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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
15
16 See also Documentation/power/runtime_pm.txt, pci=noacpi
17
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
23
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.
30
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.
36
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.
44
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.
58
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
68
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.
72
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.
88
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.
93
94 acpi_irq_balance [HW,ACPI]
95 ACPI will balance active IRQs
96 default in APIC mode
97
98 acpi_irq_nobalance [HW,ACPI]
99 ACPI will not move active IRQs (default)
100 default in PIC mode
101
102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
103 Format: <irq>,<irq>...
104
105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
106 use by PCI
107 Format: <irq>,<irq>...
108
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>
117 Support masking of GPEs numbered from 0x00 to 0x7f.
118
119 acpi_no_auto_serialize [HW,ACPI]
120 Disable auto-serialization of AML methods
121 AML control methods that contain the opcodes to create
122 named objects will be marked as "Serialized" by the
123 auto-serialization feature.
124 This feature is enabled by default.
125 This option allows to turn off the feature.
126
127 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
128 kernels.
129
130 acpi_no_static_ssdt [HW,ACPI]
131 Disable installation of static SSDTs at early boot time
132 By default, SSDTs contained in the RSDT/XSDT will be
133 installed automatically and they will appear under
134 /sys/firmware/acpi/tables.
135 This option turns off this feature.
136 Note that specifying this option does not affect
137 dynamic table installation which will install SSDT
138 tables to /sys/firmware/acpi/tables/dynamic.
139
140 acpi_rsdp= [ACPI,EFI,KEXEC]
141 Pass the RSDP address to the kernel, mostly used
142 on machines running EFI runtime service to boot the
143 second kernel for kdump.
144
145 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
146 Format: To spoof as Windows 98: ="Microsoft Windows"
147
148 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
149 of 2 which is mandated by ACPI 6) as the supported ACPI
150 specification revision (when using this switch, it may
151 be necessary to carry out a cold reboot _twice_ in a
152 row to make it take effect on the platform firmware).
153
154 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
155 acpi_osi="string1" # add string1
156 acpi_osi="!string2" # remove string2
157 acpi_osi=!* # remove all strings
158 acpi_osi=! # disable all built-in OS vendor
159 strings
160 acpi_osi=!! # enable all built-in OS vendor
161 strings
162 acpi_osi= # disable all strings
163
164 'acpi_osi=!' can be used in combination with single or
165 multiple 'acpi_osi="string1"' to support specific OS
166 vendor string(s). Note that such command can only
167 affect the default state of the OS vendor strings, thus
168 it cannot affect the default state of the feature group
169 strings and the current state of the OS vendor strings,
170 specifying it multiple times through kernel command line
171 is meaningless. This command is useful when one do not
172 care about the state of the feature group strings which
173 should be controlled by the OSPM.
174 Examples:
175 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
176 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
177 can make '_OSI("Windows 2000")' TRUE.
178
179 'acpi_osi=' cannot be used in combination with other
180 'acpi_osi=' command lines, the _OSI method will not
181 exist in the ACPI namespace. NOTE that such command can
182 only affect the _OSI support state, thus specifying it
183 multiple times through kernel command line is also
184 meaningless.
185 Examples:
186 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
187 FALSE.
188
189 'acpi_osi=!*' can be used in combination with single or
190 multiple 'acpi_osi="string1"' to support specific
191 string(s). Note that such command can affect the
192 current state of both the OS vendor strings and the
193 feature group strings, thus specifying it multiple times
194 through kernel command line is meaningful. But it may
195 still not able to affect the final state of a string if
196 there are quirks related to this string. This command
197 is useful when one want to control the state of the
198 feature group strings to debug BIOS issues related to
199 the OSPM features.
200 Examples:
201 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
202 '_OSI("Module Device")' FALSE.
203 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
204 '_OSI("Module Device")' TRUE.
205 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
206 equivalent to
207 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
208 and
209 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
210 they all will make '_OSI("Windows 2000")' TRUE.
211
212 acpi_pm_good [X86]
213 Override the pmtimer bug detection: force the kernel
214 to assume that this machine's pmtimer latches its value
215 and always returns good values.
216
217 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
218 Format: { level | edge | high | low }
219
220 acpi_skip_timer_override [HW,ACPI]
221 Recognize and ignore IRQ0/pin2 Interrupt Override.
222 For broken nForce2 BIOS resulting in XT-PIC timer.
223
224 acpi_sleep= [HW,ACPI] Sleep options
225 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
226 old_ordering, nonvs, sci_force_enable }
227 See Documentation/power/video.txt for information on
228 s3_bios and s3_mode.
229 s3_beep is for debugging; it makes the PC's speaker beep
230 as soon as the kernel's real-mode entry point is called.
231 s4_nohwsig prevents ACPI hardware signature from being
232 used during resume from hibernation.
233 old_ordering causes the ACPI 1.0 ordering of the _PTS
234 control method, with respect to putting devices into
235 low power states, to be enforced (the ACPI 2.0 ordering
236 of _PTS is used by default).
237 nonvs prevents the kernel from saving/restoring the
238 ACPI NVS memory during suspend/hibernation and resume.
239 sci_force_enable causes the kernel to set SCI_EN directly
240 on resume from S1/S3 (which is against the ACPI spec,
241 but some broken systems don't work without it).
242
243 acpi_use_timer_override [HW,ACPI]
244 Use timer override. For some broken Nvidia NF5 boards
245 that require a timer override, but don't have HPET
246
247 add_efi_memmap [EFI; X86] Include EFI memory map in
248 kernel's map of available physical RAM.
249
250 agp= [AGP]
251 { off | try_unsupported }
252 off: disable AGP support
253 try_unsupported: try to drive unsupported chipsets
254 (may crash computer or cause data corruption)
255
256 ALSA [HW,ALSA]
257 See Documentation/sound/alsa/alsa-parameters.txt
258
259 alignment= [KNL,ARM]
260 Allow the default userspace alignment fault handler
261 behaviour to be specified. Bit 0 enables warnings,
262 bit 1 enables fixups, and bit 2 sends a segfault.
263
264 align_va_addr= [X86-64]
265 Align virtual addresses by clearing slice [14:12] when
266 allocating a VMA at process creation time. This option
267 gives you up to 3% performance improvement on AMD F15h
268 machines (where it is enabled by default) for a
269 CPU-intensive style benchmark, and it can vary highly in
270 a microbenchmark depending on workload and compiler.
271
272 32: only for 32-bit processes
273 64: only for 64-bit processes
274 on: enable for both 32- and 64-bit processes
275 off: disable for both 32- and 64-bit processes
276
277 alloc_snapshot [FTRACE]
278 Allocate the ftrace snapshot buffer on boot up when the
279 main buffer is allocated. This is handy if debugging
280 and you need to use tracing_snapshot() on boot up, and
281 do not want to use tracing_snapshot_alloc() as it needs
282 to be done where GFP_KERNEL allocations are allowed.
283
284 amd_iommu= [HW,X86-64]
285 Pass parameters to the AMD IOMMU driver in the system.
286 Possible values are:
287 fullflush - enable flushing of IO/TLB entries when
288 they are unmapped. Otherwise they are
289 flushed before they will be reused, which
290 is a lot of faster
291 off - do not initialize any AMD IOMMU found in
292 the system
293 force_isolation - Force device isolation for all
294 devices. The IOMMU driver is not
295 allowed anymore to lift isolation
296 requirements as needed. This option
297 does not override iommu=pt
298
299 amd_iommu_dump= [HW,X86-64]
300 Enable AMD IOMMU driver option to dump the ACPI table
301 for AMD IOMMU. With this option enabled, AMD IOMMU
302 driver will print ACPI tables for AMD IOMMU during
303 IOMMU initialization.
304
305 amd_iommu_intr= [HW,X86-64]
306 Specifies one of the following AMD IOMMU interrupt
307 remapping modes:
308 legacy - Use legacy interrupt remapping mode.
309 vapic - Use virtual APIC mode, which allows IOMMU
310 to inject interrupts directly into guest.
311 This mode requires kvm-amd.avic=1.
312 (Default when IOMMU HW support is present.)
313
314 amijoy.map= [HW,JOY] Amiga joystick support
315 Map of devices attached to JOY0DAT and JOY1DAT
316 Format: <a>,<b>
317 See also Documentation/input/joydev/joystick.rst
318
319 analog.map= [HW,JOY] Analog joystick and gamepad support
320 Specifies type or capabilities of an analog joystick
321 connected to one of 16 gameports
322 Format: <type1>,<type2>,..<type16>
323
324 apc= [HW,SPARC]
325 Power management functions (SPARCstation-4/5 + deriv.)
326 Format: noidle
327 Disable APC CPU standby support. SPARCstation-Fox does
328 not play well with APC CPU idle - disable it if you have
329 APC and your system crashes randomly.
330
331 apic= [APIC,X86] Advanced Programmable Interrupt Controller
332 Change the output verbosity whilst booting
333 Format: { quiet (default) | verbose | debug }
334 Change the amount of debugging information output
335 when initialising the APIC and IO-APIC components.
336 For X86-32, this can also be used to specify an APIC
337 driver name.
338 Format: apic=driver_name
339 Examples: apic=bigsmp
340
341 apic_extnmi= [APIC,X86] External NMI delivery setting
342 Format: { bsp (default) | all | none }
343 bsp: External NMI is delivered only to CPU 0
344 all: External NMIs are broadcast to all CPUs as a
345 backup of CPU 0
346 none: External NMI is masked for all CPUs. This is
347 useful so that a dump capture kernel won't be
348 shot down by NMI
349
350 autoconf= [IPV6]
351 See Documentation/networking/ipv6.txt.
352
353 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
354 Limit apic dumping. The parameter defines the maximal
355 number of local apics being dumped. Also it is possible
356 to set it to "all" by meaning -- no limit here.
357 Format: { 1 (default) | 2 | ... | all }.
358 The parameter valid if only apic=debug or
359 apic=verbose is specified.
360 Example: apic=debug show_lapic=all
361
362 apm= [APM] Advanced Power Management
363 See header of arch/x86/kernel/apm_32.c.
364
365 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
366 Format: <io>,<irq>,<nodeID>
367
368 ataflop= [HW,M68k]
369
370 atarimouse= [HW,MOUSE] Atari Mouse
371
372 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
373 EzKey and similar keyboards
374
375 atkbd.reset= [HW] Reset keyboard during initialization
376
377 atkbd.set= [HW] Select keyboard code set
378 Format: <int> (2 = AT (default), 3 = PS/2)
379
380 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
381 keyboards
382
383 atkbd.softraw= [HW] Choose between synthetic and real raw mode
384 Format: <bool> (0 = real, 1 = synthetic (default))
385
386 atkbd.softrepeat= [HW]
387 Use software keyboard repeat
388
389 audit= [KNL] Enable the audit sub-system
390 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
391 0 - kernel audit is disabled and can not be enabled
392 until the next reboot
393 unset - kernel audit is initialized but disabled and
394 will be fully enabled by the userspace auditd.
395 1 - kernel audit is initialized and partially enabled,
396 storing at most audit_backlog_limit messages in
397 RAM until it is fully enabled by the userspace
398 auditd.
399 Default: unset
400
401 audit_backlog_limit= [KNL] Set the audit queue size limit.
402 Format: <int> (must be >=0)
403 Default: 64
404
405 bau= [X86_UV] Enable the BAU on SGI UV. The default
406 behavior is to disable the BAU (i.e. bau=0).
407 Format: { "0" | "1" }
408 0 - Disable the BAU.
409 1 - Enable the BAU.
410 unset - Disable the BAU.
411
412 baycom_epp= [HW,AX25]
413 Format: <io>,<mode>
414
415 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
416 Format: <io>,<mode>
417 See header of drivers/net/hamradio/baycom_par.c.
418
419 baycom_ser_fdx= [HW,AX25]
420 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
421 Format: <io>,<irq>,<mode>[,<baud>]
422 See header of drivers/net/hamradio/baycom_ser_fdx.c.
423
424 baycom_ser_hdx= [HW,AX25]
425 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
426 Format: <io>,<irq>,<mode>
427 See header of drivers/net/hamradio/baycom_ser_hdx.c.
428
429 blkdevparts= Manual partition parsing of block device(s) for
430 embedded devices based on command line input.
431 See Documentation/block/cmdline-partition.txt
432
433 boot_delay= Milliseconds to delay each printk during boot.
434 Values larger than 10 seconds (10000) are changed to
435 no delay (0).
436 Format: integer
437
438 bootmem_debug [KNL] Enable bootmem allocator debug messages.
439
440 bert_disable [ACPI]
441 Disable BERT OS support on buggy BIOSes.
442
443 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
444 bttv.radio= Most important insmod options are available as
445 kernel args too.
446 bttv.pll= See Documentation/media/v4l-drivers/bttv.rst
447 bttv.tuner=
448
449 bulk_remove=off [PPC] This parameter disables the use of the pSeries
450 firmware feature for flushing multiple hpte entries
451 at a time.
452
453 c101= [NET] Moxa C101 synchronous serial card
454
455 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
456 Sometimes CPU hardware bugs make them report the cache
457 size incorrectly. The kernel will attempt work arounds
458 to fix known problems, but for some CPUs it is not
459 possible to determine what the correct size should be.
460 This option provides an override for these situations.
461
462 ca_keys= [KEYS] This parameter identifies a specific key(s) on
463 the system trusted keyring to be used for certificate
464 trust validation.
465 format: { id:<keyid> | builtin }
466
467 cca= [MIPS] Override the kernel pages' cache coherency
468 algorithm. Accepted values range from 0 to 7
469 inclusive. See arch/mips/include/asm/pgtable-bits.h
470 for platform specific values (SB1, Loongson3 and
471 others).
472
473 ccw_timeout_log [S390]
474 See Documentation/s390/CommonIO for details.
475
476 cgroup_disable= [KNL] Disable a particular controller
477 Format: {name of the controller(s) to disable}
478 The effects of cgroup_disable=foo are:
479 - foo isn't auto-mounted if you mount all cgroups in
480 a single hierarchy
481 - foo isn't visible as an individually mountable
482 subsystem
483 {Currently only "memory" controller deal with this and
484 cut the overhead, others just disable the usage. So
485 only cgroup_disable=memory is actually worthy}
486
487 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
488 Format: { controller[,controller...] | "all" }
489 Like cgroup_disable, but only applies to cgroup v1;
490 the blacklisted controllers remain available in cgroup2.
491
492 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
493 Format: <string>
494 nosocket -- Disable socket memory accounting.
495 nokmem -- Disable kernel memory accounting.
496
497 checkreqprot [SELINUX] Set initial checkreqprot flag value.
498 Format: { "0" | "1" }
499 See security/selinux/Kconfig help text.
500 0 -- check protection applied by kernel (includes
501 any implied execute protection).
502 1 -- check protection requested by application.
503 Default value is set via a kernel config option.
504 Value can be changed at runtime via
505 /selinux/checkreqprot.
506
507 cio_ignore= [S390]
508 See Documentation/s390/CommonIO for details.
509 clk_ignore_unused
510 [CLK]
511 Prevents the clock framework from automatically gating
512 clocks that have not been explicitly enabled by a Linux
513 device driver but are enabled in hardware at reset or
514 by the bootloader/firmware. Note that this does not
515 force such clocks to be always-on nor does it reserve
516 those clocks in any way. This parameter is useful for
517 debug and development, but should not be needed on a
518 platform with proper driver support. For more
519 information, see Documentation/clk.txt.
520
521 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
522 [Deprecated]
523 Forces specified clocksource (if available) to be used
524 when calculating gettimeofday(). If specified
525 clocksource is not available, it defaults to PIT.
526 Format: { pit | tsc | cyclone | pmtmr }
527
528 clocksource= Override the default clocksource
529 Format: <string>
530 Override the default clocksource and use the clocksource
531 with the name specified.
532 Some clocksource names to choose from, depending on
533 the platform:
534 [all] jiffies (this is the base, fallback clocksource)
535 [ACPI] acpi_pm
536 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
537 pxa_timer,timer3,32k_counter,timer0_1
538 [X86-32] pit,hpet,tsc;
539 scx200_hrt on Geode; cyclone on IBM x440
540 [MIPS] MIPS
541 [PARISC] cr16
542 [S390] tod
543 [SH] SuperH
544 [SPARC64] tick
545 [X86-64] hpet,tsc
546
547 clocksource.arm_arch_timer.evtstrm=
548 [ARM,ARM64]
549 Format: <bool>
550 Enable/disable the eventstream feature of the ARM
551 architected timer so that code using WFE-based polling
552 loops can be debugged more effectively on production
553 systems.
554
555 clearcpuid=BITNUM [X86]
556 Disable CPUID feature X for the kernel. See
557 arch/x86/include/asm/cpufeatures.h for the valid bit
558 numbers. Note the Linux specific bits are not necessarily
559 stable over kernel options, but the vendor specific
560 ones should be.
561 Also note that user programs calling CPUID directly
562 or using the feature without checking anything
563 will still see it. This just prevents it from
564 being used by the kernel or shown in /proc/cpuinfo.
565 Also note the kernel might malfunction if you disable
566 some critical bits.
567
568 cma=nn[MG]@[start[MG][-end[MG]]]
569 [ARM,X86,KNL]
570 Sets the size of kernel global memory area for
571 contiguous memory allocations and optionally the
572 placement constraint by the physical address range of
573 memory allocations. A value of 0 disables CMA
574 altogether. For more information, see
575 include/linux/dma-contiguous.h
576
577 cmo_free_hint= [PPC] Format: { yes | no }
578 Specify whether pages are marked as being inactive
579 when they are freed. This is used in CMO environments
580 to determine OS memory pressure for page stealing by
581 a hypervisor.
582 Default: yes
583
584 coherent_pool=nn[KMG] [ARM,KNL]
585 Sets the size of memory pool for coherent, atomic dma
586 allocations, by default set to 256K.
587
588 code_bytes [X86] How many bytes of object code to print
589 in an oops report.
590 Range: 0 - 8192
591 Default: 64
592
593 com20020= [HW,NET] ARCnet - COM20020 chipset
594 Format:
595 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
596
597 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
598 Format: <io>[,<irq>]
599
600 com90xx= [HW,NET]
601 ARCnet - COM90xx chipset (memory-mapped buffers)
602 Format: <io>[,<irq>[,<memstart>]]
603
604 condev= [HW,S390] console device
605 conmode=
606
607 console= [KNL] Output console device and options.
608
609 tty<n> Use the virtual console device <n>.
610
611 ttyS<n>[,options]
612 ttyUSB0[,options]
613 Use the specified serial port. The options are of
614 the form "bbbbpnf", where "bbbb" is the baud rate,
615 "p" is parity ("n", "o", or "e"), "n" is number of
616 bits, and "f" is flow control ("r" for RTS or
617 omit it). Default is "9600n8".
618
619 See Documentation/admin-guide/serial-console.rst for more
620 information. See
621 Documentation/networking/netconsole.txt for an
622 alternative.
623
624 uart[8250],io,<addr>[,options]
625 uart[8250],mmio,<addr>[,options]
626 uart[8250],mmio16,<addr>[,options]
627 uart[8250],mmio32,<addr>[,options]
628 uart[8250],0x<addr>[,options]
629 Start an early, polled-mode console on the 8250/16550
630 UART at the specified I/O port or MMIO address,
631 switching to the matching ttyS device later.
632 MMIO inter-register address stride is either 8-bit
633 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
634 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
635 to be equivalent to 'mmio'. 'options' are specified in
636 the same format described for ttyS above; if unspecified,
637 the h/w is not re-initialized.
638
639 hvc<n> Use the hypervisor console device <n>. This is for
640 both Xen and PowerPC hypervisors.
641
642 If the device connected to the port is not a TTY but a braille
643 device, prepend "brl," before the device type, for instance
644 console=brl,ttyS0
645 For now, only VisioBraille is supported.
646
647 consoleblank= [KNL] The console blank (screen saver) timeout in
648 seconds. A value of 0 disables the blank timer.
649 Defaults to 0.
650
651 coredump_filter=
652 [KNL] Change the default value for
653 /proc/<pid>/coredump_filter.
654 See also Documentation/filesystems/proc.txt.
655
656 coresight_cpu_debug.enable
657 [ARM,ARM64]
658 Format: <bool>
659 Enable/disable the CPU sampling based debugging.
660 0: default value, disable debugging
661 1: enable debugging at boot time
662
663 cpufreq_driver= [X86] Allow only the named cpu frequency scaling driver
664 to register. Example: cpufreq_driver=powernow-k8
665 Format: { none | STRING }
666
667 cpuidle.off=1 [CPU_IDLE]
668 disable the cpuidle sub-system
669
670 cpufreq.off=1 [CPU_FREQ]
671 disable the cpufreq sub-system
672
673 cpu_init_udelay=N
674 [X86] Delay for N microsec between assert and de-assert
675 of APIC INIT to start processors. This delay occurs
676 on every CPU online, such as boot, and resume from suspend.
677 Default: 10000
678
679 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
680 Format:
681 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
682
683 crashkernel=size[KMG][@offset[KMG]]
684 [KNL] Using kexec, Linux can switch to a 'crash kernel'
685 upon panic. This parameter reserves the physical
686 memory region [offset, offset + size] for that kernel
687 image. If '@offset' is omitted, then a suitable offset
688 is selected automatically. Check
689 Documentation/kdump/kdump.txt for further details.
690
691 crashkernel=range1:size1[,range2:size2,...][@offset]
692 [KNL] Same as above, but depends on the memory
693 in the running system. The syntax of range is
694 start-[end] where start and end are both
695 a memory unit (amount[KMG]). See also
696 Documentation/kdump/kdump.txt for an example.
697
698 crashkernel=size[KMG],high
699 [KNL, x86_64] range could be above 4G. Allow kernel
700 to allocate physical memory region from top, so could
701 be above 4G if system have more than 4G ram installed.
702 Otherwise memory region will be allocated below 4G, if
703 available.
704 It will be ignored if crashkernel=X is specified.
705 crashkernel=size[KMG],low
706 [KNL, x86_64] range under 4G. When crashkernel=X,high
707 is passed, kernel could allocate physical memory region
708 above 4G, that cause second kernel crash on system
709 that require some amount of low memory, e.g. swiotlb
710 requires at least 64M+32K low memory, also enough extra
711 low memory is needed to make sure DMA buffers for 32-bit
712 devices won't run out. Kernel would try to allocate at
713 at least 256M below 4G automatically.
714 This one let user to specify own low range under 4G
715 for second kernel instead.
716 0: to disable low allocation.
717 It will be ignored when crashkernel=X,high is not used
718 or memory reserved is below 4G.
719
720 cryptomgr.notests
721 [KNL] Disable crypto self-tests
722
723 cs89x0_dma= [HW,NET]
724 Format: <dma>
725
726 cs89x0_media= [HW,NET]
727 Format: { rj45 | aui | bnc }
728
729 dasd= [HW,NET]
730 See header of drivers/s390/block/dasd_devmap.c.
731
732 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
733 (one device per port)
734 Format: <port#>,<type>
735 See also Documentation/input/devices/joystick-parport.rst
736
737 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
738 time. See
739 Documentation/admin-guide/dynamic-debug-howto.rst for
740 details. Deprecated, see dyndbg.
741
742 debug [KNL] Enable kernel debugging (events log level).
743
744 debug_locks_verbose=
745 [KNL] verbose self-tests
746 Format=<0|1>
747 Print debugging info while doing the locking API
748 self-tests.
749 We default to 0 (no extra messages), setting it to
750 1 will print _a lot_ more information - normally
751 only useful to kernel developers.
752
753 debug_objects [KNL] Enable object debugging
754
755 no_debug_objects
756 [KNL] Disable object debugging
757
758 debug_guardpage_minorder=
759 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
760 parameter allows control of the order of pages that will
761 be intentionally kept free (and hence protected) by the
762 buddy allocator. Bigger value increase the probability
763 of catching random memory corruption, but reduce the
764 amount of memory for normal system use. The maximum
765 possible value is MAX_ORDER/2. Setting this parameter
766 to 1 or 2 should be enough to identify most random
767 memory corruption problems caused by bugs in kernel or
768 driver code when a CPU writes to (or reads from) a
769 random memory location. Note that there exists a class
770 of memory corruptions problems caused by buggy H/W or
771 F/W or by drivers badly programing DMA (basically when
772 memory is written at bus level and the CPU MMU is
773 bypassed) which are not detectable by
774 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
775 tracking down these problems.
776
777 debug_pagealloc=
778 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
779 parameter enables the feature at boot time. In
780 default, it is disabled. We can avoid allocating huge
781 chunk of memory for debug pagealloc if we don't enable
782 it at boot time and the system will work mostly same
783 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
784 on: enable the feature
785
786 debugpat [X86] Enable PAT debugging
787
788 decnet.addr= [HW,NET]
789 Format: <area>[,<node>]
790 See also Documentation/networking/decnet.txt.
791
792 default_hugepagesz=
793 [same as hugepagesz=] The size of the default
794 HugeTLB page size. This is the size represented by
795 the legacy /proc/ hugepages APIs, used for SHM, and
796 default size when mounting hugetlbfs filesystems.
797 Defaults to the default architecture's huge page size
798 if not specified.
799
800 dhash_entries= [KNL]
801 Set number of hash buckets for dentry cache.
802
803 disable_1tb_segments [PPC]
804 Disables the use of 1TB hash page table segments. This
805 causes the kernel to fall back to 256MB segments which
806 can be useful when debugging issues that require an SLB
807 miss to occur.
808
809 disable= [IPV6]
810 See Documentation/networking/ipv6.txt.
811
812 disable_radix [PPC]
813 Disable RADIX MMU mode on POWER9
814
815 disable_cpu_apicid= [X86,APIC,SMP]
816 Format: <int>
817 The number of initial APIC ID for the
818 corresponding CPU to be disabled at boot,
819 mostly used for the kdump 2nd kernel to
820 disable BSP to wake up multiple CPUs without
821 causing system reset or hang due to sending
822 INIT from AP to BSP.
823
824 disable_ddw [PPC/PSERIES]
825 Disable Dynamic DMA Window support. Use this if
826 to workaround buggy firmware.
827
828 disable_ipv6= [IPV6]
829 See Documentation/networking/ipv6.txt.
830
831 disable_mtrr_cleanup [X86]
832 The kernel tries to adjust MTRR layout from continuous
833 to discrete, to make X server driver able to add WB
834 entry later. This parameter disables that.
835
836 disable_mtrr_trim [X86, Intel and AMD only]
837 By default the kernel will trim any uncacheable
838 memory out of your available memory pool based on
839 MTRR settings. This parameter disables that behavior,
840 possibly causing your machine to run very slowly.
841
842 disable_timer_pin_1 [X86]
843 Disable PIN 1 of APIC timer
844 Can be useful to work around chipset bugs.
845
846 dis_ucode_ldr [X86] Disable the microcode loader.
847
848 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
849 this option disables the debugging code at boot.
850
851 dma_debug_entries=<number>
852 This option allows to tune the number of preallocated
853 entries for DMA-API debugging code. One entry is
854 required per DMA-API allocation. Use this if the
855 DMA-API debugging code disables itself because the
856 architectural default is too low.
857
858 dma_debug_driver=<driver_name>
859 With this option the DMA-API debugging driver
860 filter feature can be enabled at boot time. Just
861 pass the driver to filter for as the parameter.
862 The filter can be disabled or changed to another
863 driver later using sysfs.
864
865 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
866 Broken monitors, graphic adapters, KVMs and EDIDless
867 panels may send no or incorrect EDID data sets.
868 This parameter allows to specify an EDID data sets
869 in the /lib/firmware directory that are used instead.
870 Generic built-in EDID data sets are used, if one of
871 edid/1024x768.bin, edid/1280x1024.bin,
872 edid/1680x1050.bin, or edid/1920x1080.bin is given
873 and no file with the same name exists. Details and
874 instructions how to build your own EDID data are
875 available in Documentation/EDID/HOWTO.txt. An EDID
876 data set will only be used for a particular connector,
877 if its name and a colon are prepended to the EDID
878 name. Each connector may use a unique EDID data
879 set by separating the files with a comma. An EDID
880 data set with no connector name will be used for
881 any connectors not explicitly specified.
882
883 dscc4.setup= [NET]
884
885 dt_cpu_ftrs= [PPC]
886 Format: {"off" | "known"}
887 Control how the dt_cpu_ftrs device-tree binding is
888 used for CPU feature discovery and setup (if it
889 exists).
890 off: Do not use it, fall back to legacy cpu table.
891 known: Do not pass through unknown features to guests
892 or userspace, only those that the kernel is aware of.
893
894 dump_apple_properties [X86]
895 Dump name and content of EFI device properties on
896 x86 Macs. Useful for driver authors to determine
897 what data is available or for reverse-engineering.
898
899 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
900 module.dyndbg[="val"]
901 Enable debug messages at boot time. See
902 Documentation/admin-guide/dynamic-debug-howto.rst
903 for details.
904
905 nompx [X86] Disables Intel Memory Protection Extensions.
906 See Documentation/x86/intel_mpx.txt for more
907 information about the feature.
908
909 nopku [X86] Disable Memory Protection Keys CPU feature found
910 in some Intel CPUs.
911
912 module.async_probe [KNL]
913 Enable asynchronous probe on this module.
914
915 early_ioremap_debug [KNL]
916 Enable debug messages in early_ioremap support. This
917 is useful for tracking down temporary early mappings
918 which are not unmapped.
919
920 earlycon= [KNL] Output early console device and options.
921
922 When used with no options, the early console is
923 determined by the stdout-path property in device
924 tree's chosen node.
925
926 cdns,<addr>[,options]
927 Start an early, polled-mode console on a Cadence
928 (xuartps) serial port at the specified address. Only
929 supported option is baud rate. If baud rate is not
930 specified, the serial port must already be setup and
931 configured.
932
933 uart[8250],io,<addr>[,options]
934 uart[8250],mmio,<addr>[,options]
935 uart[8250],mmio32,<addr>[,options]
936 uart[8250],mmio32be,<addr>[,options]
937 uart[8250],0x<addr>[,options]
938 Start an early, polled-mode console on the 8250/16550
939 UART at the specified I/O port or MMIO address.
940 MMIO inter-register address stride is either 8-bit
941 (mmio) or 32-bit (mmio32 or mmio32be).
942 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
943 to be equivalent to 'mmio'. 'options' are specified
944 in the same format described for "console=ttyS<n>"; if
945 unspecified, the h/w is not initialized.
946
947 pl011,<addr>
948 pl011,mmio32,<addr>
949 Start an early, polled-mode console on a pl011 serial
950 port at the specified address. The pl011 serial port
951 must already be setup and configured. Options are not
952 yet supported. If 'mmio32' is specified, then only
953 the driver will use only 32-bit accessors to read/write
954 the device registers.
955
956 meson,<addr>
957 Start an early, polled-mode console on a meson serial
958 port at the specified address. The serial port must
959 already be setup and configured. Options are not yet
960 supported.
961
962 msm_serial,<addr>
963 Start an early, polled-mode console on an msm serial
964 port at the specified address. The serial port
965 must already be setup and configured. Options are not
966 yet supported.
967
968 msm_serial_dm,<addr>
969 Start an early, polled-mode console on an msm serial
970 dm port at the specified address. The serial port
971 must already be setup and configured. Options are not
972 yet supported.
973
974 owl,<addr>
975 Start an early, polled-mode console on a serial port
976 of an Actions Semi SoC, such as S500 or S900, at the
977 specified address. The serial port must already be
978 setup and configured. Options are not yet supported.
979
980 smh Use ARM semihosting calls for early console.
981
982 s3c2410,<addr>
983 s3c2412,<addr>
984 s3c2440,<addr>
985 s3c6400,<addr>
986 s5pv210,<addr>
987 exynos4210,<addr>
988 Use early console provided by serial driver available
989 on Samsung SoCs, requires selecting proper type and
990 a correct base address of the selected UART port. The
991 serial port must already be setup and configured.
992 Options are not yet supported.
993
994 lantiq,<addr>
995 Start an early, polled-mode console on a lantiq serial
996 (lqasc) port at the specified address. The serial port
997 must already be setup and configured. Options are not
998 yet supported.
999
1000 lpuart,<addr>
1001 lpuart32,<addr>
1002 Use early console provided by Freescale LP UART driver
1003 found on Freescale Vybrid and QorIQ LS1021A processors.
1004 A valid base address must be provided, and the serial
1005 port must already be setup and configured.
1006
1007 ar3700_uart,<addr>
1008 Start an early, polled-mode console on the
1009 Armada 3700 serial port at the specified
1010 address. The serial port must already be setup
1011 and configured. Options are not yet supported.
1012
1013 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k,S390]
1014 earlyprintk=vga
1015 earlyprintk=efi
1016 earlyprintk=sclp
1017 earlyprintk=xen
1018 earlyprintk=serial[,ttySn[,baudrate]]
1019 earlyprintk=serial[,0x...[,baudrate]]
1020 earlyprintk=ttySn[,baudrate]
1021 earlyprintk=dbgp[debugController#]
1022 earlyprintk=pciserial,bus:device.function[,baudrate]
1023 earlyprintk=xdbc[xhciController#]
1024
1025 earlyprintk is useful when the kernel crashes before
1026 the normal console is initialized. It is not enabled by
1027 default because it has some cosmetic problems.
1028
1029 Append ",keep" to not disable it when the real console
1030 takes over.
1031
1032 Only one of vga, efi, serial, or usb debug port can
1033 be used at a time.
1034
1035 Currently only ttyS0 and ttyS1 may be specified by
1036 name. Other I/O ports may be explicitly specified
1037 on some architectures (x86 and arm at least) by
1038 replacing ttySn with an I/O port address, like this:
1039 earlyprintk=serial,0x1008,115200
1040 You can find the port for a given device in
1041 /proc/tty/driver/serial:
1042 2: uart:ST16650V2 port:00001008 irq:18 ...
1043
1044 Interaction with the standard serial driver is not
1045 very good.
1046
1047 The VGA and EFI output is eventually overwritten by
1048 the real console.
1049
1050 The xen output can only be used by Xen PV guests.
1051
1052 The sclp output can only be used on s390.
1053
1054 edac_report= [HW,EDAC] Control how to report EDAC event
1055 Format: {"on" | "off" | "force"}
1056 on: enable EDAC to report H/W event. May be overridden
1057 by other higher priority error reporting module.
1058 off: disable H/W event reporting through EDAC.
1059 force: enforce the use of EDAC to report H/W event.
1060 default: on.
1061
1062 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1063 ekgdboc=kbd
1064
1065 This is designed to be used in conjunction with
1066 the boot argument: earlyprintk=vga
1067
1068 edd= [EDD]
1069 Format: {"off" | "on" | "skip[mbr]"}
1070
1071 efi= [EFI]
1072 Format: { "old_map", "nochunk", "noruntime", "debug" }
1073 old_map [X86-64]: switch to the old ioremap-based EFI
1074 runtime services mapping. 32-bit still uses this one by
1075 default.
1076 nochunk: disable reading files in "chunks" in the EFI
1077 boot stub, as chunking can cause problems with some
1078 firmware implementations.
1079 noruntime : disable EFI runtime services support
1080 debug: enable misc debug output
1081
1082 efi_no_storage_paranoia [EFI; X86]
1083 Using this parameter you can use more than 50% of
1084 your efi variable storage. Use this parameter only if
1085 you are really sure that your UEFI does sane gc and
1086 fulfills the spec otherwise your board may brick.
1087
1088 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1089 Add arbitrary attribute to specific memory range by
1090 updating original EFI memory map.
1091 Region of memory which aa attribute is added to is
1092 from ss to ss+nn.
1093 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1094 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1095 attribute is added to range 0x100000000-0x180000000 and
1096 0x10a0000000-0x1120000000.
1097
1098 Using this parameter you can do debugging of EFI memmap
1099 related feature. For example, you can do debugging of
1100 Address Range Mirroring feature even if your box
1101 doesn't support it.
1102
1103 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1104 that is to be dynamically loaded by Linux. If there are
1105 multiple variables with the same name but with different
1106 vendor GUIDs, all of them will be loaded. See
1107 Documentation/acpi/ssdt-overlays.txt for details.
1108
1109
1110 eisa_irq_edge= [PARISC,HW]
1111 See header of drivers/parisc/eisa.c.
1112
1113 elanfreq= [X86-32]
1114 See comment before function elanfreq_setup() in
1115 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1116
1117 elevator= [IOSCHED]
1118 Format: {"cfq" | "deadline" | "noop"}
1119 See Documentation/block/cfq-iosched.txt and
1120 Documentation/block/deadline-iosched.txt for details.
1121
1122 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1123 Specifies physical address of start of kernel core
1124 image elf header and optionally the size. Generally
1125 kexec loader will pass this option to capture kernel.
1126 See Documentation/kdump/kdump.txt for details.
1127
1128 enable_mtrr_cleanup [X86]
1129 The kernel tries to adjust MTRR layout from continuous
1130 to discrete, to make X server driver able to add WB
1131 entry later. This parameter enables that.
1132
1133 enable_timer_pin_1 [X86]
1134 Enable PIN 1 of APIC timer
1135 Can be useful to work around chipset bugs
1136 (in particular on some ATI chipsets).
1137 The kernel tries to set a reasonable default.
1138
1139 enforcing [SELINUX] Set initial enforcing status.
1140 Format: {"0" | "1"}
1141 See security/selinux/Kconfig help text.
1142 0 -- permissive (log only, no denials).
1143 1 -- enforcing (deny and log).
1144 Default value is 0.
1145 Value can be changed at runtime via /selinux/enforce.
1146
1147 erst_disable [ACPI]
1148 Disable Error Record Serialization Table (ERST)
1149 support.
1150
1151 ether= [HW,NET] Ethernet cards parameters
1152 This option is obsoleted by the "netdev=" option, which
1153 has equivalent usage. See its documentation for details.
1154
1155 evm= [EVM]
1156 Format: { "fix" }
1157 Permit 'security.evm' to be updated regardless of
1158 current integrity status.
1159
1160 failslab=
1161 fail_page_alloc=
1162 fail_make_request=[KNL]
1163 General fault injection mechanism.
1164 Format: <interval>,<probability>,<space>,<times>
1165 See also Documentation/fault-injection/.
1166
1167 floppy= [HW]
1168 See Documentation/blockdev/floppy.txt.
1169
1170 force_pal_cache_flush
1171 [IA-64] Avoid check_sal_cache_flush which may hang on
1172 buggy SAL_CACHE_FLUSH implementations. Using this
1173 parameter will force ia64_sal_cache_flush to call
1174 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1175
1176 forcepae [X86-32]
1177 Forcefully enable Physical Address Extension (PAE).
1178 Many Pentium M systems disable PAE but may have a
1179 functionally usable PAE implementation.
1180 Warning: use of this parameter will taint the kernel
1181 and may cause unknown problems.
1182
1183 ftrace=[tracer]
1184 [FTRACE] will set and start the specified tracer
1185 as early as possible in order to facilitate early
1186 boot debugging.
1187
1188 ftrace_dump_on_oops[=orig_cpu]
1189 [FTRACE] will dump the trace buffers on oops.
1190 If no parameter is passed, ftrace will dump
1191 buffers of all CPUs, but if you pass orig_cpu, it will
1192 dump only the buffer of the CPU that triggered the
1193 oops.
1194
1195 ftrace_filter=[function-list]
1196 [FTRACE] Limit the functions traced by the function
1197 tracer at boot up. function-list is a comma separated
1198 list of functions. This list can be changed at run
1199 time by the set_ftrace_filter file in the debugfs
1200 tracing directory.
1201
1202 ftrace_notrace=[function-list]
1203 [FTRACE] Do not trace the functions specified in
1204 function-list. This list can be changed at run time
1205 by the set_ftrace_notrace file in the debugfs
1206 tracing directory.
1207
1208 ftrace_graph_filter=[function-list]
1209 [FTRACE] Limit the top level callers functions traced
1210 by the function graph tracer at boot up.
1211 function-list is a comma separated list of functions
1212 that can be changed at run time by the
1213 set_graph_function file in the debugfs tracing directory.
1214
1215 ftrace_graph_notrace=[function-list]
1216 [FTRACE] Do not trace from the functions specified in
1217 function-list. This list is a comma separated list of
1218 functions that can be changed at run time by the
1219 set_graph_notrace file in the debugfs tracing directory.
1220
1221 ftrace_graph_max_depth=<uint>
1222 [FTRACE] Used with the function graph tracer. This is
1223 the max depth it will trace into a function. This value
1224 can be changed at run time by the max_graph_depth file
1225 in the tracefs tracing directory. default: 0 (no limit)
1226
1227 gamecon.map[2|3]=
1228 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1229 support via parallel port (up to 5 devices per port)
1230 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1231 See also Documentation/input/devices/joystick-parport.rst
1232
1233 gamma= [HW,DRM]
1234
1235 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1236 Format: off | on
1237 default: on
1238
1239 gcov_persist= [GCOV] When non-zero (default), profiling data for
1240 kernel modules is saved and remains accessible via
1241 debugfs, even when the module is unloaded/reloaded.
1242 When zero, profiling data is discarded and associated
1243 debugfs files are removed at module unload time.
1244
1245 goldfish [X86] Enable the goldfish android emulator platform.
1246 Don't use this when you are not running on the
1247 android emulator
1248
1249 gpt [EFI] Forces disk with valid GPT signature but
1250 invalid Protective MBR to be treated as GPT. If the
1251 primary GPT is corrupted, it enables the backup/alternate
1252 GPT to be used instead.
1253
1254 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1255 the "Enable 0" bit of the configuration register.
1256 Format: 0 | 1
1257 Default: 0
1258 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1259 the "Enable 0" bit of the configuration register.
1260 Format: 0 | 1
1261 Default: 0
1262 grcan.select= [HW] Select which physical interface to use.
1263 Format: 0 | 1
1264 Default: 0
1265 grcan.txsize= [HW] Sets the size of the tx buffer.
1266 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1267 Default: 1024
1268 grcan.rxsize= [HW] Sets the size of the rx buffer.
1269 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1270 Default: 1024
1271
1272 gpio-mockup.gpio_mockup_ranges
1273 [HW] Sets the ranges of gpiochip of for this device.
1274 Format: <start1>,<end1>,<start2>,<end2>...
1275
1276 hardlockup_all_cpu_backtrace=
1277 [KNL] Should the hard-lockup detector generate
1278 backtraces on all cpus.
1279 Format: <integer>
1280
1281 hashdist= [KNL,NUMA] Large hashes allocated during boot
1282 are distributed across NUMA nodes. Defaults on
1283 for 64-bit NUMA, off otherwise.
1284 Format: 0 | 1 (for off | on)
1285
1286 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1287
1288 hd= [EIDE] (E)IDE hard drive subsystem geometry
1289 Format: <cyl>,<head>,<sect>
1290
1291 hest_disable [ACPI]
1292 Disable Hardware Error Source Table (HEST) support;
1293 corresponding firmware-first mode error processing
1294 logic will be disabled.
1295
1296 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1297 size of <nn>. This works even on boxes that have no
1298 highmem otherwise. This also works to reduce highmem
1299 size on bigger boxes.
1300
1301 highres= [KNL] Enable/disable high resolution timer mode.
1302 Valid parameters: "on", "off"
1303 Default: "on"
1304
1305 hisax= [HW,ISDN]
1306 See Documentation/isdn/README.HiSax.
1307
1308 hlt [BUGS=ARM,SH]
1309
1310 hpet= [X86-32,HPET] option to control HPET usage
1311 Format: { enable (default) | disable | force |
1312 verbose }
1313 disable: disable HPET and use PIT instead
1314 force: allow force enabled of undocumented chips (ICH4,
1315 VIA, nVidia)
1316 verbose: show contents of HPET registers during setup
1317
1318 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1319 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1320
1321 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1322 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1323 On x86-64 and powerpc, this option can be specified
1324 multiple times interleaved with hugepages= to reserve
1325 huge pages of different sizes. Valid pages sizes on
1326 x86-64 are 2M (when the CPU supports "pse") and 1G
1327 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1328
1329 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1330 terminal devices. Valid values: 0..8
1331 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1332 If specified, z/VM IUCV HVC accepts connections
1333 from listed z/VM user IDs only.
1334
1335 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1336 hardware thread id mappings.
1337 Format: <cpu>:<hwthread>
1338
1339 keep_bootcon [KNL]
1340 Do not unregister boot console at start. This is only
1341 useful for debugging when something happens in the window
1342 between unregistering the boot console and initializing
1343 the real console.
1344
1345 i2c_bus= [HW] Override the default board specific I2C bus speed
1346 or register an additional I2C bus that is not
1347 registered from board initialization code.
1348 Format:
1349 <bus_id>,<clkrate>
1350
1351 i8042.debug [HW] Toggle i8042 debug mode
1352 i8042.unmask_kbd_data
1353 [HW] Enable printing of interrupt data from the KBD port
1354 (disabled by default, and as a pre-condition
1355 requires that i8042.debug=1 be enabled)
1356 i8042.direct [HW] Put keyboard port into non-translated mode
1357 i8042.dumbkbd [HW] Pretend that controller can only read data from
1358 keyboard and cannot control its state
1359 (Don't attempt to blink the leds)
1360 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1361 i8042.nokbd [HW] Don't check/create keyboard port
1362 i8042.noloop [HW] Disable the AUX Loopback command while probing
1363 for the AUX port
1364 i8042.nomux [HW] Don't check presence of an active multiplexing
1365 controller
1366 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1367 controllers
1368 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1369 i8042.reset [HW] Reset the controller during init, cleanup and
1370 suspend-to-ram transitions, only during s2r
1371 transitions, or never reset
1372 Format: { 1 | Y | y | 0 | N | n }
1373 1, Y, y: always reset controller
1374 0, N, n: don't ever reset controller
1375 Default: only on s2r transitions on x86; most other
1376 architectures force reset to be always executed
1377 i8042.unlock [HW] Unlock (ignore) the keylock
1378 i8042.kbdreset [HW] Reset device connected to KBD port
1379
1380 i810= [HW,DRM]
1381
1382 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1383 indicates that the driver is running on unsupported
1384 hardware.
1385 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1386 does not match list of supported models.
1387 i8k.power_status
1388 [HW] Report power status in /proc/i8k
1389 (disabled by default)
1390 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1391 capability is set.
1392
1393 i915.invert_brightness=
1394 [DRM] Invert the sense of the variable that is used to
1395 set the brightness of the panel backlight. Normally a
1396 brightness value of 0 indicates backlight switched off,
1397 and the maximum of the brightness value sets the backlight
1398 to maximum brightness. If this parameter is set to 0
1399 (default) and the machine requires it, or this parameter
1400 is set to 1, a brightness value of 0 sets the backlight
1401 to maximum brightness, and the maximum of the brightness
1402 value switches the backlight off.
1403 -1 -- never invert brightness
1404 0 -- machine default
1405 1 -- force brightness inversion
1406
1407 icn= [HW,ISDN]
1408 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1409
1410 ide-core.nodma= [HW] (E)IDE subsystem
1411 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1412 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1413 .cdrom .chs .ignore_cable are additional options
1414 See Documentation/ide/ide.txt.
1415
1416 ide-generic.probe-mask= [HW] (E)IDE subsystem
1417 Format: <int>
1418 Probe mask for legacy ISA IDE ports. Depending on
1419 platform up to 6 ports are supported, enabled by
1420 setting corresponding bits in the mask to 1. The
1421 default value is 0x0, which has a special meaning.
1422 On systems that have PCI, it triggers scanning the
1423 PCI bus for the first and the second port, which
1424 are then probed. On systems without PCI the value
1425 of 0x0 enables probing the two first ports as if it
1426 was 0x3.
1427
1428 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1429 Claim all unknown PCI IDE storage controllers.
1430
1431 idle= [X86]
1432 Format: idle=poll, idle=halt, idle=nomwait
1433 Poll forces a polling idle loop that can slightly
1434 improve the performance of waking up a idle CPU, but
1435 will use a lot of power and make the system run hot.
1436 Not recommended.
1437 idle=halt: Halt is forced to be used for CPU idle.
1438 In such case C2/C3 won't be used again.
1439 idle=nomwait: Disable mwait for CPU C-states
1440
1441 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1442 Format: { strict | legacy | 2008 | relaxed }
1443 Default: strict
1444
1445 Choose which programs will be accepted for execution
1446 based on the IEEE 754 NaN encoding(s) supported by
1447 the FPU and the NaN encoding requested with the value
1448 of an ELF file header flag individually set by each
1449 binary. Hardware implementations are permitted to
1450 support either or both of the legacy and the 2008 NaN
1451 encoding mode.
1452
1453 Available settings are as follows:
1454 strict accept binaries that request a NaN encoding
1455 supported by the FPU
1456 legacy only accept legacy-NaN binaries, if supported
1457 by the FPU
1458 2008 only accept 2008-NaN binaries, if supported
1459 by the FPU
1460 relaxed accept any binaries regardless of whether
1461 supported by the FPU
1462
1463 The FPU emulator is always able to support both NaN
1464 encodings, so if no FPU hardware is present or it has
1465 been disabled with 'nofpu', then the settings of
1466 'legacy' and '2008' strap the emulator accordingly,
1467 'relaxed' straps the emulator for both legacy-NaN and
1468 2008-NaN, whereas 'strict' enables legacy-NaN only on
1469 legacy processors and both NaN encodings on MIPS32 or
1470 MIPS64 CPUs.
1471
1472 The setting for ABS.fmt/NEG.fmt instruction execution
1473 mode generally follows that for the NaN encoding,
1474 except where unsupported by hardware.
1475
1476 ignore_loglevel [KNL]
1477 Ignore loglevel setting - this will print /all/
1478 kernel messages to the console. Useful for debugging.
1479 We also add it as printk module parameter, so users
1480 could change it dynamically, usually by
1481 /sys/module/printk/parameters/ignore_loglevel.
1482
1483 ignore_rlimit_data
1484 Ignore RLIMIT_DATA setting for data mappings,
1485 print warning at first misuse. Can be changed via
1486 /sys/module/kernel/parameters/ignore_rlimit_data.
1487
1488 ihash_entries= [KNL]
1489 Set number of hash buckets for inode cache.
1490
1491 ima_appraise= [IMA] appraise integrity measurements
1492 Format: { "off" | "enforce" | "fix" | "log" }
1493 default: "enforce"
1494
1495 ima_appraise_tcb [IMA]
1496 The builtin appraise policy appraises all files
1497 owned by uid=0.
1498
1499 ima_canonical_fmt [IMA]
1500 Use the canonical format for the binary runtime
1501 measurements, instead of host native format.
1502
1503 ima_hash= [IMA]
1504 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1505 | sha512 | ... }
1506 default: "sha1"
1507
1508 The list of supported hash algorithms is defined
1509 in crypto/hash_info.h.
1510
1511 ima_policy= [IMA]
1512 The builtin policies to load during IMA setup.
1513 Format: "tcb | appraise_tcb | secure_boot"
1514
1515 The "tcb" policy measures all programs exec'd, files
1516 mmap'd for exec, and all files opened with the read
1517 mode bit set by either the effective uid (euid=0) or
1518 uid=0.
1519
1520 The "appraise_tcb" policy appraises the integrity of
1521 all files owned by root. (This is the equivalent
1522 of ima_appraise_tcb.)
1523
1524 The "secure_boot" policy appraises the integrity
1525 of files (eg. kexec kernel image, kernel modules,
1526 firmware, policy, etc) based on file signatures.
1527
1528 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1529 Load a policy which meets the needs of the Trusted
1530 Computing Base. This means IMA will measure all
1531 programs exec'd, files mmap'd for exec, and all files
1532 opened for read by uid=0.
1533
1534 ima_template= [IMA]
1535 Select one of defined IMA measurements template formats.
1536 Formats: { "ima" | "ima-ng" | "ima-sig" }
1537 Default: "ima-ng"
1538
1539 ima_template_fmt=
1540 [IMA] Define a custom template format.
1541 Format: { "field1|...|fieldN" }
1542
1543 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1544 Format: <min_file_size>
1545 Set the minimal file size for using asynchronous hash.
1546 If left unspecified, ahash usage is disabled.
1547
1548 ahash performance varies for different data sizes on
1549 different crypto accelerators. This option can be used
1550 to achieve the best performance for a particular HW.
1551
1552 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1553 Format: <bufsize>
1554 Set hashing buffer size. Default: 4k.
1555
1556 ahash performance varies for different chunk sizes on
1557 different crypto accelerators. This option can be used
1558 to achieve best performance for particular HW.
1559
1560 init= [KNL]
1561 Format: <full_path>
1562 Run specified binary instead of /sbin/init as init
1563 process.
1564
1565 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1566 for working out where the kernel is dying during
1567 startup.
1568
1569 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1570 initcall functions. Useful for debugging built-in
1571 modules and initcalls.
1572
1573 initrd= [BOOT] Specify the location of the initial ramdisk
1574
1575 init_pkru= [x86] Specify the default memory protection keys rights
1576 register contents for all processes. 0x55555554 by
1577 default (disallow access to all but pkey 0). Can
1578 override in debugfs after boot.
1579
1580 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1581 Format: <irq>
1582
1583 int_pln_enable [x86] Enable power limit notification interrupt
1584
1585 integrity_audit=[IMA]
1586 Format: { "0" | "1" }
1587 0 -- basic integrity auditing messages. (Default)
1588 1 -- additional integrity auditing messages.
1589
1590 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1591 on
1592 Enable intel iommu driver.
1593 off
1594 Disable intel iommu driver.
1595 igfx_off [Default Off]
1596 By default, gfx is mapped as normal device. If a gfx
1597 device has a dedicated DMAR unit, the DMAR unit is
1598 bypassed by not enabling DMAR with this option. In
1599 this case, gfx device will use physical address for
1600 DMA.
1601 forcedac [x86_64]
1602 With this option iommu will not optimize to look
1603 for io virtual address below 32-bit forcing dual
1604 address cycle on pci bus for cards supporting greater
1605 than 32-bit addressing. The default is to look
1606 for translation below 32-bit and if not available
1607 then look in the higher range.
1608 strict [Default Off]
1609 With this option on every unmap_single operation will
1610 result in a hardware IOTLB flush operation as opposed
1611 to batching them for performance.
1612 sp_off [Default Off]
1613 By default, super page will be supported if Intel IOMMU
1614 has the capability. With this option, super page will
1615 not be supported.
1616 ecs_off [Default Off]
1617 By default, extended context tables will be supported if
1618 the hardware advertises that it has support both for the
1619 extended tables themselves, and also PASID support. With
1620 this option set, extended tables will not be used even
1621 on hardware which claims to support them.
1622 tboot_noforce [Default Off]
1623 Do not force the Intel IOMMU enabled under tboot.
1624 By default, tboot will force Intel IOMMU on, which
1625 could harm performance of some high-throughput
1626 devices like 40GBit network cards, even if identity
1627 mapping is enabled.
1628 Note that using this option lowers the security
1629 provided by tboot because it makes the system
1630 vulnerable to DMA attacks.
1631
1632 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1633 0 disables intel_idle and fall back on acpi_idle.
1634 1 to 9 specify maximum depth of C-state.
1635
1636 intel_pstate= [X86]
1637 disable
1638 Do not enable intel_pstate as the default
1639 scaling driver for the supported processors
1640 passive
1641 Use intel_pstate as a scaling driver, but configure it
1642 to work with generic cpufreq governors (instead of
1643 enabling its internal governor). This mode cannot be
1644 used along with the hardware-managed P-states (HWP)
1645 feature.
1646 force
1647 Enable intel_pstate on systems that prohibit it by default
1648 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1649 instead of acpi-cpufreq may disable platform features, such
1650 as thermal controls and power capping, that rely on ACPI
1651 P-States information being indicated to OSPM and therefore
1652 should be used with caution. This option does not work with
1653 processors that aren't supported by the intel_pstate driver
1654 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1655 no_hwp
1656 Do not enable hardware P state control (HWP)
1657 if available.
1658 hwp_only
1659 Only load intel_pstate on systems which support
1660 hardware P state control (HWP) if available.
1661 support_acpi_ppc
1662 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1663 Description Table, specifies preferred power management
1664 profile as "Enterprise Server" or "Performance Server",
1665 then this feature is turned on by default.
1666 per_cpu_perf_limits
1667 Allow per-logical-CPU P-State performance control limits using
1668 cpufreq sysfs interface
1669
1670 intremap= [X86-64, Intel-IOMMU]
1671 on enable Interrupt Remapping (default)
1672 off disable Interrupt Remapping
1673 nosid disable Source ID checking
1674 no_x2apic_optout
1675 BIOS x2APIC opt-out request will be ignored
1676 nopost disable Interrupt Posting
1677
1678 iomem= Disable strict checking of access to MMIO memory
1679 strict regions from userspace.
1680 relaxed
1681
1682 iommu= [x86]
1683 off
1684 force
1685 noforce
1686 biomerge
1687 panic
1688 nopanic
1689 merge
1690 nomerge
1691 forcesac
1692 soft
1693 pt [x86, IA-64]
1694 nobypass [PPC/POWERNV]
1695 Disable IOMMU bypass, using IOMMU for PCI devices.
1696
1697 iommu.strict= [ARM64] Configure TLB invalidation behaviour
1698 Format: { "0" | "1" }
1699 0 - Lazy mode.
1700 Request that DMA unmap operations use deferred
1701 invalidation of hardware TLBs, for increased
1702 throughput at the cost of reduced device isolation.
1703 Will fall back to strict mode if not supported by
1704 the relevant IOMMU driver.
1705 1 - Strict mode (default).
1706 DMA unmap operations invalidate IOMMU hardware TLBs
1707 synchronously.
1708
1709 iommu.passthrough=
1710 [ARM64] Configure DMA to bypass the IOMMU by default.
1711 Format: { "0" | "1" }
1712 0 - Use IOMMU translation for DMA.
1713 1 - Bypass the IOMMU for DMA.
1714 unset - Use IOMMU translation for DMA.
1715
1716 io7= [HW] IO7 for Marvel based alpha systems
1717 See comment before marvel_specify_io7 in
1718 arch/alpha/kernel/core_marvel.c.
1719
1720 io_delay= [X86] I/O delay method
1721 0x80
1722 Standard port 0x80 based delay
1723 0xed
1724 Alternate port 0xed based delay (needed on some systems)
1725 udelay
1726 Simple two microseconds delay
1727 none
1728 No delay
1729
1730 ip= [IP_PNP]
1731 See Documentation/filesystems/nfs/nfsroot.txt.
1732
1733 irqaffinity= [SMP] Set the default irq affinity mask
1734 The argument is a cpu list, as described above.
1735
1736 irqchip.gicv2_force_probe=
1737 [ARM, ARM64]
1738 Format: <bool>
1739 Force the kernel to look for the second 4kB page
1740 of a GICv2 controller even if the memory range
1741 exposed by the device tree is too small.
1742
1743 irqfixup [HW]
1744 When an interrupt is not handled search all handlers
1745 for it. Intended to get systems with badly broken
1746 firmware running.
1747
1748 irqpoll [HW]
1749 When an interrupt is not handled search all handlers
1750 for it. Also check all handlers each timer
1751 interrupt. Intended to get systems with badly broken
1752 firmware running.
1753
1754 isapnp= [ISAPNP]
1755 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1756
1757 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1758 [Deprecated - use cpusets instead]
1759 Format: [flag-list,]<cpu-list>
1760
1761 Specify one or more CPUs to isolate from disturbances
1762 specified in the flag list (default: domain):
1763
1764 nohz
1765 Disable the tick when a single task runs.
1766 domain
1767 Isolate from the general SMP balancing and scheduling
1768 algorithms. Note that performing domain isolation this way
1769 is irreversible: it's not possible to bring back a CPU to
1770 the domains once isolated through isolcpus. It's strongly
1771 advised to use cpusets instead to disable scheduler load
1772 balancing through the "cpuset.sched_load_balance" file.
1773 It offers a much more flexible interface where CPUs can
1774 move in and out of an isolated set anytime.
1775
1776 You can move a process onto or off an "isolated" CPU via
1777 the CPU affinity syscalls or cpuset.
1778 <cpu number> begins at 0 and the maximum value is
1779 "number of CPUs in system - 1".
1780
1781 The format of <cpu-list> is described above.
1782
1783
1784
1785 iucv= [HW,NET]
1786
1787 ivrs_ioapic [HW,X86_64]
1788 Provide an override to the IOAPIC-ID<->DEVICE-ID
1789 mapping provided in the IVRS ACPI table. For
1790 example, to map IOAPIC-ID decimal 10 to
1791 PCI device 00:14.0 write the parameter as:
1792 ivrs_ioapic[10]=00:14.0
1793
1794 ivrs_hpet [HW,X86_64]
1795 Provide an override to the HPET-ID<->DEVICE-ID
1796 mapping provided in the IVRS ACPI table. For
1797 example, to map HPET-ID decimal 0 to
1798 PCI device 00:14.0 write the parameter as:
1799 ivrs_hpet[0]=00:14.0
1800
1801 ivrs_acpihid [HW,X86_64]
1802 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1803 mapping provided in the IVRS ACPI table. For
1804 example, to map UART-HID:UID AMD0020:0 to
1805 PCI device 00:14.5 write the parameter as:
1806 ivrs_acpihid[00:14.5]=AMD0020:0
1807
1808 js= [HW,JOY] Analog joystick
1809 See Documentation/input/joydev/joystick.rst.
1810
1811 nokaslr [KNL]
1812 When CONFIG_RANDOMIZE_BASE is set, this disables
1813 kernel and module base offset ASLR (Address Space
1814 Layout Randomization).
1815
1816 kasan_multi_shot
1817 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1818 report on every invalid memory access. Without this
1819 parameter KASAN will print report only for the first
1820 invalid access.
1821
1822 keepinitrd [HW,ARM]
1823
1824 kernelcore= [KNL,X86,IA-64,PPC]
1825 Format: nn[KMGTPE] | "mirror"
1826 This parameter
1827 specifies the amount of memory usable by the kernel
1828 for non-movable allocations. The requested amount is
1829 spread evenly throughout all nodes in the system. The
1830 remaining memory in each node is used for Movable
1831 pages. In the event, a node is too small to have both
1832 kernelcore and Movable pages, kernelcore pages will
1833 take priority and other nodes will have a larger number
1834 of Movable pages. The Movable zone is used for the
1835 allocation of pages that may be reclaimed or moved
1836 by the page migration subsystem. This means that
1837 HugeTLB pages may not be allocated from this zone.
1838 Note that allocations like PTEs-from-HighMem still
1839 use the HighMem zone if it exists, and the Normal
1840 zone if it does not.
1841
1842 Instead of specifying the amount of memory (nn[KMGTPE]),
1843 you can specify "mirror" option. In case "mirror"
1844 option is specified, mirrored (reliable) memory is used
1845 for non-movable allocations and remaining memory is used
1846 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1847 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1848 time.
1849
1850 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1851 Format: <Controller#>[,poll interval]
1852 The controller # is the number of the ehci usb debug
1853 port as it is probed via PCI. The poll interval is
1854 optional and is the number seconds in between
1855 each poll cycle to the debug port in case you need
1856 the functionality for interrupting the kernel with
1857 gdb or control-c on the dbgp connection. When
1858 not using this parameter you use sysrq-g to break into
1859 the kernel debugger.
1860
1861 kgdboc= [KGDB,HW] kgdb over consoles.
1862 Requires a tty driver that supports console polling,
1863 or a supported polling keyboard driver (non-usb).
1864 Serial only format: <serial_device>[,baud]
1865 keyboard only format: kbd
1866 keyboard and serial format: kbd,<serial_device>[,baud]
1867 Optional Kernel mode setting:
1868 kms, kbd format: kms,kbd
1869 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1870
1871 kgdbwait [KGDB] Stop kernel execution and enter the
1872 kernel debugger at the earliest opportunity.
1873
1874 kmac= [MIPS] korina ethernet MAC address.
1875 Configure the RouterBoard 532 series on-chip
1876 Ethernet adapter MAC address.
1877
1878 kmemleak= [KNL] Boot-time kmemleak enable/disable
1879 Valid arguments: on, off
1880 Default: on
1881 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1882 the default is off.
1883
1884 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1885 Default is 0 (don't ignore, but inject #GP)
1886
1887 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1888 KVM MMU at runtime.
1889 Default is 0 (off)
1890
1891 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1892 Default is 1 (enabled)
1893
1894 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1895 for all guests.
1896 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1897
1898 kvm-arm.vgic_v3_group0_trap=
1899 [KVM,ARM] Trap guest accesses to GICv3 group-0
1900 system registers
1901
1902 kvm-arm.vgic_v3_group1_trap=
1903 [KVM,ARM] Trap guest accesses to GICv3 group-1
1904 system registers
1905
1906 kvm-arm.vgic_v3_common_trap=
1907 [KVM,ARM] Trap guest accesses to GICv3 common
1908 system registers
1909
1910 kvm-arm.vgic_v4_enable=
1911 [KVM,ARM] Allow use of GICv4 for direct injection of
1912 LPIs.
1913
1914 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1915 (virtualized MMU) support on capable Intel chips.
1916 Default is 1 (enabled)
1917
1918 kvm-intel.emulate_invalid_guest_state=
1919 [KVM,Intel] Enable emulation of invalid guest states
1920 Default is 0 (disabled)
1921
1922 kvm-intel.flexpriority=
1923 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1924 Default is 1 (enabled)
1925
1926 kvm-intel.nested=
1927 [KVM,Intel] Enable VMX nesting (nVMX).
1928 Default is 0 (disabled)
1929
1930 kvm-intel.unrestricted_guest=
1931 [KVM,Intel] Disable unrestricted guest feature
1932 (virtualized real and unpaged mode) on capable
1933 Intel chips. Default is 1 (enabled)
1934
1935 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
1936 CVE-2018-3620.
1937
1938 Valid arguments: never, cond, always
1939
1940 always: L1D cache flush on every VMENTER.
1941 cond: Flush L1D on VMENTER only when the code between
1942 VMEXIT and VMENTER can leak host memory.
1943 never: Disables the mitigation
1944
1945 Default is cond (do L1 cache flush in specific instances)
1946
1947 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1948 feature (tagged TLBs) on capable Intel chips.
1949 Default is 1 (enabled)
1950
1951 l1tf= [X86] Control mitigation of the L1TF vulnerability on
1952 affected CPUs
1953
1954 The kernel PTE inversion protection is unconditionally
1955 enabled and cannot be disabled.
1956
1957 full
1958 Provides all available mitigations for the
1959 L1TF vulnerability. Disables SMT and
1960 enables all mitigations in the
1961 hypervisors, i.e. unconditional L1D flush.
1962
1963 SMT control and L1D flush control via the
1964 sysfs interface is still possible after
1965 boot. Hypervisors will issue a warning
1966 when the first VM is started in a
1967 potentially insecure configuration,
1968 i.e. SMT enabled or L1D flush disabled.
1969
1970 full,force
1971 Same as 'full', but disables SMT and L1D
1972 flush runtime control. Implies the
1973 'nosmt=force' command line option.
1974 (i.e. sysfs control of SMT is disabled.)
1975
1976 flush
1977 Leaves SMT enabled and enables the default
1978 hypervisor mitigation, i.e. conditional
1979 L1D flush.
1980
1981 SMT control and L1D flush control via the
1982 sysfs interface is still possible after
1983 boot. Hypervisors will issue a warning
1984 when the first VM is started in a
1985 potentially insecure configuration,
1986 i.e. SMT enabled or L1D flush disabled.
1987
1988 flush,nosmt
1989
1990 Disables SMT and enables the default
1991 hypervisor mitigation.
1992
1993 SMT control and L1D flush control via the
1994 sysfs interface is still possible after
1995 boot. Hypervisors will issue a warning
1996 when the first VM is started in a
1997 potentially insecure configuration,
1998 i.e. SMT enabled or L1D flush disabled.
1999
2000 flush,nowarn
2001 Same as 'flush', but hypervisors will not
2002 warn when a VM is started in a potentially
2003 insecure configuration.
2004
2005 off
2006 Disables hypervisor mitigations and doesn't
2007 emit any warnings.
2008
2009 Default is 'flush'.
2010
2011 For details see: Documentation/admin-guide/l1tf.rst
2012
2013 l2cr= [PPC]
2014
2015 l3cr= [PPC]
2016
2017 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2018 disabled it.
2019
2020 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2021 value for LAPIC timer one-shot implementation. Default
2022 back to the programmable timer unit in the LAPIC.
2023
2024 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2025 in C2 power state.
2026
2027 libata.dma= [LIBATA] DMA control
2028 libata.dma=0 Disable all PATA and SATA DMA
2029 libata.dma=1 PATA and SATA Disk DMA only
2030 libata.dma=2 ATAPI (CDROM) DMA only
2031 libata.dma=4 Compact Flash DMA only
2032 Combinations also work, so libata.dma=3 enables DMA
2033 for disks and CDROMs, but not CFs.
2034
2035 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2036 libata.ignore_hpa=0 keep BIOS limits (default)
2037 libata.ignore_hpa=1 ignore limits, using full disk
2038
2039 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2040 when set.
2041 Format: <int>
2042
2043 libata.force= [LIBATA] Force configurations. The format is comma
2044 separated list of "[ID:]VAL" where ID is
2045 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2046 matching port, link or device. Basically, it matches
2047 the ATA ID string printed on console by libata. If
2048 the whole ID part is omitted, the last PORT and DEVICE
2049 values are used. If ID hasn't been specified yet, the
2050 configuration applies to all ports, links and devices.
2051
2052 If only DEVICE is omitted, the parameter applies to
2053 the port and all links and devices behind it. DEVICE
2054 number of 0 either selects the first device or the
2055 first fan-out link behind PMP device. It does not
2056 select the host link. DEVICE number of 15 selects the
2057 host link and device attached to it.
2058
2059 The VAL specifies the configuration to force. As long
2060 as there's no ambiguity shortcut notation is allowed.
2061 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2062 The following configurations can be forced.
2063
2064 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2065 Any ID with matching PORT is used.
2066
2067 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2068
2069 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2070 udma[/][16,25,33,44,66,100,133] notation is also
2071 allowed.
2072
2073 * [no]ncq: Turn on or off NCQ.
2074
2075 * [no]ncqtrim: Turn off queued DSM TRIM.
2076
2077 * nohrst, nosrst, norst: suppress hard, soft
2078 and both resets.
2079
2080 * rstonce: only attempt one reset during
2081 hot-unplug link recovery
2082
2083 * dump_id: dump IDENTIFY data.
2084
2085 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2086
2087 * disable: Disable this device.
2088
2089 If there are multiple matching configurations changing
2090 the same attribute, the last one is used.
2091
2092 memblock=debug [KNL] Enable memblock debug messages.
2093
2094 load_ramdisk= [RAM] List of ramdisks to load from floppy
2095 See Documentation/blockdev/ramdisk.txt.
2096
2097 lockd.nlm_grace_period=P [NFS] Assign grace period.
2098 Format: <integer>
2099
2100 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2101 Format: <integer>
2102
2103 lockd.nlm_timeout=T [NFS] Assign timeout value.
2104 Format: <integer>
2105
2106 lockd.nlm_udpport=M [NFS] Assign UDP port.
2107 Format: <integer>
2108
2109 locktorture.nreaders_stress= [KNL]
2110 Set the number of locking read-acquisition kthreads.
2111 Defaults to being automatically set based on the
2112 number of online CPUs.
2113
2114 locktorture.nwriters_stress= [KNL]
2115 Set the number of locking write-acquisition kthreads.
2116
2117 locktorture.onoff_holdoff= [KNL]
2118 Set time (s) after boot for CPU-hotplug testing.
2119
2120 locktorture.onoff_interval= [KNL]
2121 Set time (s) between CPU-hotplug operations, or
2122 zero to disable CPU-hotplug testing.
2123
2124 locktorture.shuffle_interval= [KNL]
2125 Set task-shuffle interval (jiffies). Shuffling
2126 tasks allows some CPUs to go into dyntick-idle
2127 mode during the locktorture test.
2128
2129 locktorture.shutdown_secs= [KNL]
2130 Set time (s) after boot system shutdown. This
2131 is useful for hands-off automated testing.
2132
2133 locktorture.stat_interval= [KNL]
2134 Time (s) between statistics printk()s.
2135
2136 locktorture.stutter= [KNL]
2137 Time (s) to stutter testing, for example,
2138 specifying five seconds causes the test to run for
2139 five seconds, wait for five seconds, and so on.
2140 This tests the locking primitive's ability to
2141 transition abruptly to and from idle.
2142
2143 locktorture.torture_runnable= [BOOT]
2144 Start locktorture running at boot time.
2145
2146 locktorture.torture_type= [KNL]
2147 Specify the locking implementation to test.
2148
2149 locktorture.verbose= [KNL]
2150 Enable additional printk() statements.
2151
2152 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2153 Format: <irq>
2154
2155 loglevel= All Kernel Messages with a loglevel smaller than the
2156 console loglevel will be printed to the console. It can
2157 also be changed with klogd or other programs. The
2158 loglevels are defined as follows:
2159
2160 0 (KERN_EMERG) system is unusable
2161 1 (KERN_ALERT) action must be taken immediately
2162 2 (KERN_CRIT) critical conditions
2163 3 (KERN_ERR) error conditions
2164 4 (KERN_WARNING) warning conditions
2165 5 (KERN_NOTICE) normal but significant condition
2166 6 (KERN_INFO) informational
2167 7 (KERN_DEBUG) debug-level messages
2168
2169 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2170 in bytes. n must be a power of two and greater
2171 than the minimal size. The minimal size is defined
2172 by LOG_BUF_SHIFT kernel config parameter. There is
2173 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2174 that allows to increase the default size depending on
2175 the number of CPUs. See init/Kconfig for more details.
2176
2177 logo.nologo [FB] Disables display of the built-in Linux logo.
2178 This may be used to provide more screen space for
2179 kernel log messages and is useful when debugging
2180 kernel boot problems.
2181
2182 lp=0 [LP] Specify parallel ports to use, e.g,
2183 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2184 lp=reset first parallel port). 'lp=0' disables the
2185 lp=auto printer driver. 'lp=reset' (which can be
2186 specified in addition to the ports) causes
2187 attached printers to be reset. Using
2188 lp=port1,port2,... specifies the parallel ports
2189 to associate lp devices with, starting with
2190 lp0. A port specification may be 'none' to skip
2191 that lp device, or a parport name such as
2192 'parport0'. Specifying 'lp=auto' instead of a
2193 port specification list means that device IDs
2194 from each port should be examined, to see if
2195 an IEEE 1284-compliant printer is attached; if
2196 so, the driver will manage that printer.
2197 See also header of drivers/char/lp.c.
2198
2199 lpj=n [KNL]
2200 Sets loops_per_jiffy to given constant, thus avoiding
2201 time-consuming boot-time autodetection (up to 250 ms per
2202 CPU). 0 enables autodetection (default). To determine
2203 the correct value for your kernel, boot with normal
2204 autodetection and see what value is printed. Note that
2205 on SMP systems the preset will be applied to all CPUs,
2206 which is likely to cause problems if your CPUs need
2207 significantly divergent settings. An incorrect value
2208 will cause delays in the kernel to be wrong, leading to
2209 unpredictable I/O errors and other breakage. Although
2210 unlikely, in the extreme case this might damage your
2211 hardware.
2212
2213 ltpc= [NET]
2214 Format: <io>,<irq>,<dma>
2215
2216 machvec= [IA-64] Force the use of a particular machine-vector
2217 (machvec) in a generic kernel.
2218 Example: machvec=hpzx1_swiotlb
2219
2220 machtype= [Loongson] Share the same kernel image file between different
2221 yeeloong laptop.
2222 Example: machtype=lemote-yeeloong-2f-7inch
2223
2224 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2225 than or equal to this physical address is ignored.
2226
2227 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2228 will bring up during bootup. maxcpus=n : n >= 0 limits
2229 the kernel to bring up 'n' processors. Surely after
2230 bootup you can bring up the other plugged cpu by executing
2231 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2232 only takes effect during system bootup.
2233 While n=0 is a special case, it is equivalent to "nosmp",
2234 which also disables the IO APIC.
2235
2236 max_loop= [LOOP] The number of loop block devices that get
2237 (loop.max_loop) unconditionally pre-created at init time. The default
2238 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2239 of statically allocating a predefined number, loop
2240 devices can be requested on-demand with the
2241 /dev/loop-control interface.
2242
2243 mce [X86-32] Machine Check Exception
2244
2245 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2246
2247 md= [HW] RAID subsystems devices and level
2248 See Documentation/admin-guide/md.rst.
2249
2250 mdacon= [MDA]
2251 Format: <first>,<last>
2252 Specifies range of consoles to be captured by the MDA.
2253
2254 mds= [X86,INTEL]
2255 Control mitigation for the Micro-architectural Data
2256 Sampling (MDS) vulnerability.
2257
2258 Certain CPUs are vulnerable to an exploit against CPU
2259 internal buffers which can forward information to a
2260 disclosure gadget under certain conditions.
2261
2262 In vulnerable processors, the speculatively
2263 forwarded data can be used in a cache side channel
2264 attack, to access data to which the attacker does
2265 not have direct access.
2266
2267 This parameter controls the MDS mitigation. The
2268 options are:
2269
2270 full - Enable MDS mitigation on vulnerable CPUs
2271 full,nosmt - Enable MDS mitigation and disable
2272 SMT on vulnerable CPUs
2273 off - Unconditionally disable MDS mitigation
2274
2275 Not specifying this option is equivalent to
2276 mds=full.
2277
2278 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2279 Amount of memory to be used when the kernel is not able
2280 to see the whole system memory or for test.
2281 [X86] Work as limiting max address. Use together
2282 with memmap= to avoid physical address space collisions.
2283 Without memmap= PCI devices could be placed at addresses
2284 belonging to unused RAM.
2285
2286 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2287 memory.
2288
2289 memchunk=nn[KMG]
2290 [KNL,SH] Allow user to override the default size for
2291 per-device physically contiguous DMA buffers.
2292
2293 memhp_default_state=online/offline
2294 [KNL] Set the initial state for the memory hotplug
2295 onlining policy. If not specified, the default value is
2296 set according to the
2297 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2298 option.
2299 See Documentation/memory-hotplug.txt.
2300
2301 memmap=exactmap [KNL,X86] Enable setting of an exact
2302 E820 memory map, as specified by the user.
2303 Such memmap=exactmap lines can be constructed based on
2304 BIOS output or other requirements. See the memmap=nn@ss
2305 option description.
2306
2307 memmap=nn[KMG]@ss[KMG]
2308 [KNL] Force usage of a specific region of memory.
2309 Region of memory to be used is from ss to ss+nn.
2310 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2311 which limits max address to nn[KMG].
2312 Multiple different regions can be specified,
2313 comma delimited.
2314 Example:
2315 memmap=100M@2G,100M#3G,1G!1024G
2316
2317 memmap=nn[KMG]#ss[KMG]
2318 [KNL,ACPI] Mark specific memory as ACPI data.
2319 Region of memory to be marked is from ss to ss+nn.
2320
2321 memmap=nn[KMG]$ss[KMG]
2322 [KNL,ACPI] Mark specific memory as reserved.
2323 Region of memory to be reserved is from ss to ss+nn.
2324 Example: Exclude memory from 0x18690000-0x1869ffff
2325 memmap=64K$0x18690000
2326 or
2327 memmap=0x10000$0x18690000
2328 Some bootloaders may need an escape character before '$',
2329 like Grub2, otherwise '$' and the following number
2330 will be eaten.
2331
2332 memmap=nn[KMG]!ss[KMG]
2333 [KNL,X86] Mark specific memory as protected.
2334 Region of memory to be used, from ss to ss+nn.
2335 The memory region may be marked as e820 type 12 (0xc)
2336 and is NVDIMM or ADR memory.
2337
2338 memory_corruption_check=0/1 [X86]
2339 Some BIOSes seem to corrupt the first 64k of
2340 memory when doing things like suspend/resume.
2341 Setting this option will scan the memory
2342 looking for corruption. Enabling this will
2343 both detect corruption and prevent the kernel
2344 from using the memory being corrupted.
2345 However, its intended as a diagnostic tool; if
2346 repeatable BIOS-originated corruption always
2347 affects the same memory, you can use memmap=
2348 to prevent the kernel from using that memory.
2349
2350 memory_corruption_check_size=size [X86]
2351 By default it checks for corruption in the low
2352 64k, making this memory unavailable for normal
2353 use. Use this parameter to scan for
2354 corruption in more or less memory.
2355
2356 memory_corruption_check_period=seconds [X86]
2357 By default it checks for corruption every 60
2358 seconds. Use this parameter to check at some
2359 other rate. 0 disables periodic checking.
2360
2361 memtest= [KNL,X86,ARM] Enable memtest
2362 Format: <integer>
2363 default : 0 <disable>
2364 Specifies the number of memtest passes to be
2365 performed. Each pass selects another test
2366 pattern from a given set of patterns. Memtest
2367 fills the memory with this pattern, validates
2368 memory contents and reserves bad memory
2369 regions that are detected.
2370
2371 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2372 Valid arguments: on, off
2373 Default (depends on kernel configuration option):
2374 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2375 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2376 mem_encrypt=on: Activate SME
2377 mem_encrypt=off: Do not activate SME
2378
2379 Refer to Documentation/x86/amd-memory-encryption.txt
2380 for details on when memory encryption can be activated.
2381
2382 mem_sleep_default= [SUSPEND] Default system suspend mode:
2383 s2idle - Suspend-To-Idle
2384 shallow - Power-On Suspend or equivalent (if supported)
2385 deep - Suspend-To-RAM or equivalent (if supported)
2386 See Documentation/admin-guide/pm/sleep-states.rst.
2387
2388 meye.*= [HW] Set MotionEye Camera parameters
2389 See Documentation/media/v4l-drivers/meye.rst.
2390
2391 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2392 Multi-Function General Purpose Timers on AMD Geode
2393 platforms.
2394
2395 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2396 the BIOS has incorrectly applied a workaround. TinyBIOS
2397 version 0.98 is known to be affected, 0.99 fixes the
2398 problem by letting the user disable the workaround.
2399
2400 mga= [HW,DRM]
2401
2402 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2403 physical address is ignored.
2404
2405 mini2440= [ARM,HW,KNL]
2406 Format:[0..2][b][c][t]
2407 Default: "0tb"
2408 MINI2440 configuration specification:
2409 0 - The attached screen is the 3.5" TFT
2410 1 - The attached screen is the 7" TFT
2411 2 - The VGA Shield is attached (1024x768)
2412 Leaving out the screen size parameter will not load
2413 the TFT driver, and the framebuffer will be left
2414 unconfigured.
2415 b - Enable backlight. The TFT backlight pin will be
2416 linked to the kernel VESA blanking code and a GPIO
2417 LED. This parameter is not necessary when using the
2418 VGA shield.
2419 c - Enable the s3c camera interface.
2420 t - Reserved for enabling touchscreen support. The
2421 touchscreen support is not enabled in the mainstream
2422 kernel as of 2.6.30, a preliminary port can be found
2423 in the "bleeding edge" mini2440 support kernel at
2424 http://repo.or.cz/w/linux-2.6/mini2440.git
2425
2426 mminit_loglevel=
2427 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2428 parameter allows control of the logging verbosity for
2429 the additional memory initialisation checks. A value
2430 of 0 disables mminit logging and a level of 4 will
2431 log everything. Information is printed at KERN_DEBUG
2432 so loglevel=8 may also need to be specified.
2433
2434 module.sig_enforce
2435 [KNL] When CONFIG_MODULE_SIG is set, this means that
2436 modules without (valid) signatures will fail to load.
2437 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2438 is always true, so this option does nothing.
2439
2440 module_blacklist= [KNL] Do not load a comma-separated list of
2441 modules. Useful for debugging problem modules.
2442
2443 mousedev.tap_time=
2444 [MOUSE] Maximum time between finger touching and
2445 leaving touchpad surface for touch to be considered
2446 a tap and be reported as a left button click (for
2447 touchpads working in absolute mode only).
2448 Format: <msecs>
2449 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2450 reporting absolute coordinates, such as tablets
2451 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2452 reporting absolute coordinates, such as tablets
2453
2454 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2455 is similar to kernelcore except it specifies the
2456 amount of memory used for migratable allocations.
2457 If both kernelcore and movablecore is specified,
2458 then kernelcore will be at *least* the specified
2459 value but may be more. If movablecore on its own
2460 is specified, the administrator must be careful
2461 that the amount of memory usable for all allocations
2462 is not too small.
2463
2464 movable_node [KNL] Boot-time switch to make hotplugable memory
2465 NUMA nodes to be movable. This means that the memory
2466 of such nodes will be usable only for movable
2467 allocations which rules out almost all kernel
2468 allocations. Use with caution!
2469
2470 MTD_Partition= [MTD]
2471 Format: <name>,<region-number>,<size>,<offset>
2472
2473 MTD_Region= [MTD] Format:
2474 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2475
2476 mtdparts= [MTD]
2477 See drivers/mtd/cmdlinepart.c.
2478
2479 multitce=off [PPC] This parameter disables the use of the pSeries
2480 firmware feature for updating multiple TCE entries
2481 at a time.
2482
2483 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2484
2485 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2486
2487 boundary - index of last SLC block on Flex-OneNAND.
2488 The remaining blocks are configured as MLC blocks.
2489 lock - Configure if Flex-OneNAND boundary should be locked.
2490 Once locked, the boundary cannot be changed.
2491 1 indicates lock status, 0 indicates unlock status.
2492
2493 mtdset= [ARM]
2494 ARM/S3C2412 JIVE boot control
2495
2496 See arch/arm/mach-s3c2412/mach-jive.c
2497
2498 mtouchusb.raw_coordinates=
2499 [HW] Make the MicroTouch USB driver use raw coordinates
2500 ('y', default) or cooked coordinates ('n')
2501
2502 mtrr_chunk_size=nn[KMG] [X86]
2503 used for mtrr cleanup. It is largest continuous chunk
2504 that could hold holes aka. UC entries.
2505
2506 mtrr_gran_size=nn[KMG] [X86]
2507 Used for mtrr cleanup. It is granularity of mtrr block.
2508 Default is 1.
2509 Large value could prevent small alignment from
2510 using up MTRRs.
2511
2512 mtrr_spare_reg_nr=n [X86]
2513 Format: <integer>
2514 Range: 0,7 : spare reg number
2515 Default : 1
2516 Used for mtrr cleanup. It is spare mtrr entries number.
2517 Set to 2 or more if your graphical card needs more.
2518
2519 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2520
2521 netdev= [NET] Network devices parameters
2522 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2523 Note that mem_start is often overloaded to mean
2524 something different and driver-specific.
2525 This usage is only documented in each driver source
2526 file if at all.
2527
2528 nf_conntrack.acct=
2529 [NETFILTER] Enable connection tracking flow accounting
2530 0 to disable accounting
2531 1 to enable accounting
2532 Default value is 0.
2533
2534 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2535 See Documentation/filesystems/nfs/nfsroot.txt.
2536
2537 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2538 See Documentation/filesystems/nfs/nfsroot.txt.
2539
2540 nfsrootdebug [NFS] enable nfsroot debugging messages.
2541 See Documentation/filesystems/nfs/nfsroot.txt.
2542
2543 nfs.callback_nr_threads=
2544 [NFSv4] set the total number of threads that the
2545 NFS client will assign to service NFSv4 callback
2546 requests.
2547
2548 nfs.callback_tcpport=
2549 [NFS] set the TCP port on which the NFSv4 callback
2550 channel should listen.
2551
2552 nfs.cache_getent=
2553 [NFS] sets the pathname to the program which is used
2554 to update the NFS client cache entries.
2555
2556 nfs.cache_getent_timeout=
2557 [NFS] sets the timeout after which an attempt to
2558 update a cache entry is deemed to have failed.
2559
2560 nfs.idmap_cache_timeout=
2561 [NFS] set the maximum lifetime for idmapper cache
2562 entries.
2563
2564 nfs.enable_ino64=
2565 [NFS] enable 64-bit inode numbers.
2566 If zero, the NFS client will fake up a 32-bit inode
2567 number for the readdir() and stat() syscalls instead
2568 of returning the full 64-bit number.
2569 The default is to return 64-bit inode numbers.
2570
2571 nfs.max_session_cb_slots=
2572 [NFSv4.1] Sets the maximum number of session
2573 slots the client will assign to the callback
2574 channel. This determines the maximum number of
2575 callbacks the client will process in parallel for
2576 a particular server.
2577
2578 nfs.max_session_slots=
2579 [NFSv4.1] Sets the maximum number of session slots
2580 the client will attempt to negotiate with the server.
2581 This limits the number of simultaneous RPC requests
2582 that the client can send to the NFSv4.1 server.
2583 Note that there is little point in setting this
2584 value higher than the max_tcp_slot_table_limit.
2585
2586 nfs.nfs4_disable_idmapping=
2587 [NFSv4] When set to the default of '1', this option
2588 ensures that both the RPC level authentication
2589 scheme and the NFS level operations agree to use
2590 numeric uids/gids if the mount is using the
2591 'sec=sys' security flavour. In effect it is
2592 disabling idmapping, which can make migration from
2593 legacy NFSv2/v3 systems to NFSv4 easier.
2594 Servers that do not support this mode of operation
2595 will be autodetected by the client, and it will fall
2596 back to using the idmapper.
2597 To turn off this behaviour, set the value to '0'.
2598 nfs.nfs4_unique_id=
2599 [NFS4] Specify an additional fixed unique ident-
2600 ification string that NFSv4 clients can insert into
2601 their nfs_client_id4 string. This is typically a
2602 UUID that is generated at system install time.
2603
2604 nfs.send_implementation_id =
2605 [NFSv4.1] Send client implementation identification
2606 information in exchange_id requests.
2607 If zero, no implementation identification information
2608 will be sent.
2609 The default is to send the implementation identification
2610 information.
2611
2612 nfs.recover_lost_locks =
2613 [NFSv4] Attempt to recover locks that were lost due
2614 to a lease timeout on the server. Please note that
2615 doing this risks data corruption, since there are
2616 no guarantees that the file will remain unchanged
2617 after the locks are lost.
2618 If you want to enable the kernel legacy behaviour of
2619 attempting to recover these locks, then set this
2620 parameter to '1'.
2621 The default parameter value of '0' causes the kernel
2622 not to attempt recovery of lost locks.
2623
2624 nfs4.layoutstats_timer =
2625 [NFSv4.2] Change the rate at which the kernel sends
2626 layoutstats to the pNFS metadata server.
2627
2628 Setting this to value to 0 causes the kernel to use
2629 whatever value is the default set by the layout
2630 driver. A non-zero value sets the minimum interval
2631 in seconds between layoutstats transmissions.
2632
2633 nfsd.nfs4_disable_idmapping=
2634 [NFSv4] When set to the default of '1', the NFSv4
2635 server will return only numeric uids and gids to
2636 clients using auth_sys, and will accept numeric uids
2637 and gids from such clients. This is intended to ease
2638 migration from NFSv2/v3.
2639
2640 nmi_debug= [KNL,SH] Specify one or more actions to take
2641 when a NMI is triggered.
2642 Format: [state][,regs][,debounce][,die]
2643
2644 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2645 Format: [panic,][nopanic,][num]
2646 Valid num: 0 or 1
2647 0 - turn hardlockup detector in nmi_watchdog off
2648 1 - turn hardlockup detector in nmi_watchdog on
2649 When panic is specified, panic when an NMI watchdog
2650 timeout occurs (or 'nopanic' to override the opposite
2651 default). To disable both hard and soft lockup detectors,
2652 please see 'nowatchdog'.
2653 This is useful when you use a panic=... timeout and
2654 need the box quickly up again.
2655
2656 netpoll.carrier_timeout=
2657 [NET] Specifies amount of time (in seconds) that
2658 netpoll should wait for a carrier. By default netpoll
2659 waits 4 seconds.
2660
2661 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2662 emulation library even if a 387 maths coprocessor
2663 is present.
2664
2665 no_console_suspend
2666 [HW] Never suspend the console
2667 Disable suspending of consoles during suspend and
2668 hibernate operations. Once disabled, debugging
2669 messages can reach various consoles while the rest
2670 of the system is being put to sleep (ie, while
2671 debugging driver suspend/resume hooks). This may
2672 not work reliably with all consoles, but is known
2673 to work with serial and VGA consoles.
2674 To facilitate more flexible debugging, we also add
2675 console_suspend, a printk module parameter to control
2676 it. Users could use console_suspend (usually
2677 /sys/module/printk/parameters/console_suspend) to
2678 turn on/off it dynamically.
2679
2680 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2681 caches in the slab allocator. Saves per-node memory,
2682 but will impact performance.
2683
2684 noalign [KNL,ARM]
2685
2686 noaltinstr [S390] Disables alternative instructions patching
2687 (CPU alternatives feature).
2688
2689 noapic [SMP,APIC] Tells the kernel to not make use of any
2690 IOAPICs that may be present in the system.
2691
2692 noautogroup Disable scheduler automatic task group creation.
2693
2694 nobats [PPC] Do not use BATs for mapping kernel lowmem
2695 on "Classic" PPC cores.
2696
2697 nocache [ARM]
2698
2699 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2700
2701 nodelayacct [KNL] Disable per-task delay accounting
2702
2703 nodsp [SH] Disable hardware DSP at boot time.
2704
2705 noefi Disable EFI runtime services support.
2706
2707 noexec [IA-64]
2708
2709 noexec [X86]
2710 On X86-32 available only on PAE configured kernels.
2711 noexec=on: enable non-executable mappings (default)
2712 noexec=off: disable non-executable mappings
2713
2714 nosmap [X86]
2715 Disable SMAP (Supervisor Mode Access Prevention)
2716 even if it is supported by processor.
2717
2718 nosmep [X86]
2719 Disable SMEP (Supervisor Mode Execution Prevention)
2720 even if it is supported by processor.
2721
2722 noexec32 [X86-64]
2723 This affects only 32-bit executables.
2724 noexec32=on: enable non-executable mappings (default)
2725 read doesn't imply executable mappings
2726 noexec32=off: disable non-executable mappings
2727 read implies executable mappings
2728
2729 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2730
2731 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2732 register save and restore. The kernel will only save
2733 legacy floating-point registers on task switch.
2734
2735 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2736
2737 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2738 Equivalent to smt=1.
2739
2740 [KNL,x86] Disable symmetric multithreading (SMT).
2741 nosmt=force: Force disable SMT, cannot be undone
2742 via the sysfs control file.
2743
2744 nospectre_v2 [X86] Disable all mitigations for the Spectre variant 2
2745 (indirect branch prediction) vulnerability. System may
2746 allow data leaks with this option, which is equivalent
2747 to spectre_v2=off.
2748
2749 nospec_store_bypass_disable
2750 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
2751
2752 noxsave [BUGS=X86] Disables x86 extended register state save
2753 and restore using xsave. The kernel will fallback to
2754 enabling legacy floating-point and sse state.
2755
2756 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2757 register states. The kernel will fall back to use
2758 xsave to save the states. By using this parameter,
2759 performance of saving the states is degraded because
2760 xsave doesn't support modified optimization while
2761 xsaveopt supports it on xsaveopt enabled systems.
2762
2763 noxsaves [X86] Disables xsaves and xrstors used in saving and
2764 restoring x86 extended register state in compacted
2765 form of xsave area. The kernel will fall back to use
2766 xsaveopt and xrstor to save and restore the states
2767 in standard form of xsave area. By using this
2768 parameter, xsave area per process might occupy more
2769 memory on xsaves enabled systems.
2770
2771 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2772 wfi(ARM) instruction doesn't work correctly and not to
2773 use it. This is also useful when using JTAG debugger.
2774
2775 no_file_caps Tells the kernel not to honor file capabilities. The
2776 only way then for a file to be executed with privilege
2777 is to be setuid root or executed by root.
2778
2779 nohalt [IA-64] Tells the kernel not to use the power saving
2780 function PAL_HALT_LIGHT when idle. This increases
2781 power-consumption. On the positive side, it reduces
2782 interrupt wake-up latency, which may improve performance
2783 in certain environments such as networked servers or
2784 real-time systems.
2785
2786 nohibernate [HIBERNATION] Disable hibernation and resume.
2787
2788 nohz= [KNL] Boottime enable/disable dynamic ticks
2789 Valid arguments: on, off
2790 Default: on
2791
2792 nohz_full= [KNL,BOOT,SMP,ISOL]
2793 The argument is a cpu list, as described above.
2794 In kernels built with CONFIG_NO_HZ_FULL=y, set
2795 the specified list of CPUs whose tick will be stopped
2796 whenever possible. The boot CPU will be forced outside
2797 the range to maintain the timekeeping. Any CPUs
2798 in this list will have their RCU callbacks offloaded,
2799 just as if they had also been called out in the
2800 rcu_nocbs= boot parameter.
2801
2802 noiotrap [SH] Disables trapped I/O port accesses.
2803
2804 noirqdebug [X86-32] Disables the code which attempts to detect and
2805 disable unhandled interrupt sources.
2806
2807 no_timer_check [X86,APIC] Disables the code which tests for
2808 broken timer IRQ sources.
2809
2810 noisapnp [ISAPNP] Disables ISA PnP code.
2811
2812 noinitrd [RAM] Tells the kernel not to load any configured
2813 initial RAM disk.
2814
2815 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2816 remapping.
2817 [Deprecated - use intremap=off]
2818
2819 nointroute [IA-64]
2820
2821 noinvpcid [X86] Disable the INVPCID cpu feature.
2822
2823 nojitter [IA-64] Disables jitter checking for ITC timers.
2824
2825 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2826
2827 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2828 fault handling.
2829
2830 no-vmw-sched-clock
2831 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2832 clock and use the default one.
2833
2834 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2835 steal time is computed, but won't influence scheduler
2836 behaviour
2837
2838 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2839
2840 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2841
2842 noltlbs [PPC] Do not use large page/tlb entries for kernel
2843 lowmem mapping on PPC40x and PPC8xx
2844
2845 nomca [IA-64] Disable machine check abort handling
2846
2847 nomce [X86-32] Disable Machine Check Exception
2848
2849 nomfgpt [X86-32] Disable Multi-Function General Purpose
2850 Timer usage (for AMD Geode machines).
2851
2852 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2853 shutdown the other cpus. Instead use the REBOOT_VECTOR
2854 irq.
2855
2856 nomodule Disable module load
2857
2858 nopat [X86] Disable PAT (page attribute table extension of
2859 pagetables) support.
2860
2861 nopcid [X86-64] Disable the PCID cpu feature.
2862
2863 norandmaps Don't use address space randomization. Equivalent to
2864 echo 0 > /proc/sys/kernel/randomize_va_space
2865
2866 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2867 with UP alternatives
2868
2869 nordrand [X86] Disable kernel use of the RDRAND and
2870 RDSEED instructions even if they are supported
2871 by the processor. RDRAND and RDSEED are still
2872 available to user space applications.
2873
2874 noresume [SWSUSP] Disables resume and restores original swap
2875 space.
2876
2877 no-scroll [VGA] Disables scrollback.
2878 This is required for the Braillex ib80-piezo Braille
2879 reader made by F.H. Papenmeier (Germany).
2880
2881 nosbagart [IA-64]
2882
2883 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2884
2885 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2886 and disable the IO APIC. legacy for "maxcpus=0".
2887
2888 nosoftlockup [KNL] Disable the soft-lockup detector.
2889
2890 nosync [HW,M68K] Disables sync negotiation for all devices.
2891
2892 notsc [BUGS=X86-32] Disable Time Stamp Counter
2893
2894 nowatchdog [KNL] Disable both lockup detectors, i.e.
2895 soft-lockup and NMI watchdog (hard-lockup).
2896
2897 nowb [ARM]
2898
2899 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2900
2901 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2902 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2903 Some features depend on CPU0. Known dependencies are:
2904 1. Resume from suspend/hibernate depends on CPU0.
2905 Suspend/hibernate will fail if CPU0 is offline and you
2906 need to online CPU0 before suspend/hibernate.
2907 2. PIC interrupts also depend on CPU0. CPU0 can't be
2908 removed if a PIC interrupt is detected.
2909 It's said poweroff/reboot may depend on CPU0 on some
2910 machines although I haven't seen such issues so far
2911 after CPU0 is offline on a few tested machines.
2912 If the dependencies are under your control, you can
2913 turn on cpu0_hotplug.
2914
2915 nps_mtm_hs_ctr= [KNL,ARC]
2916 This parameter sets the maximum duration, in
2917 cycles, each HW thread of the CTOP can run
2918 without interruptions, before HW switches it.
2919 The actual maximum duration is 16 times this
2920 parameter's value.
2921 Format: integer between 1 and 255
2922 Default: 255
2923
2924 nptcg= [IA-64] Override max number of concurrent global TLB
2925 purges which is reported from either PAL_VM_SUMMARY or
2926 SAL PALO.
2927
2928 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2929 could support. nr_cpus=n : n >= 1 limits the kernel to
2930 support 'n' processors. It could be larger than the
2931 number of already plugged CPU during bootup, later in
2932 runtime you can physically add extra cpu until it reaches
2933 n. So during boot up some boot time memory for per-cpu
2934 variables need be pre-allocated for later physical cpu
2935 hot plugging.
2936
2937 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2938
2939 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2940 Allowed values are enable and disable
2941
2942 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2943 'node', 'default' can be specified
2944 This can be set from sysctl after boot.
2945 See Documentation/sysctl/vm.txt for details.
2946
2947 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2948 See Documentation/debugging-via-ohci1394.txt for more
2949 info.
2950
2951 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2952 Rather than timing out after 20 ms if an EC
2953 command is not properly ACKed, override the length
2954 of the timeout. We have interrupts disabled while
2955 waiting for the ACK, so if this is set too high
2956 interrupts *may* be lost!
2957
2958 omap_mux= [OMAP] Override bootloader pin multiplexing.
2959 Format: <mux_mode0.mode_name=value>...
2960 For example, to override I2C bus2:
2961 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2962
2963 oprofile.timer= [HW]
2964 Use timer interrupt instead of performance counters
2965
2966 oprofile.cpu_type= Force an oprofile cpu type
2967 This might be useful if you have an older oprofile
2968 userland or if you want common events.
2969 Format: { arch_perfmon }
2970 arch_perfmon: [X86] Force use of architectural
2971 perfmon on Intel CPUs instead of the
2972 CPU specific event set.
2973 timer: [X86] Force use of architectural NMI
2974 timer mode (see also oprofile.timer
2975 for generic hr timer mode)
2976
2977 oops=panic Always panic on oopses. Default is to just kill the
2978 process, but there is a small probability of
2979 deadlocking the machine.
2980 This will also cause panics on machine check exceptions.
2981 Useful together with panic=30 to trigger a reboot.
2982
2983 OSS [HW,OSS]
2984 See Documentation/sound/oss/oss-parameters.txt
2985
2986 page_owner= [KNL] Boot-time page_owner enabling option.
2987 Storage of the information about who allocated
2988 each page is disabled in default. With this switch,
2989 we can turn it on.
2990 on: enable the feature
2991
2992 page_poison= [KNL] Boot-time parameter changing the state of
2993 poisoning on the buddy allocator.
2994 off: turn off poisoning
2995 on: turn on poisoning
2996
2997 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2998 timeout > 0: seconds before rebooting
2999 timeout = 0: wait forever
3000 timeout < 0: reboot immediately
3001 Format: <timeout>
3002
3003 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3004 on a WARN().
3005
3006 crash_kexec_post_notifiers
3007 Run kdump after running panic-notifiers and dumping
3008 kmsg. This only for the users who doubt kdump always
3009 succeeds in any situation.
3010 Note that this also increases risks of kdump failure,
3011 because some panic notifiers can make the crashed
3012 kernel more unstable.
3013
3014 parkbd.port= [HW] Parallel port number the keyboard adapter is
3015 connected to, default is 0.
3016 Format: <parport#>
3017 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3018 0 for XT, 1 for AT (default is AT).
3019 Format: <mode>
3020
3021 parport= [HW,PPT] Specify parallel ports. 0 disables.
3022 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3023 Use 'auto' to force the driver to use any
3024 IRQ/DMA settings detected (the default is to
3025 ignore detected IRQ/DMA settings because of
3026 possible conflicts). You can specify the base
3027 address, IRQ, and DMA settings; IRQ and DMA
3028 should be numbers, or 'auto' (for using detected
3029 settings on that particular port), or 'nofifo'
3030 (to avoid using a FIFO even if it is detected).
3031 Parallel ports are assigned in the order they
3032 are specified on the command line, starting
3033 with parport0.
3034
3035 parport_init_mode= [HW,PPT]
3036 Configure VIA parallel port to operate in
3037 a specific mode. This is necessary on Pegasos
3038 computer where firmware has no options for setting
3039 up parallel port mode and sets it to spp.
3040 Currently this function knows 686a and 8231 chips.
3041 Format: [spp|ps2|epp|ecp|ecpepp]
3042
3043 pause_on_oops=
3044 Halt all CPUs after the first oops has been printed for
3045 the specified number of seconds. This is to be used if
3046 your oopses keep scrolling off the screen.
3047
3048 pcbit= [HW,ISDN]
3049
3050 pcd. [PARIDE]
3051 See header of drivers/block/paride/pcd.c.
3052 See also Documentation/blockdev/paride.txt.
3053
3054 pci=option[,option...] [PCI] various PCI subsystem options:
3055 earlydump [X86] dump PCI config space before the kernel
3056 changes anything
3057 off [X86] don't probe for the PCI bus
3058 bios [X86-32] force use of PCI BIOS, don't access
3059 the hardware directly. Use this if your machine
3060 has a non-standard PCI host bridge.
3061 nobios [X86-32] disallow use of PCI BIOS, only direct
3062 hardware access methods are allowed. Use this
3063 if you experience crashes upon bootup and you
3064 suspect they are caused by the BIOS.
3065 conf1 [X86] Force use of PCI Configuration Access
3066 Mechanism 1 (config address in IO port 0xCF8,
3067 data in IO port 0xCFC, both 32-bit).
3068 conf2 [X86] Force use of PCI Configuration Access
3069 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3070 the function, IO port 0xCFA, also 8-bit, sets
3071 bus number. The config space is then accessed
3072 through ports 0xC000-0xCFFF).
3073 See http://wiki.osdev.org/PCI for more info
3074 on the configuration access mechanisms.
3075 noaer [PCIE] If the PCIEAER kernel config parameter is
3076 enabled, this kernel boot option can be used to
3077 disable the use of PCIE advanced error reporting.
3078 nodomains [PCI] Disable support for multiple PCI
3079 root domains (aka PCI segments, in ACPI-speak).
3080 nommconf [X86] Disable use of MMCONFIG for PCI
3081 Configuration
3082 check_enable_amd_mmconf [X86] check for and enable
3083 properly configured MMIO access to PCI
3084 config space on AMD family 10h CPU
3085 nomsi [MSI] If the PCI_MSI kernel config parameter is
3086 enabled, this kernel boot option can be used to
3087 disable the use of MSI interrupts system-wide.
3088 clearmsi [X86] Clears MSI/MSI-X enable bits early in boot
3089 time in order to avoid issues like adapters
3090 screaming irqs and preventing boot progress.
3091 Also, it enforces the PCI Local Bus spec
3092 rule that those bits should be 0 in system reset
3093 events (useful for kexec/kdump cases).
3094 noioapicquirk [APIC] Disable all boot interrupt quirks.
3095 Safety option to keep boot IRQs enabled. This
3096 should never be necessary.
3097 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3098 primary IO-APIC for bridges that cannot disable
3099 boot IRQs. This fixes a source of spurious IRQs
3100 when the system masks IRQs.
3101 noioapicreroute [APIC] Disable workaround that uses the
3102 boot IRQ equivalent of an IRQ that connects to
3103 a chipset where boot IRQs cannot be disabled.
3104 The opposite of ioapicreroute.
3105 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3106 routing table. These calls are known to be buggy
3107 on several machines and they hang the machine
3108 when used, but on other computers it's the only
3109 way to get the interrupt routing table. Try
3110 this option if the kernel is unable to allocate
3111 IRQs or discover secondary PCI buses on your
3112 motherboard.
3113 rom [X86] Assign address space to expansion ROMs.
3114 Use with caution as certain devices share
3115 address decoders between ROMs and other
3116 resources.
3117 norom [X86] Do not assign address space to
3118 expansion ROMs that do not already have
3119 BIOS assigned address ranges.
3120 nobar [X86] Do not assign address space to the
3121 BARs that weren't assigned by the BIOS.
3122 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3123 assigned automatically to PCI devices. You can
3124 make the kernel exclude IRQs of your ISA cards
3125 this way.
3126 pirqaddr=0xAAAAA [X86] Specify the physical address
3127 of the PIRQ table (normally generated
3128 by the BIOS) if it is outside the
3129 F0000h-100000h range.
3130 lastbus=N [X86] Scan all buses thru bus #N. Can be
3131 useful if the kernel is unable to find your
3132 secondary buses and you want to tell it
3133 explicitly which ones they are.
3134 assign-busses [X86] Always assign all PCI bus
3135 numbers ourselves, overriding
3136 whatever the firmware may have done.
3137 usepirqmask [X86] Honor the possible IRQ mask stored
3138 in the BIOS $PIR table. This is needed on
3139 some systems with broken BIOSes, notably
3140 some HP Pavilion N5400 and Omnibook XE3
3141 notebooks. This will have no effect if ACPI
3142 IRQ routing is enabled.
3143 noacpi [X86] Do not use ACPI for IRQ routing
3144 or for PCI scanning.
3145 use_crs [X86] Use PCI host bridge window information
3146 from ACPI. On BIOSes from 2008 or later, this
3147 is enabled by default. If you need to use this,
3148 please report a bug.
3149 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3150 If you need to use this, please report a bug.
3151 routeirq Do IRQ routing for all PCI devices.
3152 This is normally done in pci_enable_device(),
3153 so this option is a temporary workaround
3154 for broken drivers that don't call it.
3155 skip_isa_align [X86] do not align io start addr, so can
3156 handle more pci cards
3157 noearly [X86] Don't do any early type 1 scanning.
3158 This might help on some broken boards which
3159 machine check when some devices' config space
3160 is read. But various workarounds are disabled
3161 and some IOMMU drivers will not work.
3162 bfsort Sort PCI devices into breadth-first order.
3163 This sorting is done to get a device
3164 order compatible with older (<= 2.4) kernels.
3165 nobfsort Don't sort PCI devices into breadth-first order.
3166 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3167 tuning and use the BIOS-configured MPS defaults.
3168 pcie_bus_safe Set every device's MPS to the largest value
3169 supported by all devices below the root complex.
3170 pcie_bus_perf Set device MPS to the largest allowable MPS
3171 based on its parent bus. Also set MRRS (Max
3172 Read Request Size) to the largest supported
3173 value (no larger than the MPS that the device
3174 or bus can support) for best performance.
3175 pcie_bus_peer2peer Set every device's MPS to 128B, which
3176 every device is guaranteed to support. This
3177 configuration allows peer-to-peer DMA between
3178 any pair of devices, possibly at the cost of
3179 reduced performance. This also guarantees
3180 that hot-added devices will work.
3181 cbiosize=nn[KMG] The fixed amount of bus space which is
3182 reserved for the CardBus bridge's IO window.
3183 The default value is 256 bytes.
3184 cbmemsize=nn[KMG] The fixed amount of bus space which is
3185 reserved for the CardBus bridge's memory
3186 window. The default value is 64 megabytes.
3187 resource_alignment=
3188 Format:
3189 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3190 [<order of align>@]pci:<vendor>:<device>\
3191 [:<subvendor>:<subdevice>][; ...]
3192 Specifies alignment and device to reassign
3193 aligned memory resources.
3194 If <order of align> is not specified,
3195 PAGE_SIZE is used as alignment.
3196 PCI-PCI bridge can be specified, if resource
3197 windows need to be expanded.
3198 To specify the alignment for several
3199 instances of a device, the PCI vendor,
3200 device, subvendor, and subdevice may be
3201 specified, e.g., 4096@pci:8086:9c22:103c:198f
3202 ecrc= Enable/disable PCIe ECRC (transaction layer
3203 end-to-end CRC checking).
3204 bios: Use BIOS/firmware settings. This is the
3205 the default.
3206 off: Turn ECRC off
3207 on: Turn ECRC on.
3208 hpiosize=nn[KMG] The fixed amount of bus space which is
3209 reserved for hotplug bridge's IO window.
3210 Default size is 256 bytes.
3211 hpmemsize=nn[KMG] The fixed amount of bus space which is
3212 reserved for hotplug bridge's memory window.
3213 Default size is 2 megabytes.
3214 hpbussize=nn The minimum amount of additional bus numbers
3215 reserved for buses below a hotplug bridge.
3216 Default is 1.
3217 realloc= Enable/disable reallocating PCI bridge resources
3218 if allocations done by BIOS are too small to
3219 accommodate resources required by all child
3220 devices.
3221 off: Turn realloc off
3222 on: Turn realloc on
3223 realloc same as realloc=on
3224 noari do not use PCIe ARI.
3225 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3226 only look for one device below a PCIe downstream
3227 port.
3228 big_root_window Try to add a big 64bit memory window to the PCIe
3229 root complex on AMD CPUs. Some GFX hardware
3230 can resize a BAR to allow access to all VRAM.
3231 Adding the window is slightly risky (it may
3232 conflict with unreported devices), so this
3233 taints the kernel.
3234
3235 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3236 Management.
3237 off Disable ASPM.
3238 force Enable ASPM even on devices that claim not to support it.
3239 WARNING: Forcing ASPM on may cause system lockups.
3240
3241 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3242 nomsi Do not use MSI for PCI Express Native Hotplug (this
3243 makes all PCIe ports use INTx for hotplug services).
3244
3245 pcie_ports= [PCIE] PCIe ports handling:
3246 auto Ask the BIOS whether or not to use native PCIe services
3247 associated with PCIe ports (PME, hot-plug, AER). Use
3248 them only if that is allowed by the BIOS.
3249 native Use native PCIe services associated with PCIe ports
3250 unconditionally.
3251 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3252 ports driver.
3253
3254 pcie_port_pm= [PCIE] PCIe port power management handling:
3255 off Disable power management of all PCIe ports
3256 force Forcibly enable power management of all PCIe ports
3257
3258 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3259 nomsi Do not use MSI for native PCIe PME signaling (this makes
3260 all PCIe root ports use INTx for all services).
3261
3262 pcmv= [HW,PCMCIA] BadgePAD 4
3263
3264 pd_ignore_unused
3265 [PM]
3266 Keep all power-domains already enabled by bootloader on,
3267 even if no driver has claimed them. This is useful
3268 for debug and development, but should not be
3269 needed on a platform with proper driver support.
3270
3271 pd. [PARIDE]
3272 See Documentation/blockdev/paride.txt.
3273
3274 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3275 boot time.
3276 Format: { 0 | 1 }
3277 See arch/parisc/kernel/pdc_chassis.c
3278
3279 percpu_alloc= Select which percpu first chunk allocator to use.
3280 Currently supported values are "embed" and "page".
3281 Archs may support subset or none of the selections.
3282 See comments in mm/percpu.c for details on each
3283 allocator. This parameter is primarily for debugging
3284 and performance comparison.
3285
3286 pf. [PARIDE]
3287 See Documentation/blockdev/paride.txt.
3288
3289 pg. [PARIDE]
3290 See Documentation/blockdev/paride.txt.
3291
3292 pirq= [SMP,APIC] Manual mp-table setup
3293 See Documentation/x86/i386/IO-APIC.txt.
3294
3295 plip= [PPT,NET] Parallel port network link
3296 Format: { parport<nr> | timid | 0 }
3297 See also Documentation/admin-guide/parport.rst.
3298
3299 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3300 Override pmtimer IOPort with a hex value.
3301 e.g. pmtmr=0x508
3302
3303 pnp.debug=1 [PNP]
3304 Enable PNP debug messages (depends on the
3305 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3306 via /sys/module/pnp/parameters/debug. We always show
3307 current resource usage; turning this on also shows
3308 possible settings and some assignment information.
3309
3310 pnpacpi= [ACPI]
3311 { off }
3312
3313 pnpbios= [ISAPNP]
3314 { on | off | curr | res | no-curr | no-res }
3315
3316 pnp_reserve_irq=
3317 [ISAPNP] Exclude IRQs for the autoconfiguration
3318
3319 pnp_reserve_dma=
3320 [ISAPNP] Exclude DMAs for the autoconfiguration
3321
3322 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3323 Ranges are in pairs (I/O port base and size).
3324
3325 pnp_reserve_mem=
3326 [ISAPNP] Exclude memory regions for the
3327 autoconfiguration.
3328 Ranges are in pairs (memory base and size).
3329
3330 ports= [IP_VS_FTP] IPVS ftp helper module
3331 Default is 21.
3332 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3333 may be specified.
3334 Format: <port>,<port>....
3335
3336 powersave=off [PPC] This option disables power saving features.
3337 It specifically disables cpuidle and sets the
3338 platform machine description specific power_save
3339 function to NULL. On Idle the CPU just reduces
3340 execution priority.
3341
3342 ppc_strict_facility_enable
3343 [PPC] This option catches any kernel floating point,
3344 Altivec, VSX and SPE outside of regions specifically
3345 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3346 There is some performance impact when enabling this.
3347
3348 ppc_tm= [PPC]
3349 Format: {"off"}
3350 Disable Hardware Transactional Memory
3351
3352 print-fatal-signals=
3353 [KNL] debug: print fatal signals
3354
3355 If enabled, warn about various signal handling
3356 related application anomalies: too many signals,
3357 too many POSIX.1 timers, fatal signals causing a
3358 coredump - etc.
3359
3360 If you hit the warning due to signal overflow,
3361 you might want to try "ulimit -i unlimited".
3362
3363 default: off.
3364
3365 printk.always_kmsg_dump=
3366 Trigger kmsg_dump for cases other than kernel oops or
3367 panics
3368 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3369 default: disabled
3370
3371 printk.devkmsg={on,off,ratelimit}
3372 Control writing to /dev/kmsg.
3373 on - unlimited logging to /dev/kmsg from userspace
3374 off - logging to /dev/kmsg disabled
3375 ratelimit - ratelimit the logging
3376 Default: ratelimit
3377
3378 printk.time= Show timing data prefixed to each printk message line
3379 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3380
3381 processor.max_cstate= [HW,ACPI]
3382 Limit processor to maximum C-state
3383 max_cstate=9 overrides any DMI blacklist limit.
3384
3385 processor.nocst [HW,ACPI]
3386 Ignore the _CST method to determine C-states,
3387 instead using the legacy FADT method
3388
3389 profile= [KNL] Enable kernel profiling via /proc/profile
3390 Format: [<profiletype>,]<number>
3391 Param: <profiletype>: "schedule", "sleep", or "kvm"
3392 [defaults to kernel profiling]
3393 Param: "schedule" - profile schedule points.
3394 Param: "sleep" - profile D-state sleeping (millisecs).
3395 Requires CONFIG_SCHEDSTATS
3396 Param: "kvm" - profile VM exits.
3397 Param: <number> - step/bucket size as a power of 2 for
3398 statistical time based profiling.
3399
3400 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3401 before loading.
3402 See Documentation/blockdev/ramdisk.txt.
3403
3404 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3405 probe for; one of (bare|imps|exps|lifebook|any).
3406 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3407 per second.
3408 psmouse.resetafter= [HW,MOUSE]
3409 Try to reset the device after so many bad packets
3410 (0 = never).
3411 psmouse.resolution=
3412 [HW,MOUSE] Set desired mouse resolution, in dpi.
3413 psmouse.smartscroll=
3414 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3415 0 = disabled, 1 = enabled (default).
3416
3417 pstore.backend= Specify the name of the pstore backend to use
3418
3419 pt. [PARIDE]
3420 See Documentation/blockdev/paride.txt.
3421
3422 pti= [X86_64] Control Page Table Isolation of user and
3423 kernel address spaces. Disabling this feature
3424 removes hardening, but improves performance of
3425 system calls and interrupts.
3426
3427 on - unconditionally enable
3428 off - unconditionally disable
3429 auto - kernel detects whether your CPU model is
3430 vulnerable to issues that PTI mitigates
3431
3432 Not specifying this option is equivalent to pti=auto.
3433
3434 nopti [X86_64]
3435 Equivalent to pti=off
3436
3437 pty.legacy_count=
3438 [KNL] Number of legacy pty's. Overwrites compiled-in
3439 default number.
3440
3441 quiet [KNL] Disable most log messages
3442
3443 r128= [HW,DRM]
3444
3445 raid= [HW,RAID]
3446 See Documentation/admin-guide/md.rst.
3447
3448 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3449 See Documentation/blockdev/ramdisk.txt.
3450
3451 ras=option[,option,...] [KNL] RAS-specific options
3452
3453 cec_disable [X86]
3454 Disable the Correctable Errors Collector,
3455 see CONFIG_RAS_CEC help text.
3456
3457 rcu_nocbs= [KNL]
3458 The argument is a cpu list, as described above.
3459
3460 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3461 the specified list of CPUs to be no-callback CPUs.
3462 Invocation of these CPUs' RCU callbacks will
3463 be offloaded to "rcuox/N" kthreads created for
3464 that purpose, where "x" is "b" for RCU-bh, "p"
3465 for RCU-preempt, and "s" for RCU-sched, and "N"
3466 is the CPU number. This reduces OS jitter on the
3467 offloaded CPUs, which can be useful for HPC and
3468 real-time workloads. It can also improve energy
3469 efficiency for asymmetric multiprocessors.
3470
3471 rcu_nocb_poll [KNL]
3472 Rather than requiring that offloaded CPUs
3473 (specified by rcu_nocbs= above) explicitly
3474 awaken the corresponding "rcuoN" kthreads,
3475 make these kthreads poll for callbacks.
3476 This improves the real-time response for the
3477 offloaded CPUs by relieving them of the need to
3478 wake up the corresponding kthread, but degrades
3479 energy efficiency by requiring that the kthreads
3480 periodically wake up to do the polling.
3481
3482 rcutree.blimit= [KNL]
3483 Set maximum number of finished RCU callbacks to
3484 process in one batch.
3485
3486 rcutree.dump_tree= [KNL]
3487 Dump the structure of the rcu_node combining tree
3488 out at early boot. This is used for diagnostic
3489 purposes, to verify correct tree setup.
3490
3491 rcutree.gp_cleanup_delay= [KNL]
3492 Set the number of jiffies to delay each step of
3493 RCU grace-period cleanup.
3494
3495 rcutree.gp_init_delay= [KNL]
3496 Set the number of jiffies to delay each step of
3497 RCU grace-period initialization.
3498
3499 rcutree.gp_preinit_delay= [KNL]
3500 Set the number of jiffies to delay each step of
3501 RCU grace-period pre-initialization, that is,
3502 the propagation of recent CPU-hotplug changes up
3503 the rcu_node combining tree.
3504
3505 rcutree.rcu_fanout_exact= [KNL]
3506 Disable autobalancing of the rcu_node combining
3507 tree. This is used by rcutorture, and might
3508 possibly be useful for architectures having high
3509 cache-to-cache transfer latencies.
3510
3511 rcutree.rcu_fanout_leaf= [KNL]
3512 Change the number of CPUs assigned to each
3513 leaf rcu_node structure. Useful for very
3514 large systems, which will choose the value 64,
3515 and for NUMA systems with large remote-access
3516 latencies, which will choose a value aligned
3517 with the appropriate hardware boundaries.
3518
3519 rcutree.jiffies_till_sched_qs= [KNL]
3520 Set required age in jiffies for a
3521 given grace period before RCU starts
3522 soliciting quiescent-state help from
3523 rcu_note_context_switch().
3524
3525 rcutree.jiffies_till_first_fqs= [KNL]
3526 Set delay from grace-period initialization to
3527 first attempt to force quiescent states.
3528 Units are jiffies, minimum value is zero,
3529 and maximum value is HZ.
3530
3531 rcutree.jiffies_till_next_fqs= [KNL]
3532 Set delay between subsequent attempts to force
3533 quiescent states. Units are jiffies, minimum
3534 value is one, and maximum value is HZ.
3535
3536 rcutree.kthread_prio= [KNL,BOOT]
3537 Set the SCHED_FIFO priority of the RCU per-CPU
3538 kthreads (rcuc/N). This value is also used for
3539 the priority of the RCU boost threads (rcub/N)
3540 and for the RCU grace-period kthreads (rcu_bh,
3541 rcu_preempt, and rcu_sched). If RCU_BOOST is
3542 set, valid values are 1-99 and the default is 1
3543 (the least-favored priority). Otherwise, when
3544 RCU_BOOST is not set, valid values are 0-99 and
3545 the default is zero (non-realtime operation).
3546
3547 rcutree.rcu_nocb_leader_stride= [KNL]
3548 Set the number of NOCB kthread groups, which
3549 defaults to the square root of the number of
3550 CPUs. Larger numbers reduces the wakeup overhead
3551 on the per-CPU grace-period kthreads, but increases
3552 that same overhead on each group's leader.
3553
3554 rcutree.qhimark= [KNL]
3555 Set threshold of queued RCU callbacks beyond which
3556 batch limiting is disabled.
3557
3558 rcutree.qlowmark= [KNL]
3559 Set threshold of queued RCU callbacks below which
3560 batch limiting is re-enabled.
3561
3562 rcutree.rcu_idle_gp_delay= [KNL]
3563 Set wakeup interval for idle CPUs that have
3564 RCU callbacks (RCU_FAST_NO_HZ=y).
3565
3566 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3567 Set wakeup interval for idle CPUs that have
3568 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3569 Lazy RCU callbacks are those which RCU can
3570 prove do nothing more than free memory.
3571
3572 rcutree.rcu_kick_kthreads= [KNL]
3573 Cause the grace-period kthread to get an extra
3574 wake_up() if it sleeps three times longer than
3575 it should at force-quiescent-state time.
3576 This wake_up() will be accompanied by a
3577 WARN_ONCE() splat and an ftrace_dump().
3578
3579 rcuperf.gp_async= [KNL]
3580 Measure performance of asynchronous
3581 grace-period primitives such as call_rcu().
3582
3583 rcuperf.gp_async_max= [KNL]
3584 Specify the maximum number of outstanding
3585 callbacks per writer thread. When a writer
3586 thread exceeds this limit, it invokes the
3587 corresponding flavor of rcu_barrier() to allow
3588 previously posted callbacks to drain.
3589
3590 rcuperf.gp_exp= [KNL]
3591 Measure performance of expedited synchronous
3592 grace-period primitives.
3593
3594 rcuperf.holdoff= [KNL]
3595 Set test-start holdoff period. The purpose of
3596 this parameter is to delay the start of the
3597 test until boot completes in order to avoid
3598 interference.
3599
3600 rcuperf.nreaders= [KNL]
3601 Set number of RCU readers. The value -1 selects
3602 N, where N is the number of CPUs. A value
3603 "n" less than -1 selects N-n+1, where N is again
3604 the number of CPUs. For example, -2 selects N
3605 (the number of CPUs), -3 selects N+1, and so on.
3606 A value of "n" less than or equal to -N selects
3607 a single reader.
3608
3609 rcuperf.nwriters= [KNL]
3610 Set number of RCU writers. The values operate
3611 the same as for rcuperf.nreaders.
3612 N, where N is the number of CPUs
3613
3614 rcuperf.perf_runnable= [BOOT]
3615 Start rcuperf running at boot time.
3616
3617 rcuperf.perf_type= [KNL]
3618 Specify the RCU implementation to test.
3619
3620 rcuperf.shutdown= [KNL]
3621 Shut the system down after performance tests
3622 complete. This is useful for hands-off automated
3623 testing.
3624
3625 rcuperf.verbose= [KNL]
3626 Enable additional printk() statements.
3627
3628 rcuperf.writer_holdoff= [KNL]
3629 Write-side holdoff between grace periods,
3630 in microseconds. The default of zero says
3631 no holdoff.
3632
3633 rcutorture.cbflood_inter_holdoff= [KNL]
3634 Set holdoff time (jiffies) between successive
3635 callback-flood tests.
3636
3637 rcutorture.cbflood_intra_holdoff= [KNL]
3638 Set holdoff time (jiffies) between successive
3639 bursts of callbacks within a given callback-flood
3640 test.
3641
3642 rcutorture.cbflood_n_burst= [KNL]
3643 Set the number of bursts making up a given
3644 callback-flood test. Set this to zero to
3645 disable callback-flood testing.
3646
3647 rcutorture.cbflood_n_per_burst= [KNL]
3648 Set the number of callbacks to be registered
3649 in a given burst of a callback-flood test.
3650
3651 rcutorture.fqs_duration= [KNL]
3652 Set duration of force_quiescent_state bursts
3653 in microseconds.
3654
3655 rcutorture.fqs_holdoff= [KNL]
3656 Set holdoff time within force_quiescent_state bursts
3657 in microseconds.
3658
3659 rcutorture.fqs_stutter= [KNL]
3660 Set wait time between force_quiescent_state bursts
3661 in seconds.
3662
3663 rcutorture.gp_cond= [KNL]
3664 Use conditional/asynchronous update-side
3665 primitives, if available.
3666
3667 rcutorture.gp_exp= [KNL]
3668 Use expedited update-side primitives, if available.
3669
3670 rcutorture.gp_normal= [KNL]
3671 Use normal (non-expedited) asynchronous
3672 update-side primitives, if available.
3673
3674 rcutorture.gp_sync= [KNL]
3675 Use normal (non-expedited) synchronous
3676 update-side primitives, if available. If all
3677 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3678 rcutorture.gp_normal=, and rcutorture.gp_sync=
3679 are zero, rcutorture acts as if is interpreted
3680 they are all non-zero.
3681
3682 rcutorture.n_barrier_cbs= [KNL]
3683 Set callbacks/threads for rcu_barrier() testing.
3684
3685 rcutorture.nfakewriters= [KNL]
3686 Set number of concurrent RCU writers. These just
3687 stress RCU, they don't participate in the actual
3688 test, hence the "fake".
3689
3690 rcutorture.nreaders= [KNL]
3691 Set number of RCU readers. The value -1 selects
3692 N-1, where N is the number of CPUs. A value
3693 "n" less than -1 selects N-n-2, where N is again
3694 the number of CPUs. For example, -2 selects N
3695 (the number of CPUs), -3 selects N+1, and so on.
3696
3697 rcutorture.object_debug= [KNL]
3698 Enable debug-object double-call_rcu() testing.
3699
3700 rcutorture.onoff_holdoff= [KNL]
3701 Set time (s) after boot for CPU-hotplug testing.
3702
3703 rcutorture.onoff_interval= [KNL]
3704 Set time (s) between CPU-hotplug operations, or
3705 zero to disable CPU-hotplug testing.
3706
3707 rcutorture.shuffle_interval= [KNL]
3708 Set task-shuffle interval (s). Shuffling tasks
3709 allows some CPUs to go into dyntick-idle mode
3710 during the rcutorture test.
3711
3712 rcutorture.shutdown_secs= [KNL]
3713 Set time (s) after boot system shutdown. This
3714 is useful for hands-off automated testing.
3715
3716 rcutorture.stall_cpu= [KNL]
3717 Duration of CPU stall (s) to test RCU CPU stall
3718 warnings, zero to disable.
3719
3720 rcutorture.stall_cpu_holdoff= [KNL]
3721 Time to wait (s) after boot before inducing stall.
3722
3723 rcutorture.stall_cpu_irqsoff= [KNL]
3724 Disable interrupts while stalling if set.
3725
3726 rcutorture.stat_interval= [KNL]
3727 Time (s) between statistics printk()s.
3728
3729 rcutorture.stutter= [KNL]
3730 Time (s) to stutter testing, for example, specifying
3731 five seconds causes the test to run for five seconds,
3732 wait for five seconds, and so on. This tests RCU's
3733 ability to transition abruptly to and from idle.
3734
3735 rcutorture.test_boost= [KNL]
3736 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3737 "Maybe" means test if the RCU implementation
3738 under test support RCU priority boosting.
3739
3740 rcutorture.test_boost_duration= [KNL]
3741 Duration (s) of each individual boost test.
3742
3743 rcutorture.test_boost_interval= [KNL]
3744 Interval (s) between each boost test.
3745
3746 rcutorture.test_no_idle_hz= [KNL]
3747 Test RCU's dyntick-idle handling. See also the
3748 rcutorture.shuffle_interval parameter.
3749
3750 rcutorture.torture_runnable= [BOOT]
3751 Start rcutorture running at boot time.
3752
3753 rcutorture.torture_type= [KNL]
3754 Specify the RCU implementation to test.
3755
3756 rcutorture.verbose= [KNL]
3757 Enable additional printk() statements.
3758
3759 rcupdate.rcu_cpu_stall_suppress= [KNL]
3760 Suppress RCU CPU stall warning messages.
3761
3762 rcupdate.rcu_cpu_stall_timeout= [KNL]
3763 Set timeout for RCU CPU stall warning messages.
3764
3765 rcupdate.rcu_expedited= [KNL]
3766 Use expedited grace-period primitives, for
3767 example, synchronize_rcu_expedited() instead
3768 of synchronize_rcu(). This reduces latency,
3769 but can increase CPU utilization, degrade
3770 real-time latency, and degrade energy efficiency.
3771 No effect on CONFIG_TINY_RCU kernels.
3772
3773 rcupdate.rcu_normal= [KNL]
3774 Use only normal grace-period primitives,
3775 for example, synchronize_rcu() instead of
3776 synchronize_rcu_expedited(). This improves
3777 real-time latency, CPU utilization, and
3778 energy efficiency, but can expose users to
3779 increased grace-period latency. This parameter
3780 overrides rcupdate.rcu_expedited. No effect on
3781 CONFIG_TINY_RCU kernels.
3782
3783 rcupdate.rcu_normal_after_boot= [KNL]
3784 Once boot has completed (that is, after
3785 rcu_end_inkernel_boot() has been invoked), use
3786 only normal grace-period primitives. No effect
3787 on CONFIG_TINY_RCU kernels.
3788
3789 rcupdate.rcu_task_stall_timeout= [KNL]
3790 Set timeout in jiffies for RCU task stall warning
3791 messages. Disable with a value less than or equal
3792 to zero.
3793
3794 rcupdate.rcu_self_test= [KNL]
3795 Run the RCU early boot self tests
3796
3797 rcupdate.rcu_self_test_bh= [KNL]
3798 Run the RCU bh early boot self tests
3799
3800 rcupdate.rcu_self_test_sched= [KNL]
3801 Run the RCU sched early boot self tests
3802
3803 rdinit= [KNL]
3804 Format: <full_path>
3805 Run specified binary instead of /init from the ramdisk,
3806 used for early userspace startup. See initrd.
3807
3808 rdt= [HW,X86,RDT]
3809 Turn on/off individual RDT features. List is:
3810 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
3811 mba.
3812 E.g. to turn on cmt and turn off mba use:
3813 rdt=cmt,!mba
3814
3815 reboot= [KNL]
3816 Format (x86 or x86_64):
3817 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3818 [[,]s[mp]#### \
3819 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3820 [[,]f[orce]
3821 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3822 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3823 reboot_force is either force or not specified,
3824 reboot_cpu is s[mp]#### with #### being the processor
3825 to be used for rebooting.
3826
3827 relax_domain_level=
3828 [KNL, SMP] Set scheduler's default relax_domain_level.
3829 See Documentation/cgroup-v1/cpusets.txt.
3830
3831 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3832
3833 reservetop= [X86-32]
3834 Format: nn[KMG]
3835 Reserves a hole at the top of the kernel virtual
3836 address space.
3837
3838 reservelow= [X86]
3839 Format: nn[K]
3840 Set the amount of memory to reserve for BIOS at
3841 the bottom of the address space.
3842
3843 reset_devices [KNL] Force drivers to reset the underlying device
3844 during initialization.
3845
3846 resume= [SWSUSP]
3847 Specify the partition device for software suspend
3848 Format:
3849 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3850
3851 resume_offset= [SWSUSP]
3852 Specify the offset from the beginning of the partition
3853 given by "resume=" at which the swap header is located,
3854 in <PAGE_SIZE> units (needed only for swap files).
3855 See Documentation/power/swsusp-and-swap-files.txt
3856
3857 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3858 read the resume files
3859
3860 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3861 Useful for devices that are detected asynchronously
3862 (e.g. USB and MMC devices).
3863
3864 hibernate= [HIBERNATION]
3865 noresume Don't check if there's a hibernation image
3866 present during boot.
3867 nocompress Don't compress/decompress hibernation images.
3868 no Disable hibernation and resume.
3869 protect_image Turn on image protection during restoration
3870 (that will set all pages holding image data
3871 during restoration read-only).
3872
3873 retain_initrd [RAM] Keep initrd memory after extraction
3874
3875 rfkill.default_state=
3876 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3877 etc. communication is blocked by default.
3878 1 Unblocked.
3879
3880 rfkill.master_switch_mode=
3881 0 The "airplane mode" button does nothing.
3882 1 The "airplane mode" button toggles between everything
3883 blocked and the previous configuration.
3884 2 The "airplane mode" button toggles between everything
3885 blocked and everything unblocked.
3886
3887 rhash_entries= [KNL,NET]
3888 Set number of hash buckets for route cache
3889
3890 ring3mwait=disable
3891 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
3892 CPUs.
3893
3894 ro [KNL] Mount root device read-only on boot
3895
3896 rodata= [KNL]
3897 on Mark read-only kernel memory as read-only (default).
3898 off Leave read-only kernel memory writable for debugging.
3899
3900 rockchip.usb_uart
3901 Enable the uart passthrough on the designated usb port
3902 on Rockchip SoCs. When active, the signals of the
3903 debug-uart get routed to the D+ and D- pins of the usb
3904 port and the regular usb controller gets disabled.
3905
3906 root= [KNL] Root filesystem
3907 See name_to_dev_t comment in init/do_mounts.c.
3908
3909 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3910 mount the root filesystem
3911
3912 rootflags= [KNL] Set root filesystem mount option string
3913
3914 rootfstype= [KNL] Set root filesystem type
3915
3916 rootwait [KNL] Wait (indefinitely) for root device to show up.
3917 Useful for devices that are detected asynchronously
3918 (e.g. USB and MMC devices).
3919
3920 rproc_mem=nn[KMG][@address]
3921 [KNL,ARM,CMA] Remoteproc physical memory block.
3922 Memory area to be used by remote processor image,
3923 managed by CMA.
3924
3925 rw [KNL] Mount root device read-write on boot
3926
3927 S [KNL] Run init in single mode
3928
3929 s390_iommu= [HW,S390]
3930 Set s390 IOTLB flushing mode
3931 strict
3932 With strict flushing every unmap operation will result in
3933 an IOTLB flush. Default is lazy flushing before reuse,
3934 which is faster.
3935
3936 sa1100ir [NET]
3937 See drivers/net/irda/sa1100_ir.c.
3938
3939 sbni= [NET] Granch SBNI12 leased line adapter
3940
3941 sched_debug [KNL] Enables verbose scheduler debug messages.
3942
3943 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3944 Allowed values are enable and disable. This feature
3945 incurs a small amount of overhead in the scheduler
3946 but is useful for debugging and performance tuning.
3947
3948 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3949 xtime_lock contention on larger systems, and/or RCU lock
3950 contention on all systems with CONFIG_MAXSMP set.
3951 Format: { "0" | "1" }
3952 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3953 1 -- enable.
3954 Note: increases power consumption, thus should only be
3955 enabled if running jitter sensitive (HPC/RT) workloads.
3956
3957 security= [SECURITY] Choose a security module to enable at boot.
3958 If this boot parameter is not specified, only the first
3959 security module asking for security registration will be
3960 loaded. An invalid security module name will be treated
3961 as if no module has been chosen.
3962
3963 selinux= [SELINUX] Disable or enable SELinux at boot time.
3964 Format: { "0" | "1" }
3965 See security/selinux/Kconfig help text.
3966 0 -- disable.
3967 1 -- enable.
3968 Default value is set via kernel config option.
3969 If enabled at boot time, /selinux/disable can be used
3970 later to disable prior to initial policy load.
3971
3972 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3973 Format: { "0" | "1" }
3974 See security/apparmor/Kconfig help text
3975 0 -- disable.
3976 1 -- enable.
3977 Default value is set via kernel config option.
3978
3979 serialnumber [BUGS=X86-32]
3980
3981 shapers= [NET]
3982 Maximal number of shapers.
3983
3984 simeth= [IA-64]
3985 simscsi=
3986
3987 slram= [HW,MTD]
3988
3989 slab_nomerge [MM]
3990 Disable merging of slabs with similar size. May be
3991 necessary if there is some reason to distinguish
3992 allocs to different slabs, especially in hardened
3993 environments where the risk of heap overflows and
3994 layout control by attackers can usually be
3995 frustrated by disabling merging. This will reduce
3996 most of the exposure of a heap attack to a single
3997 cache (risks via metadata attacks are mostly
3998 unchanged). Debug options disable merging on their
3999 own.
4000 For more information see Documentation/vm/slub.txt.
4001
4002 slab_max_order= [MM, SLAB]
4003 Determines the maximum allowed order for slabs.
4004 A high setting may cause OOMs due to memory
4005 fragmentation. Defaults to 1 for systems with
4006 more than 32MB of RAM, 0 otherwise.
4007
4008 slub_debug[=options[,slabs]] [MM, SLUB]
4009 Enabling slub_debug allows one to determine the
4010 culprit if slab objects become corrupted. Enabling
4011 slub_debug can create guard zones around objects and
4012 may poison objects when not in use. Also tracks the
4013 last alloc / free. For more information see
4014 Documentation/vm/slub.txt.
4015
4016 slub_memcg_sysfs= [MM, SLUB]
4017 Determines whether to enable sysfs directories for
4018 memory cgroup sub-caches. 1 to enable, 0 to disable.
4019 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
4020 Enabling this can lead to a very high number of debug
4021 directories and files being created under
4022 /sys/kernel/slub.
4023
4024 slub_max_order= [MM, SLUB]
4025 Determines the maximum allowed order for slabs.
4026 A high setting may cause OOMs due to memory
4027 fragmentation. For more information see
4028 Documentation/vm/slub.txt.
4029
4030 slub_min_objects= [MM, SLUB]
4031 The minimum number of objects per slab. SLUB will
4032 increase the slab order up to slub_max_order to
4033 generate a sufficiently large slab able to contain
4034 the number of objects indicated. The higher the number
4035 of objects the smaller the overhead of tracking slabs
4036 and the less frequently locks need to be acquired.
4037 For more information see Documentation/vm/slub.txt.
4038
4039 slub_min_order= [MM, SLUB]
4040 Determines the minimum page order for slabs. Must be
4041 lower than slub_max_order.
4042 For more information see Documentation/vm/slub.txt.
4043
4044 slub_nomerge [MM, SLUB]
4045 Same with slab_nomerge. This is supported for legacy.
4046 See slab_nomerge for more information.
4047
4048 smart2= [HW]
4049 Format: <io1>[,<io2>[,...,<io8>]]
4050
4051 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4052 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4053 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4054 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4055 smsc-ircc2.ircc_irq= [HW] IRQ line
4056 smsc-ircc2.ircc_dma= [HW] DMA channel
4057 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4058 0: Toshiba Satellite 1800 (GP data pin select)
4059 1: Fast pin select (default)
4060 2: ATC IRMode
4061
4062 smt [KNL,S390] Set the maximum number of threads (logical
4063 CPUs) to use per physical CPU on systems capable of
4064 symmetric multithreading (SMT). Will be capped to the
4065 actual hardware limit.
4066 Format: <integer>
4067 Default: -1 (no limit)
4068
4069 softlockup_panic=
4070 [KNL] Should the soft-lockup detector generate panics.
4071 Format: <integer>
4072
4073 A nonzero value instructs the soft-lockup detector
4074 to panic the machine when a soft-lockup occurs. This
4075 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
4076 which is the respective build-time switch to that
4077 functionality.
4078
4079 softlockup_all_cpu_backtrace=
4080 [KNL] Should the soft-lockup detector generate
4081 backtraces on all cpus.
4082 Format: <integer>
4083
4084 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4085 See Documentation/laptops/sonypi.txt
4086
4087 spectre_v2= [X86] Control mitigation of Spectre variant 2
4088 (indirect branch speculation) vulnerability.
4089 The default operation protects the kernel from
4090 user space attacks.
4091
4092 on - unconditionally enable, implies
4093 spectre_v2_user=on
4094 off - unconditionally disable, implies
4095 spectre_v2_user=off
4096 auto - kernel detects whether your CPU model is
4097 vulnerable
4098
4099 Selecting 'on' will, and 'auto' may, choose a
4100 mitigation method at run time according to the
4101 CPU, the available microcode, the setting of the
4102 CONFIG_RETPOLINE configuration option, and the
4103 compiler with which the kernel was built.
4104
4105 Selecting 'on' will also enable the mitigation
4106 against user space to user space task attacks.
4107
4108 Selecting 'off' will disable both the kernel and
4109 the user space protections.
4110
4111 Specific mitigations can also be selected manually:
4112
4113 retpoline - replace indirect branches
4114 retpoline,generic - google's original retpoline
4115 retpoline,amd - AMD-specific minimal thunk
4116
4117 Not specifying this option is equivalent to
4118 spectre_v2=auto.
4119
4120 spectre_v2_user=
4121 [X86] Control mitigation of Spectre variant 2
4122 (indirect branch speculation) vulnerability between
4123 user space tasks
4124
4125 on - Unconditionally enable mitigations. Is
4126 enforced by spectre_v2=on
4127
4128 off - Unconditionally disable mitigations. Is
4129 enforced by spectre_v2=off
4130
4131 prctl - Indirect branch speculation is enabled,
4132 but mitigation can be enabled via prctl
4133 per thread. The mitigation control state
4134 is inherited on fork.
4135
4136 prctl,ibpb
4137 - Like "prctl" above, but only STIBP is
4138 controlled per thread. IBPB is issued
4139 always when switching between different user
4140 space processes.
4141
4142 seccomp
4143 - Same as "prctl" above, but all seccomp
4144 threads will enable the mitigation unless
4145 they explicitly opt out.
4146
4147 seccomp,ibpb
4148 - Like "seccomp" above, but only STIBP is
4149 controlled per thread. IBPB is issued
4150 always when switching between different
4151 user space processes.
4152
4153 auto - Kernel selects the mitigation depending on
4154 the available CPU features and vulnerability.
4155
4156 Default mitigation:
4157 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
4158
4159 Not specifying this option is equivalent to
4160 spectre_v2_user=auto.
4161
4162 spec_store_bypass_disable=
4163 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4164 (Speculative Store Bypass vulnerability)
4165
4166 Certain CPUs are vulnerable to an exploit against a
4167 a common industry wide performance optimization known
4168 as "Speculative Store Bypass" in which recent stores
4169 to the same memory location may not be observed by
4170 later loads during speculative execution. The idea
4171 is that such stores are unlikely and that they can
4172 be detected prior to instruction retirement at the
4173 end of a particular speculation execution window.
4174
4175 In vulnerable processors, the speculatively forwarded
4176 store can be used in a cache side channel attack, for
4177 example to read memory to which the attacker does not
4178 directly have access (e.g. inside sandboxed code).
4179
4180 This parameter controls whether the Speculative Store
4181 Bypass optimization is used.
4182
4183 on - Unconditionally disable Speculative Store Bypass
4184 off - Unconditionally enable Speculative Store Bypass
4185 auto - Kernel detects whether the CPU model contains an
4186 implementation of Speculative Store Bypass and
4187 picks the most appropriate mitigation. If the
4188 CPU is not vulnerable, "off" is selected. If the
4189 CPU is vulnerable the default mitigation is
4190 architecture and Kconfig dependent. See below.
4191 prctl - Control Speculative Store Bypass per thread
4192 via prctl. Speculative Store Bypass is enabled
4193 for a process by default. The state of the control
4194 is inherited on fork.
4195 seccomp - Same as "prctl" above, but all seccomp threads
4196 will disable SSB unless they explicitly opt out.
4197
4198 Not specifying this option is equivalent to
4199 spec_store_bypass_disable=auto.
4200
4201 Default mitigations:
4202 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4203
4204 spia_io_base= [HW,MTD]
4205 spia_fio_base=
4206 spia_pedr=
4207 spia_peddr=
4208
4209 srcutree.counter_wrap_check [KNL]
4210 Specifies how frequently to check for
4211 grace-period sequence counter wrap for the
4212 srcu_data structure's ->srcu_gp_seq_needed field.
4213 The greater the number of bits set in this kernel
4214 parameter, the less frequently counter wrap will
4215 be checked for. Note that the bottom two bits
4216 are ignored.
4217
4218 srcutree.exp_holdoff [KNL]
4219 Specifies how many nanoseconds must elapse
4220 since the end of the last SRCU grace period for
4221 a given srcu_struct until the next normal SRCU
4222 grace period will be considered for automatic
4223 expediting. Set to zero to disable automatic
4224 expediting.
4225
4226 ssbd= [ARM64,HW]
4227 Speculative Store Bypass Disable control
4228
4229 On CPUs that are vulnerable to the Speculative
4230 Store Bypass vulnerability and offer a
4231 firmware based mitigation, this parameter
4232 indicates how the mitigation should be used:
4233
4234 force-on: Unconditionally enable mitigation for
4235 for both kernel and userspace
4236 force-off: Unconditionally disable mitigation for
4237 for both kernel and userspace
4238 kernel: Always enable mitigation in the
4239 kernel, and offer a prctl interface
4240 to allow userspace to register its
4241 interest in being mitigated too.
4242
4243 stack_guard_gap= [MM]
4244 override the default stack gap protection. The value
4245 is in page units and it defines how many pages prior
4246 to (for stacks growing down) resp. after (for stacks
4247 growing up) the main stack are reserved for no other
4248 mapping. Default value is 256 pages.
4249
4250 stacktrace [FTRACE]
4251 Enabled the stack tracer on boot up.
4252
4253 stacktrace_filter=[function-list]
4254 [FTRACE] Limit the functions that the stack tracer
4255 will trace at boot up. function-list is a comma separated
4256 list of functions. This list can be changed at run
4257 time by the stack_trace_filter file in the debugfs
4258 tracing directory. Note, this enables stack tracing
4259 and the stacktrace above is not needed.
4260
4261 sti= [PARISC,HW]
4262 Format: <num>
4263 Set the STI (builtin display/keyboard on the HP-PARISC
4264 machines) console (graphic card) which should be used
4265 as the initial boot-console.
4266 See also comment in drivers/video/console/sticore.c.
4267
4268 sti_font= [HW]
4269 See comment in drivers/video/console/sticore.c.
4270
4271 stifb= [HW]
4272 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4273
4274 sunrpc.min_resvport=
4275 sunrpc.max_resvport=
4276 [NFS,SUNRPC]
4277 SunRPC servers often require that client requests
4278 originate from a privileged port (i.e. a port in the
4279 range 0 < portnr < 1024).
4280 An administrator who wishes to reserve some of these
4281 ports for other uses may adjust the range that the
4282 kernel's sunrpc client considers to be privileged
4283 using these two parameters to set the minimum and
4284 maximum port values.
4285
4286 sunrpc.svc_rpc_per_connection_limit=
4287 [NFS,SUNRPC]
4288 Limit the number of requests that the server will
4289 process in parallel from a single connection.
4290 The default value is 0 (no limit).
4291
4292 sunrpc.pool_mode=
4293 [NFS]
4294 Control how the NFS server code allocates CPUs to
4295 service thread pools. Depending on how many NICs
4296 you have and where their interrupts are bound, this
4297 option will affect which CPUs will do NFS serving.
4298 Note: this parameter cannot be changed while the
4299 NFS server is running.
4300
4301 auto the server chooses an appropriate mode
4302 automatically using heuristics
4303 global a single global pool contains all CPUs
4304 percpu one pool for each CPU
4305 pernode one pool for each NUMA node (equivalent
4306 to global on non-NUMA machines)
4307
4308 sunrpc.tcp_slot_table_entries=
4309 sunrpc.udp_slot_table_entries=
4310 [NFS,SUNRPC]
4311 Sets the upper limit on the number of simultaneous
4312 RPC calls that can be sent from the client to a
4313 server. Increasing these values may allow you to
4314 improve throughput, but will also increase the
4315 amount of memory reserved for use by the client.
4316
4317 suspend.pm_test_delay=
4318 [SUSPEND]
4319 Sets the number of seconds to remain in a suspend test
4320 mode before resuming the system (see
4321 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4322 is set. Default value is 5.
4323
4324 swapaccount=[0|1]
4325 [KNL] Enable accounting of swap in memory resource
4326 controller if no parameter or 1 is given or disable
4327 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4328
4329 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4330 Format: { <int> | force | noforce }
4331 <int> -- Number of I/O TLB slabs
4332 force -- force using of bounce buffers even if they
4333 wouldn't be automatically used by the kernel
4334 noforce -- Never use bounce buffers (for debugging)
4335
4336 switches= [HW,M68k]
4337
4338 sysfs.deprecated=0|1 [KNL]
4339 Enable/disable old style sysfs layout for old udev
4340 on older distributions. When this option is enabled
4341 very new udev will not work anymore. When this option
4342 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4343 in older udev will not work anymore.
4344 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4345 the kernel configuration.
4346
4347 sysrq_always_enabled
4348 [KNL]
4349 Ignore sysrq setting - this boot parameter will
4350 neutralize any effect of /proc/sys/kernel/sysrq.
4351 Useful for debugging.
4352
4353 tcpmhash_entries= [KNL,NET]
4354 Set the number of tcp_metrics_hash slots.
4355 Default value is 8192 or 16384 depending on total
4356 ram pages. This is used to specify the TCP metrics
4357 cache size. See Documentation/networking/ip-sysctl.txt
4358 "tcp_no_metrics_save" section for more details.
4359
4360 tdfx= [HW,DRM]
4361
4362 test_suspend= [SUSPEND][,N]
4363 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4364 standby suspend) or "freeze" (for suspend type freeze)
4365 as the system sleep state during system startup with
4366 the optional capability to repeat N number of times.
4367 The system is woken from this state using a
4368 wakeup-capable RTC alarm.
4369
4370 thash_entries= [KNL,NET]
4371 Set number of hash buckets for TCP connection
4372
4373 thermal.act= [HW,ACPI]
4374 -1: disable all active trip points in all thermal zones
4375 <degrees C>: override all lowest active trip points
4376
4377 thermal.crt= [HW,ACPI]
4378 -1: disable all critical trip points in all thermal zones
4379 <degrees C>: override all critical trip points
4380
4381 thermal.nocrt= [HW,ACPI]
4382 Set to disable actions on ACPI thermal zone
4383 critical and hot trip points.
4384
4385 thermal.off= [HW,ACPI]
4386 1: disable ACPI thermal control
4387
4388 thermal.psv= [HW,ACPI]
4389 -1: disable all passive trip points
4390 <degrees C>: override all passive trip points to this
4391 value
4392
4393 thermal.tzp= [HW,ACPI]
4394 Specify global default ACPI thermal zone polling rate
4395 <deci-seconds>: poll all this frequency
4396 0: no polling (default)
4397
4398 threadirqs [KNL]
4399 Force threading of all interrupt handlers except those
4400 marked explicitly IRQF_NO_THREAD.
4401
4402 tmem [KNL,XEN]
4403 Enable the Transcendent memory driver if built-in.
4404
4405 tmem.cleancache=0|1 [KNL, XEN]
4406 Default is on (1). Disable the usage of the cleancache
4407 API to send anonymous pages to the hypervisor.
4408
4409 tmem.frontswap=0|1 [KNL, XEN]
4410 Default is on (1). Disable the usage of the frontswap
4411 API to send swap pages to the hypervisor. If disabled
4412 the selfballooning and selfshrinking are force disabled.
4413
4414 tmem.selfballooning=0|1 [KNL, XEN]
4415 Default is on (1). Disable the driving of swap pages
4416 to the hypervisor.
4417
4418 tmem.selfshrinking=0|1 [KNL, XEN]
4419 Default is on (1). Partial swapoff that immediately
4420 transfers pages from Xen hypervisor back to the
4421 kernel based on different criteria.
4422
4423 topology= [S390]
4424 Format: {off | on}
4425 Specify if the kernel should make use of the cpu
4426 topology information if the hardware supports this.
4427 The scheduler will make use of this information and
4428 e.g. base its process migration decisions on it.
4429 Default is on.
4430
4431 topology_updates= [KNL, PPC, NUMA]
4432 Format: {off}
4433 Specify if the kernel should ignore (off)
4434 topology updates sent by the hypervisor to this
4435 LPAR.
4436
4437 tp720= [HW,PS2]
4438
4439 tpm_suspend_pcr=[HW,TPM]
4440 Format: integer pcr id
4441 Specify that at suspend time, the tpm driver
4442 should extend the specified pcr with zeros,
4443 as a workaround for some chips which fail to
4444 flush the last written pcr on TPM_SaveState.
4445 This will guarantee that all the other pcrs
4446 are saved.
4447
4448 trace_buf_size=nn[KMG]
4449 [FTRACE] will set tracing buffer size on each cpu.
4450
4451 trace_event=[event-list]
4452 [FTRACE] Set and start specified trace events in order
4453 to facilitate early boot debugging. The event-list is a
4454 comma separated list of trace events to enable. See
4455 also Documentation/trace/events.txt
4456
4457 trace_options=[option-list]
4458 [FTRACE] Enable or disable tracer options at boot.
4459 The option-list is a comma delimited list of options
4460 that can be enabled or disabled just as if you were
4461 to echo the option name into
4462
4463 /sys/kernel/debug/tracing/trace_options
4464
4465 For example, to enable stacktrace option (to dump the
4466 stack trace of each event), add to the command line:
4467
4468 trace_options=stacktrace
4469
4470 See also Documentation/trace/ftrace.txt "trace options"
4471 section.
4472
4473 tp_printk[FTRACE]
4474 Have the tracepoints sent to printk as well as the
4475 tracing ring buffer. This is useful for early boot up
4476 where the system hangs or reboots and does not give the
4477 option for reading the tracing buffer or performing a
4478 ftrace_dump_on_oops.
4479
4480 To turn off having tracepoints sent to printk,
4481 echo 0 > /proc/sys/kernel/tracepoint_printk
4482 Note, echoing 1 into this file without the
4483 tracepoint_printk kernel cmdline option has no effect.
4484
4485 ** CAUTION **
4486
4487 Having tracepoints sent to printk() and activating high
4488 frequency tracepoints such as irq or sched, can cause
4489 the system to live lock.
4490
4491 traceoff_on_warning
4492 [FTRACE] enable this option to disable tracing when a
4493 warning is hit. This turns off "tracing_on". Tracing can
4494 be enabled again by echoing '1' into the "tracing_on"
4495 file located in /sys/kernel/debug/tracing/
4496
4497 This option is useful, as it disables the trace before
4498 the WARNING dump is called, which prevents the trace to
4499 be filled with content caused by the warning output.
4500
4501 This option can also be set at run time via the sysctl
4502 option: kernel/traceoff_on_warning
4503
4504 transparent_hugepage=
4505 [KNL]
4506 Format: [always|madvise|never]
4507 Can be used to control the default behavior of the system
4508 with respect to transparent hugepages.
4509 See Documentation/vm/transhuge.txt for more details.
4510
4511 tsc= Disable clocksource stability checks for TSC.
4512 Format: <string>
4513 [x86] reliable: mark tsc clocksource as reliable, this
4514 disables clocksource verification at runtime, as well
4515 as the stability checks done at bootup. Used to enable
4516 high-resolution timer mode on older hardware, and in
4517 virtualized environment.
4518 [x86] noirqtime: Do not use TSC to do irq accounting.
4519 Used to run time disable IRQ_TIME_ACCOUNTING on any
4520 platforms where RDTSC is slow and this accounting
4521 can add overhead.
4522 [x86] unstable: mark the TSC clocksource as unstable, this
4523 marks the TSC unconditionally unstable at bootup and
4524 avoids any further wobbles once the TSC watchdog notices.
4525
4526 turbografx.map[2|3]= [HW,JOY]
4527 TurboGraFX parallel port interface
4528 Format:
4529 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4530 See also Documentation/input/devices/joystick-parport.rst
4531
4532 udbg-immortal [PPC] When debugging early kernel crashes that
4533 happen after console_init() and before a proper
4534 console driver takes over, this boot options might
4535 help "seeing" what's going on.
4536
4537 uhash_entries= [KNL,NET]
4538 Set number of hash buckets for UDP/UDP-Lite connections
4539
4540 uhci-hcd.ignore_oc=
4541 [USB] Ignore overcurrent events (default N).
4542 Some badly-designed motherboards generate lots of
4543 bogus events, for ports that aren't wired to
4544 anything. Set this parameter to avoid log spamming.
4545 Note that genuine overcurrent events won't be
4546 reported either.
4547
4548 unknown_nmi_panic
4549 [X86] Cause panic on unknown NMI.
4550
4551 usbcore.authorized_default=
4552 [USB] Default USB device authorization:
4553 (default -1 = authorized except for wireless USB,
4554 0 = not authorized, 1 = authorized)
4555
4556 usbcore.autosuspend=
4557 [USB] The autosuspend time delay (in seconds) used
4558 for newly-detected USB devices (default 2). This
4559 is the time required before an idle device will be
4560 autosuspended. Devices for which the delay is set
4561 to a negative value won't be autosuspended at all.
4562
4563 usbcore.usbfs_snoop=
4564 [USB] Set to log all usbfs traffic (default 0 = off).
4565
4566 usbcore.usbfs_snoop_max=
4567 [USB] Maximum number of bytes to snoop in each URB
4568 (default = 65536).
4569
4570 usbcore.blinkenlights=
4571 [USB] Set to cycle leds on hubs (default 0 = off).
4572
4573 usbcore.old_scheme_first=
4574 [USB] Start with the old device initialization
4575 scheme (default 0 = off).
4576
4577 usbcore.usbfs_memory_mb=
4578 [USB] Memory limit (in MB) for buffers allocated by
4579 usbfs (default = 16, 0 = max = 2047).
4580
4581 usbcore.use_both_schemes=
4582 [USB] Try the other device initialization scheme
4583 if the first one fails (default 1 = enabled).
4584
4585 usbcore.initial_descriptor_timeout=
4586 [USB] Specifies timeout for the initial 64-byte
4587 USB_REQ_GET_DESCRIPTOR request in milliseconds
4588 (default 5000 = 5.0 seconds).
4589
4590 usbcore.nousb [USB] Disable the USB subsystem
4591
4592 usbcore.quirks=
4593 [USB] A list of quirk entries to augment the built-in
4594 usb core quirk list. List entries are separated by
4595 commas. Each entry has the form
4596 VendorID:ProductID:Flags. The IDs are 4-digit hex
4597 numbers and Flags is a set of letters. Each letter
4598 will change the built-in quirk; setting it if it is
4599 clear and clearing it if it is set. The letters have
4600 the following meanings:
4601 a = USB_QUIRK_STRING_FETCH_255 (string
4602 descriptors must not be fetched using
4603 a 255-byte read);
4604 b = USB_QUIRK_RESET_RESUME (device can't resume
4605 correctly so reset it instead);
4606 c = USB_QUIRK_NO_SET_INTF (device can't handle
4607 Set-Interface requests);
4608 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
4609 handle its Configuration or Interface
4610 strings);
4611 e = USB_QUIRK_RESET (device can't be reset
4612 (e.g morph devices), don't use reset);
4613 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
4614 more interface descriptions than the
4615 bNumInterfaces count, and can't handle
4616 talking to these interfaces);
4617 g = USB_QUIRK_DELAY_INIT (device needs a pause
4618 during initialization, after we read
4619 the device descriptor);
4620 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
4621 high speed and super speed interrupt
4622 endpoints, the USB 2.0 and USB 3.0 spec
4623 require the interval in microframes (1
4624 microframe = 125 microseconds) to be
4625 calculated as interval = 2 ^
4626 (bInterval-1).
4627 Devices with this quirk report their
4628 bInterval as the result of this
4629 calculation instead of the exponent
4630 variable used in the calculation);
4631 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
4632 handle device_qualifier descriptor
4633 requests);
4634 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
4635 generates spurious wakeup, ignore
4636 remote wakeup capability);
4637 k = USB_QUIRK_NO_LPM (device can't handle Link
4638 Power Management);
4639 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
4640 (Device reports its bInterval as linear
4641 frames instead of the USB 2.0
4642 calculation);
4643 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
4644 to be disconnected before suspend to
4645 prevent spurious wakeup);
4646 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
4647 pause after every control message);
4648 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
4649 delay after resetting its port);
4650 Example: quirks=0781:5580:bk,0a5c:5834:gij
4651
4652 usbhid.mousepoll=
4653 [USBHID] The interval which mice are to be polled at.
4654
4655 usbhid.jspoll=
4656 [USBHID] The interval which joysticks are to be polled at.
4657
4658 usb-storage.delay_use=
4659 [UMS] The delay in seconds before a new device is
4660 scanned for Logical Units (default 1).
4661
4662 usb-storage.quirks=
4663 [UMS] A list of quirks entries to supplement or
4664 override the built-in unusual_devs list. List
4665 entries are separated by commas. Each entry has
4666 the form VID:PID:Flags where VID and PID are Vendor
4667 and Product ID values (4-digit hex numbers) and
4668 Flags is a set of characters, each corresponding
4669 to a common usb-storage quirk flag as follows:
4670 a = SANE_SENSE (collect more than 18 bytes
4671 of sense data);
4672 b = BAD_SENSE (don't collect more than 18
4673 bytes of sense data);
4674 c = FIX_CAPACITY (decrease the reported
4675 device capacity by one sector);
4676 d = NO_READ_DISC_INFO (don't use
4677 READ_DISC_INFO command);
4678 e = NO_READ_CAPACITY_16 (don't use
4679 READ_CAPACITY_16 command);
4680 f = NO_REPORT_OPCODES (don't use report opcodes
4681 command, uas only);
4682 g = MAX_SECTORS_240 (don't transfer more than
4683 240 sectors at a time, uas only);
4684 h = CAPACITY_HEURISTICS (decrease the
4685 reported device capacity by one
4686 sector if the number is odd);
4687 i = IGNORE_DEVICE (don't bind to this
4688 device);
4689 j = NO_REPORT_LUNS (don't use report luns
4690 command, uas only);
4691 l = NOT_LOCKABLE (don't try to lock and
4692 unlock ejectable media);
4693 m = MAX_SECTORS_64 (don't transfer more
4694 than 64 sectors = 32 KB at a time);
4695 n = INITIAL_READ10 (force a retry of the
4696 initial READ(10) command);
4697 o = CAPACITY_OK (accept the capacity
4698 reported by the device);
4699 p = WRITE_CACHE (the device cache is ON
4700 by default);
4701 r = IGNORE_RESIDUE (the device reports
4702 bogus residue values);
4703 s = SINGLE_LUN (the device has only one
4704 Logical Unit);
4705 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4706 commands, uas only);
4707 u = IGNORE_UAS (don't bind to the uas driver);
4708 w = NO_WP_DETECT (don't test whether the
4709 medium is write-protected).
4710 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4711 even if the device claims no cache)
4712 Example: quirks=0419:aaf5:rl,0421:0433:rc
4713
4714 user_debug= [KNL,ARM]
4715 Format: <int>
4716 See arch/arm/Kconfig.debug help text.
4717 1 - undefined instruction events
4718 2 - system calls
4719 4 - invalid data aborts
4720 8 - SIGSEGV faults
4721 16 - SIGBUS faults
4722 Example: user_debug=31
4723
4724 userpte=
4725 [X86] Flags controlling user PTE allocations.
4726
4727 nohigh = do not allocate PTE pages in
4728 HIGHMEM regardless of setting
4729 of CONFIG_HIGHPTE.
4730
4731 vdso= [X86,SH]
4732 On X86_32, this is an alias for vdso32=. Otherwise:
4733
4734 vdso=1: enable VDSO (the default)
4735 vdso=0: disable VDSO mapping
4736
4737 vdso32= [X86] Control the 32-bit vDSO
4738 vdso32=1: enable 32-bit VDSO
4739 vdso32=0 or vdso32=2: disable 32-bit VDSO
4740
4741 See the help text for CONFIG_COMPAT_VDSO for more
4742 details. If CONFIG_COMPAT_VDSO is set, the default is
4743 vdso32=0; otherwise, the default is vdso32=1.
4744
4745 For compatibility with older kernels, vdso32=2 is an
4746 alias for vdso32=0.
4747
4748 Try vdso32=0 if you encounter an error that says:
4749 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4750
4751 vector= [IA-64,SMP]
4752 vector=percpu: enable percpu vector domain
4753
4754 video= [FB] Frame buffer configuration
4755 See Documentation/fb/modedb.txt.
4756
4757 video.brightness_switch_enabled= [0,1]
4758 If set to 1, on receiving an ACPI notify event
4759 generated by hotkey, video driver will adjust brightness
4760 level and then send out the event to user space through
4761 the allocated input device; If set to 0, video driver
4762 will only send out the event without touching backlight
4763 brightness level.
4764 default: 1
4765
4766 virtio_mmio.device=
4767 [VMMIO] Memory mapped virtio (platform) device.
4768
4769 <size>@<baseaddr>:<irq>[:<id>]
4770 where:
4771 <size> := size (can use standard suffixes
4772 like K, M and G)
4773 <baseaddr> := physical base address
4774 <irq> := interrupt number (as passed to
4775 request_irq())
4776 <id> := (optional) platform device id
4777 example:
4778 virtio_mmio.device=1K@0x100b0000:48:7
4779
4780 Can be used multiple times for multiple devices.
4781
4782 vga= [BOOT,X86-32] Select a particular video mode
4783 See Documentation/x86/boot.txt and
4784 Documentation/svga.txt.
4785 Use vga=ask for menu.
4786 This is actually a boot loader parameter; the value is
4787 passed to the kernel using a special protocol.
4788
4789 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4790 size of <nn>. This can be used to increase the
4791 minimum size (128MB on x86). It can also be used to
4792 decrease the size and leave more room for directly
4793 mapped kernel RAM.
4794
4795 vmcp_cma=nn[MG] [KNL,S390]
4796 Sets the memory size reserved for contiguous memory
4797 allocations for the vmcp device driver.
4798
4799 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4800 Format: <command>
4801
4802 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4803 Format: <command>
4804
4805 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4806 Format: <command>
4807
4808 vsyscall= [X86-64]
4809 Controls the behavior of vsyscalls (i.e. calls to
4810 fixed addresses of 0xffffffffff600x00 from legacy
4811 code). Most statically-linked binaries and older
4812 versions of glibc use these calls. Because these
4813 functions are at fixed addresses, they make nice
4814 targets for exploits that can control RIP.
4815
4816 emulate [default] Vsyscalls turn into traps and are
4817 emulated reasonably safely.
4818
4819 native Vsyscalls are native syscall instructions.
4820 This is a little bit faster than trapping
4821 and makes a few dynamic recompilers work
4822 better than they would in emulation mode.
4823 It also makes exploits much easier to write.
4824
4825 none Vsyscalls don't work at all. This makes
4826 them quite hard to use for exploits but
4827 might break your system.
4828
4829 vt.color= [VT] Default text color.
4830 Format: 0xYX, X = foreground, Y = background.
4831 Default: 0x07 = light gray on black.
4832
4833 vt.cur_default= [VT] Default cursor shape.
4834 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4835 the parameters of the <Esc>[?A;B;Cc escape sequence;
4836 see VGA-softcursor.txt. Default: 2 = underline.
4837
4838 vt.default_blu= [VT]
4839 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4840 Change the default blue palette of the console.
4841 This is a 16-member array composed of values
4842 ranging from 0-255.
4843
4844 vt.default_grn= [VT]
4845 Format: <green0>,<green1>,<green2>,...,<green15>
4846 Change the default green palette of the console.
4847 This is a 16-member array composed of values
4848 ranging from 0-255.
4849
4850 vt.default_red= [VT]
4851 Format: <red0>,<red1>,<red2>,...,<red15>
4852 Change the default red palette of the console.
4853 This is a 16-member array composed of values
4854 ranging from 0-255.
4855
4856 vt.default_utf8=
4857 [VT]
4858 Format=<0|1>
4859 Set system-wide default UTF-8 mode for all tty's.
4860 Default is 1, i.e. UTF-8 mode is enabled for all
4861 newly opened terminals.
4862
4863 vt.global_cursor_default=
4864 [VT]
4865 Format=<-1|0|1>
4866 Set system-wide default for whether a cursor
4867 is shown on new VTs. Default is -1,
4868 i.e. cursors will be created by default unless
4869 overridden by individual drivers. 0 will hide
4870 cursors, 1 will display them.
4871
4872 vt.italic= [VT] Default color for italic text; 0-15.
4873 Default: 2 = green.
4874
4875 vt.underline= [VT] Default color for underlined text; 0-15.
4876 Default: 3 = cyan.
4877
4878 watchdog timers [HW,WDT] For information on watchdog timers,
4879 see Documentation/watchdog/watchdog-parameters.txt
4880 or other driver-specific files in the
4881 Documentation/watchdog/ directory.
4882
4883 workqueue.watchdog_thresh=
4884 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4885 warn stall conditions and dump internal state to
4886 help debugging. 0 disables workqueue stall
4887 detection; otherwise, it's the stall threshold
4888 duration in seconds. The default value is 30 and
4889 it can be updated at runtime by writing to the
4890 corresponding sysfs file.
4891
4892 workqueue.disable_numa
4893 By default, all work items queued to unbound
4894 workqueues are affine to the NUMA nodes they're
4895 issued on, which results in better behavior in
4896 general. If NUMA affinity needs to be disabled for
4897 whatever reason, this option can be used. Note
4898 that this also can be controlled per-workqueue for
4899 workqueues visible under /sys/bus/workqueue/.
4900
4901 workqueue.power_efficient
4902 Per-cpu workqueues are generally preferred because
4903 they show better performance thanks to cache
4904 locality; unfortunately, per-cpu workqueues tend to
4905 be more power hungry than unbound workqueues.
4906
4907 Enabling this makes the per-cpu workqueues which
4908 were observed to contribute significantly to power
4909 consumption unbound, leading to measurably lower
4910 power usage at the cost of small performance
4911 overhead.
4912
4913 The default value of this parameter is determined by
4914 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4915
4916 workqueue.debug_force_rr_cpu
4917 Workqueue used to implicitly guarantee that work
4918 items queued without explicit CPU specified are put
4919 on the local CPU. This guarantee is no longer true
4920 and while local CPU is still preferred work items
4921 may be put on foreign CPUs. This debug option
4922 forces round-robin CPU selection to flush out
4923 usages which depend on the now broken guarantee.
4924 When enabled, memory and cache locality will be
4925 impacted.
4926
4927 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4928 default x2apic cluster mode on platforms
4929 supporting x2apic.
4930
4931 x86_intel_mid_timer= [X86-32,APBT]
4932 Choose timer option for x86 Intel MID platform.
4933 Two valid options are apbt timer only and lapic timer
4934 plus one apbt timer for broadcast timer.
4935 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4936
4937 xen_512gb_limit [KNL,X86-64,XEN]
4938 Restricts the kernel running paravirtualized under Xen
4939 to use only up to 512 GB of RAM. The reason to do so is
4940 crash analysis tools and Xen tools for doing domain
4941 save/restore/migration must be enabled to handle larger
4942 domains.
4943
4944 xen_emul_unplug= [HW,X86,XEN]
4945 Unplug Xen emulated devices
4946 Format: [unplug0,][unplug1]
4947 ide-disks -- unplug primary master IDE devices
4948 aux-ide-disks -- unplug non-primary-master IDE devices
4949 nics -- unplug network devices
4950 all -- unplug all emulated devices (NICs and IDE disks)
4951 unnecessary -- unplugging emulated devices is
4952 unnecessary even if the host did not respond to
4953 the unplug protocol
4954 never -- do not unplug even if version check succeeds
4955
4956 xen_nopvspin [X86,XEN]
4957 Disables the ticketlock slowpath using Xen PV
4958 optimizations.
4959
4960 xen_nopv [X86]
4961 Disables the PV optimizations forcing the HVM guest to
4962 run as generic HVM guest with no PV drivers.
4963
4964 xirc2ps_cs= [NET,PCMCIA]
4965 Format:
4966 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]