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.
649 consoleblank= [KNL] The console blank (screen saver) timeout in
650 seconds. A value of 0 disables the blank timer.
654 [KNL] Change the default value for
655 /proc/<pid>/coredump_filter.
656 See also Documentation/filesystems/proc.txt.
658 coresight_cpu_debug.enable
661 Enable/disable the CPU sampling based debugging.
662 0: default value, disable debugging
663 1: enable debugging at boot time
665 cpuidle.off=1 [CPU_IDLE]
666 disable the cpuidle sub-system
668 cpufreq.off=1 [CPU_FREQ]
669 disable the cpufreq sub-system
672 [X86] Delay for N microsec between assert and de-assert
673 of APIC INIT to start processors. This delay occurs
674 on every CPU online, such as boot, and resume from suspend.
677 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
679 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
681 crashkernel=size[KMG][@offset[KMG]]
682 [KNL] Using kexec, Linux can switch to a 'crash kernel'
683 upon panic. This parameter reserves the physical
684 memory region [offset, offset + size] for that kernel
685 image. If '@offset' is omitted, then a suitable offset
686 is selected automatically. Check
687 Documentation/kdump/kdump.txt for further details.
689 crashkernel=range1:size1[,range2:size2,...][@offset]
690 [KNL] Same as above, but depends on the memory
691 in the running system. The syntax of range is
692 start-[end] where start and end are both
693 a memory unit (amount[KMG]). See also
694 Documentation/kdump/kdump.txt for an example.
696 crashkernel=size[KMG],high
697 [KNL, x86_64] range could be above 4G. Allow kernel
698 to allocate physical memory region from top, so could
699 be above 4G if system have more than 4G ram installed.
700 Otherwise memory region will be allocated below 4G, if
702 It will be ignored if crashkernel=X is specified.
703 crashkernel=size[KMG],low
704 [KNL, x86_64] range under 4G. When crashkernel=X,high
705 is passed, kernel could allocate physical memory region
706 above 4G, that cause second kernel crash on system
707 that require some amount of low memory, e.g. swiotlb
708 requires at least 64M+32K low memory, also enough extra
709 low memory is needed to make sure DMA buffers for 32-bit
710 devices won't run out. Kernel would try to allocate at
711 at least 256M below 4G automatically.
712 This one let user to specify own low range under 4G
713 for second kernel instead.
714 0: to disable low allocation.
715 It will be ignored when crashkernel=X,high is not used
716 or memory reserved is below 4G.
719 [KNL] Disable crypto self-tests
724 cs89x0_media= [HW,NET]
725 Format: { rj45 | aui | bnc }
728 See header of drivers/s390/block/dasd_devmap.c.
730 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
731 (one device per port)
732 Format: <port#>,<type>
733 See also Documentation/input/devices/joystick-parport.rst
735 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
737 Documentation/admin-guide/dynamic-debug-howto.rst for
738 details. Deprecated, see dyndbg.
740 debug [KNL] Enable kernel debugging (events log level).
743 [KNL] verbose self-tests
745 Print debugging info while doing the locking API
747 We default to 0 (no extra messages), setting it to
748 1 will print _a lot_ more information - normally
749 only useful to kernel developers.
751 debug_objects [KNL] Enable object debugging
754 [KNL] Disable object debugging
756 debug_guardpage_minorder=
757 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
758 parameter allows control of the order of pages that will
759 be intentionally kept free (and hence protected) by the
760 buddy allocator. Bigger value increase the probability
761 of catching random memory corruption, but reduce the
762 amount of memory for normal system use. The maximum
763 possible value is MAX_ORDER/2. Setting this parameter
764 to 1 or 2 should be enough to identify most random
765 memory corruption problems caused by bugs in kernel or
766 driver code when a CPU writes to (or reads from) a
767 random memory location. Note that there exists a class
768 of memory corruptions problems caused by buggy H/W or
769 F/W or by drivers badly programing DMA (basically when
770 memory is written at bus level and the CPU MMU is
771 bypassed) which are not detectable by
772 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
773 tracking down these problems.
776 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
777 parameter enables the feature at boot time. In
778 default, it is disabled. We can avoid allocating huge
779 chunk of memory for debug pagealloc if we don't enable
780 it at boot time and the system will work mostly same
781 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
782 on: enable the feature
784 debugpat [X86] Enable PAT debugging
786 decnet.addr= [HW,NET]
787 Format: <area>[,<node>]
788 See also Documentation/networking/decnet.txt.
791 [same as hugepagesz=] The size of the default
792 HugeTLB page size. This is the size represented by
793 the legacy /proc/ hugepages APIs, used for SHM, and
794 default size when mounting hugetlbfs filesystems.
795 Defaults to the default architecture's huge page size
799 Set number of hash buckets for dentry cache.
801 disable_1tb_segments [PPC]
802 Disables the use of 1TB hash page table segments. This
803 causes the kernel to fall back to 256MB segments which
804 can be useful when debugging issues that require an SLB
808 See Documentation/networking/ipv6.txt.
811 Disable RADIX MMU mode on POWER9
813 disable_cpu_apicid= [X86,APIC,SMP]
815 The number of initial APIC ID for the
816 corresponding CPU to be disabled at boot,
817 mostly used for the kdump 2nd kernel to
818 disable BSP to wake up multiple CPUs without
819 causing system reset or hang due to sending
822 disable_ddw [PPC/PSERIES]
823 Disable Dynamic DMA Window support. Use this if
824 to workaround buggy firmware.
827 See Documentation/networking/ipv6.txt.
829 disable_mtrr_cleanup [X86]
830 The kernel tries to adjust MTRR layout from continuous
831 to discrete, to make X server driver able to add WB
832 entry later. This parameter disables that.
834 disable_mtrr_trim [X86, Intel and AMD only]
835 By default the kernel will trim any uncacheable
836 memory out of your available memory pool based on
837 MTRR settings. This parameter disables that behavior,
838 possibly causing your machine to run very slowly.
840 disable_timer_pin_1 [X86]
841 Disable PIN 1 of APIC timer
842 Can be useful to work around chipset bugs.
844 dis_ucode_ldr [X86] Disable the microcode loader.
846 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
847 this option disables the debugging code at boot.
849 dma_debug_entries=<number>
850 This option allows to tune the number of preallocated
851 entries for DMA-API debugging code. One entry is
852 required per DMA-API allocation. Use this if the
853 DMA-API debugging code disables itself because the
854 architectural default is too low.
856 dma_debug_driver=<driver_name>
857 With this option the DMA-API debugging driver
858 filter feature can be enabled at boot time. Just
859 pass the driver to filter for as the parameter.
860 The filter can be disabled or changed to another
861 driver later using sysfs.
863 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
864 Broken monitors, graphic adapters, KVMs and EDIDless
865 panels may send no or incorrect EDID data sets.
866 This parameter allows to specify an EDID data sets
867 in the /lib/firmware directory that are used instead.
868 Generic built-in EDID data sets are used, if one of
869 edid/1024x768.bin, edid/1280x1024.bin,
870 edid/1680x1050.bin, or edid/1920x1080.bin is given
871 and no file with the same name exists. Details and
872 instructions how to build your own EDID data are
873 available in Documentation/EDID/HOWTO.txt. An EDID
874 data set will only be used for a particular connector,
875 if its name and a colon are prepended to the EDID
876 name. Each connector may use a unique EDID data
877 set by separating the files with a comma. An EDID
878 data set with no connector name will be used for
879 any connectors not explicitly specified.
884 Format: {"off" | "known"}
885 Control how the dt_cpu_ftrs device-tree binding is
886 used for CPU feature discovery and setup (if it
888 off: Do not use it, fall back to legacy cpu table.
889 known: Do not pass through unknown features to guests
890 or userspace, only those that the kernel is aware of.
892 dump_apple_properties [X86]
893 Dump name and content of EFI device properties on
894 x86 Macs. Useful for driver authors to determine
895 what data is available or for reverse-engineering.
897 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
898 module.dyndbg[="val"]
899 Enable debug messages at boot time. See
900 Documentation/admin-guide/dynamic-debug-howto.rst
903 nompx [X86] Disables Intel Memory Protection Extensions.
904 See Documentation/x86/intel_mpx.txt for more
905 information about the feature.
907 nopku [X86] Disable Memory Protection Keys CPU feature found
910 module.async_probe [KNL]
911 Enable asynchronous probe on this module.
913 early_ioremap_debug [KNL]
914 Enable debug messages in early_ioremap support. This
915 is useful for tracking down temporary early mappings
916 which are not unmapped.
918 earlycon= [KNL] Output early console device and options.
920 [ARM64] The early console is determined by the
921 stdout-path property in device tree's chosen node,
922 or determined by the ACPI SPCR table.
924 [X86] When used with no options the early console is
925 determined by the ACPI SPCR table.
927 cdns,<addr>[,options]
928 Start an early, polled-mode console on a Cadence
929 (xuartps) serial port at the specified address. Only
930 supported option is baud rate. If baud rate is not
931 specified, the serial port must already be setup and
934 uart[8250],io,<addr>[,options]
935 uart[8250],mmio,<addr>[,options]
936 uart[8250],mmio32,<addr>[,options]
937 uart[8250],mmio32be,<addr>[,options]
938 uart[8250],0x<addr>[,options]
939 Start an early, polled-mode console on the 8250/16550
940 UART at the specified I/O port or MMIO address.
941 MMIO inter-register address stride is either 8-bit
942 (mmio) or 32-bit (mmio32 or mmio32be).
943 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
944 to be equivalent to 'mmio'. 'options' are specified
945 in the same format described for "console=ttyS<n>"; if
946 unspecified, the h/w is not initialized.
950 Start an early, polled-mode console on a pl011 serial
951 port at the specified address. The pl011 serial port
952 must already be setup and configured. Options are not
953 yet supported. If 'mmio32' is specified, then only
954 the driver will use only 32-bit accessors to read/write
955 the device registers.
958 Start an early, polled-mode console on a meson serial
959 port at the specified address. The serial port must
960 already be setup and configured. Options are not yet
964 Start an early, polled-mode console on an msm serial
965 port at the specified address. The serial port
966 must already be setup and configured. Options are not
970 Start an early, polled-mode console on an msm serial
971 dm port at the specified address. The serial port
972 must already be setup and configured. Options are not
976 Start an early, polled-mode console on a serial port
977 of an Actions Semi SoC, such as S500 or S900, at the
978 specified address. The serial port must already be
979 setup and configured. Options are not yet supported.
981 smh Use ARM semihosting calls for early console.
989 Use early console provided by serial driver available
990 on Samsung SoCs, requires selecting proper type and
991 a correct base address of the selected UART port. The
992 serial port must already be setup and configured.
993 Options are not yet supported.
996 Start an early, polled-mode console on a lantiq serial
997 (lqasc) port at the specified address. The serial port
998 must already be setup and configured. Options are not
1003 Use early console provided by Freescale LP UART driver
1004 found on Freescale Vybrid and QorIQ LS1021A processors.
1005 A valid base address must be provided, and the serial
1006 port must already be setup and configured.
1009 Start an early, polled-mode console on the
1010 Armada 3700 serial port at the specified
1011 address. The serial port must already be setup
1012 and configured. Options are not yet supported.
1014 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k,S390]
1019 earlyprintk=serial[,ttySn[,baudrate]]
1020 earlyprintk=serial[,0x...[,baudrate]]
1021 earlyprintk=ttySn[,baudrate]
1022 earlyprintk=dbgp[debugController#]
1023 earlyprintk=pciserial,bus:device.function[,baudrate]
1024 earlyprintk=xdbc[xhciController#]
1026 earlyprintk is useful when the kernel crashes before
1027 the normal console is initialized. It is not enabled by
1028 default because it has some cosmetic problems.
1030 Append ",keep" to not disable it when the real console
1033 Only one of vga, efi, serial, or usb debug port can
1036 Currently only ttyS0 and ttyS1 may be specified by
1037 name. Other I/O ports may be explicitly specified
1038 on some architectures (x86 and arm at least) by
1039 replacing ttySn with an I/O port address, like this:
1040 earlyprintk=serial,0x1008,115200
1041 You can find the port for a given device in
1042 /proc/tty/driver/serial:
1043 2: uart:ST16650V2 port:00001008 irq:18 ...
1045 Interaction with the standard serial driver is not
1048 The VGA and EFI output is eventually overwritten by
1051 The xen output can only be used by Xen PV guests.
1053 The sclp output can only be used on s390.
1055 edac_report= [HW,EDAC] Control how to report EDAC event
1056 Format: {"on" | "off" | "force"}
1057 on: enable EDAC to report H/W event. May be overridden
1058 by other higher priority error reporting module.
1059 off: disable H/W event reporting through EDAC.
1060 force: enforce the use of EDAC to report H/W event.
1063 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1066 This is designed to be used in conjunction with
1067 the boot argument: earlyprintk=vga
1070 Format: {"off" | "on" | "skip[mbr]"}
1073 Format: { "old_map", "nochunk", "noruntime", "debug" }
1074 old_map [X86-64]: switch to the old ioremap-based EFI
1075 runtime services mapping. 32-bit still uses this one by
1077 nochunk: disable reading files in "chunks" in the EFI
1078 boot stub, as chunking can cause problems with some
1079 firmware implementations.
1080 noruntime : disable EFI runtime services support
1081 debug: enable misc debug output
1083 efi_no_storage_paranoia [EFI; X86]
1084 Using this parameter you can use more than 50% of
1085 your efi variable storage. Use this parameter only if
1086 you are really sure that your UEFI does sane gc and
1087 fulfills the spec otherwise your board may brick.
1089 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1090 Add arbitrary attribute to specific memory range by
1091 updating original EFI memory map.
1092 Region of memory which aa attribute is added to is
1094 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1095 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1096 attribute is added to range 0x100000000-0x180000000 and
1097 0x10a0000000-0x1120000000.
1099 Using this parameter you can do debugging of EFI memmap
1100 related feature. For example, you can do debugging of
1101 Address Range Mirroring feature even if your box
1104 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1105 that is to be dynamically loaded by Linux. If there are
1106 multiple variables with the same name but with different
1107 vendor GUIDs, all of them will be loaded. See
1108 Documentation/acpi/ssdt-overlays.txt for details.
1111 eisa_irq_edge= [PARISC,HW]
1112 See header of drivers/parisc/eisa.c.
1115 See comment before function elanfreq_setup() in
1116 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1119 Format: {"cfq" | "deadline" | "noop"}
1120 See Documentation/block/cfq-iosched.txt and
1121 Documentation/block/deadline-iosched.txt for details.
1123 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1124 Specifies physical address of start of kernel core
1125 image elf header and optionally the size. Generally
1126 kexec loader will pass this option to capture kernel.
1127 See Documentation/kdump/kdump.txt for details.
1129 enable_mtrr_cleanup [X86]
1130 The kernel tries to adjust MTRR layout from continuous
1131 to discrete, to make X server driver able to add WB
1132 entry later. This parameter enables that.
1134 enable_timer_pin_1 [X86]
1135 Enable PIN 1 of APIC timer
1136 Can be useful to work around chipset bugs
1137 (in particular on some ATI chipsets).
1138 The kernel tries to set a reasonable default.
1140 enforcing [SELINUX] Set initial enforcing status.
1142 See security/selinux/Kconfig help text.
1143 0 -- permissive (log only, no denials).
1144 1 -- enforcing (deny and log).
1146 Value can be changed at runtime via /selinux/enforce.
1149 Disable Error Record Serialization Table (ERST)
1152 ether= [HW,NET] Ethernet cards parameters
1153 This option is obsoleted by the "netdev=" option, which
1154 has equivalent usage. See its documentation for details.
1158 Permit 'security.evm' to be updated regardless of
1159 current integrity status.
1163 fail_make_request=[KNL]
1164 General fault injection mechanism.
1165 Format: <interval>,<probability>,<space>,<times>
1166 See also Documentation/fault-injection/.
1169 See Documentation/blockdev/floppy.txt.
1171 force_pal_cache_flush
1172 [IA-64] Avoid check_sal_cache_flush which may hang on
1173 buggy SAL_CACHE_FLUSH implementations. Using this
1174 parameter will force ia64_sal_cache_flush to call
1175 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1178 Forcefully enable Physical Address Extension (PAE).
1179 Many Pentium M systems disable PAE but may have a
1180 functionally usable PAE implementation.
1181 Warning: use of this parameter will taint the kernel
1182 and may cause unknown problems.
1185 [FTRACE] will set and start the specified tracer
1186 as early as possible in order to facilitate early
1189 ftrace_dump_on_oops[=orig_cpu]
1190 [FTRACE] will dump the trace buffers on oops.
1191 If no parameter is passed, ftrace will dump
1192 buffers of all CPUs, but if you pass orig_cpu, it will
1193 dump only the buffer of the CPU that triggered the
1196 ftrace_filter=[function-list]
1197 [FTRACE] Limit the functions traced by the function
1198 tracer at boot up. function-list is a comma separated
1199 list of functions. This list can be changed at run
1200 time by the set_ftrace_filter file in the debugfs
1203 ftrace_notrace=[function-list]
1204 [FTRACE] Do not trace the functions specified in
1205 function-list. This list can be changed at run time
1206 by the set_ftrace_notrace file in the debugfs
1209 ftrace_graph_filter=[function-list]
1210 [FTRACE] Limit the top level callers functions traced
1211 by the function graph tracer at boot up.
1212 function-list is a comma separated list of functions
1213 that can be changed at run time by the
1214 set_graph_function file in the debugfs tracing directory.
1216 ftrace_graph_notrace=[function-list]
1217 [FTRACE] Do not trace from the functions specified in
1218 function-list. This list is a comma separated list of
1219 functions that can be changed at run time by the
1220 set_graph_notrace file in the debugfs tracing directory.
1222 ftrace_graph_max_depth=<uint>
1223 [FTRACE] Used with the function graph tracer. This is
1224 the max depth it will trace into a function. This value
1225 can be changed at run time by the max_graph_depth file
1226 in the tracefs tracing directory. default: 0 (no limit)
1229 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1230 support via parallel port (up to 5 devices per port)
1231 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1232 See also Documentation/input/devices/joystick-parport.rst
1236 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1240 gcov_persist= [GCOV] When non-zero (default), profiling data for
1241 kernel modules is saved and remains accessible via
1242 debugfs, even when the module is unloaded/reloaded.
1243 When zero, profiling data is discarded and associated
1244 debugfs files are removed at module unload time.
1246 goldfish [X86] Enable the goldfish android emulator platform.
1247 Don't use this when you are not running on the
1250 gpt [EFI] Forces disk with valid GPT signature but
1251 invalid Protective MBR to be treated as GPT. If the
1252 primary GPT is corrupted, it enables the backup/alternate
1253 GPT to be used instead.
1255 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1256 the "Enable 0" bit of the configuration register.
1259 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1260 the "Enable 0" bit of the configuration register.
1263 grcan.select= [HW] Select which physical interface to use.
1266 grcan.txsize= [HW] Sets the size of the tx buffer.
1267 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1269 grcan.rxsize= [HW] Sets the size of the rx buffer.
1270 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1273 gpio-mockup.gpio_mockup_ranges
1274 [HW] Sets the ranges of gpiochip of for this device.
1275 Format: <start1>,<end1>,<start2>,<end2>...
1277 hardlockup_all_cpu_backtrace=
1278 [KNL] Should the hard-lockup detector generate
1279 backtraces on all cpus.
1282 hashdist= [KNL,NUMA] Large hashes allocated during boot
1283 are distributed across NUMA nodes. Defaults on
1284 for 64-bit NUMA, off otherwise.
1285 Format: 0 | 1 (for off | on)
1287 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1289 hd= [EIDE] (E)IDE hard drive subsystem geometry
1290 Format: <cyl>,<head>,<sect>
1293 Disable Hardware Error Source Table (HEST) support;
1294 corresponding firmware-first mode error processing
1295 logic will be disabled.
1297 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1298 size of <nn>. This works even on boxes that have no
1299 highmem otherwise. This also works to reduce highmem
1300 size on bigger boxes.
1302 highres= [KNL] Enable/disable high resolution timer mode.
1303 Valid parameters: "on", "off"
1307 See Documentation/isdn/README.HiSax.
1311 hpet= [X86-32,HPET] option to control HPET usage
1312 Format: { enable (default) | disable | force |
1314 disable: disable HPET and use PIT instead
1315 force: allow force enabled of undocumented chips (ICH4,
1317 verbose: show contents of HPET registers during setup
1319 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1320 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1322 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1323 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1324 On x86-64 and powerpc, this option can be specified
1325 multiple times interleaved with hugepages= to reserve
1326 huge pages of different sizes. Valid pages sizes on
1327 x86-64 are 2M (when the CPU supports "pse") and 1G
1328 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1330 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1331 terminal devices. Valid values: 0..8
1332 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1333 If specified, z/VM IUCV HVC accepts connections
1334 from listed z/VM user IDs only.
1336 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1337 hardware thread id mappings.
1338 Format: <cpu>:<hwthread>
1341 Do not unregister boot console at start. This is only
1342 useful for debugging when something happens in the window
1343 between unregistering the boot console and initializing
1346 i2c_bus= [HW] Override the default board specific I2C bus speed
1347 or register an additional I2C bus that is not
1348 registered from board initialization code.
1352 i8042.debug [HW] Toggle i8042 debug mode
1353 i8042.unmask_kbd_data
1354 [HW] Enable printing of interrupt data from the KBD port
1355 (disabled by default, and as a pre-condition
1356 requires that i8042.debug=1 be enabled)
1357 i8042.direct [HW] Put keyboard port into non-translated mode
1358 i8042.dumbkbd [HW] Pretend that controller can only read data from
1359 keyboard and cannot control its state
1360 (Don't attempt to blink the leds)
1361 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1362 i8042.nokbd [HW] Don't check/create keyboard port
1363 i8042.noloop [HW] Disable the AUX Loopback command while probing
1365 i8042.nomux [HW] Don't check presence of an active multiplexing
1367 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1369 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1370 i8042.reset [HW] Reset the controller during init, cleanup and
1371 suspend-to-ram transitions, only during s2r
1372 transitions, or never reset
1373 Format: { 1 | Y | y | 0 | N | n }
1374 1, Y, y: always reset controller
1375 0, N, n: don't ever reset controller
1376 Default: only on s2r transitions on x86; most other
1377 architectures force reset to be always executed
1378 i8042.unlock [HW] Unlock (ignore) the keylock
1379 i8042.kbdreset [HW] Reset device connected to KBD port
1383 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1384 indicates that the driver is running on unsupported
1386 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1387 does not match list of supported models.
1389 [HW] Report power status in /proc/i8k
1390 (disabled by default)
1391 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1394 i915.invert_brightness=
1395 [DRM] Invert the sense of the variable that is used to
1396 set the brightness of the panel backlight. Normally a
1397 brightness value of 0 indicates backlight switched off,
1398 and the maximum of the brightness value sets the backlight
1399 to maximum brightness. If this parameter is set to 0
1400 (default) and the machine requires it, or this parameter
1401 is set to 1, a brightness value of 0 sets the backlight
1402 to maximum brightness, and the maximum of the brightness
1403 value switches the backlight off.
1404 -1 -- never invert brightness
1405 0 -- machine default
1406 1 -- force brightness inversion
1409 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1411 ide-core.nodma= [HW] (E)IDE subsystem
1412 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1413 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1414 .cdrom .chs .ignore_cable are additional options
1415 See Documentation/ide/ide.txt.
1417 ide-generic.probe-mask= [HW] (E)IDE subsystem
1419 Probe mask for legacy ISA IDE ports. Depending on
1420 platform up to 6 ports are supported, enabled by
1421 setting corresponding bits in the mask to 1. The
1422 default value is 0x0, which has a special meaning.
1423 On systems that have PCI, it triggers scanning the
1424 PCI bus for the first and the second port, which
1425 are then probed. On systems without PCI the value
1426 of 0x0 enables probing the two first ports as if it
1429 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1430 Claim all unknown PCI IDE storage controllers.
1433 Format: idle=poll, idle=halt, idle=nomwait
1434 Poll forces a polling idle loop that can slightly
1435 improve the performance of waking up a idle CPU, but
1436 will use a lot of power and make the system run hot.
1438 idle=halt: Halt is forced to be used for CPU idle.
1439 In such case C2/C3 won't be used again.
1440 idle=nomwait: Disable mwait for CPU C-states
1442 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1443 Format: { strict | legacy | 2008 | relaxed }
1446 Choose which programs will be accepted for execution
1447 based on the IEEE 754 NaN encoding(s) supported by
1448 the FPU and the NaN encoding requested with the value
1449 of an ELF file header flag individually set by each
1450 binary. Hardware implementations are permitted to
1451 support either or both of the legacy and the 2008 NaN
1454 Available settings are as follows:
1455 strict accept binaries that request a NaN encoding
1456 supported by the FPU
1457 legacy only accept legacy-NaN binaries, if supported
1459 2008 only accept 2008-NaN binaries, if supported
1461 relaxed accept any binaries regardless of whether
1462 supported by the FPU
1464 The FPU emulator is always able to support both NaN
1465 encodings, so if no FPU hardware is present or it has
1466 been disabled with 'nofpu', then the settings of
1467 'legacy' and '2008' strap the emulator accordingly,
1468 'relaxed' straps the emulator for both legacy-NaN and
1469 2008-NaN, whereas 'strict' enables legacy-NaN only on
1470 legacy processors and both NaN encodings on MIPS32 or
1473 The setting for ABS.fmt/NEG.fmt instruction execution
1474 mode generally follows that for the NaN encoding,
1475 except where unsupported by hardware.
1477 ignore_loglevel [KNL]
1478 Ignore loglevel setting - this will print /all/
1479 kernel messages to the console. Useful for debugging.
1480 We also add it as printk module parameter, so users
1481 could change it dynamically, usually by
1482 /sys/module/printk/parameters/ignore_loglevel.
1485 Ignore RLIMIT_DATA setting for data mappings,
1486 print warning at first misuse. Can be changed via
1487 /sys/module/kernel/parameters/ignore_rlimit_data.
1489 ihash_entries= [KNL]
1490 Set number of hash buckets for inode cache.
1492 ima_appraise= [IMA] appraise integrity measurements
1493 Format: { "off" | "enforce" | "fix" | "log" }
1496 ima_appraise_tcb [IMA]
1497 The builtin appraise policy appraises all files
1500 ima_canonical_fmt [IMA]
1501 Use the canonical format for the binary runtime
1502 measurements, instead of host native format.
1505 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1509 The list of supported hash algorithms is defined
1510 in crypto/hash_info.h.
1513 The builtin policies to load during IMA setup.
1514 Format: "tcb | appraise_tcb | secure_boot"
1516 The "tcb" policy measures all programs exec'd, files
1517 mmap'd for exec, and all files opened with the read
1518 mode bit set by either the effective uid (euid=0) or
1521 The "appraise_tcb" policy appraises the integrity of
1522 all files owned by root. (This is the equivalent
1523 of ima_appraise_tcb.)
1525 The "secure_boot" policy appraises the integrity
1526 of files (eg. kexec kernel image, kernel modules,
1527 firmware, policy, etc) based on file signatures.
1529 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1530 Load a policy which meets the needs of the Trusted
1531 Computing Base. This means IMA will measure all
1532 programs exec'd, files mmap'd for exec, and all files
1533 opened for read by uid=0.
1536 Select one of defined IMA measurements template formats.
1537 Formats: { "ima" | "ima-ng" | "ima-sig" }
1541 [IMA] Define a custom template format.
1542 Format: { "field1|...|fieldN" }
1544 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1545 Format: <min_file_size>
1546 Set the minimal file size for using asynchronous hash.
1547 If left unspecified, ahash usage is disabled.
1549 ahash performance varies for different data sizes on
1550 different crypto accelerators. This option can be used
1551 to achieve the best performance for a particular HW.
1553 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1555 Set hashing buffer size. Default: 4k.
1557 ahash performance varies for different chunk sizes on
1558 different crypto accelerators. This option can be used
1559 to achieve best performance for particular HW.
1563 Run specified binary instead of /sbin/init as init
1566 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1567 for working out where the kernel is dying during
1570 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1571 initcall functions. Useful for debugging built-in
1572 modules and initcalls.
1574 initrd= [BOOT] Specify the location of the initial ramdisk
1576 init_pkru= [x86] Specify the default memory protection keys rights
1577 register contents for all processes. 0x55555554 by
1578 default (disallow access to all but pkey 0). Can
1579 override in debugfs after boot.
1581 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1584 int_pln_enable [x86] Enable power limit notification interrupt
1586 integrity_audit=[IMA]
1587 Format: { "0" | "1" }
1588 0 -- basic integrity auditing messages. (Default)
1589 1 -- additional integrity auditing messages.
1591 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1593 Enable intel iommu driver.
1595 Disable intel iommu driver.
1596 igfx_off [Default Off]
1597 By default, gfx is mapped as normal device. If a gfx
1598 device has a dedicated DMAR unit, the DMAR unit is
1599 bypassed by not enabling DMAR with this option. In
1600 this case, gfx device will use physical address for
1603 With this option iommu will not optimize to look
1604 for io virtual address below 32-bit forcing dual
1605 address cycle on pci bus for cards supporting greater
1606 than 32-bit addressing. The default is to look
1607 for translation below 32-bit and if not available
1608 then look in the higher range.
1609 strict [Default Off]
1610 With this option on every unmap_single operation will
1611 result in a hardware IOTLB flush operation as opposed
1612 to batching them for performance.
1613 sp_off [Default Off]
1614 By default, super page will be supported if Intel IOMMU
1615 has the capability. With this option, super page will
1617 ecs_off [Default Off]
1618 By default, extended context tables will be supported if
1619 the hardware advertises that it has support both for the
1620 extended tables themselves, and also PASID support. With
1621 this option set, extended tables will not be used even
1622 on hardware which claims to support them.
1623 tboot_noforce [Default Off]
1624 Do not force the Intel IOMMU enabled under tboot.
1625 By default, tboot will force Intel IOMMU on, which
1626 could harm performance of some high-throughput
1627 devices like 40GBit network cards, even if identity
1629 Note that using this option lowers the security
1630 provided by tboot because it makes the system
1631 vulnerable to DMA attacks.
1633 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1634 0 disables intel_idle and fall back on acpi_idle.
1635 1 to 9 specify maximum depth of C-state.
1639 Do not enable intel_pstate as the default
1640 scaling driver for the supported processors
1642 Use intel_pstate as a scaling driver, but configure it
1643 to work with generic cpufreq governors (instead of
1644 enabling its internal governor). This mode cannot be
1645 used along with the hardware-managed P-states (HWP)
1648 Enable intel_pstate on systems that prohibit it by default
1649 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1650 instead of acpi-cpufreq may disable platform features, such
1651 as thermal controls and power capping, that rely on ACPI
1652 P-States information being indicated to OSPM and therefore
1653 should be used with caution. This option does not work with
1654 processors that aren't supported by the intel_pstate driver
1655 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1657 Do not enable hardware P state control (HWP)
1660 Only load intel_pstate on systems which support
1661 hardware P state control (HWP) if available.
1663 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1664 Description Table, specifies preferred power management
1665 profile as "Enterprise Server" or "Performance Server",
1666 then this feature is turned on by default.
1668 Allow per-logical-CPU P-State performance control limits using
1669 cpufreq sysfs interface
1671 intremap= [X86-64, Intel-IOMMU]
1672 on enable Interrupt Remapping (default)
1673 off disable Interrupt Remapping
1674 nosid disable Source ID checking
1676 BIOS x2APIC opt-out request will be ignored
1677 nopost disable Interrupt Posting
1679 iomem= Disable strict checking of access to MMIO memory
1680 strict regions from userspace.
1695 nobypass [PPC/POWERNV]
1696 Disable IOMMU bypass, using IOMMU for PCI devices.
1699 [ARM64] Configure DMA to bypass the IOMMU by default.
1700 Format: { "0" | "1" }
1701 0 - Use IOMMU translation for DMA.
1702 1 - Bypass the IOMMU for DMA.
1703 unset - Use IOMMU translation for DMA.
1705 io7= [HW] IO7 for Marvel based alpha systems
1706 See comment before marvel_specify_io7 in
1707 arch/alpha/kernel/core_marvel.c.
1709 io_delay= [X86] I/O delay method
1711 Standard port 0x80 based delay
1713 Alternate port 0xed based delay (needed on some systems)
1715 Simple two microseconds delay
1720 See Documentation/filesystems/nfs/nfsroot.txt.
1722 irqaffinity= [SMP] Set the default irq affinity mask
1723 The argument is a cpu list, as described above.
1725 irqchip.gicv2_force_probe=
1728 Force the kernel to look for the second 4kB page
1729 of a GICv2 controller even if the memory range
1730 exposed by the device tree is too small.
1733 When an interrupt is not handled search all handlers
1734 for it. Intended to get systems with badly broken
1738 When an interrupt is not handled search all handlers
1739 for it. Also check all handlers each timer
1740 interrupt. Intended to get systems with badly broken
1744 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1746 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1747 [Deprecated - use cpusets instead]
1748 Format: [flag-list,]<cpu-list>
1750 Specify one or more CPUs to isolate from disturbances
1751 specified in the flag list (default: domain):
1754 Disable the tick when a single task runs.
1756 Isolate from the general SMP balancing and scheduling
1757 algorithms. Note that performing domain isolation this way
1758 is irreversible: it's not possible to bring back a CPU to
1759 the domains once isolated through isolcpus. It's strongly
1760 advised to use cpusets instead to disable scheduler load
1761 balancing through the "cpuset.sched_load_balance" file.
1762 It offers a much more flexible interface where CPUs can
1763 move in and out of an isolated set anytime.
1765 You can move a process onto or off an "isolated" CPU via
1766 the CPU affinity syscalls or cpuset.
1767 <cpu number> begins at 0 and the maximum value is
1768 "number of CPUs in system - 1".
1770 The format of <cpu-list> is described above.
1776 ivrs_ioapic [HW,X86_64]
1777 Provide an override to the IOAPIC-ID<->DEVICE-ID
1778 mapping provided in the IVRS ACPI table. For
1779 example, to map IOAPIC-ID decimal 10 to
1780 PCI device 00:14.0 write the parameter as:
1781 ivrs_ioapic[10]=00:14.0
1783 ivrs_hpet [HW,X86_64]
1784 Provide an override to the HPET-ID<->DEVICE-ID
1785 mapping provided in the IVRS ACPI table. For
1786 example, to map HPET-ID decimal 0 to
1787 PCI device 00:14.0 write the parameter as:
1788 ivrs_hpet[0]=00:14.0
1790 ivrs_acpihid [HW,X86_64]
1791 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1792 mapping provided in the IVRS ACPI table. For
1793 example, to map UART-HID:UID AMD0020:0 to
1794 PCI device 00:14.5 write the parameter as:
1795 ivrs_acpihid[00:14.5]=AMD0020:0
1797 js= [HW,JOY] Analog joystick
1798 See Documentation/input/joydev/joystick.rst.
1801 When CONFIG_RANDOMIZE_BASE is set, this disables
1802 kernel and module base offset ASLR (Address Space
1803 Layout Randomization).
1806 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1807 report on every invalid memory access. Without this
1808 parameter KASAN will print report only for the first
1813 kernelcore= [KNL,X86,IA-64,PPC]
1814 Format: nn[KMGTPE] | "mirror"
1816 specifies the amount of memory usable by the kernel
1817 for non-movable allocations. The requested amount is
1818 spread evenly throughout all nodes in the system. The
1819 remaining memory in each node is used for Movable
1820 pages. In the event, a node is too small to have both
1821 kernelcore and Movable pages, kernelcore pages will
1822 take priority and other nodes will have a larger number
1823 of Movable pages. The Movable zone is used for the
1824 allocation of pages that may be reclaimed or moved
1825 by the page migration subsystem. This means that
1826 HugeTLB pages may not be allocated from this zone.
1827 Note that allocations like PTEs-from-HighMem still
1828 use the HighMem zone if it exists, and the Normal
1829 zone if it does not.
1831 Instead of specifying the amount of memory (nn[KMGTPE]),
1832 you can specify "mirror" option. In case "mirror"
1833 option is specified, mirrored (reliable) memory is used
1834 for non-movable allocations and remaining memory is used
1835 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1836 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1839 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1840 Format: <Controller#>[,poll interval]
1841 The controller # is the number of the ehci usb debug
1842 port as it is probed via PCI. The poll interval is
1843 optional and is the number seconds in between
1844 each poll cycle to the debug port in case you need
1845 the functionality for interrupting the kernel with
1846 gdb or control-c on the dbgp connection. When
1847 not using this parameter you use sysrq-g to break into
1848 the kernel debugger.
1850 kgdboc= [KGDB,HW] kgdb over consoles.
1851 Requires a tty driver that supports console polling,
1852 or a supported polling keyboard driver (non-usb).
1853 Serial only format: <serial_device>[,baud]
1854 keyboard only format: kbd
1855 keyboard and serial format: kbd,<serial_device>[,baud]
1856 Optional Kernel mode setting:
1857 kms, kbd format: kms,kbd
1858 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1860 kgdbwait [KGDB] Stop kernel execution and enter the
1861 kernel debugger at the earliest opportunity.
1863 kmac= [MIPS] korina ethernet MAC address.
1864 Configure the RouterBoard 532 series on-chip
1865 Ethernet adapter MAC address.
1867 kmemleak= [KNL] Boot-time kmemleak enable/disable
1868 Valid arguments: on, off
1870 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1873 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1874 Default is 0 (don't ignore, but inject #GP)
1876 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1880 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1881 Default is 1 (enabled)
1883 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1885 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1887 kvm-arm.vgic_v3_group0_trap=
1888 [KVM,ARM] Trap guest accesses to GICv3 group-0
1891 kvm-arm.vgic_v3_group1_trap=
1892 [KVM,ARM] Trap guest accesses to GICv3 group-1
1895 kvm-arm.vgic_v3_common_trap=
1896 [KVM,ARM] Trap guest accesses to GICv3 common
1899 kvm-arm.vgic_v4_enable=
1900 [KVM,ARM] Allow use of GICv4 for direct injection of
1903 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1904 (virtualized MMU) support on capable Intel chips.
1905 Default is 1 (enabled)
1907 kvm-intel.emulate_invalid_guest_state=
1908 [KVM,Intel] Enable emulation of invalid guest states
1909 Default is 0 (disabled)
1911 kvm-intel.flexpriority=
1912 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1913 Default is 1 (enabled)
1916 [KVM,Intel] Enable VMX nesting (nVMX).
1917 Default is 0 (disabled)
1919 kvm-intel.unrestricted_guest=
1920 [KVM,Intel] Disable unrestricted guest feature
1921 (virtualized real and unpaged mode) on capable
1922 Intel chips. Default is 1 (enabled)
1924 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1925 feature (tagged TLBs) on capable Intel chips.
1926 Default is 1 (enabled)
1932 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1935 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1936 value for LAPIC timer one-shot implementation. Default
1937 back to the programmable timer unit in the LAPIC.
1939 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1942 libata.dma= [LIBATA] DMA control
1943 libata.dma=0 Disable all PATA and SATA DMA
1944 libata.dma=1 PATA and SATA Disk DMA only
1945 libata.dma=2 ATAPI (CDROM) DMA only
1946 libata.dma=4 Compact Flash DMA only
1947 Combinations also work, so libata.dma=3 enables DMA
1948 for disks and CDROMs, but not CFs.
1950 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1951 libata.ignore_hpa=0 keep BIOS limits (default)
1952 libata.ignore_hpa=1 ignore limits, using full disk
1954 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1958 libata.force= [LIBATA] Force configurations. The format is comma
1959 separated list of "[ID:]VAL" where ID is
1960 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1961 matching port, link or device. Basically, it matches
1962 the ATA ID string printed on console by libata. If
1963 the whole ID part is omitted, the last PORT and DEVICE
1964 values are used. If ID hasn't been specified yet, the
1965 configuration applies to all ports, links and devices.
1967 If only DEVICE is omitted, the parameter applies to
1968 the port and all links and devices behind it. DEVICE
1969 number of 0 either selects the first device or the
1970 first fan-out link behind PMP device. It does not
1971 select the host link. DEVICE number of 15 selects the
1972 host link and device attached to it.
1974 The VAL specifies the configuration to force. As long
1975 as there's no ambiguity shortcut notation is allowed.
1976 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1977 The following configurations can be forced.
1979 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1980 Any ID with matching PORT is used.
1982 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1984 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1985 udma[/][16,25,33,44,66,100,133] notation is also
1988 * [no]ncq: Turn on or off NCQ.
1990 * [no]ncqtrim: Turn off queued DSM TRIM.
1992 * nohrst, nosrst, norst: suppress hard, soft
1995 * rstonce: only attempt one reset during
1996 hot-unplug link recovery
1998 * dump_id: dump IDENTIFY data.
2000 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2002 * disable: Disable this device.
2004 If there are multiple matching configurations changing
2005 the same attribute, the last one is used.
2007 memblock=debug [KNL] Enable memblock debug messages.
2009 load_ramdisk= [RAM] List of ramdisks to load from floppy
2010 See Documentation/blockdev/ramdisk.txt.
2012 lockd.nlm_grace_period=P [NFS] Assign grace period.
2015 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2018 lockd.nlm_timeout=T [NFS] Assign timeout value.
2021 lockd.nlm_udpport=M [NFS] Assign UDP port.
2024 locktorture.nreaders_stress= [KNL]
2025 Set the number of locking read-acquisition kthreads.
2026 Defaults to being automatically set based on the
2027 number of online CPUs.
2029 locktorture.nwriters_stress= [KNL]
2030 Set the number of locking write-acquisition kthreads.
2032 locktorture.onoff_holdoff= [KNL]
2033 Set time (s) after boot for CPU-hotplug testing.
2035 locktorture.onoff_interval= [KNL]
2036 Set time (s) between CPU-hotplug operations, or
2037 zero to disable CPU-hotplug testing.
2039 locktorture.shuffle_interval= [KNL]
2040 Set task-shuffle interval (jiffies). Shuffling
2041 tasks allows some CPUs to go into dyntick-idle
2042 mode during the locktorture test.
2044 locktorture.shutdown_secs= [KNL]
2045 Set time (s) after boot system shutdown. This
2046 is useful for hands-off automated testing.
2048 locktorture.stat_interval= [KNL]
2049 Time (s) between statistics printk()s.
2051 locktorture.stutter= [KNL]
2052 Time (s) to stutter testing, for example,
2053 specifying five seconds causes the test to run for
2054 five seconds, wait for five seconds, and so on.
2055 This tests the locking primitive's ability to
2056 transition abruptly to and from idle.
2058 locktorture.torture_runnable= [BOOT]
2059 Start locktorture running at boot time.
2061 locktorture.torture_type= [KNL]
2062 Specify the locking implementation to test.
2064 locktorture.verbose= [KNL]
2065 Enable additional printk() statements.
2067 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2070 loglevel= All Kernel Messages with a loglevel smaller than the
2071 console loglevel will be printed to the console. It can
2072 also be changed with klogd or other programs. The
2073 loglevels are defined as follows:
2075 0 (KERN_EMERG) system is unusable
2076 1 (KERN_ALERT) action must be taken immediately
2077 2 (KERN_CRIT) critical conditions
2078 3 (KERN_ERR) error conditions
2079 4 (KERN_WARNING) warning conditions
2080 5 (KERN_NOTICE) normal but significant condition
2081 6 (KERN_INFO) informational
2082 7 (KERN_DEBUG) debug-level messages
2084 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2085 in bytes. n must be a power of two and greater
2086 than the minimal size. The minimal size is defined
2087 by LOG_BUF_SHIFT kernel config parameter. There is
2088 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2089 that allows to increase the default size depending on
2090 the number of CPUs. See init/Kconfig for more details.
2092 logo.nologo [FB] Disables display of the built-in Linux logo.
2093 This may be used to provide more screen space for
2094 kernel log messages and is useful when debugging
2095 kernel boot problems.
2097 lp=0 [LP] Specify parallel ports to use, e.g,
2098 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2099 lp=reset first parallel port). 'lp=0' disables the
2100 lp=auto printer driver. 'lp=reset' (which can be
2101 specified in addition to the ports) causes
2102 attached printers to be reset. Using
2103 lp=port1,port2,... specifies the parallel ports
2104 to associate lp devices with, starting with
2105 lp0. A port specification may be 'none' to skip
2106 that lp device, or a parport name such as
2107 'parport0'. Specifying 'lp=auto' instead of a
2108 port specification list means that device IDs
2109 from each port should be examined, to see if
2110 an IEEE 1284-compliant printer is attached; if
2111 so, the driver will manage that printer.
2112 See also header of drivers/char/lp.c.
2115 Sets loops_per_jiffy to given constant, thus avoiding
2116 time-consuming boot-time autodetection (up to 250 ms per
2117 CPU). 0 enables autodetection (default). To determine
2118 the correct value for your kernel, boot with normal
2119 autodetection and see what value is printed. Note that
2120 on SMP systems the preset will be applied to all CPUs,
2121 which is likely to cause problems if your CPUs need
2122 significantly divergent settings. An incorrect value
2123 will cause delays in the kernel to be wrong, leading to
2124 unpredictable I/O errors and other breakage. Although
2125 unlikely, in the extreme case this might damage your
2129 Format: <io>,<irq>,<dma>
2131 machvec= [IA-64] Force the use of a particular machine-vector
2132 (machvec) in a generic kernel.
2133 Example: machvec=hpzx1_swiotlb
2135 machtype= [Loongson] Share the same kernel image file between different
2137 Example: machtype=lemote-yeeloong-2f-7inch
2139 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2140 than or equal to this physical address is ignored.
2142 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2143 will bring up during bootup. maxcpus=n : n >= 0 limits
2144 the kernel to bring up 'n' processors. Surely after
2145 bootup you can bring up the other plugged cpu by executing
2146 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2147 only takes effect during system bootup.
2148 While n=0 is a special case, it is equivalent to "nosmp",
2149 which also disables the IO APIC.
2151 max_loop= [LOOP] The number of loop block devices that get
2152 (loop.max_loop) unconditionally pre-created at init time. The default
2153 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2154 of statically allocating a predefined number, loop
2155 devices can be requested on-demand with the
2156 /dev/loop-control interface.
2158 mce [X86-32] Machine Check Exception
2160 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2162 md= [HW] RAID subsystems devices and level
2163 See Documentation/admin-guide/md.rst.
2166 Format: <first>,<last>
2167 Specifies range of consoles to be captured by the MDA.
2169 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2170 Amount of memory to be used when the kernel is not able
2171 to see the whole system memory or for test.
2172 [X86] Work as limiting max address. Use together
2173 with memmap= to avoid physical address space collisions.
2174 Without memmap= PCI devices could be placed at addresses
2175 belonging to unused RAM.
2177 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2181 [KNL,SH] Allow user to override the default size for
2182 per-device physically contiguous DMA buffers.
2184 memhp_default_state=online/offline
2185 [KNL] Set the initial state for the memory hotplug
2186 onlining policy. If not specified, the default value is
2187 set according to the
2188 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2190 See Documentation/memory-hotplug.txt.
2192 memmap=exactmap [KNL,X86] Enable setting of an exact
2193 E820 memory map, as specified by the user.
2194 Such memmap=exactmap lines can be constructed based on
2195 BIOS output or other requirements. See the memmap=nn@ss
2198 memmap=nn[KMG]@ss[KMG]
2199 [KNL] Force usage of a specific region of memory.
2200 Region of memory to be used is from ss to ss+nn.
2201 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2202 which limits max address to nn[KMG].
2203 Multiple different regions can be specified,
2206 memmap=100M@2G,100M#3G,1G!1024G
2208 memmap=nn[KMG]#ss[KMG]
2209 [KNL,ACPI] Mark specific memory as ACPI data.
2210 Region of memory to be marked is from ss to ss+nn.
2212 memmap=nn[KMG]$ss[KMG]
2213 [KNL,ACPI] Mark specific memory as reserved.
2214 Region of memory to be reserved is from ss to ss+nn.
2215 Example: Exclude memory from 0x18690000-0x1869ffff
2216 memmap=64K$0x18690000
2218 memmap=0x10000$0x18690000
2219 Some bootloaders may need an escape character before '$',
2220 like Grub2, otherwise '$' and the following number
2223 memmap=nn[KMG]!ss[KMG]
2224 [KNL,X86] Mark specific memory as protected.
2225 Region of memory to be used, from ss to ss+nn.
2226 The memory region may be marked as e820 type 12 (0xc)
2227 and is NVDIMM or ADR memory.
2229 memory_corruption_check=0/1 [X86]
2230 Some BIOSes seem to corrupt the first 64k of
2231 memory when doing things like suspend/resume.
2232 Setting this option will scan the memory
2233 looking for corruption. Enabling this will
2234 both detect corruption and prevent the kernel
2235 from using the memory being corrupted.
2236 However, its intended as a diagnostic tool; if
2237 repeatable BIOS-originated corruption always
2238 affects the same memory, you can use memmap=
2239 to prevent the kernel from using that memory.
2241 memory_corruption_check_size=size [X86]
2242 By default it checks for corruption in the low
2243 64k, making this memory unavailable for normal
2244 use. Use this parameter to scan for
2245 corruption in more or less memory.
2247 memory_corruption_check_period=seconds [X86]
2248 By default it checks for corruption every 60
2249 seconds. Use this parameter to check at some
2250 other rate. 0 disables periodic checking.
2252 memtest= [KNL,X86,ARM] Enable memtest
2254 default : 0 <disable>
2255 Specifies the number of memtest passes to be
2256 performed. Each pass selects another test
2257 pattern from a given set of patterns. Memtest
2258 fills the memory with this pattern, validates
2259 memory contents and reserves bad memory
2260 regions that are detected.
2262 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2263 Valid arguments: on, off
2264 Default (depends on kernel configuration option):
2265 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2266 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2267 mem_encrypt=on: Activate SME
2268 mem_encrypt=off: Do not activate SME
2270 Refer to Documentation/x86/amd-memory-encryption.txt
2271 for details on when memory encryption can be activated.
2273 mem_sleep_default= [SUSPEND] Default system suspend mode:
2274 s2idle - Suspend-To-Idle
2275 shallow - Power-On Suspend or equivalent (if supported)
2276 deep - Suspend-To-RAM or equivalent (if supported)
2277 See Documentation/admin-guide/pm/sleep-states.rst.
2279 meye.*= [HW] Set MotionEye Camera parameters
2280 See Documentation/media/v4l-drivers/meye.rst.
2282 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2283 Multi-Function General Purpose Timers on AMD Geode
2286 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2287 the BIOS has incorrectly applied a workaround. TinyBIOS
2288 version 0.98 is known to be affected, 0.99 fixes the
2289 problem by letting the user disable the workaround.
2293 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2294 physical address is ignored.
2296 mini2440= [ARM,HW,KNL]
2297 Format:[0..2][b][c][t]
2299 MINI2440 configuration specification:
2300 0 - The attached screen is the 3.5" TFT
2301 1 - The attached screen is the 7" TFT
2302 2 - The VGA Shield is attached (1024x768)
2303 Leaving out the screen size parameter will not load
2304 the TFT driver, and the framebuffer will be left
2306 b - Enable backlight. The TFT backlight pin will be
2307 linked to the kernel VESA blanking code and a GPIO
2308 LED. This parameter is not necessary when using the
2310 c - Enable the s3c camera interface.
2311 t - Reserved for enabling touchscreen support. The
2312 touchscreen support is not enabled in the mainstream
2313 kernel as of 2.6.30, a preliminary port can be found
2314 in the "bleeding edge" mini2440 support kernel at
2315 http://repo.or.cz/w/linux-2.6/mini2440.git
2318 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2319 parameter allows control of the logging verbosity for
2320 the additional memory initialisation checks. A value
2321 of 0 disables mminit logging and a level of 4 will
2322 log everything. Information is printed at KERN_DEBUG
2323 so loglevel=8 may also need to be specified.
2326 [KNL] When CONFIG_MODULE_SIG is set, this means that
2327 modules without (valid) signatures will fail to load.
2328 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2329 is always true, so this option does nothing.
2331 module_blacklist= [KNL] Do not load a comma-separated list of
2332 modules. Useful for debugging problem modules.
2335 [MOUSE] Maximum time between finger touching and
2336 leaving touchpad surface for touch to be considered
2337 a tap and be reported as a left button click (for
2338 touchpads working in absolute mode only).
2340 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2341 reporting absolute coordinates, such as tablets
2342 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2343 reporting absolute coordinates, such as tablets
2345 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2346 is similar to kernelcore except it specifies the
2347 amount of memory used for migratable allocations.
2348 If both kernelcore and movablecore is specified,
2349 then kernelcore will be at *least* the specified
2350 value but may be more. If movablecore on its own
2351 is specified, the administrator must be careful
2352 that the amount of memory usable for all allocations
2355 movable_node [KNL] Boot-time switch to make hotplugable memory
2356 NUMA nodes to be movable. This means that the memory
2357 of such nodes will be usable only for movable
2358 allocations which rules out almost all kernel
2359 allocations. Use with caution!
2361 MTD_Partition= [MTD]
2362 Format: <name>,<region-number>,<size>,<offset>
2364 MTD_Region= [MTD] Format:
2365 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2368 See drivers/mtd/cmdlinepart.c.
2370 multitce=off [PPC] This parameter disables the use of the pSeries
2371 firmware feature for updating multiple TCE entries
2374 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2376 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2378 boundary - index of last SLC block on Flex-OneNAND.
2379 The remaining blocks are configured as MLC blocks.
2380 lock - Configure if Flex-OneNAND boundary should be locked.
2381 Once locked, the boundary cannot be changed.
2382 1 indicates lock status, 0 indicates unlock status.
2385 ARM/S3C2412 JIVE boot control
2387 See arch/arm/mach-s3c2412/mach-jive.c
2389 mtouchusb.raw_coordinates=
2390 [HW] Make the MicroTouch USB driver use raw coordinates
2391 ('y', default) or cooked coordinates ('n')
2393 mtrr_chunk_size=nn[KMG] [X86]
2394 used for mtrr cleanup. It is largest continuous chunk
2395 that could hold holes aka. UC entries.
2397 mtrr_gran_size=nn[KMG] [X86]
2398 Used for mtrr cleanup. It is granularity of mtrr block.
2400 Large value could prevent small alignment from
2403 mtrr_spare_reg_nr=n [X86]
2405 Range: 0,7 : spare reg number
2407 Used for mtrr cleanup. It is spare mtrr entries number.
2408 Set to 2 or more if your graphical card needs more.
2410 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2412 netdev= [NET] Network devices parameters
2413 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2414 Note that mem_start is often overloaded to mean
2415 something different and driver-specific.
2416 This usage is only documented in each driver source
2420 [NETFILTER] Enable connection tracking flow accounting
2421 0 to disable accounting
2422 1 to enable accounting
2425 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2426 See Documentation/filesystems/nfs/nfsroot.txt.
2428 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2429 See Documentation/filesystems/nfs/nfsroot.txt.
2431 nfsrootdebug [NFS] enable nfsroot debugging messages.
2432 See Documentation/filesystems/nfs/nfsroot.txt.
2434 nfs.callback_nr_threads=
2435 [NFSv4] set the total number of threads that the
2436 NFS client will assign to service NFSv4 callback
2439 nfs.callback_tcpport=
2440 [NFS] set the TCP port on which the NFSv4 callback
2441 channel should listen.
2444 [NFS] sets the pathname to the program which is used
2445 to update the NFS client cache entries.
2447 nfs.cache_getent_timeout=
2448 [NFS] sets the timeout after which an attempt to
2449 update a cache entry is deemed to have failed.
2451 nfs.idmap_cache_timeout=
2452 [NFS] set the maximum lifetime for idmapper cache
2456 [NFS] enable 64-bit inode numbers.
2457 If zero, the NFS client will fake up a 32-bit inode
2458 number for the readdir() and stat() syscalls instead
2459 of returning the full 64-bit number.
2460 The default is to return 64-bit inode numbers.
2462 nfs.max_session_cb_slots=
2463 [NFSv4.1] Sets the maximum number of session
2464 slots the client will assign to the callback
2465 channel. This determines the maximum number of
2466 callbacks the client will process in parallel for
2467 a particular server.
2469 nfs.max_session_slots=
2470 [NFSv4.1] Sets the maximum number of session slots
2471 the client will attempt to negotiate with the server.
2472 This limits the number of simultaneous RPC requests
2473 that the client can send to the NFSv4.1 server.
2474 Note that there is little point in setting this
2475 value higher than the max_tcp_slot_table_limit.
2477 nfs.nfs4_disable_idmapping=
2478 [NFSv4] When set to the default of '1', this option
2479 ensures that both the RPC level authentication
2480 scheme and the NFS level operations agree to use
2481 numeric uids/gids if the mount is using the
2482 'sec=sys' security flavour. In effect it is
2483 disabling idmapping, which can make migration from
2484 legacy NFSv2/v3 systems to NFSv4 easier.
2485 Servers that do not support this mode of operation
2486 will be autodetected by the client, and it will fall
2487 back to using the idmapper.
2488 To turn off this behaviour, set the value to '0'.
2490 [NFS4] Specify an additional fixed unique ident-
2491 ification string that NFSv4 clients can insert into
2492 their nfs_client_id4 string. This is typically a
2493 UUID that is generated at system install time.
2495 nfs.send_implementation_id =
2496 [NFSv4.1] Send client implementation identification
2497 information in exchange_id requests.
2498 If zero, no implementation identification information
2500 The default is to send the implementation identification
2503 nfs.recover_lost_locks =
2504 [NFSv4] Attempt to recover locks that were lost due
2505 to a lease timeout on the server. Please note that
2506 doing this risks data corruption, since there are
2507 no guarantees that the file will remain unchanged
2508 after the locks are lost.
2509 If you want to enable the kernel legacy behaviour of
2510 attempting to recover these locks, then set this
2512 The default parameter value of '0' causes the kernel
2513 not to attempt recovery of lost locks.
2515 nfs4.layoutstats_timer =
2516 [NFSv4.2] Change the rate at which the kernel sends
2517 layoutstats to the pNFS metadata server.
2519 Setting this to value to 0 causes the kernel to use
2520 whatever value is the default set by the layout
2521 driver. A non-zero value sets the minimum interval
2522 in seconds between layoutstats transmissions.
2524 nfsd.nfs4_disable_idmapping=
2525 [NFSv4] When set to the default of '1', the NFSv4
2526 server will return only numeric uids and gids to
2527 clients using auth_sys, and will accept numeric uids
2528 and gids from such clients. This is intended to ease
2529 migration from NFSv2/v3.
2531 nmi_debug= [KNL,SH] Specify one or more actions to take
2532 when a NMI is triggered.
2533 Format: [state][,regs][,debounce][,die]
2535 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2536 Format: [panic,][nopanic,][num]
2538 0 - turn hardlockup detector in nmi_watchdog off
2539 1 - turn hardlockup detector in nmi_watchdog on
2540 When panic is specified, panic when an NMI watchdog
2541 timeout occurs (or 'nopanic' to override the opposite
2542 default). To disable both hard and soft lockup detectors,
2543 please see 'nowatchdog'.
2544 This is useful when you use a panic=... timeout and
2545 need the box quickly up again.
2547 netpoll.carrier_timeout=
2548 [NET] Specifies amount of time (in seconds) that
2549 netpoll should wait for a carrier. By default netpoll
2552 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2553 emulation library even if a 387 maths coprocessor
2557 [HW] Never suspend the console
2558 Disable suspending of consoles during suspend and
2559 hibernate operations. Once disabled, debugging
2560 messages can reach various consoles while the rest
2561 of the system is being put to sleep (ie, while
2562 debugging driver suspend/resume hooks). This may
2563 not work reliably with all consoles, but is known
2564 to work with serial and VGA consoles.
2565 To facilitate more flexible debugging, we also add
2566 console_suspend, a printk module parameter to control
2567 it. Users could use console_suspend (usually
2568 /sys/module/printk/parameters/console_suspend) to
2569 turn on/off it dynamically.
2571 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2572 caches in the slab allocator. Saves per-node memory,
2573 but will impact performance.
2577 noaltinstr [S390] Disables alternative instructions patching
2578 (CPU alternatives feature).
2580 noapic [SMP,APIC] Tells the kernel to not make use of any
2581 IOAPICs that may be present in the system.
2583 noautogroup Disable scheduler automatic task group creation.
2585 nobats [PPC] Do not use BATs for mapping kernel lowmem
2586 on "Classic" PPC cores.
2590 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2592 nodelayacct [KNL] Disable per-task delay accounting
2594 nodsp [SH] Disable hardware DSP at boot time.
2596 noefi Disable EFI runtime services support.
2601 On X86-32 available only on PAE configured kernels.
2602 noexec=on: enable non-executable mappings (default)
2603 noexec=off: disable non-executable mappings
2606 Disable SMAP (Supervisor Mode Access Prevention)
2607 even if it is supported by processor.
2610 Disable SMEP (Supervisor Mode Execution Prevention)
2611 even if it is supported by processor.
2614 This affects only 32-bit executables.
2615 noexec32=on: enable non-executable mappings (default)
2616 read doesn't imply executable mappings
2617 noexec32=off: disable non-executable mappings
2618 read implies executable mappings
2620 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2622 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2623 register save and restore. The kernel will only save
2624 legacy floating-point registers on task switch.
2626 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2628 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2629 Equivalent to smt=1.
2631 nospectre_v2 [X86] Disable all mitigations for the Spectre variant 2
2632 (indirect branch prediction) vulnerability. System may
2633 allow data leaks with this option, which is equivalent
2636 noxsave [BUGS=X86] Disables x86 extended register state save
2637 and restore using xsave. The kernel will fallback to
2638 enabling legacy floating-point and sse state.
2640 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2641 register states. The kernel will fall back to use
2642 xsave to save the states. By using this parameter,
2643 performance of saving the states is degraded because
2644 xsave doesn't support modified optimization while
2645 xsaveopt supports it on xsaveopt enabled systems.
2647 noxsaves [X86] Disables xsaves and xrstors used in saving and
2648 restoring x86 extended register state in compacted
2649 form of xsave area. The kernel will fall back to use
2650 xsaveopt and xrstor to save and restore the states
2651 in standard form of xsave area. By using this
2652 parameter, xsave area per process might occupy more
2653 memory on xsaves enabled systems.
2655 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2656 wfi(ARM) instruction doesn't work correctly and not to
2657 use it. This is also useful when using JTAG debugger.
2659 no_file_caps Tells the kernel not to honor file capabilities. The
2660 only way then for a file to be executed with privilege
2661 is to be setuid root or executed by root.
2663 nohalt [IA-64] Tells the kernel not to use the power saving
2664 function PAL_HALT_LIGHT when idle. This increases
2665 power-consumption. On the positive side, it reduces
2666 interrupt wake-up latency, which may improve performance
2667 in certain environments such as networked servers or
2670 nohibernate [HIBERNATION] Disable hibernation and resume.
2672 nohz= [KNL] Boottime enable/disable dynamic ticks
2673 Valid arguments: on, off
2676 nohz_full= [KNL,BOOT,SMP,ISOL]
2677 The argument is a cpu list, as described above.
2678 In kernels built with CONFIG_NO_HZ_FULL=y, set
2679 the specified list of CPUs whose tick will be stopped
2680 whenever possible. The boot CPU will be forced outside
2681 the range to maintain the timekeeping. Any CPUs
2682 in this list will have their RCU callbacks offloaded,
2683 just as if they had also been called out in the
2684 rcu_nocbs= boot parameter.
2686 noiotrap [SH] Disables trapped I/O port accesses.
2688 noirqdebug [X86-32] Disables the code which attempts to detect and
2689 disable unhandled interrupt sources.
2691 no_timer_check [X86,APIC] Disables the code which tests for
2692 broken timer IRQ sources.
2694 noisapnp [ISAPNP] Disables ISA PnP code.
2696 noinitrd [RAM] Tells the kernel not to load any configured
2699 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2701 [Deprecated - use intremap=off]
2705 noinvpcid [X86] Disable the INVPCID cpu feature.
2707 nojitter [IA-64] Disables jitter checking for ITC timers.
2709 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2711 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2715 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2716 clock and use the default one.
2718 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2719 steal time is computed, but won't influence scheduler
2722 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2724 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2726 noltlbs [PPC] Do not use large page/tlb entries for kernel
2727 lowmem mapping on PPC40x and PPC8xx
2729 nomca [IA-64] Disable machine check abort handling
2731 nomce [X86-32] Disable Machine Check Exception
2733 nomfgpt [X86-32] Disable Multi-Function General Purpose
2734 Timer usage (for AMD Geode machines).
2736 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2737 shutdown the other cpus. Instead use the REBOOT_VECTOR
2740 nomodule Disable module load
2742 nopat [X86] Disable PAT (page attribute table extension of
2743 pagetables) support.
2745 nopcid [X86-64] Disable the PCID cpu feature.
2747 norandmaps Don't use address space randomization. Equivalent to
2748 echo 0 > /proc/sys/kernel/randomize_va_space
2750 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2752 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2753 with UP alternatives
2755 nordrand [X86] Disable kernel use of the RDRAND and
2756 RDSEED instructions even if they are supported
2757 by the processor. RDRAND and RDSEED are still
2758 available to user space applications.
2760 noresume [SWSUSP] Disables resume and restores original swap
2763 no-scroll [VGA] Disables scrollback.
2764 This is required for the Braillex ib80-piezo Braille
2765 reader made by F.H. Papenmeier (Germany).
2769 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2771 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2772 and disable the IO APIC. legacy for "maxcpus=0".
2774 nosoftlockup [KNL] Disable the soft-lockup detector.
2776 nosync [HW,M68K] Disables sync negotiation for all devices.
2778 notsc [BUGS=X86-32] Disable Time Stamp Counter
2780 nowatchdog [KNL] Disable both lockup detectors, i.e.
2781 soft-lockup and NMI watchdog (hard-lockup).
2785 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2787 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2788 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2789 Some features depend on CPU0. Known dependencies are:
2790 1. Resume from suspend/hibernate depends on CPU0.
2791 Suspend/hibernate will fail if CPU0 is offline and you
2792 need to online CPU0 before suspend/hibernate.
2793 2. PIC interrupts also depend on CPU0. CPU0 can't be
2794 removed if a PIC interrupt is detected.
2795 It's said poweroff/reboot may depend on CPU0 on some
2796 machines although I haven't seen such issues so far
2797 after CPU0 is offline on a few tested machines.
2798 If the dependencies are under your control, you can
2799 turn on cpu0_hotplug.
2801 nps_mtm_hs_ctr= [KNL,ARC]
2802 This parameter sets the maximum duration, in
2803 cycles, each HW thread of the CTOP can run
2804 without interruptions, before HW switches it.
2805 The actual maximum duration is 16 times this
2807 Format: integer between 1 and 255
2810 nptcg= [IA-64] Override max number of concurrent global TLB
2811 purges which is reported from either PAL_VM_SUMMARY or
2814 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2815 could support. nr_cpus=n : n >= 1 limits the kernel to
2816 support 'n' processors. It could be larger than the
2817 number of already plugged CPU during bootup, later in
2818 runtime you can physically add extra cpu until it reaches
2819 n. So during boot up some boot time memory for per-cpu
2820 variables need be pre-allocated for later physical cpu
2823 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2825 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2826 Allowed values are enable and disable
2828 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2829 'node', 'default' can be specified
2830 This can be set from sysctl after boot.
2831 See Documentation/sysctl/vm.txt for details.
2833 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2834 See Documentation/debugging-via-ohci1394.txt for more
2837 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2838 Rather than timing out after 20 ms if an EC
2839 command is not properly ACKed, override the length
2840 of the timeout. We have interrupts disabled while
2841 waiting for the ACK, so if this is set too high
2842 interrupts *may* be lost!
2844 omap_mux= [OMAP] Override bootloader pin multiplexing.
2845 Format: <mux_mode0.mode_name=value>...
2846 For example, to override I2C bus2:
2847 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2849 oprofile.timer= [HW]
2850 Use timer interrupt instead of performance counters
2852 oprofile.cpu_type= Force an oprofile cpu type
2853 This might be useful if you have an older oprofile
2854 userland or if you want common events.
2855 Format: { arch_perfmon }
2856 arch_perfmon: [X86] Force use of architectural
2857 perfmon on Intel CPUs instead of the
2858 CPU specific event set.
2859 timer: [X86] Force use of architectural NMI
2860 timer mode (see also oprofile.timer
2861 for generic hr timer mode)
2863 oops=panic Always panic on oopses. Default is to just kill the
2864 process, but there is a small probability of
2865 deadlocking the machine.
2866 This will also cause panics on machine check exceptions.
2867 Useful together with panic=30 to trigger a reboot.
2870 See Documentation/sound/oss/oss-parameters.txt
2872 page_owner= [KNL] Boot-time page_owner enabling option.
2873 Storage of the information about who allocated
2874 each page is disabled in default. With this switch,
2876 on: enable the feature
2878 page_poison= [KNL] Boot-time parameter changing the state of
2879 poisoning on the buddy allocator.
2880 off: turn off poisoning
2881 on: turn on poisoning
2883 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2884 timeout > 0: seconds before rebooting
2885 timeout = 0: wait forever
2886 timeout < 0: reboot immediately
2889 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2892 crash_kexec_post_notifiers
2893 Run kdump after running panic-notifiers and dumping
2894 kmsg. This only for the users who doubt kdump always
2895 succeeds in any situation.
2896 Note that this also increases risks of kdump failure,
2897 because some panic notifiers can make the crashed
2898 kernel more unstable.
2900 parkbd.port= [HW] Parallel port number the keyboard adapter is
2901 connected to, default is 0.
2903 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2904 0 for XT, 1 for AT (default is AT).
2907 parport= [HW,PPT] Specify parallel ports. 0 disables.
2908 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2909 Use 'auto' to force the driver to use any
2910 IRQ/DMA settings detected (the default is to
2911 ignore detected IRQ/DMA settings because of
2912 possible conflicts). You can specify the base
2913 address, IRQ, and DMA settings; IRQ and DMA
2914 should be numbers, or 'auto' (for using detected
2915 settings on that particular port), or 'nofifo'
2916 (to avoid using a FIFO even if it is detected).
2917 Parallel ports are assigned in the order they
2918 are specified on the command line, starting
2921 parport_init_mode= [HW,PPT]
2922 Configure VIA parallel port to operate in
2923 a specific mode. This is necessary on Pegasos
2924 computer where firmware has no options for setting
2925 up parallel port mode and sets it to spp.
2926 Currently this function knows 686a and 8231 chips.
2927 Format: [spp|ps2|epp|ecp|ecpepp]
2930 Halt all CPUs after the first oops has been printed for
2931 the specified number of seconds. This is to be used if
2932 your oopses keep scrolling off the screen.
2937 See header of drivers/block/paride/pcd.c.
2938 See also Documentation/blockdev/paride.txt.
2940 pci=option[,option...] [PCI] various PCI subsystem options:
2941 earlydump [X86] dump PCI config space before the kernel
2943 off [X86] don't probe for the PCI bus
2944 bios [X86-32] force use of PCI BIOS, don't access
2945 the hardware directly. Use this if your machine
2946 has a non-standard PCI host bridge.
2947 nobios [X86-32] disallow use of PCI BIOS, only direct
2948 hardware access methods are allowed. Use this
2949 if you experience crashes upon bootup and you
2950 suspect they are caused by the BIOS.
2951 conf1 [X86] Force use of PCI Configuration Access
2952 Mechanism 1 (config address in IO port 0xCF8,
2953 data in IO port 0xCFC, both 32-bit).
2954 conf2 [X86] Force use of PCI Configuration Access
2955 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2956 the function, IO port 0xCFA, also 8-bit, sets
2957 bus number. The config space is then accessed
2958 through ports 0xC000-0xCFFF).
2959 See http://wiki.osdev.org/PCI for more info
2960 on the configuration access mechanisms.
2961 noaer [PCIE] If the PCIEAER kernel config parameter is
2962 enabled, this kernel boot option can be used to
2963 disable the use of PCIE advanced error reporting.
2964 nodomains [PCI] Disable support for multiple PCI
2965 root domains (aka PCI segments, in ACPI-speak).
2966 nommconf [X86] Disable use of MMCONFIG for PCI
2968 check_enable_amd_mmconf [X86] check for and enable
2969 properly configured MMIO access to PCI
2970 config space on AMD family 10h CPU
2971 nomsi [MSI] If the PCI_MSI kernel config parameter is
2972 enabled, this kernel boot option can be used to
2973 disable the use of MSI interrupts system-wide.
2974 noioapicquirk [APIC] Disable all boot interrupt quirks.
2975 Safety option to keep boot IRQs enabled. This
2976 should never be necessary.
2977 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2978 primary IO-APIC for bridges that cannot disable
2979 boot IRQs. This fixes a source of spurious IRQs
2980 when the system masks IRQs.
2981 noioapicreroute [APIC] Disable workaround that uses the
2982 boot IRQ equivalent of an IRQ that connects to
2983 a chipset where boot IRQs cannot be disabled.
2984 The opposite of ioapicreroute.
2985 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2986 routing table. These calls are known to be buggy
2987 on several machines and they hang the machine
2988 when used, but on other computers it's the only
2989 way to get the interrupt routing table. Try
2990 this option if the kernel is unable to allocate
2991 IRQs or discover secondary PCI buses on your
2993 rom [X86] Assign address space to expansion ROMs.
2994 Use with caution as certain devices share
2995 address decoders between ROMs and other
2997 norom [X86] Do not assign address space to
2998 expansion ROMs that do not already have
2999 BIOS assigned address ranges.
3000 nobar [X86] Do not assign address space to the
3001 BARs that weren't assigned by the BIOS.
3002 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3003 assigned automatically to PCI devices. You can
3004 make the kernel exclude IRQs of your ISA cards
3006 pirqaddr=0xAAAAA [X86] Specify the physical address
3007 of the PIRQ table (normally generated
3008 by the BIOS) if it is outside the
3009 F0000h-100000h range.
3010 lastbus=N [X86] Scan all buses thru bus #N. Can be
3011 useful if the kernel is unable to find your
3012 secondary buses and you want to tell it
3013 explicitly which ones they are.
3014 assign-busses [X86] Always assign all PCI bus
3015 numbers ourselves, overriding
3016 whatever the firmware may have done.
3017 usepirqmask [X86] Honor the possible IRQ mask stored
3018 in the BIOS $PIR table. This is needed on
3019 some systems with broken BIOSes, notably
3020 some HP Pavilion N5400 and Omnibook XE3
3021 notebooks. This will have no effect if ACPI
3022 IRQ routing is enabled.
3023 noacpi [X86] Do not use ACPI for IRQ routing
3024 or for PCI scanning.
3025 use_crs [X86] Use PCI host bridge window information
3026 from ACPI. On BIOSes from 2008 or later, this
3027 is enabled by default. If you need to use this,
3028 please report a bug.
3029 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3030 If you need to use this, please report a bug.
3031 routeirq Do IRQ routing for all PCI devices.
3032 This is normally done in pci_enable_device(),
3033 so this option is a temporary workaround
3034 for broken drivers that don't call it.
3035 skip_isa_align [X86] do not align io start addr, so can
3036 handle more pci cards
3037 noearly [X86] Don't do any early type 1 scanning.
3038 This might help on some broken boards which
3039 machine check when some devices' config space
3040 is read. But various workarounds are disabled
3041 and some IOMMU drivers will not work.
3042 bfsort Sort PCI devices into breadth-first order.
3043 This sorting is done to get a device
3044 order compatible with older (<= 2.4) kernels.
3045 nobfsort Don't sort PCI devices into breadth-first order.
3046 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3047 tuning and use the BIOS-configured MPS defaults.
3048 pcie_bus_safe Set every device's MPS to the largest value
3049 supported by all devices below the root complex.
3050 pcie_bus_perf Set device MPS to the largest allowable MPS
3051 based on its parent bus. Also set MRRS (Max
3052 Read Request Size) to the largest supported
3053 value (no larger than the MPS that the device
3054 or bus can support) for best performance.
3055 pcie_bus_peer2peer Set every device's MPS to 128B, which
3056 every device is guaranteed to support. This
3057 configuration allows peer-to-peer DMA between
3058 any pair of devices, possibly at the cost of
3059 reduced performance. This also guarantees
3060 that hot-added devices will work.
3061 cbiosize=nn[KMG] The fixed amount of bus space which is
3062 reserved for the CardBus bridge's IO window.
3063 The default value is 256 bytes.
3064 cbmemsize=nn[KMG] The fixed amount of bus space which is
3065 reserved for the CardBus bridge's memory
3066 window. The default value is 64 megabytes.
3069 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3070 [<order of align>@]pci:<vendor>:<device>\
3071 [:<subvendor>:<subdevice>][; ...]
3072 Specifies alignment and device to reassign
3073 aligned memory resources.
3074 If <order of align> is not specified,
3075 PAGE_SIZE is used as alignment.
3076 PCI-PCI bridge can be specified, if resource
3077 windows need to be expanded.
3078 To specify the alignment for several
3079 instances of a device, the PCI vendor,
3080 device, subvendor, and subdevice may be
3081 specified, e.g., 4096@pci:8086:9c22:103c:198f
3082 ecrc= Enable/disable PCIe ECRC (transaction layer
3083 end-to-end CRC checking).
3084 bios: Use BIOS/firmware settings. This is the
3088 hpiosize=nn[KMG] The fixed amount of bus space which is
3089 reserved for hotplug bridge's IO window.
3090 Default size is 256 bytes.
3091 hpmemsize=nn[KMG] The fixed amount of bus space which is
3092 reserved for hotplug bridge's memory window.
3093 Default size is 2 megabytes.
3094 hpbussize=nn The minimum amount of additional bus numbers
3095 reserved for buses below a hotplug bridge.
3097 realloc= Enable/disable reallocating PCI bridge resources
3098 if allocations done by BIOS are too small to
3099 accommodate resources required by all child
3101 off: Turn realloc off
3103 realloc same as realloc=on
3104 noari do not use PCIe ARI.
3105 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3106 only look for one device below a PCIe downstream
3108 big_root_window Try to add a big 64bit memory window to the PCIe
3109 root complex on AMD CPUs. Some GFX hardware
3110 can resize a BAR to allow access to all VRAM.
3111 Adding the window is slightly risky (it may
3112 conflict with unreported devices), so this
3115 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3118 force Enable ASPM even on devices that claim not to support it.
3119 WARNING: Forcing ASPM on may cause system lockups.
3121 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3122 nomsi Do not use MSI for PCI Express Native Hotplug (this
3123 makes all PCIe ports use INTx for hotplug services).
3125 pcie_ports= [PCIE] PCIe ports handling:
3126 auto Ask the BIOS whether or not to use native PCIe services
3127 associated with PCIe ports (PME, hot-plug, AER). Use
3128 them only if that is allowed by the BIOS.
3129 native Use native PCIe services associated with PCIe ports
3131 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3134 pcie_port_pm= [PCIE] PCIe port power management handling:
3135 off Disable power management of all PCIe ports
3136 force Forcibly enable power management of all PCIe ports
3138 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3139 nomsi Do not use MSI for native PCIe PME signaling (this makes
3140 all PCIe root ports use INTx for all services).
3142 pcmv= [HW,PCMCIA] BadgePAD 4
3146 Keep all power-domains already enabled by bootloader on,
3147 even if no driver has claimed them. This is useful
3148 for debug and development, but should not be
3149 needed on a platform with proper driver support.
3152 See Documentation/blockdev/paride.txt.
3154 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3157 See arch/parisc/kernel/pdc_chassis.c
3159 percpu_alloc= Select which percpu first chunk allocator to use.
3160 Currently supported values are "embed" and "page".
3161 Archs may support subset or none of the selections.
3162 See comments in mm/percpu.c for details on each
3163 allocator. This parameter is primarily for debugging
3164 and performance comparison.
3167 See Documentation/blockdev/paride.txt.
3170 See Documentation/blockdev/paride.txt.
3172 pirq= [SMP,APIC] Manual mp-table setup
3173 See Documentation/x86/i386/IO-APIC.txt.
3175 plip= [PPT,NET] Parallel port network link
3176 Format: { parport<nr> | timid | 0 }
3177 See also Documentation/admin-guide/parport.rst.
3179 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3180 Override pmtimer IOPort with a hex value.
3184 Enable PNP debug messages (depends on the
3185 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3186 via /sys/module/pnp/parameters/debug. We always show
3187 current resource usage; turning this on also shows
3188 possible settings and some assignment information.
3194 { on | off | curr | res | no-curr | no-res }
3197 [ISAPNP] Exclude IRQs for the autoconfiguration
3200 [ISAPNP] Exclude DMAs for the autoconfiguration
3202 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3203 Ranges are in pairs (I/O port base and size).
3206 [ISAPNP] Exclude memory regions for the
3208 Ranges are in pairs (memory base and size).
3210 ports= [IP_VS_FTP] IPVS ftp helper module
3212 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3214 Format: <port>,<port>....
3216 powersave=off [PPC] This option disables power saving features.
3217 It specifically disables cpuidle and sets the
3218 platform machine description specific power_save
3219 function to NULL. On Idle the CPU just reduces
3222 ppc_strict_facility_enable
3223 [PPC] This option catches any kernel floating point,
3224 Altivec, VSX and SPE outside of regions specifically
3225 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3226 There is some performance impact when enabling this.
3230 Disable Hardware Transactional Memory
3232 print-fatal-signals=
3233 [KNL] debug: print fatal signals
3235 If enabled, warn about various signal handling
3236 related application anomalies: too many signals,
3237 too many POSIX.1 timers, fatal signals causing a
3240 If you hit the warning due to signal overflow,
3241 you might want to try "ulimit -i unlimited".
3245 printk.always_kmsg_dump=
3246 Trigger kmsg_dump for cases other than kernel oops or
3248 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3251 printk.devkmsg={on,off,ratelimit}
3252 Control writing to /dev/kmsg.
3253 on - unlimited logging to /dev/kmsg from userspace
3254 off - logging to /dev/kmsg disabled
3255 ratelimit - ratelimit the logging
3258 printk.time= Show timing data prefixed to each printk message line
3259 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3261 processor.max_cstate= [HW,ACPI]
3262 Limit processor to maximum C-state
3263 max_cstate=9 overrides any DMI blacklist limit.
3265 processor.nocst [HW,ACPI]
3266 Ignore the _CST method to determine C-states,
3267 instead using the legacy FADT method
3269 profile= [KNL] Enable kernel profiling via /proc/profile
3270 Format: [<profiletype>,]<number>
3271 Param: <profiletype>: "schedule", "sleep", or "kvm"
3272 [defaults to kernel profiling]
3273 Param: "schedule" - profile schedule points.
3274 Param: "sleep" - profile D-state sleeping (millisecs).
3275 Requires CONFIG_SCHEDSTATS
3276 Param: "kvm" - profile VM exits.
3277 Param: <number> - step/bucket size as a power of 2 for
3278 statistical time based profiling.
3280 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3282 See Documentation/blockdev/ramdisk.txt.
3284 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3285 probe for; one of (bare|imps|exps|lifebook|any).
3286 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3288 psmouse.resetafter= [HW,MOUSE]
3289 Try to reset the device after so many bad packets
3292 [HW,MOUSE] Set desired mouse resolution, in dpi.
3293 psmouse.smartscroll=
3294 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3295 0 = disabled, 1 = enabled (default).
3297 pstore.backend= Specify the name of the pstore backend to use
3300 See Documentation/blockdev/paride.txt.
3302 pti= [X86_64] Control Page Table Isolation of user and
3303 kernel address spaces. Disabling this feature
3304 removes hardening, but improves performance of
3305 system calls and interrupts.
3307 on - unconditionally enable
3308 off - unconditionally disable
3309 auto - kernel detects whether your CPU model is
3310 vulnerable to issues that PTI mitigates
3312 Not specifying this option is equivalent to pti=auto.
3315 Equivalent to pti=off
3318 [KNL] Number of legacy pty's. Overwrites compiled-in
3321 quiet [KNL] Disable most log messages
3326 See Documentation/admin-guide/md.rst.
3328 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3329 See Documentation/blockdev/ramdisk.txt.
3331 ras=option[,option,...] [KNL] RAS-specific options
3334 Disable the Correctable Errors Collector,
3335 see CONFIG_RAS_CEC help text.
3338 The argument is a cpu list, as described above.
3340 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3341 the specified list of CPUs to be no-callback CPUs.
3342 Invocation of these CPUs' RCU callbacks will
3343 be offloaded to "rcuox/N" kthreads created for
3344 that purpose, where "x" is "b" for RCU-bh, "p"
3345 for RCU-preempt, and "s" for RCU-sched, and "N"
3346 is the CPU number. This reduces OS jitter on the
3347 offloaded CPUs, which can be useful for HPC and
3348 real-time workloads. It can also improve energy
3349 efficiency for asymmetric multiprocessors.
3352 Rather than requiring that offloaded CPUs
3353 (specified by rcu_nocbs= above) explicitly
3354 awaken the corresponding "rcuoN" kthreads,
3355 make these kthreads poll for callbacks.
3356 This improves the real-time response for the
3357 offloaded CPUs by relieving them of the need to
3358 wake up the corresponding kthread, but degrades
3359 energy efficiency by requiring that the kthreads
3360 periodically wake up to do the polling.
3362 rcutree.blimit= [KNL]
3363 Set maximum number of finished RCU callbacks to
3364 process in one batch.
3366 rcutree.dump_tree= [KNL]
3367 Dump the structure of the rcu_node combining tree
3368 out at early boot. This is used for diagnostic
3369 purposes, to verify correct tree setup.
3371 rcutree.gp_cleanup_delay= [KNL]
3372 Set the number of jiffies to delay each step of
3373 RCU grace-period cleanup.
3375 rcutree.gp_init_delay= [KNL]
3376 Set the number of jiffies to delay each step of
3377 RCU grace-period initialization.
3379 rcutree.gp_preinit_delay= [KNL]
3380 Set the number of jiffies to delay each step of
3381 RCU grace-period pre-initialization, that is,
3382 the propagation of recent CPU-hotplug changes up
3383 the rcu_node combining tree.
3385 rcutree.rcu_fanout_exact= [KNL]
3386 Disable autobalancing of the rcu_node combining
3387 tree. This is used by rcutorture, and might
3388 possibly be useful for architectures having high
3389 cache-to-cache transfer latencies.
3391 rcutree.rcu_fanout_leaf= [KNL]
3392 Change the number of CPUs assigned to each
3393 leaf rcu_node structure. Useful for very
3394 large systems, which will choose the value 64,
3395 and for NUMA systems with large remote-access
3396 latencies, which will choose a value aligned
3397 with the appropriate hardware boundaries.
3399 rcutree.jiffies_till_sched_qs= [KNL]
3400 Set required age in jiffies for a
3401 given grace period before RCU starts
3402 soliciting quiescent-state help from
3403 rcu_note_context_switch().
3405 rcutree.jiffies_till_first_fqs= [KNL]
3406 Set delay from grace-period initialization to
3407 first attempt to force quiescent states.
3408 Units are jiffies, minimum value is zero,
3409 and maximum value is HZ.
3411 rcutree.jiffies_till_next_fqs= [KNL]
3412 Set delay between subsequent attempts to force
3413 quiescent states. Units are jiffies, minimum
3414 value is one, and maximum value is HZ.
3416 rcutree.kthread_prio= [KNL,BOOT]
3417 Set the SCHED_FIFO priority of the RCU per-CPU
3418 kthreads (rcuc/N). This value is also used for
3419 the priority of the RCU boost threads (rcub/N)
3420 and for the RCU grace-period kthreads (rcu_bh,
3421 rcu_preempt, and rcu_sched). If RCU_BOOST is
3422 set, valid values are 1-99 and the default is 1
3423 (the least-favored priority). Otherwise, when
3424 RCU_BOOST is not set, valid values are 0-99 and
3425 the default is zero (non-realtime operation).
3427 rcutree.rcu_nocb_leader_stride= [KNL]
3428 Set the number of NOCB kthread groups, which
3429 defaults to the square root of the number of
3430 CPUs. Larger numbers reduces the wakeup overhead
3431 on the per-CPU grace-period kthreads, but increases
3432 that same overhead on each group's leader.
3434 rcutree.qhimark= [KNL]
3435 Set threshold of queued RCU callbacks beyond which
3436 batch limiting is disabled.
3438 rcutree.qlowmark= [KNL]
3439 Set threshold of queued RCU callbacks below which
3440 batch limiting is re-enabled.
3442 rcutree.rcu_idle_gp_delay= [KNL]
3443 Set wakeup interval for idle CPUs that have
3444 RCU callbacks (RCU_FAST_NO_HZ=y).
3446 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3447 Set wakeup interval for idle CPUs that have
3448 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3449 Lazy RCU callbacks are those which RCU can
3450 prove do nothing more than free memory.
3452 rcutree.rcu_kick_kthreads= [KNL]
3453 Cause the grace-period kthread to get an extra
3454 wake_up() if it sleeps three times longer than
3455 it should at force-quiescent-state time.
3456 This wake_up() will be accompanied by a
3457 WARN_ONCE() splat and an ftrace_dump().
3459 rcuperf.gp_async= [KNL]
3460 Measure performance of asynchronous
3461 grace-period primitives such as call_rcu().
3463 rcuperf.gp_async_max= [KNL]
3464 Specify the maximum number of outstanding
3465 callbacks per writer thread. When a writer
3466 thread exceeds this limit, it invokes the
3467 corresponding flavor of rcu_barrier() to allow
3468 previously posted callbacks to drain.
3470 rcuperf.gp_exp= [KNL]
3471 Measure performance of expedited synchronous
3472 grace-period primitives.
3474 rcuperf.holdoff= [KNL]
3475 Set test-start holdoff period. The purpose of
3476 this parameter is to delay the start of the
3477 test until boot completes in order to avoid
3480 rcuperf.nreaders= [KNL]
3481 Set number of RCU readers. The value -1 selects
3482 N, where N is the number of CPUs. A value
3483 "n" less than -1 selects N-n+1, where N is again
3484 the number of CPUs. For example, -2 selects N
3485 (the number of CPUs), -3 selects N+1, and so on.
3486 A value of "n" less than or equal to -N selects
3489 rcuperf.nwriters= [KNL]
3490 Set number of RCU writers. The values operate
3491 the same as for rcuperf.nreaders.
3492 N, where N is the number of CPUs
3494 rcuperf.perf_runnable= [BOOT]
3495 Start rcuperf running at boot time.
3497 rcuperf.perf_type= [KNL]
3498 Specify the RCU implementation to test.
3500 rcuperf.shutdown= [KNL]
3501 Shut the system down after performance tests
3502 complete. This is useful for hands-off automated
3505 rcuperf.verbose= [KNL]
3506 Enable additional printk() statements.
3508 rcuperf.writer_holdoff= [KNL]
3509 Write-side holdoff between grace periods,
3510 in microseconds. The default of zero says
3513 rcutorture.cbflood_inter_holdoff= [KNL]
3514 Set holdoff time (jiffies) between successive
3515 callback-flood tests.
3517 rcutorture.cbflood_intra_holdoff= [KNL]
3518 Set holdoff time (jiffies) between successive
3519 bursts of callbacks within a given callback-flood
3522 rcutorture.cbflood_n_burst= [KNL]
3523 Set the number of bursts making up a given
3524 callback-flood test. Set this to zero to
3525 disable callback-flood testing.
3527 rcutorture.cbflood_n_per_burst= [KNL]
3528 Set the number of callbacks to be registered
3529 in a given burst of a callback-flood test.
3531 rcutorture.fqs_duration= [KNL]
3532 Set duration of force_quiescent_state bursts
3535 rcutorture.fqs_holdoff= [KNL]
3536 Set holdoff time within force_quiescent_state bursts
3539 rcutorture.fqs_stutter= [KNL]
3540 Set wait time between force_quiescent_state bursts
3543 rcutorture.gp_cond= [KNL]
3544 Use conditional/asynchronous update-side
3545 primitives, if available.
3547 rcutorture.gp_exp= [KNL]
3548 Use expedited update-side primitives, if available.
3550 rcutorture.gp_normal= [KNL]
3551 Use normal (non-expedited) asynchronous
3552 update-side primitives, if available.
3554 rcutorture.gp_sync= [KNL]
3555 Use normal (non-expedited) synchronous
3556 update-side primitives, if available. If all
3557 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3558 rcutorture.gp_normal=, and rcutorture.gp_sync=
3559 are zero, rcutorture acts as if is interpreted
3560 they are all non-zero.
3562 rcutorture.n_barrier_cbs= [KNL]
3563 Set callbacks/threads for rcu_barrier() testing.
3565 rcutorture.nfakewriters= [KNL]
3566 Set number of concurrent RCU writers. These just
3567 stress RCU, they don't participate in the actual
3568 test, hence the "fake".
3570 rcutorture.nreaders= [KNL]
3571 Set number of RCU readers. The value -1 selects
3572 N-1, where N is the number of CPUs. A value
3573 "n" less than -1 selects N-n-2, where N is again
3574 the number of CPUs. For example, -2 selects N
3575 (the number of CPUs), -3 selects N+1, and so on.
3577 rcutorture.object_debug= [KNL]
3578 Enable debug-object double-call_rcu() testing.
3580 rcutorture.onoff_holdoff= [KNL]
3581 Set time (s) after boot for CPU-hotplug testing.
3583 rcutorture.onoff_interval= [KNL]
3584 Set time (s) between CPU-hotplug operations, or
3585 zero to disable CPU-hotplug testing.
3587 rcutorture.shuffle_interval= [KNL]
3588 Set task-shuffle interval (s). Shuffling tasks
3589 allows some CPUs to go into dyntick-idle mode
3590 during the rcutorture test.
3592 rcutorture.shutdown_secs= [KNL]
3593 Set time (s) after boot system shutdown. This
3594 is useful for hands-off automated testing.
3596 rcutorture.stall_cpu= [KNL]
3597 Duration of CPU stall (s) to test RCU CPU stall
3598 warnings, zero to disable.
3600 rcutorture.stall_cpu_holdoff= [KNL]
3601 Time to wait (s) after boot before inducing stall.
3603 rcutorture.stall_cpu_irqsoff= [KNL]
3604 Disable interrupts while stalling if set.
3606 rcutorture.stat_interval= [KNL]
3607 Time (s) between statistics printk()s.
3609 rcutorture.stutter= [KNL]
3610 Time (s) to stutter testing, for example, specifying
3611 five seconds causes the test to run for five seconds,
3612 wait for five seconds, and so on. This tests RCU's
3613 ability to transition abruptly to and from idle.
3615 rcutorture.test_boost= [KNL]
3616 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3617 "Maybe" means test if the RCU implementation
3618 under test support RCU priority boosting.
3620 rcutorture.test_boost_duration= [KNL]
3621 Duration (s) of each individual boost test.
3623 rcutorture.test_boost_interval= [KNL]
3624 Interval (s) between each boost test.
3626 rcutorture.test_no_idle_hz= [KNL]
3627 Test RCU's dyntick-idle handling. See also the
3628 rcutorture.shuffle_interval parameter.
3630 rcutorture.torture_runnable= [BOOT]
3631 Start rcutorture running at boot time.
3633 rcutorture.torture_type= [KNL]
3634 Specify the RCU implementation to test.
3636 rcutorture.verbose= [KNL]
3637 Enable additional printk() statements.
3639 rcupdate.rcu_cpu_stall_suppress= [KNL]
3640 Suppress RCU CPU stall warning messages.
3642 rcupdate.rcu_cpu_stall_timeout= [KNL]
3643 Set timeout for RCU CPU stall warning messages.
3645 rcupdate.rcu_expedited= [KNL]
3646 Use expedited grace-period primitives, for
3647 example, synchronize_rcu_expedited() instead
3648 of synchronize_rcu(). This reduces latency,
3649 but can increase CPU utilization, degrade
3650 real-time latency, and degrade energy efficiency.
3651 No effect on CONFIG_TINY_RCU kernels.
3653 rcupdate.rcu_normal= [KNL]
3654 Use only normal grace-period primitives,
3655 for example, synchronize_rcu() instead of
3656 synchronize_rcu_expedited(). This improves
3657 real-time latency, CPU utilization, and
3658 energy efficiency, but can expose users to
3659 increased grace-period latency. This parameter
3660 overrides rcupdate.rcu_expedited. No effect on
3661 CONFIG_TINY_RCU kernels.
3663 rcupdate.rcu_normal_after_boot= [KNL]
3664 Once boot has completed (that is, after
3665 rcu_end_inkernel_boot() has been invoked), use
3666 only normal grace-period primitives. No effect
3667 on CONFIG_TINY_RCU kernels.
3669 rcupdate.rcu_task_stall_timeout= [KNL]
3670 Set timeout in jiffies for RCU task stall warning
3671 messages. Disable with a value less than or equal
3674 rcupdate.rcu_self_test= [KNL]
3675 Run the RCU early boot self tests
3677 rcupdate.rcu_self_test_bh= [KNL]
3678 Run the RCU bh early boot self tests
3680 rcupdate.rcu_self_test_sched= [KNL]
3681 Run the RCU sched early boot self tests
3685 Run specified binary instead of /init from the ramdisk,
3686 used for early userspace startup. See initrd.
3689 Turn on/off individual RDT features. List is:
3690 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, mba.
3691 E.g. to turn on cmt and turn off mba use:
3695 Format (x86 or x86_64):
3696 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3698 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3700 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3701 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3702 reboot_force is either force or not specified,
3703 reboot_cpu is s[mp]#### with #### being the processor
3704 to be used for rebooting.
3707 [KNL, SMP] Set scheduler's default relax_domain_level.
3708 See Documentation/cgroup-v1/cpusets.txt.
3710 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3712 reservetop= [X86-32]
3714 Reserves a hole at the top of the kernel virtual
3719 Set the amount of memory to reserve for BIOS at
3720 the bottom of the address space.
3722 reset_devices [KNL] Force drivers to reset the underlying device
3723 during initialization.
3726 Specify the partition device for software suspend
3728 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3730 resume_offset= [SWSUSP]
3731 Specify the offset from the beginning of the partition
3732 given by "resume=" at which the swap header is located,
3733 in <PAGE_SIZE> units (needed only for swap files).
3734 See Documentation/power/swsusp-and-swap-files.txt
3736 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3737 read the resume files
3739 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3740 Useful for devices that are detected asynchronously
3741 (e.g. USB and MMC devices).
3743 hibernate= [HIBERNATION]
3744 noresume Don't check if there's a hibernation image
3745 present during boot.
3746 nocompress Don't compress/decompress hibernation images.
3747 no Disable hibernation and resume.
3748 protect_image Turn on image protection during restoration
3749 (that will set all pages holding image data
3750 during restoration read-only).
3752 retain_initrd [RAM] Keep initrd memory after extraction
3754 rfkill.default_state=
3755 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3756 etc. communication is blocked by default.
3759 rfkill.master_switch_mode=
3760 0 The "airplane mode" button does nothing.
3761 1 The "airplane mode" button toggles between everything
3762 blocked and the previous configuration.
3763 2 The "airplane mode" button toggles between everything
3764 blocked and everything unblocked.
3766 rhash_entries= [KNL,NET]
3767 Set number of hash buckets for route cache
3770 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
3773 ro [KNL] Mount root device read-only on boot
3776 on Mark read-only kernel memory as read-only (default).
3777 off Leave read-only kernel memory writable for debugging.
3780 Enable the uart passthrough on the designated usb port
3781 on Rockchip SoCs. When active, the signals of the
3782 debug-uart get routed to the D+ and D- pins of the usb
3783 port and the regular usb controller gets disabled.
3785 root= [KNL] Root filesystem
3786 See name_to_dev_t comment in init/do_mounts.c.
3788 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3789 mount the root filesystem
3791 rootflags= [KNL] Set root filesystem mount option string
3793 rootfstype= [KNL] Set root filesystem type
3795 rootwait [KNL] Wait (indefinitely) for root device to show up.
3796 Useful for devices that are detected asynchronously
3797 (e.g. USB and MMC devices).
3799 rproc_mem=nn[KMG][@address]
3800 [KNL,ARM,CMA] Remoteproc physical memory block.
3801 Memory area to be used by remote processor image,
3804 rw [KNL] Mount root device read-write on boot
3806 S [KNL] Run init in single mode
3808 s390_iommu= [HW,S390]
3809 Set s390 IOTLB flushing mode
3811 With strict flushing every unmap operation will result in
3812 an IOTLB flush. Default is lazy flushing before reuse,
3816 See drivers/net/irda/sa1100_ir.c.
3818 sbni= [NET] Granch SBNI12 leased line adapter
3820 sched_debug [KNL] Enables verbose scheduler debug messages.
3822 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3823 Allowed values are enable and disable. This feature
3824 incurs a small amount of overhead in the scheduler
3825 but is useful for debugging and performance tuning.
3827 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3828 xtime_lock contention on larger systems, and/or RCU lock
3829 contention on all systems with CONFIG_MAXSMP set.
3830 Format: { "0" | "1" }
3831 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3833 Note: increases power consumption, thus should only be
3834 enabled if running jitter sensitive (HPC/RT) workloads.
3836 security= [SECURITY] Choose a security module to enable at boot.
3837 If this boot parameter is not specified, only the first
3838 security module asking for security registration will be
3839 loaded. An invalid security module name will be treated
3840 as if no module has been chosen.
3842 selinux= [SELINUX] Disable or enable SELinux at boot time.
3843 Format: { "0" | "1" }
3844 See security/selinux/Kconfig help text.
3847 Default value is set via kernel config option.
3848 If enabled at boot time, /selinux/disable can be used
3849 later to disable prior to initial policy load.
3851 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3852 Format: { "0" | "1" }
3853 See security/apparmor/Kconfig help text
3856 Default value is set via kernel config option.
3858 serialnumber [BUGS=X86-32]
3861 Maximal number of shapers.
3869 Disable merging of slabs with similar size. May be
3870 necessary if there is some reason to distinguish
3871 allocs to different slabs, especially in hardened
3872 environments where the risk of heap overflows and
3873 layout control by attackers can usually be
3874 frustrated by disabling merging. This will reduce
3875 most of the exposure of a heap attack to a single
3876 cache (risks via metadata attacks are mostly
3877 unchanged). Debug options disable merging on their
3879 For more information see Documentation/vm/slub.txt.
3881 slab_max_order= [MM, SLAB]
3882 Determines the maximum allowed order for slabs.
3883 A high setting may cause OOMs due to memory
3884 fragmentation. Defaults to 1 for systems with
3885 more than 32MB of RAM, 0 otherwise.
3887 slub_debug[=options[,slabs]] [MM, SLUB]
3888 Enabling slub_debug allows one to determine the
3889 culprit if slab objects become corrupted. Enabling
3890 slub_debug can create guard zones around objects and
3891 may poison objects when not in use. Also tracks the
3892 last alloc / free. For more information see
3893 Documentation/vm/slub.txt.
3895 slub_memcg_sysfs= [MM, SLUB]
3896 Determines whether to enable sysfs directories for
3897 memory cgroup sub-caches. 1 to enable, 0 to disable.
3898 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
3899 Enabling this can lead to a very high number of debug
3900 directories and files being created under
3903 slub_max_order= [MM, SLUB]
3904 Determines the maximum allowed order for slabs.
3905 A high setting may cause OOMs due to memory
3906 fragmentation. For more information see
3907 Documentation/vm/slub.txt.
3909 slub_min_objects= [MM, SLUB]
3910 The minimum number of objects per slab. SLUB will
3911 increase the slab order up to slub_max_order to
3912 generate a sufficiently large slab able to contain
3913 the number of objects indicated. The higher the number
3914 of objects the smaller the overhead of tracking slabs
3915 and the less frequently locks need to be acquired.
3916 For more information see Documentation/vm/slub.txt.
3918 slub_min_order= [MM, SLUB]
3919 Determines the minimum page order for slabs. Must be
3920 lower than slub_max_order.
3921 For more information see Documentation/vm/slub.txt.
3923 slub_nomerge [MM, SLUB]
3924 Same with slab_nomerge. This is supported for legacy.
3925 See slab_nomerge for more information.
3928 Format: <io1>[,<io2>[,...,<io8>]]
3930 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3931 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3932 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3933 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3934 smsc-ircc2.ircc_irq= [HW] IRQ line
3935 smsc-ircc2.ircc_dma= [HW] DMA channel
3936 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3937 0: Toshiba Satellite 1800 (GP data pin select)
3938 1: Fast pin select (default)
3941 smt [KNL,S390] Set the maximum number of threads (logical
3942 CPUs) to use per physical CPU on systems capable of
3943 symmetric multithreading (SMT). Will be capped to the
3944 actual hardware limit.
3946 Default: -1 (no limit)
3949 [KNL] Should the soft-lockup detector generate panics.
3952 A nonzero value instructs the soft-lockup detector
3953 to panic the machine when a soft-lockup occurs. This
3954 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
3955 which is the respective build-time switch to that
3958 softlockup_all_cpu_backtrace=
3959 [KNL] Should the soft-lockup detector generate
3960 backtraces on all cpus.
3963 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3964 See Documentation/laptops/sonypi.txt
3966 spectre_v2= [X86] Control mitigation of Spectre variant 2
3967 (indirect branch speculation) vulnerability.
3969 on - unconditionally enable
3970 off - unconditionally disable
3971 auto - kernel detects whether your CPU model is
3974 Selecting 'on' will, and 'auto' may, choose a
3975 mitigation method at run time according to the
3976 CPU, the available microcode, the setting of the
3977 CONFIG_RETPOLINE configuration option, and the
3978 compiler with which the kernel was built.
3980 Specific mitigations can also be selected manually:
3982 retpoline - replace indirect branches
3983 retpoline,generic - google's original retpoline
3984 retpoline,amd - AMD-specific minimal thunk
3986 Not specifying this option is equivalent to
3989 spia_io_base= [HW,MTD]
3994 srcutree.counter_wrap_check [KNL]
3995 Specifies how frequently to check for
3996 grace-period sequence counter wrap for the
3997 srcu_data structure's ->srcu_gp_seq_needed field.
3998 The greater the number of bits set in this kernel
3999 parameter, the less frequently counter wrap will
4000 be checked for. Note that the bottom two bits
4003 srcutree.exp_holdoff [KNL]
4004 Specifies how many nanoseconds must elapse
4005 since the end of the last SRCU grace period for
4006 a given srcu_struct until the next normal SRCU
4007 grace period will be considered for automatic
4008 expediting. Set to zero to disable automatic
4011 stack_guard_gap= [MM]
4012 override the default stack gap protection. The value
4013 is in page units and it defines how many pages prior
4014 to (for stacks growing down) resp. after (for stacks
4015 growing up) the main stack are reserved for no other
4016 mapping. Default value is 256 pages.
4019 Enabled the stack tracer on boot up.
4021 stacktrace_filter=[function-list]
4022 [FTRACE] Limit the functions that the stack tracer
4023 will trace at boot up. function-list is a comma separated
4024 list of functions. This list can be changed at run
4025 time by the stack_trace_filter file in the debugfs
4026 tracing directory. Note, this enables stack tracing
4027 and the stacktrace above is not needed.
4031 Set the STI (builtin display/keyboard on the HP-PARISC
4032 machines) console (graphic card) which should be used
4033 as the initial boot-console.
4034 See also comment in drivers/video/console/sticore.c.
4037 See comment in drivers/video/console/sticore.c.
4040 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4042 sunrpc.min_resvport=
4043 sunrpc.max_resvport=
4045 SunRPC servers often require that client requests
4046 originate from a privileged port (i.e. a port in the
4047 range 0 < portnr < 1024).
4048 An administrator who wishes to reserve some of these
4049 ports for other uses may adjust the range that the
4050 kernel's sunrpc client considers to be privileged
4051 using these two parameters to set the minimum and
4052 maximum port values.
4054 sunrpc.svc_rpc_per_connection_limit=
4056 Limit the number of requests that the server will
4057 process in parallel from a single connection.
4058 The default value is 0 (no limit).
4062 Control how the NFS server code allocates CPUs to
4063 service thread pools. Depending on how many NICs
4064 you have and where their interrupts are bound, this
4065 option will affect which CPUs will do NFS serving.
4066 Note: this parameter cannot be changed while the
4067 NFS server is running.
4069 auto the server chooses an appropriate mode
4070 automatically using heuristics
4071 global a single global pool contains all CPUs
4072 percpu one pool for each CPU
4073 pernode one pool for each NUMA node (equivalent
4074 to global on non-NUMA machines)
4076 sunrpc.tcp_slot_table_entries=
4077 sunrpc.udp_slot_table_entries=
4079 Sets the upper limit on the number of simultaneous
4080 RPC calls that can be sent from the client to a
4081 server. Increasing these values may allow you to
4082 improve throughput, but will also increase the
4083 amount of memory reserved for use by the client.
4085 suspend.pm_test_delay=
4087 Sets the number of seconds to remain in a suspend test
4088 mode before resuming the system (see
4089 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4090 is set. Default value is 5.
4093 [KNL] Enable accounting of swap in memory resource
4094 controller if no parameter or 1 is given or disable
4095 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4097 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4098 Format: { <int> | force | noforce }
4099 <int> -- Number of I/O TLB slabs
4100 force -- force using of bounce buffers even if they
4101 wouldn't be automatically used by the kernel
4102 noforce -- Never use bounce buffers (for debugging)
4106 sysfs.deprecated=0|1 [KNL]
4107 Enable/disable old style sysfs layout for old udev
4108 on older distributions. When this option is enabled
4109 very new udev will not work anymore. When this option
4110 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4111 in older udev will not work anymore.
4112 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4113 the kernel configuration.
4115 sysrq_always_enabled
4117 Ignore sysrq setting - this boot parameter will
4118 neutralize any effect of /proc/sys/kernel/sysrq.
4119 Useful for debugging.
4121 tcpmhash_entries= [KNL,NET]
4122 Set the number of tcp_metrics_hash slots.
4123 Default value is 8192 or 16384 depending on total
4124 ram pages. This is used to specify the TCP metrics
4125 cache size. See Documentation/networking/ip-sysctl.txt
4126 "tcp_no_metrics_save" section for more details.
4130 test_suspend= [SUSPEND][,N]
4131 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4132 standby suspend) or "freeze" (for suspend type freeze)
4133 as the system sleep state during system startup with
4134 the optional capability to repeat N number of times.
4135 The system is woken from this state using a
4136 wakeup-capable RTC alarm.
4138 thash_entries= [KNL,NET]
4139 Set number of hash buckets for TCP connection
4141 thermal.act= [HW,ACPI]
4142 -1: disable all active trip points in all thermal zones
4143 <degrees C>: override all lowest active trip points
4145 thermal.crt= [HW,ACPI]
4146 -1: disable all critical trip points in all thermal zones
4147 <degrees C>: override all critical trip points
4149 thermal.nocrt= [HW,ACPI]
4150 Set to disable actions on ACPI thermal zone
4151 critical and hot trip points.
4153 thermal.off= [HW,ACPI]
4154 1: disable ACPI thermal control
4156 thermal.psv= [HW,ACPI]
4157 -1: disable all passive trip points
4158 <degrees C>: override all passive trip points to this
4161 thermal.tzp= [HW,ACPI]
4162 Specify global default ACPI thermal zone polling rate
4163 <deci-seconds>: poll all this frequency
4164 0: no polling (default)
4167 Force threading of all interrupt handlers except those
4168 marked explicitly IRQF_NO_THREAD.
4171 Enable the Transcendent memory driver if built-in.
4173 tmem.cleancache=0|1 [KNL, XEN]
4174 Default is on (1). Disable the usage of the cleancache
4175 API to send anonymous pages to the hypervisor.
4177 tmem.frontswap=0|1 [KNL, XEN]
4178 Default is on (1). Disable the usage of the frontswap
4179 API to send swap pages to the hypervisor. If disabled
4180 the selfballooning and selfshrinking are force disabled.
4182 tmem.selfballooning=0|1 [KNL, XEN]
4183 Default is on (1). Disable the driving of swap pages
4186 tmem.selfshrinking=0|1 [KNL, XEN]
4187 Default is on (1). Partial swapoff that immediately
4188 transfers pages from Xen hypervisor back to the
4189 kernel based on different criteria.
4193 Specify if the kernel should make use of the cpu
4194 topology information if the hardware supports this.
4195 The scheduler will make use of this information and
4196 e.g. base its process migration decisions on it.
4199 topology_updates= [KNL, PPC, NUMA]
4201 Specify if the kernel should ignore (off)
4202 topology updates sent by the hypervisor to this
4207 tpm_suspend_pcr=[HW,TPM]
4208 Format: integer pcr id
4209 Specify that at suspend time, the tpm driver
4210 should extend the specified pcr with zeros,
4211 as a workaround for some chips which fail to
4212 flush the last written pcr on TPM_SaveState.
4213 This will guarantee that all the other pcrs
4216 trace_buf_size=nn[KMG]
4217 [FTRACE] will set tracing buffer size on each cpu.
4219 trace_event=[event-list]
4220 [FTRACE] Set and start specified trace events in order
4221 to facilitate early boot debugging. The event-list is a
4222 comma separated list of trace events to enable. See
4223 also Documentation/trace/events.txt
4225 trace_options=[option-list]
4226 [FTRACE] Enable or disable tracer options at boot.
4227 The option-list is a comma delimited list of options
4228 that can be enabled or disabled just as if you were
4229 to echo the option name into
4231 /sys/kernel/debug/tracing/trace_options
4233 For example, to enable stacktrace option (to dump the
4234 stack trace of each event), add to the command line:
4236 trace_options=stacktrace
4238 See also Documentation/trace/ftrace.txt "trace options"
4242 Have the tracepoints sent to printk as well as the
4243 tracing ring buffer. This is useful for early boot up
4244 where the system hangs or reboots and does not give the
4245 option for reading the tracing buffer or performing a
4246 ftrace_dump_on_oops.
4248 To turn off having tracepoints sent to printk,
4249 echo 0 > /proc/sys/kernel/tracepoint_printk
4250 Note, echoing 1 into this file without the
4251 tracepoint_printk kernel cmdline option has no effect.
4255 Having tracepoints sent to printk() and activating high
4256 frequency tracepoints such as irq or sched, can cause
4257 the system to live lock.
4260 [FTRACE] enable this option to disable tracing when a
4261 warning is hit. This turns off "tracing_on". Tracing can
4262 be enabled again by echoing '1' into the "tracing_on"
4263 file located in /sys/kernel/debug/tracing/
4265 This option is useful, as it disables the trace before
4266 the WARNING dump is called, which prevents the trace to
4267 be filled with content caused by the warning output.
4269 This option can also be set at run time via the sysctl
4270 option: kernel/traceoff_on_warning
4272 transparent_hugepage=
4274 Format: [always|madvise|never]
4275 Can be used to control the default behavior of the system
4276 with respect to transparent hugepages.
4277 See Documentation/vm/transhuge.txt for more details.
4279 tsc= Disable clocksource stability checks for TSC.
4281 [x86] reliable: mark tsc clocksource as reliable, this
4282 disables clocksource verification at runtime, as well
4283 as the stability checks done at bootup. Used to enable
4284 high-resolution timer mode on older hardware, and in
4285 virtualized environment.
4286 [x86] noirqtime: Do not use TSC to do irq accounting.
4287 Used to run time disable IRQ_TIME_ACCOUNTING on any
4288 platforms where RDTSC is slow and this accounting
4290 [x86] unstable: mark the TSC clocksource as unstable, this
4291 marks the TSC unconditionally unstable at bootup and
4292 avoids any further wobbles once the TSC watchdog notices.
4294 turbografx.map[2|3]= [HW,JOY]
4295 TurboGraFX parallel port interface
4297 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4298 See also Documentation/input/devices/joystick-parport.rst
4300 udbg-immortal [PPC] When debugging early kernel crashes that
4301 happen after console_init() and before a proper
4302 console driver takes over, this boot options might
4303 help "seeing" what's going on.
4305 uhash_entries= [KNL,NET]
4306 Set number of hash buckets for UDP/UDP-Lite connections
4309 [USB] Ignore overcurrent events (default N).
4310 Some badly-designed motherboards generate lots of
4311 bogus events, for ports that aren't wired to
4312 anything. Set this parameter to avoid log spamming.
4313 Note that genuine overcurrent events won't be
4317 [X86] Cause panic on unknown NMI.
4319 usbcore.authorized_default=
4320 [USB] Default USB device authorization:
4321 (default -1 = authorized except for wireless USB,
4322 0 = not authorized, 1 = authorized)
4324 usbcore.autosuspend=
4325 [USB] The autosuspend time delay (in seconds) used
4326 for newly-detected USB devices (default 2). This
4327 is the time required before an idle device will be
4328 autosuspended. Devices for which the delay is set
4329 to a negative value won't be autosuspended at all.
4331 usbcore.usbfs_snoop=
4332 [USB] Set to log all usbfs traffic (default 0 = off).
4334 usbcore.usbfs_snoop_max=
4335 [USB] Maximum number of bytes to snoop in each URB
4338 usbcore.blinkenlights=
4339 [USB] Set to cycle leds on hubs (default 0 = off).
4341 usbcore.old_scheme_first=
4342 [USB] Start with the old device initialization
4343 scheme (default 0 = off).
4345 usbcore.usbfs_memory_mb=
4346 [USB] Memory limit (in MB) for buffers allocated by
4347 usbfs (default = 16, 0 = max = 2047).
4349 usbcore.use_both_schemes=
4350 [USB] Try the other device initialization scheme
4351 if the first one fails (default 1 = enabled).
4353 usbcore.initial_descriptor_timeout=
4354 [USB] Specifies timeout for the initial 64-byte
4355 USB_REQ_GET_DESCRIPTOR request in milliseconds
4356 (default 5000 = 5.0 seconds).
4358 usbcore.nousb [USB] Disable the USB subsystem
4361 [USBHID] The interval which mice are to be polled at.
4364 [USBHID] The interval which joysticks are to be polled at.
4366 usb-storage.delay_use=
4367 [UMS] The delay in seconds before a new device is
4368 scanned for Logical Units (default 1).
4371 [UMS] A list of quirks entries to supplement or
4372 override the built-in unusual_devs list. List
4373 entries are separated by commas. Each entry has
4374 the form VID:PID:Flags where VID and PID are Vendor
4375 and Product ID values (4-digit hex numbers) and
4376 Flags is a set of characters, each corresponding
4377 to a common usb-storage quirk flag as follows:
4378 a = SANE_SENSE (collect more than 18 bytes
4380 b = BAD_SENSE (don't collect more than 18
4381 bytes of sense data);
4382 c = FIX_CAPACITY (decrease the reported
4383 device capacity by one sector);
4384 d = NO_READ_DISC_INFO (don't use
4385 READ_DISC_INFO command);
4386 e = NO_READ_CAPACITY_16 (don't use
4387 READ_CAPACITY_16 command);
4388 f = NO_REPORT_OPCODES (don't use report opcodes
4390 g = MAX_SECTORS_240 (don't transfer more than
4391 240 sectors at a time, uas only);
4392 h = CAPACITY_HEURISTICS (decrease the
4393 reported device capacity by one
4394 sector if the number is odd);
4395 i = IGNORE_DEVICE (don't bind to this
4397 j = NO_REPORT_LUNS (don't use report luns
4399 l = NOT_LOCKABLE (don't try to lock and
4400 unlock ejectable media);
4401 m = MAX_SECTORS_64 (don't transfer more
4402 than 64 sectors = 32 KB at a time);
4403 n = INITIAL_READ10 (force a retry of the
4404 initial READ(10) command);
4405 o = CAPACITY_OK (accept the capacity
4406 reported by the device);
4407 p = WRITE_CACHE (the device cache is ON
4409 r = IGNORE_RESIDUE (the device reports
4410 bogus residue values);
4411 s = SINGLE_LUN (the device has only one
4413 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4414 commands, uas only);
4415 u = IGNORE_UAS (don't bind to the uas driver);
4416 w = NO_WP_DETECT (don't test whether the
4417 medium is write-protected).
4418 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4419 even if the device claims no cache)
4420 Example: quirks=0419:aaf5:rl,0421:0433:rc
4422 user_debug= [KNL,ARM]
4424 See arch/arm/Kconfig.debug help text.
4425 1 - undefined instruction events
4427 4 - invalid data aborts
4430 Example: user_debug=31
4433 [X86] Flags controlling user PTE allocations.
4435 nohigh = do not allocate PTE pages in
4436 HIGHMEM regardless of setting
4440 On X86_32, this is an alias for vdso32=. Otherwise:
4442 vdso=1: enable VDSO (the default)
4443 vdso=0: disable VDSO mapping
4445 vdso32= [X86] Control the 32-bit vDSO
4446 vdso32=1: enable 32-bit VDSO
4447 vdso32=0 or vdso32=2: disable 32-bit VDSO
4449 See the help text for CONFIG_COMPAT_VDSO for more
4450 details. If CONFIG_COMPAT_VDSO is set, the default is
4451 vdso32=0; otherwise, the default is vdso32=1.
4453 For compatibility with older kernels, vdso32=2 is an
4456 Try vdso32=0 if you encounter an error that says:
4457 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4460 vector=percpu: enable percpu vector domain
4462 video= [FB] Frame buffer configuration
4463 See Documentation/fb/modedb.txt.
4465 video.brightness_switch_enabled= [0,1]
4466 If set to 1, on receiving an ACPI notify event
4467 generated by hotkey, video driver will adjust brightness
4468 level and then send out the event to user space through
4469 the allocated input device; If set to 0, video driver
4470 will only send out the event without touching backlight
4475 [VMMIO] Memory mapped virtio (platform) device.
4477 <size>@<baseaddr>:<irq>[:<id>]
4479 <size> := size (can use standard suffixes
4481 <baseaddr> := physical base address
4482 <irq> := interrupt number (as passed to
4484 <id> := (optional) platform device id
4486 virtio_mmio.device=1K@0x100b0000:48:7
4488 Can be used multiple times for multiple devices.
4490 vga= [BOOT,X86-32] Select a particular video mode
4491 See Documentation/x86/boot.txt and
4492 Documentation/svga.txt.
4493 Use vga=ask for menu.
4494 This is actually a boot loader parameter; the value is
4495 passed to the kernel using a special protocol.
4497 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4498 size of <nn>. This can be used to increase the
4499 minimum size (128MB on x86). It can also be used to
4500 decrease the size and leave more room for directly
4503 vmcp_cma=nn[MG] [KNL,S390]
4504 Sets the memory size reserved for contiguous memory
4505 allocations for the vmcp device driver.
4507 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4510 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4513 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4517 Controls the behavior of vsyscalls (i.e. calls to
4518 fixed addresses of 0xffffffffff600x00 from legacy
4519 code). Most statically-linked binaries and older
4520 versions of glibc use these calls. Because these
4521 functions are at fixed addresses, they make nice
4522 targets for exploits that can control RIP.
4524 emulate [default] Vsyscalls turn into traps and are
4525 emulated reasonably safely.
4527 native Vsyscalls are native syscall instructions.
4528 This is a little bit faster than trapping
4529 and makes a few dynamic recompilers work
4530 better than they would in emulation mode.
4531 It also makes exploits much easier to write.
4533 none Vsyscalls don't work at all. This makes
4534 them quite hard to use for exploits but
4535 might break your system.
4537 vt.color= [VT] Default text color.
4538 Format: 0xYX, X = foreground, Y = background.
4539 Default: 0x07 = light gray on black.
4541 vt.cur_default= [VT] Default cursor shape.
4542 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4543 the parameters of the <Esc>[?A;B;Cc escape sequence;
4544 see VGA-softcursor.txt. Default: 2 = underline.
4546 vt.default_blu= [VT]
4547 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4548 Change the default blue palette of the console.
4549 This is a 16-member array composed of values
4552 vt.default_grn= [VT]
4553 Format: <green0>,<green1>,<green2>,...,<green15>
4554 Change the default green palette of the console.
4555 This is a 16-member array composed of values
4558 vt.default_red= [VT]
4559 Format: <red0>,<red1>,<red2>,...,<red15>
4560 Change the default red palette of the console.
4561 This is a 16-member array composed of values
4567 Set system-wide default UTF-8 mode for all tty's.
4568 Default is 1, i.e. UTF-8 mode is enabled for all
4569 newly opened terminals.
4571 vt.global_cursor_default=
4574 Set system-wide default for whether a cursor
4575 is shown on new VTs. Default is -1,
4576 i.e. cursors will be created by default unless
4577 overridden by individual drivers. 0 will hide
4578 cursors, 1 will display them.
4580 vt.italic= [VT] Default color for italic text; 0-15.
4583 vt.underline= [VT] Default color for underlined text; 0-15.
4586 watchdog timers [HW,WDT] For information on watchdog timers,
4587 see Documentation/watchdog/watchdog-parameters.txt
4588 or other driver-specific files in the
4589 Documentation/watchdog/ directory.
4591 workqueue.watchdog_thresh=
4592 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4593 warn stall conditions and dump internal state to
4594 help debugging. 0 disables workqueue stall
4595 detection; otherwise, it's the stall threshold
4596 duration in seconds. The default value is 30 and
4597 it can be updated at runtime by writing to the
4598 corresponding sysfs file.
4600 workqueue.disable_numa
4601 By default, all work items queued to unbound
4602 workqueues are affine to the NUMA nodes they're
4603 issued on, which results in better behavior in
4604 general. If NUMA affinity needs to be disabled for
4605 whatever reason, this option can be used. Note
4606 that this also can be controlled per-workqueue for
4607 workqueues visible under /sys/bus/workqueue/.
4609 workqueue.power_efficient
4610 Per-cpu workqueues are generally preferred because
4611 they show better performance thanks to cache
4612 locality; unfortunately, per-cpu workqueues tend to
4613 be more power hungry than unbound workqueues.
4615 Enabling this makes the per-cpu workqueues which
4616 were observed to contribute significantly to power
4617 consumption unbound, leading to measurably lower
4618 power usage at the cost of small performance
4621 The default value of this parameter is determined by
4622 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4624 workqueue.debug_force_rr_cpu
4625 Workqueue used to implicitly guarantee that work
4626 items queued without explicit CPU specified are put
4627 on the local CPU. This guarantee is no longer true
4628 and while local CPU is still preferred work items
4629 may be put on foreign CPUs. This debug option
4630 forces round-robin CPU selection to flush out
4631 usages which depend on the now broken guarantee.
4632 When enabled, memory and cache locality will be
4635 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4636 default x2apic cluster mode on platforms
4639 x86_intel_mid_timer= [X86-32,APBT]
4640 Choose timer option for x86 Intel MID platform.
4641 Two valid options are apbt timer only and lapic timer
4642 plus one apbt timer for broadcast timer.
4643 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4645 xen_512gb_limit [KNL,X86-64,XEN]
4646 Restricts the kernel running paravirtualized under Xen
4647 to use only up to 512 GB of RAM. The reason to do so is
4648 crash analysis tools and Xen tools for doing domain
4649 save/restore/migration must be enabled to handle larger
4652 xen_emul_unplug= [HW,X86,XEN]
4653 Unplug Xen emulated devices
4654 Format: [unplug0,][unplug1]
4655 ide-disks -- unplug primary master IDE devices
4656 aux-ide-disks -- unplug non-primary-master IDE devices
4657 nics -- unplug network devices
4658 all -- unplug all emulated devices (NICs and IDE disks)
4659 unnecessary -- unplugging emulated devices is
4660 unnecessary even if the host did not respond to
4662 never -- do not unplug even if version check succeeds
4664 xen_nopvspin [X86,XEN]
4665 Disables the ticketlock slowpath using Xen PV
4669 Disables the PV optimizations forcing the HVM guest to
4670 run as generic HVM guest with no PV drivers.
4672 xirc2ps_cs= [NET,PCMCIA]
4674 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
git.samba.org / sfrench / cifs-2.6.git / blob