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.txt, 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/acpi/debug.txt for more information about
57 debug layers and levels.
59 Enable processor driver info messages:
60 acpi.debug_layer=0x20000000
61 Enable PCI/PCI interrupt routing info messages:
62 acpi.debug_layer=0x400000
63 Enable AML "Debug" output, i.e., stores to the Debug
64 object while interpreting AML:
65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
66 Enable all messages related to ACPI hardware:
67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
69 Some values produce so much output that the system is
70 unusable. The "log_buf_len" parameter may be useful
71 if you need to capture more output.
73 acpi_enforce_resources= [ACPI]
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.txt 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 whilst booting
335 Format: { quiet (default) | verbose | debug }
336 Change the amount of debugging information output
337 when initialising the APIC and IO-APIC components.
338 For X86-32, this can also be used to specify an APIC
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.txt
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 ca_keys= [KEYS] This parameter identifies a specific key(s) on
465 the system trusted keyring to be used for certificate
466 trust validation.
467 format: { id:<keyid> | builtin }
469 cca= [MIPS] Override the kernel pages' cache coherency
470 algorithm. Accepted values range from 0 to 7
471 inclusive. See arch/mips/include/asm/pgtable-bits.h
472 for platform specific values (SB1, Loongson3 and
473 others).
475 ccw_timeout_log [S390]
476 See Documentation/s390/CommonIO for details.
478 cgroup_disable= [KNL] Disable a particular controller
479 Format: {name of the controller(s) to disable}
480 The effects of cgroup_disable=foo are:
481 - foo isn't auto-mounted if you mount all cgroups in
482 a single hierarchy
483 - foo isn't visible as an individually mountable
484 subsystem
485 {Currently only "memory" controller deal with this and
486 cut the overhead, others just disable the usage. So
487 only cgroup_disable=memory is actually worthy}
489 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
490 Format: { controller[,controller...] | "all" }
491 Like cgroup_disable, but only applies to cgroup v1;
492 the blacklisted controllers remain available in cgroup2.
494 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
495 Format: <string>
496 nosocket -- Disable socket memory accounting.
497 nokmem -- Disable kernel memory accounting.
499 checkreqprot [SELINUX] Set initial checkreqprot flag value.
500 Format: { "0" | "1" }
501 See security/selinux/Kconfig help text.
502 0 -- check protection applied by kernel (includes
503 any implied execute protection).
504 1 -- check protection requested by application.
505 Default value is set via a kernel config option.
506 Value can be changed at runtime via
507 /selinux/checkreqprot.
509 cio_ignore= [S390]
510 See Documentation/s390/CommonIO for details.
511 clk_ignore_unused
512 [CLK]
513 Prevents the clock framework from automatically gating
514 clocks that have not been explicitly enabled by a Linux
515 device driver but are enabled in hardware at reset or
516 by the bootloader/firmware. Note that this does not
517 force such clocks to be always-on nor does it reserve
518 those clocks in any way. This parameter is useful for
519 debug and development, but should not be needed on a
520 platform with proper driver support. For more
521 information, see Documentation/driver-api/clk.rst.
523 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
524 [Deprecated]
525 Forces specified clocksource (if available) to be used
526 when calculating gettimeofday(). If specified
527 clocksource is not available, it defaults to PIT.
528 Format: { pit | tsc | cyclone | pmtmr }
530 clocksource= Override the default clocksource
531 Format: <string>
532 Override the default clocksource and use the clocksource
533 with the name specified.
534 Some clocksource names to choose from, depending on
535 the platform:
536 [all] jiffies (this is the base, fallback clocksource)
537 [ACPI] acpi_pm
538 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
539 pxa_timer,timer3,32k_counter,timer0_1
540 [X86-32] pit,hpet,tsc;
541 scx200_hrt on Geode; cyclone on IBM x440
542 [MIPS] MIPS
543 [PARISC] cr16
544 [S390] tod
545 [SH] SuperH
546 [SPARC64] tick
547 [X86-64] hpet,tsc
549 clocksource.arm_arch_timer.evtstrm=
550 [ARM,ARM64]
551 Format: <bool>
552 Enable/disable the eventstream feature of the ARM
553 architected timer so that code using WFE-based polling
554 loops can be debugged more effectively on production
555 systems.
557 clearcpuid=BITNUM [X86]
558 Disable CPUID feature X for the kernel. See
559 arch/x86/include/asm/cpufeatures.h for the valid bit
560 numbers. Note the Linux specific bits are not necessarily
561 stable over kernel options, but the vendor specific
562 ones should be.
563 Also note that user programs calling CPUID directly
564 or using the feature without checking anything
565 will still see it. This just prevents it from
566 being used by the kernel or shown in /proc/cpuinfo.
567 Also note the kernel might malfunction if you disable
568 some critical bits.
570 cma=nn[MG]@[start[MG][-end[MG]]]
571 [ARM,X86,KNL]
572 Sets the size of kernel global memory area for
573 contiguous memory allocations and optionally the
574 placement constraint by the physical address range of
575 memory allocations. A value of 0 disables CMA
576 altogether. For more information, see
577 include/linux/dma-contiguous.h
579 cmo_free_hint= [PPC] Format: { yes | no }
580 Specify whether pages are marked as being inactive
581 when they are freed. This is used in CMO environments
582 to determine OS memory pressure for page stealing by
583 a hypervisor.
584 Default: yes
586 coherent_pool=nn[KMG] [ARM,KNL]
587 Sets the size of memory pool for coherent, atomic dma
588 allocations, by default set to 256K.
590 com20020= [HW,NET] ARCnet - COM20020 chipset
591 Format:
592 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
594 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
595 Format: <io>[,<irq>]
597 com90xx= [HW,NET]
598 ARCnet - COM90xx chipset (memory-mapped buffers)
599 Format: <io>[,<irq>[,<memstart>]]
601 condev= [HW,S390] console device
602 conmode=
604 console= [KNL] Output console device and options.
606 tty<n> Use the virtual console device <n>.
608 ttyS<n>[,options]
609 ttyUSB0[,options]
610 Use the specified serial port. The options are of
611 the form "bbbbpnf", where "bbbb" is the baud rate,
612 "p" is parity ("n", "o", or "e"), "n" is number of
613 bits, and "f" is flow control ("r" for RTS or
614 omit it). Default is "9600n8".
616 See Documentation/admin-guide/serial-console.rst for more
617 information. See
618 Documentation/networking/netconsole.txt for an
619 alternative.
621 uart[8250],io,<addr>[,options]
622 uart[8250],mmio,<addr>[,options]
623 uart[8250],mmio16,<addr>[,options]
624 uart[8250],mmio32,<addr>[,options]
625 uart[8250],0x<addr>[,options]
626 Start an early, polled-mode console on the 8250/16550
627 UART at the specified I/O port or MMIO address,
628 switching to the matching ttyS device later.
629 MMIO inter-register address stride is either 8-bit
630 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
631 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
632 to be equivalent to 'mmio'. 'options' are specified in
633 the same format described for ttyS above; if unspecified,
634 the h/w is not re-initialized.
636 hvc<n> Use the hypervisor console device <n>. This is for
637 both Xen and PowerPC hypervisors.
639 If the device connected to the port is not a TTY but a braille
640 device, prepend "brl," before the device type, for instance
641 console=brl,ttyS0
642 For now, only VisioBraille is supported.
644 console_msg_format=
645 [KNL] Change console messages format
646 default
647 By default we print messages on consoles in
648 "[time stamp] text\n" format (time stamp may not be
649 printed, depending on CONFIG_PRINTK_TIME or
650 `printk_time' param).
651 syslog
652 Switch to syslog format: "<%u>[time stamp] text\n"
653 IOW, each message will have a facility and loglevel
654 prefix. The format is similar to one used by syslog()
655 syscall, or to executing "dmesg -S --raw" or to reading
656 from /proc/kmsg.
658 consoleblank= [KNL] The console blank (screen saver) timeout in
659 seconds. A value of 0 disables the blank timer.
660 Defaults to 0.
662 coredump_filter=
663 [KNL] Change the default value for
664 /proc/<pid>/coredump_filter.
665 See also Documentation/filesystems/proc.txt.
667 coresight_cpu_debug.enable
668 [ARM,ARM64]
669 Format: <bool>
670 Enable/disable the CPU sampling based debugging.
671 0: default value, disable debugging
672 1: enable debugging at boot time
674 cpuidle.off=1 [CPU_IDLE]
675 disable the cpuidle sub-system
677 cpufreq.off=1 [CPU_FREQ]
678 disable the cpufreq sub-system
680 cpu_init_udelay=N
681 [X86] Delay for N microsec between assert and de-assert
682 of APIC INIT to start processors. This delay occurs
683 on every CPU online, such as boot, and resume from suspend.
684 Default: 10000
686 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
687 Format:
688 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
690 crashkernel=size[KMG][@offset[KMG]]
691 [KNL] Using kexec, Linux can switch to a 'crash kernel'
692 upon panic. This parameter reserves the physical
693 memory region [offset, offset + size] for that kernel
694 image. If '@offset' is omitted, then a suitable offset
695 is selected automatically. Check
696 Documentation/kdump/kdump.txt for further details.
698 crashkernel=range1:size1[,range2:size2,...][@offset]
699 [KNL] Same as above, but depends on the memory
700 in the running system. The syntax of range is
701 start-[end] where start and end are both
702 a memory unit (amount[KMG]). See also
703 Documentation/kdump/kdump.txt for an example.
705 crashkernel=size[KMG],high
706 [KNL, x86_64] range could be above 4G. Allow kernel
707 to allocate physical memory region from top, so could
708 be above 4G if system have more than 4G ram installed.
709 Otherwise memory region will be allocated below 4G, if
710 available.
711 It will be ignored if crashkernel=X is specified.
712 crashkernel=size[KMG],low
713 [KNL, x86_64] range under 4G. When crashkernel=X,high
714 is passed, kernel could allocate physical memory region
715 above 4G, that cause second kernel crash on system
716 that require some amount of low memory, e.g. swiotlb
717 requires at least 64M+32K low memory, also enough extra
718 low memory is needed to make sure DMA buffers for 32-bit
719 devices won't run out. Kernel would try to allocate at
720 at least 256M below 4G automatically.
721 This one let user to specify own low range under 4G
722 for second kernel instead.
723 0: to disable low allocation.
724 It will be ignored when crashkernel=X,high is not used
725 or memory reserved is below 4G.
727 cryptomgr.notests
728 [KNL] Disable crypto self-tests
730 cs89x0_dma= [HW,NET]
731 Format: <dma>
733 cs89x0_media= [HW,NET]
734 Format: { rj45 | aui | bnc }
736 dasd= [HW,NET]
737 See header of drivers/s390/block/dasd_devmap.c.
739 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
740 (one device per port)
741 Format: <port#>,<type>
742 See also Documentation/input/devices/joystick-parport.rst
744 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
745 time. See
746 Documentation/admin-guide/dynamic-debug-howto.rst for
747 details. Deprecated, see dyndbg.
749 debug [KNL] Enable kernel debugging (events log level).
751 debug_boot_weak_hash
752 [KNL] Enable printing [hashed] pointers early in the
753 boot sequence. If enabled, we use a weak hash instead
754 of siphash to hash pointers. Use this option if you are
755 seeing instances of '(___ptrval___)') and need to see a
756 value (hashed pointer) instead. Cryptographically
757 insecure, please do not use on production kernels.
759 debug_locks_verbose=
760 [KNL] verbose self-tests
761 Format=<0|1>
762 Print debugging info while doing the locking API
763 self-tests.
764 We default to 0 (no extra messages), setting it to
765 1 will print _a lot_ more information - normally
766 only useful to kernel developers.
768 debug_objects [KNL] Enable object debugging
770 no_debug_objects
771 [KNL] Disable object debugging
773 debug_guardpage_minorder=
774 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
775 parameter allows control of the order of pages that will
776 be intentionally kept free (and hence protected) by the
777 buddy allocator. Bigger value increase the probability
778 of catching random memory corruption, but reduce the
779 amount of memory for normal system use. The maximum
780 possible value is MAX_ORDER/2. Setting this parameter
781 to 1 or 2 should be enough to identify most random
782 memory corruption problems caused by bugs in kernel or
783 driver code when a CPU writes to (or reads from) a
784 random memory location. Note that there exists a class
785 of memory corruptions problems caused by buggy H/W or
786 F/W or by drivers badly programing DMA (basically when
787 memory is written at bus level and the CPU MMU is
788 bypassed) which are not detectable by
789 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
790 tracking down these problems.
792 debug_pagealloc=
793 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
794 parameter enables the feature at boot time. In
795 default, it is disabled. We can avoid allocating huge
796 chunk of memory for debug pagealloc if we don't enable
797 it at boot time and the system will work mostly same
798 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
799 on: enable the feature
801 debugpat [X86] Enable PAT debugging
803 decnet.addr= [HW,NET]
804 Format: <area>[,<node>]
805 See also Documentation/networking/decnet.txt.
807 default_hugepagesz=
808 [same as hugepagesz=] The size of the default
809 HugeTLB page size. This is the size represented by
810 the legacy /proc/ hugepages APIs, used for SHM, and
811 default size when mounting hugetlbfs filesystems.
812 Defaults to the default architecture's huge page size
813 if not specified.
815 deferred_probe_timeout=
816 [KNL] Debugging option to set a timeout in seconds for
817 deferred probe to give up waiting on dependencies to
818 probe. Only specific dependencies (subsystems or
819 drivers) that have opted in will be ignored. A timeout of 0
820 will timeout at the end of initcalls. This option will also
821 dump out devices still on the deferred probe list after
822 retrying.
824 dhash_entries= [KNL]
825 Set number of hash buckets for dentry cache.
827 disable_1tb_segments [PPC]
828 Disables the use of 1TB hash page table segments. This
829 causes the kernel to fall back to 256MB segments which
830 can be useful when debugging issues that require an SLB
831 miss to occur.
833 disable= [IPV6]
834 See Documentation/networking/ipv6.txt.
836 hardened_usercopy=
837 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
838 hardening is enabled for this boot. Hardened
839 usercopy checking is used to protect the kernel
840 from reading or writing beyond known memory
841 allocation boundaries as a proactive defense
842 against bounds-checking flaws in the kernel's
843 copy_to_user()/copy_from_user() interface.
844 on Perform hardened usercopy checks (default).
845 off Disable hardened usercopy checks.
847 disable_radix [PPC]
848 Disable RADIX MMU mode on POWER9
850 disable_cpu_apicid= [X86,APIC,SMP]
851 Format: <int>
852 The number of initial APIC ID for the
853 corresponding CPU to be disabled at boot,
854 mostly used for the kdump 2nd kernel to
855 disable BSP to wake up multiple CPUs without
856 causing system reset or hang due to sending
857 INIT from AP to BSP.
859 disable_ddw [PPC/PSERIES]
860 Disable Dynamic DMA Window support. Use this if
861 to workaround buggy firmware.
863 disable_ipv6= [IPV6]
864 See Documentation/networking/ipv6.txt.
866 disable_mtrr_cleanup [X86]
867 The kernel tries to adjust MTRR layout from continuous
868 to discrete, to make X server driver able to add WB
869 entry later. This parameter disables that.
871 disable_mtrr_trim [X86, Intel and AMD only]
872 By default the kernel will trim any uncacheable
873 memory out of your available memory pool based on
874 MTRR settings. This parameter disables that behavior,
875 possibly causing your machine to run very slowly.
877 disable_timer_pin_1 [X86]
878 Disable PIN 1 of APIC timer
879 Can be useful to work around chipset bugs.
881 dis_ucode_ldr [X86] Disable the microcode loader.
883 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
884 this option disables the debugging code at boot.
886 dma_debug_entries=<number>
887 This option allows to tune the number of preallocated
888 entries for DMA-API debugging code. One entry is
889 required per DMA-API allocation. Use this if the
890 DMA-API debugging code disables itself because the
891 architectural default is too low.
893 dma_debug_driver=<driver_name>
894 With this option the DMA-API debugging driver
895 filter feature can be enabled at boot time. Just
896 pass the driver to filter for as the parameter.
897 The filter can be disabled or changed to another
898 driver later using sysfs.
900 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
901 Broken monitors, graphic adapters, KVMs and EDIDless
902 panels may send no or incorrect EDID data sets.
903 This parameter allows to specify an EDID data sets
904 in the /lib/firmware directory that are used instead.
905 Generic built-in EDID data sets are used, if one of
906 edid/1024x768.bin, edid/1280x1024.bin,
907 edid/1680x1050.bin, or edid/1920x1080.bin is given
908 and no file with the same name exists. Details and
909 instructions how to build your own EDID data are
910 available in Documentation/EDID/HOWTO.txt. An EDID
911 data set will only be used for a particular connector,
912 if its name and a colon are prepended to the EDID
913 name. Each connector may use a unique EDID data
914 set by separating the files with a comma. An EDID
915 data set with no connector name will be used for
916 any connectors not explicitly specified.
918 dscc4.setup= [NET]
920 dt_cpu_ftrs= [PPC]
921 Format: {"off" | "known"}
922 Control how the dt_cpu_ftrs device-tree binding is
923 used for CPU feature discovery and setup (if it
924 exists).
925 off: Do not use it, fall back to legacy cpu table.
926 known: Do not pass through unknown features to guests
927 or userspace, only those that the kernel is aware of.
929 dump_apple_properties [X86]
930 Dump name and content of EFI device properties on
931 x86 Macs. Useful for driver authors to determine
932 what data is available or for reverse-engineering.
934 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
935 module.dyndbg[="val"]
936 Enable debug messages at boot time. See
937 Documentation/admin-guide/dynamic-debug-howto.rst
938 for details.
940 nompx [X86] Disables Intel Memory Protection Extensions.
941 See Documentation/x86/intel_mpx.txt for more
942 information about the feature.
944 nopku [X86] Disable Memory Protection Keys CPU feature found
945 in some Intel CPUs.
947 module.async_probe [KNL]
948 Enable asynchronous probe on this module.
950 early_ioremap_debug [KNL]
951 Enable debug messages in early_ioremap support. This
952 is useful for tracking down temporary early mappings
953 which are not unmapped.
955 earlycon= [KNL] Output early console device and options.
957 [ARM64] The early console is determined by the
958 stdout-path property in device tree's chosen node,
959 or determined by the ACPI SPCR table.
961 [X86] When used with no options the early console is
962 determined by the ACPI SPCR table.
964 cdns,<addr>[,options]
965 Start an early, polled-mode console on a Cadence
966 (xuartps) serial port at the specified address. Only
967 supported option is baud rate. If baud rate is not
968 specified, the serial port must already be setup and
969 configured.
971 uart[8250],io,<addr>[,options]
972 uart[8250],mmio,<addr>[,options]
973 uart[8250],mmio32,<addr>[,options]
974 uart[8250],mmio32be,<addr>[,options]
975 uart[8250],0x<addr>[,options]
976 Start an early, polled-mode console on the 8250/16550
977 UART at the specified I/O port or MMIO address.
978 MMIO inter-register address stride is either 8-bit
979 (mmio) or 32-bit (mmio32 or mmio32be).
980 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
981 to be equivalent to 'mmio'. 'options' are specified
982 in the same format described for "console=ttyS<n>"; if
983 unspecified, the h/w is not initialized.
985 pl011,<addr>
986 pl011,mmio32,<addr>
987 Start an early, polled-mode console on a pl011 serial
988 port at the specified address. The pl011 serial port
989 must already be setup and configured. Options are not
990 yet supported. If 'mmio32' is specified, then only
991 the driver will use only 32-bit accessors to read/write
992 the device registers.
994 meson,<addr>
995 Start an early, polled-mode console on a meson serial
996 port at the specified address. The serial port must
997 already be setup and configured. Options are not yet
998 supported.
1000 msm_serial,<addr>
1001 Start an early, polled-mode console on an msm serial
1002 port at the specified address. The serial port
1003 must already be setup and configured. Options are not
1004 yet supported.
1006 msm_serial_dm,<addr>
1007 Start an early, polled-mode console on an msm serial
1008 dm port at the specified address. The serial port
1009 must already be setup and configured. Options are not
1010 yet supported.
1012 owl,<addr>
1013 Start an early, polled-mode console on a serial port
1014 of an Actions Semi SoC, such as S500 or S900, at the
1015 specified address. The serial port must already be
1016 setup and configured. Options are not yet supported.
1018 smh Use ARM semihosting calls for early console.
1020 s3c2410,<addr>
1021 s3c2412,<addr>
1022 s3c2440,<addr>
1023 s3c6400,<addr>
1024 s5pv210,<addr>
1025 exynos4210,<addr>
1026 Use early console provided by serial driver available
1027 on Samsung SoCs, requires selecting proper type and
1028 a correct base address of the selected UART port. The
1029 serial port must already be setup and configured.
1030 Options are not yet supported.
1032 lantiq,<addr>
1033 Start an early, polled-mode console on a lantiq serial
1034 (lqasc) port at the specified address. The serial port
1035 must already be setup and configured. Options are not
1036 yet supported.
1038 lpuart,<addr>
1039 lpuart32,<addr>
1040 Use early console provided by Freescale LP UART driver
1041 found on Freescale Vybrid and QorIQ LS1021A processors.
1042 A valid base address must be provided, and the serial
1043 port must already be setup and configured.
1045 ar3700_uart,<addr>
1046 Start an early, polled-mode console on the
1047 Armada 3700 serial port at the specified
1048 address. The serial port must already be setup
1049 and configured. Options are not yet supported.
1051 qcom_geni,<addr>
1052 Start an early, polled-mode console on a Qualcomm
1053 Generic Interface (GENI) based serial port at the
1054 specified address. The serial port must already be
1055 setup and configured. Options are not yet supported.
1057 earlyprintk= [X86,SH,ARM,M68k,S390]
1058 earlyprintk=vga
1059 earlyprintk=efi
1060 earlyprintk=sclp
1061 earlyprintk=xen
1062 earlyprintk=serial[,ttySn[,baudrate]]
1063 earlyprintk=serial[,0x...[,baudrate]]
1064 earlyprintk=ttySn[,baudrate]
1065 earlyprintk=dbgp[debugController#]
1066 earlyprintk=pciserial,bus:device.function[,baudrate]
1067 earlyprintk=xdbc[xhciController#]
1069 earlyprintk is useful when the kernel crashes before
1070 the normal console is initialized. It is not enabled by
1071 default because it has some cosmetic problems.
1073 Append ",keep" to not disable it when the real console
1074 takes over.
1076 Only one of vga, efi, serial, or usb debug port can
1077 be used at a time.
1079 Currently only ttyS0 and ttyS1 may be specified by
1080 name. Other I/O ports may be explicitly specified
1081 on some architectures (x86 and arm at least) by
1082 replacing ttySn with an I/O port address, like this:
1083 earlyprintk=serial,0x1008,115200
1084 You can find the port for a given device in
1085 /proc/tty/driver/serial:
1086 2: uart:ST16650V2 port:00001008 irq:18 ...
1088 Interaction with the standard serial driver is not
1089 very good.
1091 The VGA and EFI output is eventually overwritten by
1092 the real console.
1094 The xen output can only be used by Xen PV guests.
1096 The sclp output can only be used on s390.
1098 edac_report= [HW,EDAC] Control how to report EDAC event
1099 Format: {"on" | "off" | "force"}
1100 on: enable EDAC to report H/W event. May be overridden
1101 by other higher priority error reporting module.
1102 off: disable H/W event reporting through EDAC.
1103 force: enforce the use of EDAC to report H/W event.
1104 default: on.
1106 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1107 ekgdboc=kbd
1109 This is designed to be used in conjunction with
1110 the boot argument: earlyprintk=vga
1112 edd= [EDD]
1113 Format: {"off" | "on" | "skip[mbr]"}
1115 efi= [EFI]
1116 Format: { "old_map", "nochunk", "noruntime", "debug" }
1117 old_map [X86-64]: switch to the old ioremap-based EFI
1118 runtime services mapping. 32-bit still uses this one by
1119 default.
1120 nochunk: disable reading files in "chunks" in the EFI
1121 boot stub, as chunking can cause problems with some
1122 firmware implementations.
1123 noruntime : disable EFI runtime services support
1124 debug: enable misc debug output
1126 efi_no_storage_paranoia [EFI; X86]
1127 Using this parameter you can use more than 50% of
1128 your efi variable storage. Use this parameter only if
1129 you are really sure that your UEFI does sane gc and
1130 fulfills the spec otherwise your board may brick.
1132 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1133 Add arbitrary attribute to specific memory range by
1134 updating original EFI memory map.
1135 Region of memory which aa attribute is added to is
1136 from ss to ss+nn.
1137 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1138 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1139 attribute is added to range 0x100000000-0x180000000 and
1140 0x10a0000000-0x1120000000.
1142 Using this parameter you can do debugging of EFI memmap
1143 related feature. For example, you can do debugging of
1144 Address Range Mirroring feature even if your box
1145 doesn't support it.
1147 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1148 that is to be dynamically loaded by Linux. If there are
1149 multiple variables with the same name but with different
1150 vendor GUIDs, all of them will be loaded. See
1151 Documentation/acpi/ssdt-overlays.txt for details.
1154 eisa_irq_edge= [PARISC,HW]
1155 See header of drivers/parisc/eisa.c.
1157 elanfreq= [X86-32]
1158 See comment before function elanfreq_setup() in
1159 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1161 elevator= [IOSCHED]
1162 Format: {"cfq" | "deadline" | "noop"}
1163 See Documentation/block/cfq-iosched.txt and
1164 Documentation/block/deadline-iosched.txt for details.
1166 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1167 Specifies physical address of start of kernel core
1168 image elf header and optionally the size. Generally
1169 kexec loader will pass this option to capture kernel.
1170 See Documentation/kdump/kdump.txt for details.
1172 enable_mtrr_cleanup [X86]
1173 The kernel tries to adjust MTRR layout from continuous
1174 to discrete, to make X server driver able to add WB
1175 entry later. This parameter enables that.
1177 enable_timer_pin_1 [X86]
1178 Enable PIN 1 of APIC timer
1179 Can be useful to work around chipset bugs
1180 (in particular on some ATI chipsets).
1181 The kernel tries to set a reasonable default.
1183 enforcing [SELINUX] Set initial enforcing status.
1184 Format: {"0" | "1"}
1185 See security/selinux/Kconfig help text.
1186 0 -- permissive (log only, no denials).
1187 1 -- enforcing (deny and log).
1188 Default value is 0.
1189 Value can be changed at runtime via /selinux/enforce.
1191 erst_disable [ACPI]
1192 Disable Error Record Serialization Table (ERST)
1193 support.
1195 ether= [HW,NET] Ethernet cards parameters
1196 This option is obsoleted by the "netdev=" option, which
1197 has equivalent usage. See its documentation for details.
1199 evm= [EVM]
1200 Format: { "fix" }
1201 Permit 'security.evm' to be updated regardless of
1202 current integrity status.
1204 failslab=
1205 fail_page_alloc=
1206 fail_make_request=[KNL]
1207 General fault injection mechanism.
1208 Format: <interval>,<probability>,<space>,<times>
1209 See also Documentation/fault-injection/.
1211 floppy= [HW]
1212 See Documentation/blockdev/floppy.txt.
1214 force_pal_cache_flush
1215 [IA-64] Avoid check_sal_cache_flush which may hang on
1216 buggy SAL_CACHE_FLUSH implementations. Using this
1217 parameter will force ia64_sal_cache_flush to call
1218 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1220 forcepae [X86-32]
1221 Forcefully enable Physical Address Extension (PAE).
1222 Many Pentium M systems disable PAE but may have a
1223 functionally usable PAE implementation.
1224 Warning: use of this parameter will taint the kernel
1225 and may cause unknown problems.
1227 ftrace=[tracer]
1228 [FTRACE] will set and start the specified tracer
1229 as early as possible in order to facilitate early
1230 boot debugging.
1232 ftrace_dump_on_oops[=orig_cpu]
1233 [FTRACE] will dump the trace buffers on oops.
1234 If no parameter is passed, ftrace will dump
1235 buffers of all CPUs, but if you pass orig_cpu, it will
1236 dump only the buffer of the CPU that triggered the
1237 oops.
1239 ftrace_filter=[function-list]
1240 [FTRACE] Limit the functions traced by the function
1241 tracer at boot up. function-list is a comma separated
1242 list of functions. This list can be changed at run
1243 time by the set_ftrace_filter file in the debugfs
1244 tracing directory.
1246 ftrace_notrace=[function-list]
1247 [FTRACE] Do not trace the functions specified in
1248 function-list. This list can be changed at run time
1249 by the set_ftrace_notrace file in the debugfs
1250 tracing directory.
1252 ftrace_graph_filter=[function-list]
1253 [FTRACE] Limit the top level callers functions traced
1254 by the function graph tracer at boot up.
1255 function-list is a comma separated list of functions
1256 that can be changed at run time by the
1257 set_graph_function file in the debugfs tracing directory.
1259 ftrace_graph_notrace=[function-list]
1260 [FTRACE] Do not trace from the functions specified in
1261 function-list. This list is a comma separated list of
1262 functions that can be changed at run time by the
1263 set_graph_notrace file in the debugfs tracing directory.
1265 ftrace_graph_max_depth=<uint>
1266 [FTRACE] Used with the function graph tracer. This is
1267 the max depth it will trace into a function. This value
1268 can be changed at run time by the max_graph_depth file
1269 in the tracefs tracing directory. default: 0 (no limit)
1271 gamecon.map[2|3]=
1272 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1273 support via parallel port (up to 5 devices per port)
1274 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1275 See also Documentation/input/devices/joystick-parport.rst
1277 gamma= [HW,DRM]
1279 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1280 Format: off | on
1281 default: on
1283 gcov_persist= [GCOV] When non-zero (default), profiling data for
1284 kernel modules is saved and remains accessible via
1285 debugfs, even when the module is unloaded/reloaded.
1286 When zero, profiling data is discarded and associated
1287 debugfs files are removed at module unload time.
1289 goldfish [X86] Enable the goldfish android emulator platform.
1290 Don't use this when you are not running on the
1291 android emulator
1293 gpt [EFI] Forces disk with valid GPT signature but
1294 invalid Protective MBR to be treated as GPT. If the
1295 primary GPT is corrupted, it enables the backup/alternate
1296 GPT to be used instead.
1298 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1299 the "Enable 0" bit of the configuration register.
1300 Format: 0 | 1
1301 Default: 0
1302 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1303 the "Enable 0" bit of the configuration register.
1304 Format: 0 | 1
1305 Default: 0
1306 grcan.select= [HW] Select which physical interface to use.
1307 Format: 0 | 1
1308 Default: 0
1309 grcan.txsize= [HW] Sets the size of the tx buffer.
1310 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1311 Default: 1024
1312 grcan.rxsize= [HW] Sets the size of the rx buffer.
1313 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1314 Default: 1024
1316 gpio-mockup.gpio_mockup_ranges
1317 [HW] Sets the ranges of gpiochip of for this device.
1318 Format: <start1>,<end1>,<start2>,<end2>...
1320 hardlockup_all_cpu_backtrace=
1321 [KNL] Should the hard-lockup detector generate
1322 backtraces on all cpus.
1323 Format: <integer>
1325 hashdist= [KNL,NUMA] Large hashes allocated during boot
1326 are distributed across NUMA nodes. Defaults on
1327 for 64-bit NUMA, off otherwise.
1328 Format: 0 | 1 (for off | on)
1330 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1332 hd= [EIDE] (E)IDE hard drive subsystem geometry
1333 Format: <cyl>,<head>,<sect>
1335 hest_disable [ACPI]
1336 Disable Hardware Error Source Table (HEST) support;
1337 corresponding firmware-first mode error processing
1338 logic will be disabled.
1340 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1341 size of <nn>. This works even on boxes that have no
1342 highmem otherwise. This also works to reduce highmem
1343 size on bigger boxes.
1345 highres= [KNL] Enable/disable high resolution timer mode.
1346 Valid parameters: "on", "off"
1347 Default: "on"
1349 hisax= [HW,ISDN]
1350 See Documentation/isdn/README.HiSax.
1352 hlt [BUGS=ARM,SH]
1354 hpet= [X86-32,HPET] option to control HPET usage
1355 Format: { enable (default) | disable | force |
1356 verbose }
1357 disable: disable HPET and use PIT instead
1358 force: allow force enabled of undocumented chips (ICH4,
1359 VIA, nVidia)
1360 verbose: show contents of HPET registers during setup
1362 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1363 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1365 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1366 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1367 On x86-64 and powerpc, this option can be specified
1368 multiple times interleaved with hugepages= to reserve
1369 huge pages of different sizes. Valid pages sizes on
1370 x86-64 are 2M (when the CPU supports "pse") and 1G
1371 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1373 hung_task_panic=
1374 [KNL] Should the hung task detector generate panics.
1375 Format: <integer>
1377 A nonzero value instructs the kernel to panic when a
1378 hung task is detected. The default value is controlled
1379 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1380 option. The value selected by this boot parameter can
1381 be changed later by the kernel.hung_task_panic sysctl.
1383 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1384 terminal devices. Valid values: 0..8
1385 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1386 If specified, z/VM IUCV HVC accepts connections
1387 from listed z/VM user IDs only.
1388 keep_bootcon [KNL]
1389 Do not unregister boot console at start. This is only
1390 useful for debugging when something happens in the window
1391 between unregistering the boot console and initializing
1392 the real console.
1394 i2c_bus= [HW] Override the default board specific I2C bus speed
1395 or register an additional I2C bus that is not
1396 registered from board initialization code.
1397 Format:
1398 <bus_id>,<clkrate>
1400 i8042.debug [HW] Toggle i8042 debug mode
1401 i8042.unmask_kbd_data
1402 [HW] Enable printing of interrupt data from the KBD port
1403 (disabled by default, and as a pre-condition
1404 requires that i8042.debug=1 be enabled)
1405 i8042.direct [HW] Put keyboard port into non-translated mode
1406 i8042.dumbkbd [HW] Pretend that controller can only read data from
1407 keyboard and cannot control its state
1408 (Don't attempt to blink the leds)
1409 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1410 i8042.nokbd [HW] Don't check/create keyboard port
1411 i8042.noloop [HW] Disable the AUX Loopback command while probing
1412 for the AUX port
1413 i8042.nomux [HW] Don't check presence of an active multiplexing
1414 controller
1415 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1416 controllers
1417 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1418 i8042.reset [HW] Reset the controller during init, cleanup and
1419 suspend-to-ram transitions, only during s2r
1420 transitions, or never reset
1421 Format: { 1 | Y | y | 0 | N | n }
1422 1, Y, y: always reset controller
1423 0, N, n: don't ever reset controller
1424 Default: only on s2r transitions on x86; most other
1425 architectures force reset to be always executed
1426 i8042.unlock [HW] Unlock (ignore) the keylock
1427 i8042.kbdreset [HW] Reset device connected to KBD port
1429 i810= [HW,DRM]
1431 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1432 indicates that the driver is running on unsupported
1433 hardware.
1434 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1435 does not match list of supported models.
1436 i8k.power_status
1437 [HW] Report power status in /proc/i8k
1438 (disabled by default)
1439 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1440 capability is set.
1442 i915.invert_brightness=
1443 [DRM] Invert the sense of the variable that is used to
1444 set the brightness of the panel backlight. Normally a
1445 brightness value of 0 indicates backlight switched off,
1446 and the maximum of the brightness value sets the backlight
1447 to maximum brightness. If this parameter is set to 0
1448 (default) and the machine requires it, or this parameter
1449 is set to 1, a brightness value of 0 sets the backlight
1450 to maximum brightness, and the maximum of the brightness
1451 value switches the backlight off.
1452 -1 -- never invert brightness
1453 0 -- machine default
1454 1 -- force brightness inversion
1456 icn= [HW,ISDN]
1457 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1459 ide-core.nodma= [HW] (E)IDE subsystem
1460 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1461 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1462 .cdrom .chs .ignore_cable are additional options
1463 See Documentation/ide/ide.txt.
1465 ide-generic.probe-mask= [HW] (E)IDE subsystem
1466 Format: <int>
1467 Probe mask for legacy ISA IDE ports. Depending on
1468 platform up to 6 ports are supported, enabled by
1469 setting corresponding bits in the mask to 1. The
1470 default value is 0x0, which has a special meaning.
1471 On systems that have PCI, it triggers scanning the
1472 PCI bus for the first and the second port, which
1473 are then probed. On systems without PCI the value
1474 of 0x0 enables probing the two first ports as if it
1475 was 0x3.
1477 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1478 Claim all unknown PCI IDE storage controllers.
1480 idle= [X86]
1481 Format: idle=poll, idle=halt, idle=nomwait
1482 Poll forces a polling idle loop that can slightly
1483 improve the performance of waking up a idle CPU, but
1484 will use a lot of power and make the system run hot.
1485 Not recommended.
1486 idle=halt: Halt is forced to be used for CPU idle.
1487 In such case C2/C3 won't be used again.
1488 idle=nomwait: Disable mwait for CPU C-states
1490 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1491 Format: { strict | legacy | 2008 | relaxed }
1492 Default: strict
1494 Choose which programs will be accepted for execution
1495 based on the IEEE 754 NaN encoding(s) supported by
1496 the FPU and the NaN encoding requested with the value
1497 of an ELF file header flag individually set by each
1498 binary. Hardware implementations are permitted to
1499 support either or both of the legacy and the 2008 NaN
1500 encoding mode.
1502 Available settings are as follows:
1503 strict accept binaries that request a NaN encoding
1504 supported by the FPU
1505 legacy only accept legacy-NaN binaries, if supported
1506 by the FPU
1507 2008 only accept 2008-NaN binaries, if supported
1508 by the FPU
1509 relaxed accept any binaries regardless of whether
1510 supported by the FPU
1512 The FPU emulator is always able to support both NaN
1513 encodings, so if no FPU hardware is present or it has
1514 been disabled with 'nofpu', then the settings of
1515 'legacy' and '2008' strap the emulator accordingly,
1516 'relaxed' straps the emulator for both legacy-NaN and
1517 2008-NaN, whereas 'strict' enables legacy-NaN only on
1518 legacy processors and both NaN encodings on MIPS32 or
1519 MIPS64 CPUs.
1521 The setting for ABS.fmt/NEG.fmt instruction execution
1522 mode generally follows that for the NaN encoding,
1523 except where unsupported by hardware.
1525 ignore_loglevel [KNL]
1526 Ignore loglevel setting - this will print /all/
1527 kernel messages to the console. Useful for debugging.
1528 We also add it as printk module parameter, so users
1529 could change it dynamically, usually by
1530 /sys/module/printk/parameters/ignore_loglevel.
1532 ignore_rlimit_data
1533 Ignore RLIMIT_DATA setting for data mappings,
1534 print warning at first misuse. Can be changed via
1535 /sys/module/kernel/parameters/ignore_rlimit_data.
1537 ihash_entries= [KNL]
1538 Set number of hash buckets for inode cache.
1540 ima_appraise= [IMA] appraise integrity measurements
1541 Format: { "off" | "enforce" | "fix" | "log" }
1542 default: "enforce"
1544 ima_appraise_tcb [IMA]
1545 The builtin appraise policy appraises all files
1546 owned by uid=0.
1548 ima_canonical_fmt [IMA]
1549 Use the canonical format for the binary runtime
1550 measurements, instead of host native format.
1552 ima_hash= [IMA]
1553 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1554 | sha512 | ... }
1555 default: "sha1"
1557 The list of supported hash algorithms is defined
1558 in crypto/hash_info.h.
1560 ima_policy= [IMA]
1561 The builtin policies to load during IMA setup.
1562 Format: "tcb | appraise_tcb | secure_boot |
1563 fail_securely"
1565 The "tcb" policy measures all programs exec'd, files
1566 mmap'd for exec, and all files opened with the read
1567 mode bit set by either the effective uid (euid=0) or
1568 uid=0.
1570 The "appraise_tcb" policy appraises the integrity of
1571 all files owned by root. (This is the equivalent
1572 of ima_appraise_tcb.)
1574 The "secure_boot" policy appraises the integrity
1575 of files (eg. kexec kernel image, kernel modules,
1576 firmware, policy, etc) based on file signatures.
1578 The "fail_securely" policy forces file signature
1579 verification failure also on privileged mounted
1580 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1581 flag.
1583 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1584 Load a policy which meets the needs of the Trusted
1585 Computing Base. This means IMA will measure all
1586 programs exec'd, files mmap'd for exec, and all files
1587 opened for read by uid=0.
1589 ima_template= [IMA]
1590 Select one of defined IMA measurements template formats.
1591 Formats: { "ima" | "ima-ng" | "ima-sig" }
1592 Default: "ima-ng"
1594 ima_template_fmt=
1595 [IMA] Define a custom template format.
1596 Format: { "field1|...|fieldN" }
1598 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1599 Format: <min_file_size>
1600 Set the minimal file size for using asynchronous hash.
1601 If left unspecified, ahash usage is disabled.
1603 ahash performance varies for different data sizes on
1604 different crypto accelerators. This option can be used
1605 to achieve the best performance for a particular HW.
1607 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1608 Format: <bufsize>
1609 Set hashing buffer size. Default: 4k.
1611 ahash performance varies for different chunk sizes on
1612 different crypto accelerators. This option can be used
1613 to achieve best performance for particular HW.
1615 init= [KNL]
1616 Format: <full_path>
1617 Run specified binary instead of /sbin/init as init
1618 process.
1620 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1621 for working out where the kernel is dying during
1622 startup.
1624 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1625 initcall functions. Useful for debugging built-in
1626 modules and initcalls.
1628 initrd= [BOOT] Specify the location of the initial ramdisk
1630 init_pkru= [x86] Specify the default memory protection keys rights
1631 register contents for all processes. 0x55555554 by
1632 default (disallow access to all but pkey 0). Can
1633 override in debugfs after boot.
1635 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1636 Format: <irq>
1638 int_pln_enable [x86] Enable power limit notification interrupt
1640 integrity_audit=[IMA]
1641 Format: { "0" | "1" }
1642 0 -- basic integrity auditing messages. (Default)
1643 1 -- additional integrity auditing messages.
1645 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1646 on
1647 Enable intel iommu driver.
1648 off
1649 Disable intel iommu driver.
1650 igfx_off [Default Off]
1651 By default, gfx is mapped as normal device. If a gfx
1652 device has a dedicated DMAR unit, the DMAR unit is
1653 bypassed by not enabling DMAR with this option. In
1654 this case, gfx device will use physical address for
1655 DMA.
1656 forcedac [x86_64]
1657 With this option iommu will not optimize to look
1658 for io virtual address below 32-bit forcing dual
1659 address cycle on pci bus for cards supporting greater
1660 than 32-bit addressing. The default is to look
1661 for translation below 32-bit and if not available
1662 then look in the higher range.
1663 strict [Default Off]
1664 With this option on every unmap_single operation will
1665 result in a hardware IOTLB flush operation as opposed
1666 to batching them for performance.
1667 sp_off [Default Off]
1668 By default, super page will be supported if Intel IOMMU
1669 has the capability. With this option, super page will
1670 not be supported.
1671 ecs_off [Default Off]
1672 By default, extended context tables will be supported if
1673 the hardware advertises that it has support both for the
1674 extended tables themselves, and also PASID support. With
1675 this option set, extended tables will not be used even
1676 on hardware which claims to support them.
1677 tboot_noforce [Default Off]
1678 Do not force the Intel IOMMU enabled under tboot.
1679 By default, tboot will force Intel IOMMU on, which
1680 could harm performance of some high-throughput
1681 devices like 40GBit network cards, even if identity
1682 mapping is enabled.
1683 Note that using this option lowers the security
1684 provided by tboot because it makes the system
1685 vulnerable to DMA attacks.
1687 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1688 0 disables intel_idle and fall back on acpi_idle.
1689 1 to 9 specify maximum depth of C-state.
1691 intel_pstate= [X86]
1692 disable
1693 Do not enable intel_pstate as the default
1694 scaling driver for the supported processors
1695 passive
1696 Use intel_pstate as a scaling driver, but configure it
1697 to work with generic cpufreq governors (instead of
1698 enabling its internal governor). This mode cannot be
1699 used along with the hardware-managed P-states (HWP)
1700 feature.
1701 force
1702 Enable intel_pstate on systems that prohibit it by default
1703 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1704 instead of acpi-cpufreq may disable platform features, such
1705 as thermal controls and power capping, that rely on ACPI
1706 P-States information being indicated to OSPM and therefore
1707 should be used with caution. This option does not work with
1708 processors that aren't supported by the intel_pstate driver
1709 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1710 no_hwp
1711 Do not enable hardware P state control (HWP)
1712 if available.
1713 hwp_only
1714 Only load intel_pstate on systems which support
1715 hardware P state control (HWP) if available.
1716 support_acpi_ppc
1717 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1718 Description Table, specifies preferred power management
1719 profile as "Enterprise Server" or "Performance Server",
1720 then this feature is turned on by default.
1721 per_cpu_perf_limits
1722 Allow per-logical-CPU P-State performance control limits using
1723 cpufreq sysfs interface
1725 intremap= [X86-64, Intel-IOMMU]
1726 on enable Interrupt Remapping (default)
1727 off disable Interrupt Remapping
1728 nosid disable Source ID checking
1729 no_x2apic_optout
1730 BIOS x2APIC opt-out request will be ignored
1731 nopost disable Interrupt Posting
1733 iomem= Disable strict checking of access to MMIO memory
1734 strict regions from userspace.
1735 relaxed
1737 iommu= [x86]
1738 off
1739 force
1740 noforce
1741 biomerge
1742 panic
1743 nopanic
1744 merge
1745 nomerge
1746 soft
1747 pt [x86]
1748 nopt [x86]
1749 nobypass [PPC/POWERNV]
1750 Disable IOMMU bypass, using IOMMU for PCI devices.
1752 iommu.passthrough=
1753 [ARM64] Configure DMA to bypass the IOMMU by default.
1754 Format: { "0" | "1" }
1755 0 - Use IOMMU translation for DMA.
1756 1 - Bypass the IOMMU for DMA.
1757 unset - Use IOMMU translation for DMA.
1759 io7= [HW] IO7 for Marvel based alpha systems
1760 See comment before marvel_specify_io7 in
1761 arch/alpha/kernel/core_marvel.c.
1763 io_delay= [X86] I/O delay method
1764 0x80
1765 Standard port 0x80 based delay
1766 0xed
1767 Alternate port 0xed based delay (needed on some systems)
1768 udelay
1769 Simple two microseconds delay
1770 none
1771 No delay
1773 ip= [IP_PNP]
1774 See Documentation/filesystems/nfs/nfsroot.txt.
1776 irqaffinity= [SMP] Set the default irq affinity mask
1777 The argument is a cpu list, as described above.
1779 irqchip.gicv2_force_probe=
1780 [ARM, ARM64]
1781 Format: <bool>
1782 Force the kernel to look for the second 4kB page
1783 of a GICv2 controller even if the memory range
1784 exposed by the device tree is too small.
1786 irqchip.gicv3_nolpi=
1787 [ARM, ARM64]
1788 Force the kernel to ignore the availability of
1789 LPIs (and by consequence ITSs). Intended for system
1790 that use the kernel as a bootloader, and thus want
1791 to let secondary kernels in charge of setting up
1792 LPIs.
1794 irqfixup [HW]
1795 When an interrupt is not handled search all handlers
1796 for it. Intended to get systems with badly broken
1797 firmware running.
1799 irqpoll [HW]
1800 When an interrupt is not handled search all handlers
1801 for it. Also check all handlers each timer
1802 interrupt. Intended to get systems with badly broken
1803 firmware running.
1805 isapnp= [ISAPNP]
1806 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1808 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1809 [Deprecated - use cpusets instead]
1810 Format: [flag-list,]<cpu-list>
1812 Specify one or more CPUs to isolate from disturbances
1813 specified in the flag list (default: domain):
1815 nohz
1816 Disable the tick when a single task runs.
1818 A residual 1Hz tick is offloaded to workqueues, which you
1819 need to affine to housekeeping through the global
1820 workqueue's affinity configured via the
1821 /sys/devices/virtual/workqueue/cpumask sysfs file, or
1822 by using the 'domain' flag described below.
1824 NOTE: by default the global workqueue runs on all CPUs,
1825 so to protect individual CPUs the 'cpumask' file has to
1826 be configured manually after bootup.
1828 domain
1829 Isolate from the general SMP balancing and scheduling
1830 algorithms. Note that performing domain isolation this way
1831 is irreversible: it's not possible to bring back a CPU to
1832 the domains once isolated through isolcpus. It's strongly
1833 advised to use cpusets instead to disable scheduler load
1834 balancing through the "cpuset.sched_load_balance" file.
1835 It offers a much more flexible interface where CPUs can
1836 move in and out of an isolated set anytime.
1838 You can move a process onto or off an "isolated" CPU via
1839 the CPU affinity syscalls or cpuset.
1840 <cpu number> begins at 0 and the maximum value is
1841 "number of CPUs in system - 1".
1843 The format of <cpu-list> is described above.
1847 iucv= [HW,NET]
1849 ivrs_ioapic [HW,X86_64]
1850 Provide an override to the IOAPIC-ID<->DEVICE-ID
1851 mapping provided in the IVRS ACPI table. For
1852 example, to map IOAPIC-ID decimal 10 to
1853 PCI device 00:14.0 write the parameter as:
1854 ivrs_ioapic[10]=00:14.0
1856 ivrs_hpet [HW,X86_64]
1857 Provide an override to the HPET-ID<->DEVICE-ID
1858 mapping provided in the IVRS ACPI table. For
1859 example, to map HPET-ID decimal 0 to
1860 PCI device 00:14.0 write the parameter as:
1861 ivrs_hpet[0]=00:14.0
1863 ivrs_acpihid [HW,X86_64]
1864 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1865 mapping provided in the IVRS ACPI table. For
1866 example, to map UART-HID:UID AMD0020:0 to
1867 PCI device 00:14.5 write the parameter as:
1868 ivrs_acpihid[00:14.5]=AMD0020:0
1870 js= [HW,JOY] Analog joystick
1871 See Documentation/input/joydev/joystick.rst.
1873 nokaslr [KNL]
1874 When CONFIG_RANDOMIZE_BASE is set, this disables
1875 kernel and module base offset ASLR (Address Space
1876 Layout Randomization).
1878 kasan_multi_shot
1879 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1880 report on every invalid memory access. Without this
1881 parameter KASAN will print report only for the first
1882 invalid access.
1884 keepinitrd [HW,ARM]
1886 kernelcore= [KNL,X86,IA-64,PPC]
1887 Format: nn[KMGTPE] | nn% | "mirror"
1888 This parameter specifies the amount of memory usable by
1889 the kernel for non-movable allocations. The requested
1890 amount is spread evenly throughout all nodes in the
1891 system as ZONE_NORMAL. The remaining memory is used for
1892 movable memory in its own zone, ZONE_MOVABLE. In the
1893 event, a node is too small to have both ZONE_NORMAL and
1894 ZONE_MOVABLE, kernelcore memory will take priority and
1895 other nodes will have a larger ZONE_MOVABLE.
1897 ZONE_MOVABLE is used for the allocation of pages that
1898 may be reclaimed or moved by the page migration
1899 subsystem. Note that allocations like PTEs-from-HighMem
1900 still use the HighMem zone if it exists, and the Normal
1901 zone if it does not.
1903 It is possible to specify the exact amount of memory in
1904 the form of "nn[KMGTPE]", a percentage of total system
1905 memory in the form of "nn%", or "mirror". If "mirror"
1906 option is specified, mirrored (reliable) memory is used
1907 for non-movable allocations and remaining memory is used
1908 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
1909 are exclusive, so you cannot specify multiple forms.
1911 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1912 Format: <Controller#>[,poll interval]
1913 The controller # is the number of the ehci usb debug
1914 port as it is probed via PCI. The poll interval is
1915 optional and is the number seconds in between
1916 each poll cycle to the debug port in case you need
1917 the functionality for interrupting the kernel with
1918 gdb or control-c on the dbgp connection. When
1919 not using this parameter you use sysrq-g to break into
1920 the kernel debugger.
1922 kgdboc= [KGDB,HW] kgdb over consoles.
1923 Requires a tty driver that supports console polling,
1924 or a supported polling keyboard driver (non-usb).
1925 Serial only format: <serial_device>[,baud]
1926 keyboard only format: kbd
1927 keyboard and serial format: kbd,<serial_device>[,baud]
1928 Optional Kernel mode setting:
1929 kms, kbd format: kms,kbd
1930 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1932 kgdbwait [KGDB] Stop kernel execution and enter the
1933 kernel debugger at the earliest opportunity.
1935 kmac= [MIPS] korina ethernet MAC address.
1936 Configure the RouterBoard 532 series on-chip
1937 Ethernet adapter MAC address.
1939 kmemleak= [KNL] Boot-time kmemleak enable/disable
1940 Valid arguments: on, off
1941 Default: on
1942 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1943 the default is off.
1945 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1946 Default is 0 (don't ignore, but inject #GP)
1948 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
1949 Default is false (don't support).
1951 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1952 KVM MMU at runtime.
1953 Default is 0 (off)
1955 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1956 Default is 1 (enabled)
1958 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1959 for all guests.
1960 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1962 kvm-arm.vgic_v3_group0_trap=
1963 [KVM,ARM] Trap guest accesses to GICv3 group-0
1964 system registers
1966 kvm-arm.vgic_v3_group1_trap=
1967 [KVM,ARM] Trap guest accesses to GICv3 group-1
1968 system registers
1970 kvm-arm.vgic_v3_common_trap=
1971 [KVM,ARM] Trap guest accesses to GICv3 common
1972 system registers
1974 kvm-arm.vgic_v4_enable=
1975 [KVM,ARM] Allow use of GICv4 for direct injection of
1976 LPIs.
1978 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1979 (virtualized MMU) support on capable Intel chips.
1980 Default is 1 (enabled)
1982 kvm-intel.emulate_invalid_guest_state=
1983 [KVM,Intel] Enable emulation of invalid guest states
1984 Default is 0 (disabled)
1986 kvm-intel.flexpriority=
1987 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1988 Default is 1 (enabled)
1990 kvm-intel.nested=
1991 [KVM,Intel] Enable VMX nesting (nVMX).
1992 Default is 0 (disabled)
1994 kvm-intel.unrestricted_guest=
1995 [KVM,Intel] Disable unrestricted guest feature
1996 (virtualized real and unpaged mode) on capable
1997 Intel chips. Default is 1 (enabled)
1999 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2000 CVE-2018-3620.
2002 Valid arguments: never, cond, always
2004 always: L1D cache flush on every VMENTER.
2005 cond: Flush L1D on VMENTER only when the code between
2006 VMEXIT and VMENTER can leak host memory.
2007 never: Disables the mitigation
2009 Default is cond (do L1 cache flush in specific instances)
2011 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2012 feature (tagged TLBs) on capable Intel chips.
2013 Default is 1 (enabled)
2015 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2016 affected CPUs
2018 The kernel PTE inversion protection is unconditionally
2019 enabled and cannot be disabled.
2021 full
2022 Provides all available mitigations for the
2023 L1TF vulnerability. Disables SMT and
2024 enables all mitigations in the
2025 hypervisors, i.e. unconditional L1D flush.
2027 SMT control and L1D flush control via the
2028 sysfs interface is still possible after
2029 boot. Hypervisors will issue a warning
2030 when the first VM is started in a
2031 potentially insecure configuration,
2032 i.e. SMT enabled or L1D flush disabled.
2034 full,force
2035 Same as 'full', but disables SMT and L1D
2036 flush runtime control. Implies the
2037 'nosmt=force' command line option.
2038 (i.e. sysfs control of SMT is disabled.)
2040 flush
2041 Leaves SMT enabled and enables the default
2042 hypervisor mitigation, i.e. conditional
2043 L1D flush.
2045 SMT control and L1D flush control via the
2046 sysfs interface is still possible after
2047 boot. Hypervisors will issue a warning
2048 when the first VM is started in a
2049 potentially insecure configuration,
2050 i.e. SMT enabled or L1D flush disabled.
2052 flush,nosmt
2054 Disables SMT and enables the default
2055 hypervisor mitigation.
2057 SMT control and L1D flush control via the
2058 sysfs interface is still possible after
2059 boot. Hypervisors will issue a warning
2060 when the first VM is started in a
2061 potentially insecure configuration,
2062 i.e. SMT enabled or L1D flush disabled.
2064 flush,nowarn
2065 Same as 'flush', but hypervisors will not
2066 warn when a VM is started in a potentially
2067 insecure configuration.
2069 off
2070 Disables hypervisor mitigations and doesn't
2071 emit any warnings.
2073 Default is 'flush'.
2075 For details see: Documentation/admin-guide/l1tf.rst
2077 l2cr= [PPC]
2079 l3cr= [PPC]
2081 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2082 disabled it.
2084 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2085 value for LAPIC timer one-shot implementation. Default
2086 back to the programmable timer unit in the LAPIC.
2088 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2089 in C2 power state.
2091 libata.dma= [LIBATA] DMA control
2092 libata.dma=0 Disable all PATA and SATA DMA
2093 libata.dma=1 PATA and SATA Disk DMA only
2094 libata.dma=2 ATAPI (CDROM) DMA only
2095 libata.dma=4 Compact Flash DMA only
2096 Combinations also work, so libata.dma=3 enables DMA
2097 for disks and CDROMs, but not CFs.
2099 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2100 libata.ignore_hpa=0 keep BIOS limits (default)
2101 libata.ignore_hpa=1 ignore limits, using full disk
2103 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2104 when set.
2105 Format: <int>
2107 libata.force= [LIBATA] Force configurations. The format is comma
2108 separated list of "[ID:]VAL" where ID is
2109 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2110 matching port, link or device. Basically, it matches
2111 the ATA ID string printed on console by libata. If
2112 the whole ID part is omitted, the last PORT and DEVICE
2113 values are used. If ID hasn't been specified yet, the
2114 configuration applies to all ports, links and devices.
2116 If only DEVICE is omitted, the parameter applies to
2117 the port and all links and devices behind it. DEVICE
2118 number of 0 either selects the first device or the
2119 first fan-out link behind PMP device. It does not
2120 select the host link. DEVICE number of 15 selects the
2121 host link and device attached to it.
2123 The VAL specifies the configuration to force. As long
2124 as there's no ambiguity shortcut notation is allowed.
2125 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2126 The following configurations can be forced.
2128 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2129 Any ID with matching PORT is used.
2131 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2133 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2134 udma[/][16,25,33,44,66,100,133] notation is also
2135 allowed.
2137 * [no]ncq: Turn on or off NCQ.
2139 * [no]ncqtrim: Turn off queued DSM TRIM.
2141 * nohrst, nosrst, norst: suppress hard, soft
2142 and both resets.
2144 * rstonce: only attempt one reset during
2145 hot-unplug link recovery
2147 * dump_id: dump IDENTIFY data.
2149 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2151 * disable: Disable this device.
2153 If there are multiple matching configurations changing
2154 the same attribute, the last one is used.
2156 memblock=debug [KNL] Enable memblock debug messages.
2158 load_ramdisk= [RAM] List of ramdisks to load from floppy
2159 See Documentation/blockdev/ramdisk.txt.
2161 lockd.nlm_grace_period=P [NFS] Assign grace period.
2162 Format: <integer>
2164 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2165 Format: <integer>
2167 lockd.nlm_timeout=T [NFS] Assign timeout value.
2168 Format: <integer>
2170 lockd.nlm_udpport=M [NFS] Assign UDP port.
2171 Format: <integer>
2173 locktorture.nreaders_stress= [KNL]
2174 Set the number of locking read-acquisition kthreads.
2175 Defaults to being automatically set based on the
2176 number of online CPUs.
2178 locktorture.nwriters_stress= [KNL]
2179 Set the number of locking write-acquisition kthreads.
2181 locktorture.onoff_holdoff= [KNL]
2182 Set time (s) after boot for CPU-hotplug testing.
2184 locktorture.onoff_interval= [KNL]
2185 Set time (s) between CPU-hotplug operations, or
2186 zero to disable CPU-hotplug testing.
2188 locktorture.shuffle_interval= [KNL]
2189 Set task-shuffle interval (jiffies). Shuffling
2190 tasks allows some CPUs to go into dyntick-idle
2191 mode during the locktorture test.
2193 locktorture.shutdown_secs= [KNL]
2194 Set time (s) after boot system shutdown. This
2195 is useful for hands-off automated testing.
2197 locktorture.stat_interval= [KNL]
2198 Time (s) between statistics printk()s.
2200 locktorture.stutter= [KNL]
2201 Time (s) to stutter testing, for example,
2202 specifying five seconds causes the test to run for
2203 five seconds, wait for five seconds, and so on.
2204 This tests the locking primitive's ability to
2205 transition abruptly to and from idle.
2207 locktorture.torture_type= [KNL]
2208 Specify the locking implementation to test.
2210 locktorture.verbose= [KNL]
2211 Enable additional printk() statements.
2213 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2214 Format: <irq>
2216 loglevel= All Kernel Messages with a loglevel smaller than the
2217 console loglevel will be printed to the console. It can
2218 also be changed with klogd or other programs. The
2219 loglevels are defined as follows:
2221 0 (KERN_EMERG) system is unusable
2222 1 (KERN_ALERT) action must be taken immediately
2223 2 (KERN_CRIT) critical conditions
2224 3 (KERN_ERR) error conditions
2225 4 (KERN_WARNING) warning conditions
2226 5 (KERN_NOTICE) normal but significant condition
2227 6 (KERN_INFO) informational
2228 7 (KERN_DEBUG) debug-level messages
2230 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2231 in bytes. n must be a power of two and greater
2232 than the minimal size. The minimal size is defined
2233 by LOG_BUF_SHIFT kernel config parameter. There is
2234 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2235 that allows to increase the default size depending on
2236 the number of CPUs. See init/Kconfig for more details.
2238 logo.nologo [FB] Disables display of the built-in Linux logo.
2239 This may be used to provide more screen space for
2240 kernel log messages and is useful when debugging
2241 kernel boot problems.
2243 lp=0 [LP] Specify parallel ports to use, e.g,
2244 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2245 lp=reset first parallel port). 'lp=0' disables the
2246 lp=auto printer driver. 'lp=reset' (which can be
2247 specified in addition to the ports) causes
2248 attached printers to be reset. Using
2249 lp=port1,port2,... specifies the parallel ports
2250 to associate lp devices with, starting with
2251 lp0. A port specification may be 'none' to skip
2252 that lp device, or a parport name such as
2253 'parport0'. Specifying 'lp=auto' instead of a
2254 port specification list means that device IDs
2255 from each port should be examined, to see if
2256 an IEEE 1284-compliant printer is attached; if
2257 so, the driver will manage that printer.
2258 See also header of drivers/char/lp.c.
2260 lpj=n [KNL]
2261 Sets loops_per_jiffy to given constant, thus avoiding
2262 time-consuming boot-time autodetection (up to 250 ms per
2263 CPU). 0 enables autodetection (default). To determine
2264 the correct value for your kernel, boot with normal
2265 autodetection and see what value is printed. Note that
2266 on SMP systems the preset will be applied to all CPUs,
2267 which is likely to cause problems if your CPUs need
2268 significantly divergent settings. An incorrect value
2269 will cause delays in the kernel to be wrong, leading to
2270 unpredictable I/O errors and other breakage. Although
2271 unlikely, in the extreme case this might damage your
2272 hardware.
2274 ltpc= [NET]
2275 Format: <io>,<irq>,<dma>
2277 machvec= [IA-64] Force the use of a particular machine-vector
2278 (machvec) in a generic kernel.
2279 Example: machvec=hpzx1_swiotlb
2281 machtype= [Loongson] Share the same kernel image file between different
2282 yeeloong laptop.
2283 Example: machtype=lemote-yeeloong-2f-7inch
2285 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2286 than or equal to this physical address is ignored.
2288 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2289 will bring up during bootup. maxcpus=n : n >= 0 limits
2290 the kernel to bring up 'n' processors. Surely after
2291 bootup you can bring up the other plugged cpu by executing
2292 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2293 only takes effect during system bootup.
2294 While n=0 is a special case, it is equivalent to "nosmp",
2295 which also disables the IO APIC.
2297 max_loop= [LOOP] The number of loop block devices that get
2298 (loop.max_loop) unconditionally pre-created at init time. The default
2299 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2300 of statically allocating a predefined number, loop
2301 devices can be requested on-demand with the
2302 /dev/loop-control interface.
2304 mce [X86-32] Machine Check Exception
2306 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2308 md= [HW] RAID subsystems devices and level
2309 See Documentation/admin-guide/md.rst.
2311 mdacon= [MDA]
2312 Format: <first>,<last>
2313 Specifies range of consoles to be captured by the MDA.
2315 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2316 Amount of memory to be used when the kernel is not able
2317 to see the whole system memory or for test.
2318 [X86] Work as limiting max address. Use together
2319 with memmap= to avoid physical address space collisions.
2320 Without memmap= PCI devices could be placed at addresses
2321 belonging to unused RAM.
2323 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2324 memory.
2326 memchunk=nn[KMG]
2327 [KNL,SH] Allow user to override the default size for
2328 per-device physically contiguous DMA buffers.
2330 memhp_default_state=online/offline
2331 [KNL] Set the initial state for the memory hotplug
2332 onlining policy. If not specified, the default value is
2333 set according to the
2334 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2335 option.
2336 See Documentation/memory-hotplug.txt.
2338 memmap=exactmap [KNL,X86] Enable setting of an exact
2339 E820 memory map, as specified by the user.
2340 Such memmap=exactmap lines can be constructed based on
2341 BIOS output or other requirements. See the memmap=nn@ss
2342 option description.
2344 memmap=nn[KMG]@ss[KMG]
2345 [KNL] Force usage of a specific region of memory.
2346 Region of memory to be used is from ss to ss+nn.
2347 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2348 which limits max address to nn[KMG].
2349 Multiple different regions can be specified,
2350 comma delimited.
2351 Example:
2352 memmap=100M@2G,100M#3G,1G!1024G
2354 memmap=nn[KMG]#ss[KMG]
2355 [KNL,ACPI] Mark specific memory as ACPI data.
2356 Region of memory to be marked is from ss to ss+nn.
2358 memmap=nn[KMG]$ss[KMG]
2359 [KNL,ACPI] Mark specific memory as reserved.
2360 Region of memory to be reserved is from ss to ss+nn.
2361 Example: Exclude memory from 0x18690000-0x1869ffff
2362 memmap=64K$0x18690000
2363 or
2364 memmap=0x10000$0x18690000
2365 Some bootloaders may need an escape character before '$',
2366 like Grub2, otherwise '$' and the following number
2367 will be eaten.
2369 memmap=nn[KMG]!ss[KMG]
2370 [KNL,X86] Mark specific memory as protected.
2371 Region of memory to be used, from ss to ss+nn.
2372 The memory region may be marked as e820 type 12 (0xc)
2373 and is NVDIMM or ADR memory.
2375 memmap=<size>%<offset>-<oldtype>+<newtype>
2376 [KNL,ACPI] Convert memory within the specified region
2377 from <oldtype> to <newtype>. If "-<oldtype>" is left
2378 out, the whole region will be marked as <newtype>,
2379 even if previously unavailable. If "+<newtype>" is left
2380 out, matching memory will be removed. Types are
2381 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2382 3 = ACPI, 12 = PRAM.
2384 memory_corruption_check=0/1 [X86]
2385 Some BIOSes seem to corrupt the first 64k of
2386 memory when doing things like suspend/resume.
2387 Setting this option will scan the memory
2388 looking for corruption. Enabling this will
2389 both detect corruption and prevent the kernel
2390 from using the memory being corrupted.
2391 However, its intended as a diagnostic tool; if
2392 repeatable BIOS-originated corruption always
2393 affects the same memory, you can use memmap=
2394 to prevent the kernel from using that memory.
2396 memory_corruption_check_size=size [X86]
2397 By default it checks for corruption in the low
2398 64k, making this memory unavailable for normal
2399 use. Use this parameter to scan for
2400 corruption in more or less memory.
2402 memory_corruption_check_period=seconds [X86]
2403 By default it checks for corruption every 60
2404 seconds. Use this parameter to check at some
2405 other rate. 0 disables periodic checking.
2407 memtest= [KNL,X86,ARM] Enable memtest
2408 Format: <integer>
2409 default : 0 <disable>
2410 Specifies the number of memtest passes to be
2411 performed. Each pass selects another test
2412 pattern from a given set of patterns. Memtest
2413 fills the memory with this pattern, validates
2414 memory contents and reserves bad memory
2415 regions that are detected.
2417 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2418 Valid arguments: on, off
2419 Default (depends on kernel configuration option):
2420 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2421 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2422 mem_encrypt=on: Activate SME
2423 mem_encrypt=off: Do not activate SME
2425 Refer to Documentation/x86/amd-memory-encryption.txt
2426 for details on when memory encryption can be activated.
2428 mem_sleep_default= [SUSPEND] Default system suspend mode:
2429 s2idle - Suspend-To-Idle
2430 shallow - Power-On Suspend or equivalent (if supported)
2431 deep - Suspend-To-RAM or equivalent (if supported)
2432 See Documentation/admin-guide/pm/sleep-states.rst.
2434 meye.*= [HW] Set MotionEye Camera parameters
2435 See Documentation/media/v4l-drivers/meye.rst.
2437 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2438 Multi-Function General Purpose Timers on AMD Geode
2439 platforms.
2441 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2442 the BIOS has incorrectly applied a workaround. TinyBIOS
2443 version 0.98 is known to be affected, 0.99 fixes the
2444 problem by letting the user disable the workaround.
2446 mga= [HW,DRM]
2448 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2449 physical address is ignored.
2451 mini2440= [ARM,HW,KNL]
2452 Format:[0..2][b][c][t]
2453 Default: "0tb"
2454 MINI2440 configuration specification:
2455 0 - The attached screen is the 3.5" TFT
2456 1 - The attached screen is the 7" TFT
2457 2 - The VGA Shield is attached (1024x768)
2458 Leaving out the screen size parameter will not load
2459 the TFT driver, and the framebuffer will be left
2460 unconfigured.
2461 b - Enable backlight. The TFT backlight pin will be
2462 linked to the kernel VESA blanking code and a GPIO
2463 LED. This parameter is not necessary when using the
2464 VGA shield.
2465 c - Enable the s3c camera interface.
2466 t - Reserved for enabling touchscreen support. The
2467 touchscreen support is not enabled in the mainstream
2468 kernel as of 2.6.30, a preliminary port can be found
2469 in the "bleeding edge" mini2440 support kernel at
2470 http://repo.or.cz/w/linux-2.6/mini2440.git
2472 mminit_loglevel=
2473 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2474 parameter allows control of the logging verbosity for
2475 the additional memory initialisation checks. A value
2476 of 0 disables mminit logging and a level of 4 will
2477 log everything. Information is printed at KERN_DEBUG
2478 so loglevel=8 may also need to be specified.
2480 module.sig_enforce
2481 [KNL] When CONFIG_MODULE_SIG is set, this means that
2482 modules without (valid) signatures will fail to load.
2483 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2484 is always true, so this option does nothing.
2486 module_blacklist= [KNL] Do not load a comma-separated list of
2487 modules. Useful for debugging problem modules.
2489 mousedev.tap_time=
2490 [MOUSE] Maximum time between finger touching and
2491 leaving touchpad surface for touch to be considered
2492 a tap and be reported as a left button click (for
2493 touchpads working in absolute mode only).
2494 Format: <msecs>
2495 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2496 reporting absolute coordinates, such as tablets
2497 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2498 reporting absolute coordinates, such as tablets
2500 movablecore= [KNL,X86,IA-64,PPC]
2501 Format: nn[KMGTPE] | nn%
2502 This parameter is the complement to kernelcore=, it
2503 specifies the amount of memory used for migratable
2504 allocations. If both kernelcore and movablecore is
2505 specified, then kernelcore will be at *least* the
2506 specified value but may be more. If movablecore on its
2507 own is specified, the administrator must be careful
2508 that the amount of memory usable for all allocations
2509 is not too small.
2511 movable_node [KNL] Boot-time switch to make hotplugable memory
2512 NUMA nodes to be movable. This means that the memory
2513 of such nodes will be usable only for movable
2514 allocations which rules out almost all kernel
2515 allocations. Use with caution!
2517 MTD_Partition= [MTD]
2518 Format: <name>,<region-number>,<size>,<offset>
2520 MTD_Region= [MTD] Format:
2521 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2523 mtdparts= [MTD]
2524 See drivers/mtd/cmdlinepart.c.
2526 multitce=off [PPC] This parameter disables the use of the pSeries
2527 firmware feature for updating multiple TCE entries
2528 at a time.
2530 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2532 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2534 boundary - index of last SLC block on Flex-OneNAND.
2535 The remaining blocks are configured as MLC blocks.
2536 lock - Configure if Flex-OneNAND boundary should be locked.
2537 Once locked, the boundary cannot be changed.
2538 1 indicates lock status, 0 indicates unlock status.
2540 mtdset= [ARM]
2541 ARM/S3C2412 JIVE boot control
2543 See arch/arm/mach-s3c2412/mach-jive.c
2545 mtouchusb.raw_coordinates=
2546 [HW] Make the MicroTouch USB driver use raw coordinates
2547 ('y', default) or cooked coordinates ('n')
2549 mtrr_chunk_size=nn[KMG] [X86]
2550 used for mtrr cleanup. It is largest continuous chunk
2551 that could hold holes aka. UC entries.
2553 mtrr_gran_size=nn[KMG] [X86]
2554 Used for mtrr cleanup. It is granularity of mtrr block.
2555 Default is 1.
2556 Large value could prevent small alignment from
2557 using up MTRRs.
2559 mtrr_spare_reg_nr=n [X86]
2560 Format: <integer>
2561 Range: 0,7 : spare reg number
2562 Default : 1
2563 Used for mtrr cleanup. It is spare mtrr entries number.
2564 Set to 2 or more if your graphical card needs more.
2566 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2568 netdev= [NET] Network devices parameters
2569 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2570 Note that mem_start is often overloaded to mean
2571 something different and driver-specific.
2572 This usage is only documented in each driver source
2573 file if at all.
2575 nf_conntrack.acct=
2576 [NETFILTER] Enable connection tracking flow accounting
2577 0 to disable accounting
2578 1 to enable accounting
2579 Default value is 0.
2581 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2582 See Documentation/filesystems/nfs/nfsroot.txt.
2584 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2585 See Documentation/filesystems/nfs/nfsroot.txt.
2587 nfsrootdebug [NFS] enable nfsroot debugging messages.
2588 See Documentation/filesystems/nfs/nfsroot.txt.
2590 nfs.callback_nr_threads=
2591 [NFSv4] set the total number of threads that the
2592 NFS client will assign to service NFSv4 callback
2593 requests.
2595 nfs.callback_tcpport=
2596 [NFS] set the TCP port on which the NFSv4 callback
2597 channel should listen.
2599 nfs.cache_getent=
2600 [NFS] sets the pathname to the program which is used
2601 to update the NFS client cache entries.
2603 nfs.cache_getent_timeout=
2604 [NFS] sets the timeout after which an attempt to
2605 update a cache entry is deemed to have failed.
2607 nfs.idmap_cache_timeout=
2608 [NFS] set the maximum lifetime for idmapper cache
2609 entries.
2611 nfs.enable_ino64=
2612 [NFS] enable 64-bit inode numbers.
2613 If zero, the NFS client will fake up a 32-bit inode
2614 number for the readdir() and stat() syscalls instead
2615 of returning the full 64-bit number.
2616 The default is to return 64-bit inode numbers.
2618 nfs.max_session_cb_slots=
2619 [NFSv4.1] Sets the maximum number of session
2620 slots the client will assign to the callback
2621 channel. This determines the maximum number of
2622 callbacks the client will process in parallel for
2623 a particular server.
2625 nfs.max_session_slots=
2626 [NFSv4.1] Sets the maximum number of session slots
2627 the client will attempt to negotiate with the server.
2628 This limits the number of simultaneous RPC requests
2629 that the client can send to the NFSv4.1 server.
2630 Note that there is little point in setting this
2631 value higher than the max_tcp_slot_table_limit.
2633 nfs.nfs4_disable_idmapping=
2634 [NFSv4] When set to the default of '1', this option
2635 ensures that both the RPC level authentication
2636 scheme and the NFS level operations agree to use
2637 numeric uids/gids if the mount is using the
2638 'sec=sys' security flavour. In effect it is
2639 disabling idmapping, which can make migration from
2640 legacy NFSv2/v3 systems to NFSv4 easier.
2641 Servers that do not support this mode of operation
2642 will be autodetected by the client, and it will fall
2643 back to using the idmapper.
2644 To turn off this behaviour, set the value to '0'.
2645 nfs.nfs4_unique_id=
2646 [NFS4] Specify an additional fixed unique ident-
2647 ification string that NFSv4 clients can insert into
2648 their nfs_client_id4 string. This is typically a
2649 UUID that is generated at system install time.
2651 nfs.send_implementation_id =
2652 [NFSv4.1] Send client implementation identification
2653 information in exchange_id requests.
2654 If zero, no implementation identification information
2655 will be sent.
2656 The default is to send the implementation identification
2657 information.
2659 nfs.recover_lost_locks =
2660 [NFSv4] Attempt to recover locks that were lost due
2661 to a lease timeout on the server. Please note that
2662 doing this risks data corruption, since there are
2663 no guarantees that the file will remain unchanged
2664 after the locks are lost.
2665 If you want to enable the kernel legacy behaviour of
2666 attempting to recover these locks, then set this
2667 parameter to '1'.
2668 The default parameter value of '0' causes the kernel
2669 not to attempt recovery of lost locks.
2671 nfs4.layoutstats_timer =
2672 [NFSv4.2] Change the rate at which the kernel sends
2673 layoutstats to the pNFS metadata server.
2675 Setting this to value to 0 causes the kernel to use
2676 whatever value is the default set by the layout
2677 driver. A non-zero value sets the minimum interval
2678 in seconds between layoutstats transmissions.
2680 nfsd.nfs4_disable_idmapping=
2681 [NFSv4] When set to the default of '1', the NFSv4
2682 server will return only numeric uids and gids to
2683 clients using auth_sys, and will accept numeric uids
2684 and gids from such clients. This is intended to ease
2685 migration from NFSv2/v3.
2687 nmi_debug= [KNL,SH] Specify one or more actions to take
2688 when a NMI is triggered.
2689 Format: [state][,regs][,debounce][,die]
2691 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2692 Format: [panic,][nopanic,][num]
2693 Valid num: 0 or 1
2694 0 - turn hardlockup detector in nmi_watchdog off
2695 1 - turn hardlockup detector in nmi_watchdog on
2696 When panic is specified, panic when an NMI watchdog
2697 timeout occurs (or 'nopanic' to override the opposite
2698 default). To disable both hard and soft lockup detectors,
2699 please see 'nowatchdog'.
2700 This is useful when you use a panic=... timeout and
2701 need the box quickly up again.
2703 These settings can be accessed at runtime via
2704 the nmi_watchdog and hardlockup_panic sysctls.
2706 netpoll.carrier_timeout=
2707 [NET] Specifies amount of time (in seconds) that
2708 netpoll should wait for a carrier. By default netpoll
2709 waits 4 seconds.
2711 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2712 emulation library even if a 387 maths coprocessor
2713 is present.
2715 no5lvl [X86-64] Disable 5-level paging mode. Forces
2716 kernel to use 4-level paging instead.
2718 no_console_suspend
2719 [HW] Never suspend the console
2720 Disable suspending of consoles during suspend and
2721 hibernate operations. Once disabled, debugging
2722 messages can reach various consoles while the rest
2723 of the system is being put to sleep (ie, while
2724 debugging driver suspend/resume hooks). This may
2725 not work reliably with all consoles, but is known
2726 to work with serial and VGA consoles.
2727 To facilitate more flexible debugging, we also add
2728 console_suspend, a printk module parameter to control
2729 it. Users could use console_suspend (usually
2730 /sys/module/printk/parameters/console_suspend) to
2731 turn on/off it dynamically.
2733 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2734 caches in the slab allocator. Saves per-node memory,
2735 but will impact performance.
2737 noalign [KNL,ARM]
2739 noaltinstr [S390] Disables alternative instructions patching
2740 (CPU alternatives feature).
2742 noapic [SMP,APIC] Tells the kernel to not make use of any
2743 IOAPICs that may be present in the system.
2745 noautogroup Disable scheduler automatic task group creation.
2747 nobats [PPC] Do not use BATs for mapping kernel lowmem
2748 on "Classic" PPC cores.
2750 nocache [ARM]
2752 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2754 nodelayacct [KNL] Disable per-task delay accounting
2756 nodsp [SH] Disable hardware DSP at boot time.
2758 noefi Disable EFI runtime services support.
2760 noexec [IA-64]
2762 noexec [X86]
2763 On X86-32 available only on PAE configured kernels.
2764 noexec=on: enable non-executable mappings (default)
2765 noexec=off: disable non-executable mappings
2767 nosmap [X86]
2768 Disable SMAP (Supervisor Mode Access Prevention)
2769 even if it is supported by processor.
2771 nosmep [X86]
2772 Disable SMEP (Supervisor Mode Execution Prevention)
2773 even if it is supported by processor.
2775 noexec32 [X86-64]
2776 This affects only 32-bit executables.
2777 noexec32=on: enable non-executable mappings (default)
2778 read doesn't imply executable mappings
2779 noexec32=off: disable non-executable mappings
2780 read implies executable mappings
2782 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2784 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2785 register save and restore. The kernel will only save
2786 legacy floating-point registers on task switch.
2788 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2790 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2791 Equivalent to smt=1.
2793 [KNL,x86] Disable symmetric multithreading (SMT).
2794 nosmt=force: Force disable SMT, cannot be undone
2795 via the sysfs control file.
2797 nospectre_v1 [PPC] Disable mitigations for Spectre Variant 1 (bounds
2798 check bypass). With this option data leaks are possible
2799 in the system.
2801 nospectre_v2 [X86] Disable all mitigations for the Spectre variant 2
2802 (indirect branch prediction) vulnerability. System may
2803 allow data leaks with this option, which is equivalent
2804 to spectre_v2=off.
2806 nospec_store_bypass_disable
2807 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
2809 noxsave [BUGS=X86] Disables x86 extended register state save
2810 and restore using xsave. The kernel will fallback to
2811 enabling legacy floating-point and sse state.
2813 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2814 register states. The kernel will fall back to use
2815 xsave to save the states. By using this parameter,
2816 performance of saving the states is degraded because
2817 xsave doesn't support modified optimization while
2818 xsaveopt supports it on xsaveopt enabled systems.
2820 noxsaves [X86] Disables xsaves and xrstors used in saving and
2821 restoring x86 extended register state in compacted
2822 form of xsave area. The kernel will fall back to use
2823 xsaveopt and xrstor to save and restore the states
2824 in standard form of xsave area. By using this
2825 parameter, xsave area per process might occupy more
2826 memory on xsaves enabled systems.
2828 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2829 wfi(ARM) instruction doesn't work correctly and not to
2830 use it. This is also useful when using JTAG debugger.
2832 no_file_caps Tells the kernel not to honor file capabilities. The
2833 only way then for a file to be executed with privilege
2834 is to be setuid root or executed by root.
2836 nohalt [IA-64] Tells the kernel not to use the power saving
2837 function PAL_HALT_LIGHT when idle. This increases
2838 power-consumption. On the positive side, it reduces
2839 interrupt wake-up latency, which may improve performance
2840 in certain environments such as networked servers or
2841 real-time systems.
2843 nohibernate [HIBERNATION] Disable hibernation and resume.
2845 nohz= [KNL] Boottime enable/disable dynamic ticks
2846 Valid arguments: on, off
2847 Default: on
2849 nohz_full= [KNL,BOOT,SMP,ISOL]
2850 The argument is a cpu list, as described above.
2851 In kernels built with CONFIG_NO_HZ_FULL=y, set
2852 the specified list of CPUs whose tick will be stopped
2853 whenever possible. The boot CPU will be forced outside
2854 the range to maintain the timekeeping. Any CPUs
2855 in this list will have their RCU callbacks offloaded,
2856 just as if they had also been called out in the
2857 rcu_nocbs= boot parameter.
2859 noiotrap [SH] Disables trapped I/O port accesses.
2861 noirqdebug [X86-32] Disables the code which attempts to detect and
2862 disable unhandled interrupt sources.
2864 no_timer_check [X86,APIC] Disables the code which tests for
2865 broken timer IRQ sources.
2867 noisapnp [ISAPNP] Disables ISA PnP code.
2869 noinitrd [RAM] Tells the kernel not to load any configured
2870 initial RAM disk.
2872 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2873 remapping.
2874 [Deprecated - use intremap=off]
2876 nointroute [IA-64]
2878 noinvpcid [X86] Disable the INVPCID cpu feature.
2880 nojitter [IA-64] Disables jitter checking for ITC timers.
2882 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2884 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2885 fault handling.
2887 no-vmw-sched-clock
2888 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2889 clock and use the default one.
2891 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2892 steal time is computed, but won't influence scheduler
2893 behaviour
2895 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2897 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2899 noltlbs [PPC] Do not use large page/tlb entries for kernel
2900 lowmem mapping on PPC40x and PPC8xx
2902 nomca [IA-64] Disable machine check abort handling
2904 nomce [X86-32] Disable Machine Check Exception
2906 nomfgpt [X86-32] Disable Multi-Function General Purpose
2907 Timer usage (for AMD Geode machines).
2909 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2910 shutdown the other cpus. Instead use the REBOOT_VECTOR
2911 irq.
2913 nomodule Disable module load
2915 nopat [X86] Disable PAT (page attribute table extension of
2916 pagetables) support.
2918 nopcid [X86-64] Disable the PCID cpu feature.
2920 norandmaps Don't use address space randomization. Equivalent to
2921 echo 0 > /proc/sys/kernel/randomize_va_space
2923 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2924 with UP alternatives
2926 nordrand [X86] Disable kernel use of the RDRAND and
2927 RDSEED instructions even if they are supported
2928 by the processor. RDRAND and RDSEED are still
2929 available to user space applications.
2931 noresume [SWSUSP] Disables resume and restores original swap
2932 space.
2934 no-scroll [VGA] Disables scrollback.
2935 This is required for the Braillex ib80-piezo Braille
2936 reader made by F.H. Papenmeier (Germany).
2938 nosbagart [IA-64]
2940 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2942 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2943 and disable the IO APIC. legacy for "maxcpus=0".
2945 nosoftlockup [KNL] Disable the soft-lockup detector.
2947 nosync [HW,M68K] Disables sync negotiation for all devices.
2949 nowatchdog [KNL] Disable both lockup detectors, i.e.
2950 soft-lockup and NMI watchdog (hard-lockup).
2952 nowb [ARM]
2954 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2956 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2957 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2958 Some features depend on CPU0. Known dependencies are:
2959 1. Resume from suspend/hibernate depends on CPU0.
2960 Suspend/hibernate will fail if CPU0 is offline and you
2961 need to online CPU0 before suspend/hibernate.
2962 2. PIC interrupts also depend on CPU0. CPU0 can't be
2963 removed if a PIC interrupt is detected.
2964 It's said poweroff/reboot may depend on CPU0 on some
2965 machines although I haven't seen such issues so far
2966 after CPU0 is offline on a few tested machines.
2967 If the dependencies are under your control, you can
2968 turn on cpu0_hotplug.
2970 nps_mtm_hs_ctr= [KNL,ARC]
2971 This parameter sets the maximum duration, in
2972 cycles, each HW thread of the CTOP can run
2973 without interruptions, before HW switches it.
2974 The actual maximum duration is 16 times this
2975 parameter's value.
2976 Format: integer between 1 and 255
2977 Default: 255
2979 nptcg= [IA-64] Override max number of concurrent global TLB
2980 purges which is reported from either PAL_VM_SUMMARY or
2981 SAL PALO.
2983 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2984 could support. nr_cpus=n : n >= 1 limits the kernel to
2985 support 'n' processors. It could be larger than the
2986 number of already plugged CPU during bootup, later in
2987 runtime you can physically add extra cpu until it reaches
2988 n. So during boot up some boot time memory for per-cpu
2989 variables need be pre-allocated for later physical cpu
2990 hot plugging.
2992 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2994 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2995 Allowed values are enable and disable
2997 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2998 'node', 'default' can be specified
2999 This can be set from sysctl after boot.
3000 See Documentation/sysctl/vm.txt for details.
3002 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3003 See Documentation/debugging-via-ohci1394.txt for more
3004 info.
3006 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3007 Rather than timing out after 20 ms if an EC
3008 command is not properly ACKed, override the length
3009 of the timeout. We have interrupts disabled while
3010 waiting for the ACK, so if this is set too high
3011 interrupts *may* be lost!
3013 omap_mux= [OMAP] Override bootloader pin multiplexing.
3014 Format: <mux_mode0.mode_name=value>...
3015 For example, to override I2C bus2:
3016 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3018 oprofile.timer= [HW]
3019 Use timer interrupt instead of performance counters
3021 oprofile.cpu_type= Force an oprofile cpu type
3022 This might be useful if you have an older oprofile
3023 userland or if you want common events.
3024 Format: { arch_perfmon }
3025 arch_perfmon: [X86] Force use of architectural
3026 perfmon on Intel CPUs instead of the
3027 CPU specific event set.
3028 timer: [X86] Force use of architectural NMI
3029 timer mode (see also oprofile.timer
3030 for generic hr timer mode)
3032 oops=panic Always panic on oopses. Default is to just kill the
3033 process, but there is a small probability of
3034 deadlocking the machine.
3035 This will also cause panics on machine check exceptions.
3036 Useful together with panic=30 to trigger a reboot.
3038 page_owner= [KNL] Boot-time page_owner enabling option.
3039 Storage of the information about who allocated
3040 each page is disabled in default. With this switch,
3041 we can turn it on.
3042 on: enable the feature
3044 page_poison= [KNL] Boot-time parameter changing the state of
3045 poisoning on the buddy allocator, available with
3046 CONFIG_PAGE_POISONING=y.
3047 off: turn off poisoning (default)
3048 on: turn on poisoning
3050 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3051 timeout > 0: seconds before rebooting
3052 timeout = 0: wait forever
3053 timeout < 0: reboot immediately
3054 Format: <timeout>
3056 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3057 on a WARN().
3059 crash_kexec_post_notifiers
3060 Run kdump after running panic-notifiers and dumping
3061 kmsg. This only for the users who doubt kdump always
3062 succeeds in any situation.
3063 Note that this also increases risks of kdump failure,
3064 because some panic notifiers can make the crashed
3065 kernel more unstable.
3067 parkbd.port= [HW] Parallel port number the keyboard adapter is
3068 connected to, default is 0.
3069 Format: <parport#>
3070 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3071 0 for XT, 1 for AT (default is AT).
3072 Format: <mode>
3074 parport= [HW,PPT] Specify parallel ports. 0 disables.
3075 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3076 Use 'auto' to force the driver to use any
3077 IRQ/DMA settings detected (the default is to
3078 ignore detected IRQ/DMA settings because of
3079 possible conflicts). You can specify the base
3080 address, IRQ, and DMA settings; IRQ and DMA
3081 should be numbers, or 'auto' (for using detected
3082 settings on that particular port), or 'nofifo'
3083 (to avoid using a FIFO even if it is detected).
3084 Parallel ports are assigned in the order they
3085 are specified on the command line, starting
3086 with parport0.
3088 parport_init_mode= [HW,PPT]
3089 Configure VIA parallel port to operate in
3090 a specific mode. This is necessary on Pegasos
3091 computer where firmware has no options for setting
3092 up parallel port mode and sets it to spp.
3093 Currently this function knows 686a and 8231 chips.
3094 Format: [spp|ps2|epp|ecp|ecpepp]
3096 pause_on_oops=
3097 Halt all CPUs after the first oops has been printed for
3098 the specified number of seconds. This is to be used if
3099 your oopses keep scrolling off the screen.
3101 pcbit= [HW,ISDN]
3103 pcd. [PARIDE]
3104 See header of drivers/block/paride/pcd.c.
3105 See also Documentation/blockdev/paride.txt.
3107 pci=option[,option...] [PCI] various PCI subsystem options.
3109 Some options herein operate on a specific device
3110 or a set of devices (<pci_dev>). These are
3111 specified in one of the following formats:
3113 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
3114 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
3116 Note: the first format specifies a PCI
3117 bus/device/function address which may change
3118 if new hardware is inserted, if motherboard
3119 firmware changes, or due to changes caused
3120 by other kernel parameters. If the
3121 domain is left unspecified, it is
3122 taken to be zero. Optionally, a path
3123 to a device through multiple device/function
3124 addresses can be specified after the base
3125 address (this is more robust against
3126 renumbering issues). The second format
3127 selects devices using IDs from the
3128 configuration space which may match multiple
3129 devices in the system.
3131 earlydump dump PCI config space before the kernel
3132 changes anything
3133 off [X86] don't probe for the PCI bus
3134 bios [X86-32] force use of PCI BIOS, don't access
3135 the hardware directly. Use this if your machine
3136 has a non-standard PCI host bridge.
3137 nobios [X86-32] disallow use of PCI BIOS, only direct
3138 hardware access methods are allowed. Use this
3139 if you experience crashes upon bootup and you
3140 suspect they are caused by the BIOS.
3141 conf1 [X86] Force use of PCI Configuration Access
3142 Mechanism 1 (config address in IO port 0xCF8,
3143 data in IO port 0xCFC, both 32-bit).
3144 conf2 [X86] Force use of PCI Configuration Access
3145 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3146 the function, IO port 0xCFA, also 8-bit, sets
3147 bus number. The config space is then accessed
3148 through ports 0xC000-0xCFFF).
3149 See http://wiki.osdev.org/PCI for more info
3150 on the configuration access mechanisms.
3151 noaer [PCIE] If the PCIEAER kernel config parameter is
3152 enabled, this kernel boot option can be used to
3153 disable the use of PCIE advanced error reporting.
3154 nodomains [PCI] Disable support for multiple PCI
3155 root domains (aka PCI segments, in ACPI-speak).
3156 nommconf [X86] Disable use of MMCONFIG for PCI
3157 Configuration
3158 check_enable_amd_mmconf [X86] check for and enable
3159 properly configured MMIO access to PCI
3160 config space on AMD family 10h CPU
3161 nomsi [MSI] If the PCI_MSI kernel config parameter is
3162 enabled, this kernel boot option can be used to
3163 disable the use of MSI interrupts system-wide.
3164 noioapicquirk [APIC] Disable all boot interrupt quirks.
3165 Safety option to keep boot IRQs enabled. This
3166 should never be necessary.
3167 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3168 primary IO-APIC for bridges that cannot disable
3169 boot IRQs. This fixes a source of spurious IRQs
3170 when the system masks IRQs.
3171 noioapicreroute [APIC] Disable workaround that uses the
3172 boot IRQ equivalent of an IRQ that connects to
3173 a chipset where boot IRQs cannot be disabled.
3174 The opposite of ioapicreroute.
3175 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3176 routing table. These calls are known to be buggy
3177 on several machines and they hang the machine
3178 when used, but on other computers it's the only
3179 way to get the interrupt routing table. Try
3180 this option if the kernel is unable to allocate
3181 IRQs or discover secondary PCI buses on your
3182 motherboard.
3183 rom [X86] Assign address space to expansion ROMs.
3184 Use with caution as certain devices share
3185 address decoders between ROMs and other
3186 resources.
3187 norom [X86] Do not assign address space to
3188 expansion ROMs that do not already have
3189 BIOS assigned address ranges.
3190 nobar [X86] Do not assign address space to the
3191 BARs that weren't assigned by the BIOS.
3192 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3193 assigned automatically to PCI devices. You can
3194 make the kernel exclude IRQs of your ISA cards
3195 this way.
3196 pirqaddr=0xAAAAA [X86] Specify the physical address
3197 of the PIRQ table (normally generated
3198 by the BIOS) if it is outside the
3199 F0000h-100000h range.
3200 lastbus=N [X86] Scan all buses thru bus #N. Can be
3201 useful if the kernel is unable to find your
3202 secondary buses and you want to tell it
3203 explicitly which ones they are.
3204 assign-busses [X86] Always assign all PCI bus
3205 numbers ourselves, overriding
3206 whatever the firmware may have done.
3207 usepirqmask [X86] Honor the possible IRQ mask stored
3208 in the BIOS $PIR table. This is needed on
3209 some systems with broken BIOSes, notably
3210 some HP Pavilion N5400 and Omnibook XE3
3211 notebooks. This will have no effect if ACPI
3212 IRQ routing is enabled.
3213 noacpi [X86] Do not use ACPI for IRQ routing
3214 or for PCI scanning.
3215 use_crs [X86] Use PCI host bridge window information
3216 from ACPI. On BIOSes from 2008 or later, this
3217 is enabled by default. If you need to use this,
3218 please report a bug.
3219 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3220 If you need to use this, please report a bug.
3221 routeirq Do IRQ routing for all PCI devices.
3222 This is normally done in pci_enable_device(),
3223 so this option is a temporary workaround
3224 for broken drivers that don't call it.
3225 skip_isa_align [X86] do not align io start addr, so can
3226 handle more pci cards
3227 noearly [X86] Don't do any early type 1 scanning.
3228 This might help on some broken boards which
3229 machine check when some devices' config space
3230 is read. But various workarounds are disabled
3231 and some IOMMU drivers will not work.
3232 bfsort Sort PCI devices into breadth-first order.
3233 This sorting is done to get a device
3234 order compatible with older (<= 2.4) kernels.
3235 nobfsort Don't sort PCI devices into breadth-first order.
3236 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3237 tuning and use the BIOS-configured MPS defaults.
3238 pcie_bus_safe Set every device's MPS to the largest value
3239 supported by all devices below the root complex.
3240 pcie_bus_perf Set device MPS to the largest allowable MPS
3241 based on its parent bus. Also set MRRS (Max
3242 Read Request Size) to the largest supported
3243 value (no larger than the MPS that the device
3244 or bus can support) for best performance.
3245 pcie_bus_peer2peer Set every device's MPS to 128B, which
3246 every device is guaranteed to support. This
3247 configuration allows peer-to-peer DMA between
3248 any pair of devices, possibly at the cost of
3249 reduced performance. This also guarantees
3250 that hot-added devices will work.
3251 cbiosize=nn[KMG] The fixed amount of bus space which is
3252 reserved for the CardBus bridge's IO window.
3253 The default value is 256 bytes.
3254 cbmemsize=nn[KMG] The fixed amount of bus space which is
3255 reserved for the CardBus bridge's memory
3256 window. The default value is 64 megabytes.
3257 resource_alignment=
3258 Format:
3259 [<order of align>@]<pci_dev>[; ...]
3260 Specifies alignment and device to reassign
3261 aligned memory resources. How to
3262 specify the device is described above.
3263 If <order of align> is not specified,
3264 PAGE_SIZE is used as alignment.
3265 PCI-PCI bridge can be specified, if resource
3266 windows need to be expanded.
3267 To specify the alignment for several
3268 instances of a device, the PCI vendor,
3269 device, subvendor, and subdevice may be
3270 specified, e.g., 4096@pci:8086:9c22:103c:198f
3271 ecrc= Enable/disable PCIe ECRC (transaction layer
3272 end-to-end CRC checking).
3273 bios: Use BIOS/firmware settings. This is the
3274 the default.
3275 off: Turn ECRC off
3276 on: Turn ECRC on.
3277 hpiosize=nn[KMG] The fixed amount of bus space which is
3278 reserved for hotplug bridge's IO window.
3279 Default size is 256 bytes.
3280 hpmemsize=nn[KMG] The fixed amount of bus space which is
3281 reserved for hotplug bridge's memory window.
3282 Default size is 2 megabytes.
3283 hpbussize=nn The minimum amount of additional bus numbers
3284 reserved for buses below a hotplug bridge.
3285 Default is 1.
3286 realloc= Enable/disable reallocating PCI bridge resources
3287 if allocations done by BIOS are too small to
3288 accommodate resources required by all child
3289 devices.
3290 off: Turn realloc off
3291 on: Turn realloc on
3292 realloc same as realloc=on
3293 noari do not use PCIe ARI.
3294 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
3295 do not use PCIe ATS (and IOMMU device IOTLB).
3296 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3297 only look for one device below a PCIe downstream
3298 port.
3299 big_root_window Try to add a big 64bit memory window to the PCIe
3300 root complex on AMD CPUs. Some GFX hardware
3301 can resize a BAR to allow access to all VRAM.
3302 Adding the window is slightly risky (it may
3303 conflict with unreported devices), so this
3304 taints the kernel.
3305 disable_acs_redir=<pci_dev>[; ...]
3306 Specify one or more PCI devices (in the format
3307 specified above) separated by semicolons.
3308 Each device specified will have the PCI ACS
3309 redirect capabilities forced off which will
3310 allow P2P traffic between devices through
3311 bridges without forcing it upstream. Note:
3312 this removes isolation between devices and
3313 may put more devices in an IOMMU group.
3315 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3316 Management.
3317 off Disable ASPM.
3318 force Enable ASPM even on devices that claim not to support it.
3319 WARNING: Forcing ASPM on may cause system lockups.
3321 pcie_ports= [PCIE] PCIe port services handling:
3322 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
3323 even if the platform doesn't give the OS permission to
3324 use them. This may cause conflicts if the platform
3325 also tries to use these services.
3326 compat Disable native PCIe services (PME, AER, DPC, PCIe
3327 hotplug).
3329 pcie_port_pm= [PCIE] PCIe port power management handling:
3330 off Disable power management of all PCIe ports
3331 force Forcibly enable power management of all PCIe ports
3333 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3334 nomsi Do not use MSI for native PCIe PME signaling (this makes
3335 all PCIe root ports use INTx for all services).
3337 pcmv= [HW,PCMCIA] BadgePAD 4
3339 pd_ignore_unused
3340 [PM]
3341 Keep all power-domains already enabled by bootloader on,
3342 even if no driver has claimed them. This is useful
3343 for debug and development, but should not be
3344 needed on a platform with proper driver support.
3346 pd. [PARIDE]
3347 See Documentation/blockdev/paride.txt.
3349 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3350 boot time.
3351 Format: { 0 | 1 }
3352 See arch/parisc/kernel/pdc_chassis.c
3354 percpu_alloc= Select which percpu first chunk allocator to use.
3355 Currently supported values are "embed" and "page".
3356 Archs may support subset or none of the selections.
3357 See comments in mm/percpu.c for details on each
3358 allocator. This parameter is primarily for debugging
3359 and performance comparison.
3361 pf. [PARIDE]
3362 See Documentation/blockdev/paride.txt.
3364 pg. [PARIDE]
3365 See Documentation/blockdev/paride.txt.
3367 pirq= [SMP,APIC] Manual mp-table setup
3368 See Documentation/x86/i386/IO-APIC.txt.
3370 plip= [PPT,NET] Parallel port network link
3371 Format: { parport<nr> | timid | 0 }
3372 See also Documentation/admin-guide/parport.rst.
3374 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3375 Override pmtimer IOPort with a hex value.
3376 e.g. pmtmr=0x508
3378 pnp.debug=1 [PNP]
3379 Enable PNP debug messages (depends on the
3380 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3381 via /sys/module/pnp/parameters/debug. We always show
3382 current resource usage; turning this on also shows
3383 possible settings and some assignment information.
3385 pnpacpi= [ACPI]
3386 { off }
3388 pnpbios= [ISAPNP]
3389 { on | off | curr | res | no-curr | no-res }
3391 pnp_reserve_irq=
3392 [ISAPNP] Exclude IRQs for the autoconfiguration
3394 pnp_reserve_dma=
3395 [ISAPNP] Exclude DMAs for the autoconfiguration
3397 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3398 Ranges are in pairs (I/O port base and size).
3400 pnp_reserve_mem=
3401 [ISAPNP] Exclude memory regions for the
3402 autoconfiguration.
3403 Ranges are in pairs (memory base and size).
3405 ports= [IP_VS_FTP] IPVS ftp helper module
3406 Default is 21.
3407 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3408 may be specified.
3409 Format: <port>,<port>....
3411 powersave=off [PPC] This option disables power saving features.
3412 It specifically disables cpuidle and sets the
3413 platform machine description specific power_save
3414 function to NULL. On Idle the CPU just reduces
3415 execution priority.
3417 ppc_strict_facility_enable
3418 [PPC] This option catches any kernel floating point,
3419 Altivec, VSX and SPE outside of regions specifically
3420 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3421 There is some performance impact when enabling this.
3423 ppc_tm= [PPC]
3424 Format: {"off"}
3425 Disable Hardware Transactional Memory
3427 print-fatal-signals=
3428 [KNL] debug: print fatal signals
3430 If enabled, warn about various signal handling
3431 related application anomalies: too many signals,
3432 too many POSIX.1 timers, fatal signals causing a
3433 coredump - etc.
3435 If you hit the warning due to signal overflow,
3436 you might want to try "ulimit -i unlimited".
3438 default: off.
3440 printk.always_kmsg_dump=
3441 Trigger kmsg_dump for cases other than kernel oops or
3442 panics
3443 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3444 default: disabled
3446 printk.devkmsg={on,off,ratelimit}
3447 Control writing to /dev/kmsg.
3448 on - unlimited logging to /dev/kmsg from userspace
3449 off - logging to /dev/kmsg disabled
3450 ratelimit - ratelimit the logging
3451 Default: ratelimit
3453 printk.time= Show timing data prefixed to each printk message line
3454 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3456 processor.max_cstate= [HW,ACPI]
3457 Limit processor to maximum C-state
3458 max_cstate=9 overrides any DMI blacklist limit.
3460 processor.nocst [HW,ACPI]
3461 Ignore the _CST method to determine C-states,
3462 instead using the legacy FADT method
3464 profile= [KNL] Enable kernel profiling via /proc/profile
3465 Format: [<profiletype>,]<number>
3466 Param: <profiletype>: "schedule", "sleep", or "kvm"
3467 [defaults to kernel profiling]
3468 Param: "schedule" - profile schedule points.
3469 Param: "sleep" - profile D-state sleeping (millisecs).
3470 Requires CONFIG_SCHEDSTATS
3471 Param: "kvm" - profile VM exits.
3472 Param: <number> - step/bucket size as a power of 2 for
3473 statistical time based profiling.
3475 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3476 before loading.
3477 See Documentation/blockdev/ramdisk.txt.
3479 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3480 probe for; one of (bare|imps|exps|lifebook|any).
3481 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3482 per second.
3483 psmouse.resetafter= [HW,MOUSE]
3484 Try to reset the device after so many bad packets
3485 (0 = never).
3486 psmouse.resolution=
3487 [HW,MOUSE] Set desired mouse resolution, in dpi.
3488 psmouse.smartscroll=
3489 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3490 0 = disabled, 1 = enabled (default).
3492 pstore.backend= Specify the name of the pstore backend to use
3494 pt. [PARIDE]
3495 See Documentation/blockdev/paride.txt.
3497 pti= [X86_64] Control Page Table Isolation of user and
3498 kernel address spaces. Disabling this feature
3499 removes hardening, but improves performance of
3500 system calls and interrupts.
3502 on - unconditionally enable
3503 off - unconditionally disable
3504 auto - kernel detects whether your CPU model is
3505 vulnerable to issues that PTI mitigates
3507 Not specifying this option is equivalent to pti=auto.
3509 nopti [X86_64]
3510 Equivalent to pti=off
3512 pty.legacy_count=
3513 [KNL] Number of legacy pty's. Overwrites compiled-in
3514 default number.
3516 quiet [KNL] Disable most log messages
3518 r128= [HW,DRM]
3520 raid= [HW,RAID]
3521 See Documentation/admin-guide/md.rst.
3523 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3524 See Documentation/blockdev/ramdisk.txt.
3526 random.trust_cpu={on,off}
3527 [KNL] Enable or disable trusting the use of the
3528 CPU's random number generator (if available) to
3529 fully seed the kernel's CRNG. Default is controlled
3530 by CONFIG_RANDOM_TRUST_CPU.
3532 ras=option[,option,...] [KNL] RAS-specific options
3534 cec_disable [X86]
3535 Disable the Correctable Errors Collector,
3536 see CONFIG_RAS_CEC help text.
3538 rcu_nocbs= [KNL]
3539 The argument is a cpu list, as described above.
3541 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3542 the specified list of CPUs to be no-callback CPUs.
3543 Invocation of these CPUs' RCU callbacks will
3544 be offloaded to "rcuox/N" kthreads created for
3545 that purpose, where "x" is "b" for RCU-bh, "p"
3546 for RCU-preempt, and "s" for RCU-sched, and "N"
3547 is the CPU number. This reduces OS jitter on the
3548 offloaded CPUs, which can be useful for HPC and
3549 real-time workloads. It can also improve energy
3550 efficiency for asymmetric multiprocessors.
3552 rcu_nocb_poll [KNL]
3553 Rather than requiring that offloaded CPUs
3554 (specified by rcu_nocbs= above) explicitly
3555 awaken the corresponding "rcuoN" kthreads,
3556 make these kthreads poll for callbacks.
3557 This improves the real-time response for the
3558 offloaded CPUs by relieving them of the need to
3559 wake up the corresponding kthread, but degrades
3560 energy efficiency by requiring that the kthreads
3561 periodically wake up to do the polling.
3563 rcutree.blimit= [KNL]
3564 Set maximum number of finished RCU callbacks to
3565 process in one batch.
3567 rcutree.dump_tree= [KNL]
3568 Dump the structure of the rcu_node combining tree
3569 out at early boot. This is used for diagnostic
3570 purposes, to verify correct tree setup.
3572 rcutree.gp_cleanup_delay= [KNL]
3573 Set the number of jiffies to delay each step of
3574 RCU grace-period cleanup.
3576 rcutree.gp_init_delay= [KNL]
3577 Set the number of jiffies to delay each step of
3578 RCU grace-period initialization.
3580 rcutree.gp_preinit_delay= [KNL]
3581 Set the number of jiffies to delay each step of
3582 RCU grace-period pre-initialization, that is,
3583 the propagation of recent CPU-hotplug changes up
3584 the rcu_node combining tree.
3586 rcutree.rcu_fanout_exact= [KNL]
3587 Disable autobalancing of the rcu_node combining
3588 tree. This is used by rcutorture, and might
3589 possibly be useful for architectures having high
3590 cache-to-cache transfer latencies.
3592 rcutree.rcu_fanout_leaf= [KNL]
3593 Change the number of CPUs assigned to each
3594 leaf rcu_node structure. Useful for very
3595 large systems, which will choose the value 64,
3596 and for NUMA systems with large remote-access
3597 latencies, which will choose a value aligned
3598 with the appropriate hardware boundaries.
3600 rcutree.jiffies_till_sched_qs= [KNL]
3601 Set required age in jiffies for a
3602 given grace period before RCU starts
3603 soliciting quiescent-state help from
3604 rcu_note_context_switch().
3606 rcutree.jiffies_till_first_fqs= [KNL]
3607 Set delay from grace-period initialization to
3608 first attempt to force quiescent states.
3609 Units are jiffies, minimum value is zero,
3610 and maximum value is HZ.
3612 rcutree.jiffies_till_next_fqs= [KNL]
3613 Set delay between subsequent attempts to force
3614 quiescent states. Units are jiffies, minimum
3615 value is one, and maximum value is HZ.
3617 rcutree.kthread_prio= [KNL,BOOT]
3618 Set the SCHED_FIFO priority of the RCU per-CPU
3619 kthreads (rcuc/N). This value is also used for
3620 the priority of the RCU boost threads (rcub/N)
3621 and for the RCU grace-period kthreads (rcu_bh,
3622 rcu_preempt, and rcu_sched). If RCU_BOOST is
3623 set, valid values are 1-99 and the default is 1
3624 (the least-favored priority). Otherwise, when
3625 RCU_BOOST is not set, valid values are 0-99 and
3626 the default is zero (non-realtime operation).
3628 rcutree.rcu_nocb_leader_stride= [KNL]
3629 Set the number of NOCB kthread groups, which
3630 defaults to the square root of the number of
3631 CPUs. Larger numbers reduces the wakeup overhead
3632 on the per-CPU grace-period kthreads, but increases
3633 that same overhead on each group's leader.
3635 rcutree.qhimark= [KNL]
3636 Set threshold of queued RCU callbacks beyond which
3637 batch limiting is disabled.
3639 rcutree.qlowmark= [KNL]
3640 Set threshold of queued RCU callbacks below which
3641 batch limiting is re-enabled.
3643 rcutree.rcu_idle_gp_delay= [KNL]
3644 Set wakeup interval for idle CPUs that have
3645 RCU callbacks (RCU_FAST_NO_HZ=y).
3647 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3648 Set wakeup interval for idle CPUs that have
3649 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3650 Lazy RCU callbacks are those which RCU can
3651 prove do nothing more than free memory.
3653 rcutree.rcu_kick_kthreads= [KNL]
3654 Cause the grace-period kthread to get an extra
3655 wake_up() if it sleeps three times longer than
3656 it should at force-quiescent-state time.
3657 This wake_up() will be accompanied by a
3658 WARN_ONCE() splat and an ftrace_dump().
3660 rcuperf.gp_async= [KNL]
3661 Measure performance of asynchronous
3662 grace-period primitives such as call_rcu().
3664 rcuperf.gp_async_max= [KNL]
3665 Specify the maximum number of outstanding
3666 callbacks per writer thread. When a writer
3667 thread exceeds this limit, it invokes the
3668 corresponding flavor of rcu_barrier() to allow
3669 previously posted callbacks to drain.
3671 rcuperf.gp_exp= [KNL]
3672 Measure performance of expedited synchronous
3673 grace-period primitives.
3675 rcuperf.holdoff= [KNL]
3676 Set test-start holdoff period. The purpose of
3677 this parameter is to delay the start of the
3678 test until boot completes in order to avoid
3679 interference.
3681 rcuperf.nreaders= [KNL]
3682 Set number of RCU readers. The value -1 selects
3683 N, where N is the number of CPUs. A value
3684 "n" less than -1 selects N-n+1, where N is again
3685 the number of CPUs. For example, -2 selects N
3686 (the number of CPUs), -3 selects N+1, and so on.
3687 A value of "n" less than or equal to -N selects
3688 a single reader.
3690 rcuperf.nwriters= [KNL]
3691 Set number of RCU writers. The values operate
3692 the same as for rcuperf.nreaders.
3693 N, where N is the number of CPUs
3695 rcuperf.perf_type= [KNL]
3696 Specify the RCU implementation to test.
3698 rcuperf.shutdown= [KNL]
3699 Shut the system down after performance tests
3700 complete. This is useful for hands-off automated
3701 testing.
3703 rcuperf.verbose= [KNL]
3704 Enable additional printk() statements.
3706 rcuperf.writer_holdoff= [KNL]
3707 Write-side holdoff between grace periods,
3708 in microseconds. The default of zero says
3709 no holdoff.
3711 rcutorture.cbflood_inter_holdoff= [KNL]
3712 Set holdoff time (jiffies) between successive
3713 callback-flood tests.
3715 rcutorture.cbflood_intra_holdoff= [KNL]
3716 Set holdoff time (jiffies) between successive
3717 bursts of callbacks within a given callback-flood
3718 test.
3720 rcutorture.cbflood_n_burst= [KNL]
3721 Set the number of bursts making up a given
3722 callback-flood test. Set this to zero to
3723 disable callback-flood testing.
3725 rcutorture.cbflood_n_per_burst= [KNL]
3726 Set the number of callbacks to be registered
3727 in a given burst of a callback-flood test.
3729 rcutorture.fqs_duration= [KNL]
3730 Set duration of force_quiescent_state bursts
3731 in microseconds.
3733 rcutorture.fqs_holdoff= [KNL]
3734 Set holdoff time within force_quiescent_state bursts
3735 in microseconds.
3737 rcutorture.fqs_stutter= [KNL]
3738 Set wait time between force_quiescent_state bursts
3739 in seconds.
3741 rcutorture.gp_cond= [KNL]
3742 Use conditional/asynchronous update-side
3743 primitives, if available.
3745 rcutorture.gp_exp= [KNL]
3746 Use expedited update-side primitives, if available.
3748 rcutorture.gp_normal= [KNL]
3749 Use normal (non-expedited) asynchronous
3750 update-side primitives, if available.
3752 rcutorture.gp_sync= [KNL]
3753 Use normal (non-expedited) synchronous
3754 update-side primitives, if available. If all
3755 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3756 rcutorture.gp_normal=, and rcutorture.gp_sync=
3757 are zero, rcutorture acts as if is interpreted
3758 they are all non-zero.
3760 rcutorture.n_barrier_cbs= [KNL]
3761 Set callbacks/threads for rcu_barrier() testing.
3763 rcutorture.nfakewriters= [KNL]
3764 Set number of concurrent RCU writers. These just
3765 stress RCU, they don't participate in the actual
3766 test, hence the "fake".
3768 rcutorture.nreaders= [KNL]
3769 Set number of RCU readers. The value -1 selects
3770 N-1, where N is the number of CPUs. A value
3771 "n" less than -1 selects N-n-2, where N is again
3772 the number of CPUs. For example, -2 selects N
3773 (the number of CPUs), -3 selects N+1, and so on.
3775 rcutorture.object_debug= [KNL]
3776 Enable debug-object double-call_rcu() testing.
3778 rcutorture.onoff_holdoff= [KNL]
3779 Set time (s) after boot for CPU-hotplug testing.
3781 rcutorture.onoff_interval= [KNL]
3782 Set time (jiffies) between CPU-hotplug operations,
3783 or zero to disable CPU-hotplug testing.
3785 rcutorture.shuffle_interval= [KNL]
3786 Set task-shuffle interval (s). Shuffling tasks
3787 allows some CPUs to go into dyntick-idle mode
3788 during the rcutorture test.
3790 rcutorture.shutdown_secs= [KNL]
3791 Set time (s) after boot system shutdown. This
3792 is useful for hands-off automated testing.
3794 rcutorture.stall_cpu= [KNL]
3795 Duration of CPU stall (s) to test RCU CPU stall
3796 warnings, zero to disable.
3798 rcutorture.stall_cpu_holdoff= [KNL]
3799 Time to wait (s) after boot before inducing stall.
3801 rcutorture.stall_cpu_irqsoff= [KNL]
3802 Disable interrupts while stalling if set.
3804 rcutorture.stat_interval= [KNL]
3805 Time (s) between statistics printk()s.
3807 rcutorture.stutter= [KNL]
3808 Time (s) to stutter testing, for example, specifying
3809 five seconds causes the test to run for five seconds,
3810 wait for five seconds, and so on. This tests RCU's
3811 ability to transition abruptly to and from idle.
3813 rcutorture.test_boost= [KNL]
3814 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3815 "Maybe" means test if the RCU implementation
3816 under test support RCU priority boosting.
3818 rcutorture.test_boost_duration= [KNL]
3819 Duration (s) of each individual boost test.
3821 rcutorture.test_boost_interval= [KNL]
3822 Interval (s) between each boost test.
3824 rcutorture.test_no_idle_hz= [KNL]
3825 Test RCU's dyntick-idle handling. See also the
3826 rcutorture.shuffle_interval parameter.
3828 rcutorture.torture_type= [KNL]
3829 Specify the RCU implementation to test.
3831 rcutorture.verbose= [KNL]
3832 Enable additional printk() statements.
3834 rcupdate.rcu_cpu_stall_suppress= [KNL]
3835 Suppress RCU CPU stall warning messages.
3837 rcupdate.rcu_cpu_stall_timeout= [KNL]
3838 Set timeout for RCU CPU stall warning messages.
3840 rcupdate.rcu_expedited= [KNL]
3841 Use expedited grace-period primitives, for
3842 example, synchronize_rcu_expedited() instead
3843 of synchronize_rcu(). This reduces latency,
3844 but can increase CPU utilization, degrade
3845 real-time latency, and degrade energy efficiency.
3846 No effect on CONFIG_TINY_RCU kernels.
3848 rcupdate.rcu_normal= [KNL]
3849 Use only normal grace-period primitives,
3850 for example, synchronize_rcu() instead of
3851 synchronize_rcu_expedited(). This improves
3852 real-time latency, CPU utilization, and
3853 energy efficiency, but can expose users to
3854 increased grace-period latency. This parameter
3855 overrides rcupdate.rcu_expedited. No effect on
3856 CONFIG_TINY_RCU kernels.
3858 rcupdate.rcu_normal_after_boot= [KNL]
3859 Once boot has completed (that is, after
3860 rcu_end_inkernel_boot() has been invoked), use
3861 only normal grace-period primitives. No effect
3862 on CONFIG_TINY_RCU kernels.
3864 rcupdate.rcu_task_stall_timeout= [KNL]
3865 Set timeout in jiffies for RCU task stall warning
3866 messages. Disable with a value less than or equal
3867 to zero.
3869 rcupdate.rcu_self_test= [KNL]
3870 Run the RCU early boot self tests
3872 rcupdate.rcu_self_test_bh= [KNL]
3873 Run the RCU bh early boot self tests
3875 rcupdate.rcu_self_test_sched= [KNL]
3876 Run the RCU sched early boot self tests
3878 rdinit= [KNL]
3879 Format: <full_path>
3880 Run specified binary instead of /init from the ramdisk,
3881 used for early userspace startup. See initrd.
3883 rdt= [HW,X86,RDT]
3884 Turn on/off individual RDT features. List is:
3885 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
3886 mba.
3887 E.g. to turn on cmt and turn off mba use:
3888 rdt=cmt,!mba
3890 reboot= [KNL]
3891 Format (x86 or x86_64):
3892 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3893 [[,]s[mp]#### \
3894 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3895 [[,]f[orce]
3896 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3897 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3898 reboot_force is either force or not specified,
3899 reboot_cpu is s[mp]#### with #### being the processor
3900 to be used for rebooting.
3902 relax_domain_level=
3903 [KNL, SMP] Set scheduler's default relax_domain_level.
3904 See Documentation/cgroup-v1/cpusets.txt.
3906 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
3907 Format: <base1>,<size1>[,<base2>,<size2>,...]
3908 Reserve I/O ports or memory so the kernel won't use
3909 them. If <base> is less than 0x10000, the region
3910 is assumed to be I/O ports; otherwise it is memory.
3912 reservetop= [X86-32]
3913 Format: nn[KMG]
3914 Reserves a hole at the top of the kernel virtual
3915 address space.
3917 reservelow= [X86]
3918 Format: nn[K]
3919 Set the amount of memory to reserve for BIOS at
3920 the bottom of the address space.
3922 reset_devices [KNL] Force drivers to reset the underlying device
3923 during initialization.
3925 resume= [SWSUSP]
3926 Specify the partition device for software suspend
3927 Format:
3928 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3930 resume_offset= [SWSUSP]
3931 Specify the offset from the beginning of the partition
3932 given by "resume=" at which the swap header is located,
3933 in <PAGE_SIZE> units (needed only for swap files).
3934 See Documentation/power/swsusp-and-swap-files.txt
3936 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3937 read the resume files
3939 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3940 Useful for devices that are detected asynchronously
3941 (e.g. USB and MMC devices).
3943 hibernate= [HIBERNATION]
3944 noresume Don't check if there's a hibernation image
3945 present during boot.
3946 nocompress Don't compress/decompress hibernation images.
3947 no Disable hibernation and resume.
3948 protect_image Turn on image protection during restoration
3949 (that will set all pages holding image data
3950 during restoration read-only).
3952 retain_initrd [RAM] Keep initrd memory after extraction
3954 rfkill.default_state=
3955 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3956 etc. communication is blocked by default.
3957 1 Unblocked.
3959 rfkill.master_switch_mode=
3960 0 The "airplane mode" button does nothing.
3961 1 The "airplane mode" button toggles between everything
3962 blocked and the previous configuration.
3963 2 The "airplane mode" button toggles between everything
3964 blocked and everything unblocked.
3966 rhash_entries= [KNL,NET]
3967 Set number of hash buckets for route cache
3969 ring3mwait=disable
3970 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
3971 CPUs.
3973 ro [KNL] Mount root device read-only on boot
3975 rodata= [KNL]
3976 on Mark read-only kernel memory as read-only (default).
3977 off Leave read-only kernel memory writable for debugging.
3979 rockchip.usb_uart
3980 Enable the uart passthrough on the designated usb port
3981 on Rockchip SoCs. When active, the signals of the
3982 debug-uart get routed to the D+ and D- pins of the usb
3983 port and the regular usb controller gets disabled.
3985 root= [KNL] Root filesystem
3986 See name_to_dev_t comment in init/do_mounts.c.
3988 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3989 mount the root filesystem
3991 rootflags= [KNL] Set root filesystem mount option string
3993 rootfstype= [KNL] Set root filesystem type
3995 rootwait [KNL] Wait (indefinitely) for root device to show up.
3996 Useful for devices that are detected asynchronously
3997 (e.g. USB and MMC devices).
3999 rproc_mem=nn[KMG][@address]
4000 [KNL,ARM,CMA] Remoteproc physical memory block.
4001 Memory area to be used by remote processor image,
4002 managed by CMA.
4004 rw [KNL] Mount root device read-write on boot
4006 S [KNL] Run init in single mode
4008 s390_iommu= [HW,S390]
4009 Set s390 IOTLB flushing mode
4010 strict
4011 With strict flushing every unmap operation will result in
4012 an IOTLB flush. Default is lazy flushing before reuse,
4013 which is faster.
4015 sa1100ir [NET]
4016 See drivers/net/irda/sa1100_ir.c.
4018 sbni= [NET] Granch SBNI12 leased line adapter
4020 sched_debug [KNL] Enables verbose scheduler debug messages.
4022 schedstats= [KNL,X86] Enable or disable scheduled statistics.
4023 Allowed values are enable and disable. This feature
4024 incurs a small amount of overhead in the scheduler
4025 but is useful for debugging and performance tuning.
4027 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
4028 xtime_lock contention on larger systems, and/or RCU lock
4029 contention on all systems with CONFIG_MAXSMP set.
4030 Format: { "0" | "1" }
4031 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
4032 1 -- enable.
4033 Note: increases power consumption, thus should only be
4034 enabled if running jitter sensitive (HPC/RT) workloads.
4036 security= [SECURITY] Choose a security module to enable at boot.
4037 If this boot parameter is not specified, only the first
4038 security module asking for security registration will be
4039 loaded. An invalid security module name will be treated
4040 as if no module has been chosen.
4042 selinux= [SELINUX] Disable or enable SELinux at boot time.
4043 Format: { "0" | "1" }
4044 See security/selinux/Kconfig help text.
4045 0 -- disable.
4046 1 -- enable.
4047 Default value is set via kernel config option.
4048 If enabled at boot time, /selinux/disable can be used
4049 later to disable prior to initial policy load.
4051 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
4052 Format: { "0" | "1" }
4053 See security/apparmor/Kconfig help text
4054 0 -- disable.
4055 1 -- enable.
4056 Default value is set via kernel config option.
4058 serialnumber [BUGS=X86-32]
4060 shapers= [NET]
4061 Maximal number of shapers.
4063 simeth= [IA-64]
4064 simscsi=
4066 slram= [HW,MTD]
4068 slab_nomerge [MM]
4069 Disable merging of slabs with similar size. May be
4070 necessary if there is some reason to distinguish
4071 allocs to different slabs, especially in hardened
4072 environments where the risk of heap overflows and
4073 layout control by attackers can usually be
4074 frustrated by disabling merging. This will reduce
4075 most of the exposure of a heap attack to a single
4076 cache (risks via metadata attacks are mostly
4077 unchanged). Debug options disable merging on their
4078 own.
4079 For more information see Documentation/vm/slub.rst.
4081 slab_max_order= [MM, SLAB]
4082 Determines the maximum allowed order for slabs.
4083 A high setting may cause OOMs due to memory
4084 fragmentation. Defaults to 1 for systems with
4085 more than 32MB of RAM, 0 otherwise.
4087 slub_debug[=options[,slabs]] [MM, SLUB]
4088 Enabling slub_debug allows one to determine the
4089 culprit if slab objects become corrupted. Enabling
4090 slub_debug can create guard zones around objects and
4091 may poison objects when not in use. Also tracks the
4092 last alloc / free. For more information see
4093 Documentation/vm/slub.rst.
4095 slub_memcg_sysfs= [MM, SLUB]
4096 Determines whether to enable sysfs directories for
4097 memory cgroup sub-caches. 1 to enable, 0 to disable.
4098 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
4099 Enabling this can lead to a very high number of debug
4100 directories and files being created under
4101 /sys/kernel/slub.
4103 slub_max_order= [MM, SLUB]
4104 Determines the maximum allowed order for slabs.
4105 A high setting may cause OOMs due to memory
4106 fragmentation. For more information see
4107 Documentation/vm/slub.rst.
4109 slub_min_objects= [MM, SLUB]
4110 The minimum number of objects per slab. SLUB will
4111 increase the slab order up to slub_max_order to
4112 generate a sufficiently large slab able to contain
4113 the number of objects indicated. The higher the number
4114 of objects the smaller the overhead of tracking slabs
4115 and the less frequently locks need to be acquired.
4116 For more information see Documentation/vm/slub.rst.
4118 slub_min_order= [MM, SLUB]
4119 Determines the minimum page order for slabs. Must be
4120 lower than slub_max_order.
4121 For more information see Documentation/vm/slub.rst.
4123 slub_nomerge [MM, SLUB]
4124 Same with slab_nomerge. This is supported for legacy.
4125 See slab_nomerge for more information.
4127 smart2= [HW]
4128 Format: <io1>[,<io2>[,...,<io8>]]
4130 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4131 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4132 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4133 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4134 smsc-ircc2.ircc_irq= [HW] IRQ line
4135 smsc-ircc2.ircc_dma= [HW] DMA channel
4136 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4137 0: Toshiba Satellite 1800 (GP data pin select)
4138 1: Fast pin select (default)
4139 2: ATC IRMode
4141 smt [KNL,S390] Set the maximum number of threads (logical
4142 CPUs) to use per physical CPU on systems capable of
4143 symmetric multithreading (SMT). Will be capped to the
4144 actual hardware limit.
4145 Format: <integer>
4146 Default: -1 (no limit)
4148 softlockup_panic=
4149 [KNL] Should the soft-lockup detector generate panics.
4150 Format: <integer>
4152 A nonzero value instructs the soft-lockup detector
4153 to panic the machine when a soft-lockup occurs. This
4154 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
4155 which is the respective build-time switch to that
4156 functionality.
4158 softlockup_all_cpu_backtrace=
4159 [KNL] Should the soft-lockup detector generate
4160 backtraces on all cpus.
4161 Format: <integer>
4163 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4164 See Documentation/laptops/sonypi.txt
4166 spectre_v2= [X86] Control mitigation of Spectre variant 2
4167 (indirect branch speculation) vulnerability.
4169 on - unconditionally enable
4170 off - unconditionally disable
4171 auto - kernel detects whether your CPU model is
4172 vulnerable
4174 Selecting 'on' will, and 'auto' may, choose a
4175 mitigation method at run time according to the
4176 CPU, the available microcode, the setting of the
4177 CONFIG_RETPOLINE configuration option, and the
4178 compiler with which the kernel was built.
4180 Specific mitigations can also be selected manually:
4182 retpoline - replace indirect branches
4183 retpoline,generic - google's original retpoline
4184 retpoline,amd - AMD-specific minimal thunk
4186 Not specifying this option is equivalent to
4187 spectre_v2=auto.
4189 spec_store_bypass_disable=
4190 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4191 (Speculative Store Bypass vulnerability)
4193 Certain CPUs are vulnerable to an exploit against a
4194 a common industry wide performance optimization known
4195 as "Speculative Store Bypass" in which recent stores
4196 to the same memory location may not be observed by
4197 later loads during speculative execution. The idea
4198 is that such stores are unlikely and that they can
4199 be detected prior to instruction retirement at the
4200 end of a particular speculation execution window.
4202 In vulnerable processors, the speculatively forwarded
4203 store can be used in a cache side channel attack, for
4204 example to read memory to which the attacker does not
4205 directly have access (e.g. inside sandboxed code).
4207 This parameter controls whether the Speculative Store
4208 Bypass optimization is used.
4210 On x86 the options are:
4212 on - Unconditionally disable Speculative Store Bypass
4213 off - Unconditionally enable Speculative Store Bypass
4214 auto - Kernel detects whether the CPU model contains an
4215 implementation of Speculative Store Bypass and
4216 picks the most appropriate mitigation. If the
4217 CPU is not vulnerable, "off" is selected. If the
4218 CPU is vulnerable the default mitigation is
4219 architecture and Kconfig dependent. See below.
4220 prctl - Control Speculative Store Bypass per thread
4221 via prctl. Speculative Store Bypass is enabled
4222 for a process by default. The state of the control
4223 is inherited on fork.
4224 seccomp - Same as "prctl" above, but all seccomp threads
4225 will disable SSB unless they explicitly opt out.
4227 Default mitigations:
4228 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4230 On powerpc the options are:
4232 on,auto - On Power8 and Power9 insert a store-forwarding
4233 barrier on kernel entry and exit. On Power7
4234 perform a software flush on kernel entry and
4235 exit.
4236 off - No action.
4238 Not specifying this option is equivalent to
4239 spec_store_bypass_disable=auto.
4241 spia_io_base= [HW,MTD]
4242 spia_fio_base=
4243 spia_pedr=
4244 spia_peddr=
4246 srcutree.counter_wrap_check [KNL]
4247 Specifies how frequently to check for
4248 grace-period sequence counter wrap for the
4249 srcu_data structure's ->srcu_gp_seq_needed field.
4250 The greater the number of bits set in this kernel
4251 parameter, the less frequently counter wrap will
4252 be checked for. Note that the bottom two bits
4253 are ignored.
4255 srcutree.exp_holdoff [KNL]
4256 Specifies how many nanoseconds must elapse
4257 since the end of the last SRCU grace period for
4258 a given srcu_struct until the next normal SRCU
4259 grace period will be considered for automatic
4260 expediting. Set to zero to disable automatic
4261 expediting.
4263 ssbd= [ARM64,HW]
4264 Speculative Store Bypass Disable control
4266 On CPUs that are vulnerable to the Speculative
4267 Store Bypass vulnerability and offer a
4268 firmware based mitigation, this parameter
4269 indicates how the mitigation should be used:
4271 force-on: Unconditionally enable mitigation for
4272 for both kernel and userspace
4273 force-off: Unconditionally disable mitigation for
4274 for both kernel and userspace
4275 kernel: Always enable mitigation in the
4276 kernel, and offer a prctl interface
4277 to allow userspace to register its
4278 interest in being mitigated too.
4280 stack_guard_gap= [MM]
4281 override the default stack gap protection. The value
4282 is in page units and it defines how many pages prior
4283 to (for stacks growing down) resp. after (for stacks
4284 growing up) the main stack are reserved for no other
4285 mapping. Default value is 256 pages.
4287 stacktrace [FTRACE]
4288 Enabled the stack tracer on boot up.
4290 stacktrace_filter=[function-list]
4291 [FTRACE] Limit the functions that the stack tracer
4292 will trace at boot up. function-list is a comma separated
4293 list of functions. This list can be changed at run
4294 time by the stack_trace_filter file in the debugfs
4295 tracing directory. Note, this enables stack tracing
4296 and the stacktrace above is not needed.
4298 sti= [PARISC,HW]
4299 Format: <num>
4300 Set the STI (builtin display/keyboard on the HP-PARISC
4301 machines) console (graphic card) which should be used
4302 as the initial boot-console.
4303 See also comment in drivers/video/console/sticore.c.
4305 sti_font= [HW]
4306 See comment in drivers/video/console/sticore.c.
4308 stifb= [HW]
4309 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4311 sunrpc.min_resvport=
4312 sunrpc.max_resvport=
4313 [NFS,SUNRPC]
4314 SunRPC servers often require that client requests
4315 originate from a privileged port (i.e. a port in the
4316 range 0 < portnr < 1024).
4317 An administrator who wishes to reserve some of these
4318 ports for other uses may adjust the range that the
4319 kernel's sunrpc client considers to be privileged
4320 using these two parameters to set the minimum and
4321 maximum port values.
4323 sunrpc.svc_rpc_per_connection_limit=
4324 [NFS,SUNRPC]
4325 Limit the number of requests that the server will
4326 process in parallel from a single connection.
4327 The default value is 0 (no limit).
4329 sunrpc.pool_mode=
4330 [NFS]
4331 Control how the NFS server code allocates CPUs to
4332 service thread pools. Depending on how many NICs
4333 you have and where their interrupts are bound, this
4334 option will affect which CPUs will do NFS serving.
4335 Note: this parameter cannot be changed while the
4336 NFS server is running.
4338 auto the server chooses an appropriate mode
4339 automatically using heuristics
4340 global a single global pool contains all CPUs
4341 percpu one pool for each CPU
4342 pernode one pool for each NUMA node (equivalent
4343 to global on non-NUMA machines)
4345 sunrpc.tcp_slot_table_entries=
4346 sunrpc.udp_slot_table_entries=
4347 [NFS,SUNRPC]
4348 Sets the upper limit on the number of simultaneous
4349 RPC calls that can be sent from the client to a
4350 server. Increasing these values may allow you to
4351 improve throughput, but will also increase the
4352 amount of memory reserved for use by the client.
4354 suspend.pm_test_delay=
4355 [SUSPEND]
4356 Sets the number of seconds to remain in a suspend test
4357 mode before resuming the system (see
4358 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4359 is set. Default value is 5.
4361 swapaccount=[0|1]
4362 [KNL] Enable accounting of swap in memory resource
4363 controller if no parameter or 1 is given or disable
4364 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4366 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4367 Format: { <int> | force | noforce }
4368 <int> -- Number of I/O TLB slabs
4369 force -- force using of bounce buffers even if they
4370 wouldn't be automatically used by the kernel
4371 noforce -- Never use bounce buffers (for debugging)
4373 switches= [HW,M68k]
4375 sysfs.deprecated=0|1 [KNL]
4376 Enable/disable old style sysfs layout for old udev
4377 on older distributions. When this option is enabled
4378 very new udev will not work anymore. When this option
4379 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4380 in older udev will not work anymore.
4381 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4382 the kernel configuration.
4384 sysrq_always_enabled
4385 [KNL]
4386 Ignore sysrq setting - this boot parameter will
4387 neutralize any effect of /proc/sys/kernel/sysrq.
4388 Useful for debugging.
4390 tcpmhash_entries= [KNL,NET]
4391 Set the number of tcp_metrics_hash slots.
4392 Default value is 8192 or 16384 depending on total
4393 ram pages. This is used to specify the TCP metrics
4394 cache size. See Documentation/networking/ip-sysctl.txt
4395 "tcp_no_metrics_save" section for more details.
4397 tdfx= [HW,DRM]
4399 test_suspend= [SUSPEND][,N]
4400 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4401 standby suspend) or "freeze" (for suspend type freeze)
4402 as the system sleep state during system startup with
4403 the optional capability to repeat N number of times.
4404 The system is woken from this state using a
4405 wakeup-capable RTC alarm.
4407 thash_entries= [KNL,NET]
4408 Set number of hash buckets for TCP connection
4410 thermal.act= [HW,ACPI]
4411 -1: disable all active trip points in all thermal zones
4412 <degrees C>: override all lowest active trip points
4414 thermal.crt= [HW,ACPI]
4415 -1: disable all critical trip points in all thermal zones
4416 <degrees C>: override all critical trip points
4418 thermal.nocrt= [HW,ACPI]
4419 Set to disable actions on ACPI thermal zone
4420 critical and hot trip points.
4422 thermal.off= [HW,ACPI]
4423 1: disable ACPI thermal control
4425 thermal.psv= [HW,ACPI]
4426 -1: disable all passive trip points
4427 <degrees C>: override all passive trip points to this
4428 value
4430 thermal.tzp= [HW,ACPI]
4431 Specify global default ACPI thermal zone polling rate
4432 <deci-seconds>: poll all this frequency
4433 0: no polling (default)
4435 threadirqs [KNL]
4436 Force threading of all interrupt handlers except those
4437 marked explicitly IRQF_NO_THREAD.
4439 tmem [KNL,XEN]
4440 Enable the Transcendent memory driver if built-in.
4442 tmem.cleancache=0|1 [KNL, XEN]
4443 Default is on (1). Disable the usage of the cleancache
4444 API to send anonymous pages to the hypervisor.
4446 tmem.frontswap=0|1 [KNL, XEN]
4447 Default is on (1). Disable the usage of the frontswap
4448 API to send swap pages to the hypervisor. If disabled
4449 the selfballooning and selfshrinking are force disabled.
4451 tmem.selfballooning=0|1 [KNL, XEN]
4452 Default is on (1). Disable the driving of swap pages
4453 to the hypervisor.
4455 tmem.selfshrinking=0|1 [KNL, XEN]
4456 Default is on (1). Partial swapoff that immediately
4457 transfers pages from Xen hypervisor back to the
4458 kernel based on different criteria.
4460 topology= [S390]
4461 Format: {off | on}
4462 Specify if the kernel should make use of the cpu
4463 topology information if the hardware supports this.
4464 The scheduler will make use of this information and
4465 e.g. base its process migration decisions on it.
4466 Default is on.
4468 topology_updates= [KNL, PPC, NUMA]
4469 Format: {off}
4470 Specify if the kernel should ignore (off)
4471 topology updates sent by the hypervisor to this
4472 LPAR.
4474 tp720= [HW,PS2]
4476 tpm_suspend_pcr=[HW,TPM]
4477 Format: integer pcr id
4478 Specify that at suspend time, the tpm driver
4479 should extend the specified pcr with zeros,
4480 as a workaround for some chips which fail to
4481 flush the last written pcr on TPM_SaveState.
4482 This will guarantee that all the other pcrs
4483 are saved.
4485 trace_buf_size=nn[KMG]
4486 [FTRACE] will set tracing buffer size on each cpu.
4488 trace_event=[event-list]
4489 [FTRACE] Set and start specified trace events in order
4490 to facilitate early boot debugging. The event-list is a
4491 comma separated list of trace events to enable. See
4492 also Documentation/trace/events.rst
4494 trace_options=[option-list]
4495 [FTRACE] Enable or disable tracer options at boot.
4496 The option-list is a comma delimited list of options
4497 that can be enabled or disabled just as if you were
4498 to echo the option name into
4500 /sys/kernel/debug/tracing/trace_options
4502 For example, to enable stacktrace option (to dump the
4503 stack trace of each event), add to the command line:
4505 trace_options=stacktrace
4507 See also Documentation/trace/ftrace.rst "trace options"
4508 section.
4510 tp_printk[FTRACE]
4511 Have the tracepoints sent to printk as well as the
4512 tracing ring buffer. This is useful for early boot up
4513 where the system hangs or reboots and does not give the
4514 option for reading the tracing buffer or performing a
4515 ftrace_dump_on_oops.
4517 To turn off having tracepoints sent to printk,
4518 echo 0 > /proc/sys/kernel/tracepoint_printk
4519 Note, echoing 1 into this file without the
4520 tracepoint_printk kernel cmdline option has no effect.
4522 ** CAUTION **
4524 Having tracepoints sent to printk() and activating high
4525 frequency tracepoints such as irq or sched, can cause
4526 the system to live lock.
4528 traceoff_on_warning
4529 [FTRACE] enable this option to disable tracing when a
4530 warning is hit. This turns off "tracing_on". Tracing can
4531 be enabled again by echoing '1' into the "tracing_on"
4532 file located in /sys/kernel/debug/tracing/
4534 This option is useful, as it disables the trace before
4535 the WARNING dump is called, which prevents the trace to
4536 be filled with content caused by the warning output.
4538 This option can also be set at run time via the sysctl
4539 option: kernel/traceoff_on_warning
4541 transparent_hugepage=
4542 [KNL]
4543 Format: [always|madvise|never]
4544 Can be used to control the default behavior of the system
4545 with respect to transparent hugepages.
4546 See Documentation/admin-guide/mm/transhuge.rst
4547 for more details.
4549 tsc= Disable clocksource stability checks for TSC.
4550 Format: <string>
4551 [x86] reliable: mark tsc clocksource as reliable, this
4552 disables clocksource verification at runtime, as well
4553 as the stability checks done at bootup. Used to enable
4554 high-resolution timer mode on older hardware, and in
4555 virtualized environment.
4556 [x86] noirqtime: Do not use TSC to do irq accounting.
4557 Used to run time disable IRQ_TIME_ACCOUNTING on any
4558 platforms where RDTSC is slow and this accounting
4559 can add overhead.
4560 [x86] unstable: mark the TSC clocksource as unstable, this
4561 marks the TSC unconditionally unstable at bootup and
4562 avoids any further wobbles once the TSC watchdog notices.
4564 turbografx.map[2|3]= [HW,JOY]
4565 TurboGraFX parallel port interface
4566 Format:
4567 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4568 See also Documentation/input/devices/joystick-parport.rst
4570 udbg-immortal [PPC] When debugging early kernel crashes that
4571 happen after console_init() and before a proper
4572 console driver takes over, this boot options might
4573 help "seeing" what's going on.
4575 uhash_entries= [KNL,NET]
4576 Set number of hash buckets for UDP/UDP-Lite connections
4578 uhci-hcd.ignore_oc=
4579 [USB] Ignore overcurrent events (default N).
4580 Some badly-designed motherboards generate lots of
4581 bogus events, for ports that aren't wired to
4582 anything. Set this parameter to avoid log spamming.
4583 Note that genuine overcurrent events won't be
4584 reported either.
4586 unknown_nmi_panic
4587 [X86] Cause panic on unknown NMI.
4589 usbcore.authorized_default=
4590 [USB] Default USB device authorization:
4591 (default -1 = authorized except for wireless USB,
4592 0 = not authorized, 1 = authorized)
4594 usbcore.autosuspend=
4595 [USB] The autosuspend time delay (in seconds) used
4596 for newly-detected USB devices (default 2). This
4597 is the time required before an idle device will be
4598 autosuspended. Devices for which the delay is set
4599 to a negative value won't be autosuspended at all.
4601 usbcore.usbfs_snoop=
4602 [USB] Set to log all usbfs traffic (default 0 = off).
4604 usbcore.usbfs_snoop_max=
4605 [USB] Maximum number of bytes to snoop in each URB
4606 (default = 65536).
4608 usbcore.blinkenlights=
4609 [USB] Set to cycle leds on hubs (default 0 = off).
4611 usbcore.old_scheme_first=
4612 [USB] Start with the old device initialization
4613 scheme (default 0 = off).
4615 usbcore.usbfs_memory_mb=
4616 [USB] Memory limit (in MB) for buffers allocated by
4617 usbfs (default = 16, 0 = max = 2047).
4619 usbcore.use_both_schemes=
4620 [USB] Try the other device initialization scheme
4621 if the first one fails (default 1 = enabled).
4623 usbcore.initial_descriptor_timeout=
4624 [USB] Specifies timeout for the initial 64-byte
4625 USB_REQ_GET_DESCRIPTOR request in milliseconds
4626 (default 5000 = 5.0 seconds).
4628 usbcore.nousb [USB] Disable the USB subsystem
4630 usbcore.quirks=
4631 [USB] A list of quirk entries to augment the built-in
4632 usb core quirk list. List entries are separated by
4633 commas. Each entry has the form
4634 VendorID:ProductID:Flags. The IDs are 4-digit hex
4635 numbers and Flags is a set of letters. Each letter
4636 will change the built-in quirk; setting it if it is
4637 clear and clearing it if it is set. The letters have
4638 the following meanings:
4639 a = USB_QUIRK_STRING_FETCH_255 (string
4640 descriptors must not be fetched using
4641 a 255-byte read);
4642 b = USB_QUIRK_RESET_RESUME (device can't resume
4643 correctly so reset it instead);
4644 c = USB_QUIRK_NO_SET_INTF (device can't handle
4645 Set-Interface requests);
4646 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
4647 handle its Configuration or Interface
4648 strings);
4649 e = USB_QUIRK_RESET (device can't be reset
4650 (e.g morph devices), don't use reset);
4651 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
4652 more interface descriptions than the
4653 bNumInterfaces count, and can't handle
4654 talking to these interfaces);
4655 g = USB_QUIRK_DELAY_INIT (device needs a pause
4656 during initialization, after we read
4657 the device descriptor);
4658 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
4659 high speed and super speed interrupt
4660 endpoints, the USB 2.0 and USB 3.0 spec
4661 require the interval in microframes (1
4662 microframe = 125 microseconds) to be
4663 calculated as interval = 2 ^
4664 (bInterval-1).
4665 Devices with this quirk report their
4666 bInterval as the result of this
4667 calculation instead of the exponent
4668 variable used in the calculation);
4669 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
4670 handle device_qualifier descriptor
4671 requests);
4672 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
4673 generates spurious wakeup, ignore
4674 remote wakeup capability);
4675 k = USB_QUIRK_NO_LPM (device can't handle Link
4676 Power Management);
4677 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
4678 (Device reports its bInterval as linear
4679 frames instead of the USB 2.0
4680 calculation);
4681 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
4682 to be disconnected before suspend to
4683 prevent spurious wakeup);
4684 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
4685 pause after every control message);
4686 Example: quirks=0781:5580:bk,0a5c:5834:gij
4688 usbhid.mousepoll=
4689 [USBHID] The interval which mice are to be polled at.
4691 usbhid.jspoll=
4692 [USBHID] The interval which joysticks are to be polled at.
4694 usbhid.kbpoll=
4695 [USBHID] The interval which keyboards are to be polled at.
4697 usb-storage.delay_use=
4698 [UMS] The delay in seconds before a new device is
4699 scanned for Logical Units (default 1).
4701 usb-storage.quirks=
4702 [UMS] A list of quirks entries to supplement or
4703 override the built-in unusual_devs list. List
4704 entries are separated by commas. Each entry has
4705 the form VID:PID:Flags where VID and PID are Vendor
4706 and Product ID values (4-digit hex numbers) and
4707 Flags is a set of characters, each corresponding
4708 to a common usb-storage quirk flag as follows:
4709 a = SANE_SENSE (collect more than 18 bytes
4710 of sense data);
4711 b = BAD_SENSE (don't collect more than 18
4712 bytes of sense data);
4713 c = FIX_CAPACITY (decrease the reported
4714 device capacity by one sector);
4715 d = NO_READ_DISC_INFO (don't use
4716 READ_DISC_INFO command);
4717 e = NO_READ_CAPACITY_16 (don't use
4718 READ_CAPACITY_16 command);
4719 f = NO_REPORT_OPCODES (don't use report opcodes
4720 command, uas only);
4721 g = MAX_SECTORS_240 (don't transfer more than
4722 240 sectors at a time, uas only);
4723 h = CAPACITY_HEURISTICS (decrease the
4724 reported device capacity by one
4725 sector if the number is odd);
4726 i = IGNORE_DEVICE (don't bind to this
4727 device);
4728 j = NO_REPORT_LUNS (don't use report luns
4729 command, uas only);
4730 l = NOT_LOCKABLE (don't try to lock and
4731 unlock ejectable media);
4732 m = MAX_SECTORS_64 (don't transfer more
4733 than 64 sectors = 32 KB at a time);
4734 n = INITIAL_READ10 (force a retry of the
4735 initial READ(10) command);
4736 o = CAPACITY_OK (accept the capacity
4737 reported by the device);
4738 p = WRITE_CACHE (the device cache is ON
4739 by default);
4740 r = IGNORE_RESIDUE (the device reports
4741 bogus residue values);
4742 s = SINGLE_LUN (the device has only one
4743 Logical Unit);
4744 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4745 commands, uas only);
4746 u = IGNORE_UAS (don't bind to the uas driver);
4747 w = NO_WP_DETECT (don't test whether the
4748 medium is write-protected).
4749 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4750 even if the device claims no cache)
4751 Example: quirks=0419:aaf5:rl,0421:0433:rc
4753 user_debug= [KNL,ARM]
4754 Format: <int>
4755 See arch/arm/Kconfig.debug help text.
4756 1 - undefined instruction events
4757 2 - system calls
4758 4 - invalid data aborts
4759 8 - SIGSEGV faults
4760 16 - SIGBUS faults
4761 Example: user_debug=31
4763 userpte=
4764 [X86] Flags controlling user PTE allocations.
4766 nohigh = do not allocate PTE pages in
4767 HIGHMEM regardless of setting
4768 of CONFIG_HIGHPTE.
4770 vdso= [X86,SH]
4771 On X86_32, this is an alias for vdso32=. Otherwise:
4773 vdso=1: enable VDSO (the default)
4774 vdso=0: disable VDSO mapping
4776 vdso32= [X86] Control the 32-bit vDSO
4777 vdso32=1: enable 32-bit VDSO
4778 vdso32=0 or vdso32=2: disable 32-bit VDSO
4780 See the help text for CONFIG_COMPAT_VDSO for more
4781 details. If CONFIG_COMPAT_VDSO is set, the default is
4782 vdso32=0; otherwise, the default is vdso32=1.
4784 For compatibility with older kernels, vdso32=2 is an
4785 alias for vdso32=0.
4787 Try vdso32=0 if you encounter an error that says:
4788 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4790 vector= [IA-64,SMP]
4791 vector=percpu: enable percpu vector domain
4793 video= [FB] Frame buffer configuration
4794 See Documentation/fb/modedb.txt.
4796 video.brightness_switch_enabled= [0,1]
4797 If set to 1, on receiving an ACPI notify event
4798 generated by hotkey, video driver will adjust brightness
4799 level and then send out the event to user space through
4800 the allocated input device; If set to 0, video driver
4801 will only send out the event without touching backlight
4802 brightness level.
4803 default: 1
4805 virtio_mmio.device=
4806 [VMMIO] Memory mapped virtio (platform) device.
4808 <size>@<baseaddr>:<irq>[:<id>]
4809 where:
4810 <size> := size (can use standard suffixes
4811 like K, M and G)
4812 <baseaddr> := physical base address
4813 <irq> := interrupt number (as passed to
4814 request_irq())
4815 <id> := (optional) platform device id
4816 example:
4817 virtio_mmio.device=1K@0x100b0000:48:7
4819 Can be used multiple times for multiple devices.
4821 vga= [BOOT,X86-32] Select a particular video mode
4822 See Documentation/x86/boot.txt and
4823 Documentation/svga.txt.
4824 Use vga=ask for menu.
4825 This is actually a boot loader parameter; the value is
4826 passed to the kernel using a special protocol.
4828 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4829 size of <nn>. This can be used to increase the
4830 minimum size (128MB on x86). It can also be used to
4831 decrease the size and leave more room for directly
4832 mapped kernel RAM.
4834 vmcp_cma=nn[MG] [KNL,S390]
4835 Sets the memory size reserved for contiguous memory
4836 allocations for the vmcp device driver.
4838 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4839 Format: <command>
4841 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4842 Format: <command>
4844 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4845 Format: <command>
4847 vsyscall= [X86-64]
4848 Controls the behavior of vsyscalls (i.e. calls to
4849 fixed addresses of 0xffffffffff600x00 from legacy
4850 code). Most statically-linked binaries and older
4851 versions of glibc use these calls. Because these
4852 functions are at fixed addresses, they make nice
4853 targets for exploits that can control RIP.
4855 emulate [default] Vsyscalls turn into traps and are
4856 emulated reasonably safely.
4858 native Vsyscalls are native syscall instructions.
4859 This is a little bit faster than trapping
4860 and makes a few dynamic recompilers work
4861 better than they would in emulation mode.
4862 It also makes exploits much easier to write.
4864 none Vsyscalls don't work at all. This makes
4865 them quite hard to use for exploits but
4866 might break your system.
4868 vt.color= [VT] Default text color.
4869 Format: 0xYX, X = foreground, Y = background.
4870 Default: 0x07 = light gray on black.
4872 vt.cur_default= [VT] Default cursor shape.
4873 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4874 the parameters of the <Esc>[?A;B;Cc escape sequence;
4875 see VGA-softcursor.txt. Default: 2 = underline.
4877 vt.default_blu= [VT]
4878 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4879 Change the default blue palette of the console.
4880 This is a 16-member array composed of values
4881 ranging from 0-255.
4883 vt.default_grn= [VT]
4884 Format: <green0>,<green1>,<green2>,...,<green15>
4885 Change the default green palette of the console.
4886 This is a 16-member array composed of values
4887 ranging from 0-255.
4889 vt.default_red= [VT]
4890 Format: <red0>,<red1>,<red2>,...,<red15>
4891 Change the default red palette of the console.
4892 This is a 16-member array composed of values
4893 ranging from 0-255.
4895 vt.default_utf8=
4896 [VT]
4897 Format=<0|1>
4898 Set system-wide default UTF-8 mode for all tty's.
4899 Default is 1, i.e. UTF-8 mode is enabled for all
4900 newly opened terminals.
4902 vt.global_cursor_default=
4903 [VT]
4904 Format=<-1|0|1>
4905 Set system-wide default for whether a cursor
4906 is shown on new VTs. Default is -1,
4907 i.e. cursors will be created by default unless
4908 overridden by individual drivers. 0 will hide
4909 cursors, 1 will display them.
4911 vt.italic= [VT] Default color for italic text; 0-15.
4912 Default: 2 = green.
4914 vt.underline= [VT] Default color for underlined text; 0-15.
4915 Default: 3 = cyan.
4917 watchdog timers [HW,WDT] For information on watchdog timers,
4918 see Documentation/watchdog/watchdog-parameters.txt
4919 or other driver-specific files in the
4920 Documentation/watchdog/ directory.
4922 workqueue.watchdog_thresh=
4923 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4924 warn stall conditions and dump internal state to
4925 help debugging. 0 disables workqueue stall
4926 detection; otherwise, it's the stall threshold
4927 duration in seconds. The default value is 30 and
4928 it can be updated at runtime by writing to the
4929 corresponding sysfs file.
4931 workqueue.disable_numa
4932 By default, all work items queued to unbound
4933 workqueues are affine to the NUMA nodes they're
4934 issued on, which results in better behavior in
4935 general. If NUMA affinity needs to be disabled for
4936 whatever reason, this option can be used. Note
4937 that this also can be controlled per-workqueue for
4938 workqueues visible under /sys/bus/workqueue/.
4940 workqueue.power_efficient
4941 Per-cpu workqueues are generally preferred because
4942 they show better performance thanks to cache
4943 locality; unfortunately, per-cpu workqueues tend to
4944 be more power hungry than unbound workqueues.
4946 Enabling this makes the per-cpu workqueues which
4947 were observed to contribute significantly to power
4948 consumption unbound, leading to measurably lower
4949 power usage at the cost of small performance
4950 overhead.
4952 The default value of this parameter is determined by
4953 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4955 workqueue.debug_force_rr_cpu
4956 Workqueue used to implicitly guarantee that work
4957 items queued without explicit CPU specified are put
4958 on the local CPU. This guarantee is no longer true
4959 and while local CPU is still preferred work items
4960 may be put on foreign CPUs. This debug option
4961 forces round-robin CPU selection to flush out
4962 usages which depend on the now broken guarantee.
4963 When enabled, memory and cache locality will be
4964 impacted.
4966 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4967 default x2apic cluster mode on platforms
4968 supporting x2apic.
4970 x86_intel_mid_timer= [X86-32,APBT]
4971 Choose timer option for x86 Intel MID platform.
4972 Two valid options are apbt timer only and lapic timer
4973 plus one apbt timer for broadcast timer.
4974 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4976 xen_512gb_limit [KNL,X86-64,XEN]
4977 Restricts the kernel running paravirtualized under Xen
4978 to use only up to 512 GB of RAM. The reason to do so is
4979 crash analysis tools and Xen tools for doing domain
4980 save/restore/migration must be enabled to handle larger
4981 domains.
4983 xen_emul_unplug= [HW,X86,XEN]
4984 Unplug Xen emulated devices
4985 Format: [unplug0,][unplug1]
4986 ide-disks -- unplug primary master IDE devices
4987 aux-ide-disks -- unplug non-primary-master IDE devices
4988 nics -- unplug network devices
4989 all -- unplug all emulated devices (NICs and IDE disks)
4990 unnecessary -- unplugging emulated devices is
4991 unnecessary even if the host did not respond to
4992 the unplug protocol
4993 never -- do not unplug even if version check succeeds
4995 xen_nopvspin [X86,XEN]
4996 Disables the ticketlock slowpath using Xen PV
4997 optimizations.
4999 xen_nopv [X86]
5000 Disables the PV optimizations forcing the HVM guest to
5001 run as generic HVM guest with no PV drivers.
5003 xen_scrub_pages= [XEN]
5004 Boolean option to control scrubbing pages before giving them back
5005 to Xen, for use by other domains. Can be also changed at runtime
5006 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
5007 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
5009 xirc2ps_cs= [NET,PCMCIA]
5010 Format:
5011 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
5013 xhci-hcd.quirks [USB,KNL]
5014 A hex value specifying bitmask with supplemental xhci
5015 host controller quirks. Meaning of each bit can be
5016 consulted in header drivers/usb/host/xhci.h.