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-configuration.rst
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 while 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" | "off" | "on" }
393 0 | off - kernel audit is disabled and can not be
394 enabled until the next reboot
395 unset - kernel audit is initialized but disabled and
396 will be fully enabled by the userspace auditd.
397 1 | on - kernel audit is initialized and partially
398 enabled, storing at most audit_backlog_limit
399 messages in RAM until it is fully enabled by the
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.
465 [NET] Specifies amount of time (in seconds) that
466 the kernel should wait for a network carrier. By default
467 it waits 120 seconds.
469 ca_keys= [KEYS] This parameter identifies a specific key(s) on
470 the system trusted keyring to be used for certificate
472 format: { id:<keyid> | builtin }
474 cca= [MIPS] Override the kernel pages' cache coherency
475 algorithm. Accepted values range from 0 to 7
476 inclusive. See arch/mips/include/asm/pgtable-bits.h
477 for platform specific values (SB1, Loongson3 and
480 ccw_timeout_log [S390]
481 See Documentation/s390/CommonIO for details.
483 cgroup_disable= [KNL] Disable a particular controller
484 Format: {name of the controller(s) to disable}
485 The effects of cgroup_disable=foo are:
486 - foo isn't auto-mounted if you mount all cgroups in
488 - foo isn't visible as an individually mountable
490 {Currently only "memory" controller deal with this and
491 cut the overhead, others just disable the usage. So
492 only cgroup_disable=memory is actually worthy}
494 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1
495 Format: { { controller | "all" | "named" }
496 [,{ controller | "all" | "named" }...] }
497 Like cgroup_disable, but only applies to cgroup v1;
498 the blacklisted controllers remain available in cgroup2.
499 "all" blacklists all controllers and "named" disables
500 named mounts. Specifying both "all" and "named" disables
503 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
505 nosocket -- Disable socket memory accounting.
506 nokmem -- Disable kernel memory accounting.
508 checkreqprot [SELINUX] Set initial checkreqprot flag value.
509 Format: { "0" | "1" }
510 See security/selinux/Kconfig help text.
511 0 -- check protection applied by kernel (includes
512 any implied execute protection).
513 1 -- check protection requested by application.
514 Default value is set via a kernel config option.
515 Value can be changed at runtime via
516 /selinux/checkreqprot.
519 See Documentation/s390/CommonIO for details.
522 Prevents the clock framework from automatically gating
523 clocks that have not been explicitly enabled by a Linux
524 device driver but are enabled in hardware at reset or
525 by the bootloader/firmware. Note that this does not
526 force such clocks to be always-on nor does it reserve
527 those clocks in any way. This parameter is useful for
528 debug and development, but should not be needed on a
529 platform with proper driver support. For more
530 information, see Documentation/driver-api/clk.rst.
532 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
534 Forces specified clocksource (if available) to be used
535 when calculating gettimeofday(). If specified
536 clocksource is not available, it defaults to PIT.
537 Format: { pit | tsc | cyclone | pmtmr }
539 clocksource= Override the default clocksource
541 Override the default clocksource and use the clocksource
542 with the name specified.
543 Some clocksource names to choose from, depending on
545 [all] jiffies (this is the base, fallback clocksource)
547 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
548 pxa_timer,timer3,32k_counter,timer0_1
549 [X86-32] pit,hpet,tsc;
550 scx200_hrt on Geode; cyclone on IBM x440
558 clocksource.arm_arch_timer.evtstrm=
561 Enable/disable the eventstream feature of the ARM
562 architected timer so that code using WFE-based polling
563 loops can be debugged more effectively on production
566 clearcpuid=BITNUM [X86]
567 Disable CPUID feature X for the kernel. See
568 arch/x86/include/asm/cpufeatures.h for the valid bit
569 numbers. Note the Linux specific bits are not necessarily
570 stable over kernel options, but the vendor specific
572 Also note that user programs calling CPUID directly
573 or using the feature without checking anything
574 will still see it. This just prevents it from
575 being used by the kernel or shown in /proc/cpuinfo.
576 Also note the kernel might malfunction if you disable
579 cma=nn[MG]@[start[MG][-end[MG]]]
581 Sets the size of kernel global memory area for
582 contiguous memory allocations and optionally the
583 placement constraint by the physical address range of
584 memory allocations. A value of 0 disables CMA
585 altogether. For more information, see
586 include/linux/dma-contiguous.h
588 cmo_free_hint= [PPC] Format: { yes | no }
589 Specify whether pages are marked as being inactive
590 when they are freed. This is used in CMO environments
591 to determine OS memory pressure for page stealing by
595 coherent_pool=nn[KMG] [ARM,KNL]
596 Sets the size of memory pool for coherent, atomic dma
597 allocations, by default set to 256K.
599 com20020= [HW,NET] ARCnet - COM20020 chipset
601 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
603 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
607 ARCnet - COM90xx chipset (memory-mapped buffers)
608 Format: <io>[,<irq>[,<memstart>]]
610 condev= [HW,S390] console device
613 console= [KNL] Output console device and options.
615 tty<n> Use the virtual console device <n>.
619 Use the specified serial port. The options are of
620 the form "bbbbpnf", where "bbbb" is the baud rate,
621 "p" is parity ("n", "o", or "e"), "n" is number of
622 bits, and "f" is flow control ("r" for RTS or
623 omit it). Default is "9600n8".
625 See Documentation/admin-guide/serial-console.rst for more
627 Documentation/networking/netconsole.txt for an
630 uart[8250],io,<addr>[,options]
631 uart[8250],mmio,<addr>[,options]
632 uart[8250],mmio16,<addr>[,options]
633 uart[8250],mmio32,<addr>[,options]
634 uart[8250],0x<addr>[,options]
635 Start an early, polled-mode console on the 8250/16550
636 UART at the specified I/O port or MMIO address,
637 switching to the matching ttyS device later.
638 MMIO inter-register address stride is either 8-bit
639 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
640 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
641 to be equivalent to 'mmio'. 'options' are specified in
642 the same format described for ttyS above; if unspecified,
643 the h/w is not re-initialized.
645 hvc<n> Use the hypervisor console device <n>. This is for
646 both Xen and PowerPC hypervisors.
648 If the device connected to the port is not a TTY but a braille
649 device, prepend "brl," before the device type, for instance
651 For now, only VisioBraille is supported.
654 [KNL] Change console messages format
656 By default we print messages on consoles in
657 "[time stamp] text\n" format (time stamp may not be
658 printed, depending on CONFIG_PRINTK_TIME or
659 `printk_time' param).
661 Switch to syslog format: "<%u>[time stamp] text\n"
662 IOW, each message will have a facility and loglevel
663 prefix. The format is similar to one used by syslog()
664 syscall, or to executing "dmesg -S --raw" or to reading
667 consoleblank= [KNL] The console blank (screen saver) timeout in
668 seconds. A value of 0 disables the blank timer.
672 [KNL] Change the default value for
673 /proc/<pid>/coredump_filter.
674 See also Documentation/filesystems/proc.txt.
676 coresight_cpu_debug.enable
679 Enable/disable the CPU sampling based debugging.
680 0: default value, disable debugging
681 1: enable debugging at boot time
683 cpuidle.off=1 [CPU_IDLE]
684 disable the cpuidle sub-system
687 [CPU_IDLE] Name of the cpuidle governor to use.
689 cpufreq.off=1 [CPU_FREQ]
690 disable the cpufreq sub-system
693 [X86] Delay for N microsec between assert and de-assert
694 of APIC INIT to start processors. This delay occurs
695 on every CPU online, such as boot, and resume from suspend.
698 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
700 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
702 crashkernel=size[KMG][@offset[KMG]]
703 [KNL] Using kexec, Linux can switch to a 'crash kernel'
704 upon panic. This parameter reserves the physical
705 memory region [offset, offset + size] for that kernel
706 image. If '@offset' is omitted, then a suitable offset
707 is selected automatically.
708 [KNL, x86_64] select a region under 4G first, and
709 fall back to reserve region above 4G when '@offset'
710 hasn't been specified.
711 See Documentation/kdump/kdump.txt for further details.
713 crashkernel=range1:size1[,range2:size2,...][@offset]
714 [KNL] Same as above, but depends on the memory
715 in the running system. The syntax of range is
716 start-[end] where start and end are both
717 a memory unit (amount[KMG]). See also
718 Documentation/kdump/kdump.txt for an example.
720 crashkernel=size[KMG],high
721 [KNL, x86_64] range could be above 4G. Allow kernel
722 to allocate physical memory region from top, so could
723 be above 4G if system have more than 4G ram installed.
724 Otherwise memory region will be allocated below 4G, if
726 It will be ignored if crashkernel=X is specified.
727 crashkernel=size[KMG],low
728 [KNL, x86_64] range under 4G. When crashkernel=X,high
729 is passed, kernel could allocate physical memory region
730 above 4G, that cause second kernel crash on system
731 that require some amount of low memory, e.g. swiotlb
732 requires at least 64M+32K low memory, also enough extra
733 low memory is needed to make sure DMA buffers for 32-bit
734 devices won't run out. Kernel would try to allocate at
735 at least 256M below 4G automatically.
736 This one let user to specify own low range under 4G
737 for second kernel instead.
738 0: to disable low allocation.
739 It will be ignored when crashkernel=X,high is not used
740 or memory reserved is below 4G.
743 [KNL] Disable crypto self-tests
748 cs89x0_media= [HW,NET]
749 Format: { rj45 | aui | bnc }
752 See header of drivers/s390/block/dasd_devmap.c.
754 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
755 (one device per port)
756 Format: <port#>,<type>
757 See also Documentation/input/devices/joystick-parport.rst
759 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
761 Documentation/admin-guide/dynamic-debug-howto.rst for
762 details. Deprecated, see dyndbg.
764 debug [KNL] Enable kernel debugging (events log level).
767 [KNL] Enable printing [hashed] pointers early in the
768 boot sequence. If enabled, we use a weak hash instead
769 of siphash to hash pointers. Use this option if you are
770 seeing instances of '(___ptrval___)') and need to see a
771 value (hashed pointer) instead. Cryptographically
772 insecure, please do not use on production kernels.
775 [KNL] verbose self-tests
777 Print debugging info while doing the locking API
779 We default to 0 (no extra messages), setting it to
780 1 will print _a lot_ more information - normally
781 only useful to kernel developers.
783 debug_objects [KNL] Enable object debugging
786 [KNL] Disable object debugging
788 debug_guardpage_minorder=
789 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
790 parameter allows control of the order of pages that will
791 be intentionally kept free (and hence protected) by the
792 buddy allocator. Bigger value increase the probability
793 of catching random memory corruption, but reduce the
794 amount of memory for normal system use. The maximum
795 possible value is MAX_ORDER/2. Setting this parameter
796 to 1 or 2 should be enough to identify most random
797 memory corruption problems caused by bugs in kernel or
798 driver code when a CPU writes to (or reads from) a
799 random memory location. Note that there exists a class
800 of memory corruptions problems caused by buggy H/W or
801 F/W or by drivers badly programing DMA (basically when
802 memory is written at bus level and the CPU MMU is
803 bypassed) which are not detectable by
804 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
805 tracking down these problems.
808 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
809 parameter enables the feature at boot time. In
810 default, it is disabled. We can avoid allocating huge
811 chunk of memory for debug pagealloc if we don't enable
812 it at boot time and the system will work mostly same
813 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
814 on: enable the feature
816 debugpat [X86] Enable PAT debugging
818 decnet.addr= [HW,NET]
819 Format: <area>[,<node>]
820 See also Documentation/networking/decnet.txt.
823 [same as hugepagesz=] The size of the default
824 HugeTLB page size. This is the size represented by
825 the legacy /proc/ hugepages APIs, used for SHM, and
826 default size when mounting hugetlbfs filesystems.
827 Defaults to the default architecture's huge page size
830 deferred_probe_timeout=
831 [KNL] Debugging option to set a timeout in seconds for
832 deferred probe to give up waiting on dependencies to
833 probe. Only specific dependencies (subsystems or
834 drivers) that have opted in will be ignored. A timeout of 0
835 will timeout at the end of initcalls. This option will also
836 dump out devices still on the deferred probe list after
840 Set number of hash buckets for dentry cache.
842 disable_1tb_segments [PPC]
843 Disables the use of 1TB hash page table segments. This
844 causes the kernel to fall back to 256MB segments which
845 can be useful when debugging issues that require an SLB
849 See Documentation/networking/ipv6.txt.
852 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
853 hardening is enabled for this boot. Hardened
854 usercopy checking is used to protect the kernel
855 from reading or writing beyond known memory
856 allocation boundaries as a proactive defense
857 against bounds-checking flaws in the kernel's
858 copy_to_user()/copy_from_user() interface.
859 on Perform hardened usercopy checks (default).
860 off Disable hardened usercopy checks.
863 Disable RADIX MMU mode on POWER9
865 disable_cpu_apicid= [X86,APIC,SMP]
867 The number of initial APIC ID for the
868 corresponding CPU to be disabled at boot,
869 mostly used for the kdump 2nd kernel to
870 disable BSP to wake up multiple CPUs without
871 causing system reset or hang due to sending
874 perf_v4_pmi= [X86,INTEL]
876 Disable Intel PMU counter freezing feature.
877 The feature only exists starting from
878 Arch Perfmon v4 (Skylake and newer).
880 disable_ddw [PPC/PSERIES]
881 Disable Dynamic DMA Window support. Use this if
882 to workaround buggy firmware.
885 See Documentation/networking/ipv6.txt.
887 disable_mtrr_cleanup [X86]
888 The kernel tries to adjust MTRR layout from continuous
889 to discrete, to make X server driver able to add WB
890 entry later. This parameter disables that.
892 disable_mtrr_trim [X86, Intel and AMD only]
893 By default the kernel will trim any uncacheable
894 memory out of your available memory pool based on
895 MTRR settings. This parameter disables that behavior,
896 possibly causing your machine to run very slowly.
898 disable_timer_pin_1 [X86]
899 Disable PIN 1 of APIC timer
900 Can be useful to work around chipset bugs.
902 dis_ucode_ldr [X86] Disable the microcode loader.
904 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
905 this option disables the debugging code at boot.
907 dma_debug_entries=<number>
908 This option allows to tune the number of preallocated
909 entries for DMA-API debugging code. One entry is
910 required per DMA-API allocation. Use this if the
911 DMA-API debugging code disables itself because the
912 architectural default is too low.
914 dma_debug_driver=<driver_name>
915 With this option the DMA-API debugging driver
916 filter feature can be enabled at boot time. Just
917 pass the driver to filter for as the parameter.
918 The filter can be disabled or changed to another
919 driver later using sysfs.
921 driver_async_probe= [KNL]
922 List of driver names to be probed asynchronously.
923 Format: <driver_name1>,<driver_name2>...
925 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
926 Broken monitors, graphic adapters, KVMs and EDIDless
927 panels may send no or incorrect EDID data sets.
928 This parameter allows to specify an EDID data sets
929 in the /lib/firmware directory that are used instead.
930 Generic built-in EDID data sets are used, if one of
931 edid/1024x768.bin, edid/1280x1024.bin,
932 edid/1680x1050.bin, or edid/1920x1080.bin is given
933 and no file with the same name exists. Details and
934 instructions how to build your own EDID data are
935 available in Documentation/EDID/HOWTO.txt. An EDID
936 data set will only be used for a particular connector,
937 if its name and a colon are prepended to the EDID
938 name. Each connector may use a unique EDID data
939 set by separating the files with a comma. An EDID
940 data set with no connector name will be used for
941 any connectors not explicitly specified.
946 Format: {"off" | "known"}
947 Control how the dt_cpu_ftrs device-tree binding is
948 used for CPU feature discovery and setup (if it
950 off: Do not use it, fall back to legacy cpu table.
951 known: Do not pass through unknown features to guests
952 or userspace, only those that the kernel is aware of.
954 dump_apple_properties [X86]
955 Dump name and content of EFI device properties on
956 x86 Macs. Useful for driver authors to determine
957 what data is available or for reverse-engineering.
959 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
960 module.dyndbg[="val"]
961 Enable debug messages at boot time. See
962 Documentation/admin-guide/dynamic-debug-howto.rst
965 nompx [X86] Disables Intel Memory Protection Extensions.
966 See Documentation/x86/intel_mpx.txt for more
967 information about the feature.
969 nopku [X86] Disable Memory Protection Keys CPU feature found
972 module.async_probe [KNL]
973 Enable asynchronous probe on this module.
975 early_ioremap_debug [KNL]
976 Enable debug messages in early_ioremap support. This
977 is useful for tracking down temporary early mappings
978 which are not unmapped.
980 earlycon= [KNL] Output early console device and options.
982 [ARM64] The early console is determined by the
983 stdout-path property in device tree's chosen node,
984 or determined by the ACPI SPCR table.
986 [X86] When used with no options the early console is
987 determined by the ACPI SPCR table.
989 cdns,<addr>[,options]
990 Start an early, polled-mode console on a Cadence
991 (xuartps) serial port at the specified address. Only
992 supported option is baud rate. If baud rate is not
993 specified, the serial port must already be setup and
996 uart[8250],io,<addr>[,options]
997 uart[8250],mmio,<addr>[,options]
998 uart[8250],mmio32,<addr>[,options]
999 uart[8250],mmio32be,<addr>[,options]
1000 uart[8250],0x<addr>[,options]
1001 Start an early, polled-mode console on the 8250/16550
1002 UART at the specified I/O port or MMIO address.
1003 MMIO inter-register address stride is either 8-bit
1004 (mmio) or 32-bit (mmio32 or mmio32be).
1005 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1006 to be equivalent to 'mmio'. 'options' are specified
1007 in the same format described for "console=ttyS<n>"; if
1008 unspecified, the h/w is not initialized.
1012 Start an early, polled-mode console on a pl011 serial
1013 port at the specified address. The pl011 serial port
1014 must already be setup and configured. Options are not
1015 yet supported. If 'mmio32' is specified, then only
1016 the driver will use only 32-bit accessors to read/write
1017 the device registers.
1020 Start an early, polled-mode console on a meson serial
1021 port at the specified address. The serial port must
1022 already be setup and configured. Options are not yet
1026 Start an early, polled-mode console on an msm serial
1027 port at the specified address. The serial port
1028 must already be setup and configured. Options are not
1031 msm_serial_dm,<addr>
1032 Start an early, polled-mode console on an msm serial
1033 dm port at the specified address. The serial port
1034 must already be setup and configured. Options are not
1038 Start an early, polled-mode console on a serial port
1039 of an Actions Semi SoC, such as S500 or S900, at the
1040 specified address. The serial port must already be
1041 setup and configured. Options are not yet supported.
1044 Start an early, polled-mode console on a serial port
1045 of an RDA Micro SoC, such as RDA8810PL, at the
1046 specified address. The serial port must already be
1047 setup and configured. Options are not yet supported.
1049 smh Use ARM semihosting calls for early console.
1057 Use early console provided by serial driver available
1058 on Samsung SoCs, requires selecting proper type and
1059 a correct base address of the selected UART port. The
1060 serial port must already be setup and configured.
1061 Options are not yet supported.
1064 Start an early, polled-mode console on a lantiq serial
1065 (lqasc) port at the specified address. The serial port
1066 must already be setup and configured. Options are not
1071 Use early console provided by Freescale LP UART driver
1072 found on Freescale Vybrid and QorIQ LS1021A processors.
1073 A valid base address must be provided, and the serial
1074 port must already be setup and configured.
1077 Start an early, polled-mode console on the
1078 Armada 3700 serial port at the specified
1079 address. The serial port must already be setup
1080 and configured. Options are not yet supported.
1083 Start an early, polled-mode console on a Qualcomm
1084 Generic Interface (GENI) based serial port at the
1085 specified address. The serial port must already be
1086 setup and configured. Options are not yet supported.
1089 Start an early, unaccelerated console on the EFI
1090 memory mapped framebuffer (if available). On cache
1091 coherent non-x86 systems that use system memory for
1092 the framebuffer, pass the 'ram' option so that it is
1093 mapped with the correct attributes.
1095 earlyprintk= [X86,SH,ARM,M68k,S390]
1099 earlyprintk=serial[,ttySn[,baudrate]]
1100 earlyprintk=serial[,0x...[,baudrate]]
1101 earlyprintk=ttySn[,baudrate]
1102 earlyprintk=dbgp[debugController#]
1103 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1104 earlyprintk=xdbc[xhciController#]
1106 earlyprintk is useful when the kernel crashes before
1107 the normal console is initialized. It is not enabled by
1108 default because it has some cosmetic problems.
1110 Append ",keep" to not disable it when the real console
1113 Only one of vga, efi, serial, or usb debug port can
1116 Currently only ttyS0 and ttyS1 may be specified by
1117 name. Other I/O ports may be explicitly specified
1118 on some architectures (x86 and arm at least) by
1119 replacing ttySn with an I/O port address, like this:
1120 earlyprintk=serial,0x1008,115200
1121 You can find the port for a given device in
1122 /proc/tty/driver/serial:
1123 2: uart:ST16650V2 port:00001008 irq:18 ...
1125 Interaction with the standard serial driver is not
1128 The VGA and EFI output is eventually overwritten by
1131 The xen output can only be used by Xen PV guests.
1133 The sclp output can only be used on s390.
1135 The optional "force" to "pciserial" enables use of a
1136 PCI device even when its classcode is not of the
1139 edac_report= [HW,EDAC] Control how to report EDAC event
1140 Format: {"on" | "off" | "force"}
1141 on: enable EDAC to report H/W event. May be overridden
1142 by other higher priority error reporting module.
1143 off: disable H/W event reporting through EDAC.
1144 force: enforce the use of EDAC to report H/W event.
1147 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1150 This is designed to be used in conjunction with
1151 the boot argument: earlyprintk=vga
1154 Format: {"off" | "on" | "skip[mbr]"}
1157 Format: { "old_map", "nochunk", "noruntime", "debug" }
1158 old_map [X86-64]: switch to the old ioremap-based EFI
1159 runtime services mapping. 32-bit still uses this one by
1161 nochunk: disable reading files in "chunks" in the EFI
1162 boot stub, as chunking can cause problems with some
1163 firmware implementations.
1164 noruntime : disable EFI runtime services support
1165 debug: enable misc debug output
1167 efi_no_storage_paranoia [EFI; X86]
1168 Using this parameter you can use more than 50% of
1169 your efi variable storage. Use this parameter only if
1170 you are really sure that your UEFI does sane gc and
1171 fulfills the spec otherwise your board may brick.
1173 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1174 Add arbitrary attribute to specific memory range by
1175 updating original EFI memory map.
1176 Region of memory which aa attribute is added to is
1178 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1179 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1180 attribute is added to range 0x100000000-0x180000000 and
1181 0x10a0000000-0x1120000000.
1183 Using this parameter you can do debugging of EFI memmap
1184 related feature. For example, you can do debugging of
1185 Address Range Mirroring feature even if your box
1188 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1189 that is to be dynamically loaded by Linux. If there are
1190 multiple variables with the same name but with different
1191 vendor GUIDs, all of them will be loaded. See
1192 Documentation/acpi/ssdt-overlays.txt for details.
1195 eisa_irq_edge= [PARISC,HW]
1196 See header of drivers/parisc/eisa.c.
1199 See comment before function elanfreq_setup() in
1200 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1203 Format: { "mq-deadline" | "kyber" | "bfq" }
1204 See Documentation/block/deadline-iosched.txt,
1205 Documentation/block/kyber-iosched.txt and
1206 Documentation/block/bfq-iosched.txt for details.
1208 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1209 Specifies physical address of start of kernel core
1210 image elf header and optionally the size. Generally
1211 kexec loader will pass this option to capture kernel.
1212 See Documentation/kdump/kdump.txt for details.
1214 enable_mtrr_cleanup [X86]
1215 The kernel tries to adjust MTRR layout from continuous
1216 to discrete, to make X server driver able to add WB
1217 entry later. This parameter enables that.
1219 enable_timer_pin_1 [X86]
1220 Enable PIN 1 of APIC timer
1221 Can be useful to work around chipset bugs
1222 (in particular on some ATI chipsets).
1223 The kernel tries to set a reasonable default.
1225 enforcing [SELINUX] Set initial enforcing status.
1227 See security/selinux/Kconfig help text.
1228 0 -- permissive (log only, no denials).
1229 1 -- enforcing (deny and log).
1231 Value can be changed at runtime via /selinux/enforce.
1234 Disable Error Record Serialization Table (ERST)
1237 ether= [HW,NET] Ethernet cards parameters
1238 This option is obsoleted by the "netdev=" option, which
1239 has equivalent usage. See its documentation for details.
1243 Permit 'security.evm' to be updated regardless of
1244 current integrity status.
1248 fail_make_request=[KNL]
1249 General fault injection mechanism.
1250 Format: <interval>,<probability>,<space>,<times>
1251 See also Documentation/fault-injection/.
1254 See Documentation/blockdev/floppy.txt.
1256 force_pal_cache_flush
1257 [IA-64] Avoid check_sal_cache_flush which may hang on
1258 buggy SAL_CACHE_FLUSH implementations. Using this
1259 parameter will force ia64_sal_cache_flush to call
1260 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1263 Forcefully enable Physical Address Extension (PAE).
1264 Many Pentium M systems disable PAE but may have a
1265 functionally usable PAE implementation.
1266 Warning: use of this parameter will taint the kernel
1267 and may cause unknown problems.
1270 [FTRACE] will set and start the specified tracer
1271 as early as possible in order to facilitate early
1274 ftrace_dump_on_oops[=orig_cpu]
1275 [FTRACE] will dump the trace buffers on oops.
1276 If no parameter is passed, ftrace will dump
1277 buffers of all CPUs, but if you pass orig_cpu, it will
1278 dump only the buffer of the CPU that triggered the
1281 ftrace_filter=[function-list]
1282 [FTRACE] Limit the functions traced by the function
1283 tracer at boot up. function-list is a comma separated
1284 list of functions. This list can be changed at run
1285 time by the set_ftrace_filter file in the debugfs
1288 ftrace_notrace=[function-list]
1289 [FTRACE] Do not trace the functions specified in
1290 function-list. This list can be changed at run time
1291 by the set_ftrace_notrace file in the debugfs
1294 ftrace_graph_filter=[function-list]
1295 [FTRACE] Limit the top level callers functions traced
1296 by the function graph tracer at boot up.
1297 function-list is a comma separated list of functions
1298 that can be changed at run time by the
1299 set_graph_function file in the debugfs tracing directory.
1301 ftrace_graph_notrace=[function-list]
1302 [FTRACE] Do not trace from the functions specified in
1303 function-list. This list is a comma separated list of
1304 functions that can be changed at run time by the
1305 set_graph_notrace file in the debugfs tracing directory.
1307 ftrace_graph_max_depth=<uint>
1308 [FTRACE] Used with the function graph tracer. This is
1309 the max depth it will trace into a function. This value
1310 can be changed at run time by the max_graph_depth file
1311 in the tracefs tracing directory. default: 0 (no limit)
1314 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1315 support via parallel port (up to 5 devices per port)
1316 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1317 See also Documentation/input/devices/joystick-parport.rst
1321 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1325 gcov_persist= [GCOV] When non-zero (default), profiling data for
1326 kernel modules is saved and remains accessible via
1327 debugfs, even when the module is unloaded/reloaded.
1328 When zero, profiling data is discarded and associated
1329 debugfs files are removed at module unload time.
1331 goldfish [X86] Enable the goldfish android emulator platform.
1332 Don't use this when you are not running on the
1335 gpt [EFI] Forces disk with valid GPT signature but
1336 invalid Protective MBR to be treated as GPT. If the
1337 primary GPT is corrupted, it enables the backup/alternate
1338 GPT to be used instead.
1340 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1341 the "Enable 0" bit of the configuration register.
1344 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1345 the "Enable 0" bit of the configuration register.
1348 grcan.select= [HW] Select which physical interface to use.
1351 grcan.txsize= [HW] Sets the size of the tx buffer.
1352 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1354 grcan.rxsize= [HW] Sets the size of the rx buffer.
1355 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1358 gpio-mockup.gpio_mockup_ranges
1359 [HW] Sets the ranges of gpiochip of for this device.
1360 Format: <start1>,<end1>,<start2>,<end2>...
1362 hardlockup_all_cpu_backtrace=
1363 [KNL] Should the hard-lockup detector generate
1364 backtraces on all cpus.
1367 hashdist= [KNL,NUMA] Large hashes allocated during boot
1368 are distributed across NUMA nodes. Defaults on
1369 for 64-bit NUMA, off otherwise.
1370 Format: 0 | 1 (for off | on)
1372 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1374 hd= [EIDE] (E)IDE hard drive subsystem geometry
1375 Format: <cyl>,<head>,<sect>
1378 Disable Hardware Error Source Table (HEST) support;
1379 corresponding firmware-first mode error processing
1380 logic will be disabled.
1382 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1383 size of <nn>. This works even on boxes that have no
1384 highmem otherwise. This also works to reduce highmem
1385 size on bigger boxes.
1387 highres= [KNL] Enable/disable high resolution timer mode.
1388 Valid parameters: "on", "off"
1392 See Documentation/isdn/README.HiSax.
1396 hpet= [X86-32,HPET] option to control HPET usage
1397 Format: { enable (default) | disable | force |
1399 disable: disable HPET and use PIT instead
1400 force: allow force enabled of undocumented chips (ICH4,
1402 verbose: show contents of HPET registers during setup
1404 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1405 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1407 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1408 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1409 On x86-64 and powerpc, this option can be specified
1410 multiple times interleaved with hugepages= to reserve
1411 huge pages of different sizes. Valid pages sizes on
1412 x86-64 are 2M (when the CPU supports "pse") and 1G
1413 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1416 [KNL] Should the hung task detector generate panics.
1419 A nonzero value instructs the kernel to panic when a
1420 hung task is detected. The default value is controlled
1421 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1422 option. The value selected by this boot parameter can
1423 be changed later by the kernel.hung_task_panic sysctl.
1425 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1426 terminal devices. Valid values: 0..8
1427 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1428 If specified, z/VM IUCV HVC accepts connections
1429 from listed z/VM user IDs only.
1431 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations
1432 which allow the hypervisor to 'idle' the
1433 guest on lock contention.
1436 Do not unregister boot console at start. This is only
1437 useful for debugging when something happens in the window
1438 between unregistering the boot console and initializing
1441 i2c_bus= [HW] Override the default board specific I2C bus speed
1442 or register an additional I2C bus that is not
1443 registered from board initialization code.
1447 i8042.debug [HW] Toggle i8042 debug mode
1448 i8042.unmask_kbd_data
1449 [HW] Enable printing of interrupt data from the KBD port
1450 (disabled by default, and as a pre-condition
1451 requires that i8042.debug=1 be enabled)
1452 i8042.direct [HW] Put keyboard port into non-translated mode
1453 i8042.dumbkbd [HW] Pretend that controller can only read data from
1454 keyboard and cannot control its state
1455 (Don't attempt to blink the leds)
1456 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1457 i8042.nokbd [HW] Don't check/create keyboard port
1458 i8042.noloop [HW] Disable the AUX Loopback command while probing
1460 i8042.nomux [HW] Don't check presence of an active multiplexing
1462 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1464 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1465 i8042.reset [HW] Reset the controller during init, cleanup and
1466 suspend-to-ram transitions, only during s2r
1467 transitions, or never reset
1468 Format: { 1 | Y | y | 0 | N | n }
1469 1, Y, y: always reset controller
1470 0, N, n: don't ever reset controller
1471 Default: only on s2r transitions on x86; most other
1472 architectures force reset to be always executed
1473 i8042.unlock [HW] Unlock (ignore) the keylock
1474 i8042.kbdreset [HW] Reset device connected to KBD port
1478 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1479 indicates that the driver is running on unsupported
1481 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1482 does not match list of supported models.
1484 [HW] Report power status in /proc/i8k
1485 (disabled by default)
1486 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1489 i915.invert_brightness=
1490 [DRM] Invert the sense of the variable that is used to
1491 set the brightness of the panel backlight. Normally a
1492 brightness value of 0 indicates backlight switched off,
1493 and the maximum of the brightness value sets the backlight
1494 to maximum brightness. If this parameter is set to 0
1495 (default) and the machine requires it, or this parameter
1496 is set to 1, a brightness value of 0 sets the backlight
1497 to maximum brightness, and the maximum of the brightness
1498 value switches the backlight off.
1499 -1 -- never invert brightness
1500 0 -- machine default
1501 1 -- force brightness inversion
1504 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1506 ide-core.nodma= [HW] (E)IDE subsystem
1507 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1508 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1509 .cdrom .chs .ignore_cable are additional options
1510 See Documentation/ide/ide.txt.
1512 ide-generic.probe-mask= [HW] (E)IDE subsystem
1514 Probe mask for legacy ISA IDE ports. Depending on
1515 platform up to 6 ports are supported, enabled by
1516 setting corresponding bits in the mask to 1. The
1517 default value is 0x0, which has a special meaning.
1518 On systems that have PCI, it triggers scanning the
1519 PCI bus for the first and the second port, which
1520 are then probed. On systems without PCI the value
1521 of 0x0 enables probing the two first ports as if it
1524 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1525 Claim all unknown PCI IDE storage controllers.
1528 Format: idle=poll, idle=halt, idle=nomwait
1529 Poll forces a polling idle loop that can slightly
1530 improve the performance of waking up a idle CPU, but
1531 will use a lot of power and make the system run hot.
1533 idle=halt: Halt is forced to be used for CPU idle.
1534 In such case C2/C3 won't be used again.
1535 idle=nomwait: Disable mwait for CPU C-states
1537 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1538 Format: { strict | legacy | 2008 | relaxed }
1541 Choose which programs will be accepted for execution
1542 based on the IEEE 754 NaN encoding(s) supported by
1543 the FPU and the NaN encoding requested with the value
1544 of an ELF file header flag individually set by each
1545 binary. Hardware implementations are permitted to
1546 support either or both of the legacy and the 2008 NaN
1549 Available settings are as follows:
1550 strict accept binaries that request a NaN encoding
1551 supported by the FPU
1552 legacy only accept legacy-NaN binaries, if supported
1554 2008 only accept 2008-NaN binaries, if supported
1556 relaxed accept any binaries regardless of whether
1557 supported by the FPU
1559 The FPU emulator is always able to support both NaN
1560 encodings, so if no FPU hardware is present or it has
1561 been disabled with 'nofpu', then the settings of
1562 'legacy' and '2008' strap the emulator accordingly,
1563 'relaxed' straps the emulator for both legacy-NaN and
1564 2008-NaN, whereas 'strict' enables legacy-NaN only on
1565 legacy processors and both NaN encodings on MIPS32 or
1568 The setting for ABS.fmt/NEG.fmt instruction execution
1569 mode generally follows that for the NaN encoding,
1570 except where unsupported by hardware.
1572 ignore_loglevel [KNL]
1573 Ignore loglevel setting - this will print /all/
1574 kernel messages to the console. Useful for debugging.
1575 We also add it as printk module parameter, so users
1576 could change it dynamically, usually by
1577 /sys/module/printk/parameters/ignore_loglevel.
1580 Ignore RLIMIT_DATA setting for data mappings,
1581 print warning at first misuse. Can be changed via
1582 /sys/module/kernel/parameters/ignore_rlimit_data.
1584 ihash_entries= [KNL]
1585 Set number of hash buckets for inode cache.
1587 ima_appraise= [IMA] appraise integrity measurements
1588 Format: { "off" | "enforce" | "fix" | "log" }
1591 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead.
1592 The builtin appraise policy appraises all files
1595 ima_canonical_fmt [IMA]
1596 Use the canonical format for the binary runtime
1597 measurements, instead of host native format.
1600 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1604 The list of supported hash algorithms is defined
1605 in crypto/hash_info.h.
1608 The builtin policies to load during IMA setup.
1609 Format: "tcb | appraise_tcb | secure_boot |
1612 The "tcb" policy measures all programs exec'd, files
1613 mmap'd for exec, and all files opened with the read
1614 mode bit set by either the effective uid (euid=0) or
1617 The "appraise_tcb" policy appraises the integrity of
1618 all files owned by root.
1620 The "secure_boot" policy appraises the integrity
1621 of files (eg. kexec kernel image, kernel modules,
1622 firmware, policy, etc) based on file signatures.
1624 The "fail_securely" policy forces file signature
1625 verification failure also on privileged mounted
1626 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1629 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1630 Load a policy which meets the needs of the Trusted
1631 Computing Base. This means IMA will measure all
1632 programs exec'd, files mmap'd for exec, and all files
1633 opened for read by uid=0.
1636 Select one of defined IMA measurements template formats.
1637 Formats: { "ima" | "ima-ng" | "ima-sig" }
1641 [IMA] Define a custom template format.
1642 Format: { "field1|...|fieldN" }
1644 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1645 Format: <min_file_size>
1646 Set the minimal file size for using asynchronous hash.
1647 If left unspecified, ahash usage is disabled.
1649 ahash performance varies for different data sizes on
1650 different crypto accelerators. This option can be used
1651 to achieve the best performance for a particular HW.
1653 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1655 Set hashing buffer size. Default: 4k.
1657 ahash performance varies for different chunk sizes on
1658 different crypto accelerators. This option can be used
1659 to achieve best performance for particular HW.
1663 Run specified binary instead of /sbin/init as init
1666 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1667 for working out where the kernel is dying during
1670 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1671 initcall functions. Useful for debugging built-in
1672 modules and initcalls.
1674 initrd= [BOOT] Specify the location of the initial ramdisk
1676 init_pkru= [x86] Specify the default memory protection keys rights
1677 register contents for all processes. 0x55555554 by
1678 default (disallow access to all but pkey 0). Can
1679 override in debugfs after boot.
1681 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1684 int_pln_enable [x86] Enable power limit notification interrupt
1686 integrity_audit=[IMA]
1687 Format: { "0" | "1" }
1688 0 -- basic integrity auditing messages. (Default)
1689 1 -- additional integrity auditing messages.
1691 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1693 Enable intel iommu driver.
1695 Disable intel iommu driver.
1696 igfx_off [Default Off]
1697 By default, gfx is mapped as normal device. If a gfx
1698 device has a dedicated DMAR unit, the DMAR unit is
1699 bypassed by not enabling DMAR with this option. In
1700 this case, gfx device will use physical address for
1703 With this option iommu will not optimize to look
1704 for io virtual address below 32-bit forcing dual
1705 address cycle on pci bus for cards supporting greater
1706 than 32-bit addressing. The default is to look
1707 for translation below 32-bit and if not available
1708 then look in the higher range.
1709 strict [Default Off]
1710 With this option on every unmap_single operation will
1711 result in a hardware IOTLB flush operation as opposed
1712 to batching them for performance.
1713 sp_off [Default Off]
1714 By default, super page will be supported if Intel IOMMU
1715 has the capability. With this option, super page will
1718 By default, scalable mode will be disabled even if the
1719 hardware advertises that it has support for the scalable
1720 mode translation. With this option set, scalable mode
1721 will be used on hardware which claims to support it.
1722 tboot_noforce [Default Off]
1723 Do not force the Intel IOMMU enabled under tboot.
1724 By default, tboot will force Intel IOMMU on, which
1725 could harm performance of some high-throughput
1726 devices like 40GBit network cards, even if identity
1728 Note that using this option lowers the security
1729 provided by tboot because it makes the system
1730 vulnerable to DMA attacks.
1732 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1733 0 disables intel_idle and fall back on acpi_idle.
1734 1 to 9 specify maximum depth of C-state.
1738 Do not enable intel_pstate as the default
1739 scaling driver for the supported processors
1741 Use intel_pstate as a scaling driver, but configure it
1742 to work with generic cpufreq governors (instead of
1743 enabling its internal governor). This mode cannot be
1744 used along with the hardware-managed P-states (HWP)
1747 Enable intel_pstate on systems that prohibit it by default
1748 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1749 instead of acpi-cpufreq may disable platform features, such
1750 as thermal controls and power capping, that rely on ACPI
1751 P-States information being indicated to OSPM and therefore
1752 should be used with caution. This option does not work with
1753 processors that aren't supported by the intel_pstate driver
1754 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1756 Do not enable hardware P state control (HWP)
1759 Only load intel_pstate on systems which support
1760 hardware P state control (HWP) if available.
1762 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1763 Description Table, specifies preferred power management
1764 profile as "Enterprise Server" or "Performance Server",
1765 then this feature is turned on by default.
1767 Allow per-logical-CPU P-State performance control limits using
1768 cpufreq sysfs interface
1770 intremap= [X86-64, Intel-IOMMU]
1771 on enable Interrupt Remapping (default)
1772 off disable Interrupt Remapping
1773 nosid disable Source ID checking
1775 BIOS x2APIC opt-out request will be ignored
1776 nopost disable Interrupt Posting
1778 iomem= Disable strict checking of access to MMIO memory
1779 strict regions from userspace.
1794 nobypass [PPC/POWERNV]
1795 Disable IOMMU bypass, using IOMMU for PCI devices.
1797 iommu.strict= [ARM64] Configure TLB invalidation behaviour
1798 Format: { "0" | "1" }
1800 Request that DMA unmap operations use deferred
1801 invalidation of hardware TLBs, for increased
1802 throughput at the cost of reduced device isolation.
1803 Will fall back to strict mode if not supported by
1804 the relevant IOMMU driver.
1805 1 - Strict mode (default).
1806 DMA unmap operations invalidate IOMMU hardware TLBs
1810 [ARM64] Configure DMA to bypass the IOMMU by default.
1811 Format: { "0" | "1" }
1812 0 - Use IOMMU translation for DMA.
1813 1 - Bypass the IOMMU for DMA.
1814 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
1816 io7= [HW] IO7 for Marvel based alpha systems
1817 See comment before marvel_specify_io7 in
1818 arch/alpha/kernel/core_marvel.c.
1820 io_delay= [X86] I/O delay method
1822 Standard port 0x80 based delay
1824 Alternate port 0xed based delay (needed on some systems)
1826 Simple two microseconds delay
1831 See Documentation/filesystems/nfs/nfsroot.txt.
1833 irqaffinity= [SMP] Set the default irq affinity mask
1834 The argument is a cpu list, as described above.
1836 irqchip.gicv2_force_probe=
1839 Force the kernel to look for the second 4kB page
1840 of a GICv2 controller even if the memory range
1841 exposed by the device tree is too small.
1843 irqchip.gicv3_nolpi=
1845 Force the kernel to ignore the availability of
1846 LPIs (and by consequence ITSs). Intended for system
1847 that use the kernel as a bootloader, and thus want
1848 to let secondary kernels in charge of setting up
1851 irqchip.gicv3_pseudo_nmi= [ARM64]
1852 Enables support for pseudo-NMIs in the kernel. This
1853 requires the kernel to be built with
1854 CONFIG_ARM64_PSEUDO_NMI.
1857 When an interrupt is not handled search all handlers
1858 for it. Intended to get systems with badly broken
1862 When an interrupt is not handled search all handlers
1863 for it. Also check all handlers each timer
1864 interrupt. Intended to get systems with badly broken
1868 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1870 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1871 [Deprecated - use cpusets instead]
1872 Format: [flag-list,]<cpu-list>
1874 Specify one or more CPUs to isolate from disturbances
1875 specified in the flag list (default: domain):
1878 Disable the tick when a single task runs.
1880 A residual 1Hz tick is offloaded to workqueues, which you
1881 need to affine to housekeeping through the global
1882 workqueue's affinity configured via the
1883 /sys/devices/virtual/workqueue/cpumask sysfs file, or
1884 by using the 'domain' flag described below.
1886 NOTE: by default the global workqueue runs on all CPUs,
1887 so to protect individual CPUs the 'cpumask' file has to
1888 be configured manually after bootup.
1891 Isolate from the general SMP balancing and scheduling
1892 algorithms. Note that performing domain isolation this way
1893 is irreversible: it's not possible to bring back a CPU to
1894 the domains once isolated through isolcpus. It's strongly
1895 advised to use cpusets instead to disable scheduler load
1896 balancing through the "cpuset.sched_load_balance" file.
1897 It offers a much more flexible interface where CPUs can
1898 move in and out of an isolated set anytime.
1900 You can move a process onto or off an "isolated" CPU via
1901 the CPU affinity syscalls or cpuset.
1902 <cpu number> begins at 0 and the maximum value is
1903 "number of CPUs in system - 1".
1905 The format of <cpu-list> is described above.
1911 ivrs_ioapic [HW,X86_64]
1912 Provide an override to the IOAPIC-ID<->DEVICE-ID
1913 mapping provided in the IVRS ACPI table. For
1914 example, to map IOAPIC-ID decimal 10 to
1915 PCI device 00:14.0 write the parameter as:
1916 ivrs_ioapic[10]=00:14.0
1918 ivrs_hpet [HW,X86_64]
1919 Provide an override to the HPET-ID<->DEVICE-ID
1920 mapping provided in the IVRS ACPI table. For
1921 example, to map HPET-ID decimal 0 to
1922 PCI device 00:14.0 write the parameter as:
1923 ivrs_hpet[0]=00:14.0
1925 ivrs_acpihid [HW,X86_64]
1926 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1927 mapping provided in the IVRS ACPI table. For
1928 example, to map UART-HID:UID AMD0020:0 to
1929 PCI device 00:14.5 write the parameter as:
1930 ivrs_acpihid[00:14.5]=AMD0020:0
1932 js= [HW,JOY] Analog joystick
1933 See Documentation/input/joydev/joystick.rst.
1936 When CONFIG_RANDOMIZE_BASE is set, this disables
1937 kernel and module base offset ASLR (Address Space
1938 Layout Randomization).
1941 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1942 report on every invalid memory access. Without this
1943 parameter KASAN will print report only for the first
1948 kernelcore= [KNL,X86,IA-64,PPC]
1949 Format: nn[KMGTPE] | nn% | "mirror"
1950 This parameter specifies the amount of memory usable by
1951 the kernel for non-movable allocations. The requested
1952 amount is spread evenly throughout all nodes in the
1953 system as ZONE_NORMAL. The remaining memory is used for
1954 movable memory in its own zone, ZONE_MOVABLE. In the
1955 event, a node is too small to have both ZONE_NORMAL and
1956 ZONE_MOVABLE, kernelcore memory will take priority and
1957 other nodes will have a larger ZONE_MOVABLE.
1959 ZONE_MOVABLE is used for the allocation of pages that
1960 may be reclaimed or moved by the page migration
1961 subsystem. Note that allocations like PTEs-from-HighMem
1962 still use the HighMem zone if it exists, and the Normal
1963 zone if it does not.
1965 It is possible to specify the exact amount of memory in
1966 the form of "nn[KMGTPE]", a percentage of total system
1967 memory in the form of "nn%", or "mirror". If "mirror"
1968 option is specified, mirrored (reliable) memory is used
1969 for non-movable allocations and remaining memory is used
1970 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
1971 are exclusive, so you cannot specify multiple forms.
1973 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1974 Format: <Controller#>[,poll interval]
1975 The controller # is the number of the ehci usb debug
1976 port as it is probed via PCI. The poll interval is
1977 optional and is the number seconds in between
1978 each poll cycle to the debug port in case you need
1979 the functionality for interrupting the kernel with
1980 gdb or control-c on the dbgp connection. When
1981 not using this parameter you use sysrq-g to break into
1982 the kernel debugger.
1984 kgdboc= [KGDB,HW] kgdb over consoles.
1985 Requires a tty driver that supports console polling,
1986 or a supported polling keyboard driver (non-usb).
1987 Serial only format: <serial_device>[,baud]
1988 keyboard only format: kbd
1989 keyboard and serial format: kbd,<serial_device>[,baud]
1990 Optional Kernel mode setting:
1991 kms, kbd format: kms,kbd
1992 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1994 kgdbwait [KGDB] Stop kernel execution and enter the
1995 kernel debugger at the earliest opportunity.
1997 kmac= [MIPS] korina ethernet MAC address.
1998 Configure the RouterBoard 532 series on-chip
1999 Ethernet adapter MAC address.
2001 kmemleak= [KNL] Boot-time kmemleak enable/disable
2002 Valid arguments: on, off
2004 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
2007 kpti= [ARM64] Control page table isolation of user
2008 and kernel address spaces.
2009 Default: enabled on cores which need mitigation.
2013 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
2014 Default is 0 (don't ignore, but inject #GP)
2016 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
2017 Default is false (don't support).
2019 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
2023 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
2024 Default is 1 (enabled)
2026 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
2028 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
2030 kvm-arm.vgic_v3_group0_trap=
2031 [KVM,ARM] Trap guest accesses to GICv3 group-0
2034 kvm-arm.vgic_v3_group1_trap=
2035 [KVM,ARM] Trap guest accesses to GICv3 group-1
2038 kvm-arm.vgic_v3_common_trap=
2039 [KVM,ARM] Trap guest accesses to GICv3 common
2042 kvm-arm.vgic_v4_enable=
2043 [KVM,ARM] Allow use of GICv4 for direct injection of
2046 kvm-intel.ept= [KVM,Intel] Disable extended page tables
2047 (virtualized MMU) support on capable Intel chips.
2048 Default is 1 (enabled)
2050 kvm-intel.emulate_invalid_guest_state=
2051 [KVM,Intel] Enable emulation of invalid guest states
2052 Default is 0 (disabled)
2054 kvm-intel.flexpriority=
2055 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
2056 Default is 1 (enabled)
2059 [KVM,Intel] Enable VMX nesting (nVMX).
2060 Default is 0 (disabled)
2062 kvm-intel.unrestricted_guest=
2063 [KVM,Intel] Disable unrestricted guest feature
2064 (virtualized real and unpaged mode) on capable
2065 Intel chips. Default is 1 (enabled)
2067 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2070 Valid arguments: never, cond, always
2072 always: L1D cache flush on every VMENTER.
2073 cond: Flush L1D on VMENTER only when the code between
2074 VMEXIT and VMENTER can leak host memory.
2075 never: Disables the mitigation
2077 Default is cond (do L1 cache flush in specific instances)
2079 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2080 feature (tagged TLBs) on capable Intel chips.
2081 Default is 1 (enabled)
2083 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2086 The kernel PTE inversion protection is unconditionally
2087 enabled and cannot be disabled.
2090 Provides all available mitigations for the
2091 L1TF vulnerability. Disables SMT and
2092 enables all mitigations in the
2093 hypervisors, i.e. unconditional L1D flush.
2095 SMT control and L1D flush control via the
2096 sysfs interface is still possible after
2097 boot. Hypervisors will issue a warning
2098 when the first VM is started in a
2099 potentially insecure configuration,
2100 i.e. SMT enabled or L1D flush disabled.
2103 Same as 'full', but disables SMT and L1D
2104 flush runtime control. Implies the
2105 'nosmt=force' command line option.
2106 (i.e. sysfs control of SMT is disabled.)
2109 Leaves SMT enabled and enables the default
2110 hypervisor mitigation, i.e. conditional
2113 SMT control and L1D flush control via the
2114 sysfs interface is still possible after
2115 boot. Hypervisors will issue a warning
2116 when the first VM is started in a
2117 potentially insecure configuration,
2118 i.e. SMT enabled or L1D flush disabled.
2122 Disables SMT and enables the default
2123 hypervisor mitigation.
2125 SMT control and L1D flush control via the
2126 sysfs interface is still possible after
2127 boot. Hypervisors will issue a warning
2128 when the first VM is started in a
2129 potentially insecure configuration,
2130 i.e. SMT enabled or L1D flush disabled.
2133 Same as 'flush', but hypervisors will not
2134 warn when a VM is started in a potentially
2135 insecure configuration.
2138 Disables hypervisor mitigations and doesn't
2140 It also drops the swap size and available
2141 RAM limit restriction on both hypervisor and
2146 For details see: Documentation/admin-guide/l1tf.rst
2152 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2155 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2156 value for LAPIC timer one-shot implementation. Default
2157 back to the programmable timer unit in the LAPIC.
2159 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2162 libata.dma= [LIBATA] DMA control
2163 libata.dma=0 Disable all PATA and SATA DMA
2164 libata.dma=1 PATA and SATA Disk DMA only
2165 libata.dma=2 ATAPI (CDROM) DMA only
2166 libata.dma=4 Compact Flash DMA only
2167 Combinations also work, so libata.dma=3 enables DMA
2168 for disks and CDROMs, but not CFs.
2170 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2171 libata.ignore_hpa=0 keep BIOS limits (default)
2172 libata.ignore_hpa=1 ignore limits, using full disk
2174 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2178 libata.force= [LIBATA] Force configurations. The format is comma
2179 separated list of "[ID:]VAL" where ID is
2180 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2181 matching port, link or device. Basically, it matches
2182 the ATA ID string printed on console by libata. If
2183 the whole ID part is omitted, the last PORT and DEVICE
2184 values are used. If ID hasn't been specified yet, the
2185 configuration applies to all ports, links and devices.
2187 If only DEVICE is omitted, the parameter applies to
2188 the port and all links and devices behind it. DEVICE
2189 number of 0 either selects the first device or the
2190 first fan-out link behind PMP device. It does not
2191 select the host link. DEVICE number of 15 selects the
2192 host link and device attached to it.
2194 The VAL specifies the configuration to force. As long
2195 as there's no ambiguity shortcut notation is allowed.
2196 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2197 The following configurations can be forced.
2199 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2200 Any ID with matching PORT is used.
2202 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2204 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2205 udma[/][16,25,33,44,66,100,133] notation is also
2208 * [no]ncq: Turn on or off NCQ.
2210 * [no]ncqtrim: Turn off queued DSM TRIM.
2212 * nohrst, nosrst, norst: suppress hard, soft
2215 * rstonce: only attempt one reset during
2216 hot-unplug link recovery
2218 * dump_id: dump IDENTIFY data.
2220 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2222 * disable: Disable this device.
2224 If there are multiple matching configurations changing
2225 the same attribute, the last one is used.
2227 memblock=debug [KNL] Enable memblock debug messages.
2229 load_ramdisk= [RAM] List of ramdisks to load from floppy
2230 See Documentation/blockdev/ramdisk.txt.
2232 lockd.nlm_grace_period=P [NFS] Assign grace period.
2235 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2238 lockd.nlm_timeout=T [NFS] Assign timeout value.
2241 lockd.nlm_udpport=M [NFS] Assign UDP port.
2244 locktorture.nreaders_stress= [KNL]
2245 Set the number of locking read-acquisition kthreads.
2246 Defaults to being automatically set based on the
2247 number of online CPUs.
2249 locktorture.nwriters_stress= [KNL]
2250 Set the number of locking write-acquisition kthreads.
2252 locktorture.onoff_holdoff= [KNL]
2253 Set time (s) after boot for CPU-hotplug testing.
2255 locktorture.onoff_interval= [KNL]
2256 Set time (s) between CPU-hotplug operations, or
2257 zero to disable CPU-hotplug testing.
2259 locktorture.shuffle_interval= [KNL]
2260 Set task-shuffle interval (jiffies). Shuffling
2261 tasks allows some CPUs to go into dyntick-idle
2262 mode during the locktorture test.
2264 locktorture.shutdown_secs= [KNL]
2265 Set time (s) after boot system shutdown. This
2266 is useful for hands-off automated testing.
2268 locktorture.stat_interval= [KNL]
2269 Time (s) between statistics printk()s.
2271 locktorture.stutter= [KNL]
2272 Time (s) to stutter testing, for example,
2273 specifying five seconds causes the test to run for
2274 five seconds, wait for five seconds, and so on.
2275 This tests the locking primitive's ability to
2276 transition abruptly to and from idle.
2278 locktorture.torture_type= [KNL]
2279 Specify the locking implementation to test.
2281 locktorture.verbose= [KNL]
2282 Enable additional printk() statements.
2284 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2287 loglevel= All Kernel Messages with a loglevel smaller than the
2288 console loglevel will be printed to the console. It can
2289 also be changed with klogd or other programs. The
2290 loglevels are defined as follows:
2292 0 (KERN_EMERG) system is unusable
2293 1 (KERN_ALERT) action must be taken immediately
2294 2 (KERN_CRIT) critical conditions
2295 3 (KERN_ERR) error conditions
2296 4 (KERN_WARNING) warning conditions
2297 5 (KERN_NOTICE) normal but significant condition
2298 6 (KERN_INFO) informational
2299 7 (KERN_DEBUG) debug-level messages
2301 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2302 in bytes. n must be a power of two and greater
2303 than the minimal size. The minimal size is defined
2304 by LOG_BUF_SHIFT kernel config parameter. There is
2305 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2306 that allows to increase the default size depending on
2307 the number of CPUs. See init/Kconfig for more details.
2309 logo.nologo [FB] Disables display of the built-in Linux logo.
2310 This may be used to provide more screen space for
2311 kernel log messages and is useful when debugging
2312 kernel boot problems.
2314 lp=0 [LP] Specify parallel ports to use, e.g,
2315 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2316 lp=reset first parallel port). 'lp=0' disables the
2317 lp=auto printer driver. 'lp=reset' (which can be
2318 specified in addition to the ports) causes
2319 attached printers to be reset. Using
2320 lp=port1,port2,... specifies the parallel ports
2321 to associate lp devices with, starting with
2322 lp0. A port specification may be 'none' to skip
2323 that lp device, or a parport name such as
2324 'parport0'. Specifying 'lp=auto' instead of a
2325 port specification list means that device IDs
2326 from each port should be examined, to see if
2327 an IEEE 1284-compliant printer is attached; if
2328 so, the driver will manage that printer.
2329 See also header of drivers/char/lp.c.
2332 Sets loops_per_jiffy to given constant, thus avoiding
2333 time-consuming boot-time autodetection (up to 250 ms per
2334 CPU). 0 enables autodetection (default). To determine
2335 the correct value for your kernel, boot with normal
2336 autodetection and see what value is printed. Note that
2337 on SMP systems the preset will be applied to all CPUs,
2338 which is likely to cause problems if your CPUs need
2339 significantly divergent settings. An incorrect value
2340 will cause delays in the kernel to be wrong, leading to
2341 unpredictable I/O errors and other breakage. Although
2342 unlikely, in the extreme case this might damage your
2346 Format: <io>,<irq>,<dma>
2348 lsm.debug [SECURITY] Enable LSM initialization debugging output.
2351 [SECURITY] Choose order of LSM initialization. This
2352 overrides CONFIG_LSM, and the "security=" parameter.
2354 machvec= [IA-64] Force the use of a particular machine-vector
2355 (machvec) in a generic kernel.
2356 Example: machvec=hpzx1_swiotlb
2358 machtype= [Loongson] Share the same kernel image file between different
2360 Example: machtype=lemote-yeeloong-2f-7inch
2362 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2363 than or equal to this physical address is ignored.
2365 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2366 will bring up during bootup. maxcpus=n : n >= 0 limits
2367 the kernel to bring up 'n' processors. Surely after
2368 bootup you can bring up the other plugged cpu by executing
2369 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2370 only takes effect during system bootup.
2371 While n=0 is a special case, it is equivalent to "nosmp",
2372 which also disables the IO APIC.
2374 max_loop= [LOOP] The number of loop block devices that get
2375 (loop.max_loop) unconditionally pre-created at init time. The default
2376 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2377 of statically allocating a predefined number, loop
2378 devices can be requested on-demand with the
2379 /dev/loop-control interface.
2381 mce [X86-32] Machine Check Exception
2383 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2385 md= [HW] RAID subsystems devices and level
2386 See Documentation/admin-guide/md.rst.
2389 Format: <first>,<last>
2390 Specifies range of consoles to be captured by the MDA.
2392 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2393 Amount of memory to be used when the kernel is not able
2394 to see the whole system memory or for test.
2395 [X86] Work as limiting max address. Use together
2396 with memmap= to avoid physical address space collisions.
2397 Without memmap= PCI devices could be placed at addresses
2398 belonging to unused RAM.
2400 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2404 [KNL,SH] Allow user to override the default size for
2405 per-device physically contiguous DMA buffers.
2407 memhp_default_state=online/offline
2408 [KNL] Set the initial state for the memory hotplug
2409 onlining policy. If not specified, the default value is
2410 set according to the
2411 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2413 See Documentation/memory-hotplug.txt.
2415 memmap=exactmap [KNL,X86] Enable setting of an exact
2416 E820 memory map, as specified by the user.
2417 Such memmap=exactmap lines can be constructed based on
2418 BIOS output or other requirements. See the memmap=nn@ss
2421 memmap=nn[KMG]@ss[KMG]
2422 [KNL] Force usage of a specific region of memory.
2423 Region of memory to be used is from ss to ss+nn.
2424 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2425 which limits max address to nn[KMG].
2426 Multiple different regions can be specified,
2429 memmap=100M@2G,100M#3G,1G!1024G
2431 memmap=nn[KMG]#ss[KMG]
2432 [KNL,ACPI] Mark specific memory as ACPI data.
2433 Region of memory to be marked is from ss to ss+nn.
2435 memmap=nn[KMG]$ss[KMG]
2436 [KNL,ACPI] Mark specific memory as reserved.
2437 Region of memory to be reserved is from ss to ss+nn.
2438 Example: Exclude memory from 0x18690000-0x1869ffff
2439 memmap=64K$0x18690000
2441 memmap=0x10000$0x18690000
2442 Some bootloaders may need an escape character before '$',
2443 like Grub2, otherwise '$' and the following number
2446 memmap=nn[KMG]!ss[KMG]
2447 [KNL,X86] Mark specific memory as protected.
2448 Region of memory to be used, from ss to ss+nn.
2449 The memory region may be marked as e820 type 12 (0xc)
2450 and is NVDIMM or ADR memory.
2452 memmap=<size>%<offset>-<oldtype>+<newtype>
2453 [KNL,ACPI] Convert memory within the specified region
2454 from <oldtype> to <newtype>. If "-<oldtype>" is left
2455 out, the whole region will be marked as <newtype>,
2456 even if previously unavailable. If "+<newtype>" is left
2457 out, matching memory will be removed. Types are
2458 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2459 3 = ACPI, 12 = PRAM.
2461 memory_corruption_check=0/1 [X86]
2462 Some BIOSes seem to corrupt the first 64k of
2463 memory when doing things like suspend/resume.
2464 Setting this option will scan the memory
2465 looking for corruption. Enabling this will
2466 both detect corruption and prevent the kernel
2467 from using the memory being corrupted.
2468 However, its intended as a diagnostic tool; if
2469 repeatable BIOS-originated corruption always
2470 affects the same memory, you can use memmap=
2471 to prevent the kernel from using that memory.
2473 memory_corruption_check_size=size [X86]
2474 By default it checks for corruption in the low
2475 64k, making this memory unavailable for normal
2476 use. Use this parameter to scan for
2477 corruption in more or less memory.
2479 memory_corruption_check_period=seconds [X86]
2480 By default it checks for corruption every 60
2481 seconds. Use this parameter to check at some
2482 other rate. 0 disables periodic checking.
2484 memtest= [KNL,X86,ARM,PPC] Enable memtest
2486 default : 0 <disable>
2487 Specifies the number of memtest passes to be
2488 performed. Each pass selects another test
2489 pattern from a given set of patterns. Memtest
2490 fills the memory with this pattern, validates
2491 memory contents and reserves bad memory
2492 regions that are detected.
2494 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2495 Valid arguments: on, off
2496 Default (depends on kernel configuration option):
2497 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2498 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2499 mem_encrypt=on: Activate SME
2500 mem_encrypt=off: Do not activate SME
2502 Refer to Documentation/x86/amd-memory-encryption.txt
2503 for details on when memory encryption can be activated.
2505 mem_sleep_default= [SUSPEND] Default system suspend mode:
2506 s2idle - Suspend-To-Idle
2507 shallow - Power-On Suspend or equivalent (if supported)
2508 deep - Suspend-To-RAM or equivalent (if supported)
2509 See Documentation/admin-guide/pm/sleep-states.rst.
2511 meye.*= [HW] Set MotionEye Camera parameters
2512 See Documentation/media/v4l-drivers/meye.rst.
2514 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2515 Multi-Function General Purpose Timers on AMD Geode
2518 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2519 the BIOS has incorrectly applied a workaround. TinyBIOS
2520 version 0.98 is known to be affected, 0.99 fixes the
2521 problem by letting the user disable the workaround.
2525 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2526 physical address is ignored.
2528 mini2440= [ARM,HW,KNL]
2529 Format:[0..2][b][c][t]
2531 MINI2440 configuration specification:
2532 0 - The attached screen is the 3.5" TFT
2533 1 - The attached screen is the 7" TFT
2534 2 - The VGA Shield is attached (1024x768)
2535 Leaving out the screen size parameter will not load
2536 the TFT driver, and the framebuffer will be left
2538 b - Enable backlight. The TFT backlight pin will be
2539 linked to the kernel VESA blanking code and a GPIO
2540 LED. This parameter is not necessary when using the
2542 c - Enable the s3c camera interface.
2543 t - Reserved for enabling touchscreen support. The
2544 touchscreen support is not enabled in the mainstream
2545 kernel as of 2.6.30, a preliminary port can be found
2546 in the "bleeding edge" mini2440 support kernel at
2547 http://repo.or.cz/w/linux-2.6/mini2440.git
2550 [X86,PPC,S390,ARM64] Control optional mitigations for
2551 CPU vulnerabilities. This is a set of curated,
2552 arch-independent options, each of which is an
2553 aggregation of existing arch-specific options.
2556 Disable all optional CPU mitigations. This
2557 improves system performance, but it may also
2558 expose users to several CPU vulnerabilities.
2559 Equivalent to: nopti [X86,PPC]
2563 nospectre_v2 [X86,PPC,S390,ARM64]
2564 spectre_v2_user=off [X86]
2565 spec_store_bypass_disable=off [X86,PPC]
2566 ssbd=force-off [ARM64]
2570 Mitigate all CPU vulnerabilities, but leave SMT
2571 enabled, even if it's vulnerable. This is for
2572 users who don't want to be surprised by SMT
2573 getting disabled across kernel upgrades, or who
2574 have other ways of avoiding SMT-based attacks.
2575 Equivalent to: (default behavior)
2578 Mitigate all CPU vulnerabilities, disabling SMT
2579 if needed. This is for users who always want to
2580 be fully mitigated, even if it means losing SMT.
2581 Equivalent to: l1tf=flush,nosmt [X86]
2584 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2585 parameter allows control of the logging verbosity for
2586 the additional memory initialisation checks. A value
2587 of 0 disables mminit logging and a level of 4 will
2588 log everything. Information is printed at KERN_DEBUG
2589 so loglevel=8 may also need to be specified.
2592 [KNL] When CONFIG_MODULE_SIG is set, this means that
2593 modules without (valid) signatures will fail to load.
2594 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2595 is always true, so this option does nothing.
2597 module_blacklist= [KNL] Do not load a comma-separated list of
2598 modules. Useful for debugging problem modules.
2601 [MOUSE] Maximum time between finger touching and
2602 leaving touchpad surface for touch to be considered
2603 a tap and be reported as a left button click (for
2604 touchpads working in absolute mode only).
2606 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2607 reporting absolute coordinates, such as tablets
2608 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2609 reporting absolute coordinates, such as tablets
2611 movablecore= [KNL,X86,IA-64,PPC]
2612 Format: nn[KMGTPE] | nn%
2613 This parameter is the complement to kernelcore=, it
2614 specifies the amount of memory used for migratable
2615 allocations. If both kernelcore and movablecore is
2616 specified, then kernelcore will be at *least* the
2617 specified value but may be more. If movablecore on its
2618 own is specified, the administrator must be careful
2619 that the amount of memory usable for all allocations
2622 movable_node [KNL] Boot-time switch to make hotplugable memory
2623 NUMA nodes to be movable. This means that the memory
2624 of such nodes will be usable only for movable
2625 allocations which rules out almost all kernel
2626 allocations. Use with caution!
2628 MTD_Partition= [MTD]
2629 Format: <name>,<region-number>,<size>,<offset>
2631 MTD_Region= [MTD] Format:
2632 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2635 See drivers/mtd/cmdlinepart.c.
2637 multitce=off [PPC] This parameter disables the use of the pSeries
2638 firmware feature for updating multiple TCE entries
2641 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2643 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2645 boundary - index of last SLC block on Flex-OneNAND.
2646 The remaining blocks are configured as MLC blocks.
2647 lock - Configure if Flex-OneNAND boundary should be locked.
2648 Once locked, the boundary cannot be changed.
2649 1 indicates lock status, 0 indicates unlock status.
2652 ARM/S3C2412 JIVE boot control
2654 See arch/arm/mach-s3c2412/mach-jive.c
2656 mtouchusb.raw_coordinates=
2657 [HW] Make the MicroTouch USB driver use raw coordinates
2658 ('y', default) or cooked coordinates ('n')
2660 mtrr_chunk_size=nn[KMG] [X86]
2661 used for mtrr cleanup. It is largest continuous chunk
2662 that could hold holes aka. UC entries.
2664 mtrr_gran_size=nn[KMG] [X86]
2665 Used for mtrr cleanup. It is granularity of mtrr block.
2667 Large value could prevent small alignment from
2670 mtrr_spare_reg_nr=n [X86]
2672 Range: 0,7 : spare reg number
2674 Used for mtrr cleanup. It is spare mtrr entries number.
2675 Set to 2 or more if your graphical card needs more.
2677 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2679 netdev= [NET] Network devices parameters
2680 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2681 Note that mem_start is often overloaded to mean
2682 something different and driver-specific.
2683 This usage is only documented in each driver source
2687 [NETFILTER] Enable connection tracking flow accounting
2688 0 to disable accounting
2689 1 to enable accounting
2692 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2693 See Documentation/filesystems/nfs/nfsroot.txt.
2695 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2696 See Documentation/filesystems/nfs/nfsroot.txt.
2698 nfsrootdebug [NFS] enable nfsroot debugging messages.
2699 See Documentation/filesystems/nfs/nfsroot.txt.
2701 nfs.callback_nr_threads=
2702 [NFSv4] set the total number of threads that the
2703 NFS client will assign to service NFSv4 callback
2706 nfs.callback_tcpport=
2707 [NFS] set the TCP port on which the NFSv4 callback
2708 channel should listen.
2711 [NFS] sets the pathname to the program which is used
2712 to update the NFS client cache entries.
2714 nfs.cache_getent_timeout=
2715 [NFS] sets the timeout after which an attempt to
2716 update a cache entry is deemed to have failed.
2718 nfs.idmap_cache_timeout=
2719 [NFS] set the maximum lifetime for idmapper cache
2723 [NFS] enable 64-bit inode numbers.
2724 If zero, the NFS client will fake up a 32-bit inode
2725 number for the readdir() and stat() syscalls instead
2726 of returning the full 64-bit number.
2727 The default is to return 64-bit inode numbers.
2729 nfs.max_session_cb_slots=
2730 [NFSv4.1] Sets the maximum number of session
2731 slots the client will assign to the callback
2732 channel. This determines the maximum number of
2733 callbacks the client will process in parallel for
2734 a particular server.
2736 nfs.max_session_slots=
2737 [NFSv4.1] Sets the maximum number of session slots
2738 the client will attempt to negotiate with the server.
2739 This limits the number of simultaneous RPC requests
2740 that the client can send to the NFSv4.1 server.
2741 Note that there is little point in setting this
2742 value higher than the max_tcp_slot_table_limit.
2744 nfs.nfs4_disable_idmapping=
2745 [NFSv4] When set to the default of '1', this option
2746 ensures that both the RPC level authentication
2747 scheme and the NFS level operations agree to use
2748 numeric uids/gids if the mount is using the
2749 'sec=sys' security flavour. In effect it is
2750 disabling idmapping, which can make migration from
2751 legacy NFSv2/v3 systems to NFSv4 easier.
2752 Servers that do not support this mode of operation
2753 will be autodetected by the client, and it will fall
2754 back to using the idmapper.
2755 To turn off this behaviour, set the value to '0'.
2757 [NFS4] Specify an additional fixed unique ident-
2758 ification string that NFSv4 clients can insert into
2759 their nfs_client_id4 string. This is typically a
2760 UUID that is generated at system install time.
2762 nfs.send_implementation_id =
2763 [NFSv4.1] Send client implementation identification
2764 information in exchange_id requests.
2765 If zero, no implementation identification information
2767 The default is to send the implementation identification
2770 nfs.recover_lost_locks =
2771 [NFSv4] Attempt to recover locks that were lost due
2772 to a lease timeout on the server. Please note that
2773 doing this risks data corruption, since there are
2774 no guarantees that the file will remain unchanged
2775 after the locks are lost.
2776 If you want to enable the kernel legacy behaviour of
2777 attempting to recover these locks, then set this
2779 The default parameter value of '0' causes the kernel
2780 not to attempt recovery of lost locks.
2782 nfs4.layoutstats_timer =
2783 [NFSv4.2] Change the rate at which the kernel sends
2784 layoutstats to the pNFS metadata server.
2786 Setting this to value to 0 causes the kernel to use
2787 whatever value is the default set by the layout
2788 driver. A non-zero value sets the minimum interval
2789 in seconds between layoutstats transmissions.
2791 nfsd.nfs4_disable_idmapping=
2792 [NFSv4] When set to the default of '1', the NFSv4
2793 server will return only numeric uids and gids to
2794 clients using auth_sys, and will accept numeric uids
2795 and gids from such clients. This is intended to ease
2796 migration from NFSv2/v3.
2798 nmi_debug= [KNL,SH] Specify one or more actions to take
2799 when a NMI is triggered.
2800 Format: [state][,regs][,debounce][,die]
2802 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2803 Format: [panic,][nopanic,][num]
2805 0 - turn hardlockup detector in nmi_watchdog off
2806 1 - turn hardlockup detector in nmi_watchdog on
2807 When panic is specified, panic when an NMI watchdog
2808 timeout occurs (or 'nopanic' to override the opposite
2809 default). To disable both hard and soft lockup detectors,
2810 please see 'nowatchdog'.
2811 This is useful when you use a panic=... timeout and
2812 need the box quickly up again.
2814 These settings can be accessed at runtime via
2815 the nmi_watchdog and hardlockup_panic sysctls.
2817 netpoll.carrier_timeout=
2818 [NET] Specifies amount of time (in seconds) that
2819 netpoll should wait for a carrier. By default netpoll
2822 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2823 emulation library even if a 387 maths coprocessor
2826 no5lvl [X86-64] Disable 5-level paging mode. Forces
2827 kernel to use 4-level paging instead.
2830 [HW] Never suspend the console
2831 Disable suspending of consoles during suspend and
2832 hibernate operations. Once disabled, debugging
2833 messages can reach various consoles while the rest
2834 of the system is being put to sleep (ie, while
2835 debugging driver suspend/resume hooks). This may
2836 not work reliably with all consoles, but is known
2837 to work with serial and VGA consoles.
2838 To facilitate more flexible debugging, we also add
2839 console_suspend, a printk module parameter to control
2840 it. Users could use console_suspend (usually
2841 /sys/module/printk/parameters/console_suspend) to
2842 turn on/off it dynamically.
2844 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2845 caches in the slab allocator. Saves per-node memory,
2846 but will impact performance.
2850 noaltinstr [S390] Disables alternative instructions patching
2851 (CPU alternatives feature).
2853 noapic [SMP,APIC] Tells the kernel to not make use of any
2854 IOAPICs that may be present in the system.
2856 noautogroup Disable scheduler automatic task group creation.
2858 nobats [PPC] Do not use BATs for mapping kernel lowmem
2859 on "Classic" PPC cores.
2863 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2865 nodelayacct [KNL] Disable per-task delay accounting
2867 nodsp [SH] Disable hardware DSP at boot time.
2869 noefi Disable EFI runtime services support.
2874 On X86-32 available only on PAE configured kernels.
2875 noexec=on: enable non-executable mappings (default)
2876 noexec=off: disable non-executable mappings
2879 Disable SMAP (Supervisor Mode Access Prevention)
2880 even if it is supported by processor.
2883 Disable SMEP (Supervisor Mode Execution Prevention)
2884 even if it is supported by processor.
2887 This affects only 32-bit executables.
2888 noexec32=on: enable non-executable mappings (default)
2889 read doesn't imply executable mappings
2890 noexec32=off: disable non-executable mappings
2891 read implies executable mappings
2893 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2895 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2896 register save and restore. The kernel will only save
2897 legacy floating-point registers on task switch.
2899 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2901 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2902 Equivalent to smt=1.
2904 [KNL,x86] Disable symmetric multithreading (SMT).
2905 nosmt=force: Force disable SMT, cannot be undone
2906 via the sysfs control file.
2908 nospectre_v1 [PPC] Disable mitigations for Spectre Variant 1 (bounds
2909 check bypass). With this option data leaks are possible
2912 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for
2913 the Spectre variant 2 (indirect branch prediction)
2914 vulnerability. System may allow data leaks with this
2917 nospec_store_bypass_disable
2918 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
2920 noxsave [BUGS=X86] Disables x86 extended register state save
2921 and restore using xsave. The kernel will fallback to
2922 enabling legacy floating-point and sse state.
2924 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2925 register states. The kernel will fall back to use
2926 xsave to save the states. By using this parameter,
2927 performance of saving the states is degraded because
2928 xsave doesn't support modified optimization while
2929 xsaveopt supports it on xsaveopt enabled systems.
2931 noxsaves [X86] Disables xsaves and xrstors used in saving and
2932 restoring x86 extended register state in compacted
2933 form of xsave area. The kernel will fall back to use
2934 xsaveopt and xrstor to save and restore the states
2935 in standard form of xsave area. By using this
2936 parameter, xsave area per process might occupy more
2937 memory on xsaves enabled systems.
2939 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2940 wfi(ARM) instruction doesn't work correctly and not to
2941 use it. This is also useful when using JTAG debugger.
2943 no_file_caps Tells the kernel not to honor file capabilities. The
2944 only way then for a file to be executed with privilege
2945 is to be setuid root or executed by root.
2947 nohalt [IA-64] Tells the kernel not to use the power saving
2948 function PAL_HALT_LIGHT when idle. This increases
2949 power-consumption. On the positive side, it reduces
2950 interrupt wake-up latency, which may improve performance
2951 in certain environments such as networked servers or
2954 nohibernate [HIBERNATION] Disable hibernation and resume.
2956 nohz= [KNL] Boottime enable/disable dynamic ticks
2957 Valid arguments: on, off
2960 nohz_full= [KNL,BOOT,SMP,ISOL]
2961 The argument is a cpu list, as described above.
2962 In kernels built with CONFIG_NO_HZ_FULL=y, set
2963 the specified list of CPUs whose tick will be stopped
2964 whenever possible. The boot CPU will be forced outside
2965 the range to maintain the timekeeping. Any CPUs
2966 in this list will have their RCU callbacks offloaded,
2967 just as if they had also been called out in the
2968 rcu_nocbs= boot parameter.
2970 noiotrap [SH] Disables trapped I/O port accesses.
2972 noirqdebug [X86-32] Disables the code which attempts to detect and
2973 disable unhandled interrupt sources.
2975 no_timer_check [X86,APIC] Disables the code which tests for
2976 broken timer IRQ sources.
2978 noisapnp [ISAPNP] Disables ISA PnP code.
2980 noinitrd [RAM] Tells the kernel not to load any configured
2983 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2985 [Deprecated - use intremap=off]
2989 noinvpcid [X86] Disable the INVPCID cpu feature.
2991 nojitter [IA-64] Disables jitter checking for ITC timers.
2993 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2995 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2999 [X86,PV_OPS] Disable paravirtualized VMware scheduler
3000 clock and use the default one.
3002 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
3003 steal time is computed, but won't influence scheduler
3006 nolapic [X86-32,APIC] Do not enable or use the local APIC.
3008 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
3010 noltlbs [PPC] Do not use large page/tlb entries for kernel
3011 lowmem mapping on PPC40x and PPC8xx
3013 nomca [IA-64] Disable machine check abort handling
3015 nomce [X86-32] Disable Machine Check Exception
3017 nomfgpt [X86-32] Disable Multi-Function General Purpose
3018 Timer usage (for AMD Geode machines).
3020 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
3021 shutdown the other cpus. Instead use the REBOOT_VECTOR
3024 nomodule Disable module load
3026 nopat [X86] Disable PAT (page attribute table extension of
3027 pagetables) support.
3029 nopcid [X86-64] Disable the PCID cpu feature.
3031 norandmaps Don't use address space randomization. Equivalent to
3032 echo 0 > /proc/sys/kernel/randomize_va_space
3034 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
3035 with UP alternatives
3037 nordrand [X86] Disable kernel use of the RDRAND and
3038 RDSEED instructions even if they are supported
3039 by the processor. RDRAND and RDSEED are still
3040 available to user space applications.
3042 noresume [SWSUSP] Disables resume and restores original swap
3045 no-scroll [VGA] Disables scrollback.
3046 This is required for the Braillex ib80-piezo Braille
3047 reader made by F.H. Papenmeier (Germany).
3051 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
3053 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
3054 and disable the IO APIC. legacy for "maxcpus=0".
3056 nosoftlockup [KNL] Disable the soft-lockup detector.
3058 nosync [HW,M68K] Disables sync negotiation for all devices.
3060 nowatchdog [KNL] Disable both lockup detectors, i.e.
3061 soft-lockup and NMI watchdog (hard-lockup).
3065 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
3067 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
3068 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
3069 Some features depend on CPU0. Known dependencies are:
3070 1. Resume from suspend/hibernate depends on CPU0.
3071 Suspend/hibernate will fail if CPU0 is offline and you
3072 need to online CPU0 before suspend/hibernate.
3073 2. PIC interrupts also depend on CPU0. CPU0 can't be
3074 removed if a PIC interrupt is detected.
3075 It's said poweroff/reboot may depend on CPU0 on some
3076 machines although I haven't seen such issues so far
3077 after CPU0 is offline on a few tested machines.
3078 If the dependencies are under your control, you can
3079 turn on cpu0_hotplug.
3081 nps_mtm_hs_ctr= [KNL,ARC]
3082 This parameter sets the maximum duration, in
3083 cycles, each HW thread of the CTOP can run
3084 without interruptions, before HW switches it.
3085 The actual maximum duration is 16 times this
3087 Format: integer between 1 and 255
3090 nptcg= [IA-64] Override max number of concurrent global TLB
3091 purges which is reported from either PAL_VM_SUMMARY or
3094 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
3095 could support. nr_cpus=n : n >= 1 limits the kernel to
3096 support 'n' processors. It could be larger than the
3097 number of already plugged CPU during bootup, later in
3098 runtime you can physically add extra cpu until it reaches
3099 n. So during boot up some boot time memory for per-cpu
3100 variables need be pre-allocated for later physical cpu
3103 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3105 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
3106 Allowed values are enable and disable
3108 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3109 'node', 'default' can be specified
3110 This can be set from sysctl after boot.
3111 See Documentation/sysctl/vm.txt for details.
3113 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3114 See Documentation/debugging-via-ohci1394.txt for more
3117 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3118 Rather than timing out after 20 ms if an EC
3119 command is not properly ACKed, override the length
3120 of the timeout. We have interrupts disabled while
3121 waiting for the ACK, so if this is set too high
3122 interrupts *may* be lost!
3124 omap_mux= [OMAP] Override bootloader pin multiplexing.
3125 Format: <mux_mode0.mode_name=value>...
3126 For example, to override I2C bus2:
3127 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3129 oprofile.timer= [HW]
3130 Use timer interrupt instead of performance counters
3132 oprofile.cpu_type= Force an oprofile cpu type
3133 This might be useful if you have an older oprofile
3134 userland or if you want common events.
3135 Format: { arch_perfmon }
3136 arch_perfmon: [X86] Force use of architectural
3137 perfmon on Intel CPUs instead of the
3138 CPU specific event set.
3139 timer: [X86] Force use of architectural NMI
3140 timer mode (see also oprofile.timer
3141 for generic hr timer mode)
3143 oops=panic Always panic on oopses. Default is to just kill the
3144 process, but there is a small probability of
3145 deadlocking the machine.
3146 This will also cause panics on machine check exceptions.
3147 Useful together with panic=30 to trigger a reboot.
3149 page_owner= [KNL] Boot-time page_owner enabling option.
3150 Storage of the information about who allocated
3151 each page is disabled in default. With this switch,
3153 on: enable the feature
3155 page_poison= [KNL] Boot-time parameter changing the state of
3156 poisoning on the buddy allocator, available with
3157 CONFIG_PAGE_POISONING=y.
3158 off: turn off poisoning (default)
3159 on: turn on poisoning
3161 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3162 timeout > 0: seconds before rebooting
3163 timeout = 0: wait forever
3164 timeout < 0: reboot immediately
3167 panic_print= Bitmask for printing system info when panic happens.
3168 User can chose combination of the following bits:
3169 bit 0: print all tasks info
3170 bit 1: print system memory info
3171 bit 2: print timer info
3172 bit 3: print locks info if CONFIG_LOCKDEP is on
3173 bit 4: print ftrace buffer
3175 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3178 crash_kexec_post_notifiers
3179 Run kdump after running panic-notifiers and dumping
3180 kmsg. This only for the users who doubt kdump always
3181 succeeds in any situation.
3182 Note that this also increases risks of kdump failure,
3183 because some panic notifiers can make the crashed
3184 kernel more unstable.
3186 parkbd.port= [HW] Parallel port number the keyboard adapter is
3187 connected to, default is 0.
3189 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3190 0 for XT, 1 for AT (default is AT).
3193 parport= [HW,PPT] Specify parallel ports. 0 disables.
3194 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3195 Use 'auto' to force the driver to use any
3196 IRQ/DMA settings detected (the default is to
3197 ignore detected IRQ/DMA settings because of
3198 possible conflicts). You can specify the base
3199 address, IRQ, and DMA settings; IRQ and DMA
3200 should be numbers, or 'auto' (for using detected
3201 settings on that particular port), or 'nofifo'
3202 (to avoid using a FIFO even if it is detected).
3203 Parallel ports are assigned in the order they
3204 are specified on the command line, starting
3207 parport_init_mode= [HW,PPT]
3208 Configure VIA parallel port to operate in
3209 a specific mode. This is necessary on Pegasos
3210 computer where firmware has no options for setting
3211 up parallel port mode and sets it to spp.
3212 Currently this function knows 686a and 8231 chips.
3213 Format: [spp|ps2|epp|ecp|ecpepp]
3216 Halt all CPUs after the first oops has been printed for
3217 the specified number of seconds. This is to be used if
3218 your oopses keep scrolling off the screen.
3223 See header of drivers/block/paride/pcd.c.
3224 See also Documentation/blockdev/paride.txt.
3226 pci=option[,option...] [PCI] various PCI subsystem options.
3228 Some options herein operate on a specific device
3229 or a set of devices (<pci_dev>). These are
3230 specified in one of the following formats:
3232 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
3233 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
3235 Note: the first format specifies a PCI
3236 bus/device/function address which may change
3237 if new hardware is inserted, if motherboard
3238 firmware changes, or due to changes caused
3239 by other kernel parameters. If the
3240 domain is left unspecified, it is
3241 taken to be zero. Optionally, a path
3242 to a device through multiple device/function
3243 addresses can be specified after the base
3244 address (this is more robust against
3245 renumbering issues). The second format
3246 selects devices using IDs from the
3247 configuration space which may match multiple
3248 devices in the system.
3250 earlydump dump PCI config space before the kernel
3252 off [X86] don't probe for the PCI bus
3253 bios [X86-32] force use of PCI BIOS, don't access
3254 the hardware directly. Use this if your machine
3255 has a non-standard PCI host bridge.
3256 nobios [X86-32] disallow use of PCI BIOS, only direct
3257 hardware access methods are allowed. Use this
3258 if you experience crashes upon bootup and you
3259 suspect they are caused by the BIOS.
3260 conf1 [X86] Force use of PCI Configuration Access
3261 Mechanism 1 (config address in IO port 0xCF8,
3262 data in IO port 0xCFC, both 32-bit).
3263 conf2 [X86] Force use of PCI Configuration Access
3264 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3265 the function, IO port 0xCFA, also 8-bit, sets
3266 bus number. The config space is then accessed
3267 through ports 0xC000-0xCFFF).
3268 See http://wiki.osdev.org/PCI for more info
3269 on the configuration access mechanisms.
3270 noaer [PCIE] If the PCIEAER kernel config parameter is
3271 enabled, this kernel boot option can be used to
3272 disable the use of PCIE advanced error reporting.
3273 nodomains [PCI] Disable support for multiple PCI
3274 root domains (aka PCI segments, in ACPI-speak).
3275 nommconf [X86] Disable use of MMCONFIG for PCI
3277 check_enable_amd_mmconf [X86] check for and enable
3278 properly configured MMIO access to PCI
3279 config space on AMD family 10h CPU
3280 nomsi [MSI] If the PCI_MSI kernel config parameter is
3281 enabled, this kernel boot option can be used to
3282 disable the use of MSI interrupts system-wide.
3283 noioapicquirk [APIC] Disable all boot interrupt quirks.
3284 Safety option to keep boot IRQs enabled. This
3285 should never be necessary.
3286 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3287 primary IO-APIC for bridges that cannot disable
3288 boot IRQs. This fixes a source of spurious IRQs
3289 when the system masks IRQs.
3290 noioapicreroute [APIC] Disable workaround that uses the
3291 boot IRQ equivalent of an IRQ that connects to
3292 a chipset where boot IRQs cannot be disabled.
3293 The opposite of ioapicreroute.
3294 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3295 routing table. These calls are known to be buggy
3296 on several machines and they hang the machine
3297 when used, but on other computers it's the only
3298 way to get the interrupt routing table. Try
3299 this option if the kernel is unable to allocate
3300 IRQs or discover secondary PCI buses on your
3302 rom [X86] Assign address space to expansion ROMs.
3303 Use with caution as certain devices share
3304 address decoders between ROMs and other
3306 norom [X86] Do not assign address space to
3307 expansion ROMs that do not already have
3308 BIOS assigned address ranges.
3309 nobar [X86] Do not assign address space to the
3310 BARs that weren't assigned by the BIOS.
3311 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3312 assigned automatically to PCI devices. You can
3313 make the kernel exclude IRQs of your ISA cards
3315 pirqaddr=0xAAAAA [X86] Specify the physical address
3316 of the PIRQ table (normally generated
3317 by the BIOS) if it is outside the
3318 F0000h-100000h range.
3319 lastbus=N [X86] Scan all buses thru bus #N. Can be
3320 useful if the kernel is unable to find your
3321 secondary buses and you want to tell it
3322 explicitly which ones they are.
3323 assign-busses [X86] Always assign all PCI bus
3324 numbers ourselves, overriding
3325 whatever the firmware may have done.
3326 usepirqmask [X86] Honor the possible IRQ mask stored
3327 in the BIOS $PIR table. This is needed on
3328 some systems with broken BIOSes, notably
3329 some HP Pavilion N5400 and Omnibook XE3
3330 notebooks. This will have no effect if ACPI
3331 IRQ routing is enabled.
3332 noacpi [X86] Do not use ACPI for IRQ routing
3333 or for PCI scanning.
3334 use_crs [X86] Use PCI host bridge window information
3335 from ACPI. On BIOSes from 2008 or later, this
3336 is enabled by default. If you need to use this,
3337 please report a bug.
3338 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3339 If you need to use this, please report a bug.
3340 routeirq Do IRQ routing for all PCI devices.
3341 This is normally done in pci_enable_device(),
3342 so this option is a temporary workaround
3343 for broken drivers that don't call it.
3344 skip_isa_align [X86] do not align io start addr, so can
3345 handle more pci cards
3346 noearly [X86] Don't do any early type 1 scanning.
3347 This might help on some broken boards which
3348 machine check when some devices' config space
3349 is read. But various workarounds are disabled
3350 and some IOMMU drivers will not work.
3351 bfsort Sort PCI devices into breadth-first order.
3352 This sorting is done to get a device
3353 order compatible with older (<= 2.4) kernels.
3354 nobfsort Don't sort PCI devices into breadth-first order.
3355 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3356 tuning and use the BIOS-configured MPS defaults.
3357 pcie_bus_safe Set every device's MPS to the largest value
3358 supported by all devices below the root complex.
3359 pcie_bus_perf Set device MPS to the largest allowable MPS
3360 based on its parent bus. Also set MRRS (Max
3361 Read Request Size) to the largest supported
3362 value (no larger than the MPS that the device
3363 or bus can support) for best performance.
3364 pcie_bus_peer2peer Set every device's MPS to 128B, which
3365 every device is guaranteed to support. This
3366 configuration allows peer-to-peer DMA between
3367 any pair of devices, possibly at the cost of
3368 reduced performance. This also guarantees
3369 that hot-added devices will work.
3370 cbiosize=nn[KMG] The fixed amount of bus space which is
3371 reserved for the CardBus bridge's IO window.
3372 The default value is 256 bytes.
3373 cbmemsize=nn[KMG] The fixed amount of bus space which is
3374 reserved for the CardBus bridge's memory
3375 window. The default value is 64 megabytes.
3378 [<order of align>@]<pci_dev>[; ...]
3379 Specifies alignment and device to reassign
3380 aligned memory resources. How to
3381 specify the device is described above.
3382 If <order of align> is not specified,
3383 PAGE_SIZE is used as alignment.
3384 PCI-PCI bridge can be specified, if resource
3385 windows need to be expanded.
3386 To specify the alignment for several
3387 instances of a device, the PCI vendor,
3388 device, subvendor, and subdevice may be
3389 specified, e.g., 4096@pci:8086:9c22:103c:198f
3390 ecrc= Enable/disable PCIe ECRC (transaction layer
3391 end-to-end CRC checking).
3392 bios: Use BIOS/firmware settings. This is the
3396 hpiosize=nn[KMG] The fixed amount of bus space which is
3397 reserved for hotplug bridge's IO window.
3398 Default size is 256 bytes.
3399 hpmemsize=nn[KMG] The fixed amount of bus space which is
3400 reserved for hotplug bridge's memory window.
3401 Default size is 2 megabytes.
3402 hpbussize=nn The minimum amount of additional bus numbers
3403 reserved for buses below a hotplug bridge.
3405 realloc= Enable/disable reallocating PCI bridge resources
3406 if allocations done by BIOS are too small to
3407 accommodate resources required by all child
3409 off: Turn realloc off
3411 realloc same as realloc=on
3412 noari do not use PCIe ARI.
3413 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
3414 do not use PCIe ATS (and IOMMU device IOTLB).
3415 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3416 only look for one device below a PCIe downstream
3418 big_root_window Try to add a big 64bit memory window to the PCIe
3419 root complex on AMD CPUs. Some GFX hardware
3420 can resize a BAR to allow access to all VRAM.
3421 Adding the window is slightly risky (it may
3422 conflict with unreported devices), so this
3424 disable_acs_redir=<pci_dev>[; ...]
3425 Specify one or more PCI devices (in the format
3426 specified above) separated by semicolons.
3427 Each device specified will have the PCI ACS
3428 redirect capabilities forced off which will
3429 allow P2P traffic between devices through
3430 bridges without forcing it upstream. Note:
3431 this removes isolation between devices and
3432 may put more devices in an IOMMU group.
3433 force_floating [S390] Force usage of floating interrupts.
3434 nomio [S390] Do not use MIO instructions.
3436 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3439 force Enable ASPM even on devices that claim not to support it.
3440 WARNING: Forcing ASPM on may cause system lockups.
3442 pcie_ports= [PCIE] PCIe port services handling:
3443 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
3444 even if the platform doesn't give the OS permission to
3445 use them. This may cause conflicts if the platform
3446 also tries to use these services.
3447 compat Disable native PCIe services (PME, AER, DPC, PCIe
3450 pcie_port_pm= [PCIE] PCIe port power management handling:
3451 off Disable power management of all PCIe ports
3452 force Forcibly enable power management of all PCIe ports
3454 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3455 nomsi Do not use MSI for native PCIe PME signaling (this makes
3456 all PCIe root ports use INTx for all services).
3458 pcmv= [HW,PCMCIA] BadgePAD 4
3462 Keep all power-domains already enabled by bootloader on,
3463 even if no driver has claimed them. This is useful
3464 for debug and development, but should not be
3465 needed on a platform with proper driver support.
3468 See Documentation/blockdev/paride.txt.
3470 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3473 See arch/parisc/kernel/pdc_chassis.c
3475 percpu_alloc= Select which percpu first chunk allocator to use.
3476 Currently supported values are "embed" and "page".
3477 Archs may support subset or none of the selections.
3478 See comments in mm/percpu.c for details on each
3479 allocator. This parameter is primarily for debugging
3480 and performance comparison.
3483 See Documentation/blockdev/paride.txt.
3486 See Documentation/blockdev/paride.txt.
3488 pirq= [SMP,APIC] Manual mp-table setup
3489 See Documentation/x86/i386/IO-APIC.txt.
3491 plip= [PPT,NET] Parallel port network link
3492 Format: { parport<nr> | timid | 0 }
3493 See also Documentation/admin-guide/parport.rst.
3495 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3496 Override pmtimer IOPort with a hex value.
3500 Enable PNP debug messages (depends on the
3501 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3502 via /sys/module/pnp/parameters/debug. We always show
3503 current resource usage; turning this on also shows
3504 possible settings and some assignment information.
3510 { on | off | curr | res | no-curr | no-res }
3513 [ISAPNP] Exclude IRQs for the autoconfiguration
3516 [ISAPNP] Exclude DMAs for the autoconfiguration
3518 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3519 Ranges are in pairs (I/O port base and size).
3522 [ISAPNP] Exclude memory regions for the
3524 Ranges are in pairs (memory base and size).
3526 ports= [IP_VS_FTP] IPVS ftp helper module
3528 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3530 Format: <port>,<port>....
3532 powersave=off [PPC] This option disables power saving features.
3533 It specifically disables cpuidle and sets the
3534 platform machine description specific power_save
3535 function to NULL. On Idle the CPU just reduces
3538 ppc_strict_facility_enable
3539 [PPC] This option catches any kernel floating point,
3540 Altivec, VSX and SPE outside of regions specifically
3541 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3542 There is some performance impact when enabling this.
3546 Disable Hardware Transactional Memory
3548 print-fatal-signals=
3549 [KNL] debug: print fatal signals
3551 If enabled, warn about various signal handling
3552 related application anomalies: too many signals,
3553 too many POSIX.1 timers, fatal signals causing a
3556 If you hit the warning due to signal overflow,
3557 you might want to try "ulimit -i unlimited".
3561 printk.always_kmsg_dump=
3562 Trigger kmsg_dump for cases other than kernel oops or
3564 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3567 printk.devkmsg={on,off,ratelimit}
3568 Control writing to /dev/kmsg.
3569 on - unlimited logging to /dev/kmsg from userspace
3570 off - logging to /dev/kmsg disabled
3571 ratelimit - ratelimit the logging
3574 printk.time= Show timing data prefixed to each printk message line
3575 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3577 processor.max_cstate= [HW,ACPI]
3578 Limit processor to maximum C-state
3579 max_cstate=9 overrides any DMI blacklist limit.
3581 processor.nocst [HW,ACPI]
3582 Ignore the _CST method to determine C-states,
3583 instead using the legacy FADT method
3585 profile= [KNL] Enable kernel profiling via /proc/profile
3586 Format: [<profiletype>,]<number>
3587 Param: <profiletype>: "schedule", "sleep", or "kvm"
3588 [defaults to kernel profiling]
3589 Param: "schedule" - profile schedule points.
3590 Param: "sleep" - profile D-state sleeping (millisecs).
3591 Requires CONFIG_SCHEDSTATS
3592 Param: "kvm" - profile VM exits.
3593 Param: <number> - step/bucket size as a power of 2 for
3594 statistical time based profiling.
3596 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3598 See Documentation/blockdev/ramdisk.txt.
3600 psi= [KNL] Enable or disable pressure stall information
3604 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3605 probe for; one of (bare|imps|exps|lifebook|any).
3606 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3608 psmouse.resetafter= [HW,MOUSE]
3609 Try to reset the device after so many bad packets
3612 [HW,MOUSE] Set desired mouse resolution, in dpi.
3613 psmouse.smartscroll=
3614 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3615 0 = disabled, 1 = enabled (default).
3617 pstore.backend= Specify the name of the pstore backend to use
3620 See Documentation/blockdev/paride.txt.
3622 pti= [X86_64] Control Page Table Isolation of user and
3623 kernel address spaces. Disabling this feature
3624 removes hardening, but improves performance of
3625 system calls and interrupts.
3627 on - unconditionally enable
3628 off - unconditionally disable
3629 auto - kernel detects whether your CPU model is
3630 vulnerable to issues that PTI mitigates
3632 Not specifying this option is equivalent to pti=auto.
3635 Equivalent to pti=off
3638 [KNL] Number of legacy pty's. Overwrites compiled-in
3641 quiet [KNL] Disable most log messages
3646 See Documentation/admin-guide/md.rst.
3648 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3649 See Documentation/blockdev/ramdisk.txt.
3651 random.trust_cpu={on,off}
3652 [KNL] Enable or disable trusting the use of the
3653 CPU's random number generator (if available) to
3654 fully seed the kernel's CRNG. Default is controlled
3655 by CONFIG_RANDOM_TRUST_CPU.
3657 ras=option[,option,...] [KNL] RAS-specific options
3660 Disable the Correctable Errors Collector,
3661 see CONFIG_RAS_CEC help text.
3664 The argument is a cpu list, as described above,
3665 except that the string "all" can be used to
3666 specify every CPU on the system.
3668 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3669 the specified list of CPUs to be no-callback CPUs.
3670 Invocation of these CPUs' RCU callbacks will be
3671 offloaded to "rcuox/N" kthreads created for that
3672 purpose, where "x" is "p" for RCU-preempt, and
3673 "s" for RCU-sched, and "N" is the CPU number.
3674 This reduces OS jitter on the offloaded CPUs,
3675 which can be useful for HPC and real-time
3676 workloads. It can also improve energy efficiency
3677 for asymmetric multiprocessors.
3680 Rather than requiring that offloaded CPUs
3681 (specified by rcu_nocbs= above) explicitly
3682 awaken the corresponding "rcuoN" kthreads,
3683 make these kthreads poll for callbacks.
3684 This improves the real-time response for the
3685 offloaded CPUs by relieving them of the need to
3686 wake up the corresponding kthread, but degrades
3687 energy efficiency by requiring that the kthreads
3688 periodically wake up to do the polling.
3690 rcutree.blimit= [KNL]
3691 Set maximum number of finished RCU callbacks to
3692 process in one batch.
3694 rcutree.dump_tree= [KNL]
3695 Dump the structure of the rcu_node combining tree
3696 out at early boot. This is used for diagnostic
3697 purposes, to verify correct tree setup.
3699 rcutree.gp_cleanup_delay= [KNL]
3700 Set the number of jiffies to delay each step of
3701 RCU grace-period cleanup.
3703 rcutree.gp_init_delay= [KNL]
3704 Set the number of jiffies to delay each step of
3705 RCU grace-period initialization.
3707 rcutree.gp_preinit_delay= [KNL]
3708 Set the number of jiffies to delay each step of
3709 RCU grace-period pre-initialization, that is,
3710 the propagation of recent CPU-hotplug changes up
3711 the rcu_node combining tree.
3713 rcutree.rcu_fanout_exact= [KNL]
3714 Disable autobalancing of the rcu_node combining
3715 tree. This is used by rcutorture, and might
3716 possibly be useful for architectures having high
3717 cache-to-cache transfer latencies.
3719 rcutree.rcu_fanout_leaf= [KNL]
3720 Change the number of CPUs assigned to each
3721 leaf rcu_node structure. Useful for very
3722 large systems, which will choose the value 64,
3723 and for NUMA systems with large remote-access
3724 latencies, which will choose a value aligned
3725 with the appropriate hardware boundaries.
3727 rcutree.jiffies_till_first_fqs= [KNL]
3728 Set delay from grace-period initialization to
3729 first attempt to force quiescent states.
3730 Units are jiffies, minimum value is zero,
3731 and maximum value is HZ.
3733 rcutree.jiffies_till_next_fqs= [KNL]
3734 Set delay between subsequent attempts to force
3735 quiescent states. Units are jiffies, minimum
3736 value is one, and maximum value is HZ.
3738 rcutree.jiffies_till_sched_qs= [KNL]
3739 Set required age in jiffies for a
3740 given grace period before RCU starts
3741 soliciting quiescent-state help from
3742 rcu_note_context_switch() and cond_resched().
3743 If not specified, the kernel will calculate
3744 a value based on the most recent settings
3745 of rcutree.jiffies_till_first_fqs
3746 and rcutree.jiffies_till_next_fqs.
3747 This calculated value may be viewed in
3748 rcutree.jiffies_to_sched_qs. Any attempt to set
3749 rcutree.jiffies_to_sched_qs will be cheerfully
3752 rcutree.kthread_prio= [KNL,BOOT]
3753 Set the SCHED_FIFO priority of the RCU per-CPU
3754 kthreads (rcuc/N). This value is also used for
3755 the priority of the RCU boost threads (rcub/N)
3756 and for the RCU grace-period kthreads (rcu_bh,
3757 rcu_preempt, and rcu_sched). If RCU_BOOST is
3758 set, valid values are 1-99 and the default is 1
3759 (the least-favored priority). Otherwise, when
3760 RCU_BOOST is not set, valid values are 0-99 and
3761 the default is zero (non-realtime operation).
3763 rcutree.rcu_nocb_leader_stride= [KNL]
3764 Set the number of NOCB kthread groups, which
3765 defaults to the square root of the number of
3766 CPUs. Larger numbers reduces the wakeup overhead
3767 on the per-CPU grace-period kthreads, but increases
3768 that same overhead on each group's leader.
3770 rcutree.qhimark= [KNL]
3771 Set threshold of queued RCU callbacks beyond which
3772 batch limiting is disabled.
3774 rcutree.qlowmark= [KNL]
3775 Set threshold of queued RCU callbacks below which
3776 batch limiting is re-enabled.
3778 rcutree.rcu_idle_gp_delay= [KNL]
3779 Set wakeup interval for idle CPUs that have
3780 RCU callbacks (RCU_FAST_NO_HZ=y).
3782 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3783 Set wakeup interval for idle CPUs that have
3784 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3785 Lazy RCU callbacks are those which RCU can
3786 prove do nothing more than free memory.
3788 rcutree.rcu_kick_kthreads= [KNL]
3789 Cause the grace-period kthread to get an extra
3790 wake_up() if it sleeps three times longer than
3791 it should at force-quiescent-state time.
3792 This wake_up() will be accompanied by a
3793 WARN_ONCE() splat and an ftrace_dump().
3795 rcutree.sysrq_rcu= [KNL]
3796 Commandeer a sysrq key to dump out Tree RCU's
3797 rcu_node tree with an eye towards determining
3798 why a new grace period has not yet started.
3800 rcuperf.gp_async= [KNL]
3801 Measure performance of asynchronous
3802 grace-period primitives such as call_rcu().
3804 rcuperf.gp_async_max= [KNL]
3805 Specify the maximum number of outstanding
3806 callbacks per writer thread. When a writer
3807 thread exceeds this limit, it invokes the
3808 corresponding flavor of rcu_barrier() to allow
3809 previously posted callbacks to drain.
3811 rcuperf.gp_exp= [KNL]
3812 Measure performance of expedited synchronous
3813 grace-period primitives.
3815 rcuperf.holdoff= [KNL]
3816 Set test-start holdoff period. The purpose of
3817 this parameter is to delay the start of the
3818 test until boot completes in order to avoid
3821 rcuperf.nreaders= [KNL]
3822 Set number of RCU readers. The value -1 selects
3823 N, where N is the number of CPUs. A value
3824 "n" less than -1 selects N-n+1, where N is again
3825 the number of CPUs. For example, -2 selects N
3826 (the number of CPUs), -3 selects N+1, and so on.
3827 A value of "n" less than or equal to -N selects
3830 rcuperf.nwriters= [KNL]
3831 Set number of RCU writers. The values operate
3832 the same as for rcuperf.nreaders.
3833 N, where N is the number of CPUs
3835 rcuperf.perf_type= [KNL]
3836 Specify the RCU implementation to test.
3838 rcuperf.shutdown= [KNL]
3839 Shut the system down after performance tests
3840 complete. This is useful for hands-off automated
3843 rcuperf.verbose= [KNL]
3844 Enable additional printk() statements.
3846 rcuperf.writer_holdoff= [KNL]
3847 Write-side holdoff between grace periods,
3848 in microseconds. The default of zero says
3851 rcutorture.fqs_duration= [KNL]
3852 Set duration of force_quiescent_state bursts
3855 rcutorture.fqs_holdoff= [KNL]
3856 Set holdoff time within force_quiescent_state bursts
3859 rcutorture.fqs_stutter= [KNL]
3860 Set wait time between force_quiescent_state bursts
3863 rcutorture.fwd_progress= [KNL]
3864 Enable RCU grace-period forward-progress testing
3865 for the types of RCU supporting this notion.
3867 rcutorture.fwd_progress_div= [KNL]
3868 Specify the fraction of a CPU-stall-warning
3869 period to do tight-loop forward-progress testing.
3871 rcutorture.fwd_progress_holdoff= [KNL]
3872 Number of seconds to wait between successive
3873 forward-progress tests.
3875 rcutorture.fwd_progress_need_resched= [KNL]
3876 Enclose cond_resched() calls within checks for
3877 need_resched() during tight-loop forward-progress
3880 rcutorture.gp_cond= [KNL]
3881 Use conditional/asynchronous update-side
3882 primitives, if available.
3884 rcutorture.gp_exp= [KNL]
3885 Use expedited update-side primitives, if available.
3887 rcutorture.gp_normal= [KNL]
3888 Use normal (non-expedited) asynchronous
3889 update-side primitives, if available.
3891 rcutorture.gp_sync= [KNL]
3892 Use normal (non-expedited) synchronous
3893 update-side primitives, if available. If all
3894 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3895 rcutorture.gp_normal=, and rcutorture.gp_sync=
3896 are zero, rcutorture acts as if is interpreted
3897 they are all non-zero.
3899 rcutorture.n_barrier_cbs= [KNL]
3900 Set callbacks/threads for rcu_barrier() testing.
3902 rcutorture.nfakewriters= [KNL]
3903 Set number of concurrent RCU writers. These just
3904 stress RCU, they don't participate in the actual
3905 test, hence the "fake".
3907 rcutorture.nreaders= [KNL]
3908 Set number of RCU readers. The value -1 selects
3909 N-1, where N is the number of CPUs. A value
3910 "n" less than -1 selects N-n-2, where N is again
3911 the number of CPUs. For example, -2 selects N
3912 (the number of CPUs), -3 selects N+1, and so on.
3914 rcutorture.object_debug= [KNL]
3915 Enable debug-object double-call_rcu() testing.
3917 rcutorture.onoff_holdoff= [KNL]
3918 Set time (s) after boot for CPU-hotplug testing.
3920 rcutorture.onoff_interval= [KNL]
3921 Set time (jiffies) between CPU-hotplug operations,
3922 or zero to disable CPU-hotplug testing.
3924 rcutorture.shuffle_interval= [KNL]
3925 Set task-shuffle interval (s). Shuffling tasks
3926 allows some CPUs to go into dyntick-idle mode
3927 during the rcutorture test.
3929 rcutorture.shutdown_secs= [KNL]
3930 Set time (s) after boot system shutdown. This
3931 is useful for hands-off automated testing.
3933 rcutorture.stall_cpu= [KNL]
3934 Duration of CPU stall (s) to test RCU CPU stall
3935 warnings, zero to disable.
3937 rcutorture.stall_cpu_holdoff= [KNL]
3938 Time to wait (s) after boot before inducing stall.
3940 rcutorture.stall_cpu_irqsoff= [KNL]
3941 Disable interrupts while stalling if set.
3943 rcutorture.stat_interval= [KNL]
3944 Time (s) between statistics printk()s.
3946 rcutorture.stutter= [KNL]
3947 Time (s) to stutter testing, for example, specifying
3948 five seconds causes the test to run for five seconds,
3949 wait for five seconds, and so on. This tests RCU's
3950 ability to transition abruptly to and from idle.
3952 rcutorture.test_boost= [KNL]
3953 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3954 "Maybe" means test if the RCU implementation
3955 under test support RCU priority boosting.
3957 rcutorture.test_boost_duration= [KNL]
3958 Duration (s) of each individual boost test.
3960 rcutorture.test_boost_interval= [KNL]
3961 Interval (s) between each boost test.
3963 rcutorture.test_no_idle_hz= [KNL]
3964 Test RCU's dyntick-idle handling. See also the
3965 rcutorture.shuffle_interval parameter.
3967 rcutorture.torture_type= [KNL]
3968 Specify the RCU implementation to test.
3970 rcutorture.verbose= [KNL]
3971 Enable additional printk() statements.
3973 rcupdate.rcu_cpu_stall_suppress= [KNL]
3974 Suppress RCU CPU stall warning messages.
3976 rcupdate.rcu_cpu_stall_timeout= [KNL]
3977 Set timeout for RCU CPU stall warning messages.
3979 rcupdate.rcu_expedited= [KNL]
3980 Use expedited grace-period primitives, for
3981 example, synchronize_rcu_expedited() instead
3982 of synchronize_rcu(). This reduces latency,
3983 but can increase CPU utilization, degrade
3984 real-time latency, and degrade energy efficiency.
3985 No effect on CONFIG_TINY_RCU kernels.
3987 rcupdate.rcu_normal= [KNL]
3988 Use only normal grace-period primitives,
3989 for example, synchronize_rcu() instead of
3990 synchronize_rcu_expedited(). This improves
3991 real-time latency, CPU utilization, and
3992 energy efficiency, but can expose users to
3993 increased grace-period latency. This parameter
3994 overrides rcupdate.rcu_expedited. No effect on
3995 CONFIG_TINY_RCU kernels.
3997 rcupdate.rcu_normal_after_boot= [KNL]
3998 Once boot has completed (that is, after
3999 rcu_end_inkernel_boot() has been invoked), use
4000 only normal grace-period primitives. No effect
4001 on CONFIG_TINY_RCU kernels.
4003 rcupdate.rcu_task_stall_timeout= [KNL]
4004 Set timeout in jiffies for RCU task stall warning
4005 messages. Disable with a value less than or equal
4008 rcupdate.rcu_self_test= [KNL]
4009 Run the RCU early boot self tests
4013 Run specified binary instead of /init from the ramdisk,
4014 used for early userspace startup. See initrd.
4017 Turn on/off individual RDT features. List is:
4018 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
4020 E.g. to turn on cmt and turn off mba use:
4024 Format (x86 or x86_64):
4025 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
4027 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
4029 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
4030 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
4031 reboot_force is either force or not specified,
4032 reboot_cpu is s[mp]#### with #### being the processor
4033 to be used for rebooting.
4036 [KNL, SMP] Set scheduler's default relax_domain_level.
4037 See Documentation/cgroup-v1/cpusets.txt.
4039 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
4040 Format: <base1>,<size1>[,<base2>,<size2>,...]
4041 Reserve I/O ports or memory so the kernel won't use
4042 them. If <base> is less than 0x10000, the region
4043 is assumed to be I/O ports; otherwise it is memory.
4045 reservetop= [X86-32]
4047 Reserves a hole at the top of the kernel virtual
4052 Set the amount of memory to reserve for BIOS at
4053 the bottom of the address space.
4055 reset_devices [KNL] Force drivers to reset the underlying device
4056 during initialization.
4059 Specify the partition device for software suspend
4061 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
4063 resume_offset= [SWSUSP]
4064 Specify the offset from the beginning of the partition
4065 given by "resume=" at which the swap header is located,
4066 in <PAGE_SIZE> units (needed only for swap files).
4067 See Documentation/power/swsusp-and-swap-files.txt
4069 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
4070 read the resume files
4072 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
4073 Useful for devices that are detected asynchronously
4074 (e.g. USB and MMC devices).
4076 hibernate= [HIBERNATION]
4077 noresume Don't check if there's a hibernation image
4078 present during boot.
4079 nocompress Don't compress/decompress hibernation images.
4080 no Disable hibernation and resume.
4081 protect_image Turn on image protection during restoration
4082 (that will set all pages holding image data
4083 during restoration read-only).
4085 retain_initrd [RAM] Keep initrd memory after extraction
4087 rfkill.default_state=
4088 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
4089 etc. communication is blocked by default.
4092 rfkill.master_switch_mode=
4093 0 The "airplane mode" button does nothing.
4094 1 The "airplane mode" button toggles between everything
4095 blocked and the previous configuration.
4096 2 The "airplane mode" button toggles between everything
4097 blocked and everything unblocked.
4099 rhash_entries= [KNL,NET]
4100 Set number of hash buckets for route cache
4103 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
4106 ro [KNL] Mount root device read-only on boot
4109 on Mark read-only kernel memory as read-only (default).
4110 off Leave read-only kernel memory writable for debugging.
4113 Enable the uart passthrough on the designated usb port
4114 on Rockchip SoCs. When active, the signals of the
4115 debug-uart get routed to the D+ and D- pins of the usb
4116 port and the regular usb controller gets disabled.
4118 root= [KNL] Root filesystem
4119 See name_to_dev_t comment in init/do_mounts.c.
4121 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
4122 mount the root filesystem
4124 rootflags= [KNL] Set root filesystem mount option string
4126 rootfstype= [KNL] Set root filesystem type
4128 rootwait [KNL] Wait (indefinitely) for root device to show up.
4129 Useful for devices that are detected asynchronously
4130 (e.g. USB and MMC devices).
4132 rproc_mem=nn[KMG][@address]
4133 [KNL,ARM,CMA] Remoteproc physical memory block.
4134 Memory area to be used by remote processor image,
4137 rw [KNL] Mount root device read-write on boot
4139 S [KNL] Run init in single mode
4141 s390_iommu= [HW,S390]
4142 Set s390 IOTLB flushing mode
4144 With strict flushing every unmap operation will result in
4145 an IOTLB flush. Default is lazy flushing before reuse,
4149 See drivers/net/irda/sa1100_ir.c.
4151 sbni= [NET] Granch SBNI12 leased line adapter
4153 sched_debug [KNL] Enables verbose scheduler debug messages.
4155 schedstats= [KNL,X86] Enable or disable scheduled statistics.
4156 Allowed values are enable and disable. This feature
4157 incurs a small amount of overhead in the scheduler
4158 but is useful for debugging and performance tuning.
4160 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
4161 xtime_lock contention on larger systems, and/or RCU lock
4162 contention on all systems with CONFIG_MAXSMP set.
4163 Format: { "0" | "1" }
4164 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
4166 Note: increases power consumption, thus should only be
4167 enabled if running jitter sensitive (HPC/RT) workloads.
4169 security= [SECURITY] Choose a legacy "major" security module to
4170 enable at boot. This has been deprecated by the
4173 selinux= [SELINUX] Disable or enable SELinux at boot time.
4174 Format: { "0" | "1" }
4175 See security/selinux/Kconfig help text.
4178 Default value is set via kernel config option.
4179 If enabled at boot time, /selinux/disable can be used
4180 later to disable prior to initial policy load.
4182 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
4183 Format: { "0" | "1" }
4184 See security/apparmor/Kconfig help text
4187 Default value is set via kernel config option.
4189 serialnumber [BUGS=X86-32]
4192 Maximal number of shapers.
4200 Disable merging of slabs with similar size. May be
4201 necessary if there is some reason to distinguish
4202 allocs to different slabs, especially in hardened
4203 environments where the risk of heap overflows and
4204 layout control by attackers can usually be
4205 frustrated by disabling merging. This will reduce
4206 most of the exposure of a heap attack to a single
4207 cache (risks via metadata attacks are mostly
4208 unchanged). Debug options disable merging on their
4210 For more information see Documentation/vm/slub.rst.
4212 slab_max_order= [MM, SLAB]
4213 Determines the maximum allowed order for slabs.
4214 A high setting may cause OOMs due to memory
4215 fragmentation. Defaults to 1 for systems with
4216 more than 32MB of RAM, 0 otherwise.
4218 slub_debug[=options[,slabs]] [MM, SLUB]
4219 Enabling slub_debug allows one to determine the
4220 culprit if slab objects become corrupted. Enabling
4221 slub_debug can create guard zones around objects and
4222 may poison objects when not in use. Also tracks the
4223 last alloc / free. For more information see
4224 Documentation/vm/slub.rst.
4226 slub_memcg_sysfs= [MM, SLUB]
4227 Determines whether to enable sysfs directories for
4228 memory cgroup sub-caches. 1 to enable, 0 to disable.
4229 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
4230 Enabling this can lead to a very high number of debug
4231 directories and files being created under
4234 slub_max_order= [MM, SLUB]
4235 Determines the maximum allowed order for slabs.
4236 A high setting may cause OOMs due to memory
4237 fragmentation. For more information see
4238 Documentation/vm/slub.rst.
4240 slub_min_objects= [MM, SLUB]
4241 The minimum number of objects per slab. SLUB will
4242 increase the slab order up to slub_max_order to
4243 generate a sufficiently large slab able to contain
4244 the number of objects indicated. The higher the number
4245 of objects the smaller the overhead of tracking slabs
4246 and the less frequently locks need to be acquired.
4247 For more information see Documentation/vm/slub.rst.
4249 slub_min_order= [MM, SLUB]
4250 Determines the minimum page order for slabs. Must be
4251 lower than slub_max_order.
4252 For more information see Documentation/vm/slub.rst.
4254 slub_nomerge [MM, SLUB]
4255 Same with slab_nomerge. This is supported for legacy.
4256 See slab_nomerge for more information.
4259 Format: <io1>[,<io2>[,...,<io8>]]
4261 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4262 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4263 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4264 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4265 smsc-ircc2.ircc_irq= [HW] IRQ line
4266 smsc-ircc2.ircc_dma= [HW] DMA channel
4267 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4268 0: Toshiba Satellite 1800 (GP data pin select)
4269 1: Fast pin select (default)
4272 smt [KNL,S390] Set the maximum number of threads (logical
4273 CPUs) to use per physical CPU on systems capable of
4274 symmetric multithreading (SMT). Will be capped to the
4275 actual hardware limit.
4277 Default: -1 (no limit)
4280 [KNL] Should the soft-lockup detector generate panics.
4283 A nonzero value instructs the soft-lockup detector
4284 to panic the machine when a soft-lockup occurs. This
4285 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
4286 which is the respective build-time switch to that
4289 softlockup_all_cpu_backtrace=
4290 [KNL] Should the soft-lockup detector generate
4291 backtraces on all cpus.
4294 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4295 See Documentation/laptops/sonypi.txt
4297 spectre_v2= [X86] Control mitigation of Spectre variant 2
4298 (indirect branch speculation) vulnerability.
4299 The default operation protects the kernel from
4302 on - unconditionally enable, implies
4304 off - unconditionally disable, implies
4306 auto - kernel detects whether your CPU model is
4309 Selecting 'on' will, and 'auto' may, choose a
4310 mitigation method at run time according to the
4311 CPU, the available microcode, the setting of the
4312 CONFIG_RETPOLINE configuration option, and the
4313 compiler with which the kernel was built.
4315 Selecting 'on' will also enable the mitigation
4316 against user space to user space task attacks.
4318 Selecting 'off' will disable both the kernel and
4319 the user space protections.
4321 Specific mitigations can also be selected manually:
4323 retpoline - replace indirect branches
4324 retpoline,generic - google's original retpoline
4325 retpoline,amd - AMD-specific minimal thunk
4327 Not specifying this option is equivalent to
4331 [X86] Control mitigation of Spectre variant 2
4332 (indirect branch speculation) vulnerability between
4335 on - Unconditionally enable mitigations. Is
4336 enforced by spectre_v2=on
4338 off - Unconditionally disable mitigations. Is
4339 enforced by spectre_v2=off
4341 prctl - Indirect branch speculation is enabled,
4342 but mitigation can be enabled via prctl
4343 per thread. The mitigation control state
4344 is inherited on fork.
4347 - Like "prctl" above, but only STIBP is
4348 controlled per thread. IBPB is issued
4349 always when switching between different user
4353 - Same as "prctl" above, but all seccomp
4354 threads will enable the mitigation unless
4355 they explicitly opt out.
4358 - Like "seccomp" above, but only STIBP is
4359 controlled per thread. IBPB is issued
4360 always when switching between different
4361 user space processes.
4363 auto - Kernel selects the mitigation depending on
4364 the available CPU features and vulnerability.
4367 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
4369 Not specifying this option is equivalent to
4370 spectre_v2_user=auto.
4372 spec_store_bypass_disable=
4373 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4374 (Speculative Store Bypass vulnerability)
4376 Certain CPUs are vulnerable to an exploit against a
4377 a common industry wide performance optimization known
4378 as "Speculative Store Bypass" in which recent stores
4379 to the same memory location may not be observed by
4380 later loads during speculative execution. The idea
4381 is that such stores are unlikely and that they can
4382 be detected prior to instruction retirement at the
4383 end of a particular speculation execution window.
4385 In vulnerable processors, the speculatively forwarded
4386 store can be used in a cache side channel attack, for
4387 example to read memory to which the attacker does not
4388 directly have access (e.g. inside sandboxed code).
4390 This parameter controls whether the Speculative Store
4391 Bypass optimization is used.
4393 On x86 the options are:
4395 on - Unconditionally disable Speculative Store Bypass
4396 off - Unconditionally enable Speculative Store Bypass
4397 auto - Kernel detects whether the CPU model contains an
4398 implementation of Speculative Store Bypass and
4399 picks the most appropriate mitigation. If the
4400 CPU is not vulnerable, "off" is selected. If the
4401 CPU is vulnerable the default mitigation is
4402 architecture and Kconfig dependent. See below.
4403 prctl - Control Speculative Store Bypass per thread
4404 via prctl. Speculative Store Bypass is enabled
4405 for a process by default. The state of the control
4406 is inherited on fork.
4407 seccomp - Same as "prctl" above, but all seccomp threads
4408 will disable SSB unless they explicitly opt out.
4410 Default mitigations:
4411 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4413 On powerpc the options are:
4415 on,auto - On Power8 and Power9 insert a store-forwarding
4416 barrier on kernel entry and exit. On Power7
4417 perform a software flush on kernel entry and
4421 Not specifying this option is equivalent to
4422 spec_store_bypass_disable=auto.
4424 spia_io_base= [HW,MTD]
4429 srcutree.counter_wrap_check [KNL]
4430 Specifies how frequently to check for
4431 grace-period sequence counter wrap for the
4432 srcu_data structure's ->srcu_gp_seq_needed field.
4433 The greater the number of bits set in this kernel
4434 parameter, the less frequently counter wrap will
4435 be checked for. Note that the bottom two bits
4438 srcutree.exp_holdoff [KNL]
4439 Specifies how many nanoseconds must elapse
4440 since the end of the last SRCU grace period for
4441 a given srcu_struct until the next normal SRCU
4442 grace period will be considered for automatic
4443 expediting. Set to zero to disable automatic
4447 Speculative Store Bypass Disable control
4449 On CPUs that are vulnerable to the Speculative
4450 Store Bypass vulnerability and offer a
4451 firmware based mitigation, this parameter
4452 indicates how the mitigation should be used:
4454 force-on: Unconditionally enable mitigation for
4455 for both kernel and userspace
4456 force-off: Unconditionally disable mitigation for
4457 for both kernel and userspace
4458 kernel: Always enable mitigation in the
4459 kernel, and offer a prctl interface
4460 to allow userspace to register its
4461 interest in being mitigated too.
4463 stack_guard_gap= [MM]
4464 override the default stack gap protection. The value
4465 is in page units and it defines how many pages prior
4466 to (for stacks growing down) resp. after (for stacks
4467 growing up) the main stack are reserved for no other
4468 mapping. Default value is 256 pages.
4471 Enabled the stack tracer on boot up.
4473 stacktrace_filter=[function-list]
4474 [FTRACE] Limit the functions that the stack tracer
4475 will trace at boot up. function-list is a comma separated
4476 list of functions. This list can be changed at run
4477 time by the stack_trace_filter file in the debugfs
4478 tracing directory. Note, this enables stack tracing
4479 and the stacktrace above is not needed.
4483 Set the STI (builtin display/keyboard on the HP-PARISC
4484 machines) console (graphic card) which should be used
4485 as the initial boot-console.
4486 See also comment in drivers/video/console/sticore.c.
4489 See comment in drivers/video/console/sticore.c.
4492 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4494 sunrpc.min_resvport=
4495 sunrpc.max_resvport=
4497 SunRPC servers often require that client requests
4498 originate from a privileged port (i.e. a port in the
4499 range 0 < portnr < 1024).
4500 An administrator who wishes to reserve some of these
4501 ports for other uses may adjust the range that the
4502 kernel's sunrpc client considers to be privileged
4503 using these two parameters to set the minimum and
4504 maximum port values.
4506 sunrpc.svc_rpc_per_connection_limit=
4508 Limit the number of requests that the server will
4509 process in parallel from a single connection.
4510 The default value is 0 (no limit).
4514 Control how the NFS server code allocates CPUs to
4515 service thread pools. Depending on how many NICs
4516 you have and where their interrupts are bound, this
4517 option will affect which CPUs will do NFS serving.
4518 Note: this parameter cannot be changed while the
4519 NFS server is running.
4521 auto the server chooses an appropriate mode
4522 automatically using heuristics
4523 global a single global pool contains all CPUs
4524 percpu one pool for each CPU
4525 pernode one pool for each NUMA node (equivalent
4526 to global on non-NUMA machines)
4528 sunrpc.tcp_slot_table_entries=
4529 sunrpc.udp_slot_table_entries=
4531 Sets the upper limit on the number of simultaneous
4532 RPC calls that can be sent from the client to a
4533 server. Increasing these values may allow you to
4534 improve throughput, but will also increase the
4535 amount of memory reserved for use by the client.
4537 suspend.pm_test_delay=
4539 Sets the number of seconds to remain in a suspend test
4540 mode before resuming the system (see
4541 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4542 is set. Default value is 5.
4545 [KNL] Enable accounting of swap in memory resource
4546 controller if no parameter or 1 is given or disable
4547 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4549 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4550 Format: { <int> | force | noforce }
4551 <int> -- Number of I/O TLB slabs
4552 force -- force using of bounce buffers even if they
4553 wouldn't be automatically used by the kernel
4554 noforce -- Never use bounce buffers (for debugging)
4558 sysfs.deprecated=0|1 [KNL]
4559 Enable/disable old style sysfs layout for old udev
4560 on older distributions. When this option is enabled
4561 very new udev will not work anymore. When this option
4562 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4563 in older udev will not work anymore.
4564 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4565 the kernel configuration.
4567 sysrq_always_enabled
4569 Ignore sysrq setting - this boot parameter will
4570 neutralize any effect of /proc/sys/kernel/sysrq.
4571 Useful for debugging.
4573 tcpmhash_entries= [KNL,NET]
4574 Set the number of tcp_metrics_hash slots.
4575 Default value is 8192 or 16384 depending on total
4576 ram pages. This is used to specify the TCP metrics
4577 cache size. See Documentation/networking/ip-sysctl.txt
4578 "tcp_no_metrics_save" section for more details.
4582 test_suspend= [SUSPEND][,N]
4583 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4584 standby suspend) or "freeze" (for suspend type freeze)
4585 as the system sleep state during system startup with
4586 the optional capability to repeat N number of times.
4587 The system is woken from this state using a
4588 wakeup-capable RTC alarm.
4590 thash_entries= [KNL,NET]
4591 Set number of hash buckets for TCP connection
4593 thermal.act= [HW,ACPI]
4594 -1: disable all active trip points in all thermal zones
4595 <degrees C>: override all lowest active trip points
4597 thermal.crt= [HW,ACPI]
4598 -1: disable all critical trip points in all thermal zones
4599 <degrees C>: override all critical trip points
4601 thermal.nocrt= [HW,ACPI]
4602 Set to disable actions on ACPI thermal zone
4603 critical and hot trip points.
4605 thermal.off= [HW,ACPI]
4606 1: disable ACPI thermal control
4608 thermal.psv= [HW,ACPI]
4609 -1: disable all passive trip points
4610 <degrees C>: override all passive trip points to this
4613 thermal.tzp= [HW,ACPI]
4614 Specify global default ACPI thermal zone polling rate
4615 <deci-seconds>: poll all this frequency
4616 0: no polling (default)
4619 Force threading of all interrupt handlers except those
4620 marked explicitly IRQF_NO_THREAD.
4623 Enable the Transcendent memory driver if built-in.
4625 tmem.cleancache=0|1 [KNL, XEN]
4626 Default is on (1). Disable the usage of the cleancache
4627 API to send anonymous pages to the hypervisor.
4629 tmem.frontswap=0|1 [KNL, XEN]
4630 Default is on (1). Disable the usage of the frontswap
4631 API to send swap pages to the hypervisor. If disabled
4632 the selfballooning and selfshrinking are force disabled.
4634 tmem.selfballooning=0|1 [KNL, XEN]
4635 Default is on (1). Disable the driving of swap pages
4638 tmem.selfshrinking=0|1 [KNL, XEN]
4639 Default is on (1). Partial swapoff that immediately
4640 transfers pages from Xen hypervisor back to the
4641 kernel based on different criteria.
4645 Specify if the kernel should make use of the cpu
4646 topology information if the hardware supports this.
4647 The scheduler will make use of this information and
4648 e.g. base its process migration decisions on it.
4651 topology_updates= [KNL, PPC, NUMA]
4653 Specify if the kernel should ignore (off)
4654 topology updates sent by the hypervisor to this
4659 tpm_suspend_pcr=[HW,TPM]
4660 Format: integer pcr id
4661 Specify that at suspend time, the tpm driver
4662 should extend the specified pcr with zeros,
4663 as a workaround for some chips which fail to
4664 flush the last written pcr on TPM_SaveState.
4665 This will guarantee that all the other pcrs
4668 trace_buf_size=nn[KMG]
4669 [FTRACE] will set tracing buffer size on each cpu.
4671 trace_event=[event-list]
4672 [FTRACE] Set and start specified trace events in order
4673 to facilitate early boot debugging. The event-list is a
4674 comma separated list of trace events to enable. See
4675 also Documentation/trace/events.rst
4677 trace_options=[option-list]
4678 [FTRACE] Enable or disable tracer options at boot.
4679 The option-list is a comma delimited list of options
4680 that can be enabled or disabled just as if you were
4681 to echo the option name into
4683 /sys/kernel/debug/tracing/trace_options
4685 For example, to enable stacktrace option (to dump the
4686 stack trace of each event), add to the command line:
4688 trace_options=stacktrace
4690 See also Documentation/trace/ftrace.rst "trace options"
4694 Have the tracepoints sent to printk as well as the
4695 tracing ring buffer. This is useful for early boot up
4696 where the system hangs or reboots and does not give the
4697 option for reading the tracing buffer or performing a
4698 ftrace_dump_on_oops.
4700 To turn off having tracepoints sent to printk,
4701 echo 0 > /proc/sys/kernel/tracepoint_printk
4702 Note, echoing 1 into this file without the
4703 tracepoint_printk kernel cmdline option has no effect.
4707 Having tracepoints sent to printk() and activating high
4708 frequency tracepoints such as irq or sched, can cause
4709 the system to live lock.
4712 [FTRACE] enable this option to disable tracing when a
4713 warning is hit. This turns off "tracing_on". Tracing can
4714 be enabled again by echoing '1' into the "tracing_on"
4715 file located in /sys/kernel/debug/tracing/
4717 This option is useful, as it disables the trace before
4718 the WARNING dump is called, which prevents the trace to
4719 be filled with content caused by the warning output.
4721 This option can also be set at run time via the sysctl
4722 option: kernel/traceoff_on_warning
4724 transparent_hugepage=
4726 Format: [always|madvise|never]
4727 Can be used to control the default behavior of the system
4728 with respect to transparent hugepages.
4729 See Documentation/admin-guide/mm/transhuge.rst
4732 tsc= Disable clocksource stability checks for TSC.
4734 [x86] reliable: mark tsc clocksource as reliable, this
4735 disables clocksource verification at runtime, as well
4736 as the stability checks done at bootup. Used to enable
4737 high-resolution timer mode on older hardware, and in
4738 virtualized environment.
4739 [x86] noirqtime: Do not use TSC to do irq accounting.
4740 Used to run time disable IRQ_TIME_ACCOUNTING on any
4741 platforms where RDTSC is slow and this accounting
4743 [x86] unstable: mark the TSC clocksource as unstable, this
4744 marks the TSC unconditionally unstable at bootup and
4745 avoids any further wobbles once the TSC watchdog notices.
4746 [x86] nowatchdog: disable clocksource watchdog. Used
4747 in situations with strict latency requirements (where
4748 interruptions from clocksource watchdog are not
4751 turbografx.map[2|3]= [HW,JOY]
4752 TurboGraFX parallel port interface
4754 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4755 See also Documentation/input/devices/joystick-parport.rst
4757 udbg-immortal [PPC] When debugging early kernel crashes that
4758 happen after console_init() and before a proper
4759 console driver takes over, this boot options might
4760 help "seeing" what's going on.
4762 uhash_entries= [KNL,NET]
4763 Set number of hash buckets for UDP/UDP-Lite connections
4766 [USB] Ignore overcurrent events (default N).
4767 Some badly-designed motherboards generate lots of
4768 bogus events, for ports that aren't wired to
4769 anything. Set this parameter to avoid log spamming.
4770 Note that genuine overcurrent events won't be
4774 [X86] Cause panic on unknown NMI.
4776 usbcore.authorized_default=
4777 [USB] Default USB device authorization:
4778 (default -1 = authorized except for wireless USB,
4779 0 = not authorized, 1 = authorized, 2 = authorized
4780 if device connected to internal port)
4782 usbcore.autosuspend=
4783 [USB] The autosuspend time delay (in seconds) used
4784 for newly-detected USB devices (default 2). This
4785 is the time required before an idle device will be
4786 autosuspended. Devices for which the delay is set
4787 to a negative value won't be autosuspended at all.
4789 usbcore.usbfs_snoop=
4790 [USB] Set to log all usbfs traffic (default 0 = off).
4792 usbcore.usbfs_snoop_max=
4793 [USB] Maximum number of bytes to snoop in each URB
4796 usbcore.blinkenlights=
4797 [USB] Set to cycle leds on hubs (default 0 = off).
4799 usbcore.old_scheme_first=
4800 [USB] Start with the old device initialization
4801 scheme, applies only to low and full-speed devices
4804 usbcore.usbfs_memory_mb=
4805 [USB] Memory limit (in MB) for buffers allocated by
4806 usbfs (default = 16, 0 = max = 2047).
4808 usbcore.use_both_schemes=
4809 [USB] Try the other device initialization scheme
4810 if the first one fails (default 1 = enabled).
4812 usbcore.initial_descriptor_timeout=
4813 [USB] Specifies timeout for the initial 64-byte
4814 USB_REQ_GET_DESCRIPTOR request in milliseconds
4815 (default 5000 = 5.0 seconds).
4817 usbcore.nousb [USB] Disable the USB subsystem
4820 [USB] A list of quirk entries to augment the built-in
4821 usb core quirk list. List entries are separated by
4822 commas. Each entry has the form
4823 VendorID:ProductID:Flags. The IDs are 4-digit hex
4824 numbers and Flags is a set of letters. Each letter
4825 will change the built-in quirk; setting it if it is
4826 clear and clearing it if it is set. The letters have
4827 the following meanings:
4828 a = USB_QUIRK_STRING_FETCH_255 (string
4829 descriptors must not be fetched using
4831 b = USB_QUIRK_RESET_RESUME (device can't resume
4832 correctly so reset it instead);
4833 c = USB_QUIRK_NO_SET_INTF (device can't handle
4834 Set-Interface requests);
4835 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
4836 handle its Configuration or Interface
4838 e = USB_QUIRK_RESET (device can't be reset
4839 (e.g morph devices), don't use reset);
4840 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
4841 more interface descriptions than the
4842 bNumInterfaces count, and can't handle
4843 talking to these interfaces);
4844 g = USB_QUIRK_DELAY_INIT (device needs a pause
4845 during initialization, after we read
4846 the device descriptor);
4847 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
4848 high speed and super speed interrupt
4849 endpoints, the USB 2.0 and USB 3.0 spec
4850 require the interval in microframes (1
4851 microframe = 125 microseconds) to be
4852 calculated as interval = 2 ^
4854 Devices with this quirk report their
4855 bInterval as the result of this
4856 calculation instead of the exponent
4857 variable used in the calculation);
4858 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
4859 handle device_qualifier descriptor
4861 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
4862 generates spurious wakeup, ignore
4863 remote wakeup capability);
4864 k = USB_QUIRK_NO_LPM (device can't handle Link
4866 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
4867 (Device reports its bInterval as linear
4868 frames instead of the USB 2.0
4870 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
4871 to be disconnected before suspend to
4872 prevent spurious wakeup);
4873 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
4874 pause after every control message);
4875 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
4876 delay after resetting its port);
4877 Example: quirks=0781:5580:bk,0a5c:5834:gij
4880 [USBHID] The interval which mice are to be polled at.
4883 [USBHID] The interval which joysticks are to be polled at.
4886 [USBHID] The interval which keyboards are to be polled at.
4888 usb-storage.delay_use=
4889 [UMS] The delay in seconds before a new device is
4890 scanned for Logical Units (default 1).
4893 [UMS] A list of quirks entries to supplement or
4894 override the built-in unusual_devs list. List
4895 entries are separated by commas. Each entry has
4896 the form VID:PID:Flags where VID and PID are Vendor
4897 and Product ID values (4-digit hex numbers) and
4898 Flags is a set of characters, each corresponding
4899 to a common usb-storage quirk flag as follows:
4900 a = SANE_SENSE (collect more than 18 bytes
4902 b = BAD_SENSE (don't collect more than 18
4903 bytes of sense data);
4904 c = FIX_CAPACITY (decrease the reported
4905 device capacity by one sector);
4906 d = NO_READ_DISC_INFO (don't use
4907 READ_DISC_INFO command);
4908 e = NO_READ_CAPACITY_16 (don't use
4909 READ_CAPACITY_16 command);
4910 f = NO_REPORT_OPCODES (don't use report opcodes
4912 g = MAX_SECTORS_240 (don't transfer more than
4913 240 sectors at a time, uas only);
4914 h = CAPACITY_HEURISTICS (decrease the
4915 reported device capacity by one
4916 sector if the number is odd);
4917 i = IGNORE_DEVICE (don't bind to this
4919 j = NO_REPORT_LUNS (don't use report luns
4921 l = NOT_LOCKABLE (don't try to lock and
4922 unlock ejectable media);
4923 m = MAX_SECTORS_64 (don't transfer more
4924 than 64 sectors = 32 KB at a time);
4925 n = INITIAL_READ10 (force a retry of the
4926 initial READ(10) command);
4927 o = CAPACITY_OK (accept the capacity
4928 reported by the device);
4929 p = WRITE_CACHE (the device cache is ON
4931 r = IGNORE_RESIDUE (the device reports
4932 bogus residue values);
4933 s = SINGLE_LUN (the device has only one
4935 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4936 commands, uas only);
4937 u = IGNORE_UAS (don't bind to the uas driver);
4938 w = NO_WP_DETECT (don't test whether the
4939 medium is write-protected).
4940 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4941 even if the device claims no cache)
4942 Example: quirks=0419:aaf5:rl,0421:0433:rc
4944 user_debug= [KNL,ARM]
4946 See arch/arm/Kconfig.debug help text.
4947 1 - undefined instruction events
4949 4 - invalid data aborts
4952 Example: user_debug=31
4955 [X86] Flags controlling user PTE allocations.
4957 nohigh = do not allocate PTE pages in
4958 HIGHMEM regardless of setting
4962 On X86_32, this is an alias for vdso32=. Otherwise:
4964 vdso=1: enable VDSO (the default)
4965 vdso=0: disable VDSO mapping
4967 vdso32= [X86] Control the 32-bit vDSO
4968 vdso32=1: enable 32-bit VDSO
4969 vdso32=0 or vdso32=2: disable 32-bit VDSO
4971 See the help text for CONFIG_COMPAT_VDSO for more
4972 details. If CONFIG_COMPAT_VDSO is set, the default is
4973 vdso32=0; otherwise, the default is vdso32=1.
4975 For compatibility with older kernels, vdso32=2 is an
4978 Try vdso32=0 if you encounter an error that says:
4979 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4982 vector=percpu: enable percpu vector domain
4984 video= [FB] Frame buffer configuration
4985 See Documentation/fb/modedb.txt.
4987 video.brightness_switch_enabled= [0,1]
4988 If set to 1, on receiving an ACPI notify event
4989 generated by hotkey, video driver will adjust brightness
4990 level and then send out the event to user space through
4991 the allocated input device; If set to 0, video driver
4992 will only send out the event without touching backlight
4997 [VMMIO] Memory mapped virtio (platform) device.
4999 <size>@<baseaddr>:<irq>[:<id>]
5001 <size> := size (can use standard suffixes
5003 <baseaddr> := physical base address
5004 <irq> := interrupt number (as passed to
5006 <id> := (optional) platform device id
5008 virtio_mmio.device=1K@0x100b0000:48:7
5010 Can be used multiple times for multiple devices.
5012 vga= [BOOT,X86-32] Select a particular video mode
5013 See Documentation/x86/boot.txt and
5014 Documentation/svga.txt.
5015 Use vga=ask for menu.
5016 This is actually a boot loader parameter; the value is
5017 passed to the kernel using a special protocol.
5019 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
5020 May slow down system boot speed, especially when
5021 enabled on systems with a large amount of memory.
5022 All options are enabled by default, and this
5023 interface is meant to allow for selectively
5024 enabling or disabling specific virtual memory
5027 Available options are:
5028 P Enable page structure init time poisoning
5029 - Disable all of the above options
5031 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
5032 size of <nn>. This can be used to increase the
5033 minimum size (128MB on x86). It can also be used to
5034 decrease the size and leave more room for directly
5037 vmcp_cma=nn[MG] [KNL,S390]
5038 Sets the memory size reserved for contiguous memory
5039 allocations for the vmcp device driver.
5041 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
5044 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
5047 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
5051 Controls the behavior of vsyscalls (i.e. calls to
5052 fixed addresses of 0xffffffffff600x00 from legacy
5053 code). Most statically-linked binaries and older
5054 versions of glibc use these calls. Because these
5055 functions are at fixed addresses, they make nice
5056 targets for exploits that can control RIP.
5058 emulate [default] Vsyscalls turn into traps and are
5059 emulated reasonably safely.
5061 native Vsyscalls are native syscall instructions.
5062 This is a little bit faster than trapping
5063 and makes a few dynamic recompilers work
5064 better than they would in emulation mode.
5065 It also makes exploits much easier to write.
5067 none Vsyscalls don't work at all. This makes
5068 them quite hard to use for exploits but
5069 might break your system.
5071 vt.color= [VT] Default text color.
5072 Format: 0xYX, X = foreground, Y = background.
5073 Default: 0x07 = light gray on black.
5075 vt.cur_default= [VT] Default cursor shape.
5076 Format: 0xCCBBAA, where AA, BB, and CC are the same as
5077 the parameters of the <Esc>[?A;B;Cc escape sequence;
5078 see VGA-softcursor.txt. Default: 2 = underline.
5080 vt.default_blu= [VT]
5081 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
5082 Change the default blue palette of the console.
5083 This is a 16-member array composed of values
5086 vt.default_grn= [VT]
5087 Format: <green0>,<green1>,<green2>,...,<green15>
5088 Change the default green palette of the console.
5089 This is a 16-member array composed of values
5092 vt.default_red= [VT]
5093 Format: <red0>,<red1>,<red2>,...,<red15>
5094 Change the default red palette of the console.
5095 This is a 16-member array composed of values
5101 Set system-wide default UTF-8 mode for all tty's.
5102 Default is 1, i.e. UTF-8 mode is enabled for all
5103 newly opened terminals.
5105 vt.global_cursor_default=
5108 Set system-wide default for whether a cursor
5109 is shown on new VTs. Default is -1,
5110 i.e. cursors will be created by default unless
5111 overridden by individual drivers. 0 will hide
5112 cursors, 1 will display them.
5114 vt.italic= [VT] Default color for italic text; 0-15.
5117 vt.underline= [VT] Default color for underlined text; 0-15.
5120 watchdog timers [HW,WDT] For information on watchdog timers,
5121 see Documentation/watchdog/watchdog-parameters.txt
5122 or other driver-specific files in the
5123 Documentation/watchdog/ directory.
5127 Set the hard lockup detector stall duration
5128 threshold in seconds. The soft lockup detector
5129 threshold is set to twice the value. A value of 0
5130 disables both lockup detectors. Default is 10
5133 workqueue.watchdog_thresh=
5134 If CONFIG_WQ_WATCHDOG is configured, workqueue can
5135 warn stall conditions and dump internal state to
5136 help debugging. 0 disables workqueue stall
5137 detection; otherwise, it's the stall threshold
5138 duration in seconds. The default value is 30 and
5139 it can be updated at runtime by writing to the
5140 corresponding sysfs file.
5142 workqueue.disable_numa
5143 By default, all work items queued to unbound
5144 workqueues are affine to the NUMA nodes they're
5145 issued on, which results in better behavior in
5146 general. If NUMA affinity needs to be disabled for
5147 whatever reason, this option can be used. Note
5148 that this also can be controlled per-workqueue for
5149 workqueues visible under /sys/bus/workqueue/.
5151 workqueue.power_efficient
5152 Per-cpu workqueues are generally preferred because
5153 they show better performance thanks to cache
5154 locality; unfortunately, per-cpu workqueues tend to
5155 be more power hungry than unbound workqueues.
5157 Enabling this makes the per-cpu workqueues which
5158 were observed to contribute significantly to power
5159 consumption unbound, leading to measurably lower
5160 power usage at the cost of small performance
5163 The default value of this parameter is determined by
5164 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
5166 workqueue.debug_force_rr_cpu
5167 Workqueue used to implicitly guarantee that work
5168 items queued without explicit CPU specified are put
5169 on the local CPU. This guarantee is no longer true
5170 and while local CPU is still preferred work items
5171 may be put on foreign CPUs. This debug option
5172 forces round-robin CPU selection to flush out
5173 usages which depend on the now broken guarantee.
5174 When enabled, memory and cache locality will be
5177 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
5178 default x2apic cluster mode on platforms
5181 x86_intel_mid_timer= [X86-32,APBT]
5182 Choose timer option for x86 Intel MID platform.
5183 Two valid options are apbt timer only and lapic timer
5184 plus one apbt timer for broadcast timer.
5185 x86_intel_mid_timer=apbt_only | lapic_and_apbt
5187 xen_512gb_limit [KNL,X86-64,XEN]
5188 Restricts the kernel running paravirtualized under Xen
5189 to use only up to 512 GB of RAM. The reason to do so is
5190 crash analysis tools and Xen tools for doing domain
5191 save/restore/migration must be enabled to handle larger
5194 xen_emul_unplug= [HW,X86,XEN]
5195 Unplug Xen emulated devices
5196 Format: [unplug0,][unplug1]
5197 ide-disks -- unplug primary master IDE devices
5198 aux-ide-disks -- unplug non-primary-master IDE devices
5199 nics -- unplug network devices
5200 all -- unplug all emulated devices (NICs and IDE disks)
5201 unnecessary -- unplugging emulated devices is
5202 unnecessary even if the host did not respond to
5204 never -- do not unplug even if version check succeeds
5206 xen_nopvspin [X86,XEN]
5207 Disables the ticketlock slowpath using Xen PV
5211 Disables the PV optimizations forcing the HVM guest to
5212 run as generic HVM guest with no PV drivers.
5214 xen_scrub_pages= [XEN]
5215 Boolean option to control scrubbing pages before giving them back
5216 to Xen, for use by other domains. Can be also changed at runtime
5217 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
5218 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
5220 xirc2ps_cs= [NET,PCMCIA]
5222 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
5224 xhci-hcd.quirks [USB,KNL]
5225 A hex value specifying bitmask with supplemental xhci
5226 host controller quirks. Meaning of each bit can be
5227 consulted in header drivers/usb/host/xhci.h.
git.samba.org / sfrench / cifs-2.6.git / blob