1 acpi= [HW,ACPI,X86,ARM64]
2 Advanced Configuration and Power Interface
3 Format: { force | on | off | strict | noirq | rsdt |
5 force -- enable ACPI if default was off
6 on -- enable ACPI but allow fallback to DT [arm64]
7 off -- disable ACPI if default was on
8 noirq -- do not use ACPI for IRQ routing
9 strict -- Be less tolerant of platforms that are not
10 strictly ACPI specification compliant.
11 rsdt -- prefer RSDT over (default) XSDT
12 copy_dsdt -- copy DSDT to memory
13 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"
16 See also Documentation/power/runtime_pm.txt, pci=noacpi
18 acpi_apic_instance= [ACPI, IOAPIC]
20 2: use 2nd APIC table, if available
21 1,0: use 1st APIC table
24 acpi_backlight= [HW,ACPI]
27 If set to vendor, prefer vendor specific driver
28 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
29 of the ACPI video.ko driver.
31 acpi_force_32bit_fadt_addr
32 force FADT to use 32 bit addresses rather than the
33 64 bit X_* addresses. Some firmware have broken 64
34 bit addresses for force ACPI ignore these and use
35 the older legacy 32 bit addresses.
37 acpica_no_return_repair [HW, ACPI]
38 Disable AML predefined validation mechanism
39 This mechanism can repair the evaluation result to make
40 the return objects more ACPI specification compliant.
41 This option is useful for developers to identify the
42 root cause of an AML interpreter issue when the issue
43 has something to do with the repair mechanism.
45 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
46 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
48 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
49 debug output. Bits in debug_layer correspond to a
50 _COMPONENT in an ACPI source file, e.g.,
51 #define _COMPONENT ACPI_PCI_COMPONENT
52 Bits in debug_level correspond to a level in
53 ACPI_DEBUG_PRINT statements, e.g.,
54 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
55 The debug_level mask defaults to "info". See
56 Documentation/acpi/debug.txt for more information about
57 debug layers and levels.
59 Enable processor driver info messages:
60 acpi.debug_layer=0x20000000
61 Enable PCI/PCI interrupt routing info messages:
62 acpi.debug_layer=0x400000
63 Enable AML "Debug" output, i.e., stores to the Debug
64 object while interpreting AML:
65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
66 Enable all messages related to ACPI hardware:
67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
69 Some values produce so much output that the system is
70 unusable. The "log_buf_len" parameter may be useful
71 if you need to capture more output.
73 acpi_enforce_resources= [ACPI]
75 Check for resource conflicts between native drivers
76 and ACPI OperationRegions (SystemIO and SystemMemory
77 only). IO ports and memory declared in ACPI might be
78 used by the ACPI subsystem in arbitrary AML code and
79 can interfere with legacy drivers.
80 strict (default): access to resources claimed by ACPI
81 is denied; legacy drivers trying to access reserved
82 resources will fail to bind to device using them.
83 lax: access to resources claimed by ACPI is allowed;
84 legacy drivers trying to access reserved resources
85 will bind successfully but a warning message is logged.
86 no: ACPI OperationRegions are not marked as reserved,
87 no further checks are performed.
89 acpi_force_table_verification [HW,ACPI]
90 Enable table checksum verification during early stage.
91 By default, this is disabled due to x86 early mapping
94 acpi_irq_balance [HW,ACPI]
95 ACPI will balance active IRQs
98 acpi_irq_nobalance [HW,ACPI]
99 ACPI will not move active IRQs (default)
102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
103 Format: <irq>,<irq>...
105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
107 Format: <irq>,<irq>...
109 acpi_mask_gpe= [HW,ACPI]
110 Due to the existence of _Lxx/_Exx, some GPEs triggered
111 by unsupported hardware/firmware features can result in
112 GPE floodings that cannot be automatically disabled by
114 This facility can be used to prevent such uncontrolled
118 acpi_no_auto_serialize [HW,ACPI]
119 Disable auto-serialization of AML methods
120 AML control methods that contain the opcodes to create
121 named objects will be marked as "Serialized" by the
122 auto-serialization feature.
123 This feature is enabled by default.
124 This option allows to turn off the feature.
126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
129 acpi_no_static_ssdt [HW,ACPI]
130 Disable installation of static SSDTs at early boot time
131 By default, SSDTs contained in the RSDT/XSDT will be
132 installed automatically and they will appear under
133 /sys/firmware/acpi/tables.
134 This option turns off this feature.
135 Note that specifying this option does not affect
136 dynamic table installation which will install SSDT
137 tables to /sys/firmware/acpi/tables/dynamic.
139 acpi_rsdp= [ACPI,EFI,KEXEC]
140 Pass the RSDP address to the kernel, mostly used
141 on machines running EFI runtime service to boot the
142 second kernel for kdump.
144 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
145 Format: To spoof as Windows 98: ="Microsoft Windows"
147 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
148 of 2 which is mandated by ACPI 6) as the supported ACPI
149 specification revision (when using this switch, it may
150 be necessary to carry out a cold reboot _twice_ in a
151 row to make it take effect on the platform firmware).
153 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
154 acpi_osi="string1" # add string1
155 acpi_osi="!string2" # remove string2
156 acpi_osi=!* # remove all strings
157 acpi_osi=! # disable all built-in OS vendor
159 acpi_osi=!! # enable all built-in OS vendor
161 acpi_osi= # disable all strings
163 'acpi_osi=!' can be used in combination with single or
164 multiple 'acpi_osi="string1"' to support specific OS
165 vendor string(s). Note that such command can only
166 affect the default state of the OS vendor strings, thus
167 it cannot affect the default state of the feature group
168 strings and the current state of the OS vendor strings,
169 specifying it multiple times through kernel command line
170 is meaningless. This command is useful when one do not
171 care about the state of the feature group strings which
172 should be controlled by the OSPM.
174 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
175 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
176 can make '_OSI("Windows 2000")' TRUE.
178 'acpi_osi=' cannot be used in combination with other
179 'acpi_osi=' command lines, the _OSI method will not
180 exist in the ACPI namespace. NOTE that such command can
181 only affect the _OSI support state, thus specifying it
182 multiple times through kernel command line is also
185 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
188 'acpi_osi=!*' can be used in combination with single or
189 multiple 'acpi_osi="string1"' to support specific
190 string(s). Note that such command can affect the
191 current state of both the OS vendor strings and the
192 feature group strings, thus specifying it multiple times
193 through kernel command line is meaningful. But it may
194 still not able to affect the final state of a string if
195 there are quirks related to this string. This command
196 is useful when one want to control the state of the
197 feature group strings to debug BIOS issues related to
200 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
201 '_OSI("Module Device")' FALSE.
202 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
203 '_OSI("Module Device")' TRUE.
204 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
206 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
208 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
209 they all will make '_OSI("Windows 2000")' TRUE.
212 Override the pmtimer bug detection: force the kernel
213 to assume that this machine's pmtimer latches its value
214 and always returns good values.
216 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
217 Format: { level | edge | high | low }
219 acpi_skip_timer_override [HW,ACPI]
220 Recognize and ignore IRQ0/pin2 Interrupt Override.
221 For broken nForce2 BIOS resulting in XT-PIC timer.
223 acpi_sleep= [HW,ACPI] Sleep options
224 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
225 old_ordering, nonvs, sci_force_enable, nobl }
226 See Documentation/power/video.txt for information on
228 s3_beep is for debugging; it makes the PC's speaker beep
229 as soon as the kernel's real-mode entry point is called.
230 s4_nohwsig prevents ACPI hardware signature from being
231 used during resume from hibernation.
232 old_ordering causes the ACPI 1.0 ordering of the _PTS
233 control method, with respect to putting devices into
234 low power states, to be enforced (the ACPI 2.0 ordering
235 of _PTS is used by default).
236 nonvs prevents the kernel from saving/restoring the
237 ACPI NVS memory during suspend/hibernation and resume.
238 sci_force_enable causes the kernel to set SCI_EN directly
239 on resume from S1/S3 (which is against the ACPI spec,
240 but some broken systems don't work without it).
241 nobl causes the internal blacklist of systems known to
242 behave incorrectly in some ways with respect to system
243 suspend and resume to be ignored (use wisely).
245 acpi_use_timer_override [HW,ACPI]
246 Use timer override. For some broken Nvidia NF5 boards
247 that require a timer override, but don't have HPET
249 add_efi_memmap [EFI; X86] Include EFI memory map in
250 kernel's map of available physical RAM.
253 { off | try_unsupported }
254 off: disable AGP support
255 try_unsupported: try to drive unsupported chipsets
256 (may crash computer or cause data corruption)
259 See Documentation/sound/alsa/alsa-parameters.txt
262 Allow the default userspace alignment fault handler
263 behaviour to be specified. Bit 0 enables warnings,
264 bit 1 enables fixups, and bit 2 sends a segfault.
266 align_va_addr= [X86-64]
267 Align virtual addresses by clearing slice [14:12] when
268 allocating a VMA at process creation time. This option
269 gives you up to 3% performance improvement on AMD F15h
270 machines (where it is enabled by default) for a
271 CPU-intensive style benchmark, and it can vary highly in
272 a microbenchmark depending on workload and compiler.
274 32: only for 32-bit processes
275 64: only for 64-bit processes
276 on: enable for both 32- and 64-bit processes
277 off: disable for both 32- and 64-bit processes
279 alloc_snapshot [FTRACE]
280 Allocate the ftrace snapshot buffer on boot up when the
281 main buffer is allocated. This is handy if debugging
282 and you need to use tracing_snapshot() on boot up, and
283 do not want to use tracing_snapshot_alloc() as it needs
284 to be done where GFP_KERNEL allocations are allowed.
286 amd_iommu= [HW,X86-64]
287 Pass parameters to the AMD IOMMU driver in the system.
289 fullflush - enable flushing of IO/TLB entries when
290 they are unmapped. Otherwise they are
291 flushed before they will be reused, which
293 off - do not initialize any AMD IOMMU found in
295 force_isolation - Force device isolation for all
296 devices. The IOMMU driver is not
297 allowed anymore to lift isolation
298 requirements as needed. This option
299 does not override iommu=pt
301 amd_iommu_dump= [HW,X86-64]
302 Enable AMD IOMMU driver option to dump the ACPI table
303 for AMD IOMMU. With this option enabled, AMD IOMMU
304 driver will print ACPI tables for AMD IOMMU during
305 IOMMU initialization.
307 amd_iommu_intr= [HW,X86-64]
308 Specifies one of the following AMD IOMMU interrupt
310 legacy - Use legacy interrupt remapping mode.
311 vapic - Use virtual APIC mode, which allows IOMMU
312 to inject interrupts directly into guest.
313 This mode requires kvm-amd.avic=1.
314 (Default when IOMMU HW support is present.)
316 amijoy.map= [HW,JOY] Amiga joystick support
317 Map of devices attached to JOY0DAT and JOY1DAT
319 See also Documentation/input/joydev/joystick.rst
321 analog.map= [HW,JOY] Analog joystick and gamepad support
322 Specifies type or capabilities of an analog joystick
323 connected to one of 16 gameports
324 Format: <type1>,<type2>,..<type16>
327 Power management functions (SPARCstation-4/5 + deriv.)
329 Disable APC CPU standby support. SPARCstation-Fox does
330 not play well with APC CPU idle - disable it if you have
331 APC and your system crashes randomly.
333 apic= [APIC,X86] Advanced Programmable Interrupt Controller
334 Change the output verbosity whilst booting
335 Format: { quiet (default) | verbose | debug }
336 Change the amount of debugging information output
337 when initialising the APIC and IO-APIC components.
338 For X86-32, this can also be used to specify an APIC
340 Format: apic=driver_name
341 Examples: apic=bigsmp
343 apic_extnmi= [APIC,X86] External NMI delivery setting
344 Format: { bsp (default) | all | none }
345 bsp: External NMI is delivered only to CPU 0
346 all: External NMIs are broadcast to all CPUs as a
348 none: External NMI is masked for all CPUs. This is
349 useful so that a dump capture kernel won't be
353 See Documentation/networking/ipv6.txt.
355 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
356 Limit apic dumping. The parameter defines the maximal
357 number of local apics being dumped. Also it is possible
358 to set it to "all" by meaning -- no limit here.
359 Format: { 1 (default) | 2 | ... | all }.
360 The parameter valid if only apic=debug or
361 apic=verbose is specified.
362 Example: apic=debug show_lapic=all
364 apm= [APM] Advanced Power Management
365 See header of arch/x86/kernel/apm_32.c.
367 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
368 Format: <io>,<irq>,<nodeID>
372 atarimouse= [HW,MOUSE] Atari Mouse
374 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
375 EzKey and similar keyboards
377 atkbd.reset= [HW] Reset keyboard during initialization
379 atkbd.set= [HW] Select keyboard code set
380 Format: <int> (2 = AT (default), 3 = PS/2)
382 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
385 atkbd.softraw= [HW] Choose between synthetic and real raw mode
386 Format: <bool> (0 = real, 1 = synthetic (default))
388 atkbd.softrepeat= [HW]
389 Use software keyboard repeat
391 audit= [KNL] Enable the audit sub-system
392 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
393 0 - kernel audit is disabled and can not be enabled
394 until the next reboot
395 unset - kernel audit is initialized but disabled and
396 will be fully enabled by the userspace auditd.
397 1 - kernel audit is initialized and partially enabled,
398 storing at most audit_backlog_limit messages in
399 RAM until it is fully enabled by the userspace
403 audit_backlog_limit= [KNL] Set the audit queue size limit.
404 Format: <int> (must be >=0)
407 bau= [X86_UV] Enable the BAU on SGI UV. The default
408 behavior is to disable the BAU (i.e. bau=0).
409 Format: { "0" | "1" }
412 unset - Disable the BAU.
414 baycom_epp= [HW,AX25]
417 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
419 See header of drivers/net/hamradio/baycom_par.c.
421 baycom_ser_fdx= [HW,AX25]
422 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
423 Format: <io>,<irq>,<mode>[,<baud>]
424 See header of drivers/net/hamradio/baycom_ser_fdx.c.
426 baycom_ser_hdx= [HW,AX25]
427 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
428 Format: <io>,<irq>,<mode>
429 See header of drivers/net/hamradio/baycom_ser_hdx.c.
431 blkdevparts= Manual partition parsing of block device(s) for
432 embedded devices based on command line input.
433 See Documentation/block/cmdline-partition.txt
435 boot_delay= Milliseconds to delay each printk during boot.
436 Values larger than 10 seconds (10000) are changed to
440 bootmem_debug [KNL] Enable bootmem allocator debug messages.
443 Disable BERT OS support on buggy BIOSes.
445 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
446 bttv.radio= Most important insmod options are available as
448 bttv.pll= See Documentation/media/v4l-drivers/bttv.rst
451 bulk_remove=off [PPC] This parameter disables the use of the pSeries
452 firmware feature for flushing multiple hpte entries
455 c101= [NET] Moxa C101 synchronous serial card
457 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
458 Sometimes CPU hardware bugs make them report the cache
459 size incorrectly. The kernel will attempt work arounds
460 to fix known problems, but for some CPUs it is not
461 possible to determine what the correct size should be.
462 This option provides an override for these situations.
464 ca_keys= [KEYS] This parameter identifies a specific key(s) on
465 the system trusted keyring to be used for certificate
467 format: { id:<keyid> | builtin }
469 cca= [MIPS] Override the kernel pages' cache coherency
470 algorithm. Accepted values range from 0 to 7
471 inclusive. See arch/mips/include/asm/pgtable-bits.h
472 for platform specific values (SB1, Loongson3 and
475 ccw_timeout_log [S390]
476 See Documentation/s390/CommonIO for details.
478 cgroup_disable= [KNL] Disable a particular controller
479 Format: {name of the controller(s) to disable}
480 The effects of cgroup_disable=foo are:
481 - foo isn't auto-mounted if you mount all cgroups in
483 - foo isn't visible as an individually mountable
485 {Currently only "memory" controller deal with this and
486 cut the overhead, others just disable the usage. So
487 only cgroup_disable=memory is actually worthy}
489 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
490 Format: { controller[,controller...] | "all" }
491 Like cgroup_disable, but only applies to cgroup v1;
492 the blacklisted controllers remain available in cgroup2.
494 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
496 nosocket -- Disable socket memory accounting.
497 nokmem -- Disable kernel memory accounting.
499 checkreqprot [SELINUX] Set initial checkreqprot flag value.
500 Format: { "0" | "1" }
501 See security/selinux/Kconfig help text.
502 0 -- check protection applied by kernel (includes
503 any implied execute protection).
504 1 -- check protection requested by application.
505 Default value is set via a kernel config option.
506 Value can be changed at runtime via
507 /selinux/checkreqprot.
510 See Documentation/s390/CommonIO for details.
513 Prevents the clock framework from automatically gating
514 clocks that have not been explicitly enabled by a Linux
515 device driver but are enabled in hardware at reset or
516 by the bootloader/firmware. Note that this does not
517 force such clocks to be always-on nor does it reserve
518 those clocks in any way. This parameter is useful for
519 debug and development, but should not be needed on a
520 platform with proper driver support. For more
521 information, see Documentation/clk.txt.
523 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
525 Forces specified clocksource (if available) to be used
526 when calculating gettimeofday(). If specified
527 clocksource is not available, it defaults to PIT.
528 Format: { pit | tsc | cyclone | pmtmr }
530 clocksource= Override the default clocksource
532 Override the default clocksource and use the clocksource
533 with the name specified.
534 Some clocksource names to choose from, depending on
536 [all] jiffies (this is the base, fallback clocksource)
538 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
539 pxa_timer,timer3,32k_counter,timer0_1
540 [X86-32] pit,hpet,tsc;
541 scx200_hrt on Geode; cyclone on IBM x440
549 clocksource.arm_arch_timer.evtstrm=
552 Enable/disable the eventstream feature of the ARM
553 architected timer so that code using WFE-based polling
554 loops can be debugged more effectively on production
557 clearcpuid=BITNUM [X86]
558 Disable CPUID feature X for the kernel. See
559 arch/x86/include/asm/cpufeatures.h for the valid bit
560 numbers. Note the Linux specific bits are not necessarily
561 stable over kernel options, but the vendor specific
563 Also note that user programs calling CPUID directly
564 or using the feature without checking anything
565 will still see it. This just prevents it from
566 being used by the kernel or shown in /proc/cpuinfo.
567 Also note the kernel might malfunction if you disable
570 cma=nn[MG]@[start[MG][-end[MG]]]
572 Sets the size of kernel global memory area for
573 contiguous memory allocations and optionally the
574 placement constraint by the physical address range of
575 memory allocations. A value of 0 disables CMA
576 altogether. For more information, see
577 include/linux/dma-contiguous.h
579 cmo_free_hint= [PPC] Format: { yes | no }
580 Specify whether pages are marked as being inactive
581 when they are freed. This is used in CMO environments
582 to determine OS memory pressure for page stealing by
586 coherent_pool=nn[KMG] [ARM,KNL]
587 Sets the size of memory pool for coherent, atomic dma
588 allocations, by default set to 256K.
590 code_bytes [X86] How many bytes of object code to print
595 com20020= [HW,NET] ARCnet - COM20020 chipset
597 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
599 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
603 ARCnet - COM90xx chipset (memory-mapped buffers)
604 Format: <io>[,<irq>[,<memstart>]]
606 condev= [HW,S390] console device
609 console= [KNL] Output console device and options.
611 tty<n> Use the virtual console device <n>.
615 Use the specified serial port. The options are of
616 the form "bbbbpnf", where "bbbb" is the baud rate,
617 "p" is parity ("n", "o", or "e"), "n" is number of
618 bits, and "f" is flow control ("r" for RTS or
619 omit it). Default is "9600n8".
621 See Documentation/admin-guide/serial-console.rst for more
623 Documentation/networking/netconsole.txt for an
626 uart[8250],io,<addr>[,options]
627 uart[8250],mmio,<addr>[,options]
628 uart[8250],mmio16,<addr>[,options]
629 uart[8250],mmio32,<addr>[,options]
630 uart[8250],0x<addr>[,options]
631 Start an early, polled-mode console on the 8250/16550
632 UART at the specified I/O port or MMIO address,
633 switching to the matching ttyS device later.
634 MMIO inter-register address stride is either 8-bit
635 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
636 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
637 to be equivalent to 'mmio'. 'options' are specified in
638 the same format described for ttyS above; if unspecified,
639 the h/w is not re-initialized.
641 hvc<n> Use the hypervisor console device <n>. This is for
642 both Xen and PowerPC hypervisors.
644 If the device connected to the port is not a TTY but a braille
645 device, prepend "brl," before the device type, for instance
647 For now, only VisioBraille is supported.
650 [KNL] Change console messages format
652 By default we print messages on consoles in
653 "[time stamp] text\n" format (time stamp may not be
654 printed, depending on CONFIG_PRINTK_TIME or
655 `printk_time' param).
657 Switch to syslog format: "<%u>[time stamp] text\n"
658 IOW, each message will have a facility and loglevel
659 prefix. The format is similar to one used by syslog()
660 syscall, or to executing "dmesg -S --raw" or to reading
663 consoleblank= [KNL] The console blank (screen saver) timeout in
664 seconds. A value of 0 disables the blank timer.
668 [KNL] Change the default value for
669 /proc/<pid>/coredump_filter.
670 See also Documentation/filesystems/proc.txt.
672 coresight_cpu_debug.enable
675 Enable/disable the CPU sampling based debugging.
676 0: default value, disable debugging
677 1: enable debugging at boot time
679 cpuidle.off=1 [CPU_IDLE]
680 disable the cpuidle sub-system
682 cpufreq.off=1 [CPU_FREQ]
683 disable the cpufreq sub-system
686 [X86] Delay for N microsec between assert and de-assert
687 of APIC INIT to start processors. This delay occurs
688 on every CPU online, such as boot, and resume from suspend.
691 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
693 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
695 crashkernel=size[KMG][@offset[KMG]]
696 [KNL] Using kexec, Linux can switch to a 'crash kernel'
697 upon panic. This parameter reserves the physical
698 memory region [offset, offset + size] for that kernel
699 image. If '@offset' is omitted, then a suitable offset
700 is selected automatically. Check
701 Documentation/kdump/kdump.txt for further details.
703 crashkernel=range1:size1[,range2:size2,...][@offset]
704 [KNL] Same as above, but depends on the memory
705 in the running system. The syntax of range is
706 start-[end] where start and end are both
707 a memory unit (amount[KMG]). See also
708 Documentation/kdump/kdump.txt for an example.
710 crashkernel=size[KMG],high
711 [KNL, x86_64] range could be above 4G. Allow kernel
712 to allocate physical memory region from top, so could
713 be above 4G if system have more than 4G ram installed.
714 Otherwise memory region will be allocated below 4G, if
716 It will be ignored if crashkernel=X is specified.
717 crashkernel=size[KMG],low
718 [KNL, x86_64] range under 4G. When crashkernel=X,high
719 is passed, kernel could allocate physical memory region
720 above 4G, that cause second kernel crash on system
721 that require some amount of low memory, e.g. swiotlb
722 requires at least 64M+32K low memory, also enough extra
723 low memory is needed to make sure DMA buffers for 32-bit
724 devices won't run out. Kernel would try to allocate at
725 at least 256M below 4G automatically.
726 This one let user to specify own low range under 4G
727 for second kernel instead.
728 0: to disable low allocation.
729 It will be ignored when crashkernel=X,high is not used
730 or memory reserved is below 4G.
733 [KNL] Disable crypto self-tests
738 cs89x0_media= [HW,NET]
739 Format: { rj45 | aui | bnc }
742 See header of drivers/s390/block/dasd_devmap.c.
744 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
745 (one device per port)
746 Format: <port#>,<type>
747 See also Documentation/input/devices/joystick-parport.rst
749 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
751 Documentation/admin-guide/dynamic-debug-howto.rst for
752 details. Deprecated, see dyndbg.
754 debug [KNL] Enable kernel debugging (events log level).
757 [KNL] verbose self-tests
759 Print debugging info while doing the locking API
761 We default to 0 (no extra messages), setting it to
762 1 will print _a lot_ more information - normally
763 only useful to kernel developers.
765 debug_objects [KNL] Enable object debugging
768 [KNL] Disable object debugging
770 debug_guardpage_minorder=
771 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
772 parameter allows control of the order of pages that will
773 be intentionally kept free (and hence protected) by the
774 buddy allocator. Bigger value increase the probability
775 of catching random memory corruption, but reduce the
776 amount of memory for normal system use. The maximum
777 possible value is MAX_ORDER/2. Setting this parameter
778 to 1 or 2 should be enough to identify most random
779 memory corruption problems caused by bugs in kernel or
780 driver code when a CPU writes to (or reads from) a
781 random memory location. Note that there exists a class
782 of memory corruptions problems caused by buggy H/W or
783 F/W or by drivers badly programing DMA (basically when
784 memory is written at bus level and the CPU MMU is
785 bypassed) which are not detectable by
786 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
787 tracking down these problems.
790 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
791 parameter enables the feature at boot time. In
792 default, it is disabled. We can avoid allocating huge
793 chunk of memory for debug pagealloc if we don't enable
794 it at boot time and the system will work mostly same
795 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
796 on: enable the feature
798 debugpat [X86] Enable PAT debugging
800 decnet.addr= [HW,NET]
801 Format: <area>[,<node>]
802 See also Documentation/networking/decnet.txt.
805 [same as hugepagesz=] The size of the default
806 HugeTLB page size. This is the size represented by
807 the legacy /proc/ hugepages APIs, used for SHM, and
808 default size when mounting hugetlbfs filesystems.
809 Defaults to the default architecture's huge page size
813 Set number of hash buckets for dentry cache.
815 disable_1tb_segments [PPC]
816 Disables the use of 1TB hash page table segments. This
817 causes the kernel to fall back to 256MB segments which
818 can be useful when debugging issues that require an SLB
822 See Documentation/networking/ipv6.txt.
825 Disable RADIX MMU mode on POWER9
827 disable_cpu_apicid= [X86,APIC,SMP]
829 The number of initial APIC ID for the
830 corresponding CPU to be disabled at boot,
831 mostly used for the kdump 2nd kernel to
832 disable BSP to wake up multiple CPUs without
833 causing system reset or hang due to sending
836 disable_ddw [PPC/PSERIES]
837 Disable Dynamic DMA Window support. Use this if
838 to workaround buggy firmware.
841 See Documentation/networking/ipv6.txt.
843 disable_mtrr_cleanup [X86]
844 The kernel tries to adjust MTRR layout from continuous
845 to discrete, to make X server driver able to add WB
846 entry later. This parameter disables that.
848 disable_mtrr_trim [X86, Intel and AMD only]
849 By default the kernel will trim any uncacheable
850 memory out of your available memory pool based on
851 MTRR settings. This parameter disables that behavior,
852 possibly causing your machine to run very slowly.
854 disable_timer_pin_1 [X86]
855 Disable PIN 1 of APIC timer
856 Can be useful to work around chipset bugs.
858 dis_ucode_ldr [X86] Disable the microcode loader.
860 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
861 this option disables the debugging code at boot.
863 dma_debug_entries=<number>
864 This option allows to tune the number of preallocated
865 entries for DMA-API debugging code. One entry is
866 required per DMA-API allocation. Use this if the
867 DMA-API debugging code disables itself because the
868 architectural default is too low.
870 dma_debug_driver=<driver_name>
871 With this option the DMA-API debugging driver
872 filter feature can be enabled at boot time. Just
873 pass the driver to filter for as the parameter.
874 The filter can be disabled or changed to another
875 driver later using sysfs.
877 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
878 Broken monitors, graphic adapters, KVMs and EDIDless
879 panels may send no or incorrect EDID data sets.
880 This parameter allows to specify an EDID data sets
881 in the /lib/firmware directory that are used instead.
882 Generic built-in EDID data sets are used, if one of
883 edid/1024x768.bin, edid/1280x1024.bin,
884 edid/1680x1050.bin, or edid/1920x1080.bin is given
885 and no file with the same name exists. Details and
886 instructions how to build your own EDID data are
887 available in Documentation/EDID/HOWTO.txt. An EDID
888 data set will only be used for a particular connector,
889 if its name and a colon are prepended to the EDID
890 name. Each connector may use a unique EDID data
891 set by separating the files with a comma. An EDID
892 data set with no connector name will be used for
893 any connectors not explicitly specified.
898 Format: {"off" | "known"}
899 Control how the dt_cpu_ftrs device-tree binding is
900 used for CPU feature discovery and setup (if it
902 off: Do not use it, fall back to legacy cpu table.
903 known: Do not pass through unknown features to guests
904 or userspace, only those that the kernel is aware of.
906 dump_apple_properties [X86]
907 Dump name and content of EFI device properties on
908 x86 Macs. Useful for driver authors to determine
909 what data is available or for reverse-engineering.
911 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
912 module.dyndbg[="val"]
913 Enable debug messages at boot time. See
914 Documentation/admin-guide/dynamic-debug-howto.rst
917 nompx [X86] Disables Intel Memory Protection Extensions.
918 See Documentation/x86/intel_mpx.txt for more
919 information about the feature.
921 nopku [X86] Disable Memory Protection Keys CPU feature found
924 module.async_probe [KNL]
925 Enable asynchronous probe on this module.
927 early_ioremap_debug [KNL]
928 Enable debug messages in early_ioremap support. This
929 is useful for tracking down temporary early mappings
930 which are not unmapped.
932 earlycon= [KNL] Output early console device and options.
934 [ARM64] The early console is determined by the
935 stdout-path property in device tree's chosen node,
936 or determined by the ACPI SPCR table.
938 [X86] When used with no options the early console is
939 determined by the ACPI SPCR table.
941 cdns,<addr>[,options]
942 Start an early, polled-mode console on a Cadence
943 (xuartps) serial port at the specified address. Only
944 supported option is baud rate. If baud rate is not
945 specified, the serial port must already be setup and
948 uart[8250],io,<addr>[,options]
949 uart[8250],mmio,<addr>[,options]
950 uart[8250],mmio32,<addr>[,options]
951 uart[8250],mmio32be,<addr>[,options]
952 uart[8250],0x<addr>[,options]
953 Start an early, polled-mode console on the 8250/16550
954 UART at the specified I/O port or MMIO address.
955 MMIO inter-register address stride is either 8-bit
956 (mmio) or 32-bit (mmio32 or mmio32be).
957 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
958 to be equivalent to 'mmio'. 'options' are specified
959 in the same format described for "console=ttyS<n>"; if
960 unspecified, the h/w is not initialized.
964 Start an early, polled-mode console on a pl011 serial
965 port at the specified address. The pl011 serial port
966 must already be setup and configured. Options are not
967 yet supported. If 'mmio32' is specified, then only
968 the driver will use only 32-bit accessors to read/write
969 the device registers.
972 Start an early, polled-mode console on a meson serial
973 port at the specified address. The serial port must
974 already be setup and configured. Options are not yet
978 Start an early, polled-mode console on an msm serial
979 port at the specified address. The serial port
980 must already be setup and configured. Options are not
984 Start an early, polled-mode console on an msm serial
985 dm port at the specified address. The serial port
986 must already be setup and configured. Options are not
990 Start an early, polled-mode console on a serial port
991 of an Actions Semi SoC, such as S500 or S900, at the
992 specified address. The serial port must already be
993 setup and configured. Options are not yet supported.
995 smh Use ARM semihosting calls for early console.
1003 Use early console provided by serial driver available
1004 on Samsung SoCs, requires selecting proper type and
1005 a correct base address of the selected UART port. The
1006 serial port must already be setup and configured.
1007 Options are not yet supported.
1010 Start an early, polled-mode console on a lantiq serial
1011 (lqasc) port at the specified address. The serial port
1012 must already be setup and configured. Options are not
1017 Use early console provided by Freescale LP UART driver
1018 found on Freescale Vybrid and QorIQ LS1021A processors.
1019 A valid base address must be provided, and the serial
1020 port must already be setup and configured.
1023 Start an early, polled-mode console on the
1024 Armada 3700 serial port at the specified
1025 address. The serial port must already be setup
1026 and configured. Options are not yet supported.
1028 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k,S390]
1033 earlyprintk=serial[,ttySn[,baudrate]]
1034 earlyprintk=serial[,0x...[,baudrate]]
1035 earlyprintk=ttySn[,baudrate]
1036 earlyprintk=dbgp[debugController#]
1037 earlyprintk=pciserial,bus:device.function[,baudrate]
1038 earlyprintk=xdbc[xhciController#]
1040 earlyprintk is useful when the kernel crashes before
1041 the normal console is initialized. It is not enabled by
1042 default because it has some cosmetic problems.
1044 Append ",keep" to not disable it when the real console
1047 Only one of vga, efi, serial, or usb debug port can
1050 Currently only ttyS0 and ttyS1 may be specified by
1051 name. Other I/O ports may be explicitly specified
1052 on some architectures (x86 and arm at least) by
1053 replacing ttySn with an I/O port address, like this:
1054 earlyprintk=serial,0x1008,115200
1055 You can find the port for a given device in
1056 /proc/tty/driver/serial:
1057 2: uart:ST16650V2 port:00001008 irq:18 ...
1059 Interaction with the standard serial driver is not
1062 The VGA and EFI output is eventually overwritten by
1065 The xen output can only be used by Xen PV guests.
1067 The sclp output can only be used on s390.
1069 edac_report= [HW,EDAC] Control how to report EDAC event
1070 Format: {"on" | "off" | "force"}
1071 on: enable EDAC to report H/W event. May be overridden
1072 by other higher priority error reporting module.
1073 off: disable H/W event reporting through EDAC.
1074 force: enforce the use of EDAC to report H/W event.
1077 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1080 This is designed to be used in conjunction with
1081 the boot argument: earlyprintk=vga
1084 Format: {"off" | "on" | "skip[mbr]"}
1087 Format: { "old_map", "nochunk", "noruntime", "debug" }
1088 old_map [X86-64]: switch to the old ioremap-based EFI
1089 runtime services mapping. 32-bit still uses this one by
1091 nochunk: disable reading files in "chunks" in the EFI
1092 boot stub, as chunking can cause problems with some
1093 firmware implementations.
1094 noruntime : disable EFI runtime services support
1095 debug: enable misc debug output
1097 efi_no_storage_paranoia [EFI; X86]
1098 Using this parameter you can use more than 50% of
1099 your efi variable storage. Use this parameter only if
1100 you are really sure that your UEFI does sane gc and
1101 fulfills the spec otherwise your board may brick.
1103 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1104 Add arbitrary attribute to specific memory range by
1105 updating original EFI memory map.
1106 Region of memory which aa attribute is added to is
1108 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1109 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1110 attribute is added to range 0x100000000-0x180000000 and
1111 0x10a0000000-0x1120000000.
1113 Using this parameter you can do debugging of EFI memmap
1114 related feature. For example, you can do debugging of
1115 Address Range Mirroring feature even if your box
1118 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1119 that is to be dynamically loaded by Linux. If there are
1120 multiple variables with the same name but with different
1121 vendor GUIDs, all of them will be loaded. See
1122 Documentation/acpi/ssdt-overlays.txt for details.
1125 eisa_irq_edge= [PARISC,HW]
1126 See header of drivers/parisc/eisa.c.
1129 See comment before function elanfreq_setup() in
1130 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1133 Format: {"cfq" | "deadline" | "noop"}
1134 See Documentation/block/cfq-iosched.txt and
1135 Documentation/block/deadline-iosched.txt for details.
1137 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1138 Specifies physical address of start of kernel core
1139 image elf header and optionally the size. Generally
1140 kexec loader will pass this option to capture kernel.
1141 See Documentation/kdump/kdump.txt for details.
1143 enable_mtrr_cleanup [X86]
1144 The kernel tries to adjust MTRR layout from continuous
1145 to discrete, to make X server driver able to add WB
1146 entry later. This parameter enables that.
1148 enable_timer_pin_1 [X86]
1149 Enable PIN 1 of APIC timer
1150 Can be useful to work around chipset bugs
1151 (in particular on some ATI chipsets).
1152 The kernel tries to set a reasonable default.
1154 enforcing [SELINUX] Set initial enforcing status.
1156 See security/selinux/Kconfig help text.
1157 0 -- permissive (log only, no denials).
1158 1 -- enforcing (deny and log).
1160 Value can be changed at runtime via /selinux/enforce.
1163 Disable Error Record Serialization Table (ERST)
1166 ether= [HW,NET] Ethernet cards parameters
1167 This option is obsoleted by the "netdev=" option, which
1168 has equivalent usage. See its documentation for details.
1172 Permit 'security.evm' to be updated regardless of
1173 current integrity status.
1177 fail_make_request=[KNL]
1178 General fault injection mechanism.
1179 Format: <interval>,<probability>,<space>,<times>
1180 See also Documentation/fault-injection/.
1183 See Documentation/blockdev/floppy.txt.
1185 force_pal_cache_flush
1186 [IA-64] Avoid check_sal_cache_flush which may hang on
1187 buggy SAL_CACHE_FLUSH implementations. Using this
1188 parameter will force ia64_sal_cache_flush to call
1189 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1192 Forcefully enable Physical Address Extension (PAE).
1193 Many Pentium M systems disable PAE but may have a
1194 functionally usable PAE implementation.
1195 Warning: use of this parameter will taint the kernel
1196 and may cause unknown problems.
1199 [FTRACE] will set and start the specified tracer
1200 as early as possible in order to facilitate early
1203 ftrace_dump_on_oops[=orig_cpu]
1204 [FTRACE] will dump the trace buffers on oops.
1205 If no parameter is passed, ftrace will dump
1206 buffers of all CPUs, but if you pass orig_cpu, it will
1207 dump only the buffer of the CPU that triggered the
1210 ftrace_filter=[function-list]
1211 [FTRACE] Limit the functions traced by the function
1212 tracer at boot up. function-list is a comma separated
1213 list of functions. This list can be changed at run
1214 time by the set_ftrace_filter file in the debugfs
1217 ftrace_notrace=[function-list]
1218 [FTRACE] Do not trace the functions specified in
1219 function-list. This list can be changed at run time
1220 by the set_ftrace_notrace file in the debugfs
1223 ftrace_graph_filter=[function-list]
1224 [FTRACE] Limit the top level callers functions traced
1225 by the function graph tracer at boot up.
1226 function-list is a comma separated list of functions
1227 that can be changed at run time by the
1228 set_graph_function file in the debugfs tracing directory.
1230 ftrace_graph_notrace=[function-list]
1231 [FTRACE] Do not trace from the functions specified in
1232 function-list. This list is a comma separated list of
1233 functions that can be changed at run time by the
1234 set_graph_notrace file in the debugfs tracing directory.
1236 ftrace_graph_max_depth=<uint>
1237 [FTRACE] Used with the function graph tracer. This is
1238 the max depth it will trace into a function. This value
1239 can be changed at run time by the max_graph_depth file
1240 in the tracefs tracing directory. default: 0 (no limit)
1243 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1244 support via parallel port (up to 5 devices per port)
1245 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1246 See also Documentation/input/devices/joystick-parport.rst
1250 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1254 gcov_persist= [GCOV] When non-zero (default), profiling data for
1255 kernel modules is saved and remains accessible via
1256 debugfs, even when the module is unloaded/reloaded.
1257 When zero, profiling data is discarded and associated
1258 debugfs files are removed at module unload time.
1260 goldfish [X86] Enable the goldfish android emulator platform.
1261 Don't use this when you are not running on the
1264 gpt [EFI] Forces disk with valid GPT signature but
1265 invalid Protective MBR to be treated as GPT. If the
1266 primary GPT is corrupted, it enables the backup/alternate
1267 GPT to be used instead.
1269 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1270 the "Enable 0" bit of the configuration register.
1273 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1274 the "Enable 0" bit of the configuration register.
1277 grcan.select= [HW] Select which physical interface to use.
1280 grcan.txsize= [HW] Sets the size of the tx buffer.
1281 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1283 grcan.rxsize= [HW] Sets the size of the rx buffer.
1284 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1287 gpio-mockup.gpio_mockup_ranges
1288 [HW] Sets the ranges of gpiochip of for this device.
1289 Format: <start1>,<end1>,<start2>,<end2>...
1291 hardlockup_all_cpu_backtrace=
1292 [KNL] Should the hard-lockup detector generate
1293 backtraces on all cpus.
1296 hashdist= [KNL,NUMA] Large hashes allocated during boot
1297 are distributed across NUMA nodes. Defaults on
1298 for 64-bit NUMA, off otherwise.
1299 Format: 0 | 1 (for off | on)
1301 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1303 hd= [EIDE] (E)IDE hard drive subsystem geometry
1304 Format: <cyl>,<head>,<sect>
1307 Disable Hardware Error Source Table (HEST) support;
1308 corresponding firmware-first mode error processing
1309 logic will be disabled.
1311 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1312 size of <nn>. This works even on boxes that have no
1313 highmem otherwise. This also works to reduce highmem
1314 size on bigger boxes.
1316 highres= [KNL] Enable/disable high resolution timer mode.
1317 Valid parameters: "on", "off"
1321 See Documentation/isdn/README.HiSax.
1325 hpet= [X86-32,HPET] option to control HPET usage
1326 Format: { enable (default) | disable | force |
1328 disable: disable HPET and use PIT instead
1329 force: allow force enabled of undocumented chips (ICH4,
1331 verbose: show contents of HPET registers during setup
1333 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1334 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1336 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1337 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1338 On x86-64 and powerpc, this option can be specified
1339 multiple times interleaved with hugepages= to reserve
1340 huge pages of different sizes. Valid pages sizes on
1341 x86-64 are 2M (when the CPU supports "pse") and 1G
1342 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1344 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1345 terminal devices. Valid values: 0..8
1346 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1347 If specified, z/VM IUCV HVC accepts connections
1348 from listed z/VM user IDs only.
1351 Do not unregister boot console at start. This is only
1352 useful for debugging when something happens in the window
1353 between unregistering the boot console and initializing
1356 i2c_bus= [HW] Override the default board specific I2C bus speed
1357 or register an additional I2C bus that is not
1358 registered from board initialization code.
1362 i8042.debug [HW] Toggle i8042 debug mode
1363 i8042.unmask_kbd_data
1364 [HW] Enable printing of interrupt data from the KBD port
1365 (disabled by default, and as a pre-condition
1366 requires that i8042.debug=1 be enabled)
1367 i8042.direct [HW] Put keyboard port into non-translated mode
1368 i8042.dumbkbd [HW] Pretend that controller can only read data from
1369 keyboard and cannot control its state
1370 (Don't attempt to blink the leds)
1371 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1372 i8042.nokbd [HW] Don't check/create keyboard port
1373 i8042.noloop [HW] Disable the AUX Loopback command while probing
1375 i8042.nomux [HW] Don't check presence of an active multiplexing
1377 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1379 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1380 i8042.reset [HW] Reset the controller during init, cleanup and
1381 suspend-to-ram transitions, only during s2r
1382 transitions, or never reset
1383 Format: { 1 | Y | y | 0 | N | n }
1384 1, Y, y: always reset controller
1385 0, N, n: don't ever reset controller
1386 Default: only on s2r transitions on x86; most other
1387 architectures force reset to be always executed
1388 i8042.unlock [HW] Unlock (ignore) the keylock
1389 i8042.kbdreset [HW] Reset device connected to KBD port
1393 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1394 indicates that the driver is running on unsupported
1396 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1397 does not match list of supported models.
1399 [HW] Report power status in /proc/i8k
1400 (disabled by default)
1401 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1404 i915.invert_brightness=
1405 [DRM] Invert the sense of the variable that is used to
1406 set the brightness of the panel backlight. Normally a
1407 brightness value of 0 indicates backlight switched off,
1408 and the maximum of the brightness value sets the backlight
1409 to maximum brightness. If this parameter is set to 0
1410 (default) and the machine requires it, or this parameter
1411 is set to 1, a brightness value of 0 sets the backlight
1412 to maximum brightness, and the maximum of the brightness
1413 value switches the backlight off.
1414 -1 -- never invert brightness
1415 0 -- machine default
1416 1 -- force brightness inversion
1419 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1421 ide-core.nodma= [HW] (E)IDE subsystem
1422 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1423 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1424 .cdrom .chs .ignore_cable are additional options
1425 See Documentation/ide/ide.txt.
1427 ide-generic.probe-mask= [HW] (E)IDE subsystem
1429 Probe mask for legacy ISA IDE ports. Depending on
1430 platform up to 6 ports are supported, enabled by
1431 setting corresponding bits in the mask to 1. The
1432 default value is 0x0, which has a special meaning.
1433 On systems that have PCI, it triggers scanning the
1434 PCI bus for the first and the second port, which
1435 are then probed. On systems without PCI the value
1436 of 0x0 enables probing the two first ports as if it
1439 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1440 Claim all unknown PCI IDE storage controllers.
1443 Format: idle=poll, idle=halt, idle=nomwait
1444 Poll forces a polling idle loop that can slightly
1445 improve the performance of waking up a idle CPU, but
1446 will use a lot of power and make the system run hot.
1448 idle=halt: Halt is forced to be used for CPU idle.
1449 In such case C2/C3 won't be used again.
1450 idle=nomwait: Disable mwait for CPU C-states
1452 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1453 Format: { strict | legacy | 2008 | relaxed }
1456 Choose which programs will be accepted for execution
1457 based on the IEEE 754 NaN encoding(s) supported by
1458 the FPU and the NaN encoding requested with the value
1459 of an ELF file header flag individually set by each
1460 binary. Hardware implementations are permitted to
1461 support either or both of the legacy and the 2008 NaN
1464 Available settings are as follows:
1465 strict accept binaries that request a NaN encoding
1466 supported by the FPU
1467 legacy only accept legacy-NaN binaries, if supported
1469 2008 only accept 2008-NaN binaries, if supported
1471 relaxed accept any binaries regardless of whether
1472 supported by the FPU
1474 The FPU emulator is always able to support both NaN
1475 encodings, so if no FPU hardware is present or it has
1476 been disabled with 'nofpu', then the settings of
1477 'legacy' and '2008' strap the emulator accordingly,
1478 'relaxed' straps the emulator for both legacy-NaN and
1479 2008-NaN, whereas 'strict' enables legacy-NaN only on
1480 legacy processors and both NaN encodings on MIPS32 or
1483 The setting for ABS.fmt/NEG.fmt instruction execution
1484 mode generally follows that for the NaN encoding,
1485 except where unsupported by hardware.
1487 ignore_loglevel [KNL]
1488 Ignore loglevel setting - this will print /all/
1489 kernel messages to the console. Useful for debugging.
1490 We also add it as printk module parameter, so users
1491 could change it dynamically, usually by
1492 /sys/module/printk/parameters/ignore_loglevel.
1495 Ignore RLIMIT_DATA setting for data mappings,
1496 print warning at first misuse. Can be changed via
1497 /sys/module/kernel/parameters/ignore_rlimit_data.
1499 ihash_entries= [KNL]
1500 Set number of hash buckets for inode cache.
1502 ima_appraise= [IMA] appraise integrity measurements
1503 Format: { "off" | "enforce" | "fix" | "log" }
1506 ima_appraise_tcb [IMA]
1507 The builtin appraise policy appraises all files
1510 ima_canonical_fmt [IMA]
1511 Use the canonical format for the binary runtime
1512 measurements, instead of host native format.
1515 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1519 The list of supported hash algorithms is defined
1520 in crypto/hash_info.h.
1523 The builtin policies to load during IMA setup.
1524 Format: "tcb | appraise_tcb | secure_boot"
1526 The "tcb" policy measures all programs exec'd, files
1527 mmap'd for exec, and all files opened with the read
1528 mode bit set by either the effective uid (euid=0) or
1531 The "appraise_tcb" policy appraises the integrity of
1532 all files owned by root. (This is the equivalent
1533 of ima_appraise_tcb.)
1535 The "secure_boot" policy appraises the integrity
1536 of files (eg. kexec kernel image, kernel modules,
1537 firmware, policy, etc) based on file signatures.
1539 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1540 Load a policy which meets the needs of the Trusted
1541 Computing Base. This means IMA will measure all
1542 programs exec'd, files mmap'd for exec, and all files
1543 opened for read by uid=0.
1546 Select one of defined IMA measurements template formats.
1547 Formats: { "ima" | "ima-ng" | "ima-sig" }
1551 [IMA] Define a custom template format.
1552 Format: { "field1|...|fieldN" }
1554 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1555 Format: <min_file_size>
1556 Set the minimal file size for using asynchronous hash.
1557 If left unspecified, ahash usage is disabled.
1559 ahash performance varies for different data sizes on
1560 different crypto accelerators. This option can be used
1561 to achieve the best performance for a particular HW.
1563 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1565 Set hashing buffer size. Default: 4k.
1567 ahash performance varies for different chunk sizes on
1568 different crypto accelerators. This option can be used
1569 to achieve best performance for particular HW.
1573 Run specified binary instead of /sbin/init as init
1576 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1577 for working out where the kernel is dying during
1580 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1581 initcall functions. Useful for debugging built-in
1582 modules and initcalls.
1584 initrd= [BOOT] Specify the location of the initial ramdisk
1586 init_pkru= [x86] Specify the default memory protection keys rights
1587 register contents for all processes. 0x55555554 by
1588 default (disallow access to all but pkey 0). Can
1589 override in debugfs after boot.
1591 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1594 int_pln_enable [x86] Enable power limit notification interrupt
1596 integrity_audit=[IMA]
1597 Format: { "0" | "1" }
1598 0 -- basic integrity auditing messages. (Default)
1599 1 -- additional integrity auditing messages.
1601 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1603 Enable intel iommu driver.
1605 Disable intel iommu driver.
1606 igfx_off [Default Off]
1607 By default, gfx is mapped as normal device. If a gfx
1608 device has a dedicated DMAR unit, the DMAR unit is
1609 bypassed by not enabling DMAR with this option. In
1610 this case, gfx device will use physical address for
1613 With this option iommu will not optimize to look
1614 for io virtual address below 32-bit forcing dual
1615 address cycle on pci bus for cards supporting greater
1616 than 32-bit addressing. The default is to look
1617 for translation below 32-bit and if not available
1618 then look in the higher range.
1619 strict [Default Off]
1620 With this option on every unmap_single operation will
1621 result in a hardware IOTLB flush operation as opposed
1622 to batching them for performance.
1623 sp_off [Default Off]
1624 By default, super page will be supported if Intel IOMMU
1625 has the capability. With this option, super page will
1627 ecs_off [Default Off]
1628 By default, extended context tables will be supported if
1629 the hardware advertises that it has support both for the
1630 extended tables themselves, and also PASID support. With
1631 this option set, extended tables will not be used even
1632 on hardware which claims to support them.
1633 tboot_noforce [Default Off]
1634 Do not force the Intel IOMMU enabled under tboot.
1635 By default, tboot will force Intel IOMMU on, which
1636 could harm performance of some high-throughput
1637 devices like 40GBit network cards, even if identity
1639 Note that using this option lowers the security
1640 provided by tboot because it makes the system
1641 vulnerable to DMA attacks.
1643 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1644 0 disables intel_idle and fall back on acpi_idle.
1645 1 to 9 specify maximum depth of C-state.
1649 Do not enable intel_pstate as the default
1650 scaling driver for the supported processors
1652 Use intel_pstate as a scaling driver, but configure it
1653 to work with generic cpufreq governors (instead of
1654 enabling its internal governor). This mode cannot be
1655 used along with the hardware-managed P-states (HWP)
1658 Enable intel_pstate on systems that prohibit it by default
1659 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1660 instead of acpi-cpufreq may disable platform features, such
1661 as thermal controls and power capping, that rely on ACPI
1662 P-States information being indicated to OSPM and therefore
1663 should be used with caution. This option does not work with
1664 processors that aren't supported by the intel_pstate driver
1665 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1667 Do not enable hardware P state control (HWP)
1670 Only load intel_pstate on systems which support
1671 hardware P state control (HWP) if available.
1673 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1674 Description Table, specifies preferred power management
1675 profile as "Enterprise Server" or "Performance Server",
1676 then this feature is turned on by default.
1678 Allow per-logical-CPU P-State performance control limits using
1679 cpufreq sysfs interface
1681 intremap= [X86-64, Intel-IOMMU]
1682 on enable Interrupt Remapping (default)
1683 off disable Interrupt Remapping
1684 nosid disable Source ID checking
1686 BIOS x2APIC opt-out request will be ignored
1687 nopost disable Interrupt Posting
1689 iomem= Disable strict checking of access to MMIO memory
1690 strict regions from userspace.
1705 nobypass [PPC/POWERNV]
1706 Disable IOMMU bypass, using IOMMU for PCI devices.
1709 [ARM64] Configure DMA to bypass the IOMMU by default.
1710 Format: { "0" | "1" }
1711 0 - Use IOMMU translation for DMA.
1712 1 - Bypass the IOMMU for DMA.
1713 unset - Use IOMMU translation for DMA.
1715 io7= [HW] IO7 for Marvel based alpha systems
1716 See comment before marvel_specify_io7 in
1717 arch/alpha/kernel/core_marvel.c.
1719 io_delay= [X86] I/O delay method
1721 Standard port 0x80 based delay
1723 Alternate port 0xed based delay (needed on some systems)
1725 Simple two microseconds delay
1730 See Documentation/filesystems/nfs/nfsroot.txt.
1732 irqaffinity= [SMP] Set the default irq affinity mask
1733 The argument is a cpu list, as described above.
1735 irqchip.gicv2_force_probe=
1738 Force the kernel to look for the second 4kB page
1739 of a GICv2 controller even if the memory range
1740 exposed by the device tree is too small.
1743 When an interrupt is not handled search all handlers
1744 for it. Intended to get systems with badly broken
1748 When an interrupt is not handled search all handlers
1749 for it. Also check all handlers each timer
1750 interrupt. Intended to get systems with badly broken
1754 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1756 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1757 [Deprecated - use cpusets instead]
1758 Format: [flag-list,]<cpu-list>
1760 Specify one or more CPUs to isolate from disturbances
1761 specified in the flag list (default: domain):
1764 Disable the tick when a single task runs.
1766 Isolate from the general SMP balancing and scheduling
1767 algorithms. Note that performing domain isolation this way
1768 is irreversible: it's not possible to bring back a CPU to
1769 the domains once isolated through isolcpus. It's strongly
1770 advised to use cpusets instead to disable scheduler load
1771 balancing through the "cpuset.sched_load_balance" file.
1772 It offers a much more flexible interface where CPUs can
1773 move in and out of an isolated set anytime.
1775 You can move a process onto or off an "isolated" CPU via
1776 the CPU affinity syscalls or cpuset.
1777 <cpu number> begins at 0 and the maximum value is
1778 "number of CPUs in system - 1".
1780 The format of <cpu-list> is described above.
1786 ivrs_ioapic [HW,X86_64]
1787 Provide an override to the IOAPIC-ID<->DEVICE-ID
1788 mapping provided in the IVRS ACPI table. For
1789 example, to map IOAPIC-ID decimal 10 to
1790 PCI device 00:14.0 write the parameter as:
1791 ivrs_ioapic[10]=00:14.0
1793 ivrs_hpet [HW,X86_64]
1794 Provide an override to the HPET-ID<->DEVICE-ID
1795 mapping provided in the IVRS ACPI table. For
1796 example, to map HPET-ID decimal 0 to
1797 PCI device 00:14.0 write the parameter as:
1798 ivrs_hpet[0]=00:14.0
1800 ivrs_acpihid [HW,X86_64]
1801 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1802 mapping provided in the IVRS ACPI table. For
1803 example, to map UART-HID:UID AMD0020:0 to
1804 PCI device 00:14.5 write the parameter as:
1805 ivrs_acpihid[00:14.5]=AMD0020:0
1807 js= [HW,JOY] Analog joystick
1808 See Documentation/input/joydev/joystick.rst.
1811 When CONFIG_RANDOMIZE_BASE is set, this disables
1812 kernel and module base offset ASLR (Address Space
1813 Layout Randomization).
1816 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1817 report on every invalid memory access. Without this
1818 parameter KASAN will print report only for the first
1823 kernelcore= [KNL,X86,IA-64,PPC]
1824 Format: nn[KMGTPE] | "mirror"
1826 specifies the amount of memory usable by the kernel
1827 for non-movable allocations. The requested amount is
1828 spread evenly throughout all nodes in the system. The
1829 remaining memory in each node is used for Movable
1830 pages. In the event, a node is too small to have both
1831 kernelcore and Movable pages, kernelcore pages will
1832 take priority and other nodes will have a larger number
1833 of Movable pages. The Movable zone is used for the
1834 allocation of pages that may be reclaimed or moved
1835 by the page migration subsystem. This means that
1836 HugeTLB pages may not be allocated from this zone.
1837 Note that allocations like PTEs-from-HighMem still
1838 use the HighMem zone if it exists, and the Normal
1839 zone if it does not.
1841 Instead of specifying the amount of memory (nn[KMGTPE]),
1842 you can specify "mirror" option. In case "mirror"
1843 option is specified, mirrored (reliable) memory is used
1844 for non-movable allocations and remaining memory is used
1845 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1846 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1849 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1850 Format: <Controller#>[,poll interval]
1851 The controller # is the number of the ehci usb debug
1852 port as it is probed via PCI. The poll interval is
1853 optional and is the number seconds in between
1854 each poll cycle to the debug port in case you need
1855 the functionality for interrupting the kernel with
1856 gdb or control-c on the dbgp connection. When
1857 not using this parameter you use sysrq-g to break into
1858 the kernel debugger.
1860 kgdboc= [KGDB,HW] kgdb over consoles.
1861 Requires a tty driver that supports console polling,
1862 or a supported polling keyboard driver (non-usb).
1863 Serial only format: <serial_device>[,baud]
1864 keyboard only format: kbd
1865 keyboard and serial format: kbd,<serial_device>[,baud]
1866 Optional Kernel mode setting:
1867 kms, kbd format: kms,kbd
1868 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1870 kgdbwait [KGDB] Stop kernel execution and enter the
1871 kernel debugger at the earliest opportunity.
1873 kmac= [MIPS] korina ethernet MAC address.
1874 Configure the RouterBoard 532 series on-chip
1875 Ethernet adapter MAC address.
1877 kmemleak= [KNL] Boot-time kmemleak enable/disable
1878 Valid arguments: on, off
1880 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1883 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1884 Default is 0 (don't ignore, but inject #GP)
1886 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1890 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1891 Default is 1 (enabled)
1893 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1895 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1897 kvm-arm.vgic_v3_group0_trap=
1898 [KVM,ARM] Trap guest accesses to GICv3 group-0
1901 kvm-arm.vgic_v3_group1_trap=
1902 [KVM,ARM] Trap guest accesses to GICv3 group-1
1905 kvm-arm.vgic_v3_common_trap=
1906 [KVM,ARM] Trap guest accesses to GICv3 common
1909 kvm-arm.vgic_v4_enable=
1910 [KVM,ARM] Allow use of GICv4 for direct injection of
1913 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1914 (virtualized MMU) support on capable Intel chips.
1915 Default is 1 (enabled)
1917 kvm-intel.emulate_invalid_guest_state=
1918 [KVM,Intel] Enable emulation of invalid guest states
1919 Default is 0 (disabled)
1921 kvm-intel.flexpriority=
1922 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1923 Default is 1 (enabled)
1926 [KVM,Intel] Enable VMX nesting (nVMX).
1927 Default is 0 (disabled)
1929 kvm-intel.unrestricted_guest=
1930 [KVM,Intel] Disable unrestricted guest feature
1931 (virtualized real and unpaged mode) on capable
1932 Intel chips. Default is 1 (enabled)
1934 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1935 feature (tagged TLBs) on capable Intel chips.
1936 Default is 1 (enabled)
1942 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1945 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1946 value for LAPIC timer one-shot implementation. Default
1947 back to the programmable timer unit in the LAPIC.
1949 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1952 libata.dma= [LIBATA] DMA control
1953 libata.dma=0 Disable all PATA and SATA DMA
1954 libata.dma=1 PATA and SATA Disk DMA only
1955 libata.dma=2 ATAPI (CDROM) DMA only
1956 libata.dma=4 Compact Flash DMA only
1957 Combinations also work, so libata.dma=3 enables DMA
1958 for disks and CDROMs, but not CFs.
1960 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1961 libata.ignore_hpa=0 keep BIOS limits (default)
1962 libata.ignore_hpa=1 ignore limits, using full disk
1964 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1968 libata.force= [LIBATA] Force configurations. The format is comma
1969 separated list of "[ID:]VAL" where ID is
1970 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1971 matching port, link or device. Basically, it matches
1972 the ATA ID string printed on console by libata. If
1973 the whole ID part is omitted, the last PORT and DEVICE
1974 values are used. If ID hasn't been specified yet, the
1975 configuration applies to all ports, links and devices.
1977 If only DEVICE is omitted, the parameter applies to
1978 the port and all links and devices behind it. DEVICE
1979 number of 0 either selects the first device or the
1980 first fan-out link behind PMP device. It does not
1981 select the host link. DEVICE number of 15 selects the
1982 host link and device attached to it.
1984 The VAL specifies the configuration to force. As long
1985 as there's no ambiguity shortcut notation is allowed.
1986 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1987 The following configurations can be forced.
1989 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1990 Any ID with matching PORT is used.
1992 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1994 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1995 udma[/][16,25,33,44,66,100,133] notation is also
1998 * [no]ncq: Turn on or off NCQ.
2000 * [no]ncqtrim: Turn off queued DSM TRIM.
2002 * nohrst, nosrst, norst: suppress hard, soft
2005 * rstonce: only attempt one reset during
2006 hot-unplug link recovery
2008 * dump_id: dump IDENTIFY data.
2010 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2012 * disable: Disable this device.
2014 If there are multiple matching configurations changing
2015 the same attribute, the last one is used.
2017 memblock=debug [KNL] Enable memblock debug messages.
2019 load_ramdisk= [RAM] List of ramdisks to load from floppy
2020 See Documentation/blockdev/ramdisk.txt.
2022 lockd.nlm_grace_period=P [NFS] Assign grace period.
2025 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2028 lockd.nlm_timeout=T [NFS] Assign timeout value.
2031 lockd.nlm_udpport=M [NFS] Assign UDP port.
2034 locktorture.nreaders_stress= [KNL]
2035 Set the number of locking read-acquisition kthreads.
2036 Defaults to being automatically set based on the
2037 number of online CPUs.
2039 locktorture.nwriters_stress= [KNL]
2040 Set the number of locking write-acquisition kthreads.
2042 locktorture.onoff_holdoff= [KNL]
2043 Set time (s) after boot for CPU-hotplug testing.
2045 locktorture.onoff_interval= [KNL]
2046 Set time (s) between CPU-hotplug operations, or
2047 zero to disable CPU-hotplug testing.
2049 locktorture.shuffle_interval= [KNL]
2050 Set task-shuffle interval (jiffies). Shuffling
2051 tasks allows some CPUs to go into dyntick-idle
2052 mode during the locktorture test.
2054 locktorture.shutdown_secs= [KNL]
2055 Set time (s) after boot system shutdown. This
2056 is useful for hands-off automated testing.
2058 locktorture.stat_interval= [KNL]
2059 Time (s) between statistics printk()s.
2061 locktorture.stutter= [KNL]
2062 Time (s) to stutter testing, for example,
2063 specifying five seconds causes the test to run for
2064 five seconds, wait for five seconds, and so on.
2065 This tests the locking primitive's ability to
2066 transition abruptly to and from idle.
2068 locktorture.torture_type= [KNL]
2069 Specify the locking implementation to test.
2071 locktorture.verbose= [KNL]
2072 Enable additional printk() statements.
2074 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2077 loglevel= All Kernel Messages with a loglevel smaller than the
2078 console loglevel will be printed to the console. It can
2079 also be changed with klogd or other programs. The
2080 loglevels are defined as follows:
2082 0 (KERN_EMERG) system is unusable
2083 1 (KERN_ALERT) action must be taken immediately
2084 2 (KERN_CRIT) critical conditions
2085 3 (KERN_ERR) error conditions
2086 4 (KERN_WARNING) warning conditions
2087 5 (KERN_NOTICE) normal but significant condition
2088 6 (KERN_INFO) informational
2089 7 (KERN_DEBUG) debug-level messages
2091 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2092 in bytes. n must be a power of two and greater
2093 than the minimal size. The minimal size is defined
2094 by LOG_BUF_SHIFT kernel config parameter. There is
2095 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2096 that allows to increase the default size depending on
2097 the number of CPUs. See init/Kconfig for more details.
2099 logo.nologo [FB] Disables display of the built-in Linux logo.
2100 This may be used to provide more screen space for
2101 kernel log messages and is useful when debugging
2102 kernel boot problems.
2104 lp=0 [LP] Specify parallel ports to use, e.g,
2105 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2106 lp=reset first parallel port). 'lp=0' disables the
2107 lp=auto printer driver. 'lp=reset' (which can be
2108 specified in addition to the ports) causes
2109 attached printers to be reset. Using
2110 lp=port1,port2,... specifies the parallel ports
2111 to associate lp devices with, starting with
2112 lp0. A port specification may be 'none' to skip
2113 that lp device, or a parport name such as
2114 'parport0'. Specifying 'lp=auto' instead of a
2115 port specification list means that device IDs
2116 from each port should be examined, to see if
2117 an IEEE 1284-compliant printer is attached; if
2118 so, the driver will manage that printer.
2119 See also header of drivers/char/lp.c.
2122 Sets loops_per_jiffy to given constant, thus avoiding
2123 time-consuming boot-time autodetection (up to 250 ms per
2124 CPU). 0 enables autodetection (default). To determine
2125 the correct value for your kernel, boot with normal
2126 autodetection and see what value is printed. Note that
2127 on SMP systems the preset will be applied to all CPUs,
2128 which is likely to cause problems if your CPUs need
2129 significantly divergent settings. An incorrect value
2130 will cause delays in the kernel to be wrong, leading to
2131 unpredictable I/O errors and other breakage. Although
2132 unlikely, in the extreme case this might damage your
2136 Format: <io>,<irq>,<dma>
2138 machvec= [IA-64] Force the use of a particular machine-vector
2139 (machvec) in a generic kernel.
2140 Example: machvec=hpzx1_swiotlb
2142 machtype= [Loongson] Share the same kernel image file between different
2144 Example: machtype=lemote-yeeloong-2f-7inch
2146 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2147 than or equal to this physical address is ignored.
2149 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2150 will bring up during bootup. maxcpus=n : n >= 0 limits
2151 the kernel to bring up 'n' processors. Surely after
2152 bootup you can bring up the other plugged cpu by executing
2153 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2154 only takes effect during system bootup.
2155 While n=0 is a special case, it is equivalent to "nosmp",
2156 which also disables the IO APIC.
2158 max_loop= [LOOP] The number of loop block devices that get
2159 (loop.max_loop) unconditionally pre-created at init time. The default
2160 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2161 of statically allocating a predefined number, loop
2162 devices can be requested on-demand with the
2163 /dev/loop-control interface.
2165 mce [X86-32] Machine Check Exception
2167 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2169 md= [HW] RAID subsystems devices and level
2170 See Documentation/admin-guide/md.rst.
2173 Format: <first>,<last>
2174 Specifies range of consoles to be captured by the MDA.
2176 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2177 Amount of memory to be used when the kernel is not able
2178 to see the whole system memory or for test.
2179 [X86] Work as limiting max address. Use together
2180 with memmap= to avoid physical address space collisions.
2181 Without memmap= PCI devices could be placed at addresses
2182 belonging to unused RAM.
2184 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2188 [KNL,SH] Allow user to override the default size for
2189 per-device physically contiguous DMA buffers.
2191 memhp_default_state=online/offline
2192 [KNL] Set the initial state for the memory hotplug
2193 onlining policy. If not specified, the default value is
2194 set according to the
2195 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2197 See Documentation/memory-hotplug.txt.
2199 memmap=exactmap [KNL,X86] Enable setting of an exact
2200 E820 memory map, as specified by the user.
2201 Such memmap=exactmap lines can be constructed based on
2202 BIOS output or other requirements. See the memmap=nn@ss
2205 memmap=nn[KMG]@ss[KMG]
2206 [KNL] Force usage of a specific region of memory.
2207 Region of memory to be used is from ss to ss+nn.
2208 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2209 which limits max address to nn[KMG].
2210 Multiple different regions can be specified,
2213 memmap=100M@2G,100M#3G,1G!1024G
2215 memmap=nn[KMG]#ss[KMG]
2216 [KNL,ACPI] Mark specific memory as ACPI data.
2217 Region of memory to be marked is from ss to ss+nn.
2219 memmap=nn[KMG]$ss[KMG]
2220 [KNL,ACPI] Mark specific memory as reserved.
2221 Region of memory to be reserved is from ss to ss+nn.
2222 Example: Exclude memory from 0x18690000-0x1869ffff
2223 memmap=64K$0x18690000
2225 memmap=0x10000$0x18690000
2226 Some bootloaders may need an escape character before '$',
2227 like Grub2, otherwise '$' and the following number
2230 memmap=nn[KMG]!ss[KMG]
2231 [KNL,X86] Mark specific memory as protected.
2232 Region of memory to be used, from ss to ss+nn.
2233 The memory region may be marked as e820 type 12 (0xc)
2234 and is NVDIMM or ADR memory.
2236 memory_corruption_check=0/1 [X86]
2237 Some BIOSes seem to corrupt the first 64k of
2238 memory when doing things like suspend/resume.
2239 Setting this option will scan the memory
2240 looking for corruption. Enabling this will
2241 both detect corruption and prevent the kernel
2242 from using the memory being corrupted.
2243 However, its intended as a diagnostic tool; if
2244 repeatable BIOS-originated corruption always
2245 affects the same memory, you can use memmap=
2246 to prevent the kernel from using that memory.
2248 memory_corruption_check_size=size [X86]
2249 By default it checks for corruption in the low
2250 64k, making this memory unavailable for normal
2251 use. Use this parameter to scan for
2252 corruption in more or less memory.
2254 memory_corruption_check_period=seconds [X86]
2255 By default it checks for corruption every 60
2256 seconds. Use this parameter to check at some
2257 other rate. 0 disables periodic checking.
2259 memtest= [KNL,X86,ARM] Enable memtest
2261 default : 0 <disable>
2262 Specifies the number of memtest passes to be
2263 performed. Each pass selects another test
2264 pattern from a given set of patterns. Memtest
2265 fills the memory with this pattern, validates
2266 memory contents and reserves bad memory
2267 regions that are detected.
2269 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2270 Valid arguments: on, off
2271 Default (depends on kernel configuration option):
2272 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2273 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2274 mem_encrypt=on: Activate SME
2275 mem_encrypt=off: Do not activate SME
2277 Refer to Documentation/x86/amd-memory-encryption.txt
2278 for details on when memory encryption can be activated.
2280 mem_sleep_default= [SUSPEND] Default system suspend mode:
2281 s2idle - Suspend-To-Idle
2282 shallow - Power-On Suspend or equivalent (if supported)
2283 deep - Suspend-To-RAM or equivalent (if supported)
2284 See Documentation/admin-guide/pm/sleep-states.rst.
2286 meye.*= [HW] Set MotionEye Camera parameters
2287 See Documentation/media/v4l-drivers/meye.rst.
2289 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2290 Multi-Function General Purpose Timers on AMD Geode
2293 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2294 the BIOS has incorrectly applied a workaround. TinyBIOS
2295 version 0.98 is known to be affected, 0.99 fixes the
2296 problem by letting the user disable the workaround.
2300 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2301 physical address is ignored.
2303 mini2440= [ARM,HW,KNL]
2304 Format:[0..2][b][c][t]
2306 MINI2440 configuration specification:
2307 0 - The attached screen is the 3.5" TFT
2308 1 - The attached screen is the 7" TFT
2309 2 - The VGA Shield is attached (1024x768)
2310 Leaving out the screen size parameter will not load
2311 the TFT driver, and the framebuffer will be left
2313 b - Enable backlight. The TFT backlight pin will be
2314 linked to the kernel VESA blanking code and a GPIO
2315 LED. This parameter is not necessary when using the
2317 c - Enable the s3c camera interface.
2318 t - Reserved for enabling touchscreen support. The
2319 touchscreen support is not enabled in the mainstream
2320 kernel as of 2.6.30, a preliminary port can be found
2321 in the "bleeding edge" mini2440 support kernel at
2322 http://repo.or.cz/w/linux-2.6/mini2440.git
2325 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2326 parameter allows control of the logging verbosity for
2327 the additional memory initialisation checks. A value
2328 of 0 disables mminit logging and a level of 4 will
2329 log everything. Information is printed at KERN_DEBUG
2330 so loglevel=8 may also need to be specified.
2333 [KNL] When CONFIG_MODULE_SIG is set, this means that
2334 modules without (valid) signatures will fail to load.
2335 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2336 is always true, so this option does nothing.
2338 module_blacklist= [KNL] Do not load a comma-separated list of
2339 modules. Useful for debugging problem modules.
2342 [MOUSE] Maximum time between finger touching and
2343 leaving touchpad surface for touch to be considered
2344 a tap and be reported as a left button click (for
2345 touchpads working in absolute mode only).
2347 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2348 reporting absolute coordinates, such as tablets
2349 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2350 reporting absolute coordinates, such as tablets
2352 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2353 is similar to kernelcore except it specifies the
2354 amount of memory used for migratable allocations.
2355 If both kernelcore and movablecore is specified,
2356 then kernelcore will be at *least* the specified
2357 value but may be more. If movablecore on its own
2358 is specified, the administrator must be careful
2359 that the amount of memory usable for all allocations
2362 movable_node [KNL] Boot-time switch to make hotplugable memory
2363 NUMA nodes to be movable. This means that the memory
2364 of such nodes will be usable only for movable
2365 allocations which rules out almost all kernel
2366 allocations. Use with caution!
2368 MTD_Partition= [MTD]
2369 Format: <name>,<region-number>,<size>,<offset>
2371 MTD_Region= [MTD] Format:
2372 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2375 See drivers/mtd/cmdlinepart.c.
2377 multitce=off [PPC] This parameter disables the use of the pSeries
2378 firmware feature for updating multiple TCE entries
2381 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2383 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2385 boundary - index of last SLC block on Flex-OneNAND.
2386 The remaining blocks are configured as MLC blocks.
2387 lock - Configure if Flex-OneNAND boundary should be locked.
2388 Once locked, the boundary cannot be changed.
2389 1 indicates lock status, 0 indicates unlock status.
2392 ARM/S3C2412 JIVE boot control
2394 See arch/arm/mach-s3c2412/mach-jive.c
2396 mtouchusb.raw_coordinates=
2397 [HW] Make the MicroTouch USB driver use raw coordinates
2398 ('y', default) or cooked coordinates ('n')
2400 mtrr_chunk_size=nn[KMG] [X86]
2401 used for mtrr cleanup. It is largest continuous chunk
2402 that could hold holes aka. UC entries.
2404 mtrr_gran_size=nn[KMG] [X86]
2405 Used for mtrr cleanup. It is granularity of mtrr block.
2407 Large value could prevent small alignment from
2410 mtrr_spare_reg_nr=n [X86]
2412 Range: 0,7 : spare reg number
2414 Used for mtrr cleanup. It is spare mtrr entries number.
2415 Set to 2 or more if your graphical card needs more.
2417 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2419 netdev= [NET] Network devices parameters
2420 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2421 Note that mem_start is often overloaded to mean
2422 something different and driver-specific.
2423 This usage is only documented in each driver source
2427 [NETFILTER] Enable connection tracking flow accounting
2428 0 to disable accounting
2429 1 to enable accounting
2432 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2433 See Documentation/filesystems/nfs/nfsroot.txt.
2435 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2436 See Documentation/filesystems/nfs/nfsroot.txt.
2438 nfsrootdebug [NFS] enable nfsroot debugging messages.
2439 See Documentation/filesystems/nfs/nfsroot.txt.
2441 nfs.callback_nr_threads=
2442 [NFSv4] set the total number of threads that the
2443 NFS client will assign to service NFSv4 callback
2446 nfs.callback_tcpport=
2447 [NFS] set the TCP port on which the NFSv4 callback
2448 channel should listen.
2451 [NFS] sets the pathname to the program which is used
2452 to update the NFS client cache entries.
2454 nfs.cache_getent_timeout=
2455 [NFS] sets the timeout after which an attempt to
2456 update a cache entry is deemed to have failed.
2458 nfs.idmap_cache_timeout=
2459 [NFS] set the maximum lifetime for idmapper cache
2463 [NFS] enable 64-bit inode numbers.
2464 If zero, the NFS client will fake up a 32-bit inode
2465 number for the readdir() and stat() syscalls instead
2466 of returning the full 64-bit number.
2467 The default is to return 64-bit inode numbers.
2469 nfs.max_session_cb_slots=
2470 [NFSv4.1] Sets the maximum number of session
2471 slots the client will assign to the callback
2472 channel. This determines the maximum number of
2473 callbacks the client will process in parallel for
2474 a particular server.
2476 nfs.max_session_slots=
2477 [NFSv4.1] Sets the maximum number of session slots
2478 the client will attempt to negotiate with the server.
2479 This limits the number of simultaneous RPC requests
2480 that the client can send to the NFSv4.1 server.
2481 Note that there is little point in setting this
2482 value higher than the max_tcp_slot_table_limit.
2484 nfs.nfs4_disable_idmapping=
2485 [NFSv4] When set to the default of '1', this option
2486 ensures that both the RPC level authentication
2487 scheme and the NFS level operations agree to use
2488 numeric uids/gids if the mount is using the
2489 'sec=sys' security flavour. In effect it is
2490 disabling idmapping, which can make migration from
2491 legacy NFSv2/v3 systems to NFSv4 easier.
2492 Servers that do not support this mode of operation
2493 will be autodetected by the client, and it will fall
2494 back to using the idmapper.
2495 To turn off this behaviour, set the value to '0'.
2497 [NFS4] Specify an additional fixed unique ident-
2498 ification string that NFSv4 clients can insert into
2499 their nfs_client_id4 string. This is typically a
2500 UUID that is generated at system install time.
2502 nfs.send_implementation_id =
2503 [NFSv4.1] Send client implementation identification
2504 information in exchange_id requests.
2505 If zero, no implementation identification information
2507 The default is to send the implementation identification
2510 nfs.recover_lost_locks =
2511 [NFSv4] Attempt to recover locks that were lost due
2512 to a lease timeout on the server. Please note that
2513 doing this risks data corruption, since there are
2514 no guarantees that the file will remain unchanged
2515 after the locks are lost.
2516 If you want to enable the kernel legacy behaviour of
2517 attempting to recover these locks, then set this
2519 The default parameter value of '0' causes the kernel
2520 not to attempt recovery of lost locks.
2522 nfs4.layoutstats_timer =
2523 [NFSv4.2] Change the rate at which the kernel sends
2524 layoutstats to the pNFS metadata server.
2526 Setting this to value to 0 causes the kernel to use
2527 whatever value is the default set by the layout
2528 driver. A non-zero value sets the minimum interval
2529 in seconds between layoutstats transmissions.
2531 nfsd.nfs4_disable_idmapping=
2532 [NFSv4] When set to the default of '1', the NFSv4
2533 server will return only numeric uids and gids to
2534 clients using auth_sys, and will accept numeric uids
2535 and gids from such clients. This is intended to ease
2536 migration from NFSv2/v3.
2538 nmi_debug= [KNL,SH] Specify one or more actions to take
2539 when a NMI is triggered.
2540 Format: [state][,regs][,debounce][,die]
2542 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2543 Format: [panic,][nopanic,][num]
2545 0 - turn hardlockup detector in nmi_watchdog off
2546 1 - turn hardlockup detector in nmi_watchdog on
2547 When panic is specified, panic when an NMI watchdog
2548 timeout occurs (or 'nopanic' to override the opposite
2549 default). To disable both hard and soft lockup detectors,
2550 please see 'nowatchdog'.
2551 This is useful when you use a panic=... timeout and
2552 need the box quickly up again.
2554 These settings can be accessed at runtime via
2555 the nmi_watchdog and hardlockup_panic sysctls.
2557 netpoll.carrier_timeout=
2558 [NET] Specifies amount of time (in seconds) that
2559 netpoll should wait for a carrier. By default netpoll
2562 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2563 emulation library even if a 387 maths coprocessor
2567 [HW] Never suspend the console
2568 Disable suspending of consoles during suspend and
2569 hibernate operations. Once disabled, debugging
2570 messages can reach various consoles while the rest
2571 of the system is being put to sleep (ie, while
2572 debugging driver suspend/resume hooks). This may
2573 not work reliably with all consoles, but is known
2574 to work with serial and VGA consoles.
2575 To facilitate more flexible debugging, we also add
2576 console_suspend, a printk module parameter to control
2577 it. Users could use console_suspend (usually
2578 /sys/module/printk/parameters/console_suspend) to
2579 turn on/off it dynamically.
2581 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2582 caches in the slab allocator. Saves per-node memory,
2583 but will impact performance.
2587 noaltinstr [S390] Disables alternative instructions patching
2588 (CPU alternatives feature).
2590 noapic [SMP,APIC] Tells the kernel to not make use of any
2591 IOAPICs that may be present in the system.
2593 noautogroup Disable scheduler automatic task group creation.
2595 nobats [PPC] Do not use BATs for mapping kernel lowmem
2596 on "Classic" PPC cores.
2600 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2602 nodelayacct [KNL] Disable per-task delay accounting
2604 nodsp [SH] Disable hardware DSP at boot time.
2606 noefi Disable EFI runtime services support.
2611 On X86-32 available only on PAE configured kernels.
2612 noexec=on: enable non-executable mappings (default)
2613 noexec=off: disable non-executable mappings
2616 Disable SMAP (Supervisor Mode Access Prevention)
2617 even if it is supported by processor.
2620 Disable SMEP (Supervisor Mode Execution Prevention)
2621 even if it is supported by processor.
2624 This affects only 32-bit executables.
2625 noexec32=on: enable non-executable mappings (default)
2626 read doesn't imply executable mappings
2627 noexec32=off: disable non-executable mappings
2628 read implies executable mappings
2630 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2632 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2633 register save and restore. The kernel will only save
2634 legacy floating-point registers on task switch.
2636 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2638 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2639 Equivalent to smt=1.
2641 nospectre_v2 [X86] Disable all mitigations for the Spectre variant 2
2642 (indirect branch prediction) vulnerability. System may
2643 allow data leaks with this option, which is equivalent
2646 noxsave [BUGS=X86] Disables x86 extended register state save
2647 and restore using xsave. The kernel will fallback to
2648 enabling legacy floating-point and sse state.
2650 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2651 register states. The kernel will fall back to use
2652 xsave to save the states. By using this parameter,
2653 performance of saving the states is degraded because
2654 xsave doesn't support modified optimization while
2655 xsaveopt supports it on xsaveopt enabled systems.
2657 noxsaves [X86] Disables xsaves and xrstors used in saving and
2658 restoring x86 extended register state in compacted
2659 form of xsave area. The kernel will fall back to use
2660 xsaveopt and xrstor to save and restore the states
2661 in standard form of xsave area. By using this
2662 parameter, xsave area per process might occupy more
2663 memory on xsaves enabled systems.
2665 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2666 wfi(ARM) instruction doesn't work correctly and not to
2667 use it. This is also useful when using JTAG debugger.
2669 no_file_caps Tells the kernel not to honor file capabilities. The
2670 only way then for a file to be executed with privilege
2671 is to be setuid root or executed by root.
2673 nohalt [IA-64] Tells the kernel not to use the power saving
2674 function PAL_HALT_LIGHT when idle. This increases
2675 power-consumption. On the positive side, it reduces
2676 interrupt wake-up latency, which may improve performance
2677 in certain environments such as networked servers or
2680 nohibernate [HIBERNATION] Disable hibernation and resume.
2682 nohz= [KNL] Boottime enable/disable dynamic ticks
2683 Valid arguments: on, off
2686 nohz_full= [KNL,BOOT,SMP,ISOL]
2687 The argument is a cpu list, as described above.
2688 In kernels built with CONFIG_NO_HZ_FULL=y, set
2689 the specified list of CPUs whose tick will be stopped
2690 whenever possible. The boot CPU will be forced outside
2691 the range to maintain the timekeeping. Any CPUs
2692 in this list will have their RCU callbacks offloaded,
2693 just as if they had also been called out in the
2694 rcu_nocbs= boot parameter.
2696 noiotrap [SH] Disables trapped I/O port accesses.
2698 noirqdebug [X86-32] Disables the code which attempts to detect and
2699 disable unhandled interrupt sources.
2701 no_timer_check [X86,APIC] Disables the code which tests for
2702 broken timer IRQ sources.
2704 noisapnp [ISAPNP] Disables ISA PnP code.
2706 noinitrd [RAM] Tells the kernel not to load any configured
2709 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2711 [Deprecated - use intremap=off]
2715 noinvpcid [X86] Disable the INVPCID cpu feature.
2717 nojitter [IA-64] Disables jitter checking for ITC timers.
2719 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2721 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2725 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2726 clock and use the default one.
2728 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2729 steal time is computed, but won't influence scheduler
2732 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2734 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2736 noltlbs [PPC] Do not use large page/tlb entries for kernel
2737 lowmem mapping on PPC40x and PPC8xx
2739 nomca [IA-64] Disable machine check abort handling
2741 nomce [X86-32] Disable Machine Check Exception
2743 nomfgpt [X86-32] Disable Multi-Function General Purpose
2744 Timer usage (for AMD Geode machines).
2746 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2747 shutdown the other cpus. Instead use the REBOOT_VECTOR
2750 nomodule Disable module load
2752 nopat [X86] Disable PAT (page attribute table extension of
2753 pagetables) support.
2755 nopcid [X86-64] Disable the PCID cpu feature.
2757 norandmaps Don't use address space randomization. Equivalent to
2758 echo 0 > /proc/sys/kernel/randomize_va_space
2760 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2761 with UP alternatives
2763 nordrand [X86] Disable kernel use of the RDRAND and
2764 RDSEED instructions even if they are supported
2765 by the processor. RDRAND and RDSEED are still
2766 available to user space applications.
2768 noresume [SWSUSP] Disables resume and restores original swap
2771 no-scroll [VGA] Disables scrollback.
2772 This is required for the Braillex ib80-piezo Braille
2773 reader made by F.H. Papenmeier (Germany).
2777 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2779 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2780 and disable the IO APIC. legacy for "maxcpus=0".
2782 nosoftlockup [KNL] Disable the soft-lockup detector.
2784 nosync [HW,M68K] Disables sync negotiation for all devices.
2786 notsc [BUGS=X86-32] Disable Time Stamp Counter
2788 nowatchdog [KNL] Disable both lockup detectors, i.e.
2789 soft-lockup and NMI watchdog (hard-lockup).
2793 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2795 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2796 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2797 Some features depend on CPU0. Known dependencies are:
2798 1. Resume from suspend/hibernate depends on CPU0.
2799 Suspend/hibernate will fail if CPU0 is offline and you
2800 need to online CPU0 before suspend/hibernate.
2801 2. PIC interrupts also depend on CPU0. CPU0 can't be
2802 removed if a PIC interrupt is detected.
2803 It's said poweroff/reboot may depend on CPU0 on some
2804 machines although I haven't seen such issues so far
2805 after CPU0 is offline on a few tested machines.
2806 If the dependencies are under your control, you can
2807 turn on cpu0_hotplug.
2809 nps_mtm_hs_ctr= [KNL,ARC]
2810 This parameter sets the maximum duration, in
2811 cycles, each HW thread of the CTOP can run
2812 without interruptions, before HW switches it.
2813 The actual maximum duration is 16 times this
2815 Format: integer between 1 and 255
2818 nptcg= [IA-64] Override max number of concurrent global TLB
2819 purges which is reported from either PAL_VM_SUMMARY or
2822 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2823 could support. nr_cpus=n : n >= 1 limits the kernel to
2824 support 'n' processors. It could be larger than the
2825 number of already plugged CPU during bootup, later in
2826 runtime you can physically add extra cpu until it reaches
2827 n. So during boot up some boot time memory for per-cpu
2828 variables need be pre-allocated for later physical cpu
2831 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2833 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2834 Allowed values are enable and disable
2836 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2837 'node', 'default' can be specified
2838 This can be set from sysctl after boot.
2839 See Documentation/sysctl/vm.txt for details.
2841 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2842 See Documentation/debugging-via-ohci1394.txt for more
2845 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2846 Rather than timing out after 20 ms if an EC
2847 command is not properly ACKed, override the length
2848 of the timeout. We have interrupts disabled while
2849 waiting for the ACK, so if this is set too high
2850 interrupts *may* be lost!
2852 omap_mux= [OMAP] Override bootloader pin multiplexing.
2853 Format: <mux_mode0.mode_name=value>...
2854 For example, to override I2C bus2:
2855 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2857 oprofile.timer= [HW]
2858 Use timer interrupt instead of performance counters
2860 oprofile.cpu_type= Force an oprofile cpu type
2861 This might be useful if you have an older oprofile
2862 userland or if you want common events.
2863 Format: { arch_perfmon }
2864 arch_perfmon: [X86] Force use of architectural
2865 perfmon on Intel CPUs instead of the
2866 CPU specific event set.
2867 timer: [X86] Force use of architectural NMI
2868 timer mode (see also oprofile.timer
2869 for generic hr timer mode)
2871 oops=panic Always panic on oopses. Default is to just kill the
2872 process, but there is a small probability of
2873 deadlocking the machine.
2874 This will also cause panics on machine check exceptions.
2875 Useful together with panic=30 to trigger a reboot.
2878 See Documentation/sound/oss/oss-parameters.txt
2880 page_owner= [KNL] Boot-time page_owner enabling option.
2881 Storage of the information about who allocated
2882 each page is disabled in default. With this switch,
2884 on: enable the feature
2886 page_poison= [KNL] Boot-time parameter changing the state of
2887 poisoning on the buddy allocator.
2888 off: turn off poisoning
2889 on: turn on poisoning
2891 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2892 timeout > 0: seconds before rebooting
2893 timeout = 0: wait forever
2894 timeout < 0: reboot immediately
2897 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2900 crash_kexec_post_notifiers
2901 Run kdump after running panic-notifiers and dumping
2902 kmsg. This only for the users who doubt kdump always
2903 succeeds in any situation.
2904 Note that this also increases risks of kdump failure,
2905 because some panic notifiers can make the crashed
2906 kernel more unstable.
2908 parkbd.port= [HW] Parallel port number the keyboard adapter is
2909 connected to, default is 0.
2911 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2912 0 for XT, 1 for AT (default is AT).
2915 parport= [HW,PPT] Specify parallel ports. 0 disables.
2916 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2917 Use 'auto' to force the driver to use any
2918 IRQ/DMA settings detected (the default is to
2919 ignore detected IRQ/DMA settings because of
2920 possible conflicts). You can specify the base
2921 address, IRQ, and DMA settings; IRQ and DMA
2922 should be numbers, or 'auto' (for using detected
2923 settings on that particular port), or 'nofifo'
2924 (to avoid using a FIFO even if it is detected).
2925 Parallel ports are assigned in the order they
2926 are specified on the command line, starting
2929 parport_init_mode= [HW,PPT]
2930 Configure VIA parallel port to operate in
2931 a specific mode. This is necessary on Pegasos
2932 computer where firmware has no options for setting
2933 up parallel port mode and sets it to spp.
2934 Currently this function knows 686a and 8231 chips.
2935 Format: [spp|ps2|epp|ecp|ecpepp]
2938 Halt all CPUs after the first oops has been printed for
2939 the specified number of seconds. This is to be used if
2940 your oopses keep scrolling off the screen.
2945 See header of drivers/block/paride/pcd.c.
2946 See also Documentation/blockdev/paride.txt.
2948 pci=option[,option...] [PCI] various PCI subsystem options:
2949 earlydump [X86] dump PCI config space before the kernel
2951 off [X86] don't probe for the PCI bus
2952 bios [X86-32] force use of PCI BIOS, don't access
2953 the hardware directly. Use this if your machine
2954 has a non-standard PCI host bridge.
2955 nobios [X86-32] disallow use of PCI BIOS, only direct
2956 hardware access methods are allowed. Use this
2957 if you experience crashes upon bootup and you
2958 suspect they are caused by the BIOS.
2959 conf1 [X86] Force use of PCI Configuration Access
2960 Mechanism 1 (config address in IO port 0xCF8,
2961 data in IO port 0xCFC, both 32-bit).
2962 conf2 [X86] Force use of PCI Configuration Access
2963 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2964 the function, IO port 0xCFA, also 8-bit, sets
2965 bus number. The config space is then accessed
2966 through ports 0xC000-0xCFFF).
2967 See http://wiki.osdev.org/PCI for more info
2968 on the configuration access mechanisms.
2969 noaer [PCIE] If the PCIEAER kernel config parameter is
2970 enabled, this kernel boot option can be used to
2971 disable the use of PCIE advanced error reporting.
2972 nodomains [PCI] Disable support for multiple PCI
2973 root domains (aka PCI segments, in ACPI-speak).
2974 nommconf [X86] Disable use of MMCONFIG for PCI
2976 check_enable_amd_mmconf [X86] check for and enable
2977 properly configured MMIO access to PCI
2978 config space on AMD family 10h CPU
2979 nomsi [MSI] If the PCI_MSI kernel config parameter is
2980 enabled, this kernel boot option can be used to
2981 disable the use of MSI interrupts system-wide.
2982 noioapicquirk [APIC] Disable all boot interrupt quirks.
2983 Safety option to keep boot IRQs enabled. This
2984 should never be necessary.
2985 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2986 primary IO-APIC for bridges that cannot disable
2987 boot IRQs. This fixes a source of spurious IRQs
2988 when the system masks IRQs.
2989 noioapicreroute [APIC] Disable workaround that uses the
2990 boot IRQ equivalent of an IRQ that connects to
2991 a chipset where boot IRQs cannot be disabled.
2992 The opposite of ioapicreroute.
2993 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2994 routing table. These calls are known to be buggy
2995 on several machines and they hang the machine
2996 when used, but on other computers it's the only
2997 way to get the interrupt routing table. Try
2998 this option if the kernel is unable to allocate
2999 IRQs or discover secondary PCI buses on your
3001 rom [X86] Assign address space to expansion ROMs.
3002 Use with caution as certain devices share
3003 address decoders between ROMs and other
3005 norom [X86] Do not assign address space to
3006 expansion ROMs that do not already have
3007 BIOS assigned address ranges.
3008 nobar [X86] Do not assign address space to the
3009 BARs that weren't assigned by the BIOS.
3010 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3011 assigned automatically to PCI devices. You can
3012 make the kernel exclude IRQs of your ISA cards
3014 pirqaddr=0xAAAAA [X86] Specify the physical address
3015 of the PIRQ table (normally generated
3016 by the BIOS) if it is outside the
3017 F0000h-100000h range.
3018 lastbus=N [X86] Scan all buses thru bus #N. Can be
3019 useful if the kernel is unable to find your
3020 secondary buses and you want to tell it
3021 explicitly which ones they are.
3022 assign-busses [X86] Always assign all PCI bus
3023 numbers ourselves, overriding
3024 whatever the firmware may have done.
3025 usepirqmask [X86] Honor the possible IRQ mask stored
3026 in the BIOS $PIR table. This is needed on
3027 some systems with broken BIOSes, notably
3028 some HP Pavilion N5400 and Omnibook XE3
3029 notebooks. This will have no effect if ACPI
3030 IRQ routing is enabled.
3031 noacpi [X86] Do not use ACPI for IRQ routing
3032 or for PCI scanning.
3033 use_crs [X86] Use PCI host bridge window information
3034 from ACPI. On BIOSes from 2008 or later, this
3035 is enabled by default. If you need to use this,
3036 please report a bug.
3037 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3038 If you need to use this, please report a bug.
3039 routeirq Do IRQ routing for all PCI devices.
3040 This is normally done in pci_enable_device(),
3041 so this option is a temporary workaround
3042 for broken drivers that don't call it.
3043 skip_isa_align [X86] do not align io start addr, so can
3044 handle more pci cards
3045 noearly [X86] Don't do any early type 1 scanning.
3046 This might help on some broken boards which
3047 machine check when some devices' config space
3048 is read. But various workarounds are disabled
3049 and some IOMMU drivers will not work.
3050 bfsort Sort PCI devices into breadth-first order.
3051 This sorting is done to get a device
3052 order compatible with older (<= 2.4) kernels.
3053 nobfsort Don't sort PCI devices into breadth-first order.
3054 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3055 tuning and use the BIOS-configured MPS defaults.
3056 pcie_bus_safe Set every device's MPS to the largest value
3057 supported by all devices below the root complex.
3058 pcie_bus_perf Set device MPS to the largest allowable MPS
3059 based on its parent bus. Also set MRRS (Max
3060 Read Request Size) to the largest supported
3061 value (no larger than the MPS that the device
3062 or bus can support) for best performance.
3063 pcie_bus_peer2peer Set every device's MPS to 128B, which
3064 every device is guaranteed to support. This
3065 configuration allows peer-to-peer DMA between
3066 any pair of devices, possibly at the cost of
3067 reduced performance. This also guarantees
3068 that hot-added devices will work.
3069 cbiosize=nn[KMG] The fixed amount of bus space which is
3070 reserved for the CardBus bridge's IO window.
3071 The default value is 256 bytes.
3072 cbmemsize=nn[KMG] The fixed amount of bus space which is
3073 reserved for the CardBus bridge's memory
3074 window. The default value is 64 megabytes.
3077 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3078 [<order of align>@]pci:<vendor>:<device>\
3079 [:<subvendor>:<subdevice>][; ...]
3080 Specifies alignment and device to reassign
3081 aligned memory resources.
3082 If <order of align> is not specified,
3083 PAGE_SIZE is used as alignment.
3084 PCI-PCI bridge can be specified, if resource
3085 windows need to be expanded.
3086 To specify the alignment for several
3087 instances of a device, the PCI vendor,
3088 device, subvendor, and subdevice may be
3089 specified, e.g., 4096@pci:8086:9c22:103c:198f
3090 ecrc= Enable/disable PCIe ECRC (transaction layer
3091 end-to-end CRC checking).
3092 bios: Use BIOS/firmware settings. This is the
3096 hpiosize=nn[KMG] The fixed amount of bus space which is
3097 reserved for hotplug bridge's IO window.
3098 Default size is 256 bytes.
3099 hpmemsize=nn[KMG] The fixed amount of bus space which is
3100 reserved for hotplug bridge's memory window.
3101 Default size is 2 megabytes.
3102 hpbussize=nn The minimum amount of additional bus numbers
3103 reserved for buses below a hotplug bridge.
3105 realloc= Enable/disable reallocating PCI bridge resources
3106 if allocations done by BIOS are too small to
3107 accommodate resources required by all child
3109 off: Turn realloc off
3111 realloc same as realloc=on
3112 noari do not use PCIe ARI.
3113 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3114 only look for one device below a PCIe downstream
3116 big_root_window Try to add a big 64bit memory window to the PCIe
3117 root complex on AMD CPUs. Some GFX hardware
3118 can resize a BAR to allow access to all VRAM.
3119 Adding the window is slightly risky (it may
3120 conflict with unreported devices), so this
3123 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3126 force Enable ASPM even on devices that claim not to support it.
3127 WARNING: Forcing ASPM on may cause system lockups.
3129 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3130 nomsi Do not use MSI for PCI Express Native Hotplug (this
3131 makes all PCIe ports use INTx for hotplug services).
3133 pcie_ports= [PCIE] PCIe ports handling:
3134 auto Ask the BIOS whether or not to use native PCIe services
3135 associated with PCIe ports (PME, hot-plug, AER). Use
3136 them only if that is allowed by the BIOS.
3137 native Use native PCIe services associated with PCIe ports
3139 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3142 pcie_port_pm= [PCIE] PCIe port power management handling:
3143 off Disable power management of all PCIe ports
3144 force Forcibly enable power management of all PCIe ports
3146 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3147 nomsi Do not use MSI for native PCIe PME signaling (this makes
3148 all PCIe root ports use INTx for all services).
3150 pcmv= [HW,PCMCIA] BadgePAD 4
3154 Keep all power-domains already enabled by bootloader on,
3155 even if no driver has claimed them. This is useful
3156 for debug and development, but should not be
3157 needed on a platform with proper driver support.
3160 See Documentation/blockdev/paride.txt.
3162 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3165 See arch/parisc/kernel/pdc_chassis.c
3167 percpu_alloc= Select which percpu first chunk allocator to use.
3168 Currently supported values are "embed" and "page".
3169 Archs may support subset or none of the selections.
3170 See comments in mm/percpu.c for details on each
3171 allocator. This parameter is primarily for debugging
3172 and performance comparison.
3175 See Documentation/blockdev/paride.txt.
3178 See Documentation/blockdev/paride.txt.
3180 pirq= [SMP,APIC] Manual mp-table setup
3181 See Documentation/x86/i386/IO-APIC.txt.
3183 plip= [PPT,NET] Parallel port network link
3184 Format: { parport<nr> | timid | 0 }
3185 See also Documentation/admin-guide/parport.rst.
3187 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3188 Override pmtimer IOPort with a hex value.
3192 Enable PNP debug messages (depends on the
3193 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3194 via /sys/module/pnp/parameters/debug. We always show
3195 current resource usage; turning this on also shows
3196 possible settings and some assignment information.
3202 { on | off | curr | res | no-curr | no-res }
3205 [ISAPNP] Exclude IRQs for the autoconfiguration
3208 [ISAPNP] Exclude DMAs for the autoconfiguration
3210 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3211 Ranges are in pairs (I/O port base and size).
3214 [ISAPNP] Exclude memory regions for the
3216 Ranges are in pairs (memory base and size).
3218 ports= [IP_VS_FTP] IPVS ftp helper module
3220 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3222 Format: <port>,<port>....
3224 powersave=off [PPC] This option disables power saving features.
3225 It specifically disables cpuidle and sets the
3226 platform machine description specific power_save
3227 function to NULL. On Idle the CPU just reduces
3230 ppc_strict_facility_enable
3231 [PPC] This option catches any kernel floating point,
3232 Altivec, VSX and SPE outside of regions specifically
3233 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3234 There is some performance impact when enabling this.
3238 Disable Hardware Transactional Memory
3240 print-fatal-signals=
3241 [KNL] debug: print fatal signals
3243 If enabled, warn about various signal handling
3244 related application anomalies: too many signals,
3245 too many POSIX.1 timers, fatal signals causing a
3248 If you hit the warning due to signal overflow,
3249 you might want to try "ulimit -i unlimited".
3253 printk.always_kmsg_dump=
3254 Trigger kmsg_dump for cases other than kernel oops or
3256 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3259 printk.devkmsg={on,off,ratelimit}
3260 Control writing to /dev/kmsg.
3261 on - unlimited logging to /dev/kmsg from userspace
3262 off - logging to /dev/kmsg disabled
3263 ratelimit - ratelimit the logging
3266 printk.time= Show timing data prefixed to each printk message line
3267 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3269 processor.max_cstate= [HW,ACPI]
3270 Limit processor to maximum C-state
3271 max_cstate=9 overrides any DMI blacklist limit.
3273 processor.nocst [HW,ACPI]
3274 Ignore the _CST method to determine C-states,
3275 instead using the legacy FADT method
3277 profile= [KNL] Enable kernel profiling via /proc/profile
3278 Format: [<profiletype>,]<number>
3279 Param: <profiletype>: "schedule", "sleep", or "kvm"
3280 [defaults to kernel profiling]
3281 Param: "schedule" - profile schedule points.
3282 Param: "sleep" - profile D-state sleeping (millisecs).
3283 Requires CONFIG_SCHEDSTATS
3284 Param: "kvm" - profile VM exits.
3285 Param: <number> - step/bucket size as a power of 2 for
3286 statistical time based profiling.
3288 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3290 See Documentation/blockdev/ramdisk.txt.
3292 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3293 probe for; one of (bare|imps|exps|lifebook|any).
3294 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3296 psmouse.resetafter= [HW,MOUSE]
3297 Try to reset the device after so many bad packets
3300 [HW,MOUSE] Set desired mouse resolution, in dpi.
3301 psmouse.smartscroll=
3302 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3303 0 = disabled, 1 = enabled (default).
3305 pstore.backend= Specify the name of the pstore backend to use
3308 See Documentation/blockdev/paride.txt.
3310 pti= [X86_64] Control Page Table Isolation of user and
3311 kernel address spaces. Disabling this feature
3312 removes hardening, but improves performance of
3313 system calls and interrupts.
3315 on - unconditionally enable
3316 off - unconditionally disable
3317 auto - kernel detects whether your CPU model is
3318 vulnerable to issues that PTI mitigates
3320 Not specifying this option is equivalent to pti=auto.
3323 Equivalent to pti=off
3326 [KNL] Number of legacy pty's. Overwrites compiled-in
3329 quiet [KNL] Disable most log messages
3334 See Documentation/admin-guide/md.rst.
3336 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3337 See Documentation/blockdev/ramdisk.txt.
3339 ras=option[,option,...] [KNL] RAS-specific options
3342 Disable the Correctable Errors Collector,
3343 see CONFIG_RAS_CEC help text.
3346 The argument is a cpu list, as described above.
3348 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3349 the specified list of CPUs to be no-callback CPUs.
3350 Invocation of these CPUs' RCU callbacks will
3351 be offloaded to "rcuox/N" kthreads created for
3352 that purpose, where "x" is "b" for RCU-bh, "p"
3353 for RCU-preempt, and "s" for RCU-sched, and "N"
3354 is the CPU number. This reduces OS jitter on the
3355 offloaded CPUs, which can be useful for HPC and
3356 real-time workloads. It can also improve energy
3357 efficiency for asymmetric multiprocessors.
3360 Rather than requiring that offloaded CPUs
3361 (specified by rcu_nocbs= above) explicitly
3362 awaken the corresponding "rcuoN" kthreads,
3363 make these kthreads poll for callbacks.
3364 This improves the real-time response for the
3365 offloaded CPUs by relieving them of the need to
3366 wake up the corresponding kthread, but degrades
3367 energy efficiency by requiring that the kthreads
3368 periodically wake up to do the polling.
3370 rcutree.blimit= [KNL]
3371 Set maximum number of finished RCU callbacks to
3372 process in one batch.
3374 rcutree.dump_tree= [KNL]
3375 Dump the structure of the rcu_node combining tree
3376 out at early boot. This is used for diagnostic
3377 purposes, to verify correct tree setup.
3379 rcutree.gp_cleanup_delay= [KNL]
3380 Set the number of jiffies to delay each step of
3381 RCU grace-period cleanup.
3383 rcutree.gp_init_delay= [KNL]
3384 Set the number of jiffies to delay each step of
3385 RCU grace-period initialization.
3387 rcutree.gp_preinit_delay= [KNL]
3388 Set the number of jiffies to delay each step of
3389 RCU grace-period pre-initialization, that is,
3390 the propagation of recent CPU-hotplug changes up
3391 the rcu_node combining tree.
3393 rcutree.rcu_fanout_exact= [KNL]
3394 Disable autobalancing of the rcu_node combining
3395 tree. This is used by rcutorture, and might
3396 possibly be useful for architectures having high
3397 cache-to-cache transfer latencies.
3399 rcutree.rcu_fanout_leaf= [KNL]
3400 Change the number of CPUs assigned to each
3401 leaf rcu_node structure. Useful for very
3402 large systems, which will choose the value 64,
3403 and for NUMA systems with large remote-access
3404 latencies, which will choose a value aligned
3405 with the appropriate hardware boundaries.
3407 rcutree.jiffies_till_sched_qs= [KNL]
3408 Set required age in jiffies for a
3409 given grace period before RCU starts
3410 soliciting quiescent-state help from
3411 rcu_note_context_switch().
3413 rcutree.jiffies_till_first_fqs= [KNL]
3414 Set delay from grace-period initialization to
3415 first attempt to force quiescent states.
3416 Units are jiffies, minimum value is zero,
3417 and maximum value is HZ.
3419 rcutree.jiffies_till_next_fqs= [KNL]
3420 Set delay between subsequent attempts to force
3421 quiescent states. Units are jiffies, minimum
3422 value is one, and maximum value is HZ.
3424 rcutree.kthread_prio= [KNL,BOOT]
3425 Set the SCHED_FIFO priority of the RCU per-CPU
3426 kthreads (rcuc/N). This value is also used for
3427 the priority of the RCU boost threads (rcub/N)
3428 and for the RCU grace-period kthreads (rcu_bh,
3429 rcu_preempt, and rcu_sched). If RCU_BOOST is
3430 set, valid values are 1-99 and the default is 1
3431 (the least-favored priority). Otherwise, when
3432 RCU_BOOST is not set, valid values are 0-99 and
3433 the default is zero (non-realtime operation).
3435 rcutree.rcu_nocb_leader_stride= [KNL]
3436 Set the number of NOCB kthread groups, which
3437 defaults to the square root of the number of
3438 CPUs. Larger numbers reduces the wakeup overhead
3439 on the per-CPU grace-period kthreads, but increases
3440 that same overhead on each group's leader.
3442 rcutree.qhimark= [KNL]
3443 Set threshold of queued RCU callbacks beyond which
3444 batch limiting is disabled.
3446 rcutree.qlowmark= [KNL]
3447 Set threshold of queued RCU callbacks below which
3448 batch limiting is re-enabled.
3450 rcutree.rcu_idle_gp_delay= [KNL]
3451 Set wakeup interval for idle CPUs that have
3452 RCU callbacks (RCU_FAST_NO_HZ=y).
3454 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3455 Set wakeup interval for idle CPUs that have
3456 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3457 Lazy RCU callbacks are those which RCU can
3458 prove do nothing more than free memory.
3460 rcutree.rcu_kick_kthreads= [KNL]
3461 Cause the grace-period kthread to get an extra
3462 wake_up() if it sleeps three times longer than
3463 it should at force-quiescent-state time.
3464 This wake_up() will be accompanied by a
3465 WARN_ONCE() splat and an ftrace_dump().
3467 rcuperf.gp_async= [KNL]
3468 Measure performance of asynchronous
3469 grace-period primitives such as call_rcu().
3471 rcuperf.gp_async_max= [KNL]
3472 Specify the maximum number of outstanding
3473 callbacks per writer thread. When a writer
3474 thread exceeds this limit, it invokes the
3475 corresponding flavor of rcu_barrier() to allow
3476 previously posted callbacks to drain.
3478 rcuperf.gp_exp= [KNL]
3479 Measure performance of expedited synchronous
3480 grace-period primitives.
3482 rcuperf.holdoff= [KNL]
3483 Set test-start holdoff period. The purpose of
3484 this parameter is to delay the start of the
3485 test until boot completes in order to avoid
3488 rcuperf.nreaders= [KNL]
3489 Set number of RCU readers. The value -1 selects
3490 N, where N is the number of CPUs. A value
3491 "n" less than -1 selects N-n+1, where N is again
3492 the number of CPUs. For example, -2 selects N
3493 (the number of CPUs), -3 selects N+1, and so on.
3494 A value of "n" less than or equal to -N selects
3497 rcuperf.nwriters= [KNL]
3498 Set number of RCU writers. The values operate
3499 the same as for rcuperf.nreaders.
3500 N, where N is the number of CPUs
3502 rcuperf.perf_type= [KNL]
3503 Specify the RCU implementation to test.
3505 rcuperf.shutdown= [KNL]
3506 Shut the system down after performance tests
3507 complete. This is useful for hands-off automated
3510 rcuperf.verbose= [KNL]
3511 Enable additional printk() statements.
3513 rcuperf.writer_holdoff= [KNL]
3514 Write-side holdoff between grace periods,
3515 in microseconds. The default of zero says
3518 rcutorture.cbflood_inter_holdoff= [KNL]
3519 Set holdoff time (jiffies) between successive
3520 callback-flood tests.
3522 rcutorture.cbflood_intra_holdoff= [KNL]
3523 Set holdoff time (jiffies) between successive
3524 bursts of callbacks within a given callback-flood
3527 rcutorture.cbflood_n_burst= [KNL]
3528 Set the number of bursts making up a given
3529 callback-flood test. Set this to zero to
3530 disable callback-flood testing.
3532 rcutorture.cbflood_n_per_burst= [KNL]
3533 Set the number of callbacks to be registered
3534 in a given burst of a callback-flood test.
3536 rcutorture.fqs_duration= [KNL]
3537 Set duration of force_quiescent_state bursts
3540 rcutorture.fqs_holdoff= [KNL]
3541 Set holdoff time within force_quiescent_state bursts
3544 rcutorture.fqs_stutter= [KNL]
3545 Set wait time between force_quiescent_state bursts
3548 rcutorture.gp_cond= [KNL]
3549 Use conditional/asynchronous update-side
3550 primitives, if available.
3552 rcutorture.gp_exp= [KNL]
3553 Use expedited update-side primitives, if available.
3555 rcutorture.gp_normal= [KNL]
3556 Use normal (non-expedited) asynchronous
3557 update-side primitives, if available.
3559 rcutorture.gp_sync= [KNL]
3560 Use normal (non-expedited) synchronous
3561 update-side primitives, if available. If all
3562 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3563 rcutorture.gp_normal=, and rcutorture.gp_sync=
3564 are zero, rcutorture acts as if is interpreted
3565 they are all non-zero.
3567 rcutorture.n_barrier_cbs= [KNL]
3568 Set callbacks/threads for rcu_barrier() testing.
3570 rcutorture.nfakewriters= [KNL]
3571 Set number of concurrent RCU writers. These just
3572 stress RCU, they don't participate in the actual
3573 test, hence the "fake".
3575 rcutorture.nreaders= [KNL]
3576 Set number of RCU readers. The value -1 selects
3577 N-1, where N is the number of CPUs. A value
3578 "n" less than -1 selects N-n-2, where N is again
3579 the number of CPUs. For example, -2 selects N
3580 (the number of CPUs), -3 selects N+1, and so on.
3582 rcutorture.object_debug= [KNL]
3583 Enable debug-object double-call_rcu() testing.
3585 rcutorture.onoff_holdoff= [KNL]
3586 Set time (s) after boot for CPU-hotplug testing.
3588 rcutorture.onoff_interval= [KNL]
3589 Set time (s) between CPU-hotplug operations, or
3590 zero to disable CPU-hotplug testing.
3592 rcutorture.shuffle_interval= [KNL]
3593 Set task-shuffle interval (s). Shuffling tasks
3594 allows some CPUs to go into dyntick-idle mode
3595 during the rcutorture test.
3597 rcutorture.shutdown_secs= [KNL]
3598 Set time (s) after boot system shutdown. This
3599 is useful for hands-off automated testing.
3601 rcutorture.stall_cpu= [KNL]
3602 Duration of CPU stall (s) to test RCU CPU stall
3603 warnings, zero to disable.
3605 rcutorture.stall_cpu_holdoff= [KNL]
3606 Time to wait (s) after boot before inducing stall.
3608 rcutorture.stall_cpu_irqsoff= [KNL]
3609 Disable interrupts while stalling if set.
3611 rcutorture.stat_interval= [KNL]
3612 Time (s) between statistics printk()s.
3614 rcutorture.stutter= [KNL]
3615 Time (s) to stutter testing, for example, specifying
3616 five seconds causes the test to run for five seconds,
3617 wait for five seconds, and so on. This tests RCU's
3618 ability to transition abruptly to and from idle.
3620 rcutorture.test_boost= [KNL]
3621 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3622 "Maybe" means test if the RCU implementation
3623 under test support RCU priority boosting.
3625 rcutorture.test_boost_duration= [KNL]
3626 Duration (s) of each individual boost test.
3628 rcutorture.test_boost_interval= [KNL]
3629 Interval (s) between each boost test.
3631 rcutorture.test_no_idle_hz= [KNL]
3632 Test RCU's dyntick-idle handling. See also the
3633 rcutorture.shuffle_interval parameter.
3635 rcutorture.torture_type= [KNL]
3636 Specify the RCU implementation to test.
3638 rcutorture.verbose= [KNL]
3639 Enable additional printk() statements.
3641 rcupdate.rcu_cpu_stall_suppress= [KNL]
3642 Suppress RCU CPU stall warning messages.
3644 rcupdate.rcu_cpu_stall_timeout= [KNL]
3645 Set timeout for RCU CPU stall warning messages.
3647 rcupdate.rcu_expedited= [KNL]
3648 Use expedited grace-period primitives, for
3649 example, synchronize_rcu_expedited() instead
3650 of synchronize_rcu(). This reduces latency,
3651 but can increase CPU utilization, degrade
3652 real-time latency, and degrade energy efficiency.
3653 No effect on CONFIG_TINY_RCU kernels.
3655 rcupdate.rcu_normal= [KNL]
3656 Use only normal grace-period primitives,
3657 for example, synchronize_rcu() instead of
3658 synchronize_rcu_expedited(). This improves
3659 real-time latency, CPU utilization, and
3660 energy efficiency, but can expose users to
3661 increased grace-period latency. This parameter
3662 overrides rcupdate.rcu_expedited. No effect on
3663 CONFIG_TINY_RCU kernels.
3665 rcupdate.rcu_normal_after_boot= [KNL]
3666 Once boot has completed (that is, after
3667 rcu_end_inkernel_boot() has been invoked), use
3668 only normal grace-period primitives. No effect
3669 on CONFIG_TINY_RCU kernels.
3671 rcupdate.rcu_task_stall_timeout= [KNL]
3672 Set timeout in jiffies for RCU task stall warning
3673 messages. Disable with a value less than or equal
3676 rcupdate.rcu_self_test= [KNL]
3677 Run the RCU early boot self tests
3679 rcupdate.rcu_self_test_bh= [KNL]
3680 Run the RCU bh early boot self tests
3682 rcupdate.rcu_self_test_sched= [KNL]
3683 Run the RCU sched early boot self tests
3687 Run specified binary instead of /init from the ramdisk,
3688 used for early userspace startup. See initrd.
3691 Turn on/off individual RDT features. List is:
3692 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
3694 E.g. to turn on cmt and turn off mba use:
3698 Format (x86 or x86_64):
3699 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3701 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3703 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3704 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3705 reboot_force is either force or not specified,
3706 reboot_cpu is s[mp]#### with #### being the processor
3707 to be used for rebooting.
3710 [KNL, SMP] Set scheduler's default relax_domain_level.
3711 See Documentation/cgroup-v1/cpusets.txt.
3713 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
3714 Format: <base1>,<size1>[,<base2>,<size2>,...]
3715 Reserve I/O ports or memory so the kernel won't use
3716 them. If <base> is less than 0x10000, the region
3717 is assumed to be I/O ports; otherwise it is memory.
3719 reservetop= [X86-32]
3721 Reserves a hole at the top of the kernel virtual
3726 Set the amount of memory to reserve for BIOS at
3727 the bottom of the address space.
3729 reset_devices [KNL] Force drivers to reset the underlying device
3730 during initialization.
3733 Specify the partition device for software suspend
3735 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3737 resume_offset= [SWSUSP]
3738 Specify the offset from the beginning of the partition
3739 given by "resume=" at which the swap header is located,
3740 in <PAGE_SIZE> units (needed only for swap files).
3741 See Documentation/power/swsusp-and-swap-files.txt
3743 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3744 read the resume files
3746 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3747 Useful for devices that are detected asynchronously
3748 (e.g. USB and MMC devices).
3750 hibernate= [HIBERNATION]
3751 noresume Don't check if there's a hibernation image
3752 present during boot.
3753 nocompress Don't compress/decompress hibernation images.
3754 no Disable hibernation and resume.
3755 protect_image Turn on image protection during restoration
3756 (that will set all pages holding image data
3757 during restoration read-only).
3759 retain_initrd [RAM] Keep initrd memory after extraction
3761 rfkill.default_state=
3762 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3763 etc. communication is blocked by default.
3766 rfkill.master_switch_mode=
3767 0 The "airplane mode" button does nothing.
3768 1 The "airplane mode" button toggles between everything
3769 blocked and the previous configuration.
3770 2 The "airplane mode" button toggles between everything
3771 blocked and everything unblocked.
3773 rhash_entries= [KNL,NET]
3774 Set number of hash buckets for route cache
3777 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
3780 ro [KNL] Mount root device read-only on boot
3783 on Mark read-only kernel memory as read-only (default).
3784 off Leave read-only kernel memory writable for debugging.
3787 Enable the uart passthrough on the designated usb port
3788 on Rockchip SoCs. When active, the signals of the
3789 debug-uart get routed to the D+ and D- pins of the usb
3790 port and the regular usb controller gets disabled.
3792 root= [KNL] Root filesystem
3793 See name_to_dev_t comment in init/do_mounts.c.
3795 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3796 mount the root filesystem
3798 rootflags= [KNL] Set root filesystem mount option string
3800 rootfstype= [KNL] Set root filesystem type
3802 rootwait [KNL] Wait (indefinitely) for root device to show up.
3803 Useful for devices that are detected asynchronously
3804 (e.g. USB and MMC devices).
3806 rproc_mem=nn[KMG][@address]
3807 [KNL,ARM,CMA] Remoteproc physical memory block.
3808 Memory area to be used by remote processor image,
3811 rw [KNL] Mount root device read-write on boot
3813 S [KNL] Run init in single mode
3815 s390_iommu= [HW,S390]
3816 Set s390 IOTLB flushing mode
3818 With strict flushing every unmap operation will result in
3819 an IOTLB flush. Default is lazy flushing before reuse,
3823 See drivers/net/irda/sa1100_ir.c.
3825 sbni= [NET] Granch SBNI12 leased line adapter
3827 sched_debug [KNL] Enables verbose scheduler debug messages.
3829 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3830 Allowed values are enable and disable. This feature
3831 incurs a small amount of overhead in the scheduler
3832 but is useful for debugging and performance tuning.
3834 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3835 xtime_lock contention on larger systems, and/or RCU lock
3836 contention on all systems with CONFIG_MAXSMP set.
3837 Format: { "0" | "1" }
3838 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3840 Note: increases power consumption, thus should only be
3841 enabled if running jitter sensitive (HPC/RT) workloads.
3843 security= [SECURITY] Choose a security module to enable at boot.
3844 If this boot parameter is not specified, only the first
3845 security module asking for security registration will be
3846 loaded. An invalid security module name will be treated
3847 as if no module has been chosen.
3849 selinux= [SELINUX] Disable or enable SELinux at boot time.
3850 Format: { "0" | "1" }
3851 See security/selinux/Kconfig help text.
3854 Default value is set via kernel config option.
3855 If enabled at boot time, /selinux/disable can be used
3856 later to disable prior to initial policy load.
3858 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3859 Format: { "0" | "1" }
3860 See security/apparmor/Kconfig help text
3863 Default value is set via kernel config option.
3865 serialnumber [BUGS=X86-32]
3868 Maximal number of shapers.
3876 Disable merging of slabs with similar size. May be
3877 necessary if there is some reason to distinguish
3878 allocs to different slabs, especially in hardened
3879 environments where the risk of heap overflows and
3880 layout control by attackers can usually be
3881 frustrated by disabling merging. This will reduce
3882 most of the exposure of a heap attack to a single
3883 cache (risks via metadata attacks are mostly
3884 unchanged). Debug options disable merging on their
3886 For more information see Documentation/vm/slub.txt.
3888 slab_max_order= [MM, SLAB]
3889 Determines the maximum allowed order for slabs.
3890 A high setting may cause OOMs due to memory
3891 fragmentation. Defaults to 1 for systems with
3892 more than 32MB of RAM, 0 otherwise.
3894 slub_debug[=options[,slabs]] [MM, SLUB]
3895 Enabling slub_debug allows one to determine the
3896 culprit if slab objects become corrupted. Enabling
3897 slub_debug can create guard zones around objects and
3898 may poison objects when not in use. Also tracks the
3899 last alloc / free. For more information see
3900 Documentation/vm/slub.txt.
3902 slub_memcg_sysfs= [MM, SLUB]
3903 Determines whether to enable sysfs directories for
3904 memory cgroup sub-caches. 1 to enable, 0 to disable.
3905 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
3906 Enabling this can lead to a very high number of debug
3907 directories and files being created under
3910 slub_max_order= [MM, SLUB]
3911 Determines the maximum allowed order for slabs.
3912 A high setting may cause OOMs due to memory
3913 fragmentation. For more information see
3914 Documentation/vm/slub.txt.
3916 slub_min_objects= [MM, SLUB]
3917 The minimum number of objects per slab. SLUB will
3918 increase the slab order up to slub_max_order to
3919 generate a sufficiently large slab able to contain
3920 the number of objects indicated. The higher the number
3921 of objects the smaller the overhead of tracking slabs
3922 and the less frequently locks need to be acquired.
3923 For more information see Documentation/vm/slub.txt.
3925 slub_min_order= [MM, SLUB]
3926 Determines the minimum page order for slabs. Must be
3927 lower than slub_max_order.
3928 For more information see Documentation/vm/slub.txt.
3930 slub_nomerge [MM, SLUB]
3931 Same with slab_nomerge. This is supported for legacy.
3932 See slab_nomerge for more information.
3935 Format: <io1>[,<io2>[,...,<io8>]]
3937 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3938 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3939 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3940 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3941 smsc-ircc2.ircc_irq= [HW] IRQ line
3942 smsc-ircc2.ircc_dma= [HW] DMA channel
3943 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3944 0: Toshiba Satellite 1800 (GP data pin select)
3945 1: Fast pin select (default)
3948 smt [KNL,S390] Set the maximum number of threads (logical
3949 CPUs) to use per physical CPU on systems capable of
3950 symmetric multithreading (SMT). Will be capped to the
3951 actual hardware limit.
3953 Default: -1 (no limit)
3956 [KNL] Should the soft-lockup detector generate panics.
3959 A nonzero value instructs the soft-lockup detector
3960 to panic the machine when a soft-lockup occurs. This
3961 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
3962 which is the respective build-time switch to that
3965 softlockup_all_cpu_backtrace=
3966 [KNL] Should the soft-lockup detector generate
3967 backtraces on all cpus.
3970 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3971 See Documentation/laptops/sonypi.txt
3973 spectre_v2= [X86] Control mitigation of Spectre variant 2
3974 (indirect branch speculation) vulnerability.
3976 on - unconditionally enable
3977 off - unconditionally disable
3978 auto - kernel detects whether your CPU model is
3981 Selecting 'on' will, and 'auto' may, choose a
3982 mitigation method at run time according to the
3983 CPU, the available microcode, the setting of the
3984 CONFIG_RETPOLINE configuration option, and the
3985 compiler with which the kernel was built.
3987 Specific mitigations can also be selected manually:
3989 retpoline - replace indirect branches
3990 retpoline,generic - google's original retpoline
3991 retpoline,amd - AMD-specific minimal thunk
3993 Not specifying this option is equivalent to
3996 spia_io_base= [HW,MTD]
4001 srcutree.counter_wrap_check [KNL]
4002 Specifies how frequently to check for
4003 grace-period sequence counter wrap for the
4004 srcu_data structure's ->srcu_gp_seq_needed field.
4005 The greater the number of bits set in this kernel
4006 parameter, the less frequently counter wrap will
4007 be checked for. Note that the bottom two bits
4010 srcutree.exp_holdoff [KNL]
4011 Specifies how many nanoseconds must elapse
4012 since the end of the last SRCU grace period for
4013 a given srcu_struct until the next normal SRCU
4014 grace period will be considered for automatic
4015 expediting. Set to zero to disable automatic
4018 stack_guard_gap= [MM]
4019 override the default stack gap protection. The value
4020 is in page units and it defines how many pages prior
4021 to (for stacks growing down) resp. after (for stacks
4022 growing up) the main stack are reserved for no other
4023 mapping. Default value is 256 pages.
4026 Enabled the stack tracer on boot up.
4028 stacktrace_filter=[function-list]
4029 [FTRACE] Limit the functions that the stack tracer
4030 will trace at boot up. function-list is a comma separated
4031 list of functions. This list can be changed at run
4032 time by the stack_trace_filter file in the debugfs
4033 tracing directory. Note, this enables stack tracing
4034 and the stacktrace above is not needed.
4038 Set the STI (builtin display/keyboard on the HP-PARISC
4039 machines) console (graphic card) which should be used
4040 as the initial boot-console.
4041 See also comment in drivers/video/console/sticore.c.
4044 See comment in drivers/video/console/sticore.c.
4047 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4049 sunrpc.min_resvport=
4050 sunrpc.max_resvport=
4052 SunRPC servers often require that client requests
4053 originate from a privileged port (i.e. a port in the
4054 range 0 < portnr < 1024).
4055 An administrator who wishes to reserve some of these
4056 ports for other uses may adjust the range that the
4057 kernel's sunrpc client considers to be privileged
4058 using these two parameters to set the minimum and
4059 maximum port values.
4061 sunrpc.svc_rpc_per_connection_limit=
4063 Limit the number of requests that the server will
4064 process in parallel from a single connection.
4065 The default value is 0 (no limit).
4069 Control how the NFS server code allocates CPUs to
4070 service thread pools. Depending on how many NICs
4071 you have and where their interrupts are bound, this
4072 option will affect which CPUs will do NFS serving.
4073 Note: this parameter cannot be changed while the
4074 NFS server is running.
4076 auto the server chooses an appropriate mode
4077 automatically using heuristics
4078 global a single global pool contains all CPUs
4079 percpu one pool for each CPU
4080 pernode one pool for each NUMA node (equivalent
4081 to global on non-NUMA machines)
4083 sunrpc.tcp_slot_table_entries=
4084 sunrpc.udp_slot_table_entries=
4086 Sets the upper limit on the number of simultaneous
4087 RPC calls that can be sent from the client to a
4088 server. Increasing these values may allow you to
4089 improve throughput, but will also increase the
4090 amount of memory reserved for use by the client.
4092 suspend.pm_test_delay=
4094 Sets the number of seconds to remain in a suspend test
4095 mode before resuming the system (see
4096 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4097 is set. Default value is 5.
4100 [KNL] Enable accounting of swap in memory resource
4101 controller if no parameter or 1 is given or disable
4102 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4104 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4105 Format: { <int> | force | noforce }
4106 <int> -- Number of I/O TLB slabs
4107 force -- force using of bounce buffers even if they
4108 wouldn't be automatically used by the kernel
4109 noforce -- Never use bounce buffers (for debugging)
4113 sysfs.deprecated=0|1 [KNL]
4114 Enable/disable old style sysfs layout for old udev
4115 on older distributions. When this option is enabled
4116 very new udev will not work anymore. When this option
4117 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4118 in older udev will not work anymore.
4119 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4120 the kernel configuration.
4122 sysrq_always_enabled
4124 Ignore sysrq setting - this boot parameter will
4125 neutralize any effect of /proc/sys/kernel/sysrq.
4126 Useful for debugging.
4128 tcpmhash_entries= [KNL,NET]
4129 Set the number of tcp_metrics_hash slots.
4130 Default value is 8192 or 16384 depending on total
4131 ram pages. This is used to specify the TCP metrics
4132 cache size. See Documentation/networking/ip-sysctl.txt
4133 "tcp_no_metrics_save" section for more details.
4137 test_suspend= [SUSPEND][,N]
4138 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4139 standby suspend) or "freeze" (for suspend type freeze)
4140 as the system sleep state during system startup with
4141 the optional capability to repeat N number of times.
4142 The system is woken from this state using a
4143 wakeup-capable RTC alarm.
4145 thash_entries= [KNL,NET]
4146 Set number of hash buckets for TCP connection
4148 thermal.act= [HW,ACPI]
4149 -1: disable all active trip points in all thermal zones
4150 <degrees C>: override all lowest active trip points
4152 thermal.crt= [HW,ACPI]
4153 -1: disable all critical trip points in all thermal zones
4154 <degrees C>: override all critical trip points
4156 thermal.nocrt= [HW,ACPI]
4157 Set to disable actions on ACPI thermal zone
4158 critical and hot trip points.
4160 thermal.off= [HW,ACPI]
4161 1: disable ACPI thermal control
4163 thermal.psv= [HW,ACPI]
4164 -1: disable all passive trip points
4165 <degrees C>: override all passive trip points to this
4168 thermal.tzp= [HW,ACPI]
4169 Specify global default ACPI thermal zone polling rate
4170 <deci-seconds>: poll all this frequency
4171 0: no polling (default)
4174 Force threading of all interrupt handlers except those
4175 marked explicitly IRQF_NO_THREAD.
4178 Enable the Transcendent memory driver if built-in.
4180 tmem.cleancache=0|1 [KNL, XEN]
4181 Default is on (1). Disable the usage of the cleancache
4182 API to send anonymous pages to the hypervisor.
4184 tmem.frontswap=0|1 [KNL, XEN]
4185 Default is on (1). Disable the usage of the frontswap
4186 API to send swap pages to the hypervisor. If disabled
4187 the selfballooning and selfshrinking are force disabled.
4189 tmem.selfballooning=0|1 [KNL, XEN]
4190 Default is on (1). Disable the driving of swap pages
4193 tmem.selfshrinking=0|1 [KNL, XEN]
4194 Default is on (1). Partial swapoff that immediately
4195 transfers pages from Xen hypervisor back to the
4196 kernel based on different criteria.
4200 Specify if the kernel should make use of the cpu
4201 topology information if the hardware supports this.
4202 The scheduler will make use of this information and
4203 e.g. base its process migration decisions on it.
4206 topology_updates= [KNL, PPC, NUMA]
4208 Specify if the kernel should ignore (off)
4209 topology updates sent by the hypervisor to this
4214 tpm_suspend_pcr=[HW,TPM]
4215 Format: integer pcr id
4216 Specify that at suspend time, the tpm driver
4217 should extend the specified pcr with zeros,
4218 as a workaround for some chips which fail to
4219 flush the last written pcr on TPM_SaveState.
4220 This will guarantee that all the other pcrs
4223 trace_buf_size=nn[KMG]
4224 [FTRACE] will set tracing buffer size on each cpu.
4226 trace_event=[event-list]
4227 [FTRACE] Set and start specified trace events in order
4228 to facilitate early boot debugging. The event-list is a
4229 comma separated list of trace events to enable. See
4230 also Documentation/trace/events.txt
4232 trace_options=[option-list]
4233 [FTRACE] Enable or disable tracer options at boot.
4234 The option-list is a comma delimited list of options
4235 that can be enabled or disabled just as if you were
4236 to echo the option name into
4238 /sys/kernel/debug/tracing/trace_options
4240 For example, to enable stacktrace option (to dump the
4241 stack trace of each event), add to the command line:
4243 trace_options=stacktrace
4245 See also Documentation/trace/ftrace.txt "trace options"
4249 Have the tracepoints sent to printk as well as the
4250 tracing ring buffer. This is useful for early boot up
4251 where the system hangs or reboots and does not give the
4252 option for reading the tracing buffer or performing a
4253 ftrace_dump_on_oops.
4255 To turn off having tracepoints sent to printk,
4256 echo 0 > /proc/sys/kernel/tracepoint_printk
4257 Note, echoing 1 into this file without the
4258 tracepoint_printk kernel cmdline option has no effect.
4262 Having tracepoints sent to printk() and activating high
4263 frequency tracepoints such as irq or sched, can cause
4264 the system to live lock.
4267 [FTRACE] enable this option to disable tracing when a
4268 warning is hit. This turns off "tracing_on". Tracing can
4269 be enabled again by echoing '1' into the "tracing_on"
4270 file located in /sys/kernel/debug/tracing/
4272 This option is useful, as it disables the trace before
4273 the WARNING dump is called, which prevents the trace to
4274 be filled with content caused by the warning output.
4276 This option can also be set at run time via the sysctl
4277 option: kernel/traceoff_on_warning
4279 transparent_hugepage=
4281 Format: [always|madvise|never]
4282 Can be used to control the default behavior of the system
4283 with respect to transparent hugepages.
4284 See Documentation/vm/transhuge.txt for more details.
4286 tsc= Disable clocksource stability checks for TSC.
4288 [x86] reliable: mark tsc clocksource as reliable, this
4289 disables clocksource verification at runtime, as well
4290 as the stability checks done at bootup. Used to enable
4291 high-resolution timer mode on older hardware, and in
4292 virtualized environment.
4293 [x86] noirqtime: Do not use TSC to do irq accounting.
4294 Used to run time disable IRQ_TIME_ACCOUNTING on any
4295 platforms where RDTSC is slow and this accounting
4297 [x86] unstable: mark the TSC clocksource as unstable, this
4298 marks the TSC unconditionally unstable at bootup and
4299 avoids any further wobbles once the TSC watchdog notices.
4301 turbografx.map[2|3]= [HW,JOY]
4302 TurboGraFX parallel port interface
4304 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4305 See also Documentation/input/devices/joystick-parport.rst
4307 udbg-immortal [PPC] When debugging early kernel crashes that
4308 happen after console_init() and before a proper
4309 console driver takes over, this boot options might
4310 help "seeing" what's going on.
4312 uhash_entries= [KNL,NET]
4313 Set number of hash buckets for UDP/UDP-Lite connections
4316 [USB] Ignore overcurrent events (default N).
4317 Some badly-designed motherboards generate lots of
4318 bogus events, for ports that aren't wired to
4319 anything. Set this parameter to avoid log spamming.
4320 Note that genuine overcurrent events won't be
4324 [X86] Cause panic on unknown NMI.
4326 usbcore.authorized_default=
4327 [USB] Default USB device authorization:
4328 (default -1 = authorized except for wireless USB,
4329 0 = not authorized, 1 = authorized)
4331 usbcore.autosuspend=
4332 [USB] The autosuspend time delay (in seconds) used
4333 for newly-detected USB devices (default 2). This
4334 is the time required before an idle device will be
4335 autosuspended. Devices for which the delay is set
4336 to a negative value won't be autosuspended at all.
4338 usbcore.usbfs_snoop=
4339 [USB] Set to log all usbfs traffic (default 0 = off).
4341 usbcore.usbfs_snoop_max=
4342 [USB] Maximum number of bytes to snoop in each URB
4345 usbcore.blinkenlights=
4346 [USB] Set to cycle leds on hubs (default 0 = off).
4348 usbcore.old_scheme_first=
4349 [USB] Start with the old device initialization
4350 scheme (default 0 = off).
4352 usbcore.usbfs_memory_mb=
4353 [USB] Memory limit (in MB) for buffers allocated by
4354 usbfs (default = 16, 0 = max = 2047).
4356 usbcore.use_both_schemes=
4357 [USB] Try the other device initialization scheme
4358 if the first one fails (default 1 = enabled).
4360 usbcore.initial_descriptor_timeout=
4361 [USB] Specifies timeout for the initial 64-byte
4362 USB_REQ_GET_DESCRIPTOR request in milliseconds
4363 (default 5000 = 5.0 seconds).
4365 usbcore.nousb [USB] Disable the USB subsystem
4368 [USBHID] The interval which mice are to be polled at.
4371 [USBHID] The interval which joysticks are to be polled at.
4373 usb-storage.delay_use=
4374 [UMS] The delay in seconds before a new device is
4375 scanned for Logical Units (default 1).
4378 [UMS] A list of quirks entries to supplement or
4379 override the built-in unusual_devs list. List
4380 entries are separated by commas. Each entry has
4381 the form VID:PID:Flags where VID and PID are Vendor
4382 and Product ID values (4-digit hex numbers) and
4383 Flags is a set of characters, each corresponding
4384 to a common usb-storage quirk flag as follows:
4385 a = SANE_SENSE (collect more than 18 bytes
4387 b = BAD_SENSE (don't collect more than 18
4388 bytes of sense data);
4389 c = FIX_CAPACITY (decrease the reported
4390 device capacity by one sector);
4391 d = NO_READ_DISC_INFO (don't use
4392 READ_DISC_INFO command);
4393 e = NO_READ_CAPACITY_16 (don't use
4394 READ_CAPACITY_16 command);
4395 f = NO_REPORT_OPCODES (don't use report opcodes
4397 g = MAX_SECTORS_240 (don't transfer more than
4398 240 sectors at a time, uas only);
4399 h = CAPACITY_HEURISTICS (decrease the
4400 reported device capacity by one
4401 sector if the number is odd);
4402 i = IGNORE_DEVICE (don't bind to this
4404 j = NO_REPORT_LUNS (don't use report luns
4406 l = NOT_LOCKABLE (don't try to lock and
4407 unlock ejectable media);
4408 m = MAX_SECTORS_64 (don't transfer more
4409 than 64 sectors = 32 KB at a time);
4410 n = INITIAL_READ10 (force a retry of the
4411 initial READ(10) command);
4412 o = CAPACITY_OK (accept the capacity
4413 reported by the device);
4414 p = WRITE_CACHE (the device cache is ON
4416 r = IGNORE_RESIDUE (the device reports
4417 bogus residue values);
4418 s = SINGLE_LUN (the device has only one
4420 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4421 commands, uas only);
4422 u = IGNORE_UAS (don't bind to the uas driver);
4423 w = NO_WP_DETECT (don't test whether the
4424 medium is write-protected).
4425 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4426 even if the device claims no cache)
4427 Example: quirks=0419:aaf5:rl,0421:0433:rc
4429 user_debug= [KNL,ARM]
4431 See arch/arm/Kconfig.debug help text.
4432 1 - undefined instruction events
4434 4 - invalid data aborts
4437 Example: user_debug=31
4440 [X86] Flags controlling user PTE allocations.
4442 nohigh = do not allocate PTE pages in
4443 HIGHMEM regardless of setting
4447 On X86_32, this is an alias for vdso32=. Otherwise:
4449 vdso=1: enable VDSO (the default)
4450 vdso=0: disable VDSO mapping
4452 vdso32= [X86] Control the 32-bit vDSO
4453 vdso32=1: enable 32-bit VDSO
4454 vdso32=0 or vdso32=2: disable 32-bit VDSO
4456 See the help text for CONFIG_COMPAT_VDSO for more
4457 details. If CONFIG_COMPAT_VDSO is set, the default is
4458 vdso32=0; otherwise, the default is vdso32=1.
4460 For compatibility with older kernels, vdso32=2 is an
4463 Try vdso32=0 if you encounter an error that says:
4464 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4467 vector=percpu: enable percpu vector domain
4469 video= [FB] Frame buffer configuration
4470 See Documentation/fb/modedb.txt.
4472 video.brightness_switch_enabled= [0,1]
4473 If set to 1, on receiving an ACPI notify event
4474 generated by hotkey, video driver will adjust brightness
4475 level and then send out the event to user space through
4476 the allocated input device; If set to 0, video driver
4477 will only send out the event without touching backlight
4482 [VMMIO] Memory mapped virtio (platform) device.
4484 <size>@<baseaddr>:<irq>[:<id>]
4486 <size> := size (can use standard suffixes
4488 <baseaddr> := physical base address
4489 <irq> := interrupt number (as passed to
4491 <id> := (optional) platform device id
4493 virtio_mmio.device=1K@0x100b0000:48:7
4495 Can be used multiple times for multiple devices.
4497 vga= [BOOT,X86-32] Select a particular video mode
4498 See Documentation/x86/boot.txt and
4499 Documentation/svga.txt.
4500 Use vga=ask for menu.
4501 This is actually a boot loader parameter; the value is
4502 passed to the kernel using a special protocol.
4504 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4505 size of <nn>. This can be used to increase the
4506 minimum size (128MB on x86). It can also be used to
4507 decrease the size and leave more room for directly
4510 vmcp_cma=nn[MG] [KNL,S390]
4511 Sets the memory size reserved for contiguous memory
4512 allocations for the vmcp device driver.
4514 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4517 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4520 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4524 Controls the behavior of vsyscalls (i.e. calls to
4525 fixed addresses of 0xffffffffff600x00 from legacy
4526 code). Most statically-linked binaries and older
4527 versions of glibc use these calls. Because these
4528 functions are at fixed addresses, they make nice
4529 targets for exploits that can control RIP.
4531 emulate [default] Vsyscalls turn into traps and are
4532 emulated reasonably safely.
4534 native Vsyscalls are native syscall instructions.
4535 This is a little bit faster than trapping
4536 and makes a few dynamic recompilers work
4537 better than they would in emulation mode.
4538 It also makes exploits much easier to write.
4540 none Vsyscalls don't work at all. This makes
4541 them quite hard to use for exploits but
4542 might break your system.
4544 vt.color= [VT] Default text color.
4545 Format: 0xYX, X = foreground, Y = background.
4546 Default: 0x07 = light gray on black.
4548 vt.cur_default= [VT] Default cursor shape.
4549 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4550 the parameters of the <Esc>[?A;B;Cc escape sequence;
4551 see VGA-softcursor.txt. Default: 2 = underline.
4553 vt.default_blu= [VT]
4554 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4555 Change the default blue palette of the console.
4556 This is a 16-member array composed of values
4559 vt.default_grn= [VT]
4560 Format: <green0>,<green1>,<green2>,...,<green15>
4561 Change the default green palette of the console.
4562 This is a 16-member array composed of values
4565 vt.default_red= [VT]
4566 Format: <red0>,<red1>,<red2>,...,<red15>
4567 Change the default red palette of the console.
4568 This is a 16-member array composed of values
4574 Set system-wide default UTF-8 mode for all tty's.
4575 Default is 1, i.e. UTF-8 mode is enabled for all
4576 newly opened terminals.
4578 vt.global_cursor_default=
4581 Set system-wide default for whether a cursor
4582 is shown on new VTs. Default is -1,
4583 i.e. cursors will be created by default unless
4584 overridden by individual drivers. 0 will hide
4585 cursors, 1 will display them.
4587 vt.italic= [VT] Default color for italic text; 0-15.
4590 vt.underline= [VT] Default color for underlined text; 0-15.
4593 watchdog timers [HW,WDT] For information on watchdog timers,
4594 see Documentation/watchdog/watchdog-parameters.txt
4595 or other driver-specific files in the
4596 Documentation/watchdog/ directory.
4598 workqueue.watchdog_thresh=
4599 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4600 warn stall conditions and dump internal state to
4601 help debugging. 0 disables workqueue stall
4602 detection; otherwise, it's the stall threshold
4603 duration in seconds. The default value is 30 and
4604 it can be updated at runtime by writing to the
4605 corresponding sysfs file.
4607 workqueue.disable_numa
4608 By default, all work items queued to unbound
4609 workqueues are affine to the NUMA nodes they're
4610 issued on, which results in better behavior in
4611 general. If NUMA affinity needs to be disabled for
4612 whatever reason, this option can be used. Note
4613 that this also can be controlled per-workqueue for
4614 workqueues visible under /sys/bus/workqueue/.
4616 workqueue.power_efficient
4617 Per-cpu workqueues are generally preferred because
4618 they show better performance thanks to cache
4619 locality; unfortunately, per-cpu workqueues tend to
4620 be more power hungry than unbound workqueues.
4622 Enabling this makes the per-cpu workqueues which
4623 were observed to contribute significantly to power
4624 consumption unbound, leading to measurably lower
4625 power usage at the cost of small performance
4628 The default value of this parameter is determined by
4629 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4631 workqueue.debug_force_rr_cpu
4632 Workqueue used to implicitly guarantee that work
4633 items queued without explicit CPU specified are put
4634 on the local CPU. This guarantee is no longer true
4635 and while local CPU is still preferred work items
4636 may be put on foreign CPUs. This debug option
4637 forces round-robin CPU selection to flush out
4638 usages which depend on the now broken guarantee.
4639 When enabled, memory and cache locality will be
4642 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4643 default x2apic cluster mode on platforms
4646 x86_intel_mid_timer= [X86-32,APBT]
4647 Choose timer option for x86 Intel MID platform.
4648 Two valid options are apbt timer only and lapic timer
4649 plus one apbt timer for broadcast timer.
4650 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4652 xen_512gb_limit [KNL,X86-64,XEN]
4653 Restricts the kernel running paravirtualized under Xen
4654 to use only up to 512 GB of RAM. The reason to do so is
4655 crash analysis tools and Xen tools for doing domain
4656 save/restore/migration must be enabled to handle larger
4659 xen_emul_unplug= [HW,X86,XEN]
4660 Unplug Xen emulated devices
4661 Format: [unplug0,][unplug1]
4662 ide-disks -- unplug primary master IDE devices
4663 aux-ide-disks -- unplug non-primary-master IDE devices
4664 nics -- unplug network devices
4665 all -- unplug all emulated devices (NICs and IDE disks)
4666 unnecessary -- unplugging emulated devices is
4667 unnecessary even if the host did not respond to
4669 never -- do not unplug even if version check succeeds
4671 xen_nopvspin [X86,XEN]
4672 Disables the ticketlock slowpath using Xen PV
4676 Disables the PV optimizations forcing the HVM guest to
4677 run as generic HVM guest with no PV drivers.
4679 xirc2ps_cs= [NET,PCMCIA]
4681 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
projects / linux-2.6-block.git / blob