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/firmware-guide/acpi/debug.rst for more information about
57 debug layers and levels.
59 Enable processor driver info messages:
60 acpi.debug_layer=0x20000000
61 Enable PCI/PCI interrupt routing info messages:
62 acpi.debug_layer=0x400000
63 Enable AML "Debug" output, i.e., stores to the Debug
64 object while interpreting AML:
65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
66 Enable all messages related to ACPI hardware:
67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
69 Some values produce so much output that the system is
70 unusable. The "log_buf_len" parameter may be useful
71 if you need to capture more output.
73 acpi_enforce_resources= [ACPI]
75 Check for resource conflicts between native drivers
76 and ACPI OperationRegions (SystemIO and SystemMemory
77 only). IO ports and memory declared in ACPI might be
78 used by the ACPI subsystem in arbitrary AML code and
79 can interfere with legacy drivers.
80 strict (default): access to resources claimed by ACPI
81 is denied; legacy drivers trying to access reserved
82 resources will fail to bind to device using them.
83 lax: access to resources claimed by ACPI is allowed;
84 legacy drivers trying to access reserved resources
85 will bind successfully but a warning message is logged.
86 no: ACPI OperationRegions are not marked as reserved,
87 no further checks are performed.
89 acpi_force_table_verification [HW,ACPI]
90 Enable table checksum verification during early stage.
91 By default, this is disabled due to x86 early mapping
94 acpi_irq_balance [HW,ACPI]
95 ACPI will balance active IRQs
98 acpi_irq_nobalance [HW,ACPI]
99 ACPI will not move active IRQs (default)
102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
103 Format: <irq>,<irq>...
105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
107 Format: <irq>,<irq>...
109 acpi_mask_gpe= [HW,ACPI]
110 Due to the existence of _Lxx/_Exx, some GPEs triggered
111 by unsupported hardware/firmware features can result in
112 GPE floodings that cannot be automatically disabled by
114 This facility can be used to prevent such uncontrolled
118 acpi_no_auto_serialize [HW,ACPI]
119 Disable auto-serialization of AML methods
120 AML control methods that contain the opcodes to create
121 named objects will be marked as "Serialized" by the
122 auto-serialization feature.
123 This feature is enabled by default.
124 This option allows to turn off the feature.
126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
129 acpi_no_static_ssdt [HW,ACPI]
130 Disable installation of static SSDTs at early boot time
131 By default, SSDTs contained in the RSDT/XSDT will be
132 installed automatically and they will appear under
133 /sys/firmware/acpi/tables.
134 This option turns off this feature.
135 Note that specifying this option does not affect
136 dynamic table installation which will install SSDT
137 tables to /sys/firmware/acpi/tables/dynamic.
139 acpi_rsdp= [ACPI,EFI,KEXEC]
140 Pass the RSDP address to the kernel, mostly used
141 on machines running EFI runtime service to boot the
142 second kernel for kdump.
144 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
145 Format: To spoof as Windows 98: ="Microsoft Windows"
147 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
148 of 2 which is mandated by ACPI 6) as the supported ACPI
149 specification revision (when using this switch, it may
150 be necessary to carry out a cold reboot _twice_ in a
151 row to make it take effect on the platform firmware).
153 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
154 acpi_osi="string1" # add string1
155 acpi_osi="!string2" # remove string2
156 acpi_osi=!* # remove all strings
157 acpi_osi=! # disable all built-in OS vendor
159 acpi_osi=!! # enable all built-in OS vendor
161 acpi_osi= # disable all strings
163 'acpi_osi=!' can be used in combination with single or
164 multiple 'acpi_osi="string1"' to support specific OS
165 vendor string(s). Note that such command can only
166 affect the default state of the OS vendor strings, thus
167 it cannot affect the default state of the feature group
168 strings and the current state of the OS vendor strings,
169 specifying it multiple times through kernel command line
170 is meaningless. This command is useful when one do not
171 care about the state of the feature group strings which
172 should be controlled by the OSPM.
174 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
175 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
176 can make '_OSI("Windows 2000")' TRUE.
178 'acpi_osi=' cannot be used in combination with other
179 'acpi_osi=' command lines, the _OSI method will not
180 exist in the ACPI namespace. NOTE that such command can
181 only affect the _OSI support state, thus specifying it
182 multiple times through kernel command line is also
185 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
188 'acpi_osi=!*' can be used in combination with single or
189 multiple 'acpi_osi="string1"' to support specific
190 string(s). Note that such command can affect the
191 current state of both the OS vendor strings and the
192 feature group strings, thus specifying it multiple times
193 through kernel command line is meaningful. But it may
194 still not able to affect the final state of a string if
195 there are quirks related to this string. This command
196 is useful when one want to control the state of the
197 feature group strings to debug BIOS issues related to
200 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
201 '_OSI("Module Device")' FALSE.
202 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
203 '_OSI("Module Device")' TRUE.
204 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
206 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
208 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
209 they all will make '_OSI("Windows 2000")' TRUE.
212 Override the pmtimer bug detection: force the kernel
213 to assume that this machine's pmtimer latches its value
214 and always returns good values.
216 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
217 Format: { level | edge | high | low }
219 acpi_skip_timer_override [HW,ACPI]
220 Recognize and ignore IRQ0/pin2 Interrupt Override.
221 For broken nForce2 BIOS resulting in XT-PIC timer.
223 acpi_sleep= [HW,ACPI] Sleep options
224 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
225 old_ordering, nonvs, sci_force_enable, nobl }
226 See Documentation/power/video.txt for information on
228 s3_beep is for debugging; it makes the PC's speaker beep
229 as soon as the kernel's real-mode entry point is called.
230 s4_nohwsig prevents ACPI hardware signature from being
231 used during resume from hibernation.
232 old_ordering causes the ACPI 1.0 ordering of the _PTS
233 control method, with respect to putting devices into
234 low power states, to be enforced (the ACPI 2.0 ordering
235 of _PTS is used by default).
236 nonvs prevents the kernel from saving/restoring the
237 ACPI NVS memory during suspend/hibernation and resume.
238 sci_force_enable causes the kernel to set SCI_EN directly
239 on resume from S1/S3 (which is against the ACPI spec,
240 but some broken systems don't work without it).
241 nobl causes the internal blacklist of systems known to
242 behave incorrectly in some ways with respect to system
243 suspend and resume to be ignored (use wisely).
245 acpi_use_timer_override [HW,ACPI]
246 Use timer override. For some broken Nvidia NF5 boards
247 that require a timer override, but don't have HPET
249 add_efi_memmap [EFI; X86] Include EFI memory map in
250 kernel's map of available physical RAM.
253 { off | try_unsupported }
254 off: disable AGP support
255 try_unsupported: try to drive unsupported chipsets
256 (may crash computer or cause data corruption)
259 See Documentation/sound/alsa-configuration.rst
262 Allow the default userspace alignment fault handler
263 behaviour to be specified. Bit 0 enables warnings,
264 bit 1 enables fixups, and bit 2 sends a segfault.
266 align_va_addr= [X86-64]
267 Align virtual addresses by clearing slice [14:12] when
268 allocating a VMA at process creation time. This option
269 gives you up to 3% performance improvement on AMD F15h
270 machines (where it is enabled by default) for a
271 CPU-intensive style benchmark, and it can vary highly in
272 a microbenchmark depending on workload and compiler.
274 32: only for 32-bit processes
275 64: only for 64-bit processes
276 on: enable for both 32- and 64-bit processes
277 off: disable for both 32- and 64-bit processes
279 alloc_snapshot [FTRACE]
280 Allocate the ftrace snapshot buffer on boot up when the
281 main buffer is allocated. This is handy if debugging
282 and you need to use tracing_snapshot() on boot up, and
283 do not want to use tracing_snapshot_alloc() as it needs
284 to be done where GFP_KERNEL allocations are allowed.
286 amd_iommu= [HW,X86-64]
287 Pass parameters to the AMD IOMMU driver in the system.
289 fullflush - enable flushing of IO/TLB entries when
290 they are unmapped. Otherwise they are
291 flushed before they will be reused, which
293 off - do not initialize any AMD IOMMU found in
295 force_isolation - Force device isolation for all
296 devices. The IOMMU driver is not
297 allowed anymore to lift isolation
298 requirements as needed. This option
299 does not override iommu=pt
301 amd_iommu_dump= [HW,X86-64]
302 Enable AMD IOMMU driver option to dump the ACPI table
303 for AMD IOMMU. With this option enabled, AMD IOMMU
304 driver will print ACPI tables for AMD IOMMU during
305 IOMMU initialization.
307 amd_iommu_intr= [HW,X86-64]
308 Specifies one of the following AMD IOMMU interrupt
310 legacy - Use legacy interrupt remapping mode.
311 vapic - Use virtual APIC mode, which allows IOMMU
312 to inject interrupts directly into guest.
313 This mode requires kvm-amd.avic=1.
314 (Default when IOMMU HW support is present.)
316 amijoy.map= [HW,JOY] Amiga joystick support
317 Map of devices attached to JOY0DAT and JOY1DAT
319 See also Documentation/input/joydev/joystick.rst
321 analog.map= [HW,JOY] Analog joystick and gamepad support
322 Specifies type or capabilities of an analog joystick
323 connected to one of 16 gameports
324 Format: <type1>,<type2>,..<type16>
327 Power management functions (SPARCstation-4/5 + deriv.)
329 Disable APC CPU standby support. SPARCstation-Fox does
330 not play well with APC CPU idle - disable it if you have
331 APC and your system crashes randomly.
333 apic= [APIC,X86] Advanced Programmable Interrupt Controller
334 Change the output verbosity while booting
335 Format: { quiet (default) | verbose | debug }
336 Change the amount of debugging information output
337 when initialising the APIC and IO-APIC components.
338 For X86-32, this can also be used to specify an APIC
340 Format: apic=driver_name
341 Examples: apic=bigsmp
343 apic_extnmi= [APIC,X86] External NMI delivery setting
344 Format: { bsp (default) | all | none }
345 bsp: External NMI is delivered only to CPU 0
346 all: External NMIs are broadcast to all CPUs as a
348 none: External NMI is masked for all CPUs. This is
349 useful so that a dump capture kernel won't be
353 See Documentation/networking/ipv6.txt.
355 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
356 Limit apic dumping. The parameter defines the maximal
357 number of local apics being dumped. Also it is possible
358 to set it to "all" by meaning -- no limit here.
359 Format: { 1 (default) | 2 | ... | all }.
360 The parameter valid if only apic=debug or
361 apic=verbose is specified.
362 Example: apic=debug show_lapic=all
364 apm= [APM] Advanced Power Management
365 See header of arch/x86/kernel/apm_32.c.
367 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
368 Format: <io>,<irq>,<nodeID>
372 atarimouse= [HW,MOUSE] Atari Mouse
374 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
375 EzKey and similar keyboards
377 atkbd.reset= [HW] Reset keyboard during initialization
379 atkbd.set= [HW] Select keyboard code set
380 Format: <int> (2 = AT (default), 3 = PS/2)
382 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
385 atkbd.softraw= [HW] Choose between synthetic and real raw mode
386 Format: <bool> (0 = real, 1 = synthetic (default))
388 atkbd.softrepeat= [HW]
389 Use software keyboard repeat
391 audit= [KNL] Enable the audit sub-system
392 Format: { "0" | "1" | "off" | "on" }
393 0 | off - kernel audit is disabled and can not be
394 enabled until the next reboot
395 unset - kernel audit is initialized but disabled and
396 will be fully enabled by the userspace auditd.
397 1 | on - kernel audit is initialized and partially
398 enabled, storing at most audit_backlog_limit
399 messages in RAM until it is fully enabled by the
403 audit_backlog_limit= [KNL] Set the audit queue size limit.
404 Format: <int> (must be >=0)
407 bau= [X86_UV] Enable the BAU on SGI UV. The default
408 behavior is to disable the BAU (i.e. bau=0).
409 Format: { "0" | "1" }
412 unset - Disable the BAU.
414 baycom_epp= [HW,AX25]
417 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
419 See header of drivers/net/hamradio/baycom_par.c.
421 baycom_ser_fdx= [HW,AX25]
422 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
423 Format: <io>,<irq>,<mode>[,<baud>]
424 See header of drivers/net/hamradio/baycom_ser_fdx.c.
426 baycom_ser_hdx= [HW,AX25]
427 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
428 Format: <io>,<irq>,<mode>
429 See header of drivers/net/hamradio/baycom_ser_hdx.c.
431 blkdevparts= Manual partition parsing of block device(s) for
432 embedded devices based on command line input.
433 See Documentation/block/cmdline-partition.txt
435 boot_delay= Milliseconds to delay each printk during boot.
436 Values larger than 10 seconds (10000) are changed to
440 bootmem_debug [KNL] Enable bootmem allocator debug messages.
443 Disable BERT OS support on buggy BIOSes.
445 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
446 bttv.radio= Most important insmod options are available as
448 bttv.pll= See Documentation/media/v4l-drivers/bttv.rst
451 bulk_remove=off [PPC] This parameter disables the use of the pSeries
452 firmware feature for flushing multiple hpte entries
455 c101= [NET] Moxa C101 synchronous serial card
457 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
458 Sometimes CPU hardware bugs make them report the cache
459 size incorrectly. The kernel will attempt work arounds
460 to fix known problems, but for some CPUs it is not
461 possible to determine what the correct size should be.
462 This option provides an override for these situations.
465 [NET] Specifies amount of time (in seconds) that
466 the kernel should wait for a network carrier. By default
467 it waits 120 seconds.
469 ca_keys= [KEYS] This parameter identifies a specific key(s) on
470 the system trusted keyring to be used for certificate
472 format: { id:<keyid> | builtin }
474 cca= [MIPS] Override the kernel pages' cache coherency
475 algorithm. Accepted values range from 0 to 7
476 inclusive. See arch/mips/include/asm/pgtable-bits.h
477 for platform specific values (SB1, Loongson3 and
480 ccw_timeout_log [S390]
481 See Documentation/s390/common_io.rst for details.
483 cgroup_disable= [KNL] Disable a particular controller
484 Format: {name of the controller(s) to disable}
485 The effects of cgroup_disable=foo are:
486 - foo isn't auto-mounted if you mount all cgroups in
488 - foo isn't visible as an individually mountable
490 {Currently only "memory" controller deal with this and
491 cut the overhead, others just disable the usage. So
492 only cgroup_disable=memory is actually worthy}
494 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1
495 Format: { { controller | "all" | "named" }
496 [,{ controller | "all" | "named" }...] }
497 Like cgroup_disable, but only applies to cgroup v1;
498 the blacklisted controllers remain available in cgroup2.
499 "all" blacklists all controllers and "named" disables
500 named mounts. Specifying both "all" and "named" disables
503 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
505 nosocket -- Disable socket memory accounting.
506 nokmem -- Disable kernel memory accounting.
508 checkreqprot [SELINUX] Set initial checkreqprot flag value.
509 Format: { "0" | "1" }
510 See security/selinux/Kconfig help text.
511 0 -- check protection applied by kernel (includes
512 any implied execute protection).
513 1 -- check protection requested by application.
514 Default value is set via a kernel config option.
515 Value can be changed at runtime via
516 /selinux/checkreqprot.
519 See Documentation/s390/common_io.rst for details.
522 Prevents the clock framework from automatically gating
523 clocks that have not been explicitly enabled by a Linux
524 device driver but are enabled in hardware at reset or
525 by the bootloader/firmware. Note that this does not
526 force such clocks to be always-on nor does it reserve
527 those clocks in any way. This parameter is useful for
528 debug and development, but should not be needed on a
529 platform with proper driver support. For more
530 information, see Documentation/driver-api/clk.rst.
532 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
534 Forces specified clocksource (if available) to be used
535 when calculating gettimeofday(). If specified
536 clocksource is not available, it defaults to PIT.
537 Format: { pit | tsc | cyclone | pmtmr }
539 clocksource= Override the default clocksource
541 Override the default clocksource and use the clocksource
542 with the name specified.
543 Some clocksource names to choose from, depending on
545 [all] jiffies (this is the base, fallback clocksource)
547 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
548 pxa_timer,timer3,32k_counter,timer0_1
549 [X86-32] pit,hpet,tsc;
550 scx200_hrt on Geode; cyclone on IBM x440
558 clocksource.arm_arch_timer.evtstrm=
561 Enable/disable the eventstream feature of the ARM
562 architected timer so that code using WFE-based polling
563 loops can be debugged more effectively on production
566 clearcpuid=BITNUM [X86]
567 Disable CPUID feature X for the kernel. See
568 arch/x86/include/asm/cpufeatures.h for the valid bit
569 numbers. Note the Linux specific bits are not necessarily
570 stable over kernel options, but the vendor specific
572 Also note that user programs calling CPUID directly
573 or using the feature without checking anything
574 will still see it. This just prevents it from
575 being used by the kernel or shown in /proc/cpuinfo.
576 Also note the kernel might malfunction if you disable
579 cma=nn[MG]@[start[MG][-end[MG]]]
581 Sets the size of kernel global memory area for
582 contiguous memory allocations and optionally the
583 placement constraint by the physical address range of
584 memory allocations. A value of 0 disables CMA
585 altogether. For more information, see
586 include/linux/dma-contiguous.h
588 cmo_free_hint= [PPC] Format: { yes | no }
589 Specify whether pages are marked as being inactive
590 when they are freed. This is used in CMO environments
591 to determine OS memory pressure for page stealing by
595 coherent_pool=nn[KMG] [ARM,KNL]
596 Sets the size of memory pool for coherent, atomic dma
597 allocations, by default set to 256K.
599 com20020= [HW,NET] ARCnet - COM20020 chipset
601 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
603 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
607 ARCnet - COM90xx chipset (memory-mapped buffers)
608 Format: <io>[,<irq>[,<memstart>]]
610 condev= [HW,S390] console device
613 console= [KNL] Output console device and options.
615 tty<n> Use the virtual console device <n>.
619 Use the specified serial port. The options are of
620 the form "bbbbpnf", where "bbbb" is the baud rate,
621 "p" is parity ("n", "o", or "e"), "n" is number of
622 bits, and "f" is flow control ("r" for RTS or
623 omit it). Default is "9600n8".
625 See Documentation/admin-guide/serial-console.rst for more
627 Documentation/networking/netconsole.txt for an
630 uart[8250],io,<addr>[,options]
631 uart[8250],mmio,<addr>[,options]
632 uart[8250],mmio16,<addr>[,options]
633 uart[8250],mmio32,<addr>[,options]
634 uart[8250],0x<addr>[,options]
635 Start an early, polled-mode console on the 8250/16550
636 UART at the specified I/O port or MMIO address,
637 switching to the matching ttyS device later.
638 MMIO inter-register address stride is either 8-bit
639 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
640 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
641 to be equivalent to 'mmio'. 'options' are specified in
642 the same format described for ttyS above; if unspecified,
643 the h/w is not re-initialized.
645 hvc<n> Use the hypervisor console device <n>. This is for
646 both Xen and PowerPC hypervisors.
648 If the device connected to the port is not a TTY but a braille
649 device, prepend "brl," before the device type, for instance
651 For now, only VisioBraille is supported.
654 [KNL] Change console messages format
656 By default we print messages on consoles in
657 "[time stamp] text\n" format (time stamp may not be
658 printed, depending on CONFIG_PRINTK_TIME or
659 `printk_time' param).
661 Switch to syslog format: "<%u>[time stamp] text\n"
662 IOW, each message will have a facility and loglevel
663 prefix. The format is similar to one used by syslog()
664 syscall, or to executing "dmesg -S --raw" or to reading
667 consoleblank= [KNL] The console blank (screen saver) timeout in
668 seconds. A value of 0 disables the blank timer.
672 [KNL] Change the default value for
673 /proc/<pid>/coredump_filter.
674 See also Documentation/filesystems/proc.txt.
676 coresight_cpu_debug.enable
679 Enable/disable the CPU sampling based debugging.
680 0: default value, disable debugging
681 1: enable debugging at boot time
683 cpuidle.off=1 [CPU_IDLE]
684 disable the cpuidle sub-system
687 [CPU_IDLE] Name of the cpuidle governor to use.
689 cpufreq.off=1 [CPU_FREQ]
690 disable the cpufreq sub-system
693 [X86] Delay for N microsec between assert and de-assert
694 of APIC INIT to start processors. This delay occurs
695 on every CPU online, such as boot, and resume from suspend.
698 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
700 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
702 crashkernel=size[KMG][@offset[KMG]]
703 [KNL] Using kexec, Linux can switch to a 'crash kernel'
704 upon panic. This parameter reserves the physical
705 memory region [offset, offset + size] for that kernel
706 image. If '@offset' is omitted, then a suitable offset
707 is selected automatically.
708 [KNL, x86_64] select a region under 4G first, and
709 fall back to reserve region above 4G when '@offset'
710 hasn't been specified.
711 See Documentation/kdump/kdump.rst for further details.
713 crashkernel=range1:size1[,range2:size2,...][@offset]
714 [KNL] Same as above, but depends on the memory
715 in the running system. The syntax of range is
716 start-[end] where start and end are both
717 a memory unit (amount[KMG]). See also
718 Documentation/kdump/kdump.rst for an example.
720 crashkernel=size[KMG],high
721 [KNL, x86_64] range could be above 4G. Allow kernel
722 to allocate physical memory region from top, so could
723 be above 4G if system have more than 4G ram installed.
724 Otherwise memory region will be allocated below 4G, if
726 It will be ignored if crashkernel=X is specified.
727 crashkernel=size[KMG],low
728 [KNL, x86_64] range under 4G. When crashkernel=X,high
729 is passed, kernel could allocate physical memory region
730 above 4G, that cause second kernel crash on system
731 that require some amount of low memory, e.g. swiotlb
732 requires at least 64M+32K low memory, also enough extra
733 low memory is needed to make sure DMA buffers for 32-bit
734 devices won't run out. Kernel would try to allocate at
735 at least 256M below 4G automatically.
736 This one let user to specify own low range under 4G
737 for second kernel instead.
738 0: to disable low allocation.
739 It will be ignored when crashkernel=X,high is not used
740 or memory reserved is below 4G.
743 [KNL] Disable crypto self-tests
748 cs89x0_media= [HW,NET]
749 Format: { rj45 | aui | bnc }
752 See header of drivers/s390/block/dasd_devmap.c.
754 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
755 (one device per port)
756 Format: <port#>,<type>
757 See also Documentation/input/devices/joystick-parport.rst
759 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
761 Documentation/admin-guide/dynamic-debug-howto.rst for
762 details. Deprecated, see dyndbg.
764 debug [KNL] Enable kernel debugging (events log level).
767 [KNL] Enable printing [hashed] pointers early in the
768 boot sequence. If enabled, we use a weak hash instead
769 of siphash to hash pointers. Use this option if you are
770 seeing instances of '(___ptrval___)') and need to see a
771 value (hashed pointer) instead. Cryptographically
772 insecure, please do not use on production kernels.
775 [KNL] verbose self-tests
777 Print debugging info while doing the locking API
779 We default to 0 (no extra messages), setting it to
780 1 will print _a lot_ more information - normally
781 only useful to kernel developers.
783 debug_objects [KNL] Enable object debugging
786 [KNL] Disable object debugging
788 debug_guardpage_minorder=
789 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
790 parameter allows control of the order of pages that will
791 be intentionally kept free (and hence protected) by the
792 buddy allocator. Bigger value increase the probability
793 of catching random memory corruption, but reduce the
794 amount of memory for normal system use. The maximum
795 possible value is MAX_ORDER/2. Setting this parameter
796 to 1 or 2 should be enough to identify most random
797 memory corruption problems caused by bugs in kernel or
798 driver code when a CPU writes to (or reads from) a
799 random memory location. Note that there exists a class
800 of memory corruptions problems caused by buggy H/W or
801 F/W or by drivers badly programing DMA (basically when
802 memory is written at bus level and the CPU MMU is
803 bypassed) which are not detectable by
804 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
805 tracking down these problems.
808 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
809 parameter enables the feature at boot time. In
810 default, it is disabled. We can avoid allocating huge
811 chunk of memory for debug pagealloc if we don't enable
812 it at boot time and the system will work mostly same
813 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
814 on: enable the feature
816 debugpat [X86] Enable PAT debugging
818 decnet.addr= [HW,NET]
819 Format: <area>[,<node>]
820 See also Documentation/networking/decnet.txt.
823 [same as hugepagesz=] The size of the default
824 HugeTLB page size. This is the size represented by
825 the legacy /proc/ hugepages APIs, used for SHM, and
826 default size when mounting hugetlbfs filesystems.
827 Defaults to the default architecture's huge page size
830 deferred_probe_timeout=
831 [KNL] Debugging option to set a timeout in seconds for
832 deferred probe to give up waiting on dependencies to
833 probe. Only specific dependencies (subsystems or
834 drivers) that have opted in will be ignored. A timeout of 0
835 will timeout at the end of initcalls. This option will also
836 dump out devices still on the deferred probe list after
840 Set number of hash buckets for dentry cache.
842 disable_1tb_segments [PPC]
843 Disables the use of 1TB hash page table segments. This
844 causes the kernel to fall back to 256MB segments which
845 can be useful when debugging issues that require an SLB
849 See Documentation/networking/ipv6.txt.
852 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
853 hardening is enabled for this boot. Hardened
854 usercopy checking is used to protect the kernel
855 from reading or writing beyond known memory
856 allocation boundaries as a proactive defense
857 against bounds-checking flaws in the kernel's
858 copy_to_user()/copy_from_user() interface.
859 on Perform hardened usercopy checks (default).
860 off Disable hardened usercopy checks.
863 Disable RADIX MMU mode on POWER9
865 disable_cpu_apicid= [X86,APIC,SMP]
867 The number of initial APIC ID for the
868 corresponding CPU to be disabled at boot,
869 mostly used for the kdump 2nd kernel to
870 disable BSP to wake up multiple CPUs without
871 causing system reset or hang due to sending
874 perf_v4_pmi= [X86,INTEL]
876 Disable Intel PMU counter freezing feature.
877 The feature only exists starting from
878 Arch Perfmon v4 (Skylake and newer).
880 disable_ddw [PPC/PSERIES]
881 Disable Dynamic DMA Window support. Use this if
882 to workaround buggy firmware.
885 See Documentation/networking/ipv6.txt.
887 disable_mtrr_cleanup [X86]
888 The kernel tries to adjust MTRR layout from continuous
889 to discrete, to make X server driver able to add WB
890 entry later. This parameter disables that.
892 disable_mtrr_trim [X86, Intel and AMD only]
893 By default the kernel will trim any uncacheable
894 memory out of your available memory pool based on
895 MTRR settings. This parameter disables that behavior,
896 possibly causing your machine to run very slowly.
898 disable_timer_pin_1 [X86]
899 Disable PIN 1 of APIC timer
900 Can be useful to work around chipset bugs.
902 dis_ucode_ldr [X86] Disable the microcode loader.
904 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
905 this option disables the debugging code at boot.
907 dma_debug_entries=<number>
908 This option allows to tune the number of preallocated
909 entries for DMA-API debugging code. One entry is
910 required per DMA-API allocation. Use this if the
911 DMA-API debugging code disables itself because the
912 architectural default is too low.
914 dma_debug_driver=<driver_name>
915 With this option the DMA-API debugging driver
916 filter feature can be enabled at boot time. Just
917 pass the driver to filter for as the parameter.
918 The filter can be disabled or changed to another
919 driver later using sysfs.
921 driver_async_probe= [KNL]
922 List of driver names to be probed asynchronously.
923 Format: <driver_name1>,<driver_name2>...
925 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
926 Broken monitors, graphic adapters, KVMs and EDIDless
927 panels may send no or incorrect EDID data sets.
928 This parameter allows to specify an EDID data sets
929 in the /lib/firmware directory that are used instead.
930 Generic built-in EDID data sets are used, if one of
931 edid/1024x768.bin, edid/1280x1024.bin,
932 edid/1680x1050.bin, or edid/1920x1080.bin is given
933 and no file with the same name exists. Details and
934 instructions how to build your own EDID data are
935 available in Documentation/EDID/howto.rst. An EDID
936 data set will only be used for a particular connector,
937 if its name and a colon are prepended to the EDID
938 name. Each connector may use a unique EDID data
939 set by separating the files with a comma. An EDID
940 data set with no connector name will be used for
941 any connectors not explicitly specified.
946 Format: {"off" | "known"}
947 Control how the dt_cpu_ftrs device-tree binding is
948 used for CPU feature discovery and setup (if it
950 off: Do not use it, fall back to legacy cpu table.
951 known: Do not pass through unknown features to guests
952 or userspace, only those that the kernel is aware of.
954 dump_apple_properties [X86]
955 Dump name and content of EFI device properties on
956 x86 Macs. Useful for driver authors to determine
957 what data is available or for reverse-engineering.
959 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
960 module.dyndbg[="val"]
961 Enable debug messages at boot time. See
962 Documentation/admin-guide/dynamic-debug-howto.rst
965 nompx [X86] Disables Intel Memory Protection Extensions.
966 See Documentation/x86/intel_mpx.rst for more
967 information about the feature.
969 nopku [X86] Disable Memory Protection Keys CPU feature found
972 module.async_probe [KNL]
973 Enable asynchronous probe on this module.
975 early_ioremap_debug [KNL]
976 Enable debug messages in early_ioremap support. This
977 is useful for tracking down temporary early mappings
978 which are not unmapped.
980 earlycon= [KNL] Output early console device and options.
982 [ARM64] The early console is determined by the
983 stdout-path property in device tree's chosen node,
984 or determined by the ACPI SPCR table.
986 [X86] When used with no options the early console is
987 determined by the ACPI SPCR table.
989 cdns,<addr>[,options]
990 Start an early, polled-mode console on a Cadence
991 (xuartps) serial port at the specified address. Only
992 supported option is baud rate. If baud rate is not
993 specified, the serial port must already be setup and
996 uart[8250],io,<addr>[,options]
997 uart[8250],mmio,<addr>[,options]
998 uart[8250],mmio32,<addr>[,options]
999 uart[8250],mmio32be,<addr>[,options]
1000 uart[8250],0x<addr>[,options]
1001 Start an early, polled-mode console on the 8250/16550
1002 UART at the specified I/O port or MMIO address.
1003 MMIO inter-register address stride is either 8-bit
1004 (mmio) or 32-bit (mmio32 or mmio32be).
1005 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1006 to be equivalent to 'mmio'. 'options' are specified
1007 in the same format described for "console=ttyS<n>"; if
1008 unspecified, the h/w is not initialized.
1012 Start an early, polled-mode console on a pl011 serial
1013 port at the specified address. The pl011 serial port
1014 must already be setup and configured. Options are not
1015 yet supported. If 'mmio32' is specified, then only
1016 the driver will use only 32-bit accessors to read/write
1017 the device registers.
1020 Start an early, polled-mode console on a meson serial
1021 port at the specified address. The serial port must
1022 already be setup and configured. Options are not yet
1026 Start an early, polled-mode console on an msm serial
1027 port at the specified address. The serial port
1028 must already be setup and configured. Options are not
1031 msm_serial_dm,<addr>
1032 Start an early, polled-mode console on an msm serial
1033 dm port at the specified address. The serial port
1034 must already be setup and configured. Options are not
1038 Start an early, polled-mode console on a serial port
1039 of an Actions Semi SoC, such as S500 or S900, at the
1040 specified address. The serial port must already be
1041 setup and configured. Options are not yet supported.
1044 Start an early, polled-mode console on a serial port
1045 of an RDA Micro SoC, such as RDA8810PL, at the
1046 specified address. The serial port must already be
1047 setup and configured. Options are not yet supported.
1049 smh Use ARM semihosting calls for early console.
1057 Use early console provided by serial driver available
1058 on Samsung SoCs, requires selecting proper type and
1059 a correct base address of the selected UART port. The
1060 serial port must already be setup and configured.
1061 Options are not yet supported.
1064 Start an early, polled-mode console on a lantiq serial
1065 (lqasc) port at the specified address. The serial port
1066 must already be setup and configured. Options are not
1071 Use early console provided by Freescale LP UART driver
1072 found on Freescale Vybrid and QorIQ LS1021A processors.
1073 A valid base address must be provided, and the serial
1074 port must already be setup and configured.
1077 Start an early, polled-mode console on the
1078 Armada 3700 serial port at the specified
1079 address. The serial port must already be setup
1080 and configured. Options are not yet supported.
1083 Start an early, polled-mode console on a Qualcomm
1084 Generic Interface (GENI) based serial port at the
1085 specified address. The serial port must already be
1086 setup and configured. Options are not yet supported.
1089 Start an early, unaccelerated console on the EFI
1090 memory mapped framebuffer (if available). On cache
1091 coherent non-x86 systems that use system memory for
1092 the framebuffer, pass the 'ram' option so that it is
1093 mapped with the correct attributes.
1095 earlyprintk= [X86,SH,ARM,M68k,S390]
1099 earlyprintk=serial[,ttySn[,baudrate]]
1100 earlyprintk=serial[,0x...[,baudrate]]
1101 earlyprintk=ttySn[,baudrate]
1102 earlyprintk=dbgp[debugController#]
1103 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1104 earlyprintk=xdbc[xhciController#]
1106 earlyprintk is useful when the kernel crashes before
1107 the normal console is initialized. It is not enabled by
1108 default because it has some cosmetic problems.
1110 Append ",keep" to not disable it when the real console
1113 Only one of vga, efi, serial, or usb debug port can
1116 Currently only ttyS0 and ttyS1 may be specified by
1117 name. Other I/O ports may be explicitly specified
1118 on some architectures (x86 and arm at least) by
1119 replacing ttySn with an I/O port address, like this:
1120 earlyprintk=serial,0x1008,115200
1121 You can find the port for a given device in
1122 /proc/tty/driver/serial:
1123 2: uart:ST16650V2 port:00001008 irq:18 ...
1125 Interaction with the standard serial driver is not
1128 The VGA and EFI output is eventually overwritten by
1131 The xen output can only be used by Xen PV guests.
1133 The sclp output can only be used on s390.
1135 The optional "force" to "pciserial" enables use of a
1136 PCI device even when its classcode is not of the
1139 edac_report= [HW,EDAC] Control how to report EDAC event
1140 Format: {"on" | "off" | "force"}
1141 on: enable EDAC to report H/W event. May be overridden
1142 by other higher priority error reporting module.
1143 off: disable H/W event reporting through EDAC.
1144 force: enforce the use of EDAC to report H/W event.
1147 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1150 This is designed to be used in conjunction with
1151 the boot argument: earlyprintk=vga
1154 Format: {"off" | "on" | "skip[mbr]"}
1157 Format: { "old_map", "nochunk", "noruntime", "debug" }
1158 old_map [X86-64]: switch to the old ioremap-based EFI
1159 runtime services mapping. 32-bit still uses this one by
1161 nochunk: disable reading files in "chunks" in the EFI
1162 boot stub, as chunking can cause problems with some
1163 firmware implementations.
1164 noruntime : disable EFI runtime services support
1165 debug: enable misc debug output
1167 efi_no_storage_paranoia [EFI; X86]
1168 Using this parameter you can use more than 50% of
1169 your efi variable storage. Use this parameter only if
1170 you are really sure that your UEFI does sane gc and
1171 fulfills the spec otherwise your board may brick.
1173 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1174 Add arbitrary attribute to specific memory range by
1175 updating original EFI memory map.
1176 Region of memory which aa attribute is added to is
1178 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1179 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1180 attribute is added to range 0x100000000-0x180000000 and
1181 0x10a0000000-0x1120000000.
1183 Using this parameter you can do debugging of EFI memmap
1184 related feature. For example, you can do debugging of
1185 Address Range Mirroring feature even if your box
1188 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1189 that is to be dynamically loaded by Linux. If there are
1190 multiple variables with the same name but with different
1191 vendor GUIDs, all of them will be loaded. See
1192 Documentation/admin-guide/acpi/ssdt-overlays.rst for details.
1195 eisa_irq_edge= [PARISC,HW]
1196 See header of drivers/parisc/eisa.c.
1199 See comment before function elanfreq_setup() in
1200 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1203 Format: { "mq-deadline" | "kyber" | "bfq" }
1204 See Documentation/block/deadline-iosched.txt,
1205 Documentation/block/kyber-iosched.txt and
1206 Documentation/block/bfq-iosched.txt for details.
1208 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1209 Specifies physical address of start of kernel core
1210 image elf header and optionally the size. Generally
1211 kexec loader will pass this option to capture kernel.
1212 See Documentation/kdump/kdump.rst for details.
1214 enable_mtrr_cleanup [X86]
1215 The kernel tries to adjust MTRR layout from continuous
1216 to discrete, to make X server driver able to add WB
1217 entry later. This parameter enables that.
1219 enable_timer_pin_1 [X86]
1220 Enable PIN 1 of APIC timer
1221 Can be useful to work around chipset bugs
1222 (in particular on some ATI chipsets).
1223 The kernel tries to set a reasonable default.
1225 enforcing [SELINUX] Set initial enforcing status.
1227 See security/selinux/Kconfig help text.
1228 0 -- permissive (log only, no denials).
1229 1 -- enforcing (deny and log).
1231 Value can be changed at runtime via /selinux/enforce.
1234 Disable Error Record Serialization Table (ERST)
1237 ether= [HW,NET] Ethernet cards parameters
1238 This option is obsoleted by the "netdev=" option, which
1239 has equivalent usage. See its documentation for details.
1243 Permit 'security.evm' to be updated regardless of
1244 current integrity status.
1248 fail_make_request=[KNL]
1249 General fault injection mechanism.
1250 Format: <interval>,<probability>,<space>,<times>
1251 See also Documentation/fault-injection/.
1254 See Documentation/blockdev/floppy.txt.
1256 force_pal_cache_flush
1257 [IA-64] Avoid check_sal_cache_flush which may hang on
1258 buggy SAL_CACHE_FLUSH implementations. Using this
1259 parameter will force ia64_sal_cache_flush to call
1260 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1263 Forcefully enable Physical Address Extension (PAE).
1264 Many Pentium M systems disable PAE but may have a
1265 functionally usable PAE implementation.
1266 Warning: use of this parameter will taint the kernel
1267 and may cause unknown problems.
1270 [FTRACE] will set and start the specified tracer
1271 as early as possible in order to facilitate early
1274 ftrace_dump_on_oops[=orig_cpu]
1275 [FTRACE] will dump the trace buffers on oops.
1276 If no parameter is passed, ftrace will dump
1277 buffers of all CPUs, but if you pass orig_cpu, it will
1278 dump only the buffer of the CPU that triggered the
1281 ftrace_filter=[function-list]
1282 [FTRACE] Limit the functions traced by the function
1283 tracer at boot up. function-list is a comma separated
1284 list of functions. This list can be changed at run
1285 time by the set_ftrace_filter file in the debugfs
1288 ftrace_notrace=[function-list]
1289 [FTRACE] Do not trace the functions specified in
1290 function-list. This list can be changed at run time
1291 by the set_ftrace_notrace file in the debugfs
1294 ftrace_graph_filter=[function-list]
1295 [FTRACE] Limit the top level callers functions traced
1296 by the function graph tracer at boot up.
1297 function-list is a comma separated list of functions
1298 that can be changed at run time by the
1299 set_graph_function file in the debugfs tracing directory.
1301 ftrace_graph_notrace=[function-list]
1302 [FTRACE] Do not trace from the functions specified in
1303 function-list. This list is a comma separated list of
1304 functions that can be changed at run time by the
1305 set_graph_notrace file in the debugfs tracing directory.
1307 ftrace_graph_max_depth=<uint>
1308 [FTRACE] Used with the function graph tracer. This is
1309 the max depth it will trace into a function. This value
1310 can be changed at run time by the max_graph_depth file
1311 in the tracefs tracing directory. default: 0 (no limit)
1314 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1315 support via parallel port (up to 5 devices per port)
1316 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1317 See also Documentation/input/devices/joystick-parport.rst
1321 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1325 gcov_persist= [GCOV] When non-zero (default), profiling data for
1326 kernel modules is saved and remains accessible via
1327 debugfs, even when the module is unloaded/reloaded.
1328 When zero, profiling data is discarded and associated
1329 debugfs files are removed at module unload time.
1331 goldfish [X86] Enable the goldfish android emulator platform.
1332 Don't use this when you are not running on the
1335 gpt [EFI] Forces disk with valid GPT signature but
1336 invalid Protective MBR to be treated as GPT. If the
1337 primary GPT is corrupted, it enables the backup/alternate
1338 GPT to be used instead.
1340 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1341 the "Enable 0" bit of the configuration register.
1344 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1345 the "Enable 0" bit of the configuration register.
1348 grcan.select= [HW] Select which physical interface to use.
1351 grcan.txsize= [HW] Sets the size of the tx buffer.
1352 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1354 grcan.rxsize= [HW] Sets the size of the rx buffer.
1355 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1358 gpio-mockup.gpio_mockup_ranges
1359 [HW] Sets the ranges of gpiochip of for this device.
1360 Format: <start1>,<end1>,<start2>,<end2>...
1362 hardlockup_all_cpu_backtrace=
1363 [KNL] Should the hard-lockup detector generate
1364 backtraces on all cpus.
1367 hashdist= [KNL,NUMA] Large hashes allocated during boot
1368 are distributed across NUMA nodes. Defaults on
1369 for 64-bit NUMA, off otherwise.
1370 Format: 0 | 1 (for off | on)
1372 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1374 hd= [EIDE] (E)IDE hard drive subsystem geometry
1375 Format: <cyl>,<head>,<sect>
1378 Disable Hardware Error Source Table (HEST) support;
1379 corresponding firmware-first mode error processing
1380 logic will be disabled.
1382 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1383 size of <nn>. This works even on boxes that have no
1384 highmem otherwise. This also works to reduce highmem
1385 size on bigger boxes.
1387 highres= [KNL] Enable/disable high resolution timer mode.
1388 Valid parameters: "on", "off"
1393 hpet= [X86-32,HPET] option to control HPET usage
1394 Format: { enable (default) | disable | force |
1396 disable: disable HPET and use PIT instead
1397 force: allow force enabled of undocumented chips (ICH4,
1399 verbose: show contents of HPET registers during setup
1401 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1402 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1404 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1405 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1406 On x86-64 and powerpc, this option can be specified
1407 multiple times interleaved with hugepages= to reserve
1408 huge pages of different sizes. Valid pages sizes on
1409 x86-64 are 2M (when the CPU supports "pse") and 1G
1410 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1413 [KNL] Should the hung task detector generate panics.
1416 A nonzero value instructs the kernel to panic when a
1417 hung task is detected. The default value is controlled
1418 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1419 option. The value selected by this boot parameter can
1420 be changed later by the kernel.hung_task_panic sysctl.
1422 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1423 terminal devices. Valid values: 0..8
1424 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1425 If specified, z/VM IUCV HVC accepts connections
1426 from listed z/VM user IDs only.
1428 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations
1429 which allow the hypervisor to 'idle' the
1430 guest on lock contention.
1433 Do not unregister boot console at start. This is only
1434 useful for debugging when something happens in the window
1435 between unregistering the boot console and initializing
1438 i2c_bus= [HW] Override the default board specific I2C bus speed
1439 or register an additional I2C bus that is not
1440 registered from board initialization code.
1444 i8042.debug [HW] Toggle i8042 debug mode
1445 i8042.unmask_kbd_data
1446 [HW] Enable printing of interrupt data from the KBD port
1447 (disabled by default, and as a pre-condition
1448 requires that i8042.debug=1 be enabled)
1449 i8042.direct [HW] Put keyboard port into non-translated mode
1450 i8042.dumbkbd [HW] Pretend that controller can only read data from
1451 keyboard and cannot control its state
1452 (Don't attempt to blink the leds)
1453 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1454 i8042.nokbd [HW] Don't check/create keyboard port
1455 i8042.noloop [HW] Disable the AUX Loopback command while probing
1457 i8042.nomux [HW] Don't check presence of an active multiplexing
1459 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1461 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1462 i8042.reset [HW] Reset the controller during init, cleanup and
1463 suspend-to-ram transitions, only during s2r
1464 transitions, or never reset
1465 Format: { 1 | Y | y | 0 | N | n }
1466 1, Y, y: always reset controller
1467 0, N, n: don't ever reset controller
1468 Default: only on s2r transitions on x86; most other
1469 architectures force reset to be always executed
1470 i8042.unlock [HW] Unlock (ignore) the keylock
1471 i8042.kbdreset [HW] Reset device connected to KBD port
1475 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1476 indicates that the driver is running on unsupported
1478 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1479 does not match list of supported models.
1481 [HW] Report power status in /proc/i8k
1482 (disabled by default)
1483 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1486 i915.invert_brightness=
1487 [DRM] Invert the sense of the variable that is used to
1488 set the brightness of the panel backlight. Normally a
1489 brightness value of 0 indicates backlight switched off,
1490 and the maximum of the brightness value sets the backlight
1491 to maximum brightness. If this parameter is set to 0
1492 (default) and the machine requires it, or this parameter
1493 is set to 1, a brightness value of 0 sets the backlight
1494 to maximum brightness, and the maximum of the brightness
1495 value switches the backlight off.
1496 -1 -- never invert brightness
1497 0 -- machine default
1498 1 -- force brightness inversion
1501 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1503 ide-core.nodma= [HW] (E)IDE subsystem
1504 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1505 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1506 .cdrom .chs .ignore_cable are additional options
1507 See Documentation/ide/ide.rst.
1509 ide-generic.probe-mask= [HW] (E)IDE subsystem
1511 Probe mask for legacy ISA IDE ports. Depending on
1512 platform up to 6 ports are supported, enabled by
1513 setting corresponding bits in the mask to 1. The
1514 default value is 0x0, which has a special meaning.
1515 On systems that have PCI, it triggers scanning the
1516 PCI bus for the first and the second port, which
1517 are then probed. On systems without PCI the value
1518 of 0x0 enables probing the two first ports as if it
1521 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1522 Claim all unknown PCI IDE storage controllers.
1525 Format: idle=poll, idle=halt, idle=nomwait
1526 Poll forces a polling idle loop that can slightly
1527 improve the performance of waking up a idle CPU, but
1528 will use a lot of power and make the system run hot.
1530 idle=halt: Halt is forced to be used for CPU idle.
1531 In such case C2/C3 won't be used again.
1532 idle=nomwait: Disable mwait for CPU C-states
1534 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1535 Format: { strict | legacy | 2008 | relaxed }
1538 Choose which programs will be accepted for execution
1539 based on the IEEE 754 NaN encoding(s) supported by
1540 the FPU and the NaN encoding requested with the value
1541 of an ELF file header flag individually set by each
1542 binary. Hardware implementations are permitted to
1543 support either or both of the legacy and the 2008 NaN
1546 Available settings are as follows:
1547 strict accept binaries that request a NaN encoding
1548 supported by the FPU
1549 legacy only accept legacy-NaN binaries, if supported
1551 2008 only accept 2008-NaN binaries, if supported
1553 relaxed accept any binaries regardless of whether
1554 supported by the FPU
1556 The FPU emulator is always able to support both NaN
1557 encodings, so if no FPU hardware is present or it has
1558 been disabled with 'nofpu', then the settings of
1559 'legacy' and '2008' strap the emulator accordingly,
1560 'relaxed' straps the emulator for both legacy-NaN and
1561 2008-NaN, whereas 'strict' enables legacy-NaN only on
1562 legacy processors and both NaN encodings on MIPS32 or
1565 The setting for ABS.fmt/NEG.fmt instruction execution
1566 mode generally follows that for the NaN encoding,
1567 except where unsupported by hardware.
1569 ignore_loglevel [KNL]
1570 Ignore loglevel setting - this will print /all/
1571 kernel messages to the console. Useful for debugging.
1572 We also add it as printk module parameter, so users
1573 could change it dynamically, usually by
1574 /sys/module/printk/parameters/ignore_loglevel.
1577 Ignore RLIMIT_DATA setting for data mappings,
1578 print warning at first misuse. Can be changed via
1579 /sys/module/kernel/parameters/ignore_rlimit_data.
1581 ihash_entries= [KNL]
1582 Set number of hash buckets for inode cache.
1584 ima_appraise= [IMA] appraise integrity measurements
1585 Format: { "off" | "enforce" | "fix" | "log" }
1588 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead.
1589 The builtin appraise policy appraises all files
1592 ima_canonical_fmt [IMA]
1593 Use the canonical format for the binary runtime
1594 measurements, instead of host native format.
1597 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1601 The list of supported hash algorithms is defined
1602 in crypto/hash_info.h.
1605 The builtin policies to load during IMA setup.
1606 Format: "tcb | appraise_tcb | secure_boot |
1609 The "tcb" policy measures all programs exec'd, files
1610 mmap'd for exec, and all files opened with the read
1611 mode bit set by either the effective uid (euid=0) or
1614 The "appraise_tcb" policy appraises the integrity of
1615 all files owned by root.
1617 The "secure_boot" policy appraises the integrity
1618 of files (eg. kexec kernel image, kernel modules,
1619 firmware, policy, etc) based on file signatures.
1621 The "fail_securely" policy forces file signature
1622 verification failure also on privileged mounted
1623 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1626 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1627 Load a policy which meets the needs of the Trusted
1628 Computing Base. This means IMA will measure all
1629 programs exec'd, files mmap'd for exec, and all files
1630 opened for read by uid=0.
1633 Select one of defined IMA measurements template formats.
1634 Formats: { "ima" | "ima-ng" | "ima-sig" }
1638 [IMA] Define a custom template format.
1639 Format: { "field1|...|fieldN" }
1641 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1642 Format: <min_file_size>
1643 Set the minimal file size for using asynchronous hash.
1644 If left unspecified, ahash usage is disabled.
1646 ahash performance varies for different data sizes on
1647 different crypto accelerators. This option can be used
1648 to achieve the best performance for a particular HW.
1650 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1652 Set hashing buffer size. Default: 4k.
1654 ahash performance varies for different chunk sizes on
1655 different crypto accelerators. This option can be used
1656 to achieve best performance for particular HW.
1660 Run specified binary instead of /sbin/init as init
1663 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1664 for working out where the kernel is dying during
1667 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1668 initcall functions. Useful for debugging built-in
1669 modules and initcalls.
1671 initrd= [BOOT] Specify the location of the initial ramdisk
1673 init_pkru= [x86] Specify the default memory protection keys rights
1674 register contents for all processes. 0x55555554 by
1675 default (disallow access to all but pkey 0). Can
1676 override in debugfs after boot.
1678 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1681 int_pln_enable [x86] Enable power limit notification interrupt
1683 integrity_audit=[IMA]
1684 Format: { "0" | "1" }
1685 0 -- basic integrity auditing messages. (Default)
1686 1 -- additional integrity auditing messages.
1688 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1690 Enable intel iommu driver.
1692 Disable intel iommu driver.
1693 igfx_off [Default Off]
1694 By default, gfx is mapped as normal device. If a gfx
1695 device has a dedicated DMAR unit, the DMAR unit is
1696 bypassed by not enabling DMAR with this option. In
1697 this case, gfx device will use physical address for
1700 With this option iommu will not optimize to look
1701 for io virtual address below 32-bit forcing dual
1702 address cycle on pci bus for cards supporting greater
1703 than 32-bit addressing. The default is to look
1704 for translation below 32-bit and if not available
1705 then look in the higher range.
1706 strict [Default Off]
1707 With this option on every unmap_single operation will
1708 result in a hardware IOTLB flush operation as opposed
1709 to batching them for performance.
1710 sp_off [Default Off]
1711 By default, super page will be supported if Intel IOMMU
1712 has the capability. With this option, super page will
1715 By default, scalable mode will be disabled even if the
1716 hardware advertises that it has support for the scalable
1717 mode translation. With this option set, scalable mode
1718 will be used on hardware which claims to support it.
1719 tboot_noforce [Default Off]
1720 Do not force the Intel IOMMU enabled under tboot.
1721 By default, tboot will force Intel IOMMU on, which
1722 could harm performance of some high-throughput
1723 devices like 40GBit network cards, even if identity
1725 Note that using this option lowers the security
1726 provided by tboot because it makes the system
1727 vulnerable to DMA attacks.
1729 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1730 0 disables intel_idle and fall back on acpi_idle.
1731 1 to 9 specify maximum depth of C-state.
1735 Do not enable intel_pstate as the default
1736 scaling driver for the supported processors
1738 Use intel_pstate as a scaling driver, but configure it
1739 to work with generic cpufreq governors (instead of
1740 enabling its internal governor). This mode cannot be
1741 used along with the hardware-managed P-states (HWP)
1744 Enable intel_pstate on systems that prohibit it by default
1745 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1746 instead of acpi-cpufreq may disable platform features, such
1747 as thermal controls and power capping, that rely on ACPI
1748 P-States information being indicated to OSPM and therefore
1749 should be used with caution. This option does not work with
1750 processors that aren't supported by the intel_pstate driver
1751 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1753 Do not enable hardware P state control (HWP)
1756 Only load intel_pstate on systems which support
1757 hardware P state control (HWP) if available.
1759 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1760 Description Table, specifies preferred power management
1761 profile as "Enterprise Server" or "Performance Server",
1762 then this feature is turned on by default.
1764 Allow per-logical-CPU P-State performance control limits using
1765 cpufreq sysfs interface
1767 intremap= [X86-64, Intel-IOMMU]
1768 on enable Interrupt Remapping (default)
1769 off disable Interrupt Remapping
1770 nosid disable Source ID checking
1772 BIOS x2APIC opt-out request will be ignored
1773 nopost disable Interrupt Posting
1775 iomem= Disable strict checking of access to MMIO memory
1776 strict regions from userspace.
1791 nobypass [PPC/POWERNV]
1792 Disable IOMMU bypass, using IOMMU for PCI devices.
1794 iommu.strict= [ARM64] Configure TLB invalidation behaviour
1795 Format: { "0" | "1" }
1797 Request that DMA unmap operations use deferred
1798 invalidation of hardware TLBs, for increased
1799 throughput at the cost of reduced device isolation.
1800 Will fall back to strict mode if not supported by
1801 the relevant IOMMU driver.
1802 1 - Strict mode (default).
1803 DMA unmap operations invalidate IOMMU hardware TLBs
1807 [ARM64] Configure DMA to bypass the IOMMU by default.
1808 Format: { "0" | "1" }
1809 0 - Use IOMMU translation for DMA.
1810 1 - Bypass the IOMMU for DMA.
1811 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
1813 io7= [HW] IO7 for Marvel based alpha systems
1814 See comment before marvel_specify_io7 in
1815 arch/alpha/kernel/core_marvel.c.
1817 io_delay= [X86] I/O delay method
1819 Standard port 0x80 based delay
1821 Alternate port 0xed based delay (needed on some systems)
1823 Simple two microseconds delay
1828 See Documentation/filesystems/nfs/nfsroot.txt.
1830 ipcmni_extend [KNL] Extend the maximum number of unique System V
1831 IPC identifiers from 32,768 to 16,777,216.
1833 irqaffinity= [SMP] Set the default irq affinity mask
1834 The argument is a cpu list, as described above.
1836 irqchip.gicv2_force_probe=
1839 Force the kernel to look for the second 4kB page
1840 of a GICv2 controller even if the memory range
1841 exposed by the device tree is too small.
1843 irqchip.gicv3_nolpi=
1845 Force the kernel to ignore the availability of
1846 LPIs (and by consequence ITSs). Intended for system
1847 that use the kernel as a bootloader, and thus want
1848 to let secondary kernels in charge of setting up
1851 irqchip.gicv3_pseudo_nmi= [ARM64]
1852 Enables support for pseudo-NMIs in the kernel. This
1853 requires the kernel to be built with
1854 CONFIG_ARM64_PSEUDO_NMI.
1857 When an interrupt is not handled search all handlers
1858 for it. Intended to get systems with badly broken
1862 When an interrupt is not handled search all handlers
1863 for it. Also check all handlers each timer
1864 interrupt. Intended to get systems with badly broken
1868 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1870 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1871 [Deprecated - use cpusets instead]
1872 Format: [flag-list,]<cpu-list>
1874 Specify one or more CPUs to isolate from disturbances
1875 specified in the flag list (default: domain):
1878 Disable the tick when a single task runs.
1880 A residual 1Hz tick is offloaded to workqueues, which you
1881 need to affine to housekeeping through the global
1882 workqueue's affinity configured via the
1883 /sys/devices/virtual/workqueue/cpumask sysfs file, or
1884 by using the 'domain' flag described below.
1886 NOTE: by default the global workqueue runs on all CPUs,
1887 so to protect individual CPUs the 'cpumask' file has to
1888 be configured manually after bootup.
1891 Isolate from the general SMP balancing and scheduling
1892 algorithms. Note that performing domain isolation this way
1893 is irreversible: it's not possible to bring back a CPU to
1894 the domains once isolated through isolcpus. It's strongly
1895 advised to use cpusets instead to disable scheduler load
1896 balancing through the "cpuset.sched_load_balance" file.
1897 It offers a much more flexible interface where CPUs can
1898 move in and out of an isolated set anytime.
1900 You can move a process onto or off an "isolated" CPU via
1901 the CPU affinity syscalls or cpuset.
1902 <cpu number> begins at 0 and the maximum value is
1903 "number of CPUs in system - 1".
1905 The format of <cpu-list> is described above.
1911 ivrs_ioapic [HW,X86_64]
1912 Provide an override to the IOAPIC-ID<->DEVICE-ID
1913 mapping provided in the IVRS ACPI table. For
1914 example, to map IOAPIC-ID decimal 10 to
1915 PCI device 00:14.0 write the parameter as:
1916 ivrs_ioapic[10]=00:14.0
1918 ivrs_hpet [HW,X86_64]
1919 Provide an override to the HPET-ID<->DEVICE-ID
1920 mapping provided in the IVRS ACPI table. For
1921 example, to map HPET-ID decimal 0 to
1922 PCI device 00:14.0 write the parameter as:
1923 ivrs_hpet[0]=00:14.0
1925 ivrs_acpihid [HW,X86_64]
1926 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1927 mapping provided in the IVRS ACPI table. For
1928 example, to map UART-HID:UID AMD0020:0 to
1929 PCI device 00:14.5 write the parameter as:
1930 ivrs_acpihid[00:14.5]=AMD0020:0
1932 js= [HW,JOY] Analog joystick
1933 See Documentation/input/joydev/joystick.rst.
1936 When CONFIG_RANDOMIZE_BASE is set, this disables
1937 kernel and module base offset ASLR (Address Space
1938 Layout Randomization).
1941 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1942 report on every invalid memory access. Without this
1943 parameter KASAN will print report only for the first
1948 kernelcore= [KNL,X86,IA-64,PPC]
1949 Format: nn[KMGTPE] | nn% | "mirror"
1950 This parameter specifies the amount of memory usable by
1951 the kernel for non-movable allocations. The requested
1952 amount is spread evenly throughout all nodes in the
1953 system as ZONE_NORMAL. The remaining memory is used for
1954 movable memory in its own zone, ZONE_MOVABLE. In the
1955 event, a node is too small to have both ZONE_NORMAL and
1956 ZONE_MOVABLE, kernelcore memory will take priority and
1957 other nodes will have a larger ZONE_MOVABLE.
1959 ZONE_MOVABLE is used for the allocation of pages that
1960 may be reclaimed or moved by the page migration
1961 subsystem. Note that allocations like PTEs-from-HighMem
1962 still use the HighMem zone if it exists, and the Normal
1963 zone if it does not.
1965 It is possible to specify the exact amount of memory in
1966 the form of "nn[KMGTPE]", a percentage of total system
1967 memory in the form of "nn%", or "mirror". If "mirror"
1968 option is specified, mirrored (reliable) memory is used
1969 for non-movable allocations and remaining memory is used
1970 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
1971 are exclusive, so you cannot specify multiple forms.
1973 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1974 Format: <Controller#>[,poll interval]
1975 The controller # is the number of the ehci usb debug
1976 port as it is probed via PCI. The poll interval is
1977 optional and is the number seconds in between
1978 each poll cycle to the debug port in case you need
1979 the functionality for interrupting the kernel with
1980 gdb or control-c on the dbgp connection. When
1981 not using this parameter you use sysrq-g to break into
1982 the kernel debugger.
1984 kgdboc= [KGDB,HW] kgdb over consoles.
1985 Requires a tty driver that supports console polling,
1986 or a supported polling keyboard driver (non-usb).
1987 Serial only format: <serial_device>[,baud]
1988 keyboard only format: kbd
1989 keyboard and serial format: kbd,<serial_device>[,baud]
1990 Optional Kernel mode setting:
1991 kms, kbd format: kms,kbd
1992 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1994 kgdbwait [KGDB] Stop kernel execution and enter the
1995 kernel debugger at the earliest opportunity.
1997 kmac= [MIPS] korina ethernet MAC address.
1998 Configure the RouterBoard 532 series on-chip
1999 Ethernet adapter MAC address.
2001 kmemleak= [KNL] Boot-time kmemleak enable/disable
2002 Valid arguments: on, off
2004 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
2007 kpti= [ARM64] Control page table isolation of user
2008 and kernel address spaces.
2009 Default: enabled on cores which need mitigation.
2013 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
2014 Default is 0 (don't ignore, but inject #GP)
2016 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
2017 Default is false (don't support).
2019 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
2023 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
2024 Default is 1 (enabled)
2026 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
2028 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
2030 kvm-arm.vgic_v3_group0_trap=
2031 [KVM,ARM] Trap guest accesses to GICv3 group-0
2034 kvm-arm.vgic_v3_group1_trap=
2035 [KVM,ARM] Trap guest accesses to GICv3 group-1
2038 kvm-arm.vgic_v3_common_trap=
2039 [KVM,ARM] Trap guest accesses to GICv3 common
2042 kvm-arm.vgic_v4_enable=
2043 [KVM,ARM] Allow use of GICv4 for direct injection of
2046 kvm-intel.ept= [KVM,Intel] Disable extended page tables
2047 (virtualized MMU) support on capable Intel chips.
2048 Default is 1 (enabled)
2050 kvm-intel.emulate_invalid_guest_state=
2051 [KVM,Intel] Enable emulation of invalid guest states
2052 Default is 0 (disabled)
2054 kvm-intel.flexpriority=
2055 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
2056 Default is 1 (enabled)
2059 [KVM,Intel] Enable VMX nesting (nVMX).
2060 Default is 0 (disabled)
2062 kvm-intel.unrestricted_guest=
2063 [KVM,Intel] Disable unrestricted guest feature
2064 (virtualized real and unpaged mode) on capable
2065 Intel chips. Default is 1 (enabled)
2067 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2070 Valid arguments: never, cond, always
2072 always: L1D cache flush on every VMENTER.
2073 cond: Flush L1D on VMENTER only when the code between
2074 VMEXIT and VMENTER can leak host memory.
2075 never: Disables the mitigation
2077 Default is cond (do L1 cache flush in specific instances)
2079 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2080 feature (tagged TLBs) on capable Intel chips.
2081 Default is 1 (enabled)
2083 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2086 The kernel PTE inversion protection is unconditionally
2087 enabled and cannot be disabled.
2090 Provides all available mitigations for the
2091 L1TF vulnerability. Disables SMT and
2092 enables all mitigations in the
2093 hypervisors, i.e. unconditional L1D flush.
2095 SMT control and L1D flush control via the
2096 sysfs interface is still possible after
2097 boot. Hypervisors will issue a warning
2098 when the first VM is started in a
2099 potentially insecure configuration,
2100 i.e. SMT enabled or L1D flush disabled.
2103 Same as 'full', but disables SMT and L1D
2104 flush runtime control. Implies the
2105 'nosmt=force' command line option.
2106 (i.e. sysfs control of SMT is disabled.)
2109 Leaves SMT enabled and enables the default
2110 hypervisor mitigation, i.e. conditional
2113 SMT control and L1D flush control via the
2114 sysfs interface is still possible after
2115 boot. Hypervisors will issue a warning
2116 when the first VM is started in a
2117 potentially insecure configuration,
2118 i.e. SMT enabled or L1D flush disabled.
2122 Disables SMT and enables the default
2123 hypervisor mitigation.
2125 SMT control and L1D flush control via the
2126 sysfs interface is still possible after
2127 boot. Hypervisors will issue a warning
2128 when the first VM is started in a
2129 potentially insecure configuration,
2130 i.e. SMT enabled or L1D flush disabled.
2133 Same as 'flush', but hypervisors will not
2134 warn when a VM is started in a potentially
2135 insecure configuration.
2138 Disables hypervisor mitigations and doesn't
2140 It also drops the swap size and available
2141 RAM limit restriction on both hypervisor and
2146 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
2152 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2155 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2156 value for LAPIC timer one-shot implementation. Default
2157 back to the programmable timer unit in the LAPIC.
2159 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2162 libata.dma= [LIBATA] DMA control
2163 libata.dma=0 Disable all PATA and SATA DMA
2164 libata.dma=1 PATA and SATA Disk DMA only
2165 libata.dma=2 ATAPI (CDROM) DMA only
2166 libata.dma=4 Compact Flash DMA only
2167 Combinations also work, so libata.dma=3 enables DMA
2168 for disks and CDROMs, but not CFs.
2170 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2171 libata.ignore_hpa=0 keep BIOS limits (default)
2172 libata.ignore_hpa=1 ignore limits, using full disk
2174 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2178 libata.force= [LIBATA] Force configurations. The format is comma
2179 separated list of "[ID:]VAL" where ID is
2180 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2181 matching port, link or device. Basically, it matches
2182 the ATA ID string printed on console by libata. If
2183 the whole ID part is omitted, the last PORT and DEVICE
2184 values are used. If ID hasn't been specified yet, the
2185 configuration applies to all ports, links and devices.
2187 If only DEVICE is omitted, the parameter applies to
2188 the port and all links and devices behind it. DEVICE
2189 number of 0 either selects the first device or the
2190 first fan-out link behind PMP device. It does not
2191 select the host link. DEVICE number of 15 selects the
2192 host link and device attached to it.
2194 The VAL specifies the configuration to force. As long
2195 as there's no ambiguity shortcut notation is allowed.
2196 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2197 The following configurations can be forced.
2199 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2200 Any ID with matching PORT is used.
2202 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2204 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2205 udma[/][16,25,33,44,66,100,133] notation is also
2208 * [no]ncq: Turn on or off NCQ.
2210 * [no]ncqtrim: Turn off queued DSM TRIM.
2212 * nohrst, nosrst, norst: suppress hard, soft
2215 * rstonce: only attempt one reset during
2216 hot-unplug link recovery
2218 * dump_id: dump IDENTIFY data.
2220 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2222 * disable: Disable this device.
2224 If there are multiple matching configurations changing
2225 the same attribute, the last one is used.
2227 memblock=debug [KNL] Enable memblock debug messages.
2229 load_ramdisk= [RAM] List of ramdisks to load from floppy
2230 See Documentation/blockdev/ramdisk.txt.
2232 lockd.nlm_grace_period=P [NFS] Assign grace period.
2235 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2238 lockd.nlm_timeout=T [NFS] Assign timeout value.
2241 lockd.nlm_udpport=M [NFS] Assign UDP port.
2244 locktorture.nreaders_stress= [KNL]
2245 Set the number of locking read-acquisition kthreads.
2246 Defaults to being automatically set based on the
2247 number of online CPUs.
2249 locktorture.nwriters_stress= [KNL]
2250 Set the number of locking write-acquisition kthreads.
2252 locktorture.onoff_holdoff= [KNL]
2253 Set time (s) after boot for CPU-hotplug testing.
2255 locktorture.onoff_interval= [KNL]
2256 Set time (s) between CPU-hotplug operations, or
2257 zero to disable CPU-hotplug testing.
2259 locktorture.shuffle_interval= [KNL]
2260 Set task-shuffle interval (jiffies). Shuffling
2261 tasks allows some CPUs to go into dyntick-idle
2262 mode during the locktorture test.
2264 locktorture.shutdown_secs= [KNL]
2265 Set time (s) after boot system shutdown. This
2266 is useful for hands-off automated testing.
2268 locktorture.stat_interval= [KNL]
2269 Time (s) between statistics printk()s.
2271 locktorture.stutter= [KNL]
2272 Time (s) to stutter testing, for example,
2273 specifying five seconds causes the test to run for
2274 five seconds, wait for five seconds, and so on.
2275 This tests the locking primitive's ability to
2276 transition abruptly to and from idle.
2278 locktorture.torture_type= [KNL]
2279 Specify the locking implementation to test.
2281 locktorture.verbose= [KNL]
2282 Enable additional printk() statements.
2284 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2287 loglevel= All Kernel Messages with a loglevel smaller than the
2288 console loglevel will be printed to the console. It can
2289 also be changed with klogd or other programs. The
2290 loglevels are defined as follows:
2292 0 (KERN_EMERG) system is unusable
2293 1 (KERN_ALERT) action must be taken immediately
2294 2 (KERN_CRIT) critical conditions
2295 3 (KERN_ERR) error conditions
2296 4 (KERN_WARNING) warning conditions
2297 5 (KERN_NOTICE) normal but significant condition
2298 6 (KERN_INFO) informational
2299 7 (KERN_DEBUG) debug-level messages
2301 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2302 in bytes. n must be a power of two and greater
2303 than the minimal size. The minimal size is defined
2304 by LOG_BUF_SHIFT kernel config parameter. There is
2305 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2306 that allows to increase the default size depending on
2307 the number of CPUs. See init/Kconfig for more details.
2309 logo.nologo [FB] Disables display of the built-in Linux logo.
2310 This may be used to provide more screen space for
2311 kernel log messages and is useful when debugging
2312 kernel boot problems.
2314 lp=0 [LP] Specify parallel ports to use, e.g,
2315 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2316 lp=reset first parallel port). 'lp=0' disables the
2317 lp=auto printer driver. 'lp=reset' (which can be
2318 specified in addition to the ports) causes
2319 attached printers to be reset. Using
2320 lp=port1,port2,... specifies the parallel ports
2321 to associate lp devices with, starting with
2322 lp0. A port specification may be 'none' to skip
2323 that lp device, or a parport name such as
2324 'parport0'. Specifying 'lp=auto' instead of a
2325 port specification list means that device IDs
2326 from each port should be examined, to see if
2327 an IEEE 1284-compliant printer is attached; if
2328 so, the driver will manage that printer.
2329 See also header of drivers/char/lp.c.
2332 Sets loops_per_jiffy to given constant, thus avoiding
2333 time-consuming boot-time autodetection (up to 250 ms per
2334 CPU). 0 enables autodetection (default). To determine
2335 the correct value for your kernel, boot with normal
2336 autodetection and see what value is printed. Note that
2337 on SMP systems the preset will be applied to all CPUs,
2338 which is likely to cause problems if your CPUs need
2339 significantly divergent settings. An incorrect value
2340 will cause delays in the kernel to be wrong, leading to
2341 unpredictable I/O errors and other breakage. Although
2342 unlikely, in the extreme case this might damage your
2346 Format: <io>,<irq>,<dma>
2348 lsm.debug [SECURITY] Enable LSM initialization debugging output.
2351 [SECURITY] Choose order of LSM initialization. This
2352 overrides CONFIG_LSM, and the "security=" parameter.
2354 machvec= [IA-64] Force the use of a particular machine-vector
2355 (machvec) in a generic kernel.
2356 Example: machvec=hpzx1_swiotlb
2358 machtype= [Loongson] Share the same kernel image file between different
2360 Example: machtype=lemote-yeeloong-2f-7inch
2362 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2363 than or equal to this physical address is ignored.
2365 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2366 will bring up during bootup. maxcpus=n : n >= 0 limits
2367 the kernel to bring up 'n' processors. Surely after
2368 bootup you can bring up the other plugged cpu by executing
2369 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2370 only takes effect during system bootup.
2371 While n=0 is a special case, it is equivalent to "nosmp",
2372 which also disables the IO APIC.
2374 max_loop= [LOOP] The number of loop block devices that get
2375 (loop.max_loop) unconditionally pre-created at init time. The default
2376 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2377 of statically allocating a predefined number, loop
2378 devices can be requested on-demand with the
2379 /dev/loop-control interface.
2381 mce [X86-32] Machine Check Exception
2383 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst
2385 md= [HW] RAID subsystems devices and level
2386 See Documentation/admin-guide/md.rst.
2389 Format: <first>,<last>
2390 Specifies range of consoles to be captured by the MDA.
2393 Control mitigation for the Micro-architectural Data
2394 Sampling (MDS) vulnerability.
2396 Certain CPUs are vulnerable to an exploit against CPU
2397 internal buffers which can forward information to a
2398 disclosure gadget under certain conditions.
2400 In vulnerable processors, the speculatively
2401 forwarded data can be used in a cache side channel
2402 attack, to access data to which the attacker does
2403 not have direct access.
2405 This parameter controls the MDS mitigation. The
2408 full - Enable MDS mitigation on vulnerable CPUs
2409 full,nosmt - Enable MDS mitigation and disable
2410 SMT on vulnerable CPUs
2411 off - Unconditionally disable MDS mitigation
2413 Not specifying this option is equivalent to
2416 For details see: Documentation/admin-guide/hw-vuln/mds.rst
2418 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2419 Amount of memory to be used when the kernel is not able
2420 to see the whole system memory or for test.
2421 [X86] Work as limiting max address. Use together
2422 with memmap= to avoid physical address space collisions.
2423 Without memmap= PCI devices could be placed at addresses
2424 belonging to unused RAM.
2426 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2430 [KNL,SH] Allow user to override the default size for
2431 per-device physically contiguous DMA buffers.
2433 memhp_default_state=online/offline
2434 [KNL] Set the initial state for the memory hotplug
2435 onlining policy. If not specified, the default value is
2436 set according to the
2437 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2439 See Documentation/admin-guide/mm/memory-hotplug.rst.
2441 memmap=exactmap [KNL,X86] Enable setting of an exact
2442 E820 memory map, as specified by the user.
2443 Such memmap=exactmap lines can be constructed based on
2444 BIOS output or other requirements. See the memmap=nn@ss
2447 memmap=nn[KMG]@ss[KMG]
2448 [KNL] Force usage of a specific region of memory.
2449 Region of memory to be used is from ss to ss+nn.
2450 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2451 which limits max address to nn[KMG].
2452 Multiple different regions can be specified,
2455 memmap=100M@2G,100M#3G,1G!1024G
2457 memmap=nn[KMG]#ss[KMG]
2458 [KNL,ACPI] Mark specific memory as ACPI data.
2459 Region of memory to be marked is from ss to ss+nn.
2461 memmap=nn[KMG]$ss[KMG]
2462 [KNL,ACPI] Mark specific memory as reserved.
2463 Region of memory to be reserved is from ss to ss+nn.
2464 Example: Exclude memory from 0x18690000-0x1869ffff
2465 memmap=64K$0x18690000
2467 memmap=0x10000$0x18690000
2468 Some bootloaders may need an escape character before '$',
2469 like Grub2, otherwise '$' and the following number
2472 memmap=nn[KMG]!ss[KMG]
2473 [KNL,X86] Mark specific memory as protected.
2474 Region of memory to be used, from ss to ss+nn.
2475 The memory region may be marked as e820 type 12 (0xc)
2476 and is NVDIMM or ADR memory.
2478 memmap=<size>%<offset>-<oldtype>+<newtype>
2479 [KNL,ACPI] Convert memory within the specified region
2480 from <oldtype> to <newtype>. If "-<oldtype>" is left
2481 out, the whole region will be marked as <newtype>,
2482 even if previously unavailable. If "+<newtype>" is left
2483 out, matching memory will be removed. Types are
2484 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2485 3 = ACPI, 12 = PRAM.
2487 memory_corruption_check=0/1 [X86]
2488 Some BIOSes seem to corrupt the first 64k of
2489 memory when doing things like suspend/resume.
2490 Setting this option will scan the memory
2491 looking for corruption. Enabling this will
2492 both detect corruption and prevent the kernel
2493 from using the memory being corrupted.
2494 However, its intended as a diagnostic tool; if
2495 repeatable BIOS-originated corruption always
2496 affects the same memory, you can use memmap=
2497 to prevent the kernel from using that memory.
2499 memory_corruption_check_size=size [X86]
2500 By default it checks for corruption in the low
2501 64k, making this memory unavailable for normal
2502 use. Use this parameter to scan for
2503 corruption in more or less memory.
2505 memory_corruption_check_period=seconds [X86]
2506 By default it checks for corruption every 60
2507 seconds. Use this parameter to check at some
2508 other rate. 0 disables periodic checking.
2510 memtest= [KNL,X86,ARM,PPC] Enable memtest
2512 default : 0 <disable>
2513 Specifies the number of memtest passes to be
2514 performed. Each pass selects another test
2515 pattern from a given set of patterns. Memtest
2516 fills the memory with this pattern, validates
2517 memory contents and reserves bad memory
2518 regions that are detected.
2520 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2521 Valid arguments: on, off
2522 Default (depends on kernel configuration option):
2523 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2524 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2525 mem_encrypt=on: Activate SME
2526 mem_encrypt=off: Do not activate SME
2528 Refer to Documentation/virtual/kvm/amd-memory-encryption.rst
2529 for details on when memory encryption can be activated.
2531 mem_sleep_default= [SUSPEND] Default system suspend mode:
2532 s2idle - Suspend-To-Idle
2533 shallow - Power-On Suspend or equivalent (if supported)
2534 deep - Suspend-To-RAM or equivalent (if supported)
2535 See Documentation/admin-guide/pm/sleep-states.rst.
2537 meye.*= [HW] Set MotionEye Camera parameters
2538 See Documentation/media/v4l-drivers/meye.rst.
2540 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2541 Multi-Function General Purpose Timers on AMD Geode
2544 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2545 the BIOS has incorrectly applied a workaround. TinyBIOS
2546 version 0.98 is known to be affected, 0.99 fixes the
2547 problem by letting the user disable the workaround.
2551 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2552 physical address is ignored.
2554 mini2440= [ARM,HW,KNL]
2555 Format:[0..2][b][c][t]
2557 MINI2440 configuration specification:
2558 0 - The attached screen is the 3.5" TFT
2559 1 - The attached screen is the 7" TFT
2560 2 - The VGA Shield is attached (1024x768)
2561 Leaving out the screen size parameter will not load
2562 the TFT driver, and the framebuffer will be left
2564 b - Enable backlight. The TFT backlight pin will be
2565 linked to the kernel VESA blanking code and a GPIO
2566 LED. This parameter is not necessary when using the
2568 c - Enable the s3c camera interface.
2569 t - Reserved for enabling touchscreen support. The
2570 touchscreen support is not enabled in the mainstream
2571 kernel as of 2.6.30, a preliminary port can be found
2572 in the "bleeding edge" mini2440 support kernel at
2573 http://repo.or.cz/w/linux-2.6/mini2440.git
2576 [X86,PPC,S390,ARM64] Control optional mitigations for
2577 CPU vulnerabilities. This is a set of curated,
2578 arch-independent options, each of which is an
2579 aggregation of existing arch-specific options.
2582 Disable all optional CPU mitigations. This
2583 improves system performance, but it may also
2584 expose users to several CPU vulnerabilities.
2585 Equivalent to: nopti [X86,PPC]
2589 nospectre_v2 [X86,PPC,S390,ARM64]
2590 spectre_v2_user=off [X86]
2591 spec_store_bypass_disable=off [X86,PPC]
2592 ssbd=force-off [ARM64]
2597 Mitigate all CPU vulnerabilities, but leave SMT
2598 enabled, even if it's vulnerable. This is for
2599 users who don't want to be surprised by SMT
2600 getting disabled across kernel upgrades, or who
2601 have other ways of avoiding SMT-based attacks.
2602 Equivalent to: (default behavior)
2605 Mitigate all CPU vulnerabilities, disabling SMT
2606 if needed. This is for users who always want to
2607 be fully mitigated, even if it means losing SMT.
2608 Equivalent to: l1tf=flush,nosmt [X86]
2609 mds=full,nosmt [X86]
2612 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2613 parameter allows control of the logging verbosity for
2614 the additional memory initialisation checks. A value
2615 of 0 disables mminit logging and a level of 4 will
2616 log everything. Information is printed at KERN_DEBUG
2617 so loglevel=8 may also need to be specified.
2620 [KNL] When CONFIG_MODULE_SIG is set, this means that
2621 modules without (valid) signatures will fail to load.
2622 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2623 is always true, so this option does nothing.
2625 module_blacklist= [KNL] Do not load a comma-separated list of
2626 modules. Useful for debugging problem modules.
2629 [MOUSE] Maximum time between finger touching and
2630 leaving touchpad surface for touch to be considered
2631 a tap and be reported as a left button click (for
2632 touchpads working in absolute mode only).
2634 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2635 reporting absolute coordinates, such as tablets
2636 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2637 reporting absolute coordinates, such as tablets
2639 movablecore= [KNL,X86,IA-64,PPC]
2640 Format: nn[KMGTPE] | nn%
2641 This parameter is the complement to kernelcore=, it
2642 specifies the amount of memory used for migratable
2643 allocations. If both kernelcore and movablecore is
2644 specified, then kernelcore will be at *least* the
2645 specified value but may be more. If movablecore on its
2646 own is specified, the administrator must be careful
2647 that the amount of memory usable for all allocations
2650 movable_node [KNL] Boot-time switch to make hotplugable memory
2651 NUMA nodes to be movable. This means that the memory
2652 of such nodes will be usable only for movable
2653 allocations which rules out almost all kernel
2654 allocations. Use with caution!
2656 MTD_Partition= [MTD]
2657 Format: <name>,<region-number>,<size>,<offset>
2659 MTD_Region= [MTD] Format:
2660 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2663 See drivers/mtd/cmdlinepart.c.
2665 multitce=off [PPC] This parameter disables the use of the pSeries
2666 firmware feature for updating multiple TCE entries
2669 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2671 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2673 boundary - index of last SLC block on Flex-OneNAND.
2674 The remaining blocks are configured as MLC blocks.
2675 lock - Configure if Flex-OneNAND boundary should be locked.
2676 Once locked, the boundary cannot be changed.
2677 1 indicates lock status, 0 indicates unlock status.
2680 ARM/S3C2412 JIVE boot control
2682 See arch/arm/mach-s3c2412/mach-jive.c
2684 mtouchusb.raw_coordinates=
2685 [HW] Make the MicroTouch USB driver use raw coordinates
2686 ('y', default) or cooked coordinates ('n')
2688 mtrr_chunk_size=nn[KMG] [X86]
2689 used for mtrr cleanup. It is largest continuous chunk
2690 that could hold holes aka. UC entries.
2692 mtrr_gran_size=nn[KMG] [X86]
2693 Used for mtrr cleanup. It is granularity of mtrr block.
2695 Large value could prevent small alignment from
2698 mtrr_spare_reg_nr=n [X86]
2700 Range: 0,7 : spare reg number
2702 Used for mtrr cleanup. It is spare mtrr entries number.
2703 Set to 2 or more if your graphical card needs more.
2705 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2707 netdev= [NET] Network devices parameters
2708 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2709 Note that mem_start is often overloaded to mean
2710 something different and driver-specific.
2711 This usage is only documented in each driver source
2715 [NETFILTER] Enable connection tracking flow accounting
2716 0 to disable accounting
2717 1 to enable accounting
2720 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2721 See Documentation/filesystems/nfs/nfsroot.txt.
2723 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2724 See Documentation/filesystems/nfs/nfsroot.txt.
2726 nfsrootdebug [NFS] enable nfsroot debugging messages.
2727 See Documentation/filesystems/nfs/nfsroot.txt.
2729 nfs.callback_nr_threads=
2730 [NFSv4] set the total number of threads that the
2731 NFS client will assign to service NFSv4 callback
2734 nfs.callback_tcpport=
2735 [NFS] set the TCP port on which the NFSv4 callback
2736 channel should listen.
2739 [NFS] sets the pathname to the program which is used
2740 to update the NFS client cache entries.
2742 nfs.cache_getent_timeout=
2743 [NFS] sets the timeout after which an attempt to
2744 update a cache entry is deemed to have failed.
2746 nfs.idmap_cache_timeout=
2747 [NFS] set the maximum lifetime for idmapper cache
2751 [NFS] enable 64-bit inode numbers.
2752 If zero, the NFS client will fake up a 32-bit inode
2753 number for the readdir() and stat() syscalls instead
2754 of returning the full 64-bit number.
2755 The default is to return 64-bit inode numbers.
2757 nfs.max_session_cb_slots=
2758 [NFSv4.1] Sets the maximum number of session
2759 slots the client will assign to the callback
2760 channel. This determines the maximum number of
2761 callbacks the client will process in parallel for
2762 a particular server.
2764 nfs.max_session_slots=
2765 [NFSv4.1] Sets the maximum number of session slots
2766 the client will attempt to negotiate with the server.
2767 This limits the number of simultaneous RPC requests
2768 that the client can send to the NFSv4.1 server.
2769 Note that there is little point in setting this
2770 value higher than the max_tcp_slot_table_limit.
2772 nfs.nfs4_disable_idmapping=
2773 [NFSv4] When set to the default of '1', this option
2774 ensures that both the RPC level authentication
2775 scheme and the NFS level operations agree to use
2776 numeric uids/gids if the mount is using the
2777 'sec=sys' security flavour. In effect it is
2778 disabling idmapping, which can make migration from
2779 legacy NFSv2/v3 systems to NFSv4 easier.
2780 Servers that do not support this mode of operation
2781 will be autodetected by the client, and it will fall
2782 back to using the idmapper.
2783 To turn off this behaviour, set the value to '0'.
2785 [NFS4] Specify an additional fixed unique ident-
2786 ification string that NFSv4 clients can insert into
2787 their nfs_client_id4 string. This is typically a
2788 UUID that is generated at system install time.
2790 nfs.send_implementation_id =
2791 [NFSv4.1] Send client implementation identification
2792 information in exchange_id requests.
2793 If zero, no implementation identification information
2795 The default is to send the implementation identification
2798 nfs.recover_lost_locks =
2799 [NFSv4] Attempt to recover locks that were lost due
2800 to a lease timeout on the server. Please note that
2801 doing this risks data corruption, since there are
2802 no guarantees that the file will remain unchanged
2803 after the locks are lost.
2804 If you want to enable the kernel legacy behaviour of
2805 attempting to recover these locks, then set this
2807 The default parameter value of '0' causes the kernel
2808 not to attempt recovery of lost locks.
2810 nfs4.layoutstats_timer =
2811 [NFSv4.2] Change the rate at which the kernel sends
2812 layoutstats to the pNFS metadata server.
2814 Setting this to value to 0 causes the kernel to use
2815 whatever value is the default set by the layout
2816 driver. A non-zero value sets the minimum interval
2817 in seconds between layoutstats transmissions.
2819 nfsd.nfs4_disable_idmapping=
2820 [NFSv4] When set to the default of '1', the NFSv4
2821 server will return only numeric uids and gids to
2822 clients using auth_sys, and will accept numeric uids
2823 and gids from such clients. This is intended to ease
2824 migration from NFSv2/v3.
2826 nmi_debug= [KNL,SH] Specify one or more actions to take
2827 when a NMI is triggered.
2828 Format: [state][,regs][,debounce][,die]
2830 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2831 Format: [panic,][nopanic,][num]
2833 0 - turn hardlockup detector in nmi_watchdog off
2834 1 - turn hardlockup detector in nmi_watchdog on
2835 When panic is specified, panic when an NMI watchdog
2836 timeout occurs (or 'nopanic' to not panic on an NMI
2837 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set)
2838 To disable both hard and soft lockup detectors,
2839 please see 'nowatchdog'.
2840 This is useful when you use a panic=... timeout and
2841 need the box quickly up again.
2843 These settings can be accessed at runtime via
2844 the nmi_watchdog and hardlockup_panic sysctls.
2846 netpoll.carrier_timeout=
2847 [NET] Specifies amount of time (in seconds) that
2848 netpoll should wait for a carrier. By default netpoll
2851 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2852 emulation library even if a 387 maths coprocessor
2855 no5lvl [X86-64] Disable 5-level paging mode. Forces
2856 kernel to use 4-level paging instead.
2859 [HW] Never suspend the console
2860 Disable suspending of consoles during suspend and
2861 hibernate operations. Once disabled, debugging
2862 messages can reach various consoles while the rest
2863 of the system is being put to sleep (ie, while
2864 debugging driver suspend/resume hooks). This may
2865 not work reliably with all consoles, but is known
2866 to work with serial and VGA consoles.
2867 To facilitate more flexible debugging, we also add
2868 console_suspend, a printk module parameter to control
2869 it. Users could use console_suspend (usually
2870 /sys/module/printk/parameters/console_suspend) to
2871 turn on/off it dynamically.
2873 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2874 caches in the slab allocator. Saves per-node memory,
2875 but will impact performance.
2879 noaltinstr [S390] Disables alternative instructions patching
2880 (CPU alternatives feature).
2882 noapic [SMP,APIC] Tells the kernel to not make use of any
2883 IOAPICs that may be present in the system.
2885 noautogroup Disable scheduler automatic task group creation.
2887 nobats [PPC] Do not use BATs for mapping kernel lowmem
2888 on "Classic" PPC cores.
2892 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2894 nodelayacct [KNL] Disable per-task delay accounting
2896 nodsp [SH] Disable hardware DSP at boot time.
2898 noefi Disable EFI runtime services support.
2903 On X86-32 available only on PAE configured kernels.
2904 noexec=on: enable non-executable mappings (default)
2905 noexec=off: disable non-executable mappings
2908 Disable SMAP (Supervisor Mode Access Prevention)
2909 even if it is supported by processor.
2912 Disable SMEP (Supervisor Mode Execution Prevention)
2913 even if it is supported by processor.
2916 This affects only 32-bit executables.
2917 noexec32=on: enable non-executable mappings (default)
2918 read doesn't imply executable mappings
2919 noexec32=off: disable non-executable mappings
2920 read implies executable mappings
2922 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2924 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2925 register save and restore. The kernel will only save
2926 legacy floating-point registers on task switch.
2928 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2930 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2931 Equivalent to smt=1.
2933 [KNL,x86] Disable symmetric multithreading (SMT).
2934 nosmt=force: Force disable SMT, cannot be undone
2935 via the sysfs control file.
2937 nospectre_v1 [PPC] Disable mitigations for Spectre Variant 1 (bounds
2938 check bypass). With this option data leaks are possible
2941 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for
2942 the Spectre variant 2 (indirect branch prediction)
2943 vulnerability. System may allow data leaks with this
2946 nospec_store_bypass_disable
2947 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
2949 noxsave [BUGS=X86] Disables x86 extended register state save
2950 and restore using xsave. The kernel will fallback to
2951 enabling legacy floating-point and sse state.
2953 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2954 register states. The kernel will fall back to use
2955 xsave to save the states. By using this parameter,
2956 performance of saving the states is degraded because
2957 xsave doesn't support modified optimization while
2958 xsaveopt supports it on xsaveopt enabled systems.
2960 noxsaves [X86] Disables xsaves and xrstors used in saving and
2961 restoring x86 extended register state in compacted
2962 form of xsave area. The kernel will fall back to use
2963 xsaveopt and xrstor to save and restore the states
2964 in standard form of xsave area. By using this
2965 parameter, xsave area per process might occupy more
2966 memory on xsaves enabled systems.
2968 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2969 wfi(ARM) instruction doesn't work correctly and not to
2970 use it. This is also useful when using JTAG debugger.
2972 no_file_caps Tells the kernel not to honor file capabilities. The
2973 only way then for a file to be executed with privilege
2974 is to be setuid root or executed by root.
2976 nohalt [IA-64] Tells the kernel not to use the power saving
2977 function PAL_HALT_LIGHT when idle. This increases
2978 power-consumption. On the positive side, it reduces
2979 interrupt wake-up latency, which may improve performance
2980 in certain environments such as networked servers or
2983 nohibernate [HIBERNATION] Disable hibernation and resume.
2985 nohz= [KNL] Boottime enable/disable dynamic ticks
2986 Valid arguments: on, off
2989 nohz_full= [KNL,BOOT,SMP,ISOL]
2990 The argument is a cpu list, as described above.
2991 In kernels built with CONFIG_NO_HZ_FULL=y, set
2992 the specified list of CPUs whose tick will be stopped
2993 whenever possible. The boot CPU will be forced outside
2994 the range to maintain the timekeeping. Any CPUs
2995 in this list will have their RCU callbacks offloaded,
2996 just as if they had also been called out in the
2997 rcu_nocbs= boot parameter.
2999 noiotrap [SH] Disables trapped I/O port accesses.
3001 noirqdebug [X86-32] Disables the code which attempts to detect and
3002 disable unhandled interrupt sources.
3004 no_timer_check [X86,APIC] Disables the code which tests for
3005 broken timer IRQ sources.
3007 noisapnp [ISAPNP] Disables ISA PnP code.
3009 noinitrd [RAM] Tells the kernel not to load any configured
3012 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
3014 [Deprecated - use intremap=off]
3018 noinvpcid [X86] Disable the INVPCID cpu feature.
3020 nojitter [IA-64] Disables jitter checking for ITC timers.
3022 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
3024 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
3028 [X86,PV_OPS] Disable paravirtualized VMware scheduler
3029 clock and use the default one.
3031 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
3032 steal time is computed, but won't influence scheduler
3035 nolapic [X86-32,APIC] Do not enable or use the local APIC.
3037 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
3039 noltlbs [PPC] Do not use large page/tlb entries for kernel
3040 lowmem mapping on PPC40x and PPC8xx
3042 nomca [IA-64] Disable machine check abort handling
3044 nomce [X86-32] Disable Machine Check Exception
3046 nomfgpt [X86-32] Disable Multi-Function General Purpose
3047 Timer usage (for AMD Geode machines).
3049 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
3050 shutdown the other cpus. Instead use the REBOOT_VECTOR
3053 nomodule Disable module load
3055 nopat [X86] Disable PAT (page attribute table extension of
3056 pagetables) support.
3058 nopcid [X86-64] Disable the PCID cpu feature.
3060 norandmaps Don't use address space randomization. Equivalent to
3061 echo 0 > /proc/sys/kernel/randomize_va_space
3063 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
3064 with UP alternatives
3066 nordrand [X86] Disable kernel use of the RDRAND and
3067 RDSEED instructions even if they are supported
3068 by the processor. RDRAND and RDSEED are still
3069 available to user space applications.
3071 noresume [SWSUSP] Disables resume and restores original swap
3074 no-scroll [VGA] Disables scrollback.
3075 This is required for the Braillex ib80-piezo Braille
3076 reader made by F.H. Papenmeier (Germany).
3080 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
3082 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
3083 and disable the IO APIC. legacy for "maxcpus=0".
3085 nosoftlockup [KNL] Disable the soft-lockup detector.
3087 nosync [HW,M68K] Disables sync negotiation for all devices.
3089 nowatchdog [KNL] Disable both lockup detectors, i.e.
3090 soft-lockup and NMI watchdog (hard-lockup).
3094 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
3096 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
3097 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
3098 Some features depend on CPU0. Known dependencies are:
3099 1. Resume from suspend/hibernate depends on CPU0.
3100 Suspend/hibernate will fail if CPU0 is offline and you
3101 need to online CPU0 before suspend/hibernate.
3102 2. PIC interrupts also depend on CPU0. CPU0 can't be
3103 removed if a PIC interrupt is detected.
3104 It's said poweroff/reboot may depend on CPU0 on some
3105 machines although I haven't seen such issues so far
3106 after CPU0 is offline on a few tested machines.
3107 If the dependencies are under your control, you can
3108 turn on cpu0_hotplug.
3110 nps_mtm_hs_ctr= [KNL,ARC]
3111 This parameter sets the maximum duration, in
3112 cycles, each HW thread of the CTOP can run
3113 without interruptions, before HW switches it.
3114 The actual maximum duration is 16 times this
3116 Format: integer between 1 and 255
3119 nptcg= [IA-64] Override max number of concurrent global TLB
3120 purges which is reported from either PAL_VM_SUMMARY or
3123 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
3124 could support. nr_cpus=n : n >= 1 limits the kernel to
3125 support 'n' processors. It could be larger than the
3126 number of already plugged CPU during bootup, later in
3127 runtime you can physically add extra cpu until it reaches
3128 n. So during boot up some boot time memory for per-cpu
3129 variables need be pre-allocated for later physical cpu
3132 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3134 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
3135 Allowed values are enable and disable
3137 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3138 'node', 'default' can be specified
3139 This can be set from sysctl after boot.
3140 See Documentation/sysctl/vm.txt for details.
3142 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3143 See Documentation/debugging-via-ohci1394.txt for more
3146 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3147 Rather than timing out after 20 ms if an EC
3148 command is not properly ACKed, override the length
3149 of the timeout. We have interrupts disabled while
3150 waiting for the ACK, so if this is set too high
3151 interrupts *may* be lost!
3153 omap_mux= [OMAP] Override bootloader pin multiplexing.
3154 Format: <mux_mode0.mode_name=value>...
3155 For example, to override I2C bus2:
3156 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3158 oprofile.timer= [HW]
3159 Use timer interrupt instead of performance counters
3161 oprofile.cpu_type= Force an oprofile cpu type
3162 This might be useful if you have an older oprofile
3163 userland or if you want common events.
3164 Format: { arch_perfmon }
3165 arch_perfmon: [X86] Force use of architectural
3166 perfmon on Intel CPUs instead of the
3167 CPU specific event set.
3168 timer: [X86] Force use of architectural NMI
3169 timer mode (see also oprofile.timer
3170 for generic hr timer mode)
3172 oops=panic Always panic on oopses. Default is to just kill the
3173 process, but there is a small probability of
3174 deadlocking the machine.
3175 This will also cause panics on machine check exceptions.
3176 Useful together with panic=30 to trigger a reboot.
3179 [KNL] Boolean flag to control whether the page allocator
3180 should randomize its free lists. The randomization may
3181 be automatically enabled if the kernel detects it is
3182 running on a platform with a direct-mapped memory-side
3183 cache, and this parameter can be used to
3184 override/disable that behavior. The state of the flag
3185 can be read from sysfs at:
3186 /sys/module/page_alloc/parameters/shuffle.
3188 page_owner= [KNL] Boot-time page_owner enabling option.
3189 Storage of the information about who allocated
3190 each page is disabled in default. With this switch,
3192 on: enable the feature
3194 page_poison= [KNL] Boot-time parameter changing the state of
3195 poisoning on the buddy allocator, available with
3196 CONFIG_PAGE_POISONING=y.
3197 off: turn off poisoning (default)
3198 on: turn on poisoning
3200 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3201 timeout > 0: seconds before rebooting
3202 timeout = 0: wait forever
3203 timeout < 0: reboot immediately
3206 panic_print= Bitmask for printing system info when panic happens.
3207 User can chose combination of the following bits:
3208 bit 0: print all tasks info
3209 bit 1: print system memory info
3210 bit 2: print timer info
3211 bit 3: print locks info if CONFIG_LOCKDEP is on
3212 bit 4: print ftrace buffer
3213 bit 5: print all printk messages in buffer
3215 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3218 crash_kexec_post_notifiers
3219 Run kdump after running panic-notifiers and dumping
3220 kmsg. This only for the users who doubt kdump always
3221 succeeds in any situation.
3222 Note that this also increases risks of kdump failure,
3223 because some panic notifiers can make the crashed
3224 kernel more unstable.
3226 parkbd.port= [HW] Parallel port number the keyboard adapter is
3227 connected to, default is 0.
3229 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3230 0 for XT, 1 for AT (default is AT).
3233 parport= [HW,PPT] Specify parallel ports. 0 disables.
3234 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3235 Use 'auto' to force the driver to use any
3236 IRQ/DMA settings detected (the default is to
3237 ignore detected IRQ/DMA settings because of
3238 possible conflicts). You can specify the base
3239 address, IRQ, and DMA settings; IRQ and DMA
3240 should be numbers, or 'auto' (for using detected
3241 settings on that particular port), or 'nofifo'
3242 (to avoid using a FIFO even if it is detected).
3243 Parallel ports are assigned in the order they
3244 are specified on the command line, starting
3247 parport_init_mode= [HW,PPT]
3248 Configure VIA parallel port to operate in
3249 a specific mode. This is necessary on Pegasos
3250 computer where firmware has no options for setting
3251 up parallel port mode and sets it to spp.
3252 Currently this function knows 686a and 8231 chips.
3253 Format: [spp|ps2|epp|ecp|ecpepp]
3256 Halt all CPUs after the first oops has been printed for
3257 the specified number of seconds. This is to be used if
3258 your oopses keep scrolling off the screen.
3263 See header of drivers/block/paride/pcd.c.
3264 See also Documentation/blockdev/paride.txt.
3266 pci=option[,option...] [PCI] various PCI subsystem options.
3268 Some options herein operate on a specific device
3269 or a set of devices (<pci_dev>). These are
3270 specified in one of the following formats:
3272 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
3273 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
3275 Note: the first format specifies a PCI
3276 bus/device/function address which may change
3277 if new hardware is inserted, if motherboard
3278 firmware changes, or due to changes caused
3279 by other kernel parameters. If the
3280 domain is left unspecified, it is
3281 taken to be zero. Optionally, a path
3282 to a device through multiple device/function
3283 addresses can be specified after the base
3284 address (this is more robust against
3285 renumbering issues). The second format
3286 selects devices using IDs from the
3287 configuration space which may match multiple
3288 devices in the system.
3290 earlydump dump PCI config space before the kernel
3292 off [X86] don't probe for the PCI bus
3293 bios [X86-32] force use of PCI BIOS, don't access
3294 the hardware directly. Use this if your machine
3295 has a non-standard PCI host bridge.
3296 nobios [X86-32] disallow use of PCI BIOS, only direct
3297 hardware access methods are allowed. Use this
3298 if you experience crashes upon bootup and you
3299 suspect they are caused by the BIOS.
3300 conf1 [X86] Force use of PCI Configuration Access
3301 Mechanism 1 (config address in IO port 0xCF8,
3302 data in IO port 0xCFC, both 32-bit).
3303 conf2 [X86] Force use of PCI Configuration Access
3304 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3305 the function, IO port 0xCFA, also 8-bit, sets
3306 bus number. The config space is then accessed
3307 through ports 0xC000-0xCFFF).
3308 See http://wiki.osdev.org/PCI for more info
3309 on the configuration access mechanisms.
3310 noaer [PCIE] If the PCIEAER kernel config parameter is
3311 enabled, this kernel boot option can be used to
3312 disable the use of PCIE advanced error reporting.
3313 nodomains [PCI] Disable support for multiple PCI
3314 root domains (aka PCI segments, in ACPI-speak).
3315 nommconf [X86] Disable use of MMCONFIG for PCI
3317 check_enable_amd_mmconf [X86] check for and enable
3318 properly configured MMIO access to PCI
3319 config space on AMD family 10h CPU
3320 nomsi [MSI] If the PCI_MSI kernel config parameter is
3321 enabled, this kernel boot option can be used to
3322 disable the use of MSI interrupts system-wide.
3323 noioapicquirk [APIC] Disable all boot interrupt quirks.
3324 Safety option to keep boot IRQs enabled. This
3325 should never be necessary.
3326 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3327 primary IO-APIC for bridges that cannot disable
3328 boot IRQs. This fixes a source of spurious IRQs
3329 when the system masks IRQs.
3330 noioapicreroute [APIC] Disable workaround that uses the
3331 boot IRQ equivalent of an IRQ that connects to
3332 a chipset where boot IRQs cannot be disabled.
3333 The opposite of ioapicreroute.
3334 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3335 routing table. These calls are known to be buggy
3336 on several machines and they hang the machine
3337 when used, but on other computers it's the only
3338 way to get the interrupt routing table. Try
3339 this option if the kernel is unable to allocate
3340 IRQs or discover secondary PCI buses on your
3342 rom [X86] Assign address space to expansion ROMs.
3343 Use with caution as certain devices share
3344 address decoders between ROMs and other
3346 norom [X86] Do not assign address space to
3347 expansion ROMs that do not already have
3348 BIOS assigned address ranges.
3349 nobar [X86] Do not assign address space to the
3350 BARs that weren't assigned by the BIOS.
3351 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3352 assigned automatically to PCI devices. You can
3353 make the kernel exclude IRQs of your ISA cards
3355 pirqaddr=0xAAAAA [X86] Specify the physical address
3356 of the PIRQ table (normally generated
3357 by the BIOS) if it is outside the
3358 F0000h-100000h range.
3359 lastbus=N [X86] Scan all buses thru bus #N. Can be
3360 useful if the kernel is unable to find your
3361 secondary buses and you want to tell it
3362 explicitly which ones they are.
3363 assign-busses [X86] Always assign all PCI bus
3364 numbers ourselves, overriding
3365 whatever the firmware may have done.
3366 usepirqmask [X86] Honor the possible IRQ mask stored
3367 in the BIOS $PIR table. This is needed on
3368 some systems with broken BIOSes, notably
3369 some HP Pavilion N5400 and Omnibook XE3
3370 notebooks. This will have no effect if ACPI
3371 IRQ routing is enabled.
3372 noacpi [X86] Do not use ACPI for IRQ routing
3373 or for PCI scanning.
3374 use_crs [X86] Use PCI host bridge window information
3375 from ACPI. On BIOSes from 2008 or later, this
3376 is enabled by default. If you need to use this,
3377 please report a bug.
3378 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3379 If you need to use this, please report a bug.
3380 routeirq Do IRQ routing for all PCI devices.
3381 This is normally done in pci_enable_device(),
3382 so this option is a temporary workaround
3383 for broken drivers that don't call it.
3384 skip_isa_align [X86] do not align io start addr, so can
3385 handle more pci cards
3386 noearly [X86] Don't do any early type 1 scanning.
3387 This might help on some broken boards which
3388 machine check when some devices' config space
3389 is read. But various workarounds are disabled
3390 and some IOMMU drivers will not work.
3391 bfsort Sort PCI devices into breadth-first order.
3392 This sorting is done to get a device
3393 order compatible with older (<= 2.4) kernels.
3394 nobfsort Don't sort PCI devices into breadth-first order.
3395 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3396 tuning and use the BIOS-configured MPS defaults.
3397 pcie_bus_safe Set every device's MPS to the largest value
3398 supported by all devices below the root complex.
3399 pcie_bus_perf Set device MPS to the largest allowable MPS
3400 based on its parent bus. Also set MRRS (Max
3401 Read Request Size) to the largest supported
3402 value (no larger than the MPS that the device
3403 or bus can support) for best performance.
3404 pcie_bus_peer2peer Set every device's MPS to 128B, which
3405 every device is guaranteed to support. This
3406 configuration allows peer-to-peer DMA between
3407 any pair of devices, possibly at the cost of
3408 reduced performance. This also guarantees
3409 that hot-added devices will work.
3410 cbiosize=nn[KMG] The fixed amount of bus space which is
3411 reserved for the CardBus bridge's IO window.
3412 The default value is 256 bytes.
3413 cbmemsize=nn[KMG] The fixed amount of bus space which is
3414 reserved for the CardBus bridge's memory
3415 window. The default value is 64 megabytes.
3418 [<order of align>@]<pci_dev>[; ...]
3419 Specifies alignment and device to reassign
3420 aligned memory resources. How to
3421 specify the device is described above.
3422 If <order of align> is not specified,
3423 PAGE_SIZE is used as alignment.
3424 PCI-PCI bridge can be specified, if resource
3425 windows need to be expanded.
3426 To specify the alignment for several
3427 instances of a device, the PCI vendor,
3428 device, subvendor, and subdevice may be
3429 specified, e.g., 4096@pci:8086:9c22:103c:198f
3430 ecrc= Enable/disable PCIe ECRC (transaction layer
3431 end-to-end CRC checking).
3432 bios: Use BIOS/firmware settings. This is the
3436 hpiosize=nn[KMG] The fixed amount of bus space which is
3437 reserved for hotplug bridge's IO window.
3438 Default size is 256 bytes.
3439 hpmemsize=nn[KMG] The fixed amount of bus space which is
3440 reserved for hotplug bridge's memory window.
3441 Default size is 2 megabytes.
3442 hpbussize=nn The minimum amount of additional bus numbers
3443 reserved for buses below a hotplug bridge.
3445 realloc= Enable/disable reallocating PCI bridge resources
3446 if allocations done by BIOS are too small to
3447 accommodate resources required by all child
3449 off: Turn realloc off
3451 realloc same as realloc=on
3452 noari do not use PCIe ARI.
3453 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
3454 do not use PCIe ATS (and IOMMU device IOTLB).
3455 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3456 only look for one device below a PCIe downstream
3458 big_root_window Try to add a big 64bit memory window to the PCIe
3459 root complex on AMD CPUs. Some GFX hardware
3460 can resize a BAR to allow access to all VRAM.
3461 Adding the window is slightly risky (it may
3462 conflict with unreported devices), so this
3464 disable_acs_redir=<pci_dev>[; ...]
3465 Specify one or more PCI devices (in the format
3466 specified above) separated by semicolons.
3467 Each device specified will have the PCI ACS
3468 redirect capabilities forced off which will
3469 allow P2P traffic between devices through
3470 bridges without forcing it upstream. Note:
3471 this removes isolation between devices and
3472 may put more devices in an IOMMU group.
3473 force_floating [S390] Force usage of floating interrupts.
3474 nomio [S390] Do not use MIO instructions.
3476 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3479 force Enable ASPM even on devices that claim not to support it.
3480 WARNING: Forcing ASPM on may cause system lockups.
3482 pcie_ports= [PCIE] PCIe port services handling:
3483 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
3484 even if the platform doesn't give the OS permission to
3485 use them. This may cause conflicts if the platform
3486 also tries to use these services.
3487 compat Disable native PCIe services (PME, AER, DPC, PCIe
3490 pcie_port_pm= [PCIE] PCIe port power management handling:
3491 off Disable power management of all PCIe ports
3492 force Forcibly enable power management of all PCIe ports
3494 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3495 nomsi Do not use MSI for native PCIe PME signaling (this makes
3496 all PCIe root ports use INTx for all services).
3498 pcmv= [HW,PCMCIA] BadgePAD 4
3502 Keep all power-domains already enabled by bootloader on,
3503 even if no driver has claimed them. This is useful
3504 for debug and development, but should not be
3505 needed on a platform with proper driver support.
3508 See Documentation/blockdev/paride.txt.
3510 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3513 See arch/parisc/kernel/pdc_chassis.c
3515 percpu_alloc= Select which percpu first chunk allocator to use.
3516 Currently supported values are "embed" and "page".
3517 Archs may support subset or none of the selections.
3518 See comments in mm/percpu.c for details on each
3519 allocator. This parameter is primarily for debugging
3520 and performance comparison.
3523 See Documentation/blockdev/paride.txt.
3526 See Documentation/blockdev/paride.txt.
3528 pirq= [SMP,APIC] Manual mp-table setup
3529 See Documentation/x86/i386/IO-APIC.rst.
3531 plip= [PPT,NET] Parallel port network link
3532 Format: { parport<nr> | timid | 0 }
3533 See also Documentation/admin-guide/parport.rst.
3535 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3536 Override pmtimer IOPort with a hex value.
3540 Enable PNP debug messages (depends on the
3541 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3542 via /sys/module/pnp/parameters/debug. We always show
3543 current resource usage; turning this on also shows
3544 possible settings and some assignment information.
3550 { on | off | curr | res | no-curr | no-res }
3553 [ISAPNP] Exclude IRQs for the autoconfiguration
3556 [ISAPNP] Exclude DMAs for the autoconfiguration
3558 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3559 Ranges are in pairs (I/O port base and size).
3562 [ISAPNP] Exclude memory regions for the
3564 Ranges are in pairs (memory base and size).
3566 ports= [IP_VS_FTP] IPVS ftp helper module
3568 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3570 Format: <port>,<port>....
3572 powersave=off [PPC] This option disables power saving features.
3573 It specifically disables cpuidle and sets the
3574 platform machine description specific power_save
3575 function to NULL. On Idle the CPU just reduces
3578 ppc_strict_facility_enable
3579 [PPC] This option catches any kernel floating point,
3580 Altivec, VSX and SPE outside of regions specifically
3581 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3582 There is some performance impact when enabling this.
3586 Disable Hardware Transactional Memory
3588 print-fatal-signals=
3589 [KNL] debug: print fatal signals
3591 If enabled, warn about various signal handling
3592 related application anomalies: too many signals,
3593 too many POSIX.1 timers, fatal signals causing a
3596 If you hit the warning due to signal overflow,
3597 you might want to try "ulimit -i unlimited".
3601 printk.always_kmsg_dump=
3602 Trigger kmsg_dump for cases other than kernel oops or
3604 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3607 printk.devkmsg={on,off,ratelimit}
3608 Control writing to /dev/kmsg.
3609 on - unlimited logging to /dev/kmsg from userspace
3610 off - logging to /dev/kmsg disabled
3611 ratelimit - ratelimit the logging
3614 printk.time= Show timing data prefixed to each printk message line
3615 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3617 processor.max_cstate= [HW,ACPI]
3618 Limit processor to maximum C-state
3619 max_cstate=9 overrides any DMI blacklist limit.
3621 processor.nocst [HW,ACPI]
3622 Ignore the _CST method to determine C-states,
3623 instead using the legacy FADT method
3625 profile= [KNL] Enable kernel profiling via /proc/profile
3626 Format: [<profiletype>,]<number>
3627 Param: <profiletype>: "schedule", "sleep", or "kvm"
3628 [defaults to kernel profiling]
3629 Param: "schedule" - profile schedule points.
3630 Param: "sleep" - profile D-state sleeping (millisecs).
3631 Requires CONFIG_SCHEDSTATS
3632 Param: "kvm" - profile VM exits.
3633 Param: <number> - step/bucket size as a power of 2 for
3634 statistical time based profiling.
3636 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3638 See Documentation/blockdev/ramdisk.txt.
3640 psi= [KNL] Enable or disable pressure stall information
3644 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3645 probe for; one of (bare|imps|exps|lifebook|any).
3646 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3648 psmouse.resetafter= [HW,MOUSE]
3649 Try to reset the device after so many bad packets
3652 [HW,MOUSE] Set desired mouse resolution, in dpi.
3653 psmouse.smartscroll=
3654 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3655 0 = disabled, 1 = enabled (default).
3657 pstore.backend= Specify the name of the pstore backend to use
3660 See Documentation/blockdev/paride.txt.
3662 pti= [X86_64] Control Page Table Isolation of user and
3663 kernel address spaces. Disabling this feature
3664 removes hardening, but improves performance of
3665 system calls and interrupts.
3667 on - unconditionally enable
3668 off - unconditionally disable
3669 auto - kernel detects whether your CPU model is
3670 vulnerable to issues that PTI mitigates
3672 Not specifying this option is equivalent to pti=auto.
3675 Equivalent to pti=off
3678 [KNL] Number of legacy pty's. Overwrites compiled-in
3681 quiet [KNL] Disable most log messages
3686 See Documentation/admin-guide/md.rst.
3688 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3689 See Documentation/blockdev/ramdisk.txt.
3691 random.trust_cpu={on,off}
3692 [KNL] Enable or disable trusting the use of the
3693 CPU's random number generator (if available) to
3694 fully seed the kernel's CRNG. Default is controlled
3695 by CONFIG_RANDOM_TRUST_CPU.
3697 ras=option[,option,...] [KNL] RAS-specific options
3700 Disable the Correctable Errors Collector,
3701 see CONFIG_RAS_CEC help text.
3704 The argument is a cpu list, as described above,
3705 except that the string "all" can be used to
3706 specify every CPU on the system.
3708 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3709 the specified list of CPUs to be no-callback CPUs.
3710 Invocation of these CPUs' RCU callbacks will be
3711 offloaded to "rcuox/N" kthreads created for that
3712 purpose, where "x" is "p" for RCU-preempt, and
3713 "s" for RCU-sched, and "N" is the CPU number.
3714 This reduces OS jitter on the offloaded CPUs,
3715 which can be useful for HPC and real-time
3716 workloads. It can also improve energy efficiency
3717 for asymmetric multiprocessors.
3720 Rather than requiring that offloaded CPUs
3721 (specified by rcu_nocbs= above) explicitly
3722 awaken the corresponding "rcuoN" kthreads,
3723 make these kthreads poll for callbacks.
3724 This improves the real-time response for the
3725 offloaded CPUs by relieving them of the need to
3726 wake up the corresponding kthread, but degrades
3727 energy efficiency by requiring that the kthreads
3728 periodically wake up to do the polling.
3730 rcutree.blimit= [KNL]
3731 Set maximum number of finished RCU callbacks to
3732 process in one batch.
3734 rcutree.dump_tree= [KNL]
3735 Dump the structure of the rcu_node combining tree
3736 out at early boot. This is used for diagnostic
3737 purposes, to verify correct tree setup.
3739 rcutree.gp_cleanup_delay= [KNL]
3740 Set the number of jiffies to delay each step of
3741 RCU grace-period cleanup.
3743 rcutree.gp_init_delay= [KNL]
3744 Set the number of jiffies to delay each step of
3745 RCU grace-period initialization.
3747 rcutree.gp_preinit_delay= [KNL]
3748 Set the number of jiffies to delay each step of
3749 RCU grace-period pre-initialization, that is,
3750 the propagation of recent CPU-hotplug changes up
3751 the rcu_node combining tree.
3753 rcutree.use_softirq= [KNL]
3754 If set to zero, move all RCU_SOFTIRQ processing to
3755 per-CPU rcuc kthreads. Defaults to a non-zero
3756 value, meaning that RCU_SOFTIRQ is used by default.
3757 Specify rcutree.use_softirq=0 to use rcuc kthreads.
3759 rcutree.rcu_fanout_exact= [KNL]
3760 Disable autobalancing of the rcu_node combining
3761 tree. This is used by rcutorture, and might
3762 possibly be useful for architectures having high
3763 cache-to-cache transfer latencies.
3765 rcutree.rcu_fanout_leaf= [KNL]
3766 Change the number of CPUs assigned to each
3767 leaf rcu_node structure. Useful for very
3768 large systems, which will choose the value 64,
3769 and for NUMA systems with large remote-access
3770 latencies, which will choose a value aligned
3771 with the appropriate hardware boundaries.
3773 rcutree.jiffies_till_first_fqs= [KNL]
3774 Set delay from grace-period initialization to
3775 first attempt to force quiescent states.
3776 Units are jiffies, minimum value is zero,
3777 and maximum value is HZ.
3779 rcutree.jiffies_till_next_fqs= [KNL]
3780 Set delay between subsequent attempts to force
3781 quiescent states. Units are jiffies, minimum
3782 value is one, and maximum value is HZ.
3784 rcutree.jiffies_till_sched_qs= [KNL]
3785 Set required age in jiffies for a
3786 given grace period before RCU starts
3787 soliciting quiescent-state help from
3788 rcu_note_context_switch() and cond_resched().
3789 If not specified, the kernel will calculate
3790 a value based on the most recent settings
3791 of rcutree.jiffies_till_first_fqs
3792 and rcutree.jiffies_till_next_fqs.
3793 This calculated value may be viewed in
3794 rcutree.jiffies_to_sched_qs. Any attempt to set
3795 rcutree.jiffies_to_sched_qs will be cheerfully
3798 rcutree.kthread_prio= [KNL,BOOT]
3799 Set the SCHED_FIFO priority of the RCU per-CPU
3800 kthreads (rcuc/N). This value is also used for
3801 the priority of the RCU boost threads (rcub/N)
3802 and for the RCU grace-period kthreads (rcu_bh,
3803 rcu_preempt, and rcu_sched). If RCU_BOOST is
3804 set, valid values are 1-99 and the default is 1
3805 (the least-favored priority). Otherwise, when
3806 RCU_BOOST is not set, valid values are 0-99 and
3807 the default is zero (non-realtime operation).
3809 rcutree.rcu_nocb_leader_stride= [KNL]
3810 Set the number of NOCB kthread groups, which
3811 defaults to the square root of the number of
3812 CPUs. Larger numbers reduces the wakeup overhead
3813 on the per-CPU grace-period kthreads, but increases
3814 that same overhead on each group's leader.
3816 rcutree.qhimark= [KNL]
3817 Set threshold of queued RCU callbacks beyond which
3818 batch limiting is disabled.
3820 rcutree.qlowmark= [KNL]
3821 Set threshold of queued RCU callbacks below which
3822 batch limiting is re-enabled.
3824 rcutree.rcu_idle_gp_delay= [KNL]
3825 Set wakeup interval for idle CPUs that have
3826 RCU callbacks (RCU_FAST_NO_HZ=y).
3828 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3829 Set wakeup interval for idle CPUs that have
3830 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3831 Lazy RCU callbacks are those which RCU can
3832 prove do nothing more than free memory.
3834 rcutree.rcu_kick_kthreads= [KNL]
3835 Cause the grace-period kthread to get an extra
3836 wake_up() if it sleeps three times longer than
3837 it should at force-quiescent-state time.
3838 This wake_up() will be accompanied by a
3839 WARN_ONCE() splat and an ftrace_dump().
3841 rcutree.sysrq_rcu= [KNL]
3842 Commandeer a sysrq key to dump out Tree RCU's
3843 rcu_node tree with an eye towards determining
3844 why a new grace period has not yet started.
3846 rcuperf.gp_async= [KNL]
3847 Measure performance of asynchronous
3848 grace-period primitives such as call_rcu().
3850 rcuperf.gp_async_max= [KNL]
3851 Specify the maximum number of outstanding
3852 callbacks per writer thread. When a writer
3853 thread exceeds this limit, it invokes the
3854 corresponding flavor of rcu_barrier() to allow
3855 previously posted callbacks to drain.
3857 rcuperf.gp_exp= [KNL]
3858 Measure performance of expedited synchronous
3859 grace-period primitives.
3861 rcuperf.holdoff= [KNL]
3862 Set test-start holdoff period. The purpose of
3863 this parameter is to delay the start of the
3864 test until boot completes in order to avoid
3867 rcuperf.nreaders= [KNL]
3868 Set number of RCU readers. The value -1 selects
3869 N, where N is the number of CPUs. A value
3870 "n" less than -1 selects N-n+1, where N is again
3871 the number of CPUs. For example, -2 selects N
3872 (the number of CPUs), -3 selects N+1, and so on.
3873 A value of "n" less than or equal to -N selects
3876 rcuperf.nwriters= [KNL]
3877 Set number of RCU writers. The values operate
3878 the same as for rcuperf.nreaders.
3879 N, where N is the number of CPUs
3881 rcuperf.perf_type= [KNL]
3882 Specify the RCU implementation to test.
3884 rcuperf.shutdown= [KNL]
3885 Shut the system down after performance tests
3886 complete. This is useful for hands-off automated
3889 rcuperf.verbose= [KNL]
3890 Enable additional printk() statements.
3892 rcuperf.writer_holdoff= [KNL]
3893 Write-side holdoff between grace periods,
3894 in microseconds. The default of zero says
3897 rcutorture.fqs_duration= [KNL]
3898 Set duration of force_quiescent_state bursts
3901 rcutorture.fqs_holdoff= [KNL]
3902 Set holdoff time within force_quiescent_state bursts
3905 rcutorture.fqs_stutter= [KNL]
3906 Set wait time between force_quiescent_state bursts
3909 rcutorture.fwd_progress= [KNL]
3910 Enable RCU grace-period forward-progress testing
3911 for the types of RCU supporting this notion.
3913 rcutorture.fwd_progress_div= [KNL]
3914 Specify the fraction of a CPU-stall-warning
3915 period to do tight-loop forward-progress testing.
3917 rcutorture.fwd_progress_holdoff= [KNL]
3918 Number of seconds to wait between successive
3919 forward-progress tests.
3921 rcutorture.fwd_progress_need_resched= [KNL]
3922 Enclose cond_resched() calls within checks for
3923 need_resched() during tight-loop forward-progress
3926 rcutorture.gp_cond= [KNL]
3927 Use conditional/asynchronous update-side
3928 primitives, if available.
3930 rcutorture.gp_exp= [KNL]
3931 Use expedited update-side primitives, if available.
3933 rcutorture.gp_normal= [KNL]
3934 Use normal (non-expedited) asynchronous
3935 update-side primitives, if available.
3937 rcutorture.gp_sync= [KNL]
3938 Use normal (non-expedited) synchronous
3939 update-side primitives, if available. If all
3940 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3941 rcutorture.gp_normal=, and rcutorture.gp_sync=
3942 are zero, rcutorture acts as if is interpreted
3943 they are all non-zero.
3945 rcutorture.n_barrier_cbs= [KNL]
3946 Set callbacks/threads for rcu_barrier() testing.
3948 rcutorture.nfakewriters= [KNL]
3949 Set number of concurrent RCU writers. These just
3950 stress RCU, they don't participate in the actual
3951 test, hence the "fake".
3953 rcutorture.nreaders= [KNL]
3954 Set number of RCU readers. The value -1 selects
3955 N-1, where N is the number of CPUs. A value
3956 "n" less than -1 selects N-n-2, where N is again
3957 the number of CPUs. For example, -2 selects N
3958 (the number of CPUs), -3 selects N+1, and so on.
3960 rcutorture.object_debug= [KNL]
3961 Enable debug-object double-call_rcu() testing.
3963 rcutorture.onoff_holdoff= [KNL]
3964 Set time (s) after boot for CPU-hotplug testing.
3966 rcutorture.onoff_interval= [KNL]
3967 Set time (jiffies) between CPU-hotplug operations,
3968 or zero to disable CPU-hotplug testing.
3970 rcutorture.shuffle_interval= [KNL]
3971 Set task-shuffle interval (s). Shuffling tasks
3972 allows some CPUs to go into dyntick-idle mode
3973 during the rcutorture test.
3975 rcutorture.shutdown_secs= [KNL]
3976 Set time (s) after boot system shutdown. This
3977 is useful for hands-off automated testing.
3979 rcutorture.stall_cpu= [KNL]
3980 Duration of CPU stall (s) to test RCU CPU stall
3981 warnings, zero to disable.
3983 rcutorture.stall_cpu_holdoff= [KNL]
3984 Time to wait (s) after boot before inducing stall.
3986 rcutorture.stall_cpu_irqsoff= [KNL]
3987 Disable interrupts while stalling if set.
3989 rcutorture.stat_interval= [KNL]
3990 Time (s) between statistics printk()s.
3992 rcutorture.stutter= [KNL]
3993 Time (s) to stutter testing, for example, specifying
3994 five seconds causes the test to run for five seconds,
3995 wait for five seconds, and so on. This tests RCU's
3996 ability to transition abruptly to and from idle.
3998 rcutorture.test_boost= [KNL]
3999 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
4000 "Maybe" means test if the RCU implementation
4001 under test support RCU priority boosting.
4003 rcutorture.test_boost_duration= [KNL]
4004 Duration (s) of each individual boost test.
4006 rcutorture.test_boost_interval= [KNL]
4007 Interval (s) between each boost test.
4009 rcutorture.test_no_idle_hz= [KNL]
4010 Test RCU's dyntick-idle handling. See also the
4011 rcutorture.shuffle_interval parameter.
4013 rcutorture.torture_type= [KNL]
4014 Specify the RCU implementation to test.
4016 rcutorture.verbose= [KNL]
4017 Enable additional printk() statements.
4019 rcupdate.rcu_cpu_stall_suppress= [KNL]
4020 Suppress RCU CPU stall warning messages.
4022 rcupdate.rcu_cpu_stall_timeout= [KNL]
4023 Set timeout for RCU CPU stall warning messages.
4025 rcupdate.rcu_expedited= [KNL]
4026 Use expedited grace-period primitives, for
4027 example, synchronize_rcu_expedited() instead
4028 of synchronize_rcu(). This reduces latency,
4029 but can increase CPU utilization, degrade
4030 real-time latency, and degrade energy efficiency.
4031 No effect on CONFIG_TINY_RCU kernels.
4033 rcupdate.rcu_normal= [KNL]
4034 Use only normal grace-period primitives,
4035 for example, synchronize_rcu() instead of
4036 synchronize_rcu_expedited(). This improves
4037 real-time latency, CPU utilization, and
4038 energy efficiency, but can expose users to
4039 increased grace-period latency. This parameter
4040 overrides rcupdate.rcu_expedited. No effect on
4041 CONFIG_TINY_RCU kernels.
4043 rcupdate.rcu_normal_after_boot= [KNL]
4044 Once boot has completed (that is, after
4045 rcu_end_inkernel_boot() has been invoked), use
4046 only normal grace-period primitives. No effect
4047 on CONFIG_TINY_RCU kernels.
4049 rcupdate.rcu_task_stall_timeout= [KNL]
4050 Set timeout in jiffies for RCU task stall warning
4051 messages. Disable with a value less than or equal
4054 rcupdate.rcu_self_test= [KNL]
4055 Run the RCU early boot self tests
4059 Run specified binary instead of /init from the ramdisk,
4060 used for early userspace startup. See initrd.
4063 Turn on/off individual RDT features. List is:
4064 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
4066 E.g. to turn on cmt and turn off mba use:
4070 Format (x86 or x86_64):
4071 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
4073 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
4075 Where reboot_mode is one of warm (soft) or cold (hard) or gpio
4076 (prefix with 'panic_' to set mode for panic
4078 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
4079 reboot_force is either force or not specified,
4080 reboot_cpu is s[mp]#### with #### being the processor
4081 to be used for rebooting.
4084 [KNL, SMP] Set scheduler's default relax_domain_level.
4085 See Documentation/cgroup-v1/cpusets.rst.
4087 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
4088 Format: <base1>,<size1>[,<base2>,<size2>,...]
4089 Reserve I/O ports or memory so the kernel won't use
4090 them. If <base> is less than 0x10000, the region
4091 is assumed to be I/O ports; otherwise it is memory.
4093 reservetop= [X86-32]
4095 Reserves a hole at the top of the kernel virtual
4100 Set the amount of memory to reserve for BIOS at
4101 the bottom of the address space.
4103 reset_devices [KNL] Force drivers to reset the underlying device
4104 during initialization.
4107 Specify the partition device for software suspend
4109 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
4111 resume_offset= [SWSUSP]
4112 Specify the offset from the beginning of the partition
4113 given by "resume=" at which the swap header is located,
4114 in <PAGE_SIZE> units (needed only for swap files).
4115 See Documentation/power/swsusp-and-swap-files.txt
4117 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
4118 read the resume files
4120 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
4121 Useful for devices that are detected asynchronously
4122 (e.g. USB and MMC devices).
4124 hibernate= [HIBERNATION]
4125 noresume Don't check if there's a hibernation image
4126 present during boot.
4127 nocompress Don't compress/decompress hibernation images.
4128 no Disable hibernation and resume.
4129 protect_image Turn on image protection during restoration
4130 (that will set all pages holding image data
4131 during restoration read-only).
4133 retain_initrd [RAM] Keep initrd memory after extraction
4135 rfkill.default_state=
4136 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
4137 etc. communication is blocked by default.
4140 rfkill.master_switch_mode=
4141 0 The "airplane mode" button does nothing.
4142 1 The "airplane mode" button toggles between everything
4143 blocked and the previous configuration.
4144 2 The "airplane mode" button toggles between everything
4145 blocked and everything unblocked.
4147 rhash_entries= [KNL,NET]
4148 Set number of hash buckets for route cache
4151 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
4154 ro [KNL] Mount root device read-only on boot
4157 on Mark read-only kernel memory as read-only (default).
4158 off Leave read-only kernel memory writable for debugging.
4161 Enable the uart passthrough on the designated usb port
4162 on Rockchip SoCs. When active, the signals of the
4163 debug-uart get routed to the D+ and D- pins of the usb
4164 port and the regular usb controller gets disabled.
4166 root= [KNL] Root filesystem
4167 See name_to_dev_t comment in init/do_mounts.c.
4169 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
4170 mount the root filesystem
4172 rootflags= [KNL] Set root filesystem mount option string
4174 rootfstype= [KNL] Set root filesystem type
4176 rootwait [KNL] Wait (indefinitely) for root device to show up.
4177 Useful for devices that are detected asynchronously
4178 (e.g. USB and MMC devices).
4180 rproc_mem=nn[KMG][@address]
4181 [KNL,ARM,CMA] Remoteproc physical memory block.
4182 Memory area to be used by remote processor image,
4185 rw [KNL] Mount root device read-write on boot
4187 S [KNL] Run init in single mode
4189 s390_iommu= [HW,S390]
4190 Set s390 IOTLB flushing mode
4192 With strict flushing every unmap operation will result in
4193 an IOTLB flush. Default is lazy flushing before reuse,
4197 See drivers/net/irda/sa1100_ir.c.
4199 sbni= [NET] Granch SBNI12 leased line adapter
4201 sched_debug [KNL] Enables verbose scheduler debug messages.
4203 schedstats= [KNL,X86] Enable or disable scheduled statistics.
4204 Allowed values are enable and disable. This feature
4205 incurs a small amount of overhead in the scheduler
4206 but is useful for debugging and performance tuning.
4208 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
4209 xtime_lock contention on larger systems, and/or RCU lock
4210 contention on all systems with CONFIG_MAXSMP set.
4211 Format: { "0" | "1" }
4212 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
4214 Note: increases power consumption, thus should only be
4215 enabled if running jitter sensitive (HPC/RT) workloads.
4217 security= [SECURITY] Choose a legacy "major" security module to
4218 enable at boot. This has been deprecated by the
4221 selinux= [SELINUX] Disable or enable SELinux at boot time.
4222 Format: { "0" | "1" }
4223 See security/selinux/Kconfig help text.
4226 Default value is set via kernel config option.
4227 If enabled at boot time, /selinux/disable can be used
4228 later to disable prior to initial policy load.
4230 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
4231 Format: { "0" | "1" }
4232 See security/apparmor/Kconfig help text
4235 Default value is set via kernel config option.
4237 serialnumber [BUGS=X86-32]
4240 Maximal number of shapers.
4248 Disable merging of slabs with similar size. May be
4249 necessary if there is some reason to distinguish
4250 allocs to different slabs, especially in hardened
4251 environments where the risk of heap overflows and
4252 layout control by attackers can usually be
4253 frustrated by disabling merging. This will reduce
4254 most of the exposure of a heap attack to a single
4255 cache (risks via metadata attacks are mostly
4256 unchanged). Debug options disable merging on their
4258 For more information see Documentation/vm/slub.rst.
4260 slab_max_order= [MM, SLAB]
4261 Determines the maximum allowed order for slabs.
4262 A high setting may cause OOMs due to memory
4263 fragmentation. Defaults to 1 for systems with
4264 more than 32MB of RAM, 0 otherwise.
4266 slub_debug[=options[,slabs]] [MM, SLUB]
4267 Enabling slub_debug allows one to determine the
4268 culprit if slab objects become corrupted. Enabling
4269 slub_debug can create guard zones around objects and
4270 may poison objects when not in use. Also tracks the
4271 last alloc / free. For more information see
4272 Documentation/vm/slub.rst.
4274 slub_memcg_sysfs= [MM, SLUB]
4275 Determines whether to enable sysfs directories for
4276 memory cgroup sub-caches. 1 to enable, 0 to disable.
4277 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
4278 Enabling this can lead to a very high number of debug
4279 directories and files being created under
4282 slub_max_order= [MM, SLUB]
4283 Determines the maximum allowed order for slabs.
4284 A high setting may cause OOMs due to memory
4285 fragmentation. For more information see
4286 Documentation/vm/slub.rst.
4288 slub_min_objects= [MM, SLUB]
4289 The minimum number of objects per slab. SLUB will
4290 increase the slab order up to slub_max_order to
4291 generate a sufficiently large slab able to contain
4292 the number of objects indicated. The higher the number
4293 of objects the smaller the overhead of tracking slabs
4294 and the less frequently locks need to be acquired.
4295 For more information see Documentation/vm/slub.rst.
4297 slub_min_order= [MM, SLUB]
4298 Determines the minimum page order for slabs. Must be
4299 lower than slub_max_order.
4300 For more information see Documentation/vm/slub.rst.
4302 slub_nomerge [MM, SLUB]
4303 Same with slab_nomerge. This is supported for legacy.
4304 See slab_nomerge for more information.
4307 Format: <io1>[,<io2>[,...,<io8>]]
4309 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4310 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4311 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4312 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4313 smsc-ircc2.ircc_irq= [HW] IRQ line
4314 smsc-ircc2.ircc_dma= [HW] DMA channel
4315 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4316 0: Toshiba Satellite 1800 (GP data pin select)
4317 1: Fast pin select (default)
4320 smt [KNL,S390] Set the maximum number of threads (logical
4321 CPUs) to use per physical CPU on systems capable of
4322 symmetric multithreading (SMT). Will be capped to the
4323 actual hardware limit.
4325 Default: -1 (no limit)
4328 [KNL] Should the soft-lockup detector generate panics.
4331 A nonzero value instructs the soft-lockup detector
4332 to panic the machine when a soft-lockup occurs. This
4333 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
4334 which is the respective build-time switch to that
4337 softlockup_all_cpu_backtrace=
4338 [KNL] Should the soft-lockup detector generate
4339 backtraces on all cpus.
4342 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4343 See Documentation/laptops/sonypi.txt
4345 spectre_v2= [X86] Control mitigation of Spectre variant 2
4346 (indirect branch speculation) vulnerability.
4347 The default operation protects the kernel from
4350 on - unconditionally enable, implies
4352 off - unconditionally disable, implies
4354 auto - kernel detects whether your CPU model is
4357 Selecting 'on' will, and 'auto' may, choose a
4358 mitigation method at run time according to the
4359 CPU, the available microcode, the setting of the
4360 CONFIG_RETPOLINE configuration option, and the
4361 compiler with which the kernel was built.
4363 Selecting 'on' will also enable the mitigation
4364 against user space to user space task attacks.
4366 Selecting 'off' will disable both the kernel and
4367 the user space protections.
4369 Specific mitigations can also be selected manually:
4371 retpoline - replace indirect branches
4372 retpoline,generic - google's original retpoline
4373 retpoline,amd - AMD-specific minimal thunk
4375 Not specifying this option is equivalent to
4379 [X86] Control mitigation of Spectre variant 2
4380 (indirect branch speculation) vulnerability between
4383 on - Unconditionally enable mitigations. Is
4384 enforced by spectre_v2=on
4386 off - Unconditionally disable mitigations. Is
4387 enforced by spectre_v2=off
4389 prctl - Indirect branch speculation is enabled,
4390 but mitigation can be enabled via prctl
4391 per thread. The mitigation control state
4392 is inherited on fork.
4395 - Like "prctl" above, but only STIBP is
4396 controlled per thread. IBPB is issued
4397 always when switching between different user
4401 - Same as "prctl" above, but all seccomp
4402 threads will enable the mitigation unless
4403 they explicitly opt out.
4406 - Like "seccomp" above, but only STIBP is
4407 controlled per thread. IBPB is issued
4408 always when switching between different
4409 user space processes.
4411 auto - Kernel selects the mitigation depending on
4412 the available CPU features and vulnerability.
4415 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
4417 Not specifying this option is equivalent to
4418 spectre_v2_user=auto.
4420 spec_store_bypass_disable=
4421 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4422 (Speculative Store Bypass vulnerability)
4424 Certain CPUs are vulnerable to an exploit against a
4425 a common industry wide performance optimization known
4426 as "Speculative Store Bypass" in which recent stores
4427 to the same memory location may not be observed by
4428 later loads during speculative execution. The idea
4429 is that such stores are unlikely and that they can
4430 be detected prior to instruction retirement at the
4431 end of a particular speculation execution window.
4433 In vulnerable processors, the speculatively forwarded
4434 store can be used in a cache side channel attack, for
4435 example to read memory to which the attacker does not
4436 directly have access (e.g. inside sandboxed code).
4438 This parameter controls whether the Speculative Store
4439 Bypass optimization is used.
4441 On x86 the options are:
4443 on - Unconditionally disable Speculative Store Bypass
4444 off - Unconditionally enable Speculative Store Bypass
4445 auto - Kernel detects whether the CPU model contains an
4446 implementation of Speculative Store Bypass and
4447 picks the most appropriate mitigation. If the
4448 CPU is not vulnerable, "off" is selected. If the
4449 CPU is vulnerable the default mitigation is
4450 architecture and Kconfig dependent. See below.
4451 prctl - Control Speculative Store Bypass per thread
4452 via prctl. Speculative Store Bypass is enabled
4453 for a process by default. The state of the control
4454 is inherited on fork.
4455 seccomp - Same as "prctl" above, but all seccomp threads
4456 will disable SSB unless they explicitly opt out.
4458 Default mitigations:
4459 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4461 On powerpc the options are:
4463 on,auto - On Power8 and Power9 insert a store-forwarding
4464 barrier on kernel entry and exit. On Power7
4465 perform a software flush on kernel entry and
4469 Not specifying this option is equivalent to
4470 spec_store_bypass_disable=auto.
4472 spia_io_base= [HW,MTD]
4477 srcutree.counter_wrap_check [KNL]
4478 Specifies how frequently to check for
4479 grace-period sequence counter wrap for the
4480 srcu_data structure's ->srcu_gp_seq_needed field.
4481 The greater the number of bits set in this kernel
4482 parameter, the less frequently counter wrap will
4483 be checked for. Note that the bottom two bits
4486 srcutree.exp_holdoff [KNL]
4487 Specifies how many nanoseconds must elapse
4488 since the end of the last SRCU grace period for
4489 a given srcu_struct until the next normal SRCU
4490 grace period will be considered for automatic
4491 expediting. Set to zero to disable automatic
4495 Speculative Store Bypass Disable control
4497 On CPUs that are vulnerable to the Speculative
4498 Store Bypass vulnerability and offer a
4499 firmware based mitigation, this parameter
4500 indicates how the mitigation should be used:
4502 force-on: Unconditionally enable mitigation for
4503 for both kernel and userspace
4504 force-off: Unconditionally disable mitigation for
4505 for both kernel and userspace
4506 kernel: Always enable mitigation in the
4507 kernel, and offer a prctl interface
4508 to allow userspace to register its
4509 interest in being mitigated too.
4511 stack_guard_gap= [MM]
4512 override the default stack gap protection. The value
4513 is in page units and it defines how many pages prior
4514 to (for stacks growing down) resp. after (for stacks
4515 growing up) the main stack are reserved for no other
4516 mapping. Default value is 256 pages.
4519 Enabled the stack tracer on boot up.
4521 stacktrace_filter=[function-list]
4522 [FTRACE] Limit the functions that the stack tracer
4523 will trace at boot up. function-list is a comma separated
4524 list of functions. This list can be changed at run
4525 time by the stack_trace_filter file in the debugfs
4526 tracing directory. Note, this enables stack tracing
4527 and the stacktrace above is not needed.
4531 Set the STI (builtin display/keyboard on the HP-PARISC
4532 machines) console (graphic card) which should be used
4533 as the initial boot-console.
4534 See also comment in drivers/video/console/sticore.c.
4537 See comment in drivers/video/console/sticore.c.
4540 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4542 sunrpc.min_resvport=
4543 sunrpc.max_resvport=
4545 SunRPC servers often require that client requests
4546 originate from a privileged port (i.e. a port in the
4547 range 0 < portnr < 1024).
4548 An administrator who wishes to reserve some of these
4549 ports for other uses may adjust the range that the
4550 kernel's sunrpc client considers to be privileged
4551 using these two parameters to set the minimum and
4552 maximum port values.
4554 sunrpc.svc_rpc_per_connection_limit=
4556 Limit the number of requests that the server will
4557 process in parallel from a single connection.
4558 The default value is 0 (no limit).
4562 Control how the NFS server code allocates CPUs to
4563 service thread pools. Depending on how many NICs
4564 you have and where their interrupts are bound, this
4565 option will affect which CPUs will do NFS serving.
4566 Note: this parameter cannot be changed while the
4567 NFS server is running.
4569 auto the server chooses an appropriate mode
4570 automatically using heuristics
4571 global a single global pool contains all CPUs
4572 percpu one pool for each CPU
4573 pernode one pool for each NUMA node (equivalent
4574 to global on non-NUMA machines)
4576 sunrpc.tcp_slot_table_entries=
4577 sunrpc.udp_slot_table_entries=
4579 Sets the upper limit on the number of simultaneous
4580 RPC calls that can be sent from the client to a
4581 server. Increasing these values may allow you to
4582 improve throughput, but will also increase the
4583 amount of memory reserved for use by the client.
4585 suspend.pm_test_delay=
4587 Sets the number of seconds to remain in a suspend test
4588 mode before resuming the system (see
4589 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4590 is set. Default value is 5.
4593 [KNL] Enable accounting of swap in memory resource
4594 controller if no parameter or 1 is given or disable
4595 it if 0 is given (See Documentation/cgroup-v1/memory.rst)
4597 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4598 Format: { <int> | force | noforce }
4599 <int> -- Number of I/O TLB slabs
4600 force -- force using of bounce buffers even if they
4601 wouldn't be automatically used by the kernel
4602 noforce -- Never use bounce buffers (for debugging)
4606 sysfs.deprecated=0|1 [KNL]
4607 Enable/disable old style sysfs layout for old udev
4608 on older distributions. When this option is enabled
4609 very new udev will not work anymore. When this option
4610 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4611 in older udev will not work anymore.
4612 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4613 the kernel configuration.
4615 sysrq_always_enabled
4617 Ignore sysrq setting - this boot parameter will
4618 neutralize any effect of /proc/sys/kernel/sysrq.
4619 Useful for debugging.
4621 tcpmhash_entries= [KNL,NET]
4622 Set the number of tcp_metrics_hash slots.
4623 Default value is 8192 or 16384 depending on total
4624 ram pages. This is used to specify the TCP metrics
4625 cache size. See Documentation/networking/ip-sysctl.txt
4626 "tcp_no_metrics_save" section for more details.
4630 test_suspend= [SUSPEND][,N]
4631 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4632 standby suspend) or "freeze" (for suspend type freeze)
4633 as the system sleep state during system startup with
4634 the optional capability to repeat N number of times.
4635 The system is woken from this state using a
4636 wakeup-capable RTC alarm.
4638 thash_entries= [KNL,NET]
4639 Set number of hash buckets for TCP connection
4641 thermal.act= [HW,ACPI]
4642 -1: disable all active trip points in all thermal zones
4643 <degrees C>: override all lowest active trip points
4645 thermal.crt= [HW,ACPI]
4646 -1: disable all critical trip points in all thermal zones
4647 <degrees C>: override all critical trip points
4649 thermal.nocrt= [HW,ACPI]
4650 Set to disable actions on ACPI thermal zone
4651 critical and hot trip points.
4653 thermal.off= [HW,ACPI]
4654 1: disable ACPI thermal control
4656 thermal.psv= [HW,ACPI]
4657 -1: disable all passive trip points
4658 <degrees C>: override all passive trip points to this
4661 thermal.tzp= [HW,ACPI]
4662 Specify global default ACPI thermal zone polling rate
4663 <deci-seconds>: poll all this frequency
4664 0: no polling (default)
4667 Force threading of all interrupt handlers except those
4668 marked explicitly IRQF_NO_THREAD.
4671 Enable the Transcendent memory driver if built-in.
4673 tmem.cleancache=0|1 [KNL, XEN]
4674 Default is on (1). Disable the usage of the cleancache
4675 API to send anonymous pages to the hypervisor.
4677 tmem.frontswap=0|1 [KNL, XEN]
4678 Default is on (1). Disable the usage of the frontswap
4679 API to send swap pages to the hypervisor. If disabled
4680 the selfballooning and selfshrinking are force disabled.
4682 tmem.selfballooning=0|1 [KNL, XEN]
4683 Default is on (1). Disable the driving of swap pages
4686 tmem.selfshrinking=0|1 [KNL, XEN]
4687 Default is on (1). Partial swapoff that immediately
4688 transfers pages from Xen hypervisor back to the
4689 kernel based on different criteria.
4693 Specify if the kernel should make use of the cpu
4694 topology information if the hardware supports this.
4695 The scheduler will make use of this information and
4696 e.g. base its process migration decisions on it.
4699 topology_updates= [KNL, PPC, NUMA]
4701 Specify if the kernel should ignore (off)
4702 topology updates sent by the hypervisor to this
4707 tpm_suspend_pcr=[HW,TPM]
4708 Format: integer pcr id
4709 Specify that at suspend time, the tpm driver
4710 should extend the specified pcr with zeros,
4711 as a workaround for some chips which fail to
4712 flush the last written pcr on TPM_SaveState.
4713 This will guarantee that all the other pcrs
4716 trace_buf_size=nn[KMG]
4717 [FTRACE] will set tracing buffer size on each cpu.
4719 trace_event=[event-list]
4720 [FTRACE] Set and start specified trace events in order
4721 to facilitate early boot debugging. The event-list is a
4722 comma separated list of trace events to enable. See
4723 also Documentation/trace/events.rst
4725 trace_options=[option-list]
4726 [FTRACE] Enable or disable tracer options at boot.
4727 The option-list is a comma delimited list of options
4728 that can be enabled or disabled just as if you were
4729 to echo the option name into
4731 /sys/kernel/debug/tracing/trace_options
4733 For example, to enable stacktrace option (to dump the
4734 stack trace of each event), add to the command line:
4736 trace_options=stacktrace
4738 See also Documentation/trace/ftrace.rst "trace options"
4742 Have the tracepoints sent to printk as well as the
4743 tracing ring buffer. This is useful for early boot up
4744 where the system hangs or reboots and does not give the
4745 option for reading the tracing buffer or performing a
4746 ftrace_dump_on_oops.
4748 To turn off having tracepoints sent to printk,
4749 echo 0 > /proc/sys/kernel/tracepoint_printk
4750 Note, echoing 1 into this file without the
4751 tracepoint_printk kernel cmdline option has no effect.
4755 Having tracepoints sent to printk() and activating high
4756 frequency tracepoints such as irq or sched, can cause
4757 the system to live lock.
4760 [FTRACE] enable this option to disable tracing when a
4761 warning is hit. This turns off "tracing_on". Tracing can
4762 be enabled again by echoing '1' into the "tracing_on"
4763 file located in /sys/kernel/debug/tracing/
4765 This option is useful, as it disables the trace before
4766 the WARNING dump is called, which prevents the trace to
4767 be filled with content caused by the warning output.
4769 This option can also be set at run time via the sysctl
4770 option: kernel/traceoff_on_warning
4772 transparent_hugepage=
4774 Format: [always|madvise|never]
4775 Can be used to control the default behavior of the system
4776 with respect to transparent hugepages.
4777 See Documentation/admin-guide/mm/transhuge.rst
4780 tsc= Disable clocksource stability checks for TSC.
4782 [x86] reliable: mark tsc clocksource as reliable, this
4783 disables clocksource verification at runtime, as well
4784 as the stability checks done at bootup. Used to enable
4785 high-resolution timer mode on older hardware, and in
4786 virtualized environment.
4787 [x86] noirqtime: Do not use TSC to do irq accounting.
4788 Used to run time disable IRQ_TIME_ACCOUNTING on any
4789 platforms where RDTSC is slow and this accounting
4791 [x86] unstable: mark the TSC clocksource as unstable, this
4792 marks the TSC unconditionally unstable at bootup and
4793 avoids any further wobbles once the TSC watchdog notices.
4794 [x86] nowatchdog: disable clocksource watchdog. Used
4795 in situations with strict latency requirements (where
4796 interruptions from clocksource watchdog are not
4799 turbografx.map[2|3]= [HW,JOY]
4800 TurboGraFX parallel port interface
4802 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4803 See also Documentation/input/devices/joystick-parport.rst
4805 udbg-immortal [PPC] When debugging early kernel crashes that
4806 happen after console_init() and before a proper
4807 console driver takes over, this boot options might
4808 help "seeing" what's going on.
4810 uhash_entries= [KNL,NET]
4811 Set number of hash buckets for UDP/UDP-Lite connections
4814 [USB] Ignore overcurrent events (default N).
4815 Some badly-designed motherboards generate lots of
4816 bogus events, for ports that aren't wired to
4817 anything. Set this parameter to avoid log spamming.
4818 Note that genuine overcurrent events won't be
4822 [X86] Cause panic on unknown NMI.
4824 usbcore.authorized_default=
4825 [USB] Default USB device authorization:
4826 (default -1 = authorized except for wireless USB,
4827 0 = not authorized, 1 = authorized, 2 = authorized
4828 if device connected to internal port)
4830 usbcore.autosuspend=
4831 [USB] The autosuspend time delay (in seconds) used
4832 for newly-detected USB devices (default 2). This
4833 is the time required before an idle device will be
4834 autosuspended. Devices for which the delay is set
4835 to a negative value won't be autosuspended at all.
4837 usbcore.usbfs_snoop=
4838 [USB] Set to log all usbfs traffic (default 0 = off).
4840 usbcore.usbfs_snoop_max=
4841 [USB] Maximum number of bytes to snoop in each URB
4844 usbcore.blinkenlights=
4845 [USB] Set to cycle leds on hubs (default 0 = off).
4847 usbcore.old_scheme_first=
4848 [USB] Start with the old device initialization
4849 scheme, applies only to low and full-speed devices
4852 usbcore.usbfs_memory_mb=
4853 [USB] Memory limit (in MB) for buffers allocated by
4854 usbfs (default = 16, 0 = max = 2047).
4856 usbcore.use_both_schemes=
4857 [USB] Try the other device initialization scheme
4858 if the first one fails (default 1 = enabled).
4860 usbcore.initial_descriptor_timeout=
4861 [USB] Specifies timeout for the initial 64-byte
4862 USB_REQ_GET_DESCRIPTOR request in milliseconds
4863 (default 5000 = 5.0 seconds).
4865 usbcore.nousb [USB] Disable the USB subsystem
4868 [USB] A list of quirk entries to augment the built-in
4869 usb core quirk list. List entries are separated by
4870 commas. Each entry has the form
4871 VendorID:ProductID:Flags. The IDs are 4-digit hex
4872 numbers and Flags is a set of letters. Each letter
4873 will change the built-in quirk; setting it if it is
4874 clear and clearing it if it is set. The letters have
4875 the following meanings:
4876 a = USB_QUIRK_STRING_FETCH_255 (string
4877 descriptors must not be fetched using
4879 b = USB_QUIRK_RESET_RESUME (device can't resume
4880 correctly so reset it instead);
4881 c = USB_QUIRK_NO_SET_INTF (device can't handle
4882 Set-Interface requests);
4883 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
4884 handle its Configuration or Interface
4886 e = USB_QUIRK_RESET (device can't be reset
4887 (e.g morph devices), don't use reset);
4888 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
4889 more interface descriptions than the
4890 bNumInterfaces count, and can't handle
4891 talking to these interfaces);
4892 g = USB_QUIRK_DELAY_INIT (device needs a pause
4893 during initialization, after we read
4894 the device descriptor);
4895 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
4896 high speed and super speed interrupt
4897 endpoints, the USB 2.0 and USB 3.0 spec
4898 require the interval in microframes (1
4899 microframe = 125 microseconds) to be
4900 calculated as interval = 2 ^
4902 Devices with this quirk report their
4903 bInterval as the result of this
4904 calculation instead of the exponent
4905 variable used in the calculation);
4906 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
4907 handle device_qualifier descriptor
4909 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
4910 generates spurious wakeup, ignore
4911 remote wakeup capability);
4912 k = USB_QUIRK_NO_LPM (device can't handle Link
4914 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
4915 (Device reports its bInterval as linear
4916 frames instead of the USB 2.0
4918 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
4919 to be disconnected before suspend to
4920 prevent spurious wakeup);
4921 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
4922 pause after every control message);
4923 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
4924 delay after resetting its port);
4925 Example: quirks=0781:5580:bk,0a5c:5834:gij
4928 [USBHID] The interval which mice are to be polled at.
4931 [USBHID] The interval which joysticks are to be polled at.
4934 [USBHID] The interval which keyboards are to be polled at.
4936 usb-storage.delay_use=
4937 [UMS] The delay in seconds before a new device is
4938 scanned for Logical Units (default 1).
4941 [UMS] A list of quirks entries to supplement or
4942 override the built-in unusual_devs list. List
4943 entries are separated by commas. Each entry has
4944 the form VID:PID:Flags where VID and PID are Vendor
4945 and Product ID values (4-digit hex numbers) and
4946 Flags is a set of characters, each corresponding
4947 to a common usb-storage quirk flag as follows:
4948 a = SANE_SENSE (collect more than 18 bytes
4950 b = BAD_SENSE (don't collect more than 18
4951 bytes of sense data);
4952 c = FIX_CAPACITY (decrease the reported
4953 device capacity by one sector);
4954 d = NO_READ_DISC_INFO (don't use
4955 READ_DISC_INFO command);
4956 e = NO_READ_CAPACITY_16 (don't use
4957 READ_CAPACITY_16 command);
4958 f = NO_REPORT_OPCODES (don't use report opcodes
4960 g = MAX_SECTORS_240 (don't transfer more than
4961 240 sectors at a time, uas only);
4962 h = CAPACITY_HEURISTICS (decrease the
4963 reported device capacity by one
4964 sector if the number is odd);
4965 i = IGNORE_DEVICE (don't bind to this
4967 j = NO_REPORT_LUNS (don't use report luns
4969 l = NOT_LOCKABLE (don't try to lock and
4970 unlock ejectable media);
4971 m = MAX_SECTORS_64 (don't transfer more
4972 than 64 sectors = 32 KB at a time);
4973 n = INITIAL_READ10 (force a retry of the
4974 initial READ(10) command);
4975 o = CAPACITY_OK (accept the capacity
4976 reported by the device);
4977 p = WRITE_CACHE (the device cache is ON
4979 r = IGNORE_RESIDUE (the device reports
4980 bogus residue values);
4981 s = SINGLE_LUN (the device has only one
4983 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4984 commands, uas only);
4985 u = IGNORE_UAS (don't bind to the uas driver);
4986 w = NO_WP_DETECT (don't test whether the
4987 medium is write-protected).
4988 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4989 even if the device claims no cache)
4990 Example: quirks=0419:aaf5:rl,0421:0433:rc
4992 user_debug= [KNL,ARM]
4994 See arch/arm/Kconfig.debug help text.
4995 1 - undefined instruction events
4997 4 - invalid data aborts
5000 Example: user_debug=31
5003 [X86] Flags controlling user PTE allocations.
5005 nohigh = do not allocate PTE pages in
5006 HIGHMEM regardless of setting
5010 On X86_32, this is an alias for vdso32=. Otherwise:
5012 vdso=1: enable VDSO (the default)
5013 vdso=0: disable VDSO mapping
5015 vdso32= [X86] Control the 32-bit vDSO
5016 vdso32=1: enable 32-bit VDSO
5017 vdso32=0 or vdso32=2: disable 32-bit VDSO
5019 See the help text for CONFIG_COMPAT_VDSO for more
5020 details. If CONFIG_COMPAT_VDSO is set, the default is
5021 vdso32=0; otherwise, the default is vdso32=1.
5023 For compatibility with older kernels, vdso32=2 is an
5026 Try vdso32=0 if you encounter an error that says:
5027 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
5030 vector=percpu: enable percpu vector domain
5032 video= [FB] Frame buffer configuration
5033 See Documentation/fb/modedb.rst.
5035 video.brightness_switch_enabled= [0,1]
5036 If set to 1, on receiving an ACPI notify event
5037 generated by hotkey, video driver will adjust brightness
5038 level and then send out the event to user space through
5039 the allocated input device; If set to 0, video driver
5040 will only send out the event without touching backlight
5045 [VMMIO] Memory mapped virtio (platform) device.
5047 <size>@<baseaddr>:<irq>[:<id>]
5049 <size> := size (can use standard suffixes
5051 <baseaddr> := physical base address
5052 <irq> := interrupt number (as passed to
5054 <id> := (optional) platform device id
5056 virtio_mmio.device=1K@0x100b0000:48:7
5058 Can be used multiple times for multiple devices.
5060 vga= [BOOT,X86-32] Select a particular video mode
5061 See Documentation/x86/boot.rst and
5062 Documentation/svga.txt.
5063 Use vga=ask for menu.
5064 This is actually a boot loader parameter; the value is
5065 passed to the kernel using a special protocol.
5067 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
5068 May slow down system boot speed, especially when
5069 enabled on systems with a large amount of memory.
5070 All options are enabled by default, and this
5071 interface is meant to allow for selectively
5072 enabling or disabling specific virtual memory
5075 Available options are:
5076 P Enable page structure init time poisoning
5077 - Disable all of the above options
5079 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
5080 size of <nn>. This can be used to increase the
5081 minimum size (128MB on x86). It can also be used to
5082 decrease the size and leave more room for directly
5085 vmcp_cma=nn[MG] [KNL,S390]
5086 Sets the memory size reserved for contiguous memory
5087 allocations for the vmcp device driver.
5089 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
5092 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
5095 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
5099 Controls the behavior of vsyscalls (i.e. calls to
5100 fixed addresses of 0xffffffffff600x00 from legacy
5101 code). Most statically-linked binaries and older
5102 versions of glibc use these calls. Because these
5103 functions are at fixed addresses, they make nice
5104 targets for exploits that can control RIP.
5106 emulate [default] Vsyscalls turn into traps and are
5107 emulated reasonably safely. The vsyscall
5110 xonly Vsyscalls turn into traps and are
5111 emulated reasonably safely. The vsyscall
5112 page is not readable.
5114 none Vsyscalls don't work at all. This makes
5115 them quite hard to use for exploits but
5116 might break your system.
5118 vt.color= [VT] Default text color.
5119 Format: 0xYX, X = foreground, Y = background.
5120 Default: 0x07 = light gray on black.
5122 vt.cur_default= [VT] Default cursor shape.
5123 Format: 0xCCBBAA, where AA, BB, and CC are the same as
5124 the parameters of the <Esc>[?A;B;Cc escape sequence;
5125 see VGA-softcursor.txt. Default: 2 = underline.
5127 vt.default_blu= [VT]
5128 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
5129 Change the default blue palette of the console.
5130 This is a 16-member array composed of values
5133 vt.default_grn= [VT]
5134 Format: <green0>,<green1>,<green2>,...,<green15>
5135 Change the default green palette of the console.
5136 This is a 16-member array composed of values
5139 vt.default_red= [VT]
5140 Format: <red0>,<red1>,<red2>,...,<red15>
5141 Change the default red palette of the console.
5142 This is a 16-member array composed of values
5148 Set system-wide default UTF-8 mode for all tty's.
5149 Default is 1, i.e. UTF-8 mode is enabled for all
5150 newly opened terminals.
5152 vt.global_cursor_default=
5155 Set system-wide default for whether a cursor
5156 is shown on new VTs. Default is -1,
5157 i.e. cursors will be created by default unless
5158 overridden by individual drivers. 0 will hide
5159 cursors, 1 will display them.
5161 vt.italic= [VT] Default color for italic text; 0-15.
5164 vt.underline= [VT] Default color for underlined text; 0-15.
5167 watchdog timers [HW,WDT] For information on watchdog timers,
5168 see Documentation/watchdog/watchdog-parameters.rst
5169 or other driver-specific files in the
5170 Documentation/watchdog/ directory.
5174 Set the hard lockup detector stall duration
5175 threshold in seconds. The soft lockup detector
5176 threshold is set to twice the value. A value of 0
5177 disables both lockup detectors. Default is 10
5180 workqueue.watchdog_thresh=
5181 If CONFIG_WQ_WATCHDOG is configured, workqueue can
5182 warn stall conditions and dump internal state to
5183 help debugging. 0 disables workqueue stall
5184 detection; otherwise, it's the stall threshold
5185 duration in seconds. The default value is 30 and
5186 it can be updated at runtime by writing to the
5187 corresponding sysfs file.
5189 workqueue.disable_numa
5190 By default, all work items queued to unbound
5191 workqueues are affine to the NUMA nodes they're
5192 issued on, which results in better behavior in
5193 general. If NUMA affinity needs to be disabled for
5194 whatever reason, this option can be used. Note
5195 that this also can be controlled per-workqueue for
5196 workqueues visible under /sys/bus/workqueue/.
5198 workqueue.power_efficient
5199 Per-cpu workqueues are generally preferred because
5200 they show better performance thanks to cache
5201 locality; unfortunately, per-cpu workqueues tend to
5202 be more power hungry than unbound workqueues.
5204 Enabling this makes the per-cpu workqueues which
5205 were observed to contribute significantly to power
5206 consumption unbound, leading to measurably lower
5207 power usage at the cost of small performance
5210 The default value of this parameter is determined by
5211 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
5213 workqueue.debug_force_rr_cpu
5214 Workqueue used to implicitly guarantee that work
5215 items queued without explicit CPU specified are put
5216 on the local CPU. This guarantee is no longer true
5217 and while local CPU is still preferred work items
5218 may be put on foreign CPUs. This debug option
5219 forces round-robin CPU selection to flush out
5220 usages which depend on the now broken guarantee.
5221 When enabled, memory and cache locality will be
5224 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
5225 default x2apic cluster mode on platforms
5228 x86_intel_mid_timer= [X86-32,APBT]
5229 Choose timer option for x86 Intel MID platform.
5230 Two valid options are apbt timer only and lapic timer
5231 plus one apbt timer for broadcast timer.
5232 x86_intel_mid_timer=apbt_only | lapic_and_apbt
5234 xen_512gb_limit [KNL,X86-64,XEN]
5235 Restricts the kernel running paravirtualized under Xen
5236 to use only up to 512 GB of RAM. The reason to do so is
5237 crash analysis tools and Xen tools for doing domain
5238 save/restore/migration must be enabled to handle larger
5241 xen_emul_unplug= [HW,X86,XEN]
5242 Unplug Xen emulated devices
5243 Format: [unplug0,][unplug1]
5244 ide-disks -- unplug primary master IDE devices
5245 aux-ide-disks -- unplug non-primary-master IDE devices
5246 nics -- unplug network devices
5247 all -- unplug all emulated devices (NICs and IDE disks)
5248 unnecessary -- unplugging emulated devices is
5249 unnecessary even if the host did not respond to
5251 never -- do not unplug even if version check succeeds
5253 xen_nopvspin [X86,XEN]
5254 Disables the ticketlock slowpath using Xen PV
5258 Disables the PV optimizations forcing the HVM guest to
5259 run as generic HVM guest with no PV drivers.
5261 xen_scrub_pages= [XEN]
5262 Boolean option to control scrubbing pages before giving them back
5263 to Xen, for use by other domains. Can be also changed at runtime
5264 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
5265 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
5267 xen_timer_slop= [X86-64,XEN]
5268 Set the timer slop (in nanoseconds) for the virtual Xen
5269 timers (default is 100000). This adjusts the minimum
5270 delta of virtualized Xen timers, where lower values
5271 improve timer resolution at the expense of processing
5272 more timer interrupts.
5274 xirc2ps_cs= [NET,PCMCIA]
5276 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
5278 xhci-hcd.quirks [USB,KNL]
5279 A hex value specifying bitmask with supplemental xhci
5280 host controller quirks. Meaning of each bit can be
5281 consulted in header drivers/usb/host/xhci.h.
git.samba.org / sfrench / cifs-2.6.git / blob