Linux源码研究-用户管理员手册-内核命令行参数
2024-06-05 19:45:37
下面的列表是__setup(), core_param()和module_param()宏实现的内核参数，内核从命令-开始解析参数，如果参数不被识别，也不包含“.”，参数会被用来启动，含“=”的参数会初始化环境，其他的参数会被用作命令行参数初始化。
模块参数可以以两种方式指定，通过内核命令行（使用模块名前缀），或通过modprobe
(kernel command line) usbcore.blinkenlights=1
(modprobe command line) modprobe usbcore blinkenlights=1编译到内核的模块，参数需通过内核命令行指定，当加载一个模块时，modprobe会查找内核命令行（/proc/cmdline）并搜集内核参数，所以内核命令行也可以用来加载模块。
在参数名中，-和_是等价的。
log_buf_len=1M print-fatal-signals=1双引各可以保留值中的空格
param="spaces in here"有一些内核参数取值为CPU列值，如：
<cpu number>,...,<cpu number>特殊情况下，可以使用如下，group size表示组大小，used size表示每个组中选择几个使用。
<cpu number>-cpu number>:<used size>/<group size>isolcpus=1,2,10-20,100-2000:2/25上面表示CPUs 100，101，125，126，150，151...
通过modinfo -p ${modulename}可以获取加载模块的参数列表，模块运行在内核时，也可以在/sys/module/${modulename}/parameters/下找到参数，一些参数可以运行时通过命令改变 。
echo -n ${value} > /sys/module/${modulename}/parameters/${parm}.下面列出的参数，只有内核编译选项开启，并且存在硬件进，才可用。
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.
ARM ARM architecture is enabled.
AX25 Appropriate AX.25 support 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
EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
EFI EFI Partitioning (GPT) is enabled
EIDE EIDE/ATAPI support is enabled.
EVM Extended Verification Module
FB The frame buffer device is enabled.
FTRACE Function tracing enabled.
GCOV GCOV profiling is enabled.
HW Appropriate hardware is enabled.
IA-64 IA-64 architecture is enabled.
IMA Integrity measurement architecture is enabled.
IOSCHED More than one I/O scheduler is enabled.
IP_PNP IP DHCP, BOOTP, or RARP is enabled.
IPV6 IPv6 support is enabled.
ISAPNP ISA PnP code is enabled.
ISDN Appropriate ISDN support 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
LP Printer support is enabled.
LOOP Loopback device support is enabled.
M68k M68k architecture is enabled.These options have more detailed description inside ofDocumentation/m68k/kernel-options.txt.
MDA MDA console support is enabled.
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.
NUMA NUMA support is enabled.
NFS Appropriate NFS support is enabled.
OSS OSS sound support is enabled.
PV_OPS A paravirtualized kernel is enabled.
PARIDE The ParIDE (parallel port IDE) subsystem 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.
RAM RAM disk support is enabled.
RDT Intel Resource Director Technology.
S390 S390 architecture is enabled.
SCSI Appropriate SCSI support is enabled.A lot of drivers have their options described insidethe Documentation/scsi/ sub-directory.
SECURITY Different security models are enabled.
SELINUX SELinux support is enabled.
APPARMOR AppArmor 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.
SWSUSP Software suspend (hibernation) is enabled.
SUSPEND System suspend states are enabled.
TPM TPM drivers are enabled.
TS Appropriate touchscreen support is enabled.
UMS USB Mass Storage support is enabled.
USB USB support is enabled.
USBHID USB Human Interface Device support is enabled.
V4L Video For Linux support is enabled.
VMMIO Driver for memory mapped virtio devices is enabled.
VGA The VGA console has been enabled.
VT Virtual terminal support is enabled.
WDT Watchdog support is enabled.
XT IBM PC/XT MFM hard disk support is enabled.
X86-32 X86-32, aka i386 architecture is enabled.
X86-64 X86-64 architecture is enabled.More X86-64 boot options can be found inDocumentation/x86/x86_64/boot-options.txt .
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下面的是编译选项
BUGS= Relates to possible processor bugs on the said processor.
KNL Is a kernel start-up parameter.
BOOT Is a boot loader parameter.BOOT表示的参数会被boot loader解释，对内核没有任合意义。尽量不要修改boot loader参数，如果修改可以参考Documentation/x86/boot.txt。
有一些架构特定的内核参数可以在Documentation/x86/x86_64/boot-options.txt找到。
所有的内核参数都是大小写敏感的，以=结尾的参数表示环境变量，内核参数的数量不是限制的，但是命令行的长度却是有限制的，这个大小和架构有关，在256~4096之间，定义在./include/asm/setup.h 中的COMMAND_LINE_SIZE。
acpi= [HW,ACPI,X86,ARM64]Advanced Configuration and Power Interface（电源接口）Format: { force | on | off | strict | noirq | rsdt |copy_dsdt }force -- enable ACPI if default was offon -- enable ACPI but allow fallback to DT [arm64]off -- disable ACPI if default was onnoirq -- do not use ACPI for IRQ routingstrict -- Be less tolerant of platforms that are notstrictly ACPI specification compliant.rsdt -- prefer RSDT over (default) XSDTcopy_dsdt -- copy DSDT to memoryFor ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"are availableSee also Documentation/power/runtime_pm.txt, pci=noacpiacpi_apic_instance= [ACPI, IOAPIC]Format: <int>2: use 2nd APIC table, if available1,0: use 1st APIC tabledefault: 0acpi_backlight= [HW,ACPI]acpi_backlight=vendoracpi_backlight=videoIf set to vendor, prefer vendor specific driver(e.g. thinkpad_acpi, sony_acpi, etc.) insteadof the ACPI video.ko driver.acpi_force_32bit_fadt_addrforce FADT to use 32 bit addresses rather than the64 bit X_* addresses. Some firmware have broken 64bit addresses for force ACPI ignore these and usethe older legacy 32 bit addresses.acpica_no_return_repair [HW, ACPI]Disable AML predefined validation mechanismThis mechanism can repair the evaluation result to makethe return objects more ACPI specification compliant.This option is useful for developers to identify theroot cause of an AML interpreter issue when the issuehas 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 ACPIdebug output. Bits in debug_layer correspond to a_COMPONENT in an ACPI source file, e.g.,#define _COMPONENT ACPI_PCI_COMPONENTBits in debug_level correspond to a level inACPI_DEBUG_PRINT statements, e.g.,ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...The debug_level mask defaults to "info". SeeDocumentation/acpi/debug.txt for more information aboutdebug layers and levels.Enable processor driver info messages:acpi.debug_layer=0x20000000Enable PCI/PCI interrupt routing info messages:acpi.debug_layer=0x400000Enable AML "Debug" output, i.e., stores to the Debugobject while interpreting AML:acpi.debug_layer=0xffffffff acpi.debug_level=0x2Enable all messages related to ACPI hardware:acpi.debug_layer=0x2 acpi.debug_level=0xffffffffSome values produce so much output that the system isunusable. The "log_buf_len" parameter may be usefulif you need to capture more output.acpi_enforce_resources= [ACPI]{ strict | lax | no }Check for resource conflicts between native driversand ACPI OperationRegions (SystemIO and SystemMemoryonly). IO ports and memory declared in ACPI might beused by the ACPI subsystem in arbitrary AML code andcan interfere with legacy drivers.strict (default): access to resources claimed by ACPIis denied; legacy drivers trying to access reservedresources will fail to bind to device using them.lax: access to resources claimed by ACPI is allowed;legacy drivers trying to access reserved resourceswill 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]Enable table checksum verification during early stage.By default, this is disabled due to x86 early mappingsize limitation.acpi_irq_balance [HW,ACPI]ACPI will balance active IRQsdefault in APIC modeacpi_irq_nobalance [HW,ACPI]ACPI will not move active IRQs (default)default in PIC modeacpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISAFormat: <irq>,<irq>...acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs foruse by PCIFormat: <irq>,<irq>...acpi_mask_gpe= [HW,ACPI]Due to the existence of _Lxx/_Exx, some GPEs triggeredby unsupported hardware/firmware features can result inGPE floodings that cannot be automatically disabled bythe GPE dispatcher.This facility can be used to prevent such uncontrolledGPE floodings.Format: <int>acpi_no_auto_serialize [HW,ACPI]Disable auto-serialization of AML methodsAML control methods that contain the opcodes to createnamed objects will be marked as "Serialized" by theauto-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 kdumpkernels.acpi_no_static_ssdt [HW,ACPI]Disable installation of static SSDTs at early boot timeBy default, SSDTs contained in the RSDT/XSDT will beinstalled automatically and they will appear under/sys/firmware/acpi/tables.This option turns off this feature.Note that specifying this option does not affectdynamic table installation which will install SSDTtables to /sys/firmware/acpi/tables/dynamic.acpi_rsdp= [ACPI,EFI,KEXEC]Pass the RSDP address to the kernel, mostly usedon machines running EFI runtime service to boot thesecond kernel for kdump.acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OSFormat: To spoof as Windows 98: ="Microsoft Windows"acpi_rev_override [ACPI] Override the _REV object to return 5 (insteadof 2 which is mandated by ACPI 6) as the supported ACPIspecification revision (when using this switch, it maybe necessary to carry out a cold reboot _twice_ in arow to make it take effect on the platform firmware).acpi_osi= [HW,ACPI] Modify list of supported OS interface stringsacpi_osi="string1" # add string1acpi_osi="!string2" # remove string2acpi_osi=!* # remove all stringsacpi_osi=! # disable all built-in OS vendorstringsacpi_osi=!! # enable all built-in OS vendorstringsacpi_osi= # disable all strings'acpi_osi=!' can be used in combination with single ormultiple 'acpi_osi="string1"' to support specific OSvendor string(s). Note that such command can onlyaffect the default state of the OS vendor strings, thusit cannot affect the default state of the feature groupstrings and the current state of the OS vendor strings,specifying it multiple times through kernel command lineis meaningless. This command is useful when one do notcare about the state of the feature group strings whichshould be controlled by the OSPM.Examples:1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalentto 'acpi_osi="Windows 2000" acpi_osi=!', they allcan make '_OSI("Windows 2000")' TRUE.'acpi_osi=' cannot be used in combination with other'acpi_osi=' command lines, the _OSI method will notexist in the ACPI namespace. NOTE that such command canonly affect the _OSI support state, thus specifying itmultiple times through kernel command line is alsomeaningless.Examples:1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'FALSE.'acpi_osi=!*' can be used in combination with single ormultiple 'acpi_osi="string1"' to support specificstring(s). Note that such command can affect thecurrent state of both the OS vendor strings and thefeature group strings, thus specifying it multiple timesthrough kernel command line is meaningful. But it maystill not able to affect the final state of a string ifthere are quirks related to this string. This commandis useful when one want to control the state of thefeature group strings to debug BIOS issues related tothe 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"' isequivalent 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 kernelto assume that this machine's pmtimer latches its valueand always returns good values.acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger modeFormat: { level | edge | high | low }acpi_skip_timer_override [HW,ACPI]Recognize and ignore IRQ0/pin2 Interrupt Override.For broken nForce2 BIOS resulting in XT-PIC timer.acpi_sleep= [HW,ACPI] Sleep optionsFormat: { s3_bios, s3_mode, s3_beep, s4_nohwsig,old_ordering, nonvs, sci_force_enable, nobl }See Documentation/power/video.txt for information ons3_bios and s3_mode.s3_beep is for debugging; it makes the PC's speaker beepas soon as the kernel's real-mode entry point is called.s4_nohwsig prevents ACPI hardware signature from beingused during resume from hibernation.old_ordering causes the ACPI 1.0 ordering of the _PTScontrol method, with respect to putting devices intolow power states, to be enforced (the ACPI 2.0 orderingof _PTS is used by default).nonvs prevents the kernel from saving/restoring theACPI NVS memory during suspend/hibernation and resume.sci_force_enable causes the kernel to set SCI_EN directlyon 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 tobehave incorrectly in some ways with respect to systemsuspend and resume to be ignored (use wisely).acpi_use_timer_override [HW,ACPI]Use timer override. For some broken Nvidia NF5 boardsthat require a timer override, but don't have HPETadd_efi_memmap [EFI; X86] Include EFI memory map inkernel's map of available physical RAM.agp= [AGP]{ off | try_unsupported }off: disable AGP supporttry_unsupported: try to drive unsupported chipsets(may crash computer or cause data corruption)ALSA [HW,ALSA]See Documentation/sound/alsa/alsa-parameters.txtalignment= [KNL,ARM]Allow the default userspace alignment fault handlerbehaviour 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] whenallocating a VMA at process creation time. This optiongives you up to 3% performance improvement on AMD F15hmachines (where it is enabled by default) for aCPU-intensive style benchmark, and it can vary highly ina microbenchmark depending on workload and compiler.32: only for 32-bit processes64: only for 64-bit processeson: enable for both 32- and 64-bit processesoff: disable for both 32- and 64-bit processesalloc_snapshot [FTRACE]Allocate the ftrace snapshot buffer on boot up when themain buffer is allocated. This is handy if debuggingand you need to use tracing_snapshot() on boot up, anddo not want to use tracing_snapshot_alloc() as it needsto be done where GFP_KERNEL allocations are allowed.amd_iommu= [HW,X86-64]Pass parameters to the AMD IOMMU driver in the system.Possible values are:fullflush - enable flushing of IO/TLB entries whenthey are unmapped. Otherwise they areflushed before they will be reused, whichis a lot of fasteroff - do not initialize any AMD IOMMU found inthe systemforce_isolation - Force device isolation for alldevices. The IOMMU driver is notallowed anymore to lift isolationrequirements as needed. This optiondoes not override iommu=ptamd_iommu_dump= [HW,X86-64]Enable AMD IOMMU driver option to dump the ACPI tablefor AMD IOMMU. With this option enabled, AMD IOMMUdriver will print ACPI tables for AMD IOMMU duringIOMMU initialization.amd_iommu_intr= [HW,X86-64]Specifies one of the following AMD IOMMU interruptremapping modes:legacy - Use legacy interrupt remapping mode.vapic - Use virtual APIC mode, which allows IOMMUto inject interrupts directly into guest.This mode requires kvm-amd.avic=1.(Default when IOMMU HW support is present.)amijoy.map= [HW,JOY] Amiga joystick supportMap of devices attached to JOY0DAT and JOY1DATFormat: <a>,<b>See also Documentation/input/joydev/joystick.rstanalog.map= [HW,JOY] Analog joystick and gamepad supportSpecifies type or capabilities of an analog joystickconnected to one of 16 gameportsFormat: <type1>,<type2>,..<type16>apc= [HW,SPARC]Power management functions (SPARCstation-4/5 + deriv.)Format: noidleDisable APC CPU standby support. SPARCstation-Fox doesnot play well with APC CPU idle - disable it if you haveAPC and your system crashes randomly.apic= [APIC,X86] Advanced Programmable Interrupt ControllerChange the output verbosity whilst bootingFormat: { quiet (default) | verbose | debug }Change the amount of debugging information outputwhen initialising the APIC and IO-APIC components.For X86-32, this can also be used to specify an APICdriver name.Format: apic=driver_nameExamples: apic=bigsmpapic_extnmi= [APIC,X86] External NMI delivery settingFormat: { bsp (default) | all | none }bsp: External NMI is delivered only to CPU 0all: External NMIs are broadcast to all CPUs as abackup of CPU 0none: External NMI is masked for all CPUs. This isuseful so that a dump capture kernel won't beshot down by NMIautoconf= [IPV6]See Documentation/networking/ipv6.txt.show_lapic= [APIC,X86] Advanced Programmable Interrupt ControllerLimit apic dumping. The parameter defines the maximalnumber of local apics being dumped. Also it is possibleto set it to "all" by meaning -- no limit here.Format: { 1 (default) | 2 | ... | all }.The parameter valid if only apic=debug orapic=verbose is specified.Example: apic=debug show_lapic=allapm= [APM] Advanced Power ManagementSee header of arch/x86/kernel/apm_32.c.arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cardsFormat: <io>,<irq>,<nodeID>ataflop= [HW,M68k]atarimouse= [HW,MOUSE] Atari Mouseatkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,EzKey and similar keyboardsatkbd.reset= [HW] Reset keyboard during initializationatkbd.set= [HW] Select keyboard code setFormat: <int> (2 = AT (default), 3 = PS/2)atkbd.scroll= [HW] Enable scroll wheel on MS Office and similarkeyboardsatkbd.softraw= [HW] Choose between synthetic and real raw modeFormat: <bool> (0 = real, 1 = synthetic (default))atkbd.softrepeat= [HW]Use software keyboard repeataudit= [KNL] Enable the audit sub-systemFormat: { "0" | "1" | "off" | "on" }0 | off - kernel audit is disabled and can not beenabled until the next rebootunset - kernel audit is initialized but disabled andwill be fully enabled by the userspace auditd.1 | on - kernel audit is initialized and partiallyenabled, storing at most audit_backlog_limitmessages in RAM until it is fully enabled by theuserspace auditd.Default: unsetaudit_backlog_limit= [KNL] Set the audit queue size limit.Format: <int> (must be >=0)Default: 64bau= [X86_UV] Enable the BAU on SGI UV. The defaultbehavior is to disable the BAU (i.e. bau=0).Format: { "0" | "1" }0 - Disable the BAU.1 - Enable the BAU.unset - Disable the BAU.baycom_epp= [HW,AX25]Format: <io>,<mode>baycom_par= [HW,AX25] BayCom Parallel Port AX.25 ModemFormat: <io>,<mode>See header of drivers/net/hamradio/baycom_par.c.baycom_ser_fdx= [HW,AX25]BayCom Serial Port AX.25 Modem (Full Duplex Mode)Format: <io>,<irq>,<mode>[,<baud>]See header of drivers/net/hamradio/baycom_ser_fdx.c.baycom_ser_hdx= [HW,AX25]BayCom Serial Port AX.25 Modem (Half Duplex Mode)Format: <io>,<irq>,<mode>See header of drivers/net/hamradio/baycom_ser_hdx.c.blkdevparts= Manual partition parsing of block device(s) forembedded devices based on command line input.See Documentation/block/cmdline-partition.txtboot_delay= Milliseconds to delay each printk during boot.Values larger than 10 seconds (10000) are changed tono delay (0).Format: integerbootmem_debug [KNL] Enable bootmem allocator debug messages.bert_disable [ACPI]Disable BERT OS support on buggy BIOSes.bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)bttv.radio= Most important insmod options are available askernel args too.bttv.pll= See Documentation/media/v4l-drivers/bttv.rstbttv.tuner=bulk_remove=off [PPC] This parameter disables the use of the pSeriesfirmware feature for flushing multiple hpte entriesat a time.c101= [NET] Moxa C101 synchronous serial cardcachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.Sometimes CPU hardware bugs make them report the cachesize incorrectly. The kernel will attempt work aroundsto fix known problems, but for some CPUs it is notpossible to determine what the correct size should be.This option provides an override for these situations.ca_keys= [KEYS] This parameter identifies a specific key(s) onthe system trusted keyring to be used for certificatetrust validation.format: { id:<keyid> | builtin }cca= [MIPS] Override the kernel pages' cache coherencyalgorithm. Accepted values range from 0 to 7inclusive. See arch/mips/include/asm/pgtable-bits.hfor platform specific values (SB1, Loongson3 andothers).ccw_timeout_log [S390]See Documentation/s390/CommonIO for details.cgroup_disable= [KNL] Disable a particular controllerFormat: {name of the controller(s) to disable}The effects of cgroup_disable=foo are:- foo isn't auto-mounted if you mount all cgroups ina single hierarchy- foo isn't visible as an individually mountablesubsystem{Currently only "memory" controller deal with this andcut the overhead, others just disable the usage. Soonly cgroup_disable=memory is actually worthy}cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1Format: { controller[,controller...] | "all" }Like cgroup_disable, but only applies to cgroup v1;the blacklisted controllers remain available in cgroup2.cgroup.memory= [KNL] Pass options to the cgroup memory controller.Format: <string>nosocket -- Disable socket memory accounting.nokmem -- Disable kernel memory accounting.checkreqprot [SELINUX] Set initial checkreqprot flag value.Format: { "0" | "1" }See security/selinux/Kconfig help text.0 -- check protection applied by kernel (includesany 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/selinux/checkreqprot.cio_ignore= [S390]See Documentation/s390/CommonIO for details.clk_ignore_unused[CLK]Prevents the clock framework from automatically gatingclocks that have not been explicitly enabled by a Linuxdevice driver but are enabled in hardware at reset orby the bootloader/firmware. Note that this does notforce such clocks to be always-on nor does it reservethose clocks in any way. This parameter is useful fordebug and development, but should not be needed on aplatform with proper driver support. For moreinformation, see Documentation/clk.txt.clock= [BUGS=X86-32, HW] gettimeofday clocksource override.[Deprecated]Forces specified clocksource (if available) to be usedwhen calculating gettimeofday(). If specifiedclocksource is not available, it defaults to PIT.Format: { pit | tsc | cyclone | pmtmr }clocksource= Override the default clocksourceFormat: <string>Override the default clocksource and use the clocksourcewith the name specified.Some clocksource names to choose from, depending onthe 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,tscclocksource.arm_arch_timer.evtstrm=[ARM,ARM64]Format: <bool>Enable/disable the eventstream feature of the ARMarchitected timer so that code using WFE-based pollingloops can be debugged more effectively on productionsystems.clearcpuid=BITNUM [X86]Disable CPUID feature X for the kernel. Seearch/x86/include/asm/cpufeatures.h for the valid bitnumbers. Note the Linux specific bits are not necessarilystable over kernel options, but the vendor specificones should be.Also note that user programs calling CPUID directlyor using the feature without checking anythingwill still see it. This just prevents it frombeing used by the kernel or shown in /proc/cpuinfo.Also note the kernel might malfunction if you disablesome critical bits.cma=nn[MG]@[start[MG][-end[MG]]][ARM,X86,KNL]Sets the size of kernel global memory area forcontiguous memory allocations and optionally theplacement constraint by the physical address range ofmemory allocations. A value of 0 disables CMAaltogether. For more information, seeinclude/linux/dma-contiguous.hcmo_free_hint= [PPC] Format: { yes | no }Specify whether pages are marked as being inactivewhen they are freed. This is used in CMO environmentsto determine OS memory pressure for page stealing bya hypervisor.Default: yescoherent_pool=nn[KMG] [ARM,KNL]Sets the size of memory pool for coherent, atomic dmaallocations, by default set to 256K.code_bytes [X86] How many bytes of object code to printin an oops report.Range: 0 - 8192Default: 64com20020= [HW,NET] ARCnet - COM20020 chipsetFormat:<io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)Format: <io>[,<irq>]com90xx= [HW,NET]ARCnet - COM90xx chipset (memory-mapped buffers)Format: <io>[,<irq>[,<memstart>]]condev= [HW,S390] console deviceconmode=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 ofthe form "bbbbpnf", where "bbbb" is the baud rate,"p" is parity ("n", "o", or "e"), "n" is number ofbits, and "f" is flow control ("r" for RTS oromit it). Default is "9600n8".See Documentation/admin-guide/serial-console.rst for moreinformation. SeeDocumentation/networking/netconsole.txt for analternative.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 8250/16550UART 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 assumedto be equivalent to 'mmio'. 'options' are specified inthe 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 forboth Xen and PowerPC hypervisors.If the device connected to the port is not a TTY but a brailledevice, prepend "brl," before the device type, for instanceconsole=brl,ttyS0For now, only VisioBraille is supported.console_msg_format=[KNL] Change console messages formatdefaultBy default we print messages on consoles in"[time stamp] text\n" format (time stamp may not beprinted, depending on CONFIG_PRINTK_TIME or`printk_time' param).syslogSwitch to syslog format: "<%u>[time stamp] text\n"IOW, each message will have a facility and loglevelprefix. The format is similar to one used by syslog()syscall, or to executing "dmesg -S --raw" or to readingfrom /proc/kmsg.consoleblank= [KNL] The console blank (screen saver) timeout inseconds. 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.txt.coresight_cpu_debug.enable[ARM,ARM64]Format: <bool>Enable/disable the CPU sampling based debugging.0: default value, disable debugging1: enable debugging at boot timecpuidle.off=1 [CPU_IDLE]disable the cpuidle sub-systemcpufreq.off=1 [CPU_FREQ]disable the cpufreq sub-systemcpu_init_udelay=N[X86] Delay for N microsec between assert and de-assertof APIC INIT to start processors. This delay occurson every CPU online, such as boot, and resume from suspend.Default: 10000cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driverFormat:<first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]crashkernel=size[KMG][@offset[KMG]][KNL] Using kexec, Linux can switch to a 'crash kernel'upon panic. This parameter reserves the physicalmemory region [offset, offset + size] for that kernelimage. If '@offset' is omitted, then a suitable offsetis selected automatically. CheckDocumentation/kdump/kdump.txt for further details.crashkernel=range1:size1[,range2:size2,...][@offset][KNL] Same as above, but depends on the memoryin the running system. The syntax of range isstart-[end] where start and end are botha memory unit (amount[KMG]). See alsoDocumentation/kdump/kdump.txt for an example.crashkernel=size[KMG],high[KNL, x86_64] range could be above 4G. Allow kernelto allocate physical memory region from top, so couldbe above 4G if system have more than 4G ram installed.Otherwise memory region will be allocated below 4G, ifavailable.It will be ignored if crashkernel=X is specified.crashkernel=size[KMG],low[KNL, x86_64] range under 4G. When crashkernel=X,highis passed, kernel could allocate physical memory regionabove 4G, that cause second kernel crash on systemthat require some amount of low memory, e.g. swiotlbrequires at least 64M+32K low memory, also enough extralow memory is needed to make sure DMA buffers for 32-bitdevices won't run out. Kernel would try to allocate atat least 256M below 4G automatically.This one let user to specify own low range under 4Gfor second kernel instead.0: to disable low allocation.It will be ignored when crashkernel=X,high is not usedor memory reserved is below 4G.cryptomgr.notests[KNL] Disable crypto self-testscs89x0_dma= [HW,NET]Format: <dma>cs89x0_media= [HW,NET]Format: { rj45 | aui | bnc }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.rstddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boottime. SeeDocumentation/admin-guide/dynamic-debug-howto.rst fordetails. Deprecated, see dyndbg.debug [KNL] Enable kernel debugging (events log level).debug_locks_verbose=[KNL] verbose self-testsFormat=<0|1>Print debugging info while doing the locking APIself-tests.We default to 0 (no extra messages), setting it to1 will print _a lot_ more information - normallyonly useful to kernel developers.debug_objects [KNL] Enable object debuggingno_debug_objects[KNL] Disable object debuggingdebug_guardpage_minorder=[KNL] When CONFIG_DEBUG_PAGEALLOC is set, thisparameter allows control of the order of pages that willbe intentionally kept free (and hence protected) by thebuddy allocator. Bigger value increase the probabilityof catching random memory corruption, but reduce theamount of memory for normal system use. The maximumpossible value is MAX_ORDER/2. Setting this parameterto 1 or 2 should be enough to identify most randommemory corruption problems caused by bugs in kernel ordriver code when a CPU writes to (or reads from) arandom memory location. Note that there exists a classof memory corruptions problems caused by buggy H/W orF/W or by drivers badly programing DMA (basically whenmemory is written at bus level and the CPU MMU isbypassed) which are not detectable byCONFIG_DEBUG_PAGEALLOC, hence this option will not helptracking down these problems.debug_pagealloc=[KNL] When CONFIG_DEBUG_PAGEALLOC is set, thisparameter enables the feature at boot time. Indefault, it is disabled. We can avoid allocating hugechunk of memory for debug pagealloc if we don't enableit at boot time and the system will work mostly samewith the kernel built without CONFIG_DEBUG_PAGEALLOC.on: enable the featuredebugpat [X86] Enable PAT debuggingdecnet.addr= [HW,NET]Format: <area>[,<node>]See also Documentation/networking/decnet.txt.default_hugepagesz=[same as hugepagesz=] The size of the defaultHugeTLB page size. This is the size represented bythe legacy /proc/ hugepages APIs, used for SHM, anddefault size when mounting hugetlbfs filesystems.Defaults to the default architecture's huge page sizeif not specified.dhash_entries= [KNL]Set number of hash buckets for dentry cache.disable_1tb_segments [PPC]Disables the use of 1TB hash page table segments. Thiscauses the kernel to fall back to 256MB segments whichcan be useful when debugging issues that require an SLBmiss to occur.disable= [IPV6]See Documentation/networking/ipv6.txt.disable_radix [PPC]Disable RADIX MMU mode on POWER9disable_cpu_apicid= [X86,APIC,SMP]Format: <int>The number of initial APIC ID for thecorresponding CPU to be disabled at boot,mostly used for the kdump 2nd kernel todisable BSP to wake up multiple CPUs withoutcausing system reset or hang due to sendingINIT from AP to BSP.disable_ddw [PPC/PSERIES]Disable Dynamic DMA Window support. Use this ifto workaround buggy firmware.disable_ipv6= [IPV6]See Documentation/networking/ipv6.txt.disable_mtrr_cleanup [X86]The kernel tries to adjust MTRR layout from continuousto discrete, to make X server driver able to add WBentry later. This parameter disables that.disable_mtrr_trim [X86, Intel and AMD only]By default the kernel will trim any uncacheablememory out of your available memory pool based onMTRR settings. This parameter disables that behavior,possibly causing your machine to run very slowly.disable_timer_pin_1 [X86]Disable PIN 1 of APIC timerCan 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 preallocatedentries for DMA-API debugging code. One entry isrequired per DMA-API allocation. Use this if theDMA-API debugging code disables itself because thearchitectural default is too low.dma_debug_driver=<driver_name>With this option the DMA-API debugging driverfilter feature can be enabled at boot time. Justpass the driver to filter for as the parameter.The filter can be disabled or changed to anotherdriver later using sysfs.drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]Broken monitors, graphic adapters, KVMs and EDIDlesspanels may send no or incorrect EDID data sets.This parameter allows to specify an EDID data setsin the /lib/firmware directory that are used instead.Generic built-in EDID data sets are used, if one ofedid/1024x768.bin, edid/1280x1024.bin,edid/1680x1050.bin, or edid/1920x1080.bin is givenand no file with the same name exists. Details andinstructions how to build your own EDID data areavailable in Documentation/EDID/HOWTO.txt. An EDIDdata set will only be used for a particular connector,if its name and a colon are prepended to the EDIDname. Each connector may use a unique EDID dataset by separating the files with a comma. An EDIDdata set with no connector name will be used forany connectors not explicitly specified.dscc4.setup= [NET]dt_cpu_ftrs= [PPC]Format: {"off" | "known"}Control how the dt_cpu_ftrs device-tree binding isused for CPU feature discovery and setup (if itexists).off: Do not use it, fall back to legacy cpu table.known: Do not pass through unknown features to guestsor userspace, only those that the kernel is aware of.dump_apple_properties [X86]Dump name and content of EFI device properties onx86 Macs. Useful for driver authors to determinewhat data is available or for reverse-engineering.dyndbg[="val"] [KNL,DYNAMIC_DEBUG]module.dyndbg[="val"]Enable debug messages at boot time. SeeDocumentation/admin-guide/dynamic-debug-howto.rstfor details.nompx [X86] Disables Intel Memory Protection Extensions.See Documentation/x86/intel_mpx.txt for moreinformation about the feature.nopku [X86] Disable Memory Protection Keys CPU feature foundin some Intel CPUs.module.async_probe [KNL]Enable asynchronous probe on this module.early_ioremap_debug [KNL]Enable debug messages in early_ioremap support. Thisis useful for tracking down temporary early mappingswhich are not unmapped.earlycon= [KNL] Output early console device and options.[ARM64] The early console is determined by thestdout-path property in device tree's chosen node,or determined by the ACPI SPCR table.[X86] When used with no options the early console isdetermined by the ACPI SPCR table.cdns,<addr>[,options]Start an early, polled-mode console on a Cadence(xuartps) serial port at the specified address. Onlysupported option is baud rate. If baud rate is notspecified, the serial port must already be setup andconfigured.uart[8250],io,<addr>[,options]uart[8250],mmio,<addr>[,options]uart[8250],mmio32,<addr>[,options]uart[8250],mmio32be,<addr>[,options]uart[8250],0x<addr>[,options]Start an early, polled-mode console on the 8250/16550UART 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 assumedto be equivalent to 'mmio'. 'options' are specifiedin the same format described for "console=ttyS<n>"; ifunspecified, the h/w is not initialized.pl011,<addr>pl011,mmio32,<addr>Start an early, polled-mode console on a pl011 serialport at the specified address. The pl011 serial portmust already be setup and configured. Options are notyet supported. If 'mmio32' is specified, then onlythe driver will use only 32-bit accessors to read/writethe device registers.meson,<addr>Start an early, polled-mode console on a meson serialport at the specified address. The serial port mustalready be setup and configured. Options are not yetsupported.msm_serial,<addr>Start an early, polled-mode console on an msm serialport at the specified address. The serial portmust already be setup and configured. Options are notyet supported.msm_serial_dm,<addr>Start an early, polled-mode console on an msm serialdm port at the specified address. The serial portmust already be setup and configured. Options are notyet supported.owl,<addr>Start an early, polled-mode console on a serial portof an Actions Semi SoC, such as S500 or S900, at thespecified address. The serial port must already besetup and configured. Options are not yet supported.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 availableon Samsung SoCs, requires selecting proper type anda correct base address of the selected UART port. Theserial 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 portmust already be setup and configured. Options are notyet supported.lpuart,<addr>lpuart32,<addr>Use early console provided by Freescale LP UART driverfound on Freescale Vybrid and QorIQ LS1021A processors.A valid base address must be provided, and the serialport must already be setup and configured.ar3700_uart,<addr>Start an early, polled-mode console on theArmada 3700 serial port at the specifiedaddress. The serial port must already be setupand configured. Options are not yet supported.earlyprintk= [X86,SH,ARM,M68k,S390]earlyprintk=vgaearlyprintk=efiearlyprintk=sclpearlyprintk=xenearlyprintk=serial[,ttySn[,baudrate]]earlyprintk=serial[,0x...[,baudrate]]earlyprintk=ttySn[,baudrate]earlyprintk=dbgp[debugController#]earlyprintk=pciserial,bus:device.function[,baudrate]earlyprintk=xdbc[xhciController#]earlyprintk is useful when the kernel crashes beforethe normal console is initialized. It is not enabled bydefault because it has some cosmetic problems.Append ",keep" to not disable it when the real consoletakes over.Only one of vga, efi, serial, or usb debug port canbe used at a time.Currently only ttyS0 and ttyS1 may be specified byname. Other I/O ports may be explicitly specifiedon some architectures (x86 and arm at least) byreplacing ttySn with an I/O port address, like this:earlyprintk=serial,0x1008,115200You 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 notvery good.The VGA and EFI output is eventually overwritten bythe real console.The xen output can only be used by Xen PV guests.The sclp output can only be used on s390.edac_report= [HW,EDAC] Control how to report EDAC eventFormat: {"on" | "off" | "force"}on: enable EDAC to report H/W event. May be overriddenby 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.ekgdboc= [X86,KGDB] Allow early kernel console debuggingekgdboc=kbdThis is designed to be used in conjunction withthe boot argument: earlyprintk=vgaedd= [EDD]Format: {"off" | "on" | "skip[mbr]"}efi= [EFI]Format: { "old_map", "nochunk", "noruntime", "debug" }old_map [X86-64]: switch to the old ioremap-based EFIruntime services mapping. 32-bit still uses this one bydefault.nochunk: disable reading files in "chunks" in the EFIboot stub, as chunking can cause problems with somefirmware implementations.noruntime : disable EFI runtime services supportdebug: enable misc debug outputefi_no_storage_paranoia [EFI; X86]Using this parameter you can use more than 50% ofyour efi variable storage. Use this parameter only ifyou are really sure that your UEFI does sane gc andfulfills the spec otherwise your board may brick.efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]Add arbitrary attribute to specific memory range byupdating original EFI memory map.Region of memory which aa attribute is added to isfrom ss to ss+nn.If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)attribute is added to range 0x100000000-0x180000000 and0x10a0000000-0x1120000000.Using this parameter you can do debugging of EFI memmaprelated feature. For example, you can do debugging ofAddress Range Mirroring feature even if your boxdoesn't support it.efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDTthat is to be dynamically loaded by Linux. If there aremultiple variables with the same name but with differentvendor GUIDs, all of them will be loaded. SeeDocumentation/acpi/ssdt-overlays.txt for details.eisa_irq_edge= [PARISC,HW]See header of drivers/parisc/eisa.c.elanfreq= [X86-32]See comment before function elanfreq_setup() inarch/x86/kernel/cpu/cpufreq/elanfreq.c.elevator= [IOSCHED]Format: {"cfq" | "deadline" | "noop"}See Documentation/block/cfq-iosched.txt andDocumentation/block/deadline-iosched.txt for details.elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]Specifies physical address of start of kernel coreimage elf header and optionally the size. Generallykexec loader will pass this option to capture kernel.See Documentation/kdump/kdump.txt for details.enable_mtrr_cleanup [X86]The kernel tries to adjust MTRR layout from continuousto discrete, to make X server driver able to add WBentry later. This parameter enables that.enable_timer_pin_1 [X86]Enable PIN 1 of APIC timerCan 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 /selinux/enforce.erst_disable [ACPI]Disable Error Record Serialization Table (ERST)support.ether= [HW,NET] Ethernet cards parametersThis option is obsoleted by the "netdev=" option, whichhas equivalent usage. See its documentation for details.evm= [EVM]Format: { "fix" }Permit 'security.evm' to be updated regardless ofcurrent integrity status.failslab=fail_page_alloc=fail_make_request=[KNL]General fault injection mechanism.Format: <interval>,<probability>,<space>,<times>See also Documentation/fault-injection/.floppy= [HW]See Documentation/blockdev/floppy.txt.force_pal_cache_flush[IA-64] Avoid check_sal_cache_flush which may hang onbuggy SAL_CACHE_FLUSH implementations. Using thisparameter will force ia64_sal_cache_flush to callia64_pal_cache_flush instead of SAL_CACHE_FLUSH.forcepae [X86-32]Forcefully enable Physical Address Extension (PAE).Many Pentium M systems disable PAE but may have afunctionally usable PAE implementation.Warning: use of this parameter will taint the kerneland may cause unknown problems.ftrace=[tracer][FTRACE] will set and start the specified traceras early as possible in order to facilitate earlyboot debugging.ftrace_dump_on_oops[=orig_cpu][FTRACE] will dump the trace buffers on oops.If no parameter is passed, ftrace will dumpbuffers of all CPUs, but if you pass orig_cpu, it willdump only the buffer of the CPU that triggered theoops.ftrace_filter=[function-list][FTRACE] Limit the functions traced by the functiontracer at boot up. function-list is a comma separatedlist of functions. This list can be changed at runtime by the set_ftrace_filter file in the debugfstracing directory.ftrace_notrace=[function-list][FTRACE] Do not trace the functions specified infunction-list. This list can be changed at run timeby the set_ftrace_notrace file in the debugfstracing directory.ftrace_graph_filter=[function-list][FTRACE] Limit the top level callers functions tracedby the function graph tracer at boot up.function-list is a comma separated list of functionsthat can be changed at run time by theset_graph_function file in the debugfs tracing directory.ftrace_graph_notrace=[function-list][FTRACE] Do not trace from the functions specified infunction-list. This list is a comma separated list offunctions that can be changed at run time by theset_graph_notrace file in the debugfs tracing directory.ftrace_graph_max_depth=<uint>[FTRACE] Used with the function graph tracer. This isthe max depth it will trace into a function. This valuecan be changed at run time by the max_graph_depth filein the tracefs tracing directory. default: 0 (no limit)gamecon.map[2|3]=[HW,JOY] Multisystem joystick and NES/SNES/PSX padsupport via parallel port (up to 5 devices per port)Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>See also Documentation/input/devices/joystick-parport.rstgamma= [HW,DRM]gart_fix_e820= [X86_64] disable the fix e820 for K8 GARTFormat: off | ondefault: ongcov_persist= [GCOV] When non-zero (default), profiling data forkernel modules is saved and remains accessible viadebugfs, even when the module is unloaded/reloaded.When zero, profiling data is discarded and associateddebugfs 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 theandroid emulatorgpt [EFI] Forces disk with valid GPT signature butinvalid Protective MBR to be treated as GPT. If theprimary GPT is corrupted, it enables the backup/alternateGPT to be used instead.grcan.enable0= [HW] Configuration of physical interface 0. Determinesthe "Enable 0" bit of the configuration register.Format: 0 | 1Default: 0grcan.enable1= [HW] Configuration of physical interface 1. Determinesthe "Enable 0" bit of the configuration register.Format: 0 | 1Default: 0grcan.select= [HW] Select which physical interface to use.Format: 0 | 1Default: 0grcan.txsize= [HW] Sets the size of the tx buffer.Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.Default: 1024grcan.rxsize= [HW] Sets the size of the rx buffer.Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.Default: 1024gpio-mockup.gpio_mockup_ranges[HW] Sets the ranges of gpiochip of for this device.Format: <start1>,<end1>,<start2>,<end2>...hardlockup_all_cpu_backtrace=[KNL] Should the hard-lockup detector generatebacktraces on all cpus.Format: <integer>hashdist= [KNL,NUMA] Large hashes allocated during bootare distributed across NUMA nodes. Defaults onfor 64-bit NUMA, off otherwise.Format: 0 | 1 (for off | on)hcl= [IA-64] SGI's Hardware Graph compatibility layerhd= [EIDE] (E)IDE hard drive subsystem geometryFormat: <cyl>,<head>,<sect>hest_disable [ACPI]Disable Hardware Error Source Table (HEST) support;corresponding firmware-first mode error processinglogic will be disabled.highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exactsize of <nn>. This works even on boxes that have nohighmem otherwise. This also works to reduce highmemsize on bigger boxes.highres= [KNL] Enable/disable high resolution timer mode.Valid parameters: "on", "off"Default: "on"hisax= [HW,ISDN]See Documentation/isdn/README.HiSax.hlt [BUGS=ARM,SH]hpet= [X86-32,HPET] option to control HPET usageFormat: { enable (default) | disable | force |verbose }disable: disable HPET and use PIT insteadforce: allow force enabled of undocumented chips (ICH4,VIA, nVidia)verbose: show contents of HPET registers during setuphpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPETregisters. Default set by CONFIG_HPET_MMAP_DEFAULT.hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.On x86-64 and powerpc, this option can be specifiedmultiple times interleaved with hugepages= to reservehuge pages of different sizes. Valid pages sizes onx86-64 are 2M (when the CPU supports "pse") and 1G(when the CPU supports the "pdpe1gb" cpuinfo flag).hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)terminal devices. Valid values: 0..8hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.If specified, z/VM IUCV HVC accepts connectionsfrom listed z/VM user IDs only.keep_bootcon [KNL]Do not unregister boot console at start. This is onlyuseful for debugging when something happens in the windowbetween unregistering the boot console and initializingthe real console.i2c_bus= [HW] Override the default board specific I2C bus speedor register an additional I2C bus that is notregistered from board initialization code.Format:<bus_id>,<clkrate>i8042.debug [HW] Toggle i8042 debug modei8042.unmask_kbd_data[HW] Enable printing of interrupt data from the KBD port(disabled by default, and as a pre-conditionrequires that i8042.debug=1 be enabled)i8042.direct [HW] Put keyboard port into non-translated modei8042.dumbkbd [HW] Pretend that controller can only read data fromkeyboard and cannot control its state(Don't attempt to blink the leds)i8042.noaux [HW] Don't check for auxiliary (== mouse) porti8042.nokbd [HW] Don't check/create keyboard porti8042.noloop [HW] Disable the AUX Loopback command while probingfor the AUX porti8042.nomux [HW] Don't check presence of an active multiplexingcontrolleri8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUXcontrollersi8042.notimeout [HW] Ignore timeout condition signalled by controlleri8042.reset [HW] Reset the controller during init, cleanup andsuspend-to-ram transitions, only during s2rtransitions, or never resetFormat: { 1 | Y | y | 0 | N | n }1, Y, y: always reset controller0, N, n: don't ever reset controllerDefault: only on s2r transitions on x86; most otherarchitectures force reset to be always executedi8042.unlock [HW] Unlock (ignore) the keylocki8042.kbdreset [HW] Reset device connected to KBD porti810= [HW,DRM]i8k.ignore_dmi [HW] Continue probing hardware even if DMI dataindicates that the driver is running on unsupportedhardware.i8k.force [HW] Activate i8k driver even if SMM BIOS signaturedoes not match list of supported models.i8k.power_status[HW] Report power status in /proc/i8k(disabled by default)i8k.restricted [HW] Allow controlling fans only if SYS_ADMINcapability is set.i915.invert_brightness=[DRM] Invert the sense of the variable that is used toset the brightness of the panel backlight. Normally abrightness value of 0 indicates backlight switched off,and the maximum of the brightness value sets the backlightto maximum brightness. If this parameter is set to 0(default) and the machine requires it, or this parameteris set to 1, a brightness value of 0 sets the backlightto maximum brightness, and the maximum of the brightnessvalue switches the backlight off.-1 -- never invert brightness0 -- machine default1 -- force brightness inversionicn= [HW,ISDN]Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]ide-core.nodma= [HW] (E)IDE subsystemFormat: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc.vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr.cdrom .chs .ignore_cable are additional optionsSee Documentation/ide/ide.txt.ide-generic.probe-mask= [HW] (E)IDE subsystemFormat: <int>Probe mask for legacy ISA IDE ports. Depending onplatform up to 6 ports are supported, enabled bysetting corresponding bits in the mask to 1. Thedefault value is 0x0, which has a special meaning.On systems that have PCI, it triggers scanning thePCI bus for the first and the second port, whichare then probed. On systems without PCI the valueof 0x0 enables probing the two first ports as if itwas 0x3.ide-pci-generic.all-generic-ide [HW] (E)IDE subsystemClaim all unknown PCI IDE storage controllers.idle= [X86]Format: idle=poll, idle=halt, idle=nomwaitPoll forces a polling idle loop that can slightlyimprove the performance of waking up a idle CPU, butwill use a lot of power and make the system run hot.Not recommended.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-statesieee754= [MIPS] Select IEEE Std 754 conformance modeFormat: { strict | legacy | 2008 | relaxed }Default: strictChoose which programs will be accepted for executionbased on the IEEE 754 NaN encoding(s) supported bythe FPU and the NaN encoding requested with the valueof an ELF file header flag individually set by eachbinary. Hardware implementations are permitted tosupport either or both of the legacy and the 2008 NaNencoding mode.Available settings are as follows:strict accept binaries that request a NaN encodingsupported by the FPUlegacy only accept legacy-NaN binaries, if supportedby the FPU2008 only accept 2008-NaN binaries, if supportedby the FPUrelaxed accept any binaries regardless of whethersupported by the FPUThe FPU emulator is always able to support both NaNencodings, so if no FPU hardware is present or it hasbeen disabled with 'nofpu', then the settings of'legacy' and '2008' strap the emulator accordingly,'relaxed' straps the emulator for both legacy-NaN and2008-NaN, whereas 'strict' enables legacy-NaN only onlegacy processors and both NaN encodings on MIPS32 orMIPS64 CPUs.The setting for ABS.fmt/NEG.fmt instruction executionmode generally follows that for the NaN encoding,except where unsupported by hardware.ignore_loglevel [KNL]Ignore loglevel setting - this will print /all/kernel messages to the console. Useful for debugging.We also add it as printk module parameter, so userscould change it dynamically, usually by/sys/module/printk/parameters/ignore_loglevel.ignore_rlimit_dataIgnore 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 measurementsFormat: { "off" | "enforce" | "fix" | "log" }default: "enforce"ima_appraise_tcb [IMA]The builtin appraise policy appraises all filesowned by uid=0.ima_canonical_fmt [IMA]Use the canonical format for the binary runtimemeasurements, instead of host native format.ima_hash= [IMA]Format: { md5 | sha1 | rmd160 | sha256 | sha384| sha512 | ... }default: "sha1"The list of supported hash algorithms is definedin crypto/hash_info.h.ima_policy= [IMA]The builtin policies to load during IMA setup.Format: "tcb | appraise_tcb | secure_boot |fail_securely"The "tcb" policy measures all programs exec'd, filesmmap'd for exec, and all files opened with the readmode bit set by either the effective uid (euid=0) oruid=0.The "appraise_tcb" policy appraises the integrity ofall files owned by root. (This is the equivalentof ima_appraise_tcb.)The "secure_boot" policy appraises the integrityof files (eg. kexec kernel image, kernel modules,firmware, policy, etc) based on file signatures.The "fail_securely" policy forces file signatureverification failure also on privileged mountedfilesystems with the SB_I_UNVERIFIABLE_SIGNATUREflag.ima_tcb [IMA] Deprecated. Use ima_policy= instead.Load a policy which meets the needs of the TrustedComputing Base. This means IMA will measure allprograms exec'd, files mmap'd for exec, and all filesopened for read by uid=0.ima_template= [IMA]Select one of defined IMA measurements template formats.Formats: { "ima" | "ima-ng" | "ima-sig" }Default: "ima-ng"ima_template_fmt=[IMA] Define a custom template format.Format: { "field1|...|fieldN" }ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usageFormat: <min_file_size>Set the minimal file size for using asynchronous hash.If left unspecified, ahash usage is disabled.ahash performance varies for different data sizes ondifferent crypto accelerators. This option can be usedto achieve the best performance for a particular HW.ima.ahash_bufsize= [IMA] Asynchronous hash buffer sizeFormat: <bufsize>Set hashing buffer size. Default: 4k.ahash performance varies for different chunk sizes ondifferent crypto accelerators. This option can be usedto achieve best performance for particular HW.init= [KNL]Format: <full_path>Run specified binary instead of /sbin/init as initprocess.initcall_debug [KNL] Trace initcalls as they are executed. Usefulfor working out where the kernel is dying duringstartup.initcall_blacklist= [KNL] Do not execute a comma-separated list ofinitcall functions. Useful for debugging built-inmodules and initcalls.initrd= [BOOT] Specify the location of the initial ramdiskinit_pkru= [x86] Specify the default memory protection keys rightsregister contents for all processes. 0x55555554 bydefault (disallow access to all but pkey 0). Canoverride in debugfs after boot.inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driverFormat: <irq>int_pln_enable [x86] Enable power limit notification interruptintegrity_audit=[IMA]Format: { "0" | "1" }0 -- basic integrity auditing messages. (Default)1 -- additional integrity auditing messages.intel_iommu= [DMAR] Intel IOMMU driver (DMAR) optiononEnable intel iommu driver.offDisable intel iommu driver.igfx_off [Default Off]By default, gfx is mapped as normal device. If a gfxdevice has a dedicated DMAR unit, the DMAR unit isbypassed by not enabling DMAR with this option. Inthis case, gfx device will use physical address forDMA.forcedac [x86_64]With this option iommu will not optimize to lookfor io virtual address below 32-bit forcing dualaddress cycle on pci bus for cards supporting greaterthan 32-bit addressing. The default is to lookfor translation below 32-bit and if not availablethen look in the higher range.strict [Default Off]With this option on every unmap_single operation willresult in a hardware IOTLB flush operation as opposedto batching them for performance.sp_off [Default Off]By default, super page will be supported if Intel IOMMUhas the capability. With this option, super page willnot be supported.ecs_off [Default Off]By default, extended context tables will be supported ifthe hardware advertises that it has support both for theextended tables themselves, and also PASID support. Withthis option set, extended tables will not be used evenon hardware which claims to support them.tboot_noforce [Default Off]Do not force the Intel IOMMU enabled under tboot.By default, tboot will force Intel IOMMU on, whichcould harm performance of some high-throughputdevices like 40GBit network cards, even if identitymapping is enabled.Note that using this option lowers the securityprovided by tboot because it makes the systemvulnerable 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]disableDo not enable intel_pstate as the defaultscaling driver for the supported processorspassiveUse intel_pstate as a scaling driver, but configure itto work with generic cpufreq governors (instead ofenabling its internal governor). This mode cannot beused along with the hardware-managed P-states (HWP)feature.forceEnable intel_pstate on systems that prohibit it by defaultin favor of acpi-cpufreq. Forcing the intel_pstate driverinstead of acpi-cpufreq may disable platform features, suchas thermal controls and power capping, that rely on ACPIP-States information being indicated to OSPM and thereforeshould be used with caution. This option does not work withprocessors that aren't supported by the intel_pstate driveror on platforms that use pcc-cpufreq instead of acpi-cpufreq.no_hwpDo not enable hardware P state control (HWP)if available.hwp_onlyOnly load intel_pstate on systems which supporthardware P state control (HWP) if available.support_acpi_ppcEnforce ACPI _PPC performance limits. If the Fixed ACPIDescription Table, specifies preferred power managementprofile as "Enterprise Server" or "Performance Server",then this feature is turned on by default.per_cpu_perf_limitsAllow per-logical-CPU P-State performance control limits usingcpufreq sysfs interfaceintremap= [X86-64, Intel-IOMMU]on enable Interrupt Remapping (default)off disable Interrupt Remappingnosid disable Source ID checkingno_x2apic_optoutBIOS x2APIC opt-out request will be ignorednopost disable Interrupt Postingiomem= Disable strict checking of access to MMIO memorystrict regions from userspace.relaxediommu= [x86]offforcenoforcebiomergepanicnopanicmergenomergeforcesacsoftpt [x86, IA-64]nobypass [PPC/POWERNV]Disable IOMMU bypass, using IOMMU for PCI devices.iommu.passthrough=[ARM64] 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 IOMMU translation for DMA.io7= [HW] IO7 for Marvel based alpha systemsSee comment before marvel_specify_io7 inarch/alpha/kernel/core_marvel.c.io_delay= [X86] I/O delay method0x80Standard port 0x80 based delay0xedAlternate port 0xed based delay (needed on some systems)udelaySimple two microseconds delaynoneNo delayip= [IP_PNP]See Documentation/filesystems/nfs/nfsroot.txt.irqaffinity= [SMP] Set the default irq affinity maskThe argument is a cpu list, as described above.irqchip.gicv2_force_probe=[ARM, ARM64]Format: <bool>Force the kernel to look for the second 4kB pageof a GICv2 controller even if the memory rangeexposed by the device tree is too small.irqchip.gicv3_nolpi=[ARM, ARM64]Force the kernel to ignore the availability ofLPIs (and by consequence ITSs). Intended for systemthat use the kernel as a bootloader, and thus wantto let secondary kernels in charge of setting upLPIs.irqfixup [HW]When an interrupt is not handled search all handlersfor it. Intended to get systems with badly brokenfirmware running.irqpoll [HW]When an interrupt is not handled search all handlersfor it. Also check all handlers each timerinterrupt. Intended to get systems with badly brokenfirmware running.isapnp= [ISAPNP]Format: <RDP>,<reset>,<pci_scan>,<verbosity>isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.[Deprecated - use cpusets instead]Format: [flag-list,]<cpu-list>Specify one or more CPUs to isolate from disturbancesspecified in the flag list (default: domain):nohzDisable the tick when a single task runs.A residual 1Hz tick is offloaded to workqueues, which youneed to affine to housekeeping through the globalworkqueue's affinity configured via the/sys/devices/virtual/workqueue/cpumask sysfs file, orby 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 tobe configured manually after bootup.domainIsolate from the general SMP balancing and schedulingalgorithms. Note that performing domain isolation this wayis irreversible: it's not possible to bring back a CPU tothe domains once isolated through isolcpus. It's stronglyadvised to use cpusets instead to disable scheduler loadbalancing through the "cpuset.sched_load_balance" file.It offers a much more flexible interface where CPUs canmove in and out of an isolated set anytime.You can move a process onto or off an "isolated" CPU viathe CPU affinity syscalls or cpuset.<cpu number> begins at 0 and the maximum value is"number of CPUs in system - 1".The format of <cpu-list> is described above.iucv= [HW,NET]ivrs_ioapic [HW,X86_64]Provide an override to the IOAPIC-ID<->DEVICE-IDmapping provided in the IVRS ACPI table. Forexample, to map IOAPIC-ID decimal 10 toPCI device 00:14.0 write the parameter as:ivrs_ioapic[10]=00:14.0ivrs_hpet [HW,X86_64]Provide an override to the HPET-ID<->DEVICE-IDmapping provided in the IVRS ACPI table. Forexample, to map HPET-ID decimal 0 toPCI device 00:14.0 write the parameter as:ivrs_hpet[0]=00:14.0ivrs_acpihid [HW,X86_64]Provide an override to the ACPI-HID:UID<->DEVICE-IDmapping provided in the IVRS ACPI table. Forexample, to map UART-HID:UID AMD0020:0 toPCI device 00:14.5 write the parameter as:ivrs_acpihid[00:14.5]=AMD0020:0js= [HW,JOY] Analog joystickSee Documentation/input/joydev/joystick.rst.nokaslr [KNL]When CONFIG_RANDOMIZE_BASE is set, this disableskernel and module base offset ASLR (Address SpaceLayout Randomization).kasan_multi_shot[KNL] Enforce KASAN (Kernel Address Sanitizer) to printreport on every invalid memory access. Without thisparameter KASAN will print report only for the firstinvalid access.keepinitrd [HW,ARM]kernelcore= [KNL,X86,IA-64,PPC]Format: nn[KMGTPE] | nn% | "mirror"This parameter specifies the amount of memory usable bythe kernel for non-movable allocations. The requestedamount is spread evenly throughout all nodes in thesystem as ZONE_NORMAL. The remaining memory is used formovable memory in its own zone, ZONE_MOVABLE. In theevent, a node is too small to have both ZONE_NORMAL andZONE_MOVABLE, kernelcore memory will take priority andother nodes will have a larger ZONE_MOVABLE.ZONE_MOVABLE is used for the allocation of pages thatmay be reclaimed or moved by the page migrationsubsystem. Note that allocations like PTEs-from-HighMemstill use the HighMem zone if it exists, and the Normalzone if it does not.It is possible to specify the exact amount of memory inthe form of "nn[KMGTPE]", a percentage of total systemmemory in the form of "nn%", or "mirror". If "mirror"option is specified, mirrored (reliable) memory is usedfor non-movable allocations and remaining memory is usedfor Movable pages. "nn[KMGTPE]", "nn%", and "mirror"are exclusive, so you cannot specify multiple forms.kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.Format: <Controller#>[,poll interval]The controller # is the number of the ehci usb debugport as it is probed via PCI. The poll interval isoptional and is the number seconds in betweeneach poll cycle to the debug port in case you needthe functionality for interrupting the kernel withgdb or control-c on the dbgp connection. Whennot using this parameter you use sysrq-g to break intothe 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: kbdkeyboard and serial format: kbd,<serial_device>[,baud]Optional Kernel mode setting:kms, kbd format: kms,kbdkms, kbd and serial format: kms,kbd,<ser_dev>[,baud]kgdbwait [KGDB] Stop kernel execution and enter thekernel debugger at the earliest opportunity.kmac= [MIPS] korina ethernet MAC address.Configure the RouterBoard 532 series on-chipEthernet adapter MAC address.kmemleak= [KNL] Boot-time kmemleak enable/disableValid arguments: on, offDefault: onBuilt with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,the default is off.kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.Default is 0 (don't ignore, but inject #GP)kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.Default is false (don't support).kvm.mmu_audit= [KVM] This is a R/W parameter which allows auditKVM MMU at runtime.Default is 0 (off)kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.Default is 1 (enabled)kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)for all guests.Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.kvm-arm.vgic_v3_group0_trap=[KVM,ARM] Trap guest accesses to GICv3 group-0system registerskvm-arm.vgic_v3_group1_trap=[KVM,ARM] Trap guest accesses to GICv3 group-1system registerskvm-arm.vgic_v3_common_trap=[KVM,ARM] Trap guest accesses to GICv3 commonsystem registerskvm-arm.vgic_v4_enable=[KVM,ARM] Allow use of GICv4 for direct injection ofLPIs.kvm-intel.ept= [KVM,Intel] Disable extended page tables(virtualized MMU) support on capable Intel chips.Default is 1 (enabled)kvm-intel.emulate_invalid_guest_state=[KVM,Intel] Enable emulation of invalid guest statesDefault is 0 (disabled)kvm-intel.flexpriority=[KVM,Intel] Disable FlexPriority feature (TPR shadow).Default is 1 (enabled)kvm-intel.nested=[KVM,Intel] Enable VMX nesting (nVMX).Default is 0 (disabled)kvm-intel.unrestricted_guest=[KVM,Intel] Disable unrestricted guest feature(virtualized real and unpaged mode) on capableIntel chips. Default is 1 (enabled)kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identificationfeature (tagged TLBs) on capable Intel chips.Default is 1 (enabled)l2cr= [PPC]l3cr= [PPC]lapic [X86-32,APIC] Enable the local APIC even if BIOSdisabled it.lapic= [x86,APIC] "notscdeadline" Do not use TSC deadlinevalue for LAPIC timer one-shot implementation. Defaultback to the programmable timer unit in the LAPIC.lapic_timer_c2_ok [X86,APIC] trust the local apic timerin C2 power state.libata.dma= [LIBATA] DMA controllibata.dma=0 Disable all PATA and SATA DMAlibata.dma=1 PATA and SATA Disk DMA onlylibata.dma=2 ATAPI (CDROM) DMA onlylibata.dma=4 Compact Flash DMA onlyCombinations also work, so libata.dma=3 enables DMAfor disks and CDROMs, but not CFs.libata.ignore_hpa= [LIBATA] Ignore HPA limitlibata.ignore_hpa=0 keep BIOS limits (default)libata.ignore_hpa=1 ignore limits, using full disklibata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resumewhen set.Format: <int>libata.force= [LIBATA] Force configurations. The format is commaseparated list of "[ID:]VAL" where ID isPORT[.DEVICE]. PORT and DEVICE are decimal numbersmatching port, link or device. Basically, it matchesthe ATA ID string printed on console by libata. Ifthe whole ID part is omitted, the last PORT and DEVICEvalues are used. If ID hasn't been specified yet, theconfiguration applies to all ports, links and devices.If only DEVICE is omitted, the parameter applies tothe port and all links and devices behind it. DEVICEnumber of 0 either selects the first device or thefirst fan-out link behind PMP device. It does notselect the host link. DEVICE number of 15 selects thehost link and device attached to it.The VAL specifies the configuration to force. As longas there's 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 alsoallowed.* [no]ncq: Turn on or off NCQ.* [no]ncqtrim: Turn off queued DSM TRIM.* nohrst, nosrst, norst: suppress hard, softand both resets.* rstonce: only attempt one reset duringhot-unplug link recovery* dump_id: dump IDENTIFY data.* atapi_dmadir: Enable ATAPI DMADIR bridge support* disable: Disable this device.If there are multiple matching configurations changingthe same attribute, the last one is used.memblock=debug [KNL] Enable memblock debug messages.load_ramdisk= [RAM] List of ramdisks to load from floppySee Documentation/blockdev/ramdisk.txt.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>locktorture.nreaders_stress= [KNL]Set the number of locking read-acquisition kthreads.Defaults to being automatically set based on thenumber 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, orzero to disable CPU-hotplug testing.locktorture.shuffle_interval= [KNL]Set task-shuffle interval (jiffies). Shufflingtasks allows some CPUs to go into dyntick-idlemode during the locktorture test.locktorture.shutdown_secs= [KNL]Set time (s) after boot system shutdown. Thisis 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 forfive seconds, wait for five seconds, and so on.This tests the locking primitive's ability totransition abruptly to and from idle.locktorture.torture_type= [KNL]Specify the locking implementation to test.locktorture.verbose= [KNL]Enable additional printk() statements.logibm.irq= [HW,MOUSE] Logitech Bus Mouse DriverFormat: <irq>loglevel= All Kernel Messages with a loglevel smaller than theconsole loglevel will be printed to the console. It canalso be changed with klogd or other programs. Theloglevels are defined as follows:0 (KERN_EMERG) system is unusable1 (KERN_ALERT) action must be taken immediately2 (KERN_CRIT) critical conditions3 (KERN_ERR) error conditions4 (KERN_WARNING) warning conditions5 (KERN_NOTICE) normal but significant condition6 (KERN_INFO) informational7 (KERN_DEBUG) debug-level messageslog_buf_len=n[KMG] Sets the size of the printk ring buffer,in bytes. n must be a power of two and greaterthan the minimal size. The minimal size is definedby LOG_BUF_SHIFT kernel config parameter. There isalso CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameterthat allows to increase the default size depending onthe 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 forkernel log messages and is useful when debuggingkernel boot problems.lp=0 [LP] Specify parallel ports to use, e.g,lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 useslp=reset first parallel port). 'lp=0' disables thelp=auto printer driver. 'lp=reset' (which can bespecified in addition to the ports) causesattached printers to be reset. Usinglp=port1,port2,... specifies the parallel portsto associate lp devices with, starting withlp0. A port specification may be 'none' to skipthat lp device, or a parport name such as'parport0'. Specifying 'lp=auto' instead of aport specification list means that device IDsfrom each port should be examined, to see ifan IEEE 1284-compliant printer is attached; ifso, 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 avoidingtime-consuming boot-time autodetection (up to 250 ms perCPU). 0 enables autodetection (default). To determinethe correct value for your kernel, boot with normalautodetection and see what value is printed. Note thaton SMP systems the preset will be applied to all CPUs,which is likely to cause problems if your CPUs needsignificantly divergent settings. An incorrect valuewill cause delays in the kernel to be wrong, leading tounpredictable I/O errors and other breakage. Althoughunlikely, in the extreme case this might damage yourhardware.ltpc= [NET]Format: <io>,<irq>,<dma>machvec= [IA-64] Force the use of a particular machine-vector(machvec) in a generic kernel.Example: machvec=hpzx1_swiotlbmachtype= [Loongson] Share the same kernel image file between differentyeeloong laptop.Example: machtype=lemote-yeeloong-2f-7inchmax_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greaterthan or equal to this physical address is ignored.maxcpus= [SMP] Maximum number of processors that an SMP kernelwill bring up during bootup. maxcpus=n : n >= 0 limitsthe kernel to bring up 'n' processors. Surely afterbootup you can bring up the other plugged cpu by executing"echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpusonly 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 defaultnumber is configured by BLK_DEV_LOOP_MIN_COUNT. Insteadof statically allocating a predefined number, loopdevices can be requested on-demand with the/dev/loop-control interface.mce [X86-32] Machine Check Exceptionmce=option [X86-64] See Documentation/x86/x86_64/boot-options.txtmd= [HW] RAID subsystems devices and levelSee Documentation/admin-guide/md.rst.mdacon= [MDA]Format: <first>,<last>Specifies range of consoles to be captured by the MDA.mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memoryAmount of memory to be used when the kernel is not ableto see the whole system memory or for test.[X86] Work as limiting max address. Use togetherwith memmap= to avoid physical address space collisions.Without memmap= PCI devices could be placed at addressesbelonging to unused RAM.mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernelmemory.memchunk=nn[KMG][KNL,SH] Allow user to override the default size forper-device physically contiguous DMA buffers.memhp_default_state=online/offline[KNL] Set the initial state for the memory hotplugonlining policy. If not specified, the default value isset according to theCONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel configoption.See Documentation/memory-hotplug.txt.memmap=exactmap [KNL,X86] Enable setting of an exactE820 memory map, as specified by the user.Such memmap=exactmap lines can be constructed based onBIOS output or other requirements. See the memmap=nn@ssoption description.memmap=nn[KMG]@ss[KMG][KNL] 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!1024Gmemmap=nn[KMG]#ss[KMG][KNL,ACPI] 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] Mark specific memory as reserved.Region of memory to be reserved is from ss to ss+nn.Example: Exclude memory from 0x18690000-0x1869ffffmemmap=64K$0x18690000ormemmap=0x10000$0x18690000Some bootloaders may need an escape character before '$',like Grub2, otherwise '$' and the following numberwill be eaten.memmap=nn[KMG]!ss[KMG][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] Convert memory within the specified regionfrom <oldtype> to <newtype>. If "-<oldtype>" is leftout, the whole region will be marked as <newtype>,even if previously unavailable. If "+<newtype>" is leftout, matching memory will be removed. Types arespecified as e820 types, e.g., 1 = RAM, 2 = reserved,3 = ACPI, 12 = PRAM.memory_corruption_check=0/1 [X86]Some BIOSes seem to corrupt the first 64k ofmemory when doing things like suspend/resume.Setting this option will scan the memorylooking for corruption. Enabling this willboth detect corruption and prevent the kernelfrom using the memory being corrupted.However, its intended as a diagnostic tool; ifrepeatable BIOS-originated corruption alwaysaffects the same memory, you can use memmap=to prevent the kernel from using that memory.memory_corruption_check_size=size [X86]By default it checks for corruption in the low64k, making this memory unavailable for normaluse. Use this parameter to scan forcorruption in more or less memory.memory_corruption_check_period=seconds [X86]By default it checks for corruption every 60seconds. Use this parameter to check at someother rate. 0 disables periodic checking.memtest= [KNL,X86,ARM] Enable memtestFormat: <integer>default : 0 <disable>Specifies the number of memtest passes to beperformed. Each pass selects another testpattern from a given set of patterns. Memtestfills the memory with this pattern, validatesmemory contents and reserves bad memoryregions that are detected.mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) controlValid arguments: on, offDefault (depends on kernel configuration option):on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)mem_encrypt=on: Activate SMEmem_encrypt=off: Do not activate SMERefer to Documentation/x86/amd-memory-encryption.txtfor details on when memory encryption can be activated.mem_sleep_default= [SUSPEND] Default system suspend mode:s2idle - Suspend-To-Idleshallow - Power-On Suspend or equivalent (if supported)deep - Suspend-To-RAM or equivalent (if supported)See Documentation/admin-guide/pm/sleep-states.rst.meye.*= [HW] Set MotionEye Camera parametersSee Documentation/media/v4l-drivers/meye.rst.mfgpt_irq= [IA-32] Specify the IRQ to use for theMulti-Function General Purpose Timers on AMD Geodeplatforms.mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms whenthe BIOS has incorrectly applied a workaround. TinyBIOSversion 0.98 is known to be affected, 0.99 fixes theproblem by letting the user disable the workaround.mga= [HW,DRM]min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below thisphysical address is ignored.mini2440= [ARM,HW,KNL]Format:[0..2][b][c][t]Default: "0tb"MINI2440 configuration specification:0 - The attached screen is the 3.5" TFT1 - The attached screen is the 7" TFT2 - The VGA Shield is attached (1024x768)Leaving out the screen size parameter will not loadthe TFT driver, and the framebuffer will be leftunconfigured.b - Enable backlight. The TFT backlight pin will belinked to the kernel VESA blanking code and a GPIOLED. This parameter is not necessary when using theVGA shield.c - Enable the s3c camera interface.t - Reserved for enabling touchscreen support. Thetouchscreen support is not enabled in the mainstreamkernel as of 2.6.30, a preliminary port can be foundin the "bleeding edge" mini2440 support kernel athttp://repo.or.cz/w/linux-2.6/mini2440.gitmminit_loglevel=[KNL] When CONFIG_DEBUG_MEMORY_INIT is set, thisparameter allows control of the logging verbosity forthe additional memory initialisation checks. A valueof 0 disables mminit logging and a level of 4 willlog everything. Information is printed at KERN_DEBUGso loglevel=8 may also need to be specified.module.sig_enforce[KNL] When CONFIG_MODULE_SIG is set, this means thatmodules without (valid) signatures will fail to load.Note that if CONFIG_MODULE_SIG_FORCE is set, thatis always true, so this option does nothing.module_blacklist= [KNL] Do not load a comma-separated list ofmodules. Useful for debugging problem modules.mousedev.tap_time=[MOUSE] Maximum time between finger touching andleaving touchpad surface for touch to be considereda tap and be reported as a left button click (fortouchpads working in absolute mode only).Format: <msecs>mousedev.xres= [MOUSE] Horizontal screen resolution, used for devicesreporting absolute coordinates, such as tabletsmousedev.yres= [MOUSE] Vertical screen resolution, used for devicesreporting absolute coordinates, such as tabletsmovablecore= [KNL,X86,IA-64,PPC]Format: nn[KMGTPE] | nn%This parameter is the complement to kernelcore=, itspecifies the amount of memory used for migratableallocations. If both kernelcore and movablecore isspecified, then kernelcore will be at *least* thespecified value but may be more. If movablecore on itsown is specified, the administrator must be carefulthat the amount of memory usable for all allocationsis not too small.movable_node [KNL] Boot-time switch to make hotplugable memoryNUMA nodes to be movable. This means that the memoryof such nodes will be usable only for movableallocations which rules out almost all kernelallocations. 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/cmdlinepart.c.multitce=off [PPC] This parameter disables the use of the pSeriesfirmware feature for updating multiple TCE entriesat a time.onenand.bdry= [HW,MTD] Flex-OneNAND Boundary ConfigurationFormat: [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.mtdset= [ARM]ARM/S3C2412 JIVE boot controlSee arch/arm/mach-s3c2412/mach-jive.cmtouchusb.raw_coordinates=[HW] Make the MicroTouch USB driver use raw coordinates('y', default) or cooked coordinates ('n')mtrr_chunk_size=nn[KMG] [X86]used for mtrr cleanup. It is largest continuous chunkthat could hold holes aka. UC entries.mtrr_gran_size=nn[KMG] [X86]Used for mtrr cleanup. It is granularity of mtrr block.Default is 1.Large value could prevent small alignment fromusing up MTRRs.mtrr_spare_reg_nr=n [X86]Format: <integer>Range: 0,7 : spare reg numberDefault : 1Used for mtrr cleanup. It is spare mtrr entries number.Set to 2 or more if your graphical card needs more.n2= [NET] SDL Inc. RISCom/N2 synchronous serial cardnetdev= [NET] Network devices parametersFormat: <irq>,<io>,<mem_start>,<mem_end>,<name>Note that mem_start is often overloaded to meansomething different and driver-specific.This usage is only documented in each driver sourcefile if at all.nf_conntrack.acct=[NETFILTER] Enable connection tracking flow accounting0 to disable accounting1 to enable accountingDefault value is 0.nfsaddrs= [NFS] Deprecated. Use ip= instead.See Documentation/filesystems/nfs/nfsroot.txt.nfsroot= [NFS] nfs root filesystem for disk-less boxes.See Documentation/filesystems/nfs/nfsroot.txt.nfsrootdebug [NFS] enable nfsroot debugging messages.See Documentation/filesystems/nfs/nfsroot.txt.nfs.callback_nr_threads=[NFSv4] set the total number of threads that theNFS client will assign to service NFSv4 callbackrequests.nfs.callback_tcpport=[NFS] set the TCP port on which the NFSv4 callbackchannel should listen.nfs.cache_getent=[NFS] sets the pathname to the program which is usedto update the NFS client cache entries.nfs.cache_getent_timeout=[NFS] sets the timeout after which an attempt toupdate a cache entry is deemed to have failed.nfs.idmap_cache_timeout=[NFS] set the maximum lifetime for idmapper cacheentries.nfs.enable_ino64=[NFS] enable 64-bit inode numbers.If zero, the NFS client will fake up a 32-bit inodenumber for the readdir() and stat() syscalls insteadof returning the full 64-bit number.The default is to return 64-bit inode numbers.nfs.max_session_cb_slots=[NFSv4.1] Sets the maximum number of sessionslots the client will assign to the callbackchannel. This determines the maximum number ofcallbacks the client will process in parallel fora particular server.nfs.max_session_slots=[NFSv4.1] Sets the maximum number of session slotsthe client will attempt to negotiate with the server.This limits the number of simultaneous RPC requeststhat the client can send to the NFSv4.1 server.Note that there is little point in setting thisvalue higher than the max_tcp_slot_table_limit.nfs.nfs4_disable_idmapping=[NFSv4] When set to the default of '1', this optionensures that both the RPC level authenticationscheme and the NFS level operations agree to usenumeric uids/gids if the mount is using the'sec=sys' security flavour. In effect it isdisabling idmapping, which can make migration fromlegacy NFSv2/v3 systems to NFSv4 easier.Servers that do not support this mode of operationwill be autodetected by the client, and it will fallback 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 intotheir nfs_client_id4 string. This is typically aUUID that is generated at system install time.nfs.send_implementation_id =[NFSv4.1] Send client implementation identificationinformation in exchange_id requests.If zero, no implementation identification informationwill be sent.The default is to send the implementation identificationinformation.nfs.recover_lost_locks =[NFSv4] Attempt to recover locks that were lost dueto a lease timeout on the server. Please note thatdoing this risks data corruption, since there areno guarantees that the file will remain unchangedafter the locks are lost.If you want to enable the kernel legacy behaviour ofattempting to recover these locks, then set thisparameter to '1'.The default parameter value of '0' causes the kernelnot to attempt recovery of lost locks.nfs4.layoutstats_timer =[NFSv4.2] Change the rate at which the kernel sendslayoutstats to the pNFS metadata server.Setting this to value to 0 causes the kernel to usewhatever value is the default set by the layoutdriver. A non-zero value sets the minimum intervalin seconds between layoutstats transmissions.nfsd.nfs4_disable_idmapping=[NFSv4] When set to the default of '1', the NFSv4server will return only numeric uids and gids toclients using auth_sys, and will accept numeric uidsand gids from such clients. This is intended to easemigration from NFSv2/v3.nmi_debug= [KNL,SH] Specify one or more actions to takewhen a NMI is triggered.Format: [state][,regs][,debounce][,die]nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernelsFormat: [panic,][nopanic,][num]Valid num: 0 or 10 - turn hardlockup detector in nmi_watchdog off1 - turn hardlockup detector in nmi_watchdog onWhen panic is specified, panic when an NMI watchdogtimeout occurs (or 'nopanic' to override the oppositedefault). To disable both hard and soft lockup detectors,please see 'nowatchdog'.This is useful when you use a panic=... timeout andneed the box quickly up again.These settings can be accessed at runtime viathe nmi_watchdog and hardlockup_panic sysctls.netpoll.carrier_timeout=[NET] Specifies amount of time (in seconds) thatnetpoll should wait for a carrier. By default netpollwaits 4 seconds.no387 [BUGS=X86-32] Tells the kernel to use the 387 mathsemulation library even if a 387 maths coprocessoris present.no_console_suspend[HW] Never suspend the consoleDisable suspending of consoles during suspend andhibernate operations. Once disabled, debuggingmessages can reach various consoles while the restof the system is being put to sleep (ie, whiledebugging driver suspend/resume hooks). This maynot work reliably with all consoles, but is knownto work with serial and VGA consoles.To facilitate more flexible debugging, we also addconsole_suspend, a printk module parameter to controlit. Users could use console_suspend (usually/sys/module/printk/parameters/console_suspend) toturn on/off it dynamically.noaliencache [MM, NUMA, SLAB] Disables the allocation of aliencaches in the slab allocator. Saves per-node memory,but will impact performance.noalign [KNL,ARM]noaltinstr [S390] Disables alternative instructions patching(CPU alternatives feature).noapic [SMP,APIC] Tells the kernel to not make use of anyIOAPICs that may be present in the system.noautogroup Disable scheduler automatic task group creation.nobats [PPC] Do not use BATs for mapping kernel lowmemon "Classic" PPC cores.nocache [ARM]noclflush [BUGS=X86] Don't use the CLFLUSH instructionnodelayacct [KNL] Disable per-task delay accountingnodsp [SH] Disable hardware DSP at boot time.noefi Disable EFI runtime services support.noexec [IA-64]noexec [X86]On X86-32 available only on PAE configured kernels.noexec=on: enable non-executable mappings (default)noexec=off: disable non-executable mappingsnosmap [X86]Disable SMAP (Supervisor Mode Access Prevention)even if it is supported by processor.nosmep [X86]Disable SMEP (Supervisor Mode Execution Prevention)even if it is supported by processor.noexec32 [X86-64]This affects only 32-bit executables.noexec32=on: enable non-executable mappings (default)read doesn't imply executable mappingsnoexec32=off: disable non-executable mappingsread implies executable mappingsnofpu [MIPS,SH] Disable hardware FPU at boot time.nofxsr [BUGS=X86-32] Disables x86 floating point extendedregister save and restore. The kernel will only savelegacy floating-point registers on task switch.nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.nosmt [KNL,S390] Disable symmetric multithreading (SMT).Equivalent to smt=1.nospectre_v2 [X86] Disable all mitigations for the Spectre variant 2(indirect branch prediction) vulnerability. System mayallow data leaks with this option, which is equivalentto spectre_v2=off.noxsave [BUGS=X86] Disables x86 extended register state saveand restore using xsave. The kernel will fallback toenabling legacy floating-point and sse state.noxsaveopt [X86] Disables xsaveopt used in saving x86 extendedregister states. The kernel will fall back to usexsave to save the states. By using this parameter,performance of saving the states is degraded becausexsave doesn't support modified optimization whilexsaveopt supports it on xsaveopt enabled systems.noxsaves [X86] Disables xsaves and xrstors used in saving andrestoring x86 extended register state in compactedform of xsave area. The kernel will fall back to usexsaveopt and xrstor to save and restore the statesin standard form of xsave area. By using thisparameter, xsave area per process might occupy morememory on xsaves enabled systems.nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) orwfi(ARM) instruction doesn't work correctly and not touse it. This is also useful when using JTAG debugger.no_file_caps Tells the kernel not to honor file capabilities. Theonly way then for a file to be executed with privilegeis to be setuid root or executed by root.nohalt [IA-64] Tells the kernel not to use the power savingfunction PAL_HALT_LIGHT when idle. This increasespower-consumption. On the positive side, it reducesinterrupt wake-up latency, which may improve performancein certain environments such as networked servers orreal-time systems.nohibernate [HIBERNATION] Disable hibernation and resume.nohz= [KNL] Boottime enable/disable dynamic ticksValid arguments: on, offDefault: onnohz_full= [KNL,BOOT,SMP,ISOL]The argument is a cpu list, as described above.In kernels built with CONFIG_NO_HZ_FULL=y, setthe specified list of CPUs whose tick will be stoppedwhenever possible. The boot CPU will be forced outsidethe range to maintain the timekeeping. Any CPUsin this list will have their RCU callbacks offloaded,just as if they had also been called out in thercu_nocbs= boot parameter.noiotrap [SH] Disables trapped I/O port accesses.noirqdebug [X86-32] Disables the code which attempts to detect anddisable unhandled interrupt sources.no_timer_check [X86,APIC] Disables the code which tests forbroken timer IRQ sources.noisapnp [ISAPNP] Disables ISA PnP code.noinitrd [RAM] Tells the kernel not to load any configuredinitial RAM disk.nointremap [X86-64, Intel-IOMMU] Do not enable interruptremapping.[Deprecated - use intremap=off]nointroute [IA-64]noinvpcid [X86] Disable the INVPCID cpu feature.nojitter [IA-64] Disables jitter checking for ITC timers.no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driverno-kvmapf [X86,KVM] Disable paravirtualized asynchronous pagefault handling.no-vmw-sched-clock[X86,PV_OPS] Disable paravirtualized VMware schedulerclock and use the default one.no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.steal time is computed, but won't influence schedulerbehaviournolapic [X86-32,APIC] Do not enable or use the local APIC.nolapic_timer [X86-32,APIC] Do not use the local APIC timer.noltlbs [PPC] Do not use large page/tlb entries for kernellowmem mapping on PPC40x and PPC8xxnomca [IA-64] Disable machine check abort handlingnomce [X86-32] Disable Machine Check Exceptionnomfgpt [X86-32] Disable Multi-Function General PurposeTimer usage (for AMD Geode machines).nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot toshutdown the other cpus. Instead use the REBOOT_VECTORirq.nomodule Disable module loadnopat [X86] Disable PAT (page attribute table extension ofpagetables) support.nopcid [X86-64] Disable the PCID cpu feature.norandmaps Don't use address space randomization. Equivalent toecho 0 > /proc/sys/kernel/randomize_va_spacenoreplace-smp [X86-32,SMP] Don't replace SMP instructionswith UP alternativesnordrand [X86] Disable kernel use of the RDRAND andRDSEED instructions even if they are supportedby the processor. RDRAND and RDSEED are stillavailable to user space applications.noresume [SWSUSP] Disables resume and restores original swapspace.no-scroll [VGA] Disables scrollback.This is required for the Braillex ib80-piezo Braillereader made by F.H. Papenmeier (Germany).nosbagart [IA-64]nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.nosmp [SMP] Tells an SMP kernel to act as a UP kernel,and disable the IO APIC. legacy for "maxcpus=0".nosoftlockup [KNL] Disable the soft-lockup detector.nosync [HW,M68K] Disables sync negotiation for all devices.notsc [BUGS=X86-32] Disable Time Stamp Counternowatchdog [KNL] Disable both lockup detectors, i.e.soft-lockup and NMI watchdog (hard-lockup).nowb [ARM]nox2apic [X86-64,APIC] Do not enable x2APIC mode.cpu0_hotplug [X86] Turn on CPU0 hotplug feature whenCONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.Some features depend on CPU0. Known dependencies are:1. Resume from suspend/hibernate depends on CPU0.Suspend/hibernate will fail if CPU0 is offline and youneed to online CPU0 before suspend/hibernate.2. PIC interrupts also depend on CPU0. CPU0 can't beremoved if a PIC interrupt is detected.It's said poweroff/reboot may depend on CPU0 on somemachines although I haven't seen such issues so farafter CPU0 is offline on a few tested machines.If the dependencies are under your control, you canturn on cpu0_hotplug.nps_mtm_hs_ctr= [KNL,ARC]This parameter sets the maximum duration, incycles, each HW thread of the CTOP can runwithout interruptions, before HW switches it.The actual maximum duration is 16 times thisparameter's value.Format: integer between 1 and 255Default: 255nptcg= [IA-64] Override max number of concurrent global TLBpurges which is reported from either PAL_VM_SUMMARY orSAL PALO.nr_cpus= [SMP] Maximum number of processors that an SMP kernelcould support. nr_cpus=n : n >= 1 limits the kernel tosupport 'n' processors. It could be larger than thenumber of already plugged CPU during bootup, later inruntime you can physically add extra cpu until it reachesn. So during boot up some boot time memory for per-cpuvariables need be pre-allocated for later physical cpuhot plugging.nr_uarts= [SERIAL] maximum number of UARTs to be registered.numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.Allowed values are enable and disablenuma_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.'node', 'default' can be specifiedThis can be set from sysctl after boot.See Documentation/sysctl/vm.txt for details.ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.See Documentation/debugging-via-ohci1394.txt for moreinfo.olpc_ec_timeout= [OLPC] ms delay when issuing EC commandsRather than timing out after 20 ms if an ECcommand is not properly ACKed, override the lengthof the timeout. We have interrupts disabled whilewaiting for the ACK, so if this is set too highinterrupts *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=0x100oprofile.timer= [HW]Use timer interrupt instead of performance countersoprofile.cpu_type= Force an oprofile cpu typeThis might be useful if you have an older oprofileuserland or if you want common events.Format: { arch_perfmon }arch_perfmon: [X86] Force use of architecturalperfmon on Intel CPUs instead of theCPU specific event set.timer: [X86] Force use of architectural NMItimer mode (see also oprofile.timerfor generic hr timer mode)oops=panic Always panic on oopses. Default is to just kill theprocess, but there is a small probability ofdeadlocking the machine.This will also cause panics on machine check exceptions.Useful together with panic=30 to trigger a reboot.OSS [HW,OSS]See Documentation/sound/oss/oss-parameters.txtpage_owner= [KNL] Boot-time page_owner enabling option.Storage of the information about who allocatedeach page is disabled in default. With this switch,we can turn it on.on: enable the featurepage_poison= [KNL] Boot-time parameter changing the state ofpoisoning on the buddy allocator.off: turn off poisoningon: turn on poisoningpanic= [KNL] Kernel behaviour on panic: delay <timeout>timeout > 0: seconds before rebootingtimeout = 0: wait forevertimeout < 0: reboot immediatelyFormat: <timeout>panic_on_warn panic() instead of WARN(). Useful to cause kdumpon a WARN().crash_kexec_post_notifiersRun kdump after running panic-notifiers and dumpingkmsg. This only for the users who doubt kdump alwayssucceeds in any situation.Note that this also increases risks of kdump failure,because some panic notifiers can make the crashedkernel more unstable.parkbd.port= [HW] Parallel port number the keyboard adapter isconnected 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 anyIRQ/DMA settings detected (the default is toignore detected IRQ/DMA settings because ofpossible conflicts). You can specify the baseaddress, IRQ, and DMA settings; IRQ and DMAshould be numbers, or 'auto' (for using detectedsettings on that particular port), or 'nofifo'(to avoid using a FIFO even if it is detected).Parallel ports are assigned in the order theyare specified on the command line, startingwith parport0.parport_init_mode= [HW,PPT]Configure VIA parallel port to operate ina specific mode. This is necessary on Pegasoscomputer where firmware has no options for settingup parallel port mode and sets it to spp.Currently this function knows 686a and 8231 chips.Format: [spp|ps2|epp|ecp|ecpepp]pause_on_oops=Halt all CPUs after the first oops has been printed forthe specified number of seconds. This is to be used ifyour oopses keep scrolling off the screen.pcbit= [HW,ISDN]pcd. [PARIDE]See header of drivers/block/paride/pcd.c.See also Documentation/blockdev/paride.txt.pci=option[,option...] [PCI] various PCI subsystem options:earlydump [X86] dump PCI config space before the kernelchanges anythingoff [X86] don't probe for the PCI busbios [X86-32] force use of PCI BIOS, don't accessthe hardware directly. Use this if your machinehas a non-standard PCI host bridge.nobios [X86-32] disallow use of PCI BIOS, only directhardware access methods are allowed. Use thisif you experience crashes upon bootup and yoususpect they are caused by the BIOS.conf1 [X86] Force use of PCI Configuration AccessMechanism 1 (config address in IO port 0xCF8,data in IO port 0xCFC, both 32-bit).conf2 [X86] Force use of PCI Configuration AccessMechanism 2 (IO port 0xCF8 is an 8-bit port forthe function, IO port 0xCFA, also 8-bit, setsbus number. The config space is then accessedthrough ports 0xC000-0xCFFF).See http://wiki.osdev.org/PCI for more infoon the configuration access mechanisms.noaer [PCIE] If the PCIEAER kernel config parameter isenabled, this kernel boot option can be used todisable the use of PCIE advanced error reporting.nodomains [PCI] Disable support for multiple PCIroot domains (aka PCI segments, in ACPI-speak).nommconf [X86] Disable use of MMCONFIG for PCIConfigurationcheck_enable_amd_mmconf [X86] check for and enableproperly configured MMIO access to PCIconfig space on AMD family 10h CPUnomsi [MSI] If the PCI_MSI kernel config parameter isenabled, this kernel boot option can be used todisable the use of MSI interrupts system-wide.noioapicquirk [APIC] Disable all boot interrupt quirks.Safety option to keep boot IRQs enabled. Thisshould never be necessary.ioapicreroute [APIC] Enable rerouting of boot IRQs to theprimary IO-APIC for bridges that cannot disableboot IRQs. This fixes a source of spurious IRQswhen the system masks IRQs.noioapicreroute [APIC] Disable workaround that uses theboot IRQ equivalent of an IRQ that connects toa chipset where boot IRQs cannot be disabled.The opposite of ioapicreroute.biosirq [X86-32] Use PCI BIOS calls to get the interruptrouting table. These calls are known to be buggyon several machines and they hang the machinewhen used, but on other computers it's the onlyway to get the interrupt routing table. Trythis option if the kernel is unable to allocateIRQs or discover secondary PCI buses on yourmotherboard.rom [X86] Assign address space to expansion ROMs.Use with caution as certain devices shareaddress decoders between ROMs and otherresources.norom [X86] Do not assign address space toexpansion ROMs that do not already haveBIOS assigned address ranges.nobar [X86] Do not assign address space to theBARs that weren't assigned by the BIOS.irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to beassigned automatically to PCI devices. You canmake the kernel exclude IRQs of your ISA cardsthis way.pirqaddr=0xAAAAA [X86] Specify the physical addressof the PIRQ table (normally generatedby the BIOS) if it is outside theF0000h-100000h range.lastbus=N [X86] Scan all buses thru bus #N. Can beuseful if the kernel is unable to find yoursecondary buses and you want to tell itexplicitly which ones they are.assign-busses [X86] Always assign all PCI busnumbers ourselves, overridingwhatever the firmware may have done.usepirqmask [X86] Honor the possible IRQ mask storedin the BIOS $PIR table. This is needed onsome systems with broken BIOSes, notablysome HP Pavilion N5400 and Omnibook XE3notebooks. This will have no effect if ACPIIRQ routing is enabled.noacpi [X86] Do not use ACPI for IRQ routingor for PCI scanning.use_crs [X86] Use PCI host bridge window informationfrom ACPI. On BIOSes from 2008 or later, thisis 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.routeirq Do IRQ routing for all PCI devices.This is normally done in pci_enable_device(),so this option is a temporary workaroundfor broken drivers that don't call it.skip_isa_align [X86] do not align io start addr, so canhandle more pci cardsnoearly [X86] Don't do any early type 1 scanning.This might help on some broken boards whichmachine check when some devices' config spaceis read. But various workarounds are disabledand some IOMMU drivers will not work.bfsort Sort PCI devices into breadth-first order.This sorting is done to get a deviceorder 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 valuesupported by all devices below the root complex.pcie_bus_perf Set device MPS to the largest allowable MPSbased on its parent bus. Also set MRRS (MaxRead Request Size) to the largest supportedvalue (no larger than the MPS that the deviceor bus can support) for best performance.pcie_bus_peer2peer Set every device's MPS to 128B, whichevery device is guaranteed to support. Thisconfiguration allows peer-to-peer DMA betweenany pair of devices, possibly at the cost ofreduced performance. This also guaranteesthat hot-added devices will work.cbiosize=nn[KMG] The fixed amount of bus space which isreserved for the CardBus bridge's IO window.The default value is 256 bytes.cbmemsize=nn[KMG] The fixed amount of bus space which isreserved for the CardBus bridge's memorywindow. The default value is 64 megabytes.resource_alignment=Format:[<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...][<order of align>@]pci:<vendor>:<device>\[:<subvendor>:<subdevice>][; ...]Specifies alignment and device to reassignaligned memory resources.If <order of align> is not specified,PAGE_SIZE is used as alignment.PCI-PCI bridge can be specified, if resourcewindows need to be expanded.To specify the alignment for severalinstances of a device, the PCI vendor,device, subvendor, and subdevice may bespecified, e.g., 4096@pci:8086:9c22:103c:198fecrc= Enable/disable PCIe ECRC (transaction layerend-to-end CRC checking).bios: Use BIOS/firmware settings. This is thethe default.off: Turn ECRC offon: Turn ECRC on.hpiosize=nn[KMG] The fixed amount of bus space which isreserved for hotplug bridge's IO window.Default size is 256 bytes.hpmemsize=nn[KMG] The fixed amount of bus space which isreserved for hotplug bridge's memory window.Default size is 2 megabytes.hpbussize=nn The minimum amount of additional bus numbersreserved for buses below a hotplug bridge.Default is 1.realloc= Enable/disable reallocating PCI bridge resourcesif allocations done by BIOS are too small toaccommodate resources required by all childdevices.off: Turn realloc offon: Turn realloc onrealloc same as realloc=onnoari do not use PCIe ARI.pcie_scan_all Scan all possible PCIe devices. Otherwise weonly look for one device below a PCIe downstreamport.big_root_window Try to add a big 64bit memory window to the PCIeroot complex on AMD CPUs. Some GFX hardwarecan resize a BAR to allow access to all VRAM.Adding the window is slightly risky (it mayconflict with unreported devices), so thistaints the kernel.pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State PowerManagement.off Disable ASPM.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 touse them. This may cause conflicts if the platformalso tries to use these services.compat Disable native PCIe services (PME, AER, DPC, PCIehotplug).pcie_port_pm= [PCIE] PCIe port power management handling:off Disable power management of all PCIe portsforce Forcibly enable power management of all PCIe portspcie_pme= [PCIE,PM] Native PCIe PME signaling options:nomsi Do not use MSI for native PCIe PME signaling (this makesall PCIe root ports use INTx for all services).pcmv= [HW,PCMCIA] BadgePAD 4pd_ignore_unused[PM]Keep all power-domains already enabled by bootloader on,even if no driver has claimed them. This is usefulfor debug and development, but should not beneeded on a platform with proper driver support.pd. [PARIDE]See Documentation/blockdev/paride.txt.pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes atboot time.Format: { 0 | 1 }See arch/parisc/kernel/pdc_chassis.cpercpu_alloc= 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 eachallocator. This parameter is primarily for debuggingand performance comparison.pf. [PARIDE]See Documentation/blockdev/paride.txt.pg. [PARIDE]See Documentation/blockdev/paride.txt.pirq= [SMP,APIC] Manual mp-table setupSee Documentation/x86/i386/IO-APIC.txt.plip= [PPT,NET] Parallel port network linkFormat: { 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=0x508pnp.debug=1 [PNP]Enable PNP debug messages (depends on theCONFIG_PNP_DEBUG_MESSAGES option). Change at run-timevia /sys/module/pnp/parameters/debug. We always showcurrent resource usage; turning this on also showspossible 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 autoconfigurationpnp_reserve_dma=[ISAPNP] Exclude DMAs for the autoconfigurationpnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfigurationRanges are in pairs (I/O port base and size).pnp_reserve_mem=[ISAPNP] Exclude memory regions for theautoconfiguration.Ranges are in pairs (memory base and size).ports= [IP_VS_FTP] IPVS ftp helper moduleDefault is 21.Up to 8 (IP_VS_APP_MAX_PORTS) portsmay be specified.Format: <port>,<port>....powersave=off [PPC] This option disables power saving features.It specifically disables cpuidle and sets theplatform machine description specific power_savefunction to NULL. On Idle the CPU just reducesexecution priority.ppc_strict_facility_enable[PPC] This option catches any kernel floating point,Altivec, VSX and SPE outside of regions specificallyallowed (eg kernel_enable_fpu()/kernel_disable_fpu()).There is some performance impact when enabling this.ppc_tm= [PPC]Format: {"off"}Disable Hardware Transactional Memoryprint-fatal-signals=[KNL] debug: print fatal signalsIf enabled, warn about various signal handlingrelated application anomalies: too many signals,too many POSIX.1 timers, fatal signals causing acoredump - 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 orpanicsFormat: <bool> (1/Y/y=enable, 0/N/n=disable)default: disabledprintk.devkmsg={on,off,ratelimit}Control writing to /dev/kmsg.on - unlimited logging to /dev/kmsg from userspaceoff - logging to /dev/kmsg disabledratelimit - ratelimit the loggingDefault: ratelimitprintk.time= Show timing data prefixed to each printk message lineFormat: <bool> (1/Y/y=enable, 0/N/n=disable)processor.max_cstate= [HW,ACPI]Limit processor to maximum C-statemax_cstate=9 overrides any DMI blacklist limit.processor.nocst [HW,ACPI]Ignore the _CST method to determine C-states,instead using the legacy FADT methodprofile= [KNL] Enable kernel profiling via /proc/profileFormat: [<profiletype>,]<number>Param: <profiletype>: "schedule", "sleep", or "kvm"[defaults to kernel profiling]Param: "schedule" - profile schedule points.Param: "sleep" - profile D-state sleeping (millisecs).Requires CONFIG_SCHEDSTATSParam: "kvm" - profile VM exits.Param: <number> - step/bucket size as a power of 2 forstatistical time based profiling.prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy diskbefore loading.See Documentation/blockdev/ramdisk.txt.psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension toprobe for; one of (bare|imps|exps|lifebook|any).psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reportsper 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 usept. [PARIDE]See Documentation/blockdev/paride.txt.pti= [X86_64] Control Page Table Isolation of user andkernel address spaces. Disabling this featureremoves hardening, but improves performance ofsystem calls and interrupts.on - unconditionally enableoff - unconditionally disableauto - kernel detects whether your CPU model isvulnerable to issues that PTI mitigatesNot specifying this option is equivalent to pti=auto.nopti [X86_64]Equivalent to pti=offpty.legacy_count=[KNL] Number of legacy pty's. Overwrites compiled-indefault number.quiet [KNL] Disable most log messagesr128= [HW,DRM]raid= [HW,RAID]See Documentation/admin-guide/md.rst.ramdisk_size= [RAM] Sizes of RAM disks in kilobytesSee Documentation/blockdev/ramdisk.txt.ras=option[,option,...] [KNL] RAS-specific optionscec_disable [X86]Disable the Correctable Errors Collector,see CONFIG_RAS_CEC help text.rcu_nocbs= [KNL]The argument is a cpu list, as described above.In kernels built with CONFIG_RCU_NOCB_CPU=y, setthe specified list of CPUs to be no-callback CPUs.Invocation of these CPUs' RCU callbacks willbe offloaded to "rcuox/N" kthreads created forthat purpose, where "x" is "b" for RCU-bh, "p"for RCU-preempt, and "s" for RCU-sched, and "N"is the CPU number. This reduces OS jitter on theoffloaded CPUs, which can be useful for HPC andreal-time workloads. It can also improve energyefficiency for asymmetric multiprocessors.rcu_nocb_poll [KNL]Rather than requiring that offloaded CPUs(specified by rcu_nocbs= above) explicitlyawaken the corresponding "rcuoN" kthreads,make these kthreads poll for callbacks.This improves the real-time response for theoffloaded CPUs by relieving them of the need towake up the corresponding kthread, but degradesenergy efficiency by requiring that the kthreadsperiodically wake up to do the polling.rcutree.blimit= [KNL]Set maximum number of finished RCU callbacks toprocess in one batch.rcutree.dump_tree= [KNL]Dump the structure of the rcu_node combining treeout at early boot. This is used for diagnosticpurposes, to verify correct tree setup.rcutree.gp_cleanup_delay= [KNL]Set the number of jiffies to delay each step ofRCU grace-period cleanup.rcutree.gp_init_delay= [KNL]Set the number of jiffies to delay each step ofRCU grace-period initialization.rcutree.gp_preinit_delay= [KNL]Set the number of jiffies to delay each step ofRCU grace-period pre-initialization, that is,the propagation of recent CPU-hotplug changes upthe rcu_node combining tree.rcutree.rcu_fanout_exact= [KNL]Disable autobalancing of the rcu_node combiningtree. This is used by rcutorture, and mightpossibly be useful for architectures having highcache-to-cache transfer latencies.rcutree.rcu_fanout_leaf= [KNL]Change the number of CPUs assigned to eachleaf rcu_node structure. Useful for verylarge systems, which will choose the value 64,and for NUMA systems with large remote-accesslatencies, which will choose a value alignedwith the appropriate hardware boundaries.rcutree.jiffies_till_sched_qs= [KNL]Set required age in jiffies for agiven grace period before RCU startssoliciting quiescent-state help fromrcu_note_context_switch().rcutree.jiffies_till_first_fqs= [KNL]Set delay from grace-period initialization tofirst 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 forcequiescent states. Units are jiffies, minimumvalue is one, and maximum value is HZ.rcutree.kthread_prio= [KNL,BOOT]Set the SCHED_FIFO priority of the RCU per-CPUkthreads (rcuc/N). This value is also used forthe 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 isset, valid values are 1-99 and the default is 1(the least-favored priority). Otherwise, whenRCU_BOOST is not set, valid values are 0-99 andthe default is zero (non-realtime operation).rcutree.rcu_nocb_leader_stride= [KNL]Set the number of NOCB kthread groups, whichdefaults to the square root of the number ofCPUs. Larger numbers reduces the wakeup overheadon the per-CPU grace-period kthreads, but increasesthat same overhead on each group's leader.rcutree.qhimark= [KNL]Set threshold of queued RCU callbacks beyond whichbatch limiting is disabled.rcutree.qlowmark= [KNL]Set threshold of queued RCU callbacks below whichbatch limiting is re-enabled.rcutree.rcu_idle_gp_delay= [KNL]Set wakeup interval for idle CPUs that haveRCU callbacks (RCU_FAST_NO_HZ=y).rcutree.rcu_idle_lazy_gp_delay= [KNL]Set wakeup interval for idle CPUs that haveonly "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).Lazy RCU callbacks are those which RCU canprove do nothing more than free memory.rcutree.rcu_kick_kthreads= [KNL]Cause the grace-period kthread to get an extrawake_up() if it sleeps three times longer thanit should at force-quiescent-state time.This wake_up() will be accompanied by aWARN_ONCE() splat and an ftrace_dump().rcuperf.gp_async= [KNL]Measure performance of asynchronousgrace-period primitives such as call_rcu().rcuperf.gp_async_max= [KNL]Specify the maximum number of outstandingcallbacks per writer thread. When a writerthread exceeds this limit, it invokes thecorresponding flavor of rcu_barrier() to allowpreviously posted callbacks to drain.rcuperf.gp_exp= [KNL]Measure performance of expedited synchronousgrace-period primitives.rcuperf.holdoff= [KNL]Set test-start holdoff period. The purpose ofthis parameter is to delay the start of thetest until boot completes in order to avoidinterference.rcuperf.nreaders= [KNL]Set number of RCU readers. The value -1 selectsN, where N is the number of CPUs. A value"n" less than -1 selects N-n+1, where N is againthe 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 selectsa single reader.rcuperf.nwriters= [KNL]Set number of RCU writers. The values operatethe same as for rcuperf.nreaders.N, where N is the number of CPUsrcuperf.perf_type= [KNL]Specify the RCU implementation to test.rcuperf.shutdown= [KNL]Shut the system down after performance testscomplete. This is useful for hands-off automatedtesting.rcuperf.verbose= [KNL]Enable additional printk() statements.rcuperf.writer_holdoff= [KNL]Write-side holdoff between grace periods,in microseconds. The default of zero saysno holdoff.rcutorture.cbflood_inter_holdoff= [KNL]Set holdoff time (jiffies) between successivecallback-flood tests.rcutorture.cbflood_intra_holdoff= [KNL]Set holdoff time (jiffies) between successivebursts of callbacks within a given callback-floodtest.rcutorture.cbflood_n_burst= [KNL]Set the number of bursts making up a givencallback-flood test. Set this to zero todisable callback-flood testing.rcutorture.cbflood_n_per_burst= [KNL]Set the number of callbacks to be registeredin a given burst of a callback-flood test.rcutorture.fqs_duration= [KNL]Set duration of force_quiescent_state burstsin microseconds.rcutorture.fqs_holdoff= [KNL]Set holdoff time within force_quiescent_state burstsin microseconds.rcutorture.fqs_stutter= [KNL]Set wait time between force_quiescent_state burstsin seconds.rcutorture.gp_cond= [KNL]Use conditional/asynchronous update-sideprimitives, if available.rcutorture.gp_exp= [KNL]Use expedited update-side primitives, if available.rcutorture.gp_normal= [KNL]Use normal (non-expedited) asynchronousupdate-side primitives, if available.rcutorture.gp_sync= [KNL]Use normal (non-expedited) synchronousupdate-side primitives, if available. If allof rcutorture.gp_cond=, rcutorture.gp_exp=,rcutorture.gp_normal=, and rcutorture.gp_sync=are zero, rcutorture acts as if is interpretedthey are all non-zero.rcutorture.n_barrier_cbs= [KNL]Set callbacks/threads for rcu_barrier() testing.rcutorture.nfakewriters= [KNL]Set number of concurrent RCU writers. These juststress RCU, they don't participate in the actualtest, hence the "fake".rcutorture.nreaders= [KNL]Set number of RCU readers. The value -1 selectsN-1, where N is the number of CPUs. A value"n" less than -1 selects N-n-2, where N is againthe 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 (s) between CPU-hotplug operations, orzero to disable CPU-hotplug testing.rcutorture.shuffle_interval= [KNL]Set task-shuffle interval (s). Shuffling tasksallows some CPUs to go into dyntick-idle modeduring the rcutorture test.rcutorture.shutdown_secs= [KNL]Set time (s) after boot system shutdown. Thisis useful for hands-off automated testing.rcutorture.stall_cpu= [KNL]Duration of CPU stall (s) to test RCU CPU stallwarnings, zero to disable.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.rcutorture.stat_interval= [KNL]Time (s) between statistics printk()s.rcutorture.stutter= [KNL]Time (s) to stutter testing, for example, specifyingfive seconds causes the test to run for five seconds,wait for five seconds, and so on. This tests RCU'sability 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 implementationunder test support RCU priority boosting.rcutorture.test_boost_duration= [KNL]Duration (s) of each individual boost test.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 thercutorture.shuffle_interval parameter.rcutorture.torture_type= [KNL]Specify the RCU implementation to test.rcutorture.verbose= [KNL]Enable additional printk() statements.rcupdate.rcu_cpu_stall_suppress= [KNL]Suppress RCU CPU stall warning messages.rcupdate.rcu_cpu_stall_timeout= [KNL]Set timeout for RCU CPU stall warning messages.rcupdate.rcu_expedited= [KNL]Use expedited grace-period primitives, forexample, synchronize_rcu_expedited() insteadof synchronize_rcu(). This reduces latency,but can increase CPU utilization, degradereal-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 ofsynchronize_rcu_expedited(). This improvesreal-time latency, CPU utilization, andenergy efficiency, but can expose users toincreased grace-period latency. This parameteroverrides rcupdate.rcu_expedited. No effect onCONFIG_TINY_RCU kernels.rcupdate.rcu_normal_after_boot= [KNL]Once boot has completed (that is, afterrcu_end_inkernel_boot() has been invoked), useonly normal grace-period primitives. No effecton CONFIG_TINY_RCU kernels.rcupdate.rcu_task_stall_timeout= [KNL]Set timeout in jiffies for RCU task stall warningmessages. Disable with a value less than or equalto zero.rcupdate.rcu_self_test= [KNL]Run the RCU early boot self testsrcupdate.rcu_self_test_bh= [KNL]Run the RCU bh early boot self testsrcupdate.rcu_self_test_sched= [KNL]Run the RCU sched early boot self testsrdinit= [KNL]Format: <full_path>Run specified binary instead of /init from the ramdisk,used for early userspace startup. See initrd.rdt= [HW,X86,RDT]Turn on/off individual RDT features. List is:cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,mba.E.g. to turn on cmt and turn off mba use:rdt=cmt,!mbareboot= [KNL]Format (x86 or x86_64):[w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \[[,]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,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 processorto be used for rebooting.relax_domain_level=[KNL, SMP] Set scheduler's default relax_domain_level.See Documentation/cgroup-v1/cpusets.txt.reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memoryFormat: <base1>,<size1>[,<base2>,<size2>,...]Reserve I/O ports or memory so the kernel won't usethem. If <base> is less than 0x10000, the regionis assumed to be I/O ports; otherwise it is memory.reservetop= [X86-32]Format: nn[KMG]Reserves a hole at the top of the kernel virtualaddress space.reservelow= [X86]Format: nn[K]Set the amount of memory to reserve for BIOS atthe bottom of the address space.reset_devices [KNL] Force drivers to reset the underlying deviceduring initialization.resume= [SWSUSP]Specify the partition device for software suspendFormat:{/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}resume_offset= [SWSUSP]Specify the offset from the beginning of the partitiongiven 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.txtresumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting toread the resume filesresumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.Useful for devices that are detected asynchronously(e.g. USB and MMC devices).hibernate= [HIBERNATION]noresume Don't check if there's a hibernation imagepresent 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 dataduring restoration read-only).retain_initrd [RAM] Keep initrd memory after extractionrfkill.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 everythingblocked and the previous configuration.2 The "airplane mode" button toggles between everythingblocked and everything unblocked.rhash_entries= [KNL,NET]Set number of hash buckets for route cachering3mwait=disable[KNL] Disable ring 3 MONITOR/MWAIT feature on supportedCPUs.ro [KNL] Mount root device read-only on bootrodata= [KNL]on Mark read-only kernel memory as read-only (default).off Leave read-only kernel memory writable for debugging.rockchip.usb_uartEnable the uart passthrough on the designated usb porton Rockchip SoCs. When active, the signals of thedebug-uart get routed to the D+ and D- pins of the usbport and the regular usb controller gets disabled.root= [KNL] Root filesystemSee name_to_dev_t comment in init/do_mounts.c.rootdelay= [KNL] Delay (in seconds) to pause before attempting tomount the root filesystemrootflags= [KNL] Set root filesystem mount option stringrootfstype= [KNL] Set root filesystem typerootwait [KNL] Wait (indefinitely) for root device to show up.Useful for devices that are detected asynchronously(e.g. USB and MMC devices).rproc_mem=nn[KMG][@address][KNL,ARM,CMA] Remoteproc physical memory block.Memory area to be used by remote processor image,managed by CMA.rw [KNL] Mount root device read-write on bootS [KNL] Run init in single modes390_iommu= [HW,S390]Set s390 IOTLB flushing modestrictWith strict flushing every unmap operation will result inan IOTLB flush. Default is lazy flushing before reuse,which is faster.sa1100ir [NET]See drivers/net/irda/sa1100_ir.c.sbni= [NET] Granch SBNI12 leased line adaptersched_debug [KNL] Enables verbose scheduler debug messages.schedstats= [KNL,X86] Enable or disable scheduled statistics.Allowed values are enable and disable. This featureincurs a small amount of overhead in the schedulerbut is useful for debugging and performance tuning.skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigatextime_lock contention on larger systems, and/or RCU lockcontention 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 beenabled if running jitter sensitive (HPC/RT) workloads.security= [SECURITY] Choose a security module to enable at boot.If this boot parameter is not specified, only the firstsecurity module asking for security registration will beloaded. An invalid security module name will be treatedas if no module has been chosen.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 set via kernel config option.If enabled at boot time, /selinux/disable can be usedlater to disable prior to initial policy load.apparmor= [APPARMOR] Disable or enable AppArmor at boot timeFormat: { "0" | "1" }See security/apparmor/Kconfig help text0 -- disable.1 -- enable.Default value is set via kernel config option.serialnumber [BUGS=X86-32]shapers= [NET]Maximal number of shapers.simeth= [IA-64]simscsi=slram= [HW,MTD]slab_nomerge [MM]Disable merging of slabs with similar size. May benecessary if there is some reason to distinguishallocs to different slabs, especially in hardenedenvironments where the risk of heap overflows andlayout control by attackers can usually befrustrated by disabling merging. This will reducemost of the exposure of a heap attack to a singlecache (risks via metadata attacks are mostlyunchanged). Debug options disable merging on theirown.For more information see Documentation/vm/slub.txt.slab_max_order= [MM, SLAB]Determines the maximum allowed order for slabs.A high setting may cause OOMs due to memoryfragmentation. Defaults to 1 for systems withmore than 32MB of RAM, 0 otherwise.slub_debug[=options[,slabs]] [MM, SLUB]Enabling slub_debug allows one to determine theculprit if slab objects become corrupted. Enablingslub_debug can create guard zones around objects andmay poison objects when not in use. Also tracks thelast alloc / free. For more information seeDocumentation/vm/slub.txt.slub_memcg_sysfs= [MM, SLUB]Determines whether to enable sysfs directories formemory cgroup sub-caches. 1 to enable, 0 to disable.The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.Enabling this can lead to a very high number of debugdirectories and files being created under/sys/kernel/slub.slub_max_order= [MM, SLUB]Determines the maximum allowed order for slabs.A high setting may cause OOMs due to memoryfragmentation. For more information seeDocumentation/vm/slub.txt.slub_min_objects= [MM, SLUB]The minimum number of objects per slab. SLUB willincrease the slab order up to slub_max_order togenerate a sufficiently large slab able to containthe number of objects indicated. The higher the numberof objects the smaller the overhead of tracking slabsand the less frequently locks need to be acquired.For more information see Documentation/vm/slub.txt.slub_min_order= [MM, SLUB]Determines the minimum page order for slabs. Must belower than slub_max_order.For more information see Documentation/vm/slub.txt.slub_nomerge [MM, SLUB]Same with slab_nomerge. This is supported for legacy.See slab_nomerge for more information.smart2= [HW]Format: <io1>[,<io2>[,...,<io8>]]smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devicessmsc-ircc2.ircc_cfg= [HW] Device configuration I/O portsmsc-ircc2.ircc_sir= [HW] SIR base I/O portsmsc-ircc2.ircc_fir= [HW] FIR base I/O portsmsc-ircc2.ircc_irq= [HW] IRQ linesmsc-ircc2.ircc_dma= [HW] DMA channelsmsc-ircc2.ircc_transceiver= [HW] Transceiver type:0: Toshiba Satellite 1800 (GP data pin select)1: Fast pin select (default)2: ATC IRModesmt [KNL,S390] Set the maximum number of threads (logicalCPUs) to use per physical CPU on systems capable ofsymmetric multithreading (SMT). Will be capped to theactual hardware limit.Format: <integer>Default: -1 (no limit)softlockup_panic=[KNL] Should the soft-lockup detector generate panics.Format: <integer>A nonzero value instructs the soft-lockup detectorto panic the machine when a soft-lockup occurs. Thisis also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANICwhich is the respective build-time switch to thatfunctionality.softlockup_all_cpu_backtrace=[KNL] Should the soft-lockup detector generatebacktraces on all cpus.Format: <integer>sonypi.*= [HW] Sony Programmable I/O Control Device driverSee Documentation/laptops/sonypi.txtspectre_v2= [X86] Control mitigation of Spectre variant 2(indirect branch speculation) vulnerability.on - unconditionally enableoff - unconditionally disableauto - kernel detects whether your CPU model isvulnerableSelecting 'on' will, and 'auto' may, choose amitigation method at run time according to theCPU, the available microcode, the setting of theCONFIG_RETPOLINE configuration option, and thecompiler with which the kernel was built.Specific mitigations can also be selected manually:retpoline - replace indirect branchesretpoline,generic - google's original retpolineretpoline,amd - AMD-specific minimal thunkNot specifying this option is equivalent tospectre_v2=auto.spia_io_base= [HW,MTD]spia_fio_base=spia_pedr=spia_peddr=srcutree.counter_wrap_check [KNL]Specifies how frequently to check forgrace-period sequence counter wrap for thesrcu_data structure's ->srcu_gp_seq_needed field.The greater the number of bits set in this kernelparameter, the less frequently counter wrap willbe checked for. Note that the bottom two bitsare ignored.srcutree.exp_holdoff [KNL]Specifies how many nanoseconds must elapsesince the end of the last SRCU grace period fora given srcu_struct until the next normal SRCUgrace period will be considered for automaticexpediting. Set to zero to disable automaticexpediting.stack_guard_gap= [MM]override the default stack gap protection. The valueis in page units and it defines how many pages priorto (for stacks growing down) resp. after (for stacksgrowing up) the main stack are reserved for no othermapping. Default value is 256 pages.stacktrace [FTRACE]Enabled the stack tracer on boot up.stacktrace_filter=[function-list][FTRACE] Limit the functions that the stack tracerwill trace at boot up. function-list is a comma separatedlist of functions. This list can be changed at runtime by the stack_trace_filter file in the debugfstracing directory. Note, this enables stack tracingand the stacktrace above is not needed.sti= [PARISC,HW]Format: <num>Set the STI (builtin display/keyboard on the HP-PARISCmachines) console (graphic card) which should be usedas the initial boot-console.See also comment in drivers/video/console/sticore.c.sti_font= [HW]See comment in drivers/video/console/sticore.c.stifb= [HW]Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]sunrpc.min_resvport=sunrpc.max_resvport=[NFS,SUNRPC]SunRPC servers often require that client requestsoriginate from a privileged port (i.e. a port in therange 0 < portnr < 1024).An administrator who wishes to reserve some of theseports for other uses may adjust the range that thekernel's sunrpc client considers to be privilegedusing these two parameters to set the minimum andmaximum port values.sunrpc.svc_rpc_per_connection_limit=[NFS,SUNRPC]Limit the number of requests that the server willprocess 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 toservice thread pools. Depending on how many NICsyou have and where their interrupts are bound, thisoption will affect which CPUs will do NFS serving.Note: this parameter cannot be changed while theNFS server is running.auto the server chooses an appropriate modeautomatically using heuristicsglobal a single global pool contains all CPUspercpu one pool for each CPUpernode one pool for each NUMA node (equivalentto 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 simultaneousRPC calls that can be sent from the client to aserver. Increasing these values may allow you toimprove throughput, but will also increase theamount of memory reserved for use by the client.suspend.pm_test_delay=[SUSPEND]Sets the number of seconds to remain in a suspend testmode before resuming the system (see/sys/power/pm_test). Only available when CONFIG_PM_DEBUGis set. Default value is 5.swapaccount=[0|1][KNL] Enable accounting of swap in memory resourcecontroller if no parameter or 1 is given or disableit if 0 is given (See Documentation/cgroup-v1/memory.txt)swiotlb= [ARM,IA-64,PPC,MIPS,X86]Format: { <int> | force | noforce }<int> -- Number of I/O TLB slabsforce -- force using of bounce buffers even if theywouldn't be automatically used by the kernelnoforce -- Never use bounce buffers (for debugging)switches= [HW,M68k]sysfs.deprecated=0|1 [KNL]Enable/disable old style sysfs layout for old udevon older distributions. When this option is enabledvery new udev will not work anymore. When this optionis disabled (or CONFIG_SYSFS_DEPRECATED not compiled)in older udev will not work anymore.Default depends on CONFIG_SYSFS_DEPRECATED_V2 set inthe kernel configuration.sysrq_always_enabled[KNL]Ignore sysrq setting - this boot parameter willneutralize 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 totalram pages. This is used to specify the TCP metricscache size. See Documentation/networking/ip-sysctl.txt"tcp_no_metrics_save" section for more details.tdfx= [HW,DRM]test_suspend= [SUSPEND][,N]Specify "mem" (for Suspend-to-RAM) or "standby" (forstandby suspend) or "freeze" (for suspend type freeze)as the system sleep state during system startup withthe optional capability to repeat N number of times.The system is woken from this state using awakeup-capable RTC alarm.thash_entries= [KNL,NET]Set number of hash buckets for TCP connectionthermal.act= [HW,ACPI]-1: disable all active trip points in all thermal zones<degrees C>: override all lowest active trip pointsthermal.crt= [HW,ACPI]-1: disable all critical trip points in all thermal zones<degrees C>: override all critical trip pointsthermal.nocrt= [HW,ACPI]Set to disable actions on ACPI thermal zonecritical and hot trip points.thermal.off= [HW,ACPI]1: disable ACPI thermal controlthermal.psv= [HW,ACPI]-1: disable all passive trip points<degrees C>: override all passive trip points to thisvaluethermal.tzp= [HW,ACPI]Specify global default ACPI thermal zone polling rate<deci-seconds>: poll all this frequency0: no polling (default)threadirqs [KNL]Force threading of all interrupt handlers except thosemarked explicitly IRQF_NO_THREAD.tmem [KNL,XEN]Enable the Transcendent memory driver if built-in.tmem.cleancache=0|1 [KNL, XEN]Default is on (1). Disable the usage of the cleancacheAPI to send anonymous pages to the hypervisor.tmem.frontswap=0|1 [KNL, XEN]Default is on (1). Disable the usage of the frontswapAPI to send swap pages to the hypervisor. If disabledthe selfballooning and selfshrinking are force disabled.tmem.selfballooning=0|1 [KNL, XEN]Default is on (1). Disable the driving of swap pagesto the hypervisor.tmem.selfshrinking=0|1 [KNL, XEN]Default is on (1). Partial swapoff that immediatelytransfers pages from Xen hypervisor back to thekernel based on different criteria.topology= [S390]Format: {off | on}Specify if the kernel should make use of the cputopology information if the hardware supports this.The scheduler will make use of this information ande.g. base its process migration decisions on it.Default is on.topology_updates= [KNL, PPC, NUMA]Format: {off}Specify if the kernel should ignore (off)topology updates sent by the hypervisor to thisLPAR.tp720= [HW,PS2]tpm_suspend_pcr=[HW,TPM]Format: integer pcr idSpecify that at suspend time, the tpm drivershould extend the specified pcr with zeros,as a workaround for some chips which fail toflush the last written pcr on TPM_SaveState.This will guarantee that all the other pcrsare saved.trace_buf_size=nn[KMG][FTRACE] will set tracing buffer size on each cpu.trace_event=[event-list][FTRACE] Set and start specified trace events in orderto facilitate early boot debugging. The event-list is acomma separated list of trace events to enable. Seealso Documentation/trace/events.txttrace_options=[option-list][FTRACE] Enable or disable tracer options at boot.The option-list is a comma delimited list of optionsthat can be enabled or disabled just as if you wereto echo the option name into/sys/kernel/debug/tracing/trace_optionsFor example, to enable stacktrace option (to dump thestack trace of each event), add to the command line:trace_options=stacktraceSee also Documentation/trace/ftrace.txt "trace options"section.tp_printk[FTRACE]Have the tracepoints sent to printk as well as thetracing ring buffer. This is useful for early boot upwhere the system hangs or reboots and does not give theoption for reading the tracing buffer or performing aftrace_dump_on_oops.To turn off having tracepoints sent to printk,echo 0 > /proc/sys/kernel/tracepoint_printkNote, echoing 1 into this file without thetracepoint_printk kernel cmdline option has no effect.** CAUTION **Having tracepoints sent to printk() and activating highfrequency tracepoints such as irq or sched, can causethe system to live lock.traceoff_on_warning[FTRACE] enable this option to disable tracing when awarning is hit. This turns off "tracing_on". Tracing canbe enabled again by echoing '1' into the "tracing_on"file located in /sys/kernel/debug/tracing/This option is useful, as it disables the trace beforethe WARNING dump is called, which prevents the trace tobe filled with content caused by the warning output.This option can also be set at run time via the sysctloption: kernel/traceoff_on_warningtransparent_hugepage=[KNL]Format: [always|madvise|never]Can be used to control the default behavior of the systemwith respect to transparent hugepages.See Documentation/vm/transhuge.txt for more details.tsc= Disable clocksource stability checks for TSC.Format: <string>[x86] reliable: mark tsc clocksource as reliable, thisdisables clocksource verification at runtime, as wellas the stability checks done at bootup. Used to enablehigh-resolution timer mode on older hardware, and invirtualized environment.[x86] noirqtime: Do not use TSC to do irq accounting.Used to run time disable IRQ_TIME_ACCOUNTING on anyplatforms where RDTSC is slow and this accountingcan add overhead.[x86] unstable: mark the TSC clocksource as unstable, thismarks the TSC unconditionally unstable at bootup andavoids any further wobbles once the TSC watchdog notices.turbografx.map[2|3]= [HW,JOY]TurboGraFX parallel port interfaceFormat:<port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>See also Documentation/input/devices/joystick-parport.rstudbg-immortal [PPC] When debugging early kernel crashes thathappen after console_init() and before a properconsole driver takes over, this boot options mighthelp "seeing" what's going on.uhash_entries= [KNL,NET]Set number of hash buckets for UDP/UDP-Lite connectionsuhci-hcd.ignore_oc=[USB] Ignore overcurrent events (default N).Some badly-designed motherboards generate lots ofbogus events, for ports that aren't wired toanything. Set this parameter to avoid log spamming.Note that genuine overcurrent events won't bereported either.unknown_nmi_panic[X86] Cause panic on unknown NMI.usbcore.authorized_default=[USB] Default USB device authorization:(default -1 = authorized except for wireless USB,0 = not authorized, 1 = authorized)usbcore.autosuspend=[USB] The autosuspend time delay (in seconds) usedfor newly-detected USB devices (default 2). Thisis the time required before an idle device will beautosuspended. Devices for which the delay is setto 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 initializationscheme (default 0 = off).usbcore.usbfs_memory_mb=[USB] Memory limit (in MB) for buffers allocated byusbfs (default = 16, 0 = max = 2047).usbcore.use_both_schemes=[USB] Try the other device initialization schemeif the first one fails (default 1 = enabled).usbcore.initial_descriptor_timeout=[USB] Specifies timeout for the initial 64-byteUSB_REQ_GET_DESCRIPTOR request in milliseconds(default 5000 = 5.0 seconds).usbcore.nousb [USB] Disable the USB subsystemusbcore.quirks=[USB] A list of quirk entries to augment the built-inusb core quirk list. List entries are separated bycommas. Each entry has the formVendorID:ProductID:Flags. The IDs are 4-digit hexnumbers and Flags is a set of letters. Each letterwill change the built-in quirk; setting it if it isclear and clearing it if it is set. The letters havethe following meanings:a = USB_QUIRK_STRING_FETCH_255 (stringdescriptors must not be fetched usinga 255-byte read);b = USB_QUIRK_RESET_RESUME (device can't resumecorrectly so reset it instead);c = USB_QUIRK_NO_SET_INTF (device can't handleSet-Interface requests);d = USB_QUIRK_CONFIG_INTF_STRINGS (device can'thandle its Configuration or Interfacestrings);e = USB_QUIRK_RESET (device can't be reset(e.g morph devices), don't use reset);f = USB_QUIRK_HONOR_BNUMINTERFACES (device hasmore interface descriptions than thebNumInterfaces count, and can't handletalking to these interfaces);g = USB_QUIRK_DELAY_INIT (device needs a pauseduring initialization, after we readthe device descriptor);h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (Forhigh speed and super speed interruptendpoints, the USB 2.0 and USB 3.0 specrequire the interval in microframes (1microframe = 125 microseconds) to becalculated as interval = 2 ^(bInterval-1).Devices with this quirk report theirbInterval as the result of thiscalculation instead of the exponentvariable used in the calculation);i = USB_QUIRK_DEVICE_QUALIFIER (device can'thandle device_qualifier descriptorrequests);j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (devicegenerates spurious wakeup, ignoreremote wakeup capability);k = USB_QUIRK_NO_LPM (device can't handle LinkPower Management);l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL(Device reports its bInterval as linearframes instead of the USB 2.0calculation);m = USB_QUIRK_DISCONNECT_SUSPEND (Device needsto be disconnected before suspend toprevent spurious wakeup);n = USB_QUIRK_DELAY_CTRL_MSG (Device needs apause after every control message);Example: quirks=0781:5580:bk,0a5c:5834:gijusbhid.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 isscanned for Logical Units (default 1).usb-storage.quirks=[UMS] A list of quirks entries to supplement oroverride the built-in unusual_devs list. Listentries are separated by commas. Each entry hasthe form VID:PID:Flags where VID and PID are Vendorand Product ID values (4-digit hex numbers) andFlags is a set of characters, each correspondingto a common usb-storage quirk flag as follows:a = SANE_SENSE (collect more than 18 bytesof sense data);b = BAD_SENSE (don't collect more than 18bytes of sense data);c = FIX_CAPACITY (decrease the reporteddevice capacity by one sector);d = NO_READ_DISC_INFO (don't useREAD_DISC_INFO command);e = NO_READ_CAPACITY_16 (don't useREAD_CAPACITY_16 command);f = NO_REPORT_OPCODES (don't use report opcodescommand, uas only);g = MAX_SECTORS_240 (don't transfer more than240 sectors at a time, uas only);h = CAPACITY_HEURISTICS (decrease thereported device capacity by onesector if the number is odd);i = IGNORE_DEVICE (don't bind to thisdevice);j = NO_REPORT_LUNS (don't use report lunscommand, uas only);l = NOT_LOCKABLE (don't try to lock andunlock ejectable media);m = MAX_SECTORS_64 (don't transfer morethan 64 sectors = 32 KB at a time);n = INITIAL_READ10 (force a retry of theinitial READ(10) command);o = CAPACITY_OK (accept the capacityreported by the device);p = WRITE_CACHE (the device cache is ONby default);r = IGNORE_RESIDUE (the device reportsbogus residue values);s = SINGLE_LUN (the device has only oneLogical 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 themedium is write-protected).y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHEeven if the device claims no cache)Example: quirks=0419:aaf5:rl,0421:0433:rcuser_debug= [KNL,ARM]Format: <int>See arch/arm/Kconfig.debug help text.1 - undefined instruction events2 - system calls4 - invalid data aborts8 - SIGSEGV faults16 - SIGBUS faultsExample: user_debug=31userpte=[X86] Flags controlling user PTE allocations.nohigh = do not allocate PTE pages inHIGHMEM regardless of settingof CONFIG_HIGHPTE.vdso= [X86,SH]On X86_32, this is an alias for vdso32=. Otherwise:vdso=1: enable VDSO (the default)vdso=0: disable VDSO mappingvdso32= [X86] Control the 32-bit vDSOvdso32=1: enable 32-bit VDSOvdso32=0 or vdso32=2: disable 32-bit VDSOSee the help text for CONFIG_COMPAT_VDSO for moredetails. If CONFIG_COMPAT_VDSO is set, the default isvdso32=0; otherwise, the default is vdso32=1.For compatibility with older kernels, vdso32=2 is analias 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!vector= [IA-64,SMP]vector=percpu: enable percpu vector domainvideo= [FB] Frame buffer configurationSee Documentation/fb/modedb.txt.video.brightness_switch_enabled= [0,1]If set to 1, on receiving an ACPI notify eventgenerated by hotkey, video driver will adjust brightnesslevel and then send out the event to user space throughthe allocated input device; If set to 0, video driverwill only send out the event without touching backlightbrightness level.default: 1virtio_mmio.device=[VMMIO] Memory mapped virtio (platform) device.<size>@<baseaddr>:<irq>[:<id>]where:<size> := size (can use standard suffixeslike K, M and G)<baseaddr> := physical base address<irq> := interrupt number (as passed torequest_irq())<id> := (optional) platform device idexample:virtio_mmio.device=1K@0x100b0000:48:7Can be used multiple times for multiple devices.vga= [BOOT,X86-32] Select a particular video modeSee Documentation/x86/boot.txt andDocumentation/svga.txt.Use vga=ask for menu.This is actually a boot loader parameter; the value ispassed to the kernel using a special protocol.vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exactsize of <nn>. This can be used to increase theminimum size (128MB on x86). It can also be used todecrease the size and leave more room for directlymapped kernel RAM.vmcp_cma=nn[MG] [KNL,S390]Sets the memory size reserved for contiguous memoryallocations 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>vsyscall= [X86-64]Controls the behavior of vsyscalls (i.e. calls tofixed addresses of 0xffffffffff600x00 from legacycode). Most statically-linked binaries and olderversions of glibc use these calls. Because thesefunctions are at fixed addresses, they make nicetargets for exploits that can control RIP.emulate [default] Vsyscalls turn into traps and areemulated reasonably safely.native Vsyscalls are native syscall instructions.This is a little bit faster than trappingand makes a few dynamic recompilers workbetter than they would in emulation mode.It also makes exploits much easier to write.none Vsyscalls don't work at all. This makesthem quite hard to use for exploits butmight 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 asthe parameters of the <Esc>[?A;B;Cc escape sequence;see VGA-softcursor.txt. 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 valuesranging 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 valuesranging 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 valuesranging 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 allnewly opened terminals.vt.global_cursor_default=[VT]Format=<-1|0|1>Set system-wide default for whether a cursoris shown on new VTs. Default is -1,i.e. cursors will be created by default unlessoverridden by individual drivers. 0 will hidecursors, 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.txtor other driver-specific files in theDocumentation/watchdog/ directory.workqueue.watchdog_thresh=If CONFIG_WQ_WATCHDOG is configured, workqueue canwarn stall conditions and dump internal state tohelp debugging. 0 disables workqueue stalldetection; otherwise, it's the stall thresholdduration in seconds. The default value is 30 andit can be updated at runtime by writing to thecorresponding sysfs file.workqueue.disable_numaBy default, all work items queued to unboundworkqueues are affine to the NUMA nodes they'reissued on, which results in better behavior ingeneral. If NUMA affinity needs to be disabled forwhatever reason, this option can be used. Notethat this also can be controlled per-workqueue forworkqueues visible under /sys/bus/workqueue/.workqueue.power_efficientPer-cpu workqueues are generally preferred becausethey show better performance thanks to cachelocality; unfortunately, per-cpu workqueues tend tobe more power hungry than unbound workqueues.Enabling this makes the per-cpu workqueues whichwere observed to contribute significantly to powerconsumption unbound, leading to measurably lowerpower usage at the cost of small performanceoverhead.The default value of this parameter is determined bythe config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.workqueue.debug_force_rr_cpuWorkqueue used to implicitly guarantee that workitems queued without explicit CPU specified are puton the local CPU. This guarantee is no longer trueand while local CPU is still preferred work itemsmay be put on foreign CPUs. This debug optionforces round-robin CPU selection to flush outusages which depend on the now broken guarantee.When enabled, memory and cache locality will beimpacted.x2apic_phys [X86-64,APIC] Use x2apic physical mode instead ofdefault x2apic cluster mode on platformssupporting x2apic.x86_intel_mid_timer= [X86-32,APBT]Choose timer option for x86 Intel MID platform.Two valid options are apbt timer only and lapic timerplus one apbt timer for broadcast timer.x86_intel_mid_timer=apbt_only | lapic_and_apbtxen_512gb_limit [KNL,X86-64,XEN]Restricts the kernel running paravirtualized under Xento use only up to 512 GB of RAM. The reason to do so iscrash analysis tools and Xen tools for doing domainsave/restore/migration must be enabled to handle largerdomains.xen_emul_unplug= [HW,X86,XEN]Unplug Xen emulated devicesFormat: [unplug0,][unplug1]ide-disks -- unplug primary master IDE devicesaux-ide-disks -- unplug non-primary-master IDE devicesnics -- unplug network devicesall -- unplug all emulated devices (NICs and IDE disks)unnecessary -- unplugging emulated devices isunnecessary even if the host did not respond tothe unplug protocolnever -- do not unplug even if version check succeedsxen_nopvspin [X86,XEN]Disables the ticketlock slowpath using Xen PVoptimizations.xen_nopv [X86]Disables the PV optimizations forcing the HVM guest torun as generic HVM guest with no PV drivers.xirc2ps_cs= [NET,PCMCIA]Format:<irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
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