| blob | 46b826fcb5ad55fed0d8ca92ab10751baabf64a9 |
1 acpi= [HW,ACPI,X86,ARM64]
2 Advanced Configuration and Power Interface
3 Format: { force | on | off | strict | noirq | rsdt |
4 copy_dsdt }
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"
14 are available
16 See also Documentation/power/runtime_pm.rst, pci=noacpi
18 acpi_apic_instance= [ACPI, IOAPIC]
19 Format: <int>
20 2: use 2nd APIC table, if available
21 1,0: use 1st APIC table
22 default: 0
24 acpi_backlight= [HW,ACPI]
25 acpi_backlight=vendor
26 acpi_backlight=video
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]
47 Format: <int>
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/firmware-guide/acpi/debug.rst 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]
74 { strict | lax | no }
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
92 size limitation.
94 acpi_irq_balance [HW,ACPI]
95 ACPI will balance active IRQs
96 default in APIC mode
98 acpi_irq_nobalance [HW,ACPI]
99 ACPI will not move active IRQs (default)
100 default in PIC mode
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
106 use by PCI
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
113 the GPE dispatcher.
114 This facility can be used to prevent such uncontrolled
115 GPE floodings.
116 Format: <int>
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
127 kernels.
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
158 strings
159 acpi_osi=!! # enable all built-in OS vendor
160 strings
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.
173 Examples:
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
183 meaningless.
184 Examples:
185 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
186 FALSE.
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
198 the OSPM features.
199 Examples:
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
205 equivalent to
206 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
207 and
208 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
209 they all will make '_OSI("Windows 2000")' TRUE.
211 acpi_pm_good [X86]
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.rst for information on
227 s3_bios and s3_mode.
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.
252 agp= [AGP]
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)
258 ALSA [HW,ALSA]
259 See Documentation/sound/alsa-configuration.rst
261 alignment= [KNL,ARM]
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.
288 Possible values are:
289 fullflush - enable flushing of IO/TLB entries when
290 they are unmapped. Otherwise they are
291 flushed before they will be reused, which
292 is a lot of faster
293 off - do not initialize any AMD IOMMU found in
294 the system
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
309 remapping modes:
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
318 Format: <a>,<b>
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>
326 apc= [HW,SPARC]
327 Power management functions (SPARCstation-4/5 + deriv.)
328 Format: noidle
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
339 driver name.
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
347 backup of CPU 0
348 none: External NMI is masked for all CPUs. This is
349 useful so that a dump capture kernel won't be
350 shot down by NMI
352 autoconf= [IPV6]
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>
370 ataflop= [HW,M68k]
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
383 keyboards
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
400 userspace auditd.
401 Default: unset
403 audit_backlog_limit= [KNL] Set the audit queue size limit.
404 Format: <int> (must be >=0)
405 Default: 64
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" }
410 0 - Disable the BAU.
411 1 - Enable the BAU.
412 unset - Disable the BAU.
414 baycom_epp= [HW,AX25]
415 Format: <io>,<mode>
417 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
418 Format: <io>,<mode>
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.rst
435 boot_delay= Milliseconds to delay each printk during boot.
436 Values larger than 10 seconds (10000) are changed to
437 no delay (0).
438 Format: integer
440 bootmem_debug [KNL] Enable bootmem allocator debug messages.
442 bert_disable [ACPI]
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
447 kernel args too.
448 bttv.pll= See Documentation/media/v4l-drivers/bttv.rst
449 bttv.tuner=
451 bulk_remove=off [PPC] This parameter disables the use of the pSeries
452 firmware feature for flushing multiple hpte entries
453 at a time.
455 c101= [NET] Moxa C101 synchronous serial card
457 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
458 Sometimes CPU hardware bugs make them report the cache
459 size incorrectly. The kernel will attempt work arounds
460 to fix known problems, but for some CPUs it is not
461 possible to determine what the correct size should be.
462 This option provides an override for these situations.
464 carrier_timeout=
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
471 trust validation.
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
478 others).
480 ccw_timeout_log [S390]
481 See Documentation/s390/common_io.rst 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
487 a single hierarchy
488 - foo isn't visible as an individually mountable
489 subsystem
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
501 all v1 hierarchies.
503 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
504 Format: <string>
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.
518 cio_ignore= [S390]
519 See Documentation/s390/common_io.rst for details.
520 clk_ignore_unused
521 [CLK]
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.
533 [Deprecated]
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
540 Format: <string>
541 Override the default clocksource and use the clocksource
542 with the name specified.
543 Some clocksource names to choose from, depending on
544 the platform:
545 [all] jiffies (this is the base, fallback clocksource)
546 [ACPI] acpi_pm
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
551 [MIPS] MIPS
552 [PARISC] cr16
553 [S390] tod
554 [SH] SuperH
555 [SPARC64] tick
556 [X86-64] hpet,tsc
558 clocksource.arm_arch_timer.evtstrm=
559 [ARM,ARM64]
560 Format: <bool>
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
564 systems.
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
571 ones should be.
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
577 some critical bits.
579 cma=nn[MG]@[start[MG][-end[MG]]]
580 [ARM,X86,KNL]
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
592 a hypervisor.
593 Default: yes
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
600 Format:
601 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
603 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
604 Format: <io>[,<irq>]
606 com90xx= [HW,NET]
607 ARCnet - COM90xx chipset (memory-mapped buffers)
608 Format: <io>[,<irq>[,<memstart>]]
610 condev= [HW,S390] console device
611 conmode=
613 console= [KNL] Output console device and options.
615 tty<n> Use the virtual console device <n>.
617 ttyS<n>[,options]
618 ttyUSB0[,options]
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
626 information. See
627 Documentation/networking/netconsole.txt for an
628 alternative.
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
650 console=brl,ttyS0
651 For now, only VisioBraille is supported.
653 console_msg_format=
654 [KNL] Change console messages format
655 default
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).
660 syslog
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
665 from /proc/kmsg.
667 consoleblank= [KNL] The console blank (screen saver) timeout in
668 seconds. A value of 0 disables the blank timer.
669 Defaults to 0.
671 coredump_filter=
672 [KNL] Change the default value for
673 /proc/<pid>/coredump_filter.
674 See also Documentation/filesystems/proc.txt.
676 coresight_cpu_debug.enable
677 [ARM,ARM64]
678 Format: <bool>
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
686 cpuidle.governor=
687 [CPU_IDLE] Name of the cpuidle governor to use.
689 cpufreq.off=1 [CPU_FREQ]
690 disable the cpufreq sub-system
692 cpu_init_udelay=N
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.
696 Default: 10000
698 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
699 Format:
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/admin-guide/kdump/kdump.rst 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/admin-guide/kdump/kdump.rst 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
725 available.
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.
742 cryptomgr.notests
743 [KNL] Disable crypto self-tests
745 cs89x0_dma= [HW,NET]
746 Format: <dma>
748 cs89x0_media= [HW,NET]
749 Format: { rj45 | aui | bnc }
751 dasd= [HW,NET]
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
760 time. See
761 Documentation/admin-guide/dynamic-debug-howto.rst for
762 details. Deprecated, see dyndbg.
764 debug [KNL] Enable kernel debugging (events log level).
766 debug_boot_weak_hash
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.
774 debug_locks_verbose=
775 [KNL] verbose self-tests
776 Format=<0|1>
777 Print debugging info while doing the locking API
778 self-tests.
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
785 no_debug_objects
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.
807 debug_pagealloc=
808 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter
809 enables the feature at boot time. By default, it is
810 disabled and the system will work mostly the same as a
811 kernel built without CONFIG_DEBUG_PAGEALLOC.
812 on: enable the feature
814 debugpat [X86] Enable PAT debugging
816 decnet.addr= [HW,NET]
817 Format: <area>[,<node>]
818 See also Documentation/networking/decnet.txt.
820 default_hugepagesz=
821 [same as hugepagesz=] The size of the default
822 HugeTLB page size. This is the size represented by
823 the legacy /proc/ hugepages APIs, used for SHM, and
824 default size when mounting hugetlbfs filesystems.
825 Defaults to the default architecture's huge page size
826 if not specified.
828 deferred_probe_timeout=
829 [KNL] Debugging option to set a timeout in seconds for
830 deferred probe to give up waiting on dependencies to
831 probe. Only specific dependencies (subsystems or
832 drivers) that have opted in will be ignored. A timeout of 0
833 will timeout at the end of initcalls. This option will also
834 dump out devices still on the deferred probe list after
835 retrying.
837 dhash_entries= [KNL]
838 Set number of hash buckets for dentry cache.
840 disable_1tb_segments [PPC]
841 Disables the use of 1TB hash page table segments. This
842 causes the kernel to fall back to 256MB segments which
843 can be useful when debugging issues that require an SLB
844 miss to occur.
846 disable= [IPV6]
847 See Documentation/networking/ipv6.txt.
849 hardened_usercopy=
850 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
851 hardening is enabled for this boot. Hardened
852 usercopy checking is used to protect the kernel
853 from reading or writing beyond known memory
854 allocation boundaries as a proactive defense
855 against bounds-checking flaws in the kernel's
856 copy_to_user()/copy_from_user() interface.
857 on Perform hardened usercopy checks (default).
858 off Disable hardened usercopy checks.
860 disable_radix [PPC]
861 Disable RADIX MMU mode on POWER9
863 disable_cpu_apicid= [X86,APIC,SMP]
864 Format: <int>
865 The number of initial APIC ID for the
866 corresponding CPU to be disabled at boot,
867 mostly used for the kdump 2nd kernel to
868 disable BSP to wake up multiple CPUs without
869 causing system reset or hang due to sending
870 INIT from AP to BSP.
872 perf_v4_pmi= [X86,INTEL]
873 Format: <bool>
874 Disable Intel PMU counter freezing feature.
875 The feature only exists starting from
876 Arch Perfmon v4 (Skylake and newer).
878 disable_ddw [PPC/PSERIES]
879 Disable Dynamic DMA Window support. Use this if
880 to workaround buggy firmware.
882 disable_ipv6= [IPV6]
883 See Documentation/networking/ipv6.txt.
885 disable_mtrr_cleanup [X86]
886 The kernel tries to adjust MTRR layout from continuous
887 to discrete, to make X server driver able to add WB
888 entry later. This parameter disables that.
890 disable_mtrr_trim [X86, Intel and AMD only]
891 By default the kernel will trim any uncacheable
892 memory out of your available memory pool based on
893 MTRR settings. This parameter disables that behavior,
894 possibly causing your machine to run very slowly.
896 disable_timer_pin_1 [X86]
897 Disable PIN 1 of APIC timer
898 Can be useful to work around chipset bugs.
900 dis_ucode_ldr [X86] Disable the microcode loader.
902 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
903 this option disables the debugging code at boot.
905 dma_debug_entries=<number>
906 This option allows to tune the number of preallocated
907 entries for DMA-API debugging code. One entry is
908 required per DMA-API allocation. Use this if the
909 DMA-API debugging code disables itself because the
910 architectural default is too low.
912 dma_debug_driver=<driver_name>
913 With this option the DMA-API debugging driver
914 filter feature can be enabled at boot time. Just
915 pass the driver to filter for as the parameter.
916 The filter can be disabled or changed to another
917 driver later using sysfs.
919 driver_async_probe= [KNL]
920 List of driver names to be probed asynchronously.
921 Format: <driver_name1>,<driver_name2>...
923 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
924 Broken monitors, graphic adapters, KVMs and EDIDless
925 panels may send no or incorrect EDID data sets.
926 This parameter allows to specify an EDID data sets
927 in the /lib/firmware directory that are used instead.
928 Generic built-in EDID data sets are used, if one of
929 edid/1024x768.bin, edid/1280x1024.bin,
930 edid/1680x1050.bin, or edid/1920x1080.bin is given
931 and no file with the same name exists. Details and
932 instructions how to build your own EDID data are
933 available in Documentation/driver-api/edid.rst. An EDID
934 data set will only be used for a particular connector,
935 if its name and a colon are prepended to the EDID
936 name. Each connector may use a unique EDID data
937 set by separating the files with a comma. An EDID
938 data set with no connector name will be used for
939 any connectors not explicitly specified.
941 dscc4.setup= [NET]
943 dt_cpu_ftrs= [PPC]
944 Format: {"off" | "known"}
945 Control how the dt_cpu_ftrs device-tree binding is
946 used for CPU feature discovery and setup (if it
947 exists).
948 off: Do not use it, fall back to legacy cpu table.
949 known: Do not pass through unknown features to guests
950 or userspace, only those that the kernel is aware of.
952 dump_apple_properties [X86]
953 Dump name and content of EFI device properties on
954 x86 Macs. Useful for driver authors to determine
955 what data is available or for reverse-engineering.
957 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
958 module.dyndbg[="val"]
959 Enable debug messages at boot time. See
960 Documentation/admin-guide/dynamic-debug-howto.rst
961 for details.
963 nompx [X86] Disables Intel Memory Protection Extensions.
964 See Documentation/x86/intel_mpx.rst for more
965 information about the feature.
967 nopku [X86] Disable Memory Protection Keys CPU feature found
968 in some Intel CPUs.
970 module.async_probe [KNL]
971 Enable asynchronous probe on this module.
973 early_ioremap_debug [KNL]
974 Enable debug messages in early_ioremap support. This
975 is useful for tracking down temporary early mappings
976 which are not unmapped.
978 earlycon= [KNL] Output early console device and options.
980 [ARM64] The early console is determined by the
981 stdout-path property in device tree's chosen node,
982 or determined by the ACPI SPCR table.
984 [X86] When used with no options the early console is
985 determined by the ACPI SPCR table.
987 cdns,<addr>[,options]
988 Start an early, polled-mode console on a Cadence
989 (xuartps) serial port at the specified address. Only
990 supported option is baud rate. If baud rate is not
991 specified, the serial port must already be setup and
992 configured.
994 uart[8250],io,<addr>[,options]
995 uart[8250],mmio,<addr>[,options]
996 uart[8250],mmio32,<addr>[,options]
997 uart[8250],mmio32be,<addr>[,options]
998 uart[8250],0x<addr>[,options]
999 Start an early, polled-mode console on the 8250/16550
1000 UART at the specified I/O port or MMIO address.
1001 MMIO inter-register address stride is either 8-bit
1002 (mmio) or 32-bit (mmio32 or mmio32be).
1003 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1004 to be equivalent to 'mmio'. 'options' are specified
1005 in the same format described for "console=ttyS<n>"; if
1006 unspecified, the h/w is not initialized.
1008 pl011,<addr>
1009 pl011,mmio32,<addr>
1010 Start an early, polled-mode console on a pl011 serial
1011 port at the specified address. The pl011 serial port
1012 must already be setup and configured. Options are not
1013 yet supported. If 'mmio32' is specified, then only
1014 the driver will use only 32-bit accessors to read/write
1015 the device registers.
1017 meson,<addr>
1018 Start an early, polled-mode console on a meson serial
1019 port at the specified address. The serial port must
1020 already be setup and configured. Options are not yet
1021 supported.
1023 msm_serial,<addr>
1024 Start an early, polled-mode console on an msm serial
1025 port at the specified address. The serial port
1026 must already be setup and configured. Options are not
1027 yet supported.
1029 msm_serial_dm,<addr>
1030 Start an early, polled-mode console on an msm serial
1031 dm port at the specified address. The serial port
1032 must already be setup and configured. Options are not
1033 yet supported.
1035 owl,<addr>
1036 Start an early, polled-mode console on a serial port
1037 of an Actions Semi SoC, such as S500 or S900, at the
1038 specified address. The serial port must already be
1039 setup and configured. Options are not yet supported.
1041 rda,<addr>
1042 Start an early, polled-mode console on a serial port
1043 of an RDA Micro SoC, such as RDA8810PL, at the
1044 specified address. The serial port must already be
1045 setup and configured. Options are not yet supported.
1047 smh Use ARM semihosting calls for early console.
1049 s3c2410,<addr>
1050 s3c2412,<addr>
1051 s3c2440,<addr>
1052 s3c6400,<addr>
1053 s5pv210,<addr>
1054 exynos4210,<addr>
1055 Use early console provided by serial driver available
1056 on Samsung SoCs, requires selecting proper type and
1057 a correct base address of the selected UART port. The
1058 serial port must already be setup and configured.
1059 Options are not yet supported.
1061 lantiq,<addr>
1062 Start an early, polled-mode console on a lantiq serial
1063 (lqasc) port at the specified address. The serial port
1064 must already be setup and configured. Options are not
1065 yet supported.
1067 lpuart,<addr>
1068 lpuart32,<addr>
1069 Use early console provided by Freescale LP UART driver
1070 found on Freescale Vybrid and QorIQ LS1021A processors.
1071 A valid base address must be provided, and the serial
1072 port must already be setup and configured.
1074 ar3700_uart,<addr>
1075 Start an early, polled-mode console on the
1076 Armada 3700 serial port at the specified
1077 address. The serial port must already be setup
1078 and configured. Options are not yet supported.
1080 qcom_geni,<addr>
1081 Start an early, polled-mode console on a Qualcomm
1082 Generic Interface (GENI) based serial port at the
1083 specified address. The serial port must already be
1084 setup and configured. Options are not yet supported.
1086 efifb,[options]
1087 Start an early, unaccelerated console on the EFI
1088 memory mapped framebuffer (if available). On cache
1089 coherent non-x86 systems that use system memory for
1090 the framebuffer, pass the 'ram' option so that it is
1091 mapped with the correct attributes.
1093 earlyprintk= [X86,SH,ARM,M68k,S390]
1094 earlyprintk=vga
1095 earlyprintk=sclp
1096 earlyprintk=xen
1097 earlyprintk=serial[,ttySn[,baudrate]]
1098 earlyprintk=serial[,0x...[,baudrate]]
1099 earlyprintk=ttySn[,baudrate]
1100 earlyprintk=dbgp[debugController#]
1101 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1102 earlyprintk=xdbc[xhciController#]
1104 earlyprintk is useful when the kernel crashes before
1105 the normal console is initialized. It is not enabled by
1106 default because it has some cosmetic problems.
1108 Append ",keep" to not disable it when the real console
1109 takes over.
1111 Only one of vga, efi, serial, or usb debug port can
1112 be used at a time.
1114 Currently only ttyS0 and ttyS1 may be specified by
1115 name. Other I/O ports may be explicitly specified
1116 on some architectures (x86 and arm at least) by
1117 replacing ttySn with an I/O port address, like this:
1118 earlyprintk=serial,0x1008,115200
1119 You can find the port for a given device in
1120 /proc/tty/driver/serial:
1121 2: uart:ST16650V2 port:00001008 irq:18 ...
1123 Interaction with the standard serial driver is not
1124 very good.
1126 The VGA and EFI output is eventually overwritten by
1127 the real console.
1129 The xen output can only be used by Xen PV guests.
1131 The sclp output can only be used on s390.
1133 The optional "force" to "pciserial" enables use of a
1134 PCI device even when its classcode is not of the
1135 UART class.
1137 edac_report= [HW,EDAC] Control how to report EDAC event
1138 Format: {"on" | "off" | "force"}
1139 on: enable EDAC to report H/W event. May be overridden
1140 by other higher priority error reporting module.
1141 off: disable H/W event reporting through EDAC.
1142 force: enforce the use of EDAC to report H/W event.
1143 default: on.
1145 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1146 ekgdboc=kbd
1148 This is designed to be used in conjunction with
1149 the boot argument: earlyprintk=vga
1151 edd= [EDD]
1152 Format: {"off" | "on" | "skip[mbr]"}
1154 efi= [EFI]
1155 Format: { "old_map", "nochunk", "noruntime", "debug" }
1156 old_map [X86-64]: switch to the old ioremap-based EFI
1157 runtime services mapping. 32-bit still uses this one by
1158 default.
1159 nochunk: disable reading files in "chunks" in the EFI
1160 boot stub, as chunking can cause problems with some
1161 firmware implementations.
1162 noruntime : disable EFI runtime services support
1163 debug: enable misc debug output
1165 efi_no_storage_paranoia [EFI; X86]
1166 Using this parameter you can use more than 50% of
1167 your efi variable storage. Use this parameter only if
1168 you are really sure that your UEFI does sane gc and
1169 fulfills the spec otherwise your board may brick.
1171 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1172 Add arbitrary attribute to specific memory range by
1173 updating original EFI memory map.
1174 Region of memory which aa attribute is added to is
1175 from ss to ss+nn.
1176 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1177 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1178 attribute is added to range 0x100000000-0x180000000 and
1179 0x10a0000000-0x1120000000.
1181 Using this parameter you can do debugging of EFI memmap
1182 related feature. For example, you can do debugging of
1183 Address Range Mirroring feature even if your box
1184 doesn't support it.
1186 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1187 that is to be dynamically loaded by Linux. If there are
1188 multiple variables with the same name but with different
1189 vendor GUIDs, all of them will be loaded. See
1190 Documentation/admin-guide/acpi/ssdt-overlays.rst for details.
1193 eisa_irq_edge= [PARISC,HW]
1194 See header of drivers/parisc/eisa.c.
1196 elanfreq= [X86-32]
1197 See comment before function elanfreq_setup() in
1198 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1200 elevator= [IOSCHED]
1201 Format: { "mq-deadline" | "kyber" | "bfq" }
1202 See Documentation/block/deadline-iosched.rst,
1203 Documentation/block/kyber-iosched.rst and
1204 Documentation/block/bfq-iosched.rst for details.
1206 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1207 Specifies physical address of start of kernel core
1208 image elf header and optionally the size. Generally
1209 kexec loader will pass this option to capture kernel.
1210 See Documentation/admin-guide/kdump/kdump.rst for details.
1212 enable_mtrr_cleanup [X86]
1213 The kernel tries to adjust MTRR layout from continuous
1214 to discrete, to make X server driver able to add WB
1215 entry later. This parameter enables that.
1217 enable_timer_pin_1 [X86]
1218 Enable PIN 1 of APIC timer
1219 Can be useful to work around chipset bugs
1220 (in particular on some ATI chipsets).
1221 The kernel tries to set a reasonable default.
1223 enforcing [SELINUX] Set initial enforcing status.
1224 Format: {"0" | "1"}
1225 See security/selinux/Kconfig help text.
1226 0 -- permissive (log only, no denials).
1227 1 -- enforcing (deny and log).
1228 Default value is 0.
1229 Value can be changed at runtime via /selinux/enforce.
1231 erst_disable [ACPI]
1232 Disable Error Record Serialization Table (ERST)
1233 support.
1235 ether= [HW,NET] Ethernet cards parameters
1236 This option is obsoleted by the "netdev=" option, which
1237 has equivalent usage. See its documentation for details.
1239 evm= [EVM]
1240 Format: { "fix" }
1241 Permit 'security.evm' to be updated regardless of
1242 current integrity status.
1244 failslab=
1245 fail_page_alloc=
1246 fail_make_request=[KNL]
1247 General fault injection mechanism.
1248 Format: <interval>,<probability>,<space>,<times>
1249 See also Documentation/fault-injection/.
1251 floppy= [HW]
1252 See Documentation/admin-guide/blockdev/floppy.rst.
1254 force_pal_cache_flush
1255 [IA-64] Avoid check_sal_cache_flush which may hang on
1256 buggy SAL_CACHE_FLUSH implementations. Using this
1257 parameter will force ia64_sal_cache_flush to call
1258 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1260 forcepae [X86-32]
1261 Forcefully enable Physical Address Extension (PAE).
1262 Many Pentium M systems disable PAE but may have a
1263 functionally usable PAE implementation.
1264 Warning: use of this parameter will taint the kernel
1265 and may cause unknown problems.
1267 ftrace=[tracer]
1268 [FTRACE] will set and start the specified tracer
1269 as early as possible in order to facilitate early
1270 boot debugging.
1272 ftrace_dump_on_oops[=orig_cpu]
1273 [FTRACE] will dump the trace buffers on oops.
1274 If no parameter is passed, ftrace will dump
1275 buffers of all CPUs, but if you pass orig_cpu, it will
1276 dump only the buffer of the CPU that triggered the
1277 oops.
1279 ftrace_filter=[function-list]
1280 [FTRACE] Limit the functions traced by the function
1281 tracer at boot up. function-list is a comma separated
1282 list of functions. This list can be changed at run
1283 time by the set_ftrace_filter file in the debugfs
1284 tracing directory.
1286 ftrace_notrace=[function-list]
1287 [FTRACE] Do not trace the functions specified in
1288 function-list. This list can be changed at run time
1289 by the set_ftrace_notrace file in the debugfs
1290 tracing directory.
1292 ftrace_graph_filter=[function-list]
1293 [FTRACE] Limit the top level callers functions traced
1294 by the function graph tracer at boot up.
1295 function-list is a comma separated list of functions
1296 that can be changed at run time by the
1297 set_graph_function file in the debugfs tracing directory.
1299 ftrace_graph_notrace=[function-list]
1300 [FTRACE] Do not trace from the functions specified in
1301 function-list. This list is a comma separated list of
1302 functions that can be changed at run time by the
1303 set_graph_notrace file in the debugfs tracing directory.
1305 ftrace_graph_max_depth=<uint>
1306 [FTRACE] Used with the function graph tracer. This is
1307 the max depth it will trace into a function. This value
1308 can be changed at run time by the max_graph_depth file
1309 in the tracefs tracing directory. default: 0 (no limit)
1311 gamecon.map[2|3]=
1312 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1313 support via parallel port (up to 5 devices per port)
1314 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1315 See also Documentation/input/devices/joystick-parport.rst
1317 gamma= [HW,DRM]
1319 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1320 Format: off | on
1321 default: on
1323 gcov_persist= [GCOV] When non-zero (default), profiling data for
1324 kernel modules is saved and remains accessible via
1325 debugfs, even when the module is unloaded/reloaded.
1326 When zero, profiling data is discarded and associated
1327 debugfs files are removed at module unload time.
1329 goldfish [X86] Enable the goldfish android emulator platform.
1330 Don't use this when you are not running on the
1331 android emulator
1333 gpt [EFI] Forces disk with valid GPT signature but
1334 invalid Protective MBR to be treated as GPT. If the
1335 primary GPT is corrupted, it enables the backup/alternate
1336 GPT to be used instead.
1338 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1339 the "Enable 0" bit of the configuration register.
1340 Format: 0 | 1
1341 Default: 0
1342 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1343 the "Enable 0" bit of the configuration register.
1344 Format: 0 | 1
1345 Default: 0
1346 grcan.select= [HW] Select which physical interface to use.
1347 Format: 0 | 1
1348 Default: 0
1349 grcan.txsize= [HW] Sets the size of the tx buffer.
1350 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1351 Default: 1024
1352 grcan.rxsize= [HW] Sets the size of the rx buffer.
1353 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1354 Default: 1024
1356 gpio-mockup.gpio_mockup_ranges
1357 [HW] Sets the ranges of gpiochip of for this device.
1358 Format: <start1>,<end1>,<start2>,<end2>...
1360 hardlockup_all_cpu_backtrace=
1361 [KNL] Should the hard-lockup detector generate
1362 backtraces on all cpus.
1363 Format: <integer>
1365 hashdist= [KNL,NUMA] Large hashes allocated during boot
1366 are distributed across NUMA nodes. Defaults on
1367 for 64-bit NUMA, off otherwise.
1368 Format: 0 | 1 (for off | on)
1370 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1372 hd= [EIDE] (E)IDE hard drive subsystem geometry
1373 Format: <cyl>,<head>,<sect>
1375 hest_disable [ACPI]
1376 Disable Hardware Error Source Table (HEST) support;
1377 corresponding firmware-first mode error processing
1378 logic will be disabled.
1380 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1381 size of <nn>. This works even on boxes that have no
1382 highmem otherwise. This also works to reduce highmem
1383 size on bigger boxes.
1385 highres= [KNL] Enable/disable high resolution timer mode.
1386 Valid parameters: "on", "off"
1387 Default: "on"
1389 hlt [BUGS=ARM,SH]
1391 hpet= [X86-32,HPET] option to control HPET usage
1392 Format: { enable (default) | disable | force |
1393 verbose }
1394 disable: disable HPET and use PIT instead
1395 force: allow force enabled of undocumented chips (ICH4,
1396 VIA, nVidia)
1397 verbose: show contents of HPET registers during setup
1399 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1400 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1402 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1403 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1404 On x86-64 and powerpc, this option can be specified
1405 multiple times interleaved with hugepages= to reserve
1406 huge pages of different sizes. Valid pages sizes on
1407 x86-64 are 2M (when the CPU supports "pse") and 1G
1408 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1410 hung_task_panic=
1411 [KNL] Should the hung task detector generate panics.
1412 Format: <integer>
1414 A nonzero value instructs the kernel to panic when a
1415 hung task is detected. The default value is controlled
1416 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1417 option. The value selected by this boot parameter can
1418 be changed later by the kernel.hung_task_panic sysctl.
1420 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1421 terminal devices. Valid values: 0..8
1422 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1423 If specified, z/VM IUCV HVC accepts connections
1424 from listed z/VM user IDs only.
1426 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations
1427 which allow the hypervisor to 'idle' the
1428 guest on lock contention.
1430 keep_bootcon [KNL]
1431 Do not unregister boot console at start. This is only
1432 useful for debugging when something happens in the window
1433 between unregistering the boot console and initializing
1434 the real console.
1436 i2c_bus= [HW] Override the default board specific I2C bus speed
1437 or register an additional I2C bus that is not
1438 registered from board initialization code.
1439 Format:
1440 <bus_id>,<clkrate>
1442 i8042.debug [HW] Toggle i8042 debug mode
1443 i8042.unmask_kbd_data
1444 [HW] Enable printing of interrupt data from the KBD port
1445 (disabled by default, and as a pre-condition
1446 requires that i8042.debug=1 be enabled)
1447 i8042.direct [HW] Put keyboard port into non-translated mode
1448 i8042.dumbkbd [HW] Pretend that controller can only read data from
1449 keyboard and cannot control its state
1450 (Don't attempt to blink the leds)
1451 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1452 i8042.nokbd [HW] Don't check/create keyboard port
1453 i8042.noloop [HW] Disable the AUX Loopback command while probing
1454 for the AUX port
1455 i8042.nomux [HW] Don't check presence of an active multiplexing
1456 controller
1457 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1458 controllers
1459 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1460 i8042.reset [HW] Reset the controller during init, cleanup and
1461 suspend-to-ram transitions, only during s2r
1462 transitions, or never reset
1463 Format: { 1 | Y | y | 0 | N | n }
1464 1, Y, y: always reset controller
1465 0, N, n: don't ever reset controller
1466 Default: only on s2r transitions on x86; most other
1467 architectures force reset to be always executed
1468 i8042.unlock [HW] Unlock (ignore) the keylock
1469 i8042.kbdreset [HW] Reset device connected to KBD port
1471 i810= [HW,DRM]
1473 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1474 indicates that the driver is running on unsupported
1475 hardware.
1476 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1477 does not match list of supported models.
1478 i8k.power_status
1479 [HW] Report power status in /proc/i8k
1480 (disabled by default)
1481 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1482 capability is set.
1484 i915.invert_brightness=
1485 [DRM] Invert the sense of the variable that is used to
1486 set the brightness of the panel backlight. Normally a
1487 brightness value of 0 indicates backlight switched off,
1488 and the maximum of the brightness value sets the backlight
1489 to maximum brightness. If this parameter is set to 0
1490 (default) and the machine requires it, or this parameter
1491 is set to 1, a brightness value of 0 sets the backlight
1492 to maximum brightness, and the maximum of the brightness
1493 value switches the backlight off.
1494 -1 -- never invert brightness
1495 0 -- machine default
1496 1 -- force brightness inversion
1498 icn= [HW,ISDN]
1499 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1501 ide-core.nodma= [HW] (E)IDE subsystem
1502 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1503 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1504 .cdrom .chs .ignore_cable are additional options
1505 See Documentation/ide/ide.rst.
1507 ide-generic.probe-mask= [HW] (E)IDE subsystem
1508 Format: <int>
1509 Probe mask for legacy ISA IDE ports. Depending on
1510 platform up to 6 ports are supported, enabled by
1511 setting corresponding bits in the mask to 1. The
1512 default value is 0x0, which has a special meaning.
1513 On systems that have PCI, it triggers scanning the
1514 PCI bus for the first and the second port, which
1515 are then probed. On systems without PCI the value
1516 of 0x0 enables probing the two first ports as if it
1517 was 0x3.
1519 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1520 Claim all unknown PCI IDE storage controllers.
1522 idle= [X86]
1523 Format: idle=poll, idle=halt, idle=nomwait
1524 Poll forces a polling idle loop that can slightly
1525 improve the performance of waking up a idle CPU, but
1526 will use a lot of power and make the system run hot.
1527 Not recommended.
1528 idle=halt: Halt is forced to be used for CPU idle.
1529 In such case C2/C3 won't be used again.
1530 idle=nomwait: Disable mwait for CPU C-states
1532 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1533 Format: { strict | legacy | 2008 | relaxed }
1534 Default: strict
1536 Choose which programs will be accepted for execution
1537 based on the IEEE 754 NaN encoding(s) supported by
1538 the FPU and the NaN encoding requested with the value
1539 of an ELF file header flag individually set by each
1540 binary. Hardware implementations are permitted to
1541 support either or both of the legacy and the 2008 NaN
1542 encoding mode.
1544 Available settings are as follows:
1545 strict accept binaries that request a NaN encoding
1546 supported by the FPU
1547 legacy only accept legacy-NaN binaries, if supported
1548 by the FPU
1549 2008 only accept 2008-NaN binaries, if supported
1550 by the FPU
1551 relaxed accept any binaries regardless of whether
1552 supported by the FPU
1554 The FPU emulator is always able to support both NaN
1555 encodings, so if no FPU hardware is present or it has
1556 been disabled with 'nofpu', then the settings of
1557 'legacy' and '2008' strap the emulator accordingly,
1558 'relaxed' straps the emulator for both legacy-NaN and
1559 2008-NaN, whereas 'strict' enables legacy-NaN only on
1560 legacy processors and both NaN encodings on MIPS32 or
1561 MIPS64 CPUs.
1563 The setting for ABS.fmt/NEG.fmt instruction execution
1564 mode generally follows that for the NaN encoding,
1565 except where unsupported by hardware.
1567 ignore_loglevel [KNL]
1568 Ignore loglevel setting - this will print /all/
1569 kernel messages to the console. Useful for debugging.
1570 We also add it as printk module parameter, so users
1571 could change it dynamically, usually by
1572 /sys/module/printk/parameters/ignore_loglevel.
1574 ignore_rlimit_data
1575 Ignore RLIMIT_DATA setting for data mappings,
1576 print warning at first misuse. Can be changed via
1577 /sys/module/kernel/parameters/ignore_rlimit_data.
1579 ihash_entries= [KNL]
1580 Set number of hash buckets for inode cache.
1582 ima_appraise= [IMA] appraise integrity measurements
1583 Format: { "off" | "enforce" | "fix" | "log" }
1584 default: "enforce"
1586 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead.
1587 The builtin appraise policy appraises all files
1588 owned by uid=0.
1590 ima_canonical_fmt [IMA]
1591 Use the canonical format for the binary runtime
1592 measurements, instead of host native format.
1594 ima_hash= [IMA]
1595 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1596 | sha512 | ... }
1597 default: "sha1"
1599 The list of supported hash algorithms is defined
1600 in crypto/hash_info.h.
1602 ima_policy= [IMA]
1603 The builtin policies to load during IMA setup.
1604 Format: "tcb | appraise_tcb | secure_boot |
1605 fail_securely"
1607 The "tcb" policy measures all programs exec'd, files
1608 mmap'd for exec, and all files opened with the read
1609 mode bit set by either the effective uid (euid=0) or
1610 uid=0.
1612 The "appraise_tcb" policy appraises the integrity of
1613 all files owned by root.
1615 The "secure_boot" policy appraises the integrity
1616 of files (eg. kexec kernel image, kernel modules,
1617 firmware, policy, etc) based on file signatures.
1619 The "fail_securely" policy forces file signature
1620 verification failure also on privileged mounted
1621 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1622 flag.
1624 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1625 Load a policy which meets the needs of the Trusted
1626 Computing Base. This means IMA will measure all
1627 programs exec'd, files mmap'd for exec, and all files
1628 opened for read by uid=0.
1630 ima_template= [IMA]
1631 Select one of defined IMA measurements template formats.
1632 Formats: { "ima" | "ima-ng" | "ima-sig" }
1633 Default: "ima-ng"
1635 ima_template_fmt=
1636 [IMA] Define a custom template format.
1637 Format: { "field1|...|fieldN" }
1639 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1640 Format: <min_file_size>
1641 Set the minimal file size for using asynchronous hash.
1642 If left unspecified, ahash usage is disabled.
1644 ahash performance varies for different data sizes on
1645 different crypto accelerators. This option can be used
1646 to achieve the best performance for a particular HW.
1648 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1649 Format: <bufsize>
1650 Set hashing buffer size. Default: 4k.
1652 ahash performance varies for different chunk sizes on
1653 different crypto accelerators. This option can be used
1654 to achieve best performance for particular HW.
1656 init= [KNL]
1657 Format: <full_path>
1658 Run specified binary instead of /sbin/init as init
1659 process.
1661 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1662 for working out where the kernel is dying during
1663 startup.
1665 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1666 initcall functions. Useful for debugging built-in
1667 modules and initcalls.
1669 initrd= [BOOT] Specify the location of the initial ramdisk
1671 init_on_alloc= [MM] Fill newly allocated pages and heap objects with
1672 zeroes.
1673 Format: 0 | 1
1674 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
1676 init_on_free= [MM] Fill freed pages and heap objects with zeroes.
1677 Format: 0 | 1
1678 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.
1680 init_pkru= [x86] Specify the default memory protection keys rights
1681 register contents for all processes. 0x55555554 by
1682 default (disallow access to all but pkey 0). Can
1683 override in debugfs after boot.
1685 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1686 Format: <irq>
1688 int_pln_enable [x86] Enable power limit notification interrupt
1690 integrity_audit=[IMA]
1691 Format: { "0" | "1" }
1692 0 -- basic integrity auditing messages. (Default)
1693 1 -- additional integrity auditing messages.
1695 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1696 on
1697 Enable intel iommu driver.
1698 off
1699 Disable intel iommu driver.
1700 igfx_off [Default Off]
1701 By default, gfx is mapped as normal device. If a gfx
1702 device has a dedicated DMAR unit, the DMAR unit is
1703 bypassed by not enabling DMAR with this option. In
1704 this case, gfx device will use physical address for
1705 DMA.
1706 forcedac [x86_64]
1707 With this option iommu will not optimize to look
1708 for io virtual address below 32-bit forcing dual
1709 address cycle on pci bus for cards supporting greater
1710 than 32-bit addressing. The default is to look
1711 for translation below 32-bit and if not available
1712 then look in the higher range.
1713 strict [Default Off]
1714 With this option on every unmap_single operation will
1715 result in a hardware IOTLB flush operation as opposed
1716 to batching them for performance.
1717 sp_off [Default Off]
1718 By default, super page will be supported if Intel IOMMU
1719 has the capability. With this option, super page will
1720 not be supported.
1721 sm_on [Default Off]
1722 By default, scalable mode will be disabled even if the
1723 hardware advertises that it has support for the scalable
1724 mode translation. With this option set, scalable mode
1725 will be used on hardware which claims to support it.
1726 tboot_noforce [Default Off]
1727 Do not force the Intel IOMMU enabled under tboot.
1728 By default, tboot will force Intel IOMMU on, which
1729 could harm performance of some high-throughput
1730 devices like 40GBit network cards, even if identity
1731 mapping is enabled.
1732 Note that using this option lowers the security
1733 provided by tboot because it makes the system
1734 vulnerable to DMA attacks.
1736 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1737 0 disables intel_idle and fall back on acpi_idle.
1738 1 to 9 specify maximum depth of C-state.
1740 intel_pstate= [X86]
1741 disable
1742 Do not enable intel_pstate as the default
1743 scaling driver for the supported processors
1744 passive
1745 Use intel_pstate as a scaling driver, but configure it
1746 to work with generic cpufreq governors (instead of
1747 enabling its internal governor). This mode cannot be
1748 used along with the hardware-managed P-states (HWP)
1749 feature.
1750 force
1751 Enable intel_pstate on systems that prohibit it by default
1752 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1753 instead of acpi-cpufreq may disable platform features, such
1754 as thermal controls and power capping, that rely on ACPI
1755 P-States information being indicated to OSPM and therefore
1756 should be used with caution. This option does not work with
1757 processors that aren't supported by the intel_pstate driver
1758 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1759 no_hwp
1760 Do not enable hardware P state control (HWP)
1761 if available.
1762 hwp_only
1763 Only load intel_pstate on systems which support
1764 hardware P state control (HWP) if available.
1765 support_acpi_ppc
1766 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1767 Description Table, specifies preferred power management
1768 profile as "Enterprise Server" or "Performance Server",
1769 then this feature is turned on by default.
1770 per_cpu_perf_limits
1771 Allow per-logical-CPU P-State performance control limits using
1772 cpufreq sysfs interface
1774 intremap= [X86-64, Intel-IOMMU]
1775 on enable Interrupt Remapping (default)
1776 off disable Interrupt Remapping
1777 nosid disable Source ID checking
1778 no_x2apic_optout
1779 BIOS x2APIC opt-out request will be ignored
1780 nopost disable Interrupt Posting
1782 iomem= Disable strict checking of access to MMIO memory
1783 strict regions from userspace.
1784 relaxed
1786 iommu= [x86]
1787 off
1788 force
1789 noforce
1790 biomerge
1791 panic
1792 nopanic
1793 merge
1794 nomerge
1795 soft
1796 pt [x86]
1797 nopt [x86]
1798 nobypass [PPC/POWERNV]
1799 Disable IOMMU bypass, using IOMMU for PCI devices.
1801 iommu.strict= [ARM64] Configure TLB invalidation behaviour
1802 Format: { "0" | "1" }
1803 0 - Lazy mode.
1804 Request that DMA unmap operations use deferred
1805 invalidation of hardware TLBs, for increased
1806 throughput at the cost of reduced device isolation.
1807 Will fall back to strict mode if not supported by
1808 the relevant IOMMU driver.
1809 1 - Strict mode (default).
1810 DMA unmap operations invalidate IOMMU hardware TLBs
1811 synchronously.
1813 iommu.passthrough=
1814 [ARM64] Configure DMA to bypass the IOMMU by default.
1815 Format: { "0" | "1" }
1816 0 - Use IOMMU translation for DMA.
1817 1 - Bypass the IOMMU for DMA.
1818 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
1820 io7= [HW] IO7 for Marvel based alpha systems
1821 See comment before marvel_specify_io7 in
1822 arch/alpha/kernel/core_marvel.c.
1824 io_delay= [X86] I/O delay method
1825 0x80
1826 Standard port 0x80 based delay
1827 0xed
1828 Alternate port 0xed based delay (needed on some systems)
1829 udelay
1830 Simple two microseconds delay
1831 none
1832 No delay
1834 ip= [IP_PNP]
1835 See Documentation/filesystems/nfs/nfsroot.txt.
1837 ipcmni_extend [KNL] Extend the maximum number of unique System V
1838 IPC identifiers from 32,768 to 16,777,216.
1840 irqaffinity= [SMP] Set the default irq affinity mask
1841 The argument is a cpu list, as described above.
1843 irqchip.gicv2_force_probe=
1844 [ARM, ARM64]
1845 Format: <bool>
1846 Force the kernel to look for the second 4kB page
1847 of a GICv2 controller even if the memory range
1848 exposed by the device tree is too small.
1850 irqchip.gicv3_nolpi=
1851 [ARM, ARM64]
1852 Force the kernel to ignore the availability of
1853 LPIs (and by consequence ITSs). Intended for system
1854 that use the kernel as a bootloader, and thus want
1855 to let secondary kernels in charge of setting up
1856 LPIs.
1858 irqchip.gicv3_pseudo_nmi= [ARM64]
1859 Enables support for pseudo-NMIs in the kernel. This
1860 requires the kernel to be built with
1861 CONFIG_ARM64_PSEUDO_NMI.
1863 irqfixup [HW]
1864 When an interrupt is not handled search all handlers
1865 for it. Intended to get systems with badly broken
1866 firmware running.
1868 irqpoll [HW]
1869 When an interrupt is not handled search all handlers
1870 for it. Also check all handlers each timer
1871 interrupt. Intended to get systems with badly broken
1872 firmware running.
1874 isapnp= [ISAPNP]
1875 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1877 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1878 [Deprecated - use cpusets instead]
1879 Format: [flag-list,]<cpu-list>
1881 Specify one or more CPUs to isolate from disturbances
1882 specified in the flag list (default: domain):
1884 nohz
1885 Disable the tick when a single task runs.
1887 A residual 1Hz tick is offloaded to workqueues, which you
1888 need to affine to housekeeping through the global
1889 workqueue's affinity configured via the
1890 /sys/devices/virtual/workqueue/cpumask sysfs file, or
1891 by using the 'domain' flag described below.
1893 NOTE: by default the global workqueue runs on all CPUs,
1894 so to protect individual CPUs the 'cpumask' file has to
1895 be configured manually after bootup.
1897 domain
1898 Isolate from the general SMP balancing and scheduling
1899 algorithms. Note that performing domain isolation this way
1900 is irreversible: it's not possible to bring back a CPU to
1901 the domains once isolated through isolcpus. It's strongly
1902 advised to use cpusets instead to disable scheduler load
1903 balancing through the "cpuset.sched_load_balance" file.
1904 It offers a much more flexible interface where CPUs can
1905 move in and out of an isolated set anytime.
1907 You can move a process onto or off an "isolated" CPU via
1908 the CPU affinity syscalls or cpuset.
1909 <cpu number> begins at 0 and the maximum value is
1910 "number of CPUs in system - 1".
1912 The format of <cpu-list> is described above.
1916 iucv= [HW,NET]
1918 ivrs_ioapic [HW,X86_64]
1919 Provide an override to the IOAPIC-ID<->DEVICE-ID
1920 mapping provided in the IVRS ACPI table. For
1921 example, to map IOAPIC-ID decimal 10 to
1922 PCI device 00:14.0 write the parameter as:
1923 ivrs_ioapic[10]=00:14.0
1925 ivrs_hpet [HW,X86_64]
1926 Provide an override to the HPET-ID<->DEVICE-ID
1927 mapping provided in the IVRS ACPI table. For
1928 example, to map HPET-ID decimal 0 to
1929 PCI device 00:14.0 write the parameter as:
1930 ivrs_hpet[0]=00:14.0
1932 ivrs_acpihid [HW,X86_64]
1933 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1934 mapping provided in the IVRS ACPI table. For
1935 example, to map UART-HID:UID AMD0020:0 to
1936 PCI device 00:14.5 write the parameter as:
1937 ivrs_acpihid[00:14.5]=AMD0020:0
1939 js= [HW,JOY] Analog joystick
1940 See Documentation/input/joydev/joystick.rst.
1942 nokaslr [KNL]
1943 When CONFIG_RANDOMIZE_BASE is set, this disables
1944 kernel and module base offset ASLR (Address Space
1945 Layout Randomization).
1947 kasan_multi_shot
1948 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1949 report on every invalid memory access. Without this
1950 parameter KASAN will print report only for the first
1951 invalid access.
1953 keepinitrd [HW,ARM]
1955 kernelcore= [KNL,X86,IA-64,PPC]
1956 Format: nn[KMGTPE] | nn% | "mirror"
1957 This parameter specifies the amount of memory usable by
1958 the kernel for non-movable allocations. The requested
1959 amount is spread evenly throughout all nodes in the
1960 system as ZONE_NORMAL. The remaining memory is used for
1961 movable memory in its own zone, ZONE_MOVABLE. In the
1962 event, a node is too small to have both ZONE_NORMAL and
1963 ZONE_MOVABLE, kernelcore memory will take priority and
1964 other nodes will have a larger ZONE_MOVABLE.
1966 ZONE_MOVABLE is used for the allocation of pages that
1967 may be reclaimed or moved by the page migration
1968 subsystem. Note that allocations like PTEs-from-HighMem
1969 still use the HighMem zone if it exists, and the Normal
1970 zone if it does not.
1972 It is possible to specify the exact amount of memory in
1973 the form of "nn[KMGTPE]", a percentage of total system
1974 memory in the form of "nn%", or "mirror". If "mirror"
1975 option is specified, mirrored (reliable) memory is used
1976 for non-movable allocations and remaining memory is used
1977 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
1978 are exclusive, so you cannot specify multiple forms.
1980 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1981 Format: <Controller#>[,poll interval]
1982 The controller # is the number of the ehci usb debug
1983 port as it is probed via PCI. The poll interval is
1984 optional and is the number seconds in between
1985 each poll cycle to the debug port in case you need
1986 the functionality for interrupting the kernel with
1987 gdb or control-c on the dbgp connection. When
1988 not using this parameter you use sysrq-g to break into
1989 the kernel debugger.
1991 kgdboc= [KGDB,HW] kgdb over consoles.
1992 Requires a tty driver that supports console polling,
1993 or a supported polling keyboard driver (non-usb).
1994 Serial only format: <serial_device>[,baud]
1995 keyboard only format: kbd
1996 keyboard and serial format: kbd,<serial_device>[,baud]
1997 Optional Kernel mode setting:
1998 kms, kbd format: kms,kbd
1999 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
2001 kgdbwait [KGDB] Stop kernel execution and enter the
2002 kernel debugger at the earliest opportunity.
2004 kmac= [MIPS] korina ethernet MAC address.
2005 Configure the RouterBoard 532 series on-chip
2006 Ethernet adapter MAC address.
2008 kmemleak= [KNL] Boot-time kmemleak enable/disable
2009 Valid arguments: on, off
2010 Default: on
2011 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
2012 the default is off.
2014 kprobe_event=[probe-list]
2015 [FTRACE] Add kprobe events and enable at boot time.
2016 The probe-list is a semicolon delimited list of probe
2017 definitions. Each definition is same as kprobe_events
2018 interface, but the parameters are comma delimited.
2019 For example, to add a kprobe event on vfs_read with
2020 arg1 and arg2, add to the command line;
2022 kprobe_event=p,vfs_read,$arg1,$arg2
2024 See also Documentation/trace/kprobetrace.rst "Kernel
2025 Boot Parameter" section.
2027 kpti= [ARM64] Control page table isolation of user
2028 and kernel address spaces.
2029 Default: enabled on cores which need mitigation.
2030 0: force disabled
2031 1: force enabled
2033 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
2034 Default is 0 (don't ignore, but inject #GP)
2036 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
2037 Default is false (don't support).
2039 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
2040 KVM MMU at runtime.
2041 Default is 0 (off)
2043 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
2044 Default is 1 (enabled)
2046 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
2047 for all guests.
2048 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
2050 kvm-arm.vgic_v3_group0_trap=
2051 [KVM,ARM] Trap guest accesses to GICv3 group-0
2052 system registers
2054 kvm-arm.vgic_v3_group1_trap=
2055 [KVM,ARM] Trap guest accesses to GICv3 group-1
2056 system registers
2058 kvm-arm.vgic_v3_common_trap=
2059 [KVM,ARM] Trap guest accesses to GICv3 common
2060 system registers
2062 kvm-arm.vgic_v4_enable=
2063 [KVM,ARM] Allow use of GICv4 for direct injection of
2064 LPIs.
2066 kvm-intel.ept= [KVM,Intel] Disable extended page tables
2067 (virtualized MMU) support on capable Intel chips.
2068 Default is 1 (enabled)
2070 kvm-intel.emulate_invalid_guest_state=
2071 [KVM,Intel] Enable emulation of invalid guest states
2072 Default is 0 (disabled)
2074 kvm-intel.flexpriority=
2075 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
2076 Default is 1 (enabled)
2078 kvm-intel.nested=
2079 [KVM,Intel] Enable VMX nesting (nVMX).
2080 Default is 0 (disabled)
2082 kvm-intel.unrestricted_guest=
2083 [KVM,Intel] Disable unrestricted guest feature
2084 (virtualized real and unpaged mode) on capable
2085 Intel chips. Default is 1 (enabled)
2087 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2088 CVE-2018-3620.
2090 Valid arguments: never, cond, always
2092 always: L1D cache flush on every VMENTER.
2093 cond: Flush L1D on VMENTER only when the code between
2094 VMEXIT and VMENTER can leak host memory.
2095 never: Disables the mitigation
2097 Default is cond (do L1 cache flush in specific instances)
2099 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2100 feature (tagged TLBs) on capable Intel chips.
2101 Default is 1 (enabled)
2103 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2104 affected CPUs
2106 The kernel PTE inversion protection is unconditionally
2107 enabled and cannot be disabled.
2109 full
2110 Provides all available mitigations for the
2111 L1TF vulnerability. Disables SMT and
2112 enables all mitigations in the
2113 hypervisors, i.e. unconditional L1D flush.
2115 SMT control and L1D flush control via the
2116 sysfs interface is still possible after
2117 boot. Hypervisors will issue a warning
2118 when the first VM is started in a
2119 potentially insecure configuration,
2120 i.e. SMT enabled or L1D flush disabled.
2122 full,force
2123 Same as 'full', but disables SMT and L1D
2124 flush runtime control. Implies the
2125 'nosmt=force' command line option.
2126 (i.e. sysfs control of SMT is disabled.)
2128 flush
2129 Leaves SMT enabled and enables the default
2130 hypervisor mitigation, i.e. conditional
2131 L1D flush.
2133 SMT control and L1D flush control via the
2134 sysfs interface is still possible after
2135 boot. Hypervisors will issue a warning
2136 when the first VM is started in a
2137 potentially insecure configuration,
2138 i.e. SMT enabled or L1D flush disabled.
2140 flush,nosmt
2142 Disables SMT and enables the default
2143 hypervisor mitigation.
2145 SMT control and L1D flush control via the
2146 sysfs interface is still possible after
2147 boot. Hypervisors will issue a warning
2148 when the first VM is started in a
2149 potentially insecure configuration,
2150 i.e. SMT enabled or L1D flush disabled.
2152 flush,nowarn
2153 Same as 'flush', but hypervisors will not
2154 warn when a VM is started in a potentially
2155 insecure configuration.
2157 off
2158 Disables hypervisor mitigations and doesn't
2159 emit any warnings.
2160 It also drops the swap size and available
2161 RAM limit restriction on both hypervisor and
2162 bare metal.
2164 Default is 'flush'.
2166 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
2168 l2cr= [PPC]
2170 l3cr= [PPC]
2172 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2173 disabled it.
2175 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2176 value for LAPIC timer one-shot implementation. Default
2177 back to the programmable timer unit in the LAPIC.
2179 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2180 in C2 power state.
2182 libata.dma= [LIBATA] DMA control
2183 libata.dma=0 Disable all PATA and SATA DMA
2184 libata.dma=1 PATA and SATA Disk DMA only
2185 libata.dma=2 ATAPI (CDROM) DMA only
2186 libata.dma=4 Compact Flash DMA only
2187 Combinations also work, so libata.dma=3 enables DMA
2188 for disks and CDROMs, but not CFs.
2190 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2191 libata.ignore_hpa=0 keep BIOS limits (default)
2192 libata.ignore_hpa=1 ignore limits, using full disk
2194 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2195 when set.
2196 Format: <int>
2198 libata.force= [LIBATA] Force configurations. The format is comma
2199 separated list of "[ID:]VAL" where ID is
2200 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2201 matching port, link or device. Basically, it matches
2202 the ATA ID string printed on console by libata. If
2203 the whole ID part is omitted, the last PORT and DEVICE
2204 values are used. If ID hasn't been specified yet, the
2205 configuration applies to all ports, links and devices.
2207 If only DEVICE is omitted, the parameter applies to
2208 the port and all links and devices behind it. DEVICE
2209 number of 0 either selects the first device or the
2210 first fan-out link behind PMP device. It does not
2211 select the host link. DEVICE number of 15 selects the
2212 host link and device attached to it.
2214 The VAL specifies the configuration to force. As long
2215 as there's no ambiguity shortcut notation is allowed.
2216 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2217 The following configurations can be forced.
2219 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2220 Any ID with matching PORT is used.
2222 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2224 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2225 udma[/][16,25,33,44,66,100,133] notation is also
2226 allowed.
2228 * [no]ncq: Turn on or off NCQ.
2230 * [no]ncqtrim: Turn off queued DSM TRIM.
2232 * nohrst, nosrst, norst: suppress hard, soft
2233 and both resets.
2235 * rstonce: only attempt one reset during
2236 hot-unplug link recovery
2238 * dump_id: dump IDENTIFY data.
2240 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2242 * disable: Disable this device.
2244 If there are multiple matching configurations changing
2245 the same attribute, the last one is used.
2247 memblock=debug [KNL] Enable memblock debug messages.
2249 load_ramdisk= [RAM] List of ramdisks to load from floppy
2250 See Documentation/admin-guide/blockdev/ramdisk.rst.
2252 lockd.nlm_grace_period=P [NFS] Assign grace period.
2253 Format: <integer>
2255 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2256 Format: <integer>
2258 lockd.nlm_timeout=T [NFS] Assign timeout value.
2259 Format: <integer>
2261 lockd.nlm_udpport=M [NFS] Assign UDP port.
2262 Format: <integer>
2264 locktorture.nreaders_stress= [KNL]
2265 Set the number of locking read-acquisition kthreads.
2266 Defaults to being automatically set based on the
2267 number of online CPUs.
2269 locktorture.nwriters_stress= [KNL]
2270 Set the number of locking write-acquisition kthreads.
2272 locktorture.onoff_holdoff= [KNL]
2273 Set time (s) after boot for CPU-hotplug testing.
2275 locktorture.onoff_interval= [KNL]
2276 Set time (s) between CPU-hotplug operations, or
2277 zero to disable CPU-hotplug testing.
2279 locktorture.shuffle_interval= [KNL]
2280 Set task-shuffle interval (jiffies). Shuffling
2281 tasks allows some CPUs to go into dyntick-idle
2282 mode during the locktorture test.
2284 locktorture.shutdown_secs= [KNL]
2285 Set time (s) after boot system shutdown. This
2286 is useful for hands-off automated testing.
2288 locktorture.stat_interval= [KNL]
2289 Time (s) between statistics printk()s.
2291 locktorture.stutter= [KNL]
2292 Time (s) to stutter testing, for example,
2293 specifying five seconds causes the test to run for
2294 five seconds, wait for five seconds, and so on.
2295 This tests the locking primitive's ability to
2296 transition abruptly to and from idle.
2298 locktorture.torture_type= [KNL]
2299 Specify the locking implementation to test.
2301 locktorture.verbose= [KNL]
2302 Enable additional printk() statements.
2304 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2305 Format: <irq>
2307 loglevel= All Kernel Messages with a loglevel smaller than the
2308 console loglevel will be printed to the console. It can
2309 also be changed with klogd or other programs. The
2310 loglevels are defined as follows:
2312 0 (KERN_EMERG) system is unusable
2313 1 (KERN_ALERT) action must be taken immediately
2314 2 (KERN_CRIT) critical conditions
2315 3 (KERN_ERR) error conditions
2316 4 (KERN_WARNING) warning conditions
2317 5 (KERN_NOTICE) normal but significant condition
2318 6 (KERN_INFO) informational
2319 7 (KERN_DEBUG) debug-level messages
2321 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2322 in bytes. n must be a power of two and greater
2323 than the minimal size. The minimal size is defined
2324 by LOG_BUF_SHIFT kernel config parameter. There is
2325 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2326 that allows to increase the default size depending on
2327 the number of CPUs. See init/Kconfig for more details.
2329 logo.nologo [FB] Disables display of the built-in Linux logo.
2330 This may be used to provide more screen space for
2331 kernel log messages and is useful when debugging
2332 kernel boot problems.
2334 lp=0 [LP] Specify parallel ports to use, e.g,
2335 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2336 lp=reset first parallel port). 'lp=0' disables the
2337 lp=auto printer driver. 'lp=reset' (which can be
2338 specified in addition to the ports) causes
2339 attached printers to be reset. Using
2340 lp=port1,port2,... specifies the parallel ports
2341 to associate lp devices with, starting with
2342 lp0. A port specification may be 'none' to skip
2343 that lp device, or a parport name such as
2344 'parport0'. Specifying 'lp=auto' instead of a
2345 port specification list means that device IDs
2346 from each port should be examined, to see if
2347 an IEEE 1284-compliant printer is attached; if
2348 so, the driver will manage that printer.
2349 See also header of drivers/char/lp.c.
2351 lpj=n [KNL]
2352 Sets loops_per_jiffy to given constant, thus avoiding
2353 time-consuming boot-time autodetection (up to 250 ms per
2354 CPU). 0 enables autodetection (default). To determine
2355 the correct value for your kernel, boot with normal
2356 autodetection and see what value is printed. Note that
2357 on SMP systems the preset will be applied to all CPUs,
2358 which is likely to cause problems if your CPUs need
2359 significantly divergent settings. An incorrect value
2360 will cause delays in the kernel to be wrong, leading to
2361 unpredictable I/O errors and other breakage. Although
2362 unlikely, in the extreme case this might damage your
2363 hardware.
2365 ltpc= [NET]
2366 Format: <io>,<irq>,<dma>
2368 lsm.debug [SECURITY] Enable LSM initialization debugging output.
2370 lsm=lsm1,...,lsmN
2371 [SECURITY] Choose order of LSM initialization. This
2372 overrides CONFIG_LSM, and the "security=" parameter.
2374 machvec= [IA-64] Force the use of a particular machine-vector
2375 (machvec) in a generic kernel.
2376 Example: machvec=hpzx1_swiotlb
2378 machtype= [Loongson] Share the same kernel image file between different
2379 yeeloong laptop.
2380 Example: machtype=lemote-yeeloong-2f-7inch
2382 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2383 than or equal to this physical address is ignored.
2385 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2386 will bring up during bootup. maxcpus=n : n >= 0 limits
2387 the kernel to bring up 'n' processors. Surely after
2388 bootup you can bring up the other plugged cpu by executing
2389 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2390 only takes effect during system bootup.
2391 While n=0 is a special case, it is equivalent to "nosmp",
2392 which also disables the IO APIC.
2394 max_loop= [LOOP] The number of loop block devices that get
2395 (loop.max_loop) unconditionally pre-created at init time. The default
2396 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2397 of statically allocating a predefined number, loop
2398 devices can be requested on-demand with the
2399 /dev/loop-control interface.
2401 mce [X86-32] Machine Check Exception
2403 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst
2405 md= [HW] RAID subsystems devices and level
2406 See Documentation/admin-guide/md.rst.
2408 mdacon= [MDA]
2409 Format: <first>,<last>
2410 Specifies range of consoles to be captured by the MDA.
2412 mds= [X86,INTEL]
2413 Control mitigation for the Micro-architectural Data
2414 Sampling (MDS) vulnerability.
2416 Certain CPUs are vulnerable to an exploit against CPU
2417 internal buffers which can forward information to a
2418 disclosure gadget under certain conditions.
2420 In vulnerable processors, the speculatively
2421 forwarded data can be used in a cache side channel
2422 attack, to access data to which the attacker does
2423 not have direct access.
2425 This parameter controls the MDS mitigation. The
2426 options are:
2428 full - Enable MDS mitigation on vulnerable CPUs
2429 full,nosmt - Enable MDS mitigation and disable
2430 SMT on vulnerable CPUs
2431 off - Unconditionally disable MDS mitigation
2433 Not specifying this option is equivalent to
2434 mds=full.
2436 For details see: Documentation/admin-guide/hw-vuln/mds.rst
2438 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2439 Amount of memory to be used when the kernel is not able
2440 to see the whole system memory or for test.
2441 [X86] Work as limiting max address. Use together
2442 with memmap= to avoid physical address space collisions.
2443 Without memmap= PCI devices could be placed at addresses
2444 belonging to unused RAM.
2446 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2447 memory.
2449 memchunk=nn[KMG]
2450 [KNL,SH] Allow user to override the default size for
2451 per-device physically contiguous DMA buffers.
2453 memhp_default_state=online/offline
2454 [KNL] Set the initial state for the memory hotplug
2455 onlining policy. If not specified, the default value is
2456 set according to the
2457 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2458 option.
2459 See Documentation/admin-guide/mm/memory-hotplug.rst.
2461 memmap=exactmap [KNL,X86] Enable setting of an exact
2462 E820 memory map, as specified by the user.
2463 Such memmap=exactmap lines can be constructed based on
2464 BIOS output or other requirements. See the memmap=nn@ss
2465 option description.
2467 memmap=nn[KMG]@ss[KMG]
2468 [KNL] Force usage of a specific region of memory.
2469 Region of memory to be used is from ss to ss+nn.
2470 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2471 which limits max address to nn[KMG].
2472 Multiple different regions can be specified,
2473 comma delimited.
2474 Example:
2475 memmap=100M@2G,100M#3G,1G!1024G
2477 memmap=nn[KMG]#ss[KMG]
2478 [KNL,ACPI] Mark specific memory as ACPI data.
2479 Region of memory to be marked is from ss to ss+nn.
2481 memmap=nn[KMG]$ss[KMG]
2482 [KNL,ACPI] Mark specific memory as reserved.
2483 Region of memory to be reserved is from ss to ss+nn.
2484 Example: Exclude memory from 0x18690000-0x1869ffff
2485 memmap=64K$0x18690000
2486 or
2487 memmap=0x10000$0x18690000
2488 Some bootloaders may need an escape character before '$',
2489 like Grub2, otherwise '$' and the following number
2490 will be eaten.
2492 memmap=nn[KMG]!ss[KMG]
2493 [KNL,X86] Mark specific memory as protected.
2494 Region of memory to be used, from ss to ss+nn.
2495 The memory region may be marked as e820 type 12 (0xc)
2496 and is NVDIMM or ADR memory.
2498 memmap=<size>%<offset>-<oldtype>+<newtype>
2499 [KNL,ACPI] Convert memory within the specified region
2500 from <oldtype> to <newtype>. If "-<oldtype>" is left
2501 out, the whole region will be marked as <newtype>,
2502 even if previously unavailable. If "+<newtype>" is left
2503 out, matching memory will be removed. Types are
2504 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2505 3 = ACPI, 12 = PRAM.
2507 memory_corruption_check=0/1 [X86]
2508 Some BIOSes seem to corrupt the first 64k of
2509 memory when doing things like suspend/resume.
2510 Setting this option will scan the memory
2511 looking for corruption. Enabling this will
2512 both detect corruption and prevent the kernel
2513 from using the memory being corrupted.
2514 However, its intended as a diagnostic tool; if
2515 repeatable BIOS-originated corruption always
2516 affects the same memory, you can use memmap=
2517 to prevent the kernel from using that memory.
2519 memory_corruption_check_size=size [X86]
2520 By default it checks for corruption in the low
2521 64k, making this memory unavailable for normal
2522 use. Use this parameter to scan for
2523 corruption in more or less memory.
2525 memory_corruption_check_period=seconds [X86]
2526 By default it checks for corruption every 60
2527 seconds. Use this parameter to check at some
2528 other rate. 0 disables periodic checking.
2530 memtest= [KNL,X86,ARM,PPC] Enable memtest
2531 Format: <integer>
2532 default : 0 <disable>
2533 Specifies the number of memtest passes to be
2534 performed. Each pass selects another test
2535 pattern from a given set of patterns. Memtest
2536 fills the memory with this pattern, validates
2537 memory contents and reserves bad memory
2538 regions that are detected.
2540 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2541 Valid arguments: on, off
2542 Default (depends on kernel configuration option):
2543 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2544 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2545 mem_encrypt=on: Activate SME
2546 mem_encrypt=off: Do not activate SME
2548 Refer to Documentation/virtual/kvm/amd-memory-encryption.rst
2549 for details on when memory encryption can be activated.
2551 mem_sleep_default= [SUSPEND] Default system suspend mode:
2552 s2idle - Suspend-To-Idle
2553 shallow - Power-On Suspend or equivalent (if supported)
2554 deep - Suspend-To-RAM or equivalent (if supported)
2555 See Documentation/admin-guide/pm/sleep-states.rst.
2557 meye.*= [HW] Set MotionEye Camera parameters
2558 See Documentation/media/v4l-drivers/meye.rst.
2560 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2561 Multi-Function General Purpose Timers on AMD Geode
2562 platforms.
2564 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2565 the BIOS has incorrectly applied a workaround. TinyBIOS
2566 version 0.98 is known to be affected, 0.99 fixes the
2567 problem by letting the user disable the workaround.
2569 mga= [HW,DRM]
2571 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2572 physical address is ignored.
2574 mini2440= [ARM,HW,KNL]
2575 Format:[0..2][b][c][t]
2576 Default: "0tb"
2577 MINI2440 configuration specification:
2578 0 - The attached screen is the 3.5" TFT
2579 1 - The attached screen is the 7" TFT
2580 2 - The VGA Shield is attached (1024x768)
2581 Leaving out the screen size parameter will not load
2582 the TFT driver, and the framebuffer will be left
2583 unconfigured.
2584 b - Enable backlight. The TFT backlight pin will be
2585 linked to the kernel VESA blanking code and a GPIO
2586 LED. This parameter is not necessary when using the
2587 VGA shield.
2588 c - Enable the s3c camera interface.
2589 t - Reserved for enabling touchscreen support. The
2590 touchscreen support is not enabled in the mainstream
2591 kernel as of 2.6.30, a preliminary port can be found
2592 in the "bleeding edge" mini2440 support kernel at
2593 http://repo.or.cz/w/linux-2.6/mini2440.git
2595 mitigations=
2596 [X86,PPC,S390,ARM64] Control optional mitigations for
2597 CPU vulnerabilities. This is a set of curated,
2598 arch-independent options, each of which is an
2599 aggregation of existing arch-specific options.
2601 off
2602 Disable all optional CPU mitigations. This
2603 improves system performance, but it may also
2604 expose users to several CPU vulnerabilities.
2605 Equivalent to: nopti [X86,PPC]
2606 kpti=0 [ARM64]
2607 nospectre_v1 [PPC]
2608 nobp=0 [S390]
2609 nospectre_v2 [X86,PPC,S390,ARM64]
2610 spectre_v2_user=off [X86]
2611 spec_store_bypass_disable=off [X86,PPC]
2612 ssbd=force-off [ARM64]
2613 l1tf=off [X86]
2614 mds=off [X86]
2616 auto (default)
2617 Mitigate all CPU vulnerabilities, but leave SMT
2618 enabled, even if it's vulnerable. This is for
2619 users who don't want to be surprised by SMT
2620 getting disabled across kernel upgrades, or who
2621 have other ways of avoiding SMT-based attacks.
2622 Equivalent to: (default behavior)
2624 auto,nosmt
2625 Mitigate all CPU vulnerabilities, disabling SMT
2626 if needed. This is for users who always want to
2627 be fully mitigated, even if it means losing SMT.
2628 Equivalent to: l1tf=flush,nosmt [X86]
2629 mds=full,nosmt [X86]
2631 mminit_loglevel=
2632 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2633 parameter allows control of the logging verbosity for
2634 the additional memory initialisation checks. A value
2635 of 0 disables mminit logging and a level of 4 will
2636 log everything. Information is printed at KERN_DEBUG
2637 so loglevel=8 may also need to be specified.
2639 module.sig_enforce
2640 [KNL] When CONFIG_MODULE_SIG is set, this means that
2641 modules without (valid) signatures will fail to load.
2642 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2643 is always true, so this option does nothing.
2645 module_blacklist= [KNL] Do not load a comma-separated list of
2646 modules. Useful for debugging problem modules.
2648 mousedev.tap_time=
2649 [MOUSE] Maximum time between finger touching and
2650 leaving touchpad surface for touch to be considered
2651 a tap and be reported as a left button click (for
2652 touchpads working in absolute mode only).
2653 Format: <msecs>
2654 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2655 reporting absolute coordinates, such as tablets
2656 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2657 reporting absolute coordinates, such as tablets
2659 movablecore= [KNL,X86,IA-64,PPC]
2660 Format: nn[KMGTPE] | nn%
2661 This parameter is the complement to kernelcore=, it
2662 specifies the amount of memory used for migratable
2663 allocations. If both kernelcore and movablecore is
2664 specified, then kernelcore will be at *least* the
2665 specified value but may be more. If movablecore on its
2666 own is specified, the administrator must be careful
2667 that the amount of memory usable for all allocations
2668 is not too small.
2670 movable_node [KNL] Boot-time switch to make hotplugable memory
2671 NUMA nodes to be movable. This means that the memory
2672 of such nodes will be usable only for movable
2673 allocations which rules out almost all kernel
2674 allocations. Use with caution!
2676 MTD_Partition= [MTD]
2677 Format: <name>,<region-number>,<size>,<offset>
2679 MTD_Region= [MTD] Format:
2680 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2682 mtdparts= [MTD]
2683 See drivers/mtd/cmdlinepart.c.
2685 multitce=off [PPC] This parameter disables the use of the pSeries
2686 firmware feature for updating multiple TCE entries
2687 at a time.
2689 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2691 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2693 boundary - index of last SLC block on Flex-OneNAND.
2694 The remaining blocks are configured as MLC blocks.
2695 lock - Configure if Flex-OneNAND boundary should be locked.
2696 Once locked, the boundary cannot be changed.
2697 1 indicates lock status, 0 indicates unlock status.
2699 mtdset= [ARM]
2700 ARM/S3C2412 JIVE boot control
2702 See arch/arm/mach-s3c2412/mach-jive.c
2704 mtouchusb.raw_coordinates=
2705 [HW] Make the MicroTouch USB driver use raw coordinates
2706 ('y', default) or cooked coordinates ('n')
2708 mtrr_chunk_size=nn[KMG] [X86]
2709 used for mtrr cleanup. It is largest continuous chunk
2710 that could hold holes aka. UC entries.
2712 mtrr_gran_size=nn[KMG] [X86]
2713 Used for mtrr cleanup. It is granularity of mtrr block.
2714 Default is 1.
2715 Large value could prevent small alignment from
2716 using up MTRRs.
2718 mtrr_spare_reg_nr=n [X86]
2719 Format: <integer>
2720 Range: 0,7 : spare reg number
2721 Default : 1
2722 Used for mtrr cleanup. It is spare mtrr entries number.
2723 Set to 2 or more if your graphical card needs more.
2725 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2727 netdev= [NET] Network devices parameters
2728 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2729 Note that mem_start is often overloaded to mean
2730 something different and driver-specific.
2731 This usage is only documented in each driver source
2732 file if at all.
2734 nf_conntrack.acct=
2735 [NETFILTER] Enable connection tracking flow accounting
2736 0 to disable accounting
2737 1 to enable accounting
2738 Default value is 0.
2740 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2741 See Documentation/filesystems/nfs/nfsroot.txt.
2743 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2744 See Documentation/filesystems/nfs/nfsroot.txt.
2746 nfsrootdebug [NFS] enable nfsroot debugging messages.
2747 See Documentation/filesystems/nfs/nfsroot.txt.
2749 nfs.callback_nr_threads=
2750 [NFSv4] set the total number of threads that the
2751 NFS client will assign to service NFSv4 callback
2752 requests.
2754 nfs.callback_tcpport=
2755 [NFS] set the TCP port on which the NFSv4 callback
2756 channel should listen.
2758 nfs.cache_getent=
2759 [NFS] sets the pathname to the program which is used
2760 to update the NFS client cache entries.
2762 nfs.cache_getent_timeout=
2763 [NFS] sets the timeout after which an attempt to
2764 update a cache entry is deemed to have failed.
2766 nfs.idmap_cache_timeout=
2767 [NFS] set the maximum lifetime for idmapper cache
2768 entries.
2770 nfs.enable_ino64=
2771 [NFS] enable 64-bit inode numbers.
2772 If zero, the NFS client will fake up a 32-bit inode
2773 number for the readdir() and stat() syscalls instead
2774 of returning the full 64-bit number.
2775 The default is to return 64-bit inode numbers.
2777 nfs.max_session_cb_slots=
2778 [NFSv4.1] Sets the maximum number of session
2779 slots the client will assign to the callback
2780 channel. This determines the maximum number of
2781 callbacks the client will process in parallel for
2782 a particular server.
2784 nfs.max_session_slots=
2785 [NFSv4.1] Sets the maximum number of session slots
2786 the client will attempt to negotiate with the server.
2787 This limits the number of simultaneous RPC requests
2788 that the client can send to the NFSv4.1 server.
2789 Note that there is little point in setting this
2790 value higher than the max_tcp_slot_table_limit.
2792 nfs.nfs4_disable_idmapping=
2793 [NFSv4] When set to the default of '1', this option
2794 ensures that both the RPC level authentication
2795 scheme and the NFS level operations agree to use
2796 numeric uids/gids if the mount is using the
2797 'sec=sys' security flavour. In effect it is
2798 disabling idmapping, which can make migration from
2799 legacy NFSv2/v3 systems to NFSv4 easier.
2800 Servers that do not support this mode of operation
2801 will be autodetected by the client, and it will fall
2802 back to using the idmapper.
2803 To turn off this behaviour, set the value to '0'.
2804 nfs.nfs4_unique_id=
2805 [NFS4] Specify an additional fixed unique ident-
2806 ification string that NFSv4 clients can insert into
2807 their nfs_client_id4 string. This is typically a
2808 UUID that is generated at system install time.
2810 nfs.send_implementation_id =
2811 [NFSv4.1] Send client implementation identification
2812 information in exchange_id requests.
2813 If zero, no implementation identification information
2814 will be sent.
2815 The default is to send the implementation identification
2816 information.
2818 nfs.recover_lost_locks =
2819 [NFSv4] Attempt to recover locks that were lost due
2820 to a lease timeout on the server. Please note that
2821 doing this risks data corruption, since there are
2822 no guarantees that the file will remain unchanged
2823 after the locks are lost.
2824 If you want to enable the kernel legacy behaviour of
2825 attempting to recover these locks, then set this
2826 parameter to '1'.
2827 The default parameter value of '0' causes the kernel
2828 not to attempt recovery of lost locks.
2830 nfs4.layoutstats_timer =
2831 [NFSv4.2] Change the rate at which the kernel sends
2832 layoutstats to the pNFS metadata server.
2834 Setting this to value to 0 causes the kernel to use
2835 whatever value is the default set by the layout
2836 driver. A non-zero value sets the minimum interval
2837 in seconds between layoutstats transmissions.
2839 nfsd.nfs4_disable_idmapping=
2840 [NFSv4] When set to the default of '1', the NFSv4
2841 server will return only numeric uids and gids to
2842 clients using auth_sys, and will accept numeric uids
2843 and gids from such clients. This is intended to ease
2844 migration from NFSv2/v3.
2846 nmi_debug= [KNL,SH] Specify one or more actions to take
2847 when a NMI is triggered.
2848 Format: [state][,regs][,debounce][,die]
2850 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2851 Format: [panic,][nopanic,][num]
2852 Valid num: 0 or 1
2853 0 - turn hardlockup detector in nmi_watchdog off
2854 1 - turn hardlockup detector in nmi_watchdog on
2855 When panic is specified, panic when an NMI watchdog
2856 timeout occurs (or 'nopanic' to not panic on an NMI
2857 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set)
2858 To disable both hard and soft lockup detectors,
2859 please see 'nowatchdog'.
2860 This is useful when you use a panic=... timeout and
2861 need the box quickly up again.
2863 These settings can be accessed at runtime via
2864 the nmi_watchdog and hardlockup_panic sysctls.
2866 netpoll.carrier_timeout=
2867 [NET] Specifies amount of time (in seconds) that
2868 netpoll should wait for a carrier. By default netpoll
2869 waits 4 seconds.
2871 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2872 emulation library even if a 387 maths coprocessor
2873 is present.
2875 no5lvl [X86-64] Disable 5-level paging mode. Forces
2876 kernel to use 4-level paging instead.
2878 no_console_suspend
2879 [HW] Never suspend the console
2880 Disable suspending of consoles during suspend and
2881 hibernate operations. Once disabled, debugging
2882 messages can reach various consoles while the rest
2883 of the system is being put to sleep (ie, while
2884 debugging driver suspend/resume hooks). This may
2885 not work reliably with all consoles, but is known
2886 to work with serial and VGA consoles.
2887 To facilitate more flexible debugging, we also add
2888 console_suspend, a printk module parameter to control
2889 it. Users could use console_suspend (usually
2890 /sys/module/printk/parameters/console_suspend) to
2891 turn on/off it dynamically.
2893 novmcoredd [KNL,KDUMP]
2894 Disable device dump. Device dump allows drivers to
2895 append dump data to vmcore so you can collect driver
2896 specified debug info. Drivers can append the data
2897 without any limit and this data is stored in memory,
2898 so this may cause significant memory stress. Disabling
2899 device dump can help save memory but the driver debug
2900 data will be no longer available. This parameter
2901 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP
2902 is set.
2904 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2905 caches in the slab allocator. Saves per-node memory,
2906 but will impact performance.
2908 noalign [KNL,ARM]
2910 noaltinstr [S390] Disables alternative instructions patching
2911 (CPU alternatives feature).
2913 noapic [SMP,APIC] Tells the kernel to not make use of any
2914 IOAPICs that may be present in the system.
2916 noautogroup Disable scheduler automatic task group creation.
2918 nobats [PPC] Do not use BATs for mapping kernel lowmem
2919 on "Classic" PPC cores.
2921 nocache [ARM]
2923 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2925 nodelayacct [KNL] Disable per-task delay accounting
2927 nodsp [SH] Disable hardware DSP at boot time.
2929 noefi Disable EFI runtime services support.
2931 noexec [IA-64]
2933 noexec [X86]
2934 On X86-32 available only on PAE configured kernels.
2935 noexec=on: enable non-executable mappings (default)
2936 noexec=off: disable non-executable mappings
2938 nosmap [X86,PPC]
2939 Disable SMAP (Supervisor Mode Access Prevention)
2940 even if it is supported by processor.
2942 nosmep [X86,PPC]
2943 Disable SMEP (Supervisor Mode Execution Prevention)
2944 even if it is supported by processor.
2946 noexec32 [X86-64]
2947 This affects only 32-bit executables.
2948 noexec32=on: enable non-executable mappings (default)
2949 read doesn't imply executable mappings
2950 noexec32=off: disable non-executable mappings
2951 read implies executable mappings
2953 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2955 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2956 register save and restore. The kernel will only save
2957 legacy floating-point registers on task switch.
2959 nohugeiomap [KNL,x86,PPC] Disable kernel huge I/O mappings.
2961 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2962 Equivalent to smt=1.
2964 [KNL,x86] Disable symmetric multithreading (SMT).
2965 nosmt=force: Force disable SMT, cannot be undone
2966 via the sysfs control file.
2968 nospectre_v1 [PPC] Disable mitigations for Spectre Variant 1 (bounds
2969 check bypass). With this option data leaks are possible
2970 in the system.
2972 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for
2973 the Spectre variant 2 (indirect branch prediction)
2974 vulnerability. System may allow data leaks with this
2975 option.
2977 nospec_store_bypass_disable
2978 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
2980 noxsave [BUGS=X86] Disables x86 extended register state save
2981 and restore using xsave. The kernel will fallback to
2982 enabling legacy floating-point and sse state.
2984 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2985 register states. The kernel will fall back to use
2986 xsave to save the states. By using this parameter,
2987 performance of saving the states is degraded because
2988 xsave doesn't support modified optimization while
2989 xsaveopt supports it on xsaveopt enabled systems.
2991 noxsaves [X86] Disables xsaves and xrstors used in saving and
2992 restoring x86 extended register state in compacted
2993 form of xsave area. The kernel will fall back to use
2994 xsaveopt and xrstor to save and restore the states
2995 in standard form of xsave area. By using this
2996 parameter, xsave area per process might occupy more
2997 memory on xsaves enabled systems.
2999 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
3000 wfi(ARM) instruction doesn't work correctly and not to
3001 use it. This is also useful when using JTAG debugger.
3003 no_file_caps Tells the kernel not to honor file capabilities. The
3004 only way then for a file to be executed with privilege
3005 is to be setuid root or executed by root.
3007 nohalt [IA-64] Tells the kernel not to use the power saving
3008 function PAL_HALT_LIGHT when idle. This increases
3009 power-consumption. On the positive side, it reduces
3010 interrupt wake-up latency, which may improve performance
3011 in certain environments such as networked servers or
3012 real-time systems.
3014 nohibernate [HIBERNATION] Disable hibernation and resume.
3016 nohz= [KNL] Boottime enable/disable dynamic ticks
3017 Valid arguments: on, off
3018 Default: on
3020 nohz_full= [KNL,BOOT,SMP,ISOL]
3021 The argument is a cpu list, as described above.
3022 In kernels built with CONFIG_NO_HZ_FULL=y, set
3023 the specified list of CPUs whose tick will be stopped
3024 whenever possible. The boot CPU will be forced outside
3025 the range to maintain the timekeeping. Any CPUs
3026 in this list will have their RCU callbacks offloaded,
3027 just as if they had also been called out in the
3028 rcu_nocbs= boot parameter.
3030 noiotrap [SH] Disables trapped I/O port accesses.
3032 noirqdebug [X86-32] Disables the code which attempts to detect and
3033 disable unhandled interrupt sources.
3035 no_timer_check [X86,APIC] Disables the code which tests for
3036 broken timer IRQ sources.
3038 noisapnp [ISAPNP] Disables ISA PnP code.
3040 noinitrd [RAM] Tells the kernel not to load any configured
3041 initial RAM disk.
3043 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
3044 remapping.
3045 [Deprecated - use intremap=off]
3047 nointroute [IA-64]
3049 noinvpcid [X86] Disable the INVPCID cpu feature.
3051 nojitter [IA-64] Disables jitter checking for ITC timers.
3053 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
3055 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
3056 fault handling.
3058 no-vmw-sched-clock
3059 [X86,PV_OPS] Disable paravirtualized VMware scheduler
3060 clock and use the default one.
3062 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
3063 steal time is computed, but won't influence scheduler
3064 behaviour
3066 nolapic [X86-32,APIC] Do not enable or use the local APIC.
3068 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
3070 noltlbs [PPC] Do not use large page/tlb entries for kernel
3071 lowmem mapping on PPC40x and PPC8xx
3073 nomca [IA-64] Disable machine check abort handling
3075 nomce [X86-32] Disable Machine Check Exception
3077 nomfgpt [X86-32] Disable Multi-Function General Purpose
3078 Timer usage (for AMD Geode machines).
3080 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
3081 shutdown the other cpus. Instead use the REBOOT_VECTOR
3082 irq.
3084 nomodule Disable module load
3086 nopat [X86] Disable PAT (page attribute table extension of
3087 pagetables) support.
3089 nopcid [X86-64] Disable the PCID cpu feature.
3091 norandmaps Don't use address space randomization. Equivalent to
3092 echo 0 > /proc/sys/kernel/randomize_va_space
3094 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
3095 with UP alternatives
3097 nordrand [X86] Disable kernel use of the RDRAND and
3098 RDSEED instructions even if they are supported
3099 by the processor. RDRAND and RDSEED are still
3100 available to user space applications.
3102 noresume [SWSUSP] Disables resume and restores original swap
3103 space.
3105 no-scroll [VGA] Disables scrollback.
3106 This is required for the Braillex ib80-piezo Braille
3107 reader made by F.H. Papenmeier (Germany).
3109 nosbagart [IA-64]
3111 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
3113 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
3114 and disable the IO APIC. legacy for "maxcpus=0".
3116 nosoftlockup [KNL] Disable the soft-lockup detector.
3118 nosync [HW,M68K] Disables sync negotiation for all devices.
3120 nowatchdog [KNL] Disable both lockup detectors, i.e.
3121 soft-lockup and NMI watchdog (hard-lockup).
3123 nowb [ARM]
3125 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
3127 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
3128 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
3129 Some features depend on CPU0. Known dependencies are:
3130 1. Resume from suspend/hibernate depends on CPU0.
3131 Suspend/hibernate will fail if CPU0 is offline and you
3132 need to online CPU0 before suspend/hibernate.
3133 2. PIC interrupts also depend on CPU0. CPU0 can't be
3134 removed if a PIC interrupt is detected.
3135 It's said poweroff/reboot may depend on CPU0 on some
3136 machines although I haven't seen such issues so far
3137 after CPU0 is offline on a few tested machines.
3138 If the dependencies are under your control, you can
3139 turn on cpu0_hotplug.
3141 nps_mtm_hs_ctr= [KNL,ARC]
3142 This parameter sets the maximum duration, in
3143 cycles, each HW thread of the CTOP can run
3144 without interruptions, before HW switches it.
3145 The actual maximum duration is 16 times this
3146 parameter's value.
3147 Format: integer between 1 and 255
3148 Default: 255
3150 nptcg= [IA-64] Override max number of concurrent global TLB
3151 purges which is reported from either PAL_VM_SUMMARY or
3152 SAL PALO.
3154 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
3155 could support. nr_cpus=n : n >= 1 limits the kernel to
3156 support 'n' processors. It could be larger than the
3157 number of already plugged CPU during bootup, later in
3158 runtime you can physically add extra cpu until it reaches
3159 n. So during boot up some boot time memory for per-cpu
3160 variables need be pre-allocated for later physical cpu
3161 hot plugging.
3163 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3165 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
3166 Allowed values are enable and disable
3168 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3169 'node', 'default' can be specified
3170 This can be set from sysctl after boot.
3171 See Documentation/admin-guide/sysctl/vm.rst for details.
3173 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3174 See Documentation/debugging-via-ohci1394.txt for more
3175 info.
3177 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3178 Rather than timing out after 20 ms if an EC
3179 command is not properly ACKed, override the length
3180 of the timeout. We have interrupts disabled while
3181 waiting for the ACK, so if this is set too high
3182 interrupts *may* be lost!
3184 omap_mux= [OMAP] Override bootloader pin multiplexing.
3185 Format: <mux_mode0.mode_name=value>...
3186 For example, to override I2C bus2:
3187 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3189 oprofile.timer= [HW]
3190 Use timer interrupt instead of performance counters
3192 oprofile.cpu_type= Force an oprofile cpu type
3193 This might be useful if you have an older oprofile
3194 userland or if you want common events.
3195 Format: { arch_perfmon }
3196 arch_perfmon: [X86] Force use of architectural
3197 perfmon on Intel CPUs instead of the
3198 CPU specific event set.
3199 timer: [X86] Force use of architectural NMI
3200 timer mode (see also oprofile.timer
3201 for generic hr timer mode)
3203 oops=panic Always panic on oopses. Default is to just kill the
3204 process, but there is a small probability of
3205 deadlocking the machine.
3206 This will also cause panics on machine check exceptions.
3207 Useful together with panic=30 to trigger a reboot.
3209 page_alloc.shuffle=
3210 [KNL] Boolean flag to control whether the page allocator
3211 should randomize its free lists. The randomization may
3212 be automatically enabled if the kernel detects it is
3213 running on a platform with a direct-mapped memory-side
3214 cache, and this parameter can be used to
3215 override/disable that behavior. The state of the flag
3216 can be read from sysfs at:
3217 /sys/module/page_alloc/parameters/shuffle.
3219 page_owner= [KNL] Boot-time page_owner enabling option.
3220 Storage of the information about who allocated
3221 each page is disabled in default. With this switch,
3222 we can turn it on.
3223 on: enable the feature
3225 page_poison= [KNL] Boot-time parameter changing the state of
3226 poisoning on the buddy allocator, available with
3227 CONFIG_PAGE_POISONING=y.
3228 off: turn off poisoning (default)
3229 on: turn on poisoning
3231 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3232 timeout > 0: seconds before rebooting
3233 timeout = 0: wait forever
3234 timeout < 0: reboot immediately
3235 Format: <timeout>
3237 panic_print= Bitmask for printing system info when panic happens.
3238 User can chose combination of the following bits:
3239 bit 0: print all tasks info
3240 bit 1: print system memory info
3241 bit 2: print timer info
3242 bit 3: print locks info if CONFIG_LOCKDEP is on
3243 bit 4: print ftrace buffer
3244 bit 5: print all printk messages in buffer
3246 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3247 on a WARN().
3249 crash_kexec_post_notifiers
3250 Run kdump after running panic-notifiers and dumping
3251 kmsg. This only for the users who doubt kdump always
3252 succeeds in any situation.
3253 Note that this also increases risks of kdump failure,
3254 because some panic notifiers can make the crashed
3255 kernel more unstable.
3257 parkbd.port= [HW] Parallel port number the keyboard adapter is
3258 connected to, default is 0.
3259 Format: <parport#>
3260 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3261 0 for XT, 1 for AT (default is AT).
3262 Format: <mode>
3264 parport= [HW,PPT] Specify parallel ports. 0 disables.
3265 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3266 Use 'auto' to force the driver to use any
3267 IRQ/DMA settings detected (the default is to
3268 ignore detected IRQ/DMA settings because of
3269 possible conflicts). You can specify the base
3270 address, IRQ, and DMA settings; IRQ and DMA
3271 should be numbers, or 'auto' (for using detected
3272 settings on that particular port), or 'nofifo'
3273 (to avoid using a FIFO even if it is detected).
3274 Parallel ports are assigned in the order they
3275 are specified on the command line, starting
3276 with parport0.
3278 parport_init_mode= [HW,PPT]
3279 Configure VIA parallel port to operate in
3280 a specific mode. This is necessary on Pegasos
3281 computer where firmware has no options for setting
3282 up parallel port mode and sets it to spp.
3283 Currently this function knows 686a and 8231 chips.
3284 Format: [spp|ps2|epp|ecp|ecpepp]
3286 pause_on_oops=
3287 Halt all CPUs after the first oops has been printed for
3288 the specified number of seconds. This is to be used if
3289 your oopses keep scrolling off the screen.
3291 pcbit= [HW,ISDN]
3293 pcd. [PARIDE]
3294 See header of drivers/block/paride/pcd.c.
3295 See also Documentation/admin-guide/blockdev/paride.rst.
3297 pci=option[,option...] [PCI] various PCI subsystem options.
3299 Some options herein operate on a specific device
3300 or a set of devices (<pci_dev>). These are
3301 specified in one of the following formats:
3303 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
3304 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
3306 Note: the first format specifies a PCI
3307 bus/device/function address which may change
3308 if new hardware is inserted, if motherboard
3309 firmware changes, or due to changes caused
3310 by other kernel parameters. If the
3311 domain is left unspecified, it is
3312 taken to be zero. Optionally, a path
3313 to a device through multiple device/function
3314 addresses can be specified after the base
3315 address (this is more robust against
3316 renumbering issues). The second format
3317 selects devices using IDs from the
3318 configuration space which may match multiple
3319 devices in the system.
3321 earlydump dump PCI config space before the kernel
3322 changes anything
3323 off [X86] don't probe for the PCI bus
3324 bios [X86-32] force use of PCI BIOS, don't access
3325 the hardware directly. Use this if your machine
3326 has a non-standard PCI host bridge.
3327 nobios [X86-32] disallow use of PCI BIOS, only direct
3328 hardware access methods are allowed. Use this
3329 if you experience crashes upon bootup and you
3330 suspect they are caused by the BIOS.
3331 conf1 [X86] Force use of PCI Configuration Access
3332 Mechanism 1 (config address in IO port 0xCF8,
3333 data in IO port 0xCFC, both 32-bit).
3334 conf2 [X86] Force use of PCI Configuration Access
3335 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3336 the function, IO port 0xCFA, also 8-bit, sets
3337 bus number. The config space is then accessed
3338 through ports 0xC000-0xCFFF).
3339 See http://wiki.osdev.org/PCI for more info
3340 on the configuration access mechanisms.
3341 noaer [PCIE] If the PCIEAER kernel config parameter is
3342 enabled, this kernel boot option can be used to
3343 disable the use of PCIE advanced error reporting.
3344 nodomains [PCI] Disable support for multiple PCI
3345 root domains (aka PCI segments, in ACPI-speak).
3346 nommconf [X86] Disable use of MMCONFIG for PCI
3347 Configuration
3348 check_enable_amd_mmconf [X86] check for and enable
3349 properly configured MMIO access to PCI
3350 config space on AMD family 10h CPU
3351 nomsi [MSI] If the PCI_MSI kernel config parameter is
3352 enabled, this kernel boot option can be used to
3353 disable the use of MSI interrupts system-wide.
3354 noioapicquirk [APIC] Disable all boot interrupt quirks.
3355 Safety option to keep boot IRQs enabled. This
3356 should never be necessary.
3357 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3358 primary IO-APIC for bridges that cannot disable
3359 boot IRQs. This fixes a source of spurious IRQs
3360 when the system masks IRQs.
3361 noioapicreroute [APIC] Disable workaround that uses the
3362 boot IRQ equivalent of an IRQ that connects to
3363 a chipset where boot IRQs cannot be disabled.
3364 The opposite of ioapicreroute.
3365 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3366 routing table. These calls are known to be buggy
3367 on several machines and they hang the machine
3368 when used, but on other computers it's the only
3369 way to get the interrupt routing table. Try
3370 this option if the kernel is unable to allocate
3371 IRQs or discover secondary PCI buses on your
3372 motherboard.
3373 rom [X86] Assign address space to expansion ROMs.
3374 Use with caution as certain devices share
3375 address decoders between ROMs and other
3376 resources.
3377 norom [X86] Do not assign address space to
3378 expansion ROMs that do not already have
3379 BIOS assigned address ranges.
3380 nobar [X86] Do not assign address space to the
3381 BARs that weren't assigned by the BIOS.
3382 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3383 assigned automatically to PCI devices. You can
3384 make the kernel exclude IRQs of your ISA cards
3385 this way.
3386 pirqaddr=0xAAAAA [X86] Specify the physical address
3387 of the PIRQ table (normally generated
3388 by the BIOS) if it is outside the
3389 F0000h-100000h range.
3390 lastbus=N [X86] Scan all buses thru bus #N. Can be
3391 useful if the kernel is unable to find your
3392 secondary buses and you want to tell it
3393 explicitly which ones they are.
3394 assign-busses [X86] Always assign all PCI bus
3395 numbers ourselves, overriding
3396 whatever the firmware may have done.
3397 usepirqmask [X86] Honor the possible IRQ mask stored
3398 in the BIOS $PIR table. This is needed on
3399 some systems with broken BIOSes, notably
3400 some HP Pavilion N5400 and Omnibook XE3
3401 notebooks. This will have no effect if ACPI
3402 IRQ routing is enabled.
3403 noacpi [X86] Do not use ACPI for IRQ routing
3404 or for PCI scanning.
3405 use_crs [X86] Use PCI host bridge window information
3406 from ACPI. On BIOSes from 2008 or later, this
3407 is enabled by default. If you need to use this,
3408 please report a bug.
3409 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3410 If you need to use this, please report a bug.
3411 routeirq Do IRQ routing for all PCI devices.
3412 This is normally done in pci_enable_device(),
3413 so this option is a temporary workaround
3414 for broken drivers that don't call it.
3415 skip_isa_align [X86] do not align io start addr, so can
3416 handle more pci cards
3417 noearly [X86] Don't do any early type 1 scanning.
3418 This might help on some broken boards which
3419 machine check when some devices' config space
3420 is read. But various workarounds are disabled
3421 and some IOMMU drivers will not work.
3422 bfsort Sort PCI devices into breadth-first order.
3423 This sorting is done to get a device
3424 order compatible with older (<= 2.4) kernels.
3425 nobfsort Don't sort PCI devices into breadth-first order.
3426 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3427 tuning and use the BIOS-configured MPS defaults.
3428 pcie_bus_safe Set every device's MPS to the largest value
3429 supported by all devices below the root complex.
3430 pcie_bus_perf Set device MPS to the largest allowable MPS
3431 based on its parent bus. Also set MRRS (Max
3432 Read Request Size) to the largest supported
3433 value (no larger than the MPS that the device
3434 or bus can support) for best performance.
3435 pcie_bus_peer2peer Set every device's MPS to 128B, which
3436 every device is guaranteed to support. This
3437 configuration allows peer-to-peer DMA between
3438 any pair of devices, possibly at the cost of
3439 reduced performance. This also guarantees
3440 that hot-added devices will work.
3441 cbiosize=nn[KMG] The fixed amount of bus space which is
3442 reserved for the CardBus bridge's IO window.
3443 The default value is 256 bytes.
3444 cbmemsize=nn[KMG] The fixed amount of bus space which is
3445 reserved for the CardBus bridge's memory
3446 window. The default value is 64 megabytes.
3447 resource_alignment=
3448 Format:
3449 [<order of align>@]<pci_dev>[; ...]
3450 Specifies alignment and device to reassign
3451 aligned memory resources. How to
3452 specify the device is described above.
3453 If <order of align> is not specified,
3454 PAGE_SIZE is used as alignment.
3455 PCI-PCI bridge can be specified, if resource
3456 windows need to be expanded.
3457 To specify the alignment for several
3458 instances of a device, the PCI vendor,
3459 device, subvendor, and subdevice may be
3460 specified, e.g., 4096@pci:8086:9c22:103c:198f
3461 ecrc= Enable/disable PCIe ECRC (transaction layer
3462 end-to-end CRC checking).
3463 bios: Use BIOS/firmware settings. This is the
3464 the default.
3465 off: Turn ECRC off
3466 on: Turn ECRC on.
3467 hpiosize=nn[KMG] The fixed amount of bus space which is
3468 reserved for hotplug bridge's IO window.
3469 Default size is 256 bytes.
3470 hpmemsize=nn[KMG] The fixed amount of bus space which is
3471 reserved for hotplug bridge's memory window.
3472 Default size is 2 megabytes.
3473 hpbussize=nn The minimum amount of additional bus numbers
3474 reserved for buses below a hotplug bridge.
3475 Default is 1.
3476 realloc= Enable/disable reallocating PCI bridge resources
3477 if allocations done by BIOS are too small to
3478 accommodate resources required by all child
3479 devices.
3480 off: Turn realloc off
3481 on: Turn realloc on
3482 realloc same as realloc=on
3483 noari do not use PCIe ARI.
3484 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
3485 do not use PCIe ATS (and IOMMU device IOTLB).
3486 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3487 only look for one device below a PCIe downstream
3488 port.
3489 big_root_window Try to add a big 64bit memory window to the PCIe
3490 root complex on AMD CPUs. Some GFX hardware
3491 can resize a BAR to allow access to all VRAM.
3492 Adding the window is slightly risky (it may
3493 conflict with unreported devices), so this
3494 taints the kernel.
3495 disable_acs_redir=<pci_dev>[; ...]
3496 Specify one or more PCI devices (in the format
3497 specified above) separated by semicolons.
3498 Each device specified will have the PCI ACS
3499 redirect capabilities forced off which will
3500 allow P2P traffic between devices through
3501 bridges without forcing it upstream. Note:
3502 this removes isolation between devices and
3503 may put more devices in an IOMMU group.
3504 force_floating [S390] Force usage of floating interrupts.
3505 nomio [S390] Do not use MIO instructions.
3507 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3508 Management.
3509 off Disable ASPM.
3510 force Enable ASPM even on devices that claim not to support it.
3511 WARNING: Forcing ASPM on may cause system lockups.
3513 pcie_ports= [PCIE] PCIe port services handling:
3514 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
3515 even if the platform doesn't give the OS permission to
3516 use them. This may cause conflicts if the platform
3517 also tries to use these services.
3518 compat Disable native PCIe services (PME, AER, DPC, PCIe
3519 hotplug).
3521 pcie_port_pm= [PCIE] PCIe port power management handling:
3522 off Disable power management of all PCIe ports
3523 force Forcibly enable power management of all PCIe ports
3525 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3526 nomsi Do not use MSI for native PCIe PME signaling (this makes
3527 all PCIe root ports use INTx for all services).
3529 pcmv= [HW,PCMCIA] BadgePAD 4
3531 pd_ignore_unused
3532 [PM]
3533 Keep all power-domains already enabled by bootloader on,
3534 even if no driver has claimed them. This is useful
3535 for debug and development, but should not be
3536 needed on a platform with proper driver support.
3538 pd. [PARIDE]
3539 See Documentation/admin-guide/blockdev/paride.rst.
3541 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3542 boot time.
3543 Format: { 0 | 1 }
3544 See arch/parisc/kernel/pdc_chassis.c
3546 percpu_alloc= Select which percpu first chunk allocator to use.
3547 Currently supported values are "embed" and "page".
3548 Archs may support subset or none of the selections.
3549 See comments in mm/percpu.c for details on each
3550 allocator. This parameter is primarily for debugging
3551 and performance comparison.
3553 pf. [PARIDE]
3554 See Documentation/admin-guide/blockdev/paride.rst.
3556 pg. [PARIDE]
3557 See Documentation/admin-guide/blockdev/paride.rst.
3559 pirq= [SMP,APIC] Manual mp-table setup
3560 See Documentation/x86/i386/IO-APIC.rst.
3562 plip= [PPT,NET] Parallel port network link
3563 Format: { parport<nr> | timid | 0 }
3564 See also Documentation/admin-guide/parport.rst.
3566 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3567 Override pmtimer IOPort with a hex value.
3568 e.g. pmtmr=0x508
3570 pnp.debug=1 [PNP]
3571 Enable PNP debug messages (depends on the
3572 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3573 via /sys/module/pnp/parameters/debug. We always show
3574 current resource usage; turning this on also shows
3575 possible settings and some assignment information.
3577 pnpacpi= [ACPI]
3578 { off }
3580 pnpbios= [ISAPNP]
3581 { on | off | curr | res | no-curr | no-res }
3583 pnp_reserve_irq=
3584 [ISAPNP] Exclude IRQs for the autoconfiguration
3586 pnp_reserve_dma=
3587 [ISAPNP] Exclude DMAs for the autoconfiguration
3589 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3590 Ranges are in pairs (I/O port base and size).
3592 pnp_reserve_mem=
3593 [ISAPNP] Exclude memory regions for the
3594 autoconfiguration.
3595 Ranges are in pairs (memory base and size).
3597 ports= [IP_VS_FTP] IPVS ftp helper module
3598 Default is 21.
3599 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3600 may be specified.
3601 Format: <port>,<port>....
3603 powersave=off [PPC] This option disables power saving features.
3604 It specifically disables cpuidle and sets the
3605 platform machine description specific power_save
3606 function to NULL. On Idle the CPU just reduces
3607 execution priority.
3609 ppc_strict_facility_enable
3610 [PPC] This option catches any kernel floating point,
3611 Altivec, VSX and SPE outside of regions specifically
3612 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3613 There is some performance impact when enabling this.
3615 ppc_tm= [PPC]
3616 Format: {"off"}
3617 Disable Hardware Transactional Memory
3619 print-fatal-signals=
3620 [KNL] debug: print fatal signals
3622 If enabled, warn about various signal handling
3623 related application anomalies: too many signals,
3624 too many POSIX.1 timers, fatal signals causing a
3625 coredump - etc.
3627 If you hit the warning due to signal overflow,
3628 you might want to try "ulimit -i unlimited".
3630 default: off.
3632 printk.always_kmsg_dump=
3633 Trigger kmsg_dump for cases other than kernel oops or
3634 panics
3635 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3636 default: disabled
3638 printk.devkmsg={on,off,ratelimit}
3639 Control writing to /dev/kmsg.
3640 on - unlimited logging to /dev/kmsg from userspace
3641 off - logging to /dev/kmsg disabled
3642 ratelimit - ratelimit the logging
3643 Default: ratelimit
3645 printk.time= Show timing data prefixed to each printk message line
3646 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3648 processor.max_cstate= [HW,ACPI]
3649 Limit processor to maximum C-state
3650 max_cstate=9 overrides any DMI blacklist limit.
3652 processor.nocst [HW,ACPI]
3653 Ignore the _CST method to determine C-states,
3654 instead using the legacy FADT method
3656 profile= [KNL] Enable kernel profiling via /proc/profile
3657 Format: [<profiletype>,]<number>
3658 Param: <profiletype>: "schedule", "sleep", or "kvm"
3659 [defaults to kernel profiling]
3660 Param: "schedule" - profile schedule points.
3661 Param: "sleep" - profile D-state sleeping (millisecs).
3662 Requires CONFIG_SCHEDSTATS
3663 Param: "kvm" - profile VM exits.
3664 Param: <number> - step/bucket size as a power of 2 for
3665 statistical time based profiling.
3667 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3668 before loading.
3669 See Documentation/admin-guide/blockdev/ramdisk.rst.
3671 psi= [KNL] Enable or disable pressure stall information
3672 tracking.
3673 Format: <bool>
3675 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3676 probe for; one of (bare|imps|exps|lifebook|any).
3677 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3678 per second.
3679 psmouse.resetafter= [HW,MOUSE]
3680 Try to reset the device after so many bad packets
3681 (0 = never).
3682 psmouse.resolution=
3683 [HW,MOUSE] Set desired mouse resolution, in dpi.
3684 psmouse.smartscroll=
3685 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3686 0 = disabled, 1 = enabled (default).
3688 pstore.backend= Specify the name of the pstore backend to use
3690 pt. [PARIDE]
3691 See Documentation/admin-guide/blockdev/paride.rst.
3693 pti= [X86_64] Control Page Table Isolation of user and
3694 kernel address spaces. Disabling this feature
3695 removes hardening, but improves performance of
3696 system calls and interrupts.
3698 on - unconditionally enable
3699 off - unconditionally disable
3700 auto - kernel detects whether your CPU model is
3701 vulnerable to issues that PTI mitigates
3703 Not specifying this option is equivalent to pti=auto.
3705 nopti [X86_64]
3706 Equivalent to pti=off
3708 pty.legacy_count=
3709 [KNL] Number of legacy pty's. Overwrites compiled-in
3710 default number.
3712 quiet [KNL] Disable most log messages
3714 r128= [HW,DRM]
3716 raid= [HW,RAID]
3717 See Documentation/admin-guide/md.rst.
3719 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3720 See Documentation/admin-guide/blockdev/ramdisk.rst.
3722 random.trust_cpu={on,off}
3723 [KNL] Enable or disable trusting the use of the
3724 CPU's random number generator (if available) to
3725 fully seed the kernel's CRNG. Default is controlled
3726 by CONFIG_RANDOM_TRUST_CPU.
3728 ras=option[,option,...] [KNL] RAS-specific options
3730 cec_disable [X86]
3731 Disable the Correctable Errors Collector,
3732 see CONFIG_RAS_CEC help text.
3734 rcu_nocbs= [KNL]
3735 The argument is a cpu list, as described above,
3736 except that the string "all" can be used to
3737 specify every CPU on the system.
3739 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3740 the specified list of CPUs to be no-callback CPUs.
3741 Invocation of these CPUs' RCU callbacks will be
3742 offloaded to "rcuox/N" kthreads created for that
3743 purpose, where "x" is "p" for RCU-preempt, and
3744 "s" for RCU-sched, and "N" is the CPU number.
3745 This reduces OS jitter on the offloaded CPUs,
3746 which can be useful for HPC and real-time
3747 workloads. It can also improve energy efficiency
3748 for asymmetric multiprocessors.
3750 rcu_nocb_poll [KNL]
3751 Rather than requiring that offloaded CPUs
3752 (specified by rcu_nocbs= above) explicitly
3753 awaken the corresponding "rcuoN" kthreads,
3754 make these kthreads poll for callbacks.
3755 This improves the real-time response for the
3756 offloaded CPUs by relieving them of the need to
3757 wake up the corresponding kthread, but degrades
3758 energy efficiency by requiring that the kthreads
3759 periodically wake up to do the polling.
3761 rcutree.blimit= [KNL]
3762 Set maximum number of finished RCU callbacks to
3763 process in one batch.
3765 rcutree.dump_tree= [KNL]
3766 Dump the structure of the rcu_node combining tree
3767 out at early boot. This is used for diagnostic
3768 purposes, to verify correct tree setup.
3770 rcutree.gp_cleanup_delay= [KNL]
3771 Set the number of jiffies to delay each step of
3772 RCU grace-period cleanup.
3774 rcutree.gp_init_delay= [KNL]
3775 Set the number of jiffies to delay each step of
3776 RCU grace-period initialization.
3778 rcutree.gp_preinit_delay= [KNL]
3779 Set the number of jiffies to delay each step of
3780 RCU grace-period pre-initialization, that is,
3781 the propagation of recent CPU-hotplug changes up
3782 the rcu_node combining tree.
3784 rcutree.use_softirq= [KNL]
3785 If set to zero, move all RCU_SOFTIRQ processing to
3786 per-CPU rcuc kthreads. Defaults to a non-zero
3787 value, meaning that RCU_SOFTIRQ is used by default.
3788 Specify rcutree.use_softirq=0 to use rcuc kthreads.
3790 rcutree.rcu_fanout_exact= [KNL]
3791 Disable autobalancing of the rcu_node combining
3792 tree. This is used by rcutorture, and might
3793 possibly be useful for architectures having high
3794 cache-to-cache transfer latencies.
3796 rcutree.rcu_fanout_leaf= [KNL]
3797 Change the number of CPUs assigned to each
3798 leaf rcu_node structure. Useful for very
3799 large systems, which will choose the value 64,
3800 and for NUMA systems with large remote-access
3801 latencies, which will choose a value aligned
3802 with the appropriate hardware boundaries.
3804 rcutree.jiffies_till_first_fqs= [KNL]
3805 Set delay from grace-period initialization to
3806 first attempt to force quiescent states.
3807 Units are jiffies, minimum value is zero,
3808 and maximum value is HZ.
3810 rcutree.jiffies_till_next_fqs= [KNL]
3811 Set delay between subsequent attempts to force
3812 quiescent states. Units are jiffies, minimum
3813 value is one, and maximum value is HZ.
3815 rcutree.jiffies_till_sched_qs= [KNL]
3816 Set required age in jiffies for a
3817 given grace period before RCU starts
3818 soliciting quiescent-state help from
3819 rcu_note_context_switch() and cond_resched().
3820 If not specified, the kernel will calculate
3821 a value based on the most recent settings
3822 of rcutree.jiffies_till_first_fqs
3823 and rcutree.jiffies_till_next_fqs.
3824 This calculated value may be viewed in
3825 rcutree.jiffies_to_sched_qs. Any attempt to set
3826 rcutree.jiffies_to_sched_qs will be cheerfully
3827 overwritten.
3829 rcutree.kthread_prio= [KNL,BOOT]
3830 Set the SCHED_FIFO priority of the RCU per-CPU
3831 kthreads (rcuc/N). This value is also used for
3832 the priority of the RCU boost threads (rcub/N)
3833 and for the RCU grace-period kthreads (rcu_bh,
3834 rcu_preempt, and rcu_sched). If RCU_BOOST is
3835 set, valid values are 1-99 and the default is 1
3836 (the least-favored priority). Otherwise, when
3837 RCU_BOOST is not set, valid values are 0-99 and
3838 the default is zero (non-realtime operation).
3840 rcutree.rcu_nocb_leader_stride= [KNL]
3841 Set the number of NOCB kthread groups, which
3842 defaults to the square root of the number of
3843 CPUs. Larger numbers reduces the wakeup overhead
3844 on the per-CPU grace-period kthreads, but increases
3845 that same overhead on each group's leader.
3847 rcutree.qhimark= [KNL]
3848 Set threshold of queued RCU callbacks beyond which
3849 batch limiting is disabled.
3851 rcutree.qlowmark= [KNL]
3852 Set threshold of queued RCU callbacks below which
3853 batch limiting is re-enabled.
3855 rcutree.rcu_idle_gp_delay= [KNL]
3856 Set wakeup interval for idle CPUs that have
3857 RCU callbacks (RCU_FAST_NO_HZ=y).
3859 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3860 Set wakeup interval for idle CPUs that have
3861 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3862 Lazy RCU callbacks are those which RCU can
3863 prove do nothing more than free memory.
3865 rcutree.rcu_kick_kthreads= [KNL]
3866 Cause the grace-period kthread to get an extra
3867 wake_up() if it sleeps three times longer than
3868 it should at force-quiescent-state time.
3869 This wake_up() will be accompanied by a
3870 WARN_ONCE() splat and an ftrace_dump().
3872 rcutree.sysrq_rcu= [KNL]
3873 Commandeer a sysrq key to dump out Tree RCU's
3874 rcu_node tree with an eye towards determining
3875 why a new grace period has not yet started.
3877 rcuperf.gp_async= [KNL]
3878 Measure performance of asynchronous
3879 grace-period primitives such as call_rcu().
3881 rcuperf.gp_async_max= [KNL]
3882 Specify the maximum number of outstanding
3883 callbacks per writer thread. When a writer
3884 thread exceeds this limit, it invokes the
3885 corresponding flavor of rcu_barrier() to allow
3886 previously posted callbacks to drain.
3888 rcuperf.gp_exp= [KNL]
3889 Measure performance of expedited synchronous
3890 grace-period primitives.
3892 rcuperf.holdoff= [KNL]
3893 Set test-start holdoff period. The purpose of
3894 this parameter is to delay the start of the
3895 test until boot completes in order to avoid
3896 interference.
3898 rcuperf.nreaders= [KNL]
3899 Set number of RCU readers. The value -1 selects
3900 N, where N is the number of CPUs. A value
3901 "n" less than -1 selects N-n+1, where N is again
3902 the number of CPUs. For example, -2 selects N
3903 (the number of CPUs), -3 selects N+1, and so on.
3904 A value of "n" less than or equal to -N selects
3905 a single reader.
3907 rcuperf.nwriters= [KNL]
3908 Set number of RCU writers. The values operate
3909 the same as for rcuperf.nreaders.
3910 N, where N is the number of CPUs
3912 rcuperf.perf_type= [KNL]
3913 Specify the RCU implementation to test.
3915 rcuperf.shutdown= [KNL]
3916 Shut the system down after performance tests
3917 complete. This is useful for hands-off automated
3918 testing.
3920 rcuperf.verbose= [KNL]
3921 Enable additional printk() statements.
3923 rcuperf.writer_holdoff= [KNL]
3924 Write-side holdoff between grace periods,
3925 in microseconds. The default of zero says
3926 no holdoff.
3928 rcutorture.fqs_duration= [KNL]
3929 Set duration of force_quiescent_state bursts
3930 in microseconds.
3932 rcutorture.fqs_holdoff= [KNL]
3933 Set holdoff time within force_quiescent_state bursts
3934 in microseconds.
3936 rcutorture.fqs_stutter= [KNL]
3937 Set wait time between force_quiescent_state bursts
3938 in seconds.
3940 rcutorture.fwd_progress= [KNL]
3941 Enable RCU grace-period forward-progress testing
3942 for the types of RCU supporting this notion.
3944 rcutorture.fwd_progress_div= [KNL]
3945 Specify the fraction of a CPU-stall-warning
3946 period to do tight-loop forward-progress testing.
3948 rcutorture.fwd_progress_holdoff= [KNL]
3949 Number of seconds to wait between successive
3950 forward-progress tests.
3952 rcutorture.fwd_progress_need_resched= [KNL]
3953 Enclose cond_resched() calls within checks for
3954 need_resched() during tight-loop forward-progress
3955 testing.
3957 rcutorture.gp_cond= [KNL]
3958 Use conditional/asynchronous update-side
3959 primitives, if available.
3961 rcutorture.gp_exp= [KNL]
3962 Use expedited update-side primitives, if available.
3964 rcutorture.gp_normal= [KNL]
3965 Use normal (non-expedited) asynchronous
3966 update-side primitives, if available.
3968 rcutorture.gp_sync= [KNL]
3969 Use normal (non-expedited) synchronous
3970 update-side primitives, if available. If all
3971 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3972 rcutorture.gp_normal=, and rcutorture.gp_sync=
3973 are zero, rcutorture acts as if is interpreted
3974 they are all non-zero.
3976 rcutorture.n_barrier_cbs= [KNL]
3977 Set callbacks/threads for rcu_barrier() testing.
3979 rcutorture.nfakewriters= [KNL]
3980 Set number of concurrent RCU writers. These just
3981 stress RCU, they don't participate in the actual
3982 test, hence the "fake".
3984 rcutorture.nreaders= [KNL]
3985 Set number of RCU readers. The value -1 selects
3986 N-1, where N is the number of CPUs. A value
3987 "n" less than -1 selects N-n-2, where N is again
3988 the number of CPUs. For example, -2 selects N
3989 (the number of CPUs), -3 selects N+1, and so on.
3991 rcutorture.object_debug= [KNL]
3992 Enable debug-object double-call_rcu() testing.
3994 rcutorture.onoff_holdoff= [KNL]
3995 Set time (s) after boot for CPU-hotplug testing.
3997 rcutorture.onoff_interval= [KNL]
3998 Set time (jiffies) between CPU-hotplug operations,
3999 or zero to disable CPU-hotplug testing.
4001 rcutorture.shuffle_interval= [KNL]
4002 Set task-shuffle interval (s). Shuffling tasks
4003 allows some CPUs to go into dyntick-idle mode
4004 during the rcutorture test.
4006 rcutorture.shutdown_secs= [KNL]
4007 Set time (s) after boot system shutdown. This
4008 is useful for hands-off automated testing.
4010 rcutorture.stall_cpu= [KNL]
4011 Duration of CPU stall (s) to test RCU CPU stall
4012 warnings, zero to disable.
4014 rcutorture.stall_cpu_holdoff= [KNL]
4015 Time to wait (s) after boot before inducing stall.
4017 rcutorture.stall_cpu_irqsoff= [KNL]
4018 Disable interrupts while stalling if set.
4020 rcutorture.stat_interval= [KNL]
4021 Time (s) between statistics printk()s.
4023 rcutorture.stutter= [KNL]
4024 Time (s) to stutter testing, for example, specifying
4025 five seconds causes the test to run for five seconds,
4026 wait for five seconds, and so on. This tests RCU's
4027 ability to transition abruptly to and from idle.
4029 rcutorture.test_boost= [KNL]
4030 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
4031 "Maybe" means test if the RCU implementation
4032 under test support RCU priority boosting.
4034 rcutorture.test_boost_duration= [KNL]
4035 Duration (s) of each individual boost test.
4037 rcutorture.test_boost_interval= [KNL]
4038 Interval (s) between each boost test.
4040 rcutorture.test_no_idle_hz= [KNL]
4041 Test RCU's dyntick-idle handling. See also the
4042 rcutorture.shuffle_interval parameter.
4044 rcutorture.torture_type= [KNL]
4045 Specify the RCU implementation to test.
4047 rcutorture.verbose= [KNL]
4048 Enable additional printk() statements.
4050 rcupdate.rcu_cpu_stall_suppress= [KNL]
4051 Suppress RCU CPU stall warning messages.
4053 rcupdate.rcu_cpu_stall_timeout= [KNL]
4054 Set timeout for RCU CPU stall warning messages.
4056 rcupdate.rcu_expedited= [KNL]
4057 Use expedited grace-period primitives, for
4058 example, synchronize_rcu_expedited() instead
4059 of synchronize_rcu(). This reduces latency,
4060 but can increase CPU utilization, degrade
4061 real-time latency, and degrade energy efficiency.
4062 No effect on CONFIG_TINY_RCU kernels.
4064 rcupdate.rcu_normal= [KNL]
4065 Use only normal grace-period primitives,
4066 for example, synchronize_rcu() instead of
4067 synchronize_rcu_expedited(). This improves
4068 real-time latency, CPU utilization, and
4069 energy efficiency, but can expose users to
4070 increased grace-period latency. This parameter
4071 overrides rcupdate.rcu_expedited. No effect on
4072 CONFIG_TINY_RCU kernels.
4074 rcupdate.rcu_normal_after_boot= [KNL]
4075 Once boot has completed (that is, after
4076 rcu_end_inkernel_boot() has been invoked), use
4077 only normal grace-period primitives. No effect
4078 on CONFIG_TINY_RCU kernels.
4080 rcupdate.rcu_task_stall_timeout= [KNL]
4081 Set timeout in jiffies for RCU task stall warning
4082 messages. Disable with a value less than or equal
4083 to zero.
4085 rcupdate.rcu_self_test= [KNL]
4086 Run the RCU early boot self tests
4088 rdinit= [KNL]
4089 Format: <full_path>
4090 Run specified binary instead of /init from the ramdisk,
4091 used for early userspace startup. See initrd.
4093 rdt= [HW,X86,RDT]
4094 Turn on/off individual RDT features. List is:
4095 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
4096 mba.
4097 E.g. to turn on cmt and turn off mba use:
4098 rdt=cmt,!mba
4100 reboot= [KNL]
4101 Format (x86 or x86_64):
4102 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
4103 [[,]s[mp]#### \
4104 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
4105 [[,]f[orce]
4106 Where reboot_mode is one of warm (soft) or cold (hard) or gpio
4107 (prefix with 'panic_' to set mode for panic
4108 reboot only),
4109 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
4110 reboot_force is either force or not specified,
4111 reboot_cpu is s[mp]#### with #### being the processor
4112 to be used for rebooting.
4114 relax_domain_level=
4115 [KNL, SMP] Set scheduler's default relax_domain_level.
4116 See Documentation/admin-guide/cgroup-v1/cpusets.rst.
4118 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
4119 Format: <base1>,<size1>[,<base2>,<size2>,...]
4120 Reserve I/O ports or memory so the kernel won't use
4121 them. If <base> is less than 0x10000, the region
4122 is assumed to be I/O ports; otherwise it is memory.
4124 reservetop= [X86-32]
4125 Format: nn[KMG]
4126 Reserves a hole at the top of the kernel virtual
4127 address space.
4129 reservelow= [X86]
4130 Format: nn[K]
4131 Set the amount of memory to reserve for BIOS at
4132 the bottom of the address space.
4134 reset_devices [KNL] Force drivers to reset the underlying device
4135 during initialization.
4137 resume= [SWSUSP]
4138 Specify the partition device for software suspend
4139 Format:
4140 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
4142 resume_offset= [SWSUSP]
4143 Specify the offset from the beginning of the partition
4144 given by "resume=" at which the swap header is located,
4145 in <PAGE_SIZE> units (needed only for swap files).
4146 See Documentation/power/swsusp-and-swap-files.rst
4148 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
4149 read the resume files
4151 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
4152 Useful for devices that are detected asynchronously
4153 (e.g. USB and MMC devices).
4155 hibernate= [HIBERNATION]
4156 noresume Don't check if there's a hibernation image
4157 present during boot.
4158 nocompress Don't compress/decompress hibernation images.
4159 no Disable hibernation and resume.
4160 protect_image Turn on image protection during restoration
4161 (that will set all pages holding image data
4162 during restoration read-only).
4164 retain_initrd [RAM] Keep initrd memory after extraction
4166 rfkill.default_state=
4167 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
4168 etc. communication is blocked by default.
4169 1 Unblocked.
4171 rfkill.master_switch_mode=
4172 0 The "airplane mode" button does nothing.
4173 1 The "airplane mode" button toggles between everything
4174 blocked and the previous configuration.
4175 2 The "airplane mode" button toggles between everything
4176 blocked and everything unblocked.
4178 rhash_entries= [KNL,NET]
4179 Set number of hash buckets for route cache
4181 ring3mwait=disable
4182 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
4183 CPUs.
4185 ro [KNL] Mount root device read-only on boot
4187 rodata= [KNL]
4188 on Mark read-only kernel memory as read-only (default).
4189 off Leave read-only kernel memory writable for debugging.
4191 rockchip.usb_uart
4192 Enable the uart passthrough on the designated usb port
4193 on Rockchip SoCs. When active, the signals of the
4194 debug-uart get routed to the D+ and D- pins of the usb
4195 port and the regular usb controller gets disabled.
4197 root= [KNL] Root filesystem
4198 See name_to_dev_t comment in init/do_mounts.c.
4200 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
4201 mount the root filesystem
4203 rootflags= [KNL] Set root filesystem mount option string
4205 rootfstype= [KNL] Set root filesystem type
4207 rootwait [KNL] Wait (indefinitely) for root device to show up.
4208 Useful for devices that are detected asynchronously
4209 (e.g. USB and MMC devices).
4211 rproc_mem=nn[KMG][@address]
4212 [KNL,ARM,CMA] Remoteproc physical memory block.
4213 Memory area to be used by remote processor image,
4214 managed by CMA.
4216 rw [KNL] Mount root device read-write on boot
4218 S [KNL] Run init in single mode
4220 s390_iommu= [HW,S390]
4221 Set s390 IOTLB flushing mode
4222 strict
4223 With strict flushing every unmap operation will result in
4224 an IOTLB flush. Default is lazy flushing before reuse,
4225 which is faster.
4227 sa1100ir [NET]
4228 See drivers/net/irda/sa1100_ir.c.
4230 sbni= [NET] Granch SBNI12 leased line adapter
4232 sched_debug [KNL] Enables verbose scheduler debug messages.
4234 schedstats= [KNL,X86] Enable or disable scheduled statistics.
4235 Allowed values are enable and disable. This feature
4236 incurs a small amount of overhead in the scheduler
4237 but is useful for debugging and performance tuning.
4239 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
4240 xtime_lock contention on larger systems, and/or RCU lock
4241 contention on all systems with CONFIG_MAXSMP set.
4242 Format: { "0" | "1" }
4243 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
4244 1 -- enable.
4245 Note: increases power consumption, thus should only be
4246 enabled if running jitter sensitive (HPC/RT) workloads.
4248 security= [SECURITY] Choose a legacy "major" security module to
4249 enable at boot. This has been deprecated by the
4250 "lsm=" parameter.
4252 selinux= [SELINUX] Disable or enable SELinux at boot time.
4253 Format: { "0" | "1" }
4254 See security/selinux/Kconfig help text.
4255 0 -- disable.
4256 1 -- enable.
4257 Default value is set via kernel config option.
4258 If enabled at boot time, /selinux/disable can be used
4259 later to disable prior to initial policy load.
4261 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
4262 Format: { "0" | "1" }
4263 See security/apparmor/Kconfig help text
4264 0 -- disable.
4265 1 -- enable.
4266 Default value is set via kernel config option.
4268 serialnumber [BUGS=X86-32]
4270 shapers= [NET]
4271 Maximal number of shapers.
4273 simeth= [IA-64]
4274 simscsi=
4276 slram= [HW,MTD]
4278 slab_nomerge [MM]
4279 Disable merging of slabs with similar size. May be
4280 necessary if there is some reason to distinguish
4281 allocs to different slabs, especially in hardened
4282 environments where the risk of heap overflows and
4283 layout control by attackers can usually be
4284 frustrated by disabling merging. This will reduce
4285 most of the exposure of a heap attack to a single
4286 cache (risks via metadata attacks are mostly
4287 unchanged). Debug options disable merging on their
4288 own.
4289 For more information see Documentation/vm/slub.rst.
4291 slab_max_order= [MM, SLAB]
4292 Determines the maximum allowed order for slabs.
4293 A high setting may cause OOMs due to memory
4294 fragmentation. Defaults to 1 for systems with
4295 more than 32MB of RAM, 0 otherwise.
4297 slub_debug[=options[,slabs]] [MM, SLUB]
4298 Enabling slub_debug allows one to determine the
4299 culprit if slab objects become corrupted. Enabling
4300 slub_debug can create guard zones around objects and
4301 may poison objects when not in use. Also tracks the
4302 last alloc / free. For more information see
4303 Documentation/vm/slub.rst.
4305 slub_memcg_sysfs= [MM, SLUB]
4306 Determines whether to enable sysfs directories for
4307 memory cgroup sub-caches. 1 to enable, 0 to disable.
4308 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
4309 Enabling this can lead to a very high number of debug
4310 directories and files being created under
4311 /sys/kernel/slub.
4313 slub_max_order= [MM, SLUB]
4314 Determines the maximum allowed order for slabs.
4315 A high setting may cause OOMs due to memory
4316 fragmentation. For more information see
4317 Documentation/vm/slub.rst.
4319 slub_min_objects= [MM, SLUB]
4320 The minimum number of objects per slab. SLUB will
4321 increase the slab order up to slub_max_order to
4322 generate a sufficiently large slab able to contain
4323 the number of objects indicated. The higher the number
4324 of objects the smaller the overhead of tracking slabs
4325 and the less frequently locks need to be acquired.
4326 For more information see Documentation/vm/slub.rst.
4328 slub_min_order= [MM, SLUB]
4329 Determines the minimum page order for slabs. Must be
4330 lower than slub_max_order.
4331 For more information see Documentation/vm/slub.rst.
4333 slub_nomerge [MM, SLUB]
4334 Same with slab_nomerge. This is supported for legacy.
4335 See slab_nomerge for more information.
4337 smart2= [HW]
4338 Format: <io1>[,<io2>[,...,<io8>]]
4340 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4341 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4342 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4343 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4344 smsc-ircc2.ircc_irq= [HW] IRQ line
4345 smsc-ircc2.ircc_dma= [HW] DMA channel
4346 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4347 0: Toshiba Satellite 1800 (GP data pin select)
4348 1: Fast pin select (default)
4349 2: ATC IRMode
4351 smt [KNL,S390] Set the maximum number of threads (logical
4352 CPUs) to use per physical CPU on systems capable of
4353 symmetric multithreading (SMT). Will be capped to the
4354 actual hardware limit.
4355 Format: <integer>
4356 Default: -1 (no limit)
4358 softlockup_panic=
4359 [KNL] Should the soft-lockup detector generate panics.
4360 Format: <integer>
4362 A nonzero value instructs the soft-lockup detector
4363 to panic the machine when a soft-lockup occurs. This
4364 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
4365 which is the respective build-time switch to that
4366 functionality.
4368 softlockup_all_cpu_backtrace=
4369 [KNL] Should the soft-lockup detector generate
4370 backtraces on all cpus.
4371 Format: <integer>
4373 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4374 See Documentation/admin-guide/laptops/sonypi.rst
4376 spectre_v2= [X86] Control mitigation of Spectre variant 2
4377 (indirect branch speculation) vulnerability.
4378 The default operation protects the kernel from
4379 user space attacks.
4381 on - unconditionally enable, implies
4382 spectre_v2_user=on
4383 off - unconditionally disable, implies
4384 spectre_v2_user=off
4385 auto - kernel detects whether your CPU model is
4386 vulnerable
4388 Selecting 'on' will, and 'auto' may, choose a
4389 mitigation method at run time according to the
4390 CPU, the available microcode, the setting of the
4391 CONFIG_RETPOLINE configuration option, and the
4392 compiler with which the kernel was built.
4394 Selecting 'on' will also enable the mitigation
4395 against user space to user space task attacks.
4397 Selecting 'off' will disable both the kernel and
4398 the user space protections.
4400 Specific mitigations can also be selected manually:
4402 retpoline - replace indirect branches
4403 retpoline,generic - google's original retpoline
4404 retpoline,amd - AMD-specific minimal thunk
4406 Not specifying this option is equivalent to
4407 spectre_v2=auto.
4409 spectre_v2_user=
4410 [X86] Control mitigation of Spectre variant 2
4411 (indirect branch speculation) vulnerability between
4412 user space tasks
4414 on - Unconditionally enable mitigations. Is
4415 enforced by spectre_v2=on
4417 off - Unconditionally disable mitigations. Is
4418 enforced by spectre_v2=off
4420 prctl - Indirect branch speculation is enabled,
4421 but mitigation can be enabled via prctl
4422 per thread. The mitigation control state
4423 is inherited on fork.
4425 prctl,ibpb
4426 - Like "prctl" above, but only STIBP is
4427 controlled per thread. IBPB is issued
4428 always when switching between different user
4429 space processes.
4431 seccomp
4432 - Same as "prctl" above, but all seccomp
4433 threads will enable the mitigation unless
4434 they explicitly opt out.
4436 seccomp,ibpb
4437 - Like "seccomp" above, but only STIBP is
4438 controlled per thread. IBPB is issued
4439 always when switching between different
4440 user space processes.
4442 auto - Kernel selects the mitigation depending on
4443 the available CPU features and vulnerability.
4445 Default mitigation:
4446 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
4448 Not specifying this option is equivalent to
4449 spectre_v2_user=auto.
4451 spec_store_bypass_disable=
4452 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4453 (Speculative Store Bypass vulnerability)
4455 Certain CPUs are vulnerable to an exploit against a
4456 a common industry wide performance optimization known
4457 as "Speculative Store Bypass" in which recent stores
4458 to the same memory location may not be observed by
4459 later loads during speculative execution. The idea
4460 is that such stores are unlikely and that they can
4461 be detected prior to instruction retirement at the
4462 end of a particular speculation execution window.
4464 In vulnerable processors, the speculatively forwarded
4465 store can be used in a cache side channel attack, for
4466 example to read memory to which the attacker does not
4467 directly have access (e.g. inside sandboxed code).
4469 This parameter controls whether the Speculative Store
4470 Bypass optimization is used.
4472 On x86 the options are:
4474 on - Unconditionally disable Speculative Store Bypass
4475 off - Unconditionally enable Speculative Store Bypass
4476 auto - Kernel detects whether the CPU model contains an
4477 implementation of Speculative Store Bypass and
4478 picks the most appropriate mitigation. If the
4479 CPU is not vulnerable, "off" is selected. If the
4480 CPU is vulnerable the default mitigation is
4481 architecture and Kconfig dependent. See below.
4482 prctl - Control Speculative Store Bypass per thread
4483 via prctl. Speculative Store Bypass is enabled
4484 for a process by default. The state of the control
4485 is inherited on fork.
4486 seccomp - Same as "prctl" above, but all seccomp threads
4487 will disable SSB unless they explicitly opt out.
4489 Default mitigations:
4490 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4492 On powerpc the options are:
4494 on,auto - On Power8 and Power9 insert a store-forwarding
4495 barrier on kernel entry and exit. On Power7
4496 perform a software flush on kernel entry and
4497 exit.
4498 off - No action.
4500 Not specifying this option is equivalent to
4501 spec_store_bypass_disable=auto.
4503 spia_io_base= [HW,MTD]
4504 spia_fio_base=
4505 spia_pedr=
4506 spia_peddr=
4508 srcutree.counter_wrap_check [KNL]
4509 Specifies how frequently to check for
4510 grace-period sequence counter wrap for the
4511 srcu_data structure's ->srcu_gp_seq_needed field.
4512 The greater the number of bits set in this kernel
4513 parameter, the less frequently counter wrap will
4514 be checked for. Note that the bottom two bits
4515 are ignored.
4517 srcutree.exp_holdoff [KNL]
4518 Specifies how many nanoseconds must elapse
4519 since the end of the last SRCU grace period for
4520 a given srcu_struct until the next normal SRCU
4521 grace period will be considered for automatic
4522 expediting. Set to zero to disable automatic
4523 expediting.
4525 ssbd= [ARM64,HW]
4526 Speculative Store Bypass Disable control
4528 On CPUs that are vulnerable to the Speculative
4529 Store Bypass vulnerability and offer a
4530 firmware based mitigation, this parameter
4531 indicates how the mitigation should be used:
4533 force-on: Unconditionally enable mitigation for
4534 for both kernel and userspace
4535 force-off: Unconditionally disable mitigation for
4536 for both kernel and userspace
4537 kernel: Always enable mitigation in the
4538 kernel, and offer a prctl interface
4539 to allow userspace to register its
4540 interest in being mitigated too.
4542 stack_guard_gap= [MM]
4543 override the default stack gap protection. The value
4544 is in page units and it defines how many pages prior
4545 to (for stacks growing down) resp. after (for stacks
4546 growing up) the main stack are reserved for no other
4547 mapping. Default value is 256 pages.
4549 stacktrace [FTRACE]
4550 Enabled the stack tracer on boot up.
4552 stacktrace_filter=[function-list]
4553 [FTRACE] Limit the functions that the stack tracer
4554 will trace at boot up. function-list is a comma separated
4555 list of functions. This list can be changed at run
4556 time by the stack_trace_filter file in the debugfs
4557 tracing directory. Note, this enables stack tracing
4558 and the stacktrace above is not needed.
4560 sti= [PARISC,HW]
4561 Format: <num>
4562 Set the STI (builtin display/keyboard on the HP-PARISC
4563 machines) console (graphic card) which should be used
4564 as the initial boot-console.
4565 See also comment in drivers/video/console/sticore.c.
4567 sti_font= [HW]
4568 See comment in drivers/video/console/sticore.c.
4570 stifb= [HW]
4571 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4573 sunrpc.min_resvport=
4574 sunrpc.max_resvport=
4575 [NFS,SUNRPC]
4576 SunRPC servers often require that client requests
4577 originate from a privileged port (i.e. a port in the
4578 range 0 < portnr < 1024).
4579 An administrator who wishes to reserve some of these
4580 ports for other uses may adjust the range that the
4581 kernel's sunrpc client considers to be privileged
4582 using these two parameters to set the minimum and
4583 maximum port values.
4585 sunrpc.svc_rpc_per_connection_limit=
4586 [NFS,SUNRPC]
4587 Limit the number of requests that the server will
4588 process in parallel from a single connection.
4589 The default value is 0 (no limit).
4591 sunrpc.pool_mode=
4592 [NFS]
4593 Control how the NFS server code allocates CPUs to
4594 service thread pools. Depending on how many NICs
4595 you have and where their interrupts are bound, this
4596 option will affect which CPUs will do NFS serving.
4597 Note: this parameter cannot be changed while the
4598 NFS server is running.
4600 auto the server chooses an appropriate mode
4601 automatically using heuristics
4602 global a single global pool contains all CPUs
4603 percpu one pool for each CPU
4604 pernode one pool for each NUMA node (equivalent
4605 to global on non-NUMA machines)
4607 sunrpc.tcp_slot_table_entries=
4608 sunrpc.udp_slot_table_entries=
4609 [NFS,SUNRPC]
4610 Sets the upper limit on the number of simultaneous
4611 RPC calls that can be sent from the client to a
4612 server. Increasing these values may allow you to
4613 improve throughput, but will also increase the
4614 amount of memory reserved for use by the client.
4616 suspend.pm_test_delay=
4617 [SUSPEND]
4618 Sets the number of seconds to remain in a suspend test
4619 mode before resuming the system (see
4620 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4621 is set. Default value is 5.
4623 swapaccount=[0|1]
4624 [KNL] Enable accounting of swap in memory resource
4625 controller if no parameter or 1 is given or disable
4626 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst)
4628 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4629 Format: { <int> | force | noforce }
4630 <int> -- Number of I/O TLB slabs
4631 force -- force using of bounce buffers even if they
4632 wouldn't be automatically used by the kernel
4633 noforce -- Never use bounce buffers (for debugging)
4635 switches= [HW,M68k]
4637 sysfs.deprecated=0|1 [KNL]
4638 Enable/disable old style sysfs layout for old udev
4639 on older distributions. When this option is enabled
4640 very new udev will not work anymore. When this option
4641 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4642 in older udev will not work anymore.
4643 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4644 the kernel configuration.
4646 sysrq_always_enabled
4647 [KNL]
4648 Ignore sysrq setting - this boot parameter will
4649 neutralize any effect of /proc/sys/kernel/sysrq.
4650 Useful for debugging.
4652 tcpmhash_entries= [KNL,NET]
4653 Set the number of tcp_metrics_hash slots.
4654 Default value is 8192 or 16384 depending on total
4655 ram pages. This is used to specify the TCP metrics
4656 cache size. See Documentation/networking/ip-sysctl.txt
4657 "tcp_no_metrics_save" section for more details.
4659 tdfx= [HW,DRM]
4661 test_suspend= [SUSPEND][,N]
4662 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4663 standby suspend) or "freeze" (for suspend type freeze)
4664 as the system sleep state during system startup with
4665 the optional capability to repeat N number of times.
4666 The system is woken from this state using a
4667 wakeup-capable RTC alarm.
4669 thash_entries= [KNL,NET]
4670 Set number of hash buckets for TCP connection
4672 thermal.act= [HW,ACPI]
4673 -1: disable all active trip points in all thermal zones
4674 <degrees C>: override all lowest active trip points
4676 thermal.crt= [HW,ACPI]
4677 -1: disable all critical trip points in all thermal zones
4678 <degrees C>: override all critical trip points
4680 thermal.nocrt= [HW,ACPI]
4681 Set to disable actions on ACPI thermal zone
4682 critical and hot trip points.
4684 thermal.off= [HW,ACPI]
4685 1: disable ACPI thermal control
4687 thermal.psv= [HW,ACPI]
4688 -1: disable all passive trip points
4689 <degrees C>: override all passive trip points to this
4690 value
4692 thermal.tzp= [HW,ACPI]
4693 Specify global default ACPI thermal zone polling rate
4694 <deci-seconds>: poll all this frequency
4695 0: no polling (default)
4697 threadirqs [KNL]
4698 Force threading of all interrupt handlers except those
4699 marked explicitly IRQF_NO_THREAD.
4701 topology= [S390]
4702 Format: {off | on}
4703 Specify if the kernel should make use of the cpu
4704 topology information if the hardware supports this.
4705 The scheduler will make use of this information and
4706 e.g. base its process migration decisions on it.
4707 Default is on.
4709 topology_updates= [KNL, PPC, NUMA]
4710 Format: {off}
4711 Specify if the kernel should ignore (off)
4712 topology updates sent by the hypervisor to this
4713 LPAR.
4715 tp720= [HW,PS2]
4717 tpm_suspend_pcr=[HW,TPM]
4718 Format: integer pcr id
4719 Specify that at suspend time, the tpm driver
4720 should extend the specified pcr with zeros,
4721 as a workaround for some chips which fail to
4722 flush the last written pcr on TPM_SaveState.
4723 This will guarantee that all the other pcrs
4724 are saved.
4726 trace_buf_size=nn[KMG]
4727 [FTRACE] will set tracing buffer size on each cpu.
4729 trace_event=[event-list]
4730 [FTRACE] Set and start specified trace events in order
4731 to facilitate early boot debugging. The event-list is a
4732 comma separated list of trace events to enable. See
4733 also Documentation/trace/events.rst
4735 trace_options=[option-list]
4736 [FTRACE] Enable or disable tracer options at boot.
4737 The option-list is a comma delimited list of options
4738 that can be enabled or disabled just as if you were
4739 to echo the option name into
4741 /sys/kernel/debug/tracing/trace_options
4743 For example, to enable stacktrace option (to dump the
4744 stack trace of each event), add to the command line:
4746 trace_options=stacktrace
4748 See also Documentation/trace/ftrace.rst "trace options"
4749 section.
4751 tp_printk[FTRACE]
4752 Have the tracepoints sent to printk as well as the
4753 tracing ring buffer. This is useful for early boot up
4754 where the system hangs or reboots and does not give the
4755 option for reading the tracing buffer or performing a
4756 ftrace_dump_on_oops.
4758 To turn off having tracepoints sent to printk,
4759 echo 0 > /proc/sys/kernel/tracepoint_printk
4760 Note, echoing 1 into this file without the
4761 tracepoint_printk kernel cmdline option has no effect.
4763 ** CAUTION **
4765 Having tracepoints sent to printk() and activating high
4766 frequency tracepoints such as irq or sched, can cause
4767 the system to live lock.
4769 traceoff_on_warning
4770 [FTRACE] enable this option to disable tracing when a
4771 warning is hit. This turns off "tracing_on". Tracing can
4772 be enabled again by echoing '1' into the "tracing_on"
4773 file located in /sys/kernel/debug/tracing/
4775 This option is useful, as it disables the trace before
4776 the WARNING dump is called, which prevents the trace to
4777 be filled with content caused by the warning output.
4779 This option can also be set at run time via the sysctl
4780 option: kernel/traceoff_on_warning
4782 transparent_hugepage=
4783 [KNL]
4784 Format: [always|madvise|never]
4785 Can be used to control the default behavior of the system
4786 with respect to transparent hugepages.
4787 See Documentation/admin-guide/mm/transhuge.rst
4788 for more details.
4790 tsc= Disable clocksource stability checks for TSC.
4791 Format: <string>
4792 [x86] reliable: mark tsc clocksource as reliable, this
4793 disables clocksource verification at runtime, as well
4794 as the stability checks done at bootup. Used to enable
4795 high-resolution timer mode on older hardware, and in
4796 virtualized environment.
4797 [x86] noirqtime: Do not use TSC to do irq accounting.
4798 Used to run time disable IRQ_TIME_ACCOUNTING on any
4799 platforms where RDTSC is slow and this accounting
4800 can add overhead.
4801 [x86] unstable: mark the TSC clocksource as unstable, this
4802 marks the TSC unconditionally unstable at bootup and
4803 avoids any further wobbles once the TSC watchdog notices.
4804 [x86] nowatchdog: disable clocksource watchdog. Used
4805 in situations with strict latency requirements (where
4806 interruptions from clocksource watchdog are not
4807 acceptable).
4809 turbografx.map[2|3]= [HW,JOY]
4810 TurboGraFX parallel port interface
4811 Format:
4812 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4813 See also Documentation/input/devices/joystick-parport.rst
4815 udbg-immortal [PPC] When debugging early kernel crashes that
4816 happen after console_init() and before a proper
4817 console driver takes over, this boot options might
4818 help "seeing" what's going on.
4820 uhash_entries= [KNL,NET]
4821 Set number of hash buckets for UDP/UDP-Lite connections
4823 uhci-hcd.ignore_oc=
4824 [USB] Ignore overcurrent events (default N).
4825 Some badly-designed motherboards generate lots of
4826 bogus events, for ports that aren't wired to
4827 anything. Set this parameter to avoid log spamming.
4828 Note that genuine overcurrent events won't be
4829 reported either.
4831 unknown_nmi_panic
4832 [X86] Cause panic on unknown NMI.
4834 usbcore.authorized_default=
4835 [USB] Default USB device authorization:
4836 (default -1 = authorized except for wireless USB,
4837 0 = not authorized, 1 = authorized, 2 = authorized
4838 if device connected to internal port)
4840 usbcore.autosuspend=
4841 [USB] The autosuspend time delay (in seconds) used
4842 for newly-detected USB devices (default 2). This
4843 is the time required before an idle device will be
4844 autosuspended. Devices for which the delay is set
4845 to a negative value won't be autosuspended at all.
4847 usbcore.usbfs_snoop=
4848 [USB] Set to log all usbfs traffic (default 0 = off).
4850 usbcore.usbfs_snoop_max=
4851 [USB] Maximum number of bytes to snoop in each URB
4852 (default = 65536).
4854 usbcore.blinkenlights=
4855 [USB] Set to cycle leds on hubs (default 0 = off).
4857 usbcore.old_scheme_first=
4858 [USB] Start with the old device initialization
4859 scheme, applies only to low and full-speed devices
4860 (default 0 = off).
4862 usbcore.usbfs_memory_mb=
4863 [USB] Memory limit (in MB) for buffers allocated by
4864 usbfs (default = 16, 0 = max = 2047).
4866 usbcore.use_both_schemes=
4867 [USB] Try the other device initialization scheme
4868 if the first one fails (default 1 = enabled).
4870 usbcore.initial_descriptor_timeout=
4871 [USB] Specifies timeout for the initial 64-byte
4872 USB_REQ_GET_DESCRIPTOR request in milliseconds
4873 (default 5000 = 5.0 seconds).
4875 usbcore.nousb [USB] Disable the USB subsystem
4877 usbcore.quirks=
4878 [USB] A list of quirk entries to augment the built-in
4879 usb core quirk list. List entries are separated by
4880 commas. Each entry has the form
4881 VendorID:ProductID:Flags. The IDs are 4-digit hex
4882 numbers and Flags is a set of letters. Each letter
4883 will change the built-in quirk; setting it if it is
4884 clear and clearing it if it is set. The letters have
4885 the following meanings:
4886 a = USB_QUIRK_STRING_FETCH_255 (string
4887 descriptors must not be fetched using
4888 a 255-byte read);
4889 b = USB_QUIRK_RESET_RESUME (device can't resume
4890 correctly so reset it instead);
4891 c = USB_QUIRK_NO_SET_INTF (device can't handle
4892 Set-Interface requests);
4893 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
4894 handle its Configuration or Interface
4895 strings);
4896 e = USB_QUIRK_RESET (device can't be reset
4897 (e.g morph devices), don't use reset);
4898 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
4899 more interface descriptions than the
4900 bNumInterfaces count, and can't handle
4901 talking to these interfaces);
4902 g = USB_QUIRK_DELAY_INIT (device needs a pause
4903 during initialization, after we read
4904 the device descriptor);
4905 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
4906 high speed and super speed interrupt
4907 endpoints, the USB 2.0 and USB 3.0 spec
4908 require the interval in microframes (1
4909 microframe = 125 microseconds) to be
4910 calculated as interval = 2 ^
4911 (bInterval-1).
4912 Devices with this quirk report their
4913 bInterval as the result of this
4914 calculation instead of the exponent
4915 variable used in the calculation);
4916 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
4917 handle device_qualifier descriptor
4918 requests);
4919 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
4920 generates spurious wakeup, ignore
4921 remote wakeup capability);
4922 k = USB_QUIRK_NO_LPM (device can't handle Link
4923 Power Management);
4924 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
4925 (Device reports its bInterval as linear
4926 frames instead of the USB 2.0
4927 calculation);
4928 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
4929 to be disconnected before suspend to
4930 prevent spurious wakeup);
4931 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
4932 pause after every control message);
4933 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
4934 delay after resetting its port);
4935 Example: quirks=0781:5580:bk,0a5c:5834:gij
4937 usbhid.mousepoll=
4938 [USBHID] The interval which mice are to be polled at.
4940 usbhid.jspoll=
4941 [USBHID] The interval which joysticks are to be polled at.
4943 usbhid.kbpoll=
4944 [USBHID] The interval which keyboards are to be polled at.
4946 usb-storage.delay_use=
4947 [UMS] The delay in seconds before a new device is
4948 scanned for Logical Units (default 1).
4950 usb-storage.quirks=
4951 [UMS] A list of quirks entries to supplement or
4952 override the built-in unusual_devs list. List
4953 entries are separated by commas. Each entry has
4954 the form VID:PID:Flags where VID and PID are Vendor
4955 and Product ID values (4-digit hex numbers) and
4956 Flags is a set of characters, each corresponding
4957 to a common usb-storage quirk flag as follows:
4958 a = SANE_SENSE (collect more than 18 bytes
4959 of sense data);
4960 b = BAD_SENSE (don't collect more than 18
4961 bytes of sense data);
4962 c = FIX_CAPACITY (decrease the reported
4963 device capacity by one sector);
4964 d = NO_READ_DISC_INFO (don't use
4965 READ_DISC_INFO command);
4966 e = NO_READ_CAPACITY_16 (don't use
4967 READ_CAPACITY_16 command);
4968 f = NO_REPORT_OPCODES (don't use report opcodes
4969 command, uas only);
4970 g = MAX_SECTORS_240 (don't transfer more than
4971 240 sectors at a time, uas only);
4972 h = CAPACITY_HEURISTICS (decrease the
4973 reported device capacity by one
4974 sector if the number is odd);
4975 i = IGNORE_DEVICE (don't bind to this
4976 device);
4977 j = NO_REPORT_LUNS (don't use report luns
4978 command, uas only);
4979 l = NOT_LOCKABLE (don't try to lock and
4980 unlock ejectable media);
4981 m = MAX_SECTORS_64 (don't transfer more
4982 than 64 sectors = 32 KB at a time);
4983 n = INITIAL_READ10 (force a retry of the
4984 initial READ(10) command);
4985 o = CAPACITY_OK (accept the capacity
4986 reported by the device);
4987 p = WRITE_CACHE (the device cache is ON
4988 by default);
4989 r = IGNORE_RESIDUE (the device reports
4990 bogus residue values);
4991 s = SINGLE_LUN (the device has only one
4992 Logical Unit);
4993 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4994 commands, uas only);
4995 u = IGNORE_UAS (don't bind to the uas driver);
4996 w = NO_WP_DETECT (don't test whether the
4997 medium is write-protected).
4998 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4999 even if the device claims no cache)
5000 Example: quirks=0419:aaf5:rl,0421:0433:rc
5002 user_debug= [KNL,ARM]
5003 Format: <int>
5004 See arch/arm/Kconfig.debug help text.
5005 1 - undefined instruction events
5006 2 - system calls
5007 4 - invalid data aborts
5008 8 - SIGSEGV faults
5009 16 - SIGBUS faults
5010 Example: user_debug=31
5012 userpte=
5013 [X86] Flags controlling user PTE allocations.
5015 nohigh = do not allocate PTE pages in
5016 HIGHMEM regardless of setting
5017 of CONFIG_HIGHPTE.
5019 vdso= [X86,SH]
5020 On X86_32, this is an alias for vdso32=. Otherwise:
5022 vdso=1: enable VDSO (the default)
5023 vdso=0: disable VDSO mapping
5025 vdso32= [X86] Control the 32-bit vDSO
5026 vdso32=1: enable 32-bit VDSO
5027 vdso32=0 or vdso32=2: disable 32-bit VDSO
5029 See the help text for CONFIG_COMPAT_VDSO for more
5030 details. If CONFIG_COMPAT_VDSO is set, the default is
5031 vdso32=0; otherwise, the default is vdso32=1.
5033 For compatibility with older kernels, vdso32=2 is an
5034 alias for vdso32=0.
5036 Try vdso32=0 if you encounter an error that says:
5037 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
5039 vector= [IA-64,SMP]
5040 vector=percpu: enable percpu vector domain
5042 video= [FB] Frame buffer configuration
5043 See Documentation/fb/modedb.rst.
5045 video.brightness_switch_enabled= [0,1]
5046 If set to 1, on receiving an ACPI notify event
5047 generated by hotkey, video driver will adjust brightness
5048 level and then send out the event to user space through
5049 the allocated input device; If set to 0, video driver
5050 will only send out the event without touching backlight
5051 brightness level.
5052 default: 1
5054 virtio_mmio.device=
5055 [VMMIO] Memory mapped virtio (platform) device.
5057 <size>@<baseaddr>:<irq>[:<id>]
5058 where:
5059 <size> := size (can use standard suffixes
5060 like K, M and G)
5061 <baseaddr> := physical base address
5062 <irq> := interrupt number (as passed to
5063 request_irq())
5064 <id> := (optional) platform device id
5065 example:
5066 virtio_mmio.device=1K@0x100b0000:48:7
5068 Can be used multiple times for multiple devices.
5070 vga= [BOOT,X86-32] Select a particular video mode
5071 See Documentation/x86/boot.rst and
5072 Documentation/admin-guide/svga.rst.
5073 Use vga=ask for menu.
5074 This is actually a boot loader parameter; the value is
5075 passed to the kernel using a special protocol.
5077 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
5078 May slow down system boot speed, especially when
5079 enabled on systems with a large amount of memory.
5080 All options are enabled by default, and this
5081 interface is meant to allow for selectively
5082 enabling or disabling specific virtual memory
5083 debugging features.
5085 Available options are:
5086 P Enable page structure init time poisoning
5087 - Disable all of the above options
5089 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
5090 size of <nn>. This can be used to increase the
5091 minimum size (128MB on x86). It can also be used to
5092 decrease the size and leave more room for directly
5093 mapped kernel RAM.
5095 vmcp_cma=nn[MG] [KNL,S390]
5096 Sets the memory size reserved for contiguous memory
5097 allocations for the vmcp device driver.
5099 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
5100 Format: <command>
5102 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
5103 Format: <command>
5105 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
5106 Format: <command>
5108 vsyscall= [X86-64]
5109 Controls the behavior of vsyscalls (i.e. calls to
5110 fixed addresses of 0xffffffffff600x00 from legacy
5111 code). Most statically-linked binaries and older
5112 versions of glibc use these calls. Because these
5113 functions are at fixed addresses, they make nice
5114 targets for exploits that can control RIP.
5116 emulate [default] Vsyscalls turn into traps and are
5117 emulated reasonably safely. The vsyscall
5118 page is readable.
5120 xonly Vsyscalls turn into traps and are
5121 emulated reasonably safely. The vsyscall
5122 page is not readable.
5124 none Vsyscalls don't work at all. This makes
5125 them quite hard to use for exploits but
5126 might break your system.
5128 vt.color= [VT] Default text color.
5129 Format: 0xYX, X = foreground, Y = background.
5130 Default: 0x07 = light gray on black.
5132 vt.cur_default= [VT] Default cursor shape.
5133 Format: 0xCCBBAA, where AA, BB, and CC are the same as
5134 the parameters of the <Esc>[?A;B;Cc escape sequence;
5135 see VGA-softcursor.txt. Default: 2 = underline.
5137 vt.default_blu= [VT]
5138 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
5139 Change the default blue palette of the console.
5140 This is a 16-member array composed of values
5141 ranging from 0-255.
5143 vt.default_grn= [VT]
5144 Format: <green0>,<green1>,<green2>,...,<green15>
5145 Change the default green palette of the console.
5146 This is a 16-member array composed of values
5147 ranging from 0-255.
5149 vt.default_red= [VT]
5150 Format: <red0>,<red1>,<red2>,...,<red15>
5151 Change the default red palette of the console.
5152 This is a 16-member array composed of values
5153 ranging from 0-255.
5155 vt.default_utf8=
5156 [VT]
5157 Format=<0|1>
5158 Set system-wide default UTF-8 mode for all tty's.
5159 Default is 1, i.e. UTF-8 mode is enabled for all
5160 newly opened terminals.
5162 vt.global_cursor_default=
5163 [VT]
5164 Format=<-1|0|1>
5165 Set system-wide default for whether a cursor
5166 is shown on new VTs. Default is -1,
5167 i.e. cursors will be created by default unless
5168 overridden by individual drivers. 0 will hide
5169 cursors, 1 will display them.
5171 vt.italic= [VT] Default color for italic text; 0-15.
5172 Default: 2 = green.
5174 vt.underline= [VT] Default color for underlined text; 0-15.
5175 Default: 3 = cyan.
5177 watchdog timers [HW,WDT] For information on watchdog timers,
5178 see Documentation/watchdog/watchdog-parameters.rst
5179 or other driver-specific files in the
5180 Documentation/watchdog/ directory.
5182 watchdog_thresh=
5183 [KNL]
5184 Set the hard lockup detector stall duration
5185 threshold in seconds. The soft lockup detector
5186 threshold is set to twice the value. A value of 0
5187 disables both lockup detectors. Default is 10
5188 seconds.
5190 workqueue.watchdog_thresh=
5191 If CONFIG_WQ_WATCHDOG is configured, workqueue can
5192 warn stall conditions and dump internal state to
5193 help debugging. 0 disables workqueue stall
5194 detection; otherwise, it's the stall threshold
5195 duration in seconds. The default value is 30 and
5196 it can be updated at runtime by writing to the
5197 corresponding sysfs file.
5199 workqueue.disable_numa
5200 By default, all work items queued to unbound
5201 workqueues are affine to the NUMA nodes they're
5202 issued on, which results in better behavior in
5203 general. If NUMA affinity needs to be disabled for
5204 whatever reason, this option can be used. Note
5205 that this also can be controlled per-workqueue for
5206 workqueues visible under /sys/bus/workqueue/.
5208 workqueue.power_efficient
5209 Per-cpu workqueues are generally preferred because
5210 they show better performance thanks to cache
5211 locality; unfortunately, per-cpu workqueues tend to
5212 be more power hungry than unbound workqueues.
5214 Enabling this makes the per-cpu workqueues which
5215 were observed to contribute significantly to power
5216 consumption unbound, leading to measurably lower
5217 power usage at the cost of small performance
5218 overhead.
5220 The default value of this parameter is determined by
5221 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
5223 workqueue.debug_force_rr_cpu
5224 Workqueue used to implicitly guarantee that work
5225 items queued without explicit CPU specified are put
5226 on the local CPU. This guarantee is no longer true
5227 and while local CPU is still preferred work items
5228 may be put on foreign CPUs. This debug option
5229 forces round-robin CPU selection to flush out
5230 usages which depend on the now broken guarantee.
5231 When enabled, memory and cache locality will be
5232 impacted.
5234 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
5235 default x2apic cluster mode on platforms
5236 supporting x2apic.
5238 x86_intel_mid_timer= [X86-32,APBT]
5239 Choose timer option for x86 Intel MID platform.
5240 Two valid options are apbt timer only and lapic timer
5241 plus one apbt timer for broadcast timer.
5242 x86_intel_mid_timer=apbt_only | lapic_and_apbt
5244 xen_512gb_limit [KNL,X86-64,XEN]
5245 Restricts the kernel running paravirtualized under Xen
5246 to use only up to 512 GB of RAM. The reason to do so is
5247 crash analysis tools and Xen tools for doing domain
5248 save/restore/migration must be enabled to handle larger
5249 domains.
5251 xen_emul_unplug= [HW,X86,XEN]
5252 Unplug Xen emulated devices
5253 Format: [unplug0,][unplug1]
5254 ide-disks -- unplug primary master IDE devices
5255 aux-ide-disks -- unplug non-primary-master IDE devices
5256 nics -- unplug network devices
5257 all -- unplug all emulated devices (NICs and IDE disks)
5258 unnecessary -- unplugging emulated devices is
5259 unnecessary even if the host did not respond to
5260 the unplug protocol
5261 never -- do not unplug even if version check succeeds
5263 xen_nopvspin [X86,XEN]
5264 Disables the ticketlock slowpath using Xen PV
5265 optimizations.
5267 xen_nopv [X86]
5268 Disables the PV optimizations forcing the HVM guest to
5269 run as generic HVM guest with no PV drivers.
5270 This option is obsoleted by the "nopv" option, which
5271 has equivalent effect for XEN platform.
5273 xen_scrub_pages= [XEN]
5274 Boolean option to control scrubbing pages before giving them back
5275 to Xen, for use by other domains. Can be also changed at runtime
5276 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
5277 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
5279 xen_timer_slop= [X86-64,XEN]
5280 Set the timer slop (in nanoseconds) for the virtual Xen
5281 timers (default is 100000). This adjusts the minimum
5282 delta of virtualized Xen timers, where lower values
5283 improve timer resolution at the expense of processing
5284 more timer interrupts.
5286 nopv= [X86,XEN,KVM,HYPER_V,VMWARE]
5287 Disables the PV optimizations forcing the guest to run
5288 as generic guest with no PV drivers. Currently support
5289 XEN HVM, KVM, HYPER_V and VMWARE guest.
5291 xirc2ps_cs= [NET,PCMCIA]
5292 Format:
5293 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
5295 xive= [PPC]
5296 By default on POWER9 and above, the kernel will
5297 natively use the XIVE interrupt controller. This option
5298 allows the fallback firmware mode to be used:
5300 off Fallback to firmware control of XIVE interrupt
5301 controller on both pseries and powernv
5302 platforms. Only useful on POWER9 and above.
5304 xhci-hcd.quirks [USB,KNL]
5305 A hex value specifying bitmask with supplemental xhci
5306 host controller quirks. Meaning of each bit can be
5307 consulted in header drivers/usb/host/xhci.h.