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: { "mq-deadline" | "kyber" | "bfq" }
1201 See Documentation/block/deadline-iosched.txt,
1202 Documentation/block/kyber-iosched.txt and
1203 Documentation/block/bfq-iosched.txt for details.
1205 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1206 Specifies physical address of start of kernel core
1207 image elf header and optionally the size. Generally
1208 kexec loader will pass this option to capture kernel.
1209 See Documentation/kdump/kdump.txt for details.
1211 enable_mtrr_cleanup [X86]
1212 The kernel tries to adjust MTRR layout from continuous
1213 to discrete, to make X server driver able to add WB
1214 entry later. This parameter enables that.
1216 enable_timer_pin_1 [X86]
1217 Enable PIN 1 of APIC timer
1218 Can be useful to work around chipset bugs
1219 (in particular on some ATI chipsets).
1220 The kernel tries to set a reasonable default.
1222 enforcing [SELINUX] Set initial enforcing status.
1224 See security/selinux/Kconfig help text.
1225 0 -- permissive (log only, no denials).
1226 1 -- enforcing (deny and log).
1228 Value can be changed at runtime via /selinux/enforce.
1231 Disable Error Record Serialization Table (ERST)
1234 ether= [HW,NET] Ethernet cards parameters
1235 This option is obsoleted by the "netdev=" option, which
1236 has equivalent usage. See its documentation for details.
1240 Permit 'security.evm' to be updated regardless of
1241 current integrity status.
1245 fail_make_request=[KNL]
1246 General fault injection mechanism.
1247 Format: <interval>,<probability>,<space>,<times>
1248 See also Documentation/fault-injection/.
1251 See Documentation/blockdev/floppy.txt.
1253 force_pal_cache_flush
1254 [IA-64] Avoid check_sal_cache_flush which may hang on
1255 buggy SAL_CACHE_FLUSH implementations. Using this
1256 parameter will force ia64_sal_cache_flush to call
1257 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1260 Forcefully enable Physical Address Extension (PAE).
1261 Many Pentium M systems disable PAE but may have a
1262 functionally usable PAE implementation.
1263 Warning: use of this parameter will taint the kernel
1264 and may cause unknown problems.
1267 [FTRACE] will set and start the specified tracer
1268 as early as possible in order to facilitate early
1271 ftrace_dump_on_oops[=orig_cpu]
1272 [FTRACE] will dump the trace buffers on oops.
1273 If no parameter is passed, ftrace will dump
1274 buffers of all CPUs, but if you pass orig_cpu, it will
1275 dump only the buffer of the CPU that triggered the
1278 ftrace_filter=[function-list]
1279 [FTRACE] Limit the functions traced by the function
1280 tracer at boot up. function-list is a comma separated
1281 list of functions. This list can be changed at run
1282 time by the set_ftrace_filter file in the debugfs
1285 ftrace_notrace=[function-list]
1286 [FTRACE] Do not trace the functions specified in
1287 function-list. This list can be changed at run time
1288 by the set_ftrace_notrace file in the debugfs
1291 ftrace_graph_filter=[function-list]
1292 [FTRACE] Limit the top level callers functions traced
1293 by the function graph tracer at boot up.
1294 function-list is a comma separated list of functions
1295 that can be changed at run time by the
1296 set_graph_function file in the debugfs tracing directory.
1298 ftrace_graph_notrace=[function-list]
1299 [FTRACE] Do not trace from the functions specified in
1300 function-list. This list is a comma separated list of
1301 functions that can be changed at run time by the
1302 set_graph_notrace file in the debugfs tracing directory.
1304 ftrace_graph_max_depth=<uint>
1305 [FTRACE] Used with the function graph tracer. This is
1306 the max depth it will trace into a function. This value
1307 can be changed at run time by the max_graph_depth file
1308 in the tracefs tracing directory. default: 0 (no limit)
1311 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1312 support via parallel port (up to 5 devices per port)
1313 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1314 See also Documentation/input/devices/joystick-parport.rst
1318 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1322 gcov_persist= [GCOV] When non-zero (default), profiling data for
1323 kernel modules is saved and remains accessible via
1324 debugfs, even when the module is unloaded/reloaded.
1325 When zero, profiling data is discarded and associated
1326 debugfs files are removed at module unload time.
1328 goldfish [X86] Enable the goldfish android emulator platform.
1329 Don't use this when you are not running on the
1332 gpt [EFI] Forces disk with valid GPT signature but
1333 invalid Protective MBR to be treated as GPT. If the
1334 primary GPT is corrupted, it enables the backup/alternate
1335 GPT to be used instead.
1337 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1338 the "Enable 0" bit of the configuration register.
1341 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1342 the "Enable 0" bit of the configuration register.
1345 grcan.select= [HW] Select which physical interface to use.
1348 grcan.txsize= [HW] Sets the size of the tx buffer.
1349 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1351 grcan.rxsize= [HW] Sets the size of the rx buffer.
1352 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1355 gpio-mockup.gpio_mockup_ranges
1356 [HW] Sets the ranges of gpiochip of for this device.
1357 Format: <start1>,<end1>,<start2>,<end2>...
1359 hardlockup_all_cpu_backtrace=
1360 [KNL] Should the hard-lockup detector generate
1361 backtraces on all cpus.
1364 hashdist= [KNL,NUMA] Large hashes allocated during boot
1365 are distributed across NUMA nodes. Defaults on
1366 for 64-bit NUMA, off otherwise.
1367 Format: 0 | 1 (for off | on)
1369 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1371 hd= [EIDE] (E)IDE hard drive subsystem geometry
1372 Format: <cyl>,<head>,<sect>
1375 Disable Hardware Error Source Table (HEST) support;
1376 corresponding firmware-first mode error processing
1377 logic will be disabled.
1379 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1380 size of <nn>. This works even on boxes that have no
1381 highmem otherwise. This also works to reduce highmem
1382 size on bigger boxes.
1384 highres= [KNL] Enable/disable high resolution timer mode.
1385 Valid parameters: "on", "off"
1389 See Documentation/isdn/README.HiSax.
1393 hpet= [X86-32,HPET] option to control HPET usage
1394 Format: { enable (default) | disable | force |
1396 disable: disable HPET and use PIT instead
1397 force: allow force enabled of undocumented chips (ICH4,
1399 verbose: show contents of HPET registers during setup
1401 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1402 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1404 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1405 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1406 On x86-64 and powerpc, this option can be specified
1407 multiple times interleaved with hugepages= to reserve
1408 huge pages of different sizes. Valid pages sizes on
1409 x86-64 are 2M (when the CPU supports "pse") and 1G
1410 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1413 [KNL] Should the hung task detector generate panics.
1416 A nonzero value instructs the kernel to panic when a
1417 hung task is detected. The default value is controlled
1418 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1419 option. The value selected by this boot parameter can
1420 be changed later by the kernel.hung_task_panic sysctl.
1422 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1423 terminal devices. Valid values: 0..8
1424 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1425 If specified, z/VM IUCV HVC accepts connections
1426 from listed z/VM user IDs only.
1428 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations
1429 which allow the hypervisor to 'idle' the
1430 guest on lock contention.
1433 Do not unregister boot console at start. This is only
1434 useful for debugging when something happens in the window
1435 between unregistering the boot console and initializing
1438 i2c_bus= [HW] Override the default board specific I2C bus speed
1439 or register an additional I2C bus that is not
1440 registered from board initialization code.
1444 i8042.debug [HW] Toggle i8042 debug mode
1445 i8042.unmask_kbd_data
1446 [HW] Enable printing of interrupt data from the KBD port
1447 (disabled by default, and as a pre-condition
1448 requires that i8042.debug=1 be enabled)
1449 i8042.direct [HW] Put keyboard port into non-translated mode
1450 i8042.dumbkbd [HW] Pretend that controller can only read data from
1451 keyboard and cannot control its state
1452 (Don't attempt to blink the leds)
1453 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1454 i8042.nokbd [HW] Don't check/create keyboard port
1455 i8042.noloop [HW] Disable the AUX Loopback command while probing
1457 i8042.nomux [HW] Don't check presence of an active multiplexing
1459 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1461 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1462 i8042.reset [HW] Reset the controller during init, cleanup and
1463 suspend-to-ram transitions, only during s2r
1464 transitions, or never reset
1465 Format: { 1 | Y | y | 0 | N | n }
1466 1, Y, y: always reset controller
1467 0, N, n: don't ever reset controller
1468 Default: only on s2r transitions on x86; most other
1469 architectures force reset to be always executed
1470 i8042.unlock [HW] Unlock (ignore) the keylock
1471 i8042.kbdreset [HW] Reset device connected to KBD port
1475 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1476 indicates that the driver is running on unsupported
1478 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1479 does not match list of supported models.
1481 [HW] Report power status in /proc/i8k
1482 (disabled by default)
1483 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1486 i915.invert_brightness=
1487 [DRM] Invert the sense of the variable that is used to
1488 set the brightness of the panel backlight. Normally a
1489 brightness value of 0 indicates backlight switched off,
1490 and the maximum of the brightness value sets the backlight
1491 to maximum brightness. If this parameter is set to 0
1492 (default) and the machine requires it, or this parameter
1493 is set to 1, a brightness value of 0 sets the backlight
1494 to maximum brightness, and the maximum of the brightness
1495 value switches the backlight off.
1496 -1 -- never invert brightness
1497 0 -- machine default
1498 1 -- force brightness inversion
1501 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1503 ide-core.nodma= [HW] (E)IDE subsystem
1504 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1505 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1506 .cdrom .chs .ignore_cable are additional options
1507 See Documentation/ide/ide.txt.
1509 ide-generic.probe-mask= [HW] (E)IDE subsystem
1511 Probe mask for legacy ISA IDE ports. Depending on
1512 platform up to 6 ports are supported, enabled by
1513 setting corresponding bits in the mask to 1. The
1514 default value is 0x0, which has a special meaning.
1515 On systems that have PCI, it triggers scanning the
1516 PCI bus for the first and the second port, which
1517 are then probed. On systems without PCI the value
1518 of 0x0 enables probing the two first ports as if it
1521 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1522 Claim all unknown PCI IDE storage controllers.
1525 Format: idle=poll, idle=halt, idle=nomwait
1526 Poll forces a polling idle loop that can slightly
1527 improve the performance of waking up a idle CPU, but
1528 will use a lot of power and make the system run hot.
1530 idle=halt: Halt is forced to be used for CPU idle.
1531 In such case C2/C3 won't be used again.
1532 idle=nomwait: Disable mwait for CPU C-states
1534 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1535 Format: { strict | legacy | 2008 | relaxed }
1538 Choose which programs will be accepted for execution
1539 based on the IEEE 754 NaN encoding(s) supported by
1540 the FPU and the NaN encoding requested with the value
1541 of an ELF file header flag individually set by each
1542 binary. Hardware implementations are permitted to
1543 support either or both of the legacy and the 2008 NaN
1546 Available settings are as follows:
1547 strict accept binaries that request a NaN encoding
1548 supported by the FPU
1549 legacy only accept legacy-NaN binaries, if supported
1551 2008 only accept 2008-NaN binaries, if supported
1553 relaxed accept any binaries regardless of whether
1554 supported by the FPU
1556 The FPU emulator is always able to support both NaN
1557 encodings, so if no FPU hardware is present or it has
1558 been disabled with 'nofpu', then the settings of
1559 'legacy' and '2008' strap the emulator accordingly,
1560 'relaxed' straps the emulator for both legacy-NaN and
1561 2008-NaN, whereas 'strict' enables legacy-NaN only on
1562 legacy processors and both NaN encodings on MIPS32 or
1565 The setting for ABS.fmt/NEG.fmt instruction execution
1566 mode generally follows that for the NaN encoding,
1567 except where unsupported by hardware.
1569 ignore_loglevel [KNL]
1570 Ignore loglevel setting - this will print /all/
1571 kernel messages to the console. Useful for debugging.
1572 We also add it as printk module parameter, so users
1573 could change it dynamically, usually by
1574 /sys/module/printk/parameters/ignore_loglevel.
1577 Ignore RLIMIT_DATA setting for data mappings,
1578 print warning at first misuse. Can be changed via
1579 /sys/module/kernel/parameters/ignore_rlimit_data.
1581 ihash_entries= [KNL]
1582 Set number of hash buckets for inode cache.
1584 ima_appraise= [IMA] appraise integrity measurements
1585 Format: { "off" | "enforce" | "fix" | "log" }
1588 ima_appraise_tcb [IMA]
1589 The builtin appraise policy appraises all files
1592 ima_canonical_fmt [IMA]
1593 Use the canonical format for the binary runtime
1594 measurements, instead of host native format.
1597 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1601 The list of supported hash algorithms is defined
1602 in crypto/hash_info.h.
1605 The builtin policies to load during IMA setup.
1606 Format: "tcb | appraise_tcb | secure_boot |
1609 The "tcb" policy measures all programs exec'd, files
1610 mmap'd for exec, and all files opened with the read
1611 mode bit set by either the effective uid (euid=0) or
1614 The "appraise_tcb" policy appraises the integrity of
1615 all files owned by root. (This is the equivalent
1616 of ima_appraise_tcb.)
1618 The "secure_boot" policy appraises the integrity
1619 of files (eg. kexec kernel image, kernel modules,
1620 firmware, policy, etc) based on file signatures.
1622 The "fail_securely" policy forces file signature
1623 verification failure also on privileged mounted
1624 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1627 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1628 Load a policy which meets the needs of the Trusted
1629 Computing Base. This means IMA will measure all
1630 programs exec'd, files mmap'd for exec, and all files
1631 opened for read by uid=0.
1634 Select one of defined IMA measurements template formats.
1635 Formats: { "ima" | "ima-ng" | "ima-sig" }
1639 [IMA] Define a custom template format.
1640 Format: { "field1|...|fieldN" }
1642 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1643 Format: <min_file_size>
1644 Set the minimal file size for using asynchronous hash.
1645 If left unspecified, ahash usage is disabled.
1647 ahash performance varies for different data sizes on
1648 different crypto accelerators. This option can be used
1649 to achieve the best performance for a particular HW.
1651 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1653 Set hashing buffer size. Default: 4k.
1655 ahash performance varies for different chunk sizes on
1656 different crypto accelerators. This option can be used
1657 to achieve best performance for particular HW.
1661 Run specified binary instead of /sbin/init as init
1664 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1665 for working out where the kernel is dying during
1668 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1669 initcall functions. Useful for debugging built-in
1670 modules and initcalls.
1672 initrd= [BOOT] Specify the location of the initial ramdisk
1674 init_pkru= [x86] Specify the default memory protection keys rights
1675 register contents for all processes. 0x55555554 by
1676 default (disallow access to all but pkey 0). Can
1677 override in debugfs after boot.
1679 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1682 int_pln_enable [x86] Enable power limit notification interrupt
1684 integrity_audit=[IMA]
1685 Format: { "0" | "1" }
1686 0 -- basic integrity auditing messages. (Default)
1687 1 -- additional integrity auditing messages.
1689 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1691 Enable intel iommu driver.
1693 Disable intel iommu driver.
1694 igfx_off [Default Off]
1695 By default, gfx is mapped as normal device. If a gfx
1696 device has a dedicated DMAR unit, the DMAR unit is
1697 bypassed by not enabling DMAR with this option. In
1698 this case, gfx device will use physical address for
1701 With this option iommu will not optimize to look
1702 for io virtual address below 32-bit forcing dual
1703 address cycle on pci bus for cards supporting greater
1704 than 32-bit addressing. The default is to look
1705 for translation below 32-bit and if not available
1706 then look in the higher range.
1707 strict [Default Off]
1708 With this option on every unmap_single operation will
1709 result in a hardware IOTLB flush operation as opposed
1710 to batching them for performance.
1711 sp_off [Default Off]
1712 By default, super page will be supported if Intel IOMMU
1713 has the capability. With this option, super page will
1716 By default, scalable mode will be disabled even if the
1717 hardware advertises that it has support for the scalable
1718 mode translation. With this option set, scalable mode
1719 will be used on hardware which claims to support it.
1720 tboot_noforce [Default Off]
1721 Do not force the Intel IOMMU enabled under tboot.
1722 By default, tboot will force Intel IOMMU on, which
1723 could harm performance of some high-throughput
1724 devices like 40GBit network cards, even if identity
1726 Note that using this option lowers the security
1727 provided by tboot because it makes the system
1728 vulnerable to DMA attacks.
1730 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1731 0 disables intel_idle and fall back on acpi_idle.
1732 1 to 9 specify maximum depth of C-state.
1736 Do not enable intel_pstate as the default
1737 scaling driver for the supported processors
1739 Use intel_pstate as a scaling driver, but configure it
1740 to work with generic cpufreq governors (instead of
1741 enabling its internal governor). This mode cannot be
1742 used along with the hardware-managed P-states (HWP)
1745 Enable intel_pstate on systems that prohibit it by default
1746 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1747 instead of acpi-cpufreq may disable platform features, such
1748 as thermal controls and power capping, that rely on ACPI
1749 P-States information being indicated to OSPM and therefore
1750 should be used with caution. This option does not work with
1751 processors that aren't supported by the intel_pstate driver
1752 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1754 Do not enable hardware P state control (HWP)
1757 Only load intel_pstate on systems which support
1758 hardware P state control (HWP) if available.
1760 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1761 Description Table, specifies preferred power management
1762 profile as "Enterprise Server" or "Performance Server",
1763 then this feature is turned on by default.
1765 Allow per-logical-CPU P-State performance control limits using
1766 cpufreq sysfs interface
1768 intremap= [X86-64, Intel-IOMMU]
1769 on enable Interrupt Remapping (default)
1770 off disable Interrupt Remapping
1771 nosid disable Source ID checking
1773 BIOS x2APIC opt-out request will be ignored
1774 nopost disable Interrupt Posting
1776 iomem= Disable strict checking of access to MMIO memory
1777 strict regions from userspace.
1792 nobypass [PPC/POWERNV]
1793 Disable IOMMU bypass, using IOMMU for PCI devices.
1795 iommu.strict= [ARM64] Configure TLB invalidation behaviour
1796 Format: { "0" | "1" }
1798 Request that DMA unmap operations use deferred
1799 invalidation of hardware TLBs, for increased
1800 throughput at the cost of reduced device isolation.
1801 Will fall back to strict mode if not supported by
1802 the relevant IOMMU driver.
1803 1 - Strict mode (default).
1804 DMA unmap operations invalidate IOMMU hardware TLBs
1808 [ARM64] Configure DMA to bypass the IOMMU by default.
1809 Format: { "0" | "1" }
1810 0 - Use IOMMU translation for DMA.
1811 1 - Bypass the IOMMU for DMA.
1812 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
1814 io7= [HW] IO7 for Marvel based alpha systems
1815 See comment before marvel_specify_io7 in
1816 arch/alpha/kernel/core_marvel.c.
1818 io_delay= [X86] I/O delay method
1820 Standard port 0x80 based delay
1822 Alternate port 0xed based delay (needed on some systems)
1824 Simple two microseconds delay
1829 See Documentation/filesystems/nfs/nfsroot.txt.
1831 irqaffinity= [SMP] Set the default irq affinity mask
1832 The argument is a cpu list, as described above.
1834 irqchip.gicv2_force_probe=
1837 Force the kernel to look for the second 4kB page
1838 of a GICv2 controller even if the memory range
1839 exposed by the device tree is too small.
1841 irqchip.gicv3_nolpi=
1843 Force the kernel to ignore the availability of
1844 LPIs (and by consequence ITSs). Intended for system
1845 that use the kernel as a bootloader, and thus want
1846 to let secondary kernels in charge of setting up
1849 irqchip.gicv3_pseudo_nmi= [ARM64]
1850 Enables support for pseudo-NMIs in the kernel. This
1851 requires the kernel to be built with
1852 CONFIG_ARM64_PSEUDO_NMI.
1855 When an interrupt is not handled search all handlers
1856 for it. Intended to get systems with badly broken
1860 When an interrupt is not handled search all handlers
1861 for it. Also check all handlers each timer
1862 interrupt. Intended to get systems with badly broken
1866 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1868 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1869 [Deprecated - use cpusets instead]
1870 Format: [flag-list,]<cpu-list>
1872 Specify one or more CPUs to isolate from disturbances
1873 specified in the flag list (default: domain):
1876 Disable the tick when a single task runs.
1878 A residual 1Hz tick is offloaded to workqueues, which you
1879 need to affine to housekeeping through the global
1880 workqueue's affinity configured via the
1881 /sys/devices/virtual/workqueue/cpumask sysfs file, or
1882 by using the 'domain' flag described below.
1884 NOTE: by default the global workqueue runs on all CPUs,
1885 so to protect individual CPUs the 'cpumask' file has to
1886 be configured manually after bootup.
1889 Isolate from the general SMP balancing and scheduling
1890 algorithms. Note that performing domain isolation this way
1891 is irreversible: it's not possible to bring back a CPU to
1892 the domains once isolated through isolcpus. It's strongly
1893 advised to use cpusets instead to disable scheduler load
1894 balancing through the "cpuset.sched_load_balance" file.
1895 It offers a much more flexible interface where CPUs can
1896 move in and out of an isolated set anytime.
1898 You can move a process onto or off an "isolated" CPU via
1899 the CPU affinity syscalls or cpuset.
1900 <cpu number> begins at 0 and the maximum value is
1901 "number of CPUs in system - 1".
1903 The format of <cpu-list> is described above.
1909 ivrs_ioapic [HW,X86_64]
1910 Provide an override to the IOAPIC-ID<->DEVICE-ID
1911 mapping provided in the IVRS ACPI table. For
1912 example, to map IOAPIC-ID decimal 10 to
1913 PCI device 00:14.0 write the parameter as:
1914 ivrs_ioapic[10]=00:14.0
1916 ivrs_hpet [HW,X86_64]
1917 Provide an override to the HPET-ID<->DEVICE-ID
1918 mapping provided in the IVRS ACPI table. For
1919 example, to map HPET-ID decimal 0 to
1920 PCI device 00:14.0 write the parameter as:
1921 ivrs_hpet[0]=00:14.0
1923 ivrs_acpihid [HW,X86_64]
1924 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1925 mapping provided in the IVRS ACPI table. For
1926 example, to map UART-HID:UID AMD0020:0 to
1927 PCI device 00:14.5 write the parameter as:
1928 ivrs_acpihid[00:14.5]=AMD0020:0
1930 js= [HW,JOY] Analog joystick
1931 See Documentation/input/joydev/joystick.rst.
1934 When CONFIG_RANDOMIZE_BASE is set, this disables
1935 kernel and module base offset ASLR (Address Space
1936 Layout Randomization).
1939 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1940 report on every invalid memory access. Without this
1941 parameter KASAN will print report only for the first
1946 kernelcore= [KNL,X86,IA-64,PPC]
1947 Format: nn[KMGTPE] | nn% | "mirror"
1948 This parameter specifies the amount of memory usable by
1949 the kernel for non-movable allocations. The requested
1950 amount is spread evenly throughout all nodes in the
1951 system as ZONE_NORMAL. The remaining memory is used for
1952 movable memory in its own zone, ZONE_MOVABLE. In the
1953 event, a node is too small to have both ZONE_NORMAL and
1954 ZONE_MOVABLE, kernelcore memory will take priority and
1955 other nodes will have a larger ZONE_MOVABLE.
1957 ZONE_MOVABLE is used for the allocation of pages that
1958 may be reclaimed or moved by the page migration
1959 subsystem. Note that allocations like PTEs-from-HighMem
1960 still use the HighMem zone if it exists, and the Normal
1961 zone if it does not.
1963 It is possible to specify the exact amount of memory in
1964 the form of "nn[KMGTPE]", a percentage of total system
1965 memory in the form of "nn%", or "mirror". If "mirror"
1966 option is specified, mirrored (reliable) memory is used
1967 for non-movable allocations and remaining memory is used
1968 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
1969 are exclusive, so you cannot specify multiple forms.
1971 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1972 Format: <Controller#>[,poll interval]
1973 The controller # is the number of the ehci usb debug
1974 port as it is probed via PCI. The poll interval is
1975 optional and is the number seconds in between
1976 each poll cycle to the debug port in case you need
1977 the functionality for interrupting the kernel with
1978 gdb or control-c on the dbgp connection. When
1979 not using this parameter you use sysrq-g to break into
1980 the kernel debugger.
1982 kgdboc= [KGDB,HW] kgdb over consoles.
1983 Requires a tty driver that supports console polling,
1984 or a supported polling keyboard driver (non-usb).
1985 Serial only format: <serial_device>[,baud]
1986 keyboard only format: kbd
1987 keyboard and serial format: kbd,<serial_device>[,baud]
1988 Optional Kernel mode setting:
1989 kms, kbd format: kms,kbd
1990 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1992 kgdbwait [KGDB] Stop kernel execution and enter the
1993 kernel debugger at the earliest opportunity.
1995 kmac= [MIPS] korina ethernet MAC address.
1996 Configure the RouterBoard 532 series on-chip
1997 Ethernet adapter MAC address.
1999 kmemleak= [KNL] Boot-time kmemleak enable/disable
2000 Valid arguments: on, off
2002 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
2005 kpti= [ARM64] Control page table isolation of user
2006 and kernel address spaces.
2007 Default: enabled on cores which need mitigation.
2011 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
2012 Default is 0 (don't ignore, but inject #GP)
2014 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
2015 Default is false (don't support).
2017 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
2021 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
2022 Default is 1 (enabled)
2024 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
2026 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
2028 kvm-arm.vgic_v3_group0_trap=
2029 [KVM,ARM] Trap guest accesses to GICv3 group-0
2032 kvm-arm.vgic_v3_group1_trap=
2033 [KVM,ARM] Trap guest accesses to GICv3 group-1
2036 kvm-arm.vgic_v3_common_trap=
2037 [KVM,ARM] Trap guest accesses to GICv3 common
2040 kvm-arm.vgic_v4_enable=
2041 [KVM,ARM] Allow use of GICv4 for direct injection of
2044 kvm-intel.ept= [KVM,Intel] Disable extended page tables
2045 (virtualized MMU) support on capable Intel chips.
2046 Default is 1 (enabled)
2048 kvm-intel.emulate_invalid_guest_state=
2049 [KVM,Intel] Enable emulation of invalid guest states
2050 Default is 0 (disabled)
2052 kvm-intel.flexpriority=
2053 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
2054 Default is 1 (enabled)
2057 [KVM,Intel] Enable VMX nesting (nVMX).
2058 Default is 0 (disabled)
2060 kvm-intel.unrestricted_guest=
2061 [KVM,Intel] Disable unrestricted guest feature
2062 (virtualized real and unpaged mode) on capable
2063 Intel chips. Default is 1 (enabled)
2065 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2068 Valid arguments: never, cond, always
2070 always: L1D cache flush on every VMENTER.
2071 cond: Flush L1D on VMENTER only when the code between
2072 VMEXIT and VMENTER can leak host memory.
2073 never: Disables the mitigation
2075 Default is cond (do L1 cache flush in specific instances)
2077 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2078 feature (tagged TLBs) on capable Intel chips.
2079 Default is 1 (enabled)
2081 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2084 The kernel PTE inversion protection is unconditionally
2085 enabled and cannot be disabled.
2088 Provides all available mitigations for the
2089 L1TF vulnerability. Disables SMT and
2090 enables all mitigations in the
2091 hypervisors, i.e. unconditional L1D flush.
2093 SMT control and L1D flush control via the
2094 sysfs interface is still possible after
2095 boot. Hypervisors will issue a warning
2096 when the first VM is started in a
2097 potentially insecure configuration,
2098 i.e. SMT enabled or L1D flush disabled.
2101 Same as 'full', but disables SMT and L1D
2102 flush runtime control. Implies the
2103 'nosmt=force' command line option.
2104 (i.e. sysfs control of SMT is disabled.)
2107 Leaves SMT enabled and enables the default
2108 hypervisor mitigation, i.e. conditional
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.
2120 Disables SMT and enables the default
2121 hypervisor mitigation.
2123 SMT control and L1D flush control via the
2124 sysfs interface is still possible after
2125 boot. Hypervisors will issue a warning
2126 when the first VM is started in a
2127 potentially insecure configuration,
2128 i.e. SMT enabled or L1D flush disabled.
2131 Same as 'flush', but hypervisors will not
2132 warn when a VM is started in a potentially
2133 insecure configuration.
2136 Disables hypervisor mitigations and doesn't
2138 It also drops the swap size and available
2139 RAM limit restriction on both hypervisor and
2144 For details see: Documentation/admin-guide/l1tf.rst
2150 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2153 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2154 value for LAPIC timer one-shot implementation. Default
2155 back to the programmable timer unit in the LAPIC.
2157 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2160 libata.dma= [LIBATA] DMA control
2161 libata.dma=0 Disable all PATA and SATA DMA
2162 libata.dma=1 PATA and SATA Disk DMA only
2163 libata.dma=2 ATAPI (CDROM) DMA only
2164 libata.dma=4 Compact Flash DMA only
2165 Combinations also work, so libata.dma=3 enables DMA
2166 for disks and CDROMs, but not CFs.
2168 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2169 libata.ignore_hpa=0 keep BIOS limits (default)
2170 libata.ignore_hpa=1 ignore limits, using full disk
2172 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2176 libata.force= [LIBATA] Force configurations. The format is comma
2177 separated list of "[ID:]VAL" where ID is
2178 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2179 matching port, link or device. Basically, it matches
2180 the ATA ID string printed on console by libata. If
2181 the whole ID part is omitted, the last PORT and DEVICE
2182 values are used. If ID hasn't been specified yet, the
2183 configuration applies to all ports, links and devices.
2185 If only DEVICE is omitted, the parameter applies to
2186 the port and all links and devices behind it. DEVICE
2187 number of 0 either selects the first device or the
2188 first fan-out link behind PMP device. It does not
2189 select the host link. DEVICE number of 15 selects the
2190 host link and device attached to it.
2192 The VAL specifies the configuration to force. As long
2193 as there's no ambiguity shortcut notation is allowed.
2194 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2195 The following configurations can be forced.
2197 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2198 Any ID with matching PORT is used.
2200 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2202 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2203 udma[/][16,25,33,44,66,100,133] notation is also
2206 * [no]ncq: Turn on or off NCQ.
2208 * [no]ncqtrim: Turn off queued DSM TRIM.
2210 * nohrst, nosrst, norst: suppress hard, soft
2213 * rstonce: only attempt one reset during
2214 hot-unplug link recovery
2216 * dump_id: dump IDENTIFY data.
2218 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2220 * disable: Disable this device.
2222 If there are multiple matching configurations changing
2223 the same attribute, the last one is used.
2225 memblock=debug [KNL] Enable memblock debug messages.
2227 load_ramdisk= [RAM] List of ramdisks to load from floppy
2228 See Documentation/blockdev/ramdisk.txt.
2230 lockd.nlm_grace_period=P [NFS] Assign grace period.
2233 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2236 lockd.nlm_timeout=T [NFS] Assign timeout value.
2239 lockd.nlm_udpport=M [NFS] Assign UDP port.
2242 locktorture.nreaders_stress= [KNL]
2243 Set the number of locking read-acquisition kthreads.
2244 Defaults to being automatically set based on the
2245 number of online CPUs.
2247 locktorture.nwriters_stress= [KNL]
2248 Set the number of locking write-acquisition kthreads.
2250 locktorture.onoff_holdoff= [KNL]
2251 Set time (s) after boot for CPU-hotplug testing.
2253 locktorture.onoff_interval= [KNL]
2254 Set time (s) between CPU-hotplug operations, or
2255 zero to disable CPU-hotplug testing.
2257 locktorture.shuffle_interval= [KNL]
2258 Set task-shuffle interval (jiffies). Shuffling
2259 tasks allows some CPUs to go into dyntick-idle
2260 mode during the locktorture test.
2262 locktorture.shutdown_secs= [KNL]
2263 Set time (s) after boot system shutdown. This
2264 is useful for hands-off automated testing.
2266 locktorture.stat_interval= [KNL]
2267 Time (s) between statistics printk()s.
2269 locktorture.stutter= [KNL]
2270 Time (s) to stutter testing, for example,
2271 specifying five seconds causes the test to run for
2272 five seconds, wait for five seconds, and so on.
2273 This tests the locking primitive's ability to
2274 transition abruptly to and from idle.
2276 locktorture.torture_type= [KNL]
2277 Specify the locking implementation to test.
2279 locktorture.verbose= [KNL]
2280 Enable additional printk() statements.
2282 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2285 loglevel= All Kernel Messages with a loglevel smaller than the
2286 console loglevel will be printed to the console. It can
2287 also be changed with klogd or other programs. The
2288 loglevels are defined as follows:
2290 0 (KERN_EMERG) system is unusable
2291 1 (KERN_ALERT) action must be taken immediately
2292 2 (KERN_CRIT) critical conditions
2293 3 (KERN_ERR) error conditions
2294 4 (KERN_WARNING) warning conditions
2295 5 (KERN_NOTICE) normal but significant condition
2296 6 (KERN_INFO) informational
2297 7 (KERN_DEBUG) debug-level messages
2299 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2300 in bytes. n must be a power of two and greater
2301 than the minimal size. The minimal size is defined
2302 by LOG_BUF_SHIFT kernel config parameter. There is
2303 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2304 that allows to increase the default size depending on
2305 the number of CPUs. See init/Kconfig for more details.
2307 logo.nologo [FB] Disables display of the built-in Linux logo.
2308 This may be used to provide more screen space for
2309 kernel log messages and is useful when debugging
2310 kernel boot problems.
2312 lp=0 [LP] Specify parallel ports to use, e.g,
2313 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2314 lp=reset first parallel port). 'lp=0' disables the
2315 lp=auto printer driver. 'lp=reset' (which can be
2316 specified in addition to the ports) causes
2317 attached printers to be reset. Using
2318 lp=port1,port2,... specifies the parallel ports
2319 to associate lp devices with, starting with
2320 lp0. A port specification may be 'none' to skip
2321 that lp device, or a parport name such as
2322 'parport0'. Specifying 'lp=auto' instead of a
2323 port specification list means that device IDs
2324 from each port should be examined, to see if
2325 an IEEE 1284-compliant printer is attached; if
2326 so, the driver will manage that printer.
2327 See also header of drivers/char/lp.c.
2330 Sets loops_per_jiffy to given constant, thus avoiding
2331 time-consuming boot-time autodetection (up to 250 ms per
2332 CPU). 0 enables autodetection (default). To determine
2333 the correct value for your kernel, boot with normal
2334 autodetection and see what value is printed. Note that
2335 on SMP systems the preset will be applied to all CPUs,
2336 which is likely to cause problems if your CPUs need
2337 significantly divergent settings. An incorrect value
2338 will cause delays in the kernel to be wrong, leading to
2339 unpredictable I/O errors and other breakage. Although
2340 unlikely, in the extreme case this might damage your
2344 Format: <io>,<irq>,<dma>
2346 lsm.debug [SECURITY] Enable LSM initialization debugging output.
2349 [SECURITY] Choose order of LSM initialization. This
2350 overrides CONFIG_LSM, and the "security=" parameter.
2352 machvec= [IA-64] Force the use of a particular machine-vector
2353 (machvec) in a generic kernel.
2354 Example: machvec=hpzx1_swiotlb
2356 machtype= [Loongson] Share the same kernel image file between different
2358 Example: machtype=lemote-yeeloong-2f-7inch
2360 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2361 than or equal to this physical address is ignored.
2363 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2364 will bring up during bootup. maxcpus=n : n >= 0 limits
2365 the kernel to bring up 'n' processors. Surely after
2366 bootup you can bring up the other plugged cpu by executing
2367 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2368 only takes effect during system bootup.
2369 While n=0 is a special case, it is equivalent to "nosmp",
2370 which also disables the IO APIC.
2372 max_loop= [LOOP] The number of loop block devices that get
2373 (loop.max_loop) unconditionally pre-created at init time. The default
2374 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2375 of statically allocating a predefined number, loop
2376 devices can be requested on-demand with the
2377 /dev/loop-control interface.
2379 mce [X86-32] Machine Check Exception
2381 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2383 md= [HW] RAID subsystems devices and level
2384 See Documentation/admin-guide/md.rst.
2387 Format: <first>,<last>
2388 Specifies range of consoles to be captured by the MDA.
2390 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2391 Amount of memory to be used when the kernel is not able
2392 to see the whole system memory or for test.
2393 [X86] Work as limiting max address. Use together
2394 with memmap= to avoid physical address space collisions.
2395 Without memmap= PCI devices could be placed at addresses
2396 belonging to unused RAM.
2398 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2402 [KNL,SH] Allow user to override the default size for
2403 per-device physically contiguous DMA buffers.
2405 memhp_default_state=online/offline
2406 [KNL] Set the initial state for the memory hotplug
2407 onlining policy. If not specified, the default value is
2408 set according to the
2409 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2411 See Documentation/memory-hotplug.txt.
2413 memmap=exactmap [KNL,X86] Enable setting of an exact
2414 E820 memory map, as specified by the user.
2415 Such memmap=exactmap lines can be constructed based on
2416 BIOS output or other requirements. See the memmap=nn@ss
2419 memmap=nn[KMG]@ss[KMG]
2420 [KNL] Force usage of a specific region of memory.
2421 Region of memory to be used is from ss to ss+nn.
2422 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2423 which limits max address to nn[KMG].
2424 Multiple different regions can be specified,
2427 memmap=100M@2G,100M#3G,1G!1024G
2429 memmap=nn[KMG]#ss[KMG]
2430 [KNL,ACPI] Mark specific memory as ACPI data.
2431 Region of memory to be marked is from ss to ss+nn.
2433 memmap=nn[KMG]$ss[KMG]
2434 [KNL,ACPI] Mark specific memory as reserved.
2435 Region of memory to be reserved is from ss to ss+nn.
2436 Example: Exclude memory from 0x18690000-0x1869ffff
2437 memmap=64K$0x18690000
2439 memmap=0x10000$0x18690000
2440 Some bootloaders may need an escape character before '$',
2441 like Grub2, otherwise '$' and the following number
2444 memmap=nn[KMG]!ss[KMG]
2445 [KNL,X86] Mark specific memory as protected.
2446 Region of memory to be used, from ss to ss+nn.
2447 The memory region may be marked as e820 type 12 (0xc)
2448 and is NVDIMM or ADR memory.
2450 memmap=<size>%<offset>-<oldtype>+<newtype>
2451 [KNL,ACPI] Convert memory within the specified region
2452 from <oldtype> to <newtype>. If "-<oldtype>" is left
2453 out, the whole region will be marked as <newtype>,
2454 even if previously unavailable. If "+<newtype>" is left
2455 out, matching memory will be removed. Types are
2456 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2457 3 = ACPI, 12 = PRAM.
2459 memory_corruption_check=0/1 [X86]
2460 Some BIOSes seem to corrupt the first 64k of
2461 memory when doing things like suspend/resume.
2462 Setting this option will scan the memory
2463 looking for corruption. Enabling this will
2464 both detect corruption and prevent the kernel
2465 from using the memory being corrupted.
2466 However, its intended as a diagnostic tool; if
2467 repeatable BIOS-originated corruption always
2468 affects the same memory, you can use memmap=
2469 to prevent the kernel from using that memory.
2471 memory_corruption_check_size=size [X86]
2472 By default it checks for corruption in the low
2473 64k, making this memory unavailable for normal
2474 use. Use this parameter to scan for
2475 corruption in more or less memory.
2477 memory_corruption_check_period=seconds [X86]
2478 By default it checks for corruption every 60
2479 seconds. Use this parameter to check at some
2480 other rate. 0 disables periodic checking.
2482 memtest= [KNL,X86,ARM,PPC] Enable memtest
2484 default : 0 <disable>
2485 Specifies the number of memtest passes to be
2486 performed. Each pass selects another test
2487 pattern from a given set of patterns. Memtest
2488 fills the memory with this pattern, validates
2489 memory contents and reserves bad memory
2490 regions that are detected.
2492 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2493 Valid arguments: on, off
2494 Default (depends on kernel configuration option):
2495 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2496 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2497 mem_encrypt=on: Activate SME
2498 mem_encrypt=off: Do not activate SME
2500 Refer to Documentation/x86/amd-memory-encryption.txt
2501 for details on when memory encryption can be activated.
2503 mem_sleep_default= [SUSPEND] Default system suspend mode:
2504 s2idle - Suspend-To-Idle
2505 shallow - Power-On Suspend or equivalent (if supported)
2506 deep - Suspend-To-RAM or equivalent (if supported)
2507 See Documentation/admin-guide/pm/sleep-states.rst.
2509 meye.*= [HW] Set MotionEye Camera parameters
2510 See Documentation/media/v4l-drivers/meye.rst.
2512 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2513 Multi-Function General Purpose Timers on AMD Geode
2516 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2517 the BIOS has incorrectly applied a workaround. TinyBIOS
2518 version 0.98 is known to be affected, 0.99 fixes the
2519 problem by letting the user disable the workaround.
2523 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2524 physical address is ignored.
2526 mini2440= [ARM,HW,KNL]
2527 Format:[0..2][b][c][t]
2529 MINI2440 configuration specification:
2530 0 - The attached screen is the 3.5" TFT
2531 1 - The attached screen is the 7" TFT
2532 2 - The VGA Shield is attached (1024x768)
2533 Leaving out the screen size parameter will not load
2534 the TFT driver, and the framebuffer will be left
2536 b - Enable backlight. The TFT backlight pin will be
2537 linked to the kernel VESA blanking code and a GPIO
2538 LED. This parameter is not necessary when using the
2540 c - Enable the s3c camera interface.
2541 t - Reserved for enabling touchscreen support. The
2542 touchscreen support is not enabled in the mainstream
2543 kernel as of 2.6.30, a preliminary port can be found
2544 in the "bleeding edge" mini2440 support kernel at
2545 http://repo.or.cz/w/linux-2.6/mini2440.git
2548 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2549 parameter allows control of the logging verbosity for
2550 the additional memory initialisation checks. A value
2551 of 0 disables mminit logging and a level of 4 will
2552 log everything. Information is printed at KERN_DEBUG
2553 so loglevel=8 may also need to be specified.
2556 [KNL] When CONFIG_MODULE_SIG is set, this means that
2557 modules without (valid) signatures will fail to load.
2558 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2559 is always true, so this option does nothing.
2561 module_blacklist= [KNL] Do not load a comma-separated list of
2562 modules. Useful for debugging problem modules.
2565 [MOUSE] Maximum time between finger touching and
2566 leaving touchpad surface for touch to be considered
2567 a tap and be reported as a left button click (for
2568 touchpads working in absolute mode only).
2570 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2571 reporting absolute coordinates, such as tablets
2572 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2573 reporting absolute coordinates, such as tablets
2575 movablecore= [KNL,X86,IA-64,PPC]
2576 Format: nn[KMGTPE] | nn%
2577 This parameter is the complement to kernelcore=, it
2578 specifies the amount of memory used for migratable
2579 allocations. If both kernelcore and movablecore is
2580 specified, then kernelcore will be at *least* the
2581 specified value but may be more. If movablecore on its
2582 own is specified, the administrator must be careful
2583 that the amount of memory usable for all allocations
2586 movable_node [KNL] Boot-time switch to make hotplugable memory
2587 NUMA nodes to be movable. This means that the memory
2588 of such nodes will be usable only for movable
2589 allocations which rules out almost all kernel
2590 allocations. Use with caution!
2592 MTD_Partition= [MTD]
2593 Format: <name>,<region-number>,<size>,<offset>
2595 MTD_Region= [MTD] Format:
2596 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2599 See drivers/mtd/cmdlinepart.c.
2601 multitce=off [PPC] This parameter disables the use of the pSeries
2602 firmware feature for updating multiple TCE entries
2605 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2607 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2609 boundary - index of last SLC block on Flex-OneNAND.
2610 The remaining blocks are configured as MLC blocks.
2611 lock - Configure if Flex-OneNAND boundary should be locked.
2612 Once locked, the boundary cannot be changed.
2613 1 indicates lock status, 0 indicates unlock status.
2616 ARM/S3C2412 JIVE boot control
2618 See arch/arm/mach-s3c2412/mach-jive.c
2620 mtouchusb.raw_coordinates=
2621 [HW] Make the MicroTouch USB driver use raw coordinates
2622 ('y', default) or cooked coordinates ('n')
2624 mtrr_chunk_size=nn[KMG] [X86]
2625 used for mtrr cleanup. It is largest continuous chunk
2626 that could hold holes aka. UC entries.
2628 mtrr_gran_size=nn[KMG] [X86]
2629 Used for mtrr cleanup. It is granularity of mtrr block.
2631 Large value could prevent small alignment from
2634 mtrr_spare_reg_nr=n [X86]
2636 Range: 0,7 : spare reg number
2638 Used for mtrr cleanup. It is spare mtrr entries number.
2639 Set to 2 or more if your graphical card needs more.
2641 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2643 netdev= [NET] Network devices parameters
2644 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2645 Note that mem_start is often overloaded to mean
2646 something different and driver-specific.
2647 This usage is only documented in each driver source
2651 [NETFILTER] Enable connection tracking flow accounting
2652 0 to disable accounting
2653 1 to enable accounting
2656 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2657 See Documentation/filesystems/nfs/nfsroot.txt.
2659 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2660 See Documentation/filesystems/nfs/nfsroot.txt.
2662 nfsrootdebug [NFS] enable nfsroot debugging messages.
2663 See Documentation/filesystems/nfs/nfsroot.txt.
2665 nfs.callback_nr_threads=
2666 [NFSv4] set the total number of threads that the
2667 NFS client will assign to service NFSv4 callback
2670 nfs.callback_tcpport=
2671 [NFS] set the TCP port on which the NFSv4 callback
2672 channel should listen.
2675 [NFS] sets the pathname to the program which is used
2676 to update the NFS client cache entries.
2678 nfs.cache_getent_timeout=
2679 [NFS] sets the timeout after which an attempt to
2680 update a cache entry is deemed to have failed.
2682 nfs.idmap_cache_timeout=
2683 [NFS] set the maximum lifetime for idmapper cache
2687 [NFS] enable 64-bit inode numbers.
2688 If zero, the NFS client will fake up a 32-bit inode
2689 number for the readdir() and stat() syscalls instead
2690 of returning the full 64-bit number.
2691 The default is to return 64-bit inode numbers.
2693 nfs.max_session_cb_slots=
2694 [NFSv4.1] Sets the maximum number of session
2695 slots the client will assign to the callback
2696 channel. This determines the maximum number of
2697 callbacks the client will process in parallel for
2698 a particular server.
2700 nfs.max_session_slots=
2701 [NFSv4.1] Sets the maximum number of session slots
2702 the client will attempt to negotiate with the server.
2703 This limits the number of simultaneous RPC requests
2704 that the client can send to the NFSv4.1 server.
2705 Note that there is little point in setting this
2706 value higher than the max_tcp_slot_table_limit.
2708 nfs.nfs4_disable_idmapping=
2709 [NFSv4] When set to the default of '1', this option
2710 ensures that both the RPC level authentication
2711 scheme and the NFS level operations agree to use
2712 numeric uids/gids if the mount is using the
2713 'sec=sys' security flavour. In effect it is
2714 disabling idmapping, which can make migration from
2715 legacy NFSv2/v3 systems to NFSv4 easier.
2716 Servers that do not support this mode of operation
2717 will be autodetected by the client, and it will fall
2718 back to using the idmapper.
2719 To turn off this behaviour, set the value to '0'.
2721 [NFS4] Specify an additional fixed unique ident-
2722 ification string that NFSv4 clients can insert into
2723 their nfs_client_id4 string. This is typically a
2724 UUID that is generated at system install time.
2726 nfs.send_implementation_id =
2727 [NFSv4.1] Send client implementation identification
2728 information in exchange_id requests.
2729 If zero, no implementation identification information
2731 The default is to send the implementation identification
2734 nfs.recover_lost_locks =
2735 [NFSv4] Attempt to recover locks that were lost due
2736 to a lease timeout on the server. Please note that
2737 doing this risks data corruption, since there are
2738 no guarantees that the file will remain unchanged
2739 after the locks are lost.
2740 If you want to enable the kernel legacy behaviour of
2741 attempting to recover these locks, then set this
2743 The default parameter value of '0' causes the kernel
2744 not to attempt recovery of lost locks.
2746 nfs4.layoutstats_timer =
2747 [NFSv4.2] Change the rate at which the kernel sends
2748 layoutstats to the pNFS metadata server.
2750 Setting this to value to 0 causes the kernel to use
2751 whatever value is the default set by the layout
2752 driver. A non-zero value sets the minimum interval
2753 in seconds between layoutstats transmissions.
2755 nfsd.nfs4_disable_idmapping=
2756 [NFSv4] When set to the default of '1', the NFSv4
2757 server will return only numeric uids and gids to
2758 clients using auth_sys, and will accept numeric uids
2759 and gids from such clients. This is intended to ease
2760 migration from NFSv2/v3.
2762 nmi_debug= [KNL,SH] Specify one or more actions to take
2763 when a NMI is triggered.
2764 Format: [state][,regs][,debounce][,die]
2766 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2767 Format: [panic,][nopanic,][num]
2769 0 - turn hardlockup detector in nmi_watchdog off
2770 1 - turn hardlockup detector in nmi_watchdog on
2771 When panic is specified, panic when an NMI watchdog
2772 timeout occurs (or 'nopanic' to override the opposite
2773 default). To disable both hard and soft lockup detectors,
2774 please see 'nowatchdog'.
2775 This is useful when you use a panic=... timeout and
2776 need the box quickly up again.
2778 These settings can be accessed at runtime via
2779 the nmi_watchdog and hardlockup_panic sysctls.
2781 netpoll.carrier_timeout=
2782 [NET] Specifies amount of time (in seconds) that
2783 netpoll should wait for a carrier. By default netpoll
2786 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2787 emulation library even if a 387 maths coprocessor
2790 no5lvl [X86-64] Disable 5-level paging mode. Forces
2791 kernel to use 4-level paging instead.
2794 [HW] Never suspend the console
2795 Disable suspending of consoles during suspend and
2796 hibernate operations. Once disabled, debugging
2797 messages can reach various consoles while the rest
2798 of the system is being put to sleep (ie, while
2799 debugging driver suspend/resume hooks). This may
2800 not work reliably with all consoles, but is known
2801 to work with serial and VGA consoles.
2802 To facilitate more flexible debugging, we also add
2803 console_suspend, a printk module parameter to control
2804 it. Users could use console_suspend (usually
2805 /sys/module/printk/parameters/console_suspend) to
2806 turn on/off it dynamically.
2808 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2809 caches in the slab allocator. Saves per-node memory,
2810 but will impact performance.
2814 noaltinstr [S390] Disables alternative instructions patching
2815 (CPU alternatives feature).
2817 noapic [SMP,APIC] Tells the kernel to not make use of any
2818 IOAPICs that may be present in the system.
2820 noautogroup Disable scheduler automatic task group creation.
2822 nobats [PPC] Do not use BATs for mapping kernel lowmem
2823 on "Classic" PPC cores.
2827 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2829 nodelayacct [KNL] Disable per-task delay accounting
2831 nodsp [SH] Disable hardware DSP at boot time.
2833 noefi Disable EFI runtime services support.
2838 On X86-32 available only on PAE configured kernels.
2839 noexec=on: enable non-executable mappings (default)
2840 noexec=off: disable non-executable mappings
2843 Disable SMAP (Supervisor Mode Access Prevention)
2844 even if it is supported by processor.
2847 Disable SMEP (Supervisor Mode Execution Prevention)
2848 even if it is supported by processor.
2851 This affects only 32-bit executables.
2852 noexec32=on: enable non-executable mappings (default)
2853 read doesn't imply executable mappings
2854 noexec32=off: disable non-executable mappings
2855 read implies executable mappings
2857 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2859 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2860 register save and restore. The kernel will only save
2861 legacy floating-point registers on task switch.
2863 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2865 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2866 Equivalent to smt=1.
2868 [KNL,x86] Disable symmetric multithreading (SMT).
2869 nosmt=force: Force disable SMT, cannot be undone
2870 via the sysfs control file.
2872 nospectre_v1 [PPC] Disable mitigations for Spectre Variant 1 (bounds
2873 check bypass). With this option data leaks are possible
2876 nospectre_v2 [X86,PPC_FSL_BOOK3E] Disable all mitigations for the Spectre variant 2
2877 (indirect branch prediction) vulnerability. System may
2878 allow data leaks with this option, which is equivalent
2881 nospec_store_bypass_disable
2882 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
2884 noxsave [BUGS=X86] Disables x86 extended register state save
2885 and restore using xsave. The kernel will fallback to
2886 enabling legacy floating-point and sse state.
2888 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2889 register states. The kernel will fall back to use
2890 xsave to save the states. By using this parameter,
2891 performance of saving the states is degraded because
2892 xsave doesn't support modified optimization while
2893 xsaveopt supports it on xsaveopt enabled systems.
2895 noxsaves [X86] Disables xsaves and xrstors used in saving and
2896 restoring x86 extended register state in compacted
2897 form of xsave area. The kernel will fall back to use
2898 xsaveopt and xrstor to save and restore the states
2899 in standard form of xsave area. By using this
2900 parameter, xsave area per process might occupy more
2901 memory on xsaves enabled systems.
2903 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2904 wfi(ARM) instruction doesn't work correctly and not to
2905 use it. This is also useful when using JTAG debugger.
2907 no_file_caps Tells the kernel not to honor file capabilities. The
2908 only way then for a file to be executed with privilege
2909 is to be setuid root or executed by root.
2911 nohalt [IA-64] Tells the kernel not to use the power saving
2912 function PAL_HALT_LIGHT when idle. This increases
2913 power-consumption. On the positive side, it reduces
2914 interrupt wake-up latency, which may improve performance
2915 in certain environments such as networked servers or
2918 nohibernate [HIBERNATION] Disable hibernation and resume.
2920 nohz= [KNL] Boottime enable/disable dynamic ticks
2921 Valid arguments: on, off
2924 nohz_full= [KNL,BOOT,SMP,ISOL]
2925 The argument is a cpu list, as described above.
2926 In kernels built with CONFIG_NO_HZ_FULL=y, set
2927 the specified list of CPUs whose tick will be stopped
2928 whenever possible. The boot CPU will be forced outside
2929 the range to maintain the timekeeping. Any CPUs
2930 in this list will have their RCU callbacks offloaded,
2931 just as if they had also been called out in the
2932 rcu_nocbs= boot parameter.
2934 noiotrap [SH] Disables trapped I/O port accesses.
2936 noirqdebug [X86-32] Disables the code which attempts to detect and
2937 disable unhandled interrupt sources.
2939 no_timer_check [X86,APIC] Disables the code which tests for
2940 broken timer IRQ sources.
2942 noisapnp [ISAPNP] Disables ISA PnP code.
2944 noinitrd [RAM] Tells the kernel not to load any configured
2947 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2949 [Deprecated - use intremap=off]
2953 noinvpcid [X86] Disable the INVPCID cpu feature.
2955 nojitter [IA-64] Disables jitter checking for ITC timers.
2957 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2959 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2963 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2964 clock and use the default one.
2966 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2967 steal time is computed, but won't influence scheduler
2970 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2972 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2974 noltlbs [PPC] Do not use large page/tlb entries for kernel
2975 lowmem mapping on PPC40x and PPC8xx
2977 nomca [IA-64] Disable machine check abort handling
2979 nomce [X86-32] Disable Machine Check Exception
2981 nomfgpt [X86-32] Disable Multi-Function General Purpose
2982 Timer usage (for AMD Geode machines).
2984 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2985 shutdown the other cpus. Instead use the REBOOT_VECTOR
2988 nomodule Disable module load
2990 nopat [X86] Disable PAT (page attribute table extension of
2991 pagetables) support.
2993 nopcid [X86-64] Disable the PCID cpu feature.
2995 norandmaps Don't use address space randomization. Equivalent to
2996 echo 0 > /proc/sys/kernel/randomize_va_space
2998 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2999 with UP alternatives
3001 nordrand [X86] Disable kernel use of the RDRAND and
3002 RDSEED instructions even if they are supported
3003 by the processor. RDRAND and RDSEED are still
3004 available to user space applications.
3006 noresume [SWSUSP] Disables resume and restores original swap
3009 no-scroll [VGA] Disables scrollback.
3010 This is required for the Braillex ib80-piezo Braille
3011 reader made by F.H. Papenmeier (Germany).
3015 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
3017 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
3018 and disable the IO APIC. legacy for "maxcpus=0".
3020 nosoftlockup [KNL] Disable the soft-lockup detector.
3022 nosync [HW,M68K] Disables sync negotiation for all devices.
3024 nowatchdog [KNL] Disable both lockup detectors, i.e.
3025 soft-lockup and NMI watchdog (hard-lockup).
3029 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
3031 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
3032 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
3033 Some features depend on CPU0. Known dependencies are:
3034 1. Resume from suspend/hibernate depends on CPU0.
3035 Suspend/hibernate will fail if CPU0 is offline and you
3036 need to online CPU0 before suspend/hibernate.
3037 2. PIC interrupts also depend on CPU0. CPU0 can't be
3038 removed if a PIC interrupt is detected.
3039 It's said poweroff/reboot may depend on CPU0 on some
3040 machines although I haven't seen such issues so far
3041 after CPU0 is offline on a few tested machines.
3042 If the dependencies are under your control, you can
3043 turn on cpu0_hotplug.
3045 nps_mtm_hs_ctr= [KNL,ARC]
3046 This parameter sets the maximum duration, in
3047 cycles, each HW thread of the CTOP can run
3048 without interruptions, before HW switches it.
3049 The actual maximum duration is 16 times this
3051 Format: integer between 1 and 255
3054 nptcg= [IA-64] Override max number of concurrent global TLB
3055 purges which is reported from either PAL_VM_SUMMARY or
3058 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
3059 could support. nr_cpus=n : n >= 1 limits the kernel to
3060 support 'n' processors. It could be larger than the
3061 number of already plugged CPU during bootup, later in
3062 runtime you can physically add extra cpu until it reaches
3063 n. So during boot up some boot time memory for per-cpu
3064 variables need be pre-allocated for later physical cpu
3067 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3069 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
3070 Allowed values are enable and disable
3072 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3073 'node', 'default' can be specified
3074 This can be set from sysctl after boot.
3075 See Documentation/sysctl/vm.txt for details.
3077 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3078 See Documentation/debugging-via-ohci1394.txt for more
3081 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3082 Rather than timing out after 20 ms if an EC
3083 command is not properly ACKed, override the length
3084 of the timeout. We have interrupts disabled while
3085 waiting for the ACK, so if this is set too high
3086 interrupts *may* be lost!
3088 omap_mux= [OMAP] Override bootloader pin multiplexing.
3089 Format: <mux_mode0.mode_name=value>...
3090 For example, to override I2C bus2:
3091 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3093 oprofile.timer= [HW]
3094 Use timer interrupt instead of performance counters
3096 oprofile.cpu_type= Force an oprofile cpu type
3097 This might be useful if you have an older oprofile
3098 userland or if you want common events.
3099 Format: { arch_perfmon }
3100 arch_perfmon: [X86] Force use of architectural
3101 perfmon on Intel CPUs instead of the
3102 CPU specific event set.
3103 timer: [X86] Force use of architectural NMI
3104 timer mode (see also oprofile.timer
3105 for generic hr timer mode)
3107 oops=panic Always panic on oopses. Default is to just kill the
3108 process, but there is a small probability of
3109 deadlocking the machine.
3110 This will also cause panics on machine check exceptions.
3111 Useful together with panic=30 to trigger a reboot.
3113 page_owner= [KNL] Boot-time page_owner enabling option.
3114 Storage of the information about who allocated
3115 each page is disabled in default. With this switch,
3117 on: enable the feature
3119 page_poison= [KNL] Boot-time parameter changing the state of
3120 poisoning on the buddy allocator, available with
3121 CONFIG_PAGE_POISONING=y.
3122 off: turn off poisoning (default)
3123 on: turn on poisoning
3125 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3126 timeout > 0: seconds before rebooting
3127 timeout = 0: wait forever
3128 timeout < 0: reboot immediately
3131 panic_print= Bitmask for printing system info when panic happens.
3132 User can chose combination of the following bits:
3133 bit 0: print all tasks info
3134 bit 1: print system memory info
3135 bit 2: print timer info
3136 bit 3: print locks info if CONFIG_LOCKDEP is on
3137 bit 4: print ftrace buffer
3139 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3142 crash_kexec_post_notifiers
3143 Run kdump after running panic-notifiers and dumping
3144 kmsg. This only for the users who doubt kdump always
3145 succeeds in any situation.
3146 Note that this also increases risks of kdump failure,
3147 because some panic notifiers can make the crashed
3148 kernel more unstable.
3150 parkbd.port= [HW] Parallel port number the keyboard adapter is
3151 connected to, default is 0.
3153 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3154 0 for XT, 1 for AT (default is AT).
3157 parport= [HW,PPT] Specify parallel ports. 0 disables.
3158 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3159 Use 'auto' to force the driver to use any
3160 IRQ/DMA settings detected (the default is to
3161 ignore detected IRQ/DMA settings because of
3162 possible conflicts). You can specify the base
3163 address, IRQ, and DMA settings; IRQ and DMA
3164 should be numbers, or 'auto' (for using detected
3165 settings on that particular port), or 'nofifo'
3166 (to avoid using a FIFO even if it is detected).
3167 Parallel ports are assigned in the order they
3168 are specified on the command line, starting
3171 parport_init_mode= [HW,PPT]
3172 Configure VIA parallel port to operate in
3173 a specific mode. This is necessary on Pegasos
3174 computer where firmware has no options for setting
3175 up parallel port mode and sets it to spp.
3176 Currently this function knows 686a and 8231 chips.
3177 Format: [spp|ps2|epp|ecp|ecpepp]
3180 Halt all CPUs after the first oops has been printed for
3181 the specified number of seconds. This is to be used if
3182 your oopses keep scrolling off the screen.
3187 See header of drivers/block/paride/pcd.c.
3188 See also Documentation/blockdev/paride.txt.
3190 pci=option[,option...] [PCI] various PCI subsystem options.
3192 Some options herein operate on a specific device
3193 or a set of devices (<pci_dev>). These are
3194 specified in one of the following formats:
3196 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
3197 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
3199 Note: the first format specifies a PCI
3200 bus/device/function address which may change
3201 if new hardware is inserted, if motherboard
3202 firmware changes, or due to changes caused
3203 by other kernel parameters. If the
3204 domain is left unspecified, it is
3205 taken to be zero. Optionally, a path
3206 to a device through multiple device/function
3207 addresses can be specified after the base
3208 address (this is more robust against
3209 renumbering issues). The second format
3210 selects devices using IDs from the
3211 configuration space which may match multiple
3212 devices in the system.
3214 earlydump dump PCI config space before the kernel
3216 off [X86] don't probe for the PCI bus
3217 bios [X86-32] force use of PCI BIOS, don't access
3218 the hardware directly. Use this if your machine
3219 has a non-standard PCI host bridge.
3220 nobios [X86-32] disallow use of PCI BIOS, only direct
3221 hardware access methods are allowed. Use this
3222 if you experience crashes upon bootup and you
3223 suspect they are caused by the BIOS.
3224 conf1 [X86] Force use of PCI Configuration Access
3225 Mechanism 1 (config address in IO port 0xCF8,
3226 data in IO port 0xCFC, both 32-bit).
3227 conf2 [X86] Force use of PCI Configuration Access
3228 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3229 the function, IO port 0xCFA, also 8-bit, sets
3230 bus number. The config space is then accessed
3231 through ports 0xC000-0xCFFF).
3232 See http://wiki.osdev.org/PCI for more info
3233 on the configuration access mechanisms.
3234 noaer [PCIE] If the PCIEAER kernel config parameter is
3235 enabled, this kernel boot option can be used to
3236 disable the use of PCIE advanced error reporting.
3237 nodomains [PCI] Disable support for multiple PCI
3238 root domains (aka PCI segments, in ACPI-speak).
3239 nommconf [X86] Disable use of MMCONFIG for PCI
3241 check_enable_amd_mmconf [X86] check for and enable
3242 properly configured MMIO access to PCI
3243 config space on AMD family 10h CPU
3244 nomsi [MSI] If the PCI_MSI kernel config parameter is
3245 enabled, this kernel boot option can be used to
3246 disable the use of MSI interrupts system-wide.
3247 noioapicquirk [APIC] Disable all boot interrupt quirks.
3248 Safety option to keep boot IRQs enabled. This
3249 should never be necessary.
3250 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3251 primary IO-APIC for bridges that cannot disable
3252 boot IRQs. This fixes a source of spurious IRQs
3253 when the system masks IRQs.
3254 noioapicreroute [APIC] Disable workaround that uses the
3255 boot IRQ equivalent of an IRQ that connects to
3256 a chipset where boot IRQs cannot be disabled.
3257 The opposite of ioapicreroute.
3258 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3259 routing table. These calls are known to be buggy
3260 on several machines and they hang the machine
3261 when used, but on other computers it's the only
3262 way to get the interrupt routing table. Try
3263 this option if the kernel is unable to allocate
3264 IRQs or discover secondary PCI buses on your
3266 rom [X86] Assign address space to expansion ROMs.
3267 Use with caution as certain devices share
3268 address decoders between ROMs and other
3270 norom [X86] Do not assign address space to
3271 expansion ROMs that do not already have
3272 BIOS assigned address ranges.
3273 nobar [X86] Do not assign address space to the
3274 BARs that weren't assigned by the BIOS.
3275 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3276 assigned automatically to PCI devices. You can
3277 make the kernel exclude IRQs of your ISA cards
3279 pirqaddr=0xAAAAA [X86] Specify the physical address
3280 of the PIRQ table (normally generated
3281 by the BIOS) if it is outside the
3282 F0000h-100000h range.
3283 lastbus=N [X86] Scan all buses thru bus #N. Can be
3284 useful if the kernel is unable to find your
3285 secondary buses and you want to tell it
3286 explicitly which ones they are.
3287 assign-busses [X86] Always assign all PCI bus
3288 numbers ourselves, overriding
3289 whatever the firmware may have done.
3290 usepirqmask [X86] Honor the possible IRQ mask stored
3291 in the BIOS $PIR table. This is needed on
3292 some systems with broken BIOSes, notably
3293 some HP Pavilion N5400 and Omnibook XE3
3294 notebooks. This will have no effect if ACPI
3295 IRQ routing is enabled.
3296 noacpi [X86] Do not use ACPI for IRQ routing
3297 or for PCI scanning.
3298 use_crs [X86] Use PCI host bridge window information
3299 from ACPI. On BIOSes from 2008 or later, this
3300 is enabled by default. If you need to use this,
3301 please report a bug.
3302 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3303 If you need to use this, please report a bug.
3304 routeirq Do IRQ routing for all PCI devices.
3305 This is normally done in pci_enable_device(),
3306 so this option is a temporary workaround
3307 for broken drivers that don't call it.
3308 skip_isa_align [X86] do not align io start addr, so can
3309 handle more pci cards
3310 noearly [X86] Don't do any early type 1 scanning.
3311 This might help on some broken boards which
3312 machine check when some devices' config space
3313 is read. But various workarounds are disabled
3314 and some IOMMU drivers will not work.
3315 bfsort Sort PCI devices into breadth-first order.
3316 This sorting is done to get a device
3317 order compatible with older (<= 2.4) kernels.
3318 nobfsort Don't sort PCI devices into breadth-first order.
3319 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3320 tuning and use the BIOS-configured MPS defaults.
3321 pcie_bus_safe Set every device's MPS to the largest value
3322 supported by all devices below the root complex.
3323 pcie_bus_perf Set device MPS to the largest allowable MPS
3324 based on its parent bus. Also set MRRS (Max
3325 Read Request Size) to the largest supported
3326 value (no larger than the MPS that the device
3327 or bus can support) for best performance.
3328 pcie_bus_peer2peer Set every device's MPS to 128B, which
3329 every device is guaranteed to support. This
3330 configuration allows peer-to-peer DMA between
3331 any pair of devices, possibly at the cost of
3332 reduced performance. This also guarantees
3333 that hot-added devices will work.
3334 cbiosize=nn[KMG] The fixed amount of bus space which is
3335 reserved for the CardBus bridge's IO window.
3336 The default value is 256 bytes.
3337 cbmemsize=nn[KMG] The fixed amount of bus space which is
3338 reserved for the CardBus bridge's memory
3339 window. The default value is 64 megabytes.
3342 [<order of align>@]<pci_dev>[; ...]
3343 Specifies alignment and device to reassign
3344 aligned memory resources. How to
3345 specify the device is described above.
3346 If <order of align> is not specified,
3347 PAGE_SIZE is used as alignment.
3348 PCI-PCI bridge can be specified, if resource
3349 windows need to be expanded.
3350 To specify the alignment for several
3351 instances of a device, the PCI vendor,
3352 device, subvendor, and subdevice may be
3353 specified, e.g., 4096@pci:8086:9c22:103c:198f
3354 ecrc= Enable/disable PCIe ECRC (transaction layer
3355 end-to-end CRC checking).
3356 bios: Use BIOS/firmware settings. This is the
3360 hpiosize=nn[KMG] The fixed amount of bus space which is
3361 reserved for hotplug bridge's IO window.
3362 Default size is 256 bytes.
3363 hpmemsize=nn[KMG] The fixed amount of bus space which is
3364 reserved for hotplug bridge's memory window.
3365 Default size is 2 megabytes.
3366 hpbussize=nn The minimum amount of additional bus numbers
3367 reserved for buses below a hotplug bridge.
3369 realloc= Enable/disable reallocating PCI bridge resources
3370 if allocations done by BIOS are too small to
3371 accommodate resources required by all child
3373 off: Turn realloc off
3375 realloc same as realloc=on
3376 noari do not use PCIe ARI.
3377 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
3378 do not use PCIe ATS (and IOMMU device IOTLB).
3379 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3380 only look for one device below a PCIe downstream
3382 big_root_window Try to add a big 64bit memory window to the PCIe
3383 root complex on AMD CPUs. Some GFX hardware
3384 can resize a BAR to allow access to all VRAM.
3385 Adding the window is slightly risky (it may
3386 conflict with unreported devices), so this
3388 disable_acs_redir=<pci_dev>[; ...]
3389 Specify one or more PCI devices (in the format
3390 specified above) separated by semicolons.
3391 Each device specified will have the PCI ACS
3392 redirect capabilities forced off which will
3393 allow P2P traffic between devices through
3394 bridges without forcing it upstream. Note:
3395 this removes isolation between devices and
3396 may put more devices in an IOMMU group.
3398 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3401 force Enable ASPM even on devices that claim not to support it.
3402 WARNING: Forcing ASPM on may cause system lockups.
3404 pcie_ports= [PCIE] PCIe port services handling:
3405 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
3406 even if the platform doesn't give the OS permission to
3407 use them. This may cause conflicts if the platform
3408 also tries to use these services.
3409 compat Disable native PCIe services (PME, AER, DPC, PCIe
3412 pcie_port_pm= [PCIE] PCIe port power management handling:
3413 off Disable power management of all PCIe ports
3414 force Forcibly enable power management of all PCIe ports
3416 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3417 nomsi Do not use MSI for native PCIe PME signaling (this makes
3418 all PCIe root ports use INTx for all services).
3420 pcmv= [HW,PCMCIA] BadgePAD 4
3424 Keep all power-domains already enabled by bootloader on,
3425 even if no driver has claimed them. This is useful
3426 for debug and development, but should not be
3427 needed on a platform with proper driver support.
3430 See Documentation/blockdev/paride.txt.
3432 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3435 See arch/parisc/kernel/pdc_chassis.c
3437 percpu_alloc= Select which percpu first chunk allocator to use.
3438 Currently supported values are "embed" and "page".
3439 Archs may support subset or none of the selections.
3440 See comments in mm/percpu.c for details on each
3441 allocator. This parameter is primarily for debugging
3442 and performance comparison.
3445 See Documentation/blockdev/paride.txt.
3448 See Documentation/blockdev/paride.txt.
3450 pirq= [SMP,APIC] Manual mp-table setup
3451 See Documentation/x86/i386/IO-APIC.txt.
3453 plip= [PPT,NET] Parallel port network link
3454 Format: { parport<nr> | timid | 0 }
3455 See also Documentation/admin-guide/parport.rst.
3457 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3458 Override pmtimer IOPort with a hex value.
3462 Enable PNP debug messages (depends on the
3463 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3464 via /sys/module/pnp/parameters/debug. We always show
3465 current resource usage; turning this on also shows
3466 possible settings and some assignment information.
3472 { on | off | curr | res | no-curr | no-res }
3475 [ISAPNP] Exclude IRQs for the autoconfiguration
3478 [ISAPNP] Exclude DMAs for the autoconfiguration
3480 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3481 Ranges are in pairs (I/O port base and size).
3484 [ISAPNP] Exclude memory regions for the
3486 Ranges are in pairs (memory base and size).
3488 ports= [IP_VS_FTP] IPVS ftp helper module
3490 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3492 Format: <port>,<port>....
3494 powersave=off [PPC] This option disables power saving features.
3495 It specifically disables cpuidle and sets the
3496 platform machine description specific power_save
3497 function to NULL. On Idle the CPU just reduces
3500 ppc_strict_facility_enable
3501 [PPC] This option catches any kernel floating point,
3502 Altivec, VSX and SPE outside of regions specifically
3503 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3504 There is some performance impact when enabling this.
3508 Disable Hardware Transactional Memory
3510 print-fatal-signals=
3511 [KNL] debug: print fatal signals
3513 If enabled, warn about various signal handling
3514 related application anomalies: too many signals,
3515 too many POSIX.1 timers, fatal signals causing a
3518 If you hit the warning due to signal overflow,
3519 you might want to try "ulimit -i unlimited".
3523 printk.always_kmsg_dump=
3524 Trigger kmsg_dump for cases other than kernel oops or
3526 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3529 printk.devkmsg={on,off,ratelimit}
3530 Control writing to /dev/kmsg.
3531 on - unlimited logging to /dev/kmsg from userspace
3532 off - logging to /dev/kmsg disabled
3533 ratelimit - ratelimit the logging
3536 printk.time= Show timing data prefixed to each printk message line
3537 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3539 processor.max_cstate= [HW,ACPI]
3540 Limit processor to maximum C-state
3541 max_cstate=9 overrides any DMI blacklist limit.
3543 processor.nocst [HW,ACPI]
3544 Ignore the _CST method to determine C-states,
3545 instead using the legacy FADT method
3547 profile= [KNL] Enable kernel profiling via /proc/profile
3548 Format: [<profiletype>,]<number>
3549 Param: <profiletype>: "schedule", "sleep", or "kvm"
3550 [defaults to kernel profiling]
3551 Param: "schedule" - profile schedule points.
3552 Param: "sleep" - profile D-state sleeping (millisecs).
3553 Requires CONFIG_SCHEDSTATS
3554 Param: "kvm" - profile VM exits.
3555 Param: <number> - step/bucket size as a power of 2 for
3556 statistical time based profiling.
3558 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3560 See Documentation/blockdev/ramdisk.txt.
3562 psi= [KNL] Enable or disable pressure stall information
3566 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3567 probe for; one of (bare|imps|exps|lifebook|any).
3568 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3570 psmouse.resetafter= [HW,MOUSE]
3571 Try to reset the device after so many bad packets
3574 [HW,MOUSE] Set desired mouse resolution, in dpi.
3575 psmouse.smartscroll=
3576 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3577 0 = disabled, 1 = enabled (default).
3579 pstore.backend= Specify the name of the pstore backend to use
3582 See Documentation/blockdev/paride.txt.
3584 pti= [X86_64] Control Page Table Isolation of user and
3585 kernel address spaces. Disabling this feature
3586 removes hardening, but improves performance of
3587 system calls and interrupts.
3589 on - unconditionally enable
3590 off - unconditionally disable
3591 auto - kernel detects whether your CPU model is
3592 vulnerable to issues that PTI mitigates
3594 Not specifying this option is equivalent to pti=auto.
3597 Equivalent to pti=off
3600 [KNL] Number of legacy pty's. Overwrites compiled-in
3603 quiet [KNL] Disable most log messages
3608 See Documentation/admin-guide/md.rst.
3610 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3611 See Documentation/blockdev/ramdisk.txt.
3613 random.trust_cpu={on,off}
3614 [KNL] Enable or disable trusting the use of the
3615 CPU's random number generator (if available) to
3616 fully seed the kernel's CRNG. Default is controlled
3617 by CONFIG_RANDOM_TRUST_CPU.
3619 ras=option[,option,...] [KNL] RAS-specific options
3622 Disable the Correctable Errors Collector,
3623 see CONFIG_RAS_CEC help text.
3626 The argument is a cpu list, as described above.
3628 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3629 the specified list of CPUs to be no-callback CPUs.
3630 Invocation of these CPUs' RCU callbacks will be
3631 offloaded to "rcuox/N" kthreads created for that
3632 purpose, where "x" is "p" for RCU-preempt, and
3633 "s" for RCU-sched, and "N" is the CPU number.
3634 This reduces OS jitter on the offloaded CPUs,
3635 which can be useful for HPC and real-time
3636 workloads. It can also improve energy efficiency
3637 for asymmetric multiprocessors.
3640 Rather than requiring that offloaded CPUs
3641 (specified by rcu_nocbs= above) explicitly
3642 awaken the corresponding "rcuoN" kthreads,
3643 make these kthreads poll for callbacks.
3644 This improves the real-time response for the
3645 offloaded CPUs by relieving them of the need to
3646 wake up the corresponding kthread, but degrades
3647 energy efficiency by requiring that the kthreads
3648 periodically wake up to do the polling.
3650 rcutree.blimit= [KNL]
3651 Set maximum number of finished RCU callbacks to
3652 process in one batch.
3654 rcutree.dump_tree= [KNL]
3655 Dump the structure of the rcu_node combining tree
3656 out at early boot. This is used for diagnostic
3657 purposes, to verify correct tree setup.
3659 rcutree.gp_cleanup_delay= [KNL]
3660 Set the number of jiffies to delay each step of
3661 RCU grace-period cleanup.
3663 rcutree.gp_init_delay= [KNL]
3664 Set the number of jiffies to delay each step of
3665 RCU grace-period initialization.
3667 rcutree.gp_preinit_delay= [KNL]
3668 Set the number of jiffies to delay each step of
3669 RCU grace-period pre-initialization, that is,
3670 the propagation of recent CPU-hotplug changes up
3671 the rcu_node combining tree.
3673 rcutree.rcu_fanout_exact= [KNL]
3674 Disable autobalancing of the rcu_node combining
3675 tree. This is used by rcutorture, and might
3676 possibly be useful for architectures having high
3677 cache-to-cache transfer latencies.
3679 rcutree.rcu_fanout_leaf= [KNL]
3680 Change the number of CPUs assigned to each
3681 leaf rcu_node structure. Useful for very
3682 large systems, which will choose the value 64,
3683 and for NUMA systems with large remote-access
3684 latencies, which will choose a value aligned
3685 with the appropriate hardware boundaries.
3687 rcutree.jiffies_till_first_fqs= [KNL]
3688 Set delay from grace-period initialization to
3689 first attempt to force quiescent states.
3690 Units are jiffies, minimum value is zero,
3691 and maximum value is HZ.
3693 rcutree.jiffies_till_next_fqs= [KNL]
3694 Set delay between subsequent attempts to force
3695 quiescent states. Units are jiffies, minimum
3696 value is one, and maximum value is HZ.
3698 rcutree.jiffies_till_sched_qs= [KNL]
3699 Set required age in jiffies for a
3700 given grace period before RCU starts
3701 soliciting quiescent-state help from
3702 rcu_note_context_switch() and cond_resched().
3703 If not specified, the kernel will calculate
3704 a value based on the most recent settings
3705 of rcutree.jiffies_till_first_fqs
3706 and rcutree.jiffies_till_next_fqs.
3707 This calculated value may be viewed in
3708 rcutree.jiffies_to_sched_qs. Any attempt to set
3709 rcutree.jiffies_to_sched_qs will be cheerfully
3712 rcutree.kthread_prio= [KNL,BOOT]
3713 Set the SCHED_FIFO priority of the RCU per-CPU
3714 kthreads (rcuc/N). This value is also used for
3715 the priority of the RCU boost threads (rcub/N)
3716 and for the RCU grace-period kthreads (rcu_bh,
3717 rcu_preempt, and rcu_sched). If RCU_BOOST is
3718 set, valid values are 1-99 and the default is 1
3719 (the least-favored priority). Otherwise, when
3720 RCU_BOOST is not set, valid values are 0-99 and
3721 the default is zero (non-realtime operation).
3723 rcutree.rcu_nocb_leader_stride= [KNL]
3724 Set the number of NOCB kthread groups, which
3725 defaults to the square root of the number of
3726 CPUs. Larger numbers reduces the wakeup overhead
3727 on the per-CPU grace-period kthreads, but increases
3728 that same overhead on each group's leader.
3730 rcutree.qhimark= [KNL]
3731 Set threshold of queued RCU callbacks beyond which
3732 batch limiting is disabled.
3734 rcutree.qlowmark= [KNL]
3735 Set threshold of queued RCU callbacks below which
3736 batch limiting is re-enabled.
3738 rcutree.rcu_idle_gp_delay= [KNL]
3739 Set wakeup interval for idle CPUs that have
3740 RCU callbacks (RCU_FAST_NO_HZ=y).
3742 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3743 Set wakeup interval for idle CPUs that have
3744 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3745 Lazy RCU callbacks are those which RCU can
3746 prove do nothing more than free memory.
3748 rcutree.rcu_kick_kthreads= [KNL]
3749 Cause the grace-period kthread to get an extra
3750 wake_up() if it sleeps three times longer than
3751 it should at force-quiescent-state time.
3752 This wake_up() will be accompanied by a
3753 WARN_ONCE() splat and an ftrace_dump().
3755 rcutree.sysrq_rcu= [KNL]
3756 Commandeer a sysrq key to dump out Tree RCU's
3757 rcu_node tree with an eye towards determining
3758 why a new grace period has not yet started.
3760 rcuperf.gp_async= [KNL]
3761 Measure performance of asynchronous
3762 grace-period primitives such as call_rcu().
3764 rcuperf.gp_async_max= [KNL]
3765 Specify the maximum number of outstanding
3766 callbacks per writer thread. When a writer
3767 thread exceeds this limit, it invokes the
3768 corresponding flavor of rcu_barrier() to allow
3769 previously posted callbacks to drain.
3771 rcuperf.gp_exp= [KNL]
3772 Measure performance of expedited synchronous
3773 grace-period primitives.
3775 rcuperf.holdoff= [KNL]
3776 Set test-start holdoff period. The purpose of
3777 this parameter is to delay the start of the
3778 test until boot completes in order to avoid
3781 rcuperf.nreaders= [KNL]
3782 Set number of RCU readers. The value -1 selects
3783 N, where N is the number of CPUs. A value
3784 "n" less than -1 selects N-n+1, where N is again
3785 the number of CPUs. For example, -2 selects N
3786 (the number of CPUs), -3 selects N+1, and so on.
3787 A value of "n" less than or equal to -N selects
3790 rcuperf.nwriters= [KNL]
3791 Set number of RCU writers. The values operate
3792 the same as for rcuperf.nreaders.
3793 N, where N is the number of CPUs
3795 rcuperf.perf_type= [KNL]
3796 Specify the RCU implementation to test.
3798 rcuperf.shutdown= [KNL]
3799 Shut the system down after performance tests
3800 complete. This is useful for hands-off automated
3803 rcuperf.verbose= [KNL]
3804 Enable additional printk() statements.
3806 rcuperf.writer_holdoff= [KNL]
3807 Write-side holdoff between grace periods,
3808 in microseconds. The default of zero says
3811 rcutorture.fqs_duration= [KNL]
3812 Set duration of force_quiescent_state bursts
3815 rcutorture.fqs_holdoff= [KNL]
3816 Set holdoff time within force_quiescent_state bursts
3819 rcutorture.fqs_stutter= [KNL]
3820 Set wait time between force_quiescent_state bursts
3823 rcutorture.fwd_progress= [KNL]
3824 Enable RCU grace-period forward-progress testing
3825 for the types of RCU supporting this notion.
3827 rcutorture.fwd_progress_div= [KNL]
3828 Specify the fraction of a CPU-stall-warning
3829 period to do tight-loop forward-progress testing.
3831 rcutorture.fwd_progress_holdoff= [KNL]
3832 Number of seconds to wait between successive
3833 forward-progress tests.
3835 rcutorture.fwd_progress_need_resched= [KNL]
3836 Enclose cond_resched() calls within checks for
3837 need_resched() during tight-loop forward-progress
3840 rcutorture.gp_cond= [KNL]
3841 Use conditional/asynchronous update-side
3842 primitives, if available.
3844 rcutorture.gp_exp= [KNL]
3845 Use expedited update-side primitives, if available.
3847 rcutorture.gp_normal= [KNL]
3848 Use normal (non-expedited) asynchronous
3849 update-side primitives, if available.
3851 rcutorture.gp_sync= [KNL]
3852 Use normal (non-expedited) synchronous
3853 update-side primitives, if available. If all
3854 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3855 rcutorture.gp_normal=, and rcutorture.gp_sync=
3856 are zero, rcutorture acts as if is interpreted
3857 they are all non-zero.
3859 rcutorture.n_barrier_cbs= [KNL]
3860 Set callbacks/threads for rcu_barrier() testing.
3862 rcutorture.nfakewriters= [KNL]
3863 Set number of concurrent RCU writers. These just
3864 stress RCU, they don't participate in the actual
3865 test, hence the "fake".
3867 rcutorture.nreaders= [KNL]
3868 Set number of RCU readers. The value -1 selects
3869 N-1, where N is the number of CPUs. A value
3870 "n" less than -1 selects N-n-2, where N is again
3871 the number of CPUs. For example, -2 selects N
3872 (the number of CPUs), -3 selects N+1, and so on.
3874 rcutorture.object_debug= [KNL]
3875 Enable debug-object double-call_rcu() testing.
3877 rcutorture.onoff_holdoff= [KNL]
3878 Set time (s) after boot for CPU-hotplug testing.
3880 rcutorture.onoff_interval= [KNL]
3881 Set time (jiffies) between CPU-hotplug operations,
3882 or zero to disable CPU-hotplug testing.
3884 rcutorture.shuffle_interval= [KNL]
3885 Set task-shuffle interval (s). Shuffling tasks
3886 allows some CPUs to go into dyntick-idle mode
3887 during the rcutorture test.
3889 rcutorture.shutdown_secs= [KNL]
3890 Set time (s) after boot system shutdown. This
3891 is useful for hands-off automated testing.
3893 rcutorture.stall_cpu= [KNL]
3894 Duration of CPU stall (s) to test RCU CPU stall
3895 warnings, zero to disable.
3897 rcutorture.stall_cpu_holdoff= [KNL]
3898 Time to wait (s) after boot before inducing stall.
3900 rcutorture.stall_cpu_irqsoff= [KNL]
3901 Disable interrupts while stalling if set.
3903 rcutorture.stat_interval= [KNL]
3904 Time (s) between statistics printk()s.
3906 rcutorture.stutter= [KNL]
3907 Time (s) to stutter testing, for example, specifying
3908 five seconds causes the test to run for five seconds,
3909 wait for five seconds, and so on. This tests RCU's
3910 ability to transition abruptly to and from idle.
3912 rcutorture.test_boost= [KNL]
3913 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3914 "Maybe" means test if the RCU implementation
3915 under test support RCU priority boosting.
3917 rcutorture.test_boost_duration= [KNL]
3918 Duration (s) of each individual boost test.
3920 rcutorture.test_boost_interval= [KNL]
3921 Interval (s) between each boost test.
3923 rcutorture.test_no_idle_hz= [KNL]
3924 Test RCU's dyntick-idle handling. See also the
3925 rcutorture.shuffle_interval parameter.
3927 rcutorture.torture_type= [KNL]
3928 Specify the RCU implementation to test.
3930 rcutorture.verbose= [KNL]
3931 Enable additional printk() statements.
3933 rcupdate.rcu_cpu_stall_suppress= [KNL]
3934 Suppress RCU CPU stall warning messages.
3936 rcupdate.rcu_cpu_stall_timeout= [KNL]
3937 Set timeout for RCU CPU stall warning messages.
3939 rcupdate.rcu_expedited= [KNL]
3940 Use expedited grace-period primitives, for
3941 example, synchronize_rcu_expedited() instead
3942 of synchronize_rcu(). This reduces latency,
3943 but can increase CPU utilization, degrade
3944 real-time latency, and degrade energy efficiency.
3945 No effect on CONFIG_TINY_RCU kernels.
3947 rcupdate.rcu_normal= [KNL]
3948 Use only normal grace-period primitives,
3949 for example, synchronize_rcu() instead of
3950 synchronize_rcu_expedited(). This improves
3951 real-time latency, CPU utilization, and
3952 energy efficiency, but can expose users to
3953 increased grace-period latency. This parameter
3954 overrides rcupdate.rcu_expedited. No effect on
3955 CONFIG_TINY_RCU kernels.
3957 rcupdate.rcu_normal_after_boot= [KNL]
3958 Once boot has completed (that is, after
3959 rcu_end_inkernel_boot() has been invoked), use
3960 only normal grace-period primitives. No effect
3961 on CONFIG_TINY_RCU kernels.
3963 rcupdate.rcu_task_stall_timeout= [KNL]
3964 Set timeout in jiffies for RCU task stall warning
3965 messages. Disable with a value less than or equal
3968 rcupdate.rcu_self_test= [KNL]
3969 Run the RCU early boot self tests
3973 Run specified binary instead of /init from the ramdisk,
3974 used for early userspace startup. See initrd.
3977 Turn on/off individual RDT features. List is:
3978 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
3980 E.g. to turn on cmt and turn off mba use:
3984 Format (x86 or x86_64):
3985 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3987 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3989 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3990 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3991 reboot_force is either force or not specified,
3992 reboot_cpu is s[mp]#### with #### being the processor
3993 to be used for rebooting.
3996 [KNL, SMP] Set scheduler's default relax_domain_level.
3997 See Documentation/cgroup-v1/cpusets.txt.
3999 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
4000 Format: <base1>,<size1>[,<base2>,<size2>,...]
4001 Reserve I/O ports or memory so the kernel won't use
4002 them. If <base> is less than 0x10000, the region
4003 is assumed to be I/O ports; otherwise it is memory.
4005 reservetop= [X86-32]
4007 Reserves a hole at the top of the kernel virtual
4012 Set the amount of memory to reserve for BIOS at
4013 the bottom of the address space.
4015 reset_devices [KNL] Force drivers to reset the underlying device
4016 during initialization.
4019 Specify the partition device for software suspend
4021 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
4023 resume_offset= [SWSUSP]
4024 Specify the offset from the beginning of the partition
4025 given by "resume=" at which the swap header is located,
4026 in <PAGE_SIZE> units (needed only for swap files).
4027 See Documentation/power/swsusp-and-swap-files.txt
4029 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
4030 read the resume files
4032 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
4033 Useful for devices that are detected asynchronously
4034 (e.g. USB and MMC devices).
4036 hibernate= [HIBERNATION]
4037 noresume Don't check if there's a hibernation image
4038 present during boot.
4039 nocompress Don't compress/decompress hibernation images.
4040 no Disable hibernation and resume.
4041 protect_image Turn on image protection during restoration
4042 (that will set all pages holding image data
4043 during restoration read-only).
4045 retain_initrd [RAM] Keep initrd memory after extraction
4047 rfkill.default_state=
4048 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
4049 etc. communication is blocked by default.
4052 rfkill.master_switch_mode=
4053 0 The "airplane mode" button does nothing.
4054 1 The "airplane mode" button toggles between everything
4055 blocked and the previous configuration.
4056 2 The "airplane mode" button toggles between everything
4057 blocked and everything unblocked.
4059 rhash_entries= [KNL,NET]
4060 Set number of hash buckets for route cache
4063 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
4066 ro [KNL] Mount root device read-only on boot
4069 on Mark read-only kernel memory as read-only (default).
4070 off Leave read-only kernel memory writable for debugging.
4073 Enable the uart passthrough on the designated usb port
4074 on Rockchip SoCs. When active, the signals of the
4075 debug-uart get routed to the D+ and D- pins of the usb
4076 port and the regular usb controller gets disabled.
4078 root= [KNL] Root filesystem
4079 See name_to_dev_t comment in init/do_mounts.c.
4081 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
4082 mount the root filesystem
4084 rootflags= [KNL] Set root filesystem mount option string
4086 rootfstype= [KNL] Set root filesystem type
4088 rootwait [KNL] Wait (indefinitely) for root device to show up.
4089 Useful for devices that are detected asynchronously
4090 (e.g. USB and MMC devices).
4092 rproc_mem=nn[KMG][@address]
4093 [KNL,ARM,CMA] Remoteproc physical memory block.
4094 Memory area to be used by remote processor image,
4097 rw [KNL] Mount root device read-write on boot
4099 S [KNL] Run init in single mode
4101 s390_iommu= [HW,S390]
4102 Set s390 IOTLB flushing mode
4104 With strict flushing every unmap operation will result in
4105 an IOTLB flush. Default is lazy flushing before reuse,
4109 See drivers/net/irda/sa1100_ir.c.
4111 sbni= [NET] Granch SBNI12 leased line adapter
4113 sched_debug [KNL] Enables verbose scheduler debug messages.
4115 schedstats= [KNL,X86] Enable or disable scheduled statistics.
4116 Allowed values are enable and disable. This feature
4117 incurs a small amount of overhead in the scheduler
4118 but is useful for debugging and performance tuning.
4120 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
4121 xtime_lock contention on larger systems, and/or RCU lock
4122 contention on all systems with CONFIG_MAXSMP set.
4123 Format: { "0" | "1" }
4124 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
4126 Note: increases power consumption, thus should only be
4127 enabled if running jitter sensitive (HPC/RT) workloads.
4129 security= [SECURITY] Choose a legacy "major" security module to
4130 enable at boot. This has been deprecated by the
4133 selinux= [SELINUX] Disable or enable SELinux at boot time.
4134 Format: { "0" | "1" }
4135 See security/selinux/Kconfig help text.
4138 Default value is set via kernel config option.
4139 If enabled at boot time, /selinux/disable can be used
4140 later to disable prior to initial policy load.
4142 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
4143 Format: { "0" | "1" }
4144 See security/apparmor/Kconfig help text
4147 Default value is set via kernel config option.
4149 serialnumber [BUGS=X86-32]
4152 Maximal number of shapers.
4160 Disable merging of slabs with similar size. May be
4161 necessary if there is some reason to distinguish
4162 allocs to different slabs, especially in hardened
4163 environments where the risk of heap overflows and
4164 layout control by attackers can usually be
4165 frustrated by disabling merging. This will reduce
4166 most of the exposure of a heap attack to a single
4167 cache (risks via metadata attacks are mostly
4168 unchanged). Debug options disable merging on their
4170 For more information see Documentation/vm/slub.rst.
4172 slab_max_order= [MM, SLAB]
4173 Determines the maximum allowed order for slabs.
4174 A high setting may cause OOMs due to memory
4175 fragmentation. Defaults to 1 for systems with
4176 more than 32MB of RAM, 0 otherwise.
4178 slub_debug[=options[,slabs]] [MM, SLUB]
4179 Enabling slub_debug allows one to determine the
4180 culprit if slab objects become corrupted. Enabling
4181 slub_debug can create guard zones around objects and
4182 may poison objects when not in use. Also tracks the
4183 last alloc / free. For more information see
4184 Documentation/vm/slub.rst.
4186 slub_memcg_sysfs= [MM, SLUB]
4187 Determines whether to enable sysfs directories for
4188 memory cgroup sub-caches. 1 to enable, 0 to disable.
4189 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
4190 Enabling this can lead to a very high number of debug
4191 directories and files being created under
4194 slub_max_order= [MM, SLUB]
4195 Determines the maximum allowed order for slabs.
4196 A high setting may cause OOMs due to memory
4197 fragmentation. For more information see
4198 Documentation/vm/slub.rst.
4200 slub_min_objects= [MM, SLUB]
4201 The minimum number of objects per slab. SLUB will
4202 increase the slab order up to slub_max_order to
4203 generate a sufficiently large slab able to contain
4204 the number of objects indicated. The higher the number
4205 of objects the smaller the overhead of tracking slabs
4206 and the less frequently locks need to be acquired.
4207 For more information see Documentation/vm/slub.rst.
4209 slub_min_order= [MM, SLUB]
4210 Determines the minimum page order for slabs. Must be
4211 lower than slub_max_order.
4212 For more information see Documentation/vm/slub.rst.
4214 slub_nomerge [MM, SLUB]
4215 Same with slab_nomerge. This is supported for legacy.
4216 See slab_nomerge for more information.
4219 Format: <io1>[,<io2>[,...,<io8>]]
4221 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4222 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4223 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4224 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4225 smsc-ircc2.ircc_irq= [HW] IRQ line
4226 smsc-ircc2.ircc_dma= [HW] DMA channel
4227 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4228 0: Toshiba Satellite 1800 (GP data pin select)
4229 1: Fast pin select (default)
4232 smt [KNL,S390] Set the maximum number of threads (logical
4233 CPUs) to use per physical CPU on systems capable of
4234 symmetric multithreading (SMT). Will be capped to the
4235 actual hardware limit.
4237 Default: -1 (no limit)
4240 [KNL] Should the soft-lockup detector generate panics.
4243 A nonzero value instructs the soft-lockup detector
4244 to panic the machine when a soft-lockup occurs. This
4245 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
4246 which is the respective build-time switch to that
4249 softlockup_all_cpu_backtrace=
4250 [KNL] Should the soft-lockup detector generate
4251 backtraces on all cpus.
4254 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4255 See Documentation/laptops/sonypi.txt
4257 spectre_v2= [X86] Control mitigation of Spectre variant 2
4258 (indirect branch speculation) vulnerability.
4259 The default operation protects the kernel from
4262 on - unconditionally enable, implies
4264 off - unconditionally disable, implies
4266 auto - kernel detects whether your CPU model is
4269 Selecting 'on' will, and 'auto' may, choose a
4270 mitigation method at run time according to the
4271 CPU, the available microcode, the setting of the
4272 CONFIG_RETPOLINE configuration option, and the
4273 compiler with which the kernel was built.
4275 Selecting 'on' will also enable the mitigation
4276 against user space to user space task attacks.
4278 Selecting 'off' will disable both the kernel and
4279 the user space protections.
4281 Specific mitigations can also be selected manually:
4283 retpoline - replace indirect branches
4284 retpoline,generic - google's original retpoline
4285 retpoline,amd - AMD-specific minimal thunk
4287 Not specifying this option is equivalent to
4291 [X86] Control mitigation of Spectre variant 2
4292 (indirect branch speculation) vulnerability between
4295 on - Unconditionally enable mitigations. Is
4296 enforced by spectre_v2=on
4298 off - Unconditionally disable mitigations. Is
4299 enforced by spectre_v2=off
4301 prctl - Indirect branch speculation is enabled,
4302 but mitigation can be enabled via prctl
4303 per thread. The mitigation control state
4304 is inherited on fork.
4307 - Like "prctl" above, but only STIBP is
4308 controlled per thread. IBPB is issued
4309 always when switching between different user
4313 - Same as "prctl" above, but all seccomp
4314 threads will enable the mitigation unless
4315 they explicitly opt out.
4318 - Like "seccomp" above, but only STIBP is
4319 controlled per thread. IBPB is issued
4320 always when switching between different
4321 user space processes.
4323 auto - Kernel selects the mitigation depending on
4324 the available CPU features and vulnerability.
4327 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
4329 Not specifying this option is equivalent to
4330 spectre_v2_user=auto.
4332 spec_store_bypass_disable=
4333 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4334 (Speculative Store Bypass vulnerability)
4336 Certain CPUs are vulnerable to an exploit against a
4337 a common industry wide performance optimization known
4338 as "Speculative Store Bypass" in which recent stores
4339 to the same memory location may not be observed by
4340 later loads during speculative execution. The idea
4341 is that such stores are unlikely and that they can
4342 be detected prior to instruction retirement at the
4343 end of a particular speculation execution window.
4345 In vulnerable processors, the speculatively forwarded
4346 store can be used in a cache side channel attack, for
4347 example to read memory to which the attacker does not
4348 directly have access (e.g. inside sandboxed code).
4350 This parameter controls whether the Speculative Store
4351 Bypass optimization is used.
4353 On x86 the options are:
4355 on - Unconditionally disable Speculative Store Bypass
4356 off - Unconditionally enable Speculative Store Bypass
4357 auto - Kernel detects whether the CPU model contains an
4358 implementation of Speculative Store Bypass and
4359 picks the most appropriate mitigation. If the
4360 CPU is not vulnerable, "off" is selected. If the
4361 CPU is vulnerable the default mitigation is
4362 architecture and Kconfig dependent. See below.
4363 prctl - Control Speculative Store Bypass per thread
4364 via prctl. Speculative Store Bypass is enabled
4365 for a process by default. The state of the control
4366 is inherited on fork.
4367 seccomp - Same as "prctl" above, but all seccomp threads
4368 will disable SSB unless they explicitly opt out.
4370 Default mitigations:
4371 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4373 On powerpc the options are:
4375 on,auto - On Power8 and Power9 insert a store-forwarding
4376 barrier on kernel entry and exit. On Power7
4377 perform a software flush on kernel entry and
4381 Not specifying this option is equivalent to
4382 spec_store_bypass_disable=auto.
4384 spia_io_base= [HW,MTD]
4389 srcutree.counter_wrap_check [KNL]
4390 Specifies how frequently to check for
4391 grace-period sequence counter wrap for the
4392 srcu_data structure's ->srcu_gp_seq_needed field.
4393 The greater the number of bits set in this kernel
4394 parameter, the less frequently counter wrap will
4395 be checked for. Note that the bottom two bits
4398 srcutree.exp_holdoff [KNL]
4399 Specifies how many nanoseconds must elapse
4400 since the end of the last SRCU grace period for
4401 a given srcu_struct until the next normal SRCU
4402 grace period will be considered for automatic
4403 expediting. Set to zero to disable automatic
4407 Speculative Store Bypass Disable control
4409 On CPUs that are vulnerable to the Speculative
4410 Store Bypass vulnerability and offer a
4411 firmware based mitigation, this parameter
4412 indicates how the mitigation should be used:
4414 force-on: Unconditionally enable mitigation for
4415 for both kernel and userspace
4416 force-off: Unconditionally disable mitigation for
4417 for both kernel and userspace
4418 kernel: Always enable mitigation in the
4419 kernel, and offer a prctl interface
4420 to allow userspace to register its
4421 interest in being mitigated too.
4423 stack_guard_gap= [MM]
4424 override the default stack gap protection. The value
4425 is in page units and it defines how many pages prior
4426 to (for stacks growing down) resp. after (for stacks
4427 growing up) the main stack are reserved for no other
4428 mapping. Default value is 256 pages.
4431 Enabled the stack tracer on boot up.
4433 stacktrace_filter=[function-list]
4434 [FTRACE] Limit the functions that the stack tracer
4435 will trace at boot up. function-list is a comma separated
4436 list of functions. This list can be changed at run
4437 time by the stack_trace_filter file in the debugfs
4438 tracing directory. Note, this enables stack tracing
4439 and the stacktrace above is not needed.
4443 Set the STI (builtin display/keyboard on the HP-PARISC
4444 machines) console (graphic card) which should be used
4445 as the initial boot-console.
4446 See also comment in drivers/video/console/sticore.c.
4449 See comment in drivers/video/console/sticore.c.
4452 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4454 sunrpc.min_resvport=
4455 sunrpc.max_resvport=
4457 SunRPC servers often require that client requests
4458 originate from a privileged port (i.e. a port in the
4459 range 0 < portnr < 1024).
4460 An administrator who wishes to reserve some of these
4461 ports for other uses may adjust the range that the
4462 kernel's sunrpc client considers to be privileged
4463 using these two parameters to set the minimum and
4464 maximum port values.
4466 sunrpc.svc_rpc_per_connection_limit=
4468 Limit the number of requests that the server will
4469 process in parallel from a single connection.
4470 The default value is 0 (no limit).
4474 Control how the NFS server code allocates CPUs to
4475 service thread pools. Depending on how many NICs
4476 you have and where their interrupts are bound, this
4477 option will affect which CPUs will do NFS serving.
4478 Note: this parameter cannot be changed while the
4479 NFS server is running.
4481 auto the server chooses an appropriate mode
4482 automatically using heuristics
4483 global a single global pool contains all CPUs
4484 percpu one pool for each CPU
4485 pernode one pool for each NUMA node (equivalent
4486 to global on non-NUMA machines)
4488 sunrpc.tcp_slot_table_entries=
4489 sunrpc.udp_slot_table_entries=
4491 Sets the upper limit on the number of simultaneous
4492 RPC calls that can be sent from the client to a
4493 server. Increasing these values may allow you to
4494 improve throughput, but will also increase the
4495 amount of memory reserved for use by the client.
4497 suspend.pm_test_delay=
4499 Sets the number of seconds to remain in a suspend test
4500 mode before resuming the system (see
4501 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4502 is set. Default value is 5.
4505 [KNL] Enable accounting of swap in memory resource
4506 controller if no parameter or 1 is given or disable
4507 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4509 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4510 Format: { <int> | force | noforce }
4511 <int> -- Number of I/O TLB slabs
4512 force -- force using of bounce buffers even if they
4513 wouldn't be automatically used by the kernel
4514 noforce -- Never use bounce buffers (for debugging)
4518 sysfs.deprecated=0|1 [KNL]
4519 Enable/disable old style sysfs layout for old udev
4520 on older distributions. When this option is enabled
4521 very new udev will not work anymore. When this option
4522 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4523 in older udev will not work anymore.
4524 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4525 the kernel configuration.
4527 sysrq_always_enabled
4529 Ignore sysrq setting - this boot parameter will
4530 neutralize any effect of /proc/sys/kernel/sysrq.
4531 Useful for debugging.
4533 tcpmhash_entries= [KNL,NET]
4534 Set the number of tcp_metrics_hash slots.
4535 Default value is 8192 or 16384 depending on total
4536 ram pages. This is used to specify the TCP metrics
4537 cache size. See Documentation/networking/ip-sysctl.txt
4538 "tcp_no_metrics_save" section for more details.
4542 test_suspend= [SUSPEND][,N]
4543 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4544 standby suspend) or "freeze" (for suspend type freeze)
4545 as the system sleep state during system startup with
4546 the optional capability to repeat N number of times.
4547 The system is woken from this state using a
4548 wakeup-capable RTC alarm.
4550 thash_entries= [KNL,NET]
4551 Set number of hash buckets for TCP connection
4553 thermal.act= [HW,ACPI]
4554 -1: disable all active trip points in all thermal zones
4555 <degrees C>: override all lowest active trip points
4557 thermal.crt= [HW,ACPI]
4558 -1: disable all critical trip points in all thermal zones
4559 <degrees C>: override all critical trip points
4561 thermal.nocrt= [HW,ACPI]
4562 Set to disable actions on ACPI thermal zone
4563 critical and hot trip points.
4565 thermal.off= [HW,ACPI]
4566 1: disable ACPI thermal control
4568 thermal.psv= [HW,ACPI]
4569 -1: disable all passive trip points
4570 <degrees C>: override all passive trip points to this
4573 thermal.tzp= [HW,ACPI]
4574 Specify global default ACPI thermal zone polling rate
4575 <deci-seconds>: poll all this frequency
4576 0: no polling (default)
4579 Force threading of all interrupt handlers except those
4580 marked explicitly IRQF_NO_THREAD.
4583 Enable the Transcendent memory driver if built-in.
4585 tmem.cleancache=0|1 [KNL, XEN]
4586 Default is on (1). Disable the usage of the cleancache
4587 API to send anonymous pages to the hypervisor.
4589 tmem.frontswap=0|1 [KNL, XEN]
4590 Default is on (1). Disable the usage of the frontswap
4591 API to send swap pages to the hypervisor. If disabled
4592 the selfballooning and selfshrinking are force disabled.
4594 tmem.selfballooning=0|1 [KNL, XEN]
4595 Default is on (1). Disable the driving of swap pages
4598 tmem.selfshrinking=0|1 [KNL, XEN]
4599 Default is on (1). Partial swapoff that immediately
4600 transfers pages from Xen hypervisor back to the
4601 kernel based on different criteria.
4605 Specify if the kernel should make use of the cpu
4606 topology information if the hardware supports this.
4607 The scheduler will make use of this information and
4608 e.g. base its process migration decisions on it.
4611 topology_updates= [KNL, PPC, NUMA]
4613 Specify if the kernel should ignore (off)
4614 topology updates sent by the hypervisor to this
4619 tpm_suspend_pcr=[HW,TPM]
4620 Format: integer pcr id
4621 Specify that at suspend time, the tpm driver
4622 should extend the specified pcr with zeros,
4623 as a workaround for some chips which fail to
4624 flush the last written pcr on TPM_SaveState.
4625 This will guarantee that all the other pcrs
4628 trace_buf_size=nn[KMG]
4629 [FTRACE] will set tracing buffer size on each cpu.
4631 trace_event=[event-list]
4632 [FTRACE] Set and start specified trace events in order
4633 to facilitate early boot debugging. The event-list is a
4634 comma separated list of trace events to enable. See
4635 also Documentation/trace/events.rst
4637 trace_options=[option-list]
4638 [FTRACE] Enable or disable tracer options at boot.
4639 The option-list is a comma delimited list of options
4640 that can be enabled or disabled just as if you were
4641 to echo the option name into
4643 /sys/kernel/debug/tracing/trace_options
4645 For example, to enable stacktrace option (to dump the
4646 stack trace of each event), add to the command line:
4648 trace_options=stacktrace
4650 See also Documentation/trace/ftrace.rst "trace options"
4654 Have the tracepoints sent to printk as well as the
4655 tracing ring buffer. This is useful for early boot up
4656 where the system hangs or reboots and does not give the
4657 option for reading the tracing buffer or performing a
4658 ftrace_dump_on_oops.
4660 To turn off having tracepoints sent to printk,
4661 echo 0 > /proc/sys/kernel/tracepoint_printk
4662 Note, echoing 1 into this file without the
4663 tracepoint_printk kernel cmdline option has no effect.
4667 Having tracepoints sent to printk() and activating high
4668 frequency tracepoints such as irq or sched, can cause
4669 the system to live lock.
4672 [FTRACE] enable this option to disable tracing when a
4673 warning is hit. This turns off "tracing_on". Tracing can
4674 be enabled again by echoing '1' into the "tracing_on"
4675 file located in /sys/kernel/debug/tracing/
4677 This option is useful, as it disables the trace before
4678 the WARNING dump is called, which prevents the trace to
4679 be filled with content caused by the warning output.
4681 This option can also be set at run time via the sysctl
4682 option: kernel/traceoff_on_warning
4684 transparent_hugepage=
4686 Format: [always|madvise|never]
4687 Can be used to control the default behavior of the system
4688 with respect to transparent hugepages.
4689 See Documentation/admin-guide/mm/transhuge.rst
4692 tsc= Disable clocksource stability checks for TSC.
4694 [x86] reliable: mark tsc clocksource as reliable, this
4695 disables clocksource verification at runtime, as well
4696 as the stability checks done at bootup. Used to enable
4697 high-resolution timer mode on older hardware, and in
4698 virtualized environment.
4699 [x86] noirqtime: Do not use TSC to do irq accounting.
4700 Used to run time disable IRQ_TIME_ACCOUNTING on any
4701 platforms where RDTSC is slow and this accounting
4703 [x86] unstable: mark the TSC clocksource as unstable, this
4704 marks the TSC unconditionally unstable at bootup and
4705 avoids any further wobbles once the TSC watchdog notices.
4707 turbografx.map[2|3]= [HW,JOY]
4708 TurboGraFX parallel port interface
4710 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4711 See also Documentation/input/devices/joystick-parport.rst
4713 udbg-immortal [PPC] When debugging early kernel crashes that
4714 happen after console_init() and before a proper
4715 console driver takes over, this boot options might
4716 help "seeing" what's going on.
4718 uhash_entries= [KNL,NET]
4719 Set number of hash buckets for UDP/UDP-Lite connections
4722 [USB] Ignore overcurrent events (default N).
4723 Some badly-designed motherboards generate lots of
4724 bogus events, for ports that aren't wired to
4725 anything. Set this parameter to avoid log spamming.
4726 Note that genuine overcurrent events won't be
4730 [X86] Cause panic on unknown NMI.
4732 usbcore.authorized_default=
4733 [USB] Default USB device authorization:
4734 (default -1 = authorized except for wireless USB,
4735 0 = not authorized, 1 = authorized, 2 = authorized
4736 if device connected to internal port)
4738 usbcore.autosuspend=
4739 [USB] The autosuspend time delay (in seconds) used
4740 for newly-detected USB devices (default 2). This
4741 is the time required before an idle device will be
4742 autosuspended. Devices for which the delay is set
4743 to a negative value won't be autosuspended at all.
4745 usbcore.usbfs_snoop=
4746 [USB] Set to log all usbfs traffic (default 0 = off).
4748 usbcore.usbfs_snoop_max=
4749 [USB] Maximum number of bytes to snoop in each URB
4752 usbcore.blinkenlights=
4753 [USB] Set to cycle leds on hubs (default 0 = off).
4755 usbcore.old_scheme_first=
4756 [USB] Start with the old device initialization
4757 scheme, applies only to low and full-speed devices
4760 usbcore.usbfs_memory_mb=
4761 [USB] Memory limit (in MB) for buffers allocated by
4762 usbfs (default = 16, 0 = max = 2047).
4764 usbcore.use_both_schemes=
4765 [USB] Try the other device initialization scheme
4766 if the first one fails (default 1 = enabled).
4768 usbcore.initial_descriptor_timeout=
4769 [USB] Specifies timeout for the initial 64-byte
4770 USB_REQ_GET_DESCRIPTOR request in milliseconds
4771 (default 5000 = 5.0 seconds).
4773 usbcore.nousb [USB] Disable the USB subsystem
4776 [USB] A list of quirk entries to augment the built-in
4777 usb core quirk list. List entries are separated by
4778 commas. Each entry has the form
4779 VendorID:ProductID:Flags. The IDs are 4-digit hex
4780 numbers and Flags is a set of letters. Each letter
4781 will change the built-in quirk; setting it if it is
4782 clear and clearing it if it is set. The letters have
4783 the following meanings:
4784 a = USB_QUIRK_STRING_FETCH_255 (string
4785 descriptors must not be fetched using
4787 b = USB_QUIRK_RESET_RESUME (device can't resume
4788 correctly so reset it instead);
4789 c = USB_QUIRK_NO_SET_INTF (device can't handle
4790 Set-Interface requests);
4791 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
4792 handle its Configuration or Interface
4794 e = USB_QUIRK_RESET (device can't be reset
4795 (e.g morph devices), don't use reset);
4796 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
4797 more interface descriptions than the
4798 bNumInterfaces count, and can't handle
4799 talking to these interfaces);
4800 g = USB_QUIRK_DELAY_INIT (device needs a pause
4801 during initialization, after we read
4802 the device descriptor);
4803 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
4804 high speed and super speed interrupt
4805 endpoints, the USB 2.0 and USB 3.0 spec
4806 require the interval in microframes (1
4807 microframe = 125 microseconds) to be
4808 calculated as interval = 2 ^
4810 Devices with this quirk report their
4811 bInterval as the result of this
4812 calculation instead of the exponent
4813 variable used in the calculation);
4814 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
4815 handle device_qualifier descriptor
4817 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
4818 generates spurious wakeup, ignore
4819 remote wakeup capability);
4820 k = USB_QUIRK_NO_LPM (device can't handle Link
4822 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
4823 (Device reports its bInterval as linear
4824 frames instead of the USB 2.0
4826 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
4827 to be disconnected before suspend to
4828 prevent spurious wakeup);
4829 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
4830 pause after every control message);
4831 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
4832 delay after resetting its port);
4833 Example: quirks=0781:5580:bk,0a5c:5834:gij
4836 [USBHID] The interval which mice are to be polled at.
4839 [USBHID] The interval which joysticks are to be polled at.
4842 [USBHID] The interval which keyboards are to be polled at.
4844 usb-storage.delay_use=
4845 [UMS] The delay in seconds before a new device is
4846 scanned for Logical Units (default 1).
4849 [UMS] A list of quirks entries to supplement or
4850 override the built-in unusual_devs list. List
4851 entries are separated by commas. Each entry has
4852 the form VID:PID:Flags where VID and PID are Vendor
4853 and Product ID values (4-digit hex numbers) and
4854 Flags is a set of characters, each corresponding
4855 to a common usb-storage quirk flag as follows:
4856 a = SANE_SENSE (collect more than 18 bytes
4858 b = BAD_SENSE (don't collect more than 18
4859 bytes of sense data);
4860 c = FIX_CAPACITY (decrease the reported
4861 device capacity by one sector);
4862 d = NO_READ_DISC_INFO (don't use
4863 READ_DISC_INFO command);
4864 e = NO_READ_CAPACITY_16 (don't use
4865 READ_CAPACITY_16 command);
4866 f = NO_REPORT_OPCODES (don't use report opcodes
4868 g = MAX_SECTORS_240 (don't transfer more than
4869 240 sectors at a time, uas only);
4870 h = CAPACITY_HEURISTICS (decrease the
4871 reported device capacity by one
4872 sector if the number is odd);
4873 i = IGNORE_DEVICE (don't bind to this
4875 j = NO_REPORT_LUNS (don't use report luns
4877 l = NOT_LOCKABLE (don't try to lock and
4878 unlock ejectable media);
4879 m = MAX_SECTORS_64 (don't transfer more
4880 than 64 sectors = 32 KB at a time);
4881 n = INITIAL_READ10 (force a retry of the
4882 initial READ(10) command);
4883 o = CAPACITY_OK (accept the capacity
4884 reported by the device);
4885 p = WRITE_CACHE (the device cache is ON
4887 r = IGNORE_RESIDUE (the device reports
4888 bogus residue values);
4889 s = SINGLE_LUN (the device has only one
4891 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4892 commands, uas only);
4893 u = IGNORE_UAS (don't bind to the uas driver);
4894 w = NO_WP_DETECT (don't test whether the
4895 medium is write-protected).
4896 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4897 even if the device claims no cache)
4898 Example: quirks=0419:aaf5:rl,0421:0433:rc
4900 user_debug= [KNL,ARM]
4902 See arch/arm/Kconfig.debug help text.
4903 1 - undefined instruction events
4905 4 - invalid data aborts
4908 Example: user_debug=31
4911 [X86] Flags controlling user PTE allocations.
4913 nohigh = do not allocate PTE pages in
4914 HIGHMEM regardless of setting
4918 On X86_32, this is an alias for vdso32=. Otherwise:
4920 vdso=1: enable VDSO (the default)
4921 vdso=0: disable VDSO mapping
4923 vdso32= [X86] Control the 32-bit vDSO
4924 vdso32=1: enable 32-bit VDSO
4925 vdso32=0 or vdso32=2: disable 32-bit VDSO
4927 See the help text for CONFIG_COMPAT_VDSO for more
4928 details. If CONFIG_COMPAT_VDSO is set, the default is
4929 vdso32=0; otherwise, the default is vdso32=1.
4931 For compatibility with older kernels, vdso32=2 is an
4934 Try vdso32=0 if you encounter an error that says:
4935 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4938 vector=percpu: enable percpu vector domain
4940 video= [FB] Frame buffer configuration
4941 See Documentation/fb/modedb.txt.
4943 video.brightness_switch_enabled= [0,1]
4944 If set to 1, on receiving an ACPI notify event
4945 generated by hotkey, video driver will adjust brightness
4946 level and then send out the event to user space through
4947 the allocated input device; If set to 0, video driver
4948 will only send out the event without touching backlight
4953 [VMMIO] Memory mapped virtio (platform) device.
4955 <size>@<baseaddr>:<irq>[:<id>]
4957 <size> := size (can use standard suffixes
4959 <baseaddr> := physical base address
4960 <irq> := interrupt number (as passed to
4962 <id> := (optional) platform device id
4964 virtio_mmio.device=1K@0x100b0000:48:7
4966 Can be used multiple times for multiple devices.
4968 vga= [BOOT,X86-32] Select a particular video mode
4969 See Documentation/x86/boot.txt and
4970 Documentation/svga.txt.
4971 Use vga=ask for menu.
4972 This is actually a boot loader parameter; the value is
4973 passed to the kernel using a special protocol.
4975 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
4976 May slow down system boot speed, especially when
4977 enabled on systems with a large amount of memory.
4978 All options are enabled by default, and this
4979 interface is meant to allow for selectively
4980 enabling or disabling specific virtual memory
4983 Available options are:
4984 P Enable page structure init time poisoning
4985 - Disable all of the above options
4987 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4988 size of <nn>. This can be used to increase the
4989 minimum size (128MB on x86). It can also be used to
4990 decrease the size and leave more room for directly
4993 vmcp_cma=nn[MG] [KNL,S390]
4994 Sets the memory size reserved for contiguous memory
4995 allocations for the vmcp device driver.
4997 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
5000 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
5003 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
5007 Controls the behavior of vsyscalls (i.e. calls to
5008 fixed addresses of 0xffffffffff600x00 from legacy
5009 code). Most statically-linked binaries and older
5010 versions of glibc use these calls. Because these
5011 functions are at fixed addresses, they make nice
5012 targets for exploits that can control RIP.
5014 emulate [default] Vsyscalls turn into traps and are
5015 emulated reasonably safely.
5017 native Vsyscalls are native syscall instructions.
5018 This is a little bit faster than trapping
5019 and makes a few dynamic recompilers work
5020 better than they would in emulation mode.
5021 It also makes exploits much easier to write.
5023 none Vsyscalls don't work at all. This makes
5024 them quite hard to use for exploits but
5025 might break your system.
5027 vt.color= [VT] Default text color.
5028 Format: 0xYX, X = foreground, Y = background.
5029 Default: 0x07 = light gray on black.
5031 vt.cur_default= [VT] Default cursor shape.
5032 Format: 0xCCBBAA, where AA, BB, and CC are the same as
5033 the parameters of the <Esc>[?A;B;Cc escape sequence;
5034 see VGA-softcursor.txt. Default: 2 = underline.
5036 vt.default_blu= [VT]
5037 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
5038 Change the default blue palette of the console.
5039 This is a 16-member array composed of values
5042 vt.default_grn= [VT]
5043 Format: <green0>,<green1>,<green2>,...,<green15>
5044 Change the default green palette of the console.
5045 This is a 16-member array composed of values
5048 vt.default_red= [VT]
5049 Format: <red0>,<red1>,<red2>,...,<red15>
5050 Change the default red palette of the console.
5051 This is a 16-member array composed of values
5057 Set system-wide default UTF-8 mode for all tty's.
5058 Default is 1, i.e. UTF-8 mode is enabled for all
5059 newly opened terminals.
5061 vt.global_cursor_default=
5064 Set system-wide default for whether a cursor
5065 is shown on new VTs. Default is -1,
5066 i.e. cursors will be created by default unless
5067 overridden by individual drivers. 0 will hide
5068 cursors, 1 will display them.
5070 vt.italic= [VT] Default color for italic text; 0-15.
5073 vt.underline= [VT] Default color for underlined text; 0-15.
5076 watchdog timers [HW,WDT] For information on watchdog timers,
5077 see Documentation/watchdog/watchdog-parameters.txt
5078 or other driver-specific files in the
5079 Documentation/watchdog/ directory.
5083 Set the hard lockup detector stall duration
5084 threshold in seconds. The soft lockup detector
5085 threshold is set to twice the value. A value of 0
5086 disables both lockup detectors. Default is 10
5089 workqueue.watchdog_thresh=
5090 If CONFIG_WQ_WATCHDOG is configured, workqueue can
5091 warn stall conditions and dump internal state to
5092 help debugging. 0 disables workqueue stall
5093 detection; otherwise, it's the stall threshold
5094 duration in seconds. The default value is 30 and
5095 it can be updated at runtime by writing to the
5096 corresponding sysfs file.
5098 workqueue.disable_numa
5099 By default, all work items queued to unbound
5100 workqueues are affine to the NUMA nodes they're
5101 issued on, which results in better behavior in
5102 general. If NUMA affinity needs to be disabled for
5103 whatever reason, this option can be used. Note
5104 that this also can be controlled per-workqueue for
5105 workqueues visible under /sys/bus/workqueue/.
5107 workqueue.power_efficient
5108 Per-cpu workqueues are generally preferred because
5109 they show better performance thanks to cache
5110 locality; unfortunately, per-cpu workqueues tend to
5111 be more power hungry than unbound workqueues.
5113 Enabling this makes the per-cpu workqueues which
5114 were observed to contribute significantly to power
5115 consumption unbound, leading to measurably lower
5116 power usage at the cost of small performance
5119 The default value of this parameter is determined by
5120 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
5122 workqueue.debug_force_rr_cpu
5123 Workqueue used to implicitly guarantee that work
5124 items queued without explicit CPU specified are put
5125 on the local CPU. This guarantee is no longer true
5126 and while local CPU is still preferred work items
5127 may be put on foreign CPUs. This debug option
5128 forces round-robin CPU selection to flush out
5129 usages which depend on the now broken guarantee.
5130 When enabled, memory and cache locality will be
5133 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
5134 default x2apic cluster mode on platforms
5137 x86_intel_mid_timer= [X86-32,APBT]
5138 Choose timer option for x86 Intel MID platform.
5139 Two valid options are apbt timer only and lapic timer
5140 plus one apbt timer for broadcast timer.
5141 x86_intel_mid_timer=apbt_only | lapic_and_apbt
5143 xen_512gb_limit [KNL,X86-64,XEN]
5144 Restricts the kernel running paravirtualized under Xen
5145 to use only up to 512 GB of RAM. The reason to do so is
5146 crash analysis tools and Xen tools for doing domain
5147 save/restore/migration must be enabled to handle larger
5150 xen_emul_unplug= [HW,X86,XEN]
5151 Unplug Xen emulated devices
5152 Format: [unplug0,][unplug1]
5153 ide-disks -- unplug primary master IDE devices
5154 aux-ide-disks -- unplug non-primary-master IDE devices
5155 nics -- unplug network devices
5156 all -- unplug all emulated devices (NICs and IDE disks)
5157 unnecessary -- unplugging emulated devices is
5158 unnecessary even if the host did not respond to
5160 never -- do not unplug even if version check succeeds
5162 xen_nopvspin [X86,XEN]
5163 Disables the ticketlock slowpath using Xen PV
5167 Disables the PV optimizations forcing the HVM guest to
5168 run as generic HVM guest with no PV drivers.
5170 xen_scrub_pages= [XEN]
5171 Boolean option to control scrubbing pages before giving them back
5172 to Xen, for use by other domains. Can be also changed at runtime
5173 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
5174 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
5176 xirc2ps_cs= [NET,PCMCIA]
5178 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
5180 xhci-hcd.quirks [USB,KNL]
5181 A hex value specifying bitmask with supplemental xhci
5182 host controller quirks. Meaning of each bit can be
5183 consulted in header drivers/usb/host/xhci.h.
git.samba.org / sfrench / cifs-2.6.git / blob