1 acpi= [HW,ACPI,X86,ARM64]
2 Advanced Configuration and Power Interface
3 Format: { force | on | off | strict | noirq | rsdt |
5 force -- enable ACPI if default was off
6 on -- enable ACPI but allow fallback to DT [arm64]
7 off -- disable ACPI if default was on
8 noirq -- do not use ACPI for IRQ routing
9 strict -- Be less tolerant of platforms that are not
10 strictly ACPI specification compliant.
11 rsdt -- prefer RSDT over (default) XSDT
12 copy_dsdt -- copy DSDT to memory
13 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"
16 See also Documentation/power/runtime_pm.txt, pci=noacpi
18 acpi_apic_instance= [ACPI, IOAPIC]
20 2: use 2nd APIC table, if available
21 1,0: use 1st APIC table
24 acpi_backlight= [HW,ACPI]
27 If set to vendor, prefer vendor specific driver
28 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
29 of the ACPI video.ko driver.
31 acpi_force_32bit_fadt_addr
32 force FADT to use 32 bit addresses rather than the
33 64 bit X_* addresses. Some firmware have broken 64
34 bit addresses for force ACPI ignore these and use
35 the older legacy 32 bit addresses.
37 acpica_no_return_repair [HW, ACPI]
38 Disable AML predefined validation mechanism
39 This mechanism can repair the evaluation result to make
40 the return objects more ACPI specification compliant.
41 This option is useful for developers to identify the
42 root cause of an AML interpreter issue when the issue
43 has something to do with the repair mechanism.
45 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
46 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
48 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
49 debug output. Bits in debug_layer correspond to a
50 _COMPONENT in an ACPI source file, e.g.,
51 #define _COMPONENT ACPI_PCI_COMPONENT
52 Bits in debug_level correspond to a level in
53 ACPI_DEBUG_PRINT statements, e.g.,
54 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
55 The debug_level mask defaults to "info". See
56 Documentation/acpi/debug.txt for more information about
57 debug layers and levels.
59 Enable processor driver info messages:
60 acpi.debug_layer=0x20000000
61 Enable PCI/PCI interrupt routing info messages:
62 acpi.debug_layer=0x400000
63 Enable AML "Debug" output, i.e., stores to the Debug
64 object while interpreting AML:
65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
66 Enable all messages related to ACPI hardware:
67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
69 Some values produce so much output that the system is
70 unusable. The "log_buf_len" parameter may be useful
71 if you need to capture more output.
73 acpi_enforce_resources= [ACPI]
75 Check for resource conflicts between native drivers
76 and ACPI OperationRegions (SystemIO and SystemMemory
77 only). IO ports and memory declared in ACPI might be
78 used by the ACPI subsystem in arbitrary AML code and
79 can interfere with legacy drivers.
80 strict (default): access to resources claimed by ACPI
81 is denied; legacy drivers trying to access reserved
82 resources will fail to bind to device using them.
83 lax: access to resources claimed by ACPI is allowed;
84 legacy drivers trying to access reserved resources
85 will bind successfully but a warning message is logged.
86 no: ACPI OperationRegions are not marked as reserved,
87 no further checks are performed.
89 acpi_force_table_verification [HW,ACPI]
90 Enable table checksum verification during early stage.
91 By default, this is disabled due to x86 early mapping
94 acpi_irq_balance [HW,ACPI]
95 ACPI will balance active IRQs
98 acpi_irq_nobalance [HW,ACPI]
99 ACPI will not move active IRQs (default)
102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
103 Format: <irq>,<irq>...
105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
107 Format: <irq>,<irq>...
109 acpi_mask_gpe= [HW,ACPI]
110 Due to the existence of _Lxx/_Exx, some GPEs triggered
111 by unsupported hardware/firmware features can result in
112 GPE floodings that cannot be automatically disabled by
114 This facility can be used to prevent such uncontrolled
118 acpi_no_auto_serialize [HW,ACPI]
119 Disable auto-serialization of AML methods
120 AML control methods that contain the opcodes to create
121 named objects will be marked as "Serialized" by the
122 auto-serialization feature.
123 This feature is enabled by default.
124 This option allows to turn off the feature.
126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
129 acpi_no_static_ssdt [HW,ACPI]
130 Disable installation of static SSDTs at early boot time
131 By default, SSDTs contained in the RSDT/XSDT will be
132 installed automatically and they will appear under
133 /sys/firmware/acpi/tables.
134 This option turns off this feature.
135 Note that specifying this option does not affect
136 dynamic table installation which will install SSDT
137 tables to /sys/firmware/acpi/tables/dynamic.
139 acpi_rsdp= [ACPI,EFI,KEXEC]
140 Pass the RSDP address to the kernel, mostly used
141 on machines running EFI runtime service to boot the
142 second kernel for kdump.
144 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
145 Format: To spoof as Windows 98: ="Microsoft Windows"
147 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
148 of 2 which is mandated by ACPI 6) as the supported ACPI
149 specification revision (when using this switch, it may
150 be necessary to carry out a cold reboot _twice_ in a
151 row to make it take effect on the platform firmware).
153 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
154 acpi_osi="string1" # add string1
155 acpi_osi="!string2" # remove string2
156 acpi_osi=!* # remove all strings
157 acpi_osi=! # disable all built-in OS vendor
159 acpi_osi=!! # enable all built-in OS vendor
161 acpi_osi= # disable all strings
163 'acpi_osi=!' can be used in combination with single or
164 multiple 'acpi_osi="string1"' to support specific OS
165 vendor string(s). Note that such command can only
166 affect the default state of the OS vendor strings, thus
167 it cannot affect the default state of the feature group
168 strings and the current state of the OS vendor strings,
169 specifying it multiple times through kernel command line
170 is meaningless. This command is useful when one do not
171 care about the state of the feature group strings which
172 should be controlled by the OSPM.
174 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
175 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
176 can make '_OSI("Windows 2000")' TRUE.
178 'acpi_osi=' cannot be used in combination with other
179 'acpi_osi=' command lines, the _OSI method will not
180 exist in the ACPI namespace. NOTE that such command can
181 only affect the _OSI support state, thus specifying it
182 multiple times through kernel command line is also
185 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
188 'acpi_osi=!*' can be used in combination with single or
189 multiple 'acpi_osi="string1"' to support specific
190 string(s). Note that such command can affect the
191 current state of both the OS vendor strings and the
192 feature group strings, thus specifying it multiple times
193 through kernel command line is meaningful. But it may
194 still not able to affect the final state of a string if
195 there are quirks related to this string. This command
196 is useful when one want to control the state of the
197 feature group strings to debug BIOS issues related to
200 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
201 '_OSI("Module Device")' FALSE.
202 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
203 '_OSI("Module Device")' TRUE.
204 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
206 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
208 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
209 they all will make '_OSI("Windows 2000")' TRUE.
212 Override the pmtimer bug detection: force the kernel
213 to assume that this machine's pmtimer latches its value
214 and always returns good values.
216 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
217 Format: { level | edge | high | low }
219 acpi_skip_timer_override [HW,ACPI]
220 Recognize and ignore IRQ0/pin2 Interrupt Override.
221 For broken nForce2 BIOS resulting in XT-PIC timer.
223 acpi_sleep= [HW,ACPI] Sleep options
224 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
225 old_ordering, nonvs, sci_force_enable, nobl }
226 See Documentation/power/video.txt for information on
228 s3_beep is for debugging; it makes the PC's speaker beep
229 as soon as the kernel's real-mode entry point is called.
230 s4_nohwsig prevents ACPI hardware signature from being
231 used during resume from hibernation.
232 old_ordering causes the ACPI 1.0 ordering of the _PTS
233 control method, with respect to putting devices into
234 low power states, to be enforced (the ACPI 2.0 ordering
235 of _PTS is used by default).
236 nonvs prevents the kernel from saving/restoring the
237 ACPI NVS memory during suspend/hibernation and resume.
238 sci_force_enable causes the kernel to set SCI_EN directly
239 on resume from S1/S3 (which is against the ACPI spec,
240 but some broken systems don't work without it).
241 nobl causes the internal blacklist of systems known to
242 behave incorrectly in some ways with respect to system
243 suspend and resume to be ignored (use wisely).
245 acpi_use_timer_override [HW,ACPI]
246 Use timer override. For some broken Nvidia NF5 boards
247 that require a timer override, but don't have HPET
249 add_efi_memmap [EFI; X86] Include EFI memory map in
250 kernel's map of available physical RAM.
253 { off | try_unsupported }
254 off: disable AGP support
255 try_unsupported: try to drive unsupported chipsets
256 (may crash computer or cause data corruption)
259 See Documentation/sound/alsa-configuration.rst
262 Allow the default userspace alignment fault handler
263 behaviour to be specified. Bit 0 enables warnings,
264 bit 1 enables fixups, and bit 2 sends a segfault.
266 align_va_addr= [X86-64]
267 Align virtual addresses by clearing slice [14:12] when
268 allocating a VMA at process creation time. This option
269 gives you up to 3% performance improvement on AMD F15h
270 machines (where it is enabled by default) for a
271 CPU-intensive style benchmark, and it can vary highly in
272 a microbenchmark depending on workload and compiler.
274 32: only for 32-bit processes
275 64: only for 64-bit processes
276 on: enable for both 32- and 64-bit processes
277 off: disable for both 32- and 64-bit processes
279 alloc_snapshot [FTRACE]
280 Allocate the ftrace snapshot buffer on boot up when the
281 main buffer is allocated. This is handy if debugging
282 and you need to use tracing_snapshot() on boot up, and
283 do not want to use tracing_snapshot_alloc() as it needs
284 to be done where GFP_KERNEL allocations are allowed.
286 amd_iommu= [HW,X86-64]
287 Pass parameters to the AMD IOMMU driver in the system.
289 fullflush - enable flushing of IO/TLB entries when
290 they are unmapped. Otherwise they are
291 flushed before they will be reused, which
293 off - do not initialize any AMD IOMMU found in
295 force_isolation - Force device isolation for all
296 devices. The IOMMU driver is not
297 allowed anymore to lift isolation
298 requirements as needed. This option
299 does not override iommu=pt
301 amd_iommu_dump= [HW,X86-64]
302 Enable AMD IOMMU driver option to dump the ACPI table
303 for AMD IOMMU. With this option enabled, AMD IOMMU
304 driver will print ACPI tables for AMD IOMMU during
305 IOMMU initialization.
307 amd_iommu_intr= [HW,X86-64]
308 Specifies one of the following AMD IOMMU interrupt
310 legacy - Use legacy interrupt remapping mode.
311 vapic - Use virtual APIC mode, which allows IOMMU
312 to inject interrupts directly into guest.
313 This mode requires kvm-amd.avic=1.
314 (Default when IOMMU HW support is present.)
316 amijoy.map= [HW,JOY] Amiga joystick support
317 Map of devices attached to JOY0DAT and JOY1DAT
319 See also Documentation/input/joydev/joystick.rst
321 analog.map= [HW,JOY] Analog joystick and gamepad support
322 Specifies type or capabilities of an analog joystick
323 connected to one of 16 gameports
324 Format: <type1>,<type2>,..<type16>
327 Power management functions (SPARCstation-4/5 + deriv.)
329 Disable APC CPU standby support. SPARCstation-Fox does
330 not play well with APC CPU idle - disable it if you have
331 APC and your system crashes randomly.
333 apic= [APIC,X86] Advanced Programmable Interrupt Controller
334 Change the output verbosity while booting
335 Format: { quiet (default) | verbose | debug }
336 Change the amount of debugging information output
337 when initialising the APIC and IO-APIC components.
338 For X86-32, this can also be used to specify an APIC
340 Format: apic=driver_name
341 Examples: apic=bigsmp
343 apic_extnmi= [APIC,X86] External NMI delivery setting
344 Format: { bsp (default) | all | none }
345 bsp: External NMI is delivered only to CPU 0
346 all: External NMIs are broadcast to all CPUs as a
348 none: External NMI is masked for all CPUs. This is
349 useful so that a dump capture kernel won't be
353 See Documentation/networking/ipv6.txt.
355 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
356 Limit apic dumping. The parameter defines the maximal
357 number of local apics being dumped. Also it is possible
358 to set it to "all" by meaning -- no limit here.
359 Format: { 1 (default) | 2 | ... | all }.
360 The parameter valid if only apic=debug or
361 apic=verbose is specified.
362 Example: apic=debug show_lapic=all
364 apm= [APM] Advanced Power Management
365 See header of arch/x86/kernel/apm_32.c.
367 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
368 Format: <io>,<irq>,<nodeID>
372 atarimouse= [HW,MOUSE] Atari Mouse
374 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
375 EzKey and similar keyboards
377 atkbd.reset= [HW] Reset keyboard during initialization
379 atkbd.set= [HW] Select keyboard code set
380 Format: <int> (2 = AT (default), 3 = PS/2)
382 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
385 atkbd.softraw= [HW] Choose between synthetic and real raw mode
386 Format: <bool> (0 = real, 1 = synthetic (default))
388 atkbd.softrepeat= [HW]
389 Use software keyboard repeat
391 audit= [KNL] Enable the audit sub-system
392 Format: { "0" | "1" | "off" | "on" }
393 0 | off - kernel audit is disabled and can not be
394 enabled until the next reboot
395 unset - kernel audit is initialized but disabled and
396 will be fully enabled by the userspace auditd.
397 1 | on - kernel audit is initialized and partially
398 enabled, storing at most audit_backlog_limit
399 messages in RAM until it is fully enabled by the
403 audit_backlog_limit= [KNL] Set the audit queue size limit.
404 Format: <int> (must be >=0)
407 bau= [X86_UV] Enable the BAU on SGI UV. The default
408 behavior is to disable the BAU (i.e. bau=0).
409 Format: { "0" | "1" }
412 unset - Disable the BAU.
414 baycom_epp= [HW,AX25]
417 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
419 See header of drivers/net/hamradio/baycom_par.c.
421 baycom_ser_fdx= [HW,AX25]
422 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
423 Format: <io>,<irq>,<mode>[,<baud>]
424 See header of drivers/net/hamradio/baycom_ser_fdx.c.
426 baycom_ser_hdx= [HW,AX25]
427 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
428 Format: <io>,<irq>,<mode>
429 See header of drivers/net/hamradio/baycom_ser_hdx.c.
431 blkdevparts= Manual partition parsing of block device(s) for
432 embedded devices based on command line input.
433 See Documentation/block/cmdline-partition.txt
435 boot_delay= Milliseconds to delay each printk during boot.
436 Values larger than 10 seconds (10000) are changed to
440 bootmem_debug [KNL] Enable bootmem allocator debug messages.
443 Disable BERT OS support on buggy BIOSes.
445 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
446 bttv.radio= Most important insmod options are available as
448 bttv.pll= See Documentation/media/v4l-drivers/bttv.rst
451 bulk_remove=off [PPC] This parameter disables the use of the pSeries
452 firmware feature for flushing multiple hpte entries
455 c101= [NET] Moxa C101 synchronous serial card
457 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
458 Sometimes CPU hardware bugs make them report the cache
459 size incorrectly. The kernel will attempt work arounds
460 to fix known problems, but for some CPUs it is not
461 possible to determine what the correct size should be.
462 This option provides an override for these situations.
465 [NET] Specifies amount of time (in seconds) that
466 the kernel should wait for a network carrier. By default
467 it waits 120 seconds.
469 ca_keys= [KEYS] This parameter identifies a specific key(s) on
470 the system trusted keyring to be used for certificate
472 format: { id:<keyid> | builtin }
474 cca= [MIPS] Override the kernel pages' cache coherency
475 algorithm. Accepted values range from 0 to 7
476 inclusive. See arch/mips/include/asm/pgtable-bits.h
477 for platform specific values (SB1, Loongson3 and
480 ccw_timeout_log [S390]
481 See Documentation/s390/CommonIO for details.
483 cgroup_disable= [KNL] Disable a particular controller
484 Format: {name of the controller(s) to disable}
485 The effects of cgroup_disable=foo are:
486 - foo isn't auto-mounted if you mount all cgroups in
488 - foo isn't visible as an individually mountable
490 {Currently only "memory" controller deal with this and
491 cut the overhead, others just disable the usage. So
492 only cgroup_disable=memory is actually worthy}
494 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1
495 Format: { { controller | "all" | "named" }
496 [,{ controller | "all" | "named" }...] }
497 Like cgroup_disable, but only applies to cgroup v1;
498 the blacklisted controllers remain available in cgroup2.
499 "all" blacklists all controllers and "named" disables
500 named mounts. Specifying both "all" and "named" disables
503 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
505 nosocket -- Disable socket memory accounting.
506 nokmem -- Disable kernel memory accounting.
508 checkreqprot [SELINUX] Set initial checkreqprot flag value.
509 Format: { "0" | "1" }
510 See security/selinux/Kconfig help text.
511 0 -- check protection applied by kernel (includes
512 any implied execute protection).
513 1 -- check protection requested by application.
514 Default value is set via a kernel config option.
515 Value can be changed at runtime via
516 /selinux/checkreqprot.
519 See Documentation/s390/CommonIO for details.
522 Prevents the clock framework from automatically gating
523 clocks that have not been explicitly enabled by a Linux
524 device driver but are enabled in hardware at reset or
525 by the bootloader/firmware. Note that this does not
526 force such clocks to be always-on nor does it reserve
527 those clocks in any way. This parameter is useful for
528 debug and development, but should not be needed on a
529 platform with proper driver support. For more
530 information, see Documentation/driver-api/clk.rst.
532 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
534 Forces specified clocksource (if available) to be used
535 when calculating gettimeofday(). If specified
536 clocksource is not available, it defaults to PIT.
537 Format: { pit | tsc | cyclone | pmtmr }
539 clocksource= Override the default clocksource
541 Override the default clocksource and use the clocksource
542 with the name specified.
543 Some clocksource names to choose from, depending on
545 [all] jiffies (this is the base, fallback clocksource)
547 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
548 pxa_timer,timer3,32k_counter,timer0_1
549 [X86-32] pit,hpet,tsc;
550 scx200_hrt on Geode; cyclone on IBM x440
558 clocksource.arm_arch_timer.evtstrm=
561 Enable/disable the eventstream feature of the ARM
562 architected timer so that code using WFE-based polling
563 loops can be debugged more effectively on production
566 clearcpuid=BITNUM [X86]
567 Disable CPUID feature X for the kernel. See
568 arch/x86/include/asm/cpufeatures.h for the valid bit
569 numbers. Note the Linux specific bits are not necessarily
570 stable over kernel options, but the vendor specific
572 Also note that user programs calling CPUID directly
573 or using the feature without checking anything
574 will still see it. This just prevents it from
575 being used by the kernel or shown in /proc/cpuinfo.
576 Also note the kernel might malfunction if you disable
579 cma=nn[MG]@[start[MG][-end[MG]]]
581 Sets the size of kernel global memory area for
582 contiguous memory allocations and optionally the
583 placement constraint by the physical address range of
584 memory allocations. A value of 0 disables CMA
585 altogether. For more information, see
586 include/linux/dma-contiguous.h
588 cmo_free_hint= [PPC] Format: { yes | no }
589 Specify whether pages are marked as being inactive
590 when they are freed. This is used in CMO environments
591 to determine OS memory pressure for page stealing by
595 coherent_pool=nn[KMG] [ARM,KNL]
596 Sets the size of memory pool for coherent, atomic dma
597 allocations, by default set to 256K.
599 com20020= [HW,NET] ARCnet - COM20020 chipset
601 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
603 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
607 ARCnet - COM90xx chipset (memory-mapped buffers)
608 Format: <io>[,<irq>[,<memstart>]]
610 condev= [HW,S390] console device
613 console= [KNL] Output console device and options.
615 tty<n> Use the virtual console device <n>.
619 Use the specified serial port. The options are of
620 the form "bbbbpnf", where "bbbb" is the baud rate,
621 "p" is parity ("n", "o", or "e"), "n" is number of
622 bits, and "f" is flow control ("r" for RTS or
623 omit it). Default is "9600n8".
625 See Documentation/admin-guide/serial-console.rst for more
627 Documentation/networking/netconsole.txt for an
630 uart[8250],io,<addr>[,options]
631 uart[8250],mmio,<addr>[,options]
632 uart[8250],mmio16,<addr>[,options]
633 uart[8250],mmio32,<addr>[,options]
634 uart[8250],0x<addr>[,options]
635 Start an early, polled-mode console on the 8250/16550
636 UART at the specified I/O port or MMIO address,
637 switching to the matching ttyS device later.
638 MMIO inter-register address stride is either 8-bit
639 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
640 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
641 to be equivalent to 'mmio'. 'options' are specified in
642 the same format described for ttyS above; if unspecified,
643 the h/w is not re-initialized.
645 hvc<n> Use the hypervisor console device <n>. This is for
646 both Xen and PowerPC hypervisors.
648 If the device connected to the port is not a TTY but a braille
649 device, prepend "brl," before the device type, for instance
651 For now, only VisioBraille is supported.
654 [KNL] Change console messages format
656 By default we print messages on consoles in
657 "[time stamp] text\n" format (time stamp may not be
658 printed, depending on CONFIG_PRINTK_TIME or
659 `printk_time' param).
661 Switch to syslog format: "<%u>[time stamp] text\n"
662 IOW, each message will have a facility and loglevel
663 prefix. The format is similar to one used by syslog()
664 syscall, or to executing "dmesg -S --raw" or to reading
667 consoleblank= [KNL] The console blank (screen saver) timeout in
668 seconds. A value of 0 disables the blank timer.
672 [KNL] Change the default value for
673 /proc/<pid>/coredump_filter.
674 See also Documentation/filesystems/proc.txt.
676 coresight_cpu_debug.enable
679 Enable/disable the CPU sampling based debugging.
680 0: default value, disable debugging
681 1: enable debugging at boot time
683 cpuidle.off=1 [CPU_IDLE]
684 disable the cpuidle sub-system
687 [CPU_IDLE] Name of the cpuidle governor to use.
689 cpufreq.off=1 [CPU_FREQ]
690 disable the cpufreq sub-system
693 [X86] Delay for N microsec between assert and de-assert
694 of APIC INIT to start processors. This delay occurs
695 on every CPU online, such as boot, and resume from suspend.
698 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
700 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
702 crashkernel=size[KMG][@offset[KMG]]
703 [KNL] Using kexec, Linux can switch to a 'crash kernel'
704 upon panic. This parameter reserves the physical
705 memory region [offset, offset + size] for that kernel
706 image. If '@offset' is omitted, then a suitable offset
707 is selected automatically. Check
708 Documentation/kdump/kdump.txt for further details.
710 crashkernel=range1:size1[,range2:size2,...][@offset]
711 [KNL] Same as above, but depends on the memory
712 in the running system. The syntax of range is
713 start-[end] where start and end are both
714 a memory unit (amount[KMG]). See also
715 Documentation/kdump/kdump.txt for an example.
717 crashkernel=size[KMG],high
718 [KNL, x86_64] range could be above 4G. Allow kernel
719 to allocate physical memory region from top, so could
720 be above 4G if system have more than 4G ram installed.
721 Otherwise memory region will be allocated below 4G, if
723 It will be ignored if crashkernel=X is specified.
724 crashkernel=size[KMG],low
725 [KNL, x86_64] range under 4G. When crashkernel=X,high
726 is passed, kernel could allocate physical memory region
727 above 4G, that cause second kernel crash on system
728 that require some amount of low memory, e.g. swiotlb
729 requires at least 64M+32K low memory, also enough extra
730 low memory is needed to make sure DMA buffers for 32-bit
731 devices won't run out. Kernel would try to allocate at
732 at least 256M below 4G automatically.
733 This one let user to specify own low range under 4G
734 for second kernel instead.
735 0: to disable low allocation.
736 It will be ignored when crashkernel=X,high is not used
737 or memory reserved is below 4G.
740 [KNL] Disable crypto self-tests
745 cs89x0_media= [HW,NET]
746 Format: { rj45 | aui | bnc }
749 See header of drivers/s390/block/dasd_devmap.c.
751 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
752 (one device per port)
753 Format: <port#>,<type>
754 See also Documentation/input/devices/joystick-parport.rst
756 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
758 Documentation/admin-guide/dynamic-debug-howto.rst for
759 details. Deprecated, see dyndbg.
761 debug [KNL] Enable kernel debugging (events log level).
764 [KNL] Enable printing [hashed] pointers early in the
765 boot sequence. If enabled, we use a weak hash instead
766 of siphash to hash pointers. Use this option if you are
767 seeing instances of '(___ptrval___)') and need to see a
768 value (hashed pointer) instead. Cryptographically
769 insecure, please do not use on production kernels.
772 [KNL] verbose self-tests
774 Print debugging info while doing the locking API
776 We default to 0 (no extra messages), setting it to
777 1 will print _a lot_ more information - normally
778 only useful to kernel developers.
780 debug_objects [KNL] Enable object debugging
783 [KNL] Disable object debugging
785 debug_guardpage_minorder=
786 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
787 parameter allows control of the order of pages that will
788 be intentionally kept free (and hence protected) by the
789 buddy allocator. Bigger value increase the probability
790 of catching random memory corruption, but reduce the
791 amount of memory for normal system use. The maximum
792 possible value is MAX_ORDER/2. Setting this parameter
793 to 1 or 2 should be enough to identify most random
794 memory corruption problems caused by bugs in kernel or
795 driver code when a CPU writes to (or reads from) a
796 random memory location. Note that there exists a class
797 of memory corruptions problems caused by buggy H/W or
798 F/W or by drivers badly programing DMA (basically when
799 memory is written at bus level and the CPU MMU is
800 bypassed) which are not detectable by
801 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
802 tracking down these problems.
805 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
806 parameter enables the feature at boot time. In
807 default, it is disabled. We can avoid allocating huge
808 chunk of memory for debug pagealloc if we don't enable
809 it at boot time and the system will work mostly same
810 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
811 on: enable the feature
813 debugpat [X86] Enable PAT debugging
815 decnet.addr= [HW,NET]
816 Format: <area>[,<node>]
817 See also Documentation/networking/decnet.txt.
820 [same as hugepagesz=] The size of the default
821 HugeTLB page size. This is the size represented by
822 the legacy /proc/ hugepages APIs, used for SHM, and
823 default size when mounting hugetlbfs filesystems.
824 Defaults to the default architecture's huge page size
827 deferred_probe_timeout=
828 [KNL] Debugging option to set a timeout in seconds for
829 deferred probe to give up waiting on dependencies to
830 probe. Only specific dependencies (subsystems or
831 drivers) that have opted in will be ignored. A timeout of 0
832 will timeout at the end of initcalls. This option will also
833 dump out devices still on the deferred probe list after
837 Set number of hash buckets for dentry cache.
839 disable_1tb_segments [PPC]
840 Disables the use of 1TB hash page table segments. This
841 causes the kernel to fall back to 256MB segments which
842 can be useful when debugging issues that require an SLB
846 See Documentation/networking/ipv6.txt.
849 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
850 hardening is enabled for this boot. Hardened
851 usercopy checking is used to protect the kernel
852 from reading or writing beyond known memory
853 allocation boundaries as a proactive defense
854 against bounds-checking flaws in the kernel's
855 copy_to_user()/copy_from_user() interface.
856 on Perform hardened usercopy checks (default).
857 off Disable hardened usercopy checks.
860 Disable RADIX MMU mode on POWER9
862 disable_cpu_apicid= [X86,APIC,SMP]
864 The number of initial APIC ID for the
865 corresponding CPU to be disabled at boot,
866 mostly used for the kdump 2nd kernel to
867 disable BSP to wake up multiple CPUs without
868 causing system reset or hang due to sending
871 perf_v4_pmi= [X86,INTEL]
873 Disable Intel PMU counter freezing feature.
874 The feature only exists starting from
875 Arch Perfmon v4 (Skylake and newer).
877 disable_ddw [PPC/PSERIES]
878 Disable Dynamic DMA Window support. Use this if
879 to workaround buggy firmware.
882 See Documentation/networking/ipv6.txt.
884 disable_mtrr_cleanup [X86]
885 The kernel tries to adjust MTRR layout from continuous
886 to discrete, to make X server driver able to add WB
887 entry later. This parameter disables that.
889 disable_mtrr_trim [X86, Intel and AMD only]
890 By default the kernel will trim any uncacheable
891 memory out of your available memory pool based on
892 MTRR settings. This parameter disables that behavior,
893 possibly causing your machine to run very slowly.
895 disable_timer_pin_1 [X86]
896 Disable PIN 1 of APIC timer
897 Can be useful to work around chipset bugs.
899 dis_ucode_ldr [X86] Disable the microcode loader.
901 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
902 this option disables the debugging code at boot.
904 dma_debug_entries=<number>
905 This option allows to tune the number of preallocated
906 entries for DMA-API debugging code. One entry is
907 required per DMA-API allocation. Use this if the
908 DMA-API debugging code disables itself because the
909 architectural default is too low.
911 dma_debug_driver=<driver_name>
912 With this option the DMA-API debugging driver
913 filter feature can be enabled at boot time. Just
914 pass the driver to filter for as the parameter.
915 The filter can be disabled or changed to another
916 driver later using sysfs.
918 driver_async_probe= [KNL]
919 List of driver names to be probed asynchronously.
920 Format: <driver_name1>,<driver_name2>...
922 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
923 Broken monitors, graphic adapters, KVMs and EDIDless
924 panels may send no or incorrect EDID data sets.
925 This parameter allows to specify an EDID data sets
926 in the /lib/firmware directory that are used instead.
927 Generic built-in EDID data sets are used, if one of
928 edid/1024x768.bin, edid/1280x1024.bin,
929 edid/1680x1050.bin, or edid/1920x1080.bin is given
930 and no file with the same name exists. Details and
931 instructions how to build your own EDID data are
932 available in Documentation/EDID/HOWTO.txt. An EDID
933 data set will only be used for a particular connector,
934 if its name and a colon are prepended to the EDID
935 name. Each connector may use a unique EDID data
936 set by separating the files with a comma. An EDID
937 data set with no connector name will be used for
938 any connectors not explicitly specified.
943 Format: {"off" | "known"}
944 Control how the dt_cpu_ftrs device-tree binding is
945 used for CPU feature discovery and setup (if it
947 off: Do not use it, fall back to legacy cpu table.
948 known: Do not pass through unknown features to guests
949 or userspace, only those that the kernel is aware of.
951 dump_apple_properties [X86]
952 Dump name and content of EFI device properties on
953 x86 Macs. Useful for driver authors to determine
954 what data is available or for reverse-engineering.
956 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
957 module.dyndbg[="val"]
958 Enable debug messages at boot time. See
959 Documentation/admin-guide/dynamic-debug-howto.rst
962 nompx [X86] Disables Intel Memory Protection Extensions.
963 See Documentation/x86/intel_mpx.txt for more
964 information about the feature.
966 nopku [X86] Disable Memory Protection Keys CPU feature found
969 module.async_probe [KNL]
970 Enable asynchronous probe on this module.
972 early_ioremap_debug [KNL]
973 Enable debug messages in early_ioremap support. This
974 is useful for tracking down temporary early mappings
975 which are not unmapped.
977 earlycon= [KNL] Output early console device and options.
979 [ARM64] The early console is determined by the
980 stdout-path property in device tree's chosen node,
981 or determined by the ACPI SPCR table.
983 [X86] When used with no options the early console is
984 determined by the ACPI SPCR table.
986 cdns,<addr>[,options]
987 Start an early, polled-mode console on a Cadence
988 (xuartps) serial port at the specified address. Only
989 supported option is baud rate. If baud rate is not
990 specified, the serial port must already be setup and
993 uart[8250],io,<addr>[,options]
994 uart[8250],mmio,<addr>[,options]
995 uart[8250],mmio32,<addr>[,options]
996 uart[8250],mmio32be,<addr>[,options]
997 uart[8250],0x<addr>[,options]
998 Start an early, polled-mode console on the 8250/16550
999 UART at the specified I/O port or MMIO address.
1000 MMIO inter-register address stride is either 8-bit
1001 (mmio) or 32-bit (mmio32 or mmio32be).
1002 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1003 to be equivalent to 'mmio'. 'options' are specified
1004 in the same format described for "console=ttyS<n>"; if
1005 unspecified, the h/w is not initialized.
1009 Start an early, polled-mode console on a pl011 serial
1010 port at the specified address. The pl011 serial port
1011 must already be setup and configured. Options are not
1012 yet supported. If 'mmio32' is specified, then only
1013 the driver will use only 32-bit accessors to read/write
1014 the device registers.
1017 Start an early, polled-mode console on a meson serial
1018 port at the specified address. The serial port must
1019 already be setup and configured. Options are not yet
1023 Start an early, polled-mode console on an msm serial
1024 port at the specified address. The serial port
1025 must already be setup and configured. Options are not
1028 msm_serial_dm,<addr>
1029 Start an early, polled-mode console on an msm serial
1030 dm port at the specified address. The serial port
1031 must already be setup and configured. Options are not
1035 Start an early, polled-mode console on a serial port
1036 of an Actions Semi SoC, such as S500 or S900, at the
1037 specified address. The serial port must already be
1038 setup and configured. Options are not yet supported.
1041 Start an early, polled-mode console on a serial port
1042 of an RDA Micro SoC, such as RDA8810PL, at the
1043 specified address. The serial port must already be
1044 setup and configured. Options are not yet supported.
1046 smh Use ARM semihosting calls for early console.
1054 Use early console provided by serial driver available
1055 on Samsung SoCs, requires selecting proper type and
1056 a correct base address of the selected UART port. The
1057 serial port must already be setup and configured.
1058 Options are not yet supported.
1061 Start an early, polled-mode console on a lantiq serial
1062 (lqasc) port at the specified address. The serial port
1063 must already be setup and configured. Options are not
1068 Use early console provided by Freescale LP UART driver
1069 found on Freescale Vybrid and QorIQ LS1021A processors.
1070 A valid base address must be provided, and the serial
1071 port must already be setup and configured.
1074 Start an early, polled-mode console on the
1075 Armada 3700 serial port at the specified
1076 address. The serial port must already be setup
1077 and configured. Options are not yet supported.
1080 Start an early, polled-mode console on a Qualcomm
1081 Generic Interface (GENI) based serial port at the
1082 specified address. The serial port must already be
1083 setup and configured. Options are not yet supported.
1086 Start an early, unaccelerated console on the EFI
1087 memory mapped framebuffer (if available). On cache
1088 coherent non-x86 systems that use system memory for
1089 the framebuffer, pass the 'ram' option so that it is
1090 mapped with the correct attributes.
1092 earlyprintk= [X86,SH,ARM,M68k,S390]
1096 earlyprintk=serial[,ttySn[,baudrate]]
1097 earlyprintk=serial[,0x...[,baudrate]]
1098 earlyprintk=ttySn[,baudrate]
1099 earlyprintk=dbgp[debugController#]
1100 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1101 earlyprintk=xdbc[xhciController#]
1103 earlyprintk is useful when the kernel crashes before
1104 the normal console is initialized. It is not enabled by
1105 default because it has some cosmetic problems.
1107 Append ",keep" to not disable it when the real console
1110 Only one of vga, efi, serial, or usb debug port can
1113 Currently only ttyS0 and ttyS1 may be specified by
1114 name. Other I/O ports may be explicitly specified
1115 on some architectures (x86 and arm at least) by
1116 replacing ttySn with an I/O port address, like this:
1117 earlyprintk=serial,0x1008,115200
1118 You can find the port for a given device in
1119 /proc/tty/driver/serial:
1120 2: uart:ST16650V2 port:00001008 irq:18 ...
1122 Interaction with the standard serial driver is not
1125 The VGA and EFI output is eventually overwritten by
1128 The xen output can only be used by Xen PV guests.
1130 The sclp output can only be used on s390.
1132 The optional "force" to "pciserial" enables use of a
1133 PCI device even when its classcode is not of the
1136 edac_report= [HW,EDAC] Control how to report EDAC event
1137 Format: {"on" | "off" | "force"}
1138 on: enable EDAC to report H/W event. May be overridden
1139 by other higher priority error reporting module.
1140 off: disable H/W event reporting through EDAC.
1141 force: enforce the use of EDAC to report H/W event.
1144 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1147 This is designed to be used in conjunction with
1148 the boot argument: earlyprintk=vga
1151 Format: {"off" | "on" | "skip[mbr]"}
1154 Format: { "old_map", "nochunk", "noruntime", "debug" }
1155 old_map [X86-64]: switch to the old ioremap-based EFI
1156 runtime services mapping. 32-bit still uses this one by
1158 nochunk: disable reading files in "chunks" in the EFI
1159 boot stub, as chunking can cause problems with some
1160 firmware implementations.
1161 noruntime : disable EFI runtime services support
1162 debug: enable misc debug output
1164 efi_no_storage_paranoia [EFI; X86]
1165 Using this parameter you can use more than 50% of
1166 your efi variable storage. Use this parameter only if
1167 you are really sure that your UEFI does sane gc and
1168 fulfills the spec otherwise your board may brick.
1170 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1171 Add arbitrary attribute to specific memory range by
1172 updating original EFI memory map.
1173 Region of memory which aa attribute is added to is
1175 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1176 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1177 attribute is added to range 0x100000000-0x180000000 and
1178 0x10a0000000-0x1120000000.
1180 Using this parameter you can do debugging of EFI memmap
1181 related feature. For example, you can do debugging of
1182 Address Range Mirroring feature even if your box
1185 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1186 that is to be dynamically loaded by Linux. If there are
1187 multiple variables with the same name but with different
1188 vendor GUIDs, all of them will be loaded. See
1189 Documentation/acpi/ssdt-overlays.txt for details.
1192 eisa_irq_edge= [PARISC,HW]
1193 See header of drivers/parisc/eisa.c.
1196 See comment before function elanfreq_setup() in
1197 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1200 Format: {"cfq" | "deadline" | "noop"}
1201 See Documentation/block/cfq-iosched.txt and
1202 Documentation/block/deadline-iosched.txt for details.
1204 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1205 Specifies physical address of start of kernel core
1206 image elf header and optionally the size. Generally
1207 kexec loader will pass this option to capture kernel.
1208 See Documentation/kdump/kdump.txt for details.
1210 enable_mtrr_cleanup [X86]
1211 The kernel tries to adjust MTRR layout from continuous
1212 to discrete, to make X server driver able to add WB
1213 entry later. This parameter enables that.
1215 enable_timer_pin_1 [X86]
1216 Enable PIN 1 of APIC timer
1217 Can be useful to work around chipset bugs
1218 (in particular on some ATI chipsets).
1219 The kernel tries to set a reasonable default.
1221 enforcing [SELINUX] Set initial enforcing status.
1223 See security/selinux/Kconfig help text.
1224 0 -- permissive (log only, no denials).
1225 1 -- enforcing (deny and log).
1227 Value can be changed at runtime via /selinux/enforce.
1230 Disable Error Record Serialization Table (ERST)
1233 ether= [HW,NET] Ethernet cards parameters
1234 This option is obsoleted by the "netdev=" option, which
1235 has equivalent usage. See its documentation for details.
1239 Permit 'security.evm' to be updated regardless of
1240 current integrity status.
1244 fail_make_request=[KNL]
1245 General fault injection mechanism.
1246 Format: <interval>,<probability>,<space>,<times>
1247 See also Documentation/fault-injection/.
1250 See Documentation/blockdev/floppy.txt.
1252 force_pal_cache_flush
1253 [IA-64] Avoid check_sal_cache_flush which may hang on
1254 buggy SAL_CACHE_FLUSH implementations. Using this
1255 parameter will force ia64_sal_cache_flush to call
1256 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1259 Forcefully enable Physical Address Extension (PAE).
1260 Many Pentium M systems disable PAE but may have a
1261 functionally usable PAE implementation.
1262 Warning: use of this parameter will taint the kernel
1263 and may cause unknown problems.
1266 [FTRACE] will set and start the specified tracer
1267 as early as possible in order to facilitate early
1270 ftrace_dump_on_oops[=orig_cpu]
1271 [FTRACE] will dump the trace buffers on oops.
1272 If no parameter is passed, ftrace will dump
1273 buffers of all CPUs, but if you pass orig_cpu, it will
1274 dump only the buffer of the CPU that triggered the
1277 ftrace_filter=[function-list]
1278 [FTRACE] Limit the functions traced by the function
1279 tracer at boot up. function-list is a comma separated
1280 list of functions. This list can be changed at run
1281 time by the set_ftrace_filter file in the debugfs
1284 ftrace_notrace=[function-list]
1285 [FTRACE] Do not trace the functions specified in
1286 function-list. This list can be changed at run time
1287 by the set_ftrace_notrace file in the debugfs
1290 ftrace_graph_filter=[function-list]
1291 [FTRACE] Limit the top level callers functions traced
1292 by the function graph tracer at boot up.
1293 function-list is a comma separated list of functions
1294 that can be changed at run time by the
1295 set_graph_function file in the debugfs tracing directory.
1297 ftrace_graph_notrace=[function-list]
1298 [FTRACE] Do not trace from the functions specified in
1299 function-list. This list is a comma separated list of
1300 functions that can be changed at run time by the
1301 set_graph_notrace file in the debugfs tracing directory.
1303 ftrace_graph_max_depth=<uint>
1304 [FTRACE] Used with the function graph tracer. This is
1305 the max depth it will trace into a function. This value
1306 can be changed at run time by the max_graph_depth file
1307 in the tracefs tracing directory. default: 0 (no limit)
1310 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1311 support via parallel port (up to 5 devices per port)
1312 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1313 See also Documentation/input/devices/joystick-parport.rst
1317 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1321 gcov_persist= [GCOV] When non-zero (default), profiling data for
1322 kernel modules is saved and remains accessible via
1323 debugfs, even when the module is unloaded/reloaded.
1324 When zero, profiling data is discarded and associated
1325 debugfs files are removed at module unload time.
1327 goldfish [X86] Enable the goldfish android emulator platform.
1328 Don't use this when you are not running on the
1331 gpt [EFI] Forces disk with valid GPT signature but
1332 invalid Protective MBR to be treated as GPT. If the
1333 primary GPT is corrupted, it enables the backup/alternate
1334 GPT to be used instead.
1336 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1337 the "Enable 0" bit of the configuration register.
1340 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1341 the "Enable 0" bit of the configuration register.
1344 grcan.select= [HW] Select which physical interface to use.
1347 grcan.txsize= [HW] Sets the size of the tx buffer.
1348 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1350 grcan.rxsize= [HW] Sets the size of the rx buffer.
1351 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1354 gpio-mockup.gpio_mockup_ranges
1355 [HW] Sets the ranges of gpiochip of for this device.
1356 Format: <start1>,<end1>,<start2>,<end2>...
1358 hardlockup_all_cpu_backtrace=
1359 [KNL] Should the hard-lockup detector generate
1360 backtraces on all cpus.
1363 hashdist= [KNL,NUMA] Large hashes allocated during boot
1364 are distributed across NUMA nodes. Defaults on
1365 for 64-bit NUMA, off otherwise.
1366 Format: 0 | 1 (for off | on)
1368 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1370 hd= [EIDE] (E)IDE hard drive subsystem geometry
1371 Format: <cyl>,<head>,<sect>
1374 Disable Hardware Error Source Table (HEST) support;
1375 corresponding firmware-first mode error processing
1376 logic will be disabled.
1378 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1379 size of <nn>. This works even on boxes that have no
1380 highmem otherwise. This also works to reduce highmem
1381 size on bigger boxes.
1383 highres= [KNL] Enable/disable high resolution timer mode.
1384 Valid parameters: "on", "off"
1388 See Documentation/isdn/README.HiSax.
1392 hpet= [X86-32,HPET] option to control HPET usage
1393 Format: { enable (default) | disable | force |
1395 disable: disable HPET and use PIT instead
1396 force: allow force enabled of undocumented chips (ICH4,
1398 verbose: show contents of HPET registers during setup
1400 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1401 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1403 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1404 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1405 On x86-64 and powerpc, this option can be specified
1406 multiple times interleaved with hugepages= to reserve
1407 huge pages of different sizes. Valid pages sizes on
1408 x86-64 are 2M (when the CPU supports "pse") and 1G
1409 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1412 [KNL] Should the hung task detector generate panics.
1415 A nonzero value instructs the kernel to panic when a
1416 hung task is detected. The default value is controlled
1417 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1418 option. The value selected by this boot parameter can
1419 be changed later by the kernel.hung_task_panic sysctl.
1421 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1422 terminal devices. Valid values: 0..8
1423 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1424 If specified, z/VM IUCV HVC accepts connections
1425 from listed z/VM user IDs only.
1427 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations
1428 which allow the hypervisor to 'idle' the
1429 guest on lock contention.
1432 Do not unregister boot console at start. This is only
1433 useful for debugging when something happens in the window
1434 between unregistering the boot console and initializing
1437 i2c_bus= [HW] Override the default board specific I2C bus speed
1438 or register an additional I2C bus that is not
1439 registered from board initialization code.
1443 i8042.debug [HW] Toggle i8042 debug mode
1444 i8042.unmask_kbd_data
1445 [HW] Enable printing of interrupt data from the KBD port
1446 (disabled by default, and as a pre-condition
1447 requires that i8042.debug=1 be enabled)
1448 i8042.direct [HW] Put keyboard port into non-translated mode
1449 i8042.dumbkbd [HW] Pretend that controller can only read data from
1450 keyboard and cannot control its state
1451 (Don't attempt to blink the leds)
1452 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1453 i8042.nokbd [HW] Don't check/create keyboard port
1454 i8042.noloop [HW] Disable the AUX Loopback command while probing
1456 i8042.nomux [HW] Don't check presence of an active multiplexing
1458 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1460 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1461 i8042.reset [HW] Reset the controller during init, cleanup and
1462 suspend-to-ram transitions, only during s2r
1463 transitions, or never reset
1464 Format: { 1 | Y | y | 0 | N | n }
1465 1, Y, y: always reset controller
1466 0, N, n: don't ever reset controller
1467 Default: only on s2r transitions on x86; most other
1468 architectures force reset to be always executed
1469 i8042.unlock [HW] Unlock (ignore) the keylock
1470 i8042.kbdreset [HW] Reset device connected to KBD port
1474 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1475 indicates that the driver is running on unsupported
1477 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1478 does not match list of supported models.
1480 [HW] Report power status in /proc/i8k
1481 (disabled by default)
1482 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1485 i915.invert_brightness=
1486 [DRM] Invert the sense of the variable that is used to
1487 set the brightness of the panel backlight. Normally a
1488 brightness value of 0 indicates backlight switched off,
1489 and the maximum of the brightness value sets the backlight
1490 to maximum brightness. If this parameter is set to 0
1491 (default) and the machine requires it, or this parameter
1492 is set to 1, a brightness value of 0 sets the backlight
1493 to maximum brightness, and the maximum of the brightness
1494 value switches the backlight off.
1495 -1 -- never invert brightness
1496 0 -- machine default
1497 1 -- force brightness inversion
1500 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1502 ide-core.nodma= [HW] (E)IDE subsystem
1503 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1504 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1505 .cdrom .chs .ignore_cable are additional options
1506 See Documentation/ide/ide.txt.
1508 ide-generic.probe-mask= [HW] (E)IDE subsystem
1510 Probe mask for legacy ISA IDE ports. Depending on
1511 platform up to 6 ports are supported, enabled by
1512 setting corresponding bits in the mask to 1. The
1513 default value is 0x0, which has a special meaning.
1514 On systems that have PCI, it triggers scanning the
1515 PCI bus for the first and the second port, which
1516 are then probed. On systems without PCI the value
1517 of 0x0 enables probing the two first ports as if it
1520 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1521 Claim all unknown PCI IDE storage controllers.
1524 Format: idle=poll, idle=halt, idle=nomwait
1525 Poll forces a polling idle loop that can slightly
1526 improve the performance of waking up a idle CPU, but
1527 will use a lot of power and make the system run hot.
1529 idle=halt: Halt is forced to be used for CPU idle.
1530 In such case C2/C3 won't be used again.
1531 idle=nomwait: Disable mwait for CPU C-states
1533 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1534 Format: { strict | legacy | 2008 | relaxed }
1537 Choose which programs will be accepted for execution
1538 based on the IEEE 754 NaN encoding(s) supported by
1539 the FPU and the NaN encoding requested with the value
1540 of an ELF file header flag individually set by each
1541 binary. Hardware implementations are permitted to
1542 support either or both of the legacy and the 2008 NaN
1545 Available settings are as follows:
1546 strict accept binaries that request a NaN encoding
1547 supported by the FPU
1548 legacy only accept legacy-NaN binaries, if supported
1550 2008 only accept 2008-NaN binaries, if supported
1552 relaxed accept any binaries regardless of whether
1553 supported by the FPU
1555 The FPU emulator is always able to support both NaN
1556 encodings, so if no FPU hardware is present or it has
1557 been disabled with 'nofpu', then the settings of
1558 'legacy' and '2008' strap the emulator accordingly,
1559 'relaxed' straps the emulator for both legacy-NaN and
1560 2008-NaN, whereas 'strict' enables legacy-NaN only on
1561 legacy processors and both NaN encodings on MIPS32 or
1564 The setting for ABS.fmt/NEG.fmt instruction execution
1565 mode generally follows that for the NaN encoding,
1566 except where unsupported by hardware.
1568 ignore_loglevel [KNL]
1569 Ignore loglevel setting - this will print /all/
1570 kernel messages to the console. Useful for debugging.
1571 We also add it as printk module parameter, so users
1572 could change it dynamically, usually by
1573 /sys/module/printk/parameters/ignore_loglevel.
1576 Ignore RLIMIT_DATA setting for data mappings,
1577 print warning at first misuse. Can be changed via
1578 /sys/module/kernel/parameters/ignore_rlimit_data.
1580 ihash_entries= [KNL]
1581 Set number of hash buckets for inode cache.
1583 ima_appraise= [IMA] appraise integrity measurements
1584 Format: { "off" | "enforce" | "fix" | "log" }
1587 ima_appraise_tcb [IMA]
1588 The builtin appraise policy appraises all files
1591 ima_canonical_fmt [IMA]
1592 Use the canonical format for the binary runtime
1593 measurements, instead of host native format.
1596 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1600 The list of supported hash algorithms is defined
1601 in crypto/hash_info.h.
1604 The builtin policies to load during IMA setup.
1605 Format: "tcb | appraise_tcb | secure_boot |
1608 The "tcb" policy measures all programs exec'd, files
1609 mmap'd for exec, and all files opened with the read
1610 mode bit set by either the effective uid (euid=0) or
1613 The "appraise_tcb" policy appraises the integrity of
1614 all files owned by root. (This is the equivalent
1615 of ima_appraise_tcb.)
1617 The "secure_boot" policy appraises the integrity
1618 of files (eg. kexec kernel image, kernel modules,
1619 firmware, policy, etc) based on file signatures.
1621 The "fail_securely" policy forces file signature
1622 verification failure also on privileged mounted
1623 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1626 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1627 Load a policy which meets the needs of the Trusted
1628 Computing Base. This means IMA will measure all
1629 programs exec'd, files mmap'd for exec, and all files
1630 opened for read by uid=0.
1633 Select one of defined IMA measurements template formats.
1634 Formats: { "ima" | "ima-ng" | "ima-sig" }
1638 [IMA] Define a custom template format.
1639 Format: { "field1|...|fieldN" }
1641 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1642 Format: <min_file_size>
1643 Set the minimal file size for using asynchronous hash.
1644 If left unspecified, ahash usage is disabled.
1646 ahash performance varies for different data sizes on
1647 different crypto accelerators. This option can be used
1648 to achieve the best performance for a particular HW.
1650 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1652 Set hashing buffer size. Default: 4k.
1654 ahash performance varies for different chunk sizes on
1655 different crypto accelerators. This option can be used
1656 to achieve best performance for particular HW.
1660 Run specified binary instead of /sbin/init as init
1663 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1664 for working out where the kernel is dying during
1667 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1668 initcall functions. Useful for debugging built-in
1669 modules and initcalls.
1671 initrd= [BOOT] Specify the location of the initial ramdisk
1673 init_pkru= [x86] Specify the default memory protection keys rights
1674 register contents for all processes. 0x55555554 by
1675 default (disallow access to all but pkey 0). Can
1676 override in debugfs after boot.
1678 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1681 int_pln_enable [x86] Enable power limit notification interrupt
1683 integrity_audit=[IMA]
1684 Format: { "0" | "1" }
1685 0 -- basic integrity auditing messages. (Default)
1686 1 -- additional integrity auditing messages.
1688 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1690 Enable intel iommu driver.
1692 Disable intel iommu driver.
1693 igfx_off [Default Off]
1694 By default, gfx is mapped as normal device. If a gfx
1695 device has a dedicated DMAR unit, the DMAR unit is
1696 bypassed by not enabling DMAR with this option. In
1697 this case, gfx device will use physical address for
1700 With this option iommu will not optimize to look
1701 for io virtual address below 32-bit forcing dual
1702 address cycle on pci bus for cards supporting greater
1703 than 32-bit addressing. The default is to look
1704 for translation below 32-bit and if not available
1705 then look in the higher range.
1706 strict [Default Off]
1707 With this option on every unmap_single operation will
1708 result in a hardware IOTLB flush operation as opposed
1709 to batching them for performance.
1710 sp_off [Default Off]
1711 By default, super page will be supported if Intel IOMMU
1712 has the capability. With this option, super page will
1715 By default, scalable mode will be disabled even if the
1716 hardware advertises that it has support for the scalable
1717 mode translation. With this option set, scalable mode
1718 will be used on hardware which claims to support it.
1719 tboot_noforce [Default Off]
1720 Do not force the Intel IOMMU enabled under tboot.
1721 By default, tboot will force Intel IOMMU on, which
1722 could harm performance of some high-throughput
1723 devices like 40GBit network cards, even if identity
1725 Note that using this option lowers the security
1726 provided by tboot because it makes the system
1727 vulnerable to DMA attacks.
1729 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1730 0 disables intel_idle and fall back on acpi_idle.
1731 1 to 9 specify maximum depth of C-state.
1735 Do not enable intel_pstate as the default
1736 scaling driver for the supported processors
1738 Use intel_pstate as a scaling driver, but configure it
1739 to work with generic cpufreq governors (instead of
1740 enabling its internal governor). This mode cannot be
1741 used along with the hardware-managed P-states (HWP)
1744 Enable intel_pstate on systems that prohibit it by default
1745 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1746 instead of acpi-cpufreq may disable platform features, such
1747 as thermal controls and power capping, that rely on ACPI
1748 P-States information being indicated to OSPM and therefore
1749 should be used with caution. This option does not work with
1750 processors that aren't supported by the intel_pstate driver
1751 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1753 Do not enable hardware P state control (HWP)
1756 Only load intel_pstate on systems which support
1757 hardware P state control (HWP) if available.
1759 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1760 Description Table, specifies preferred power management
1761 profile as "Enterprise Server" or "Performance Server",
1762 then this feature is turned on by default.
1764 Allow per-logical-CPU P-State performance control limits using
1765 cpufreq sysfs interface
1767 intremap= [X86-64, Intel-IOMMU]
1768 on enable Interrupt Remapping (default)
1769 off disable Interrupt Remapping
1770 nosid disable Source ID checking
1772 BIOS x2APIC opt-out request will be ignored
1773 nopost disable Interrupt Posting
1775 iomem= Disable strict checking of access to MMIO memory
1776 strict regions from userspace.
1791 nobypass [PPC/POWERNV]
1792 Disable IOMMU bypass, using IOMMU for PCI devices.
1794 iommu.strict= [ARM64] Configure TLB invalidation behaviour
1795 Format: { "0" | "1" }
1797 Request that DMA unmap operations use deferred
1798 invalidation of hardware TLBs, for increased
1799 throughput at the cost of reduced device isolation.
1800 Will fall back to strict mode if not supported by
1801 the relevant IOMMU driver.
1802 1 - Strict mode (default).
1803 DMA unmap operations invalidate IOMMU hardware TLBs
1807 [ARM64] Configure DMA to bypass the IOMMU by default.
1808 Format: { "0" | "1" }
1809 0 - Use IOMMU translation for DMA.
1810 1 - Bypass the IOMMU for DMA.
1811 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
1813 io7= [HW] IO7 for Marvel based alpha systems
1814 See comment before marvel_specify_io7 in
1815 arch/alpha/kernel/core_marvel.c.
1817 io_delay= [X86] I/O delay method
1819 Standard port 0x80 based delay
1821 Alternate port 0xed based delay (needed on some systems)
1823 Simple two microseconds delay
1828 See Documentation/filesystems/nfs/nfsroot.txt.
1830 irqaffinity= [SMP] Set the default irq affinity mask
1831 The argument is a cpu list, as described above.
1833 irqchip.gicv2_force_probe=
1836 Force the kernel to look for the second 4kB page
1837 of a GICv2 controller even if the memory range
1838 exposed by the device tree is too small.
1840 irqchip.gicv3_nolpi=
1842 Force the kernel to ignore the availability of
1843 LPIs (and by consequence ITSs). Intended for system
1844 that use the kernel as a bootloader, and thus want
1845 to let secondary kernels in charge of setting up
1849 When an interrupt is not handled search all handlers
1850 for it. Intended to get systems with badly broken
1854 When an interrupt is not handled search all handlers
1855 for it. Also check all handlers each timer
1856 interrupt. Intended to get systems with badly broken
1860 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1862 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1863 [Deprecated - use cpusets instead]
1864 Format: [flag-list,]<cpu-list>
1866 Specify one or more CPUs to isolate from disturbances
1867 specified in the flag list (default: domain):
1870 Disable the tick when a single task runs.
1872 A residual 1Hz tick is offloaded to workqueues, which you
1873 need to affine to housekeeping through the global
1874 workqueue's affinity configured via the
1875 /sys/devices/virtual/workqueue/cpumask sysfs file, or
1876 by using the 'domain' flag described below.
1878 NOTE: by default the global workqueue runs on all CPUs,
1879 so to protect individual CPUs the 'cpumask' file has to
1880 be configured manually after bootup.
1883 Isolate from the general SMP balancing and scheduling
1884 algorithms. Note that performing domain isolation this way
1885 is irreversible: it's not possible to bring back a CPU to
1886 the domains once isolated through isolcpus. It's strongly
1887 advised to use cpusets instead to disable scheduler load
1888 balancing through the "cpuset.sched_load_balance" file.
1889 It offers a much more flexible interface where CPUs can
1890 move in and out of an isolated set anytime.
1892 You can move a process onto or off an "isolated" CPU via
1893 the CPU affinity syscalls or cpuset.
1894 <cpu number> begins at 0 and the maximum value is
1895 "number of CPUs in system - 1".
1897 The format of <cpu-list> is described above.
1903 ivrs_ioapic [HW,X86_64]
1904 Provide an override to the IOAPIC-ID<->DEVICE-ID
1905 mapping provided in the IVRS ACPI table. For
1906 example, to map IOAPIC-ID decimal 10 to
1907 PCI device 00:14.0 write the parameter as:
1908 ivrs_ioapic[10]=00:14.0
1910 ivrs_hpet [HW,X86_64]
1911 Provide an override to the HPET-ID<->DEVICE-ID
1912 mapping provided in the IVRS ACPI table. For
1913 example, to map HPET-ID decimal 0 to
1914 PCI device 00:14.0 write the parameter as:
1915 ivrs_hpet[0]=00:14.0
1917 ivrs_acpihid [HW,X86_64]
1918 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1919 mapping provided in the IVRS ACPI table. For
1920 example, to map UART-HID:UID AMD0020:0 to
1921 PCI device 00:14.5 write the parameter as:
1922 ivrs_acpihid[00:14.5]=AMD0020:0
1924 js= [HW,JOY] Analog joystick
1925 See Documentation/input/joydev/joystick.rst.
1928 When CONFIG_RANDOMIZE_BASE is set, this disables
1929 kernel and module base offset ASLR (Address Space
1930 Layout Randomization).
1933 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1934 report on every invalid memory access. Without this
1935 parameter KASAN will print report only for the first
1940 kernelcore= [KNL,X86,IA-64,PPC]
1941 Format: nn[KMGTPE] | nn% | "mirror"
1942 This parameter specifies the amount of memory usable by
1943 the kernel for non-movable allocations. The requested
1944 amount is spread evenly throughout all nodes in the
1945 system as ZONE_NORMAL. The remaining memory is used for
1946 movable memory in its own zone, ZONE_MOVABLE. In the
1947 event, a node is too small to have both ZONE_NORMAL and
1948 ZONE_MOVABLE, kernelcore memory will take priority and
1949 other nodes will have a larger ZONE_MOVABLE.
1951 ZONE_MOVABLE is used for the allocation of pages that
1952 may be reclaimed or moved by the page migration
1953 subsystem. Note that allocations like PTEs-from-HighMem
1954 still use the HighMem zone if it exists, and the Normal
1955 zone if it does not.
1957 It is possible to specify the exact amount of memory in
1958 the form of "nn[KMGTPE]", a percentage of total system
1959 memory in the form of "nn%", or "mirror". If "mirror"
1960 option is specified, mirrored (reliable) memory is used
1961 for non-movable allocations and remaining memory is used
1962 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
1963 are exclusive, so you cannot specify multiple forms.
1965 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1966 Format: <Controller#>[,poll interval]
1967 The controller # is the number of the ehci usb debug
1968 port as it is probed via PCI. The poll interval is
1969 optional and is the number seconds in between
1970 each poll cycle to the debug port in case you need
1971 the functionality for interrupting the kernel with
1972 gdb or control-c on the dbgp connection. When
1973 not using this parameter you use sysrq-g to break into
1974 the kernel debugger.
1976 kgdboc= [KGDB,HW] kgdb over consoles.
1977 Requires a tty driver that supports console polling,
1978 or a supported polling keyboard driver (non-usb).
1979 Serial only format: <serial_device>[,baud]
1980 keyboard only format: kbd
1981 keyboard and serial format: kbd,<serial_device>[,baud]
1982 Optional Kernel mode setting:
1983 kms, kbd format: kms,kbd
1984 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1986 kgdbwait [KGDB] Stop kernel execution and enter the
1987 kernel debugger at the earliest opportunity.
1989 kmac= [MIPS] korina ethernet MAC address.
1990 Configure the RouterBoard 532 series on-chip
1991 Ethernet adapter MAC address.
1993 kmemleak= [KNL] Boot-time kmemleak enable/disable
1994 Valid arguments: on, off
1996 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1999 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
2000 Default is 0 (don't ignore, but inject #GP)
2002 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
2003 Default is false (don't support).
2005 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
2009 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
2010 Default is 1 (enabled)
2012 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
2014 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
2016 kvm-arm.vgic_v3_group0_trap=
2017 [KVM,ARM] Trap guest accesses to GICv3 group-0
2020 kvm-arm.vgic_v3_group1_trap=
2021 [KVM,ARM] Trap guest accesses to GICv3 group-1
2024 kvm-arm.vgic_v3_common_trap=
2025 [KVM,ARM] Trap guest accesses to GICv3 common
2028 kvm-arm.vgic_v4_enable=
2029 [KVM,ARM] Allow use of GICv4 for direct injection of
2032 kvm-intel.ept= [KVM,Intel] Disable extended page tables
2033 (virtualized MMU) support on capable Intel chips.
2034 Default is 1 (enabled)
2036 kvm-intel.emulate_invalid_guest_state=
2037 [KVM,Intel] Enable emulation of invalid guest states
2038 Default is 0 (disabled)
2040 kvm-intel.flexpriority=
2041 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
2042 Default is 1 (enabled)
2045 [KVM,Intel] Enable VMX nesting (nVMX).
2046 Default is 0 (disabled)
2048 kvm-intel.unrestricted_guest=
2049 [KVM,Intel] Disable unrestricted guest feature
2050 (virtualized real and unpaged mode) on capable
2051 Intel chips. Default is 1 (enabled)
2053 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2056 Valid arguments: never, cond, always
2058 always: L1D cache flush on every VMENTER.
2059 cond: Flush L1D on VMENTER only when the code between
2060 VMEXIT and VMENTER can leak host memory.
2061 never: Disables the mitigation
2063 Default is cond (do L1 cache flush in specific instances)
2065 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2066 feature (tagged TLBs) on capable Intel chips.
2067 Default is 1 (enabled)
2069 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2072 The kernel PTE inversion protection is unconditionally
2073 enabled and cannot be disabled.
2076 Provides all available mitigations for the
2077 L1TF vulnerability. Disables SMT and
2078 enables all mitigations in the
2079 hypervisors, i.e. unconditional L1D flush.
2081 SMT control and L1D flush control via the
2082 sysfs interface is still possible after
2083 boot. Hypervisors will issue a warning
2084 when the first VM is started in a
2085 potentially insecure configuration,
2086 i.e. SMT enabled or L1D flush disabled.
2089 Same as 'full', but disables SMT and L1D
2090 flush runtime control. Implies the
2091 'nosmt=force' command line option.
2092 (i.e. sysfs control of SMT is disabled.)
2095 Leaves SMT enabled and enables the default
2096 hypervisor mitigation, i.e. conditional
2099 SMT control and L1D flush control via the
2100 sysfs interface is still possible after
2101 boot. Hypervisors will issue a warning
2102 when the first VM is started in a
2103 potentially insecure configuration,
2104 i.e. SMT enabled or L1D flush disabled.
2108 Disables SMT and enables the default
2109 hypervisor mitigation.
2111 SMT control and L1D flush control via the
2112 sysfs interface is still possible after
2113 boot. Hypervisors will issue a warning
2114 when the first VM is started in a
2115 potentially insecure configuration,
2116 i.e. SMT enabled or L1D flush disabled.
2119 Same as 'flush', but hypervisors will not
2120 warn when a VM is started in a potentially
2121 insecure configuration.
2124 Disables hypervisor mitigations and doesn't
2126 It also drops the swap size and available
2127 RAM limit restriction on both hypervisor and
2132 For details see: Documentation/admin-guide/l1tf.rst
2138 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2141 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2142 value for LAPIC timer one-shot implementation. Default
2143 back to the programmable timer unit in the LAPIC.
2145 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2148 libata.dma= [LIBATA] DMA control
2149 libata.dma=0 Disable all PATA and SATA DMA
2150 libata.dma=1 PATA and SATA Disk DMA only
2151 libata.dma=2 ATAPI (CDROM) DMA only
2152 libata.dma=4 Compact Flash DMA only
2153 Combinations also work, so libata.dma=3 enables DMA
2154 for disks and CDROMs, but not CFs.
2156 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2157 libata.ignore_hpa=0 keep BIOS limits (default)
2158 libata.ignore_hpa=1 ignore limits, using full disk
2160 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2164 libata.force= [LIBATA] Force configurations. The format is comma
2165 separated list of "[ID:]VAL" where ID is
2166 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2167 matching port, link or device. Basically, it matches
2168 the ATA ID string printed on console by libata. If
2169 the whole ID part is omitted, the last PORT and DEVICE
2170 values are used. If ID hasn't been specified yet, the
2171 configuration applies to all ports, links and devices.
2173 If only DEVICE is omitted, the parameter applies to
2174 the port and all links and devices behind it. DEVICE
2175 number of 0 either selects the first device or the
2176 first fan-out link behind PMP device. It does not
2177 select the host link. DEVICE number of 15 selects the
2178 host link and device attached to it.
2180 The VAL specifies the configuration to force. As long
2181 as there's no ambiguity shortcut notation is allowed.
2182 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2183 The following configurations can be forced.
2185 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2186 Any ID with matching PORT is used.
2188 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2190 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2191 udma[/][16,25,33,44,66,100,133] notation is also
2194 * [no]ncq: Turn on or off NCQ.
2196 * [no]ncqtrim: Turn off queued DSM TRIM.
2198 * nohrst, nosrst, norst: suppress hard, soft
2201 * rstonce: only attempt one reset during
2202 hot-unplug link recovery
2204 * dump_id: dump IDENTIFY data.
2206 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2208 * disable: Disable this device.
2210 If there are multiple matching configurations changing
2211 the same attribute, the last one is used.
2213 memblock=debug [KNL] Enable memblock debug messages.
2215 load_ramdisk= [RAM] List of ramdisks to load from floppy
2216 See Documentation/blockdev/ramdisk.txt.
2218 lockd.nlm_grace_period=P [NFS] Assign grace period.
2221 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2224 lockd.nlm_timeout=T [NFS] Assign timeout value.
2227 lockd.nlm_udpport=M [NFS] Assign UDP port.
2230 locktorture.nreaders_stress= [KNL]
2231 Set the number of locking read-acquisition kthreads.
2232 Defaults to being automatically set based on the
2233 number of online CPUs.
2235 locktorture.nwriters_stress= [KNL]
2236 Set the number of locking write-acquisition kthreads.
2238 locktorture.onoff_holdoff= [KNL]
2239 Set time (s) after boot for CPU-hotplug testing.
2241 locktorture.onoff_interval= [KNL]
2242 Set time (s) between CPU-hotplug operations, or
2243 zero to disable CPU-hotplug testing.
2245 locktorture.shuffle_interval= [KNL]
2246 Set task-shuffle interval (jiffies). Shuffling
2247 tasks allows some CPUs to go into dyntick-idle
2248 mode during the locktorture test.
2250 locktorture.shutdown_secs= [KNL]
2251 Set time (s) after boot system shutdown. This
2252 is useful for hands-off automated testing.
2254 locktorture.stat_interval= [KNL]
2255 Time (s) between statistics printk()s.
2257 locktorture.stutter= [KNL]
2258 Time (s) to stutter testing, for example,
2259 specifying five seconds causes the test to run for
2260 five seconds, wait for five seconds, and so on.
2261 This tests the locking primitive's ability to
2262 transition abruptly to and from idle.
2264 locktorture.torture_type= [KNL]
2265 Specify the locking implementation to test.
2267 locktorture.verbose= [KNL]
2268 Enable additional printk() statements.
2270 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2273 loglevel= All Kernel Messages with a loglevel smaller than the
2274 console loglevel will be printed to the console. It can
2275 also be changed with klogd or other programs. The
2276 loglevels are defined as follows:
2278 0 (KERN_EMERG) system is unusable
2279 1 (KERN_ALERT) action must be taken immediately
2280 2 (KERN_CRIT) critical conditions
2281 3 (KERN_ERR) error conditions
2282 4 (KERN_WARNING) warning conditions
2283 5 (KERN_NOTICE) normal but significant condition
2284 6 (KERN_INFO) informational
2285 7 (KERN_DEBUG) debug-level messages
2287 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2288 in bytes. n must be a power of two and greater
2289 than the minimal size. The minimal size is defined
2290 by LOG_BUF_SHIFT kernel config parameter. There is
2291 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2292 that allows to increase the default size depending on
2293 the number of CPUs. See init/Kconfig for more details.
2295 logo.nologo [FB] Disables display of the built-in Linux logo.
2296 This may be used to provide more screen space for
2297 kernel log messages and is useful when debugging
2298 kernel boot problems.
2300 lp=0 [LP] Specify parallel ports to use, e.g,
2301 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2302 lp=reset first parallel port). 'lp=0' disables the
2303 lp=auto printer driver. 'lp=reset' (which can be
2304 specified in addition to the ports) causes
2305 attached printers to be reset. Using
2306 lp=port1,port2,... specifies the parallel ports
2307 to associate lp devices with, starting with
2308 lp0. A port specification may be 'none' to skip
2309 that lp device, or a parport name such as
2310 'parport0'. Specifying 'lp=auto' instead of a
2311 port specification list means that device IDs
2312 from each port should be examined, to see if
2313 an IEEE 1284-compliant printer is attached; if
2314 so, the driver will manage that printer.
2315 See also header of drivers/char/lp.c.
2318 Sets loops_per_jiffy to given constant, thus avoiding
2319 time-consuming boot-time autodetection (up to 250 ms per
2320 CPU). 0 enables autodetection (default). To determine
2321 the correct value for your kernel, boot with normal
2322 autodetection and see what value is printed. Note that
2323 on SMP systems the preset will be applied to all CPUs,
2324 which is likely to cause problems if your CPUs need
2325 significantly divergent settings. An incorrect value
2326 will cause delays in the kernel to be wrong, leading to
2327 unpredictable I/O errors and other breakage. Although
2328 unlikely, in the extreme case this might damage your
2332 Format: <io>,<irq>,<dma>
2334 lsm.debug [SECURITY] Enable LSM initialization debugging output.
2336 machvec= [IA-64] Force the use of a particular machine-vector
2337 (machvec) in a generic kernel.
2338 Example: machvec=hpzx1_swiotlb
2340 machtype= [Loongson] Share the same kernel image file between different
2342 Example: machtype=lemote-yeeloong-2f-7inch
2344 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2345 than or equal to this physical address is ignored.
2347 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2348 will bring up during bootup. maxcpus=n : n >= 0 limits
2349 the kernel to bring up 'n' processors. Surely after
2350 bootup you can bring up the other plugged cpu by executing
2351 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2352 only takes effect during system bootup.
2353 While n=0 is a special case, it is equivalent to "nosmp",
2354 which also disables the IO APIC.
2356 max_loop= [LOOP] The number of loop block devices that get
2357 (loop.max_loop) unconditionally pre-created at init time. The default
2358 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2359 of statically allocating a predefined number, loop
2360 devices can be requested on-demand with the
2361 /dev/loop-control interface.
2363 mce [X86-32] Machine Check Exception
2365 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2367 md= [HW] RAID subsystems devices and level
2368 See Documentation/admin-guide/md.rst.
2371 Format: <first>,<last>
2372 Specifies range of consoles to be captured by the MDA.
2374 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2375 Amount of memory to be used when the kernel is not able
2376 to see the whole system memory or for test.
2377 [X86] Work as limiting max address. Use together
2378 with memmap= to avoid physical address space collisions.
2379 Without memmap= PCI devices could be placed at addresses
2380 belonging to unused RAM.
2382 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2386 [KNL,SH] Allow user to override the default size for
2387 per-device physically contiguous DMA buffers.
2389 memhp_default_state=online/offline
2390 [KNL] Set the initial state for the memory hotplug
2391 onlining policy. If not specified, the default value is
2392 set according to the
2393 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2395 See Documentation/memory-hotplug.txt.
2397 memmap=exactmap [KNL,X86] Enable setting of an exact
2398 E820 memory map, as specified by the user.
2399 Such memmap=exactmap lines can be constructed based on
2400 BIOS output or other requirements. See the memmap=nn@ss
2403 memmap=nn[KMG]@ss[KMG]
2404 [KNL] Force usage of a specific region of memory.
2405 Region of memory to be used is from ss to ss+nn.
2406 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2407 which limits max address to nn[KMG].
2408 Multiple different regions can be specified,
2411 memmap=100M@2G,100M#3G,1G!1024G
2413 memmap=nn[KMG]#ss[KMG]
2414 [KNL,ACPI] Mark specific memory as ACPI data.
2415 Region of memory to be marked is from ss to ss+nn.
2417 memmap=nn[KMG]$ss[KMG]
2418 [KNL,ACPI] Mark specific memory as reserved.
2419 Region of memory to be reserved is from ss to ss+nn.
2420 Example: Exclude memory from 0x18690000-0x1869ffff
2421 memmap=64K$0x18690000
2423 memmap=0x10000$0x18690000
2424 Some bootloaders may need an escape character before '$',
2425 like Grub2, otherwise '$' and the following number
2428 memmap=nn[KMG]!ss[KMG]
2429 [KNL,X86] Mark specific memory as protected.
2430 Region of memory to be used, from ss to ss+nn.
2431 The memory region may be marked as e820 type 12 (0xc)
2432 and is NVDIMM or ADR memory.
2434 memmap=<size>%<offset>-<oldtype>+<newtype>
2435 [KNL,ACPI] Convert memory within the specified region
2436 from <oldtype> to <newtype>. If "-<oldtype>" is left
2437 out, the whole region will be marked as <newtype>,
2438 even if previously unavailable. If "+<newtype>" is left
2439 out, matching memory will be removed. Types are
2440 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2441 3 = ACPI, 12 = PRAM.
2443 memory_corruption_check=0/1 [X86]
2444 Some BIOSes seem to corrupt the first 64k of
2445 memory when doing things like suspend/resume.
2446 Setting this option will scan the memory
2447 looking for corruption. Enabling this will
2448 both detect corruption and prevent the kernel
2449 from using the memory being corrupted.
2450 However, its intended as a diagnostic tool; if
2451 repeatable BIOS-originated corruption always
2452 affects the same memory, you can use memmap=
2453 to prevent the kernel from using that memory.
2455 memory_corruption_check_size=size [X86]
2456 By default it checks for corruption in the low
2457 64k, making this memory unavailable for normal
2458 use. Use this parameter to scan for
2459 corruption in more or less memory.
2461 memory_corruption_check_period=seconds [X86]
2462 By default it checks for corruption every 60
2463 seconds. Use this parameter to check at some
2464 other rate. 0 disables periodic checking.
2466 memtest= [KNL,X86,ARM,PPC] Enable memtest
2468 default : 0 <disable>
2469 Specifies the number of memtest passes to be
2470 performed. Each pass selects another test
2471 pattern from a given set of patterns. Memtest
2472 fills the memory with this pattern, validates
2473 memory contents and reserves bad memory
2474 regions that are detected.
2476 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2477 Valid arguments: on, off
2478 Default (depends on kernel configuration option):
2479 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2480 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2481 mem_encrypt=on: Activate SME
2482 mem_encrypt=off: Do not activate SME
2484 Refer to Documentation/x86/amd-memory-encryption.txt
2485 for details on when memory encryption can be activated.
2487 mem_sleep_default= [SUSPEND] Default system suspend mode:
2488 s2idle - Suspend-To-Idle
2489 shallow - Power-On Suspend or equivalent (if supported)
2490 deep - Suspend-To-RAM or equivalent (if supported)
2491 See Documentation/admin-guide/pm/sleep-states.rst.
2493 meye.*= [HW] Set MotionEye Camera parameters
2494 See Documentation/media/v4l-drivers/meye.rst.
2496 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2497 Multi-Function General Purpose Timers on AMD Geode
2500 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2501 the BIOS has incorrectly applied a workaround. TinyBIOS
2502 version 0.98 is known to be affected, 0.99 fixes the
2503 problem by letting the user disable the workaround.
2507 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2508 physical address is ignored.
2510 mini2440= [ARM,HW,KNL]
2511 Format:[0..2][b][c][t]
2513 MINI2440 configuration specification:
2514 0 - The attached screen is the 3.5" TFT
2515 1 - The attached screen is the 7" TFT
2516 2 - The VGA Shield is attached (1024x768)
2517 Leaving out the screen size parameter will not load
2518 the TFT driver, and the framebuffer will be left
2520 b - Enable backlight. The TFT backlight pin will be
2521 linked to the kernel VESA blanking code and a GPIO
2522 LED. This parameter is not necessary when using the
2524 c - Enable the s3c camera interface.
2525 t - Reserved for enabling touchscreen support. The
2526 touchscreen support is not enabled in the mainstream
2527 kernel as of 2.6.30, a preliminary port can be found
2528 in the "bleeding edge" mini2440 support kernel at
2529 http://repo.or.cz/w/linux-2.6/mini2440.git
2532 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2533 parameter allows control of the logging verbosity for
2534 the additional memory initialisation checks. A value
2535 of 0 disables mminit logging and a level of 4 will
2536 log everything. Information is printed at KERN_DEBUG
2537 so loglevel=8 may also need to be specified.
2540 [KNL] When CONFIG_MODULE_SIG is set, this means that
2541 modules without (valid) signatures will fail to load.
2542 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2543 is always true, so this option does nothing.
2545 module_blacklist= [KNL] Do not load a comma-separated list of
2546 modules. Useful for debugging problem modules.
2549 [MOUSE] Maximum time between finger touching and
2550 leaving touchpad surface for touch to be considered
2551 a tap and be reported as a left button click (for
2552 touchpads working in absolute mode only).
2554 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2555 reporting absolute coordinates, such as tablets
2556 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2557 reporting absolute coordinates, such as tablets
2559 movablecore= [KNL,X86,IA-64,PPC]
2560 Format: nn[KMGTPE] | nn%
2561 This parameter is the complement to kernelcore=, it
2562 specifies the amount of memory used for migratable
2563 allocations. If both kernelcore and movablecore is
2564 specified, then kernelcore will be at *least* the
2565 specified value but may be more. If movablecore on its
2566 own is specified, the administrator must be careful
2567 that the amount of memory usable for all allocations
2570 movable_node [KNL] Boot-time switch to make hotplugable memory
2571 NUMA nodes to be movable. This means that the memory
2572 of such nodes will be usable only for movable
2573 allocations which rules out almost all kernel
2574 allocations. Use with caution!
2576 MTD_Partition= [MTD]
2577 Format: <name>,<region-number>,<size>,<offset>
2579 MTD_Region= [MTD] Format:
2580 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2583 See drivers/mtd/cmdlinepart.c.
2585 multitce=off [PPC] This parameter disables the use of the pSeries
2586 firmware feature for updating multiple TCE entries
2589 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2591 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2593 boundary - index of last SLC block on Flex-OneNAND.
2594 The remaining blocks are configured as MLC blocks.
2595 lock - Configure if Flex-OneNAND boundary should be locked.
2596 Once locked, the boundary cannot be changed.
2597 1 indicates lock status, 0 indicates unlock status.
2600 ARM/S3C2412 JIVE boot control
2602 See arch/arm/mach-s3c2412/mach-jive.c
2604 mtouchusb.raw_coordinates=
2605 [HW] Make the MicroTouch USB driver use raw coordinates
2606 ('y', default) or cooked coordinates ('n')
2608 mtrr_chunk_size=nn[KMG] [X86]
2609 used for mtrr cleanup. It is largest continuous chunk
2610 that could hold holes aka. UC entries.
2612 mtrr_gran_size=nn[KMG] [X86]
2613 Used for mtrr cleanup. It is granularity of mtrr block.
2615 Large value could prevent small alignment from
2618 mtrr_spare_reg_nr=n [X86]
2620 Range: 0,7 : spare reg number
2622 Used for mtrr cleanup. It is spare mtrr entries number.
2623 Set to 2 or more if your graphical card needs more.
2625 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2627 netdev= [NET] Network devices parameters
2628 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2629 Note that mem_start is often overloaded to mean
2630 something different and driver-specific.
2631 This usage is only documented in each driver source
2635 [NETFILTER] Enable connection tracking flow accounting
2636 0 to disable accounting
2637 1 to enable accounting
2640 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2641 See Documentation/filesystems/nfs/nfsroot.txt.
2643 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2644 See Documentation/filesystems/nfs/nfsroot.txt.
2646 nfsrootdebug [NFS] enable nfsroot debugging messages.
2647 See Documentation/filesystems/nfs/nfsroot.txt.
2649 nfs.callback_nr_threads=
2650 [NFSv4] set the total number of threads that the
2651 NFS client will assign to service NFSv4 callback
2654 nfs.callback_tcpport=
2655 [NFS] set the TCP port on which the NFSv4 callback
2656 channel should listen.
2659 [NFS] sets the pathname to the program which is used
2660 to update the NFS client cache entries.
2662 nfs.cache_getent_timeout=
2663 [NFS] sets the timeout after which an attempt to
2664 update a cache entry is deemed to have failed.
2666 nfs.idmap_cache_timeout=
2667 [NFS] set the maximum lifetime for idmapper cache
2671 [NFS] enable 64-bit inode numbers.
2672 If zero, the NFS client will fake up a 32-bit inode
2673 number for the readdir() and stat() syscalls instead
2674 of returning the full 64-bit number.
2675 The default is to return 64-bit inode numbers.
2677 nfs.max_session_cb_slots=
2678 [NFSv4.1] Sets the maximum number of session
2679 slots the client will assign to the callback
2680 channel. This determines the maximum number of
2681 callbacks the client will process in parallel for
2682 a particular server.
2684 nfs.max_session_slots=
2685 [NFSv4.1] Sets the maximum number of session slots
2686 the client will attempt to negotiate with the server.
2687 This limits the number of simultaneous RPC requests
2688 that the client can send to the NFSv4.1 server.
2689 Note that there is little point in setting this
2690 value higher than the max_tcp_slot_table_limit.
2692 nfs.nfs4_disable_idmapping=
2693 [NFSv4] When set to the default of '1', this option
2694 ensures that both the RPC level authentication
2695 scheme and the NFS level operations agree to use
2696 numeric uids/gids if the mount is using the
2697 'sec=sys' security flavour. In effect it is
2698 disabling idmapping, which can make migration from
2699 legacy NFSv2/v3 systems to NFSv4 easier.
2700 Servers that do not support this mode of operation
2701 will be autodetected by the client, and it will fall
2702 back to using the idmapper.
2703 To turn off this behaviour, set the value to '0'.
2705 [NFS4] Specify an additional fixed unique ident-
2706 ification string that NFSv4 clients can insert into
2707 their nfs_client_id4 string. This is typically a
2708 UUID that is generated at system install time.
2710 nfs.send_implementation_id =
2711 [NFSv4.1] Send client implementation identification
2712 information in exchange_id requests.
2713 If zero, no implementation identification information
2715 The default is to send the implementation identification
2718 nfs.recover_lost_locks =
2719 [NFSv4] Attempt to recover locks that were lost due
2720 to a lease timeout on the server. Please note that
2721 doing this risks data corruption, since there are
2722 no guarantees that the file will remain unchanged
2723 after the locks are lost.
2724 If you want to enable the kernel legacy behaviour of
2725 attempting to recover these locks, then set this
2727 The default parameter value of '0' causes the kernel
2728 not to attempt recovery of lost locks.
2730 nfs4.layoutstats_timer =
2731 [NFSv4.2] Change the rate at which the kernel sends
2732 layoutstats to the pNFS metadata server.
2734 Setting this to value to 0 causes the kernel to use
2735 whatever value is the default set by the layout
2736 driver. A non-zero value sets the minimum interval
2737 in seconds between layoutstats transmissions.
2739 nfsd.nfs4_disable_idmapping=
2740 [NFSv4] When set to the default of '1', the NFSv4
2741 server will return only numeric uids and gids to
2742 clients using auth_sys, and will accept numeric uids
2743 and gids from such clients. This is intended to ease
2744 migration from NFSv2/v3.
2746 nmi_debug= [KNL,SH] Specify one or more actions to take
2747 when a NMI is triggered.
2748 Format: [state][,regs][,debounce][,die]
2750 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2751 Format: [panic,][nopanic,][num]
2753 0 - turn hardlockup detector in nmi_watchdog off
2754 1 - turn hardlockup detector in nmi_watchdog on
2755 When panic is specified, panic when an NMI watchdog
2756 timeout occurs (or 'nopanic' to override the opposite
2757 default). To disable both hard and soft lockup detectors,
2758 please see 'nowatchdog'.
2759 This is useful when you use a panic=... timeout and
2760 need the box quickly up again.
2762 These settings can be accessed at runtime via
2763 the nmi_watchdog and hardlockup_panic sysctls.
2765 netpoll.carrier_timeout=
2766 [NET] Specifies amount of time (in seconds) that
2767 netpoll should wait for a carrier. By default netpoll
2770 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2771 emulation library even if a 387 maths coprocessor
2774 no5lvl [X86-64] Disable 5-level paging mode. Forces
2775 kernel to use 4-level paging instead.
2778 [HW] Never suspend the console
2779 Disable suspending of consoles during suspend and
2780 hibernate operations. Once disabled, debugging
2781 messages can reach various consoles while the rest
2782 of the system is being put to sleep (ie, while
2783 debugging driver suspend/resume hooks). This may
2784 not work reliably with all consoles, but is known
2785 to work with serial and VGA consoles.
2786 To facilitate more flexible debugging, we also add
2787 console_suspend, a printk module parameter to control
2788 it. Users could use console_suspend (usually
2789 /sys/module/printk/parameters/console_suspend) to
2790 turn on/off it dynamically.
2792 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2793 caches in the slab allocator. Saves per-node memory,
2794 but will impact performance.
2798 noaltinstr [S390] Disables alternative instructions patching
2799 (CPU alternatives feature).
2801 noapic [SMP,APIC] Tells the kernel to not make use of any
2802 IOAPICs that may be present in the system.
2804 noautogroup Disable scheduler automatic task group creation.
2806 nobats [PPC] Do not use BATs for mapping kernel lowmem
2807 on "Classic" PPC cores.
2811 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2813 nodelayacct [KNL] Disable per-task delay accounting
2815 nodsp [SH] Disable hardware DSP at boot time.
2817 noefi Disable EFI runtime services support.
2822 On X86-32 available only on PAE configured kernels.
2823 noexec=on: enable non-executable mappings (default)
2824 noexec=off: disable non-executable mappings
2827 Disable SMAP (Supervisor Mode Access Prevention)
2828 even if it is supported by processor.
2831 Disable SMEP (Supervisor Mode Execution Prevention)
2832 even if it is supported by processor.
2835 This affects only 32-bit executables.
2836 noexec32=on: enable non-executable mappings (default)
2837 read doesn't imply executable mappings
2838 noexec32=off: disable non-executable mappings
2839 read implies executable mappings
2841 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2843 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2844 register save and restore. The kernel will only save
2845 legacy floating-point registers on task switch.
2847 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2849 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2850 Equivalent to smt=1.
2852 [KNL,x86] Disable symmetric multithreading (SMT).
2853 nosmt=force: Force disable SMT, cannot be undone
2854 via the sysfs control file.
2856 nospectre_v1 [PPC] Disable mitigations for Spectre Variant 1 (bounds
2857 check bypass). With this option data leaks are possible
2860 nospectre_v2 [X86,PPC_FSL_BOOK3E] Disable all mitigations for the Spectre variant 2
2861 (indirect branch prediction) vulnerability. System may
2862 allow data leaks with this option, which is equivalent
2865 nospec_store_bypass_disable
2866 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
2868 noxsave [BUGS=X86] Disables x86 extended register state save
2869 and restore using xsave. The kernel will fallback to
2870 enabling legacy floating-point and sse state.
2872 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2873 register states. The kernel will fall back to use
2874 xsave to save the states. By using this parameter,
2875 performance of saving the states is degraded because
2876 xsave doesn't support modified optimization while
2877 xsaveopt supports it on xsaveopt enabled systems.
2879 noxsaves [X86] Disables xsaves and xrstors used in saving and
2880 restoring x86 extended register state in compacted
2881 form of xsave area. The kernel will fall back to use
2882 xsaveopt and xrstor to save and restore the states
2883 in standard form of xsave area. By using this
2884 parameter, xsave area per process might occupy more
2885 memory on xsaves enabled systems.
2887 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2888 wfi(ARM) instruction doesn't work correctly and not to
2889 use it. This is also useful when using JTAG debugger.
2891 no_file_caps Tells the kernel not to honor file capabilities. The
2892 only way then for a file to be executed with privilege
2893 is to be setuid root or executed by root.
2895 nohalt [IA-64] Tells the kernel not to use the power saving
2896 function PAL_HALT_LIGHT when idle. This increases
2897 power-consumption. On the positive side, it reduces
2898 interrupt wake-up latency, which may improve performance
2899 in certain environments such as networked servers or
2902 nohibernate [HIBERNATION] Disable hibernation and resume.
2904 nohz= [KNL] Boottime enable/disable dynamic ticks
2905 Valid arguments: on, off
2908 nohz_full= [KNL,BOOT,SMP,ISOL]
2909 The argument is a cpu list, as described above.
2910 In kernels built with CONFIG_NO_HZ_FULL=y, set
2911 the specified list of CPUs whose tick will be stopped
2912 whenever possible. The boot CPU will be forced outside
2913 the range to maintain the timekeeping. Any CPUs
2914 in this list will have their RCU callbacks offloaded,
2915 just as if they had also been called out in the
2916 rcu_nocbs= boot parameter.
2918 noiotrap [SH] Disables trapped I/O port accesses.
2920 noirqdebug [X86-32] Disables the code which attempts to detect and
2921 disable unhandled interrupt sources.
2923 no_timer_check [X86,APIC] Disables the code which tests for
2924 broken timer IRQ sources.
2926 noisapnp [ISAPNP] Disables ISA PnP code.
2928 noinitrd [RAM] Tells the kernel not to load any configured
2931 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2933 [Deprecated - use intremap=off]
2937 noinvpcid [X86] Disable the INVPCID cpu feature.
2939 nojitter [IA-64] Disables jitter checking for ITC timers.
2941 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2943 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2947 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2948 clock and use the default one.
2950 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2951 steal time is computed, but won't influence scheduler
2954 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2956 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2958 noltlbs [PPC] Do not use large page/tlb entries for kernel
2959 lowmem mapping on PPC40x and PPC8xx
2961 nomca [IA-64] Disable machine check abort handling
2963 nomce [X86-32] Disable Machine Check Exception
2965 nomfgpt [X86-32] Disable Multi-Function General Purpose
2966 Timer usage (for AMD Geode machines).
2968 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2969 shutdown the other cpus. Instead use the REBOOT_VECTOR
2972 nomodule Disable module load
2974 nopat [X86] Disable PAT (page attribute table extension of
2975 pagetables) support.
2977 nopcid [X86-64] Disable the PCID cpu feature.
2979 norandmaps Don't use address space randomization. Equivalent to
2980 echo 0 > /proc/sys/kernel/randomize_va_space
2982 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2983 with UP alternatives
2985 nordrand [X86] Disable kernel use of the RDRAND and
2986 RDSEED instructions even if they are supported
2987 by the processor. RDRAND and RDSEED are still
2988 available to user space applications.
2990 noresume [SWSUSP] Disables resume and restores original swap
2993 no-scroll [VGA] Disables scrollback.
2994 This is required for the Braillex ib80-piezo Braille
2995 reader made by F.H. Papenmeier (Germany).
2999 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
3001 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
3002 and disable the IO APIC. legacy for "maxcpus=0".
3004 nosoftlockup [KNL] Disable the soft-lockup detector.
3006 nosync [HW,M68K] Disables sync negotiation for all devices.
3008 nowatchdog [KNL] Disable both lockup detectors, i.e.
3009 soft-lockup and NMI watchdog (hard-lockup).
3013 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
3015 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
3016 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
3017 Some features depend on CPU0. Known dependencies are:
3018 1. Resume from suspend/hibernate depends on CPU0.
3019 Suspend/hibernate will fail if CPU0 is offline and you
3020 need to online CPU0 before suspend/hibernate.
3021 2. PIC interrupts also depend on CPU0. CPU0 can't be
3022 removed if a PIC interrupt is detected.
3023 It's said poweroff/reboot may depend on CPU0 on some
3024 machines although I haven't seen such issues so far
3025 after CPU0 is offline on a few tested machines.
3026 If the dependencies are under your control, you can
3027 turn on cpu0_hotplug.
3029 nps_mtm_hs_ctr= [KNL,ARC]
3030 This parameter sets the maximum duration, in
3031 cycles, each HW thread of the CTOP can run
3032 without interruptions, before HW switches it.
3033 The actual maximum duration is 16 times this
3035 Format: integer between 1 and 255
3038 nptcg= [IA-64] Override max number of concurrent global TLB
3039 purges which is reported from either PAL_VM_SUMMARY or
3042 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
3043 could support. nr_cpus=n : n >= 1 limits the kernel to
3044 support 'n' processors. It could be larger than the
3045 number of already plugged CPU during bootup, later in
3046 runtime you can physically add extra cpu until it reaches
3047 n. So during boot up some boot time memory for per-cpu
3048 variables need be pre-allocated for later physical cpu
3051 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3053 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
3054 Allowed values are enable and disable
3056 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3057 'node', 'default' can be specified
3058 This can be set from sysctl after boot.
3059 See Documentation/sysctl/vm.txt for details.
3061 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3062 See Documentation/debugging-via-ohci1394.txt for more
3065 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3066 Rather than timing out after 20 ms if an EC
3067 command is not properly ACKed, override the length
3068 of the timeout. We have interrupts disabled while
3069 waiting for the ACK, so if this is set too high
3070 interrupts *may* be lost!
3072 omap_mux= [OMAP] Override bootloader pin multiplexing.
3073 Format: <mux_mode0.mode_name=value>...
3074 For example, to override I2C bus2:
3075 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3077 oprofile.timer= [HW]
3078 Use timer interrupt instead of performance counters
3080 oprofile.cpu_type= Force an oprofile cpu type
3081 This might be useful if you have an older oprofile
3082 userland or if you want common events.
3083 Format: { arch_perfmon }
3084 arch_perfmon: [X86] Force use of architectural
3085 perfmon on Intel CPUs instead of the
3086 CPU specific event set.
3087 timer: [X86] Force use of architectural NMI
3088 timer mode (see also oprofile.timer
3089 for generic hr timer mode)
3091 oops=panic Always panic on oopses. Default is to just kill the
3092 process, but there is a small probability of
3093 deadlocking the machine.
3094 This will also cause panics on machine check exceptions.
3095 Useful together with panic=30 to trigger a reboot.
3097 page_owner= [KNL] Boot-time page_owner enabling option.
3098 Storage of the information about who allocated
3099 each page is disabled in default. With this switch,
3101 on: enable the feature
3103 page_poison= [KNL] Boot-time parameter changing the state of
3104 poisoning on the buddy allocator, available with
3105 CONFIG_PAGE_POISONING=y.
3106 off: turn off poisoning (default)
3107 on: turn on poisoning
3109 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3110 timeout > 0: seconds before rebooting
3111 timeout = 0: wait forever
3112 timeout < 0: reboot immediately
3115 panic_print= Bitmask for printing system info when panic happens.
3116 User can chose combination of the following bits:
3117 bit 0: print all tasks info
3118 bit 1: print system memory info
3119 bit 2: print timer info
3120 bit 3: print locks info if CONFIG_LOCKDEP is on
3121 bit 4: print ftrace buffer
3123 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3126 crash_kexec_post_notifiers
3127 Run kdump after running panic-notifiers and dumping
3128 kmsg. This only for the users who doubt kdump always
3129 succeeds in any situation.
3130 Note that this also increases risks of kdump failure,
3131 because some panic notifiers can make the crashed
3132 kernel more unstable.
3134 parkbd.port= [HW] Parallel port number the keyboard adapter is
3135 connected to, default is 0.
3137 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3138 0 for XT, 1 for AT (default is AT).
3141 parport= [HW,PPT] Specify parallel ports. 0 disables.
3142 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3143 Use 'auto' to force the driver to use any
3144 IRQ/DMA settings detected (the default is to
3145 ignore detected IRQ/DMA settings because of
3146 possible conflicts). You can specify the base
3147 address, IRQ, and DMA settings; IRQ and DMA
3148 should be numbers, or 'auto' (for using detected
3149 settings on that particular port), or 'nofifo'
3150 (to avoid using a FIFO even if it is detected).
3151 Parallel ports are assigned in the order they
3152 are specified on the command line, starting
3155 parport_init_mode= [HW,PPT]
3156 Configure VIA parallel port to operate in
3157 a specific mode. This is necessary on Pegasos
3158 computer where firmware has no options for setting
3159 up parallel port mode and sets it to spp.
3160 Currently this function knows 686a and 8231 chips.
3161 Format: [spp|ps2|epp|ecp|ecpepp]
3164 Halt all CPUs after the first oops has been printed for
3165 the specified number of seconds. This is to be used if
3166 your oopses keep scrolling off the screen.
3171 See header of drivers/block/paride/pcd.c.
3172 See also Documentation/blockdev/paride.txt.
3174 pci=option[,option...] [PCI] various PCI subsystem options.
3176 Some options herein operate on a specific device
3177 or a set of devices (<pci_dev>). These are
3178 specified in one of the following formats:
3180 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
3181 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
3183 Note: the first format specifies a PCI
3184 bus/device/function address which may change
3185 if new hardware is inserted, if motherboard
3186 firmware changes, or due to changes caused
3187 by other kernel parameters. If the
3188 domain is left unspecified, it is
3189 taken to be zero. Optionally, a path
3190 to a device through multiple device/function
3191 addresses can be specified after the base
3192 address (this is more robust against
3193 renumbering issues). The second format
3194 selects devices using IDs from the
3195 configuration space which may match multiple
3196 devices in the system.
3198 earlydump dump PCI config space before the kernel
3200 off [X86] don't probe for the PCI bus
3201 bios [X86-32] force use of PCI BIOS, don't access
3202 the hardware directly. Use this if your machine
3203 has a non-standard PCI host bridge.
3204 nobios [X86-32] disallow use of PCI BIOS, only direct
3205 hardware access methods are allowed. Use this
3206 if you experience crashes upon bootup and you
3207 suspect they are caused by the BIOS.
3208 conf1 [X86] Force use of PCI Configuration Access
3209 Mechanism 1 (config address in IO port 0xCF8,
3210 data in IO port 0xCFC, both 32-bit).
3211 conf2 [X86] Force use of PCI Configuration Access
3212 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3213 the function, IO port 0xCFA, also 8-bit, sets
3214 bus number. The config space is then accessed
3215 through ports 0xC000-0xCFFF).
3216 See http://wiki.osdev.org/PCI for more info
3217 on the configuration access mechanisms.
3218 noaer [PCIE] If the PCIEAER kernel config parameter is
3219 enabled, this kernel boot option can be used to
3220 disable the use of PCIE advanced error reporting.
3221 nodomains [PCI] Disable support for multiple PCI
3222 root domains (aka PCI segments, in ACPI-speak).
3223 nommconf [X86] Disable use of MMCONFIG for PCI
3225 check_enable_amd_mmconf [X86] check for and enable
3226 properly configured MMIO access to PCI
3227 config space on AMD family 10h CPU
3228 nomsi [MSI] If the PCI_MSI kernel config parameter is
3229 enabled, this kernel boot option can be used to
3230 disable the use of MSI interrupts system-wide.
3231 noioapicquirk [APIC] Disable all boot interrupt quirks.
3232 Safety option to keep boot IRQs enabled. This
3233 should never be necessary.
3234 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3235 primary IO-APIC for bridges that cannot disable
3236 boot IRQs. This fixes a source of spurious IRQs
3237 when the system masks IRQs.
3238 noioapicreroute [APIC] Disable workaround that uses the
3239 boot IRQ equivalent of an IRQ that connects to
3240 a chipset where boot IRQs cannot be disabled.
3241 The opposite of ioapicreroute.
3242 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3243 routing table. These calls are known to be buggy
3244 on several machines and they hang the machine
3245 when used, but on other computers it's the only
3246 way to get the interrupt routing table. Try
3247 this option if the kernel is unable to allocate
3248 IRQs or discover secondary PCI buses on your
3250 rom [X86] Assign address space to expansion ROMs.
3251 Use with caution as certain devices share
3252 address decoders between ROMs and other
3254 norom [X86] Do not assign address space to
3255 expansion ROMs that do not already have
3256 BIOS assigned address ranges.
3257 nobar [X86] Do not assign address space to the
3258 BARs that weren't assigned by the BIOS.
3259 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3260 assigned automatically to PCI devices. You can
3261 make the kernel exclude IRQs of your ISA cards
3263 pirqaddr=0xAAAAA [X86] Specify the physical address
3264 of the PIRQ table (normally generated
3265 by the BIOS) if it is outside the
3266 F0000h-100000h range.
3267 lastbus=N [X86] Scan all buses thru bus #N. Can be
3268 useful if the kernel is unable to find your
3269 secondary buses and you want to tell it
3270 explicitly which ones they are.
3271 assign-busses [X86] Always assign all PCI bus
3272 numbers ourselves, overriding
3273 whatever the firmware may have done.
3274 usepirqmask [X86] Honor the possible IRQ mask stored
3275 in the BIOS $PIR table. This is needed on
3276 some systems with broken BIOSes, notably
3277 some HP Pavilion N5400 and Omnibook XE3
3278 notebooks. This will have no effect if ACPI
3279 IRQ routing is enabled.
3280 noacpi [X86] Do not use ACPI for IRQ routing
3281 or for PCI scanning.
3282 use_crs [X86] Use PCI host bridge window information
3283 from ACPI. On BIOSes from 2008 or later, this
3284 is enabled by default. If you need to use this,
3285 please report a bug.
3286 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3287 If you need to use this, please report a bug.
3288 routeirq Do IRQ routing for all PCI devices.
3289 This is normally done in pci_enable_device(),
3290 so this option is a temporary workaround
3291 for broken drivers that don't call it.
3292 skip_isa_align [X86] do not align io start addr, so can
3293 handle more pci cards
3294 noearly [X86] Don't do any early type 1 scanning.
3295 This might help on some broken boards which
3296 machine check when some devices' config space
3297 is read. But various workarounds are disabled
3298 and some IOMMU drivers will not work.
3299 bfsort Sort PCI devices into breadth-first order.
3300 This sorting is done to get a device
3301 order compatible with older (<= 2.4) kernels.
3302 nobfsort Don't sort PCI devices into breadth-first order.
3303 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3304 tuning and use the BIOS-configured MPS defaults.
3305 pcie_bus_safe Set every device's MPS to the largest value
3306 supported by all devices below the root complex.
3307 pcie_bus_perf Set device MPS to the largest allowable MPS
3308 based on its parent bus. Also set MRRS (Max
3309 Read Request Size) to the largest supported
3310 value (no larger than the MPS that the device
3311 or bus can support) for best performance.
3312 pcie_bus_peer2peer Set every device's MPS to 128B, which
3313 every device is guaranteed to support. This
3314 configuration allows peer-to-peer DMA between
3315 any pair of devices, possibly at the cost of
3316 reduced performance. This also guarantees
3317 that hot-added devices will work.
3318 cbiosize=nn[KMG] The fixed amount of bus space which is
3319 reserved for the CardBus bridge's IO window.
3320 The default value is 256 bytes.
3321 cbmemsize=nn[KMG] The fixed amount of bus space which is
3322 reserved for the CardBus bridge's memory
3323 window. The default value is 64 megabytes.
3326 [<order of align>@]<pci_dev>[; ...]
3327 Specifies alignment and device to reassign
3328 aligned memory resources. How to
3329 specify the device is described above.
3330 If <order of align> is not specified,
3331 PAGE_SIZE is used as alignment.
3332 PCI-PCI bridge can be specified, if resource
3333 windows need to be expanded.
3334 To specify the alignment for several
3335 instances of a device, the PCI vendor,
3336 device, subvendor, and subdevice may be
3337 specified, e.g., 4096@pci:8086:9c22:103c:198f
3338 ecrc= Enable/disable PCIe ECRC (transaction layer
3339 end-to-end CRC checking).
3340 bios: Use BIOS/firmware settings. This is the
3344 hpiosize=nn[KMG] The fixed amount of bus space which is
3345 reserved for hotplug bridge's IO window.
3346 Default size is 256 bytes.
3347 hpmemsize=nn[KMG] The fixed amount of bus space which is
3348 reserved for hotplug bridge's memory window.
3349 Default size is 2 megabytes.
3350 hpbussize=nn The minimum amount of additional bus numbers
3351 reserved for buses below a hotplug bridge.
3353 realloc= Enable/disable reallocating PCI bridge resources
3354 if allocations done by BIOS are too small to
3355 accommodate resources required by all child
3357 off: Turn realloc off
3359 realloc same as realloc=on
3360 noari do not use PCIe ARI.
3361 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
3362 do not use PCIe ATS (and IOMMU device IOTLB).
3363 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3364 only look for one device below a PCIe downstream
3366 big_root_window Try to add a big 64bit memory window to the PCIe
3367 root complex on AMD CPUs. Some GFX hardware
3368 can resize a BAR to allow access to all VRAM.
3369 Adding the window is slightly risky (it may
3370 conflict with unreported devices), so this
3372 disable_acs_redir=<pci_dev>[; ...]
3373 Specify one or more PCI devices (in the format
3374 specified above) separated by semicolons.
3375 Each device specified will have the PCI ACS
3376 redirect capabilities forced off which will
3377 allow P2P traffic between devices through
3378 bridges without forcing it upstream. Note:
3379 this removes isolation between devices and
3380 may put more devices in an IOMMU group.
3382 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3385 force Enable ASPM even on devices that claim not to support it.
3386 WARNING: Forcing ASPM on may cause system lockups.
3388 pcie_ports= [PCIE] PCIe port services handling:
3389 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
3390 even if the platform doesn't give the OS permission to
3391 use them. This may cause conflicts if the platform
3392 also tries to use these services.
3393 compat Disable native PCIe services (PME, AER, DPC, PCIe
3396 pcie_port_pm= [PCIE] PCIe port power management handling:
3397 off Disable power management of all PCIe ports
3398 force Forcibly enable power management of all PCIe ports
3400 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3401 nomsi Do not use MSI for native PCIe PME signaling (this makes
3402 all PCIe root ports use INTx for all services).
3404 pcmv= [HW,PCMCIA] BadgePAD 4
3408 Keep all power-domains already enabled by bootloader on,
3409 even if no driver has claimed them. This is useful
3410 for debug and development, but should not be
3411 needed on a platform with proper driver support.
3414 See Documentation/blockdev/paride.txt.
3416 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3419 See arch/parisc/kernel/pdc_chassis.c
3421 percpu_alloc= Select which percpu first chunk allocator to use.
3422 Currently supported values are "embed" and "page".
3423 Archs may support subset or none of the selections.
3424 See comments in mm/percpu.c for details on each
3425 allocator. This parameter is primarily for debugging
3426 and performance comparison.
3429 See Documentation/blockdev/paride.txt.
3432 See Documentation/blockdev/paride.txt.
3434 pirq= [SMP,APIC] Manual mp-table setup
3435 See Documentation/x86/i386/IO-APIC.txt.
3437 plip= [PPT,NET] Parallel port network link
3438 Format: { parport<nr> | timid | 0 }
3439 See also Documentation/admin-guide/parport.rst.
3441 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3442 Override pmtimer IOPort with a hex value.
3446 Enable PNP debug messages (depends on the
3447 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3448 via /sys/module/pnp/parameters/debug. We always show
3449 current resource usage; turning this on also shows
3450 possible settings and some assignment information.
3456 { on | off | curr | res | no-curr | no-res }
3459 [ISAPNP] Exclude IRQs for the autoconfiguration
3462 [ISAPNP] Exclude DMAs for the autoconfiguration
3464 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3465 Ranges are in pairs (I/O port base and size).
3468 [ISAPNP] Exclude memory regions for the
3470 Ranges are in pairs (memory base and size).
3472 ports= [IP_VS_FTP] IPVS ftp helper module
3474 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3476 Format: <port>,<port>....
3478 powersave=off [PPC] This option disables power saving features.
3479 It specifically disables cpuidle and sets the
3480 platform machine description specific power_save
3481 function to NULL. On Idle the CPU just reduces
3484 ppc_strict_facility_enable
3485 [PPC] This option catches any kernel floating point,
3486 Altivec, VSX and SPE outside of regions specifically
3487 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3488 There is some performance impact when enabling this.
3492 Disable Hardware Transactional Memory
3494 print-fatal-signals=
3495 [KNL] debug: print fatal signals
3497 If enabled, warn about various signal handling
3498 related application anomalies: too many signals,
3499 too many POSIX.1 timers, fatal signals causing a
3502 If you hit the warning due to signal overflow,
3503 you might want to try "ulimit -i unlimited".
3507 printk.always_kmsg_dump=
3508 Trigger kmsg_dump for cases other than kernel oops or
3510 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3513 printk.devkmsg={on,off,ratelimit}
3514 Control writing to /dev/kmsg.
3515 on - unlimited logging to /dev/kmsg from userspace
3516 off - logging to /dev/kmsg disabled
3517 ratelimit - ratelimit the logging
3520 printk.time= Show timing data prefixed to each printk message line
3521 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3523 processor.max_cstate= [HW,ACPI]
3524 Limit processor to maximum C-state
3525 max_cstate=9 overrides any DMI blacklist limit.
3527 processor.nocst [HW,ACPI]
3528 Ignore the _CST method to determine C-states,
3529 instead using the legacy FADT method
3531 profile= [KNL] Enable kernel profiling via /proc/profile
3532 Format: [<profiletype>,]<number>
3533 Param: <profiletype>: "schedule", "sleep", or "kvm"
3534 [defaults to kernel profiling]
3535 Param: "schedule" - profile schedule points.
3536 Param: "sleep" - profile D-state sleeping (millisecs).
3537 Requires CONFIG_SCHEDSTATS
3538 Param: "kvm" - profile VM exits.
3539 Param: <number> - step/bucket size as a power of 2 for
3540 statistical time based profiling.
3542 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3544 See Documentation/blockdev/ramdisk.txt.
3546 psi= [KNL] Enable or disable pressure stall information
3550 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3551 probe for; one of (bare|imps|exps|lifebook|any).
3552 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3554 psmouse.resetafter= [HW,MOUSE]
3555 Try to reset the device after so many bad packets
3558 [HW,MOUSE] Set desired mouse resolution, in dpi.
3559 psmouse.smartscroll=
3560 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3561 0 = disabled, 1 = enabled (default).
3563 pstore.backend= Specify the name of the pstore backend to use
3566 See Documentation/blockdev/paride.txt.
3568 pti= [X86_64] Control Page Table Isolation of user and
3569 kernel address spaces. Disabling this feature
3570 removes hardening, but improves performance of
3571 system calls and interrupts.
3573 on - unconditionally enable
3574 off - unconditionally disable
3575 auto - kernel detects whether your CPU model is
3576 vulnerable to issues that PTI mitigates
3578 Not specifying this option is equivalent to pti=auto.
3581 Equivalent to pti=off
3584 [KNL] Number of legacy pty's. Overwrites compiled-in
3587 quiet [KNL] Disable most log messages
3592 See Documentation/admin-guide/md.rst.
3594 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3595 See Documentation/blockdev/ramdisk.txt.
3597 random.trust_cpu={on,off}
3598 [KNL] Enable or disable trusting the use of the
3599 CPU's random number generator (if available) to
3600 fully seed the kernel's CRNG. Default is controlled
3601 by CONFIG_RANDOM_TRUST_CPU.
3603 ras=option[,option,...] [KNL] RAS-specific options
3606 Disable the Correctable Errors Collector,
3607 see CONFIG_RAS_CEC help text.
3610 The argument is a cpu list, as described above.
3612 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3613 the specified list of CPUs to be no-callback CPUs.
3614 Invocation of these CPUs' RCU callbacks will be
3615 offloaded to "rcuox/N" kthreads created for that
3616 purpose, where "x" is "p" for RCU-preempt, and
3617 "s" for RCU-sched, and "N" is the CPU number.
3618 This reduces OS jitter on the offloaded CPUs,
3619 which can be useful for HPC and real-time
3620 workloads. It can also improve energy efficiency
3621 for asymmetric multiprocessors.
3624 Rather than requiring that offloaded CPUs
3625 (specified by rcu_nocbs= above) explicitly
3626 awaken the corresponding "rcuoN" kthreads,
3627 make these kthreads poll for callbacks.
3628 This improves the real-time response for the
3629 offloaded CPUs by relieving them of the need to
3630 wake up the corresponding kthread, but degrades
3631 energy efficiency by requiring that the kthreads
3632 periodically wake up to do the polling.
3634 rcutree.blimit= [KNL]
3635 Set maximum number of finished RCU callbacks to
3636 process in one batch.
3638 rcutree.dump_tree= [KNL]
3639 Dump the structure of the rcu_node combining tree
3640 out at early boot. This is used for diagnostic
3641 purposes, to verify correct tree setup.
3643 rcutree.gp_cleanup_delay= [KNL]
3644 Set the number of jiffies to delay each step of
3645 RCU grace-period cleanup.
3647 rcutree.gp_init_delay= [KNL]
3648 Set the number of jiffies to delay each step of
3649 RCU grace-period initialization.
3651 rcutree.gp_preinit_delay= [KNL]
3652 Set the number of jiffies to delay each step of
3653 RCU grace-period pre-initialization, that is,
3654 the propagation of recent CPU-hotplug changes up
3655 the rcu_node combining tree.
3657 rcutree.rcu_fanout_exact= [KNL]
3658 Disable autobalancing of the rcu_node combining
3659 tree. This is used by rcutorture, and might
3660 possibly be useful for architectures having high
3661 cache-to-cache transfer latencies.
3663 rcutree.rcu_fanout_leaf= [KNL]
3664 Change the number of CPUs assigned to each
3665 leaf rcu_node structure. Useful for very
3666 large systems, which will choose the value 64,
3667 and for NUMA systems with large remote-access
3668 latencies, which will choose a value aligned
3669 with the appropriate hardware boundaries.
3671 rcutree.jiffies_till_first_fqs= [KNL]
3672 Set delay from grace-period initialization to
3673 first attempt to force quiescent states.
3674 Units are jiffies, minimum value is zero,
3675 and maximum value is HZ.
3677 rcutree.jiffies_till_next_fqs= [KNL]
3678 Set delay between subsequent attempts to force
3679 quiescent states. Units are jiffies, minimum
3680 value is one, and maximum value is HZ.
3682 rcutree.jiffies_till_sched_qs= [KNL]
3683 Set required age in jiffies for a
3684 given grace period before RCU starts
3685 soliciting quiescent-state help from
3686 rcu_note_context_switch() and cond_resched().
3687 If not specified, the kernel will calculate
3688 a value based on the most recent settings
3689 of rcutree.jiffies_till_first_fqs
3690 and rcutree.jiffies_till_next_fqs.
3691 This calculated value may be viewed in
3692 rcutree.jiffies_to_sched_qs. Any attempt to set
3693 rcutree.jiffies_to_sched_qs will be cheerfully
3696 rcutree.kthread_prio= [KNL,BOOT]
3697 Set the SCHED_FIFO priority of the RCU per-CPU
3698 kthreads (rcuc/N). This value is also used for
3699 the priority of the RCU boost threads (rcub/N)
3700 and for the RCU grace-period kthreads (rcu_bh,
3701 rcu_preempt, and rcu_sched). If RCU_BOOST is
3702 set, valid values are 1-99 and the default is 1
3703 (the least-favored priority). Otherwise, when
3704 RCU_BOOST is not set, valid values are 0-99 and
3705 the default is zero (non-realtime operation).
3707 rcutree.rcu_nocb_leader_stride= [KNL]
3708 Set the number of NOCB kthread groups, which
3709 defaults to the square root of the number of
3710 CPUs. Larger numbers reduces the wakeup overhead
3711 on the per-CPU grace-period kthreads, but increases
3712 that same overhead on each group's leader.
3714 rcutree.qhimark= [KNL]
3715 Set threshold of queued RCU callbacks beyond which
3716 batch limiting is disabled.
3718 rcutree.qlowmark= [KNL]
3719 Set threshold of queued RCU callbacks below which
3720 batch limiting is re-enabled.
3722 rcutree.rcu_idle_gp_delay= [KNL]
3723 Set wakeup interval for idle CPUs that have
3724 RCU callbacks (RCU_FAST_NO_HZ=y).
3726 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3727 Set wakeup interval for idle CPUs that have
3728 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3729 Lazy RCU callbacks are those which RCU can
3730 prove do nothing more than free memory.
3732 rcutree.rcu_kick_kthreads= [KNL]
3733 Cause the grace-period kthread to get an extra
3734 wake_up() if it sleeps three times longer than
3735 it should at force-quiescent-state time.
3736 This wake_up() will be accompanied by a
3737 WARN_ONCE() splat and an ftrace_dump().
3739 rcutree.sysrq_rcu= [KNL]
3740 Commandeer a sysrq key to dump out Tree RCU's
3741 rcu_node tree with an eye towards determining
3742 why a new grace period has not yet started.
3744 rcuperf.gp_async= [KNL]
3745 Measure performance of asynchronous
3746 grace-period primitives such as call_rcu().
3748 rcuperf.gp_async_max= [KNL]
3749 Specify the maximum number of outstanding
3750 callbacks per writer thread. When a writer
3751 thread exceeds this limit, it invokes the
3752 corresponding flavor of rcu_barrier() to allow
3753 previously posted callbacks to drain.
3755 rcuperf.gp_exp= [KNL]
3756 Measure performance of expedited synchronous
3757 grace-period primitives.
3759 rcuperf.holdoff= [KNL]
3760 Set test-start holdoff period. The purpose of
3761 this parameter is to delay the start of the
3762 test until boot completes in order to avoid
3765 rcuperf.nreaders= [KNL]
3766 Set number of RCU readers. The value -1 selects
3767 N, where N is the number of CPUs. A value
3768 "n" less than -1 selects N-n+1, where N is again
3769 the number of CPUs. For example, -2 selects N
3770 (the number of CPUs), -3 selects N+1, and so on.
3771 A value of "n" less than or equal to -N selects
3774 rcuperf.nwriters= [KNL]
3775 Set number of RCU writers. The values operate
3776 the same as for rcuperf.nreaders.
3777 N, where N is the number of CPUs
3779 rcuperf.perf_type= [KNL]
3780 Specify the RCU implementation to test.
3782 rcuperf.shutdown= [KNL]
3783 Shut the system down after performance tests
3784 complete. This is useful for hands-off automated
3787 rcuperf.verbose= [KNL]
3788 Enable additional printk() statements.
3790 rcuperf.writer_holdoff= [KNL]
3791 Write-side holdoff between grace periods,
3792 in microseconds. The default of zero says
3795 rcutorture.fqs_duration= [KNL]
3796 Set duration of force_quiescent_state bursts
3799 rcutorture.fqs_holdoff= [KNL]
3800 Set holdoff time within force_quiescent_state bursts
3803 rcutorture.fqs_stutter= [KNL]
3804 Set wait time between force_quiescent_state bursts
3807 rcutorture.fwd_progress= [KNL]
3808 Enable RCU grace-period forward-progress testing
3809 for the types of RCU supporting this notion.
3811 rcutorture.fwd_progress_div= [KNL]
3812 Specify the fraction of a CPU-stall-warning
3813 period to do tight-loop forward-progress testing.
3815 rcutorture.fwd_progress_holdoff= [KNL]
3816 Number of seconds to wait between successive
3817 forward-progress tests.
3819 rcutorture.fwd_progress_need_resched= [KNL]
3820 Enclose cond_resched() calls within checks for
3821 need_resched() during tight-loop forward-progress
3824 rcutorture.gp_cond= [KNL]
3825 Use conditional/asynchronous update-side
3826 primitives, if available.
3828 rcutorture.gp_exp= [KNL]
3829 Use expedited update-side primitives, if available.
3831 rcutorture.gp_normal= [KNL]
3832 Use normal (non-expedited) asynchronous
3833 update-side primitives, if available.
3835 rcutorture.gp_sync= [KNL]
3836 Use normal (non-expedited) synchronous
3837 update-side primitives, if available. If all
3838 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3839 rcutorture.gp_normal=, and rcutorture.gp_sync=
3840 are zero, rcutorture acts as if is interpreted
3841 they are all non-zero.
3843 rcutorture.n_barrier_cbs= [KNL]
3844 Set callbacks/threads for rcu_barrier() testing.
3846 rcutorture.nfakewriters= [KNL]
3847 Set number of concurrent RCU writers. These just
3848 stress RCU, they don't participate in the actual
3849 test, hence the "fake".
3851 rcutorture.nreaders= [KNL]
3852 Set number of RCU readers. The value -1 selects
3853 N-1, where N is the number of CPUs. A value
3854 "n" less than -1 selects N-n-2, where N is again
3855 the number of CPUs. For example, -2 selects N
3856 (the number of CPUs), -3 selects N+1, and so on.
3858 rcutorture.object_debug= [KNL]
3859 Enable debug-object double-call_rcu() testing.
3861 rcutorture.onoff_holdoff= [KNL]
3862 Set time (s) after boot for CPU-hotplug testing.
3864 rcutorture.onoff_interval= [KNL]
3865 Set time (jiffies) between CPU-hotplug operations,
3866 or zero to disable CPU-hotplug testing.
3868 rcutorture.shuffle_interval= [KNL]
3869 Set task-shuffle interval (s). Shuffling tasks
3870 allows some CPUs to go into dyntick-idle mode
3871 during the rcutorture test.
3873 rcutorture.shutdown_secs= [KNL]
3874 Set time (s) after boot system shutdown. This
3875 is useful for hands-off automated testing.
3877 rcutorture.stall_cpu= [KNL]
3878 Duration of CPU stall (s) to test RCU CPU stall
3879 warnings, zero to disable.
3881 rcutorture.stall_cpu_holdoff= [KNL]
3882 Time to wait (s) after boot before inducing stall.
3884 rcutorture.stall_cpu_irqsoff= [KNL]
3885 Disable interrupts while stalling if set.
3887 rcutorture.stat_interval= [KNL]
3888 Time (s) between statistics printk()s.
3890 rcutorture.stutter= [KNL]
3891 Time (s) to stutter testing, for example, specifying
3892 five seconds causes the test to run for five seconds,
3893 wait for five seconds, and so on. This tests RCU's
3894 ability to transition abruptly to and from idle.
3896 rcutorture.test_boost= [KNL]
3897 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3898 "Maybe" means test if the RCU implementation
3899 under test support RCU priority boosting.
3901 rcutorture.test_boost_duration= [KNL]
3902 Duration (s) of each individual boost test.
3904 rcutorture.test_boost_interval= [KNL]
3905 Interval (s) between each boost test.
3907 rcutorture.test_no_idle_hz= [KNL]
3908 Test RCU's dyntick-idle handling. See also the
3909 rcutorture.shuffle_interval parameter.
3911 rcutorture.torture_type= [KNL]
3912 Specify the RCU implementation to test.
3914 rcutorture.verbose= [KNL]
3915 Enable additional printk() statements.
3917 rcupdate.rcu_cpu_stall_suppress= [KNL]
3918 Suppress RCU CPU stall warning messages.
3920 rcupdate.rcu_cpu_stall_timeout= [KNL]
3921 Set timeout for RCU CPU stall warning messages.
3923 rcupdate.rcu_expedited= [KNL]
3924 Use expedited grace-period primitives, for
3925 example, synchronize_rcu_expedited() instead
3926 of synchronize_rcu(). This reduces latency,
3927 but can increase CPU utilization, degrade
3928 real-time latency, and degrade energy efficiency.
3929 No effect on CONFIG_TINY_RCU kernels.
3931 rcupdate.rcu_normal= [KNL]
3932 Use only normal grace-period primitives,
3933 for example, synchronize_rcu() instead of
3934 synchronize_rcu_expedited(). This improves
3935 real-time latency, CPU utilization, and
3936 energy efficiency, but can expose users to
3937 increased grace-period latency. This parameter
3938 overrides rcupdate.rcu_expedited. No effect on
3939 CONFIG_TINY_RCU kernels.
3941 rcupdate.rcu_normal_after_boot= [KNL]
3942 Once boot has completed (that is, after
3943 rcu_end_inkernel_boot() has been invoked), use
3944 only normal grace-period primitives. No effect
3945 on CONFIG_TINY_RCU kernels.
3947 rcupdate.rcu_task_stall_timeout= [KNL]
3948 Set timeout in jiffies for RCU task stall warning
3949 messages. Disable with a value less than or equal
3952 rcupdate.rcu_self_test= [KNL]
3953 Run the RCU early boot self tests
3957 Run specified binary instead of /init from the ramdisk,
3958 used for early userspace startup. See initrd.
3961 Turn on/off individual RDT features. List is:
3962 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
3964 E.g. to turn on cmt and turn off mba use:
3968 Format (x86 or x86_64):
3969 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3971 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3973 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3974 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3975 reboot_force is either force or not specified,
3976 reboot_cpu is s[mp]#### with #### being the processor
3977 to be used for rebooting.
3980 [KNL, SMP] Set scheduler's default relax_domain_level.
3981 See Documentation/cgroup-v1/cpusets.txt.
3983 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
3984 Format: <base1>,<size1>[,<base2>,<size2>,...]
3985 Reserve I/O ports or memory so the kernel won't use
3986 them. If <base> is less than 0x10000, the region
3987 is assumed to be I/O ports; otherwise it is memory.
3989 reservetop= [X86-32]
3991 Reserves a hole at the top of the kernel virtual
3996 Set the amount of memory to reserve for BIOS at
3997 the bottom of the address space.
3999 reset_devices [KNL] Force drivers to reset the underlying device
4000 during initialization.
4003 Specify the partition device for software suspend
4005 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
4007 resume_offset= [SWSUSP]
4008 Specify the offset from the beginning of the partition
4009 given by "resume=" at which the swap header is located,
4010 in <PAGE_SIZE> units (needed only for swap files).
4011 See Documentation/power/swsusp-and-swap-files.txt
4013 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
4014 read the resume files
4016 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
4017 Useful for devices that are detected asynchronously
4018 (e.g. USB and MMC devices).
4020 hibernate= [HIBERNATION]
4021 noresume Don't check if there's a hibernation image
4022 present during boot.
4023 nocompress Don't compress/decompress hibernation images.
4024 no Disable hibernation and resume.
4025 protect_image Turn on image protection during restoration
4026 (that will set all pages holding image data
4027 during restoration read-only).
4029 retain_initrd [RAM] Keep initrd memory after extraction
4031 rfkill.default_state=
4032 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
4033 etc. communication is blocked by default.
4036 rfkill.master_switch_mode=
4037 0 The "airplane mode" button does nothing.
4038 1 The "airplane mode" button toggles between everything
4039 blocked and the previous configuration.
4040 2 The "airplane mode" button toggles between everything
4041 blocked and everything unblocked.
4043 rhash_entries= [KNL,NET]
4044 Set number of hash buckets for route cache
4047 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
4050 ro [KNL] Mount root device read-only on boot
4053 on Mark read-only kernel memory as read-only (default).
4054 off Leave read-only kernel memory writable for debugging.
4057 Enable the uart passthrough on the designated usb port
4058 on Rockchip SoCs. When active, the signals of the
4059 debug-uart get routed to the D+ and D- pins of the usb
4060 port and the regular usb controller gets disabled.
4062 root= [KNL] Root filesystem
4063 See name_to_dev_t comment in init/do_mounts.c.
4065 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
4066 mount the root filesystem
4068 rootflags= [KNL] Set root filesystem mount option string
4070 rootfstype= [KNL] Set root filesystem type
4072 rootwait [KNL] Wait (indefinitely) for root device to show up.
4073 Useful for devices that are detected asynchronously
4074 (e.g. USB and MMC devices).
4076 rproc_mem=nn[KMG][@address]
4077 [KNL,ARM,CMA] Remoteproc physical memory block.
4078 Memory area to be used by remote processor image,
4081 rw [KNL] Mount root device read-write on boot
4083 S [KNL] Run init in single mode
4085 s390_iommu= [HW,S390]
4086 Set s390 IOTLB flushing mode
4088 With strict flushing every unmap operation will result in
4089 an IOTLB flush. Default is lazy flushing before reuse,
4093 See drivers/net/irda/sa1100_ir.c.
4095 sbni= [NET] Granch SBNI12 leased line adapter
4097 sched_debug [KNL] Enables verbose scheduler debug messages.
4099 schedstats= [KNL,X86] Enable or disable scheduled statistics.
4100 Allowed values are enable and disable. This feature
4101 incurs a small amount of overhead in the scheduler
4102 but is useful for debugging and performance tuning.
4104 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
4105 xtime_lock contention on larger systems, and/or RCU lock
4106 contention on all systems with CONFIG_MAXSMP set.
4107 Format: { "0" | "1" }
4108 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
4110 Note: increases power consumption, thus should only be
4111 enabled if running jitter sensitive (HPC/RT) workloads.
4113 security= [SECURITY] Choose a security module to enable at boot.
4114 If this boot parameter is not specified, only the first
4115 security module asking for security registration will be
4116 loaded. An invalid security module name will be treated
4117 as if no module has been chosen.
4119 selinux= [SELINUX] Disable or enable SELinux at boot time.
4120 Format: { "0" | "1" }
4121 See security/selinux/Kconfig help text.
4124 Default value is set via kernel config option.
4125 If enabled at boot time, /selinux/disable can be used
4126 later to disable prior to initial policy load.
4128 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
4129 Format: { "0" | "1" }
4130 See security/apparmor/Kconfig help text
4133 Default value is set via kernel config option.
4135 serialnumber [BUGS=X86-32]
4138 Maximal number of shapers.
4146 Disable merging of slabs with similar size. May be
4147 necessary if there is some reason to distinguish
4148 allocs to different slabs, especially in hardened
4149 environments where the risk of heap overflows and
4150 layout control by attackers can usually be
4151 frustrated by disabling merging. This will reduce
4152 most of the exposure of a heap attack to a single
4153 cache (risks via metadata attacks are mostly
4154 unchanged). Debug options disable merging on their
4156 For more information see Documentation/vm/slub.rst.
4158 slab_max_order= [MM, SLAB]
4159 Determines the maximum allowed order for slabs.
4160 A high setting may cause OOMs due to memory
4161 fragmentation. Defaults to 1 for systems with
4162 more than 32MB of RAM, 0 otherwise.
4164 slub_debug[=options[,slabs]] [MM, SLUB]
4165 Enabling slub_debug allows one to determine the
4166 culprit if slab objects become corrupted. Enabling
4167 slub_debug can create guard zones around objects and
4168 may poison objects when not in use. Also tracks the
4169 last alloc / free. For more information see
4170 Documentation/vm/slub.rst.
4172 slub_memcg_sysfs= [MM, SLUB]
4173 Determines whether to enable sysfs directories for
4174 memory cgroup sub-caches. 1 to enable, 0 to disable.
4175 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
4176 Enabling this can lead to a very high number of debug
4177 directories and files being created under
4180 slub_max_order= [MM, SLUB]
4181 Determines the maximum allowed order for slabs.
4182 A high setting may cause OOMs due to memory
4183 fragmentation. For more information see
4184 Documentation/vm/slub.rst.
4186 slub_min_objects= [MM, SLUB]
4187 The minimum number of objects per slab. SLUB will
4188 increase the slab order up to slub_max_order to
4189 generate a sufficiently large slab able to contain
4190 the number of objects indicated. The higher the number
4191 of objects the smaller the overhead of tracking slabs
4192 and the less frequently locks need to be acquired.
4193 For more information see Documentation/vm/slub.rst.
4195 slub_min_order= [MM, SLUB]
4196 Determines the minimum page order for slabs. Must be
4197 lower than slub_max_order.
4198 For more information see Documentation/vm/slub.rst.
4200 slub_nomerge [MM, SLUB]
4201 Same with slab_nomerge. This is supported for legacy.
4202 See slab_nomerge for more information.
4205 Format: <io1>[,<io2>[,...,<io8>]]
4207 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4208 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4209 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4210 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4211 smsc-ircc2.ircc_irq= [HW] IRQ line
4212 smsc-ircc2.ircc_dma= [HW] DMA channel
4213 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4214 0: Toshiba Satellite 1800 (GP data pin select)
4215 1: Fast pin select (default)
4218 smt [KNL,S390] Set the maximum number of threads (logical
4219 CPUs) to use per physical CPU on systems capable of
4220 symmetric multithreading (SMT). Will be capped to the
4221 actual hardware limit.
4223 Default: -1 (no limit)
4226 [KNL] Should the soft-lockup detector generate panics.
4229 A nonzero value instructs the soft-lockup detector
4230 to panic the machine when a soft-lockup occurs. This
4231 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
4232 which is the respective build-time switch to that
4235 softlockup_all_cpu_backtrace=
4236 [KNL] Should the soft-lockup detector generate
4237 backtraces on all cpus.
4240 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4241 See Documentation/laptops/sonypi.txt
4243 spectre_v2= [X86] Control mitigation of Spectre variant 2
4244 (indirect branch speculation) vulnerability.
4245 The default operation protects the kernel from
4248 on - unconditionally enable, implies
4250 off - unconditionally disable, implies
4252 auto - kernel detects whether your CPU model is
4255 Selecting 'on' will, and 'auto' may, choose a
4256 mitigation method at run time according to the
4257 CPU, the available microcode, the setting of the
4258 CONFIG_RETPOLINE configuration option, and the
4259 compiler with which the kernel was built.
4261 Selecting 'on' will also enable the mitigation
4262 against user space to user space task attacks.
4264 Selecting 'off' will disable both the kernel and
4265 the user space protections.
4267 Specific mitigations can also be selected manually:
4269 retpoline - replace indirect branches
4270 retpoline,generic - google's original retpoline
4271 retpoline,amd - AMD-specific minimal thunk
4273 Not specifying this option is equivalent to
4277 [X86] Control mitigation of Spectre variant 2
4278 (indirect branch speculation) vulnerability between
4281 on - Unconditionally enable mitigations. Is
4282 enforced by spectre_v2=on
4284 off - Unconditionally disable mitigations. Is
4285 enforced by spectre_v2=off
4287 prctl - Indirect branch speculation is enabled,
4288 but mitigation can be enabled via prctl
4289 per thread. The mitigation control state
4290 is inherited on fork.
4293 - Like "prctl" above, but only STIBP is
4294 controlled per thread. IBPB is issued
4295 always when switching between different user
4299 - Same as "prctl" above, but all seccomp
4300 threads will enable the mitigation unless
4301 they explicitly opt out.
4304 - Like "seccomp" above, but only STIBP is
4305 controlled per thread. IBPB is issued
4306 always when switching between different
4307 user space processes.
4309 auto - Kernel selects the mitigation depending on
4310 the available CPU features and vulnerability.
4313 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
4315 Not specifying this option is equivalent to
4316 spectre_v2_user=auto.
4318 spec_store_bypass_disable=
4319 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4320 (Speculative Store Bypass vulnerability)
4322 Certain CPUs are vulnerable to an exploit against a
4323 a common industry wide performance optimization known
4324 as "Speculative Store Bypass" in which recent stores
4325 to the same memory location may not be observed by
4326 later loads during speculative execution. The idea
4327 is that such stores are unlikely and that they can
4328 be detected prior to instruction retirement at the
4329 end of a particular speculation execution window.
4331 In vulnerable processors, the speculatively forwarded
4332 store can be used in a cache side channel attack, for
4333 example to read memory to which the attacker does not
4334 directly have access (e.g. inside sandboxed code).
4336 This parameter controls whether the Speculative Store
4337 Bypass optimization is used.
4339 On x86 the options are:
4341 on - Unconditionally disable Speculative Store Bypass
4342 off - Unconditionally enable Speculative Store Bypass
4343 auto - Kernel detects whether the CPU model contains an
4344 implementation of Speculative Store Bypass and
4345 picks the most appropriate mitigation. If the
4346 CPU is not vulnerable, "off" is selected. If the
4347 CPU is vulnerable the default mitigation is
4348 architecture and Kconfig dependent. See below.
4349 prctl - Control Speculative Store Bypass per thread
4350 via prctl. Speculative Store Bypass is enabled
4351 for a process by default. The state of the control
4352 is inherited on fork.
4353 seccomp - Same as "prctl" above, but all seccomp threads
4354 will disable SSB unless they explicitly opt out.
4356 Default mitigations:
4357 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4359 On powerpc the options are:
4361 on,auto - On Power8 and Power9 insert a store-forwarding
4362 barrier on kernel entry and exit. On Power7
4363 perform a software flush on kernel entry and
4367 Not specifying this option is equivalent to
4368 spec_store_bypass_disable=auto.
4370 spia_io_base= [HW,MTD]
4375 srcutree.counter_wrap_check [KNL]
4376 Specifies how frequently to check for
4377 grace-period sequence counter wrap for the
4378 srcu_data structure's ->srcu_gp_seq_needed field.
4379 The greater the number of bits set in this kernel
4380 parameter, the less frequently counter wrap will
4381 be checked for. Note that the bottom two bits
4384 srcutree.exp_holdoff [KNL]
4385 Specifies how many nanoseconds must elapse
4386 since the end of the last SRCU grace period for
4387 a given srcu_struct until the next normal SRCU
4388 grace period will be considered for automatic
4389 expediting. Set to zero to disable automatic
4393 Speculative Store Bypass Disable control
4395 On CPUs that are vulnerable to the Speculative
4396 Store Bypass vulnerability and offer a
4397 firmware based mitigation, this parameter
4398 indicates how the mitigation should be used:
4400 force-on: Unconditionally enable mitigation for
4401 for both kernel and userspace
4402 force-off: Unconditionally disable mitigation for
4403 for both kernel and userspace
4404 kernel: Always enable mitigation in the
4405 kernel, and offer a prctl interface
4406 to allow userspace to register its
4407 interest in being mitigated too.
4409 stack_guard_gap= [MM]
4410 override the default stack gap protection. The value
4411 is in page units and it defines how many pages prior
4412 to (for stacks growing down) resp. after (for stacks
4413 growing up) the main stack are reserved for no other
4414 mapping. Default value is 256 pages.
4417 Enabled the stack tracer on boot up.
4419 stacktrace_filter=[function-list]
4420 [FTRACE] Limit the functions that the stack tracer
4421 will trace at boot up. function-list is a comma separated
4422 list of functions. This list can be changed at run
4423 time by the stack_trace_filter file in the debugfs
4424 tracing directory. Note, this enables stack tracing
4425 and the stacktrace above is not needed.
4429 Set the STI (builtin display/keyboard on the HP-PARISC
4430 machines) console (graphic card) which should be used
4431 as the initial boot-console.
4432 See also comment in drivers/video/console/sticore.c.
4435 See comment in drivers/video/console/sticore.c.
4438 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4440 sunrpc.min_resvport=
4441 sunrpc.max_resvport=
4443 SunRPC servers often require that client requests
4444 originate from a privileged port (i.e. a port in the
4445 range 0 < portnr < 1024).
4446 An administrator who wishes to reserve some of these
4447 ports for other uses may adjust the range that the
4448 kernel's sunrpc client considers to be privileged
4449 using these two parameters to set the minimum and
4450 maximum port values.
4452 sunrpc.svc_rpc_per_connection_limit=
4454 Limit the number of requests that the server will
4455 process in parallel from a single connection.
4456 The default value is 0 (no limit).
4460 Control how the NFS server code allocates CPUs to
4461 service thread pools. Depending on how many NICs
4462 you have and where their interrupts are bound, this
4463 option will affect which CPUs will do NFS serving.
4464 Note: this parameter cannot be changed while the
4465 NFS server is running.
4467 auto the server chooses an appropriate mode
4468 automatically using heuristics
4469 global a single global pool contains all CPUs
4470 percpu one pool for each CPU
4471 pernode one pool for each NUMA node (equivalent
4472 to global on non-NUMA machines)
4474 sunrpc.tcp_slot_table_entries=
4475 sunrpc.udp_slot_table_entries=
4477 Sets the upper limit on the number of simultaneous
4478 RPC calls that can be sent from the client to a
4479 server. Increasing these values may allow you to
4480 improve throughput, but will also increase the
4481 amount of memory reserved for use by the client.
4483 suspend.pm_test_delay=
4485 Sets the number of seconds to remain in a suspend test
4486 mode before resuming the system (see
4487 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4488 is set. Default value is 5.
4491 [KNL] Enable accounting of swap in memory resource
4492 controller if no parameter or 1 is given or disable
4493 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4495 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4496 Format: { <int> | force | noforce }
4497 <int> -- Number of I/O TLB slabs
4498 force -- force using of bounce buffers even if they
4499 wouldn't be automatically used by the kernel
4500 noforce -- Never use bounce buffers (for debugging)
4504 sysfs.deprecated=0|1 [KNL]
4505 Enable/disable old style sysfs layout for old udev
4506 on older distributions. When this option is enabled
4507 very new udev will not work anymore. When this option
4508 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4509 in older udev will not work anymore.
4510 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4511 the kernel configuration.
4513 sysrq_always_enabled
4515 Ignore sysrq setting - this boot parameter will
4516 neutralize any effect of /proc/sys/kernel/sysrq.
4517 Useful for debugging.
4519 tcpmhash_entries= [KNL,NET]
4520 Set the number of tcp_metrics_hash slots.
4521 Default value is 8192 or 16384 depending on total
4522 ram pages. This is used to specify the TCP metrics
4523 cache size. See Documentation/networking/ip-sysctl.txt
4524 "tcp_no_metrics_save" section for more details.
4528 test_suspend= [SUSPEND][,N]
4529 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4530 standby suspend) or "freeze" (for suspend type freeze)
4531 as the system sleep state during system startup with
4532 the optional capability to repeat N number of times.
4533 The system is woken from this state using a
4534 wakeup-capable RTC alarm.
4536 thash_entries= [KNL,NET]
4537 Set number of hash buckets for TCP connection
4539 thermal.act= [HW,ACPI]
4540 -1: disable all active trip points in all thermal zones
4541 <degrees C>: override all lowest active trip points
4543 thermal.crt= [HW,ACPI]
4544 -1: disable all critical trip points in all thermal zones
4545 <degrees C>: override all critical trip points
4547 thermal.nocrt= [HW,ACPI]
4548 Set to disable actions on ACPI thermal zone
4549 critical and hot trip points.
4551 thermal.off= [HW,ACPI]
4552 1: disable ACPI thermal control
4554 thermal.psv= [HW,ACPI]
4555 -1: disable all passive trip points
4556 <degrees C>: override all passive trip points to this
4559 thermal.tzp= [HW,ACPI]
4560 Specify global default ACPI thermal zone polling rate
4561 <deci-seconds>: poll all this frequency
4562 0: no polling (default)
4565 Force threading of all interrupt handlers except those
4566 marked explicitly IRQF_NO_THREAD.
4569 Enable the Transcendent memory driver if built-in.
4571 tmem.cleancache=0|1 [KNL, XEN]
4572 Default is on (1). Disable the usage of the cleancache
4573 API to send anonymous pages to the hypervisor.
4575 tmem.frontswap=0|1 [KNL, XEN]
4576 Default is on (1). Disable the usage of the frontswap
4577 API to send swap pages to the hypervisor. If disabled
4578 the selfballooning and selfshrinking are force disabled.
4580 tmem.selfballooning=0|1 [KNL, XEN]
4581 Default is on (1). Disable the driving of swap pages
4584 tmem.selfshrinking=0|1 [KNL, XEN]
4585 Default is on (1). Partial swapoff that immediately
4586 transfers pages from Xen hypervisor back to the
4587 kernel based on different criteria.
4591 Specify if the kernel should make use of the cpu
4592 topology information if the hardware supports this.
4593 The scheduler will make use of this information and
4594 e.g. base its process migration decisions on it.
4597 topology_updates= [KNL, PPC, NUMA]
4599 Specify if the kernel should ignore (off)
4600 topology updates sent by the hypervisor to this
4605 tpm_suspend_pcr=[HW,TPM]
4606 Format: integer pcr id
4607 Specify that at suspend time, the tpm driver
4608 should extend the specified pcr with zeros,
4609 as a workaround for some chips which fail to
4610 flush the last written pcr on TPM_SaveState.
4611 This will guarantee that all the other pcrs
4614 trace_buf_size=nn[KMG]
4615 [FTRACE] will set tracing buffer size on each cpu.
4617 trace_event=[event-list]
4618 [FTRACE] Set and start specified trace events in order
4619 to facilitate early boot debugging. The event-list is a
4620 comma separated list of trace events to enable. See
4621 also Documentation/trace/events.rst
4623 trace_options=[option-list]
4624 [FTRACE] Enable or disable tracer options at boot.
4625 The option-list is a comma delimited list of options
4626 that can be enabled or disabled just as if you were
4627 to echo the option name into
4629 /sys/kernel/debug/tracing/trace_options
4631 For example, to enable stacktrace option (to dump the
4632 stack trace of each event), add to the command line:
4634 trace_options=stacktrace
4636 See also Documentation/trace/ftrace.rst "trace options"
4640 Have the tracepoints sent to printk as well as the
4641 tracing ring buffer. This is useful for early boot up
4642 where the system hangs or reboots and does not give the
4643 option for reading the tracing buffer or performing a
4644 ftrace_dump_on_oops.
4646 To turn off having tracepoints sent to printk,
4647 echo 0 > /proc/sys/kernel/tracepoint_printk
4648 Note, echoing 1 into this file without the
4649 tracepoint_printk kernel cmdline option has no effect.
4653 Having tracepoints sent to printk() and activating high
4654 frequency tracepoints such as irq or sched, can cause
4655 the system to live lock.
4658 [FTRACE] enable this option to disable tracing when a
4659 warning is hit. This turns off "tracing_on". Tracing can
4660 be enabled again by echoing '1' into the "tracing_on"
4661 file located in /sys/kernel/debug/tracing/
4663 This option is useful, as it disables the trace before
4664 the WARNING dump is called, which prevents the trace to
4665 be filled with content caused by the warning output.
4667 This option can also be set at run time via the sysctl
4668 option: kernel/traceoff_on_warning
4670 transparent_hugepage=
4672 Format: [always|madvise|never]
4673 Can be used to control the default behavior of the system
4674 with respect to transparent hugepages.
4675 See Documentation/admin-guide/mm/transhuge.rst
4678 tsc= Disable clocksource stability checks for TSC.
4680 [x86] reliable: mark tsc clocksource as reliable, this
4681 disables clocksource verification at runtime, as well
4682 as the stability checks done at bootup. Used to enable
4683 high-resolution timer mode on older hardware, and in
4684 virtualized environment.
4685 [x86] noirqtime: Do not use TSC to do irq accounting.
4686 Used to run time disable IRQ_TIME_ACCOUNTING on any
4687 platforms where RDTSC is slow and this accounting
4689 [x86] unstable: mark the TSC clocksource as unstable, this
4690 marks the TSC unconditionally unstable at bootup and
4691 avoids any further wobbles once the TSC watchdog notices.
4693 turbografx.map[2|3]= [HW,JOY]
4694 TurboGraFX parallel port interface
4696 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4697 See also Documentation/input/devices/joystick-parport.rst
4699 udbg-immortal [PPC] When debugging early kernel crashes that
4700 happen after console_init() and before a proper
4701 console driver takes over, this boot options might
4702 help "seeing" what's going on.
4704 uhash_entries= [KNL,NET]
4705 Set number of hash buckets for UDP/UDP-Lite connections
4708 [USB] Ignore overcurrent events (default N).
4709 Some badly-designed motherboards generate lots of
4710 bogus events, for ports that aren't wired to
4711 anything. Set this parameter to avoid log spamming.
4712 Note that genuine overcurrent events won't be
4716 [X86] Cause panic on unknown NMI.
4718 usbcore.authorized_default=
4719 [USB] Default USB device authorization:
4720 (default -1 = authorized except for wireless USB,
4721 0 = not authorized, 1 = authorized, 2 = authorized
4722 if device connected to internal port)
4724 usbcore.autosuspend=
4725 [USB] The autosuspend time delay (in seconds) used
4726 for newly-detected USB devices (default 2). This
4727 is the time required before an idle device will be
4728 autosuspended. Devices for which the delay is set
4729 to a negative value won't be autosuspended at all.
4731 usbcore.usbfs_snoop=
4732 [USB] Set to log all usbfs traffic (default 0 = off).
4734 usbcore.usbfs_snoop_max=
4735 [USB] Maximum number of bytes to snoop in each URB
4738 usbcore.blinkenlights=
4739 [USB] Set to cycle leds on hubs (default 0 = off).
4741 usbcore.old_scheme_first=
4742 [USB] Start with the old device initialization
4743 scheme, applies only to low and full-speed devices
4746 usbcore.usbfs_memory_mb=
4747 [USB] Memory limit (in MB) for buffers allocated by
4748 usbfs (default = 16, 0 = max = 2047).
4750 usbcore.use_both_schemes=
4751 [USB] Try the other device initialization scheme
4752 if the first one fails (default 1 = enabled).
4754 usbcore.initial_descriptor_timeout=
4755 [USB] Specifies timeout for the initial 64-byte
4756 USB_REQ_GET_DESCRIPTOR request in milliseconds
4757 (default 5000 = 5.0 seconds).
4759 usbcore.nousb [USB] Disable the USB subsystem
4762 [USB] A list of quirk entries to augment the built-in
4763 usb core quirk list. List entries are separated by
4764 commas. Each entry has the form
4765 VendorID:ProductID:Flags. The IDs are 4-digit hex
4766 numbers and Flags is a set of letters. Each letter
4767 will change the built-in quirk; setting it if it is
4768 clear and clearing it if it is set. The letters have
4769 the following meanings:
4770 a = USB_QUIRK_STRING_FETCH_255 (string
4771 descriptors must not be fetched using
4773 b = USB_QUIRK_RESET_RESUME (device can't resume
4774 correctly so reset it instead);
4775 c = USB_QUIRK_NO_SET_INTF (device can't handle
4776 Set-Interface requests);
4777 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
4778 handle its Configuration or Interface
4780 e = USB_QUIRK_RESET (device can't be reset
4781 (e.g morph devices), don't use reset);
4782 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
4783 more interface descriptions than the
4784 bNumInterfaces count, and can't handle
4785 talking to these interfaces);
4786 g = USB_QUIRK_DELAY_INIT (device needs a pause
4787 during initialization, after we read
4788 the device descriptor);
4789 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
4790 high speed and super speed interrupt
4791 endpoints, the USB 2.0 and USB 3.0 spec
4792 require the interval in microframes (1
4793 microframe = 125 microseconds) to be
4794 calculated as interval = 2 ^
4796 Devices with this quirk report their
4797 bInterval as the result of this
4798 calculation instead of the exponent
4799 variable used in the calculation);
4800 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
4801 handle device_qualifier descriptor
4803 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
4804 generates spurious wakeup, ignore
4805 remote wakeup capability);
4806 k = USB_QUIRK_NO_LPM (device can't handle Link
4808 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
4809 (Device reports its bInterval as linear
4810 frames instead of the USB 2.0
4812 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
4813 to be disconnected before suspend to
4814 prevent spurious wakeup);
4815 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
4816 pause after every control message);
4817 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
4818 delay after resetting its port);
4819 Example: quirks=0781:5580:bk,0a5c:5834:gij
4822 [USBHID] The interval which mice are to be polled at.
4825 [USBHID] The interval which joysticks are to be polled at.
4828 [USBHID] The interval which keyboards are to be polled at.
4830 usb-storage.delay_use=
4831 [UMS] The delay in seconds before a new device is
4832 scanned for Logical Units (default 1).
4835 [UMS] A list of quirks entries to supplement or
4836 override the built-in unusual_devs list. List
4837 entries are separated by commas. Each entry has
4838 the form VID:PID:Flags where VID and PID are Vendor
4839 and Product ID values (4-digit hex numbers) and
4840 Flags is a set of characters, each corresponding
4841 to a common usb-storage quirk flag as follows:
4842 a = SANE_SENSE (collect more than 18 bytes
4844 b = BAD_SENSE (don't collect more than 18
4845 bytes of sense data);
4846 c = FIX_CAPACITY (decrease the reported
4847 device capacity by one sector);
4848 d = NO_READ_DISC_INFO (don't use
4849 READ_DISC_INFO command);
4850 e = NO_READ_CAPACITY_16 (don't use
4851 READ_CAPACITY_16 command);
4852 f = NO_REPORT_OPCODES (don't use report opcodes
4854 g = MAX_SECTORS_240 (don't transfer more than
4855 240 sectors at a time, uas only);
4856 h = CAPACITY_HEURISTICS (decrease the
4857 reported device capacity by one
4858 sector if the number is odd);
4859 i = IGNORE_DEVICE (don't bind to this
4861 j = NO_REPORT_LUNS (don't use report luns
4863 l = NOT_LOCKABLE (don't try to lock and
4864 unlock ejectable media);
4865 m = MAX_SECTORS_64 (don't transfer more
4866 than 64 sectors = 32 KB at a time);
4867 n = INITIAL_READ10 (force a retry of the
4868 initial READ(10) command);
4869 o = CAPACITY_OK (accept the capacity
4870 reported by the device);
4871 p = WRITE_CACHE (the device cache is ON
4873 r = IGNORE_RESIDUE (the device reports
4874 bogus residue values);
4875 s = SINGLE_LUN (the device has only one
4877 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4878 commands, uas only);
4879 u = IGNORE_UAS (don't bind to the uas driver);
4880 w = NO_WP_DETECT (don't test whether the
4881 medium is write-protected).
4882 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4883 even if the device claims no cache)
4884 Example: quirks=0419:aaf5:rl,0421:0433:rc
4886 user_debug= [KNL,ARM]
4888 See arch/arm/Kconfig.debug help text.
4889 1 - undefined instruction events
4891 4 - invalid data aborts
4894 Example: user_debug=31
4897 [X86] Flags controlling user PTE allocations.
4899 nohigh = do not allocate PTE pages in
4900 HIGHMEM regardless of setting
4904 On X86_32, this is an alias for vdso32=. Otherwise:
4906 vdso=1: enable VDSO (the default)
4907 vdso=0: disable VDSO mapping
4909 vdso32= [X86] Control the 32-bit vDSO
4910 vdso32=1: enable 32-bit VDSO
4911 vdso32=0 or vdso32=2: disable 32-bit VDSO
4913 See the help text for CONFIG_COMPAT_VDSO for more
4914 details. If CONFIG_COMPAT_VDSO is set, the default is
4915 vdso32=0; otherwise, the default is vdso32=1.
4917 For compatibility with older kernels, vdso32=2 is an
4920 Try vdso32=0 if you encounter an error that says:
4921 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4924 vector=percpu: enable percpu vector domain
4926 video= [FB] Frame buffer configuration
4927 See Documentation/fb/modedb.txt.
4929 video.brightness_switch_enabled= [0,1]
4930 If set to 1, on receiving an ACPI notify event
4931 generated by hotkey, video driver will adjust brightness
4932 level and then send out the event to user space through
4933 the allocated input device; If set to 0, video driver
4934 will only send out the event without touching backlight
4939 [VMMIO] Memory mapped virtio (platform) device.
4941 <size>@<baseaddr>:<irq>[:<id>]
4943 <size> := size (can use standard suffixes
4945 <baseaddr> := physical base address
4946 <irq> := interrupt number (as passed to
4948 <id> := (optional) platform device id
4950 virtio_mmio.device=1K@0x100b0000:48:7
4952 Can be used multiple times for multiple devices.
4954 vga= [BOOT,X86-32] Select a particular video mode
4955 See Documentation/x86/boot.txt and
4956 Documentation/svga.txt.
4957 Use vga=ask for menu.
4958 This is actually a boot loader parameter; the value is
4959 passed to the kernel using a special protocol.
4961 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
4962 May slow down system boot speed, especially when
4963 enabled on systems with a large amount of memory.
4964 All options are enabled by default, and this
4965 interface is meant to allow for selectively
4966 enabling or disabling specific virtual memory
4969 Available options are:
4970 P Enable page structure init time poisoning
4971 - Disable all of the above options
4973 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4974 size of <nn>. This can be used to increase the
4975 minimum size (128MB on x86). It can also be used to
4976 decrease the size and leave more room for directly
4979 vmcp_cma=nn[MG] [KNL,S390]
4980 Sets the memory size reserved for contiguous memory
4981 allocations for the vmcp device driver.
4983 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4986 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4989 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4993 Controls the behavior of vsyscalls (i.e. calls to
4994 fixed addresses of 0xffffffffff600x00 from legacy
4995 code). Most statically-linked binaries and older
4996 versions of glibc use these calls. Because these
4997 functions are at fixed addresses, they make nice
4998 targets for exploits that can control RIP.
5000 emulate [default] Vsyscalls turn into traps and are
5001 emulated reasonably safely.
5003 native Vsyscalls are native syscall instructions.
5004 This is a little bit faster than trapping
5005 and makes a few dynamic recompilers work
5006 better than they would in emulation mode.
5007 It also makes exploits much easier to write.
5009 none Vsyscalls don't work at all. This makes
5010 them quite hard to use for exploits but
5011 might break your system.
5013 vt.color= [VT] Default text color.
5014 Format: 0xYX, X = foreground, Y = background.
5015 Default: 0x07 = light gray on black.
5017 vt.cur_default= [VT] Default cursor shape.
5018 Format: 0xCCBBAA, where AA, BB, and CC are the same as
5019 the parameters of the <Esc>[?A;B;Cc escape sequence;
5020 see VGA-softcursor.txt. Default: 2 = underline.
5022 vt.default_blu= [VT]
5023 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
5024 Change the default blue palette of the console.
5025 This is a 16-member array composed of values
5028 vt.default_grn= [VT]
5029 Format: <green0>,<green1>,<green2>,...,<green15>
5030 Change the default green palette of the console.
5031 This is a 16-member array composed of values
5034 vt.default_red= [VT]
5035 Format: <red0>,<red1>,<red2>,...,<red15>
5036 Change the default red palette of the console.
5037 This is a 16-member array composed of values
5043 Set system-wide default UTF-8 mode for all tty's.
5044 Default is 1, i.e. UTF-8 mode is enabled for all
5045 newly opened terminals.
5047 vt.global_cursor_default=
5050 Set system-wide default for whether a cursor
5051 is shown on new VTs. Default is -1,
5052 i.e. cursors will be created by default unless
5053 overridden by individual drivers. 0 will hide
5054 cursors, 1 will display them.
5056 vt.italic= [VT] Default color for italic text; 0-15.
5059 vt.underline= [VT] Default color for underlined text; 0-15.
5062 watchdog timers [HW,WDT] For information on watchdog timers,
5063 see Documentation/watchdog/watchdog-parameters.txt
5064 or other driver-specific files in the
5065 Documentation/watchdog/ directory.
5067 workqueue.watchdog_thresh=
5068 If CONFIG_WQ_WATCHDOG is configured, workqueue can
5069 warn stall conditions and dump internal state to
5070 help debugging. 0 disables workqueue stall
5071 detection; otherwise, it's the stall threshold
5072 duration in seconds. The default value is 30 and
5073 it can be updated at runtime by writing to the
5074 corresponding sysfs file.
5076 workqueue.disable_numa
5077 By default, all work items queued to unbound
5078 workqueues are affine to the NUMA nodes they're
5079 issued on, which results in better behavior in
5080 general. If NUMA affinity needs to be disabled for
5081 whatever reason, this option can be used. Note
5082 that this also can be controlled per-workqueue for
5083 workqueues visible under /sys/bus/workqueue/.
5085 workqueue.power_efficient
5086 Per-cpu workqueues are generally preferred because
5087 they show better performance thanks to cache
5088 locality; unfortunately, per-cpu workqueues tend to
5089 be more power hungry than unbound workqueues.
5091 Enabling this makes the per-cpu workqueues which
5092 were observed to contribute significantly to power
5093 consumption unbound, leading to measurably lower
5094 power usage at the cost of small performance
5097 The default value of this parameter is determined by
5098 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
5100 workqueue.debug_force_rr_cpu
5101 Workqueue used to implicitly guarantee that work
5102 items queued without explicit CPU specified are put
5103 on the local CPU. This guarantee is no longer true
5104 and while local CPU is still preferred work items
5105 may be put on foreign CPUs. This debug option
5106 forces round-robin CPU selection to flush out
5107 usages which depend on the now broken guarantee.
5108 When enabled, memory and cache locality will be
5111 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
5112 default x2apic cluster mode on platforms
5115 x86_intel_mid_timer= [X86-32,APBT]
5116 Choose timer option for x86 Intel MID platform.
5117 Two valid options are apbt timer only and lapic timer
5118 plus one apbt timer for broadcast timer.
5119 x86_intel_mid_timer=apbt_only | lapic_and_apbt
5121 xen_512gb_limit [KNL,X86-64,XEN]
5122 Restricts the kernel running paravirtualized under Xen
5123 to use only up to 512 GB of RAM. The reason to do so is
5124 crash analysis tools and Xen tools for doing domain
5125 save/restore/migration must be enabled to handle larger
5128 xen_emul_unplug= [HW,X86,XEN]
5129 Unplug Xen emulated devices
5130 Format: [unplug0,][unplug1]
5131 ide-disks -- unplug primary master IDE devices
5132 aux-ide-disks -- unplug non-primary-master IDE devices
5133 nics -- unplug network devices
5134 all -- unplug all emulated devices (NICs and IDE disks)
5135 unnecessary -- unplugging emulated devices is
5136 unnecessary even if the host did not respond to
5138 never -- do not unplug even if version check succeeds
5140 xen_nopvspin [X86,XEN]
5141 Disables the ticketlock slowpath using Xen PV
5145 Disables the PV optimizations forcing the HVM guest to
5146 run as generic HVM guest with no PV drivers.
5148 xen_scrub_pages= [XEN]
5149 Boolean option to control scrubbing pages before giving them back
5150 to Xen, for use by other domains. Can be also changed at runtime
5151 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
5152 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
5154 xirc2ps_cs= [NET,PCMCIA]
5156 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
5158 xhci-hcd.quirks [USB,KNL]
5159 A hex value specifying bitmask with supplemental xhci
5160 host controller quirks. Meaning of each bit can be
5161 consulted in header drivers/usb/host/xhci.h.
git.samba.org / sfrench / cifs-2.6.git / blob