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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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318 kB · 8667 lines
at master
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ACPI ACPI support is enabled. AGP AGP (Accelerated Graphics Port) is enabled. ALSA ALSA sound support is enabled. APIC APIC support is enabled. APM Advanced Power Management support is enabled. APPARMOR AppArmor support is enabled. ARM ARM architecture is enabled. ARM64 ARM64 architecture is enabled. CLK Common clock infrastructure is enabled. CMA Contiguous Memory Area support is enabled. DRM Direct Rendering Management support is enabled. DYNAMIC_DEBUG Build in debug messages and enable them at runtime EARLY Parameter processed too early to be embedded in initrd. EDD BIOS Enhanced Disk Drive Services (EDD) is enabled EFI EFI Partitioning (GPT) is enabled EVM Extended Verification Module FB The frame buffer device is enabled. FTRACE Function tracing enabled. GCOV GCOV profiling is enabled. HIBERNATION HIBERNATION is enabled. HW Appropriate hardware is enabled. HYPER_V HYPERV support is enabled. IMA Integrity measurement architecture is enabled. IP_PNP IP DHCP, BOOTP, or RARP is enabled. IPV6 IPv6 support is enabled. ISAPNP ISA PnP code is enabled. ISOL CPU Isolation is enabled. JOY Appropriate joystick support is enabled. KGDB Kernel debugger support is enabled. KVM Kernel Virtual Machine support is enabled. LIBATA Libata driver is enabled LOONGARCH LoongArch architecture is enabled. LOOP Loopback device support is enabled. LP Printer support is enabled. M68k M68k architecture is enabled. These options have more detailed description inside of Documentation/arch/m68k/kernel-options.rst. MIPS MIPS architecture is enabled. MOUSE Appropriate mouse support is enabled. MSI Message Signaled Interrupts (PCI). MTD MTD (Memory Technology Device) support is enabled. NET Appropriate network support is enabled. NFS Appropriate NFS support is enabled. NUMA NUMA support is enabled. OF Devicetree is enabled. PARISC The PA-RISC architecture is enabled. PCI PCI bus support is enabled. PCIE PCI Express support is enabled. PCMCIA The PCMCIA subsystem is enabled. PNP Plug & Play support is enabled. PPC PowerPC architecture is enabled. PPT Parallel port support is enabled. PS2 Appropriate PS/2 support is enabled. PV_OPS A paravirtualized kernel is enabled. RAM RAM disk support is enabled. RDT Intel Resource Director Technology. RISCV RISCV architecture is enabled. S390 S390 architecture is enabled. SCSI Appropriate SCSI support is enabled. A lot of drivers have their options described inside the Documentation/scsi/ sub-directory. SDW SoundWire support is enabled. SECURITY Different security models are enabled. SELINUX SELinux support is enabled. SERIAL Serial support is enabled. SH SuperH architecture is enabled. SMP The kernel is an SMP kernel. SPARC Sparc architecture is enabled. SUSPEND System suspend states are enabled. SWSUSP Software suspend (hibernation) is enabled. TPM TPM drivers are enabled. UMS USB Mass Storage support is enabled. USB USB support is enabled. NVME NVMe support is enabled USBHID USB Human Interface Device support is enabled. V4L Video For Linux support is enabled. VGA The VGA console has been enabled. VMMIO Driver for memory mapped virtio devices is enabled. VT Virtual terminal support is enabled. WDT Watchdog support is enabled. X86-32 X86-32, aka i386 architecture is enabled. X86-64 X86-64 architecture is enabled. X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64) X86_UV SGI UV support is enabled. XEN Xen support is enabled XTENSA xtensa architecture is enabled.
In addition, the following text indicates that the option
BOOT Is a boot loader parameter. BUGS= Relates to possible processor bugs on the said processor. KNL Is a kernel start-up parameter.
Kernel parameters
accept_memory= [MM] Format: { eager | lazy } default: lazy By default, unaccepted memory is accepted lazily to avoid prolonged boot times. The lazy option will add some runtime overhead until all memory is eventually accepted. In most cases the overhead is negligible. For some workloads or for debugging purposes accept_memory=eager can be used to accept all memory at once during boot.
acpi= [HW,ACPI,X86,ARM64,RISCV64,EARLY] Advanced Configuration and Power Interface Format: { force | on | off | strict | noirq | rsdt | copy_dsdt | nospcr } force -- enable ACPI if default was off on -- enable ACPI but allow fallback to DT [arm64,riscv64] off -- disable ACPI if default was on noirq -- do not use ACPI for IRQ routing strict -- Be less tolerant of platforms that are not strictly ACPI specification compliant. rsdt -- prefer RSDT over (default) XSDT copy_dsdt -- copy DSDT to memory nocmcff -- Disable firmware first mode for corrected errors. This disables parsing the HEST CMC error source to check if firmware has set the FF flag. This may result in duplicate corrected error reports. nospcr -- disable console in ACPI SPCR table as default _serial_ console on ARM64 spcr -- enable console in ACPI SPCR table as default _serial_ console on x86 For ARM64, ONLY "acpi=off", "acpi=on", "acpi=force" or "acpi=nospcr" are available For RISCV64, ONLY "acpi=off", "acpi=on" or "acpi=force" are available
See also Documentation/power/runtime_pm.rst, pci=noacpi
acpi_apic_instance= [ACPI,IOAPIC,EARLY] Format: <int> 2: use 2nd APIC table, if available 1,0: use 1st APIC table default: 0
acpi_backlight= [HW,ACPI] { vendor | video | native | none } If set to vendor, prefer vendor-specific driver (e.g. thinkpad_acpi, sony_acpi, etc.) instead of the ACPI video.ko driver. If set to video, use the ACPI video.ko driver. If set to native, use the device's native backlight mode. If set to none, disable the ACPI backlight interface.
acpi_force_32bit_fadt_addr [ACPI,EARLY] force FADT to use 32 bit addresses rather than the 64 bit X_* addresses. Some firmware have broken 64 bit addresses for force ACPI ignore these and use the older legacy 32 bit addresses.
acpica_no_return_repair [HW, ACPI] Disable AML predefined validation mechanism This mechanism can repair the evaluation result to make the return objects more ACPI specification compliant. This option is useful for developers to identify the root cause of an AML interpreter issue when the issue has something to do with the repair mechanism.
acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] acpi.debug_level= [HW,ACPI,ACPI_DEBUG] Format: <int> CONFIG_ACPI_DEBUG must be enabled to produce any ACPI debug output. Bits in debug_layer correspond to a _COMPONENT in an ACPI source file, e.g., #define _COMPONENT ACPI_EVENTS Bits in debug_level correspond to a level in ACPI_DEBUG_PRINT statements, e.g., ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... The debug_level mask defaults to "info". See Documentation/firmware-guide/acpi/debug.rst for more information about debug layers and levels.
Enable processor driver info messages: acpi.debug_layer=0x20000000 Enable AML "Debug" output, i.e., stores to the Debug object while interpreting AML: acpi.debug_layer=0xffffffff acpi.debug_level=0x2 Enable all messages related to ACPI hardware: acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
Some values produce so much output that the system is unusable. The "log_buf_len" parameter may be useful if you need to capture more output.
acpi.poweroff_on_fatal= [ACPI] {0 | 1} Causes the system to poweroff when the ACPI bytecode signals a fatal error. The default value of this setting is 1. Overriding this value should only be done for diagnosing ACPI firmware problems, as the system might behave erratically after having encountered a fatal ACPI error.
acpi_enforce_resources= [ACPI] { strict | lax | no } Check for resource conflicts between native drivers and ACPI OperationRegions (SystemIO and SystemMemory only). IO ports and memory declared in ACPI might be used by the ACPI subsystem in arbitrary AML code and can interfere with legacy drivers. strict (default): access to resources claimed by ACPI is denied; legacy drivers trying to access reserved resources will fail to bind to device using them. lax: access to resources claimed by ACPI is allowed; legacy drivers trying to access reserved resources will bind successfully but a warning message is logged. no: ACPI OperationRegions are not marked as reserved, no further checks are performed.
acpi_force_table_verification [HW,ACPI,EARLY] Enable table checksum verification during early stage. By default, this is disabled due to x86 early mapping size limitation.
acpi_irq_balance [HW,ACPI] ACPI will balance active IRQs default in APIC mode
acpi_irq_nobalance [HW,ACPI] ACPI will not move active IRQs (default) default in PIC mode
acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA Format: <irq>,<irq>...
acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for use by PCI Format: <irq>,<irq>...
acpi_mask_gpe= [HW,ACPI] Due to the existence of _Lxx/_Exx, some GPEs triggered by unsupported hardware/firmware features can result in GPE floodings that cannot be automatically disabled by the GPE dispatcher. This facility can be used to prevent such uncontrolled GPE floodings. Format: <byte> or <bitmap-list>
acpi_no_auto_serialize [HW,ACPI] Disable auto-serialization of AML methods AML control methods that contain the opcodes to create named objects will be marked as "Serialized" by the auto-serialization feature. This feature is enabled by default. This option allows to turn off the feature.
acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump kernels.
acpi_no_static_ssdt [HW,ACPI,EARLY] Disable installation of static SSDTs at early boot time By default, SSDTs contained in the RSDT/XSDT will be installed automatically and they will appear under /sys/firmware/acpi/tables. This option turns off this feature. Note that specifying this option does not affect dynamic table installation which will install SSDT tables to /sys/firmware/acpi/tables/dynamic.
acpi_no_watchdog [HW,ACPI,WDT] Ignore the ACPI-based watchdog interface (WDAT) and let a native driver control the watchdog device instead.
acpi_rsdp= [ACPI,EFI,KEXEC,EARLY] Pass the RSDP address to the kernel, mostly used on machines running EFI runtime service to boot the second kernel for kdump.
acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS Format: To spoof as Windows 98: ="Microsoft Windows"
acpi_rev_override [ACPI] Override the _REV object to return 5 (instead of 2 which is mandated by ACPI 6) as the supported ACPI specification revision (when using this switch, it may be necessary to carry out a cold reboot _twice_ in a row to make it take effect on the platform firmware).
acpi_osi= [HW,ACPI] Modify list of supported OS interface strings acpi_osi="string1" # add string1 acpi_osi="!string2" # remove string2 acpi_osi=!* # remove all strings acpi_osi=! # disable all built-in OS vendor strings acpi_osi=!! # enable all built-in OS vendor strings acpi_osi= # disable all strings
'acpi_osi=!' can be used in combination with single or multiple 'acpi_osi="string1"' to support specific OS vendor string(s). Note that such command can only affect the default state of the OS vendor strings, thus it cannot affect the default state of the feature group strings and the current state of the OS vendor strings, specifying it multiple times through kernel command line is meaningless. This command is useful when one do not care about the state of the feature group strings which should be controlled by the OSPM. Examples: 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent to 'acpi_osi="Windows 2000" acpi_osi=!', they all can make '_OSI("Windows 2000")' TRUE.
'acpi_osi=' cannot be used in combination with other 'acpi_osi=' command lines, the _OSI method will not exist in the ACPI namespace. NOTE that such command can only affect the _OSI support state, thus specifying it multiple times through kernel command line is also meaningless. Examples: 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' FALSE.
'acpi_osi=!*' can be used in combination with single or multiple 'acpi_osi="string1"' to support specific string(s). Note that such command can affect the current state of both the OS vendor strings and the feature group strings, thus specifying it multiple times through kernel command line is meaningful. But it may still not able to affect the final state of a string if there are quirks related to this string. This command is useful when one want to control the state of the feature group strings to debug BIOS issues related to the OSPM features. Examples: 1. 'acpi_osi="Module Device" acpi_osi=!*' can make '_OSI("Module Device")' FALSE. 2. 'acpi_osi=!* acpi_osi="Module Device"' can make '_OSI("Module Device")' TRUE. 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is equivalent to 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' and 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', they all will make '_OSI("Windows 2000")' TRUE.
acpi_pm_good [X86] Override the pmtimer bug detection: force the kernel to assume that this machine's pmtimer latches its value and always returns good values.
acpi_sci= [HW,ACPI,EARLY] ACPI System Control Interrupt trigger mode Format: { level | edge | high | low }
acpi_skip_timer_override [HW,ACPI,EARLY] Recognize and ignore IRQ0/pin2 Interrupt Override. For broken nForce2 BIOS resulting in XT-PIC timer.
acpi_sleep= [HW,ACPI] Sleep options Format: { s3_bios, s3_mode, s3_beep, s4_hwsig, s4_nohwsig, old_ordering, nonvs, sci_force_enable, nobl } See Documentation/power/video.rst for information on s3_bios and s3_mode. s3_beep is for debugging; it makes the PC's speaker beep as soon as the kernel's real-mode entry point is called. s4_hwsig causes the kernel to check the ACPI hardware signature during resume from hibernation, and gracefully refuse to resume if it has changed. This complies with the ACPI specification but not with reality, since Windows does not do this and many laptops do change it on docking. So the default behaviour is to allow resume and simply warn when the signature changes, unless the s4_hwsig option is enabled. s4_nohwsig prevents ACPI hardware signature from being used (or even warned about) during resume. old_ordering causes the ACPI 1.0 ordering of the _PTS control method, with respect to putting devices into low power states, to be enforced (the ACPI 2.0 ordering of _PTS is used by default). nonvs prevents the kernel from saving/restoring the ACPI NVS memory during suspend/hibernation and resume. sci_force_enable causes the kernel to set SCI_EN directly on resume from S1/S3 (which is against the ACPI spec, but some broken systems don't work without it). nobl causes the internal blacklist of systems known to behave incorrectly in some ways with respect to system suspend and resume to be ignored (use wisely).
acpi_use_timer_override [HW,ACPI,EARLY] Use timer override. For some broken Nvidia NF5 boards that require a timer override, but don't have HPET
add_efi_memmap [EFI,X86,EARLY] Include EFI memory map in kernel's map of available physical RAM.
agp= [AGP] { off | try_unsupported } off: disable AGP support try_unsupported: try to drive unsupported chipsets (may crash computer or cause data corruption)
ALSA [HW,ALSA] See Documentation/sound/alsa-configuration.rst
alignment= [KNL,ARM] Allow the default userspace alignment fault handler behaviour to be specified. Bit 0 enables warnings, bit 1 enables fixups, and bit 2 sends a segfault.
align_va_addr= [X86-64] Align virtual addresses by clearing slice [14:12] when allocating a VMA at process creation time. This option gives you up to 3% performance improvement on AMD F15h machines (where it is enabled by default) for a CPU-intensive style benchmark, and it can vary highly in a microbenchmark depending on workload and compiler.
32: only for 32-bit processes 64: only for 64-bit processes on: enable for both 32- and 64-bit processes off: disable for both 32- and 64-bit processes
alloc_snapshot [FTRACE] Allocate the ftrace snapshot buffer on boot up when the main buffer is allocated. This is handy if debugging and you need to use tracing_snapshot() on boot up, and do not want to use tracing_snapshot_alloc() as it needs to be done where GFP_KERNEL allocations are allowed.
allow_mismatched_32bit_el0 [ARM64,EARLY] Allow execve() of 32-bit applications and setting of the PER_LINUX32 personality on systems where only a strict subset of the CPUs support 32-bit EL0. When this parameter is present, the set of CPUs supporting 32-bit EL0 is indicated by /sys/devices/system/cpu/aarch32_el0 and hot-unplug operations may be restricted.
See Documentation/arch/arm64/asymmetric-32bit.rst for more information.
amd_iommu= [HW,X86-64] Pass parameters to the AMD IOMMU driver in the system. Possible values are: fullflush - Deprecated, equivalent to iommu.strict=1 off - do not initialize any AMD IOMMU found in the system force_isolation - Force device isolation for all devices. The IOMMU driver is not allowed anymore to lift isolation requirements as needed. This option does not override iommu=pt force_enable - Force enable the IOMMU on platforms known to be buggy with IOMMU enabled. Use this option with care. pgtbl_v1 - Use v1 page table for DMA-API (Default). pgtbl_v2 - Use v2 page table for DMA-API. irtcachedis - Disable Interrupt Remapping Table (IRT) caching. nohugepages - Limit page-sizes used for v1 page-tables to 4 KiB. v2_pgsizes_only - Limit page-sizes used for v1 page-tables to 4KiB/2Mib/1GiB.
amd_iommu_dump= [HW,X86-64] Enable AMD IOMMU driver option to dump the ACPI table for AMD IOMMU. With this option enabled, AMD IOMMU driver will print ACPI tables for AMD IOMMU during IOMMU initialization.
amd_iommu_intr= [HW,X86-64] Specifies one of the following AMD IOMMU interrupt remapping modes: legacy - Use legacy interrupt remapping mode. vapic - Use virtual APIC mode, which allows IOMMU to inject interrupts directly into guest. This mode requires kvm-amd.avic=1. (Default when IOMMU HW support is present.)
amd_pstate= [X86,EARLY] disable Do not enable amd_pstate as the default scaling driver for the supported processors passive Use amd_pstate with passive mode as a scaling driver. In this mode autonomous selection is disabled. Driver requests a desired performance level and platform tries to match the same performance level if it is satisfied by guaranteed performance level. active Use amd_pstate_epp driver instance as the scaling driver, driver provides a hint to the hardware if software wants to bias toward performance (0x0) or energy efficiency (0xff) to the CPPC firmware. then CPPC power algorithm will calculate the runtime workload and adjust the realtime cores frequency. guided Activate guided autonomous mode. Driver requests minimum and maximum performance level and the platform autonomously selects a performance level in this range and appropriate to the current workload.
amd_prefcore= [X86] disable Disable amd-pstate preferred core.
amd_dynamic_epp= [X86] disable Disable amd-pstate dynamic EPP. enable Enable amd-pstate dynamic EPP.
amijoy.map= [HW,JOY] Amiga joystick support Map of devices attached to JOY0DAT and JOY1DAT Format: <a>,<b> See also Documentation/input/joydev/joystick.rst
analog.map= [HW,JOY] Analog joystick and gamepad support Specifies type or capabilities of an analog joystick connected to one of 16 gameports Format: <type1>,<type2>,..<type16>
apc= [HW,SPARC] Power management functions (SPARCstation-4/5 + deriv.) Format: noidle Disable APC CPU standby support. SPARCstation-Fox does not play well with APC CPU idle - disable it if you have APC and your system crashes randomly.
apic [APIC,X86-64] Use IO-APIC. Default.
apic= [APIC,X86,EARLY] Advanced Programmable Interrupt Controller Change the output verbosity while booting Format: { quiet (default) | verbose | debug } Change the amount of debugging information output when initialising the APIC and IO-APIC components.
apic_extnmi= [APIC,X86,EARLY] External NMI delivery setting Format: { bsp (default) | all | none } bsp: External NMI is delivered only to CPU 0 all: External NMIs are broadcast to all CPUs as a backup of CPU 0 none: External NMI is masked for all CPUs. This is useful so that a dump capture kernel won't be shot down by NMI
apicpmtimer Do APIC timer calibration using the pmtimer. Implies apicmaintimer. Useful when your PIT timer is totally broken.
autoconf= [IPV6] See Documentation/networking/ipv6.rst.
apm= [APM] Advanced Power Management See header of arch/x86/kernel/apm_32.c.
apparmor= [APPARMOR] Disable or enable AppArmor at boot time Format: { "0" | "1" } See security/apparmor/Kconfig help text 0 -- disable. 1 -- enable. Default value is set via kernel config option.
arm64.no32bit_el0 [ARM64] Unconditionally disable the execution of 32 bit applications.
arm64.nobti [ARM64] Unconditionally disable Branch Target Identification support
arm64.nogcs [ARM64] Unconditionally disable Guarded Control Stack support
arm64.nomops [ARM64] Unconditionally disable Memory Copy and Memory Set instructions support
arm64.nompam [ARM64] Unconditionally disable Memory Partitioning And Monitoring support
arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension support
arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication support
arm64.nosme [ARM64] Unconditionally disable Scalable Matrix Extension support
arm64.nosve [ARM64] Unconditionally disable Scalable Vector Extension support
ataflop= [HW,M68k]
atarimouse= [HW,MOUSE] Atari Mouse
atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, EzKey and similar keyboards
atkbd.reset= [HW] Reset keyboard during initialization
atkbd.set= [HW] Select keyboard code set Format: <int> (2 = AT (default), 3 = PS/2)
atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar keyboards
atkbd.softraw= [HW] Choose between synthetic and real raw mode Format: <bool> (0 = real, 1 = synthetic (default))
atkbd.softrepeat= [HW] Use software keyboard repeat
audit= [KNL] Enable the audit sub-system Format: { "0" | "1" | "off" | "on" } 0 | off - kernel audit is disabled and can not be enabled until the next reboot unset - kernel audit is initialized but disabled and will be fully enabled by the userspace auditd. 1 | on - kernel audit is initialized and partially enabled, storing at most audit_backlog_limit messages in RAM until it is fully enabled by the userspace auditd. Default: unset
audit_backlog_limit= [KNL] Set the audit queue size limit. Format: <int> (must be >=0) Default: 64
bau= [X86_UV] Enable the BAU on SGI UV. The default behavior is to disable the BAU (i.e. bau=0). Format: { "0" | "1" } 0 - Disable the BAU. 1 - Enable the BAU. unset - Disable the BAU.
bdev_allow_write_mounted= Format: <bool> Control the ability to open a mounted block device for writing, i.e., allow / disallow writes that bypass the FS. This was implemented as a means to prevent fuzzers from crashing the kernel by overwriting the metadata underneath a mounted FS without its awareness. This also prevents destructive formatting of mounted filesystems by naive storage tooling that don't use O_EXCL. Default is Y and can be changed through the Kconfig option CONFIG_BLK_DEV_WRITE_MOUNTED.
bert_disable [ACPI] Disable BERT OS support on buggy BIOSes.
bgrt_disable [ACPI,X86,EARLY] Disable BGRT to avoid flickering OEM logo.
blkdevparts= Manual partition parsing of block device(s) for embedded devices based on command line input. See Documentation/block/cmdline-partition.rst
boot_delay= [KNL,EARLY] Milliseconds to delay each printk during boot. Only works if CONFIG_BOOT_PRINTK_DELAY is enabled, and you may also have to specify "lpj=". Boot_delay values larger than 10 seconds (10000) are assumed erroneous and ignored. Format: integer
bootconfig [KNL,EARLY] Extended command line options can be added to an initrd and this will cause the kernel to look for it.
See Documentation/admin-guide/bootconfig.rst
bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) bttv.radio= Most important insmod options are available as kernel args too. bttv.pll= See Documentation/admin-guide/media/bttv.rst bttv.tuner=
bulk_remove=off [PPC] This parameter disables the use of the pSeries firmware feature for flushing multiple hpte entries at a time.
c101= [NET] Moxa C101 synchronous serial card
cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. Sometimes CPU hardware bugs make them report the cache size incorrectly. The kernel will attempt work arounds to fix known problems, but for some CPUs it is not possible to determine what the correct size should be. This option provides an override for these situations.
carrier_timeout= [NET] Specifies amount of time (in seconds) that the kernel should wait for a network carrier. By default it waits 120 seconds.
ca_keys= [KEYS] This parameter identifies a specific key(s) on the system trusted keyring to be used for certificate trust validation. format: { id:<keyid> | builtin }
cca= [MIPS,EARLY] Override the kernel pages' cache coherency algorithm. Accepted values range from 0 to 7 inclusive. See arch/mips/include/asm/pgtable-bits.h for platform specific values (SB1, Loongson3 and others).
ccw_timeout_log [S390] See Documentation/arch/s390/common_io.rst for details.
cfi= [X86-64] Set Control Flow Integrity checking features when CONFIG_FINEIBT is enabled. Format: feature[,feature...] Default: auto
auto: Use FineIBT if IBT available, otherwise kCFI. Under FineIBT, enable "paranoid" mode when FRED is not available. off: Turn off CFI checking. kcfi: Use kCFI (disable FineIBT). fineibt: Use FineIBT (even if IBT not available). norand: Do not re-randomize CFI hashes. paranoid: Add caller hash checking under FineIBT. bhi: Enable register poisoning to stop speculation across FineIBT. (Disabled by default.) warn: Do not enforce CFI checking: warn only. debug: Report CFI initialization details.
cgroup_disable= [KNL] Disable a particular controller or optional feature Format: {name of the controller(s) or feature(s) to disable} The effects of cgroup_disable=foo are: - foo isn't auto-mounted if you mount all cgroups in a single hierarchy - foo isn't visible as an individually mountable subsystem - if foo is an optional feature then the feature is disabled and corresponding cgroup files are not created {Currently only "memory" controller deal with this and cut the overhead, others just disable the usage. So only cgroup_disable=memory is actually worthy} Specifying "pressure" disables per-cgroup pressure stall information accounting feature
cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 Format: { { controller | "all" | "named" } [,{ controller | "all" | "named" }...] } Like cgroup_disable, but only applies to cgroup v1; the blacklisted controllers remain available in cgroup2. "all" blacklists all controllers and "named" disables named mounts. Specifying both "all" and "named" disables all v1 hierarchies.
cgroup_v1_proc= [KNL] Show also missing controllers in /proc/cgroups Format: { "true" | "false" } /proc/cgroups lists only v1 controllers by default. This compatibility option enables listing also v2 controllers (whose v1 code is not compiled!), so that semi-legacy software can check this file to decide about usage of v2 (sic) controllers.
cgroup_favordynmods= [KNL] Enable or Disable favordynmods. Format: { "true" | "false" } Defaults to the value of CONFIG_CGROUP_FAVOR_DYNMODS.
cgroup.memory= [KNL] Pass options to the cgroup memory controller. Format: <string> nosocket -- Disable socket memory accounting. nokmem -- Disable kernel memory accounting. nobpf -- Disable BPF memory accounting.
check_pages= [MM,EARLY] Enable sanity checking of pages after allocations / before freeing. This adds checks to catch double-frees, use-after-frees, and other sources of page corruption by inspecting page internals (flags, mapcount/refcount, memcg_data, etc.). Format: { "0" | "1" } Default: 0 (1 if CONFIG_DEBUG_VM is set)
checkreqprot= [SELINUX] Set initial checkreqprot flag value. Format: { "0" | "1" } See security/selinux/Kconfig help text. 0 -- check protection applied by kernel (includes any implied execute protection). 1 -- check protection requested by application. Default value is set via a kernel config option. Value can be changed at runtime via /sys/fs/selinux/checkreqprot. Setting checkreqprot to 1 is deprecated.
cio_ignore= [S390] See Documentation/arch/s390/common_io.rst for details.
clk_ignore_unused [CLK] Prevents the clock framework from automatically gating clocks that have not been explicitly enabled by a Linux device driver but are enabled in hardware at reset or by the bootloader/firmware. Note that this does not force such clocks to be always-on nor does it reserve those clocks in any way. This parameter is useful for debug and development, but should not be needed on a platform with proper driver support. For more information, see Documentation/driver-api/clk.rst.
clock= [BUGS=X86-32, HW] gettimeofday clocksource override. [Deprecated] Forces specified clocksource (if available) to be used when calculating gettimeofday(). If specified clocksource is not available, it defaults to PIT. Format: { pit | tsc | cyclone | pmtmr }
clocksource= Override the default clocksource Format: <string> Override the default clocksource and use the clocksource with the name specified. Some clocksource names to choose from, depending on the platform: [all] jiffies (this is the base, fallback clocksource) [ACPI] acpi_pm [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, pxa_timer,timer3,32k_counter,timer0_1 [X86-32] pit,hpet,tsc; scx200_hrt on Geode; cyclone on IBM x440 [MIPS] MIPS [PARISC] cr16 [S390] tod [SH] SuperH [SPARC64] tick [X86-64] hpet,tsc
clocksource.arm_arch_timer.evtstrm= [ARM,ARM64,EARLY] Format: <bool> Enable/disable the eventstream feature of the ARM architected timer so that code using WFE-based polling loops can be debugged more effectively on production systems.
clocksource.verify_n_cpus= [KNL] Limit the number of CPUs checked for clocksources marked with CLOCK_SOURCE_VERIFY_PERCPU that are marked unstable due to excessive skew. A negative value says to check all CPUs, while zero says not to check any. Values larger than nr_cpu_ids are silently truncated to nr_cpu_ids. The actual CPUs are chosen randomly, with no replacement if the same CPU is chosen twice.
clocksource-wdtest.holdoff= [KNL] Set the time in seconds that the clocksource watchdog test waits before commencing its tests. Defaults to zero when built as a module and to 10 seconds when built into the kernel.
cma=nn[MG]@[start[MG][-end[MG]]] [KNL,CMA,EARLY] Sets the size of kernel global memory area for contiguous memory allocations and optionally the placement constraint by the physical address range of memory allocations. A value of 0 disables CMA altogether. For more information, see kernel/dma/contiguous.c
cma_pernuma=nn[MG] [KNL,CMA,EARLY] Sets the size of kernel per-numa memory area for contiguous memory allocations. A value of 0 disables per-numa CMA altogether. And If this option is not specified, the default value is 0. With per-numa CMA enabled, DMA users on node nid will first try to allocate buffer from the pernuma area which is located in node nid, if the allocation fails, they will fallback to the global default memory area.
numa_cma=<node>:nn[MG][,<node>:nn[MG]] [KNL,CMA,EARLY] Sets the size of kernel numa memory area for contiguous memory allocations. It will reserve CMA area for the specified node.
If it is setup together with upper 'cmd_pernuma=' (unlikely), its size setting takes priority for the specified numa nodes.
With numa CMA enabled, DMA users on node nid will first try to allocate buffer from the numa area which is located in node nid, if the allocation fails, they will fallback to the global default memory area.
cmo_free_hint= [PPC] Format: { yes | no } Specify whether pages are marked as being inactive when they are freed. This is used in CMO environments to determine OS memory pressure for page stealing by a hypervisor. Default: yes
coherent_pool=nn[KMG] [ARM,KNL,EARLY] Sets the size of memory pool for coherent, atomic dma allocations, by default set to 256K.
condev= [HW,S390] console device conmode=
con3215_drop= [S390,EARLY] 3215 console drop mode. Format: y|n|Y|N|1|0 When set to true, drop data on the 3215 console when the console buffer is full. In this case the operator using a 3270 terminal emulator (for example x3270) does not have to enter the clear key for the console output to advance and the kernel to continue. This leads to a much faster boot time when a 3270 terminal emulator is active. If no 3270 terminal emulator is used, this parameter has no effect.
console= [KNL] Output console device and options.
tty<n> Use the virtual console device <n>.
ttyS<n>[,options] ttyUSB0[,options] Use the specified serial port. The options are of the form "bbbbpnf", where "bbbb" is the baud rate, "p" is parity ("n", "o", or "e"), "n" is number of bits, and "f" is flow control ("r" for RTS or omit it). Default is "9600n8".
See Documentation/admin-guide/serial-console.rst for more information. See Documentation/networking/netconsole.rst for an alternative.
<DEVNAME>:<n>.<n>[,options] Use the specified serial port on the serial core bus. The addressing uses DEVNAME of the physical serial port device, followed by the serial core controller instance, and the serial port instance. The options are the same as documented for the ttyS addressing above.
The mapping of the serial ports to the tty instances can be viewed with:
$ ls -d /sys/bus/serial-base/devices/*:*.*/tty/* /sys/bus/serial-base/devices/00:04:0.0/tty/ttyS0
In the above example, the console can be addressed with console=00:04:0.0. Note that a console addressed this way will only get added when the related device driver is ready. The use of an earlycon parameter in addition to the console may be desired for console output early on.
uart[8250],io,<addr>[,options] uart[8250],mmio,<addr>[,options] uart[8250],mmio16,<addr>[,options] uart[8250],mmio32,<addr>[,options] uart[8250],0x<addr>[,options] Start an early, polled-mode console on the 8250/16550 UART at the specified I/O port or MMIO address, switching to the matching ttyS device later. MMIO inter-register address stride is either 8-bit (mmio), 16-bit (mmio16), or 32-bit (mmio32). If none of [io|mmio|mmio16|mmio32], <addr> is assumed to be equivalent to 'mmio'. 'options' are specified in the same format described for ttyS above; if unspecified, the h/w is not re-initialized.
hvc<n> Use the hypervisor console device <n>. This is for both Xen and PowerPC hypervisors.
{ null | "" } Use to disable console output, i.e., to have kernel console messages discarded. This must be the only console= parameter used on the kernel command line.
If the device connected to the port is not a TTY but a braille device, prepend "brl," before the device type, for instance console=brl,ttyS0 For now, only VisioBraille is supported.
console_msg_format= [KNL] Change console messages format default By default we print messages on consoles in "[time stamp] text\n" format (time stamp may not be printed, depending on CONFIG_PRINTK_TIME or `printk_time' param). syslog Switch to syslog format: "<%u>[time stamp] text\n" IOW, each message will have a facility and loglevel prefix. The format is similar to one used by syslog() syscall, or to executing "dmesg -S --raw" or to reading from /proc/kmsg.
consoleblank= [KNL] The console blank (screen saver) timeout in seconds. A value of 0 disables the blank timer. Defaults to 0.
coredump_filter= [KNL] Change the default value for /proc/<pid>/coredump_filter. See also Documentation/filesystems/proc.rst.
coresight_cpu_debug.enable [ARM,ARM64] Format: <bool> Enable/disable the CPU sampling based debugging. 0: default value, disable debugging 1: enable debugging at boot time
cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver Format: <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
cpuidle.off=1 [CPU_IDLE] disable the cpuidle sub-system
cpuidle.governor= [CPU_IDLE] Name of the cpuidle governor to use.
cpufreq.off=1 [CPU_FREQ] disable the cpufreq sub-system
cpufreq.default_governor= [CPU_FREQ] Name of the default cpufreq governor or policy to use. This governor must be registered in the kernel before the cpufreq driver probes.
cpu_init_udelay=N [X86,EARLY] Delay for N microsec between assert and de-assert of APIC INIT to start processors. This delay occurs on every CPU online, such as boot, and resume from suspend. Default: 10000
cpuhp.parallel= [SMP] Enable/disable parallel bringup of secondary CPUs Format: <bool> Default is enabled if CONFIG_HOTPLUG_PARALLEL=y. Otherwise the parameter has no effect.
crash_kexec_post_notifiers Only jump to kdump kernel after running the panic notifiers and dumping kmsg. This option increases the risks of a kdump failure, since some panic notifiers can make the crashed kernel more unstable. In configurations where kdump may not be reliable, running the panic notifiers could allow collecting more data on dmesg, like stack traces from other CPUS or extra data dumped by panic_print. Note that some configurations enable this option unconditionally, like Hyper-V, PowerPC (fadump) and AMD SEV-SNP.
crashkernel=size[KMG][@offset[KMG]] [KNL,EARLY] Using kexec, Linux can switch to a 'crash kernel' upon panic. This parameter reserves the physical memory region [offset, offset + size] for that kernel image. If '@offset' is omitted, then a suitable offset is selected automatically. [KNL, X86-64, ARM64, RISCV, LoongArch] Select a region under 4G first, and fall back to reserve region above 4G when '@offset' hasn't been specified. See Documentation/admin-guide/kdump/kdump.rst for further details.
crashkernel=range1:size1[,range2:size2,...][@offset] [KNL] Same as above, but depends on the memory in the running system. The syntax of range is start-[end] where start and end are both a memory unit (amount[KMG]). See also Documentation/admin-guide/kdump/kdump.rst for an example.
crashkernel=size[KMG],high [KNL, X86-64, ARM64, RISCV, LoongArch] range could be above 4G. Allow kernel to allocate physical memory region from top, so could be above 4G if system have more than 4G ram installed. Otherwise memory region will be allocated below 4G, if available. It will be ignored if crashkernel=X is specified. crashkernel=size[KMG],low [KNL, X86-64, ARM64, RISCV, LoongArch] range under 4G. When crashkernel=X,high is passed, kernel could allocate physical memory region above 4G, that cause second kernel crash on system that require some amount of low memory, e.g. swiotlb requires at least 64M+32K low memory, also enough extra low memory is needed to make sure DMA buffers for 32-bit devices won't run out. Kernel would try to allocate default size of memory below 4G automatically. The default size is platform dependent. --> x86: max(swiotlb_size_or_default() + 8MiB, 256MiB) --> arm64: 128MiB --> riscv: 128MiB --> loongarch: 128MiB This one lets the user specify own low range under 4G for second kernel instead. 0: to disable low allocation. It will be ignored when crashkernel=X,high is not used or memory reserved is below 4G. crashkernel=size[KMG],cma [KNL, X86, ppc] Reserve additional crash kernel memory from CMA. This reservation is usable by the first system's userspace memory and kernel movable allocations (memory balloon, zswap). Pages allocated from this memory range will not be included in the vmcore so this should not be used if dumping of userspace memory is intended and it has to be expected that some movable kernel pages may be missing from the dump.
A standard crashkernel reservation, as described above, is still needed to hold the crash kernel and initrd.
This option increases the risk of a kdump failure: DMA transfers configured by the first kernel may end up corrupting the second kernel's memory.
This reservation method is intended for systems that can't afford to sacrifice enough memory for standard crashkernel reservation and where less reliable and possibly incomplete kdump is preferable to no kdump at all.
cryptomgr.notests [KNL] Disable crypto self-tests
cs89x0_dma= [HW,NET] Format: <dma>
cs89x0_media= [HW,NET] Format: { rj45 | aui | bnc }
csdlock_debug= [KNL] Enable or disable debug add-ons of cross-CPU function call handling. When switched on, additional debug data is printed to the console in case a hanging CPU is detected, and that CPU is pinged again in order to try to resolve the hang situation. The default value of this option depends on the CSD_LOCK_WAIT_DEBUG_DEFAULT Kconfig option.
dasd= [HW,NET] See header of drivers/s390/block/dasd_devmap.c.
db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port (one device per port) Format: <port#>,<type> See also Documentation/input/devices/joystick-parport.rst
debug [KNL,EARLY] Enable kernel debugging (events log level).
debug_boot_weak_hash [KNL,EARLY] Enable printing [hashed] pointers early in the boot sequence. If enabled, we use a weak hash instead of siphash to hash pointers. Use this option if you are seeing instances of '(___ptrval___)') and need to see a value (hashed pointer) instead. Cryptographically insecure, please do not use on production kernels.
debug_locks_verbose= [KNL] verbose locking self-tests Format: <int> Print debugging info while doing the locking API self-tests. Bitmask for the various LOCKTYPE_ tests. Defaults to 0 (no extra messages), setting it to -1 (all bits set) will print _a_lot_ more information - normally only useful to lockdep developers.
debug_objects [KNL,EARLY] Enable object debugging
debug_guardpage_minorder= [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this parameter allows control of the order of pages that will be intentionally kept free (and hence protected) by the buddy allocator. Bigger value increase the probability of catching random memory corruption, but reduce the amount of memory for normal system use. The maximum possible value is MAX_PAGE_ORDER/2. Setting this parameter to 1 or 2 should be enough to identify most random memory corruption problems caused by bugs in kernel or driver code when a CPU writes to (or reads from) a random memory location. Note that there exists a class of memory corruptions problems caused by buggy H/W or F/W or by drivers badly programming DMA (basically when memory is written at bus level and the CPU MMU is bypassed) which are not detectable by CONFIG_DEBUG_PAGEALLOC, hence this option will not help tracking down these problems.
debug_pagealloc= [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this parameter enables the feature at boot time. By default, it is disabled and the system will work mostly the same as a kernel built without CONFIG_DEBUG_PAGEALLOC. Note: to get most of debug_pagealloc error reports, it's useful to also enable the page_owner functionality. on: enable the feature
debugfs= [KNL,EARLY] This parameter enables what is exposed to userspace and debugfs internal clients. Format: { on, off } on: All functions are enabled. off: Filesystem is not registered and clients get a -EPERM as result when trying to register files or directories within debugfs. This is equivalent of the runtime functionality if debugfs was not enabled in the kernel at all. Default value is set in build-time with a kernel configuration.
debugpat [X86] Enable PAT debugging
default_hugepagesz= [HW] The size of the default HugeTLB page. This is the size represented by the legacy /proc/ hugepages APIs. In addition, this is the default hugetlb size used for shmget(), mmap() and mounting hugetlbfs filesystems. If not specified, defaults to the architecture's default huge page size. Huge page sizes are architecture dependent. See also Documentation/admin-guide/mm/hugetlbpage.rst. Format: size[KMG]
deferred_probe_timeout= [KNL] Debugging option to set a timeout in seconds for deferred probe to give up waiting on dependencies to probe. Only specific dependencies (subsystems or drivers) that have opted in will be ignored. A timeout of 0 will timeout at the end of initcalls; a negative value is treated as an infinite timeout value. If the timeout hasn't expired, it'll be restarted by each successful driver registration. This option will also dump out devices still on the deferred probe list after retrying.
delayacct [KNL] Enable per-task delay accounting
dell_smm_hwmon.ignore_dmi= [HW] Continue probing hardware even if DMI data indicates that the driver is running on unsupported hardware.
dell_smm_hwmon.force= [HW] Activate driver even if SMM BIOS signature does not match list of supported models and enable otherwise blacklisted features.
dell_smm_hwmon.power_status= [HW] Report power status in /proc/i8k (disabled by default).
dell_smm_hwmon.restricted= [HW] Allow controlling fans only if SYS_ADMIN capability is set.
dell_smm_hwmon.fan_mult= [HW] Factor to multiply fan speed with.
dell_smm_hwmon.fan_max= [HW] Maximum configurable fan speed.
dfltcc= [HW,S390] Format: { on | off | def_only | inf_only | always } on: s390 zlib hardware support for compression on level 1 and decompression (default) off: No s390 zlib hardware support def_only: s390 zlib hardware support for deflate only (compression on level 1) inf_only: s390 zlib hardware support for inflate only (decompression) always: Same as 'on' but ignores the selected compression level always using hardware support (used for debugging)
dhash_entries= [KNL] Set number of hash buckets for dentry cache.
disable_1tb_segments [PPC,EARLY] Disables the use of 1TB hash page table segments. This causes the kernel to fall back to 256MB segments which can be useful when debugging issues that require an SLB miss to occur.
disable= [IPV6] See Documentation/networking/ipv6.rst.
disable_radix [PPC,EARLY] Disable RADIX MMU mode on POWER9
disable_tlbie [PPC] Disable TLBIE instruction. Currently does not work with KVM, with HASH MMU, or with coherent accelerators.
disable_ddw [PPC/PSERIES,EARLY] Disable Dynamic DMA Window support. Use this to workaround buggy firmware.
disable_ipv6= [IPV6] See Documentation/networking/ipv6.rst.
disable_mtrr_cleanup [X86,EARLY] The kernel tries to adjust MTRR layout from continuous to discrete, to make X server driver able to add WB entry later. This parameter disables that.
disable_mtrr_trim [X86, Intel and AMD only,EARLY] By default the kernel will trim any uncacheable memory out of your available memory pool based on MTRR settings. This parameter disables that behavior, possibly causing your machine to run very slowly.
disable_timer_pin_1 [X86,EARLY] Disable PIN 1 of APIC timer Can be useful to work around chipset bugs.
dis_ucode_ldr [X86] Disable the microcode loader.
dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, this option disables the debugging code at boot.
dma_debug_entries=<number> This option allows to tune the number of preallocated entries for DMA-API debugging code. One entry is required per DMA-API allocation. Use this if the DMA-API debugging code disables itself because the architectural default is too low.
dma_debug_driver=<driver_name> With this option the DMA-API debugging driver filter feature can be enabled at boot time. Just pass the driver to filter for as the parameter. The filter can be disabled or changed to another driver later using sysfs.
reg_file_data_sampling= [X86] Controls mitigation for Register File Data Sampling (RFDS) vulnerability. RFDS is a CPU vulnerability which may allow userspace to infer kernel data values previously stored in floating point registers, vector registers, or integer registers. RFDS only affects Intel Atom processors.
on: Turns ON the mitigation. off: Turns OFF the mitigation.
This parameter overrides the compile time default set by CONFIG_MITIGATION_RFDS. Mitigation cannot be disabled when other VERW based mitigations (like MDS) are enabled. In order to disable RFDS mitigation all VERW based mitigations need to be disabled.
For details see: Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst
dm_verity.keyring_unsealed= [KNL] When set to 1, leave the dm-verity keyring unsealed after initialization so userspace can provision keys. Once the keyring is restricted it becomes active and is searched during signature verification.
driver_async_probe= [KNL] List of driver names to be probed asynchronously. * matches with all driver names. If * is specified, the rest of the listed driver names are those that will NOT match the *. Format: <driver_name1>,<driver_name2>...
drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] Broken monitors, graphic adapters, KVMs and EDIDless panels may send no or incorrect EDID data sets. This parameter allows to specify an EDID data sets in the /lib/firmware directory that are used instead. An EDID data set will only be used for a particular connector, if its name and a colon are prepended to the EDID name. Each connector may use a unique EDID data set by separating the files with a comma. An EDID data set with no connector name will be used for any connectors not explicitly specified.
dscc4.setup= [NET]
dt_cpu_ftrs= [PPC,EARLY] Format: {"off" | "known"} Control how the dt_cpu_ftrs device-tree binding is used for CPU feature discovery and setup (if it exists). off: Do not use it, fall back to legacy cpu table. known: Do not pass through unknown features to guests or userspace, only those that the kernel is aware of.
dump_apple_properties [X86] Dump name and content of EFI device properties on x86 Macs. Useful for driver authors to determine what data is available or for reverse-engineering.
dyndbg[="val"] [KNL,DYNAMIC_DEBUG] <module>.dyndbg[="val"] Enable debug messages at boot time. See Documentation/admin-guide/dynamic-debug-howto.rst for details.
early_ioremap_debug [KNL,EARLY] Enable debug messages in early_ioremap support. This is useful for tracking down temporary early mappings which are not unmapped.
earlycon= [KNL,EARLY] Output early console device and options.
When used with no options, the early console is determined by stdout-path property in device tree's chosen node or the ACPI SPCR table if supported by the platform.
cdns,<addr>[,options] Start an early, polled-mode console on a Cadence (xuartps) serial port at the specified address. Only supported option is baud rate. If baud rate is not specified, the serial port must already be setup and configured.
uart[8250],io,<addr>[,options[,uartclk]] uart[8250],mmio,<addr>[,options[,uartclk]] uart[8250],mmio32,<addr>[,options[,uartclk]] uart[8250],mmio32be,<addr>[,options[,uartclk]] uart[8250],0x<addr>[,options] Start an early, polled-mode console on the 8250/16550 UART at the specified I/O port or MMIO address. MMIO inter-register address stride is either 8-bit (mmio) or 32-bit (mmio32 or mmio32be). If none of [io|mmio|mmio32|mmio32be], <addr> is assumed to be equivalent to 'mmio'. 'options' are specified in the same format described for "console=ttyS<n>"; if unspecified, the h/w is not initialized. 'uartclk' is the uart clock frequency; if unspecified, it is set to 'BASE_BAUD' * 16.
pl011,<addr> pl011,mmio32,<addr> Start an early, polled-mode console on a pl011 serial port at the specified address. The pl011 serial port must already be setup and configured. Options are not yet supported. If 'mmio32' is specified, then only the driver will use only 32-bit accessors to read/write the device registers.
liteuart,<addr> Start an early console on a litex serial port at the specified address. The serial port must already be setup and configured. Options are not yet supported.
meson,<addr> Start an early, polled-mode console on a meson serial port at the specified address. The serial port must already be setup and configured. Options are not yet supported.
msm_serial,<addr> Start an early, polled-mode console on an msm serial port at the specified address. The serial port must already be setup and configured. Options are not yet supported.
msm_serial_dm,<addr> Start an early, polled-mode console on an msm serial dm port at the specified address. The serial port must already be setup and configured. Options are not yet supported.
owl,<addr> Start an early, polled-mode console on a serial port of an Actions Semi SoC, such as S500 or S900, at the specified address. The serial port must already be setup and configured. Options are not yet supported.
rda,<addr> Start an early, polled-mode console on a serial port of an RDA Micro SoC, such as RDA8810PL, at the specified address. The serial port must already be setup and configured. Options are not yet supported.
sbi Use RISC-V SBI (Supervisor Binary Interface) for early console.
smh Use ARM semihosting calls for early console.
s3c2410,<addr> s3c2412,<addr> s3c2440,<addr> s3c6400,<addr> s5pv210,<addr> exynos4210,<addr> Use early console provided by serial driver available on Samsung SoCs, requires selecting proper type and a correct base address of the selected UART port. The serial port must already be setup and configured. Options are not yet supported.
lantiq,<addr> Start an early, polled-mode console on a lantiq serial (lqasc) port at the specified address. The serial port must already be setup and configured. Options are not yet supported.
lpuart,<addr> lpuart32,<addr> Use early console provided by Freescale LP UART driver found on Freescale Vybrid and QorIQ LS1021A processors. A valid base address must be provided, and the serial port must already be setup and configured.
ec_imx21,<addr> ec_imx6q,<addr> Start an early, polled-mode, output-only console on the Freescale i.MX UART at the specified address. The UART must already be setup and configured.
ar3700_uart,<addr> Start an early, polled-mode console on the Armada 3700 serial port at the specified address. The serial port must already be setup and configured. Options are not yet supported.
qcom_geni,<addr> Start an early, polled-mode console on a Qualcomm Generic Interface (GENI) based serial port at the specified address. The serial port must already be setup and configured. Options are not yet supported.
efifb,[options] Start an early, unaccelerated console on the EFI memory mapped framebuffer (if available). On cache coherent non-x86 systems that use system memory for the framebuffer, pass the 'ram' option so that it is mapped with the correct attributes.
linflex,<addr> Use early console provided by Freescale LINFlexD UART serial driver for NXP S32V234 SoCs. A valid base address must be provided, and the serial port must already be setup and configured.
earlyprintk= [X86,SH,ARM,M68k,S390,UM,EARLY] earlyprintk=vga earlyprintk=sclp earlyprintk=xen earlyprintk=serial[,ttySn[,baudrate]] earlyprintk=serial[,0x...[,baudrate]] earlyprintk=ttySn[,baudrate] earlyprintk=dbgp[debugController#] earlyprintk=mmio32,membase[,{nocfg|baudrate}] earlyprintk=pciserial[,force],bus:device.function[,{nocfg|baudrate}] earlyprintk=xdbc[xhciController#] earlyprintk=bios
earlyprintk is useful when the kernel crashes before the normal console is initialized. It is not enabled by default because it has some cosmetic problems.
Use "nocfg" to skip UART configuration, assume BIOS/firmware has configured UART correctly.
Append ",keep" to not disable it when the real console takes over.
Only one of vga, serial, or usb debug port can be used at a time.
Currently only ttyS0 and ttyS1 may be specified by name. Other I/O ports may be explicitly specified on some architectures (x86 and arm at least) by replacing ttySn with an I/O port address, like this: earlyprintk=serial,0x1008,115200 You can find the port for a given device in /proc/tty/driver/serial: 2: uart:ST16650V2 port:00001008 irq:18 ...
Interaction with the standard serial driver is not very good.
The VGA output is eventually overwritten by the real console.
The xen option can only be used in Xen domains.
The sclp output can only be used on s390.
The bios output can only be used on SuperH.
The optional "force" to "pciserial" enables use of a PCI device even when its classcode is not of the UART class.
edac_report= [HW,EDAC] Control how to report EDAC event Format: {"on" | "off" | "force"} on: enable EDAC to report H/W event. May be overridden by other higher priority error reporting module. off: disable H/W event reporting through EDAC. force: enforce the use of EDAC to report H/W event. default: on.
edd= [EDD] Format: {"off" | "on" | "skip[mbr]"}
efi= [EFI,EARLY] Format: { "debug", "disable_early_pci_dma", "nochunk", "noruntime", "nosoftreserve", "novamap", "no_disable_early_pci_dma" } debug: enable misc debug output. disable_early_pci_dma: disable the busmaster bit on all PCI bridges while in the EFI boot stub. nochunk: disable reading files in "chunks" in the EFI boot stub, as chunking can cause problems with some firmware implementations. noruntime : disable EFI runtime services support nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) attribute may cause the kernel to reserve the memory range for a memory mapping driver to claim. Specify efi=nosoftreserve to disable this reservation and treat the memory by its base type (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). novamap: do not call SetVirtualAddressMap(). no_disable_early_pci_dma: Leave the busmaster bit set on all PCI bridges while in the EFI boot stub
efi_no_storage_paranoia [EFI,X86,EARLY] Using this parameter you can use more than 50% of your efi variable storage. Use this parameter only if you are really sure that your UEFI does sane gc and fulfills the spec otherwise your board may brick.
efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT that is to be dynamically loaded by Linux. If there are multiple variables with the same name but with different vendor GUIDs, all of them will be loaded. See Documentation/admin-guide/acpi/ssdt-overlays.rst for details.
eisa_irq_edge= [PARISC,HW] See header of drivers/parisc/eisa.c.
ekgdboc= [X86,KGDB,EARLY] Allow early kernel console debugging Format: ekgdboc=kbd
This is designed to be used in conjunction with the boot argument: earlyprintk=vga
This parameter works in place of the kgdboc parameter but can only be used if the backing tty is available very early in the boot process. For early debugging via a serial port see kgdboc_earlycon instead.
elfcorehdr=[size[KMG]@]offset[KMG] [PPC,SH,X86,S390,EARLY] Specifies physical address of start of kernel core image elf header and optionally the size. Generally kexec loader will pass this option to capture kernel. See Documentation/admin-guide/kdump/kdump.rst for details.
enable_mtrr_cleanup [X86,EARLY] The kernel tries to adjust MTRR layout from continuous to discrete, to make X server driver able to add WB entry later. This parameter enables that.
enable_timer_pin_1 [X86] Enable PIN 1 of APIC timer Can be useful to work around chipset bugs (in particular on some ATI chipsets). The kernel tries to set a reasonable default.
enforcing= [SELINUX] Set initial enforcing status. Format: {"0" | "1"} See security/selinux/Kconfig help text. 0 -- permissive (log only, no denials). 1 -- enforcing (deny and log). Default value is 0. Value can be changed at runtime via /sys/fs/selinux/enforce.
erst_disable [ACPI] Disable Error Record Serialization Table (ERST) support.
ether= [HW,NET] Ethernet cards parameters This option is obsoleted by the "netdev=" option, which has equivalent usage. See its documentation for details.
evm= [EVM] Format: { "fix" } Permit 'security.evm' to be updated regardless of current integrity status.
early_page_ext [KNL,EARLY] Enforces page_ext initialization to earlier stages so cover more early boot allocations. Please note that as side effect some optimizations might be disabled to achieve that (e.g. parallelized memory initialization is disabled) so the boot process might take longer, especially on systems with a lot of memory. Available with CONFIG_PAGE_EXTENSION=y.
failslab= fail_usercopy= fail_page_alloc= fail_skb_realloc= fail_make_request=[KNL] General fault injection mechanism. Format: <interval>,<probability>,<space>,<times> See also Documentation/fault-injection/.
fb_tunnels= [NET] Format: { initns | none } See Documentation/admin-guide/sysctl/net.rst for fb_tunnels_only_for_init_ns
floppy= [HW] See Documentation/admin-guide/blockdev/floppy.rst.
forcepae [X86-32] Forcefully enable Physical Address Extension (PAE). Many Pentium M systems disable PAE but may have a functionally usable PAE implementation. Warning: use of this parameter will taint the kernel and may cause unknown problems.
fred= [X86-64] Enable/disable Flexible Return and Event Delivery. Format: { on | off } on: enable FRED when it's present, the default setting. off: disable FRED.
ftrace=[tracer] [FTRACE] will set and start the specified tracer as early as possible in order to facilitate early boot debugging.
ftrace_boot_snapshot [FTRACE] On boot up, a snapshot will be taken of the ftrace ring buffer that can be read at: /sys/kernel/tracing/snapshot. This is useful if you need tracing information from kernel boot up that is likely to be overridden by user space start up functionality.
Optionally, the snapshot can also be defined for a tracing instance that was created by the trace_instance= command line parameter.
trace_instance=foo,sched_switch ftrace_boot_snapshot=foo
The above will cause the "foo" tracing instance to trigger a snapshot at the end of boot up.
ftrace_dump_on_oops[=2(orig_cpu) | =<instance>][,<instance> | ,<instance>=2(orig_cpu)] [FTRACE] will dump the trace buffers on oops. If no parameter is passed, ftrace will dump global buffers of all CPUs, if you pass 2 or orig_cpu, it will dump only the buffer of the CPU that triggered the oops, or the specific instance will be dumped if its name is passed. Multiple instance dump is also supported, and instances are separated by commas. Each instance supports only dump on CPU that triggered the oops by passing 2 or orig_cpu to it.
ftrace_dump_on_oops=foo=orig_cpu
The above will dump only the buffer of "foo" instance on CPU that triggered the oops.
ftrace_dump_on_oops,foo,bar=orig_cpu
The above will dump global buffer on all CPUs, the buffer of "foo" instance on all CPUs and the buffer of "bar" instance on CPU that triggered the oops.
ftrace_filter=[function-list] [FTRACE] Limit the functions traced by the function tracer at boot up. function-list is a comma-separated list of functions. This list can be changed at run time by the set_ftrace_filter file in the debugfs tracing directory.
ftrace_notrace=[function-list] [FTRACE] Do not trace the functions specified in function-list. This list can be changed at run time by the set_ftrace_notrace file in the debugfs tracing directory.
ftrace_graph_filter=[function-list] [FTRACE] Limit the top level callers functions traced by the function graph tracer at boot up. function-list is a comma-separated list of functions that can be changed at run time by the set_graph_function file in the debugfs tracing directory.
ftrace_graph_notrace=[function-list] [FTRACE] Do not trace from the functions specified in function-list. This list is a comma-separated list of functions that can be changed at run time by the set_graph_notrace file in the debugfs tracing directory.
ftrace_graph_max_depth=<uint> [FTRACE] Used with the function graph tracer. This is the max depth it will trace into a function. This value can be changed at run time by the max_graph_depth file in the tracefs tracing directory. default: 0 (no limit)
fw_devlink= [KNL,EARLY] Create device links between consumer and supplier devices by scanning the firmware to infer the consumer/supplier relationships. This feature is especially useful when drivers are loaded as modules as it ensures proper ordering of tasks like device probing (suppliers first, then consumers), supplier boot state clean up (only after all consumers have probed), suspend/resume & runtime PM (consumers first, then suppliers). Format: { off | permissive | on | rpm } off -- Don't create device links from firmware info. permissive -- Create device links from firmware info but use it only for ordering boot state clean up (sync_state() calls). on -- Create device links from firmware info and use it to enforce probe and suspend/resume ordering. rpm -- Like "on", but also use to order runtime PM.
fw_devlink.strict=<bool> [KNL,EARLY] Treat all inferred dependencies as mandatory dependencies. This only applies for fw_devlink=on|rpm. Format: <bool>
fw_devlink.sync_state = [KNL,EARLY] When all devices that could probe have finished probing, this parameter controls what to do with devices that haven't yet received their sync_state() calls. Format: { strict | timeout } strict -- Default. Continue waiting on consumers to probe successfully. timeout -- Give up waiting on consumers and call sync_state() on any devices that haven't yet received their sync_state() calls after deferred_probe_timeout has expired or by late_initcall() if !CONFIG_MODULES.
gamecon.map[2|3]= [HW,JOY] Multisystem joystick and NES/SNES/PSX pad support via parallel port (up to 5 devices per port) Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> See also Documentation/input/devices/joystick-parport.rst
gamma= [HW,DRM]
gart_fix_e820= [X86-64,EARLY] disable the fix e820 for K8 GART Format: off | on default: on
gather_data_sampling= [X86,INTEL,EARLY] Control the Gather Data Sampling (GDS) mitigation.
Gather Data Sampling is a hardware vulnerability which allows unprivileged speculative access to data which was previously stored in vector registers.
This issue is mitigated by default in updated microcode. The mitigation may have a performance impact but can be disabled. On systems without the microcode mitigation disabling AVX serves as a mitigation.
force: Disable AVX to mitigate systems without microcode mitigation. No effect if the microcode mitigation is present. Known to cause crashes in userspace with buggy AVX enumeration.
off: Disable GDS mitigation.
gbpages [X86] Use GB pages for kernel direct mappings.
gcov_persist= [GCOV] When non-zero (default), profiling data for kernel modules is saved and remains accessible via debugfs, even when the module is unloaded/reloaded. When zero, profiling data is discarded and associated debugfs files are removed at module unload time.
goldfish [X86] Enable the goldfish android emulator platform. Don't use this when you are not running on the android emulator
gpio-mockup.gpio_mockup_ranges [HW] Sets the ranges of gpiochip of for this device. Format: <start1>,<end1>,<start2>,<end2>... gpio-mockup.gpio_mockup_named_lines [HW] Let the driver know GPIO lines should be named.
gpt [EFI] Forces disk with valid GPT signature but invalid Protective MBR to be treated as GPT. If the primary GPT is corrupted, it enables the backup/alternate GPT to be used instead.
grcan.enable0= [HW] Configuration of physical interface 0. Determines the "Enable 0" bit of the configuration register. Format: 0 | 1 Default: 0 grcan.enable1= [HW] Configuration of physical interface 1. Determines the "Enable 0" bit of the configuration register. Format: 0 | 1 Default: 0 grcan.select= [HW] Select which physical interface to use. Format: 0 | 1 Default: 0 grcan.txsize= [HW] Sets the size of the tx buffer. Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. Default: 1024 grcan.rxsize= [HW] Sets the size of the rx buffer. Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. Default: 1024
hardened_usercopy= [KNL] Under CONFIG_HARDENED_USERCOPY, whether hardening is enabled for this boot. Hardened usercopy checking is used to protect the kernel from reading or writing beyond known memory allocation boundaries as a proactive defense against bounds-checking flaws in the kernel's copy_to_user()/copy_from_user() interface. The default is determined by CONFIG_HARDENED_USERCOPY_DEFAULT_ON. on Perform hardened usercopy checks. off Disable hardened usercopy checks.
hardlockup_all_cpu_backtrace= [KNL] Should the hard-lockup detector generate backtraces on all cpus. Format: 0 | 1
hash_pointers= [KNL,EARLY] By default, when pointers are printed to the console or buffers via the %p format string, that pointer is "hashed", i.e. obscured by hashing the pointer value. This is a security feature that hides actual kernel addresses from unprivileged users, but it also makes debugging the kernel more difficult since unequal pointers can no longer be compared. The choices are: Format: { auto | always | never } Default: auto
auto - Hash pointers unless slab_debug is enabled. always - Always hash pointers (even if slab_debug is enabled). never - Never hash pointers. This option should only be specified when debugging the kernel. Do not use on production kernels. The boot param "no_hash_pointers" is an alias for this mode.
For controlling hashing dynamically at runtime, use the "kernel.kptr_restrict" sysctl instead.
hashdist= [KNL,NUMA] Large hashes allocated during boot are distributed across NUMA nodes. Defaults on for 64-bit NUMA, off otherwise. Format: 0 | 1 (for off | on)
hd= [EIDE] (E)IDE hard drive subsystem geometry Format: <cyl>,<head>,<sect>
hest_disable [ACPI] Disable Hardware Error Source Table (HEST) support; corresponding firmware-first mode error processing logic will be disabled.
hibernate= [HIBERNATION] noresume Don't check if there's a hibernation image present during boot. nocompress Don't compress/decompress hibernation images. no Disable hibernation and resume. protect_image Turn on image protection during restoration (that will set all pages holding image data during restoration read-only).
hibernate.compressor= [HIBERNATION] Compression algorithm to be used with hibernation. Format: { lzo | lz4 } Default: lzo
lzo: Select LZO compression algorithm to compress/decompress hibernation image.
lz4: Select LZ4 compression algorithm to compress/decompress hibernation image.
hibernate.pm_test_delay= [HIBERNATION] Sets the number of seconds to remain in a hibernation test mode before resuming the system (see /sys/power/pm_test). Only available when CONFIG_PM_DEBUG is set. Default value is 5.
hibernate_compression_threads= [HIBERNATION] Set the number of threads used for compressing or decompressing hibernation images.
Format: <integer> Default: 3 Minimum: 1 Example: hibernate_compression_threads=4
highmem=nn[KMG] [KNL,BOOT,EARLY] forces the highmem zone to have an exact size of <nn>. This works even on boxes that have no highmem otherwise. This also works to reduce highmem size on bigger boxes.
highres= [KNL] Enable/disable high resolution timer mode. Valid parameters: "on", "off" Default: "on"
hlt [BUGS=ARM,SH]
hostname= [KNL,EARLY] Set the hostname (aka UTS nodename). Format: <string> This allows setting the system's hostname during early startup. This sets the name returned by gethostname. Using this parameter to set the hostname makes it possible to ensure the hostname is correctly set before any userspace processes run, avoiding the possibility that a process may call gethostname before the hostname has been explicitly set, resulting in the calling process getting an incorrect result. The string must not exceed the maximum allowed hostname length (usually 64 characters) and will be truncated otherwise.
hpet= [X86-32,HPET] option to control HPET usage Format: { enable (default) | disable | force | verbose } disable: disable HPET and use PIT instead force: allow force enabled of undocumented chips (ICH4, VIA, nVidia) verbose: show contents of HPET registers during setup
hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
hugepages= [HW,EARLY] Number of HugeTLB pages to allocate at boot. If this follows hugepagesz (below), it specifies the number of pages of hugepagesz to be allocated. If this is the first HugeTLB parameter on the command line, it specifies the number of pages to allocate for the default huge page size. If using node format, the number of pages to allocate per-node can be specified. See also Documentation/admin-guide/mm/hugetlbpage.rst. Format: <integer> or (node format) <node>:<integer>[,<node>:<integer>]
hugepagesz= [HW,EARLY] The size of the HugeTLB pages. This is used in conjunction with hugepages (above) to allocate huge pages of a specific size at boot. The pair hugepagesz=X hugepages=Y can be specified once for each supported huge page size. Huge page sizes are architecture dependent. See also Documentation/admin-guide/mm/hugetlbpage.rst. Format: size[KMG]
hugepage_alloc_threads= [HW] The number of threads that should be used to allocate hugepages during boot. This option can be used to improve system bootup time when allocating a large amount of huge pages. The default value is 25% of the available hardware threads.
Note that this parameter only applies to non-gigantic huge pages.
hugetlb_cma= [HW,CMA,EARLY] The size of a CMA area used for allocation of gigantic hugepages. Or using node format, the size of a CMA area per node can be specified. Format: nn[KMGTPE] or (node format) <node>:nn[KMGTPE][,<node>:nn[KMGTPE]]
The size must be a multiple of the gigantic page size. When using node format, this applies to each per-node size. Missaligned values are dropped with a warning.
Reserve a CMA area of given size and allocate gigantic hugepages using the CMA allocator. If enabled, the boot-time allocation of gigantic hugepages is skipped.
hugetlb_cma_only= [HW,CMA,EARLY] When allocating new HugeTLB pages, only try to allocate from the CMA areas.
This option does nothing if hugetlb_cma= is not also specified.
hugetlb_free_vmemmap= [KNL] Requires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP enabled. Control if HugeTLB Vmemmap Optimization (HVO) is enabled. Allows heavy hugetlb users to free up some more memory (7 * PAGE_SIZE for each 2MB hugetlb page). Format: { on | off (default) }
on: enable HVO off: disable HVO
Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y, the default is on.
Note that the vmemmap pages may be allocated from the added memory block itself when memory_hotplug.memmap_on_memory is enabled, those vmemmap pages cannot be optimized even if this feature is enabled. Other vmemmap pages not allocated from the added memory block itself do not be affected.
hung_task_panic= [KNL] Number of hung tasks to trigger kernel panic. Format: <int>
When set to a non-zero value, a kernel panic will be triggered if the number of detected hung tasks reaches this value.
0: don't panic 1: panic immediately on first hung task N: panic after N hung tasks are detected in a single scan
The default value is controlled by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time option. The value selected by this boot parameter can be changed later by the kernel.hung_task_panic sysctl.
hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) terminal devices. Valid values: 0..8 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. If specified, z/VM IUCV HVC accepts connections from listed z/VM user IDs only.
hv_nopvspin [X86,HYPER_V,EARLY] Disables the paravirt spinlock optimizations which allow the hypervisor to 'idle' the guest on lock contention.
hw_protection= [HW] Format: reboot | shutdown
Hardware protection action taken on critical events like overtemperature or imminent voltage loss.
i2c_bus= [HW] Override the default board specific I2C bus speed or register an additional I2C bus that is not registered from board initialization code. Format: <bus_id>,<clkrate>
i2c_touchscreen_props= [HW,ACPI,X86] Set device-properties for ACPI-enumerated I2C-attached touchscreen, to e.g. fix coordinates of upside-down mounted touchscreens. If you need this option please submit a drivers/platform/x86/touchscreen_dmi.c patch adding a DMI quirk for this.
Format: <ACPI_HW_ID>:<prop_name>=<val>[:prop_name=val][:...] Where <val> is one of: Omit "=<val>" entirely Set a boolean device-property Unsigned number Set a u32 device-property Anything else Set a string device-property
Examples (split over multiple lines): i2c_touchscreen_props=GDIX1001:touchscreen-inverted-x: touchscreen-inverted-y
i2c_touchscreen_props=MSSL1680:touchscreen-size-x=1920: touchscreen-size-y=1080:touchscreen-inverted-y: firmware-name=gsl1680-vendor-model.fw:silead,home-button
i8042.debug [HW] Toggle i8042 debug mode i8042.unmask_kbd_data [HW] Enable printing of interrupt data from the KBD port (disabled by default, and as a pre-condition requires that i8042.debug=1 be enabled) i8042.direct [HW] Put keyboard port into non-translated mode i8042.dumbkbd [HW] Pretend that controller can only read data from keyboard and cannot control its state (Don't attempt to blink the leds) i8042.noaux [HW] Don't check for auxiliary (== mouse) port i8042.nokbd [HW] Don't check/create keyboard port i8042.noloop [HW] Disable the AUX Loopback command while probing for the AUX port i8042.nomux [HW] Don't check presence of an active multiplexing controller i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX controllers i8042.notimeout [HW] Ignore timeout condition signalled by controller i8042.reset [HW] Reset the controller during init, cleanup and suspend-to-ram transitions, only during s2r transitions, or never reset Format: { 1 | Y | y | 0 | N | n } 1, Y, y: always reset controller 0, N, n: don't ever reset controller Default: only on s2r transitions on x86; most other architectures force reset to be always executed i8042.unlock [HW] Unlock (ignore) the keylock i8042.kbdreset [HW] Reset device connected to KBD port i8042.probe_defer [HW] Allow deferred probing upon i8042 probe errors
i810= [HW,DRM]
i915.invert_brightness= [DRM] Invert the sense of the variable that is used to set the brightness of the panel backlight. Normally a brightness value of 0 indicates backlight switched off, and the maximum of the brightness value sets the backlight to maximum brightness. If this parameter is set to 0 (default) and the machine requires it, or this parameter is set to 1, a brightness value of 0 sets the backlight to maximum brightness, and the maximum of the brightness value switches the backlight off. -1 -- never invert brightness 0 -- machine default 1 -- force brightness inversion
ia32_emulation= [X86-64] Format: <bool> When true, allows loading 32-bit programs and executing 32-bit syscalls, essentially overriding IA32_EMULATION_DEFAULT_DISABLED at boot time. When false, unconditionally disables IA32 emulation.
idle= [X86,EARLY] Format: idle=poll, idle=halt, idle=nomwait
idle=poll: Don't do power saving in the idle loop using HLT, but poll for rescheduling event. This will make the CPUs eat a lot more power, but may be useful to get slightly better performance in multiprocessor benchmarks. It also makes some profiling using performance counters more accurate. Please note that on systems with MONITOR/MWAIT support (like Intel EM64T CPUs) this option has no performance advantage over the normal idle loop. It may also interact badly with hyperthreading.
idle=halt: Halt is forced to be used for CPU idle. In such case C2/C3 won't be used again.
idle=nomwait: Disable mwait for CPU C-states
idxd.sva= [HW] Format: <bool> Allow force disabling of Shared Virtual Memory (SVA) support for the idxd driver. By default it is set to true (1).
idxd.tc_override= [HW] Format: <bool> Allow override of default traffic class configuration for the device. By default it is set to false (0).
ieee754= [MIPS] Select IEEE Std 754 conformance mode Format: { strict | legacy | 2008 | relaxed | emulated } Default: strict
Choose which programs will be accepted for execution based on the IEEE 754 NaN encoding(s) supported by the FPU and the NaN encoding requested with the value of an ELF file header flag individually set by each binary. Hardware implementations are permitted to support either or both of the legacy and the 2008 NaN encoding mode.
Available settings are as follows: strict accept binaries that request a NaN encoding supported by the FPU legacy only accept legacy-NaN binaries, if supported by the FPU 2008 only accept 2008-NaN binaries, if supported by the FPU relaxed accept any binaries regardless of whether supported by the FPU emulated accept any binaries but enable FPU emulator if binary mode is unsupported by the FPU.
The FPU emulator is always able to support both NaN encodings, so if no FPU hardware is present or it has been disabled with 'nofpu', then the settings of 'legacy' and '2008' strap the emulator accordingly, 'relaxed' straps the emulator for both legacy-NaN and 2008-NaN, whereas 'strict' enables legacy-NaN only on legacy processors and both NaN encodings on MIPS32 or MIPS64 CPUs.
The setting for ABS.fmt/NEG.fmt instruction execution mode generally follows that for the NaN encoding, except where unsupported by hardware.
ignore_loglevel [KNL,EARLY] Ignore loglevel setting - this will print /all/ kernel messages to the console. Useful for debugging. We also add it as printk module parameter, so users could change it dynamically, usually by /sys/module/printk/parameters/ignore_loglevel.
ignore_rlimit_data Ignore RLIMIT_DATA setting for data mappings, print warning at first misuse. Can be changed via /sys/module/kernel/parameters/ignore_rlimit_data.
ihash_entries= [KNL] Set number of hash buckets for inode cache.
ima_appraise= [IMA] appraise integrity measurements Format: { "off" | "enforce" | "fix" | "log" } default: "enforce"
ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. The builtin appraise policy appraises all files owned by uid=0.
ima_canonical_fmt [IMA] Use the canonical format for the binary runtime measurements, instead of host native format.
ima_flush_htable [IMA] Flush the IMA hash table when deleting all the staged measurement records, to achieve maximum memory saving at the cost of having duplicate records across the staged measurement lists.
ima_hash= [IMA] Format: { md5 | sha1 | rmd160 | sha256 | sha384 | sha512 | ... } default: "sha1"
The list of supported hash algorithms is defined in crypto/hash_info.h.
ima_policy= [IMA] The builtin policies to load during IMA setup. Format: "tcb | appraise_tcb | secure_boot | fail_securely | critical_data"
The "tcb" policy measures all programs exec'd, files mmap'd for exec, and all files opened with the read mode bit set by either the effective uid (euid=0) or uid=0.
The "appraise_tcb" policy appraises the integrity of all files owned by root.
The "secure_boot" policy appraises the integrity of files (eg. kexec kernel image, kernel modules, firmware, policy, etc) based on file signatures.
The "fail_securely" policy forces file signature verification failure also on privileged mounted filesystems with the SB_I_UNVERIFIABLE_SIGNATURE flag.
The "critical_data" policy measures kernel integrity critical data.
ima_tcb [IMA] Deprecated. Use ima_policy= instead. Load a policy which meets the needs of the Trusted Computing Base. This means IMA will measure all programs exec'd, files mmap'd for exec, and all files opened for read by uid=0.
ima_template= [IMA] Select one of defined IMA measurements template formats. Formats: { "ima" | "ima-ng" | "ima-ngv2" | "ima-sig" | "ima-sigv2" } Default: "ima-ng"
ima_template_fmt= [IMA] Define a custom template format. Format: { "field1|...|fieldN" }
ima= [IMA] Enable or disable IMA Format: { "off" | "on" } Default: "on" Note that disabling IMA is limited to kdump kernel.
indirect_target_selection= [X86,Intel] Mitigation control for Indirect Target Selection(ITS) bug in Intel CPUs. Updated microcode is also required for a fix in IBPB.
on: Enable mitigation (default). off: Disable mitigation. force: Force the ITS bug and deploy default mitigation. vmexit: Only deploy mitigation if CPU is affected by guest/host isolation part of ITS. stuff: Deploy RSB-fill mitigation when retpoline is also deployed. Otherwise, deploy the default mitigation.
For details see: Documentation/admin-guide/hw-vuln/indirect-target-selection.rst
init= [KNL] Format: <full_path> Run specified binary instead of /sbin/init as init process.
initcall_debug [KNL] Trace initcalls as they are executed. Useful for working out where the kernel is dying during startup.
initcall_blacklist= [KNL] Do not execute a comma-separated list of initcall functions. Useful for debugging built-in modules and initcalls.
initramfs_async= [KNL] Format: <bool> Default: 1 This parameter controls whether the initramfs image is unpacked asynchronously, concurrently with devices being probed and initialized. This should normally just work, but as a debugging aid, one can get the historical behaviour of the initramfs unpacking being completed before device_ and late_ initcalls.
initrd= [BOOT,EARLY] Specify the location of the initial ramdisk
initrdmem= [KNL,EARLY] Specify a physical address and size from which to load the initrd. If an initrd is compiled in or specified in the bootparams, it takes priority over this setting. Format: ss[KMG],nn[KMG] Default is 0, 0
init_on_alloc= [MM,EARLY] Fill newly allocated pages and heap objects with zeroes. Format: 0 | 1 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
init_on_free= [MM,EARLY] Fill freed pages and heap objects with zeroes. Format: 0 | 1 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.
init_pkru= [X86] Specify the default memory protection keys rights register contents for all processes. 0x55555554 by default (disallow access to all but pkey 0). Can override in debugfs after boot.
inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver Format: <irq>
int_pln_enable [X86] Enable power limit notification interrupt
integrity_audit=[IMA] Format: { "0" | "1" } 0 -- basic integrity auditing messages. (Default) 1 -- additional integrity auditing messages.
intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option on Enable intel iommu driver. off Disable intel iommu driver. igfx_off [Default Off] By default, gfx is mapped as normal device. If a gfx device has a dedicated DMAR unit, the DMAR unit is bypassed by not enabling DMAR with this option. In this case, gfx device will use physical address for DMA. strict [Default Off] Deprecated, equivalent to iommu.strict=1. sp_off [Default Off] By default, super page will be supported if Intel IOMMU has the capability. With this option, super page will not be supported. sm_on Enable the Intel IOMMU scalable mode if the hardware advertises that it has support for the scalable mode translation. sm_off Disallow use of the Intel IOMMU scalable mode. tboot_noforce [Default Off] Do not force the Intel IOMMU enabled under tboot. By default, tboot will force Intel IOMMU on, which could harm performance of some high-throughput devices like 40GBit network cards, even if identity mapping is enabled. Note that using this option lowers the security provided by tboot because it makes the system vulnerable to DMA attacks.
intel_idle.max_cstate= [KNL,HW,ACPI,X86] 0 disables intel_idle and fall back on acpi_idle. 1 to 9 specify maximum depth of C-state.
intel_pstate= [X86,EARLY] disable Do not enable intel_pstate as the default scaling driver for the supported processors active Use intel_pstate driver to bypass the scaling governors layer of cpufreq and provides it own algorithms for p-state selection. There are two P-state selection algorithms provided by intel_pstate in the active mode: powersave and performance. The way they both operate depends on whether or not the hardware managed P-states (HWP) feature has been enabled in the processor and possibly on the processor model. passive Use intel_pstate as a scaling driver, but configure it to work with generic cpufreq governors (instead of enabling its internal governor). This mode cannot be used along with the hardware-managed P-states (HWP) feature. force Enable intel_pstate on systems that prohibit it by default in favor of acpi-cpufreq. Forcing the intel_pstate driver instead of acpi-cpufreq may disable platform features, such as thermal controls and power capping, that rely on ACPI P-States information being indicated to OSPM and therefore should be used with caution. This option does not work with processors that aren't supported by the intel_pstate driver or on platforms that use pcc-cpufreq instead of acpi-cpufreq. no_hwp Do not enable hardware P state control (HWP) if available. hwp_only Only load intel_pstate on systems which support hardware P state control (HWP) if available. support_acpi_ppc Enforce ACPI _PPC performance limits. If the Fixed ACPI Description Table, specifies preferred power management profile as "Enterprise Server" or "Performance Server", then this feature is turned on by default. per_cpu_perf_limits Allow per-logical-CPU P-State performance control limits using cpufreq sysfs interface no_cas Do not enable capacity-aware scheduling (CAS) on hybrid systems
intremap= [X86-64,Intel-IOMMU,EARLY] on enable Interrupt Remapping (default) off disable Interrupt Remapping nosid disable Source ID checking no_x2apic_optout BIOS x2APIC opt-out request will be ignored nopost disable Interrupt Posting posted_msi enable MSIs delivered as posted interrupts
iomem= Disable strict checking of access to MMIO memory strict regions from userspace. relaxed
iommu= [X86,EARLY]
off Don't initialize and use any kind of IOMMU.
force Force the use of the hardware IOMMU even when it is not actually needed (e.g. because < 3 GB memory).
noforce Don't force hardware IOMMU usage when it is not needed. (default).
merge Do scatter-gather (SG) merging. Implies "force" (experimental).
nomerge Don't do scatter-gather (SG) merging.
biomerge Do scatter-gather (SG) merging. Implies "force" (experimental). [same as "merge"]
panic Always panic when IOMMU overflows.
nopanic Don't panic on IOMMU overflows.
pt Use passththrough mode by default (Equivalent to iommu.passthrough=1)
nopt Use translated mode for DMA by default (Equivalent to iommu.passthrough=0)
soft Use software bounce buffering (SWIOTLB) (default for Intel machines). This can be used to prevent the usage of an available hardware IOMMU.
usedac Use the DAC on VIA PCI bridge (default: disable the VIA PCI bridge DAC)
AMD Gart HW IOMMU-specific options: (CONFIG_GART_IOMMU)
<size> Set the size of the remapping area in bytes.
allowed Overwrite iommu off workarounds for specific chipsets
force Overwrite iommu off workarounds for specific chipsets
fullflush Flush IOMMU on each allocation (default).
nofullflush Don't use IOMMU fullflush.
memaper[=<order>] Allocate an own aperture over RAM with size 32MB<<order. (default: order=1, i.e. 64MB)
noaperture Ask the IOMMU not to touch the aperture for AGP.
noagp Don't initialize the AGP driver and use full aperture.
iommu= [PPC/POWERNV]
nobypass Disable IOMMU bypass, using IOMMU for PCI devices.
iommu.forcedac= [ARM64,X86,EARLY] Control IOVA allocation for PCI devices. Format: { "0" | "1" } 0 - Try to allocate a 32-bit DMA address first, before falling back to the full range if needed. 1 - Allocate directly from the full usable range, forcing Dual Address Cycle for PCI cards supporting greater than 32-bit addressing.
iommu.strict= [ARM64,X86,S390,EARLY] Configure TLB invalidation behaviour Format: { "0" | "1" } 0 - Lazy mode. Request that DMA unmap operations use deferred invalidation of hardware TLBs, for increased throughput at the cost of reduced device isolation. Will fall back to strict mode if not supported by the relevant IOMMU driver. 1 - Strict mode. DMA unmap operations invalidate IOMMU hardware TLBs synchronously. unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}. Note: on x86, strict mode specified via one of the legacy driver-specific options takes precedence.
iommu.passthrough= [ARM64,X86,EARLY] Configure DMA to bypass the IOMMU by default. Format: { "0" | "1" } 0 - Use IOMMU translation for DMA. 1 - Bypass the IOMMU for DMA. unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
iommu.debug_pagealloc= [KNL,EARLY] When CONFIG_IOMMU_DEBUG_PAGEALLOC is set, this parameter enables the feature at boot time. By default, it is disabled and the system behaves the same way as a kernel built without CONFIG_IOMMU_DEBUG_PAGEALLOC. Format: { "0" | "1" } 0 - Sanitizer disabled. 1 - Sanitizer enabled, expect runtime overhead.
io7= [HW] IO7 for Marvel-based Alpha systems See comment before marvel_specify_io7 in arch/alpha/kernel/core_marvel.c.
io_delay= [X86,EARLY] I/O delay method 0x80 Standard port 0x80 based delay 0xed Alternate port 0xed based delay (needed on some systems) udelay Simple two microseconds delay none No delay
ip= [IP_PNP] See Documentation/admin-guide/nfs/nfsroot.rst.
ipcmni_extend [KNL,EARLY] Extend the maximum number of unique System V IPC identifiers from 32,768 to 16,777,216.
ipe.enforce= [IPE] Format: <bool> Determine whether IPE starts in permissive (0) or enforce (1) mode. The default is enforce.
ipe.success_audit= [IPE] Format: <bool> Start IPE with success auditing enabled, emitting an audit event when a binary is allowed. The default is 0.
irqaffinity= [SMP] Set the default irq affinity mask The argument is a cpu list, as described above.
irqchip.gicv2_force_probe= [ARM,ARM64,EARLY] Format: <bool> Force the kernel to look for the second 4kB page of a GICv2 controller even if the memory range exposed by the device tree is too small.
irqchip.gicv3_nolpi= [ARM,ARM64,EARLY] Force the kernel to ignore the availability of LPIs (and by consequence ITSs). Intended for system that use the kernel as a bootloader, and thus want to let secondary kernels in charge of setting up LPIs.
irqchip.gicv3_pseudo_nmi= [ARM64,EARLY] Enables support for pseudo-NMIs in the kernel. This requires the kernel to be built with CONFIG_ARM64_PSEUDO_NMI.
irqchip.riscv_imsic_noipi [RISC-V,EARLY] Force the kernel to not use IMSIC software injected MSIs as IPIs. Intended for system where IMSIC is trap-n-emulated, and thus want to reduce MMIO traps when triggering IPIs to multiple harts.
irqfixup [HW] When an interrupt is not handled search all handlers for it. Intended to get systems with badly broken firmware running.
irqhandler.duration_warn_us= [KNL] Warn if an IRQ handler exceeds the specified duration threshold in microseconds. Useful for identifying long-running IRQs in the system.
irqpoll [HW] When an interrupt is not handled search all handlers for it. Also check all handlers each timer interrupt. Intended to get systems with badly broken firmware running.
isapnp= [ISAPNP] Format: <RDP>,<reset>,<pci_scan>,<verbosity>
isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. Format: [flag-list,]<cpu-list>
Specify one or more CPUs to isolate from disturbances specified in the flag list (default: domain):
nohz Disable the tick when a single task runs as well as disabling other kernel noises like having RCU callbacks offloaded. This is equivalent to the nohz_full parameter.
A residual 1Hz tick is offloaded to workqueues, which you need to affine to housekeeping through the global workqueue's affinity configured via the /sys/devices/virtual/workqueue/cpumask sysfs file, or by using the 'domain' flag described below.
NOTE: by default the global workqueue runs on all CPUs, so to protect individual CPUs the 'cpumask' file has to be configured manually after bootup.
domain Isolate from the general SMP balancing and scheduling algorithms. Note that performing domain isolation this way is irreversible: it's not possible to bring back a CPU to the domains once isolated through this boot time configuration. Use cpusets for a dynamic configuration which can be altered at runtime. For details see Documentation/admin-guide/cpu-isolation.rst.
You can move a process onto or off an "isolated" CPU via the CPU affinity syscalls or cpuset. <cpu number> begins at 0 and the maximum value is "number of CPUs in system - 1".
managed_irq
Isolate from being targeted by managed interrupts which have an interrupt mask containing isolated CPUs. The affinity of managed interrupts is handled by the kernel and cannot be changed via the /proc/irq/* interfaces.
This isolation is best effort and only effective if the automatically assigned interrupt mask of a device queue contains isolated and housekeeping CPUs. If housekeeping CPUs are online then such interrupts are directed to the housekeeping CPU so that IO submitted on the housekeeping CPU cannot disturb the isolated CPU.
If a queue's affinity mask contains only isolated CPUs then this parameter has no effect on the interrupt routing decision, though interrupts are only delivered when tasks running on those isolated CPUs submit IO. IO submitted on housekeeping CPUs has no influence on those queues.
The format of <cpu-list> is described above.
iucv= [HW,NET]
ivrs_ioapic [HW,X86-64] Provide an override to the IOAPIC-ID<->DEVICE-ID mapping provided in the IVRS ACPI table. By default, PCI segment is 0, and can be omitted.
For example, to map IOAPIC-ID decimal 10 to PCI segment 0x1 and PCI device 00:14.0, write the parameter as: ivrs_ioapic=10@0001:00:14.0
Deprecated formats: * To map IOAPIC-ID decimal 10 to PCI device 00:14.0 write the parameter as: ivrs_ioapic[10]=00:14.0 * To map IOAPIC-ID decimal 10 to PCI segment 0x1 and PCI device 00:14.0 write the parameter as: ivrs_ioapic[10]=0001:00:14.0
ivrs_hpet [HW,X86-64] Provide an override to the HPET-ID<->DEVICE-ID mapping provided in the IVRS ACPI table. By default, PCI segment is 0, and can be omitted.
For example, to map HPET-ID decimal 10 to PCI segment 0x1 and PCI device 00:14.0, write the parameter as: ivrs_hpet=10@0001:00:14.0
Deprecated formats: * To map HPET-ID decimal 0 to PCI device 00:14.0 write the parameter as: ivrs_hpet[0]=00:14.0 * To map HPET-ID decimal 10 to PCI segment 0x1 and PCI device 00:14.0 write the parameter as: ivrs_ioapic[10]=0001:00:14.0
ivrs_acpihid [HW,X86-64] Provide an override to the ACPI-HID:UID<->DEVICE-ID mapping provided in the IVRS ACPI table. By default, PCI segment is 0, and can be omitted.
For example, to map UART-HID:UID AMD0020:0 to PCI segment 0x1 and PCI device ID 00:14.5, write the parameter as: ivrs_acpihid=AMD0020:0@0001:00:14.5
Deprecated formats: * To map UART-HID:UID AMD0020:0 to PCI segment is 0, PCI device ID 00:14.5, write the parameter as: ivrs_acpihid[00:14.5]=AMD0020:0 * To map UART-HID:UID AMD0020:0 to PCI segment 0x1 and PCI device ID 00:14.5, write the parameter as: ivrs_acpihid[0001:00:14.5]=AMD0020:0
js= [HW,JOY] Analog joystick See Documentation/input/joydev/joystick.rst.
kasan_multi_shot [KNL] Enforce KASAN (Kernel Address Sanitizer) to print report on every invalid memory access. Without this parameter KASAN will print report only for the first invalid access.
keep_bootcon [KNL,EARLY] Do not unregister boot console at start. This is only useful for debugging when something happens in the window between unregistering the boot console and initializing the real console.
keepinitrd [HW,ARM] See retain_initrd.
kernelcore= [KNL,X86,PPC,EARLY] Format: nn[KMGTPE] | nn% | "mirror" This parameter specifies the amount of memory usable by the kernel for non-movable allocations. The requested amount is spread evenly throughout all nodes in the system as ZONE_NORMAL. The remaining memory is used for movable memory in its own zone, ZONE_MOVABLE. In the event, a node is too small to have both ZONE_NORMAL and ZONE_MOVABLE, kernelcore memory will take priority and other nodes will have a larger ZONE_MOVABLE.
ZONE_MOVABLE is used for the allocation of pages that may be reclaimed or moved by the page migration subsystem. Note that allocations like PTEs-from-HighMem still use the HighMem zone if it exists, and the Normal zone if it does not.
It is possible to specify the exact amount of memory in the form of "nn[KMGTPE]", a percentage of total system memory in the form of "nn%", or "mirror". If "mirror" option is specified, mirrored (reliable) memory is used for non-movable allocations and remaining memory is used for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" are exclusive, so you cannot specify multiple forms.
kfence.burst= [MM,KFENCE] The number of additional successive allocations to be attempted through KFENCE for each sample interval. Format: <unsigned integer> Default: 0
kfence.check_on_panic= [MM,KFENCE] Whether to check all KFENCE-managed objects' canaries on panic. Format: <bool> Default: false
kfence.deferrable= [MM,KFENCE] Whether to use a deferrable timer to trigger allocations. This avoids forcing CPU wake-ups if the system is idle, at the risk of a less predictable sample interval. Format: <bool> Default: CONFIG_KFENCE_DEFERRABLE
kfence.fault= [MM,KFENCE] Controls the behavior when a KFENCE error is detected. report - print the error report and continue (default). oops - print the error report and oops. panic - print the error report and panic.
kfence.sample_interval= [MM,KFENCE] KFENCE's sample interval in milliseconds. Format: <unsigned integer> 0 - Disable KFENCE. >0 - Enabled KFENCE with given sample interval. Default: CONFIG_KFENCE_SAMPLE_INTERVAL
kfence.skip_covered_thresh= [MM,KFENCE] If pool utilization reaches this threshold (pool usage%), KFENCE limits currently covered allocations of the same source from further filling up the pool. Format: <unsigned integer> Default: 75
kgdbdbgp= [KGDB,HW,EARLY] kgdb over EHCI usb debug port. Format: <Controller#>[,poll interval] The controller # is the number of the ehci usb debug port as it is probed via PCI. The poll interval is optional and is the number seconds in between each poll cycle to the debug port in case you need the functionality for interrupting the kernel with gdb or control-c on the dbgp connection. When not using this parameter you use sysrq-g to break into the kernel debugger.
kgdboc= [KGDB,HW] kgdb over consoles. Requires a tty driver that supports console polling, or a supported polling keyboard driver (non-usb). Serial only format: <serial_device>[,baud] keyboard only format: kbd keyboard and serial format: kbd,<serial_device>[,baud] Optional Kernel mode setting: kms, kbd format: kms,kbd kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
kgdboc_earlycon= [KGDB,HW,EARLY] If the boot console provides the ability to read characters and can work in polling mode, you can use this parameter to tell kgdb to use it as a backend until the normal console is registered. Intended to be used together with the kgdboc parameter which specifies the normal console to transition to.
The name of the early console should be specified as the value of this parameter. Note that the name of the early console might be different than the tty name passed to kgdboc. It's OK to leave the value blank and the first boot console that implements read() will be picked.
kgdbwait [KGDB,EARLY] Stop kernel execution and enter the kernel debugger at the earliest opportunity.
kho= [KEXEC,EARLY] Format: { "0" | "1" | "off" | "on" | "y" | "n" } Enables or disables Kexec HandOver. "0" | "off" | "n" - kexec handover is disabled "1" | "on" | "y" - kexec handover is enabled
kho_scratch= [KEXEC,EARLY] Format: ll[KMG],mm[KMG],nn[KMG] | nn% Defines the size of the KHO scratch region. The KHO scratch regions are physically contiguous memory ranges that can only be used for non-kernel allocations. That way, even when memory is heavily fragmented with handed over memory, the kexeced kernel will always have enough contiguous ranges to bootstrap itself.
It is possible to specify the exact amount of memory in the form of "ll[KMG],mm[KMG],nn[KMG]" where the first parameter defines the size of a low memory scratch area, the second parameter defines the size of a global scratch area and the third parameter defines the size of additional per-node scratch areas. The form "nn%" defines scale factor (in percents) of memory that was used during boot.
kmac= [MIPS] Korina ethernet MAC address. Configure the RouterBoard 532 series on-chip Ethernet adapter MAC address.
kmemleak= [KNL,EARLY] Boot-time kmemleak enable/disable Valid arguments: on, off Default: on Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, the default is off.
kprobe_event=[probe-list] [FTRACE] Add kprobe events and enable at boot time. The probe-list is a semicolon delimited list of probe definitions. Each definition is same as kprobe_events interface, but the parameters are comma delimited. For example, to add a kprobe event on vfs_read with arg1 and arg2, add to the command line;
kprobe_event=p,vfs_read,$arg1,$arg2
See also Documentation/trace/kprobetrace.rst "Kernel Boot Parameter" section.
kpti= [ARM64,EARLY] Control page table isolation of user and kernel address spaces. Default: enabled on cores which need mitigation. 0: force disabled 1: force enabled
kunit.enable= [KUNIT] Enable executing KUnit tests. Requires CONFIG_KUNIT to be set to be fully enabled. The default value can be overridden via KUNIT_DEFAULT_ENABLED. Default is 1 (enabled)
kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. Default is 0 (don't ignore, but inject #GP)
kvm.eager_page_split= [KVM,X86] Controls whether or not KVM will try to proactively split all huge pages during dirty logging. Eager page splitting reduces interruptions to vCPU execution by eliminating the write-protection faults and MMU lock contention that would otherwise be required to split huge pages lazily.
VM workloads that rarely perform writes or that write only to a small region of VM memory may benefit from disabling eager page splitting to allow huge pages to still be used for reads.
The behavior of eager page splitting depends on whether KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If disabled, all huge pages in a memslot will be eagerly split when dirty logging is enabled on that memslot. If enabled, eager page splitting will be performed during the KVM_CLEAR_DIRTY ioctl, and only for the pages being cleared.
Eager page splitting is only supported when kvm.tdp_mmu=Y.
Default is Y (on).
kvm.enable_pmu=[KVM,X86] If enabled, KVM will virtualize PMU functionality based on the virtual CPU model defined by userspace. This can be overridden on a per-VM basis via KVM_CAP_PMU_CAPABILITY.
If disabled, KVM will not virtualize PMU functionality, e.g. MSRs, PMCs, PMIs, etc., even if userspace defines a virtual CPU model that contains PMU assets.
Note, KVM's vPMU support implicitly requires running with an in-kernel local APIC, e.g. to deliver PMIs to the guest. Running without an in-kernel local APIC is not supported, though KVM will allow such a combination (with severely degraded functionality).
See also enable_mediated_pmu.
Default is Y (on).
kvm.enable_virt_at_load=[KVM,ARM64,LOONGARCH,MIPS,RISCV,X86] If enabled, KVM will enable virtualization in hardware when KVM is loaded, and disable virtualization when KVM is unloaded (if KVM is built as a module).
If disabled, KVM will dynamically enable and disable virtualization on-demand when creating and destroying VMs, i.e. on the 0=>1 and 1=>0 transitions of the number of VMs.
Enabling virtualization at module load avoids potential latency for creation of the 0=>1 VM, as KVM serializes virtualization enabling across all online CPUs. The "cost" of enabling virtualization when KVM is loaded, is that doing so may interfere with using out-of-tree hypervisors that want to "own" virtualization hardware.
kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. Default is false (don't support).
kvm.nx_huge_pages= [KVM] Controls the software workaround for the X86_BUG_ITLB_MULTIHIT bug. force : Always deploy workaround. off : Never deploy workaround. auto : Deploy workaround based on the presence of X86_BUG_ITLB_MULTIHIT.
Default is 'auto'.
If the software workaround is enabled for the host, guests do need not to enable it for nested guests.
kvm.nx_huge_pages_recovery_ratio= [KVM] Controls how many 4KiB pages are periodically zapped back to huge pages. 0 disables the recovery, otherwise if the value is N KVM will zap 1/Nth of the 4KiB pages every period (see below). The default is 60.
kvm.nx_huge_pages_recovery_period_ms= [KVM] Controls the time period at which KVM zaps 4KiB pages back to huge pages. If the value is a non-zero N, KVM will zap a portion (see ratio above) of the pages every N msecs. If the value is 0 (the default), KVM will pick a period based on the ratio, such that a page is zapped after 1 hour on average.
kvm-{amd,intel}.enable_mediated_pmu=[KVM,AMD,INTEL] If enabled, KVM will provide a mediated virtual PMU, instead of the default perf-based virtual PMU (if kvm.enable_pmu is true and PMU is enumerated via the virtual CPU model).
With a perf-based vPMU, KVM operates as a user of perf, i.e. emulates guest PMU counters using perf events. KVM-created perf events are managed by perf as regular (guest-only) events, e.g. are scheduled in/out, contend for hardware resources, etc. Using a perf-based vPMU allows guest and host usage of the PMU to co-exist, but incurs non-trivial overhead and can result in silently dropped guest events (due to resource contention).
With a mediated vPMU, hardware PMU state is context switched around the world switch to/from the guest. KVM mediates which events the guest can utilize, but gives the guest direct access to all other PMU assets when possible (KVM may intercept some accesses if the virtual CPU model provides a subset of hardware PMU functionality). Using a mediated vPMU significantly reduces PMU virtualization overhead and eliminates lost guest events, but is mutually exclusive with using perf to profile KVM guests and adds latency to most VM-Exits (to context switch PMU state).
Default is N (off).
kvm-amd.nested= [KVM,AMD] Control nested virtualization feature in KVM/SVM. Default is 1 (enabled).
kvm-amd.npt= [KVM,AMD] Control KVM's use of Nested Page Tables, a.k.a. Two-Dimensional Page Tables. Default is 1 (enabled). Disable by KVM if hardware lacks support for NPT.
kvm-amd.ciphertext_hiding_asids= [KVM,AMD] Ciphertext hiding prevents disallowed accesses to SNP private memory from reading ciphertext. Instead, reads will see constant default values (0xff).
If ciphertext hiding is enabled, the joint SEV-ES and SEV-SNP ASID space is partitioned into separate SEV-ES and SEV-SNP ASID ranges, with the SEV-SNP range being [1..max_snp_asid] and the SEV-ES range being (max_snp_asid..min_sev_asid), where min_sev_asid is enumerated by CPUID.0x.8000_001F[EDX].
A non-zero value enables SEV-SNP ciphertext hiding and adjusts the ASID ranges for SEV-ES and SEV-SNP guests. KVM caps the number of SEV-SNP ASIDs at the maximum possible value, e.g. specifying -1u will assign all joint SEV-ES and SEV-SNP ASIDs to SEV-SNP. Note, assigning all joint ASIDs to SEV-SNP, i.e. configuring max_snp_asid == min_sev_asid-1, will effectively make SEV-ES unusable.
kvm-arm.mode= [KVM,ARM,EARLY] Select one of KVM/arm64's modes of operation.
none: Forcefully disable KVM.
nvhe: Standard nVHE-based mode, without support for protected guests.
protected: Mode with support for guests whose state is kept private from the host, using VHE or nVHE depending on HW support.
nested: VHE-based mode with support for nested virtualization. Requires at least ARMv8.4 hardware (with FEAT_NV2).
Defaults to VHE/nVHE based on hardware support. Setting mode to "protected" will disable kexec and hibernation for the host. To force nVHE on VHE hardware, add "arm64_sw.hvhe=0 id_aa64mmfr1.vh=0" to the command-line. "nested" and "protected" are experimental and should be used with extreme caution.
kvm-arm.vgic_v3_group0_trap= [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-0 system registers
kvm-arm.vgic_v3_group1_trap= [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-1 system registers
kvm-arm.vgic_v3_common_trap= [KVM,ARM,EARLY] Trap guest accesses to GICv3 common system registers
kvm-arm.vgic_v4_enable= [KVM,ARM,EARLY] Allow use of GICv4 for direct injection of LPIs.
kvm-arm.wfe_trap_policy= [KVM,ARM] Control when to set WFE instruction trap for KVM VMs. Traps are allowed but not guaranteed by the CPU architecture.
trap: set WFE instruction trap
notrap: clear WFE instruction trap
kvm-arm.wfi_trap_policy= [KVM,ARM] Control when to set WFI instruction trap for KVM VMs. Traps are allowed but not guaranteed by the CPU architecture.
trap: set WFI instruction trap
notrap: clear WFI instruction trap
kvm_cma_resv_ratio=n [PPC,EARLY] Reserves given percentage from system memory area for contiguous memory allocation for KVM hash pagetable allocation. By default it reserves 5% of total system memory. Format: <integer> Default: 5
kvm-intel.ept= [KVM,Intel] Control KVM's use of Extended Page Tables, a.k.a. Two-Dimensional Page Tables. Default is 1 (enabled). Disable by KVM if hardware lacks support for EPT.
kvm-intel.emulate_invalid_guest_state= [KVM,Intel] Control whether to emulate invalid guest state. Ignored if kvm-intel.enable_unrestricted_guest=1, as guest state is never invalid for unrestricted guests. This param doesn't apply to nested guests (L2), as KVM never emulates invalid L2 guest state. Default is 1 (enabled).
kvm-intel.flexpriority= [KVM,Intel] Control KVM's use of FlexPriority feature (TPR shadow). Default is 1 (enabled). Disable by KVM if hardware lacks support for it.
kvm-intel.nested= [KVM,Intel] Control nested virtualization feature in KVM/VMX. Default is 1 (enabled).
kvm-intel.unrestricted_guest= [KVM,Intel] Control KVM's use of unrestricted guest feature (virtualized real and unpaged mode). Default is 1 (enabled). Disable by KVM if EPT is disabled or hardware lacks support for it.
kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault CVE-2018-3620.
Valid arguments: never, cond, always
always: L1D cache flush on every VMENTER. cond: Flush L1D on VMENTER only when the code between VMEXIT and VMENTER can leak host memory. never: Disables the mitigation
Default is cond (do L1 cache flush in specific instances)
kvm-intel.vpid= [KVM,Intel] Control KVM's use of Virtual Processor Identification feature (tagged TLBs). Default is 1 (enabled). Disable by KVM if hardware lacks support for it.
l1d_flush= [X86,INTEL,EARLY] Control mitigation for L1D based snooping vulnerability.
Certain CPUs are vulnerable to an exploit against CPU internal buffers which can forward information to a disclosure gadget under certain conditions.
In vulnerable processors, the speculatively forwarded data can be used in a cache side channel attack, to access data to which the attacker does not have direct access.
This parameter controls the mitigation. The options are:
on - enable the interface for the mitigation
l1tf= [X86,EARLY] Control mitigation of the L1TF vulnerability on affected CPUs
The kernel PTE inversion protection is unconditionally enabled and cannot be disabled.
full Provides all available mitigations for the L1TF vulnerability. Disables SMT and enables all mitigations in the hypervisors, i.e. unconditional L1D flush.
SMT control and L1D flush control via the sysfs interface is still possible after boot. Hypervisors will issue a warning when the first VM is started in a potentially insecure configuration, i.e. SMT enabled or L1D flush disabled.
full,force Same as 'full', but disables SMT and L1D flush runtime control. Implies the 'nosmt=force' command line option. (i.e. sysfs control of SMT is disabled.)
flush Leaves SMT enabled and enables the default hypervisor mitigation, i.e. conditional L1D flush.
SMT control and L1D flush control via the sysfs interface is still possible after boot. Hypervisors will issue a warning when the first VM is started in a potentially insecure configuration, i.e. SMT enabled or L1D flush disabled.
flush,nosmt
Disables SMT and enables the default hypervisor mitigation.
SMT control and L1D flush control via the sysfs interface is still possible after boot. Hypervisors will issue a warning when the first VM is started in a potentially insecure configuration, i.e. SMT enabled or L1D flush disabled.
flush,nowarn Same as 'flush', but hypervisors will not warn when a VM is started in a potentially insecure configuration.
off Disables hypervisor mitigations and doesn't emit any warnings. It also drops the swap size and available RAM limit restriction on both hypervisor and bare metal.
Default is 'flush'.
For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
l2cr= [PPC]
l3cr= [PPC]
lapic [X86-32,APIC,EARLY] Enable the local APIC even if BIOS disabled it.
lapic= [X86,APIC] Do not use TSC deadline value for LAPIC timer one-shot implementation. Default back to the programmable timer unit in the LAPIC. Format: notscdeadline
lapic_timer_c2_ok [X86,APIC,EARLY] trust the local apic timer in C2 power state.
libata.dma= [LIBATA] DMA control libata.dma=0 Disable all PATA and SATA DMA libata.dma=1 PATA and SATA Disk DMA only libata.dma=2 ATAPI (CDROM) DMA only libata.dma=4 Compact Flash DMA only Combinations also work, so libata.dma=3 enables DMA for disks and CDROMs, but not CFs.
libata.ignore_hpa= [LIBATA] Ignore HPA limit libata.ignore_hpa=0 keep BIOS limits (default) libata.ignore_hpa=1 ignore limits, using full disk
libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume when set. Format: <int>
libata.force= [LIBATA] Force configurations. The format is a comma- separated list of "[ID:]VAL" where ID is PORT[.DEVICE]. PORT and DEVICE are decimal numbers matching port, link or device. Basically, it matches the ATA ID string printed on console by libata. If the whole ID part is omitted, the last PORT and DEVICE values are used. If ID hasn't been specified yet, the configuration applies to all ports, links and devices.
If only DEVICE is omitted, the parameter applies to the port and all links and devices behind it. DEVICE number of 0 either selects the first device or the first fan-out link behind PMP device. It does not select the host link. DEVICE number of 15 selects the host link and device attached to it.
The VAL specifies the configuration to force. As long as there is no ambiguity, shortcut notation is allowed. For example, both 1.5 and 1.5G would work for 1.5Gbps. The following configurations can be forced.
* Cable type: 40c, 80c, short40c, unk, ign or sata. Any ID with matching PORT is used.
* SATA link speed limit: 1.5Gbps or 3.0Gbps.
* Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. udma[/][16,25,33,44,66,100,133] notation is also allowed.
* nohrst, nosrst, norst: suppress hard, soft and both resets.
* rstonce: only attempt one reset during hot-unplug link recovery.
* [no]dbdelay: Enable or disable the extra 200ms delay before debouncing a link PHY and device presence detection.
* [no]ncq: Turn on or off NCQ.
* [no]ncqtrim: Enable or disable queued DSM TRIM.
* [no]ncqati: Enable or disable NCQ trim on ATI chipset.
* [no]trim: Enable or disable (unqueued) TRIM.
* trim_zero: Indicate that TRIM command zeroes data.
* max_trim_128m: Set 128M maximum trim size limit.
* [no]dma: Turn on or off DMA transfers.
* atapi_dmadir: Enable ATAPI DMADIR bridge support.
* atapi_mod16_dma: Enable the use of ATAPI DMA for commands that are not a multiple of 16 bytes.
* [no]dmalog: Enable or disable the use of the READ LOG DMA EXT command to access logs.
* [no]iddevlog: Enable or disable access to the identify device data log.
* [no]logdir: Enable or disable access to the general purpose log directory.
* max_sec=<sectors>: Set the transfer size limit, in number of 512-byte sectors, to the value specified in <sectors>. The value specified in <sectors> has to be a non-zero positive integer.
* max_sec_128: Set transfer size limit to 128 sectors.
* max_sec_1024: Set or clear transfer size limit to 1024 sectors.
* max_sec_lba48: Set or clear transfer size limit to 65535 sectors.
* external: Mark port as external (hotplug-capable).
* [no]lpm: Enable or disable link power management.
* [no]setxfer: Indicate if transfer speed mode setting should be skipped.
* [no]fua: Disable or enable FUA (Force Unit Access) support for devices supporting this feature.
* dump_id: Dump IDENTIFY data.
* disable: Disable this device.
If there are multiple matching configurations changing the same attribute, the last one is used.
liveupdate= [KNL,EARLY] Format: <bool> Enable Live Update Orchestrator (LUO). Default: off.
lockd.nlm_grace_period=P [NFS] Assign grace period. Format: <integer>
lockd.nlm_tcpport=N [NFS] Assign TCP port. Format: <integer>
lockd.nlm_timeout=T [NFS] Assign timeout value. Format: <integer>
lockd.nlm_udpport=M [NFS] Assign UDP port. Format: <integer>
lockdown= [SECURITY,EARLY] { integrity | confidentiality } Enable the kernel lockdown feature. If set to integrity, kernel features that allow userland to modify the running kernel are disabled. If set to confidentiality, kernel features that allow userland to extract confidential information from the kernel are also disabled.
locktorture.acq_writer_lim= [KNL] Set the time limit in jiffies for a lock acquisition. Acquisitions exceeding this limit will result in a splat once they do complete.
locktorture.bind_readers= [KNL] Specify the list of CPUs to which the readers are to be bound.
locktorture.bind_writers= [KNL] Specify the list of CPUs to which the writers are to be bound.
locktorture.call_rcu_chains= [KNL] Specify the number of self-propagating call_rcu() chains to set up. These are used to ensure that there is a high probability of an RCU grace period in progress at any given time. Defaults to 0, which disables these call_rcu() chains.
locktorture.long_hold= [KNL] Specify the duration in milliseconds for the occasional long-duration lock hold time. Defaults to 100 milliseconds. Select 0 to disable.
locktorture.nested_locks= [KNL] Specify the maximum lock nesting depth that locktorture is to exercise, up to a limit of 8 (MAX_NESTED_LOCKS). Specify zero to disable. Note that this parameter is ineffective on types of locks that do not support nested acquisition.
locktorture.nreaders_stress= [KNL] Set the number of locking read-acquisition kthreads. Defaults to being automatically set based on the number of online CPUs.
locktorture.nwriters_stress= [KNL] Set the number of locking write-acquisition kthreads.
locktorture.onoff_holdoff= [KNL] Set time (s) after boot for CPU-hotplug testing.
locktorture.onoff_interval= [KNL] Set time (s) between CPU-hotplug operations, or zero to disable CPU-hotplug testing.
locktorture.rt_boost= [KNL] Do periodic testing of real-time lock priority boosting. Select 0 to disable, 1 to boost only rt_mutex, and 2 to boost unconditionally. Defaults to 2, which might seem to be an odd choice, but which should be harmless for non-real-time spinlocks, due to their disabling of preemption. Note that non-realtime mutexes disable boosting.
locktorture.rt_boost_factor= [KNL] Number that determines how often and for how long priority boosting is exercised. This is scaled down by the number of writers, so that the number of boosts per unit time remains roughly constant as the number of writers increases. On the other hand, the duration of each boost increases with the number of writers.
locktorture.shuffle_interval= [KNL] Set task-shuffle interval (jiffies). Shuffling tasks allows some CPUs to go into dyntick-idle mode during the locktorture test.
locktorture.shutdown_secs= [KNL] Set time (s) after boot system shutdown. This is useful for hands-off automated testing.
locktorture.stat_interval= [KNL] Time (s) between statistics printk()s.
locktorture.stutter= [KNL] Time (s) to stutter testing, for example, specifying five seconds causes the test to run for five seconds, wait for five seconds, and so on. This tests the locking primitive's ability to transition abruptly to and from idle.
locktorture.torture_type= [KNL] Specify the locking implementation to test.
locktorture.verbose= [KNL] Enable additional printk() statements.
locktorture.writer_fifo= [KNL] Run the write-side locktorture kthreads at sched_set_fifo() real-time priority.
logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver Format: <irq>
loglevel= [KNL,EARLY] All Kernel Messages with a loglevel smaller than the console loglevel will be printed to the console. It can also be changed with klogd or other programs. The loglevels are defined as follows:
0 (KERN_EMERG) system is unusable 1 (KERN_ALERT) action must be taken immediately 2 (KERN_CRIT) critical conditions 3 (KERN_ERR) error conditions 4 (KERN_WARNING) warning conditions 5 (KERN_NOTICE) normal but significant condition 6 (KERN_INFO) informational 7 (KERN_DEBUG) debug-level messages
log_buf_len=n[KMG] [KNL,EARLY] Sets the size of the printk ring buffer, in bytes. n must be a power of two and greater than the minimal size. The minimal size is defined by LOG_BUF_SHIFT kernel config parameter. There is also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter that allows to increase the default size depending on the number of CPUs. See init/Kconfig for more details.
logo.nologo [FB] Disables display of the built-in Linux logo. This may be used to provide more screen space for kernel log messages and is useful when debugging kernel boot problems.
lp=0 [LP] Specify parallel ports to use, e.g, lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses lp=reset first parallel port). 'lp=0' disables the lp=auto printer driver. 'lp=reset' (which can be specified in addition to the ports) causes attached printers to be reset. Using lp=port1,port2,... specifies the parallel ports to associate lp devices with, starting with lp0. A port specification may be 'none' to skip that lp device, or a parport name such as 'parport0'. Specifying 'lp=auto' instead of a port specification list means that device IDs from each port should be examined, to see if an IEEE 1284-compliant printer is attached; if so, the driver will manage that printer. See also header of drivers/char/lp.c.
lpj=n [KNL] Sets loops_per_jiffy to given constant, thus avoiding time-consuming boot-time autodetection (up to 250 ms per CPU). 0 enables autodetection (default). To determine the correct value for your kernel, boot with normal autodetection and see what value is printed. Note that on SMP systems the preset will be applied to all CPUs, which is likely to cause problems if your CPUs need significantly divergent settings. An incorrect value will cause delays in the kernel to be wrong, leading to unpredictable I/O errors and other breakage. Although unlikely, in the extreme case this might damage your hardware.
lsm.debug [SECURITY] Enable LSM initialization debugging output.
lsm=lsm1,...,lsmN [SECURITY] Choose order of LSM initialization. This overrides CONFIG_LSM, and the "security=" parameter.
machtype= [Loongson] Share the same kernel image file between different yeeloong laptops. Example: machtype=lemote-yeeloong-2f-7inch
maxcpus= [SMP,EARLY] Maximum number of processors that an SMP kernel will bring up during bootup. maxcpus=n : n >= 0 limits the kernel to bring up 'n' processors. Surely after bootup you can bring up the other plugged cpu by executing "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus only takes effect during system bootup. While n=0 is a special case, it is equivalent to "nosmp", which also disables the IO APIC.
max_loop= [LOOP] The number of loop block devices that get (loop.max_loop) unconditionally pre-created at init time. The default number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead of statically allocating a predefined number, loop devices can be requested on-demand with the /dev/loop-control interface.
mce= [X86-{32,64}]
Please see Documentation/arch/x86/x86_64/machinecheck.rst for sysfs runtime tunables.
off disable machine check
no_cmci disable CMCI(Corrected Machine Check Interrupt) that Intel processor supports. Usually this disablement is not recommended, but it might be handy if your hardware is misbehaving.
Note that you'll get more problems without CMCI than with due to the shared banks, i.e. you might get duplicated error logs.
dont_log_ce don't make logs for corrected errors. All events reported as corrected are silently cleared by OS. This option will be useful if you have no interest in any of corrected errors.
ignore_ce disable features for corrected errors, e.g. polling timer and CMCI. All events reported as corrected are not cleared by OS and remained in its error banks.
Usually this disablement is not recommended, however if there is an agent checking/clearing corrected errors (e.g. BIOS or hardware monitoring applications), conflicting with OS's error handling, and you cannot deactivate the agent, then this option will be a help.
no_lmce do not opt-in to Local MCE delivery. Use legacy method to broadcast MCEs.
bootlog enable logging of machine checks left over from booting. Disabled by default on AMD Fam10h and older because some BIOS leave bogus ones.
If your BIOS doesn't do that it's a good idea to enable though to make sure you log even machine check events that result in a reboot. On Intel systems it is enabled by default.
nobootlog disable boot machine check logging.
monarchtimeout (number) sets the time in us to wait for other CPUs on machine checks. 0 to disable.
bios_cmci_threshold don't overwrite the bios-set CMCI threshold. This boot option prevents Linux from overwriting the CMCI threshold set by the bios. Without this option, Linux always sets the CMCI threshold to 1. Enabling this may make memory predictive failure analysis less effective if the bios sets thresholds for memory errors since we will not see details for all errors.
recovery force-enable recoverable machine check code paths
Everything else is in sysfs now.
md= [HW] RAID subsystems devices and level See Documentation/admin-guide/md.rst.
mds= [X86,INTEL,EARLY] Control mitigation for the Micro-architectural Data Sampling (MDS) vulnerability.
Certain CPUs are vulnerable to an exploit against CPU internal buffers which can forward information to a disclosure gadget under certain conditions.
In vulnerable processors, the speculatively forwarded data can be used in a cache side channel attack, to access data to which the attacker does not have direct access.
This parameter controls the MDS mitigation. The options are:
full - Enable MDS mitigation on vulnerable CPUs full,nosmt - Enable MDS mitigation and disable SMT on vulnerable CPUs off - Unconditionally disable MDS mitigation
On TAA-affected machines, mds=off can be prevented by an active TAA mitigation as both vulnerabilities are mitigated with the same mechanism so in order to disable this mitigation, you need to specify tsx_async_abort=off too.
Not specifying this option is equivalent to mds=full.
For details see: Documentation/admin-guide/hw-vuln/mds.rst
mem=nn[KMG] [HEXAGON,EARLY] Set the memory size. Must be specified, otherwise memory size will be 0.
mem=nn[KMG] [KNL,BOOT,EARLY] Force usage of a specific amount of memory Amount of memory to be used in cases as follows:
1 for test; 2 when the kernel is not able to see the whole system memory; 3 memory that lies after 'mem=' boundary is excluded from the hypervisor, then assigned to KVM guests. 4 to limit the memory available for kdump kernel.
[ARC,MICROBLAZE] - the limit applies only to low memory, high memory is not affected.
[ARM64] - only limits memory covered by the linear mapping. The NOMAP regions are not affected.
[X86] Work as limiting max address. Use together with memmap= to avoid physical address space collisions. Without memmap= PCI devices could be placed at addresses belonging to unused RAM.
Note that this only takes effects during boot time since in above case 3, memory may need be hot added after boot if system memory of hypervisor is not sufficient.
mem=nn[KMG]@ss[KMG] [ARM,MIPS,EARLY] - override the memory layout reported by firmware. Define a memory region of size nn[KMG] starting at ss[KMG]. Multiple different regions can be specified with multiple mem= parameters on the command line.
mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel memory.
memblock=debug [KNL,EARLY] Enable memblock debug messages.
memchunk=nn[KMG] [KNL,SH] Allow user to override the default size for per-device physically contiguous DMA buffers.
memhp_default_state=online/offline/online_kernel/online_movable [KNL] Set the initial state for the memory hotplug onlining policy. If not specified, the default value is set according to the CONFIG_MHP_DEFAULT_ONLINE_TYPE kernel config options. See Documentation/admin-guide/mm/memory-hotplug.rst.
memmap=exactmap [KNL,X86,EARLY] Enable setting of an exact E820 memory map, as specified by the user. Such memmap=exactmap lines can be constructed based on BIOS output or other requirements. See the memmap=nn@ss option description.
memmap=nn[KMG]@ss[KMG] [KNL, X86,MIPS,XTENSA,EARLY] Force usage of a specific region of memory. Region of memory to be used is from ss to ss+nn. If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], which limits max address to nn[KMG]. Multiple different regions can be specified, comma delimited. Example: memmap=100M@2G,100M#3G,1G!1024G
memmap=nn[KMG]#ss[KMG] [KNL,ACPI,EARLY] Mark specific memory as ACPI data. Region of memory to be marked is from ss to ss+nn.
memmap=nn[KMG]$ss[KMG] [KNL,ACPI,EARLY] Mark specific memory as reserved. Region of memory to be reserved is from ss to ss+nn. Example: Exclude memory from 0x18690000-0x1869ffff memmap=64K$0x18690000 or memmap=0x10000$0x18690000 Some bootloaders may need an escape character before '$', like Grub2, otherwise '$' and the following number will be eaten.
memmap=nn[KMG]!ss[KMG,EARLY] [KNL,X86] Mark specific memory as protected. Region of memory to be used, from ss to ss+nn. The memory region may be marked as e820 type 12 (0xc) and is NVDIMM or ADR memory.
memmap=<size>%<offset>-<oldtype>+<newtype> [KNL,ACPI,EARLY] Convert memory within the specified region from <oldtype> to <newtype>. If "-<oldtype>" is left out, the whole region will be marked as <newtype>, even if previously unavailable. If "+<newtype>" is left out, matching memory will be removed. Types are specified as e820 types, e.g., 1 = RAM, 2 = reserved, 3 = ACPI, 12 = PRAM.
memory_corruption_check=0/1 [X86,EARLY] Some BIOSes seem to corrupt the first 64k of memory when doing things like suspend/resume. Setting this option will scan the memory looking for corruption. Enabling this will both detect corruption and prevent the kernel from using the memory being corrupted. However, it's intended as a diagnostic tool; if repeatable BIOS-originated corruption always affects the same memory, you can use memmap= to prevent the kernel from using that memory.
memory_corruption_check_size=size [X86,EARLY] By default it checks for corruption in the low 64k, making this memory unavailable for normal use. Use this parameter to scan for corruption in more or less memory.
memory_corruption_check_period=seconds [X86,EARLY] By default it checks for corruption every 60 seconds. Use this parameter to check at some other rate. 0 disables periodic checking.
memory_hotplug.memmap_on_memory [KNL,X86,ARM] Boolean flag to enable this feature. Format: {on | off (default)} When enabled, runtime hotplugged memory will allocate its internal metadata (struct pages, those vmemmap pages cannot be optimized even if hugetlb_free_vmemmap is enabled) from the hotadded memory which will allow to hotadd a lot of memory without requiring additional memory to do so. This feature is disabled by default because it has some implication on large (e.g. GB) allocations in some configurations (e.g. small memory blocks). The state of the flag can be read in /sys/module/memory_hotplug/parameters/memmap_on_memory. Note that even when enabled, there are a few cases where the feature is not effective.
memtest= [KNL,X86,ARM,M68K,PPC,RISCV,EARLY] Enable memtest Format: <integer> default : 0 <disable> Specifies the number of memtest passes to be performed. Each pass selects another test pattern from a given set of patterns. Memtest fills the memory with this pattern, validates memory contents and reserves bad memory regions that are detected.
mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control Valid arguments: on, off Default: off mem_encrypt=on: Activate SME mem_encrypt=off: Do not activate SME
Refer to Documentation/virt/kvm/x86/amd-memory-encryption.rst for details on when memory encryption can be activated.
mem_sleep_default= [SUSPEND] Default system suspend mode: s2idle - Suspend-To-Idle shallow - Power-On Suspend or equivalent (if supported) deep - Suspend-To-RAM or equivalent (if supported) See Documentation/admin-guide/pm/sleep-states.rst.
mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when the BIOS has incorrectly applied a workaround. TinyBIOS version 0.98 is known to be affected, 0.99 fixes the problem by letting the user disable the workaround.
mga= [HW,DRM]
microcode= [X86] Control the behavior of the microcode loader. Available options, comma separated:
base_rev=X - with <X> with format: <u32> Set the base microcode revision of each thread when in debug mode.
dis_ucode_ldr: disable the microcode loader
force_minrev: Enable or disable the microcode minimal revision enforcement for the runtime microcode loader.
mini2440= [ARM,HW,KNL] Format:[0..2][b][c][t] Default: "0tb" MINI2440 configuration specification: 0 - The attached screen is the 3.5" TFT 1 - The attached screen is the 7" TFT 2 - The VGA Shield is attached (1024x768) Leaving out the screen size parameter will not load the TFT driver, and the framebuffer will be left unconfigured. b - Enable backlight. The TFT backlight pin will be linked to the kernel VESA blanking code and a GPIO LED. This parameter is not necessary when using the VGA shield. c - Enable the s3c camera interface. t - Reserved for enabling touchscreen support. The touchscreen support is not enabled in the mainstream kernel as of 2.6.30, a preliminary port can be found in the "bleeding edge" mini2440 support kernel at https://repo.or.cz/w/linux-2.6/mini2440.git
mitigations= [X86,PPC,S390,ARM64,EARLY] Control optional mitigations for CPU vulnerabilities. This is a set of curated, arch-independent options, each of which is an aggregation of existing arch-specific options.
Note, "mitigations" is supported if and only if the kernel was built with CPU_MITIGATIONS=y.
off Disable all optional CPU mitigations. This improves system performance, but it may also expose users to several CPU vulnerabilities. Equivalent to: if nokaslr then kpti=0 [ARM64] gather_data_sampling=off [X86] indirect_target_selection=off [X86] kvm.nx_huge_pages=off [X86] l1tf=off [X86] mds=off [X86] mmio_stale_data=off [X86] no_entry_flush [PPC] no_uaccess_flush [PPC] nobp=0 [S390] nopti [X86,PPC] nospectre_bhb [ARM64] nospectre_v1 [X86,PPC] nospectre_v2 [X86,PPC,S390,ARM64] reg_file_data_sampling=off [X86] retbleed=off [X86] spec_rstack_overflow=off [X86] spec_store_bypass_disable=off [X86,PPC] spectre_bhi=off [X86] spectre_v2_user=off [X86] srbds=off [X86,INTEL] ssbd=force-off [ARM64] tsa=off [X86,AMD] tsx_async_abort=off [X86] vmscape=off [X86]
Exceptions: This does not have any effect on kvm.nx_huge_pages when kvm.nx_huge_pages=force.
auto (default) Mitigate all CPU vulnerabilities, but leave SMT enabled, even if it's vulnerable. This is for users who don't want to be surprised by SMT getting disabled across kernel upgrades, or who have other ways of avoiding SMT-based attacks. Equivalent to: (default behavior)
auto,nosmt Mitigate all CPU vulnerabilities, disabling SMT if needed. This is for users who always want to be fully mitigated, even if it means losing SMT. Equivalent to: l1tf=flush,nosmt [X86] mds=full,nosmt [X86] tsx_async_abort=full,nosmt [X86] mmio_stale_data=full,nosmt [X86] retbleed=auto,nosmt [X86]
[X86] After one of the above options, additionally supports attack-vector based controls as documented in Documentation/admin-guide/hw-vuln/attack_vector_controls.rst
mminit_loglevel= [KNL,EARLY] When CONFIG_DEBUG_MEMORY_INIT is set, this parameter allows control of the logging verbosity for the additional memory initialisation checks. A value of 0 disables mminit logging and a level of 4 will log everything. Information is printed at KERN_DEBUG so loglevel=8 may also need to be specified.
mmio_stale_data= [X86,INTEL,EARLY] Control mitigation for the Processor MMIO Stale Data vulnerabilities.
Processor MMIO Stale Data is a class of vulnerabilities that may expose data after an MMIO operation. Exposed data could originate or end in the same CPU buffers as affected by MDS and TAA. Therefore, similar to MDS and TAA, the mitigation is to clear the affected CPU buffers.
This parameter controls the mitigation. The options are:
full - Enable mitigation on vulnerable CPUs
full,nosmt - Enable mitigation and disable SMT on vulnerable CPUs.
off - Unconditionally disable mitigation
On MDS or TAA affected machines, mmio_stale_data=off can be prevented by an active MDS or TAA mitigation as these vulnerabilities are mitigated with the same mechanism so in order to disable this mitigation, you need to specify mds=off and tsx_async_abort=off too.
Not specifying this option is equivalent to mmio_stale_data=full.
For details see: Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst
<module>.async_probe[=<bool>] [KNL] If no <bool> value is specified or if the value specified is not a valid <bool>, enable asynchronous probe on this module. Otherwise, enable/disable asynchronous probe on this module as indicated by the <bool> value. See also: module.async_probe
module.async_probe=<bool> [KNL] When set to true, modules will use async probing by default. To enable/disable async probing for a specific module, use the module specific control that is documented under <module>.async_probe. When both module.async_probe and <module>.async_probe are specified, <module>.async_probe takes precedence for the specific module.
module.enable_dups_trace [KNL] When CONFIG_MODULE_DEBUG_AUTOLOAD_DUPS is set, this means that duplicate request_module() calls will trigger a WARN_ON() instead of a pr_warn(). Note that if MODULE_DEBUG_AUTOLOAD_DUPS_TRACE is set, WARN_ON()s will always be issued and this option does nothing. module.sig_enforce [KNL] When CONFIG_MODULE_SIG is set, this means that modules without (valid) signatures will fail to load. Note that if CONFIG_MODULE_SIG_FORCE is set, that is always true, so this option does nothing.
module_blacklist= [KNL] Do not load a comma-separated list of modules. Useful for debugging problem modules.
mousedev.tap_time= [MOUSE] Maximum time between finger touching and leaving touchpad surface for touch to be considered a tap and be reported as a left button click (for touchpads working in absolute mode only). Format: <msecs> mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices reporting absolute coordinates, such as tablets mousedev.yres= [MOUSE] Vertical screen resolution, used for devices reporting absolute coordinates, such as tablets
movablecore= [KNL,X86,PPC,EARLY] Format: nn[KMGTPE] | nn% This parameter is the complement to kernelcore=, it specifies the amount of memory used for migratable allocations. If both kernelcore and movablecore is specified, then kernelcore will be at *least* the specified value but may be more. If movablecore on its own is specified, the administrator must be careful that the amount of memory usable for all allocations is not too small.
movable_node [KNL,EARLY] Boot-time switch to make hotplugable memory NUMA nodes to be movable. This means that the memory of such nodes will be usable only for movable allocations which rules out almost all kernel allocations. Use with caution!
MTD_Partition= [MTD] Format: <name>,<region-number>,<size>,<offset>
MTD_Region= [MTD] Format: <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
mtdparts= [MTD] See drivers/mtd/parsers/cmdlinepart.c
mtouchusb.raw_coordinates= [HW] Make the MicroTouch USB driver use raw coordinates ('y', default) or cooked coordinates ('n')
mtrr=debug [X86,EARLY] Enable printing debug information related to MTRR registers at boot time.
mtrr_chunk_size=nn[KMG,X86,EARLY] used for mtrr cleanup. It is largest continuous chunk that could hold holes aka. UC entries.
mtrr_gran_size=nn[KMG,X86,EARLY] Used for mtrr cleanup. It is granularity of mtrr block. Default is 1. Large value could prevent small alignment from using up MTRRs.
mtrr_spare_reg_nr=n [X86,EARLY] Format: <integer> Range: 0,7 : spare reg number Default : 1 Used for mtrr cleanup. It is spare mtrr entries number. Set to 2 or more if your graphical card needs more.
multitce=off [PPC] This parameter disables the use of the pSeries firmware feature for updating multiple TCE entries at a time.
n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
netdev= [NET] NE2000 ISA network devices parameters Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
netpoll.carrier_timeout= [NET] Specifies amount of time (in seconds) that netpoll should wait for a carrier. By default netpoll waits 4 seconds.
nf_conntrack.acct= [NETFILTER] Enable connection tracking flow accounting 0 to disable accounting 1 to enable accounting Default value is 0.
nfs.cache_getent= [NFS] sets the pathname to the program which is used to update the NFS client cache entries.
nfs.cache_getent_timeout= [NFS] sets the timeout after which an attempt to update a cache entry is deemed to have failed.
nfs.callback_nr_threads= [NFSv4] set the total number of threads that the NFS client will assign to service NFSv4 callback requests.
nfs.callback_tcpport= [NFS] set the TCP port on which the NFSv4 callback channel should listen.
nfs.delay_retrans= [NFS] specifies the number of times the NFSv4 client retries the request before returning an EAGAIN error, after a reply of NFS4ERR_DELAY from the server. Only applies if the softerr mount option is enabled, and the specified value is >= 0.
nfs.idmap_cache_timeout= [NFS] set the maximum lifetime for idmapper cache entries.
nfs.max_session_cb_slots= [NFSv4.1] Sets the maximum number of session slots the client will assign to the callback channel. This determines the maximum number of callbacks the client will process in parallel for a particular server.
nfs.max_session_slots= [NFSv4.1] Sets the maximum number of session slots the client will attempt to negotiate with the server. This limits the number of simultaneous RPC requests that the client can send to the NFSv4.1 server. Note that there is little point in setting this value higher than the max_tcp_slot_table_limit.
nfs.nfs4_disable_idmapping= [NFSv4] When set to the default of '1', this option ensures that both the RPC level authentication scheme and the NFS level operations agree to use numeric uids/gids if the mount is using the 'sec=sys' security flavour. In effect it is disabling idmapping, which can make migration from legacy NFSv2/v3 systems to NFSv4 easier. Servers that do not support this mode of operation will be autodetected by the client, and it will fall back to using the idmapper. To turn off this behaviour, set the value to '0'.
nfs.nfs4_unique_id= [NFS4] Specify an additional fixed unique ident- ification string that NFSv4 clients can insert into their nfs_client_id4 string. This is typically a UUID that is generated at system install time.
nfs.recover_lost_locks= [NFSv4] Attempt to recover locks that were lost due to a lease timeout on the server. Please note that doing this risks data corruption, since there are no guarantees that the file will remain unchanged after the locks are lost. If you want to enable the kernel legacy behaviour of attempting to recover these locks, then set this parameter to '1'. The default parameter value of '0' causes the kernel not to attempt recovery of lost locks.
nfs.send_implementation_id= [NFSv4.1] Send client implementation identification information in exchange_id requests. If zero, no implementation identification information will be sent. The default is to send the implementation identification information.
nfs4.layoutstats_timer= [NFSv4.2] Change the rate at which the kernel sends layoutstats to the pNFS metadata server.
Setting this to value to 0 causes the kernel to use whatever value is the default set by the layout driver. A non-zero value sets the minimum interval in seconds between layoutstats transmissions.
nfsd.inter_copy_offload_enable= [NFSv4.2] When set to 1, the server will support server-to-server copies for which this server is the destination of the copy.
nfsd.nfs4_disable_idmapping= [NFSv4] When set to the default of '1', the NFSv4 server will return only numeric uids and gids to clients using auth_sys, and will accept numeric uids and gids from such clients. This is intended to ease migration from NFSv2/v3.
nfsd.nfsd4_ssc_umount_timeout= [NFSv4.2] When used as the destination of a server-to-server copy, knfsd temporarily mounts the source server. It caches the mount in case it will be needed again, and discards it if not used for the number of milliseconds specified by this parameter.
nfsaddrs= [NFS] Deprecated. Use ip= instead. See Documentation/admin-guide/nfs/nfsroot.rst.
nfsroot= [NFS] nfs root filesystem for disk-less boxes. See Documentation/admin-guide/nfs/nfsroot.rst.
nfsrootdebug [NFS] enable nfsroot debugging messages. See Documentation/admin-guide/nfs/nfsroot.rst.
nmi_backtrace.backtrace_idle [KNL] Dump stacks even of idle CPUs in response to an NMI stack-backtrace request.
nmi_debug= [KNL,SH] Specify one or more actions to take when a NMI is triggered. Format: [state][,regs][,debounce][,die]
nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels Format: [panic,][nopanic,][rNNN,][num] Valid num: 0 or 1 0 - turn hardlockup detector in nmi_watchdog off 1 - turn hardlockup detector in nmi_watchdog on rNNN - configure the watchdog with raw perf event 0xNNN
When panic is specified, panic when an NMI watchdog timeout occurs (or 'nopanic' to not panic on an NMI watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) To disable both hard and soft lockup detectors, please see 'nowatchdog'. This is useful when you use a panic=... timeout and need the box quickly up again.
These settings can be accessed at runtime via the nmi_watchdog and hardlockup_panic sysctls.
no4lvl [RISCV,EARLY] Disable 4-level and 5-level paging modes. Forces kernel to use 3-level paging instead.
no5lvl [X86-64,RISCV,EARLY] Disable 5-level paging mode. Forces kernel to use 4-level paging instead.
noalign [KNL,ARM]
noapic [SMP,APIC,EARLY] Tells the kernel to not make use of any IOAPICs that may be present in the system.
noapictimer [APIC,X86] Don't set up the APIC timer
noautogroup Disable scheduler automatic task group creation.
nocache [ARM,EARLY]
no_console_suspend [HW] Never suspend the console Disable suspending of consoles during suspend and hibernate operations. Once disabled, debugging messages can reach various consoles while the rest of the system is being put to sleep (ie, while debugging driver suspend/resume hooks). This may not work reliably with all consoles, but is known to work with serial and VGA consoles. To facilitate more flexible debugging, we also add console_suspend, a printk module parameter to control it. Users could use console_suspend (usually /sys/module/printk/parameters/console_suspend) to turn on/off it dynamically.
no_debug_objects [KNL,EARLY] Disable object debugging
nodsp [SH] Disable hardware DSP at boot time.
noefi [EFI,EARLY] Disable EFI runtime services support.
no_entry_flush [PPC,EARLY] Don't flush the L1-D cache when entering the kernel.
noexec32 [X86-64] This affects only 32-bit executables. noexec32=on: enable non-executable mappings (default) read doesn't imply executable mappings noexec32=off: disable non-executable mappings read implies executable mappings
no_file_caps Tells the kernel not to honor file capabilities. The only way then for a file to be executed with privilege is to be setuid root or executed by root.
nofpu [MIPS,SH] Disable hardware FPU at boot time.
nofsgsbase [X86] Disables FSGSBASE instructions.
nofxsr [BUGS=X86-32] Disables x86 floating point extended register save and restore. The kernel will only save legacy floating-point registers on task switch.
nogbpages [X86] Do not use GB pages for kernel direct mappings.
no_hash_pointers [KNL,EARLY] Alias for "hash_pointers=never".
nohibernate [HIBERNATION] Disable hibernation and resume.
nohlt [ARM,ARM64,MICROBLAZE,MIPS,PPC,RISCV,SH] Forces the kernel to busy wait in do_idle() and not use the arch_cpu_idle() implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP to be effective. This is useful on platforms where the sleep(SH) or wfi(ARM,ARM64) instructions do not work correctly or when doing power measurements to evaluate the impact of the sleep instructions. This is also useful when using JTAG debugger.
nohpet [X86] Don't use the HPET timer.
nohugeiomap [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge I/O mappings.
nohugevmalloc [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge vmalloc mappings.
nohz= [KNL] Boottime enable/disable dynamic ticks Valid arguments: on, off Default: on
nohz_full= [KNL,BOOT,SMP,ISOL] The argument is a cpu list, as described above. In kernels built with CONFIG_NO_HZ_FULL=y, set the specified list of CPUs whose tick will be stopped whenever possible. The boot CPU will be forced outside the range to maintain the timekeeping. Any CPUs in this list will have their RCU callbacks offloaded, just as if they had also been called out in the rcu_nocbs= boot parameter.
Note that this argument takes precedence over the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.
noinitrd [Deprecated,RAM] Tells the kernel not to load any configured initial RAM disk. Currently this parameter applies to initrd only, not to initramfs. But it applies to both in EFI mode.
nointremap [X86-64,Intel-IOMMU,EARLY] Do not enable interrupt remapping. [Deprecated - use intremap=off]
noinvpcid [X86,EARLY] Disable the INVPCID cpu feature.
noiotrap [SH] Disables trapped I/O port accesses.
noirqdebug [X86-32] Disables the code which attempts to detect and disable unhandled interrupt sources.
noisapnp [ISAPNP] Disables ISA PnP code.
nokaslr [KNL,EARLY] When CONFIG_RANDOMIZE_BASE is set, this disables kernel and module base offset ASLR (Address Space Layout Randomization).
no-kvmapf [X86,KVM,EARLY] Disable paravirtualized asynchronous page fault handling.
no-kvmclock [X86,KVM,EARLY] Disable paravirtualized KVM clock driver
nolapic [X86-32,APIC,EARLY] Do not enable or use the local APIC.
nolapic_timer [X86-32,APIC,EARLY] Do not use the local APIC timer.
nomce [X86-32] Disable Machine Check Exception
nomfgpt [X86-32] Disable Multi-Function General Purpose Timer usage (for AMD Geode machines).
nomodeset Disable kernel modesetting. Most systems' firmware sets up a display mode and provides framebuffer memory for output. With nomodeset, DRM and fbdev drivers will not load if they could possibly displace the pre- initialized output. Only the system framebuffer will be available for use. The respective drivers will not perform display-mode changes or accelerated rendering.
Useful as error fallback, or for testing and debugging.
nomodule Disable module load
nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to shutdown the other cpus. Instead use the REBOOT_VECTOR irq.
nopat [X86,EARLY] Disable PAT (page attribute table extension of pagetables) support.
nopcid [X86-64,EARLY] Disable the PCID cpu feature.
nopku [X86] Disable Memory Protection Keys CPU feature found in some Intel CPUs.
nopti [X86-64,EARLY] Equivalent to pti=off
nopv= [X86,XEN,KVM,HYPER_V,VMWARE,EARLY] Disables the PV optimizations forcing the guest to run as generic guest with no PV drivers. Currently support XEN HVM, KVM, HYPER_V and VMWARE guest.
nopvspin [X86,XEN,KVM,EARLY] Disables the qspinlock slow path using PV optimizations which allow the hypervisor to 'idle' the guest on lock contention.
norandmaps Don't use address space randomization. Equivalent to echo 0 > /proc/sys/kernel/randomize_va_space
noreplace-smp [X86-32,SMP] Don't replace SMP instructions with UP alternatives
noresume [SWSUSP] Disables resume and restores original swap space.
no-scroll [VGA] Disables scrollback. This is required for the Braillex ib80-piezo Braille reader made by F.H. Papenmeier (Germany).
nosgx [X86-64,SGX,EARLY] Disables Intel SGX kernel support.
nosmap [PPC,EARLY] Disable SMAP (Supervisor Mode Access Prevention) even if it is supported by processor.
nosmep [PPC64s,EARLY] Disable SMEP (Supervisor Mode Execution Prevention) even if it is supported by processor.
nosmp [SMP,EARLY] Tells an SMP kernel to act as a UP kernel, and disable the IO APIC. legacy for "maxcpus=0".
nosmt [KNL,MIPS,PPC,EARLY] Disable symmetric multithreading (SMT). Equivalent to smt=1.
[KNL,LOONGARCH,X86,ARM64,PPC,S390] Disable symmetric multithreading (SMT). nosmt=force: Force disable SMT, cannot be undone via the sysfs control file.
nosoftlockup [KNL] Disable the soft-lockup detector.
nospec_store_bypass_disable [HW,EARLY] Disable all mitigations for the Speculative Store Bypass vulnerability
nospectre_bhb [ARM64,EARLY] Disable all mitigations for Spectre-BHB (branch history injection) vulnerability. System may allow data leaks with this option.
nospectre_v1 [X86,PPC,EARLY] Disable mitigations for Spectre Variant 1 (bounds check bypass). With this option data leaks are possible in the system.
nospectre_v2 [X86,PPC_E500,ARM64,EARLY] Disable all mitigations for the Spectre variant 2 (indirect branch prediction) vulnerability. System may allow data leaks with this option.
no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES,RISCV,LOONGARCH,EARLY] Disable paravirtualized steal time accounting. steal time is computed, but won't influence scheduler behaviour
nosync [HW,M68K] Disables sync negotiation for all devices.
no_timer_check [X86,APIC] Disables the code which tests for broken timer IRQ sources, i.e., the IO-APIC timer. This can work around problems with incorrect timer initialization on some boards.
no_uaccess_flush [PPC,EARLY] Don't flush the L1-D cache after accessing user data.
novmcoredd [KNL,KDUMP] Disable device dump. Device dump allows drivers to append dump data to vmcore so you can collect driver specified debug info. Drivers can append the data without any limit and this data is stored in memory, so this may cause significant memory stress. Disabling device dump can help save memory but the driver debug data will be no longer available. This parameter is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP is set.
no-vmw-sched-clock [X86,PV_OPS,EARLY] Disable paravirtualized VMware scheduler clock and use the default one.
nowatchdog [KNL] Disable both lockup detectors, i.e. soft-lockup and NMI watchdog (hard-lockup).
nowb [ARM,EARLY]
nox2apic [X86-64,APIC,EARLY] Do not enable x2APIC mode.
NOTE: this parameter will be ignored on systems with the LEGACY_XAPIC_DISABLED bit set in the IA32_XAPIC_DISABLE_STATUS MSR.
noxsave [BUGS=X86] Disables x86 extended register state save and restore using xsave. The kernel will fallback to enabling legacy floating-point and sse state.
noxsaveopt [X86] Disables xsaveopt used in saving x86 extended register states. The kernel will fall back to use xsave to save the states. By using this parameter, performance of saving the states is degraded because xsave doesn't support modified optimization while xsaveopt supports it on xsaveopt enabled systems.
noxsaves [X86] Disables xsaves and xrstors used in saving and restoring x86 extended register state in compacted form of xsave area. The kernel will fall back to use xsaveopt and xrstor to save and restore the states in standard form of xsave area. By using this parameter, xsave area per process might occupy more memory on xsaves enabled systems.
nr_cpus= [SMP,EARLY] Maximum number of processors that an SMP kernel could support. nr_cpus=n : n >= 1 limits the kernel to support 'n' processors. It could be larger than the number of already plugged CPU during bootup, later in runtime you can physically add extra cpu until it reaches n. So during boot up some boot time memory for per-cpu variables need be pre-allocated for later physical cpu hot plugging.
nr_uarts= [SERIAL] maximum number of UARTs to be registered.
numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86, EARLY] Disable NUMA, Only set up a single NUMA node spanning all memory.
numa=fake=<size>[MG] [KNL, ARM64, RISCV, X86, EARLY] If given as a memory unit, fills all system RAM with nodes of size interleaved over physical nodes.
numa=fake=<N> [KNL, ARM64, RISCV, X86, EARLY] If given as an integer, fills all system RAM with N fake nodes interleaved over physical nodes.
numa=fake=<N>U [KNL, ARM64, RISCV, X86, EARLY] If given as an integer followed by 'U', it will divide each physical node into N emulated nodes.
numa=noacpi [X86] Don't parse the SRAT table for NUMA setup
numa=nohmat [X86] Don't parse the HMAT table for NUMA setup, or soft-reserved memory partitioning.
numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic NUMA balancing. Allowed values are enable and disable
numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 'node', 'default' can be specified This can be set from sysctl after boot. See Documentation/admin-guide/sysctl/vm.rst for details.
nvme.quirks= [NVME] A list of quirk entries to augment the built-in nvme quirk list. List entries are separated by a '-' character. Each entry has the form VendorID:ProductID:quirk_names. The IDs are 4-digits hex numbers and quirk_names is a list of quirk names separated by commas. A quirk name can be prefixed by '^', meaning that the specified quirk must be disabled.
Example: nvme.quirks=7710:2267:bogus_nid,^identify_cns-9900:7711:broken_msi
ohci1394_dma=early [HW,EARLY] enable debugging via the ohci1394 driver. See Documentation/core-api/debugging-via-ohci1394.rst for more info.
olpc_ec_timeout= [OLPC] ms delay when issuing EC commands Rather than timing out after 20 ms if an EC command is not properly ACKed, override the length of the timeout. We have interrupts disabled while waiting for the ACK, so if this is set too high interrupts *may* be lost!
omap_mux= [OMAP] Override bootloader pin multiplexing. Format: <mux_mode0.mode_name=value>... For example, to override I2C bus2: omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
boundary - index of last SLC block on Flex-OneNAND. The remaining blocks are configured as MLC blocks. lock - Configure if Flex-OneNAND boundary should be locked. Once locked, the boundary cannot be changed. 1 indicates lock status, 0 indicates unlock status.
oops=panic [KNL,EARLY] Always panic on oopses. Default is to just kill the process, but there is a small probability of deadlocking the machine. This will also cause panics on machine check exceptions. Useful together with panic=30 to trigger a reboot.
page_alloc.shuffle= [KNL] Boolean flag to control whether the page allocator should randomize its free lists. This parameter can be used to enable/disable page randomization. The state of the flag can be read from sysfs at: /sys/module/page_alloc/parameters/shuffle. This parameter is only available if CONFIG_SHUFFLE_PAGE_ALLOCATOR=y.
page_owner= [KNL,EARLY] Boot-time page_owner enabling option. Storage of the information about who allocated each page is disabled in default. With this switch, we can turn it on. on: enable the feature
page_poison= [KNL,EARLY] Boot-time parameter changing the state of poisoning on the buddy allocator, available with CONFIG_PAGE_POISONING=y. off: turn off poisoning (default) on: turn on poisoning
page_reporting.page_reporting_order= [KNL] Minimal page reporting order Format: <integer> Adjust the minimal page reporting order. The page reporting is disabled when it exceeds MAX_PAGE_ORDER.
panic= [KNL] Kernel behaviour on panic: delay <timeout> timeout > 0: seconds before rebooting timeout = 0: wait forever timeout < 0: reboot immediately Format: <timeout>
panic_on_taint= [KNL,EARLY] Bitmask for conditionally calling panic() in add_taint() Format: <hex>[,nousertaint] Hexadecimal bitmask representing the set of TAINT flags that will cause the kernel to panic when add_taint() is called with any of the flags in this set. The optional switch "nousertaint" can be utilized to prevent userspace forced crashes by writing to sysctl /proc/sys/kernel/tainted any flagset matching with the bitmask set on panic_on_taint. See Documentation/admin-guide/tainted-kernels.rst for extra details on the taint flags that users can pick to compose the bitmask to assign to panic_on_taint.
panic_on_warn=1 panic() instead of WARN(). Useful to cause kdump on a WARN().
panic_force_cpu= [KNL,SMP] Force panic handling to execute on a specific CPU. Format: <cpu number> Some platforms require panic handling to occur on a specific CPU for the crash kernel to function correctly. This can be due to firmware limitations, interrupt routing constraints, or platform-specific requirements where only a particular CPU can safely enter the crash kernel. When set, panic() will redirect execution to the specified CPU before proceeding with the normal panic and kexec flow. If the target CPU is offline or unavailable, panic proceeds on the current CPU. This option should only be used for systems with the above constraints as it might cause the panic operation to be less reliable.
panic_print= Bitmask for printing system info when panic happens. User can chose combination of the following bits: bit 0: print all tasks info bit 1: print system memory info bit 2: print timer info bit 3: print locks info if CONFIG_LOCKDEP is on bit 4: print ftrace buffer bit 5: replay all kernel messages on consoles at the end of panic bit 6: print all CPUs backtrace (if available in the arch) bit 7: print only tasks in uninterruptible (blocked) state *Be aware* that this option may print a _lot_ of lines, so there are risks of losing older messages in the log. Use this option carefully, maybe worth to setup a bigger log buffer with "log_buf_len" along with this.
panic_sys_info= A comma separated list of extra information to be dumped on panic. Format: val[,val...] Where @val can be any of the following:
tasks: print all tasks info mem: print system memory info timers: print timers info locks: print locks info if CONFIG_LOCKDEP is on ftrace: print ftrace buffer all_bt: print all CPUs backtrace (if available in the arch) blocked_tasks: print only tasks in uninterruptible (blocked) state
This is a human readable alternative to the 'panic_print' option.
panic_console_replay When panic happens, replay all kernel messages on consoles at the end of panic.
parkbd.port= [HW] Parallel port number the keyboard adapter is connected to, default is 0. Format: <parport#> parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 0 for XT, 1 for AT (default is AT). Format: <mode>
parport= [HW,PPT] Specify parallel ports. 0 disables. Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } Use 'auto' to force the driver to use any IRQ/DMA settings detected (the default is to ignore detected IRQ/DMA settings because of possible conflicts). You can specify the base address, IRQ, and DMA settings; IRQ and DMA should be numbers, or 'auto' (for using detected settings on that particular port), or 'nofifo' (to avoid using a FIFO even if it is detected). Parallel ports are assigned in the order they are specified on the command line, starting with parport0.
parport_init_mode= [HW,PPT] Configure VIA parallel port to operate in a specific mode. This is necessary on Pegasos computer where firmware has no options for setting up parallel port mode and sets it to spp. Currently this function knows 686a and 8231 chips. Format: [spp|ps2|epp|ecp|ecpepp]
pata_legacy.all= [HW,LIBATA] Format: <int> Set to non-zero to probe primary and secondary ISA port ranges on PCI systems where no PCI PATA device has been found at either range. Disabled by default.
pata_legacy.autospeed= [HW,LIBATA] Format: <int> Set to non-zero if a chip is present that snoops speed changes. Disabled by default.
pata_legacy.ht6560a= [HW,LIBATA] Format: <int> Set to 1, 2, or 3 for HT 6560A on the primary channel, the secondary channel, or both channels respectively. Disabled by default.
pata_legacy.ht6560b= [HW,LIBATA] Format: <int> Set to 1, 2, or 3 for HT 6560B on the primary channel, the secondary channel, or both channels respectively. Disabled by default.
pata_legacy.iordy_mask= [HW,LIBATA] Format: <int> IORDY enable mask. Set individual bits to allow IORDY for the respective channel. Bit 0 is for the first legacy channel handled by this driver, bit 1 is for the second channel, and so on. The sequence will often correspond to the primary legacy channel, the secondary legacy channel, and so on, but the handling of a PCI bus and the use of other driver options may interfere with the sequence. By default IORDY is allowed across all channels.
pata_legacy.opti82c46x= [HW,LIBATA] Format: <int> Set to 1, 2, or 3 for Opti 82c611A on the primary channel, the secondary channel, or both channels respectively. Disabled by default.
pata_legacy.opti82c611a= [HW,LIBATA] Format: <int> Set to 1, 2, or 3 for Opti 82c465MV on the primary channel, the secondary channel, or both channels respectively. Disabled by default.
pata_legacy.pio_mask= [HW,LIBATA] Format: <int> PIO mode mask for autospeed devices. Set individual bits to allow the use of the respective PIO modes. Bit 0 is for mode 0, bit 1 is for mode 1, and so on. All modes allowed by default.
pata_legacy.probe_all= [HW,LIBATA] Format: <int> Set to non-zero to probe tertiary and further ISA port ranges on PCI systems. Disabled by default.
pata_legacy.probe_mask= [HW,LIBATA] Format: <int> Probe mask for legacy ISA PATA ports. Depending on platform configuration and the use of other driver options up to 6 legacy ports are supported: 0x1f0, 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing of individual ports can be disabled by setting the corresponding bits in the mask to 1. Bit 0 is for the first port in the list above (0x1f0), and so on. By default all supported ports are probed.
pata_legacy.qdi= [HW,LIBATA] Format: <int> Set to non-zero to probe QDI controllers. By default set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise.
pata_legacy.winbond= [HW,LIBATA] Format: <int> Set to non-zero to probe Winbond controllers. Use the standard I/O port (0x130) if 1, otherwise the value given is the I/O port to use (typically 0x1b0). By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE, 0 otherwise.
pata_platform.pio_mask= [HW,LIBATA] Format: <int> Supported PIO mode mask. Set individual bits to allow the use of the respective PIO modes. Bit 0 is for mode 0, bit 1 is for mode 1, and so on. Mode 0 only allowed by default.
pause_on_oops=<int> Halt all CPUs after the first oops has been printed for the specified number of seconds. This is to be used if your oopses keep scrolling off the screen.
pci=option[,option...] [PCI,EARLY] various PCI subsystem options.
Some options herein operate on a specific device or a set of devices (<pci_dev>). These are specified in one of the following formats:
[<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* pci:<vendor>:<device>[:<subvendor>:<subdevice>]
Note: the first format specifies a PCI bus/device/function address which may change if new hardware is inserted, if motherboard firmware changes, or due to changes caused by other kernel parameters. If the domain is left unspecified, it is taken to be zero. Optionally, a path to a device through multiple device/function addresses can be specified after the base address (this is more robust against renumbering issues). The second format selects devices using IDs from the configuration space which may match multiple devices in the system.
earlydump dump PCI config space before the kernel changes anything off [X86] don't probe for the PCI bus bios [X86-32] force use of PCI BIOS, don't access the hardware directly. Use this if your machine has a non-standard PCI host bridge. nobios [X86-32] disallow use of PCI BIOS, only direct hardware access methods are allowed. Use this if you experience crashes upon bootup and you suspect they are caused by the BIOS. conf1 [X86] Force use of PCI Configuration Access Mechanism 1 (config address in IO port 0xCF8, data in IO port 0xCFC, both 32-bit). conf2 [X86] Force use of PCI Configuration Access Mechanism 2 (IO port 0xCF8 is an 8-bit port for the function, IO port 0xCFA, also 8-bit, sets bus number. The config space is then accessed through ports 0xC000-0xCFFF). See http://wiki.osdev.org/PCI for more info on the configuration access mechanisms. noaer [PCIE] If the PCIEAER kernel config parameter is enabled, this kernel boot option can be used to disable the use of PCIE advanced error reporting. nodomains [PCI] Disable support for multiple PCI root domains (aka PCI segments, in ACPI-speak). nommconf [X86] Disable use of MMCONFIG for PCI Configuration check_enable_amd_mmconf [X86] check for and enable properly configured MMIO access to PCI config space on AMD family 10h CPU nomsi [MSI] If the PCI_MSI kernel config parameter is enabled, this kernel boot option can be used to disable the use of MSI interrupts system-wide. noioapicquirk [APIC] Disable all boot interrupt quirks. Safety option to keep boot IRQs enabled. This should never be necessary. ioapicreroute [APIC] Enable rerouting of boot IRQs to the primary IO-APIC for bridges that cannot disable boot IRQs. This fixes a source of spurious IRQs when the system masks IRQs. noioapicreroute [APIC] Disable workaround that uses the boot IRQ equivalent of an IRQ that connects to a chipset where boot IRQs cannot be disabled. The opposite of ioapicreroute. biosirq [X86-32] Use PCI BIOS calls to get the interrupt routing table. These calls are known to be buggy on several machines and they hang the machine when used, but on other computers it's the only way to get the interrupt routing table. Try this option if the kernel is unable to allocate IRQs or discover secondary PCI buses on your motherboard. rom [X86] Assign address space to expansion ROMs. Use with caution as certain devices share address decoders between ROMs and other resources. norom [X86] Do not assign address space to expansion ROMs that do not already have BIOS assigned address ranges. nobar [X86] Do not assign address space to the BARs that weren't assigned by the BIOS. irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be assigned automatically to PCI devices. You can make the kernel exclude IRQs of your ISA cards this way. pirqaddr=0xAAAAA [X86] Specify the physical address of the PIRQ table (normally generated by the BIOS) if it is outside the F0000h-100000h range. lastbus=N [X86] Scan all buses thru bus #N. Can be useful if the kernel is unable to find your secondary buses and you want to tell it explicitly which ones they are. assign-busses [X86] Always assign all PCI bus numbers ourselves, overriding whatever the firmware may have done. usepirqmask [X86] Honor the possible IRQ mask stored in the BIOS $PIR table. This is needed on some systems with broken BIOSes, notably some HP Pavilion N5400 and Omnibook XE3 notebooks. This will have no effect if ACPI IRQ routing is enabled. noacpi [X86] Do not use ACPI for IRQ routing or for PCI scanning. use_crs [X86] Use PCI host bridge window information from ACPI. On BIOSes from 2008 or later, this is enabled by default. If you need to use this, please report a bug. nocrs [X86] Ignore PCI host bridge windows from ACPI. If you need to use this, please report a bug. use_e820 [X86] Use E820 reservations to exclude parts of PCI host bridge windows. This is a workaround for BIOS defects in host bridge _CRS methods. If you need to use this, please report a bug to <linux-pci@vger.kernel.org>. no_e820 [X86] Ignore E820 reservations for PCI host bridge windows. This is the default on modern hardware. If you need to use this, please report a bug to <linux-pci@vger.kernel.org>. routeirq Do IRQ routing for all PCI devices. This is normally done in pci_enable_device(), so this option is a temporary workaround for broken drivers that don't call it. skip_isa_align [X86] do not align io start addr, so can handle more pci cards noearly [X86] Don't do any early type 1 scanning. This might help on some broken boards which machine check when some devices' config space is read. But various workarounds are disabled and some IOMMU drivers will not work. bfsort Sort PCI devices into breadth-first order. This sorting is done to get a device order compatible with older (<= 2.4) kernels. nobfsort Don't sort PCI devices into breadth-first order. pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) tuning and use the BIOS-configured MPS defaults. pcie_bus_safe Set every device's MPS to the largest value supported by all devices below the root complex. pcie_bus_perf Set device MPS to the largest allowable MPS based on its parent bus. Also set MRRS (Max Read Request Size) to the largest supported value (no larger than the MPS that the device or bus can support) for best performance. pcie_bus_peer2peer Set every device's MPS to 128B, which every device is guaranteed to support. This configuration allows peer-to-peer DMA between any pair of devices, possibly at the cost of reduced performance. This also guarantees that hot-added devices will work. cbiosize=nn[KMG] The fixed amount of bus space which is reserved for the CardBus bridge's IO window. The default value is 256 bytes. cbmemsize=nn[KMG] The fixed amount of bus space which is reserved for the CardBus bridge's memory window. The default value is 64 megabytes. resource_alignment= Format: [<order of align>@]<pci_dev>[; ...] Specifies alignment and device to reassign aligned memory resources. How to specify the device is described above. If <order of align> is not specified, PAGE_SIZE is used as alignment. A PCI-PCI bridge can be specified if resource windows need to be expanded. To specify the alignment for several instances of a device, the PCI vendor, device, subvendor, and subdevice may be specified, e.g., 12@pci:8086:9c22:103c:198f for 4096-byte alignment. ecrc= Enable/disable PCIe ECRC (transaction layer end-to-end CRC checking). Only effective if OS has native AER control (either granted by ACPI _OSC or forced via "pcie_ports=native") bios: Use BIOS/firmware settings. This is the the default. off: Turn ECRC off on: Turn ECRC on. hpiosize=nn[KMG] The fixed amount of bus space which is reserved for hotplug bridge's IO window. Default size is 256 bytes. hpmmiosize=nn[KMG] The fixed amount of bus space which is reserved for hotplug bridge's MMIO window. Default size is 2 megabytes. hpmmioprefsize=nn[KMG] The fixed amount of bus space which is reserved for hotplug bridge's MMIO_PREF window. Default size is 2 megabytes. hpmemsize=nn[KMG] The fixed amount of bus space which is reserved for hotplug bridge's MMIO and MMIO_PREF window. Default size is 2 megabytes. hpbussize=nn The minimum amount of additional bus numbers reserved for buses below a hotplug bridge. Default is 1. realloc= Enable/disable reallocating PCI bridge resources if allocations done by BIOS are too small to accommodate resources required by all child devices. off: Turn realloc off on: Turn realloc on realloc same as realloc=on noari do not use PCIe ARI. noats [PCIE, Intel-IOMMU, AMD-IOMMU] do not use PCIe ATS (and IOMMU device IOTLB). pcie_scan_all Scan all possible PCIe devices. Otherwise we only look for one device below a PCIe downstream port. big_root_window Try to add a big 64bit memory window to the PCIe root complex on AMD CPUs. Some GFX hardware can resize a BAR to allow access to all VRAM. Adding the window is slightly risky (it may conflict with unreported devices), so this taints the kernel. disable_acs_redir=<pci_dev>[; ...] Specify one or more PCI devices (in the format specified above) separated by semicolons. Each device specified will have the PCI ACS redirect capabilities forced off which will allow P2P traffic between devices through bridges without forcing it upstream. Note: this removes isolation between devices and may put more devices in an IOMMU group. config_acs= Format: <ACS flags>@<pci_dev>[; ...] Specify one or more PCI devices (in the format specified above) optionally prepended with flags and separated by semicolons. The respective capabilities will be enabled, disabled or unchanged based on what is specified in flags.
ACS Flags is defined as follows: bit-0 : ACS Source Validation bit-1 : ACS Translation Blocking bit-2 : ACS P2P Request Redirect bit-3 : ACS P2P Completion Redirect bit-4 : ACS Upstream Forwarding bit-5 : ACS P2P Egress Control bit-6 : ACS Direct Translated P2P Each bit can be marked as: '0' – force disabled '1' – force enabled 'x' – unchanged For example, pci=config_acs=10x@pci:0:0 would configure all devices that support ACS to enable P2P Request Redirect, disable Translation Blocking, and leave Source Validation unchanged from whatever power-up or firmware set it to.
Note: this may remove isolation between devices and may put more devices in an IOMMU group. force_floating [S390] Force usage of floating interrupts. nomio [S390] Do not use MIO instructions. norid [S390] ignore the RID field and force use of one PCI domain per PCI function notph [PCIE] If the PCIE_TPH kernel config parameter is enabled, this kernel boot option can be used to disable PCIe TLP Processing Hints support system-wide.
pcie_aspm= [PCIE] Forcibly enable or ignore PCIe Active State Power Management. off Don't touch ASPM configuration at all. Leave any configuration done by firmware unchanged. force Enable ASPM even on devices that claim not to support it. WARNING: Forcing ASPM on may cause system lockups.
pcie_ports= [PCIE] PCIe port services handling: native Use native PCIe services (PME, AER, DPC, PCIe hotplug) even if the platform doesn't give the OS permission to use them. This may cause conflicts if the platform also tries to use these services. dpc-native Use native PCIe service for DPC only. May cause conflicts if firmware uses AER or DPC. compat Disable native PCIe services (PME, AER, DPC, PCIe hotplug).
pcie_port_pm= [PCIE] PCIe port power management handling: off Disable power management of all PCIe ports force Forcibly enable power management of all PCIe ports
pcie_pme= [PCIE,PM] Native PCIe PME signaling options: nomsi Do not use MSI for native PCIe PME signaling (this makes all PCIe root ports use INTx for all services).
pcmv= [HW,PCMCIA] BadgePAD 4
pd_ignore_unused [PM] Keep all power-domains already enabled by bootloader on, even if no driver has claimed them. This is useful for debug and development, but should not be needed on a platform with proper driver support.
pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at boot time. Format: { 0 | 1 } See arch/parisc/kernel/pdc_chassis.c
percpu_alloc= [MM,EARLY] Select which percpu first chunk allocator to use. Currently supported values are "embed" and "page". Archs may support subset or none of the selections. See comments in mm/percpu.c for details on each allocator. This parameter is primarily for debugging and performance comparison.
pirq= [SMP,APIC] Manual mp-table setup See Documentation/arch/x86/i386/IO-APIC.rst.
plip= [PPT,NET] Parallel port network link Format: { parport<nr> | timid | 0 } See also Documentation/admin-guide/parport.rst.
pmtmr= [X86] Manual setup of pmtmr I/O Port. Override pmtimer IOPort with a hex value. e.g. pmtmr=0x508
pmu_override= [PPC] Override the PMU. This option takes over the PMU facility, so it is no longer usable by perf. Setting this option starts the PMU counters by setting MMCR0 to 0 (the FC bit is cleared). If a number is given, then MMCR1 is set to that number, otherwise (e.g., 'pmu_override=on'), MMCR1 remains 0.
pm_async= [PM] Format: off This parameter sets the initial value of the /sys/power/pm_async sysfs knob at boot time. If set to "off", disables asynchronous suspend and resume of devices during system-wide power transitions. This can be useful on platforms where device dependencies are not well-defined, or for debugging power management issues. Asynchronous operations are enabled by default.
pm_debug_messages [SUSPEND,KNL] Enable suspend/resume debug messages during boot up.
pnp.debug=1 [PNP] Enable PNP debug messages (depends on the CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time via /sys/module/pnp/parameters/debug. We always show current resource usage; turning this on also shows possible settings and some assignment information.
pnpacpi= [ACPI] { off }
pnpbios= [ISAPNP] { on | off | curr | res | no-curr | no-res }
pnp_reserve_irq= [ISAPNP] Exclude IRQs for the autoconfiguration
pnp_reserve_dma= [ISAPNP] Exclude DMAs for the autoconfiguration
pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration Ranges are in pairs (I/O port base and size).
pnp_reserve_mem= [ISAPNP] Exclude memory regions for the autoconfiguration. Ranges are in pairs (memory base and size).
ports= [IP_VS_FTP] IPVS ftp helper module Default is 21. Up to 8 (IP_VS_APP_MAX_PORTS) ports may be specified. Format: <port>,<port>....
possible_cpus= [SMP,S390,X86] Format: <unsigned int> Set the number of possible CPUs, overriding the regular discovery mechanisms (such as ACPI/FW, etc).
powersave=off [PPC] This option disables power saving features. It specifically disables cpuidle and sets the platform machine description specific power_save function to NULL. On Idle the CPU just reduces execution priority.
ppc_strict_facility_enable [PPC,ENABLE] This option catches any kernel floating point, Altivec, VSX and SPE outside of regions specifically allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). There is some performance impact when enabling this.
ppc_tm= [PPC,EARLY] Format: {"off"} Disable Hardware Transactional Memory
preempt= [KNL] Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC none - Limited to cond_resched() calls voluntary - Limited to cond_resched() and might_sleep() calls full - Any section that isn't explicitly preempt disabled can be preempted anytime. Tasks will also yield contended spinlocks (if the critical section isn't explicitly preempt disabled beyond the lock itself). lazy - Scheduler controlled. Similar to full but instead of preempting the task immediately, the task gets one HZ tick time to yield itself before the preemption will be forced. One preemption is when the task returns to user space.
print-fatal-signals= [KNL] debug: print fatal signals
If enabled, warn about various signal handling related application anomalies: too many signals, too many POSIX.1 timers, fatal signals causing a coredump - etc.
If you hit the warning due to signal overflow, you might want to try "ulimit -i unlimited".
default: off.
printk.always_kmsg_dump= Trigger kmsg_dump for cases other than kernel oops or panics Format: <bool> (1/Y/y=enable, 0/N/n=disable) default: disabled
printk.console_no_auto_verbose= Disable console loglevel raise on oops, panic or lockdep-detected issues (only if lock debug is on). With an exception to setups with low baudrate on serial console, keeping this 0 is a good choice in order to provide more debug information. Format: <bool> default: 0 (auto_verbose is enabled)
printk.debug_non_panic_cpus= Allows storing messages from non-panic CPUs into the printk log buffer during panic(). They are flushed to consoles by the panic-CPU on a best-effort basis. Format: <bool> (1/Y/y=enable, 0/N/n=disable) Default: disabled
printk.devkmsg={on,off,ratelimit} Control writing to /dev/kmsg. on - unlimited logging to /dev/kmsg from userspace off - logging to /dev/kmsg disabled ratelimit - ratelimit the logging Default: ratelimit
printk.time= Show timing data prefixed to each printk message line Format: <bool> (1/Y/y=enable, 0/N/n=disable)
proc_mem.force_override= [KNL] Format: {always | ptrace | never} Traditionally /proc/pid/mem allows memory permissions to be overridden without restrictions. This option may be set to restrict that. Can be one of: - 'always': traditional behavior always allows mem overrides. - 'ptrace': only allow mem overrides for active ptracers. - 'never': never allow mem overrides. If not specified, default is the CONFIG_PROC_MEM_* choice.
processor.max_cstate= [HW,ACPI] Limit processor to maximum C-state max_cstate=9 overrides any DMI blacklist limit.
processor.nocst [HW,ACPI] Ignore the _CST method to determine C-states, instead using the legacy FADT method
profile= [KNL] Enable kernel profiling via /proc/profile Format: [<profiletype>,]<number> Param: <profiletype>: "schedule" or "kvm" [defaults to kernel profiling] Param: "schedule" - profile schedule points. Param: "kvm" - profile VM exits. Param: <number> - step/bucket size as a power of 2 for statistical time based profiling.
prot_virt= [S390] enable hosting protected virtual machines isolated from the hypervisor (if hardware supports that). If enabled, the default kernel base address might be overridden even when Kernel Address Space Layout Randomization is disabled. Format: <bool>
psi= [KNL] Enable or disable pressure stall information tracking. Format: <bool>
psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to probe for; one of (bare|imps|exps|lifebook|any). psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports per second. psmouse.resetafter= [HW,MOUSE] Try to reset the device after so many bad packets (0 = never). psmouse.resolution= [HW,MOUSE] Set desired mouse resolution, in dpi. psmouse.smartscroll= [HW,MOUSE] Controls Logitech smartscroll autorepeat. 0 = disabled, 1 = enabled (default).
pstore.backend= Specify the name of the pstore backend to use
pti= [X86-64] Control Page Table Isolation of user and kernel address spaces. Disabling this feature removes hardening, but improves performance of system calls and interrupts.
on - unconditionally enable off - unconditionally disable auto - kernel detects whether your CPU model is vulnerable to issues that PTI mitigates
Not specifying this option is equivalent to pti=auto.
pty.legacy_count= [KNL] Number of legacy pty's. Overwrites compiled-in default number.
quiet [KNL,EARLY] Disable most log messages
r128= [HW,DRM]
radix_hcall_invalidate=on [PPC/PSERIES] Disable RADIX GTSE feature and use hcall for TLB invalidate.
raid= [HW,RAID] See Documentation/admin-guide/md.rst.
ramdisk_size= [RAM] Sizes of RAM disks in kilobytes See Documentation/admin-guide/blockdev/ramdisk.rst.
ramdisk_start= [Deprecated,RAM] RAM disk image start address
random.trust_cpu=off [KNL,EARLY] Disable trusting the use of the CPU's random number generator (if available) to initialize the kernel's RNG.
random.trust_bootloader=off [KNL,EARLY] Disable trusting the use of the a seed passed by the bootloader (if available) to initialize the kernel's RNG.
randomize_kstack_offset= [KNL,EARLY] Enable or disable kernel stack offset randomization, which provides roughly 5 bits of entropy, frustrating memory corruption attacks that depend on stack address determinism or cross-syscall address exposures. This is only available on architectures that have defined CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET. Format: <bool> (1/Y/y=enable, 0/N/n=disable) Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT.
ras=option[,option,...] [KNL] RAS-specific options
cec_disable [X86] Disable the Correctable Errors Collector, see CONFIG_RAS_CEC help text.
rcu_nocbs[=cpu-list] [KNL] The optional argument is a cpu list, as described above.
In kernels built with CONFIG_RCU_NOCB_CPU=y, enable the no-callback CPU mode, which prevents such CPUs' callbacks from being invoked in softirq context. Invocation of such CPUs' RCU callbacks will instead be offloaded to "rcuox/N" kthreads created for that purpose, where "x" is "p" for RCU-preempt, "s" for RCU-sched, and "g" for the kthreads that mediate grace periods; and "N" is the CPU number. This reduces OS jitter on the offloaded CPUs, which can be useful for HPC and real-time workloads. It can also improve energy efficiency for asymmetric multiprocessors.
If a cpulist is passed as an argument, the specified list of CPUs is set to no-callback mode from boot.
Otherwise, if the '=' sign and the cpulist arguments are omitted, no CPU will be set to no-callback mode from boot but the mode may be toggled at runtime via cpusets.
Note that this argument takes precedence over the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.
rcu_nocb_poll [KNL] Rather than requiring that offloaded CPUs (specified by rcu_nocbs= above) explicitly awaken the corresponding "rcuoN" kthreads, make these kthreads poll for callbacks. This improves the real-time response for the offloaded CPUs by relieving them of the need to wake up the corresponding kthread, but degrades energy efficiency by requiring that the kthreads periodically wake up to do the polling.
rcutree.blimit= [KNL] Set maximum number of finished RCU callbacks to process in one batch.
rcutree.csd_lock_suppress_rcu_stall= [KNL] Do only a one-line RCU CPU stall warning when there is an ongoing too-long CSD-lock wait.
rcutree.do_rcu_barrier= [KNL] Request a call to rcu_barrier(). This is throttled so that userspace tests can safely hammer on the sysfs variable if they so choose. If triggered before the RCU grace-period machinery is fully active, this will error out with EAGAIN.
rcutree.dump_tree= [KNL] Dump the structure of the rcu_node combining tree out at early boot. This is used for diagnostic purposes, to verify correct tree setup.
rcutree.gp_cleanup_delay= [KNL] Set the number of jiffies to delay each step of RCU grace-period cleanup.
rcutree.gp_init_delay= [KNL] Set the number of jiffies to delay each step of RCU grace-period initialization.
rcutree.gp_preinit_delay= [KNL] Set the number of jiffies to delay each step of RCU grace-period pre-initialization, that is, the propagation of recent CPU-hotplug changes up the rcu_node combining tree.
rcutree.jiffies_till_first_fqs= [KNL] Set delay from grace-period initialization to first attempt to force quiescent states. Units are jiffies, minimum value is zero, and maximum value is HZ.
rcutree.jiffies_till_next_fqs= [KNL] Set delay between subsequent attempts to force quiescent states. Units are jiffies, minimum value is one, and maximum value is HZ.
rcutree.jiffies_till_sched_qs= [KNL] Set required age in jiffies for a given grace period before RCU starts soliciting quiescent-state help from rcu_note_context_switch() and cond_resched(). If not specified, the kernel will calculate a value based on the most recent settings of rcutree.jiffies_till_first_fqs and rcutree.jiffies_till_next_fqs. This calculated value may be viewed in rcutree.jiffies_to_sched_qs. Any attempt to set rcutree.jiffies_to_sched_qs will be cheerfully overwritten.
rcutree.kthread_prio= [KNL,BOOT] Set the SCHED_FIFO priority of the RCU per-CPU kthreads (rcuc/N). This value is also used for the priority of the RCU boost threads (rcub/N) and for the RCU grace-period kthreads (rcu_bh, rcu_preempt, and rcu_sched). If RCU_BOOST is set, valid values are 1-99 and the default is 1 (the least-favored priority). Otherwise, when RCU_BOOST is not set, valid values are 0-99 and the default is zero (non-realtime operation). When RCU_NOCB_CPU is set, also adjust the priority of NOCB callback kthreads.
rcutree.nocb_nobypass_lim_per_jiffy= [KNL] On callback-offloaded (rcu_nocbs) CPUs, RCU reduces the lock contention that would otherwise be caused by callback floods through use of the ->nocb_bypass list. However, in the common non-flooded case, RCU queues directly to the main ->cblist in order to avoid the extra overhead of the ->nocb_bypass list and its lock. But if there are too many callbacks queued during a single jiffy, RCU pre-queues the callbacks into the ->nocb_bypass queue. The definition of "too many" is supplied by this kernel boot parameter.
rcutree.nohz_full_patience_delay= [KNL] On callback-offloaded (rcu_nocbs) CPUs, avoid disturbing RCU unless the grace period has reached the specified age in milliseconds. Defaults to zero. Large values will be capped at five seconds. All values will be rounded down to the nearest value representable by jiffies.
rcutree.qhimark= [KNL] Set threshold of queued RCU callbacks beyond which batch limiting is disabled.
rcutree.qlowmark= [KNL] Set threshold of queued RCU callbacks below which batch limiting is re-enabled.
rcutree.qovld= [KNL] Set threshold of queued RCU callbacks beyond which RCU's force-quiescent-state scan will aggressively enlist help from cond_resched() and sched IPIs to help CPUs more quickly reach quiescent states. Set to less than zero to make this be set based on rcutree.qhimark at boot time and to zero to disable more aggressive help enlistment.
rcutree.rcu_delay_page_cache_fill_msec= [KNL] Set the page-cache refill delay (in milliseconds) in response to low-memory conditions. The range of permitted values is in the range 0:100000.
rcutree.rcu_divisor= [KNL] Set the shift-right count to use to compute the callback-invocation batch limit bl from the number of callbacks queued on this CPU. The result will be bounded below by the value of the rcutree.blimit kernel parameter. Every bl callbacks, the softirq handler will exit in order to allow the CPU to do other work.
Please note that this callback-invocation batch limit applies only to non-offloaded callback invocation. Offloaded callbacks are instead invoked in the context of an rcuoc kthread, which scheduler will preempt as it does any other task.
rcutree.rcu_fanout_exact= [KNL] Disable autobalancing of the rcu_node combining tree. This is used by rcutorture, and might possibly be useful for architectures having high cache-to-cache transfer latencies.
rcutree.rcu_fanout_leaf= [KNL] Change the number of CPUs assigned to each leaf rcu_node structure. Useful for very large systems, which will choose the value 64, and for NUMA systems with large remote-access latencies, which will choose a value aligned with the appropriate hardware boundaries.
rcutree.rcu_min_cached_objs= [KNL] Minimum number of objects which are cached and maintained per one CPU. Object size is equal to PAGE_SIZE. The cache allows to reduce the pressure to page allocator, also it makes the whole algorithm to behave better in low memory condition.
rcutree.rcu_nocb_gp_stride= [KNL] Set the number of NOCB callback kthreads in each group, which defaults to the square root of the number of CPUs. Larger numbers reduce the wakeup overhead on the global grace-period kthread, but increases that same overhead on each group's NOCB grace-period kthread.
rcutree.rcu_kick_kthreads= [KNL] Cause the grace-period kthread to get an extra wake_up() if it sleeps three times longer than it should at force-quiescent-state time. This wake_up() will be accompanied by a WARN_ONCE() splat and an ftrace_dump().
rcutree.rcu_resched_ns= [KNL] Limit the time spend invoking a batch of RCU callbacks to the specified number of nanoseconds. By default, this limit is checked only once every 32 callbacks in order to limit the pain inflicted by local_clock() overhead.
rcutree.rcu_unlock_delay= [KNL] In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, this specifies an rcu_read_unlock()-time delay in microseconds. This defaults to zero. Larger delays increase the probability of catching RCU pointer leaks, that is, buggy use of RCU-protected pointers after the relevant rcu_read_unlock() has completed.
rcutree.sysrq_rcu= [KNL] Commandeer a sysrq key to dump out Tree RCU's rcu_node tree with an eye towards determining why a new grace period has not yet started.
rcutree.use_softirq= [KNL] If set to zero, move all RCU_SOFTIRQ processing to per-CPU rcuc kthreads. Defaults to a non-zero value, meaning that RCU_SOFTIRQ is used by default. Specify rcutree.use_softirq=0 to use rcuc kthreads.
But note that CONFIG_PREEMPT_RT=y kernels disable this kernel boot parameter, forcibly setting it to zero.
rcutree.enable_rcu_lazy= [KNL] To save power, batch RCU callbacks and flush after delay, memory pressure or callback list growing too big.
rcutree.rcu_normal_wake_from_gp= [KNL] Reduces a latency of synchronize_rcu() call. This approach maintains its own track of synchronize_rcu() callers, so it does not interact with regular callbacks because it does not use a call_rcu[_hurry]() path. Please note, this is for a normal grace period.
How to disable it:
echo 0 > /sys/module/rcutree/parameters/rcu_normal_wake_from_gp or pass a boot parameter "rcutree.rcu_normal_wake_from_gp=0"
Default is 1 if it is not explicitly disabled by the boot parameter passing 0.
rcuscale.gp_async= [KNL] Measure performance of asynchronous grace-period primitives such as call_rcu().
rcuscale.gp_async_max= [KNL] Specify the maximum number of outstanding callbacks per writer thread. When a writer thread exceeds this limit, it invokes the corresponding flavor of rcu_barrier() to allow previously posted callbacks to drain.
rcuscale.gp_exp= [KNL] Measure performance of expedited synchronous grace-period primitives.
rcuscale.holdoff= [KNL] Set test-start holdoff period. The purpose of this parameter is to delay the start of the test until boot completes in order to avoid interference.
rcuscale.kfree_by_call_rcu= [KNL] In kernels built with CONFIG_RCU_LAZY=y, test call_rcu() instead of kfree_rcu().
rcuscale.kfree_mult= [KNL] Instead of allocating an object of size kfree_obj, allocate one of kfree_mult * sizeof(kfree_obj). Defaults to 1.
rcuscale.kfree_rcu_test= [KNL] Set to measure performance of kfree_rcu() flooding.
rcuscale.kfree_rcu_test_double= [KNL] Test the double-argument variant of kfree_rcu(). If this parameter has the same value as rcuscale.kfree_rcu_test_single, both the single- and double-argument variants are tested.
rcuscale.kfree_rcu_test_single= [KNL] Test the single-argument variant of kfree_rcu(). If this parameter has the same value as rcuscale.kfree_rcu_test_double, both the single- and double-argument variants are tested.
rcuscale.kfree_nthreads= [KNL] The number of threads running loops of kfree_rcu().
rcuscale.kfree_alloc_num= [KNL] Number of allocations and frees done in an iteration.
rcuscale.kfree_loops= [KNL] Number of loops doing rcuscale.kfree_alloc_num number of allocations and frees.
rcuscale.minruntime= [KNL] Set the minimum test run time in seconds. This does not affect the data-collection interval, but instead allows better measurement of things like CPU consumption.
rcuscale.nreaders= [KNL] Set number of RCU readers. The value -1 selects N, where N is the number of CPUs. A value "n" less than -1 selects N-n+1, where N is again the number of CPUs. For example, -2 selects N (the number of CPUs), -3 selects N+1, and so on. A value of "n" less than or equal to -N selects a single reader.
rcuscale.nwriters= [KNL] Set number of RCU writers. The values operate the same as for rcuscale.nreaders. N, where N is the number of CPUs
rcuscale.scale_type= [KNL] Specify the RCU implementation to test.
rcuscale.shutdown= [KNL] Shut the system down after performance tests complete. This is useful for hands-off automated testing.
rcuscale.verbose= [KNL] Enable additional printk() statements.
rcuscale.writer_holdoff= [KNL] Write-side holdoff between grace periods, in microseconds. The default of zero says no holdoff.
rcuscale.writer_holdoff_jiffies= [KNL] Additional write-side holdoff between grace periods, but in jiffies. The default of zero says no holdoff.
rcutorture.fqs_duration= [KNL] Set duration of force_quiescent_state bursts in microseconds.
rcutorture.fqs_holdoff= [KNL] Set holdoff time within force_quiescent_state bursts in microseconds.
rcutorture.fqs_stutter= [KNL] Set wait time between force_quiescent_state bursts in seconds.
rcutorture.fwd_progress= [KNL] Specifies the number of kthreads to be used for RCU grace-period forward-progress testing for the types of RCU supporting this notion. Defaults to 1 kthread, values less than zero or greater than the number of CPUs cause the number of CPUs to be used.
rcutorture.fwd_progress_div= [KNL] Specify the fraction of a CPU-stall-warning period to do tight-loop forward-progress testing.
rcutorture.fwd_progress_holdoff= [KNL] Number of seconds to wait between successive forward-progress tests.
rcutorture.fwd_progress_need_resched= [KNL] Enclose cond_resched() calls within checks for need_resched() during tight-loop forward-progress testing.
rcutorture.gp_cond= [KNL] Use conditional/asynchronous update-side normal-grace-period primitives, if available.
rcutorture.gp_cond_exp= [KNL] Use conditional/asynchronous update-side expedited-grace-period primitives, if available.
rcutorture.gp_cond_full= [KNL] Use conditional/asynchronous update-side normal-grace-period primitives that also take concurrent expedited grace periods into account, if available.
rcutorture.gp_cond_exp_full= [KNL] Use conditional/asynchronous update-side expedited-grace-period primitives that also take concurrent normal grace periods into account, if available.
rcutorture.gp_cond_wi= [KNL] Nominal wait interval for normal conditional grace periods (specified by rcutorture's gp_cond and gp_cond_full module parameters), in microseconds. The actual wait interval will be randomly selected to nanosecond granularity up to this wait interval. Defaults to 16 jiffies, for example, 16,000 microseconds on a system with HZ=1000.
rcutorture.gp_cond_wi_exp= [KNL] Nominal wait interval for expedited conditional grace periods (specified by rcutorture's gp_cond_exp and gp_cond_exp_full module parameters), in microseconds. The actual wait interval will be randomly selected to nanosecond granularity up to this wait interval. Defaults to 128 microseconds.
rcutorture.gp_exp= [KNL] Use expedited update-side primitives, if available.
rcutorture.gp_normal= [KNL] Use normal (non-expedited) asynchronous update-side primitives, if available.
rcutorture.gp_poll= [KNL] Use polled update-side normal-grace-period primitives, if available.
rcutorture.gp_poll_exp= [KNL] Use polled update-side expedited-grace-period primitives, if available.
rcutorture.gp_poll_full= [KNL] Use polled update-side normal-grace-period primitives that also take concurrent expedited grace periods into account, if available.
rcutorture.gp_poll_exp_full= [KNL] Use polled update-side expedited-grace-period primitives that also take concurrent normal grace periods into account, if available.
rcutorture.gp_poll_wi= [KNL] Nominal wait interval for normal conditional grace periods (specified by rcutorture's gp_poll and gp_poll_full module parameters), in microseconds. The actual wait interval will be randomly selected to nanosecond granularity up to this wait interval. Defaults to 16 jiffies, for example, 16,000 microseconds on a system with HZ=1000.
rcutorture.gp_poll_wi_exp= [KNL] Nominal wait interval for expedited conditional grace periods (specified by rcutorture's gp_poll_exp and gp_poll_exp_full module parameters), in microseconds. The actual wait interval will be randomly selected to nanosecond granularity up to this wait interval. Defaults to 128 microseconds.
rcutorture.gp_sync= [KNL] Use normal (non-expedited) synchronous update-side primitives, if available. If all of rcutorture.gp_cond=, rcutorture.gp_exp=, rcutorture.gp_normal=, and rcutorture.gp_sync= are zero, rcutorture acts as if is interpreted they are all non-zero.
rcutorture.gpwrap_lag= [KNL] Enable grace-period wrap lag testing. Setting to false prevents the gpwrap lag test from running. Default is true.
rcutorture.gpwrap_lag_gps= [KNL] Set the value for grace-period wrap lag during active lag testing periods. This controls how many grace periods differences we tolerate between rdp and rnp's gp_seq before setting overflow flag. The default is always set to 8.
rcutorture.gpwrap_lag_cycle_mins= [KNL] Set the total cycle duration for gpwrap lag testing in minutes. This is the total time for one complete cycle of active and inactive testing periods. Default is 30 minutes.
rcutorture.gpwrap_lag_active_mins= [KNL] Set the duration for which gpwrap lag is active within each cycle, in minutes. During this time, the grace-period wrap lag will be set to the value specified by gpwrap_lag_gps. Default is 5 minutes.
rcutorture.irqreader= [KNL] Run RCU readers from irq handlers, or, more accurately, from a timer handler. Not all RCU flavors take kindly to this sort of thing.
rcutorture.leakpointer= [KNL] Leak an RCU-protected pointer out of the reader. This can of course result in splats, and is intended to test the ability of things like CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect such leaks.
rcutorture.n_barrier_cbs= [KNL] Set callbacks/threads for rcu_barrier() testing.
rcutorture.nfakewriters= [KNL] Set number of concurrent RCU writers. These just stress RCU, they don't participate in the actual test, hence the "fake".
rcutorture.nocbs_nthreads= [KNL] Set number of RCU callback-offload togglers. Zero (the default) disables toggling.
rcutorture.nocbs_toggle= [KNL] Set the delay in milliseconds between successive callback-offload toggling attempts.
rcutorture.nreaders= [KNL] Set number of RCU readers. The value -1 selects N-1, where N is the number of CPUs. A value "n" less than -1 selects N-n-2, where N is again the number of CPUs. For example, -2 selects N (the number of CPUs), -3 selects N+1, and so on.
rcutorture.object_debug= [KNL] Enable debug-object double-call_rcu() testing.
rcutorture.onoff_holdoff= [KNL] Set time (s) after boot for CPU-hotplug testing.
rcutorture.onoff_interval= [KNL] Set time (jiffies) between CPU-hotplug operations, or zero to disable CPU-hotplug testing.
rcutorture.preempt_duration= [KNL] Set duration (in milliseconds) of preemptions by a high-priority FIFO real-time task. Set to zero (the default) to disable. The CPUs to preempt are selected randomly from the set that are online at a given point in time. Races with CPUs going offline are ignored, with that attempt at preemption skipped.
rcutorture.preempt_interval= [KNL] Set interval (in milliseconds, defaulting to one second) between preemptions by a high-priority FIFO real-time task. This delay is mediated by an hrtimer and is further fuzzed to avoid inadvertent synchronizations.
rcutorture.read_exit_burst= [KNL] The number of times in a given read-then-exit episode that a set of read-then-exit kthreads is spawned.
rcutorture.read_exit_delay= [KNL] The delay, in seconds, between successive read-then-exit testing episodes.
rcutorture.reader_flavor= [KNL] A bit mask indicating which readers to use. If there is more than one bit set, the readers are entered from low-order bit up, and are exited in the opposite order. For SRCU, the 0x1 bit is normal readers, 0x2 NMI-safe readers, and 0x4 light-weight readers.
rcutorture.shuffle_interval= [KNL] Set task-shuffle interval (s). Shuffling tasks allows some CPUs to go into dyntick-idle mode during the rcutorture test.
rcutorture.shutdown_secs= [KNL] Set time (s) after boot system shutdown. This is useful for hands-off automated testing.
rcutorture.stall_cpu= [KNL] Duration of CPU stall (s) to test RCU CPU stall warnings, zero to disable.
rcutorture.stall_cpu_block= [KNL] Sleep while stalling if set. This will result in warnings from preemptible RCU in addition to any other stall-related activity. Note that in kernels built with CONFIG_PREEMPTION=n and CONFIG_PREEMPT_COUNT=y, this parameter will cause the CPU to pass through a quiescent state. Given CONFIG_PREEMPTION=n, this will suppress RCU CPU stall warnings, but will instead result in scheduling-while-atomic splats.
Use of this module parameter results in splats.
rcutorture.stall_cpu_holdoff= [KNL] Time to wait (s) after boot before inducing stall.
rcutorture.stall_cpu_irqsoff= [KNL] Disable interrupts while stalling if set, but only on the first stall in the set.
rcutorture.stall_cpu_repeat= [KNL] Number of times to repeat the stall sequence, so that rcutorture.stall_cpu_repeat=3 will result in four stall sequences.
rcutorture.stall_gp_kthread= [KNL] Duration (s) of forced sleep within RCU grace-period kthread to test RCU CPU stall warnings, zero to disable. If both stall_cpu and stall_gp_kthread are specified, the kthread is starved first, then the CPU.
rcutorture.stat_interval= [KNL] Time (s) between statistics printk()s.
rcutorture.stutter= [KNL] Time (s) to stutter testing, for example, specifying five seconds causes the test to run for five seconds, wait for five seconds, and so on. This tests RCU's ability to transition abruptly to and from idle.
rcutorture.test_boost= [KNL] Test RCU priority boosting? 0=no, 1=maybe, 2=yes. "Maybe" means test if the RCU implementation under test support RCU priority boosting.
rcutorture.test_boost_duration= [KNL] Duration (s) of each individual boost test.
rcutorture.test_boost_holdoff= [KNL] Holdoff time (s) from start of test to the start of RCU priority-boost testing. Defaults to zero, that is, no holdoff.
rcutorture.test_boost_interval= [KNL] Interval (s) between each boost test.
rcutorture.test_no_idle_hz= [KNL] Test RCU's dyntick-idle handling. See also the rcutorture.shuffle_interval parameter.
rcutorture.torture_type= [KNL] Specify the RCU implementation to test.
rcutorture.verbose= [KNL] Enable additional printk() statements.
rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] Dump ftrace buffer after reporting RCU CPU stall warning.
rcupdate.rcu_cpu_stall_notifiers= [KNL] Provide RCU CPU stall notifiers, but see the warnings in the RCU_CPU_STALL_NOTIFIER Kconfig option's help text. TL;DR: You almost certainly do not want rcupdate.rcu_cpu_stall_notifiers.
rcupdate.rcu_cpu_stall_suppress= [KNL] Suppress RCU CPU stall warning messages.
rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] Suppress RCU CPU stall warning messages and rcutorture writer stall warnings that occur during early boot, that is, during the time before the init task is spawned.
rcupdate.rcu_cpu_stall_timeout= [KNL] Set timeout for RCU CPU stall warning messages. The value is in seconds and the maximum allowed value is 300 seconds.
rcupdate.rcu_exp_cpu_stall_timeout= [KNL] Set timeout for expedited RCU CPU stall warning messages. The value is in milliseconds and the maximum allowed value is 21000 milliseconds. Please note that this value is adjusted to an arch timer tick resolution. Setting this to zero causes the value from rcupdate.rcu_cpu_stall_timeout to be used (after conversion from seconds to milliseconds).
rcupdate.rcu_cpu_stall_cputime= [KNL] Provide statistics on the cputime and count of interrupts and tasks during the sampling period. For multiple continuous RCU stalls, all sampling periods begin at half of the first RCU stall timeout.
rcupdate.rcu_exp_stall_task_details= [KNL] Print stack dumps of any tasks blocking the current expedited RCU grace period during an expedited RCU CPU stall warning.
rcupdate.rcu_expedited= [KNL] Use expedited grace-period primitives, for example, synchronize_rcu_expedited() instead of synchronize_rcu(). This reduces latency, but can increase CPU utilization, degrade real-time latency, and degrade energy efficiency. No effect on CONFIG_TINY_RCU kernels.
rcupdate.rcu_normal= [KNL] Use only normal grace-period primitives, for example, synchronize_rcu() instead of synchronize_rcu_expedited(). This improves real-time latency, CPU utilization, and energy efficiency, but can expose users to increased grace-period latency. This parameter overrides rcupdate.rcu_expedited. No effect on CONFIG_TINY_RCU kernels.
rcupdate.rcu_normal_after_boot= [KNL] Once boot has completed (that is, after rcu_end_inkernel_boot() has been invoked), use only normal grace-period primitives. No effect on CONFIG_TINY_RCU kernels.
But note that CONFIG_PREEMPT_RT=y kernels enables this kernel boot parameter, forcibly setting it to the value one, that is, converting any post-boot attempt at an expedited RCU grace period to instead use normal non-expedited grace-period processing.
rcupdate.rcu_task_collapse_lim= [KNL] Set the maximum number of callbacks present at the beginning of a grace period that allows the RCU Tasks flavors to collapse back to using a single callback queue. This switching only occurs when rcupdate.rcu_task_enqueue_lim is set to the default value of -1.
rcupdate.rcu_task_contend_lim= [KNL] Set the minimum number of callback-queuing-time lock-contention events per jiffy required to cause the RCU Tasks flavors to switch to per-CPU callback queuing. This switching only occurs when rcupdate.rcu_task_enqueue_lim is set to the default value of -1.
rcupdate.rcu_task_enqueue_lim= [KNL] Set the number of callback queues to use for the RCU Tasks family of RCU flavors. The default of -1 allows this to be automatically (and dynamically) adjusted. This parameter is intended for use in testing.
rcupdate.rcu_task_lazy_lim= [KNL] Number of callbacks on a given CPU that will cancel laziness on that CPU. Use -1 to disable cancellation of laziness, but be advised that doing so increases the danger of OOM due to callback flooding.
rcupdate.rcu_task_stall_info= [KNL] Set initial timeout in jiffies for RCU task stall informational messages, which give some indication of the problem for those not patient enough to wait for ten minutes. Informational messages are only printed prior to the stall-warning message for a given grace period. Disable with a value less than or equal to zero. Defaults to ten seconds. A change in value does not take effect until the beginning of the next grace period.
rcupdate.rcu_task_stall_info_mult= [KNL] Multiplier for time interval between successive RCU task stall informational messages for a given RCU tasks grace period. This value is clamped to one through ten, inclusive. It defaults to the value three, so that the first informational message is printed 10 seconds into the grace period, the second at 40 seconds, the third at 160 seconds, and then the stall warning at 600 seconds would prevent a fourth at 640 seconds.
rcupdate.rcu_task_stall_timeout= [KNL] Set timeout in jiffies for RCU task stall warning messages. Disable with a value less than or equal to zero. Defaults to ten minutes. A change in value does not take effect until the beginning of the next grace period.
rcupdate.rcu_tasks_lazy_ms= [KNL] Set timeout in milliseconds RCU Tasks asynchronous callback batching for call_rcu_tasks(). A negative value will take the default. A value of zero will disable batching. Batching is always disabled for synchronize_rcu_tasks().
rcupdate.rcu_self_test= [KNL] Run the RCU early boot self tests
rdinit= [KNL] Format: <full_path> Run specified binary instead of /init from the ramdisk, used for early userspace startup. See initrd.
rdrand= [X86,EARLY] force - Override the decision by the kernel to hide the advertisement of RDRAND support (this affects certain AMD processors because of buggy BIOS support, specifically around the suspend/resume path).
rdt= [HW,X86,RDT] Turn on/off individual RDT features. List is: cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, mba, smba, bmec, abmc, sdciae, energy[:guid], perf[:guid]. E.g. to turn on cmt and turn off mba use: rdt=cmt,!mba To turn off all energy telemetry monitoring and ensure that perf telemetry monitoring associated with guid 0x12345 is enabled use: rdt=!energy,perf:0x12345
reboot= [KNL] Format (x86 or x86_64): [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \ [[,]s[mp]#### \ [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ [[,]f[orce] Where reboot_mode is one of warm (soft) or cold (hard) or gpio (prefix with 'panic_' to set mode for panic reboot only), reboot_type is one of bios, acpi, kbd, triple, efi, or pci, reboot_force is either force or not specified, reboot_cpu is s[mp]#### with #### being the processor to be used for rebooting.
acpi Use the ACPI RESET_REG in the FADT. If ACPI is not configured or the ACPI reset does not work, the reboot path attempts the reset using the keyboard controller.
bios Use the CPU reboot vector for warm reset
cold Set the cold reboot flag
default There are some built-in platform specific "quirks" - you may see: "reboot: <name> series board detected. Selecting <type> for reboots." In the case where you think the quirk is in error (e.g. you have newer BIOS, or newer board) using this option will ignore the built-in quirk table, and use the generic default reboot actions.
efi Use efi reset_system runtime service. If EFI is not configured or the EFI reset does not work, the reboot path attempts the reset using the keyboard controller.
force Don't stop other CPUs on reboot. This can make reboot more reliable in some cases.
kbd Use the keyboard controller. cold reset (default)
pci Use a write to the PCI config space register 0xcf9 to trigger reboot.
triple Force a triple fault (init)
warm Don't set the cold reboot flag
Using warm reset will be much faster especially on big memory systems because the BIOS will not go through the memory check. Disadvantage is that not all hardware will be completely reinitialized on reboot so there may be boot problems on some systems.
refscale.holdoff= [KNL] Set test-start holdoff period. The purpose of this parameter is to delay the start of the test until boot completes in order to avoid interference.
refscale.lookup_instances= [KNL] Number of data elements to use for the forms of SLAB_TYPESAFE_BY_RCU testing. A negative number is negated and multiplied by nr_cpu_ids, while zero specifies nr_cpu_ids.
refscale.loops= [KNL] Set the number of loops over the synchronization primitive under test. Increasing this number reduces noise due to loop start/end overhead, but the default has already reduced the per-pass noise to a handful of picoseconds on ca. 2020 x86 laptops.
refscale.nreaders= [KNL] Set number of readers. The default value of -1 selects N, where N is roughly 75% of the number of CPUs. A value of zero is an interesting choice.
refscale.nruns= [KNL] Set number of runs, each of which is dumped onto the console log.
refscale.readdelay= [KNL] Set the read-side critical-section duration, measured in microseconds.
refscale.scale_type= [KNL] Specify the read-protection implementation to test.
refscale.shutdown= [KNL] Shut down the system at the end of the performance test. This defaults to 1 (shut it down) when refscale is built into the kernel and to 0 (leave it running) when refscale is built as a module.
refscale.verbose= [KNL] Enable additional printk() statements.
refscale.verbose_batched= [KNL] Batch the additional printk() statements. If zero (the default) or negative, print everything. Otherwise, print every Nth verbose statement, where N is the value specified.
regulator_ignore_unused [REGULATOR] Prevents regulator framework from disabling regulators that are unused, due no driver claiming them. This may be useful for debug and development, but should not be needed on a platform with proper driver support.
relax_domain_level= [KNL, SMP] Set scheduler's default relax_domain_level. See Documentation/admin-guide/cgroup-v1/cpusets.rst.
reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory Format: <base1>,<size1>[,<base2>,<size2>,...] Reserve I/O ports or memory so the kernel won't use them. If <base> is less than 0x10000, the region is assumed to be I/O ports; otherwise it is memory.
reserve_mem= [RAM] Format: nn[KMG]:<align>:<label> Reserve physical memory and label it with a name that other subsystems can use to access it. This is typically used for systems that do not wipe the RAM, and this command line will try to reserve the same physical memory on soft reboots. Note, it is not guaranteed to be the same location. For example, if anything about the system changes or if booting a different kernel. It can also fail if KASLR places the kernel at the location of where the RAM reservation was from a previous boot, the new reservation will be at a different location. Any subsystem using this feature must add a way to verify that the contents of the physical memory is from a previous boot, as there may be cases where the memory will not be located at the same location.
The format is size:align:label for example, to request 12 megabytes of 4096 alignment for ramoops:
reserve_mem=12M:4096:oops ramoops.mem_name=oops
reservetop= [X86-32,EARLY] Format: nn[KMG] Reserves a hole at the top of the kernel virtual address space.
reset_devices [KNL] Force drivers to reset the underlying device during initialization.
resume= [SWSUSP] Specify the partition device for software suspend Format: {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
resume_offset= [SWSUSP] Specify the offset from the beginning of the partition given by "resume=" at which the swap header is located, in <PAGE_SIZE> units (needed only for swap files). See Documentation/power/swsusp-and-swap-files.rst
resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to read the resume files
resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. Useful for devices that are detected asynchronously (e.g. USB and MMC devices).
retain_initrd [RAM] Keep initrd memory after extraction. After boot, it will be accessible via /sys/firmware/initrd.
retbleed= [X86] Control mitigation of RETBleed (Arbitrary Speculative Code Execution with Return Instructions) vulnerability.
AMD-based UNRET and IBPB mitigations alone do not stop sibling threads from influencing the predictions of other sibling threads. For that reason, STIBP is used on pro- cessors that support it, and mitigate SMT on processors that don't.
off - no mitigation auto - automatically select a mitigation auto,nosmt - automatically select a mitigation, disabling SMT if necessary for the full mitigation (only on Zen1 and older without STIBP). ibpb - On AMD, mitigate short speculation windows on basic block boundaries too. Safe, highest perf impact. It also enables STIBP if present. Not suitable on Intel. ibpb,nosmt - Like "ibpb" above but will disable SMT when STIBP is not available. This is the alternative for systems which do not have STIBP. unret - Force enable untrained return thunks, only effective on AMD f15h-f17h based systems. unret,nosmt - Like unret, but will disable SMT when STIBP is not available. This is the alternative for systems which do not have STIBP.
Selecting 'auto' will choose a mitigation method at run time according to the CPU.
Not specifying this option is equivalent to retbleed=auto.
rfkill.default_state= 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, etc. communication is blocked by default. 1 Unblocked.
rfkill.master_switch_mode= 0 The "airplane mode" button does nothing. 1 The "airplane mode" button toggles between everything blocked and the previous configuration. 2 The "airplane mode" button toggles between everything blocked and everything unblocked.
ring3mwait=disable [KNL] Disable ring 3 MONITOR/MWAIT feature on supported CPUs.
riscv_isa_fallback [RISCV,EARLY] When CONFIG_RISCV_ISA_FALLBACK is not enabled, permit falling back to detecting extension support by parsing "riscv,isa" property on devicetree systems when the replacement properties are not found. See the Kconfig entry for RISCV_ISA_FALLBACK.
riscv_nousercfi= all Disable user CFI ABI to userspace even if cpu extension are available. bcfi Disable user backward CFI ABI to userspace even if the shadow stack extension is available. fcfi Disable user forward CFI ABI to userspace even if the landing pad extension is available.
ro [KNL] Mount root device read-only on boot
rodata= [KNL,EARLY] on Mark read-only kernel memory as read-only (default). off Leave read-only kernel memory writable for debugging. noalias Mark read-only kernel memory as read-only but retain writable aliases in the direct map for regions outside of the kernel image. [arm64]
rockchip.usb_uart [EARLY] Enable the uart passthrough on the designated usb port on Rockchip SoCs. When active, the signals of the debug-uart get routed to the D+ and D- pins of the usb port and the regular usb controller gets disabled.
root= [KNL] Root filesystem Usually this is a block device specifier of some kind, see the early_lookup_bdev comment in block/early-lookup.c for details. Alternatively this can be "ram" for the legacy initial ramdisk, "nfs" and "cifs" for root on a network file system, or "mtd" and "ubi" for mounting from raw flash.
rootdelay= [KNL] Delay (in seconds) to pause before attempting to mount the root filesystem
rootflags= [KNL] Set root filesystem mount option string
rseq_slice_ext= [KNL] RSEQ based time slice extension Format: boolean Control enablement of RSEQ based time slice extension. Default is 'on'.
initramfs_options= [KNL] Specify mount options for the initramfs mount.
rootfstype= [KNL] Set root filesystem type
rootwait [KNL] Wait (indefinitely) for root device to show up. Useful for devices that are detected asynchronously (e.g. USB and MMC devices).
rootwait= [KNL] Maximum time (in seconds) to wait for root device to show up before attempting to mount the root filesystem.
rproc_mem=nn[KMG][@address] [KNL,ARM,CMA] Remoteproc physical memory block. Memory area to be used by remote processor image, managed by CMA.
rseq_debug= [KNL] Enable or disable restartable sequence debug mode. Defaults to CONFIG_RSEQ_DEBUG_DEFAULT_ENABLE. Format: <bool>
rt_group_sched= [KNL] Enable or disable SCHED_RR/FIFO group scheduling when CONFIG_RT_GROUP_SCHED=y. Defaults to !CONFIG_RT_GROUP_SCHED_DEFAULT_DISABLED. Format: <bool>
rw [KNL] Mount root device read-write on boot
S [KNL] Run init in single mode
s390_iommu= [HW,S390] Set s390 IOTLB flushing mode strict With strict flushing every unmap operation will result in an IOTLB flush. Default is lazy flushing before reuse, which is faster. Deprecated, equivalent to iommu.strict=1.
s390_iommu_aperture= [KNL,S390] Specifies the size of the per device DMA address space accessible through the DMA and IOMMU APIs as a decimal factor of the size of main memory. The default is 1 meaning that one can concurrently use as many DMA addresses as physical memory is installed, if supported by hardware, and thus map all of memory once. With a value of 2 one can map all of memory twice and so on. As a special case a factor of 0 imposes no restrictions other than those given by hardware at the cost of significant additional memory use for tables.
sched_proxy_exec= [KNL] Enables or disables "proxy execution" style solution to mutex-based priority inversion. Format: <bool>
sched_verbose [KNL,EARLY] Enables verbose scheduler debug messages.
schedstats= [KNL,X86] Enable or disable scheduled statistics. Allowed values are enable and disable. This feature incurs a small amount of overhead in the scheduler but is useful for debugging and performance tuning.
sched_thermal_decay_shift= [Deprecated] [KNL, SMP] Set a decay shift for scheduler thermal pressure signal. Thermal pressure signal follows the default decay period of other scheduler pelt signals(usually 32 ms but configurable). Setting sched_thermal_decay_shift will left shift the decay period for the thermal pressure signal by the shift value. i.e. with the default pelt decay period of 32 ms sched_thermal_decay_shift thermal pressure decay pr 1 64 ms 2 128 ms and so on. Format: integer between 0 and 10 Default is 0.
scftorture.holdoff= [KNL] Number of seconds to hold off before starting test. Defaults to zero for module insertion and to 10 seconds for built-in smp_call_function() tests.
scftorture.longwait= [KNL] Request ridiculously long waits randomly selected up to the chosen limit in seconds. Zero (the default) disables this feature. Please note that requesting even small non-zero numbers of seconds can result in RCU CPU stall warnings, softlockup complaints, and so on.
scftorture.nthreads= [KNL] Number of kthreads to spawn to invoke the smp_call_function() family of functions. The default of -1 specifies a number of kthreads equal to the number of CPUs.
scftorture.onoff_holdoff= [KNL] Number seconds to wait after the start of the test before initiating CPU-hotplug operations.
scftorture.onoff_interval= [KNL] Number seconds to wait between successive CPU-hotplug operations. Specifying zero (which is the default) disables CPU-hotplug operations.
scftorture.shutdown_secs= [KNL] The number of seconds following the start of the test after which to shut down the system. The default of zero avoids shutting down the system. Non-zero values are useful for automated tests.
scftorture.stat_interval= [KNL] The number of seconds between outputting the current test statistics to the console. A value of zero disables statistics output.
scftorture.stutter_cpus= [KNL] The number of jiffies to wait between each change to the set of CPUs under test.
scftorture.use_cpus_read_lock= [KNL] Use use_cpus_read_lock() instead of the default preempt_disable() to disable CPU hotplug while invoking one of the smp_call_function*() functions.
scftorture.verbose= [KNL] Enable additional printk() statements.
scftorture.weight_single= [KNL] The probability weighting to use for the smp_call_function_single() function with a zero "wait" parameter. A value of -1 selects the default if all other weights are -1. However, if at least one weight has some other value, a value of -1 will instead select a weight of zero.
scftorture.weight_single_wait= [KNL] The probability weighting to use for the smp_call_function_single() function with a non-zero "wait" parameter. See weight_single.
scftorture.weight_many= [KNL] The probability weighting to use for the smp_call_function_many() function with a zero "wait" parameter. See weight_single. Note well that setting a high probability for this weighting can place serious IPI load on the system.
scftorture.weight_many_wait= [KNL] The probability weighting to use for the smp_call_function_many() function with a non-zero "wait" parameter. See weight_single and weight_many.
scftorture.weight_all= [KNL] The probability weighting to use for the smp_call_function_all() function with a zero "wait" parameter. See weight_single and weight_many.
scftorture.weight_all_wait= [KNL] The probability weighting to use for the smp_call_function_all() function with a non-zero "wait" parameter. See weight_single and weight_many.
sdw_mclk_divider=[SDW] Specify the MCLK divider for Intel SoundWire buses in case the BIOS does not provide the clock rate properly.
skew_tick= [KNL,EARLY] Offset the periodic timer tick per cpu to mitigate xtime_lock contention on larger systems, and/or RCU lock contention on all systems with CONFIG_MAXSMP set. Format: { "0" | "1" } 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 1 -- enable. Note: increases power consumption, thus should only be enabled if running jitter sensitive (HPC/RT) workloads.
security= [SECURITY] Choose a legacy "major" security module to enable at boot. This has been deprecated by the "lsm=" parameter.
selinux= [SELINUX] Disable or enable SELinux at boot time. Format: { "0" | "1" } See security/selinux/Kconfig help text. 0 -- disable. 1 -- enable. Default value is 1.
serialnumber [BUGS=X86-32]
sev=option[,option...] [X86-64]
debug Enable debug messages.
nosnp Do not enable SEV-SNP (applies to host/hypervisor only). Setting 'nosnp' avoids the RMP check overhead in memory accesses when users do not want to run SEV-SNP guests.
shapers= [NET] Maximal number of shapers.
show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller Limit apic dumping. The parameter defines the maximal number of local apics being dumped. Also it is possible to set it to "all" by meaning -- no limit here. Format: { 1 (default) | 2 | ... | all }. The parameter valid if only apic=debug or apic=verbose is specified. Example: apic=debug show_lapic=all
slab_debug[=options[,slabs][;[options[,slabs]]...] [MM] Enabling slab_debug allows one to determine the culprit if slab objects become corrupted. Enabling slab_debug can create guard zones around objects and may poison objects when not in use. Also tracks the last alloc / free. For more information see Documentation/admin-guide/mm/slab.rst. (slub_debug legacy name also accepted for now)
Using this option implies the "no_hash_pointers" option which can be undone by adding the "hash_pointers=always" option.
slab_max_order= [MM] Determines the maximum allowed order for slabs. A high setting may cause OOMs due to memory fragmentation. For more information see Documentation/admin-guide/mm/slab.rst. (slub_max_order legacy name also accepted for now)
slab_merge [MM] Enable merging of slabs with similar size when the kernel is built without CONFIG_SLAB_MERGE_DEFAULT. (slub_merge legacy name also accepted for now)
slab_min_objects= [MM] The minimum number of objects per slab. SLUB will increase the slab order up to slab_max_order to generate a sufficiently large slab able to contain the number of objects indicated. The higher the number of objects the smaller the overhead of tracking slabs and the less frequently locks need to be acquired. For more information see Documentation/admin-guide/mm/slab.rst. (slub_min_objects legacy name also accepted for now)
slab_min_order= [MM] Determines the minimum page order for slabs. Must be lower or equal to slab_max_order. For more information see Documentation/admin-guide/mm/slab.rst. (slub_min_order legacy name also accepted for now)
slab_nomerge [MM] Disable merging of slabs with similar size. May be necessary if there is some reason to distinguish allocs to different slabs, especially in hardened environments where the risk of heap overflows and layout control by attackers can usually be frustrated by disabling merging. This will reduce most of the exposure of a heap attack to a single cache (risks via metadata attacks are mostly unchanged). Debug options disable merging on their own. For more information see Documentation/admin-guide/mm/slab.rst. (slub_nomerge legacy name also accepted for now)
slab_strict_numa [MM] Support memory policies on a per object level in the slab allocator. The default is for memory policies to be applied at the folio level when a new folio is needed or a partial folio is retrieved from the lists. Increases overhead in the slab fastpaths but gains more accurate NUMA kernel object placement which helps with slow interconnects in NUMA systems.
slram= [HW,MTD]
smart2= [HW] Format: <io1>[,<io2>[,...,<io8>]]
smp.csd_lock_timeout= [KNL] Specify the period of time in milliseconds that smp_call_function() and friends will wait for a CPU to release the CSD lock. This is useful when diagnosing bugs involving CPUs disabling interrupts for extended periods of time. Defaults to 5,000 milliseconds, and setting a value of zero disables this feature. This feature may be more efficiently disabled using the csdlock_debug- kernel parameter.
smp.panic_on_ipistall= [KNL] If a csd_lock_timeout extends for more than the specified number of milliseconds, panic the system. By default, let CSD-lock acquisition take as long as they take. Specifying 300,000 for this value provides a 5-minute timeout.
smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port smsc-ircc2.ircc_sir= [HW] SIR base I/O port smsc-ircc2.ircc_fir= [HW] FIR base I/O port smsc-ircc2.ircc_irq= [HW] IRQ line smsc-ircc2.ircc_dma= [HW] DMA channel smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 0: Toshiba Satellite 1800 (GP data pin select) 1: Fast pin select (default) 2: ATC IRMode
smt= [KNL,MIPS,S390,EARLY] Set the maximum number of threads (logical CPUs) to use per physical CPU on systems capable of symmetric multithreading (SMT). Will be capped to the actual hardware limit. Format: <integer> Default: -1 (no limit)
softlockup_panic= [KNL] Should the soft-lockup detector generate panics. Format: <int>
A value of non-zero instructs the soft-lockup detector to panic the machine when a soft-lockup duration exceeds N thresholds. It is also controlled by the kernel.softlockup_panic sysctl and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the respective build-time switch to that functionality.
softlockup_all_cpu_backtrace= [KNL] Should the soft-lockup detector generate backtraces on all cpus. Format: 0 | 1
sonypi.*= [HW] Sony Programmable I/O Control Device driver See Documentation/admin-guide/laptops/sonypi.rst
spectre_bhi= [X86] Control mitigation of Branch History Injection (BHI) vulnerability. This setting affects the deployment of the HW BHI control and the SW BHB clearing sequence.
on - (default) Enable the HW or SW mitigation as needed. This protects the kernel from both syscalls and VMs. vmexit - On systems which don't have the HW mitigation available, enable the SW mitigation on vmexit ONLY. On such systems, the host kernel is protected from VM-originated BHI attacks, but may still be vulnerable to syscall attacks. off - Disable the mitigation.
spectre_v2= [X86,EARLY] Control mitigation of Spectre variant 2 (indirect branch speculation) vulnerability. The default operation protects the kernel from user space attacks.
on - unconditionally enable, implies spectre_v2_user=on off - unconditionally disable, implies spectre_v2_user=off auto - kernel detects whether your CPU model is vulnerable
Selecting 'on' will, and 'auto' may, choose a mitigation method at run time according to the CPU, the available microcode, the setting of the CONFIG_MITIGATION_RETPOLINE configuration option, and the compiler with which the kernel was built.
Selecting 'on' will also enable the mitigation against user space to user space task attacks. Selecting specific mitigation does not force enable user mitigations.
Selecting 'off' will disable both the kernel and the user space protections.
Specific mitigations can also be selected manually:
retpoline - replace indirect branches retpoline,generic - Retpolines retpoline,lfence - LFENCE; indirect branch retpoline,amd - alias for retpoline,lfence eibrs - Enhanced/Auto IBRS eibrs,retpoline - Enhanced/Auto IBRS + Retpolines eibrs,lfence - Enhanced/Auto IBRS + LFENCE ibrs - use IBRS to protect kernel
Not specifying this option is equivalent to spectre_v2=auto.
spectre_v2_user= [X86] Control mitigation of Spectre variant 2 (indirect branch speculation) vulnerability between user space tasks
on - Unconditionally enable mitigations. Is enforced by spectre_v2=on
off - Unconditionally disable mitigations. Is enforced by spectre_v2=off
prctl - Indirect branch speculation is enabled, but mitigation can be enabled via prctl per thread. The mitigation control state is inherited on fork.
prctl,ibpb - Like "prctl" above, but only STIBP is controlled per thread. IBPB is issued always when switching between different user space processes.
seccomp - Same as "prctl" above, but all seccomp threads will enable the mitigation unless they explicitly opt out.
seccomp,ibpb - Like "seccomp" above, but only STIBP is controlled per thread. IBPB is issued always when switching between different user space processes.
auto - Kernel selects the mitigation depending on the available CPU features and vulnerability.
Default mitigation: "prctl"
Not specifying this option is equivalent to spectre_v2_user=auto.
spec_rstack_overflow= [X86,EARLY] Control RAS overflow mitigation on AMD Zen CPUs
off - Disable mitigation microcode - Enable microcode mitigation only safe-ret - Enable sw-only safe RET mitigation (default) ibpb - Enable mitigation by issuing IBPB on kernel entry ibpb-vmexit - Issue IBPB only on VMEXIT (cloud-specific mitigation)
spec_store_bypass_disable= [HW,EARLY] Control Speculative Store Bypass (SSB) Disable mitigation (Speculative Store Bypass vulnerability)
Certain CPUs are vulnerable to an exploit against a a common industry wide performance optimization known as "Speculative Store Bypass" in which recent stores to the same memory location may not be observed by later loads during speculative execution. The idea is that such stores are unlikely and that they can be detected prior to instruction retirement at the end of a particular speculation execution window.
In vulnerable processors, the speculatively forwarded store can be used in a cache side channel attack, for example to read memory to which the attacker does not directly have access (e.g. inside sandboxed code).
This parameter controls whether the Speculative Store Bypass optimization is used.
On x86 the options are:
on - Unconditionally disable Speculative Store Bypass off - Unconditionally enable Speculative Store Bypass auto - Kernel detects whether the CPU model contains an implementation of Speculative Store Bypass and picks the most appropriate mitigation. If the CPU is not vulnerable, "off" is selected. If the CPU is vulnerable the default mitigation is architecture and Kconfig dependent. See below. prctl - Control Speculative Store Bypass per thread via prctl. Speculative Store Bypass is enabled for a process by default. The state of the control is inherited on fork. seccomp - Same as "prctl" above, but all seccomp threads will disable SSB unless they explicitly opt out.
Default mitigations: X86: "prctl"
On powerpc the options are:
on,auto - On Power8 and Power9 insert a store-forwarding barrier on kernel entry and exit. On Power7 perform a software flush on kernel entry and exit. off - No action.
Not specifying this option is equivalent to spec_store_bypass_disable=auto.
split_llc= [X86,EARLY] Split the LLC N-ways
When set, the LLC is split this many ways by matching 'core_id % n'. This is setup before SMP bringup and used during SMP bringup before it knows the full topology. If your core count doesn't nicely divide by the number given, you get to keep the pieces.
This is mostly a debug feature to emulate multiple LLCs on hardware that only have a single LLC.
split_lock_detect= [X86] Enable split lock detection or bus lock detection
When enabled (and if hardware support is present), atomic instructions that access data across cache line boundaries will result in an alignment check exception for split lock detection or a debug exception for bus lock detection.
off - not enabled
warn - the kernel will emit rate-limited warnings about applications triggering the #AC exception or the #DB exception. This mode is the default on CPUs that support split lock detection or bus lock detection. Default behavior is by #AC if both features are enabled in hardware.
fatal - the kernel will send SIGBUS to applications that trigger the #AC exception or the #DB exception. Default behavior is by #AC if both features are enabled in hardware.
ratelimit:N - Set system wide rate limit to N bus locks per second for bus lock detection. 0 < N <= 1000.
N/A for split lock detection.
If an #AC exception is hit in the kernel or in firmware (i.e. not while executing in user mode) the kernel will oops in either "warn" or "fatal" mode.
#DB exception for bus lock is triggered only when CPL > 0.
srbds= [X86,INTEL,EARLY] Control the Special Register Buffer Data Sampling (SRBDS) mitigation.
Certain CPUs are vulnerable to an MDS-like exploit which can leak bits from the random number generator.
By default, this issue is mitigated by microcode. However, the microcode fix can cause the RDRAND and RDSEED instructions to become much slower. Among other effects, this will result in reduced throughput from /dev/urandom.
The microcode mitigation can be disabled with the following option:
off: Disable mitigation and remove performance impact to RDRAND and RDSEED
srcutree.big_cpu_lim [KNL] Specifies the number of CPUs constituting a large system, such that srcu_struct structures should immediately allocate an srcu_node array. This kernel-boot parameter defaults to 128, but takes effect only when the low-order four bits of srcutree.convert_to_big is equal to 3 (decide at boot).
srcutree.convert_to_big [KNL] Specifies under what conditions an SRCU tree srcu_struct structure will be converted to big form, that is, with an rcu_node tree:
0: Never. 1: At init_srcu_struct() time. 2: When rcutorture decides to. 3: Decide at boot time (default). 0x1X: Above plus if high contention.
Either way, the srcu_node tree will be sized based on the actual runtime number of CPUs (nr_cpu_ids) instead of the compile-time CONFIG_NR_CPUS.
srcutree.counter_wrap_check [KNL] Specifies how frequently to check for grace-period sequence counter wrap for the srcu_data structure's ->srcu_gp_seq_needed field. The greater the number of bits set in this kernel parameter, the less frequently counter wrap will be checked for. Note that the bottom two bits are ignored.
srcutree.exp_holdoff [KNL] Specifies how many nanoseconds must elapse since the end of the last SRCU grace period for a given srcu_struct until the next normal SRCU grace period will be considered for automatic expediting. Set to zero to disable automatic expediting.
srcutree.srcu_max_nodelay [KNL] Specifies the number of no-delay instances per jiffy for which the SRCU grace period worker thread will be rescheduled with zero delay. Beyond this limit, worker thread will be rescheduled with a sleep delay of one jiffy.
srcutree.srcu_max_nodelay_phase [KNL] Specifies the per-grace-period phase, number of non-sleeping polls of readers. Beyond this limit, grace period worker thread will be rescheduled with a sleep delay of one jiffy, between each rescan of the readers, for a grace period phase.
srcutree.srcu_retry_check_delay [KNL] Specifies number of microseconds of non-sleeping delay between each non-sleeping poll of readers.
srcutree.small_contention_lim [KNL] Specifies the number of update-side contention events per jiffy will be tolerated before initiating a conversion of an srcu_struct structure to big form. Note that the value of srcutree.convert_to_big must have the 0x10 bit set for contention-based conversions to occur.
ssbd= [ARM64,HW,EARLY] Speculative Store Bypass Disable control
On CPUs that are vulnerable to the Speculative Store Bypass vulnerability and offer a firmware based mitigation, this parameter indicates how the mitigation should be used:
force-on: Unconditionally enable mitigation for for both kernel and userspace force-off: Unconditionally disable mitigation for for both kernel and userspace kernel: Always enable mitigation in the kernel, and offer a prctl interface to allow userspace to register its interest in being mitigated too.
stack_guard_gap= [MM] override the default stack gap protection. The value is in page units and it defines how many pages prior to (for stacks growing down) resp. after (for stacks growing up) the main stack are reserved for no other mapping. Default value is 256 pages.
stack_depot_disable= [KNL,EARLY] Setting this to true through kernel command line will disable the stack depot thereby saving the static memory consumed by the stack hash table. By default this is set to false.
stack_depot_max_pools= [KNL,EARLY] Specify the maximum number of pools to use for storing stack traces. Pools are allocated on-demand up to this limit. Default value is 8191 pools.
stacktrace [FTRACE] Enable the stack tracer on boot up.
stacktrace_filter=[function-list] [FTRACE] Limit the functions that the stack tracer will trace at boot up. function-list is a comma-separated list of functions. This list can be changed at run time by the stack_trace_filter file in the debugfs tracing directory. Note, this enables stack tracing and the stacktrace above is not needed.
sti= [PARISC,HW] Format: <num> Set the STI (builtin display/keyboard on the HP-PARISC machines) console (graphic card) which should be used as the initial boot-console. See also comment in drivers/video/sticore.c.
sti_font= [HW] See comment in drivers/video/sticore.c.
stifb= [HW] Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
strict_sas_size= [X86] Format: <bool> Enable or disable strict sigaltstack size checks against the required signal frame size which depends on the supported FPU features. This can be used to filter out binaries which have not yet been made aware of AT_MINSIGSTKSZ.
stress_hpt [PPC,EARLY] Limits the number of kernel HPT entries in the hash page table to increase the rate of hash page table faults on kernel addresses.
stress_slb [PPC,EARLY] Limits the number of kernel SLB entries, and flushes them frequently to increase the rate of SLB faults on kernel addresses.
no_slb_preload [PPC,EARLY] Disables slb preloading for userspace.
sunrpc.min_resvport= sunrpc.max_resvport= [NFS,SUNRPC] SunRPC servers often require that client requests originate from a privileged port (i.e. a port in the range 0 < portnr < 1024). An administrator who wishes to reserve some of these ports for other uses may adjust the range that the kernel's sunrpc client considers to be privileged using these two parameters to set the minimum and maximum port values.
sunrpc.svc_rpc_per_connection_limit= [NFS,SUNRPC] Limit the number of requests that the server will process in parallel from a single connection. The default value is 0 (no limit).
sunrpc.pool_mode= [NFS] Control how the NFS server code allocates CPUs to service thread pools. Depending on how many NICs you have and where their interrupts are bound, this option will affect which CPUs will do NFS serving. Note: this parameter cannot be changed while the NFS server is running.
auto the server chooses an appropriate mode automatically using heuristics global a single global pool contains all CPUs percpu one pool for each CPU pernode one pool for each NUMA node (equivalent to global on non-NUMA machines)
sunrpc.tcp_slot_table_entries= sunrpc.udp_slot_table_entries= [NFS,SUNRPC] Sets the upper limit on the number of simultaneous RPC calls that can be sent from the client to a server. Increasing these values may allow you to improve throughput, but will also increase the amount of memory reserved for use by the client.
suspend.pm_test_delay= [SUSPEND] Sets the number of seconds to remain in a suspend test mode before resuming the system (see /sys/power/pm_test). Only available when CONFIG_PM_DEBUG is set. Default value is 5.
svm= [PPC] Format: { on | off | y | n | 1 | 0 } This parameter controls use of the Protected Execution Facility on pSeries.
swiotlb= [ARM,PPC,MIPS,X86,S390,EARLY] Format: { <int> [,<int>] | force | noforce } <int> -- Number of I/O TLB slabs <int> -- Second integer after comma. Number of swiotlb areas with their own lock. Will be rounded up to a power of 2. force -- force using of bounce buffers even if they wouldn't be automatically used by the kernel noforce -- Never use bounce buffers (for debugging)
switches= [HW,M68k,EARLY]
sysctl.*= [KNL] Set a sysctl parameter, right before loading the init process, as if the value was written to the respective /proc/sys/... file. Both '.' and '/' are recognized as separators. Unrecognized parameters and invalid values are reported in the kernel log. Sysctls registered later by a loaded module cannot be set this way. Example: sysctl.vm.swappiness=40
sysrq_always_enabled [KNL] Ignore sysrq setting - this boot parameter will neutralize any effect of /proc/sys/kernel/sysrq. Useful for debugging.
tcpmhash_entries= [KNL,NET] Set the number of tcp_metrics_hash slots. Default value is 8192 or 16384 depending on total ram pages. This is used to specify the TCP metrics cache size. See Documentation/networking/ip-sysctl.rst "tcp_no_metrics_save" section for more details.
tdfx= [HW,DRM]
test_suspend= [SUSPEND] Format: { "mem" | "standby" | "freeze" }[,N] Specify "mem" (for Suspend-to-RAM) or "standby" (for standby suspend) or "freeze" (for suspend type freeze) as the system sleep state during system startup with the optional capability to repeat N number of times. The system is woken from this state using a wakeup-capable RTC alarm.
thash_entries= [KNL,NET] Set number of hash buckets for TCP connection
thermal.act= [HW,ACPI] -1: disable all active trip points in all thermal zones <degrees C>: override all lowest active trip points
thermal.crt= [HW,ACPI] -1: disable all critical trip points in all thermal zones <degrees C>: override all critical trip points
thermal.off= [HW,ACPI] 1: disable ACPI thermal control
thermal.psv= [HW,ACPI] -1: disable all passive trip points <degrees C>: override all passive trip points to this value
thermal.tzp= [HW,ACPI] Specify global default ACPI thermal zone polling rate <deci-seconds>: poll all this frequency 0: no polling (default)
thp_anon= [KNL] Format: <size>[KMG],<size>[KMG]:<state>;<size>[KMG]-<size>[KMG]:<state> state is one of "always", "madvise", "never" or "inherit". Control the default behavior of the system with respect to anonymous transparent hugepages. Can be used multiple times for multiple anon THP sizes. See Documentation/admin-guide/mm/transhuge.rst for more details.
threadirqs [KNL,EARLY] Force threading of all interrupt handlers except those marked explicitly IRQF_NO_THREAD.
thp_shmem= [KNL] Format: <size>[KMG],<size>[KMG]:<policy>;<size>[KMG]-<size>[KMG]:<policy> Control the default policy of each hugepage size for the internal shmem mount. <policy> is one of policies available for the shmem mount ("always", "inherit", "never", "within_size", and "advise"). It can be used multiple times for multiple shmem THP sizes. See Documentation/admin-guide/mm/transhuge.rst for more details.
topology= [S390,EARLY] Format: {off | on} Specify if the kernel should make use of the cpu topology information if the hardware supports this. The scheduler will make use of this information and e.g. base its process migration decisions on it. Default is on.
torture.disable_onoff_at_boot= [KNL] Prevent the CPU-hotplug component of torturing until after init has spawned.
torture.ftrace_dump_at_shutdown= [KNL] Dump the ftrace buffer at torture-test shutdown, even if there were no errors. This can be a very costly operation when many torture tests are running concurrently, especially on systems with rotating-rust storage.
torture.verbose_sleep_frequency= [KNL] Specifies how many verbose printk()s should be emitted between each sleep. The default of zero disables verbose-printk() sleeping.
torture.verbose_sleep_duration= [KNL] Duration of each verbose-printk() sleep in jiffies.
tpm.disable_pcr_integrity= [HW,TPM] Do not protect PCR registers from unintended physical access, or interposers in the bus by the means of having an integrity protected session wrapped around TPM2_PCR_Extend command. Consider this in a situation where TPM is heavily utilized by IMA, thus protection causing a major performance hit, and the space where machines are deployed is by other means guarded.
tpm_crb_ffa.busy_timeout_ms= [ARM64,TPM] Maximum time in milliseconds to retry sending a message to the TPM service before giving up. This parameter controls how long the system will continue retrying when the TPM service is busy. Format: <unsigned int> Default: 2000 (2 seconds)
tpm_suspend_pcr=[HW,TPM] Format: integer pcr id Specify that at suspend time, the tpm driver should extend the specified pcr with zeros, as a workaround for some chips which fail to flush the last written pcr on TPM_SaveState. This will guarantee that all the other pcrs are saved.
tpm_tis.interrupts= [HW,TPM] Enable interrupts for the MMIO based physical layer for the FIFO interface. By default it is set to false (0). For more information about TPM hardware interfaces defined by Trusted Computing Group (TCG) see https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/
tp_printk [FTRACE] Have the tracepoints sent to printk as well as the tracing ring buffer. This is useful for early boot up where the system hangs or reboots and does not give the option for reading the tracing buffer or performing a ftrace_dump_on_oops.
To turn off having tracepoints sent to printk, echo 0 > /proc/sys/kernel/tracepoint_printk Note, echoing 1 into this file without the tp_printk kernel cmdline option has no effect.
The tp_printk_stop_on_boot (see below) can also be used to stop the printing of events to console at late_initcall_sync.
** CAUTION **
Having tracepoints sent to printk() and activating high frequency tracepoints such as irq or sched, can cause the system to live lock.
tp_printk_stop_on_boot [FTRACE] When tp_printk (above) is set, it can cause a lot of noise on the console. It may be useful to only include the printing of events during boot up, as user space may make the system inoperable.
This command line option will stop the printing of events to console at the late_initcall_sync() time frame.
trace_buf_size=nn[KMG] [FTRACE] will set tracing buffer size on each cpu.
trace_clock= [FTRACE] Set the clock used for tracing events at boot up. local - Use the per CPU time stamp counter (converted into nanoseconds). Fast, but depending on the architecture, may not be in sync between CPUs. global - Event time stamps are synchronized across CPUs. May be slower than the local clock, but better for some race conditions. counter - Simple counting of events (1, 2, ..) note, some counts may be skipped due to the infrastructure grabbing the clock more than once per event. uptime - Use jiffies as the time stamp. perf - Use the same clock that perf uses. mono - Use ktime_get_mono_fast_ns() for time stamps. mono_raw - Use ktime_get_raw_fast_ns() for time stamps. boot - Use ktime_get_boot_fast_ns() for time stamps. Architectures may add more clocks. See Documentation/trace/ftrace.rst for more details.
trace_event=[event-list] [FTRACE] Set and start specified trace events in order to facilitate early boot debugging. The event-list is a comma-separated list of trace events to enable. See also Documentation/trace/events.rst
To enable modules, use :mod: keyword:
trace_event=:mod:<module>
The value before :mod: will only enable specific events that are part of the module. See the above mentioned document for more information.
trace_instance=[instance-info] [FTRACE] Create a ring buffer instance early in boot up. This will be listed in:
/sys/kernel/tracing/instances
Events can be enabled at the time the instance is created via:
trace_instance=<name>,<system1>:<event1>,<system2>:<event2>
Note, the "<system*>:" portion is optional if the event is unique.
trace_instance=foo,sched:sched_switch,irq_handler_entry,initcall
will enable the "sched_switch" event (note, the "sched:" is optional, and the same thing would happen if it was left off). The irq_handler_entry event, and all events under the "initcall" system.
Flags can be added to the instance to modify its behavior when it is created. The flags are separated by '^'.
The available flags are:
traceoff - Have the tracing instance tracing disabled after it is created. traceprintk - Have trace_printk() write into this trace instance (note, "printk" and "trace_printk" can also be used)
trace_instance=foo^traceoff^traceprintk,sched,irq
The flags must come before the defined events.
If memory has been reserved (see memmap for x86), the instance can use that memory:
memmap=12M$0x284500000 trace_instance=boot_map@0x284500000:12M
The above will create a "boot_map" instance that uses the physical memory at 0x284500000 that is 12Megs. The per CPU buffers of that instance will be split up accordingly.
Alternatively, the memory can be reserved by the reserve_mem option:
reserve_mem=12M:4096:trace trace_instance=boot_map@trace
This will reserve 12 megabytes at boot up with a 4096 byte alignment and place the ring buffer in this memory. Note that due to KASLR, the memory may not be the same location each time, which will not preserve the buffer content.
Also note that the layout of the ring buffer data may change between kernel versions where the validator will fail and reset the ring buffer if the layout is not the same as the previous kernel.
If the ring buffer is used for persistent bootups and has events enabled, it is recommend to disable tracing so that events from a previous boot do not mix with events of the current boot (unless you are debugging a random crash at boot up).
reserve_mem=12M:4096:trace trace_instance=boot_map^traceoff^traceprintk@trace,sched,irq
Note, saving the trace buffer across reboots does require that the system is set up to not wipe memory. For instance, CONFIG_RESET_ATTACK_MITIGATION can force a memory reset on boot which will clear any trace that was stored. This is just one of many ways that can clear memory. Make sure your system keeps the content of memory across reboots before relying on this option.
NB: Both the mapped address and size must be page aligned for the architecture.
See also Documentation/trace/debugging.rst
trace_options=[option-list] [FTRACE] Enable or disable tracer options at boot. The option-list is a comma delimited list of options that can be enabled or disabled just as if you were to echo the option name into
/sys/kernel/tracing/trace_options
For example, to enable stacktrace option (to dump the stack trace of each event), add to the command line:
trace_options=stacktrace
See also Documentation/trace/ftrace.rst "trace options" section.
trace_trigger=[trigger-list] [FTRACE] Add an event trigger on specific events. Set a trigger on top of a specific event, with an optional filter.
The format is "trace_trigger=<event>.<trigger>[ if <filter>],..." Where more than one trigger may be specified that are comma delimited.
For example:
trace_trigger="sched_switch.stacktrace if prev_state == 2"
The above will enable the "stacktrace" trigger on the "sched_switch" event but only trigger it if the "prev_state" of the "sched_switch" event is "2" (TASK_UNINTERRUPTIBLE).
See also "Event triggers" in Documentation/trace/events.rst
traceoff_after_boot [FTRACE] Sometimes tracing is used to debug issues during the boot process. Since the trace buffer has a limited amount of storage, it may be prudent to disable tracing after the boot is finished, otherwise the critical information may be overwritten. With this option, the main tracing buffer will be turned off at the end of the boot process.
traceoff_on_warning [FTRACE] enable this option to disable tracing when a warning is hit. This turns off "tracing_on". Tracing can be enabled again by echoing '1' into the "tracing_on" file located in /sys/kernel/tracing/
This option is useful, as it disables the trace before the WARNING dump is called, which prevents the trace to be filled with content caused by the warning output.
This option can also be set at run time via the sysctl option: kernel/traceoff_on_warning
transparent_hugepage= [KNL] Format: [always|madvise|never] Can be used to control the default behavior of the system with respect to transparent hugepages. See Documentation/admin-guide/mm/transhuge.rst for more details.
transparent_hugepage_shmem= [KNL] Format: [always|within_size|advise|never|deny|force] Can be used to control the hugepage allocation policy for the internal shmem mount. See Documentation/admin-guide/mm/transhuge.rst for more details.
transparent_hugepage_tmpfs= [KNL] Format: [always|within_size|advise|never] Can be used to control the default hugepage allocation policy for the tmpfs mount. See Documentation/admin-guide/mm/transhuge.rst for more details.
trusted.source= [KEYS] Format: <string> This parameter identifies the trust source as a backend for trusted keys implementation. Supported trust sources: - "tpm" - "tee" - "caam" - "dcp" - "pkwm" If not specified then it defaults to iterating through the trust source list starting with TPM and assigns the first trust source as a backend which is initialized successfully during iteration.
trusted.debug= [KEYS] Format: <bool> Enable trusted keys debug traces at runtime when CONFIG_TRUSTED_KEYS_DEBUG=y.
To make the traces visible after enabling the option, use trusted.dyndbg='+p' as needed. By convention, the subsystem uses pr_debug() for these traces.
SAFETY: The traces can leak sensitive data, so be cautious before enabling this. They remain inactive unless this parameter is set this option to a true value.
Default: false
trusted.rng= [KEYS] Format: <string> The RNG used to generate key material for trusted keys. Can be one of: - "kernel" - the same value as trusted.source: "tpm" or "tee" - "default" If not specified, "default" is used. In this case, the RNG's choice is left to each individual trust source.
trusted.dcp_use_otp_key This is intended to be used in combination with trusted.source=dcp and will select the DCP OTP key instead of the DCP UNIQUE key blob encryption.
trusted.dcp_skip_zk_test This is intended to be used in combination with trusted.source=dcp and will disable the check if the blob key is all zeros. This is helpful for situations where having this key zero'ed is acceptable. E.g. in testing scenarios.
tsa= [X86] Control mitigation for Transient Scheduler Attacks on AMD CPUs. Search the following in your favourite search engine for more details:
"Technical guidance for mitigating transient scheduler attacks".
off - disable the mitigation on - enable the mitigation (default) user - mitigate only user/kernel transitions vm - mitigate only guest/host transitions
tsc= Disable clocksource stability checks for TSC. Format: <string> [x86] reliable: mark tsc clocksource as reliable, this disables clocksource verification at runtime, as well as the stability checks done at bootup. Used to enable high-resolution timer mode on older hardware, and in virtualized environment. [x86] noirqtime: Do not use TSC to do irq accounting. Used to run time disable IRQ_TIME_ACCOUNTING on any platforms where RDTSC is slow and this accounting can add overhead. [x86] unstable: mark the TSC clocksource as unstable, this marks the TSC unconditionally unstable at bootup and avoids any further wobbles once the TSC watchdog notices. [x86] nowatchdog: disable clocksource watchdog. Used in situations with strict latency requirements (where interruptions from clocksource watchdog are not acceptable). [x86] recalibrate: force recalibration against a HW timer (HPET or PM timer) on systems whose TSC frequency was obtained from HW or FW using either an MSR or CPUID(0x15). Warn if the difference is more than 500 ppm. [x86] watchdog: Enforce the clocksource watchdog on TSC
tsc_early_khz= [X86,EARLY] Skip early TSC calibration and use the given value instead. Useful when the early TSC frequency discovery procedure is not reliable, such as on overclocked systems with CPUID.16h support and partial CPUID.15h support. Format: <unsigned int>
tsx= [X86] Control Transactional Synchronization Extensions (TSX) feature in Intel processors that support TSX control.
This parameter controls the TSX feature. The options are:
on - Enable TSX on the system. Although there are mitigations for all known security vulnerabilities, TSX has been known to be an accelerator for several previous speculation-related CVEs, and so there may be unknown security risks associated with leaving it enabled.
off - Disable TSX on the system. (Note that this option takes effect only on newer CPUs which are not vulnerable to MDS, i.e., have MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get the new IA32_TSX_CTRL MSR through a microcode update. This new MSR allows for the reliable deactivation of the TSX functionality.)
auto - Disable TSX if X86_BUG_TAA is present, otherwise enable TSX on the system.
Not specifying this option is equivalent to tsx=off.
See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst for more details.
tsx_async_abort= [X86,INTEL,EARLY] Control mitigation for the TSX Async Abort (TAA) vulnerability.
Similar to Micro-architectural Data Sampling (MDS) certain CPUs that support Transactional Synchronization Extensions (TSX) are vulnerable to an exploit against CPU internal buffers which can forward information to a disclosure gadget under certain conditions.
In vulnerable processors, the speculatively forwarded data can be used in a cache side channel attack, to access data to which the attacker does not have direct access.
This parameter controls the TAA mitigation. The options are:
full - Enable TAA mitigation on vulnerable CPUs if TSX is enabled.
full,nosmt - Enable TAA mitigation and disable SMT on vulnerable CPUs. If TSX is disabled, SMT is not disabled because CPU is not vulnerable to cross-thread TAA attacks. off - Unconditionally disable TAA mitigation
On MDS-affected machines, tsx_async_abort=off can be prevented by an active MDS mitigation as both vulnerabilities are mitigated with the same mechanism so in order to disable this mitigation, you need to specify mds=off too.
Not specifying this option is equivalent to tsx_async_abort=full. On CPUs which are MDS affected and deploy MDS mitigation, TAA mitigation is not required and doesn't provide any additional mitigation.
For details see: Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
turbografx.map[2|3]= [HW,JOY] TurboGraFX parallel port interface Format: <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> See also Documentation/input/devices/joystick-parport.rst
udbg-immortal [PPC] When debugging early kernel crashes that happen after console_init() and before a proper console driver takes over, this boot options might help "seeing" what's going on.
uhash_entries= [KNL,NET] Set number of hash buckets for UDP/UDP-Lite connections
uhci-hcd.ignore_oc= [USB] Ignore overcurrent events (default N). Some badly-designed motherboards generate lots of bogus events, for ports that aren't wired to anything. Set this parameter to avoid log spamming. Note that genuine overcurrent events won't be reported either.
unaligned_scalar_speed= [RISCV] Format: {slow | fast | unsupported} Allow skipping scalar unaligned access speed tests. This is useful for testing alternative code paths and to skip the tests in environments where they run too slowly. All CPUs must have the same scalar unaligned access speed.
unaligned_vector_speed= [RISCV] Format: {slow | fast | unsupported} Allow skipping vector unaligned access speed tests. This is useful for testing alternative code paths and to skip the tests in environments where they run too slowly. All CPUs must have the same vector unaligned access speed.
unknown_nmi_panic [X86] Cause panic on unknown NMI.
unwind_debug [X86-64,EARLY] Enable unwinder debug output. This can be useful for debugging certain unwinder error conditions, including corrupt stacks and bad/missing unwinder metadata.
usbcore.authorized_default= [USB] Default USB device authorization: (default -1 = authorized (same as 1), 0 = not authorized, 1 = authorized, 2 = authorized if device connected to internal port)
usbcore.autosuspend= [USB] The autosuspend time delay (in seconds) used for newly-detected USB devices (default 2). This is the time required before an idle device will be autosuspended. Devices for which the delay is set to a negative value won't be autosuspended at all.
usbcore.usbfs_snoop= [USB] Set to log all usbfs traffic (default 0 = off).
usbcore.usbfs_snoop_max= [USB] Maximum number of bytes to snoop in each URB (default = 65536).
usbcore.blinkenlights= [USB] Set to cycle leds on hubs (default 0 = off).
usbcore.old_scheme_first= [USB] Start with the old device initialization scheme (default 0 = off).
usbcore.usbfs_memory_mb= [USB] Memory limit (in MB) for buffers allocated by usbfs (default = 16, 0 = max = 2047).
usbcore.use_both_schemes= [USB] Try the other device initialization scheme if the first one fails (default 1 = enabled).
usbcore.initial_descriptor_timeout= [USB] Specifies timeout for the initial 64-byte USB_REQ_GET_DESCRIPTOR request in milliseconds (default 5000 = 5.0 seconds).
usbcore.nousb [USB] Disable the USB subsystem
usbcore.quirks= [USB] A list of quirk entries to augment the built-in usb core quirk list. List entries are separated by commas. Each entry has the form VendorID:ProductID:Flags. The IDs are 4-digit hex numbers and Flags is a set of letters. Each letter will change the built-in quirk; setting it if it is clear and clearing it if it is set. The letters have the following meanings: a = USB_QUIRK_STRING_FETCH_255 (string descriptors must not be fetched using a 255-byte read); b = USB_QUIRK_RESET_RESUME (device can't resume correctly so reset it instead); c = USB_QUIRK_NO_SET_INTF (device can't handle Set-Interface requests); d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't handle its Configuration or Interface strings); e = USB_QUIRK_RESET (device can't be reset (e.g morph devices), don't use reset); f = USB_QUIRK_HONOR_BNUMINTERFACES (device has more interface descriptions than the bNumInterfaces count, and can't handle talking to these interfaces); g = USB_QUIRK_DELAY_INIT (device needs a pause during initialization, after we read the device descriptor); h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For high speed and super speed interrupt endpoints, the USB 2.0 and USB 3.0 spec require the interval in microframes (1 microframe = 125 microseconds) to be calculated as interval = 2 ^ (bInterval-1). Devices with this quirk report their bInterval as the result of this calculation instead of the exponent variable used in the calculation); i = USB_QUIRK_DEVICE_QUALIFIER (device can't handle device_qualifier descriptor requests); j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device generates spurious wakeup, ignore remote wakeup capability); k = USB_QUIRK_NO_LPM (device can't handle Link Power Management); l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL (Device reports its bInterval as linear frames instead of the USB 2.0 calculation); m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs to be disconnected before suspend to prevent spurious wakeup); n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a pause after every control message); o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra delay after resetting its port); p = USB_QUIRK_SHORT_SET_ADDRESS_REQ_TIMEOUT (Reduce timeout of the SET_ADDRESS request from 5000 ms to 500 ms); q = USB_QUIRK_FORCE_ONE_CONFIG (Device claims zero configurations, forcing to 1); Example: quirks=0781:5580:bk,0a5c:5834:gij
usbhid.mousepoll= [USBHID] The interval which mice are to be polled at.
usbhid.jspoll= [USBHID] The interval which joysticks are to be polled at.
usbhid.kbpoll= [USBHID] The interval which keyboards are to be polled at.
usb-storage.delay_use= [UMS] The delay in seconds before a new device is scanned for Logical Units (default 1). Optionally the delay in milliseconds if the value has suffix with "ms". Example: delay_use=2567ms
usb-storage.quirks= [UMS] A list of quirks entries to supplement or override the built-in unusual_devs list. List entries are separated by commas. Each entry has the form VID:PID:Flags where VID and PID are Vendor and Product ID values (4-digit hex numbers) and Flags is a set of characters, each corresponding to a common usb-storage quirk flag as follows: a = SANE_SENSE (collect more than 18 bytes of sense data, not on uas); b = BAD_SENSE (don't collect more than 18 bytes of sense data, not on uas); c = FIX_CAPACITY (decrease the reported device capacity by one sector); d = NO_READ_DISC_INFO (don't use READ_DISC_INFO command, not on uas); e = NO_READ_CAPACITY_16 (don't use READ_CAPACITY_16 command); f = NO_REPORT_OPCODES (don't use report opcodes command, uas only); g = MAX_SECTORS_240 (don't transfer more than 240 sectors at a time, uas only); h = CAPACITY_HEURISTICS (decrease the reported device capacity by one sector if the number is odd); i = IGNORE_DEVICE (don't bind to this device); j = NO_REPORT_LUNS (don't use report luns command, uas only); k = NO_SAME (do not use WRITE_SAME, uas only) l = NOT_LOCKABLE (don't try to lock and unlock ejectable media, not on uas); m = MAX_SECTORS_64 (don't transfer more than 64 sectors = 32 KB at a time, not on uas); n = INITIAL_READ10 (force a retry of the initial READ(10) command, not on uas); o = CAPACITY_OK (accept the capacity reported by the device, not on uas); p = WRITE_CACHE (the device cache is ON by default, not on uas); r = IGNORE_RESIDUE (the device reports bogus residue values, not on uas); s = SINGLE_LUN (the device has only one Logical Unit); t = NO_ATA_1X (don't allow ATA(12) and ATA(16) commands, uas only); u = IGNORE_UAS (don't bind to the uas driver); w = NO_WP_DETECT (don't test whether the medium is write-protected). y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE even if the device claims no cache, not on uas) Example: quirks=0419:aaf5:rl,0421:0433:rc
user_debug= [KNL,ARM] Format: <int> See arch/arm/Kconfig.debug help text. 1 - undefined instruction events 2 - system calls 4 - invalid data aborts 8 - SIGSEGV faults 16 - SIGBUS faults Example: user_debug=31
vdso= [X86,SH,SPARC] On X86_32, this is an alias for vdso32=. Otherwise:
vdso=1: enable VDSO (the default) vdso=0: disable VDSO mapping
vdso32= [X86] Control the 32-bit vDSO vdso32=1: enable 32-bit VDSO vdso32=0 or vdso32=2: disable 32-bit VDSO
See the help text for CONFIG_COMPAT_VDSO for more details. If CONFIG_COMPAT_VDSO is set, the default is vdso32=0; otherwise, the default is vdso32=1.
For compatibility with older kernels, vdso32=2 is an alias for vdso32=0.
Try vdso32=0 if you encounter an error that says: dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
video= [FB,EARLY] Frame buffer configuration See Documentation/fb/modedb.rst.
video.brightness_switch_enabled= [ACPI] Format: [0|1] If set to 1, on receiving an ACPI notify event generated by hotkey, video driver will adjust brightness level and then send out the event to user space through the allocated input device. If set to 0, video driver will only send out the event without touching backlight brightness level. default: 1
virtio_mmio.device= [VMMIO] Memory mapped virtio (platform) device.
<size>@<baseaddr>:<irq>[:<id>] where: <size> := size (can use standard suffixes like K, M and G) <baseaddr> := physical base address <irq> := interrupt number (as passed to request_irq()) <id> := (optional) platform device id example: virtio_mmio.device=1K@0x100b0000:48:7
Can be used multiple times for multiple devices.
vga= [BOOT,X86-32] Select a particular video mode See Documentation/arch/x86/boot.rst and Documentation/admin-guide/svga.rst. Use vga=ask for menu. This is actually a boot loader parameter; the value is passed to the kernel using a special protocol.
vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. May slow down system boot speed, especially when enabled on systems with a large amount of memory. All options are enabled by default, and this interface is meant to allow for selectively enabling or disabling specific virtual memory debugging features.
Available options are: P Enable page structure init time poisoning - Disable all of the above options
vmalloc=nn[KMG] [KNL,BOOT,EARLY] Forces the vmalloc area to have an exact size of <nn>. This can be used to increase the minimum size (128MB on x86, arm32 platforms). It can also be used to decrease the size and leave more room for directly mapped kernel RAM. Note that this parameter does not exist on many other platforms (including arm64, alpha, loongarch, arc, csky, hexagon, microblaze, mips, nios2, openrisc, parisc, m64k, powerpc, riscv, sh, um, xtensa, s390, sparc).
vmcp_cma=nn[MG] [KNL,S390,EARLY] Sets the memory size reserved for contiguous memory allocations for the vmcp device driver.
vmhalt= [KNL,S390] Perform z/VM CP command after system halt. Format: <command>
vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. Format: <command>
vmpoff= [KNL,S390] Perform z/VM CP command after power off. Format: <command>
vmscape= [X86] Controls mitigation for VMscape attacks. VMscape attacks can leak information from a userspace hypervisor to a guest via speculative side-channels.
off - disable the mitigation ibpb - use Indirect Branch Prediction Barrier (IBPB) mitigation (default) force - force vulnerability detection even on unaffected processors
vsyscall= [X86-64,EARLY] Controls the behavior of vsyscalls (i.e. calls to fixed addresses of 0xffffffffff600x00 from legacy code). Most statically-linked binaries and older versions of glibc use these calls. Because these functions are at fixed addresses, they make nice targets for exploits that can control RIP.
emulate Vsyscalls turn into traps and are emulated reasonably safely. The vsyscall page is readable. This disables the Linear Address Space Separation (LASS) security feature and makes the system less secure.
xonly [default] Vsyscalls turn into traps and are emulated reasonably safely. The vsyscall page is not readable.
none Vsyscalls don't work at all. This makes them quite hard to use for exploits but might break your system.
vt.color= [VT] Default text color. Format: 0xYX, X = foreground, Y = background. Default: 0x07 = light gray on black.
vt.cur_default= [VT] Default cursor shape. Format: 0xCCBBAA, where AA, BB, and CC are the same as the parameters of the <Esc>[?A;B;Cc escape sequence; see vga-softcursor.rst. Default: 2 = underline.
vt.default_blu= [VT] Format: <blue0>,<blue1>,<blue2>,...,<blue15> Change the default blue palette of the console. This is a 16-member array composed of values ranging from 0-255.
vt.default_grn= [VT] Format: <green0>,<green1>,<green2>,...,<green15> Change the default green palette of the console. This is a 16-member array composed of values ranging from 0-255.
vt.default_red= [VT] Format: <red0>,<red1>,<red2>,...,<red15> Change the default red palette of the console. This is a 16-member array composed of values ranging from 0-255.
vt.default_utf8= [VT] Format=<0|1> Set system-wide default UTF-8 mode for all tty's. Default is 1, i.e. UTF-8 mode is enabled for all newly opened terminals.
vt.global_cursor_default= [VT] Format=<-1|0|1> Set system-wide default for whether a cursor is shown on new VTs. Default is -1, i.e. cursors will be created by default unless overridden by individual drivers. 0 will hide cursors, 1 will display them.
vt.italic= [VT] Default color for italic text; 0-15. Default: 2 = green.
vt.underline= [VT] Default color for underlined text; 0-15. Default: 3 = cyan.
watchdog timers [HW,WDT] For information on watchdog timers, see Documentation/watchdog/watchdog-parameters.rst or other driver-specific files in the Documentation/watchdog/ directory.
watchdog_thresh= [KNL] Set the hard lockup detector stall duration threshold in seconds. The soft lockup detector threshold is set to twice the value. A value of 0 disables both lockup detectors. Default is 10 seconds.
workqueue.unbound_cpus= [KNL,SMP] Specify to constrain one or some CPUs to use in unbound workqueues. Format: <cpu-list> By default, all online CPUs are available for unbound workqueues.
workqueue.watchdog_thresh= If CONFIG_WQ_WATCHDOG is configured, workqueue can warn stall conditions and dump internal state to help debugging. 0 disables workqueue stall detection; otherwise, it's the stall threshold duration in seconds. The default value is 30 and it can be updated at runtime by writing to the corresponding sysfs file.
workqueue.panic_on_stall=<uint> Panic when workqueue stall is detected by CONFIG_WQ_WATCHDOG. It sets the number times of the stall to trigger panic.
The default is set by CONFIG_BOOTPARAM_WQ_STALL_PANIC, which is 0 (disabled) if not configured.
workqueue.panic_on_stall_time=<uint> Panic when a workqueue stall has been continuous for the specified number of seconds. Unlike panic_on_stall which counts accumulated stall events, this triggers based on the duration of a single continuous stall.
The default is 0, which disables the time-based panic.
workqueue.cpu_intensive_thresh_us= Per-cpu work items which run for longer than this threshold are automatically considered CPU intensive and excluded from concurrency management to prevent them from noticeably delaying other per-cpu work items. Default is 10000 (10ms).
If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel will report the work functions which violate this threshold repeatedly. They are likely good candidates for using WQ_UNBOUND workqueues instead.
workqueue.cpu_intensive_warning_thresh=<uint> If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel will report the work functions which violate the intensive_threshold_us repeatedly. In order to prevent spurious warnings, start printing only after a work function has violated this threshold number of times.
The default is 4 times. 0 disables the warning.
workqueue.power_efficient Per-cpu workqueues are generally preferred because they show better performance thanks to cache locality; unfortunately, per-cpu workqueues tend to be more power hungry than unbound workqueues.
Enabling this makes the per-cpu workqueues which were observed to contribute significantly to power consumption unbound, leading to measurably lower power usage at the cost of small performance overhead.
The default value of this parameter is determined by the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
workqueue.default_affinity_scope= Select the default affinity scope to use for unbound workqueues. Can be one of "cpu", "smt", "cache", "cache_shard", "numa" and "system". Default is "cache_shard". For more information, see the Affinity Scopes section in Documentation/core-api/workqueue.rst.
This can be changed after boot by writing to the matching /sys/module/workqueue/parameters file. All workqueues with the "default" affinity scope will be updated accordingly.
workqueue.debug_force_rr_cpu Workqueue used to implicitly guarantee that work items queued without explicit CPU specified are put on the local CPU. This guarantee is no longer true and while local CPU is still preferred work items may be put on foreign CPUs. This debug option forces round-robin CPU selection to flush out usages which depend on the now broken guarantee. When enabled, memory and cache locality will be impacted.
writecombine= [LOONGARCH,EARLY] Control the MAT (Memory Access Type) of ioremap_wc().
on - Enable writecombine, use WUC for ioremap_wc() off - Disable writecombine, use SUC for ioremap_wc()
x2apic_phys [X86-64,APIC,EARLY] Use x2apic physical mode instead of default x2apic cluster mode on platforms supporting x2apic.
xen_512gb_limit [KNL,X86-64,XEN] Restricts the kernel running paravirtualized under Xen to use only up to 512 GB of RAM. The reason to do so is crash analysis tools and Xen tools for doing domain save/restore/migration must be enabled to handle larger domains.
xen_console_io [XEN,EARLY] Boolean option to enable/disable the usage of the Xen console_io hypercalls to read and write to the console. Mostly useful for debugging and development.
xen_emul_unplug= [HW,X86,XEN,EARLY] Unplug Xen emulated devices Format: [unplug0,][unplug1] ide-disks -- unplug primary master IDE devices aux-ide-disks -- unplug non-primary-master IDE devices nics -- unplug network devices all -- unplug all emulated devices (NICs and IDE disks) unnecessary -- unplugging emulated devices is unnecessary even if the host did not respond to the unplug protocol never -- do not unplug even if version check succeeds
xen_legacy_crash [X86,XEN,EARLY] Crash from Xen panic notifier, without executing late panic() code such as dumping handler.
xen_mc_debug [X86,XEN,EARLY] Enable multicall debugging when running as a Xen PV guest. Enabling this feature will reduce performance a little bit, so it should only be enabled for obtaining extended debug data in case of multicall errors.
xen_msr_safe= [X86,XEN,EARLY] Format: <bool> Select whether to always use non-faulting (safe) MSR access functions when running as Xen PV guest. The default value is controlled by CONFIG_XEN_PV_MSR_SAFE.
xen_nopv [X86] Disables the PV optimizations forcing the HVM guest to run as generic HVM guest with no PV drivers. This option is obsoleted by the "nopv" option, which has equivalent effect for XEN platform.
xen_no_vector_callback [KNL,X86,XEN,EARLY] Disable the vector callback for Xen event channel interrupts.
xen_scrub_pages= [XEN] Boolean option to control scrubbing pages before giving them back to Xen, for use by other domains. Can be also changed at runtime with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
xen_timer_slop= [X86-64,XEN,EARLY] Set the timer slop (in nanoseconds) for the virtual Xen timers (default is 100000). This adjusts the minimum delta of virtualized Xen timers, where lower values improve timer resolution at the expense of processing more timer interrupts.
xen.balloon_boot_timeout= [XEN] The time (in seconds) to wait before giving up to boot in case initial ballooning fails to free enough memory. Applies only when running as HVM or PVH guest and started with less memory configured than allowed at max. Default is 180.
xen.event_eoi_delay= [XEN] How long to delay EOI handling in case of event storms (jiffies). Default is 10.
xen.event_loop_timeout= [XEN] After which time (jiffies) the event handling loop should start to delay EOI handling. Default is 2.
xen.fifo_events= [XEN] Boolean parameter to disable using fifo event handling even if available. Normally fifo event handling is preferred over the 2-level event handling, as it is fairer and the number of possible event channels is much higher. Default is on (use fifo events).
xirc2ps_cs= [NET,PCMCIA] Format: <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
xive= [PPC] By default on POWER9 and above, the kernel will natively use the XIVE interrupt controller. This option allows the fallback firmware mode to be used:
off Fallback to firmware control of XIVE interrupt controller on both pseries and powernv platforms. Only useful on POWER9 and above.
xive.store-eoi=off [PPC] By default on POWER10 and above, the kernel will use stores for EOI handling when the XIVE interrupt mode is active. This option allows the XIVE driver to use loads instead, as on POWER9.
xhci-hcd.quirks [USB,KNL] A hex value specifying bitmask with supplemental xhci host controller quirks. Meaning of each bit can be consulted in header drivers/usb/host/xhci.h.
xmon [PPC,EARLY] Format: { early | on | rw | ro | off } Controls if xmon debugger is enabled. Default is off. Passing only "xmon" is equivalent to "xmon=early". early Call xmon as early as possible on boot; xmon debugger is called from setup_arch(). on xmon debugger hooks will be installed so xmon is only called on a kernel crash. Default mode, i.e. either "ro" or "rw" mode, is controlled with CONFIG_XMON_DEFAULT_RO_MODE. rw xmon debugger hooks will be installed so xmon is called only on a kernel crash, mode is write, meaning SPR registers, memory and, other data can be written using xmon commands. ro same as "rw" option above but SPR registers, memory, and other data can't be written using xmon commands. off xmon is disabled.