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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
16 See also Documentation/power/runtime_pm.txt, pci=noacpi
18 acpi_apic_instance= [ACPI, IOAPIC]
19 Format: <int>
20 2: use 2nd APIC table, if available
21 1,0: use 1st APIC table
22 default: 0
24 acpi_backlight= [HW,ACPI]
25 acpi_backlight=vendor
26 acpi_backlight=video
27 If set to vendor, prefer vendor specific driver
28 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
29 of the ACPI video.ko driver.
31 acpi_force_32bit_fadt_addr
32 force FADT to use 32 bit addresses rather than the
33 64 bit X_* addresses. Some firmware have broken 64
34 bit addresses for force ACPI ignore these and use
35 the older legacy 32 bit addresses.
37 acpica_no_return_repair [HW, ACPI]
38 Disable AML predefined validation mechanism
39 This mechanism can repair the evaluation result to make
40 the return objects more ACPI specification compliant.
41 This option is useful for developers to identify the
42 root cause of an AML interpreter issue when the issue
43 has something to do with the repair mechanism.
45 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
46 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
47 Format: <int>
48 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
49 debug output. Bits in debug_layer correspond to a
50 _COMPONENT in an ACPI source file, e.g.,
51 #define _COMPONENT ACPI_PCI_COMPONENT
52 Bits in debug_level correspond to a level in
53 ACPI_DEBUG_PRINT statements, e.g.,
54 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
55 The debug_level mask defaults to "info". See
56 Documentation/acpi/debug.txt for more information about
57 debug layers and levels.
59 Enable processor driver info messages:
60 acpi.debug_layer=0x20000000
61 Enable PCI/PCI interrupt routing info messages:
62 acpi.debug_layer=0x400000
63 Enable AML "Debug" output, i.e., stores to the Debug
64 object while interpreting AML:
65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
66 Enable all messages related to ACPI hardware:
67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
69 Some values produce so much output that the system is
70 unusable. The "log_buf_len" parameter may be useful
71 if you need to capture more output.
73 acpi_enforce_resources= [ACPI]
74 { strict | lax | no }
75 Check for resource conflicts between native drivers
76 and ACPI OperationRegions (SystemIO and SystemMemory
77 only). IO ports and memory declared in ACPI might be
78 used by the ACPI subsystem in arbitrary AML code and
79 can interfere with legacy drivers.
80 strict (default): access to resources claimed by ACPI
81 is denied; legacy drivers trying to access reserved
82 resources will fail to bind to device using them.
83 lax: access to resources claimed by ACPI is allowed;
84 legacy drivers trying to access reserved resources
85 will bind successfully but a warning message is logged.
86 no: ACPI OperationRegions are not marked as reserved,
87 no further checks are performed.
89 acpi_force_table_verification [HW,ACPI]
90 Enable table checksum verification during early stage.
91 By default, this is disabled due to x86 early mapping
92 size limitation.
94 acpi_irq_balance [HW,ACPI]
95 ACPI will balance active IRQs
96 default in APIC mode
98 acpi_irq_nobalance [HW,ACPI]
99 ACPI will not move active IRQs (default)
100 default in PIC mode
102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
103 Format: <irq>,<irq>...
105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
106 use by PCI
107 Format: <irq>,<irq>...
109 acpi_mask_gpe= [HW,ACPI]
110 Due to the existence of _Lxx/_Exx, some GPEs triggered
111 by unsupported hardware/firmware features can result in
112 GPE floodings that cannot be automatically disabled by
113 the GPE dispatcher.
114 This facility can be used to prevent such uncontrolled
115 GPE floodings.
116 Format: <int>
118 acpi_no_auto_serialize [HW,ACPI]
119 Disable auto-serialization of AML methods
120 AML control methods that contain the opcodes to create
121 named objects will be marked as "Serialized" by the
122 auto-serialization feature.
123 This feature is enabled by default.
124 This option allows to turn off the feature.
126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
127 kernels.
129 acpi_no_static_ssdt [HW,ACPI]
130 Disable installation of static SSDTs at early boot time
131 By default, SSDTs contained in the RSDT/XSDT will be
132 installed automatically and they will appear under
133 /sys/firmware/acpi/tables.
134 This option turns off this feature.
135 Note that specifying this option does not affect
136 dynamic table installation which will install SSDT
137 tables to /sys/firmware/acpi/tables/dynamic.
139 acpi_rsdp= [ACPI,EFI,KEXEC]
140 Pass the RSDP address to the kernel, mostly used
141 on machines running EFI runtime service to boot the
142 second kernel for kdump.
144 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
145 Format: To spoof as Windows 98: ="Microsoft Windows"
147 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
148 of 2 which is mandated by ACPI 6) as the supported ACPI
149 specification revision (when using this switch, it may
150 be necessary to carry out a cold reboot _twice_ in a
151 row to make it take effect on the platform firmware).
153 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
154 acpi_osi="string1" # add string1
155 acpi_osi="!string2" # remove string2
156 acpi_osi=!* # remove all strings
157 acpi_osi=! # disable all built-in OS vendor
158 strings
159 acpi_osi=!! # enable all built-in OS vendor
160 strings
161 acpi_osi= # disable all strings
163 'acpi_osi=!' can be used in combination with single or
164 multiple 'acpi_osi="string1"' to support specific OS
165 vendor string(s). Note that such command can only
166 affect the default state of the OS vendor strings, thus
167 it cannot affect the default state of the feature group
168 strings and the current state of the OS vendor strings,
169 specifying it multiple times through kernel command line
170 is meaningless. This command is useful when one do not
171 care about the state of the feature group strings which
172 should be controlled by the OSPM.
173 Examples:
174 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
175 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
176 can make '_OSI("Windows 2000")' TRUE.
178 'acpi_osi=' cannot be used in combination with other
179 'acpi_osi=' command lines, the _OSI method will not
180 exist in the ACPI namespace. NOTE that such command can
181 only affect the _OSI support state, thus specifying it
182 multiple times through kernel command line is also
183 meaningless.
184 Examples:
185 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
186 FALSE.
188 'acpi_osi=!*' can be used in combination with single or
189 multiple 'acpi_osi="string1"' to support specific
190 string(s). Note that such command can affect the
191 current state of both the OS vendor strings and the
192 feature group strings, thus specifying it multiple times
193 through kernel command line is meaningful. But it may
194 still not able to affect the final state of a string if
195 there are quirks related to this string. This command
196 is useful when one want to control the state of the
197 feature group strings to debug BIOS issues related to
198 the OSPM features.
199 Examples:
200 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
201 '_OSI("Module Device")' FALSE.
202 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
203 '_OSI("Module Device")' TRUE.
204 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
205 equivalent to
206 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
207 and
208 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
209 they all will make '_OSI("Windows 2000")' TRUE.
211 acpi_pm_good [X86]
212 Override the pmtimer bug detection: force the kernel
213 to assume that this machine's pmtimer latches its value
214 and always returns good values.
216 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
217 Format: { level | edge | high | low }
219 acpi_skip_timer_override [HW,ACPI]
220 Recognize and ignore IRQ0/pin2 Interrupt Override.
221 For broken nForce2 BIOS resulting in XT-PIC timer.
223 acpi_sleep= [HW,ACPI] Sleep options
224 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
225 old_ordering, nonvs, sci_force_enable, nobl }
226 See Documentation/power/video.txt for information on
227 s3_bios and s3_mode.
228 s3_beep is for debugging; it makes the PC's speaker beep
229 as soon as the kernel's real-mode entry point is called.
230 s4_nohwsig prevents ACPI hardware signature from being
231 used during resume from hibernation.
232 old_ordering causes the ACPI 1.0 ordering of the _PTS
233 control method, with respect to putting devices into
234 low power states, to be enforced (the ACPI 2.0 ordering
235 of _PTS is used by default).
236 nonvs prevents the kernel from saving/restoring the
237 ACPI NVS memory during suspend/hibernation and resume.
238 sci_force_enable causes the kernel to set SCI_EN directly
239 on resume from S1/S3 (which is against the ACPI spec,
240 but some broken systems don't work without it).
241 nobl causes the internal blacklist of systems known to
242 behave incorrectly in some ways with respect to system
243 suspend and resume to be ignored (use wisely).
245 acpi_use_timer_override [HW,ACPI]
246 Use timer override. For some broken Nvidia NF5 boards
247 that require a timer override, but don't have HPET
249 add_efi_memmap [EFI; X86] Include EFI memory map in
250 kernel's map of available physical RAM.
252 agp= [AGP]
253 { off | try_unsupported }
254 off: disable AGP support
255 try_unsupported: try to drive unsupported chipsets
256 (may crash computer or cause data corruption)
258 ALSA [HW,ALSA]
259 See Documentation/sound/alsa-configuration.rst
261 alignment= [KNL,ARM]
262 Allow the default userspace alignment fault handler
263 behaviour to be specified. Bit 0 enables warnings,
264 bit 1 enables fixups, and bit 2 sends a segfault.
266 align_va_addr= [X86-64]
267 Align virtual addresses by clearing slice [14:12] when
268 allocating a VMA at process creation time. This option
269 gives you up to 3% performance improvement on AMD F15h
270 machines (where it is enabled by default) for a
271 CPU-intensive style benchmark, and it can vary highly in
272 a microbenchmark depending on workload and compiler.
274 32: only for 32-bit processes
275 64: only for 64-bit processes
276 on: enable for both 32- and 64-bit processes
277 off: disable for both 32- and 64-bit processes
279 alloc_snapshot [FTRACE]
280 Allocate the ftrace snapshot buffer on boot up when the
281 main buffer is allocated. This is handy if debugging
282 and you need to use tracing_snapshot() on boot up, and
283 do not want to use tracing_snapshot_alloc() as it needs
284 to be done where GFP_KERNEL allocations are allowed.
286 amd_iommu= [HW,X86-64]
287 Pass parameters to the AMD IOMMU driver in the system.
288 Possible values are:
289 fullflush - enable flushing of IO/TLB entries when
290 they are unmapped. Otherwise they are
291 flushed before they will be reused, which
292 is a lot of faster
293 off - do not initialize any AMD IOMMU found in
294 the system
295 force_isolation - Force device isolation for all
296 devices. The IOMMU driver is not
297 allowed anymore to lift isolation
298 requirements as needed. This option
299 does not override iommu=pt
301 amd_iommu_dump= [HW,X86-64]
302 Enable AMD IOMMU driver option to dump the ACPI table
303 for AMD IOMMU. With this option enabled, AMD IOMMU
304 driver will print ACPI tables for AMD IOMMU during
305 IOMMU initialization.
307 amd_iommu_intr= [HW,X86-64]
308 Specifies one of the following AMD IOMMU interrupt
309 remapping modes:
310 legacy - Use legacy interrupt remapping mode.
311 vapic - Use virtual APIC mode, which allows IOMMU
312 to inject interrupts directly into guest.
313 This mode requires kvm-amd.avic=1.
314 (Default when IOMMU HW support is present.)
316 amijoy.map= [HW,JOY] Amiga joystick support
317 Map of devices attached to JOY0DAT and JOY1DAT
318 Format: <a>,<b>
319 See also Documentation/input/joydev/joystick.rst
321 analog.map= [HW,JOY] Analog joystick and gamepad support
322 Specifies type or capabilities of an analog joystick
323 connected to one of 16 gameports
324 Format: <type1>,<type2>,..<type16>
326 apc= [HW,SPARC]
327 Power management functions (SPARCstation-4/5 + deriv.)
328 Format: noidle
329 Disable APC CPU standby support. SPARCstation-Fox does
330 not play well with APC CPU idle - disable it if you have
331 APC and your system crashes randomly.
333 apic= [APIC,X86] Advanced Programmable Interrupt Controller
334 Change the output verbosity whilst booting
335 Format: { quiet (default) | verbose | debug }
336 Change the amount of debugging information output
337 when initialising the APIC and IO-APIC components.
338 For X86-32, this can also be used to specify an APIC
339 driver name.
340 Format: apic=driver_name
341 Examples: apic=bigsmp
343 apic_extnmi= [APIC,X86] External NMI delivery setting
344 Format: { bsp (default) | all | none }
345 bsp: External NMI is delivered only to CPU 0
346 all: External NMIs are broadcast to all CPUs as a
347 backup of CPU 0
348 none: External NMI is masked for all CPUs. This is
349 useful so that a dump capture kernel won't be
350 shot down by NMI
352 autoconf= [IPV6]
353 See Documentation/networking/ipv6.txt.
355 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
356 Limit apic dumping. The parameter defines the maximal
357 number of local apics being dumped. Also it is possible
358 to set it to "all" by meaning -- no limit here.
359 Format: { 1 (default) | 2 | ... | all }.
360 The parameter valid if only apic=debug or
361 apic=verbose is specified.
362 Example: apic=debug show_lapic=all
364 apm= [APM] Advanced Power Management
365 See header of arch/x86/kernel/apm_32.c.
367 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
368 Format: <io>,<irq>,<nodeID>
370 ataflop= [HW,M68k]
372 atarimouse= [HW,MOUSE] Atari Mouse
374 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
375 EzKey and similar keyboards
377 atkbd.reset= [HW] Reset keyboard during initialization
379 atkbd.set= [HW] Select keyboard code set
380 Format: <int> (2 = AT (default), 3 = PS/2)
382 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
383 keyboards
385 atkbd.softraw= [HW] Choose between synthetic and real raw mode
386 Format: <bool> (0 = real, 1 = synthetic (default))
388 atkbd.softrepeat= [HW]
389 Use software keyboard repeat
391 audit= [KNL] Enable the audit sub-system
392 Format: { "0" | "1" | "off" | "on" }
393 0 | off - kernel audit is disabled and can not be
394 enabled until the next reboot
395 unset - kernel audit is initialized but disabled and
396 will be fully enabled by the userspace auditd.
397 1 | on - kernel audit is initialized and partially
398 enabled, storing at most audit_backlog_limit
399 messages in RAM until it is fully enabled by the
400 userspace auditd.
401 Default: unset
403 audit_backlog_limit= [KNL] Set the audit queue size limit.
404 Format: <int> (must be >=0)
405 Default: 64
407 bau= [X86_UV] Enable the BAU on SGI UV. The default
408 behavior is to disable the BAU (i.e. bau=0).
409 Format: { "0" | "1" }
410 0 - Disable the BAU.
411 1 - Enable the BAU.
412 unset - Disable the BAU.
414 baycom_epp= [HW,AX25]
415 Format: <io>,<mode>
417 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
418 Format: <io>,<mode>
419 See header of drivers/net/hamradio/baycom_par.c.
421 baycom_ser_fdx= [HW,AX25]
422 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
423 Format: <io>,<irq>,<mode>[,<baud>]
424 See header of drivers/net/hamradio/baycom_ser_fdx.c.
426 baycom_ser_hdx= [HW,AX25]
427 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
428 Format: <io>,<irq>,<mode>
429 See header of drivers/net/hamradio/baycom_ser_hdx.c.
431 blkdevparts= Manual partition parsing of block device(s) for
432 embedded devices based on command line input.
433 See Documentation/block/cmdline-partition.txt
435 boot_delay= Milliseconds to delay each printk during boot.
436 Values larger than 10 seconds (10000) are changed to
437 no delay (0).
438 Format: integer
440 bootmem_debug [KNL] Enable bootmem allocator debug messages.
442 bert_disable [ACPI]
443 Disable BERT OS support on buggy BIOSes.
445 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
446 bttv.radio= Most important insmod options are available as
447 kernel args too.
448 bttv.pll= See Documentation/media/v4l-drivers/bttv.rst
449 bttv.tuner=
451 bulk_remove=off [PPC] This parameter disables the use of the pSeries
452 firmware feature for flushing multiple hpte entries
453 at a time.
455 c101= [NET] Moxa C101 synchronous serial card
457 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
458 Sometimes CPU hardware bugs make them report the cache
459 size incorrectly. The kernel will attempt work arounds
460 to fix known problems, but for some CPUs it is not
461 possible to determine what the correct size should be.
462 This option provides an override for these situations.
464 ca_keys= [KEYS] This parameter identifies a specific key(s) on
465 the system trusted keyring to be used for certificate
466 trust validation.
467 format: { id:<keyid> | builtin }
469 cca= [MIPS] Override the kernel pages' cache coherency
470 algorithm. Accepted values range from 0 to 7
471 inclusive. See arch/mips/include/asm/pgtable-bits.h
472 for platform specific values (SB1, Loongson3 and
473 others).
475 ccw_timeout_log [S390]
476 See Documentation/s390/CommonIO for details.
478 cgroup_disable= [KNL] Disable a particular controller
479 Format: {name of the controller(s) to disable}
480 The effects of cgroup_disable=foo are:
481 - foo isn't auto-mounted if you mount all cgroups in
482 a single hierarchy
483 - foo isn't visible as an individually mountable
484 subsystem
485 {Currently only "memory" controller deal with this and
486 cut the overhead, others just disable the usage. So
487 only cgroup_disable=memory is actually worthy}
489 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
490 Format: { controller[,controller...] | "all" }
491 Like cgroup_disable, but only applies to cgroup v1;
492 the blacklisted controllers remain available in cgroup2.
494 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
495 Format: <string>
496 nosocket -- Disable socket memory accounting.
497 nokmem -- Disable kernel memory accounting.
499 checkreqprot [SELINUX] Set initial checkreqprot flag value.
500 Format: { "0" | "1" }
501 See security/selinux/Kconfig help text.
502 0 -- check protection applied by kernel (includes
503 any implied execute protection).
504 1 -- check protection requested by application.
505 Default value is set via a kernel config option.
506 Value can be changed at runtime via
507 /selinux/checkreqprot.
509 cio_ignore= [S390]
510 See Documentation/s390/CommonIO for details.
511 clk_ignore_unused
512 [CLK]
513 Prevents the clock framework from automatically gating
514 clocks that have not been explicitly enabled by a Linux
515 device driver but are enabled in hardware at reset or
516 by the bootloader/firmware. Note that this does not
517 force such clocks to be always-on nor does it reserve
518 those clocks in any way. This parameter is useful for
519 debug and development, but should not be needed on a
520 platform with proper driver support. For more
521 information, see Documentation/driver-api/clk.rst.
523 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
524 [Deprecated]
525 Forces specified clocksource (if available) to be used
526 when calculating gettimeofday(). If specified
527 clocksource is not available, it defaults to PIT.
528 Format: { pit | tsc | cyclone | pmtmr }
530 clocksource= Override the default clocksource
531 Format: <string>
532 Override the default clocksource and use the clocksource
533 with the name specified.
534 Some clocksource names to choose from, depending on
535 the platform:
536 [all] jiffies (this is the base, fallback clocksource)
537 [ACPI] acpi_pm
538 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
539 pxa_timer,timer3,32k_counter,timer0_1
540 [X86-32] pit,hpet,tsc;
541 scx200_hrt on Geode; cyclone on IBM x440
542 [MIPS] MIPS
543 [PARISC] cr16
544 [S390] tod
545 [SH] SuperH
546 [SPARC64] tick
547 [X86-64] hpet,tsc
549 clocksource.arm_arch_timer.evtstrm=
550 [ARM,ARM64]
551 Format: <bool>
552 Enable/disable the eventstream feature of the ARM
553 architected timer so that code using WFE-based polling
554 loops can be debugged more effectively on production
555 systems.
557 clearcpuid=BITNUM [X86]
558 Disable CPUID feature X for the kernel. See
559 arch/x86/include/asm/cpufeatures.h for the valid bit
560 numbers. Note the Linux specific bits are not necessarily
561 stable over kernel options, but the vendor specific
562 ones should be.
563 Also note that user programs calling CPUID directly
564 or using the feature without checking anything
565 will still see it. This just prevents it from
566 being used by the kernel or shown in /proc/cpuinfo.
567 Also note the kernel might malfunction if you disable
568 some critical bits.
570 cma=nn[MG]@[start[MG][-end[MG]]]
571 [ARM,X86,KNL]
572 Sets the size of kernel global memory area for
573 contiguous memory allocations and optionally the
574 placement constraint by the physical address range of
575 memory allocations. A value of 0 disables CMA
576 altogether. For more information, see
577 include/linux/dma-contiguous.h
579 cmo_free_hint= [PPC] Format: { yes | no }
580 Specify whether pages are marked as being inactive
581 when they are freed. This is used in CMO environments
582 to determine OS memory pressure for page stealing by
583 a hypervisor.
584 Default: yes
586 coherent_pool=nn[KMG] [ARM,KNL]
587 Sets the size of memory pool for coherent, atomic dma
588 allocations, by default set to 256K.
590 com20020= [HW,NET] ARCnet - COM20020 chipset
591 Format:
592 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
594 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
595 Format: <io>[,<irq>]
597 com90xx= [HW,NET]
598 ARCnet - COM90xx chipset (memory-mapped buffers)
599 Format: <io>[,<irq>[,<memstart>]]
601 condev= [HW,S390] console device
602 conmode=
604 console= [KNL] Output console device and options.
606 tty<n> Use the virtual console device <n>.
608 ttyS<n>[,options]
609 ttyUSB0[,options]
610 Use the specified serial port. The options are of
611 the form "bbbbpnf", where "bbbb" is the baud rate,
612 "p" is parity ("n", "o", or "e"), "n" is number of
613 bits, and "f" is flow control ("r" for RTS or
614 omit it). Default is "9600n8".
616 See Documentation/admin-guide/serial-console.rst for more
617 information. See
618 Documentation/networking/netconsole.txt for an
619 alternative.
621 uart[8250],io,<addr>[,options]
622 uart[8250],mmio,<addr>[,options]
623 uart[8250],mmio16,<addr>[,options]
624 uart[8250],mmio32,<addr>[,options]
625 uart[8250],0x<addr>[,options]
626 Start an early, polled-mode console on the 8250/16550
627 UART at the specified I/O port or MMIO address,
628 switching to the matching ttyS device later.
629 MMIO inter-register address stride is either 8-bit
630 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
631 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
632 to be equivalent to 'mmio'. 'options' are specified in
633 the same format described for ttyS above; if unspecified,
634 the h/w is not re-initialized.
636 hvc<n> Use the hypervisor console device <n>. This is for
637 both Xen and PowerPC hypervisors.
639 If the device connected to the port is not a TTY but a braille
640 device, prepend "brl," before the device type, for instance
641 console=brl,ttyS0
642 For now, only VisioBraille is supported.
644 console_msg_format=
645 [KNL] Change console messages format
646 default
647 By default we print messages on consoles in
648 "[time stamp] text\n" format (time stamp may not be
649 printed, depending on CONFIG_PRINTK_TIME or
650 `printk_time' param).
651 syslog
652 Switch to syslog format: "<%u>[time stamp] text\n"
653 IOW, each message will have a facility and loglevel
654 prefix. The format is similar to one used by syslog()
655 syscall, or to executing "dmesg -S --raw" or to reading
656 from /proc/kmsg.
658 consoleblank= [KNL] The console blank (screen saver) timeout in
659 seconds. A value of 0 disables the blank timer.
660 Defaults to 0.
662 coredump_filter=
663 [KNL] Change the default value for
664 /proc/<pid>/coredump_filter.
665 See also Documentation/filesystems/proc.txt.
667 coresight_cpu_debug.enable
668 [ARM,ARM64]
669 Format: <bool>
670 Enable/disable the CPU sampling based debugging.
671 0: default value, disable debugging
672 1: enable debugging at boot time
674 cpuidle.off=1 [CPU_IDLE]
675 disable the cpuidle sub-system
677 cpufreq.off=1 [CPU_FREQ]
678 disable the cpufreq sub-system
680 cpu_init_udelay=N
681 [X86] Delay for N microsec between assert and de-assert
682 of APIC INIT to start processors. This delay occurs
683 on every CPU online, such as boot, and resume from suspend.
684 Default: 10000
686 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
687 Format:
688 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
690 crashkernel=size[KMG][@offset[KMG]]
691 [KNL] Using kexec, Linux can switch to a 'crash kernel'
692 upon panic. This parameter reserves the physical
693 memory region [offset, offset + size] for that kernel
694 image. If '@offset' is omitted, then a suitable offset
695 is selected automatically. Check
696 Documentation/kdump/kdump.txt for further details.
698 crashkernel=range1:size1[,range2:size2,...][@offset]
699 [KNL] Same as above, but depends on the memory
700 in the running system. The syntax of range is
701 start-[end] where start and end are both
702 a memory unit (amount[KMG]). See also
703 Documentation/kdump/kdump.txt for an example.
705 crashkernel=size[KMG],high
706 [KNL, x86_64] range could be above 4G. Allow kernel
707 to allocate physical memory region from top, so could
708 be above 4G if system have more than 4G ram installed.
709 Otherwise memory region will be allocated below 4G, if
710 available.
711 It will be ignored if crashkernel=X is specified.
712 crashkernel=size[KMG],low
713 [KNL, x86_64] range under 4G. When crashkernel=X,high
714 is passed, kernel could allocate physical memory region
715 above 4G, that cause second kernel crash on system
716 that require some amount of low memory, e.g. swiotlb
717 requires at least 64M+32K low memory, also enough extra
718 low memory is needed to make sure DMA buffers for 32-bit
719 devices won't run out. Kernel would try to allocate at
720 at least 256M below 4G automatically.
721 This one let user to specify own low range under 4G
722 for second kernel instead.
723 0: to disable low allocation.
724 It will be ignored when crashkernel=X,high is not used
725 or memory reserved is below 4G.
727 cryptomgr.notests
728 [KNL] Disable crypto self-tests
730 cs89x0_dma= [HW,NET]
731 Format: <dma>
733 cs89x0_media= [HW,NET]
734 Format: { rj45 | aui | bnc }
736 dasd= [HW,NET]
737 See header of drivers/s390/block/dasd_devmap.c.
739 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
740 (one device per port)
741 Format: <port#>,<type>
742 See also Documentation/input/devices/joystick-parport.rst
744 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
745 time. See
746 Documentation/admin-guide/dynamic-debug-howto.rst for
747 details. Deprecated, see dyndbg.
749 debug [KNL] Enable kernel debugging (events log level).
751 debug_locks_verbose=
752 [KNL] verbose self-tests
753 Format=<0|1>
754 Print debugging info while doing the locking API
755 self-tests.
756 We default to 0 (no extra messages), setting it to
757 1 will print _a lot_ more information - normally
758 only useful to kernel developers.
760 debug_objects [KNL] Enable object debugging
762 no_debug_objects
763 [KNL] Disable object debugging
765 debug_guardpage_minorder=
766 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
767 parameter allows control of the order of pages that will
768 be intentionally kept free (and hence protected) by the
769 buddy allocator. Bigger value increase the probability
770 of catching random memory corruption, but reduce the
771 amount of memory for normal system use. The maximum
772 possible value is MAX_ORDER/2. Setting this parameter
773 to 1 or 2 should be enough to identify most random
774 memory corruption problems caused by bugs in kernel or
775 driver code when a CPU writes to (or reads from) a
776 random memory location. Note that there exists a class
777 of memory corruptions problems caused by buggy H/W or
778 F/W or by drivers badly programing DMA (basically when
779 memory is written at bus level and the CPU MMU is
780 bypassed) which are not detectable by
781 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
782 tracking down these problems.
784 debug_pagealloc=
785 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
786 parameter enables the feature at boot time. In
787 default, it is disabled. We can avoid allocating huge
788 chunk of memory for debug pagealloc if we don't enable
789 it at boot time and the system will work mostly same
790 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
791 on: enable the feature
793 debugpat [X86] Enable PAT debugging
795 decnet.addr= [HW,NET]
796 Format: <area>[,<node>]
797 See also Documentation/networking/decnet.txt.
799 default_hugepagesz=
800 [same as hugepagesz=] The size of the default
801 HugeTLB page size. This is the size represented by
802 the legacy /proc/ hugepages APIs, used for SHM, and
803 default size when mounting hugetlbfs filesystems.
804 Defaults to the default architecture's huge page size
805 if not specified.
807 dhash_entries= [KNL]
808 Set number of hash buckets for dentry cache.
810 disable_1tb_segments [PPC]
811 Disables the use of 1TB hash page table segments. This
812 causes the kernel to fall back to 256MB segments which
813 can be useful when debugging issues that require an SLB
814 miss to occur.
816 disable= [IPV6]
817 See Documentation/networking/ipv6.txt.
819 disable_radix [PPC]
820 Disable RADIX MMU mode on POWER9
822 disable_cpu_apicid= [X86,APIC,SMP]
823 Format: <int>
824 The number of initial APIC ID for the
825 corresponding CPU to be disabled at boot,
826 mostly used for the kdump 2nd kernel to
827 disable BSP to wake up multiple CPUs without
828 causing system reset or hang due to sending
829 INIT from AP to BSP.
831 disable_ddw [PPC/PSERIES]
832 Disable Dynamic DMA Window support. Use this if
833 to workaround buggy firmware.
835 disable_ipv6= [IPV6]
836 See Documentation/networking/ipv6.txt.
838 disable_mtrr_cleanup [X86]
839 The kernel tries to adjust MTRR layout from continuous
840 to discrete, to make X server driver able to add WB
841 entry later. This parameter disables that.
843 disable_mtrr_trim [X86, Intel and AMD only]
844 By default the kernel will trim any uncacheable
845 memory out of your available memory pool based on
846 MTRR settings. This parameter disables that behavior,
847 possibly causing your machine to run very slowly.
849 disable_timer_pin_1 [X86]
850 Disable PIN 1 of APIC timer
851 Can be useful to work around chipset bugs.
853 dis_ucode_ldr [X86] Disable the microcode loader.
855 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
856 this option disables the debugging code at boot.
858 dma_debug_entries=<number>
859 This option allows to tune the number of preallocated
860 entries for DMA-API debugging code. One entry is
861 required per DMA-API allocation. Use this if the
862 DMA-API debugging code disables itself because the
863 architectural default is too low.
865 dma_debug_driver=<driver_name>
866 With this option the DMA-API debugging driver
867 filter feature can be enabled at boot time. Just
868 pass the driver to filter for as the parameter.
869 The filter can be disabled or changed to another
870 driver later using sysfs.
872 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
873 Broken monitors, graphic adapters, KVMs and EDIDless
874 panels may send no or incorrect EDID data sets.
875 This parameter allows to specify an EDID data sets
876 in the /lib/firmware directory that are used instead.
877 Generic built-in EDID data sets are used, if one of
878 edid/1024x768.bin, edid/1280x1024.bin,
879 edid/1680x1050.bin, or edid/1920x1080.bin is given
880 and no file with the same name exists. Details and
881 instructions how to build your own EDID data are
882 available in Documentation/EDID/HOWTO.txt. An EDID
883 data set will only be used for a particular connector,
884 if its name and a colon are prepended to the EDID
885 name. Each connector may use a unique EDID data
886 set by separating the files with a comma. An EDID
887 data set with no connector name will be used for
888 any connectors not explicitly specified.
890 dscc4.setup= [NET]
892 dt_cpu_ftrs= [PPC]
893 Format: {"off" | "known"}
894 Control how the dt_cpu_ftrs device-tree binding is
895 used for CPU feature discovery and setup (if it
896 exists).
897 off: Do not use it, fall back to legacy cpu table.
898 known: Do not pass through unknown features to guests
899 or userspace, only those that the kernel is aware of.
901 dump_apple_properties [X86]
902 Dump name and content of EFI device properties on
903 x86 Macs. Useful for driver authors to determine
904 what data is available or for reverse-engineering.
906 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
907 module.dyndbg[="val"]
908 Enable debug messages at boot time. See
909 Documentation/admin-guide/dynamic-debug-howto.rst
910 for details.
912 nompx [X86] Disables Intel Memory Protection Extensions.
913 See Documentation/x86/intel_mpx.txt for more
914 information about the feature.
916 nopku [X86] Disable Memory Protection Keys CPU feature found
917 in some Intel CPUs.
919 module.async_probe [KNL]
920 Enable asynchronous probe on this module.
922 early_ioremap_debug [KNL]
923 Enable debug messages in early_ioremap support. This
924 is useful for tracking down temporary early mappings
925 which are not unmapped.
927 earlycon= [KNL] Output early console device and options.
929 [ARM64] The early console is determined by the
930 stdout-path property in device tree's chosen node,
931 or determined by the ACPI SPCR table.
933 [X86] When used with no options the early console is
934 determined by the ACPI SPCR table.
936 cdns,<addr>[,options]
937 Start an early, polled-mode console on a Cadence
938 (xuartps) serial port at the specified address. Only
939 supported option is baud rate. If baud rate is not
940 specified, the serial port must already be setup and
941 configured.
943 uart[8250],io,<addr>[,options]
944 uart[8250],mmio,<addr>[,options]
945 uart[8250],mmio32,<addr>[,options]
946 uart[8250],mmio32be,<addr>[,options]
947 uart[8250],0x<addr>[,options]
948 Start an early, polled-mode console on the 8250/16550
949 UART at the specified I/O port or MMIO address.
950 MMIO inter-register address stride is either 8-bit
951 (mmio) or 32-bit (mmio32 or mmio32be).
952 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
953 to be equivalent to 'mmio'. 'options' are specified
954 in the same format described for "console=ttyS<n>"; if
955 unspecified, the h/w is not initialized.
957 pl011,<addr>
958 pl011,mmio32,<addr>
959 Start an early, polled-mode console on a pl011 serial
960 port at the specified address. The pl011 serial port
961 must already be setup and configured. Options are not
962 yet supported. If 'mmio32' is specified, then only
963 the driver will use only 32-bit accessors to read/write
964 the device registers.
966 meson,<addr>
967 Start an early, polled-mode console on a meson serial
968 port at the specified address. The serial port must
969 already be setup and configured. Options are not yet
970 supported.
972 msm_serial,<addr>
973 Start an early, polled-mode console on an msm serial
974 port at the specified address. The serial port
975 must already be setup and configured. Options are not
976 yet supported.
978 msm_serial_dm,<addr>
979 Start an early, polled-mode console on an msm serial
980 dm port at the specified address. The serial port
981 must already be setup and configured. Options are not
982 yet supported.
984 owl,<addr>
985 Start an early, polled-mode console on a serial port
986 of an Actions Semi SoC, such as S500 or S900, at the
987 specified address. The serial port must already be
988 setup and configured. Options are not yet supported.
990 smh Use ARM semihosting calls for early console.
992 s3c2410,<addr>
993 s3c2412,<addr>
994 s3c2440,<addr>
995 s3c6400,<addr>
996 s5pv210,<addr>
997 exynos4210,<addr>
998 Use early console provided by serial driver available
999 on Samsung SoCs, requires selecting proper type and
1000 a correct base address of the selected UART port. The
1001 serial port must already be setup and configured.
1002 Options are not yet supported.
1004 lantiq,<addr>
1005 Start an early, polled-mode console on a lantiq serial
1006 (lqasc) port at the specified address. The serial port
1007 must already be setup and configured. Options are not
1008 yet supported.
1010 lpuart,<addr>
1011 lpuart32,<addr>
1012 Use early console provided by Freescale LP UART driver
1013 found on Freescale Vybrid and QorIQ LS1021A processors.
1014 A valid base address must be provided, and the serial
1015 port must already be setup and configured.
1017 ar3700_uart,<addr>
1018 Start an early, polled-mode console on the
1019 Armada 3700 serial port at the specified
1020 address. The serial port must already be setup
1021 and configured. Options are not yet supported.
1023 qcom_geni,<addr>
1024 Start an early, polled-mode console on a Qualcomm
1025 Generic Interface (GENI) based serial port at the
1026 specified address. The serial port must already be
1027 setup and configured. Options are not yet supported.
1029 earlyprintk= [X86,SH,ARM,M68k,S390]
1030 earlyprintk=vga
1031 earlyprintk=efi
1032 earlyprintk=sclp
1033 earlyprintk=xen
1034 earlyprintk=serial[,ttySn[,baudrate]]
1035 earlyprintk=serial[,0x...[,baudrate]]
1036 earlyprintk=ttySn[,baudrate]
1037 earlyprintk=dbgp[debugController#]
1038 earlyprintk=pciserial,bus:device.function[,baudrate]
1039 earlyprintk=xdbc[xhciController#]
1041 earlyprintk is useful when the kernel crashes before
1042 the normal console is initialized. It is not enabled by
1043 default because it has some cosmetic problems.
1045 Append ",keep" to not disable it when the real console
1046 takes over.
1048 Only one of vga, efi, serial, or usb debug port can
1049 be used at a time.
1051 Currently only ttyS0 and ttyS1 may be specified by
1052 name. Other I/O ports may be explicitly specified
1053 on some architectures (x86 and arm at least) by
1054 replacing ttySn with an I/O port address, like this:
1055 earlyprintk=serial,0x1008,115200
1056 You can find the port for a given device in
1057 /proc/tty/driver/serial:
1058 2: uart:ST16650V2 port:00001008 irq:18 ...
1060 Interaction with the standard serial driver is not
1061 very good.
1063 The VGA and EFI output is eventually overwritten by
1064 the real console.
1066 The xen output can only be used by Xen PV guests.
1068 The sclp output can only be used on s390.
1070 edac_report= [HW,EDAC] Control how to report EDAC event
1071 Format: {"on" | "off" | "force"}
1072 on: enable EDAC to report H/W event. May be overridden
1073 by other higher priority error reporting module.
1074 off: disable H/W event reporting through EDAC.
1075 force: enforce the use of EDAC to report H/W event.
1076 default: on.
1078 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1079 ekgdboc=kbd
1081 This is designed to be used in conjunction with
1082 the boot argument: earlyprintk=vga
1084 edd= [EDD]
1085 Format: {"off" | "on" | "skip[mbr]"}
1087 efi= [EFI]
1088 Format: { "old_map", "nochunk", "noruntime", "debug" }
1089 old_map [X86-64]: switch to the old ioremap-based EFI
1090 runtime services mapping. 32-bit still uses this one by
1091 default.
1092 nochunk: disable reading files in "chunks" in the EFI
1093 boot stub, as chunking can cause problems with some
1094 firmware implementations.
1095 noruntime : disable EFI runtime services support
1096 debug: enable misc debug output
1098 efi_no_storage_paranoia [EFI; X86]
1099 Using this parameter you can use more than 50% of
1100 your efi variable storage. Use this parameter only if
1101 you are really sure that your UEFI does sane gc and
1102 fulfills the spec otherwise your board may brick.
1104 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1105 Add arbitrary attribute to specific memory range by
1106 updating original EFI memory map.
1107 Region of memory which aa attribute is added to is
1108 from ss to ss+nn.
1109 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1110 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1111 attribute is added to range 0x100000000-0x180000000 and
1112 0x10a0000000-0x1120000000.
1114 Using this parameter you can do debugging of EFI memmap
1115 related feature. For example, you can do debugging of
1116 Address Range Mirroring feature even if your box
1117 doesn't support it.
1119 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1120 that is to be dynamically loaded by Linux. If there are
1121 multiple variables with the same name but with different
1122 vendor GUIDs, all of them will be loaded. See
1123 Documentation/acpi/ssdt-overlays.txt for details.
1126 eisa_irq_edge= [PARISC,HW]
1127 See header of drivers/parisc/eisa.c.
1129 elanfreq= [X86-32]
1130 See comment before function elanfreq_setup() in
1131 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1133 elevator= [IOSCHED]
1134 Format: {"cfq" | "deadline" | "noop"}
1135 See Documentation/block/cfq-iosched.txt and
1136 Documentation/block/deadline-iosched.txt for details.
1138 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1139 Specifies physical address of start of kernel core
1140 image elf header and optionally the size. Generally
1141 kexec loader will pass this option to capture kernel.
1142 See Documentation/kdump/kdump.txt for details.
1144 enable_mtrr_cleanup [X86]
1145 The kernel tries to adjust MTRR layout from continuous
1146 to discrete, to make X server driver able to add WB
1147 entry later. This parameter enables that.
1149 enable_timer_pin_1 [X86]
1150 Enable PIN 1 of APIC timer
1151 Can be useful to work around chipset bugs
1152 (in particular on some ATI chipsets).
1153 The kernel tries to set a reasonable default.
1155 enforcing [SELINUX] Set initial enforcing status.
1156 Format: {"0" | "1"}
1157 See security/selinux/Kconfig help text.
1158 0 -- permissive (log only, no denials).
1159 1 -- enforcing (deny and log).
1160 Default value is 0.
1161 Value can be changed at runtime via /selinux/enforce.
1163 erst_disable [ACPI]
1164 Disable Error Record Serialization Table (ERST)
1165 support.
1167 ether= [HW,NET] Ethernet cards parameters
1168 This option is obsoleted by the "netdev=" option, which
1169 has equivalent usage. See its documentation for details.
1171 evm= [EVM]
1172 Format: { "fix" }
1173 Permit 'security.evm' to be updated regardless of
1174 current integrity status.
1176 failslab=
1177 fail_page_alloc=
1178 fail_make_request=[KNL]
1179 General fault injection mechanism.
1180 Format: <interval>,<probability>,<space>,<times>
1181 See also Documentation/fault-injection/.
1183 floppy= [HW]
1184 See Documentation/blockdev/floppy.txt.
1186 force_pal_cache_flush
1187 [IA-64] Avoid check_sal_cache_flush which may hang on
1188 buggy SAL_CACHE_FLUSH implementations. Using this
1189 parameter will force ia64_sal_cache_flush to call
1190 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1192 forcepae [X86-32]
1193 Forcefully enable Physical Address Extension (PAE).
1194 Many Pentium M systems disable PAE but may have a
1195 functionally usable PAE implementation.
1196 Warning: use of this parameter will taint the kernel
1197 and may cause unknown problems.
1199 ftrace=[tracer]
1200 [FTRACE] will set and start the specified tracer
1201 as early as possible in order to facilitate early
1202 boot debugging.
1204 ftrace_dump_on_oops[=orig_cpu]
1205 [FTRACE] will dump the trace buffers on oops.
1206 If no parameter is passed, ftrace will dump
1207 buffers of all CPUs, but if you pass orig_cpu, it will
1208 dump only the buffer of the CPU that triggered the
1209 oops.
1211 ftrace_filter=[function-list]
1212 [FTRACE] Limit the functions traced by the function
1213 tracer at boot up. function-list is a comma separated
1214 list of functions. This list can be changed at run
1215 time by the set_ftrace_filter file in the debugfs
1216 tracing directory.
1218 ftrace_notrace=[function-list]
1219 [FTRACE] Do not trace the functions specified in
1220 function-list. This list can be changed at run time
1221 by the set_ftrace_notrace file in the debugfs
1222 tracing directory.
1224 ftrace_graph_filter=[function-list]
1225 [FTRACE] Limit the top level callers functions traced
1226 by the function graph tracer at boot up.
1227 function-list is a comma separated list of functions
1228 that can be changed at run time by the
1229 set_graph_function file in the debugfs tracing directory.
1231 ftrace_graph_notrace=[function-list]
1232 [FTRACE] Do not trace from the functions specified in
1233 function-list. This list is a comma separated list of
1234 functions that can be changed at run time by the
1235 set_graph_notrace file in the debugfs tracing directory.
1237 ftrace_graph_max_depth=<uint>
1238 [FTRACE] Used with the function graph tracer. This is
1239 the max depth it will trace into a function. This value
1240 can be changed at run time by the max_graph_depth file
1241 in the tracefs tracing directory. default: 0 (no limit)
1243 gamecon.map[2|3]=
1244 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1245 support via parallel port (up to 5 devices per port)
1246 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1247 See also Documentation/input/devices/joystick-parport.rst
1249 gamma= [HW,DRM]
1251 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1252 Format: off | on
1253 default: on
1255 gcov_persist= [GCOV] When non-zero (default), profiling data for
1256 kernel modules is saved and remains accessible via
1257 debugfs, even when the module is unloaded/reloaded.
1258 When zero, profiling data is discarded and associated
1259 debugfs files are removed at module unload time.
1261 goldfish [X86] Enable the goldfish android emulator platform.
1262 Don't use this when you are not running on the
1263 android emulator
1265 gpt [EFI] Forces disk with valid GPT signature but
1266 invalid Protective MBR to be treated as GPT. If the
1267 primary GPT is corrupted, it enables the backup/alternate
1268 GPT to be used instead.
1270 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1271 the "Enable 0" bit of the configuration register.
1272 Format: 0 | 1
1273 Default: 0
1274 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1275 the "Enable 0" bit of the configuration register.
1276 Format: 0 | 1
1277 Default: 0
1278 grcan.select= [HW] Select which physical interface to use.
1279 Format: 0 | 1
1280 Default: 0
1281 grcan.txsize= [HW] Sets the size of the tx buffer.
1282 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1283 Default: 1024
1284 grcan.rxsize= [HW] Sets the size of the rx buffer.
1285 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1286 Default: 1024
1288 gpio-mockup.gpio_mockup_ranges
1289 [HW] Sets the ranges of gpiochip of for this device.
1290 Format: <start1>,<end1>,<start2>,<end2>...
1292 hardlockup_all_cpu_backtrace=
1293 [KNL] Should the hard-lockup detector generate
1294 backtraces on all cpus.
1295 Format: <integer>
1297 hashdist= [KNL,NUMA] Large hashes allocated during boot
1298 are distributed across NUMA nodes. Defaults on
1299 for 64-bit NUMA, off otherwise.
1300 Format: 0 | 1 (for off | on)
1302 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1304 hd= [EIDE] (E)IDE hard drive subsystem geometry
1305 Format: <cyl>,<head>,<sect>
1307 hest_disable [ACPI]
1308 Disable Hardware Error Source Table (HEST) support;
1309 corresponding firmware-first mode error processing
1310 logic will be disabled.
1312 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1313 size of <nn>. This works even on boxes that have no
1314 highmem otherwise. This also works to reduce highmem
1315 size on bigger boxes.
1317 highres= [KNL] Enable/disable high resolution timer mode.
1318 Valid parameters: "on", "off"
1319 Default: "on"
1321 hisax= [HW,ISDN]
1322 See Documentation/isdn/README.HiSax.
1324 hlt [BUGS=ARM,SH]
1326 hpet= [X86-32,HPET] option to control HPET usage
1327 Format: { enable (default) | disable | force |
1328 verbose }
1329 disable: disable HPET and use PIT instead
1330 force: allow force enabled of undocumented chips (ICH4,
1331 VIA, nVidia)
1332 verbose: show contents of HPET registers during setup
1334 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1335 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1337 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1338 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1339 On x86-64 and powerpc, this option can be specified
1340 multiple times interleaved with hugepages= to reserve
1341 huge pages of different sizes. Valid pages sizes on
1342 x86-64 are 2M (when the CPU supports "pse") and 1G
1343 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1345 hung_task_panic=
1346 [KNL] Should the hung task detector generate panics.
1347 Format: <integer>
1349 A nonzero value instructs the kernel to panic when a
1350 hung task is detected. The default value is controlled
1351 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1352 option. The value selected by this boot parameter can
1353 be changed later by the kernel.hung_task_panic sysctl.
1355 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1356 terminal devices. Valid values: 0..8
1357 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1358 If specified, z/VM IUCV HVC accepts connections
1359 from listed z/VM user IDs only.
1360 keep_bootcon [KNL]
1361 Do not unregister boot console at start. This is only
1362 useful for debugging when something happens in the window
1363 between unregistering the boot console and initializing
1364 the real console.
1366 i2c_bus= [HW] Override the default board specific I2C bus speed
1367 or register an additional I2C bus that is not
1368 registered from board initialization code.
1369 Format:
1370 <bus_id>,<clkrate>
1372 i8042.debug [HW] Toggle i8042 debug mode
1373 i8042.unmask_kbd_data
1374 [HW] Enable printing of interrupt data from the KBD port
1375 (disabled by default, and as a pre-condition
1376 requires that i8042.debug=1 be enabled)
1377 i8042.direct [HW] Put keyboard port into non-translated mode
1378 i8042.dumbkbd [HW] Pretend that controller can only read data from
1379 keyboard and cannot control its state
1380 (Don't attempt to blink the leds)
1381 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1382 i8042.nokbd [HW] Don't check/create keyboard port
1383 i8042.noloop [HW] Disable the AUX Loopback command while probing
1384 for the AUX port
1385 i8042.nomux [HW] Don't check presence of an active multiplexing
1386 controller
1387 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1388 controllers
1389 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1390 i8042.reset [HW] Reset the controller during init, cleanup and
1391 suspend-to-ram transitions, only during s2r
1392 transitions, or never reset
1393 Format: { 1 | Y | y | 0 | N | n }
1394 1, Y, y: always reset controller
1395 0, N, n: don't ever reset controller
1396 Default: only on s2r transitions on x86; most other
1397 architectures force reset to be always executed
1398 i8042.unlock [HW] Unlock (ignore) the keylock
1399 i8042.kbdreset [HW] Reset device connected to KBD port
1401 i810= [HW,DRM]
1403 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1404 indicates that the driver is running on unsupported
1405 hardware.
1406 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1407 does not match list of supported models.
1408 i8k.power_status
1409 [HW] Report power status in /proc/i8k
1410 (disabled by default)
1411 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1412 capability is set.
1414 i915.invert_brightness=
1415 [DRM] Invert the sense of the variable that is used to
1416 set the brightness of the panel backlight. Normally a
1417 brightness value of 0 indicates backlight switched off,
1418 and the maximum of the brightness value sets the backlight
1419 to maximum brightness. If this parameter is set to 0
1420 (default) and the machine requires it, or this parameter
1421 is set to 1, a brightness value of 0 sets the backlight
1422 to maximum brightness, and the maximum of the brightness
1423 value switches the backlight off.
1424 -1 -- never invert brightness
1425 0 -- machine default
1426 1 -- force brightness inversion
1428 icn= [HW,ISDN]
1429 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1431 ide-core.nodma= [HW] (E)IDE subsystem
1432 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1433 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1434 .cdrom .chs .ignore_cable are additional options
1435 See Documentation/ide/ide.txt.
1437 ide-generic.probe-mask= [HW] (E)IDE subsystem
1438 Format: <int>
1439 Probe mask for legacy ISA IDE ports. Depending on
1440 platform up to 6 ports are supported, enabled by
1441 setting corresponding bits in the mask to 1. The
1442 default value is 0x0, which has a special meaning.
1443 On systems that have PCI, it triggers scanning the
1444 PCI bus for the first and the second port, which
1445 are then probed. On systems without PCI the value
1446 of 0x0 enables probing the two first ports as if it
1447 was 0x3.
1449 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1450 Claim all unknown PCI IDE storage controllers.
1452 idle= [X86]
1453 Format: idle=poll, idle=halt, idle=nomwait
1454 Poll forces a polling idle loop that can slightly
1455 improve the performance of waking up a idle CPU, but
1456 will use a lot of power and make the system run hot.
1457 Not recommended.
1458 idle=halt: Halt is forced to be used for CPU idle.
1459 In such case C2/C3 won't be used again.
1460 idle=nomwait: Disable mwait for CPU C-states
1462 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1463 Format: { strict | legacy | 2008 | relaxed }
1464 Default: strict
1466 Choose which programs will be accepted for execution
1467 based on the IEEE 754 NaN encoding(s) supported by
1468 the FPU and the NaN encoding requested with the value
1469 of an ELF file header flag individually set by each
1470 binary. Hardware implementations are permitted to
1471 support either or both of the legacy and the 2008 NaN
1472 encoding mode.
1474 Available settings are as follows:
1475 strict accept binaries that request a NaN encoding
1476 supported by the FPU
1477 legacy only accept legacy-NaN binaries, if supported
1478 by the FPU
1479 2008 only accept 2008-NaN binaries, if supported
1480 by the FPU
1481 relaxed accept any binaries regardless of whether
1482 supported by the FPU
1484 The FPU emulator is always able to support both NaN
1485 encodings, so if no FPU hardware is present or it has
1486 been disabled with 'nofpu', then the settings of
1487 'legacy' and '2008' strap the emulator accordingly,
1488 'relaxed' straps the emulator for both legacy-NaN and
1489 2008-NaN, whereas 'strict' enables legacy-NaN only on
1490 legacy processors and both NaN encodings on MIPS32 or
1491 MIPS64 CPUs.
1493 The setting for ABS.fmt/NEG.fmt instruction execution
1494 mode generally follows that for the NaN encoding,
1495 except where unsupported by hardware.
1497 ignore_loglevel [KNL]
1498 Ignore loglevel setting - this will print /all/
1499 kernel messages to the console. Useful for debugging.
1500 We also add it as printk module parameter, so users
1501 could change it dynamically, usually by
1502 /sys/module/printk/parameters/ignore_loglevel.
1504 ignore_rlimit_data
1505 Ignore RLIMIT_DATA setting for data mappings,
1506 print warning at first misuse. Can be changed via
1507 /sys/module/kernel/parameters/ignore_rlimit_data.
1509 ihash_entries= [KNL]
1510 Set number of hash buckets for inode cache.
1512 ima_appraise= [IMA] appraise integrity measurements
1513 Format: { "off" | "enforce" | "fix" | "log" }
1514 default: "enforce"
1516 ima_appraise_tcb [IMA]
1517 The builtin appraise policy appraises all files
1518 owned by uid=0.
1520 ima_canonical_fmt [IMA]
1521 Use the canonical format for the binary runtime
1522 measurements, instead of host native format.
1524 ima_hash= [IMA]
1525 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1526 | sha512 | ... }
1527 default: "sha1"
1529 The list of supported hash algorithms is defined
1530 in crypto/hash_info.h.
1532 ima_policy= [IMA]
1533 The builtin policies to load during IMA setup.
1534 Format: "tcb | appraise_tcb | secure_boot |
1535 fail_securely"
1537 The "tcb" policy measures all programs exec'd, files
1538 mmap'd for exec, and all files opened with the read
1539 mode bit set by either the effective uid (euid=0) or
1540 uid=0.
1542 The "appraise_tcb" policy appraises the integrity of
1543 all files owned by root. (This is the equivalent
1544 of ima_appraise_tcb.)
1546 The "secure_boot" policy appraises the integrity
1547 of files (eg. kexec kernel image, kernel modules,
1548 firmware, policy, etc) based on file signatures.
1550 The "fail_securely" policy forces file signature
1551 verification failure also on privileged mounted
1552 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1553 flag.
1555 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1556 Load a policy which meets the needs of the Trusted
1557 Computing Base. This means IMA will measure all
1558 programs exec'd, files mmap'd for exec, and all files
1559 opened for read by uid=0.
1561 ima_template= [IMA]
1562 Select one of defined IMA measurements template formats.
1563 Formats: { "ima" | "ima-ng" | "ima-sig" }
1564 Default: "ima-ng"
1566 ima_template_fmt=
1567 [IMA] Define a custom template format.
1568 Format: { "field1|...|fieldN" }
1570 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1571 Format: <min_file_size>
1572 Set the minimal file size for using asynchronous hash.
1573 If left unspecified, ahash usage is disabled.
1575 ahash performance varies for different data sizes on
1576 different crypto accelerators. This option can be used
1577 to achieve the best performance for a particular HW.
1579 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1580 Format: <bufsize>
1581 Set hashing buffer size. Default: 4k.
1583 ahash performance varies for different chunk sizes on
1584 different crypto accelerators. This option can be used
1585 to achieve best performance for particular HW.
1587 init= [KNL]
1588 Format: <full_path>
1589 Run specified binary instead of /sbin/init as init
1590 process.
1592 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1593 for working out where the kernel is dying during
1594 startup.
1596 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1597 initcall functions. Useful for debugging built-in
1598 modules and initcalls.
1600 initrd= [BOOT] Specify the location of the initial ramdisk
1602 init_pkru= [x86] Specify the default memory protection keys rights
1603 register contents for all processes. 0x55555554 by
1604 default (disallow access to all but pkey 0). Can
1605 override in debugfs after boot.
1607 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1608 Format: <irq>
1610 int_pln_enable [x86] Enable power limit notification interrupt
1612 integrity_audit=[IMA]
1613 Format: { "0" | "1" }
1614 0 -- basic integrity auditing messages. (Default)
1615 1 -- additional integrity auditing messages.
1617 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1618 on
1619 Enable intel iommu driver.
1620 off
1621 Disable intel iommu driver.
1622 igfx_off [Default Off]
1623 By default, gfx is mapped as normal device. If a gfx
1624 device has a dedicated DMAR unit, the DMAR unit is
1625 bypassed by not enabling DMAR with this option. In
1626 this case, gfx device will use physical address for
1627 DMA.
1628 forcedac [x86_64]
1629 With this option iommu will not optimize to look
1630 for io virtual address below 32-bit forcing dual
1631 address cycle on pci bus for cards supporting greater
1632 than 32-bit addressing. The default is to look
1633 for translation below 32-bit and if not available
1634 then look in the higher range.
1635 strict [Default Off]
1636 With this option on every unmap_single operation will
1637 result in a hardware IOTLB flush operation as opposed
1638 to batching them for performance.
1639 sp_off [Default Off]
1640 By default, super page will be supported if Intel IOMMU
1641 has the capability. With this option, super page will
1642 not be supported.
1643 ecs_off [Default Off]
1644 By default, extended context tables will be supported if
1645 the hardware advertises that it has support both for the
1646 extended tables themselves, and also PASID support. With
1647 this option set, extended tables will not be used even
1648 on hardware which claims to support them.
1649 tboot_noforce [Default Off]
1650 Do not force the Intel IOMMU enabled under tboot.
1651 By default, tboot will force Intel IOMMU on, which
1652 could harm performance of some high-throughput
1653 devices like 40GBit network cards, even if identity
1654 mapping is enabled.
1655 Note that using this option lowers the security
1656 provided by tboot because it makes the system
1657 vulnerable to DMA attacks.
1659 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1660 0 disables intel_idle and fall back on acpi_idle.
1661 1 to 9 specify maximum depth of C-state.
1663 intel_pstate= [X86]
1664 disable
1665 Do not enable intel_pstate as the default
1666 scaling driver for the supported processors
1667 passive
1668 Use intel_pstate as a scaling driver, but configure it
1669 to work with generic cpufreq governors (instead of
1670 enabling its internal governor). This mode cannot be
1671 used along with the hardware-managed P-states (HWP)
1672 feature.
1673 force
1674 Enable intel_pstate on systems that prohibit it by default
1675 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1676 instead of acpi-cpufreq may disable platform features, such
1677 as thermal controls and power capping, that rely on ACPI
1678 P-States information being indicated to OSPM and therefore
1679 should be used with caution. This option does not work with
1680 processors that aren't supported by the intel_pstate driver
1681 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1682 no_hwp
1683 Do not enable hardware P state control (HWP)
1684 if available.
1685 hwp_only
1686 Only load intel_pstate on systems which support
1687 hardware P state control (HWP) if available.
1688 support_acpi_ppc
1689 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1690 Description Table, specifies preferred power management
1691 profile as "Enterprise Server" or "Performance Server",
1692 then this feature is turned on by default.
1693 per_cpu_perf_limits
1694 Allow per-logical-CPU P-State performance control limits using
1695 cpufreq sysfs interface
1697 intremap= [X86-64, Intel-IOMMU]
1698 on enable Interrupt Remapping (default)
1699 off disable Interrupt Remapping
1700 nosid disable Source ID checking
1701 no_x2apic_optout
1702 BIOS x2APIC opt-out request will be ignored
1703 nopost disable Interrupt Posting
1705 iomem= Disable strict checking of access to MMIO memory
1706 strict regions from userspace.
1707 relaxed
1709 iommu= [x86]
1710 off
1711 force
1712 noforce
1713 biomerge
1714 panic
1715 nopanic
1716 merge
1717 nomerge
1718 soft
1719 pt [x86, IA-64]
1720 nobypass [PPC/POWERNV]
1721 Disable IOMMU bypass, using IOMMU for PCI devices.
1723 iommu.passthrough=
1724 [ARM64] Configure DMA to bypass the IOMMU by default.
1725 Format: { "0" | "1" }
1726 0 - Use IOMMU translation for DMA.
1727 1 - Bypass the IOMMU for DMA.
1728 unset - Use IOMMU translation for DMA.
1730 io7= [HW] IO7 for Marvel based alpha systems
1731 See comment before marvel_specify_io7 in
1732 arch/alpha/kernel/core_marvel.c.
1734 io_delay= [X86] I/O delay method
1735 0x80
1736 Standard port 0x80 based delay
1737 0xed
1738 Alternate port 0xed based delay (needed on some systems)
1739 udelay
1740 Simple two microseconds delay
1741 none
1742 No delay
1744 ip= [IP_PNP]
1745 See Documentation/filesystems/nfs/nfsroot.txt.
1747 irqaffinity= [SMP] Set the default irq affinity mask
1748 The argument is a cpu list, as described above.
1750 irqchip.gicv2_force_probe=
1751 [ARM, ARM64]
1752 Format: <bool>
1753 Force the kernel to look for the second 4kB page
1754 of a GICv2 controller even if the memory range
1755 exposed by the device tree is too small.
1757 irqchip.gicv3_nolpi=
1758 [ARM, ARM64]
1759 Force the kernel to ignore the availability of
1760 LPIs (and by consequence ITSs). Intended for system
1761 that use the kernel as a bootloader, and thus want
1762 to let secondary kernels in charge of setting up
1763 LPIs.
1765 irqfixup [HW]
1766 When an interrupt is not handled search all handlers
1767 for it. Intended to get systems with badly broken
1768 firmware running.
1770 irqpoll [HW]
1771 When an interrupt is not handled search all handlers
1772 for it. Also check all handlers each timer
1773 interrupt. Intended to get systems with badly broken
1774 firmware running.
1776 isapnp= [ISAPNP]
1777 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1779 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1780 [Deprecated - use cpusets instead]
1781 Format: [flag-list,]<cpu-list>
1783 Specify one or more CPUs to isolate from disturbances
1784 specified in the flag list (default: domain):
1786 nohz
1787 Disable the tick when a single task runs.
1789 A residual 1Hz tick is offloaded to workqueues, which you
1790 need to affine to housekeeping through the global
1791 workqueue's affinity configured via the
1792 /sys/devices/virtual/workqueue/cpumask sysfs file, or
1793 by using the 'domain' flag described below.
1795 NOTE: by default the global workqueue runs on all CPUs,
1796 so to protect individual CPUs the 'cpumask' file has to
1797 be configured manually after bootup.
1799 domain
1800 Isolate from the general SMP balancing and scheduling
1801 algorithms. Note that performing domain isolation this way
1802 is irreversible: it's not possible to bring back a CPU to
1803 the domains once isolated through isolcpus. It's strongly
1804 advised to use cpusets instead to disable scheduler load
1805 balancing through the "cpuset.sched_load_balance" file.
1806 It offers a much more flexible interface where CPUs can
1807 move in and out of an isolated set anytime.
1809 You can move a process onto or off an "isolated" CPU via
1810 the CPU affinity syscalls or cpuset.
1811 <cpu number> begins at 0 and the maximum value is
1812 "number of CPUs in system - 1".
1814 The format of <cpu-list> is described above.
1818 iucv= [HW,NET]
1820 ivrs_ioapic [HW,X86_64]
1821 Provide an override to the IOAPIC-ID<->DEVICE-ID
1822 mapping provided in the IVRS ACPI table. For
1823 example, to map IOAPIC-ID decimal 10 to
1824 PCI device 00:14.0 write the parameter as:
1825 ivrs_ioapic[10]=00:14.0
1827 ivrs_hpet [HW,X86_64]
1828 Provide an override to the HPET-ID<->DEVICE-ID
1829 mapping provided in the IVRS ACPI table. For
1830 example, to map HPET-ID decimal 0 to
1831 PCI device 00:14.0 write the parameter as:
1832 ivrs_hpet[0]=00:14.0
1834 ivrs_acpihid [HW,X86_64]
1835 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1836 mapping provided in the IVRS ACPI table. For
1837 example, to map UART-HID:UID AMD0020:0 to
1838 PCI device 00:14.5 write the parameter as:
1839 ivrs_acpihid[00:14.5]=AMD0020:0
1841 js= [HW,JOY] Analog joystick
1842 See Documentation/input/joydev/joystick.rst.
1844 nokaslr [KNL]
1845 When CONFIG_RANDOMIZE_BASE is set, this disables
1846 kernel and module base offset ASLR (Address Space
1847 Layout Randomization).
1849 kasan_multi_shot
1850 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1851 report on every invalid memory access. Without this
1852 parameter KASAN will print report only for the first
1853 invalid access.
1855 keepinitrd [HW,ARM]
1857 kernelcore= [KNL,X86,IA-64,PPC]
1858 Format: nn[KMGTPE] | nn% | "mirror"
1859 This parameter specifies the amount of memory usable by
1860 the kernel for non-movable allocations. The requested
1861 amount is spread evenly throughout all nodes in the
1862 system as ZONE_NORMAL. The remaining memory is used for
1863 movable memory in its own zone, ZONE_MOVABLE. In the
1864 event, a node is too small to have both ZONE_NORMAL and
1865 ZONE_MOVABLE, kernelcore memory will take priority and
1866 other nodes will have a larger ZONE_MOVABLE.
1868 ZONE_MOVABLE is used for the allocation of pages that
1869 may be reclaimed or moved by the page migration
1870 subsystem. Note that allocations like PTEs-from-HighMem
1871 still use the HighMem zone if it exists, and the Normal
1872 zone if it does not.
1874 It is possible to specify the exact amount of memory in
1875 the form of "nn[KMGTPE]", a percentage of total system
1876 memory in the form of "nn%", or "mirror". If "mirror"
1877 option is specified, mirrored (reliable) memory is used
1878 for non-movable allocations and remaining memory is used
1879 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
1880 are exclusive, so you cannot specify multiple forms.
1882 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1883 Format: <Controller#>[,poll interval]
1884 The controller # is the number of the ehci usb debug
1885 port as it is probed via PCI. The poll interval is
1886 optional and is the number seconds in between
1887 each poll cycle to the debug port in case you need
1888 the functionality for interrupting the kernel with
1889 gdb or control-c on the dbgp connection. When
1890 not using this parameter you use sysrq-g to break into
1891 the kernel debugger.
1893 kgdboc= [KGDB,HW] kgdb over consoles.
1894 Requires a tty driver that supports console polling,
1895 or a supported polling keyboard driver (non-usb).
1896 Serial only format: <serial_device>[,baud]
1897 keyboard only format: kbd
1898 keyboard and serial format: kbd,<serial_device>[,baud]
1899 Optional Kernel mode setting:
1900 kms, kbd format: kms,kbd
1901 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1903 kgdbwait [KGDB] Stop kernel execution and enter the
1904 kernel debugger at the earliest opportunity.
1906 kmac= [MIPS] korina ethernet MAC address.
1907 Configure the RouterBoard 532 series on-chip
1908 Ethernet adapter MAC address.
1910 kmemleak= [KNL] Boot-time kmemleak enable/disable
1911 Valid arguments: on, off
1912 Default: on
1913 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1914 the default is off.
1916 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1917 Default is 0 (don't ignore, but inject #GP)
1919 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
1920 Default is false (don't support).
1922 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1923 KVM MMU at runtime.
1924 Default is 0 (off)
1926 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1927 Default is 1 (enabled)
1929 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1930 for all guests.
1931 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1933 kvm-arm.vgic_v3_group0_trap=
1934 [KVM,ARM] Trap guest accesses to GICv3 group-0
1935 system registers
1937 kvm-arm.vgic_v3_group1_trap=
1938 [KVM,ARM] Trap guest accesses to GICv3 group-1
1939 system registers
1941 kvm-arm.vgic_v3_common_trap=
1942 [KVM,ARM] Trap guest accesses to GICv3 common
1943 system registers
1945 kvm-arm.vgic_v4_enable=
1946 [KVM,ARM] Allow use of GICv4 for direct injection of
1947 LPIs.
1949 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1950 (virtualized MMU) support on capable Intel chips.
1951 Default is 1 (enabled)
1953 kvm-intel.emulate_invalid_guest_state=
1954 [KVM,Intel] Enable emulation of invalid guest states
1955 Default is 0 (disabled)
1957 kvm-intel.flexpriority=
1958 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1959 Default is 1 (enabled)
1961 kvm-intel.nested=
1962 [KVM,Intel] Enable VMX nesting (nVMX).
1963 Default is 0 (disabled)
1965 kvm-intel.unrestricted_guest=
1966 [KVM,Intel] Disable unrestricted guest feature
1967 (virtualized real and unpaged mode) on capable
1968 Intel chips. Default is 1 (enabled)
1970 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
1971 CVE-2018-3620.
1973 Valid arguments: never, cond, always
1975 always: L1D cache flush on every VMENTER.
1976 cond: Flush L1D on VMENTER only when the code between
1977 VMEXIT and VMENTER can leak host memory.
1978 never: Disables the mitigation
1980 Default is cond (do L1 cache flush in specific instances)
1982 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1983 feature (tagged TLBs) on capable Intel chips.
1984 Default is 1 (enabled)
1986 l1tf= [X86] Control mitigation of the L1TF vulnerability on
1987 affected CPUs
1989 The kernel PTE inversion protection is unconditionally
1990 enabled and cannot be disabled.
1992 full
1993 Provides all available mitigations for the
1994 L1TF vulnerability. Disables SMT and
1995 enables all mitigations in the
1996 hypervisors, i.e. unconditional L1D flush.
1998 SMT control and L1D flush control via the
1999 sysfs interface is still possible after
2000 boot. Hypervisors will issue a warning
2001 when the first VM is started in a
2002 potentially insecure configuration,
2003 i.e. SMT enabled or L1D flush disabled.
2005 full,force
2006 Same as 'full', but disables SMT and L1D
2007 flush runtime control. Implies the
2008 'nosmt=force' command line option.
2009 (i.e. sysfs control of SMT is disabled.)
2011 flush
2012 Leaves SMT enabled and enables the default
2013 hypervisor mitigation, i.e. conditional
2014 L1D flush.
2016 SMT control and L1D flush control via the
2017 sysfs interface is still possible after
2018 boot. Hypervisors will issue a warning
2019 when the first VM is started in a
2020 potentially insecure configuration,
2021 i.e. SMT enabled or L1D flush disabled.
2023 flush,nosmt
2025 Disables SMT and enables the default
2026 hypervisor mitigation.
2028 SMT control and L1D flush control via the
2029 sysfs interface is still possible after
2030 boot. Hypervisors will issue a warning
2031 when the first VM is started in a
2032 potentially insecure configuration,
2033 i.e. SMT enabled or L1D flush disabled.
2035 flush,nowarn
2036 Same as 'flush', but hypervisors will not
2037 warn when a VM is started in a potentially
2038 insecure configuration.
2040 off
2041 Disables hypervisor mitigations and doesn't
2042 emit any warnings.
2044 Default is 'flush'.
2046 For details see: Documentation/admin-guide/l1tf.rst
2048 l2cr= [PPC]
2050 l3cr= [PPC]
2052 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2053 disabled it.
2055 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2056 value for LAPIC timer one-shot implementation. Default
2057 back to the programmable timer unit in the LAPIC.
2059 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2060 in C2 power state.
2062 libata.dma= [LIBATA] DMA control
2063 libata.dma=0 Disable all PATA and SATA DMA
2064 libata.dma=1 PATA and SATA Disk DMA only
2065 libata.dma=2 ATAPI (CDROM) DMA only
2066 libata.dma=4 Compact Flash DMA only
2067 Combinations also work, so libata.dma=3 enables DMA
2068 for disks and CDROMs, but not CFs.
2070 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2071 libata.ignore_hpa=0 keep BIOS limits (default)
2072 libata.ignore_hpa=1 ignore limits, using full disk
2074 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2075 when set.
2076 Format: <int>
2078 libata.force= [LIBATA] Force configurations. The format is comma
2079 separated list of "[ID:]VAL" where ID is
2080 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2081 matching port, link or device. Basically, it matches
2082 the ATA ID string printed on console by libata. If
2083 the whole ID part is omitted, the last PORT and DEVICE
2084 values are used. If ID hasn't been specified yet, the
2085 configuration applies to all ports, links and devices.
2087 If only DEVICE is omitted, the parameter applies to
2088 the port and all links and devices behind it. DEVICE
2089 number of 0 either selects the first device or the
2090 first fan-out link behind PMP device. It does not
2091 select the host link. DEVICE number of 15 selects the
2092 host link and device attached to it.
2094 The VAL specifies the configuration to force. As long
2095 as there's no ambiguity shortcut notation is allowed.
2096 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2097 The following configurations can be forced.
2099 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2100 Any ID with matching PORT is used.
2102 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2104 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2105 udma[/][16,25,33,44,66,100,133] notation is also
2106 allowed.
2108 * [no]ncq: Turn on or off NCQ.
2110 * [no]ncqtrim: Turn off queued DSM TRIM.
2112 * nohrst, nosrst, norst: suppress hard, soft
2113 and both resets.
2115 * rstonce: only attempt one reset during
2116 hot-unplug link recovery
2118 * dump_id: dump IDENTIFY data.
2120 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2122 * disable: Disable this device.
2124 If there are multiple matching configurations changing
2125 the same attribute, the last one is used.
2127 memblock=debug [KNL] Enable memblock debug messages.
2129 load_ramdisk= [RAM] List of ramdisks to load from floppy
2130 See Documentation/blockdev/ramdisk.txt.
2132 lockd.nlm_grace_period=P [NFS] Assign grace period.
2133 Format: <integer>
2135 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2136 Format: <integer>
2138 lockd.nlm_timeout=T [NFS] Assign timeout value.
2139 Format: <integer>
2141 lockd.nlm_udpport=M [NFS] Assign UDP port.
2142 Format: <integer>
2144 locktorture.nreaders_stress= [KNL]
2145 Set the number of locking read-acquisition kthreads.
2146 Defaults to being automatically set based on the
2147 number of online CPUs.
2149 locktorture.nwriters_stress= [KNL]
2150 Set the number of locking write-acquisition kthreads.
2152 locktorture.onoff_holdoff= [KNL]
2153 Set time (s) after boot for CPU-hotplug testing.
2155 locktorture.onoff_interval= [KNL]
2156 Set time (s) between CPU-hotplug operations, or
2157 zero to disable CPU-hotplug testing.
2159 locktorture.shuffle_interval= [KNL]
2160 Set task-shuffle interval (jiffies). Shuffling
2161 tasks allows some CPUs to go into dyntick-idle
2162 mode during the locktorture test.
2164 locktorture.shutdown_secs= [KNL]
2165 Set time (s) after boot system shutdown. This
2166 is useful for hands-off automated testing.
2168 locktorture.stat_interval= [KNL]
2169 Time (s) between statistics printk()s.
2171 locktorture.stutter= [KNL]
2172 Time (s) to stutter testing, for example,
2173 specifying five seconds causes the test to run for
2174 five seconds, wait for five seconds, and so on.
2175 This tests the locking primitive's ability to
2176 transition abruptly to and from idle.
2178 locktorture.torture_type= [KNL]
2179 Specify the locking implementation to test.
2181 locktorture.verbose= [KNL]
2182 Enable additional printk() statements.
2184 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2185 Format: <irq>
2187 loglevel= All Kernel Messages with a loglevel smaller than the
2188 console loglevel will be printed to the console. It can
2189 also be changed with klogd or other programs. The
2190 loglevels are defined as follows:
2192 0 (KERN_EMERG) system is unusable
2193 1 (KERN_ALERT) action must be taken immediately
2194 2 (KERN_CRIT) critical conditions
2195 3 (KERN_ERR) error conditions
2196 4 (KERN_WARNING) warning conditions
2197 5 (KERN_NOTICE) normal but significant condition
2198 6 (KERN_INFO) informational
2199 7 (KERN_DEBUG) debug-level messages
2201 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2202 in bytes. n must be a power of two and greater
2203 than the minimal size. The minimal size is defined
2204 by LOG_BUF_SHIFT kernel config parameter. There is
2205 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2206 that allows to increase the default size depending on
2207 the number of CPUs. See init/Kconfig for more details.
2209 logo.nologo [FB] Disables display of the built-in Linux logo.
2210 This may be used to provide more screen space for
2211 kernel log messages and is useful when debugging
2212 kernel boot problems.
2214 lp=0 [LP] Specify parallel ports to use, e.g,
2215 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2216 lp=reset first parallel port). 'lp=0' disables the
2217 lp=auto printer driver. 'lp=reset' (which can be
2218 specified in addition to the ports) causes
2219 attached printers to be reset. Using
2220 lp=port1,port2,... specifies the parallel ports
2221 to associate lp devices with, starting with
2222 lp0. A port specification may be 'none' to skip
2223 that lp device, or a parport name such as
2224 'parport0'. Specifying 'lp=auto' instead of a
2225 port specification list means that device IDs
2226 from each port should be examined, to see if
2227 an IEEE 1284-compliant printer is attached; if
2228 so, the driver will manage that printer.
2229 See also header of drivers/char/lp.c.
2231 lpj=n [KNL]
2232 Sets loops_per_jiffy to given constant, thus avoiding
2233 time-consuming boot-time autodetection (up to 250 ms per
2234 CPU). 0 enables autodetection (default). To determine
2235 the correct value for your kernel, boot with normal
2236 autodetection and see what value is printed. Note that
2237 on SMP systems the preset will be applied to all CPUs,
2238 which is likely to cause problems if your CPUs need
2239 significantly divergent settings. An incorrect value
2240 will cause delays in the kernel to be wrong, leading to
2241 unpredictable I/O errors and other breakage. Although
2242 unlikely, in the extreme case this might damage your
2243 hardware.
2245 ltpc= [NET]
2246 Format: <io>,<irq>,<dma>
2248 machvec= [IA-64] Force the use of a particular machine-vector
2249 (machvec) in a generic kernel.
2250 Example: machvec=hpzx1_swiotlb
2252 machtype= [Loongson] Share the same kernel image file between different
2253 yeeloong laptop.
2254 Example: machtype=lemote-yeeloong-2f-7inch
2256 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2257 than or equal to this physical address is ignored.
2259 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2260 will bring up during bootup. maxcpus=n : n >= 0 limits
2261 the kernel to bring up 'n' processors. Surely after
2262 bootup you can bring up the other plugged cpu by executing
2263 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2264 only takes effect during system bootup.
2265 While n=0 is a special case, it is equivalent to "nosmp",
2266 which also disables the IO APIC.
2268 max_loop= [LOOP] The number of loop block devices that get
2269 (loop.max_loop) unconditionally pre-created at init time. The default
2270 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2271 of statically allocating a predefined number, loop
2272 devices can be requested on-demand with the
2273 /dev/loop-control interface.
2275 mce [X86-32] Machine Check Exception
2277 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2279 md= [HW] RAID subsystems devices and level
2280 See Documentation/admin-guide/md.rst.
2282 mdacon= [MDA]
2283 Format: <first>,<last>
2284 Specifies range of consoles to be captured by the MDA.
2286 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2287 Amount of memory to be used when the kernel is not able
2288 to see the whole system memory or for test.
2289 [X86] Work as limiting max address. Use together
2290 with memmap= to avoid physical address space collisions.
2291 Without memmap= PCI devices could be placed at addresses
2292 belonging to unused RAM.
2294 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2295 memory.
2297 memchunk=nn[KMG]
2298 [KNL,SH] Allow user to override the default size for
2299 per-device physically contiguous DMA buffers.
2301 memhp_default_state=online/offline
2302 [KNL] Set the initial state for the memory hotplug
2303 onlining policy. If not specified, the default value is
2304 set according to the
2305 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2306 option.
2307 See Documentation/memory-hotplug.txt.
2309 memmap=exactmap [KNL,X86] Enable setting of an exact
2310 E820 memory map, as specified by the user.
2311 Such memmap=exactmap lines can be constructed based on
2312 BIOS output or other requirements. See the memmap=nn@ss
2313 option description.
2315 memmap=nn[KMG]@ss[KMG]
2316 [KNL] Force usage of a specific region of memory.
2317 Region of memory to be used is from ss to ss+nn.
2318 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2319 which limits max address to nn[KMG].
2320 Multiple different regions can be specified,
2321 comma delimited.
2322 Example:
2323 memmap=100M@2G,100M#3G,1G!1024G
2325 memmap=nn[KMG]#ss[KMG]
2326 [KNL,ACPI] Mark specific memory as ACPI data.
2327 Region of memory to be marked is from ss to ss+nn.
2329 memmap=nn[KMG]$ss[KMG]
2330 [KNL,ACPI] Mark specific memory as reserved.
2331 Region of memory to be reserved is from ss to ss+nn.
2332 Example: Exclude memory from 0x18690000-0x1869ffff
2333 memmap=64K$0x18690000
2334 or
2335 memmap=0x10000$0x18690000
2336 Some bootloaders may need an escape character before '$',
2337 like Grub2, otherwise '$' and the following number
2338 will be eaten.
2340 memmap=nn[KMG]!ss[KMG]
2341 [KNL,X86] Mark specific memory as protected.
2342 Region of memory to be used, from ss to ss+nn.
2343 The memory region may be marked as e820 type 12 (0xc)
2344 and is NVDIMM or ADR memory.
2346 memmap=<size>%<offset>-<oldtype>+<newtype>
2347 [KNL,ACPI] Convert memory within the specified region
2348 from <oldtype> to <newtype>. If "-<oldtype>" is left
2349 out, the whole region will be marked as <newtype>,
2350 even if previously unavailable. If "+<newtype>" is left
2351 out, matching memory will be removed. Types are
2352 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2353 3 = ACPI, 12 = PRAM.
2355 memory_corruption_check=0/1 [X86]
2356 Some BIOSes seem to corrupt the first 64k of
2357 memory when doing things like suspend/resume.
2358 Setting this option will scan the memory
2359 looking for corruption. Enabling this will
2360 both detect corruption and prevent the kernel
2361 from using the memory being corrupted.
2362 However, its intended as a diagnostic tool; if
2363 repeatable BIOS-originated corruption always
2364 affects the same memory, you can use memmap=
2365 to prevent the kernel from using that memory.
2367 memory_corruption_check_size=size [X86]
2368 By default it checks for corruption in the low
2369 64k, making this memory unavailable for normal
2370 use. Use this parameter to scan for
2371 corruption in more or less memory.
2373 memory_corruption_check_period=seconds [X86]
2374 By default it checks for corruption every 60
2375 seconds. Use this parameter to check at some
2376 other rate. 0 disables periodic checking.
2378 memtest= [KNL,X86,ARM] Enable memtest
2379 Format: <integer>
2380 default : 0 <disable>
2381 Specifies the number of memtest passes to be
2382 performed. Each pass selects another test
2383 pattern from a given set of patterns. Memtest
2384 fills the memory with this pattern, validates
2385 memory contents and reserves bad memory
2386 regions that are detected.
2388 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2389 Valid arguments: on, off
2390 Default (depends on kernel configuration option):
2391 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2392 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2393 mem_encrypt=on: Activate SME
2394 mem_encrypt=off: Do not activate SME
2396 Refer to Documentation/x86/amd-memory-encryption.txt
2397 for details on when memory encryption can be activated.
2399 mem_sleep_default= [SUSPEND] Default system suspend mode:
2400 s2idle - Suspend-To-Idle
2401 shallow - Power-On Suspend or equivalent (if supported)
2402 deep - Suspend-To-RAM or equivalent (if supported)
2403 See Documentation/admin-guide/pm/sleep-states.rst.
2405 meye.*= [HW] Set MotionEye Camera parameters
2406 See Documentation/media/v4l-drivers/meye.rst.
2408 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2409 Multi-Function General Purpose Timers on AMD Geode
2410 platforms.
2412 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2413 the BIOS has incorrectly applied a workaround. TinyBIOS
2414 version 0.98 is known to be affected, 0.99 fixes the
2415 problem by letting the user disable the workaround.
2417 mga= [HW,DRM]
2419 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2420 physical address is ignored.
2422 mini2440= [ARM,HW,KNL]
2423 Format:[0..2][b][c][t]
2424 Default: "0tb"
2425 MINI2440 configuration specification:
2426 0 - The attached screen is the 3.5" TFT
2427 1 - The attached screen is the 7" TFT
2428 2 - The VGA Shield is attached (1024x768)
2429 Leaving out the screen size parameter will not load
2430 the TFT driver, and the framebuffer will be left
2431 unconfigured.
2432 b - Enable backlight. The TFT backlight pin will be
2433 linked to the kernel VESA blanking code and a GPIO
2434 LED. This parameter is not necessary when using the
2435 VGA shield.
2436 c - Enable the s3c camera interface.
2437 t - Reserved for enabling touchscreen support. The
2438 touchscreen support is not enabled in the mainstream
2439 kernel as of 2.6.30, a preliminary port can be found
2440 in the "bleeding edge" mini2440 support kernel at
2441 http://repo.or.cz/w/linux-2.6/mini2440.git
2443 mminit_loglevel=
2444 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2445 parameter allows control of the logging verbosity for
2446 the additional memory initialisation checks. A value
2447 of 0 disables mminit logging and a level of 4 will
2448 log everything. Information is printed at KERN_DEBUG
2449 so loglevel=8 may also need to be specified.
2451 module.sig_enforce
2452 [KNL] When CONFIG_MODULE_SIG is set, this means that
2453 modules without (valid) signatures will fail to load.
2454 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2455 is always true, so this option does nothing.
2457 module_blacklist= [KNL] Do not load a comma-separated list of
2458 modules. Useful for debugging problem modules.
2460 mousedev.tap_time=
2461 [MOUSE] Maximum time between finger touching and
2462 leaving touchpad surface for touch to be considered
2463 a tap and be reported as a left button click (for
2464 touchpads working in absolute mode only).
2465 Format: <msecs>
2466 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2467 reporting absolute coordinates, such as tablets
2468 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2469 reporting absolute coordinates, such as tablets
2471 movablecore= [KNL,X86,IA-64,PPC]
2472 Format: nn[KMGTPE] | nn%
2473 This parameter is the complement to kernelcore=, it
2474 specifies the amount of memory used for migratable
2475 allocations. If both kernelcore and movablecore is
2476 specified, then kernelcore will be at *least* the
2477 specified value but may be more. If movablecore on its
2478 own is specified, the administrator must be careful
2479 that the amount of memory usable for all allocations
2480 is not too small.
2482 movable_node [KNL] Boot-time switch to make hotplugable memory
2483 NUMA nodes to be movable. This means that the memory
2484 of such nodes will be usable only for movable
2485 allocations which rules out almost all kernel
2486 allocations. Use with caution!
2488 MTD_Partition= [MTD]
2489 Format: <name>,<region-number>,<size>,<offset>
2491 MTD_Region= [MTD] Format:
2492 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2494 mtdparts= [MTD]
2495 See drivers/mtd/cmdlinepart.c.
2497 multitce=off [PPC] This parameter disables the use of the pSeries
2498 firmware feature for updating multiple TCE entries
2499 at a time.
2501 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2503 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2505 boundary - index of last SLC block on Flex-OneNAND.
2506 The remaining blocks are configured as MLC blocks.
2507 lock - Configure if Flex-OneNAND boundary should be locked.
2508 Once locked, the boundary cannot be changed.
2509 1 indicates lock status, 0 indicates unlock status.
2511 mtdset= [ARM]
2512 ARM/S3C2412 JIVE boot control
2514 See arch/arm/mach-s3c2412/mach-jive.c
2516 mtouchusb.raw_coordinates=
2517 [HW] Make the MicroTouch USB driver use raw coordinates
2518 ('y', default) or cooked coordinates ('n')
2520 mtrr_chunk_size=nn[KMG] [X86]
2521 used for mtrr cleanup. It is largest continuous chunk
2522 that could hold holes aka. UC entries.
2524 mtrr_gran_size=nn[KMG] [X86]
2525 Used for mtrr cleanup. It is granularity of mtrr block.
2526 Default is 1.
2527 Large value could prevent small alignment from
2528 using up MTRRs.
2530 mtrr_spare_reg_nr=n [X86]
2531 Format: <integer>
2532 Range: 0,7 : spare reg number
2533 Default : 1
2534 Used for mtrr cleanup. It is spare mtrr entries number.
2535 Set to 2 or more if your graphical card needs more.
2537 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2539 netdev= [NET] Network devices parameters
2540 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2541 Note that mem_start is often overloaded to mean
2542 something different and driver-specific.
2543 This usage is only documented in each driver source
2544 file if at all.
2546 nf_conntrack.acct=
2547 [NETFILTER] Enable connection tracking flow accounting
2548 0 to disable accounting
2549 1 to enable accounting
2550 Default value is 0.
2552 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2553 See Documentation/filesystems/nfs/nfsroot.txt.
2555 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2556 See Documentation/filesystems/nfs/nfsroot.txt.
2558 nfsrootdebug [NFS] enable nfsroot debugging messages.
2559 See Documentation/filesystems/nfs/nfsroot.txt.
2561 nfs.callback_nr_threads=
2562 [NFSv4] set the total number of threads that the
2563 NFS client will assign to service NFSv4 callback
2564 requests.
2566 nfs.callback_tcpport=
2567 [NFS] set the TCP port on which the NFSv4 callback
2568 channel should listen.
2570 nfs.cache_getent=
2571 [NFS] sets the pathname to the program which is used
2572 to update the NFS client cache entries.
2574 nfs.cache_getent_timeout=
2575 [NFS] sets the timeout after which an attempt to
2576 update a cache entry is deemed to have failed.
2578 nfs.idmap_cache_timeout=
2579 [NFS] set the maximum lifetime for idmapper cache
2580 entries.
2582 nfs.enable_ino64=
2583 [NFS] enable 64-bit inode numbers.
2584 If zero, the NFS client will fake up a 32-bit inode
2585 number for the readdir() and stat() syscalls instead
2586 of returning the full 64-bit number.
2587 The default is to return 64-bit inode numbers.
2589 nfs.max_session_cb_slots=
2590 [NFSv4.1] Sets the maximum number of session
2591 slots the client will assign to the callback
2592 channel. This determines the maximum number of
2593 callbacks the client will process in parallel for
2594 a particular server.
2596 nfs.max_session_slots=
2597 [NFSv4.1] Sets the maximum number of session slots
2598 the client will attempt to negotiate with the server.
2599 This limits the number of simultaneous RPC requests
2600 that the client can send to the NFSv4.1 server.
2601 Note that there is little point in setting this
2602 value higher than the max_tcp_slot_table_limit.
2604 nfs.nfs4_disable_idmapping=
2605 [NFSv4] When set to the default of '1', this option
2606 ensures that both the RPC level authentication
2607 scheme and the NFS level operations agree to use
2608 numeric uids/gids if the mount is using the
2609 'sec=sys' security flavour. In effect it is
2610 disabling idmapping, which can make migration from
2611 legacy NFSv2/v3 systems to NFSv4 easier.
2612 Servers that do not support this mode of operation
2613 will be autodetected by the client, and it will fall
2614 back to using the idmapper.
2615 To turn off this behaviour, set the value to '0'.
2616 nfs.nfs4_unique_id=
2617 [NFS4] Specify an additional fixed unique ident-
2618 ification string that NFSv4 clients can insert into
2619 their nfs_client_id4 string. This is typically a
2620 UUID that is generated at system install time.
2622 nfs.send_implementation_id =
2623 [NFSv4.1] Send client implementation identification
2624 information in exchange_id requests.
2625 If zero, no implementation identification information
2626 will be sent.
2627 The default is to send the implementation identification
2628 information.
2630 nfs.recover_lost_locks =
2631 [NFSv4] Attempt to recover locks that were lost due
2632 to a lease timeout on the server. Please note that
2633 doing this risks data corruption, since there are
2634 no guarantees that the file will remain unchanged
2635 after the locks are lost.
2636 If you want to enable the kernel legacy behaviour of
2637 attempting to recover these locks, then set this
2638 parameter to '1'.
2639 The default parameter value of '0' causes the kernel
2640 not to attempt recovery of lost locks.
2642 nfs4.layoutstats_timer =
2643 [NFSv4.2] Change the rate at which the kernel sends
2644 layoutstats to the pNFS metadata server.
2646 Setting this to value to 0 causes the kernel to use
2647 whatever value is the default set by the layout
2648 driver. A non-zero value sets the minimum interval
2649 in seconds between layoutstats transmissions.
2651 nfsd.nfs4_disable_idmapping=
2652 [NFSv4] When set to the default of '1', the NFSv4
2653 server will return only numeric uids and gids to
2654 clients using auth_sys, and will accept numeric uids
2655 and gids from such clients. This is intended to ease
2656 migration from NFSv2/v3.
2658 nmi_debug= [KNL,SH] Specify one or more actions to take
2659 when a NMI is triggered.
2660 Format: [state][,regs][,debounce][,die]
2662 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2663 Format: [panic,][nopanic,][num]
2664 Valid num: 0 or 1
2665 0 - turn hardlockup detector in nmi_watchdog off
2666 1 - turn hardlockup detector in nmi_watchdog on
2667 When panic is specified, panic when an NMI watchdog
2668 timeout occurs (or 'nopanic' to override the opposite
2669 default). To disable both hard and soft lockup detectors,
2670 please see 'nowatchdog'.
2671 This is useful when you use a panic=... timeout and
2672 need the box quickly up again.
2674 These settings can be accessed at runtime via
2675 the nmi_watchdog and hardlockup_panic sysctls.
2677 netpoll.carrier_timeout=
2678 [NET] Specifies amount of time (in seconds) that
2679 netpoll should wait for a carrier. By default netpoll
2680 waits 4 seconds.
2682 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2683 emulation library even if a 387 maths coprocessor
2684 is present.
2686 no5lvl [X86-64] Disable 5-level paging mode. Forces
2687 kernel to use 4-level paging instead.
2689 no_console_suspend
2690 [HW] Never suspend the console
2691 Disable suspending of consoles during suspend and
2692 hibernate operations. Once disabled, debugging
2693 messages can reach various consoles while the rest
2694 of the system is being put to sleep (ie, while
2695 debugging driver suspend/resume hooks). This may
2696 not work reliably with all consoles, but is known
2697 to work with serial and VGA consoles.
2698 To facilitate more flexible debugging, we also add
2699 console_suspend, a printk module parameter to control
2700 it. Users could use console_suspend (usually
2701 /sys/module/printk/parameters/console_suspend) to
2702 turn on/off it dynamically.
2704 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2705 caches in the slab allocator. Saves per-node memory,
2706 but will impact performance.
2708 noalign [KNL,ARM]
2710 noaltinstr [S390] Disables alternative instructions patching
2711 (CPU alternatives feature).
2713 noapic [SMP,APIC] Tells the kernel to not make use of any
2714 IOAPICs that may be present in the system.
2716 noautogroup Disable scheduler automatic task group creation.
2718 nobats [PPC] Do not use BATs for mapping kernel lowmem
2719 on "Classic" PPC cores.
2721 nocache [ARM]
2723 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2725 nodelayacct [KNL] Disable per-task delay accounting
2727 nodsp [SH] Disable hardware DSP at boot time.
2729 noefi Disable EFI runtime services support.
2731 noexec [IA-64]
2733 noexec [X86]
2734 On X86-32 available only on PAE configured kernels.
2735 noexec=on: enable non-executable mappings (default)
2736 noexec=off: disable non-executable mappings
2738 nosmap [X86]
2739 Disable SMAP (Supervisor Mode Access Prevention)
2740 even if it is supported by processor.
2742 nosmep [X86]
2743 Disable SMEP (Supervisor Mode Execution Prevention)
2744 even if it is supported by processor.
2746 noexec32 [X86-64]
2747 This affects only 32-bit executables.
2748 noexec32=on: enable non-executable mappings (default)
2749 read doesn't imply executable mappings
2750 noexec32=off: disable non-executable mappings
2751 read implies executable mappings
2753 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2755 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2756 register save and restore. The kernel will only save
2757 legacy floating-point registers on task switch.
2759 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2761 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2762 Equivalent to smt=1.
2764 [KNL,x86] Disable symmetric multithreading (SMT).
2765 nosmt=force: Force disable SMT, cannot be undone
2766 via the sysfs control file.
2768 nospectre_v2 [X86] Disable all mitigations for the Spectre variant 2
2769 (indirect branch prediction) vulnerability. System may
2770 allow data leaks with this option, which is equivalent
2771 to spectre_v2=off.
2773 nospec_store_bypass_disable
2774 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
2776 noxsave [BUGS=X86] Disables x86 extended register state save
2777 and restore using xsave. The kernel will fallback to
2778 enabling legacy floating-point and sse state.
2780 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2781 register states. The kernel will fall back to use
2782 xsave to save the states. By using this parameter,
2783 performance of saving the states is degraded because
2784 xsave doesn't support modified optimization while
2785 xsaveopt supports it on xsaveopt enabled systems.
2787 noxsaves [X86] Disables xsaves and xrstors used in saving and
2788 restoring x86 extended register state in compacted
2789 form of xsave area. The kernel will fall back to use
2790 xsaveopt and xrstor to save and restore the states
2791 in standard form of xsave area. By using this
2792 parameter, xsave area per process might occupy more
2793 memory on xsaves enabled systems.
2795 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2796 wfi(ARM) instruction doesn't work correctly and not to
2797 use it. This is also useful when using JTAG debugger.
2799 no_file_caps Tells the kernel not to honor file capabilities. The
2800 only way then for a file to be executed with privilege
2801 is to be setuid root or executed by root.
2803 nohalt [IA-64] Tells the kernel not to use the power saving
2804 function PAL_HALT_LIGHT when idle. This increases
2805 power-consumption. On the positive side, it reduces
2806 interrupt wake-up latency, which may improve performance
2807 in certain environments such as networked servers or
2808 real-time systems.
2810 nohibernate [HIBERNATION] Disable hibernation and resume.
2812 nohz= [KNL] Boottime enable/disable dynamic ticks
2813 Valid arguments: on, off
2814 Default: on
2816 nohz_full= [KNL,BOOT,SMP,ISOL]
2817 The argument is a cpu list, as described above.
2818 In kernels built with CONFIG_NO_HZ_FULL=y, set
2819 the specified list of CPUs whose tick will be stopped
2820 whenever possible. The boot CPU will be forced outside
2821 the range to maintain the timekeeping. Any CPUs
2822 in this list will have their RCU callbacks offloaded,
2823 just as if they had also been called out in the
2824 rcu_nocbs= boot parameter.
2826 noiotrap [SH] Disables trapped I/O port accesses.
2828 noirqdebug [X86-32] Disables the code which attempts to detect and
2829 disable unhandled interrupt sources.
2831 no_timer_check [X86,APIC] Disables the code which tests for
2832 broken timer IRQ sources.
2834 noisapnp [ISAPNP] Disables ISA PnP code.
2836 noinitrd [RAM] Tells the kernel not to load any configured
2837 initial RAM disk.
2839 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2840 remapping.
2841 [Deprecated - use intremap=off]
2843 nointroute [IA-64]
2845 noinvpcid [X86] Disable the INVPCID cpu feature.
2847 nojitter [IA-64] Disables jitter checking for ITC timers.
2849 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2851 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2852 fault handling.
2854 no-vmw-sched-clock
2855 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2856 clock and use the default one.
2858 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2859 steal time is computed, but won't influence scheduler
2860 behaviour
2862 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2864 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2866 noltlbs [PPC] Do not use large page/tlb entries for kernel
2867 lowmem mapping on PPC40x and PPC8xx
2869 nomca [IA-64] Disable machine check abort handling
2871 nomce [X86-32] Disable Machine Check Exception
2873 nomfgpt [X86-32] Disable Multi-Function General Purpose
2874 Timer usage (for AMD Geode machines).
2876 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2877 shutdown the other cpus. Instead use the REBOOT_VECTOR
2878 irq.
2880 nomodule Disable module load
2882 nopat [X86] Disable PAT (page attribute table extension of
2883 pagetables) support.
2885 nopcid [X86-64] Disable the PCID cpu feature.
2887 norandmaps Don't use address space randomization. Equivalent to
2888 echo 0 > /proc/sys/kernel/randomize_va_space
2890 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2891 with UP alternatives
2893 nordrand [X86] Disable kernel use of the RDRAND and
2894 RDSEED instructions even if they are supported
2895 by the processor. RDRAND and RDSEED are still
2896 available to user space applications.
2898 noresume [SWSUSP] Disables resume and restores original swap
2899 space.
2901 no-scroll [VGA] Disables scrollback.
2902 This is required for the Braillex ib80-piezo Braille
2903 reader made by F.H. Papenmeier (Germany).
2905 nosbagart [IA-64]
2907 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2909 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2910 and disable the IO APIC. legacy for "maxcpus=0".
2912 nosoftlockup [KNL] Disable the soft-lockup detector.
2914 nosync [HW,M68K] Disables sync negotiation for all devices.
2916 notsc [BUGS=X86-32] Disable Time Stamp Counter
2918 nowatchdog [KNL] Disable both lockup detectors, i.e.
2919 soft-lockup and NMI watchdog (hard-lockup).
2921 nowb [ARM]
2923 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2925 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2926 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2927 Some features depend on CPU0. Known dependencies are:
2928 1. Resume from suspend/hibernate depends on CPU0.
2929 Suspend/hibernate will fail if CPU0 is offline and you
2930 need to online CPU0 before suspend/hibernate.
2931 2. PIC interrupts also depend on CPU0. CPU0 can't be
2932 removed if a PIC interrupt is detected.
2933 It's said poweroff/reboot may depend on CPU0 on some
2934 machines although I haven't seen such issues so far
2935 after CPU0 is offline on a few tested machines.
2936 If the dependencies are under your control, you can
2937 turn on cpu0_hotplug.
2939 nps_mtm_hs_ctr= [KNL,ARC]
2940 This parameter sets the maximum duration, in
2941 cycles, each HW thread of the CTOP can run
2942 without interruptions, before HW switches it.
2943 The actual maximum duration is 16 times this
2944 parameter's value.
2945 Format: integer between 1 and 255
2946 Default: 255
2948 nptcg= [IA-64] Override max number of concurrent global TLB
2949 purges which is reported from either PAL_VM_SUMMARY or
2950 SAL PALO.
2952 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2953 could support. nr_cpus=n : n >= 1 limits the kernel to
2954 support 'n' processors. It could be larger than the
2955 number of already plugged CPU during bootup, later in
2956 runtime you can physically add extra cpu until it reaches
2957 n. So during boot up some boot time memory for per-cpu
2958 variables need be pre-allocated for later physical cpu
2959 hot plugging.
2961 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2963 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2964 Allowed values are enable and disable
2966 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2967 'node', 'default' can be specified
2968 This can be set from sysctl after boot.
2969 See Documentation/sysctl/vm.txt for details.
2971 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2972 See Documentation/debugging-via-ohci1394.txt for more
2973 info.
2975 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2976 Rather than timing out after 20 ms if an EC
2977 command is not properly ACKed, override the length
2978 of the timeout. We have interrupts disabled while
2979 waiting for the ACK, so if this is set too high
2980 interrupts *may* be lost!
2982 omap_mux= [OMAP] Override bootloader pin multiplexing.
2983 Format: <mux_mode0.mode_name=value>...
2984 For example, to override I2C bus2:
2985 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2987 oprofile.timer= [HW]
2988 Use timer interrupt instead of performance counters
2990 oprofile.cpu_type= Force an oprofile cpu type
2991 This might be useful if you have an older oprofile
2992 userland or if you want common events.
2993 Format: { arch_perfmon }
2994 arch_perfmon: [X86] Force use of architectural
2995 perfmon on Intel CPUs instead of the
2996 CPU specific event set.
2997 timer: [X86] Force use of architectural NMI
2998 timer mode (see also oprofile.timer
2999 for generic hr timer mode)
3001 oops=panic Always panic on oopses. Default is to just kill the
3002 process, but there is a small probability of
3003 deadlocking the machine.
3004 This will also cause panics on machine check exceptions.
3005 Useful together with panic=30 to trigger a reboot.
3007 page_owner= [KNL] Boot-time page_owner enabling option.
3008 Storage of the information about who allocated
3009 each page is disabled in default. With this switch,
3010 we can turn it on.
3011 on: enable the feature
3013 page_poison= [KNL] Boot-time parameter changing the state of
3014 poisoning on the buddy allocator.
3015 off: turn off poisoning
3016 on: turn on poisoning
3018 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3019 timeout > 0: seconds before rebooting
3020 timeout = 0: wait forever
3021 timeout < 0: reboot immediately
3022 Format: <timeout>
3024 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3025 on a WARN().
3027 crash_kexec_post_notifiers
3028 Run kdump after running panic-notifiers and dumping
3029 kmsg. This only for the users who doubt kdump always
3030 succeeds in any situation.
3031 Note that this also increases risks of kdump failure,
3032 because some panic notifiers can make the crashed
3033 kernel more unstable.
3035 parkbd.port= [HW] Parallel port number the keyboard adapter is
3036 connected to, default is 0.
3037 Format: <parport#>
3038 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3039 0 for XT, 1 for AT (default is AT).
3040 Format: <mode>
3042 parport= [HW,PPT] Specify parallel ports. 0 disables.
3043 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3044 Use 'auto' to force the driver to use any
3045 IRQ/DMA settings detected (the default is to
3046 ignore detected IRQ/DMA settings because of
3047 possible conflicts). You can specify the base
3048 address, IRQ, and DMA settings; IRQ and DMA
3049 should be numbers, or 'auto' (for using detected
3050 settings on that particular port), or 'nofifo'
3051 (to avoid using a FIFO even if it is detected).
3052 Parallel ports are assigned in the order they
3053 are specified on the command line, starting
3054 with parport0.
3056 parport_init_mode= [HW,PPT]
3057 Configure VIA parallel port to operate in
3058 a specific mode. This is necessary on Pegasos
3059 computer where firmware has no options for setting
3060 up parallel port mode and sets it to spp.
3061 Currently this function knows 686a and 8231 chips.
3062 Format: [spp|ps2|epp|ecp|ecpepp]
3064 pause_on_oops=
3065 Halt all CPUs after the first oops has been printed for
3066 the specified number of seconds. This is to be used if
3067 your oopses keep scrolling off the screen.
3069 pcbit= [HW,ISDN]
3071 pcd. [PARIDE]
3072 See header of drivers/block/paride/pcd.c.
3073 See also Documentation/blockdev/paride.txt.
3075 pci=option[,option...] [PCI] various PCI subsystem options:
3076 earlydump [X86] dump PCI config space before the kernel
3077 changes anything
3078 off [X86] don't probe for the PCI bus
3079 bios [X86-32] force use of PCI BIOS, don't access
3080 the hardware directly. Use this if your machine
3081 has a non-standard PCI host bridge.
3082 nobios [X86-32] disallow use of PCI BIOS, only direct
3083 hardware access methods are allowed. Use this
3084 if you experience crashes upon bootup and you
3085 suspect they are caused by the BIOS.
3086 conf1 [X86] Force use of PCI Configuration Access
3087 Mechanism 1 (config address in IO port 0xCF8,
3088 data in IO port 0xCFC, both 32-bit).
3089 conf2 [X86] Force use of PCI Configuration Access
3090 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3091 the function, IO port 0xCFA, also 8-bit, sets
3092 bus number. The config space is then accessed
3093 through ports 0xC000-0xCFFF).
3094 See http://wiki.osdev.org/PCI for more info
3095 on the configuration access mechanisms.
3096 noaer [PCIE] If the PCIEAER kernel config parameter is
3097 enabled, this kernel boot option can be used to
3098 disable the use of PCIE advanced error reporting.
3099 nodomains [PCI] Disable support for multiple PCI
3100 root domains (aka PCI segments, in ACPI-speak).
3101 nommconf [X86] Disable use of MMCONFIG for PCI
3102 Configuration
3103 check_enable_amd_mmconf [X86] check for and enable
3104 properly configured MMIO access to PCI
3105 config space on AMD family 10h CPU
3106 nomsi [MSI] If the PCI_MSI kernel config parameter is
3107 enabled, this kernel boot option can be used to
3108 disable the use of MSI interrupts system-wide.
3109 noioapicquirk [APIC] Disable all boot interrupt quirks.
3110 Safety option to keep boot IRQs enabled. This
3111 should never be necessary.
3112 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3113 primary IO-APIC for bridges that cannot disable
3114 boot IRQs. This fixes a source of spurious IRQs
3115 when the system masks IRQs.
3116 noioapicreroute [APIC] Disable workaround that uses the
3117 boot IRQ equivalent of an IRQ that connects to
3118 a chipset where boot IRQs cannot be disabled.
3119 The opposite of ioapicreroute.
3120 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3121 routing table. These calls are known to be buggy
3122 on several machines and they hang the machine
3123 when used, but on other computers it's the only
3124 way to get the interrupt routing table. Try
3125 this option if the kernel is unable to allocate
3126 IRQs or discover secondary PCI buses on your
3127 motherboard.
3128 rom [X86] Assign address space to expansion ROMs.
3129 Use with caution as certain devices share
3130 address decoders between ROMs and other
3131 resources.
3132 norom [X86] Do not assign address space to
3133 expansion ROMs that do not already have
3134 BIOS assigned address ranges.
3135 nobar [X86] Do not assign address space to the
3136 BARs that weren't assigned by the BIOS.
3137 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3138 assigned automatically to PCI devices. You can
3139 make the kernel exclude IRQs of your ISA cards
3140 this way.
3141 pirqaddr=0xAAAAA [X86] Specify the physical address
3142 of the PIRQ table (normally generated
3143 by the BIOS) if it is outside the
3144 F0000h-100000h range.
3145 lastbus=N [X86] Scan all buses thru bus #N. Can be
3146 useful if the kernel is unable to find your
3147 secondary buses and you want to tell it
3148 explicitly which ones they are.
3149 assign-busses [X86] Always assign all PCI bus
3150 numbers ourselves, overriding
3151 whatever the firmware may have done.
3152 usepirqmask [X86] Honor the possible IRQ mask stored
3153 in the BIOS $PIR table. This is needed on
3154 some systems with broken BIOSes, notably
3155 some HP Pavilion N5400 and Omnibook XE3
3156 notebooks. This will have no effect if ACPI
3157 IRQ routing is enabled.
3158 noacpi [X86] Do not use ACPI for IRQ routing
3159 or for PCI scanning.
3160 use_crs [X86] Use PCI host bridge window information
3161 from ACPI. On BIOSes from 2008 or later, this
3162 is enabled by default. If you need to use this,
3163 please report a bug.
3164 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3165 If you need to use this, please report a bug.
3166 routeirq Do IRQ routing for all PCI devices.
3167 This is normally done in pci_enable_device(),
3168 so this option is a temporary workaround
3169 for broken drivers that don't call it.
3170 skip_isa_align [X86] do not align io start addr, so can
3171 handle more pci cards
3172 noearly [X86] Don't do any early type 1 scanning.
3173 This might help on some broken boards which
3174 machine check when some devices' config space
3175 is read. But various workarounds are disabled
3176 and some IOMMU drivers will not work.
3177 bfsort Sort PCI devices into breadth-first order.
3178 This sorting is done to get a device
3179 order compatible with older (<= 2.4) kernels.
3180 nobfsort Don't sort PCI devices into breadth-first order.
3181 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3182 tuning and use the BIOS-configured MPS defaults.
3183 pcie_bus_safe Set every device's MPS to the largest value
3184 supported by all devices below the root complex.
3185 pcie_bus_perf Set device MPS to the largest allowable MPS
3186 based on its parent bus. Also set MRRS (Max
3187 Read Request Size) to the largest supported
3188 value (no larger than the MPS that the device
3189 or bus can support) for best performance.
3190 pcie_bus_peer2peer Set every device's MPS to 128B, which
3191 every device is guaranteed to support. This
3192 configuration allows peer-to-peer DMA between
3193 any pair of devices, possibly at the cost of
3194 reduced performance. This also guarantees
3195 that hot-added devices will work.
3196 cbiosize=nn[KMG] The fixed amount of bus space which is
3197 reserved for the CardBus bridge's IO window.
3198 The default value is 256 bytes.
3199 cbmemsize=nn[KMG] The fixed amount of bus space which is
3200 reserved for the CardBus bridge's memory
3201 window. The default value is 64 megabytes.
3202 resource_alignment=
3203 Format:
3204 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3205 [<order of align>@]pci:<vendor>:<device>\
3206 [:<subvendor>:<subdevice>][; ...]
3207 Specifies alignment and device to reassign
3208 aligned memory resources.
3209 If <order of align> is not specified,
3210 PAGE_SIZE is used as alignment.
3211 PCI-PCI bridge can be specified, if resource
3212 windows need to be expanded.
3213 To specify the alignment for several
3214 instances of a device, the PCI vendor,
3215 device, subvendor, and subdevice may be
3216 specified, e.g., 4096@pci:8086:9c22:103c:198f
3217 ecrc= Enable/disable PCIe ECRC (transaction layer
3218 end-to-end CRC checking).
3219 bios: Use BIOS/firmware settings. This is the
3220 the default.
3221 off: Turn ECRC off
3222 on: Turn ECRC on.
3223 hpiosize=nn[KMG] The fixed amount of bus space which is
3224 reserved for hotplug bridge's IO window.
3225 Default size is 256 bytes.
3226 hpmemsize=nn[KMG] The fixed amount of bus space which is
3227 reserved for hotplug bridge's memory window.
3228 Default size is 2 megabytes.
3229 hpbussize=nn The minimum amount of additional bus numbers
3230 reserved for buses below a hotplug bridge.
3231 Default is 1.
3232 realloc= Enable/disable reallocating PCI bridge resources
3233 if allocations done by BIOS are too small to
3234 accommodate resources required by all child
3235 devices.
3236 off: Turn realloc off
3237 on: Turn realloc on
3238 realloc same as realloc=on
3239 noari do not use PCIe ARI.
3240 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
3241 do not use PCIe ATS (and IOMMU device IOTLB).
3242 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3243 only look for one device below a PCIe downstream
3244 port.
3245 big_root_window Try to add a big 64bit memory window to the PCIe
3246 root complex on AMD CPUs. Some GFX hardware
3247 can resize a BAR to allow access to all VRAM.
3248 Adding the window is slightly risky (it may
3249 conflict with unreported devices), so this
3250 taints the kernel.
3252 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3253 Management.
3254 off Disable ASPM.
3255 force Enable ASPM even on devices that claim not to support it.
3256 WARNING: Forcing ASPM on may cause system lockups.
3258 pcie_ports= [PCIE] PCIe port services handling:
3259 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
3260 even if the platform doesn't give the OS permission to
3261 use them. This may cause conflicts if the platform
3262 also tries to use these services.
3263 compat Disable native PCIe services (PME, AER, DPC, PCIe
3264 hotplug).
3266 pcie_port_pm= [PCIE] PCIe port power management handling:
3267 off Disable power management of all PCIe ports
3268 force Forcibly enable power management of all PCIe ports
3270 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3271 nomsi Do not use MSI for native PCIe PME signaling (this makes
3272 all PCIe root ports use INTx for all services).
3274 pcmv= [HW,PCMCIA] BadgePAD 4
3276 pd_ignore_unused
3277 [PM]
3278 Keep all power-domains already enabled by bootloader on,
3279 even if no driver has claimed them. This is useful
3280 for debug and development, but should not be
3281 needed on a platform with proper driver support.
3283 pd. [PARIDE]
3284 See Documentation/blockdev/paride.txt.
3286 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3287 boot time.
3288 Format: { 0 | 1 }
3289 See arch/parisc/kernel/pdc_chassis.c
3291 percpu_alloc= Select which percpu first chunk allocator to use.
3292 Currently supported values are "embed" and "page".
3293 Archs may support subset or none of the selections.
3294 See comments in mm/percpu.c for details on each
3295 allocator. This parameter is primarily for debugging
3296 and performance comparison.
3298 pf. [PARIDE]
3299 See Documentation/blockdev/paride.txt.
3301 pg. [PARIDE]
3302 See Documentation/blockdev/paride.txt.
3304 pirq= [SMP,APIC] Manual mp-table setup
3305 See Documentation/x86/i386/IO-APIC.txt.
3307 plip= [PPT,NET] Parallel port network link
3308 Format: { parport<nr> | timid | 0 }
3309 See also Documentation/admin-guide/parport.rst.
3311 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3312 Override pmtimer IOPort with a hex value.
3313 e.g. pmtmr=0x508
3315 pnp.debug=1 [PNP]
3316 Enable PNP debug messages (depends on the
3317 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3318 via /sys/module/pnp/parameters/debug. We always show
3319 current resource usage; turning this on also shows
3320 possible settings and some assignment information.
3322 pnpacpi= [ACPI]
3323 { off }
3325 pnpbios= [ISAPNP]
3326 { on | off | curr | res | no-curr | no-res }
3328 pnp_reserve_irq=
3329 [ISAPNP] Exclude IRQs for the autoconfiguration
3331 pnp_reserve_dma=
3332 [ISAPNP] Exclude DMAs for the autoconfiguration
3334 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3335 Ranges are in pairs (I/O port base and size).
3337 pnp_reserve_mem=
3338 [ISAPNP] Exclude memory regions for the
3339 autoconfiguration.
3340 Ranges are in pairs (memory base and size).
3342 ports= [IP_VS_FTP] IPVS ftp helper module
3343 Default is 21.
3344 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3345 may be specified.
3346 Format: <port>,<port>....
3348 powersave=off [PPC] This option disables power saving features.
3349 It specifically disables cpuidle and sets the
3350 platform machine description specific power_save
3351 function to NULL. On Idle the CPU just reduces
3352 execution priority.
3354 ppc_strict_facility_enable
3355 [PPC] This option catches any kernel floating point,
3356 Altivec, VSX and SPE outside of regions specifically
3357 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3358 There is some performance impact when enabling this.
3360 ppc_tm= [PPC]
3361 Format: {"off"}
3362 Disable Hardware Transactional Memory
3364 print-fatal-signals=
3365 [KNL] debug: print fatal signals
3367 If enabled, warn about various signal handling
3368 related application anomalies: too many signals,
3369 too many POSIX.1 timers, fatal signals causing a
3370 coredump - etc.
3372 If you hit the warning due to signal overflow,
3373 you might want to try "ulimit -i unlimited".
3375 default: off.
3377 printk.always_kmsg_dump=
3378 Trigger kmsg_dump for cases other than kernel oops or
3379 panics
3380 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3381 default: disabled
3383 printk.devkmsg={on,off,ratelimit}
3384 Control writing to /dev/kmsg.
3385 on - unlimited logging to /dev/kmsg from userspace
3386 off - logging to /dev/kmsg disabled
3387 ratelimit - ratelimit the logging
3388 Default: ratelimit
3390 printk.time= Show timing data prefixed to each printk message line
3391 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3393 processor.max_cstate= [HW,ACPI]
3394 Limit processor to maximum C-state
3395 max_cstate=9 overrides any DMI blacklist limit.
3397 processor.nocst [HW,ACPI]
3398 Ignore the _CST method to determine C-states,
3399 instead using the legacy FADT method
3401 profile= [KNL] Enable kernel profiling via /proc/profile
3402 Format: [<profiletype>,]<number>
3403 Param: <profiletype>: "schedule", "sleep", or "kvm"
3404 [defaults to kernel profiling]
3405 Param: "schedule" - profile schedule points.
3406 Param: "sleep" - profile D-state sleeping (millisecs).
3407 Requires CONFIG_SCHEDSTATS
3408 Param: "kvm" - profile VM exits.
3409 Param: <number> - step/bucket size as a power of 2 for
3410 statistical time based profiling.
3412 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3413 before loading.
3414 See Documentation/blockdev/ramdisk.txt.
3416 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3417 probe for; one of (bare|imps|exps|lifebook|any).
3418 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3419 per second.
3420 psmouse.resetafter= [HW,MOUSE]
3421 Try to reset the device after so many bad packets
3422 (0 = never).
3423 psmouse.resolution=
3424 [HW,MOUSE] Set desired mouse resolution, in dpi.
3425 psmouse.smartscroll=
3426 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3427 0 = disabled, 1 = enabled (default).
3429 pstore.backend= Specify the name of the pstore backend to use
3431 pt. [PARIDE]
3432 See Documentation/blockdev/paride.txt.
3434 pti= [X86_64] Control Page Table Isolation of user and
3435 kernel address spaces. Disabling this feature
3436 removes hardening, but improves performance of
3437 system calls and interrupts.
3439 on - unconditionally enable
3440 off - unconditionally disable
3441 auto - kernel detects whether your CPU model is
3442 vulnerable to issues that PTI mitigates
3444 Not specifying this option is equivalent to pti=auto.
3446 nopti [X86_64]
3447 Equivalent to pti=off
3449 pty.legacy_count=
3450 [KNL] Number of legacy pty's. Overwrites compiled-in
3451 default number.
3453 quiet [KNL] Disable most log messages
3455 r128= [HW,DRM]
3457 raid= [HW,RAID]
3458 See Documentation/admin-guide/md.rst.
3460 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3461 See Documentation/blockdev/ramdisk.txt.
3463 ras=option[,option,...] [KNL] RAS-specific options
3465 cec_disable [X86]
3466 Disable the Correctable Errors Collector,
3467 see CONFIG_RAS_CEC help text.
3469 rcu_nocbs= [KNL]
3470 The argument is a cpu list, as described above.
3472 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3473 the specified list of CPUs to be no-callback CPUs.
3474 Invocation of these CPUs' RCU callbacks will
3475 be offloaded to "rcuox/N" kthreads created for
3476 that purpose, where "x" is "b" for RCU-bh, "p"
3477 for RCU-preempt, and "s" for RCU-sched, and "N"
3478 is the CPU number. This reduces OS jitter on the
3479 offloaded CPUs, which can be useful for HPC and
3480 real-time workloads. It can also improve energy
3481 efficiency for asymmetric multiprocessors.
3483 rcu_nocb_poll [KNL]
3484 Rather than requiring that offloaded CPUs
3485 (specified by rcu_nocbs= above) explicitly
3486 awaken the corresponding "rcuoN" kthreads,
3487 make these kthreads poll for callbacks.
3488 This improves the real-time response for the
3489 offloaded CPUs by relieving them of the need to
3490 wake up the corresponding kthread, but degrades
3491 energy efficiency by requiring that the kthreads
3492 periodically wake up to do the polling.
3494 rcutree.blimit= [KNL]
3495 Set maximum number of finished RCU callbacks to
3496 process in one batch.
3498 rcutree.dump_tree= [KNL]
3499 Dump the structure of the rcu_node combining tree
3500 out at early boot. This is used for diagnostic
3501 purposes, to verify correct tree setup.
3503 rcutree.gp_cleanup_delay= [KNL]
3504 Set the number of jiffies to delay each step of
3505 RCU grace-period cleanup.
3507 rcutree.gp_init_delay= [KNL]
3508 Set the number of jiffies to delay each step of
3509 RCU grace-period initialization.
3511 rcutree.gp_preinit_delay= [KNL]
3512 Set the number of jiffies to delay each step of
3513 RCU grace-period pre-initialization, that is,
3514 the propagation of recent CPU-hotplug changes up
3515 the rcu_node combining tree.
3517 rcutree.rcu_fanout_exact= [KNL]
3518 Disable autobalancing of the rcu_node combining
3519 tree. This is used by rcutorture, and might
3520 possibly be useful for architectures having high
3521 cache-to-cache transfer latencies.
3523 rcutree.rcu_fanout_leaf= [KNL]
3524 Change the number of CPUs assigned to each
3525 leaf rcu_node structure. Useful for very
3526 large systems, which will choose the value 64,
3527 and for NUMA systems with large remote-access
3528 latencies, which will choose a value aligned
3529 with the appropriate hardware boundaries.
3531 rcutree.jiffies_till_sched_qs= [KNL]
3532 Set required age in jiffies for a
3533 given grace period before RCU starts
3534 soliciting quiescent-state help from
3535 rcu_note_context_switch().
3537 rcutree.jiffies_till_first_fqs= [KNL]
3538 Set delay from grace-period initialization to
3539 first attempt to force quiescent states.
3540 Units are jiffies, minimum value is zero,
3541 and maximum value is HZ.
3543 rcutree.jiffies_till_next_fqs= [KNL]
3544 Set delay between subsequent attempts to force
3545 quiescent states. Units are jiffies, minimum
3546 value is one, and maximum value is HZ.
3548 rcutree.kthread_prio= [KNL,BOOT]
3549 Set the SCHED_FIFO priority of the RCU per-CPU
3550 kthreads (rcuc/N). This value is also used for
3551 the priority of the RCU boost threads (rcub/N)
3552 and for the RCU grace-period kthreads (rcu_bh,
3553 rcu_preempt, and rcu_sched). If RCU_BOOST is
3554 set, valid values are 1-99 and the default is 1
3555 (the least-favored priority). Otherwise, when
3556 RCU_BOOST is not set, valid values are 0-99 and
3557 the default is zero (non-realtime operation).
3559 rcutree.rcu_nocb_leader_stride= [KNL]
3560 Set the number of NOCB kthread groups, which
3561 defaults to the square root of the number of
3562 CPUs. Larger numbers reduces the wakeup overhead
3563 on the per-CPU grace-period kthreads, but increases
3564 that same overhead on each group's leader.
3566 rcutree.qhimark= [KNL]
3567 Set threshold of queued RCU callbacks beyond which
3568 batch limiting is disabled.
3570 rcutree.qlowmark= [KNL]
3571 Set threshold of queued RCU callbacks below which
3572 batch limiting is re-enabled.
3574 rcutree.rcu_idle_gp_delay= [KNL]
3575 Set wakeup interval for idle CPUs that have
3576 RCU callbacks (RCU_FAST_NO_HZ=y).
3578 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3579 Set wakeup interval for idle CPUs that have
3580 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3581 Lazy RCU callbacks are those which RCU can
3582 prove do nothing more than free memory.
3584 rcutree.rcu_kick_kthreads= [KNL]
3585 Cause the grace-period kthread to get an extra
3586 wake_up() if it sleeps three times longer than
3587 it should at force-quiescent-state time.
3588 This wake_up() will be accompanied by a
3589 WARN_ONCE() splat and an ftrace_dump().
3591 rcuperf.gp_async= [KNL]
3592 Measure performance of asynchronous
3593 grace-period primitives such as call_rcu().
3595 rcuperf.gp_async_max= [KNL]
3596 Specify the maximum number of outstanding
3597 callbacks per writer thread. When a writer
3598 thread exceeds this limit, it invokes the
3599 corresponding flavor of rcu_barrier() to allow
3600 previously posted callbacks to drain.
3602 rcuperf.gp_exp= [KNL]
3603 Measure performance of expedited synchronous
3604 grace-period primitives.
3606 rcuperf.holdoff= [KNL]
3607 Set test-start holdoff period. The purpose of
3608 this parameter is to delay the start of the
3609 test until boot completes in order to avoid
3610 interference.
3612 rcuperf.nreaders= [KNL]
3613 Set number of RCU readers. The value -1 selects
3614 N, where N is the number of CPUs. A value
3615 "n" less than -1 selects N-n+1, where N is again
3616 the number of CPUs. For example, -2 selects N
3617 (the number of CPUs), -3 selects N+1, and so on.
3618 A value of "n" less than or equal to -N selects
3619 a single reader.
3621 rcuperf.nwriters= [KNL]
3622 Set number of RCU writers. The values operate
3623 the same as for rcuperf.nreaders.
3624 N, where N is the number of CPUs
3626 rcuperf.perf_type= [KNL]
3627 Specify the RCU implementation to test.
3629 rcuperf.shutdown= [KNL]
3630 Shut the system down after performance tests
3631 complete. This is useful for hands-off automated
3632 testing.
3634 rcuperf.verbose= [KNL]
3635 Enable additional printk() statements.
3637 rcuperf.writer_holdoff= [KNL]
3638 Write-side holdoff between grace periods,
3639 in microseconds. The default of zero says
3640 no holdoff.
3642 rcutorture.cbflood_inter_holdoff= [KNL]
3643 Set holdoff time (jiffies) between successive
3644 callback-flood tests.
3646 rcutorture.cbflood_intra_holdoff= [KNL]
3647 Set holdoff time (jiffies) between successive
3648 bursts of callbacks within a given callback-flood
3649 test.
3651 rcutorture.cbflood_n_burst= [KNL]
3652 Set the number of bursts making up a given
3653 callback-flood test. Set this to zero to
3654 disable callback-flood testing.
3656 rcutorture.cbflood_n_per_burst= [KNL]
3657 Set the number of callbacks to be registered
3658 in a given burst of a callback-flood test.
3660 rcutorture.fqs_duration= [KNL]
3661 Set duration of force_quiescent_state bursts
3662 in microseconds.
3664 rcutorture.fqs_holdoff= [KNL]
3665 Set holdoff time within force_quiescent_state bursts
3666 in microseconds.
3668 rcutorture.fqs_stutter= [KNL]
3669 Set wait time between force_quiescent_state bursts
3670 in seconds.
3672 rcutorture.gp_cond= [KNL]
3673 Use conditional/asynchronous update-side
3674 primitives, if available.
3676 rcutorture.gp_exp= [KNL]
3677 Use expedited update-side primitives, if available.
3679 rcutorture.gp_normal= [KNL]
3680 Use normal (non-expedited) asynchronous
3681 update-side primitives, if available.
3683 rcutorture.gp_sync= [KNL]
3684 Use normal (non-expedited) synchronous
3685 update-side primitives, if available. If all
3686 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3687 rcutorture.gp_normal=, and rcutorture.gp_sync=
3688 are zero, rcutorture acts as if is interpreted
3689 they are all non-zero.
3691 rcutorture.n_barrier_cbs= [KNL]
3692 Set callbacks/threads for rcu_barrier() testing.
3694 rcutorture.nfakewriters= [KNL]
3695 Set number of concurrent RCU writers. These just
3696 stress RCU, they don't participate in the actual
3697 test, hence the "fake".
3699 rcutorture.nreaders= [KNL]
3700 Set number of RCU readers. The value -1 selects
3701 N-1, where N is the number of CPUs. A value
3702 "n" less than -1 selects N-n-2, where N is again
3703 the number of CPUs. For example, -2 selects N
3704 (the number of CPUs), -3 selects N+1, and so on.
3706 rcutorture.object_debug= [KNL]
3707 Enable debug-object double-call_rcu() testing.
3709 rcutorture.onoff_holdoff= [KNL]
3710 Set time (s) after boot for CPU-hotplug testing.
3712 rcutorture.onoff_interval= [KNL]
3713 Set time (s) between CPU-hotplug operations, or
3714 zero to disable CPU-hotplug testing.
3716 rcutorture.shuffle_interval= [KNL]
3717 Set task-shuffle interval (s). Shuffling tasks
3718 allows some CPUs to go into dyntick-idle mode
3719 during the rcutorture test.
3721 rcutorture.shutdown_secs= [KNL]
3722 Set time (s) after boot system shutdown. This
3723 is useful for hands-off automated testing.
3725 rcutorture.stall_cpu= [KNL]
3726 Duration of CPU stall (s) to test RCU CPU stall
3727 warnings, zero to disable.
3729 rcutorture.stall_cpu_holdoff= [KNL]
3730 Time to wait (s) after boot before inducing stall.
3732 rcutorture.stall_cpu_irqsoff= [KNL]
3733 Disable interrupts while stalling if set.
3735 rcutorture.stat_interval= [KNL]
3736 Time (s) between statistics printk()s.
3738 rcutorture.stutter= [KNL]
3739 Time (s) to stutter testing, for example, specifying
3740 five seconds causes the test to run for five seconds,
3741 wait for five seconds, and so on. This tests RCU's
3742 ability to transition abruptly to and from idle.
3744 rcutorture.test_boost= [KNL]
3745 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3746 "Maybe" means test if the RCU implementation
3747 under test support RCU priority boosting.
3749 rcutorture.test_boost_duration= [KNL]
3750 Duration (s) of each individual boost test.
3752 rcutorture.test_boost_interval= [KNL]
3753 Interval (s) between each boost test.
3755 rcutorture.test_no_idle_hz= [KNL]
3756 Test RCU's dyntick-idle handling. See also the
3757 rcutorture.shuffle_interval parameter.
3759 rcutorture.torture_type= [KNL]
3760 Specify the RCU implementation to test.
3762 rcutorture.verbose= [KNL]
3763 Enable additional printk() statements.
3765 rcupdate.rcu_cpu_stall_suppress= [KNL]
3766 Suppress RCU CPU stall warning messages.
3768 rcupdate.rcu_cpu_stall_timeout= [KNL]
3769 Set timeout for RCU CPU stall warning messages.
3771 rcupdate.rcu_expedited= [KNL]
3772 Use expedited grace-period primitives, for
3773 example, synchronize_rcu_expedited() instead
3774 of synchronize_rcu(). This reduces latency,
3775 but can increase CPU utilization, degrade
3776 real-time latency, and degrade energy efficiency.
3777 No effect on CONFIG_TINY_RCU kernels.
3779 rcupdate.rcu_normal= [KNL]
3780 Use only normal grace-period primitives,
3781 for example, synchronize_rcu() instead of
3782 synchronize_rcu_expedited(). This improves
3783 real-time latency, CPU utilization, and
3784 energy efficiency, but can expose users to
3785 increased grace-period latency. This parameter
3786 overrides rcupdate.rcu_expedited. No effect on
3787 CONFIG_TINY_RCU kernels.
3789 rcupdate.rcu_normal_after_boot= [KNL]
3790 Once boot has completed (that is, after
3791 rcu_end_inkernel_boot() has been invoked), use
3792 only normal grace-period primitives. No effect
3793 on CONFIG_TINY_RCU kernels.
3795 rcupdate.rcu_task_stall_timeout= [KNL]
3796 Set timeout in jiffies for RCU task stall warning
3797 messages. Disable with a value less than or equal
3798 to zero.
3800 rcupdate.rcu_self_test= [KNL]
3801 Run the RCU early boot self tests
3803 rcupdate.rcu_self_test_bh= [KNL]
3804 Run the RCU bh early boot self tests
3806 rcupdate.rcu_self_test_sched= [KNL]
3807 Run the RCU sched early boot self tests
3809 rdinit= [KNL]
3810 Format: <full_path>
3811 Run specified binary instead of /init from the ramdisk,
3812 used for early userspace startup. See initrd.
3814 rdt= [HW,X86,RDT]
3815 Turn on/off individual RDT features. List is:
3816 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
3817 mba.
3818 E.g. to turn on cmt and turn off mba use:
3819 rdt=cmt,!mba
3821 reboot= [KNL]
3822 Format (x86 or x86_64):
3823 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3824 [[,]s[mp]#### \
3825 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3826 [[,]f[orce]
3827 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3828 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3829 reboot_force is either force or not specified,
3830 reboot_cpu is s[mp]#### with #### being the processor
3831 to be used for rebooting.
3833 relax_domain_level=
3834 [KNL, SMP] Set scheduler's default relax_domain_level.
3835 See Documentation/cgroup-v1/cpusets.txt.
3837 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
3838 Format: <base1>,<size1>[,<base2>,<size2>,...]
3839 Reserve I/O ports or memory so the kernel won't use
3840 them. If <base> is less than 0x10000, the region
3841 is assumed to be I/O ports; otherwise it is memory.
3843 reservetop= [X86-32]
3844 Format: nn[KMG]
3845 Reserves a hole at the top of the kernel virtual
3846 address space.
3848 reservelow= [X86]
3849 Format: nn[K]
3850 Set the amount of memory to reserve for BIOS at
3851 the bottom of the address space.
3853 reset_devices [KNL] Force drivers to reset the underlying device
3854 during initialization.
3856 resume= [SWSUSP]
3857 Specify the partition device for software suspend
3858 Format:
3859 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3861 resume_offset= [SWSUSP]
3862 Specify the offset from the beginning of the partition
3863 given by "resume=" at which the swap header is located,
3864 in <PAGE_SIZE> units (needed only for swap files).
3865 See Documentation/power/swsusp-and-swap-files.txt
3867 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3868 read the resume files
3870 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3871 Useful for devices that are detected asynchronously
3872 (e.g. USB and MMC devices).
3874 hibernate= [HIBERNATION]
3875 noresume Don't check if there's a hibernation image
3876 present during boot.
3877 nocompress Don't compress/decompress hibernation images.
3878 no Disable hibernation and resume.
3879 protect_image Turn on image protection during restoration
3880 (that will set all pages holding image data
3881 during restoration read-only).
3883 retain_initrd [RAM] Keep initrd memory after extraction
3885 rfkill.default_state=
3886 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3887 etc. communication is blocked by default.
3888 1 Unblocked.
3890 rfkill.master_switch_mode=
3891 0 The "airplane mode" button does nothing.
3892 1 The "airplane mode" button toggles between everything
3893 blocked and the previous configuration.
3894 2 The "airplane mode" button toggles between everything
3895 blocked and everything unblocked.
3897 rhash_entries= [KNL,NET]
3898 Set number of hash buckets for route cache
3900 ring3mwait=disable
3901 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
3902 CPUs.
3904 ro [KNL] Mount root device read-only on boot
3906 rodata= [KNL]
3907 on Mark read-only kernel memory as read-only (default).
3908 off Leave read-only kernel memory writable for debugging.
3910 rockchip.usb_uart
3911 Enable the uart passthrough on the designated usb port
3912 on Rockchip SoCs. When active, the signals of the
3913 debug-uart get routed to the D+ and D- pins of the usb
3914 port and the regular usb controller gets disabled.
3916 root= [KNL] Root filesystem
3917 See name_to_dev_t comment in init/do_mounts.c.
3919 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3920 mount the root filesystem
3922 rootflags= [KNL] Set root filesystem mount option string
3924 rootfstype= [KNL] Set root filesystem type
3926 rootwait [KNL] Wait (indefinitely) for root device to show up.
3927 Useful for devices that are detected asynchronously
3928 (e.g. USB and MMC devices).
3930 rproc_mem=nn[KMG][@address]
3931 [KNL,ARM,CMA] Remoteproc physical memory block.
3932 Memory area to be used by remote processor image,
3933 managed by CMA.
3935 rw [KNL] Mount root device read-write on boot
3937 S [KNL] Run init in single mode
3939 s390_iommu= [HW,S390]
3940 Set s390 IOTLB flushing mode
3941 strict
3942 With strict flushing every unmap operation will result in
3943 an IOTLB flush. Default is lazy flushing before reuse,
3944 which is faster.
3946 sa1100ir [NET]
3947 See drivers/net/irda/sa1100_ir.c.
3949 sbni= [NET] Granch SBNI12 leased line adapter
3951 sched_debug [KNL] Enables verbose scheduler debug messages.
3953 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3954 Allowed values are enable and disable. This feature
3955 incurs a small amount of overhead in the scheduler
3956 but is useful for debugging and performance tuning.
3958 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3959 xtime_lock contention on larger systems, and/or RCU lock
3960 contention on all systems with CONFIG_MAXSMP set.
3961 Format: { "0" | "1" }
3962 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3963 1 -- enable.
3964 Note: increases power consumption, thus should only be
3965 enabled if running jitter sensitive (HPC/RT) workloads.
3967 security= [SECURITY] Choose a security module to enable at boot.
3968 If this boot parameter is not specified, only the first
3969 security module asking for security registration will be
3970 loaded. An invalid security module name will be treated
3971 as if no module has been chosen.
3973 selinux= [SELINUX] Disable or enable SELinux at boot time.
3974 Format: { "0" | "1" }
3975 See security/selinux/Kconfig help text.
3976 0 -- disable.
3977 1 -- enable.
3978 Default value is set via kernel config option.
3979 If enabled at boot time, /selinux/disable can be used
3980 later to disable prior to initial policy load.
3982 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3983 Format: { "0" | "1" }
3984 See security/apparmor/Kconfig help text
3985 0 -- disable.
3986 1 -- enable.
3987 Default value is set via kernel config option.
3989 serialnumber [BUGS=X86-32]
3991 shapers= [NET]
3992 Maximal number of shapers.
3994 simeth= [IA-64]
3995 simscsi=
3997 slram= [HW,MTD]
3999 slab_nomerge [MM]
4000 Disable merging of slabs with similar size. May be
4001 necessary if there is some reason to distinguish
4002 allocs to different slabs, especially in hardened
4003 environments where the risk of heap overflows and
4004 layout control by attackers can usually be
4005 frustrated by disabling merging. This will reduce
4006 most of the exposure of a heap attack to a single
4007 cache (risks via metadata attacks are mostly
4008 unchanged). Debug options disable merging on their
4009 own.
4010 For more information see Documentation/vm/slub.rst.
4012 slab_max_order= [MM, SLAB]
4013 Determines the maximum allowed order for slabs.
4014 A high setting may cause OOMs due to memory
4015 fragmentation. Defaults to 1 for systems with
4016 more than 32MB of RAM, 0 otherwise.
4018 slub_debug[=options[,slabs]] [MM, SLUB]
4019 Enabling slub_debug allows one to determine the
4020 culprit if slab objects become corrupted. Enabling
4021 slub_debug can create guard zones around objects and
4022 may poison objects when not in use. Also tracks the
4023 last alloc / free. For more information see
4024 Documentation/vm/slub.rst.
4026 slub_memcg_sysfs= [MM, SLUB]
4027 Determines whether to enable sysfs directories for
4028 memory cgroup sub-caches. 1 to enable, 0 to disable.
4029 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
4030 Enabling this can lead to a very high number of debug
4031 directories and files being created under
4032 /sys/kernel/slub.
4034 slub_max_order= [MM, SLUB]
4035 Determines the maximum allowed order for slabs.
4036 A high setting may cause OOMs due to memory
4037 fragmentation. For more information see
4038 Documentation/vm/slub.rst.
4040 slub_min_objects= [MM, SLUB]
4041 The minimum number of objects per slab. SLUB will
4042 increase the slab order up to slub_max_order to
4043 generate a sufficiently large slab able to contain
4044 the number of objects indicated. The higher the number
4045 of objects the smaller the overhead of tracking slabs
4046 and the less frequently locks need to be acquired.
4047 For more information see Documentation/vm/slub.rst.
4049 slub_min_order= [MM, SLUB]
4050 Determines the minimum page order for slabs. Must be
4051 lower than slub_max_order.
4052 For more information see Documentation/vm/slub.rst.
4054 slub_nomerge [MM, SLUB]
4055 Same with slab_nomerge. This is supported for legacy.
4056 See slab_nomerge for more information.
4058 smart2= [HW]
4059 Format: <io1>[,<io2>[,...,<io8>]]
4061 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4062 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4063 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4064 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4065 smsc-ircc2.ircc_irq= [HW] IRQ line
4066 smsc-ircc2.ircc_dma= [HW] DMA channel
4067 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4068 0: Toshiba Satellite 1800 (GP data pin select)
4069 1: Fast pin select (default)
4070 2: ATC IRMode
4072 smt [KNL,S390] Set the maximum number of threads (logical
4073 CPUs) to use per physical CPU on systems capable of
4074 symmetric multithreading (SMT). Will be capped to the
4075 actual hardware limit.
4076 Format: <integer>
4077 Default: -1 (no limit)
4079 softlockup_panic=
4080 [KNL] Should the soft-lockup detector generate panics.
4081 Format: <integer>
4083 A nonzero value instructs the soft-lockup detector
4084 to panic the machine when a soft-lockup occurs. This
4085 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
4086 which is the respective build-time switch to that
4087 functionality.
4089 softlockup_all_cpu_backtrace=
4090 [KNL] Should the soft-lockup detector generate
4091 backtraces on all cpus.
4092 Format: <integer>
4094 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4095 See Documentation/laptops/sonypi.txt
4097 spectre_v2= [X86] Control mitigation of Spectre variant 2
4098 (indirect branch speculation) vulnerability.
4100 on - unconditionally enable
4101 off - unconditionally disable
4102 auto - kernel detects whether your CPU model is
4103 vulnerable
4105 Selecting 'on' will, and 'auto' may, choose a
4106 mitigation method at run time according to the
4107 CPU, the available microcode, the setting of the
4108 CONFIG_RETPOLINE configuration option, and the
4109 compiler with which the kernel was built.
4111 Specific mitigations can also be selected manually:
4113 retpoline - replace indirect branches
4114 retpoline,generic - google's original retpoline
4115 retpoline,amd - AMD-specific minimal thunk
4117 Not specifying this option is equivalent to
4118 spectre_v2=auto.
4120 spec_store_bypass_disable=
4121 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4122 (Speculative Store Bypass vulnerability)
4124 Certain CPUs are vulnerable to an exploit against a
4125 a common industry wide performance optimization known
4126 as "Speculative Store Bypass" in which recent stores
4127 to the same memory location may not be observed by
4128 later loads during speculative execution. The idea
4129 is that such stores are unlikely and that they can
4130 be detected prior to instruction retirement at the
4131 end of a particular speculation execution window.
4133 In vulnerable processors, the speculatively forwarded
4134 store can be used in a cache side channel attack, for
4135 example to read memory to which the attacker does not
4136 directly have access (e.g. inside sandboxed code).
4138 This parameter controls whether the Speculative Store
4139 Bypass optimization is used.
4141 on - Unconditionally disable Speculative Store Bypass
4142 off - Unconditionally enable Speculative Store Bypass
4143 auto - Kernel detects whether the CPU model contains an
4144 implementation of Speculative Store Bypass and
4145 picks the most appropriate mitigation. If the
4146 CPU is not vulnerable, "off" is selected. If the
4147 CPU is vulnerable the default mitigation is
4148 architecture and Kconfig dependent. See below.
4149 prctl - Control Speculative Store Bypass per thread
4150 via prctl. Speculative Store Bypass is enabled
4151 for a process by default. The state of the control
4152 is inherited on fork.
4153 seccomp - Same as "prctl" above, but all seccomp threads
4154 will disable SSB unless they explicitly opt out.
4156 Not specifying this option is equivalent to
4157 spec_store_bypass_disable=auto.
4159 Default mitigations:
4160 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4162 spia_io_base= [HW,MTD]
4163 spia_fio_base=
4164 spia_pedr=
4165 spia_peddr=
4167 srcutree.counter_wrap_check [KNL]
4168 Specifies how frequently to check for
4169 grace-period sequence counter wrap for the
4170 srcu_data structure's ->srcu_gp_seq_needed field.
4171 The greater the number of bits set in this kernel
4172 parameter, the less frequently counter wrap will
4173 be checked for. Note that the bottom two bits
4174 are ignored.
4176 srcutree.exp_holdoff [KNL]
4177 Specifies how many nanoseconds must elapse
4178 since the end of the last SRCU grace period for
4179 a given srcu_struct until the next normal SRCU
4180 grace period will be considered for automatic
4181 expediting. Set to zero to disable automatic
4182 expediting.
4184 ssbd= [ARM64,HW]
4185 Speculative Store Bypass Disable control
4187 On CPUs that are vulnerable to the Speculative
4188 Store Bypass vulnerability and offer a
4189 firmware based mitigation, this parameter
4190 indicates how the mitigation should be used:
4192 force-on: Unconditionally enable mitigation for
4193 for both kernel and userspace
4194 force-off: Unconditionally disable mitigation for
4195 for both kernel and userspace
4196 kernel: Always enable mitigation in the
4197 kernel, and offer a prctl interface
4198 to allow userspace to register its
4199 interest in being mitigated too.
4201 stack_guard_gap= [MM]
4202 override the default stack gap protection. The value
4203 is in page units and it defines how many pages prior
4204 to (for stacks growing down) resp. after (for stacks
4205 growing up) the main stack are reserved for no other
4206 mapping. Default value is 256 pages.
4208 stacktrace [FTRACE]
4209 Enabled the stack tracer on boot up.
4211 stacktrace_filter=[function-list]
4212 [FTRACE] Limit the functions that the stack tracer
4213 will trace at boot up. function-list is a comma separated
4214 list of functions. This list can be changed at run
4215 time by the stack_trace_filter file in the debugfs
4216 tracing directory. Note, this enables stack tracing
4217 and the stacktrace above is not needed.
4219 sti= [PARISC,HW]
4220 Format: <num>
4221 Set the STI (builtin display/keyboard on the HP-PARISC
4222 machines) console (graphic card) which should be used
4223 as the initial boot-console.
4224 See also comment in drivers/video/console/sticore.c.
4226 sti_font= [HW]
4227 See comment in drivers/video/console/sticore.c.
4229 stifb= [HW]
4230 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4232 sunrpc.min_resvport=
4233 sunrpc.max_resvport=
4234 [NFS,SUNRPC]
4235 SunRPC servers often require that client requests
4236 originate from a privileged port (i.e. a port in the
4237 range 0 < portnr < 1024).
4238 An administrator who wishes to reserve some of these
4239 ports for other uses may adjust the range that the
4240 kernel's sunrpc client considers to be privileged
4241 using these two parameters to set the minimum and
4242 maximum port values.
4244 sunrpc.svc_rpc_per_connection_limit=
4245 [NFS,SUNRPC]
4246 Limit the number of requests that the server will
4247 process in parallel from a single connection.
4248 The default value is 0 (no limit).
4250 sunrpc.pool_mode=
4251 [NFS]
4252 Control how the NFS server code allocates CPUs to
4253 service thread pools. Depending on how many NICs
4254 you have and where their interrupts are bound, this
4255 option will affect which CPUs will do NFS serving.
4256 Note: this parameter cannot be changed while the
4257 NFS server is running.
4259 auto the server chooses an appropriate mode
4260 automatically using heuristics
4261 global a single global pool contains all CPUs
4262 percpu one pool for each CPU
4263 pernode one pool for each NUMA node (equivalent
4264 to global on non-NUMA machines)
4266 sunrpc.tcp_slot_table_entries=
4267 sunrpc.udp_slot_table_entries=
4268 [NFS,SUNRPC]
4269 Sets the upper limit on the number of simultaneous
4270 RPC calls that can be sent from the client to a
4271 server. Increasing these values may allow you to
4272 improve throughput, but will also increase the
4273 amount of memory reserved for use by the client.
4275 suspend.pm_test_delay=
4276 [SUSPEND]
4277 Sets the number of seconds to remain in a suspend test
4278 mode before resuming the system (see
4279 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4280 is set. Default value is 5.
4282 swapaccount=[0|1]
4283 [KNL] Enable accounting of swap in memory resource
4284 controller if no parameter or 1 is given or disable
4285 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4287 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4288 Format: { <int> | force | noforce }
4289 <int> -- Number of I/O TLB slabs
4290 force -- force using of bounce buffers even if they
4291 wouldn't be automatically used by the kernel
4292 noforce -- Never use bounce buffers (for debugging)
4294 switches= [HW,M68k]
4296 sysfs.deprecated=0|1 [KNL]
4297 Enable/disable old style sysfs layout for old udev
4298 on older distributions. When this option is enabled
4299 very new udev will not work anymore. When this option
4300 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4301 in older udev will not work anymore.
4302 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4303 the kernel configuration.
4305 sysrq_always_enabled
4306 [KNL]
4307 Ignore sysrq setting - this boot parameter will
4308 neutralize any effect of /proc/sys/kernel/sysrq.
4309 Useful for debugging.
4311 tcpmhash_entries= [KNL,NET]
4312 Set the number of tcp_metrics_hash slots.
4313 Default value is 8192 or 16384 depending on total
4314 ram pages. This is used to specify the TCP metrics
4315 cache size. See Documentation/networking/ip-sysctl.txt
4316 "tcp_no_metrics_save" section for more details.
4318 tdfx= [HW,DRM]
4320 test_suspend= [SUSPEND][,N]
4321 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4322 standby suspend) or "freeze" (for suspend type freeze)
4323 as the system sleep state during system startup with
4324 the optional capability to repeat N number of times.
4325 The system is woken from this state using a
4326 wakeup-capable RTC alarm.
4328 thash_entries= [KNL,NET]
4329 Set number of hash buckets for TCP connection
4331 thermal.act= [HW,ACPI]
4332 -1: disable all active trip points in all thermal zones
4333 <degrees C>: override all lowest active trip points
4335 thermal.crt= [HW,ACPI]
4336 -1: disable all critical trip points in all thermal zones
4337 <degrees C>: override all critical trip points
4339 thermal.nocrt= [HW,ACPI]
4340 Set to disable actions on ACPI thermal zone
4341 critical and hot trip points.
4343 thermal.off= [HW,ACPI]
4344 1: disable ACPI thermal control
4346 thermal.psv= [HW,ACPI]
4347 -1: disable all passive trip points
4348 <degrees C>: override all passive trip points to this
4349 value
4351 thermal.tzp= [HW,ACPI]
4352 Specify global default ACPI thermal zone polling rate
4353 <deci-seconds>: poll all this frequency
4354 0: no polling (default)
4356 threadirqs [KNL]
4357 Force threading of all interrupt handlers except those
4358 marked explicitly IRQF_NO_THREAD.
4360 tmem [KNL,XEN]
4361 Enable the Transcendent memory driver if built-in.
4363 tmem.cleancache=0|1 [KNL, XEN]
4364 Default is on (1). Disable the usage of the cleancache
4365 API to send anonymous pages to the hypervisor.
4367 tmem.frontswap=0|1 [KNL, XEN]
4368 Default is on (1). Disable the usage of the frontswap
4369 API to send swap pages to the hypervisor. If disabled
4370 the selfballooning and selfshrinking are force disabled.
4372 tmem.selfballooning=0|1 [KNL, XEN]
4373 Default is on (1). Disable the driving of swap pages
4374 to the hypervisor.
4376 tmem.selfshrinking=0|1 [KNL, XEN]
4377 Default is on (1). Partial swapoff that immediately
4378 transfers pages from Xen hypervisor back to the
4379 kernel based on different criteria.
4381 topology= [S390]
4382 Format: {off | on}
4383 Specify if the kernel should make use of the cpu
4384 topology information if the hardware supports this.
4385 The scheduler will make use of this information and
4386 e.g. base its process migration decisions on it.
4387 Default is on.
4389 topology_updates= [KNL, PPC, NUMA]
4390 Format: {off}
4391 Specify if the kernel should ignore (off)
4392 topology updates sent by the hypervisor to this
4393 LPAR.
4395 tp720= [HW,PS2]
4397 tpm_suspend_pcr=[HW,TPM]
4398 Format: integer pcr id
4399 Specify that at suspend time, the tpm driver
4400 should extend the specified pcr with zeros,
4401 as a workaround for some chips which fail to
4402 flush the last written pcr on TPM_SaveState.
4403 This will guarantee that all the other pcrs
4404 are saved.
4406 trace_buf_size=nn[KMG]
4407 [FTRACE] will set tracing buffer size on each cpu.
4409 trace_event=[event-list]
4410 [FTRACE] Set and start specified trace events in order
4411 to facilitate early boot debugging. The event-list is a
4412 comma separated list of trace events to enable. See
4413 also Documentation/trace/events.rst
4415 trace_options=[option-list]
4416 [FTRACE] Enable or disable tracer options at boot.
4417 The option-list is a comma delimited list of options
4418 that can be enabled or disabled just as if you were
4419 to echo the option name into
4421 /sys/kernel/debug/tracing/trace_options
4423 For example, to enable stacktrace option (to dump the
4424 stack trace of each event), add to the command line:
4426 trace_options=stacktrace
4428 See also Documentation/trace/ftrace.rst "trace options"
4429 section.
4431 tp_printk[FTRACE]
4432 Have the tracepoints sent to printk as well as the
4433 tracing ring buffer. This is useful for early boot up
4434 where the system hangs or reboots and does not give the
4435 option for reading the tracing buffer or performing a
4436 ftrace_dump_on_oops.
4438 To turn off having tracepoints sent to printk,
4439 echo 0 > /proc/sys/kernel/tracepoint_printk
4440 Note, echoing 1 into this file without the
4441 tracepoint_printk kernel cmdline option has no effect.
4443 ** CAUTION **
4445 Having tracepoints sent to printk() and activating high
4446 frequency tracepoints such as irq or sched, can cause
4447 the system to live lock.
4449 traceoff_on_warning
4450 [FTRACE] enable this option to disable tracing when a
4451 warning is hit. This turns off "tracing_on". Tracing can
4452 be enabled again by echoing '1' into the "tracing_on"
4453 file located in /sys/kernel/debug/tracing/
4455 This option is useful, as it disables the trace before
4456 the WARNING dump is called, which prevents the trace to
4457 be filled with content caused by the warning output.
4459 This option can also be set at run time via the sysctl
4460 option: kernel/traceoff_on_warning
4462 transparent_hugepage=
4463 [KNL]
4464 Format: [always|madvise|never]
4465 Can be used to control the default behavior of the system
4466 with respect to transparent hugepages.
4467 See Documentation/admin-guide/mm/transhuge.rst
4468 for more details.
4470 tsc= Disable clocksource stability checks for TSC.
4471 Format: <string>
4472 [x86] reliable: mark tsc clocksource as reliable, this
4473 disables clocksource verification at runtime, as well
4474 as the stability checks done at bootup. Used to enable
4475 high-resolution timer mode on older hardware, and in
4476 virtualized environment.
4477 [x86] noirqtime: Do not use TSC to do irq accounting.
4478 Used to run time disable IRQ_TIME_ACCOUNTING on any
4479 platforms where RDTSC is slow and this accounting
4480 can add overhead.
4481 [x86] unstable: mark the TSC clocksource as unstable, this
4482 marks the TSC unconditionally unstable at bootup and
4483 avoids any further wobbles once the TSC watchdog notices.
4485 turbografx.map[2|3]= [HW,JOY]
4486 TurboGraFX parallel port interface
4487 Format:
4488 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4489 See also Documentation/input/devices/joystick-parport.rst
4491 udbg-immortal [PPC] When debugging early kernel crashes that
4492 happen after console_init() and before a proper
4493 console driver takes over, this boot options might
4494 help "seeing" what's going on.
4496 uhash_entries= [KNL,NET]
4497 Set number of hash buckets for UDP/UDP-Lite connections
4499 uhci-hcd.ignore_oc=
4500 [USB] Ignore overcurrent events (default N).
4501 Some badly-designed motherboards generate lots of
4502 bogus events, for ports that aren't wired to
4503 anything. Set this parameter to avoid log spamming.
4504 Note that genuine overcurrent events won't be
4505 reported either.
4507 unknown_nmi_panic
4508 [X86] Cause panic on unknown NMI.
4510 usbcore.authorized_default=
4511 [USB] Default USB device authorization:
4512 (default -1 = authorized except for wireless USB,
4513 0 = not authorized, 1 = authorized)
4515 usbcore.autosuspend=
4516 [USB] The autosuspend time delay (in seconds) used
4517 for newly-detected USB devices (default 2). This
4518 is the time required before an idle device will be
4519 autosuspended. Devices for which the delay is set
4520 to a negative value won't be autosuspended at all.
4522 usbcore.usbfs_snoop=
4523 [USB] Set to log all usbfs traffic (default 0 = off).
4525 usbcore.usbfs_snoop_max=
4526 [USB] Maximum number of bytes to snoop in each URB
4527 (default = 65536).
4529 usbcore.blinkenlights=
4530 [USB] Set to cycle leds on hubs (default 0 = off).
4532 usbcore.old_scheme_first=
4533 [USB] Start with the old device initialization
4534 scheme (default 0 = off).
4536 usbcore.usbfs_memory_mb=
4537 [USB] Memory limit (in MB) for buffers allocated by
4538 usbfs (default = 16, 0 = max = 2047).
4540 usbcore.use_both_schemes=
4541 [USB] Try the other device initialization scheme
4542 if the first one fails (default 1 = enabled).
4544 usbcore.initial_descriptor_timeout=
4545 [USB] Specifies timeout for the initial 64-byte
4546 USB_REQ_GET_DESCRIPTOR request in milliseconds
4547 (default 5000 = 5.0 seconds).
4549 usbcore.nousb [USB] Disable the USB subsystem
4551 usbcore.quirks=
4552 [USB] A list of quirk entries to augment the built-in
4553 usb core quirk list. List entries are separated by
4554 commas. Each entry has the form
4555 VendorID:ProductID:Flags. The IDs are 4-digit hex
4556 numbers and Flags is a set of letters. Each letter
4557 will change the built-in quirk; setting it if it is
4558 clear and clearing it if it is set. The letters have
4559 the following meanings:
4560 a = USB_QUIRK_STRING_FETCH_255 (string
4561 descriptors must not be fetched using
4562 a 255-byte read);
4563 b = USB_QUIRK_RESET_RESUME (device can't resume
4564 correctly so reset it instead);
4565 c = USB_QUIRK_NO_SET_INTF (device can't handle
4566 Set-Interface requests);
4567 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
4568 handle its Configuration or Interface
4569 strings);
4570 e = USB_QUIRK_RESET (device can't be reset
4571 (e.g morph devices), don't use reset);
4572 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
4573 more interface descriptions than the
4574 bNumInterfaces count, and can't handle
4575 talking to these interfaces);
4576 g = USB_QUIRK_DELAY_INIT (device needs a pause
4577 during initialization, after we read
4578 the device descriptor);
4579 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
4580 high speed and super speed interrupt
4581 endpoints, the USB 2.0 and USB 3.0 spec
4582 require the interval in microframes (1
4583 microframe = 125 microseconds) to be
4584 calculated as interval = 2 ^
4585 (bInterval-1).
4586 Devices with this quirk report their
4587 bInterval as the result of this
4588 calculation instead of the exponent
4589 variable used in the calculation);
4590 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
4591 handle device_qualifier descriptor
4592 requests);
4593 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
4594 generates spurious wakeup, ignore
4595 remote wakeup capability);
4596 k = USB_QUIRK_NO_LPM (device can't handle Link
4597 Power Management);
4598 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
4599 (Device reports its bInterval as linear
4600 frames instead of the USB 2.0
4601 calculation);
4602 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
4603 to be disconnected before suspend to
4604 prevent spurious wakeup);
4605 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
4606 pause after every control message);
4607 Example: quirks=0781:5580:bk,0a5c:5834:gij
4609 usbhid.mousepoll=
4610 [USBHID] The interval which mice are to be polled at.
4612 usbhid.jspoll=
4613 [USBHID] The interval which joysticks are to be polled at.
4615 usbhid.kbpoll=
4616 [USBHID] The interval which keyboards are to be polled at.
4618 usb-storage.delay_use=
4619 [UMS] The delay in seconds before a new device is
4620 scanned for Logical Units (default 1).
4622 usb-storage.quirks=
4623 [UMS] A list of quirks entries to supplement or
4624 override the built-in unusual_devs list. List
4625 entries are separated by commas. Each entry has
4626 the form VID:PID:Flags where VID and PID are Vendor
4627 and Product ID values (4-digit hex numbers) and
4628 Flags is a set of characters, each corresponding
4629 to a common usb-storage quirk flag as follows:
4630 a = SANE_SENSE (collect more than 18 bytes
4631 of sense data);
4632 b = BAD_SENSE (don't collect more than 18
4633 bytes of sense data);
4634 c = FIX_CAPACITY (decrease the reported
4635 device capacity by one sector);
4636 d = NO_READ_DISC_INFO (don't use
4637 READ_DISC_INFO command);
4638 e = NO_READ_CAPACITY_16 (don't use
4639 READ_CAPACITY_16 command);
4640 f = NO_REPORT_OPCODES (don't use report opcodes
4641 command, uas only);
4642 g = MAX_SECTORS_240 (don't transfer more than
4643 240 sectors at a time, uas only);
4644 h = CAPACITY_HEURISTICS (decrease the
4645 reported device capacity by one
4646 sector if the number is odd);
4647 i = IGNORE_DEVICE (don't bind to this
4648 device);
4649 j = NO_REPORT_LUNS (don't use report luns
4650 command, uas only);
4651 l = NOT_LOCKABLE (don't try to lock and
4652 unlock ejectable media);
4653 m = MAX_SECTORS_64 (don't transfer more
4654 than 64 sectors = 32 KB at a time);
4655 n = INITIAL_READ10 (force a retry of the
4656 initial READ(10) command);
4657 o = CAPACITY_OK (accept the capacity
4658 reported by the device);
4659 p = WRITE_CACHE (the device cache is ON
4660 by default);
4661 r = IGNORE_RESIDUE (the device reports
4662 bogus residue values);
4663 s = SINGLE_LUN (the device has only one
4664 Logical Unit);
4665 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4666 commands, uas only);
4667 u = IGNORE_UAS (don't bind to the uas driver);
4668 w = NO_WP_DETECT (don't test whether the
4669 medium is write-protected).
4670 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4671 even if the device claims no cache)
4672 Example: quirks=0419:aaf5:rl,0421:0433:rc
4674 user_debug= [KNL,ARM]
4675 Format: <int>
4676 See arch/arm/Kconfig.debug help text.
4677 1 - undefined instruction events
4678 2 - system calls
4679 4 - invalid data aborts
4680 8 - SIGSEGV faults
4681 16 - SIGBUS faults
4682 Example: user_debug=31
4684 userpte=
4685 [X86] Flags controlling user PTE allocations.
4687 nohigh = do not allocate PTE pages in
4688 HIGHMEM regardless of setting
4689 of CONFIG_HIGHPTE.
4691 vdso= [X86,SH]
4692 On X86_32, this is an alias for vdso32=. Otherwise:
4694 vdso=1: enable VDSO (the default)
4695 vdso=0: disable VDSO mapping
4697 vdso32= [X86] Control the 32-bit vDSO
4698 vdso32=1: enable 32-bit VDSO
4699 vdso32=0 or vdso32=2: disable 32-bit VDSO
4701 See the help text for CONFIG_COMPAT_VDSO for more
4702 details. If CONFIG_COMPAT_VDSO is set, the default is
4703 vdso32=0; otherwise, the default is vdso32=1.
4705 For compatibility with older kernels, vdso32=2 is an
4706 alias for vdso32=0.
4708 Try vdso32=0 if you encounter an error that says:
4709 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4711 vector= [IA-64,SMP]
4712 vector=percpu: enable percpu vector domain
4714 video= [FB] Frame buffer configuration
4715 See Documentation/fb/modedb.txt.
4717 video.brightness_switch_enabled= [0,1]
4718 If set to 1, on receiving an ACPI notify event
4719 generated by hotkey, video driver will adjust brightness
4720 level and then send out the event to user space through
4721 the allocated input device; If set to 0, video driver
4722 will only send out the event without touching backlight
4723 brightness level.
4724 default: 1
4726 virtio_mmio.device=
4727 [VMMIO] Memory mapped virtio (platform) device.
4729 <size>@<baseaddr>:<irq>[:<id>]
4730 where:
4731 <size> := size (can use standard suffixes
4732 like K, M and G)
4733 <baseaddr> := physical base address
4734 <irq> := interrupt number (as passed to
4735 request_irq())
4736 <id> := (optional) platform device id
4737 example:
4738 virtio_mmio.device=1K@0x100b0000:48:7
4740 Can be used multiple times for multiple devices.
4742 vga= [BOOT,X86-32] Select a particular video mode
4743 See Documentation/x86/boot.txt and
4744 Documentation/svga.txt.
4745 Use vga=ask for menu.
4746 This is actually a boot loader parameter; the value is
4747 passed to the kernel using a special protocol.
4749 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4750 size of <nn>. This can be used to increase the
4751 minimum size (128MB on x86). It can also be used to
4752 decrease the size and leave more room for directly
4753 mapped kernel RAM.
4755 vmcp_cma=nn[MG] [KNL,S390]
4756 Sets the memory size reserved for contiguous memory
4757 allocations for the vmcp device driver.
4759 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4760 Format: <command>
4762 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4763 Format: <command>
4765 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4766 Format: <command>
4768 vsyscall= [X86-64]
4769 Controls the behavior of vsyscalls (i.e. calls to
4770 fixed addresses of 0xffffffffff600x00 from legacy
4771 code). Most statically-linked binaries and older
4772 versions of glibc use these calls. Because these
4773 functions are at fixed addresses, they make nice
4774 targets for exploits that can control RIP.
4776 emulate [default] Vsyscalls turn into traps and are
4777 emulated reasonably safely.
4779 native Vsyscalls are native syscall instructions.
4780 This is a little bit faster than trapping
4781 and makes a few dynamic recompilers work
4782 better than they would in emulation mode.
4783 It also makes exploits much easier to write.
4785 none Vsyscalls don't work at all. This makes
4786 them quite hard to use for exploits but
4787 might break your system.
4789 vt.color= [VT] Default text color.
4790 Format: 0xYX, X = foreground, Y = background.
4791 Default: 0x07 = light gray on black.
4793 vt.cur_default= [VT] Default cursor shape.
4794 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4795 the parameters of the <Esc>[?A;B;Cc escape sequence;
4796 see VGA-softcursor.txt. Default: 2 = underline.
4798 vt.default_blu= [VT]
4799 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4800 Change the default blue palette of the console.
4801 This is a 16-member array composed of values
4802 ranging from 0-255.
4804 vt.default_grn= [VT]
4805 Format: <green0>,<green1>,<green2>,...,<green15>
4806 Change the default green palette of the console.
4807 This is a 16-member array composed of values
4808 ranging from 0-255.
4810 vt.default_red= [VT]
4811 Format: <red0>,<red1>,<red2>,...,<red15>
4812 Change the default red palette of the console.
4813 This is a 16-member array composed of values
4814 ranging from 0-255.
4816 vt.default_utf8=
4817 [VT]
4818 Format=<0|1>
4819 Set system-wide default UTF-8 mode for all tty's.
4820 Default is 1, i.e. UTF-8 mode is enabled for all
4821 newly opened terminals.
4823 vt.global_cursor_default=
4824 [VT]
4825 Format=<-1|0|1>
4826 Set system-wide default for whether a cursor
4827 is shown on new VTs. Default is -1,
4828 i.e. cursors will be created by default unless
4829 overridden by individual drivers. 0 will hide
4830 cursors, 1 will display them.
4832 vt.italic= [VT] Default color for italic text; 0-15.
4833 Default: 2 = green.
4835 vt.underline= [VT] Default color for underlined text; 0-15.
4836 Default: 3 = cyan.
4838 watchdog timers [HW,WDT] For information on watchdog timers,
4839 see Documentation/watchdog/watchdog-parameters.txt
4840 or other driver-specific files in the
4841 Documentation/watchdog/ directory.
4843 workqueue.watchdog_thresh=
4844 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4845 warn stall conditions and dump internal state to
4846 help debugging. 0 disables workqueue stall
4847 detection; otherwise, it's the stall threshold
4848 duration in seconds. The default value is 30 and
4849 it can be updated at runtime by writing to the
4850 corresponding sysfs file.
4852 workqueue.disable_numa
4853 By default, all work items queued to unbound
4854 workqueues are affine to the NUMA nodes they're
4855 issued on, which results in better behavior in
4856 general. If NUMA affinity needs to be disabled for
4857 whatever reason, this option can be used. Note
4858 that this also can be controlled per-workqueue for
4859 workqueues visible under /sys/bus/workqueue/.
4861 workqueue.power_efficient
4862 Per-cpu workqueues are generally preferred because
4863 they show better performance thanks to cache
4864 locality; unfortunately, per-cpu workqueues tend to
4865 be more power hungry than unbound workqueues.
4867 Enabling this makes the per-cpu workqueues which
4868 were observed to contribute significantly to power
4869 consumption unbound, leading to measurably lower
4870 power usage at the cost of small performance
4871 overhead.
4873 The default value of this parameter is determined by
4874 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4876 workqueue.debug_force_rr_cpu
4877 Workqueue used to implicitly guarantee that work
4878 items queued without explicit CPU specified are put
4879 on the local CPU. This guarantee is no longer true
4880 and while local CPU is still preferred work items
4881 may be put on foreign CPUs. This debug option
4882 forces round-robin CPU selection to flush out
4883 usages which depend on the now broken guarantee.
4884 When enabled, memory and cache locality will be
4885 impacted.
4887 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4888 default x2apic cluster mode on platforms
4889 supporting x2apic.
4891 x86_intel_mid_timer= [X86-32,APBT]
4892 Choose timer option for x86 Intel MID platform.
4893 Two valid options are apbt timer only and lapic timer
4894 plus one apbt timer for broadcast timer.
4895 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4897 xen_512gb_limit [KNL,X86-64,XEN]
4898 Restricts the kernel running paravirtualized under Xen
4899 to use only up to 512 GB of RAM. The reason to do so is
4900 crash analysis tools and Xen tools for doing domain
4901 save/restore/migration must be enabled to handle larger
4902 domains.
4904 xen_emul_unplug= [HW,X86,XEN]
4905 Unplug Xen emulated devices
4906 Format: [unplug0,][unplug1]
4907 ide-disks -- unplug primary master IDE devices
4908 aux-ide-disks -- unplug non-primary-master IDE devices
4909 nics -- unplug network devices
4910 all -- unplug all emulated devices (NICs and IDE disks)
4911 unnecessary -- unplugging emulated devices is
4912 unnecessary even if the host did not respond to
4913 the unplug protocol
4914 never -- do not unplug even if version check succeeds
4916 xen_nopvspin [X86,XEN]
4917 Disables the ticketlock slowpath using Xen PV
4918 optimizations.
4920 xen_nopv [X86]
4921 Disables the PV optimizations forcing the HVM guest to
4922 run as generic HVM guest with no PV drivers.
4924 xirc2ps_cs= [NET,PCMCIA]
4925 Format:
4926 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4928 xhci-hcd.quirks [USB,KNL]
4929 A hex value specifying bitmask with supplemental xhci
4930 host controller quirks. Meaning of each bit can be
4931 consulted in header drivers/usb/host/xhci.h.