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/alsa-parameters.txt
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 whilst booting
335 Format: { quiet (default) | verbose | debug }
336 Change the amount of debugging information output
337 when initialising the APIC and IO-APIC components.
338 For X86-32, this can also be used to specify an APIC
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" } (0 = disabled, 1 = enabled)
393 0 - kernel audit is disabled and can not be enabled
394 until the next reboot
395 unset - kernel audit is initialized but disabled and
396 will be fully enabled by the userspace auditd.
397 1 - kernel audit is initialized and partially enabled,
398 storing at most audit_backlog_limit messages in
399 RAM until it is fully enabled by the userspace
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.
464 ca_keys= [KEYS] This parameter identifies a specific key(s) on
465 the system trusted keyring to be used for certificate
467 format: { id:<keyid> | builtin }
469 cca= [MIPS] Override the kernel pages' cache coherency
470 algorithm. Accepted values range from 0 to 7
471 inclusive. See arch/mips/include/asm/pgtable-bits.h
472 for platform specific values (SB1, Loongson3 and
475 ccw_timeout_log [S390]
476 See Documentation/s390/CommonIO for details.
478 cgroup_disable= [KNL] Disable a particular controller
479 Format: {name of the controller(s) to disable}
480 The effects of cgroup_disable=foo are:
481 - foo isn't auto-mounted if you mount all cgroups in
483 - foo isn't visible as an individually mountable
485 {Currently only "memory" controller deal with this and
486 cut the overhead, others just disable the usage. So
487 only cgroup_disable=memory is actually worthy}
489 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
490 Format: { controller[,controller...] | "all" }
491 Like cgroup_disable, but only applies to cgroup v1;
492 the blacklisted controllers remain available in cgroup2.
494 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
496 nosocket -- Disable socket memory accounting.
497 nokmem -- Disable kernel memory accounting.
499 checkreqprot [SELINUX] Set initial checkreqprot flag value.
500 Format: { "0" | "1" }
501 See security/selinux/Kconfig help text.
502 0 -- check protection applied by kernel (includes
503 any implied execute protection).
504 1 -- check protection requested by application.
505 Default value is set via a kernel config option.
506 Value can be changed at runtime via
507 /selinux/checkreqprot.
510 See Documentation/s390/CommonIO for details.
513 Prevents the clock framework from automatically gating
514 clocks that have not been explicitly enabled by a Linux
515 device driver but are enabled in hardware at reset or
516 by the bootloader/firmware. Note that this does not
517 force such clocks to be always-on nor does it reserve
518 those clocks in any way. This parameter is useful for
519 debug and development, but should not be needed on a
520 platform with proper driver support. For more
521 information, see Documentation/clk.txt.
523 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
525 Forces specified clocksource (if available) to be used
526 when calculating gettimeofday(). If specified
527 clocksource is not available, it defaults to PIT.
528 Format: { pit | tsc | cyclone | pmtmr }
530 clocksource= Override the default clocksource
532 Override the default clocksource and use the clocksource
533 with the name specified.
534 Some clocksource names to choose from, depending on
536 [all] jiffies (this is the base, fallback clocksource)
538 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
539 pxa_timer,timer3,32k_counter,timer0_1
540 [X86-32] pit,hpet,tsc;
541 scx200_hrt on Geode; cyclone on IBM x440
549 clocksource.arm_arch_timer.evtstrm=
552 Enable/disable the eventstream feature of the ARM
553 architected timer so that code using WFE-based polling
554 loops can be debugged more effectively on production
557 clearcpuid=BITNUM [X86]
558 Disable CPUID feature X for the kernel. See
559 arch/x86/include/asm/cpufeatures.h for the valid bit
560 numbers. Note the Linux specific bits are not necessarily
561 stable over kernel options, but the vendor specific
563 Also note that user programs calling CPUID directly
564 or using the feature without checking anything
565 will still see it. This just prevents it from
566 being used by the kernel or shown in /proc/cpuinfo.
567 Also note the kernel might malfunction if you disable
570 cma=nn[MG]@[start[MG][-end[MG]]]
572 Sets the size of kernel global memory area for
573 contiguous memory allocations and optionally the
574 placement constraint by the physical address range of
575 memory allocations. A value of 0 disables CMA
576 altogether. For more information, see
577 include/linux/dma-contiguous.h
579 cmo_free_hint= [PPC] Format: { yes | no }
580 Specify whether pages are marked as being inactive
581 when they are freed. This is used in CMO environments
582 to determine OS memory pressure for page stealing by
586 coherent_pool=nn[KMG] [ARM,KNL]
587 Sets the size of memory pool for coherent, atomic dma
588 allocations, by default set to 256K.
590 code_bytes [X86] How many bytes of object code to print
595 com20020= [HW,NET] ARCnet - COM20020 chipset
597 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
599 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
603 ARCnet - COM90xx chipset (memory-mapped buffers)
604 Format: <io>[,<irq>[,<memstart>]]
606 condev= [HW,S390] console device
609 console= [KNL] Output console device and options.
611 tty<n> Use the virtual console device <n>.
615 Use the specified serial port. The options are of
616 the form "bbbbpnf", where "bbbb" is the baud rate,
617 "p" is parity ("n", "o", or "e"), "n" is number of
618 bits, and "f" is flow control ("r" for RTS or
619 omit it). Default is "9600n8".
621 See Documentation/admin-guide/serial-console.rst for more
623 Documentation/networking/netconsole.txt for an
626 uart[8250],io,<addr>[,options]
627 uart[8250],mmio,<addr>[,options]
628 uart[8250],mmio16,<addr>[,options]
629 uart[8250],mmio32,<addr>[,options]
630 uart[8250],0x<addr>[,options]
631 Start an early, polled-mode console on the 8250/16550
632 UART at the specified I/O port or MMIO address,
633 switching to the matching ttyS device later.
634 MMIO inter-register address stride is either 8-bit
635 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
636 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
637 to be equivalent to 'mmio'. 'options' are specified in
638 the same format described for ttyS above; if unspecified,
639 the h/w is not re-initialized.
641 hvc<n> Use the hypervisor console device <n>. This is for
642 both Xen and PowerPC hypervisors.
644 If the device connected to the port is not a TTY but a braille
645 device, prepend "brl," before the device type, for instance
647 For now, only VisioBraille is supported.
650 [KNL] Change console messages format
652 By default we print messages on consoles in
653 "[time stamp] text\n" format (time stamp may not be
654 printed, depending on CONFIG_PRINTK_TIME or
655 `printk_time' param).
657 Switch to syslog format: "<%u>[time stamp] text\n"
658 IOW, each message will have a facility and loglevel
659 prefix. The format is similar to one used by syslog()
660 syscall, or to executing "dmesg -S --raw" or to reading
663 consoleblank= [KNL] The console blank (screen saver) timeout in
664 seconds. A value of 0 disables the blank timer.
668 [KNL] Change the default value for
669 /proc/<pid>/coredump_filter.
670 See also Documentation/filesystems/proc.txt.
672 coresight_cpu_debug.enable
675 Enable/disable the CPU sampling based debugging.
676 0: default value, disable debugging
677 1: enable debugging at boot time
679 cpuidle.off=1 [CPU_IDLE]
680 disable the cpuidle sub-system
682 cpufreq.off=1 [CPU_FREQ]
683 disable the cpufreq sub-system
686 [X86] Delay for N microsec between assert and de-assert
687 of APIC INIT to start processors. This delay occurs
688 on every CPU online, such as boot, and resume from suspend.
691 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
693 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
695 crashkernel=size[KMG][@offset[KMG]]
696 [KNL] Using kexec, Linux can switch to a 'crash kernel'
697 upon panic. This parameter reserves the physical
698 memory region [offset, offset + size] for that kernel
699 image. If '@offset' is omitted, then a suitable offset
700 is selected automatically. Check
701 Documentation/kdump/kdump.txt for further details.
703 crashkernel=range1:size1[,range2:size2,...][@offset]
704 [KNL] Same as above, but depends on the memory
705 in the running system. The syntax of range is
706 start-[end] where start and end are both
707 a memory unit (amount[KMG]). See also
708 Documentation/kdump/kdump.txt for an example.
710 crashkernel=size[KMG],high
711 [KNL, x86_64] range could be above 4G. Allow kernel
712 to allocate physical memory region from top, so could
713 be above 4G if system have more than 4G ram installed.
714 Otherwise memory region will be allocated below 4G, if
716 It will be ignored if crashkernel=X is specified.
717 crashkernel=size[KMG],low
718 [KNL, x86_64] range under 4G. When crashkernel=X,high
719 is passed, kernel could allocate physical memory region
720 above 4G, that cause second kernel crash on system
721 that require some amount of low memory, e.g. swiotlb
722 requires at least 64M+32K low memory, also enough extra
723 low memory is needed to make sure DMA buffers for 32-bit
724 devices won't run out. Kernel would try to allocate at
725 at least 256M below 4G automatically.
726 This one let user to specify own low range under 4G
727 for second kernel instead.
728 0: to disable low allocation.
729 It will be ignored when crashkernel=X,high is not used
730 or memory reserved is below 4G.
733 [KNL] Disable crypto self-tests
738 cs89x0_media= [HW,NET]
739 Format: { rj45 | aui | bnc }
742 See header of drivers/s390/block/dasd_devmap.c.
744 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
745 (one device per port)
746 Format: <port#>,<type>
747 See also Documentation/input/devices/joystick-parport.rst
749 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
751 Documentation/admin-guide/dynamic-debug-howto.rst for
752 details. Deprecated, see dyndbg.
754 debug [KNL] Enable kernel debugging (events log level).
757 [KNL] verbose self-tests
759 Print debugging info while doing the locking API
761 We default to 0 (no extra messages), setting it to
762 1 will print _a lot_ more information - normally
763 only useful to kernel developers.
765 debug_objects [KNL] Enable object debugging
768 [KNL] Disable object debugging
770 debug_guardpage_minorder=
771 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
772 parameter allows control of the order of pages that will
773 be intentionally kept free (and hence protected) by the
774 buddy allocator. Bigger value increase the probability
775 of catching random memory corruption, but reduce the
776 amount of memory for normal system use. The maximum
777 possible value is MAX_ORDER/2. Setting this parameter
778 to 1 or 2 should be enough to identify most random
779 memory corruption problems caused by bugs in kernel or
780 driver code when a CPU writes to (or reads from) a
781 random memory location. Note that there exists a class
782 of memory corruptions problems caused by buggy H/W or
783 F/W or by drivers badly programing DMA (basically when
784 memory is written at bus level and the CPU MMU is
785 bypassed) which are not detectable by
786 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
787 tracking down these problems.
790 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
791 parameter enables the feature at boot time. In
792 default, it is disabled. We can avoid allocating huge
793 chunk of memory for debug pagealloc if we don't enable
794 it at boot time and the system will work mostly same
795 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
796 on: enable the feature
798 debugpat [X86] Enable PAT debugging
800 decnet.addr= [HW,NET]
801 Format: <area>[,<node>]
802 See also Documentation/networking/decnet.txt.
805 [same as hugepagesz=] The size of the default
806 HugeTLB page size. This is the size represented by
807 the legacy /proc/ hugepages APIs, used for SHM, and
808 default size when mounting hugetlbfs filesystems.
809 Defaults to the default architecture's huge page size
813 Set number of hash buckets for dentry cache.
815 disable_1tb_segments [PPC]
816 Disables the use of 1TB hash page table segments. This
817 causes the kernel to fall back to 256MB segments which
818 can be useful when debugging issues that require an SLB
822 See Documentation/networking/ipv6.txt.
825 Disable RADIX MMU mode on POWER9
827 disable_cpu_apicid= [X86,APIC,SMP]
829 The number of initial APIC ID for the
830 corresponding CPU to be disabled at boot,
831 mostly used for the kdump 2nd kernel to
832 disable BSP to wake up multiple CPUs without
833 causing system reset or hang due to sending
836 disable_ddw [PPC/PSERIES]
837 Disable Dynamic DMA Window support. Use this if
838 to workaround buggy firmware.
841 See Documentation/networking/ipv6.txt.
843 disable_mtrr_cleanup [X86]
844 The kernel tries to adjust MTRR layout from continuous
845 to discrete, to make X server driver able to add WB
846 entry later. This parameter disables that.
848 disable_mtrr_trim [X86, Intel and AMD only]
849 By default the kernel will trim any uncacheable
850 memory out of your available memory pool based on
851 MTRR settings. This parameter disables that behavior,
852 possibly causing your machine to run very slowly.
854 disable_timer_pin_1 [X86]
855 Disable PIN 1 of APIC timer
856 Can be useful to work around chipset bugs.
858 dis_ucode_ldr [X86] Disable the microcode loader.
860 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
861 this option disables the debugging code at boot.
863 dma_debug_entries=<number>
864 This option allows to tune the number of preallocated
865 entries for DMA-API debugging code. One entry is
866 required per DMA-API allocation. Use this if the
867 DMA-API debugging code disables itself because the
868 architectural default is too low.
870 dma_debug_driver=<driver_name>
871 With this option the DMA-API debugging driver
872 filter feature can be enabled at boot time. Just
873 pass the driver to filter for as the parameter.
874 The filter can be disabled or changed to another
875 driver later using sysfs.
877 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
878 Broken monitors, graphic adapters, KVMs and EDIDless
879 panels may send no or incorrect EDID data sets.
880 This parameter allows to specify an EDID data sets
881 in the /lib/firmware directory that are used instead.
882 Generic built-in EDID data sets are used, if one of
883 edid/1024x768.bin, edid/1280x1024.bin,
884 edid/1680x1050.bin, or edid/1920x1080.bin is given
885 and no file with the same name exists. Details and
886 instructions how to build your own EDID data are
887 available in Documentation/EDID/HOWTO.txt. An EDID
888 data set will only be used for a particular connector,
889 if its name and a colon are prepended to the EDID
890 name. Each connector may use a unique EDID data
891 set by separating the files with a comma. An EDID
892 data set with no connector name will be used for
893 any connectors not explicitly specified.
898 Format: {"off" | "known"}
899 Control how the dt_cpu_ftrs device-tree binding is
900 used for CPU feature discovery and setup (if it
902 off: Do not use it, fall back to legacy cpu table.
903 known: Do not pass through unknown features to guests
904 or userspace, only those that the kernel is aware of.
906 dump_apple_properties [X86]
907 Dump name and content of EFI device properties on
908 x86 Macs. Useful for driver authors to determine
909 what data is available or for reverse-engineering.
911 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
912 module.dyndbg[="val"]
913 Enable debug messages at boot time. See
914 Documentation/admin-guide/dynamic-debug-howto.rst
917 nompx [X86] Disables Intel Memory Protection Extensions.
918 See Documentation/x86/intel_mpx.txt for more
919 information about the feature.
921 nopku [X86] Disable Memory Protection Keys CPU feature found
924 module.async_probe [KNL]
925 Enable asynchronous probe on this module.
927 early_ioremap_debug [KNL]
928 Enable debug messages in early_ioremap support. This
929 is useful for tracking down temporary early mappings
930 which are not unmapped.
932 earlycon= [KNL] Output early console device and options.
934 [ARM64] The early console is determined by the
935 stdout-path property in device tree's chosen node,
936 or determined by the ACPI SPCR table.
938 [X86] When used with no options the early console is
939 determined by the ACPI SPCR table.
941 cdns,<addr>[,options]
942 Start an early, polled-mode console on a Cadence
943 (xuartps) serial port at the specified address. Only
944 supported option is baud rate. If baud rate is not
945 specified, the serial port must already be setup and
948 uart[8250],io,<addr>[,options]
949 uart[8250],mmio,<addr>[,options]
950 uart[8250],mmio32,<addr>[,options]
951 uart[8250],mmio32be,<addr>[,options]
952 uart[8250],0x<addr>[,options]
953 Start an early, polled-mode console on the 8250/16550
954 UART at the specified I/O port or MMIO address.
955 MMIO inter-register address stride is either 8-bit
956 (mmio) or 32-bit (mmio32 or mmio32be).
957 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
958 to be equivalent to 'mmio'. 'options' are specified
959 in the same format described for "console=ttyS<n>"; if
960 unspecified, the h/w is not initialized.
964 Start an early, polled-mode console on a pl011 serial
965 port at the specified address. The pl011 serial port
966 must already be setup and configured. Options are not
967 yet supported. If 'mmio32' is specified, then only
968 the driver will use only 32-bit accessors to read/write
969 the device registers.
972 Start an early, polled-mode console on a meson serial
973 port at the specified address. The serial port must
974 already be setup and configured. Options are not yet
978 Start an early, polled-mode console on an msm serial
979 port at the specified address. The serial port
980 must already be setup and configured. Options are not
984 Start an early, polled-mode console on an msm serial
985 dm port at the specified address. The serial port
986 must already be setup and configured. Options are not
990 Start an early, polled-mode console on a serial port
991 of an Actions Semi SoC, such as S500 or S900, at the
992 specified address. The serial port must already be
993 setup and configured. Options are not yet supported.
995 smh Use ARM semihosting calls for early console.
1003 Use early console provided by serial driver available
1004 on Samsung SoCs, requires selecting proper type and
1005 a correct base address of the selected UART port. The
1006 serial port must already be setup and configured.
1007 Options are not yet supported.
1010 Start an early, polled-mode console on a lantiq serial
1011 (lqasc) port at the specified address. The serial port
1012 must already be setup and configured. Options are not
1017 Use early console provided by Freescale LP UART driver
1018 found on Freescale Vybrid and QorIQ LS1021A processors.
1019 A valid base address must be provided, and the serial
1020 port must already be setup and configured.
1023 Start an early, polled-mode console on the
1024 Armada 3700 serial port at the specified
1025 address. The serial port must already be setup
1026 and configured. Options are not yet supported.
1028 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k,S390]
1033 earlyprintk=serial[,ttySn[,baudrate]]
1034 earlyprintk=serial[,0x...[,baudrate]]
1035 earlyprintk=ttySn[,baudrate]
1036 earlyprintk=dbgp[debugController#]
1037 earlyprintk=pciserial,bus:device.function[,baudrate]
1038 earlyprintk=xdbc[xhciController#]
1040 earlyprintk is useful when the kernel crashes before
1041 the normal console is initialized. It is not enabled by
1042 default because it has some cosmetic problems.
1044 Append ",keep" to not disable it when the real console
1047 Only one of vga, efi, serial, or usb debug port can
1050 Currently only ttyS0 and ttyS1 may be specified by
1051 name. Other I/O ports may be explicitly specified
1052 on some architectures (x86 and arm at least) by
1053 replacing ttySn with an I/O port address, like this:
1054 earlyprintk=serial,0x1008,115200
1055 You can find the port for a given device in
1056 /proc/tty/driver/serial:
1057 2: uart:ST16650V2 port:00001008 irq:18 ...
1059 Interaction with the standard serial driver is not
1062 The VGA and EFI output is eventually overwritten by
1065 The xen output can only be used by Xen PV guests.
1067 The sclp output can only be used on s390.
1069 edac_report= [HW,EDAC] Control how to report EDAC event
1070 Format: {"on" | "off" | "force"}
1071 on: enable EDAC to report H/W event. May be overridden
1072 by other higher priority error reporting module.
1073 off: disable H/W event reporting through EDAC.
1074 force: enforce the use of EDAC to report H/W event.
1077 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1080 This is designed to be used in conjunction with
1081 the boot argument: earlyprintk=vga
1084 Format: {"off" | "on" | "skip[mbr]"}
1087 Format: { "old_map", "nochunk", "noruntime", "debug" }
1088 old_map [X86-64]: switch to the old ioremap-based EFI
1089 runtime services mapping. 32-bit still uses this one by
1091 nochunk: disable reading files in "chunks" in the EFI
1092 boot stub, as chunking can cause problems with some
1093 firmware implementations.
1094 noruntime : disable EFI runtime services support
1095 debug: enable misc debug output
1097 efi_no_storage_paranoia [EFI; X86]
1098 Using this parameter you can use more than 50% of
1099 your efi variable storage. Use this parameter only if
1100 you are really sure that your UEFI does sane gc and
1101 fulfills the spec otherwise your board may brick.
1103 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1104 Add arbitrary attribute to specific memory range by
1105 updating original EFI memory map.
1106 Region of memory which aa attribute is added to is
1108 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1109 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1110 attribute is added to range 0x100000000-0x180000000 and
1111 0x10a0000000-0x1120000000.
1113 Using this parameter you can do debugging of EFI memmap
1114 related feature. For example, you can do debugging of
1115 Address Range Mirroring feature even if your box
1118 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1119 that is to be dynamically loaded by Linux. If there are
1120 multiple variables with the same name but with different
1121 vendor GUIDs, all of them will be loaded. See
1122 Documentation/acpi/ssdt-overlays.txt for details.
1125 eisa_irq_edge= [PARISC,HW]
1126 See header of drivers/parisc/eisa.c.
1129 See comment before function elanfreq_setup() in
1130 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1133 Format: {"cfq" | "deadline" | "noop"}
1134 See Documentation/block/cfq-iosched.txt and
1135 Documentation/block/deadline-iosched.txt for details.
1137 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1138 Specifies physical address of start of kernel core
1139 image elf header and optionally the size. Generally
1140 kexec loader will pass this option to capture kernel.
1141 See Documentation/kdump/kdump.txt for details.
1143 enable_mtrr_cleanup [X86]
1144 The kernel tries to adjust MTRR layout from continuous
1145 to discrete, to make X server driver able to add WB
1146 entry later. This parameter enables that.
1148 enable_timer_pin_1 [X86]
1149 Enable PIN 1 of APIC timer
1150 Can be useful to work around chipset bugs
1151 (in particular on some ATI chipsets).
1152 The kernel tries to set a reasonable default.
1154 enforcing [SELINUX] Set initial enforcing status.
1156 See security/selinux/Kconfig help text.
1157 0 -- permissive (log only, no denials).
1158 1 -- enforcing (deny and log).
1160 Value can be changed at runtime via /selinux/enforce.
1163 Disable Error Record Serialization Table (ERST)
1166 ether= [HW,NET] Ethernet cards parameters
1167 This option is obsoleted by the "netdev=" option, which
1168 has equivalent usage. See its documentation for details.
1172 Permit 'security.evm' to be updated regardless of
1173 current integrity status.
1177 fail_make_request=[KNL]
1178 General fault injection mechanism.
1179 Format: <interval>,<probability>,<space>,<times>
1180 See also Documentation/fault-injection/.
1183 See Documentation/blockdev/floppy.txt.
1185 force_pal_cache_flush
1186 [IA-64] Avoid check_sal_cache_flush which may hang on
1187 buggy SAL_CACHE_FLUSH implementations. Using this
1188 parameter will force ia64_sal_cache_flush to call
1189 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1192 Forcefully enable Physical Address Extension (PAE).
1193 Many Pentium M systems disable PAE but may have a
1194 functionally usable PAE implementation.
1195 Warning: use of this parameter will taint the kernel
1196 and may cause unknown problems.
1199 [FTRACE] will set and start the specified tracer
1200 as early as possible in order to facilitate early
1203 ftrace_dump_on_oops[=orig_cpu]
1204 [FTRACE] will dump the trace buffers on oops.
1205 If no parameter is passed, ftrace will dump
1206 buffers of all CPUs, but if you pass orig_cpu, it will
1207 dump only the buffer of the CPU that triggered the
1210 ftrace_filter=[function-list]
1211 [FTRACE] Limit the functions traced by the function
1212 tracer at boot up. function-list is a comma separated
1213 list of functions. This list can be changed at run
1214 time by the set_ftrace_filter file in the debugfs
1217 ftrace_notrace=[function-list]
1218 [FTRACE] Do not trace the functions specified in
1219 function-list. This list can be changed at run time
1220 by the set_ftrace_notrace file in the debugfs
1223 ftrace_graph_filter=[function-list]
1224 [FTRACE] Limit the top level callers functions traced
1225 by the function graph tracer at boot up.
1226 function-list is a comma separated list of functions
1227 that can be changed at run time by the
1228 set_graph_function file in the debugfs tracing directory.
1230 ftrace_graph_notrace=[function-list]
1231 [FTRACE] Do not trace from the functions specified in
1232 function-list. This list is a comma separated list of
1233 functions that can be changed at run time by the
1234 set_graph_notrace file in the debugfs tracing directory.
1236 ftrace_graph_max_depth=<uint>
1237 [FTRACE] Used with the function graph tracer. This is
1238 the max depth it will trace into a function. This value
1239 can be changed at run time by the max_graph_depth file
1240 in the tracefs tracing directory. default: 0 (no limit)
1243 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1244 support via parallel port (up to 5 devices per port)
1245 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1246 See also Documentation/input/devices/joystick-parport.rst
1250 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1254 gcov_persist= [GCOV] When non-zero (default), profiling data for
1255 kernel modules is saved and remains accessible via
1256 debugfs, even when the module is unloaded/reloaded.
1257 When zero, profiling data is discarded and associated
1258 debugfs files are removed at module unload time.
1260 goldfish [X86] Enable the goldfish android emulator platform.
1261 Don't use this when you are not running on the
1264 gpt [EFI] Forces disk with valid GPT signature but
1265 invalid Protective MBR to be treated as GPT. If the
1266 primary GPT is corrupted, it enables the backup/alternate
1267 GPT to be used instead.
1269 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1270 the "Enable 0" bit of the configuration register.
1273 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1274 the "Enable 0" bit of the configuration register.
1277 grcan.select= [HW] Select which physical interface to use.
1280 grcan.txsize= [HW] Sets the size of the tx buffer.
1281 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1283 grcan.rxsize= [HW] Sets the size of the rx buffer.
1284 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1287 gpio-mockup.gpio_mockup_ranges
1288 [HW] Sets the ranges of gpiochip of for this device.
1289 Format: <start1>,<end1>,<start2>,<end2>...
1291 hardlockup_all_cpu_backtrace=
1292 [KNL] Should the hard-lockup detector generate
1293 backtraces on all cpus.
1296 hashdist= [KNL,NUMA] Large hashes allocated during boot
1297 are distributed across NUMA nodes. Defaults on
1298 for 64-bit NUMA, off otherwise.
1299 Format: 0 | 1 (for off | on)
1301 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1303 hd= [EIDE] (E)IDE hard drive subsystem geometry
1304 Format: <cyl>,<head>,<sect>
1307 Disable Hardware Error Source Table (HEST) support;
1308 corresponding firmware-first mode error processing
1309 logic will be disabled.
1311 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1312 size of <nn>. This works even on boxes that have no
1313 highmem otherwise. This also works to reduce highmem
1314 size on bigger boxes.
1316 highres= [KNL] Enable/disable high resolution timer mode.
1317 Valid parameters: "on", "off"
1321 See Documentation/isdn/README.HiSax.
1325 hpet= [X86-32,HPET] option to control HPET usage
1326 Format: { enable (default) | disable | force |
1328 disable: disable HPET and use PIT instead
1329 force: allow force enabled of undocumented chips (ICH4,
1331 verbose: show contents of HPET registers during setup
1333 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1334 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1336 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1337 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1338 On x86-64 and powerpc, this option can be specified
1339 multiple times interleaved with hugepages= to reserve
1340 huge pages of different sizes. Valid pages sizes on
1341 x86-64 are 2M (when the CPU supports "pse") and 1G
1342 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1344 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1345 terminal devices. Valid values: 0..8
1346 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1347 If specified, z/VM IUCV HVC accepts connections
1348 from listed z/VM user IDs only.
1350 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1351 hardware thread id mappings.
1352 Format: <cpu>:<hwthread>
1355 Do not unregister boot console at start. This is only
1356 useful for debugging when something happens in the window
1357 between unregistering the boot console and initializing
1360 i2c_bus= [HW] Override the default board specific I2C bus speed
1361 or register an additional I2C bus that is not
1362 registered from board initialization code.
1366 i8042.debug [HW] Toggle i8042 debug mode
1367 i8042.unmask_kbd_data
1368 [HW] Enable printing of interrupt data from the KBD port
1369 (disabled by default, and as a pre-condition
1370 requires that i8042.debug=1 be enabled)
1371 i8042.direct [HW] Put keyboard port into non-translated mode
1372 i8042.dumbkbd [HW] Pretend that controller can only read data from
1373 keyboard and cannot control its state
1374 (Don't attempt to blink the leds)
1375 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1376 i8042.nokbd [HW] Don't check/create keyboard port
1377 i8042.noloop [HW] Disable the AUX Loopback command while probing
1379 i8042.nomux [HW] Don't check presence of an active multiplexing
1381 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1383 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1384 i8042.reset [HW] Reset the controller during init, cleanup and
1385 suspend-to-ram transitions, only during s2r
1386 transitions, or never reset
1387 Format: { 1 | Y | y | 0 | N | n }
1388 1, Y, y: always reset controller
1389 0, N, n: don't ever reset controller
1390 Default: only on s2r transitions on x86; most other
1391 architectures force reset to be always executed
1392 i8042.unlock [HW] Unlock (ignore) the keylock
1393 i8042.kbdreset [HW] Reset device connected to KBD port
1397 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1398 indicates that the driver is running on unsupported
1400 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1401 does not match list of supported models.
1403 [HW] Report power status in /proc/i8k
1404 (disabled by default)
1405 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1408 i915.invert_brightness=
1409 [DRM] Invert the sense of the variable that is used to
1410 set the brightness of the panel backlight. Normally a
1411 brightness value of 0 indicates backlight switched off,
1412 and the maximum of the brightness value sets the backlight
1413 to maximum brightness. If this parameter is set to 0
1414 (default) and the machine requires it, or this parameter
1415 is set to 1, a brightness value of 0 sets the backlight
1416 to maximum brightness, and the maximum of the brightness
1417 value switches the backlight off.
1418 -1 -- never invert brightness
1419 0 -- machine default
1420 1 -- force brightness inversion
1423 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1425 ide-core.nodma= [HW] (E)IDE subsystem
1426 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1427 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1428 .cdrom .chs .ignore_cable are additional options
1429 See Documentation/ide/ide.txt.
1431 ide-generic.probe-mask= [HW] (E)IDE subsystem
1433 Probe mask for legacy ISA IDE ports. Depending on
1434 platform up to 6 ports are supported, enabled by
1435 setting corresponding bits in the mask to 1. The
1436 default value is 0x0, which has a special meaning.
1437 On systems that have PCI, it triggers scanning the
1438 PCI bus for the first and the second port, which
1439 are then probed. On systems without PCI the value
1440 of 0x0 enables probing the two first ports as if it
1443 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1444 Claim all unknown PCI IDE storage controllers.
1447 Format: idle=poll, idle=halt, idle=nomwait
1448 Poll forces a polling idle loop that can slightly
1449 improve the performance of waking up a idle CPU, but
1450 will use a lot of power and make the system run hot.
1452 idle=halt: Halt is forced to be used for CPU idle.
1453 In such case C2/C3 won't be used again.
1454 idle=nomwait: Disable mwait for CPU C-states
1456 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1457 Format: { strict | legacy | 2008 | relaxed }
1460 Choose which programs will be accepted for execution
1461 based on the IEEE 754 NaN encoding(s) supported by
1462 the FPU and the NaN encoding requested with the value
1463 of an ELF file header flag individually set by each
1464 binary. Hardware implementations are permitted to
1465 support either or both of the legacy and the 2008 NaN
1468 Available settings are as follows:
1469 strict accept binaries that request a NaN encoding
1470 supported by the FPU
1471 legacy only accept legacy-NaN binaries, if supported
1473 2008 only accept 2008-NaN binaries, if supported
1475 relaxed accept any binaries regardless of whether
1476 supported by the FPU
1478 The FPU emulator is always able to support both NaN
1479 encodings, so if no FPU hardware is present or it has
1480 been disabled with 'nofpu', then the settings of
1481 'legacy' and '2008' strap the emulator accordingly,
1482 'relaxed' straps the emulator for both legacy-NaN and
1483 2008-NaN, whereas 'strict' enables legacy-NaN only on
1484 legacy processors and both NaN encodings on MIPS32 or
1487 The setting for ABS.fmt/NEG.fmt instruction execution
1488 mode generally follows that for the NaN encoding,
1489 except where unsupported by hardware.
1491 ignore_loglevel [KNL]
1492 Ignore loglevel setting - this will print /all/
1493 kernel messages to the console. Useful for debugging.
1494 We also add it as printk module parameter, so users
1495 could change it dynamically, usually by
1496 /sys/module/printk/parameters/ignore_loglevel.
1499 Ignore RLIMIT_DATA setting for data mappings,
1500 print warning at first misuse. Can be changed via
1501 /sys/module/kernel/parameters/ignore_rlimit_data.
1503 ihash_entries= [KNL]
1504 Set number of hash buckets for inode cache.
1506 ima_appraise= [IMA] appraise integrity measurements
1507 Format: { "off" | "enforce" | "fix" | "log" }
1510 ima_appraise_tcb [IMA]
1511 The builtin appraise policy appraises all files
1514 ima_canonical_fmt [IMA]
1515 Use the canonical format for the binary runtime
1516 measurements, instead of host native format.
1519 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1523 The list of supported hash algorithms is defined
1524 in crypto/hash_info.h.
1527 The builtin policies to load during IMA setup.
1528 Format: "tcb | appraise_tcb | secure_boot"
1530 The "tcb" policy measures all programs exec'd, files
1531 mmap'd for exec, and all files opened with the read
1532 mode bit set by either the effective uid (euid=0) or
1535 The "appraise_tcb" policy appraises the integrity of
1536 all files owned by root. (This is the equivalent
1537 of ima_appraise_tcb.)
1539 The "secure_boot" policy appraises the integrity
1540 of files (eg. kexec kernel image, kernel modules,
1541 firmware, policy, etc) based on file signatures.
1543 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1544 Load a policy which meets the needs of the Trusted
1545 Computing Base. This means IMA will measure all
1546 programs exec'd, files mmap'd for exec, and all files
1547 opened for read by uid=0.
1550 Select one of defined IMA measurements template formats.
1551 Formats: { "ima" | "ima-ng" | "ima-sig" }
1555 [IMA] Define a custom template format.
1556 Format: { "field1|...|fieldN" }
1558 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1559 Format: <min_file_size>
1560 Set the minimal file size for using asynchronous hash.
1561 If left unspecified, ahash usage is disabled.
1563 ahash performance varies for different data sizes on
1564 different crypto accelerators. This option can be used
1565 to achieve the best performance for a particular HW.
1567 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1569 Set hashing buffer size. Default: 4k.
1571 ahash performance varies for different chunk sizes on
1572 different crypto accelerators. This option can be used
1573 to achieve best performance for particular HW.
1577 Run specified binary instead of /sbin/init as init
1580 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1581 for working out where the kernel is dying during
1584 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1585 initcall functions. Useful for debugging built-in
1586 modules and initcalls.
1588 initrd= [BOOT] Specify the location of the initial ramdisk
1590 init_pkru= [x86] Specify the default memory protection keys rights
1591 register contents for all processes. 0x55555554 by
1592 default (disallow access to all but pkey 0). Can
1593 override in debugfs after boot.
1595 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1598 int_pln_enable [x86] Enable power limit notification interrupt
1600 integrity_audit=[IMA]
1601 Format: { "0" | "1" }
1602 0 -- basic integrity auditing messages. (Default)
1603 1 -- additional integrity auditing messages.
1605 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1607 Enable intel iommu driver.
1609 Disable intel iommu driver.
1610 igfx_off [Default Off]
1611 By default, gfx is mapped as normal device. If a gfx
1612 device has a dedicated DMAR unit, the DMAR unit is
1613 bypassed by not enabling DMAR with this option. In
1614 this case, gfx device will use physical address for
1617 With this option iommu will not optimize to look
1618 for io virtual address below 32-bit forcing dual
1619 address cycle on pci bus for cards supporting greater
1620 than 32-bit addressing. The default is to look
1621 for translation below 32-bit and if not available
1622 then look in the higher range.
1623 strict [Default Off]
1624 With this option on every unmap_single operation will
1625 result in a hardware IOTLB flush operation as opposed
1626 to batching them for performance.
1627 sp_off [Default Off]
1628 By default, super page will be supported if Intel IOMMU
1629 has the capability. With this option, super page will
1631 ecs_off [Default Off]
1632 By default, extended context tables will be supported if
1633 the hardware advertises that it has support both for the
1634 extended tables themselves, and also PASID support. With
1635 this option set, extended tables will not be used even
1636 on hardware which claims to support them.
1637 tboot_noforce [Default Off]
1638 Do not force the Intel IOMMU enabled under tboot.
1639 By default, tboot will force Intel IOMMU on, which
1640 could harm performance of some high-throughput
1641 devices like 40GBit network cards, even if identity
1643 Note that using this option lowers the security
1644 provided by tboot because it makes the system
1645 vulnerable to DMA attacks.
1647 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1648 0 disables intel_idle and fall back on acpi_idle.
1649 1 to 9 specify maximum depth of C-state.
1653 Do not enable intel_pstate as the default
1654 scaling driver for the supported processors
1656 Use intel_pstate as a scaling driver, but configure it
1657 to work with generic cpufreq governors (instead of
1658 enabling its internal governor). This mode cannot be
1659 used along with the hardware-managed P-states (HWP)
1662 Enable intel_pstate on systems that prohibit it by default
1663 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1664 instead of acpi-cpufreq may disable platform features, such
1665 as thermal controls and power capping, that rely on ACPI
1666 P-States information being indicated to OSPM and therefore
1667 should be used with caution. This option does not work with
1668 processors that aren't supported by the intel_pstate driver
1669 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1671 Do not enable hardware P state control (HWP)
1674 Only load intel_pstate on systems which support
1675 hardware P state control (HWP) if available.
1677 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1678 Description Table, specifies preferred power management
1679 profile as "Enterprise Server" or "Performance Server",
1680 then this feature is turned on by default.
1682 Allow per-logical-CPU P-State performance control limits using
1683 cpufreq sysfs interface
1685 intremap= [X86-64, Intel-IOMMU]
1686 on enable Interrupt Remapping (default)
1687 off disable Interrupt Remapping
1688 nosid disable Source ID checking
1690 BIOS x2APIC opt-out request will be ignored
1691 nopost disable Interrupt Posting
1693 iomem= Disable strict checking of access to MMIO memory
1694 strict regions from userspace.
1709 nobypass [PPC/POWERNV]
1710 Disable IOMMU bypass, using IOMMU for PCI devices.
1713 [ARM64] Configure DMA to bypass the IOMMU by default.
1714 Format: { "0" | "1" }
1715 0 - Use IOMMU translation for DMA.
1716 1 - Bypass the IOMMU for DMA.
1717 unset - Use IOMMU translation for DMA.
1719 io7= [HW] IO7 for Marvel based alpha systems
1720 See comment before marvel_specify_io7 in
1721 arch/alpha/kernel/core_marvel.c.
1723 io_delay= [X86] I/O delay method
1725 Standard port 0x80 based delay
1727 Alternate port 0xed based delay (needed on some systems)
1729 Simple two microseconds delay
1734 See Documentation/filesystems/nfs/nfsroot.txt.
1736 irqaffinity= [SMP] Set the default irq affinity mask
1737 The argument is a cpu list, as described above.
1739 irqchip.gicv2_force_probe=
1742 Force the kernel to look for the second 4kB page
1743 of a GICv2 controller even if the memory range
1744 exposed by the device tree is too small.
1747 When an interrupt is not handled search all handlers
1748 for it. Intended to get systems with badly broken
1752 When an interrupt is not handled search all handlers
1753 for it. Also check all handlers each timer
1754 interrupt. Intended to get systems with badly broken
1758 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1760 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1761 [Deprecated - use cpusets instead]
1762 Format: [flag-list,]<cpu-list>
1764 Specify one or more CPUs to isolate from disturbances
1765 specified in the flag list (default: domain):
1768 Disable the tick when a single task runs.
1770 Isolate from the general SMP balancing and scheduling
1771 algorithms. Note that performing domain isolation this way
1772 is irreversible: it's not possible to bring back a CPU to
1773 the domains once isolated through isolcpus. It's strongly
1774 advised to use cpusets instead to disable scheduler load
1775 balancing through the "cpuset.sched_load_balance" file.
1776 It offers a much more flexible interface where CPUs can
1777 move in and out of an isolated set anytime.
1779 You can move a process onto or off an "isolated" CPU via
1780 the CPU affinity syscalls or cpuset.
1781 <cpu number> begins at 0 and the maximum value is
1782 "number of CPUs in system - 1".
1784 The format of <cpu-list> is described above.
1790 ivrs_ioapic [HW,X86_64]
1791 Provide an override to the IOAPIC-ID<->DEVICE-ID
1792 mapping provided in the IVRS ACPI table. For
1793 example, to map IOAPIC-ID decimal 10 to
1794 PCI device 00:14.0 write the parameter as:
1795 ivrs_ioapic[10]=00:14.0
1797 ivrs_hpet [HW,X86_64]
1798 Provide an override to the HPET-ID<->DEVICE-ID
1799 mapping provided in the IVRS ACPI table. For
1800 example, to map HPET-ID decimal 0 to
1801 PCI device 00:14.0 write the parameter as:
1802 ivrs_hpet[0]=00:14.0
1804 ivrs_acpihid [HW,X86_64]
1805 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1806 mapping provided in the IVRS ACPI table. For
1807 example, to map UART-HID:UID AMD0020:0 to
1808 PCI device 00:14.5 write the parameter as:
1809 ivrs_acpihid[00:14.5]=AMD0020:0
1811 js= [HW,JOY] Analog joystick
1812 See Documentation/input/joydev/joystick.rst.
1815 When CONFIG_RANDOMIZE_BASE is set, this disables
1816 kernel and module base offset ASLR (Address Space
1817 Layout Randomization).
1820 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1821 report on every invalid memory access. Without this
1822 parameter KASAN will print report only for the first
1827 kernelcore= [KNL,X86,IA-64,PPC]
1828 Format: nn[KMGTPE] | "mirror"
1830 specifies the amount of memory usable by the kernel
1831 for non-movable allocations. The requested amount is
1832 spread evenly throughout all nodes in the system. The
1833 remaining memory in each node is used for Movable
1834 pages. In the event, a node is too small to have both
1835 kernelcore and Movable pages, kernelcore pages will
1836 take priority and other nodes will have a larger number
1837 of Movable pages. The Movable zone is used for the
1838 allocation of pages that may be reclaimed or moved
1839 by the page migration subsystem. This means that
1840 HugeTLB pages may not be allocated from this zone.
1841 Note that allocations like PTEs-from-HighMem still
1842 use the HighMem zone if it exists, and the Normal
1843 zone if it does not.
1845 Instead of specifying the amount of memory (nn[KMGTPE]),
1846 you can specify "mirror" option. In case "mirror"
1847 option is specified, mirrored (reliable) memory is used
1848 for non-movable allocations and remaining memory is used
1849 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1850 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1853 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1854 Format: <Controller#>[,poll interval]
1855 The controller # is the number of the ehci usb debug
1856 port as it is probed via PCI. The poll interval is
1857 optional and is the number seconds in between
1858 each poll cycle to the debug port in case you need
1859 the functionality for interrupting the kernel with
1860 gdb or control-c on the dbgp connection. When
1861 not using this parameter you use sysrq-g to break into
1862 the kernel debugger.
1864 kgdboc= [KGDB,HW] kgdb over consoles.
1865 Requires a tty driver that supports console polling,
1866 or a supported polling keyboard driver (non-usb).
1867 Serial only format: <serial_device>[,baud]
1868 keyboard only format: kbd
1869 keyboard and serial format: kbd,<serial_device>[,baud]
1870 Optional Kernel mode setting:
1871 kms, kbd format: kms,kbd
1872 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1874 kgdbwait [KGDB] Stop kernel execution and enter the
1875 kernel debugger at the earliest opportunity.
1877 kmac= [MIPS] korina ethernet MAC address.
1878 Configure the RouterBoard 532 series on-chip
1879 Ethernet adapter MAC address.
1881 kmemleak= [KNL] Boot-time kmemleak enable/disable
1882 Valid arguments: on, off
1884 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1887 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1888 Default is 0 (don't ignore, but inject #GP)
1890 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1894 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1895 Default is 1 (enabled)
1897 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1899 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1901 kvm-arm.vgic_v3_group0_trap=
1902 [KVM,ARM] Trap guest accesses to GICv3 group-0
1905 kvm-arm.vgic_v3_group1_trap=
1906 [KVM,ARM] Trap guest accesses to GICv3 group-1
1909 kvm-arm.vgic_v3_common_trap=
1910 [KVM,ARM] Trap guest accesses to GICv3 common
1913 kvm-arm.vgic_v4_enable=
1914 [KVM,ARM] Allow use of GICv4 for direct injection of
1917 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1918 (virtualized MMU) support on capable Intel chips.
1919 Default is 1 (enabled)
1921 kvm-intel.emulate_invalid_guest_state=
1922 [KVM,Intel] Enable emulation of invalid guest states
1923 Default is 0 (disabled)
1925 kvm-intel.flexpriority=
1926 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1927 Default is 1 (enabled)
1930 [KVM,Intel] Enable VMX nesting (nVMX).
1931 Default is 0 (disabled)
1933 kvm-intel.unrestricted_guest=
1934 [KVM,Intel] Disable unrestricted guest feature
1935 (virtualized real and unpaged mode) on capable
1936 Intel chips. Default is 1 (enabled)
1938 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1939 feature (tagged TLBs) on capable Intel chips.
1940 Default is 1 (enabled)
1946 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1949 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1950 value for LAPIC timer one-shot implementation. Default
1951 back to the programmable timer unit in the LAPIC.
1953 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1956 libata.dma= [LIBATA] DMA control
1957 libata.dma=0 Disable all PATA and SATA DMA
1958 libata.dma=1 PATA and SATA Disk DMA only
1959 libata.dma=2 ATAPI (CDROM) DMA only
1960 libata.dma=4 Compact Flash DMA only
1961 Combinations also work, so libata.dma=3 enables DMA
1962 for disks and CDROMs, but not CFs.
1964 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1965 libata.ignore_hpa=0 keep BIOS limits (default)
1966 libata.ignore_hpa=1 ignore limits, using full disk
1968 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1972 libata.force= [LIBATA] Force configurations. The format is comma
1973 separated list of "[ID:]VAL" where ID is
1974 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1975 matching port, link or device. Basically, it matches
1976 the ATA ID string printed on console by libata. If
1977 the whole ID part is omitted, the last PORT and DEVICE
1978 values are used. If ID hasn't been specified yet, the
1979 configuration applies to all ports, links and devices.
1981 If only DEVICE is omitted, the parameter applies to
1982 the port and all links and devices behind it. DEVICE
1983 number of 0 either selects the first device or the
1984 first fan-out link behind PMP device. It does not
1985 select the host link. DEVICE number of 15 selects the
1986 host link and device attached to it.
1988 The VAL specifies the configuration to force. As long
1989 as there's no ambiguity shortcut notation is allowed.
1990 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1991 The following configurations can be forced.
1993 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1994 Any ID with matching PORT is used.
1996 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1998 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1999 udma[/][16,25,33,44,66,100,133] notation is also
2002 * [no]ncq: Turn on or off NCQ.
2004 * [no]ncqtrim: Turn off queued DSM TRIM.
2006 * nohrst, nosrst, norst: suppress hard, soft
2009 * rstonce: only attempt one reset during
2010 hot-unplug link recovery
2012 * dump_id: dump IDENTIFY data.
2014 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2016 * disable: Disable this device.
2018 If there are multiple matching configurations changing
2019 the same attribute, the last one is used.
2021 memblock=debug [KNL] Enable memblock debug messages.
2023 load_ramdisk= [RAM] List of ramdisks to load from floppy
2024 See Documentation/blockdev/ramdisk.txt.
2026 lockd.nlm_grace_period=P [NFS] Assign grace period.
2029 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2032 lockd.nlm_timeout=T [NFS] Assign timeout value.
2035 lockd.nlm_udpport=M [NFS] Assign UDP port.
2038 locktorture.nreaders_stress= [KNL]
2039 Set the number of locking read-acquisition kthreads.
2040 Defaults to being automatically set based on the
2041 number of online CPUs.
2043 locktorture.nwriters_stress= [KNL]
2044 Set the number of locking write-acquisition kthreads.
2046 locktorture.onoff_holdoff= [KNL]
2047 Set time (s) after boot for CPU-hotplug testing.
2049 locktorture.onoff_interval= [KNL]
2050 Set time (s) between CPU-hotplug operations, or
2051 zero to disable CPU-hotplug testing.
2053 locktorture.shuffle_interval= [KNL]
2054 Set task-shuffle interval (jiffies). Shuffling
2055 tasks allows some CPUs to go into dyntick-idle
2056 mode during the locktorture test.
2058 locktorture.shutdown_secs= [KNL]
2059 Set time (s) after boot system shutdown. This
2060 is useful for hands-off automated testing.
2062 locktorture.stat_interval= [KNL]
2063 Time (s) between statistics printk()s.
2065 locktorture.stutter= [KNL]
2066 Time (s) to stutter testing, for example,
2067 specifying five seconds causes the test to run for
2068 five seconds, wait for five seconds, and so on.
2069 This tests the locking primitive's ability to
2070 transition abruptly to and from idle.
2072 locktorture.torture_type= [KNL]
2073 Specify the locking implementation to test.
2075 locktorture.verbose= [KNL]
2076 Enable additional printk() statements.
2078 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2081 loglevel= All Kernel Messages with a loglevel smaller than the
2082 console loglevel will be printed to the console. It can
2083 also be changed with klogd or other programs. The
2084 loglevels are defined as follows:
2086 0 (KERN_EMERG) system is unusable
2087 1 (KERN_ALERT) action must be taken immediately
2088 2 (KERN_CRIT) critical conditions
2089 3 (KERN_ERR) error conditions
2090 4 (KERN_WARNING) warning conditions
2091 5 (KERN_NOTICE) normal but significant condition
2092 6 (KERN_INFO) informational
2093 7 (KERN_DEBUG) debug-level messages
2095 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2096 in bytes. n must be a power of two and greater
2097 than the minimal size. The minimal size is defined
2098 by LOG_BUF_SHIFT kernel config parameter. There is
2099 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2100 that allows to increase the default size depending on
2101 the number of CPUs. See init/Kconfig for more details.
2103 logo.nologo [FB] Disables display of the built-in Linux logo.
2104 This may be used to provide more screen space for
2105 kernel log messages and is useful when debugging
2106 kernel boot problems.
2108 lp=0 [LP] Specify parallel ports to use, e.g,
2109 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2110 lp=reset first parallel port). 'lp=0' disables the
2111 lp=auto printer driver. 'lp=reset' (which can be
2112 specified in addition to the ports) causes
2113 attached printers to be reset. Using
2114 lp=port1,port2,... specifies the parallel ports
2115 to associate lp devices with, starting with
2116 lp0. A port specification may be 'none' to skip
2117 that lp device, or a parport name such as
2118 'parport0'. Specifying 'lp=auto' instead of a
2119 port specification list means that device IDs
2120 from each port should be examined, to see if
2121 an IEEE 1284-compliant printer is attached; if
2122 so, the driver will manage that printer.
2123 See also header of drivers/char/lp.c.
2126 Sets loops_per_jiffy to given constant, thus avoiding
2127 time-consuming boot-time autodetection (up to 250 ms per
2128 CPU). 0 enables autodetection (default). To determine
2129 the correct value for your kernel, boot with normal
2130 autodetection and see what value is printed. Note that
2131 on SMP systems the preset will be applied to all CPUs,
2132 which is likely to cause problems if your CPUs need
2133 significantly divergent settings. An incorrect value
2134 will cause delays in the kernel to be wrong, leading to
2135 unpredictable I/O errors and other breakage. Although
2136 unlikely, in the extreme case this might damage your
2140 Format: <io>,<irq>,<dma>
2142 machvec= [IA-64] Force the use of a particular machine-vector
2143 (machvec) in a generic kernel.
2144 Example: machvec=hpzx1_swiotlb
2146 machtype= [Loongson] Share the same kernel image file between different
2148 Example: machtype=lemote-yeeloong-2f-7inch
2150 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2151 than or equal to this physical address is ignored.
2153 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2154 will bring up during bootup. maxcpus=n : n >= 0 limits
2155 the kernel to bring up 'n' processors. Surely after
2156 bootup you can bring up the other plugged cpu by executing
2157 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2158 only takes effect during system bootup.
2159 While n=0 is a special case, it is equivalent to "nosmp",
2160 which also disables the IO APIC.
2162 max_loop= [LOOP] The number of loop block devices that get
2163 (loop.max_loop) unconditionally pre-created at init time. The default
2164 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2165 of statically allocating a predefined number, loop
2166 devices can be requested on-demand with the
2167 /dev/loop-control interface.
2169 mce [X86-32] Machine Check Exception
2171 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2173 md= [HW] RAID subsystems devices and level
2174 See Documentation/admin-guide/md.rst.
2177 Format: <first>,<last>
2178 Specifies range of consoles to be captured by the MDA.
2180 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2181 Amount of memory to be used when the kernel is not able
2182 to see the whole system memory or for test.
2183 [X86] Work as limiting max address. Use together
2184 with memmap= to avoid physical address space collisions.
2185 Without memmap= PCI devices could be placed at addresses
2186 belonging to unused RAM.
2188 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2192 [KNL,SH] Allow user to override the default size for
2193 per-device physically contiguous DMA buffers.
2195 memhp_default_state=online/offline
2196 [KNL] Set the initial state for the memory hotplug
2197 onlining policy. If not specified, the default value is
2198 set according to the
2199 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2201 See Documentation/memory-hotplug.txt.
2203 memmap=exactmap [KNL,X86] Enable setting of an exact
2204 E820 memory map, as specified by the user.
2205 Such memmap=exactmap lines can be constructed based on
2206 BIOS output or other requirements. See the memmap=nn@ss
2209 memmap=nn[KMG]@ss[KMG]
2210 [KNL] Force usage of a specific region of memory.
2211 Region of memory to be used is from ss to ss+nn.
2212 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2213 which limits max address to nn[KMG].
2214 Multiple different regions can be specified,
2217 memmap=100M@2G,100M#3G,1G!1024G
2219 memmap=nn[KMG]#ss[KMG]
2220 [KNL,ACPI] Mark specific memory as ACPI data.
2221 Region of memory to be marked is from ss to ss+nn.
2223 memmap=nn[KMG]$ss[KMG]
2224 [KNL,ACPI] Mark specific memory as reserved.
2225 Region of memory to be reserved is from ss to ss+nn.
2226 Example: Exclude memory from 0x18690000-0x1869ffff
2227 memmap=64K$0x18690000
2229 memmap=0x10000$0x18690000
2230 Some bootloaders may need an escape character before '$',
2231 like Grub2, otherwise '$' and the following number
2234 memmap=nn[KMG]!ss[KMG]
2235 [KNL,X86] Mark specific memory as protected.
2236 Region of memory to be used, from ss to ss+nn.
2237 The memory region may be marked as e820 type 12 (0xc)
2238 and is NVDIMM or ADR memory.
2240 memory_corruption_check=0/1 [X86]
2241 Some BIOSes seem to corrupt the first 64k of
2242 memory when doing things like suspend/resume.
2243 Setting this option will scan the memory
2244 looking for corruption. Enabling this will
2245 both detect corruption and prevent the kernel
2246 from using the memory being corrupted.
2247 However, its intended as a diagnostic tool; if
2248 repeatable BIOS-originated corruption always
2249 affects the same memory, you can use memmap=
2250 to prevent the kernel from using that memory.
2252 memory_corruption_check_size=size [X86]
2253 By default it checks for corruption in the low
2254 64k, making this memory unavailable for normal
2255 use. Use this parameter to scan for
2256 corruption in more or less memory.
2258 memory_corruption_check_period=seconds [X86]
2259 By default it checks for corruption every 60
2260 seconds. Use this parameter to check at some
2261 other rate. 0 disables periodic checking.
2263 memtest= [KNL,X86,ARM] Enable memtest
2265 default : 0 <disable>
2266 Specifies the number of memtest passes to be
2267 performed. Each pass selects another test
2268 pattern from a given set of patterns. Memtest
2269 fills the memory with this pattern, validates
2270 memory contents and reserves bad memory
2271 regions that are detected.
2273 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2274 Valid arguments: on, off
2275 Default (depends on kernel configuration option):
2276 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2277 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2278 mem_encrypt=on: Activate SME
2279 mem_encrypt=off: Do not activate SME
2281 Refer to Documentation/x86/amd-memory-encryption.txt
2282 for details on when memory encryption can be activated.
2284 mem_sleep_default= [SUSPEND] Default system suspend mode:
2285 s2idle - Suspend-To-Idle
2286 shallow - Power-On Suspend or equivalent (if supported)
2287 deep - Suspend-To-RAM or equivalent (if supported)
2288 See Documentation/admin-guide/pm/sleep-states.rst.
2290 meye.*= [HW] Set MotionEye Camera parameters
2291 See Documentation/media/v4l-drivers/meye.rst.
2293 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2294 Multi-Function General Purpose Timers on AMD Geode
2297 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2298 the BIOS has incorrectly applied a workaround. TinyBIOS
2299 version 0.98 is known to be affected, 0.99 fixes the
2300 problem by letting the user disable the workaround.
2304 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2305 physical address is ignored.
2307 mini2440= [ARM,HW,KNL]
2308 Format:[0..2][b][c][t]
2310 MINI2440 configuration specification:
2311 0 - The attached screen is the 3.5" TFT
2312 1 - The attached screen is the 7" TFT
2313 2 - The VGA Shield is attached (1024x768)
2314 Leaving out the screen size parameter will not load
2315 the TFT driver, and the framebuffer will be left
2317 b - Enable backlight. The TFT backlight pin will be
2318 linked to the kernel VESA blanking code and a GPIO
2319 LED. This parameter is not necessary when using the
2321 c - Enable the s3c camera interface.
2322 t - Reserved for enabling touchscreen support. The
2323 touchscreen support is not enabled in the mainstream
2324 kernel as of 2.6.30, a preliminary port can be found
2325 in the "bleeding edge" mini2440 support kernel at
2326 http://repo.or.cz/w/linux-2.6/mini2440.git
2329 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2330 parameter allows control of the logging verbosity for
2331 the additional memory initialisation checks. A value
2332 of 0 disables mminit logging and a level of 4 will
2333 log everything. Information is printed at KERN_DEBUG
2334 so loglevel=8 may also need to be specified.
2337 [KNL] When CONFIG_MODULE_SIG is set, this means that
2338 modules without (valid) signatures will fail to load.
2339 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2340 is always true, so this option does nothing.
2342 module_blacklist= [KNL] Do not load a comma-separated list of
2343 modules. Useful for debugging problem modules.
2346 [MOUSE] Maximum time between finger touching and
2347 leaving touchpad surface for touch to be considered
2348 a tap and be reported as a left button click (for
2349 touchpads working in absolute mode only).
2351 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2352 reporting absolute coordinates, such as tablets
2353 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2354 reporting absolute coordinates, such as tablets
2356 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2357 is similar to kernelcore except it specifies the
2358 amount of memory used for migratable allocations.
2359 If both kernelcore and movablecore is specified,
2360 then kernelcore will be at *least* the specified
2361 value but may be more. If movablecore on its own
2362 is specified, the administrator must be careful
2363 that the amount of memory usable for all allocations
2366 movable_node [KNL] Boot-time switch to make hotplugable memory
2367 NUMA nodes to be movable. This means that the memory
2368 of such nodes will be usable only for movable
2369 allocations which rules out almost all kernel
2370 allocations. Use with caution!
2372 MTD_Partition= [MTD]
2373 Format: <name>,<region-number>,<size>,<offset>
2375 MTD_Region= [MTD] Format:
2376 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2379 See drivers/mtd/cmdlinepart.c.
2381 multitce=off [PPC] This parameter disables the use of the pSeries
2382 firmware feature for updating multiple TCE entries
2385 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2387 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2389 boundary - index of last SLC block on Flex-OneNAND.
2390 The remaining blocks are configured as MLC blocks.
2391 lock - Configure if Flex-OneNAND boundary should be locked.
2392 Once locked, the boundary cannot be changed.
2393 1 indicates lock status, 0 indicates unlock status.
2396 ARM/S3C2412 JIVE boot control
2398 See arch/arm/mach-s3c2412/mach-jive.c
2400 mtouchusb.raw_coordinates=
2401 [HW] Make the MicroTouch USB driver use raw coordinates
2402 ('y', default) or cooked coordinates ('n')
2404 mtrr_chunk_size=nn[KMG] [X86]
2405 used for mtrr cleanup. It is largest continuous chunk
2406 that could hold holes aka. UC entries.
2408 mtrr_gran_size=nn[KMG] [X86]
2409 Used for mtrr cleanup. It is granularity of mtrr block.
2411 Large value could prevent small alignment from
2414 mtrr_spare_reg_nr=n [X86]
2416 Range: 0,7 : spare reg number
2418 Used for mtrr cleanup. It is spare mtrr entries number.
2419 Set to 2 or more if your graphical card needs more.
2421 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2423 netdev= [NET] Network devices parameters
2424 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2425 Note that mem_start is often overloaded to mean
2426 something different and driver-specific.
2427 This usage is only documented in each driver source
2431 [NETFILTER] Enable connection tracking flow accounting
2432 0 to disable accounting
2433 1 to enable accounting
2436 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2437 See Documentation/filesystems/nfs/nfsroot.txt.
2439 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2440 See Documentation/filesystems/nfs/nfsroot.txt.
2442 nfsrootdebug [NFS] enable nfsroot debugging messages.
2443 See Documentation/filesystems/nfs/nfsroot.txt.
2445 nfs.callback_nr_threads=
2446 [NFSv4] set the total number of threads that the
2447 NFS client will assign to service NFSv4 callback
2450 nfs.callback_tcpport=
2451 [NFS] set the TCP port on which the NFSv4 callback
2452 channel should listen.
2455 [NFS] sets the pathname to the program which is used
2456 to update the NFS client cache entries.
2458 nfs.cache_getent_timeout=
2459 [NFS] sets the timeout after which an attempt to
2460 update a cache entry is deemed to have failed.
2462 nfs.idmap_cache_timeout=
2463 [NFS] set the maximum lifetime for idmapper cache
2467 [NFS] enable 64-bit inode numbers.
2468 If zero, the NFS client will fake up a 32-bit inode
2469 number for the readdir() and stat() syscalls instead
2470 of returning the full 64-bit number.
2471 The default is to return 64-bit inode numbers.
2473 nfs.max_session_cb_slots=
2474 [NFSv4.1] Sets the maximum number of session
2475 slots the client will assign to the callback
2476 channel. This determines the maximum number of
2477 callbacks the client will process in parallel for
2478 a particular server.
2480 nfs.max_session_slots=
2481 [NFSv4.1] Sets the maximum number of session slots
2482 the client will attempt to negotiate with the server.
2483 This limits the number of simultaneous RPC requests
2484 that the client can send to the NFSv4.1 server.
2485 Note that there is little point in setting this
2486 value higher than the max_tcp_slot_table_limit.
2488 nfs.nfs4_disable_idmapping=
2489 [NFSv4] When set to the default of '1', this option
2490 ensures that both the RPC level authentication
2491 scheme and the NFS level operations agree to use
2492 numeric uids/gids if the mount is using the
2493 'sec=sys' security flavour. In effect it is
2494 disabling idmapping, which can make migration from
2495 legacy NFSv2/v3 systems to NFSv4 easier.
2496 Servers that do not support this mode of operation
2497 will be autodetected by the client, and it will fall
2498 back to using the idmapper.
2499 To turn off this behaviour, set the value to '0'.
2501 [NFS4] Specify an additional fixed unique ident-
2502 ification string that NFSv4 clients can insert into
2503 their nfs_client_id4 string. This is typically a
2504 UUID that is generated at system install time.
2506 nfs.send_implementation_id =
2507 [NFSv4.1] Send client implementation identification
2508 information in exchange_id requests.
2509 If zero, no implementation identification information
2511 The default is to send the implementation identification
2514 nfs.recover_lost_locks =
2515 [NFSv4] Attempt to recover locks that were lost due
2516 to a lease timeout on the server. Please note that
2517 doing this risks data corruption, since there are
2518 no guarantees that the file will remain unchanged
2519 after the locks are lost.
2520 If you want to enable the kernel legacy behaviour of
2521 attempting to recover these locks, then set this
2523 The default parameter value of '0' causes the kernel
2524 not to attempt recovery of lost locks.
2526 nfs4.layoutstats_timer =
2527 [NFSv4.2] Change the rate at which the kernel sends
2528 layoutstats to the pNFS metadata server.
2530 Setting this to value to 0 causes the kernel to use
2531 whatever value is the default set by the layout
2532 driver. A non-zero value sets the minimum interval
2533 in seconds between layoutstats transmissions.
2535 nfsd.nfs4_disable_idmapping=
2536 [NFSv4] When set to the default of '1', the NFSv4
2537 server will return only numeric uids and gids to
2538 clients using auth_sys, and will accept numeric uids
2539 and gids from such clients. This is intended to ease
2540 migration from NFSv2/v3.
2542 nmi_debug= [KNL,SH] Specify one or more actions to take
2543 when a NMI is triggered.
2544 Format: [state][,regs][,debounce][,die]
2546 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2547 Format: [panic,][nopanic,][num]
2549 0 - turn hardlockup detector in nmi_watchdog off
2550 1 - turn hardlockup detector in nmi_watchdog on
2551 When panic is specified, panic when an NMI watchdog
2552 timeout occurs (or 'nopanic' to override the opposite
2553 default). To disable both hard and soft lockup detectors,
2554 please see 'nowatchdog'.
2555 This is useful when you use a panic=... timeout and
2556 need the box quickly up again.
2558 These settings can be accessed at runtime via
2559 the nmi_watchdog and hardlockup_panic sysctls.
2561 netpoll.carrier_timeout=
2562 [NET] Specifies amount of time (in seconds) that
2563 netpoll should wait for a carrier. By default netpoll
2566 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2567 emulation library even if a 387 maths coprocessor
2571 [HW] Never suspend the console
2572 Disable suspending of consoles during suspend and
2573 hibernate operations. Once disabled, debugging
2574 messages can reach various consoles while the rest
2575 of the system is being put to sleep (ie, while
2576 debugging driver suspend/resume hooks). This may
2577 not work reliably with all consoles, but is known
2578 to work with serial and VGA consoles.
2579 To facilitate more flexible debugging, we also add
2580 console_suspend, a printk module parameter to control
2581 it. Users could use console_suspend (usually
2582 /sys/module/printk/parameters/console_suspend) to
2583 turn on/off it dynamically.
2585 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2586 caches in the slab allocator. Saves per-node memory,
2587 but will impact performance.
2591 noaltinstr [S390] Disables alternative instructions patching
2592 (CPU alternatives feature).
2594 noapic [SMP,APIC] Tells the kernel to not make use of any
2595 IOAPICs that may be present in the system.
2597 noautogroup Disable scheduler automatic task group creation.
2599 nobats [PPC] Do not use BATs for mapping kernel lowmem
2600 on "Classic" PPC cores.
2604 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2606 nodelayacct [KNL] Disable per-task delay accounting
2608 nodsp [SH] Disable hardware DSP at boot time.
2610 noefi Disable EFI runtime services support.
2615 On X86-32 available only on PAE configured kernels.
2616 noexec=on: enable non-executable mappings (default)
2617 noexec=off: disable non-executable mappings
2620 Disable SMAP (Supervisor Mode Access Prevention)
2621 even if it is supported by processor.
2624 Disable SMEP (Supervisor Mode Execution Prevention)
2625 even if it is supported by processor.
2628 This affects only 32-bit executables.
2629 noexec32=on: enable non-executable mappings (default)
2630 read doesn't imply executable mappings
2631 noexec32=off: disable non-executable mappings
2632 read implies executable mappings
2634 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2636 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2637 register save and restore. The kernel will only save
2638 legacy floating-point registers on task switch.
2640 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2642 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2643 Equivalent to smt=1.
2645 nospectre_v2 [X86] Disable all mitigations for the Spectre variant 2
2646 (indirect branch prediction) vulnerability. System may
2647 allow data leaks with this option, which is equivalent
2650 noxsave [BUGS=X86] Disables x86 extended register state save
2651 and restore using xsave. The kernel will fallback to
2652 enabling legacy floating-point and sse state.
2654 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2655 register states. The kernel will fall back to use
2656 xsave to save the states. By using this parameter,
2657 performance of saving the states is degraded because
2658 xsave doesn't support modified optimization while
2659 xsaveopt supports it on xsaveopt enabled systems.
2661 noxsaves [X86] Disables xsaves and xrstors used in saving and
2662 restoring x86 extended register state in compacted
2663 form of xsave area. The kernel will fall back to use
2664 xsaveopt and xrstor to save and restore the states
2665 in standard form of xsave area. By using this
2666 parameter, xsave area per process might occupy more
2667 memory on xsaves enabled systems.
2669 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2670 wfi(ARM) instruction doesn't work correctly and not to
2671 use it. This is also useful when using JTAG debugger.
2673 no_file_caps Tells the kernel not to honor file capabilities. The
2674 only way then for a file to be executed with privilege
2675 is to be setuid root or executed by root.
2677 nohalt [IA-64] Tells the kernel not to use the power saving
2678 function PAL_HALT_LIGHT when idle. This increases
2679 power-consumption. On the positive side, it reduces
2680 interrupt wake-up latency, which may improve performance
2681 in certain environments such as networked servers or
2684 nohibernate [HIBERNATION] Disable hibernation and resume.
2686 nohz= [KNL] Boottime enable/disable dynamic ticks
2687 Valid arguments: on, off
2690 nohz_full= [KNL,BOOT,SMP,ISOL]
2691 The argument is a cpu list, as described above.
2692 In kernels built with CONFIG_NO_HZ_FULL=y, set
2693 the specified list of CPUs whose tick will be stopped
2694 whenever possible. The boot CPU will be forced outside
2695 the range to maintain the timekeeping. Any CPUs
2696 in this list will have their RCU callbacks offloaded,
2697 just as if they had also been called out in the
2698 rcu_nocbs= boot parameter.
2700 noiotrap [SH] Disables trapped I/O port accesses.
2702 noirqdebug [X86-32] Disables the code which attempts to detect and
2703 disable unhandled interrupt sources.
2705 no_timer_check [X86,APIC] Disables the code which tests for
2706 broken timer IRQ sources.
2708 noisapnp [ISAPNP] Disables ISA PnP code.
2710 noinitrd [RAM] Tells the kernel not to load any configured
2713 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2715 [Deprecated - use intremap=off]
2719 noinvpcid [X86] Disable the INVPCID cpu feature.
2721 nojitter [IA-64] Disables jitter checking for ITC timers.
2723 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2725 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2729 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2730 clock and use the default one.
2732 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2733 steal time is computed, but won't influence scheduler
2736 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2738 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2740 noltlbs [PPC] Do not use large page/tlb entries for kernel
2741 lowmem mapping on PPC40x and PPC8xx
2743 nomca [IA-64] Disable machine check abort handling
2745 nomce [X86-32] Disable Machine Check Exception
2747 nomfgpt [X86-32] Disable Multi-Function General Purpose
2748 Timer usage (for AMD Geode machines).
2750 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2751 shutdown the other cpus. Instead use the REBOOT_VECTOR
2754 nomodule Disable module load
2756 nopat [X86] Disable PAT (page attribute table extension of
2757 pagetables) support.
2759 nopcid [X86-64] Disable the PCID cpu feature.
2761 norandmaps Don't use address space randomization. Equivalent to
2762 echo 0 > /proc/sys/kernel/randomize_va_space
2764 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2765 with UP alternatives
2767 nordrand [X86] Disable kernel use of the RDRAND and
2768 RDSEED instructions even if they are supported
2769 by the processor. RDRAND and RDSEED are still
2770 available to user space applications.
2772 noresume [SWSUSP] Disables resume and restores original swap
2775 no-scroll [VGA] Disables scrollback.
2776 This is required for the Braillex ib80-piezo Braille
2777 reader made by F.H. Papenmeier (Germany).
2781 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2783 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2784 and disable the IO APIC. legacy for "maxcpus=0".
2786 nosoftlockup [KNL] Disable the soft-lockup detector.
2788 nosync [HW,M68K] Disables sync negotiation for all devices.
2790 notsc [BUGS=X86-32] Disable Time Stamp Counter
2792 nowatchdog [KNL] Disable both lockup detectors, i.e.
2793 soft-lockup and NMI watchdog (hard-lockup).
2797 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2799 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2800 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2801 Some features depend on CPU0. Known dependencies are:
2802 1. Resume from suspend/hibernate depends on CPU0.
2803 Suspend/hibernate will fail if CPU0 is offline and you
2804 need to online CPU0 before suspend/hibernate.
2805 2. PIC interrupts also depend on CPU0. CPU0 can't be
2806 removed if a PIC interrupt is detected.
2807 It's said poweroff/reboot may depend on CPU0 on some
2808 machines although I haven't seen such issues so far
2809 after CPU0 is offline on a few tested machines.
2810 If the dependencies are under your control, you can
2811 turn on cpu0_hotplug.
2813 nps_mtm_hs_ctr= [KNL,ARC]
2814 This parameter sets the maximum duration, in
2815 cycles, each HW thread of the CTOP can run
2816 without interruptions, before HW switches it.
2817 The actual maximum duration is 16 times this
2819 Format: integer between 1 and 255
2822 nptcg= [IA-64] Override max number of concurrent global TLB
2823 purges which is reported from either PAL_VM_SUMMARY or
2826 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2827 could support. nr_cpus=n : n >= 1 limits the kernel to
2828 support 'n' processors. It could be larger than the
2829 number of already plugged CPU during bootup, later in
2830 runtime you can physically add extra cpu until it reaches
2831 n. So during boot up some boot time memory for per-cpu
2832 variables need be pre-allocated for later physical cpu
2835 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2837 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2838 Allowed values are enable and disable
2840 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2841 'node', 'default' can be specified
2842 This can be set from sysctl after boot.
2843 See Documentation/sysctl/vm.txt for details.
2845 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2846 See Documentation/debugging-via-ohci1394.txt for more
2849 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2850 Rather than timing out after 20 ms if an EC
2851 command is not properly ACKed, override the length
2852 of the timeout. We have interrupts disabled while
2853 waiting for the ACK, so if this is set too high
2854 interrupts *may* be lost!
2856 omap_mux= [OMAP] Override bootloader pin multiplexing.
2857 Format: <mux_mode0.mode_name=value>...
2858 For example, to override I2C bus2:
2859 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2861 oprofile.timer= [HW]
2862 Use timer interrupt instead of performance counters
2864 oprofile.cpu_type= Force an oprofile cpu type
2865 This might be useful if you have an older oprofile
2866 userland or if you want common events.
2867 Format: { arch_perfmon }
2868 arch_perfmon: [X86] Force use of architectural
2869 perfmon on Intel CPUs instead of the
2870 CPU specific event set.
2871 timer: [X86] Force use of architectural NMI
2872 timer mode (see also oprofile.timer
2873 for generic hr timer mode)
2875 oops=panic Always panic on oopses. Default is to just kill the
2876 process, but there is a small probability of
2877 deadlocking the machine.
2878 This will also cause panics on machine check exceptions.
2879 Useful together with panic=30 to trigger a reboot.
2882 See Documentation/sound/oss/oss-parameters.txt
2884 page_owner= [KNL] Boot-time page_owner enabling option.
2885 Storage of the information about who allocated
2886 each page is disabled in default. With this switch,
2888 on: enable the feature
2890 page_poison= [KNL] Boot-time parameter changing the state of
2891 poisoning on the buddy allocator.
2892 off: turn off poisoning
2893 on: turn on poisoning
2895 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2896 timeout > 0: seconds before rebooting
2897 timeout = 0: wait forever
2898 timeout < 0: reboot immediately
2901 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2904 crash_kexec_post_notifiers
2905 Run kdump after running panic-notifiers and dumping
2906 kmsg. This only for the users who doubt kdump always
2907 succeeds in any situation.
2908 Note that this also increases risks of kdump failure,
2909 because some panic notifiers can make the crashed
2910 kernel more unstable.
2912 parkbd.port= [HW] Parallel port number the keyboard adapter is
2913 connected to, default is 0.
2915 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2916 0 for XT, 1 for AT (default is AT).
2919 parport= [HW,PPT] Specify parallel ports. 0 disables.
2920 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2921 Use 'auto' to force the driver to use any
2922 IRQ/DMA settings detected (the default is to
2923 ignore detected IRQ/DMA settings because of
2924 possible conflicts). You can specify the base
2925 address, IRQ, and DMA settings; IRQ and DMA
2926 should be numbers, or 'auto' (for using detected
2927 settings on that particular port), or 'nofifo'
2928 (to avoid using a FIFO even if it is detected).
2929 Parallel ports are assigned in the order they
2930 are specified on the command line, starting
2933 parport_init_mode= [HW,PPT]
2934 Configure VIA parallel port to operate in
2935 a specific mode. This is necessary on Pegasos
2936 computer where firmware has no options for setting
2937 up parallel port mode and sets it to spp.
2938 Currently this function knows 686a and 8231 chips.
2939 Format: [spp|ps2|epp|ecp|ecpepp]
2942 Halt all CPUs after the first oops has been printed for
2943 the specified number of seconds. This is to be used if
2944 your oopses keep scrolling off the screen.
2949 See header of drivers/block/paride/pcd.c.
2950 See also Documentation/blockdev/paride.txt.
2952 pci=option[,option...] [PCI] various PCI subsystem options:
2953 earlydump [X86] dump PCI config space before the kernel
2955 off [X86] don't probe for the PCI bus
2956 bios [X86-32] force use of PCI BIOS, don't access
2957 the hardware directly. Use this if your machine
2958 has a non-standard PCI host bridge.
2959 nobios [X86-32] disallow use of PCI BIOS, only direct
2960 hardware access methods are allowed. Use this
2961 if you experience crashes upon bootup and you
2962 suspect they are caused by the BIOS.
2963 conf1 [X86] Force use of PCI Configuration Access
2964 Mechanism 1 (config address in IO port 0xCF8,
2965 data in IO port 0xCFC, both 32-bit).
2966 conf2 [X86] Force use of PCI Configuration Access
2967 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2968 the function, IO port 0xCFA, also 8-bit, sets
2969 bus number. The config space is then accessed
2970 through ports 0xC000-0xCFFF).
2971 See http://wiki.osdev.org/PCI for more info
2972 on the configuration access mechanisms.
2973 noaer [PCIE] If the PCIEAER kernel config parameter is
2974 enabled, this kernel boot option can be used to
2975 disable the use of PCIE advanced error reporting.
2976 nodomains [PCI] Disable support for multiple PCI
2977 root domains (aka PCI segments, in ACPI-speak).
2978 nommconf [X86] Disable use of MMCONFIG for PCI
2980 check_enable_amd_mmconf [X86] check for and enable
2981 properly configured MMIO access to PCI
2982 config space on AMD family 10h CPU
2983 nomsi [MSI] If the PCI_MSI kernel config parameter is
2984 enabled, this kernel boot option can be used to
2985 disable the use of MSI interrupts system-wide.
2986 noioapicquirk [APIC] Disable all boot interrupt quirks.
2987 Safety option to keep boot IRQs enabled. This
2988 should never be necessary.
2989 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2990 primary IO-APIC for bridges that cannot disable
2991 boot IRQs. This fixes a source of spurious IRQs
2992 when the system masks IRQs.
2993 noioapicreroute [APIC] Disable workaround that uses the
2994 boot IRQ equivalent of an IRQ that connects to
2995 a chipset where boot IRQs cannot be disabled.
2996 The opposite of ioapicreroute.
2997 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2998 routing table. These calls are known to be buggy
2999 on several machines and they hang the machine
3000 when used, but on other computers it's the only
3001 way to get the interrupt routing table. Try
3002 this option if the kernel is unable to allocate
3003 IRQs or discover secondary PCI buses on your
3005 rom [X86] Assign address space to expansion ROMs.
3006 Use with caution as certain devices share
3007 address decoders between ROMs and other
3009 norom [X86] Do not assign address space to
3010 expansion ROMs that do not already have
3011 BIOS assigned address ranges.
3012 nobar [X86] Do not assign address space to the
3013 BARs that weren't assigned by the BIOS.
3014 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3015 assigned automatically to PCI devices. You can
3016 make the kernel exclude IRQs of your ISA cards
3018 pirqaddr=0xAAAAA [X86] Specify the physical address
3019 of the PIRQ table (normally generated
3020 by the BIOS) if it is outside the
3021 F0000h-100000h range.
3022 lastbus=N [X86] Scan all buses thru bus #N. Can be
3023 useful if the kernel is unable to find your
3024 secondary buses and you want to tell it
3025 explicitly which ones they are.
3026 assign-busses [X86] Always assign all PCI bus
3027 numbers ourselves, overriding
3028 whatever the firmware may have done.
3029 usepirqmask [X86] Honor the possible IRQ mask stored
3030 in the BIOS $PIR table. This is needed on
3031 some systems with broken BIOSes, notably
3032 some HP Pavilion N5400 and Omnibook XE3
3033 notebooks. This will have no effect if ACPI
3034 IRQ routing is enabled.
3035 noacpi [X86] Do not use ACPI for IRQ routing
3036 or for PCI scanning.
3037 use_crs [X86] Use PCI host bridge window information
3038 from ACPI. On BIOSes from 2008 or later, this
3039 is enabled by default. If you need to use this,
3040 please report a bug.
3041 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3042 If you need to use this, please report a bug.
3043 routeirq Do IRQ routing for all PCI devices.
3044 This is normally done in pci_enable_device(),
3045 so this option is a temporary workaround
3046 for broken drivers that don't call it.
3047 skip_isa_align [X86] do not align io start addr, so can
3048 handle more pci cards
3049 noearly [X86] Don't do any early type 1 scanning.
3050 This might help on some broken boards which
3051 machine check when some devices' config space
3052 is read. But various workarounds are disabled
3053 and some IOMMU drivers will not work.
3054 bfsort Sort PCI devices into breadth-first order.
3055 This sorting is done to get a device
3056 order compatible with older (<= 2.4) kernels.
3057 nobfsort Don't sort PCI devices into breadth-first order.
3058 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3059 tuning and use the BIOS-configured MPS defaults.
3060 pcie_bus_safe Set every device's MPS to the largest value
3061 supported by all devices below the root complex.
3062 pcie_bus_perf Set device MPS to the largest allowable MPS
3063 based on its parent bus. Also set MRRS (Max
3064 Read Request Size) to the largest supported
3065 value (no larger than the MPS that the device
3066 or bus can support) for best performance.
3067 pcie_bus_peer2peer Set every device's MPS to 128B, which
3068 every device is guaranteed to support. This
3069 configuration allows peer-to-peer DMA between
3070 any pair of devices, possibly at the cost of
3071 reduced performance. This also guarantees
3072 that hot-added devices will work.
3073 cbiosize=nn[KMG] The fixed amount of bus space which is
3074 reserved for the CardBus bridge's IO window.
3075 The default value is 256 bytes.
3076 cbmemsize=nn[KMG] The fixed amount of bus space which is
3077 reserved for the CardBus bridge's memory
3078 window. The default value is 64 megabytes.
3081 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3082 [<order of align>@]pci:<vendor>:<device>\
3083 [:<subvendor>:<subdevice>][; ...]
3084 Specifies alignment and device to reassign
3085 aligned memory resources.
3086 If <order of align> is not specified,
3087 PAGE_SIZE is used as alignment.
3088 PCI-PCI bridge can be specified, if resource
3089 windows need to be expanded.
3090 To specify the alignment for several
3091 instances of a device, the PCI vendor,
3092 device, subvendor, and subdevice may be
3093 specified, e.g., 4096@pci:8086:9c22:103c:198f
3094 ecrc= Enable/disable PCIe ECRC (transaction layer
3095 end-to-end CRC checking).
3096 bios: Use BIOS/firmware settings. This is the
3100 hpiosize=nn[KMG] The fixed amount of bus space which is
3101 reserved for hotplug bridge's IO window.
3102 Default size is 256 bytes.
3103 hpmemsize=nn[KMG] The fixed amount of bus space which is
3104 reserved for hotplug bridge's memory window.
3105 Default size is 2 megabytes.
3106 hpbussize=nn The minimum amount of additional bus numbers
3107 reserved for buses below a hotplug bridge.
3109 realloc= Enable/disable reallocating PCI bridge resources
3110 if allocations done by BIOS are too small to
3111 accommodate resources required by all child
3113 off: Turn realloc off
3115 realloc same as realloc=on
3116 noari do not use PCIe ARI.
3117 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3118 only look for one device below a PCIe downstream
3120 big_root_window Try to add a big 64bit memory window to the PCIe
3121 root complex on AMD CPUs. Some GFX hardware
3122 can resize a BAR to allow access to all VRAM.
3123 Adding the window is slightly risky (it may
3124 conflict with unreported devices), so this
3127 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3130 force Enable ASPM even on devices that claim not to support it.
3131 WARNING: Forcing ASPM on may cause system lockups.
3133 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3134 nomsi Do not use MSI for PCI Express Native Hotplug (this
3135 makes all PCIe ports use INTx for hotplug services).
3137 pcie_ports= [PCIE] PCIe ports handling:
3138 auto Ask the BIOS whether or not to use native PCIe services
3139 associated with PCIe ports (PME, hot-plug, AER). Use
3140 them only if that is allowed by the BIOS.
3141 native Use native PCIe services associated with PCIe ports
3143 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3146 pcie_port_pm= [PCIE] PCIe port power management handling:
3147 off Disable power management of all PCIe ports
3148 force Forcibly enable power management of all PCIe ports
3150 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3151 nomsi Do not use MSI for native PCIe PME signaling (this makes
3152 all PCIe root ports use INTx for all services).
3154 pcmv= [HW,PCMCIA] BadgePAD 4
3158 Keep all power-domains already enabled by bootloader on,
3159 even if no driver has claimed them. This is useful
3160 for debug and development, but should not be
3161 needed on a platform with proper driver support.
3164 See Documentation/blockdev/paride.txt.
3166 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3169 See arch/parisc/kernel/pdc_chassis.c
3171 percpu_alloc= Select which percpu first chunk allocator to use.
3172 Currently supported values are "embed" and "page".
3173 Archs may support subset or none of the selections.
3174 See comments in mm/percpu.c for details on each
3175 allocator. This parameter is primarily for debugging
3176 and performance comparison.
3179 See Documentation/blockdev/paride.txt.
3182 See Documentation/blockdev/paride.txt.
3184 pirq= [SMP,APIC] Manual mp-table setup
3185 See Documentation/x86/i386/IO-APIC.txt.
3187 plip= [PPT,NET] Parallel port network link
3188 Format: { parport<nr> | timid | 0 }
3189 See also Documentation/admin-guide/parport.rst.
3191 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3192 Override pmtimer IOPort with a hex value.
3196 Enable PNP debug messages (depends on the
3197 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3198 via /sys/module/pnp/parameters/debug. We always show
3199 current resource usage; turning this on also shows
3200 possible settings and some assignment information.
3206 { on | off | curr | res | no-curr | no-res }
3209 [ISAPNP] Exclude IRQs for the autoconfiguration
3212 [ISAPNP] Exclude DMAs for the autoconfiguration
3214 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3215 Ranges are in pairs (I/O port base and size).
3218 [ISAPNP] Exclude memory regions for the
3220 Ranges are in pairs (memory base and size).
3222 ports= [IP_VS_FTP] IPVS ftp helper module
3224 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3226 Format: <port>,<port>....
3228 powersave=off [PPC] This option disables power saving features.
3229 It specifically disables cpuidle and sets the
3230 platform machine description specific power_save
3231 function to NULL. On Idle the CPU just reduces
3234 ppc_strict_facility_enable
3235 [PPC] This option catches any kernel floating point,
3236 Altivec, VSX and SPE outside of regions specifically
3237 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3238 There is some performance impact when enabling this.
3242 Disable Hardware Transactional Memory
3244 print-fatal-signals=
3245 [KNL] debug: print fatal signals
3247 If enabled, warn about various signal handling
3248 related application anomalies: too many signals,
3249 too many POSIX.1 timers, fatal signals causing a
3252 If you hit the warning due to signal overflow,
3253 you might want to try "ulimit -i unlimited".
3257 printk.always_kmsg_dump=
3258 Trigger kmsg_dump for cases other than kernel oops or
3260 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3263 printk.devkmsg={on,off,ratelimit}
3264 Control writing to /dev/kmsg.
3265 on - unlimited logging to /dev/kmsg from userspace
3266 off - logging to /dev/kmsg disabled
3267 ratelimit - ratelimit the logging
3270 printk.time= Show timing data prefixed to each printk message line
3271 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3273 processor.max_cstate= [HW,ACPI]
3274 Limit processor to maximum C-state
3275 max_cstate=9 overrides any DMI blacklist limit.
3277 processor.nocst [HW,ACPI]
3278 Ignore the _CST method to determine C-states,
3279 instead using the legacy FADT method
3281 profile= [KNL] Enable kernel profiling via /proc/profile
3282 Format: [<profiletype>,]<number>
3283 Param: <profiletype>: "schedule", "sleep", or "kvm"
3284 [defaults to kernel profiling]
3285 Param: "schedule" - profile schedule points.
3286 Param: "sleep" - profile D-state sleeping (millisecs).
3287 Requires CONFIG_SCHEDSTATS
3288 Param: "kvm" - profile VM exits.
3289 Param: <number> - step/bucket size as a power of 2 for
3290 statistical time based profiling.
3292 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3294 See Documentation/blockdev/ramdisk.txt.
3296 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3297 probe for; one of (bare|imps|exps|lifebook|any).
3298 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3300 psmouse.resetafter= [HW,MOUSE]
3301 Try to reset the device after so many bad packets
3304 [HW,MOUSE] Set desired mouse resolution, in dpi.
3305 psmouse.smartscroll=
3306 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3307 0 = disabled, 1 = enabled (default).
3309 pstore.backend= Specify the name of the pstore backend to use
3312 See Documentation/blockdev/paride.txt.
3314 pti= [X86_64] Control Page Table Isolation of user and
3315 kernel address spaces. Disabling this feature
3316 removes hardening, but improves performance of
3317 system calls and interrupts.
3319 on - unconditionally enable
3320 off - unconditionally disable
3321 auto - kernel detects whether your CPU model is
3322 vulnerable to issues that PTI mitigates
3324 Not specifying this option is equivalent to pti=auto.
3327 Equivalent to pti=off
3330 [KNL] Number of legacy pty's. Overwrites compiled-in
3333 quiet [KNL] Disable most log messages
3338 See Documentation/admin-guide/md.rst.
3340 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3341 See Documentation/blockdev/ramdisk.txt.
3343 ras=option[,option,...] [KNL] RAS-specific options
3346 Disable the Correctable Errors Collector,
3347 see CONFIG_RAS_CEC help text.
3350 The argument is a cpu list, as described above.
3352 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3353 the specified list of CPUs to be no-callback CPUs.
3354 Invocation of these CPUs' RCU callbacks will
3355 be offloaded to "rcuox/N" kthreads created for
3356 that purpose, where "x" is "b" for RCU-bh, "p"
3357 for RCU-preempt, and "s" for RCU-sched, and "N"
3358 is the CPU number. This reduces OS jitter on the
3359 offloaded CPUs, which can be useful for HPC and
3360 real-time workloads. It can also improve energy
3361 efficiency for asymmetric multiprocessors.
3364 Rather than requiring that offloaded CPUs
3365 (specified by rcu_nocbs= above) explicitly
3366 awaken the corresponding "rcuoN" kthreads,
3367 make these kthreads poll for callbacks.
3368 This improves the real-time response for the
3369 offloaded CPUs by relieving them of the need to
3370 wake up the corresponding kthread, but degrades
3371 energy efficiency by requiring that the kthreads
3372 periodically wake up to do the polling.
3374 rcutree.blimit= [KNL]
3375 Set maximum number of finished RCU callbacks to
3376 process in one batch.
3378 rcutree.dump_tree= [KNL]
3379 Dump the structure of the rcu_node combining tree
3380 out at early boot. This is used for diagnostic
3381 purposes, to verify correct tree setup.
3383 rcutree.gp_cleanup_delay= [KNL]
3384 Set the number of jiffies to delay each step of
3385 RCU grace-period cleanup.
3387 rcutree.gp_init_delay= [KNL]
3388 Set the number of jiffies to delay each step of
3389 RCU grace-period initialization.
3391 rcutree.gp_preinit_delay= [KNL]
3392 Set the number of jiffies to delay each step of
3393 RCU grace-period pre-initialization, that is,
3394 the propagation of recent CPU-hotplug changes up
3395 the rcu_node combining tree.
3397 rcutree.rcu_fanout_exact= [KNL]
3398 Disable autobalancing of the rcu_node combining
3399 tree. This is used by rcutorture, and might
3400 possibly be useful for architectures having high
3401 cache-to-cache transfer latencies.
3403 rcutree.rcu_fanout_leaf= [KNL]
3404 Change the number of CPUs assigned to each
3405 leaf rcu_node structure. Useful for very
3406 large systems, which will choose the value 64,
3407 and for NUMA systems with large remote-access
3408 latencies, which will choose a value aligned
3409 with the appropriate hardware boundaries.
3411 rcutree.jiffies_till_sched_qs= [KNL]
3412 Set required age in jiffies for a
3413 given grace period before RCU starts
3414 soliciting quiescent-state help from
3415 rcu_note_context_switch().
3417 rcutree.jiffies_till_first_fqs= [KNL]
3418 Set delay from grace-period initialization to
3419 first attempt to force quiescent states.
3420 Units are jiffies, minimum value is zero,
3421 and maximum value is HZ.
3423 rcutree.jiffies_till_next_fqs= [KNL]
3424 Set delay between subsequent attempts to force
3425 quiescent states. Units are jiffies, minimum
3426 value is one, and maximum value is HZ.
3428 rcutree.kthread_prio= [KNL,BOOT]
3429 Set the SCHED_FIFO priority of the RCU per-CPU
3430 kthreads (rcuc/N). This value is also used for
3431 the priority of the RCU boost threads (rcub/N)
3432 and for the RCU grace-period kthreads (rcu_bh,
3433 rcu_preempt, and rcu_sched). If RCU_BOOST is
3434 set, valid values are 1-99 and the default is 1
3435 (the least-favored priority). Otherwise, when
3436 RCU_BOOST is not set, valid values are 0-99 and
3437 the default is zero (non-realtime operation).
3439 rcutree.rcu_nocb_leader_stride= [KNL]
3440 Set the number of NOCB kthread groups, which
3441 defaults to the square root of the number of
3442 CPUs. Larger numbers reduces the wakeup overhead
3443 on the per-CPU grace-period kthreads, but increases
3444 that same overhead on each group's leader.
3446 rcutree.qhimark= [KNL]
3447 Set threshold of queued RCU callbacks beyond which
3448 batch limiting is disabled.
3450 rcutree.qlowmark= [KNL]
3451 Set threshold of queued RCU callbacks below which
3452 batch limiting is re-enabled.
3454 rcutree.rcu_idle_gp_delay= [KNL]
3455 Set wakeup interval for idle CPUs that have
3456 RCU callbacks (RCU_FAST_NO_HZ=y).
3458 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3459 Set wakeup interval for idle CPUs that have
3460 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3461 Lazy RCU callbacks are those which RCU can
3462 prove do nothing more than free memory.
3464 rcutree.rcu_kick_kthreads= [KNL]
3465 Cause the grace-period kthread to get an extra
3466 wake_up() if it sleeps three times longer than
3467 it should at force-quiescent-state time.
3468 This wake_up() will be accompanied by a
3469 WARN_ONCE() splat and an ftrace_dump().
3471 rcuperf.gp_async= [KNL]
3472 Measure performance of asynchronous
3473 grace-period primitives such as call_rcu().
3475 rcuperf.gp_async_max= [KNL]
3476 Specify the maximum number of outstanding
3477 callbacks per writer thread. When a writer
3478 thread exceeds this limit, it invokes the
3479 corresponding flavor of rcu_barrier() to allow
3480 previously posted callbacks to drain.
3482 rcuperf.gp_exp= [KNL]
3483 Measure performance of expedited synchronous
3484 grace-period primitives.
3486 rcuperf.holdoff= [KNL]
3487 Set test-start holdoff period. The purpose of
3488 this parameter is to delay the start of the
3489 test until boot completes in order to avoid
3492 rcuperf.nreaders= [KNL]
3493 Set number of RCU readers. The value -1 selects
3494 N, where N is the number of CPUs. A value
3495 "n" less than -1 selects N-n+1, where N is again
3496 the number of CPUs. For example, -2 selects N
3497 (the number of CPUs), -3 selects N+1, and so on.
3498 A value of "n" less than or equal to -N selects
3501 rcuperf.nwriters= [KNL]
3502 Set number of RCU writers. The values operate
3503 the same as for rcuperf.nreaders.
3504 N, where N is the number of CPUs
3506 rcuperf.perf_type= [KNL]
3507 Specify the RCU implementation to test.
3509 rcuperf.shutdown= [KNL]
3510 Shut the system down after performance tests
3511 complete. This is useful for hands-off automated
3514 rcuperf.verbose= [KNL]
3515 Enable additional printk() statements.
3517 rcuperf.writer_holdoff= [KNL]
3518 Write-side holdoff between grace periods,
3519 in microseconds. The default of zero says
3522 rcutorture.cbflood_inter_holdoff= [KNL]
3523 Set holdoff time (jiffies) between successive
3524 callback-flood tests.
3526 rcutorture.cbflood_intra_holdoff= [KNL]
3527 Set holdoff time (jiffies) between successive
3528 bursts of callbacks within a given callback-flood
3531 rcutorture.cbflood_n_burst= [KNL]
3532 Set the number of bursts making up a given
3533 callback-flood test. Set this to zero to
3534 disable callback-flood testing.
3536 rcutorture.cbflood_n_per_burst= [KNL]
3537 Set the number of callbacks to be registered
3538 in a given burst of a callback-flood test.
3540 rcutorture.fqs_duration= [KNL]
3541 Set duration of force_quiescent_state bursts
3544 rcutorture.fqs_holdoff= [KNL]
3545 Set holdoff time within force_quiescent_state bursts
3548 rcutorture.fqs_stutter= [KNL]
3549 Set wait time between force_quiescent_state bursts
3552 rcutorture.gp_cond= [KNL]
3553 Use conditional/asynchronous update-side
3554 primitives, if available.
3556 rcutorture.gp_exp= [KNL]
3557 Use expedited update-side primitives, if available.
3559 rcutorture.gp_normal= [KNL]
3560 Use normal (non-expedited) asynchronous
3561 update-side primitives, if available.
3563 rcutorture.gp_sync= [KNL]
3564 Use normal (non-expedited) synchronous
3565 update-side primitives, if available. If all
3566 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3567 rcutorture.gp_normal=, and rcutorture.gp_sync=
3568 are zero, rcutorture acts as if is interpreted
3569 they are all non-zero.
3571 rcutorture.n_barrier_cbs= [KNL]
3572 Set callbacks/threads for rcu_barrier() testing.
3574 rcutorture.nfakewriters= [KNL]
3575 Set number of concurrent RCU writers. These just
3576 stress RCU, they don't participate in the actual
3577 test, hence the "fake".
3579 rcutorture.nreaders= [KNL]
3580 Set number of RCU readers. The value -1 selects
3581 N-1, where N is the number of CPUs. A value
3582 "n" less than -1 selects N-n-2, where N is again
3583 the number of CPUs. For example, -2 selects N
3584 (the number of CPUs), -3 selects N+1, and so on.
3586 rcutorture.object_debug= [KNL]
3587 Enable debug-object double-call_rcu() testing.
3589 rcutorture.onoff_holdoff= [KNL]
3590 Set time (s) after boot for CPU-hotplug testing.
3592 rcutorture.onoff_interval= [KNL]
3593 Set time (s) between CPU-hotplug operations, or
3594 zero to disable CPU-hotplug testing.
3596 rcutorture.shuffle_interval= [KNL]
3597 Set task-shuffle interval (s). Shuffling tasks
3598 allows some CPUs to go into dyntick-idle mode
3599 during the rcutorture test.
3601 rcutorture.shutdown_secs= [KNL]
3602 Set time (s) after boot system shutdown. This
3603 is useful for hands-off automated testing.
3605 rcutorture.stall_cpu= [KNL]
3606 Duration of CPU stall (s) to test RCU CPU stall
3607 warnings, zero to disable.
3609 rcutorture.stall_cpu_holdoff= [KNL]
3610 Time to wait (s) after boot before inducing stall.
3612 rcutorture.stall_cpu_irqsoff= [KNL]
3613 Disable interrupts while stalling if set.
3615 rcutorture.stat_interval= [KNL]
3616 Time (s) between statistics printk()s.
3618 rcutorture.stutter= [KNL]
3619 Time (s) to stutter testing, for example, specifying
3620 five seconds causes the test to run for five seconds,
3621 wait for five seconds, and so on. This tests RCU's
3622 ability to transition abruptly to and from idle.
3624 rcutorture.test_boost= [KNL]
3625 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3626 "Maybe" means test if the RCU implementation
3627 under test support RCU priority boosting.
3629 rcutorture.test_boost_duration= [KNL]
3630 Duration (s) of each individual boost test.
3632 rcutorture.test_boost_interval= [KNL]
3633 Interval (s) between each boost test.
3635 rcutorture.test_no_idle_hz= [KNL]
3636 Test RCU's dyntick-idle handling. See also the
3637 rcutorture.shuffle_interval parameter.
3639 rcutorture.torture_type= [KNL]
3640 Specify the RCU implementation to test.
3642 rcutorture.verbose= [KNL]
3643 Enable additional printk() statements.
3645 rcupdate.rcu_cpu_stall_suppress= [KNL]
3646 Suppress RCU CPU stall warning messages.
3648 rcupdate.rcu_cpu_stall_timeout= [KNL]
3649 Set timeout for RCU CPU stall warning messages.
3651 rcupdate.rcu_expedited= [KNL]
3652 Use expedited grace-period primitives, for
3653 example, synchronize_rcu_expedited() instead
3654 of synchronize_rcu(). This reduces latency,
3655 but can increase CPU utilization, degrade
3656 real-time latency, and degrade energy efficiency.
3657 No effect on CONFIG_TINY_RCU kernels.
3659 rcupdate.rcu_normal= [KNL]
3660 Use only normal grace-period primitives,
3661 for example, synchronize_rcu() instead of
3662 synchronize_rcu_expedited(). This improves
3663 real-time latency, CPU utilization, and
3664 energy efficiency, but can expose users to
3665 increased grace-period latency. This parameter
3666 overrides rcupdate.rcu_expedited. No effect on
3667 CONFIG_TINY_RCU kernels.
3669 rcupdate.rcu_normal_after_boot= [KNL]
3670 Once boot has completed (that is, after
3671 rcu_end_inkernel_boot() has been invoked), use
3672 only normal grace-period primitives. No effect
3673 on CONFIG_TINY_RCU kernels.
3675 rcupdate.rcu_task_stall_timeout= [KNL]
3676 Set timeout in jiffies for RCU task stall warning
3677 messages. Disable with a value less than or equal
3680 rcupdate.rcu_self_test= [KNL]
3681 Run the RCU early boot self tests
3683 rcupdate.rcu_self_test_bh= [KNL]
3684 Run the RCU bh early boot self tests
3686 rcupdate.rcu_self_test_sched= [KNL]
3687 Run the RCU sched early boot self tests
3691 Run specified binary instead of /init from the ramdisk,
3692 used for early userspace startup. See initrd.
3695 Turn on/off individual RDT features. List is:
3696 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
3698 E.g. to turn on cmt and turn off mba use:
3702 Format (x86 or x86_64):
3703 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3705 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3707 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3708 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3709 reboot_force is either force or not specified,
3710 reboot_cpu is s[mp]#### with #### being the processor
3711 to be used for rebooting.
3714 [KNL, SMP] Set scheduler's default relax_domain_level.
3715 See Documentation/cgroup-v1/cpusets.txt.
3717 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
3718 Format: <base1>,<size1>[,<base2>,<size2>,...]
3719 Reserve I/O ports or memory so the kernel won't use
3720 them. If <base> is less than 0x10000, the region
3721 is assumed to be I/O ports; otherwise it is memory.
3723 reservetop= [X86-32]
3725 Reserves a hole at the top of the kernel virtual
3730 Set the amount of memory to reserve for BIOS at
3731 the bottom of the address space.
3733 reset_devices [KNL] Force drivers to reset the underlying device
3734 during initialization.
3737 Specify the partition device for software suspend
3739 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3741 resume_offset= [SWSUSP]
3742 Specify the offset from the beginning of the partition
3743 given by "resume=" at which the swap header is located,
3744 in <PAGE_SIZE> units (needed only for swap files).
3745 See Documentation/power/swsusp-and-swap-files.txt
3747 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3748 read the resume files
3750 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3751 Useful for devices that are detected asynchronously
3752 (e.g. USB and MMC devices).
3754 hibernate= [HIBERNATION]
3755 noresume Don't check if there's a hibernation image
3756 present during boot.
3757 nocompress Don't compress/decompress hibernation images.
3758 no Disable hibernation and resume.
3759 protect_image Turn on image protection during restoration
3760 (that will set all pages holding image data
3761 during restoration read-only).
3763 retain_initrd [RAM] Keep initrd memory after extraction
3765 rfkill.default_state=
3766 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3767 etc. communication is blocked by default.
3770 rfkill.master_switch_mode=
3771 0 The "airplane mode" button does nothing.
3772 1 The "airplane mode" button toggles between everything
3773 blocked and the previous configuration.
3774 2 The "airplane mode" button toggles between everything
3775 blocked and everything unblocked.
3777 rhash_entries= [KNL,NET]
3778 Set number of hash buckets for route cache
3781 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
3784 ro [KNL] Mount root device read-only on boot
3787 on Mark read-only kernel memory as read-only (default).
3788 off Leave read-only kernel memory writable for debugging.
3791 Enable the uart passthrough on the designated usb port
3792 on Rockchip SoCs. When active, the signals of the
3793 debug-uart get routed to the D+ and D- pins of the usb
3794 port and the regular usb controller gets disabled.
3796 root= [KNL] Root filesystem
3797 See name_to_dev_t comment in init/do_mounts.c.
3799 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3800 mount the root filesystem
3802 rootflags= [KNL] Set root filesystem mount option string
3804 rootfstype= [KNL] Set root filesystem type
3806 rootwait [KNL] Wait (indefinitely) for root device to show up.
3807 Useful for devices that are detected asynchronously
3808 (e.g. USB and MMC devices).
3810 rproc_mem=nn[KMG][@address]
3811 [KNL,ARM,CMA] Remoteproc physical memory block.
3812 Memory area to be used by remote processor image,
3815 rw [KNL] Mount root device read-write on boot
3817 S [KNL] Run init in single mode
3819 s390_iommu= [HW,S390]
3820 Set s390 IOTLB flushing mode
3822 With strict flushing every unmap operation will result in
3823 an IOTLB flush. Default is lazy flushing before reuse,
3827 See drivers/net/irda/sa1100_ir.c.
3829 sbni= [NET] Granch SBNI12 leased line adapter
3831 sched_debug [KNL] Enables verbose scheduler debug messages.
3833 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3834 Allowed values are enable and disable. This feature
3835 incurs a small amount of overhead in the scheduler
3836 but is useful for debugging and performance tuning.
3838 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3839 xtime_lock contention on larger systems, and/or RCU lock
3840 contention on all systems with CONFIG_MAXSMP set.
3841 Format: { "0" | "1" }
3842 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3844 Note: increases power consumption, thus should only be
3845 enabled if running jitter sensitive (HPC/RT) workloads.
3847 security= [SECURITY] Choose a security module to enable at boot.
3848 If this boot parameter is not specified, only the first
3849 security module asking for security registration will be
3850 loaded. An invalid security module name will be treated
3851 as if no module has been chosen.
3853 selinux= [SELINUX] Disable or enable SELinux at boot time.
3854 Format: { "0" | "1" }
3855 See security/selinux/Kconfig help text.
3858 Default value is set via kernel config option.
3859 If enabled at boot time, /selinux/disable can be used
3860 later to disable prior to initial policy load.
3862 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3863 Format: { "0" | "1" }
3864 See security/apparmor/Kconfig help text
3867 Default value is set via kernel config option.
3869 serialnumber [BUGS=X86-32]
3872 Maximal number of shapers.
3880 Disable merging of slabs with similar size. May be
3881 necessary if there is some reason to distinguish
3882 allocs to different slabs, especially in hardened
3883 environments where the risk of heap overflows and
3884 layout control by attackers can usually be
3885 frustrated by disabling merging. This will reduce
3886 most of the exposure of a heap attack to a single
3887 cache (risks via metadata attacks are mostly
3888 unchanged). Debug options disable merging on their
3890 For more information see Documentation/vm/slub.txt.
3892 slab_max_order= [MM, SLAB]
3893 Determines the maximum allowed order for slabs.
3894 A high setting may cause OOMs due to memory
3895 fragmentation. Defaults to 1 for systems with
3896 more than 32MB of RAM, 0 otherwise.
3898 slub_debug[=options[,slabs]] [MM, SLUB]
3899 Enabling slub_debug allows one to determine the
3900 culprit if slab objects become corrupted. Enabling
3901 slub_debug can create guard zones around objects and
3902 may poison objects when not in use. Also tracks the
3903 last alloc / free. For more information see
3904 Documentation/vm/slub.txt.
3906 slub_memcg_sysfs= [MM, SLUB]
3907 Determines whether to enable sysfs directories for
3908 memory cgroup sub-caches. 1 to enable, 0 to disable.
3909 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
3910 Enabling this can lead to a very high number of debug
3911 directories and files being created under
3914 slub_max_order= [MM, SLUB]
3915 Determines the maximum allowed order for slabs.
3916 A high setting may cause OOMs due to memory
3917 fragmentation. For more information see
3918 Documentation/vm/slub.txt.
3920 slub_min_objects= [MM, SLUB]
3921 The minimum number of objects per slab. SLUB will
3922 increase the slab order up to slub_max_order to
3923 generate a sufficiently large slab able to contain
3924 the number of objects indicated. The higher the number
3925 of objects the smaller the overhead of tracking slabs
3926 and the less frequently locks need to be acquired.
3927 For more information see Documentation/vm/slub.txt.
3929 slub_min_order= [MM, SLUB]
3930 Determines the minimum page order for slabs. Must be
3931 lower than slub_max_order.
3932 For more information see Documentation/vm/slub.txt.
3934 slub_nomerge [MM, SLUB]
3935 Same with slab_nomerge. This is supported for legacy.
3936 See slab_nomerge for more information.
3939 Format: <io1>[,<io2>[,...,<io8>]]
3941 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3942 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3943 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3944 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3945 smsc-ircc2.ircc_irq= [HW] IRQ line
3946 smsc-ircc2.ircc_dma= [HW] DMA channel
3947 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3948 0: Toshiba Satellite 1800 (GP data pin select)
3949 1: Fast pin select (default)
3952 smt [KNL,S390] Set the maximum number of threads (logical
3953 CPUs) to use per physical CPU on systems capable of
3954 symmetric multithreading (SMT). Will be capped to the
3955 actual hardware limit.
3957 Default: -1 (no limit)
3960 [KNL] Should the soft-lockup detector generate panics.
3963 A nonzero value instructs the soft-lockup detector
3964 to panic the machine when a soft-lockup occurs. This
3965 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
3966 which is the respective build-time switch to that
3969 softlockup_all_cpu_backtrace=
3970 [KNL] Should the soft-lockup detector generate
3971 backtraces on all cpus.
3974 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3975 See Documentation/laptops/sonypi.txt
3977 spectre_v2= [X86] Control mitigation of Spectre variant 2
3978 (indirect branch speculation) vulnerability.
3980 on - unconditionally enable
3981 off - unconditionally disable
3982 auto - kernel detects whether your CPU model is
3985 Selecting 'on' will, and 'auto' may, choose a
3986 mitigation method at run time according to the
3987 CPU, the available microcode, the setting of the
3988 CONFIG_RETPOLINE configuration option, and the
3989 compiler with which the kernel was built.
3991 Specific mitigations can also be selected manually:
3993 retpoline - replace indirect branches
3994 retpoline,generic - google's original retpoline
3995 retpoline,amd - AMD-specific minimal thunk
3997 Not specifying this option is equivalent to
4000 spia_io_base= [HW,MTD]
4005 srcutree.counter_wrap_check [KNL]
4006 Specifies how frequently to check for
4007 grace-period sequence counter wrap for the
4008 srcu_data structure's ->srcu_gp_seq_needed field.
4009 The greater the number of bits set in this kernel
4010 parameter, the less frequently counter wrap will
4011 be checked for. Note that the bottom two bits
4014 srcutree.exp_holdoff [KNL]
4015 Specifies how many nanoseconds must elapse
4016 since the end of the last SRCU grace period for
4017 a given srcu_struct until the next normal SRCU
4018 grace period will be considered for automatic
4019 expediting. Set to zero to disable automatic
4022 stack_guard_gap= [MM]
4023 override the default stack gap protection. The value
4024 is in page units and it defines how many pages prior
4025 to (for stacks growing down) resp. after (for stacks
4026 growing up) the main stack are reserved for no other
4027 mapping. Default value is 256 pages.
4030 Enabled the stack tracer on boot up.
4032 stacktrace_filter=[function-list]
4033 [FTRACE] Limit the functions that the stack tracer
4034 will trace at boot up. function-list is a comma separated
4035 list of functions. This list can be changed at run
4036 time by the stack_trace_filter file in the debugfs
4037 tracing directory. Note, this enables stack tracing
4038 and the stacktrace above is not needed.
4042 Set the STI (builtin display/keyboard on the HP-PARISC
4043 machines) console (graphic card) which should be used
4044 as the initial boot-console.
4045 See also comment in drivers/video/console/sticore.c.
4048 See comment in drivers/video/console/sticore.c.
4051 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4053 sunrpc.min_resvport=
4054 sunrpc.max_resvport=
4056 SunRPC servers often require that client requests
4057 originate from a privileged port (i.e. a port in the
4058 range 0 < portnr < 1024).
4059 An administrator who wishes to reserve some of these
4060 ports for other uses may adjust the range that the
4061 kernel's sunrpc client considers to be privileged
4062 using these two parameters to set the minimum and
4063 maximum port values.
4065 sunrpc.svc_rpc_per_connection_limit=
4067 Limit the number of requests that the server will
4068 process in parallel from a single connection.
4069 The default value is 0 (no limit).
4073 Control how the NFS server code allocates CPUs to
4074 service thread pools. Depending on how many NICs
4075 you have and where their interrupts are bound, this
4076 option will affect which CPUs will do NFS serving.
4077 Note: this parameter cannot be changed while the
4078 NFS server is running.
4080 auto the server chooses an appropriate mode
4081 automatically using heuristics
4082 global a single global pool contains all CPUs
4083 percpu one pool for each CPU
4084 pernode one pool for each NUMA node (equivalent
4085 to global on non-NUMA machines)
4087 sunrpc.tcp_slot_table_entries=
4088 sunrpc.udp_slot_table_entries=
4090 Sets the upper limit on the number of simultaneous
4091 RPC calls that can be sent from the client to a
4092 server. Increasing these values may allow you to
4093 improve throughput, but will also increase the
4094 amount of memory reserved for use by the client.
4096 suspend.pm_test_delay=
4098 Sets the number of seconds to remain in a suspend test
4099 mode before resuming the system (see
4100 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4101 is set. Default value is 5.
4104 [KNL] Enable accounting of swap in memory resource
4105 controller if no parameter or 1 is given or disable
4106 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4108 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4109 Format: { <int> | force | noforce }
4110 <int> -- Number of I/O TLB slabs
4111 force -- force using of bounce buffers even if they
4112 wouldn't be automatically used by the kernel
4113 noforce -- Never use bounce buffers (for debugging)
4117 sysfs.deprecated=0|1 [KNL]
4118 Enable/disable old style sysfs layout for old udev
4119 on older distributions. When this option is enabled
4120 very new udev will not work anymore. When this option
4121 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4122 in older udev will not work anymore.
4123 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4124 the kernel configuration.
4126 sysrq_always_enabled
4128 Ignore sysrq setting - this boot parameter will
4129 neutralize any effect of /proc/sys/kernel/sysrq.
4130 Useful for debugging.
4132 tcpmhash_entries= [KNL,NET]
4133 Set the number of tcp_metrics_hash slots.
4134 Default value is 8192 or 16384 depending on total
4135 ram pages. This is used to specify the TCP metrics
4136 cache size. See Documentation/networking/ip-sysctl.txt
4137 "tcp_no_metrics_save" section for more details.
4141 test_suspend= [SUSPEND][,N]
4142 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4143 standby suspend) or "freeze" (for suspend type freeze)
4144 as the system sleep state during system startup with
4145 the optional capability to repeat N number of times.
4146 The system is woken from this state using a
4147 wakeup-capable RTC alarm.
4149 thash_entries= [KNL,NET]
4150 Set number of hash buckets for TCP connection
4152 thermal.act= [HW,ACPI]
4153 -1: disable all active trip points in all thermal zones
4154 <degrees C>: override all lowest active trip points
4156 thermal.crt= [HW,ACPI]
4157 -1: disable all critical trip points in all thermal zones
4158 <degrees C>: override all critical trip points
4160 thermal.nocrt= [HW,ACPI]
4161 Set to disable actions on ACPI thermal zone
4162 critical and hot trip points.
4164 thermal.off= [HW,ACPI]
4165 1: disable ACPI thermal control
4167 thermal.psv= [HW,ACPI]
4168 -1: disable all passive trip points
4169 <degrees C>: override all passive trip points to this
4172 thermal.tzp= [HW,ACPI]
4173 Specify global default ACPI thermal zone polling rate
4174 <deci-seconds>: poll all this frequency
4175 0: no polling (default)
4178 Force threading of all interrupt handlers except those
4179 marked explicitly IRQF_NO_THREAD.
4182 Enable the Transcendent memory driver if built-in.
4184 tmem.cleancache=0|1 [KNL, XEN]
4185 Default is on (1). Disable the usage of the cleancache
4186 API to send anonymous pages to the hypervisor.
4188 tmem.frontswap=0|1 [KNL, XEN]
4189 Default is on (1). Disable the usage of the frontswap
4190 API to send swap pages to the hypervisor. If disabled
4191 the selfballooning and selfshrinking are force disabled.
4193 tmem.selfballooning=0|1 [KNL, XEN]
4194 Default is on (1). Disable the driving of swap pages
4197 tmem.selfshrinking=0|1 [KNL, XEN]
4198 Default is on (1). Partial swapoff that immediately
4199 transfers pages from Xen hypervisor back to the
4200 kernel based on different criteria.
4204 Specify if the kernel should make use of the cpu
4205 topology information if the hardware supports this.
4206 The scheduler will make use of this information and
4207 e.g. base its process migration decisions on it.
4210 topology_updates= [KNL, PPC, NUMA]
4212 Specify if the kernel should ignore (off)
4213 topology updates sent by the hypervisor to this
4218 tpm_suspend_pcr=[HW,TPM]
4219 Format: integer pcr id
4220 Specify that at suspend time, the tpm driver
4221 should extend the specified pcr with zeros,
4222 as a workaround for some chips which fail to
4223 flush the last written pcr on TPM_SaveState.
4224 This will guarantee that all the other pcrs
4227 trace_buf_size=nn[KMG]
4228 [FTRACE] will set tracing buffer size on each cpu.
4230 trace_event=[event-list]
4231 [FTRACE] Set and start specified trace events in order
4232 to facilitate early boot debugging. The event-list is a
4233 comma separated list of trace events to enable. See
4234 also Documentation/trace/events.txt
4236 trace_options=[option-list]
4237 [FTRACE] Enable or disable tracer options at boot.
4238 The option-list is a comma delimited list of options
4239 that can be enabled or disabled just as if you were
4240 to echo the option name into
4242 /sys/kernel/debug/tracing/trace_options
4244 For example, to enable stacktrace option (to dump the
4245 stack trace of each event), add to the command line:
4247 trace_options=stacktrace
4249 See also Documentation/trace/ftrace.txt "trace options"
4253 Have the tracepoints sent to printk as well as the
4254 tracing ring buffer. This is useful for early boot up
4255 where the system hangs or reboots and does not give the
4256 option for reading the tracing buffer or performing a
4257 ftrace_dump_on_oops.
4259 To turn off having tracepoints sent to printk,
4260 echo 0 > /proc/sys/kernel/tracepoint_printk
4261 Note, echoing 1 into this file without the
4262 tracepoint_printk kernel cmdline option has no effect.
4266 Having tracepoints sent to printk() and activating high
4267 frequency tracepoints such as irq or sched, can cause
4268 the system to live lock.
4271 [FTRACE] enable this option to disable tracing when a
4272 warning is hit. This turns off "tracing_on". Tracing can
4273 be enabled again by echoing '1' into the "tracing_on"
4274 file located in /sys/kernel/debug/tracing/
4276 This option is useful, as it disables the trace before
4277 the WARNING dump is called, which prevents the trace to
4278 be filled with content caused by the warning output.
4280 This option can also be set at run time via the sysctl
4281 option: kernel/traceoff_on_warning
4283 transparent_hugepage=
4285 Format: [always|madvise|never]
4286 Can be used to control the default behavior of the system
4287 with respect to transparent hugepages.
4288 See Documentation/vm/transhuge.txt for more details.
4290 tsc= Disable clocksource stability checks for TSC.
4292 [x86] reliable: mark tsc clocksource as reliable, this
4293 disables clocksource verification at runtime, as well
4294 as the stability checks done at bootup. Used to enable
4295 high-resolution timer mode on older hardware, and in
4296 virtualized environment.
4297 [x86] noirqtime: Do not use TSC to do irq accounting.
4298 Used to run time disable IRQ_TIME_ACCOUNTING on any
4299 platforms where RDTSC is slow and this accounting
4301 [x86] unstable: mark the TSC clocksource as unstable, this
4302 marks the TSC unconditionally unstable at bootup and
4303 avoids any further wobbles once the TSC watchdog notices.
4305 turbografx.map[2|3]= [HW,JOY]
4306 TurboGraFX parallel port interface
4308 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4309 See also Documentation/input/devices/joystick-parport.rst
4311 udbg-immortal [PPC] When debugging early kernel crashes that
4312 happen after console_init() and before a proper
4313 console driver takes over, this boot options might
4314 help "seeing" what's going on.
4316 uhash_entries= [KNL,NET]
4317 Set number of hash buckets for UDP/UDP-Lite connections
4320 [USB] Ignore overcurrent events (default N).
4321 Some badly-designed motherboards generate lots of
4322 bogus events, for ports that aren't wired to
4323 anything. Set this parameter to avoid log spamming.
4324 Note that genuine overcurrent events won't be
4328 [X86] Cause panic on unknown NMI.
4330 usbcore.authorized_default=
4331 [USB] Default USB device authorization:
4332 (default -1 = authorized except for wireless USB,
4333 0 = not authorized, 1 = authorized)
4335 usbcore.autosuspend=
4336 [USB] The autosuspend time delay (in seconds) used
4337 for newly-detected USB devices (default 2). This
4338 is the time required before an idle device will be
4339 autosuspended. Devices for which the delay is set
4340 to a negative value won't be autosuspended at all.
4342 usbcore.usbfs_snoop=
4343 [USB] Set to log all usbfs traffic (default 0 = off).
4345 usbcore.usbfs_snoop_max=
4346 [USB] Maximum number of bytes to snoop in each URB
4349 usbcore.blinkenlights=
4350 [USB] Set to cycle leds on hubs (default 0 = off).
4352 usbcore.old_scheme_first=
4353 [USB] Start with the old device initialization
4354 scheme (default 0 = off).
4356 usbcore.usbfs_memory_mb=
4357 [USB] Memory limit (in MB) for buffers allocated by
4358 usbfs (default = 16, 0 = max = 2047).
4360 usbcore.use_both_schemes=
4361 [USB] Try the other device initialization scheme
4362 if the first one fails (default 1 = enabled).
4364 usbcore.initial_descriptor_timeout=
4365 [USB] Specifies timeout for the initial 64-byte
4366 USB_REQ_GET_DESCRIPTOR request in milliseconds
4367 (default 5000 = 5.0 seconds).
4369 usbcore.nousb [USB] Disable the USB subsystem
4372 [USBHID] The interval which mice are to be polled at.
4375 [USBHID] The interval which joysticks are to be polled at.
4377 usb-storage.delay_use=
4378 [UMS] The delay in seconds before a new device is
4379 scanned for Logical Units (default 1).
4382 [UMS] A list of quirks entries to supplement or
4383 override the built-in unusual_devs list. List
4384 entries are separated by commas. Each entry has
4385 the form VID:PID:Flags where VID and PID are Vendor
4386 and Product ID values (4-digit hex numbers) and
4387 Flags is a set of characters, each corresponding
4388 to a common usb-storage quirk flag as follows:
4389 a = SANE_SENSE (collect more than 18 bytes
4391 b = BAD_SENSE (don't collect more than 18
4392 bytes of sense data);
4393 c = FIX_CAPACITY (decrease the reported
4394 device capacity by one sector);
4395 d = NO_READ_DISC_INFO (don't use
4396 READ_DISC_INFO command);
4397 e = NO_READ_CAPACITY_16 (don't use
4398 READ_CAPACITY_16 command);
4399 f = NO_REPORT_OPCODES (don't use report opcodes
4401 g = MAX_SECTORS_240 (don't transfer more than
4402 240 sectors at a time, uas only);
4403 h = CAPACITY_HEURISTICS (decrease the
4404 reported device capacity by one
4405 sector if the number is odd);
4406 i = IGNORE_DEVICE (don't bind to this
4408 j = NO_REPORT_LUNS (don't use report luns
4410 l = NOT_LOCKABLE (don't try to lock and
4411 unlock ejectable media);
4412 m = MAX_SECTORS_64 (don't transfer more
4413 than 64 sectors = 32 KB at a time);
4414 n = INITIAL_READ10 (force a retry of the
4415 initial READ(10) command);
4416 o = CAPACITY_OK (accept the capacity
4417 reported by the device);
4418 p = WRITE_CACHE (the device cache is ON
4420 r = IGNORE_RESIDUE (the device reports
4421 bogus residue values);
4422 s = SINGLE_LUN (the device has only one
4424 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4425 commands, uas only);
4426 u = IGNORE_UAS (don't bind to the uas driver);
4427 w = NO_WP_DETECT (don't test whether the
4428 medium is write-protected).
4429 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4430 even if the device claims no cache)
4431 Example: quirks=0419:aaf5:rl,0421:0433:rc
4433 user_debug= [KNL,ARM]
4435 See arch/arm/Kconfig.debug help text.
4436 1 - undefined instruction events
4438 4 - invalid data aborts
4441 Example: user_debug=31
4444 [X86] Flags controlling user PTE allocations.
4446 nohigh = do not allocate PTE pages in
4447 HIGHMEM regardless of setting
4451 On X86_32, this is an alias for vdso32=. Otherwise:
4453 vdso=1: enable VDSO (the default)
4454 vdso=0: disable VDSO mapping
4456 vdso32= [X86] Control the 32-bit vDSO
4457 vdso32=1: enable 32-bit VDSO
4458 vdso32=0 or vdso32=2: disable 32-bit VDSO
4460 See the help text for CONFIG_COMPAT_VDSO for more
4461 details. If CONFIG_COMPAT_VDSO is set, the default is
4462 vdso32=0; otherwise, the default is vdso32=1.
4464 For compatibility with older kernels, vdso32=2 is an
4467 Try vdso32=0 if you encounter an error that says:
4468 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4471 vector=percpu: enable percpu vector domain
4473 video= [FB] Frame buffer configuration
4474 See Documentation/fb/modedb.txt.
4476 video.brightness_switch_enabled= [0,1]
4477 If set to 1, on receiving an ACPI notify event
4478 generated by hotkey, video driver will adjust brightness
4479 level and then send out the event to user space through
4480 the allocated input device; If set to 0, video driver
4481 will only send out the event without touching backlight
4486 [VMMIO] Memory mapped virtio (platform) device.
4488 <size>@<baseaddr>:<irq>[:<id>]
4490 <size> := size (can use standard suffixes
4492 <baseaddr> := physical base address
4493 <irq> := interrupt number (as passed to
4495 <id> := (optional) platform device id
4497 virtio_mmio.device=1K@0x100b0000:48:7
4499 Can be used multiple times for multiple devices.
4501 vga= [BOOT,X86-32] Select a particular video mode
4502 See Documentation/x86/boot.txt and
4503 Documentation/svga.txt.
4504 Use vga=ask for menu.
4505 This is actually a boot loader parameter; the value is
4506 passed to the kernel using a special protocol.
4508 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4509 size of <nn>. This can be used to increase the
4510 minimum size (128MB on x86). It can also be used to
4511 decrease the size and leave more room for directly
4514 vmcp_cma=nn[MG] [KNL,S390]
4515 Sets the memory size reserved for contiguous memory
4516 allocations for the vmcp device driver.
4518 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4521 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4524 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4528 Controls the behavior of vsyscalls (i.e. calls to
4529 fixed addresses of 0xffffffffff600x00 from legacy
4530 code). Most statically-linked binaries and older
4531 versions of glibc use these calls. Because these
4532 functions are at fixed addresses, they make nice
4533 targets for exploits that can control RIP.
4535 emulate [default] Vsyscalls turn into traps and are
4536 emulated reasonably safely.
4538 native Vsyscalls are native syscall instructions.
4539 This is a little bit faster than trapping
4540 and makes a few dynamic recompilers work
4541 better than they would in emulation mode.
4542 It also makes exploits much easier to write.
4544 none Vsyscalls don't work at all. This makes
4545 them quite hard to use for exploits but
4546 might break your system.
4548 vt.color= [VT] Default text color.
4549 Format: 0xYX, X = foreground, Y = background.
4550 Default: 0x07 = light gray on black.
4552 vt.cur_default= [VT] Default cursor shape.
4553 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4554 the parameters of the <Esc>[?A;B;Cc escape sequence;
4555 see VGA-softcursor.txt. Default: 2 = underline.
4557 vt.default_blu= [VT]
4558 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4559 Change the default blue palette of the console.
4560 This is a 16-member array composed of values
4563 vt.default_grn= [VT]
4564 Format: <green0>,<green1>,<green2>,...,<green15>
4565 Change the default green palette of the console.
4566 This is a 16-member array composed of values
4569 vt.default_red= [VT]
4570 Format: <red0>,<red1>,<red2>,...,<red15>
4571 Change the default red palette of the console.
4572 This is a 16-member array composed of values
4578 Set system-wide default UTF-8 mode for all tty's.
4579 Default is 1, i.e. UTF-8 mode is enabled for all
4580 newly opened terminals.
4582 vt.global_cursor_default=
4585 Set system-wide default for whether a cursor
4586 is shown on new VTs. Default is -1,
4587 i.e. cursors will be created by default unless
4588 overridden by individual drivers. 0 will hide
4589 cursors, 1 will display them.
4591 vt.italic= [VT] Default color for italic text; 0-15.
4594 vt.underline= [VT] Default color for underlined text; 0-15.
4597 watchdog timers [HW,WDT] For information on watchdog timers,
4598 see Documentation/watchdog/watchdog-parameters.txt
4599 or other driver-specific files in the
4600 Documentation/watchdog/ directory.
4602 workqueue.watchdog_thresh=
4603 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4604 warn stall conditions and dump internal state to
4605 help debugging. 0 disables workqueue stall
4606 detection; otherwise, it's the stall threshold
4607 duration in seconds. The default value is 30 and
4608 it can be updated at runtime by writing to the
4609 corresponding sysfs file.
4611 workqueue.disable_numa
4612 By default, all work items queued to unbound
4613 workqueues are affine to the NUMA nodes they're
4614 issued on, which results in better behavior in
4615 general. If NUMA affinity needs to be disabled for
4616 whatever reason, this option can be used. Note
4617 that this also can be controlled per-workqueue for
4618 workqueues visible under /sys/bus/workqueue/.
4620 workqueue.power_efficient
4621 Per-cpu workqueues are generally preferred because
4622 they show better performance thanks to cache
4623 locality; unfortunately, per-cpu workqueues tend to
4624 be more power hungry than unbound workqueues.
4626 Enabling this makes the per-cpu workqueues which
4627 were observed to contribute significantly to power
4628 consumption unbound, leading to measurably lower
4629 power usage at the cost of small performance
4632 The default value of this parameter is determined by
4633 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4635 workqueue.debug_force_rr_cpu
4636 Workqueue used to implicitly guarantee that work
4637 items queued without explicit CPU specified are put
4638 on the local CPU. This guarantee is no longer true
4639 and while local CPU is still preferred work items
4640 may be put on foreign CPUs. This debug option
4641 forces round-robin CPU selection to flush out
4642 usages which depend on the now broken guarantee.
4643 When enabled, memory and cache locality will be
4646 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4647 default x2apic cluster mode on platforms
4650 x86_intel_mid_timer= [X86-32,APBT]
4651 Choose timer option for x86 Intel MID platform.
4652 Two valid options are apbt timer only and lapic timer
4653 plus one apbt timer for broadcast timer.
4654 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4656 xen_512gb_limit [KNL,X86-64,XEN]
4657 Restricts the kernel running paravirtualized under Xen
4658 to use only up to 512 GB of RAM. The reason to do so is
4659 crash analysis tools and Xen tools for doing domain
4660 save/restore/migration must be enabled to handle larger
4663 xen_emul_unplug= [HW,X86,XEN]
4664 Unplug Xen emulated devices
4665 Format: [unplug0,][unplug1]
4666 ide-disks -- unplug primary master IDE devices
4667 aux-ide-disks -- unplug non-primary-master IDE devices
4668 nics -- unplug network devices
4669 all -- unplug all emulated devices (NICs and IDE disks)
4670 unnecessary -- unplugging emulated devices is
4671 unnecessary even if the host did not respond to
4673 never -- do not unplug even if version check succeeds
4675 xen_nopvspin [X86,XEN]
4676 Disables the ticketlock slowpath using Xen PV
4680 Disables the PV optimizations forcing the HVM guest to
4681 run as generic HVM guest with no PV drivers.
4683 xirc2ps_cs= [NET,PCMCIA]
4685 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
git.samba.org / sfrench / cifs-2.6.git / blob