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.rst
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 parameter
809 enables the feature at boot time. By default, it is
810 disabled and the system will work mostly the same as a
811 kernel built without CONFIG_DEBUG_PAGEALLOC.
812 on: enable the feature
814 debugpat [X86] Enable PAT debugging
816 decnet.addr= [HW,NET]
817 Format: <area>[,<node>]
818 See also Documentation/networking/decnet.txt.
821 [same as hugepagesz=] The size of the default
822 HugeTLB page size. This is the size represented by
823 the legacy /proc/ hugepages APIs, used for SHM, and
824 default size when mounting hugetlbfs filesystems.
825 Defaults to the default architecture's huge page size
828 deferred_probe_timeout=
829 [KNL] Debugging option to set a timeout in seconds for
830 deferred probe to give up waiting on dependencies to
831 probe. Only specific dependencies (subsystems or
832 drivers) that have opted in will be ignored. A timeout of 0
833 will timeout at the end of initcalls. This option will also
834 dump out devices still on the deferred probe list after
838 Set number of hash buckets for dentry cache.
840 disable_1tb_segments [PPC]
841 Disables the use of 1TB hash page table segments. This
842 causes the kernel to fall back to 256MB segments which
843 can be useful when debugging issues that require an SLB
847 See Documentation/networking/ipv6.txt.
850 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
851 hardening is enabled for this boot. Hardened
852 usercopy checking is used to protect the kernel
853 from reading or writing beyond known memory
854 allocation boundaries as a proactive defense
855 against bounds-checking flaws in the kernel's
856 copy_to_user()/copy_from_user() interface.
857 on Perform hardened usercopy checks (default).
858 off Disable hardened usercopy checks.
861 Disable RADIX MMU mode on POWER9
863 disable_cpu_apicid= [X86,APIC,SMP]
865 The number of initial APIC ID for the
866 corresponding CPU to be disabled at boot,
867 mostly used for the kdump 2nd kernel to
868 disable BSP to wake up multiple CPUs without
869 causing system reset or hang due to sending
872 perf_v4_pmi= [X86,INTEL]
874 Disable Intel PMU counter freezing feature.
875 The feature only exists starting from
876 Arch Perfmon v4 (Skylake and newer).
878 disable_ddw [PPC/PSERIES]
879 Disable Dynamic DMA Window support. Use this if
880 to workaround buggy firmware.
883 See Documentation/networking/ipv6.txt.
885 disable_mtrr_cleanup [X86]
886 The kernel tries to adjust MTRR layout from continuous
887 to discrete, to make X server driver able to add WB
888 entry later. This parameter disables that.
890 disable_mtrr_trim [X86, Intel and AMD only]
891 By default the kernel will trim any uncacheable
892 memory out of your available memory pool based on
893 MTRR settings. This parameter disables that behavior,
894 possibly causing your machine to run very slowly.
896 disable_timer_pin_1 [X86]
897 Disable PIN 1 of APIC timer
898 Can be useful to work around chipset bugs.
900 dis_ucode_ldr [X86] Disable the microcode loader.
902 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
903 this option disables the debugging code at boot.
905 dma_debug_entries=<number>
906 This option allows to tune the number of preallocated
907 entries for DMA-API debugging code. One entry is
908 required per DMA-API allocation. Use this if the
909 DMA-API debugging code disables itself because the
910 architectural default is too low.
912 dma_debug_driver=<driver_name>
913 With this option the DMA-API debugging driver
914 filter feature can be enabled at boot time. Just
915 pass the driver to filter for as the parameter.
916 The filter can be disabled or changed to another
917 driver later using sysfs.
919 driver_async_probe= [KNL]
920 List of driver names to be probed asynchronously.
921 Format: <driver_name1>,<driver_name2>...
923 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
924 Broken monitors, graphic adapters, KVMs and EDIDless
925 panels may send no or incorrect EDID data sets.
926 This parameter allows to specify an EDID data sets
927 in the /lib/firmware directory that are used instead.
928 Generic built-in EDID data sets are used, if one of
929 edid/1024x768.bin, edid/1280x1024.bin,
930 edid/1680x1050.bin, or edid/1920x1080.bin is given
931 and no file with the same name exists. Details and
932 instructions how to build your own EDID data are
933 available in Documentation/EDID/howto.rst. An EDID
934 data set will only be used for a particular connector,
935 if its name and a colon are prepended to the EDID
936 name. Each connector may use a unique EDID data
937 set by separating the files with a comma. An EDID
938 data set with no connector name will be used for
939 any connectors not explicitly specified.
944 Format: {"off" | "known"}
945 Control how the dt_cpu_ftrs device-tree binding is
946 used for CPU feature discovery and setup (if it
948 off: Do not use it, fall back to legacy cpu table.
949 known: Do not pass through unknown features to guests
950 or userspace, only those that the kernel is aware of.
952 dump_apple_properties [X86]
953 Dump name and content of EFI device properties on
954 x86 Macs. Useful for driver authors to determine
955 what data is available or for reverse-engineering.
957 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
958 module.dyndbg[="val"]
959 Enable debug messages at boot time. See
960 Documentation/admin-guide/dynamic-debug-howto.rst
963 nompx [X86] Disables Intel Memory Protection Extensions.
964 See Documentation/x86/intel_mpx.rst for more
965 information about the feature.
967 nopku [X86] Disable Memory Protection Keys CPU feature found
970 module.async_probe [KNL]
971 Enable asynchronous probe on this module.
973 early_ioremap_debug [KNL]
974 Enable debug messages in early_ioremap support. This
975 is useful for tracking down temporary early mappings
976 which are not unmapped.
978 earlycon= [KNL] Output early console device and options.
980 [ARM64] The early console is determined by the
981 stdout-path property in device tree's chosen node,
982 or determined by the ACPI SPCR table.
984 [X86] When used with no options the early console is
985 determined by the ACPI SPCR table.
987 cdns,<addr>[,options]
988 Start an early, polled-mode console on a Cadence
989 (xuartps) serial port at the specified address. Only
990 supported option is baud rate. If baud rate is not
991 specified, the serial port must already be setup and
994 uart[8250],io,<addr>[,options]
995 uart[8250],mmio,<addr>[,options]
996 uart[8250],mmio32,<addr>[,options]
997 uart[8250],mmio32be,<addr>[,options]
998 uart[8250],0x<addr>[,options]
999 Start an early, polled-mode console on the 8250/16550
1000 UART at the specified I/O port or MMIO address.
1001 MMIO inter-register address stride is either 8-bit
1002 (mmio) or 32-bit (mmio32 or mmio32be).
1003 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1004 to be equivalent to 'mmio'. 'options' are specified
1005 in the same format described for "console=ttyS<n>"; if
1006 unspecified, the h/w is not initialized.
1010 Start an early, polled-mode console on a pl011 serial
1011 port at the specified address. The pl011 serial port
1012 must already be setup and configured. Options are not
1013 yet supported. If 'mmio32' is specified, then only
1014 the driver will use only 32-bit accessors to read/write
1015 the device registers.
1018 Start an early, polled-mode console on a meson serial
1019 port at the specified address. The serial port must
1020 already be setup and configured. Options are not yet
1024 Start an early, polled-mode console on an msm serial
1025 port at the specified address. The serial port
1026 must already be setup and configured. Options are not
1029 msm_serial_dm,<addr>
1030 Start an early, polled-mode console on an msm serial
1031 dm port at the specified address. The serial port
1032 must already be setup and configured. Options are not
1036 Start an early, polled-mode console on a serial port
1037 of an Actions Semi SoC, such as S500 or S900, at the
1038 specified address. The serial port must already be
1039 setup and configured. Options are not yet supported.
1042 Start an early, polled-mode console on a serial port
1043 of an RDA Micro SoC, such as RDA8810PL, at the
1044 specified address. The serial port must already be
1045 setup and configured. Options are not yet supported.
1047 smh Use ARM semihosting calls for early console.
1055 Use early console provided by serial driver available
1056 on Samsung SoCs, requires selecting proper type and
1057 a correct base address of the selected UART port. The
1058 serial port must already be setup and configured.
1059 Options are not yet supported.
1062 Start an early, polled-mode console on a lantiq serial
1063 (lqasc) port at the specified address. The serial port
1064 must already be setup and configured. Options are not
1069 Use early console provided by Freescale LP UART driver
1070 found on Freescale Vybrid and QorIQ LS1021A processors.
1071 A valid base address must be provided, and the serial
1072 port must already be setup and configured.
1075 Start an early, polled-mode console on the
1076 Armada 3700 serial port at the specified
1077 address. The serial port must already be setup
1078 and configured. Options are not yet supported.
1081 Start an early, polled-mode console on a Qualcomm
1082 Generic Interface (GENI) based serial port at the
1083 specified address. The serial port must already be
1084 setup and configured. Options are not yet supported.
1087 Start an early, unaccelerated console on the EFI
1088 memory mapped framebuffer (if available). On cache
1089 coherent non-x86 systems that use system memory for
1090 the framebuffer, pass the 'ram' option so that it is
1091 mapped with the correct attributes.
1093 earlyprintk= [X86,SH,ARM,M68k,S390]
1097 earlyprintk=serial[,ttySn[,baudrate]]
1098 earlyprintk=serial[,0x...[,baudrate]]
1099 earlyprintk=ttySn[,baudrate]
1100 earlyprintk=dbgp[debugController#]
1101 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1102 earlyprintk=xdbc[xhciController#]
1104 earlyprintk is useful when the kernel crashes before
1105 the normal console is initialized. It is not enabled by
1106 default because it has some cosmetic problems.
1108 Append ",keep" to not disable it when the real console
1111 Only one of vga, efi, serial, or usb debug port can
1114 Currently only ttyS0 and ttyS1 may be specified by
1115 name. Other I/O ports may be explicitly specified
1116 on some architectures (x86 and arm at least) by
1117 replacing ttySn with an I/O port address, like this:
1118 earlyprintk=serial,0x1008,115200
1119 You can find the port for a given device in
1120 /proc/tty/driver/serial:
1121 2: uart:ST16650V2 port:00001008 irq:18 ...
1123 Interaction with the standard serial driver is not
1126 The VGA and EFI output is eventually overwritten by
1129 The xen output can only be used by Xen PV guests.
1131 The sclp output can only be used on s390.
1133 The optional "force" to "pciserial" enables use of a
1134 PCI device even when its classcode is not of the
1137 edac_report= [HW,EDAC] Control how to report EDAC event
1138 Format: {"on" | "off" | "force"}
1139 on: enable EDAC to report H/W event. May be overridden
1140 by other higher priority error reporting module.
1141 off: disable H/W event reporting through EDAC.
1142 force: enforce the use of EDAC to report H/W event.
1145 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1148 This is designed to be used in conjunction with
1149 the boot argument: earlyprintk=vga
1152 Format: {"off" | "on" | "skip[mbr]"}
1155 Format: { "old_map", "nochunk", "noruntime", "debug" }
1156 old_map [X86-64]: switch to the old ioremap-based EFI
1157 runtime services mapping. 32-bit still uses this one by
1159 nochunk: disable reading files in "chunks" in the EFI
1160 boot stub, as chunking can cause problems with some
1161 firmware implementations.
1162 noruntime : disable EFI runtime services support
1163 debug: enable misc debug output
1165 efi_no_storage_paranoia [EFI; X86]
1166 Using this parameter you can use more than 50% of
1167 your efi variable storage. Use this parameter only if
1168 you are really sure that your UEFI does sane gc and
1169 fulfills the spec otherwise your board may brick.
1171 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1172 Add arbitrary attribute to specific memory range by
1173 updating original EFI memory map.
1174 Region of memory which aa attribute is added to is
1176 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1177 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1178 attribute is added to range 0x100000000-0x180000000 and
1179 0x10a0000000-0x1120000000.
1181 Using this parameter you can do debugging of EFI memmap
1182 related feature. For example, you can do debugging of
1183 Address Range Mirroring feature even if your box
1186 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1187 that is to be dynamically loaded by Linux. If there are
1188 multiple variables with the same name but with different
1189 vendor GUIDs, all of them will be loaded. See
1190 Documentation/admin-guide/acpi/ssdt-overlays.rst for details.
1193 eisa_irq_edge= [PARISC,HW]
1194 See header of drivers/parisc/eisa.c.
1197 See comment before function elanfreq_setup() in
1198 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1201 Format: { "mq-deadline" | "kyber" | "bfq" }
1202 See Documentation/block/deadline-iosched.rst,
1203 Documentation/block/kyber-iosched.rst and
1204 Documentation/block/bfq-iosched.rst for details.
1206 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1207 Specifies physical address of start of kernel core
1208 image elf header and optionally the size. Generally
1209 kexec loader will pass this option to capture kernel.
1210 See Documentation/kdump/kdump.rst for details.
1212 enable_mtrr_cleanup [X86]
1213 The kernel tries to adjust MTRR layout from continuous
1214 to discrete, to make X server driver able to add WB
1215 entry later. This parameter enables that.
1217 enable_timer_pin_1 [X86]
1218 Enable PIN 1 of APIC timer
1219 Can be useful to work around chipset bugs
1220 (in particular on some ATI chipsets).
1221 The kernel tries to set a reasonable default.
1223 enforcing [SELINUX] Set initial enforcing status.
1225 See security/selinux/Kconfig help text.
1226 0 -- permissive (log only, no denials).
1227 1 -- enforcing (deny and log).
1229 Value can be changed at runtime via /selinux/enforce.
1232 Disable Error Record Serialization Table (ERST)
1235 ether= [HW,NET] Ethernet cards parameters
1236 This option is obsoleted by the "netdev=" option, which
1237 has equivalent usage. See its documentation for details.
1241 Permit 'security.evm' to be updated regardless of
1242 current integrity status.
1246 fail_make_request=[KNL]
1247 General fault injection mechanism.
1248 Format: <interval>,<probability>,<space>,<times>
1249 See also Documentation/fault-injection/.
1252 See Documentation/blockdev/floppy.rst.
1254 force_pal_cache_flush
1255 [IA-64] Avoid check_sal_cache_flush which may hang on
1256 buggy SAL_CACHE_FLUSH implementations. Using this
1257 parameter will force ia64_sal_cache_flush to call
1258 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1261 Forcefully enable Physical Address Extension (PAE).
1262 Many Pentium M systems disable PAE but may have a
1263 functionally usable PAE implementation.
1264 Warning: use of this parameter will taint the kernel
1265 and may cause unknown problems.
1268 [FTRACE] will set and start the specified tracer
1269 as early as possible in order to facilitate early
1272 ftrace_dump_on_oops[=orig_cpu]
1273 [FTRACE] will dump the trace buffers on oops.
1274 If no parameter is passed, ftrace will dump
1275 buffers of all CPUs, but if you pass orig_cpu, it will
1276 dump only the buffer of the CPU that triggered the
1279 ftrace_filter=[function-list]
1280 [FTRACE] Limit the functions traced by the function
1281 tracer at boot up. function-list is a comma separated
1282 list of functions. This list can be changed at run
1283 time by the set_ftrace_filter file in the debugfs
1286 ftrace_notrace=[function-list]
1287 [FTRACE] Do not trace the functions specified in
1288 function-list. This list can be changed at run time
1289 by the set_ftrace_notrace file in the debugfs
1292 ftrace_graph_filter=[function-list]
1293 [FTRACE] Limit the top level callers functions traced
1294 by the function graph tracer at boot up.
1295 function-list is a comma separated list of functions
1296 that can be changed at run time by the
1297 set_graph_function file in the debugfs tracing directory.
1299 ftrace_graph_notrace=[function-list]
1300 [FTRACE] Do not trace from the functions specified in
1301 function-list. This list is a comma separated list of
1302 functions that can be changed at run time by the
1303 set_graph_notrace file in the debugfs tracing directory.
1305 ftrace_graph_max_depth=<uint>
1306 [FTRACE] Used with the function graph tracer. This is
1307 the max depth it will trace into a function. This value
1308 can be changed at run time by the max_graph_depth file
1309 in the tracefs tracing directory. default: 0 (no limit)
1312 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1313 support via parallel port (up to 5 devices per port)
1314 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1315 See also Documentation/input/devices/joystick-parport.rst
1319 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1323 gcov_persist= [GCOV] When non-zero (default), profiling data for
1324 kernel modules is saved and remains accessible via
1325 debugfs, even when the module is unloaded/reloaded.
1326 When zero, profiling data is discarded and associated
1327 debugfs files are removed at module unload time.
1329 goldfish [X86] Enable the goldfish android emulator platform.
1330 Don't use this when you are not running on the
1333 gpt [EFI] Forces disk with valid GPT signature but
1334 invalid Protective MBR to be treated as GPT. If the
1335 primary GPT is corrupted, it enables the backup/alternate
1336 GPT to be used instead.
1338 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1339 the "Enable 0" bit of the configuration register.
1342 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1343 the "Enable 0" bit of the configuration register.
1346 grcan.select= [HW] Select which physical interface to use.
1349 grcan.txsize= [HW] Sets the size of the tx buffer.
1350 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1352 grcan.rxsize= [HW] Sets the size of the rx buffer.
1353 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1356 gpio-mockup.gpio_mockup_ranges
1357 [HW] Sets the ranges of gpiochip of for this device.
1358 Format: <start1>,<end1>,<start2>,<end2>...
1360 hardlockup_all_cpu_backtrace=
1361 [KNL] Should the hard-lockup detector generate
1362 backtraces on all cpus.
1365 hashdist= [KNL,NUMA] Large hashes allocated during boot
1366 are distributed across NUMA nodes. Defaults on
1367 for 64-bit NUMA, off otherwise.
1368 Format: 0 | 1 (for off | on)
1370 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1372 hd= [EIDE] (E)IDE hard drive subsystem geometry
1373 Format: <cyl>,<head>,<sect>
1376 Disable Hardware Error Source Table (HEST) support;
1377 corresponding firmware-first mode error processing
1378 logic will be disabled.
1380 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1381 size of <nn>. This works even on boxes that have no
1382 highmem otherwise. This also works to reduce highmem
1383 size on bigger boxes.
1385 highres= [KNL] Enable/disable high resolution timer mode.
1386 Valid parameters: "on", "off"
1391 hpet= [X86-32,HPET] option to control HPET usage
1392 Format: { enable (default) | disable | force |
1394 disable: disable HPET and use PIT instead
1395 force: allow force enabled of undocumented chips (ICH4,
1397 verbose: show contents of HPET registers during setup
1399 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1400 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1402 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1403 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1404 On x86-64 and powerpc, this option can be specified
1405 multiple times interleaved with hugepages= to reserve
1406 huge pages of different sizes. Valid pages sizes on
1407 x86-64 are 2M (when the CPU supports "pse") and 1G
1408 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1411 [KNL] Should the hung task detector generate panics.
1414 A nonzero value instructs the kernel to panic when a
1415 hung task is detected. The default value is controlled
1416 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1417 option. The value selected by this boot parameter can
1418 be changed later by the kernel.hung_task_panic sysctl.
1420 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1421 terminal devices. Valid values: 0..8
1422 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1423 If specified, z/VM IUCV HVC accepts connections
1424 from listed z/VM user IDs only.
1426 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations
1427 which allow the hypervisor to 'idle' the
1428 guest on lock contention.
1431 Do not unregister boot console at start. This is only
1432 useful for debugging when something happens in the window
1433 between unregistering the boot console and initializing
1436 i2c_bus= [HW] Override the default board specific I2C bus speed
1437 or register an additional I2C bus that is not
1438 registered from board initialization code.
1442 i8042.debug [HW] Toggle i8042 debug mode
1443 i8042.unmask_kbd_data
1444 [HW] Enable printing of interrupt data from the KBD port
1445 (disabled by default, and as a pre-condition
1446 requires that i8042.debug=1 be enabled)
1447 i8042.direct [HW] Put keyboard port into non-translated mode
1448 i8042.dumbkbd [HW] Pretend that controller can only read data from
1449 keyboard and cannot control its state
1450 (Don't attempt to blink the leds)
1451 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1452 i8042.nokbd [HW] Don't check/create keyboard port
1453 i8042.noloop [HW] Disable the AUX Loopback command while probing
1455 i8042.nomux [HW] Don't check presence of an active multiplexing
1457 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1459 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1460 i8042.reset [HW] Reset the controller during init, cleanup and
1461 suspend-to-ram transitions, only during s2r
1462 transitions, or never reset
1463 Format: { 1 | Y | y | 0 | N | n }
1464 1, Y, y: always reset controller
1465 0, N, n: don't ever reset controller
1466 Default: only on s2r transitions on x86; most other
1467 architectures force reset to be always executed
1468 i8042.unlock [HW] Unlock (ignore) the keylock
1469 i8042.kbdreset [HW] Reset device connected to KBD port
1473 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1474 indicates that the driver is running on unsupported
1476 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1477 does not match list of supported models.
1479 [HW] Report power status in /proc/i8k
1480 (disabled by default)
1481 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1484 i915.invert_brightness=
1485 [DRM] Invert the sense of the variable that is used to
1486 set the brightness of the panel backlight. Normally a
1487 brightness value of 0 indicates backlight switched off,
1488 and the maximum of the brightness value sets the backlight
1489 to maximum brightness. If this parameter is set to 0
1490 (default) and the machine requires it, or this parameter
1491 is set to 1, a brightness value of 0 sets the backlight
1492 to maximum brightness, and the maximum of the brightness
1493 value switches the backlight off.
1494 -1 -- never invert brightness
1495 0 -- machine default
1496 1 -- force brightness inversion
1499 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1501 ide-core.nodma= [HW] (E)IDE subsystem
1502 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1503 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1504 .cdrom .chs .ignore_cable are additional options
1505 See Documentation/ide/ide.rst.
1507 ide-generic.probe-mask= [HW] (E)IDE subsystem
1509 Probe mask for legacy ISA IDE ports. Depending on
1510 platform up to 6 ports are supported, enabled by
1511 setting corresponding bits in the mask to 1. The
1512 default value is 0x0, which has a special meaning.
1513 On systems that have PCI, it triggers scanning the
1514 PCI bus for the first and the second port, which
1515 are then probed. On systems without PCI the value
1516 of 0x0 enables probing the two first ports as if it
1519 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1520 Claim all unknown PCI IDE storage controllers.
1523 Format: idle=poll, idle=halt, idle=nomwait
1524 Poll forces a polling idle loop that can slightly
1525 improve the performance of waking up a idle CPU, but
1526 will use a lot of power and make the system run hot.
1528 idle=halt: Halt is forced to be used for CPU idle.
1529 In such case C2/C3 won't be used again.
1530 idle=nomwait: Disable mwait for CPU C-states
1532 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1533 Format: { strict | legacy | 2008 | relaxed }
1536 Choose which programs will be accepted for execution
1537 based on the IEEE 754 NaN encoding(s) supported by
1538 the FPU and the NaN encoding requested with the value
1539 of an ELF file header flag individually set by each
1540 binary. Hardware implementations are permitted to
1541 support either or both of the legacy and the 2008 NaN
1544 Available settings are as follows:
1545 strict accept binaries that request a NaN encoding
1546 supported by the FPU
1547 legacy only accept legacy-NaN binaries, if supported
1549 2008 only accept 2008-NaN binaries, if supported
1551 relaxed accept any binaries regardless of whether
1552 supported by the FPU
1554 The FPU emulator is always able to support both NaN
1555 encodings, so if no FPU hardware is present or it has
1556 been disabled with 'nofpu', then the settings of
1557 'legacy' and '2008' strap the emulator accordingly,
1558 'relaxed' straps the emulator for both legacy-NaN and
1559 2008-NaN, whereas 'strict' enables legacy-NaN only on
1560 legacy processors and both NaN encodings on MIPS32 or
1563 The setting for ABS.fmt/NEG.fmt instruction execution
1564 mode generally follows that for the NaN encoding,
1565 except where unsupported by hardware.
1567 ignore_loglevel [KNL]
1568 Ignore loglevel setting - this will print /all/
1569 kernel messages to the console. Useful for debugging.
1570 We also add it as printk module parameter, so users
1571 could change it dynamically, usually by
1572 /sys/module/printk/parameters/ignore_loglevel.
1575 Ignore RLIMIT_DATA setting for data mappings,
1576 print warning at first misuse. Can be changed via
1577 /sys/module/kernel/parameters/ignore_rlimit_data.
1579 ihash_entries= [KNL]
1580 Set number of hash buckets for inode cache.
1582 ima_appraise= [IMA] appraise integrity measurements
1583 Format: { "off" | "enforce" | "fix" | "log" }
1586 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead.
1587 The builtin appraise policy appraises all files
1590 ima_canonical_fmt [IMA]
1591 Use the canonical format for the binary runtime
1592 measurements, instead of host native format.
1595 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1599 The list of supported hash algorithms is defined
1600 in crypto/hash_info.h.
1603 The builtin policies to load during IMA setup.
1604 Format: "tcb | appraise_tcb | secure_boot |
1607 The "tcb" policy measures all programs exec'd, files
1608 mmap'd for exec, and all files opened with the read
1609 mode bit set by either the effective uid (euid=0) or
1612 The "appraise_tcb" policy appraises the integrity of
1613 all files owned by root.
1615 The "secure_boot" policy appraises the integrity
1616 of files (eg. kexec kernel image, kernel modules,
1617 firmware, policy, etc) based on file signatures.
1619 The "fail_securely" policy forces file signature
1620 verification failure also on privileged mounted
1621 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1624 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1625 Load a policy which meets the needs of the Trusted
1626 Computing Base. This means IMA will measure all
1627 programs exec'd, files mmap'd for exec, and all files
1628 opened for read by uid=0.
1631 Select one of defined IMA measurements template formats.
1632 Formats: { "ima" | "ima-ng" | "ima-sig" }
1636 [IMA] Define a custom template format.
1637 Format: { "field1|...|fieldN" }
1639 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1640 Format: <min_file_size>
1641 Set the minimal file size for using asynchronous hash.
1642 If left unspecified, ahash usage is disabled.
1644 ahash performance varies for different data sizes on
1645 different crypto accelerators. This option can be used
1646 to achieve the best performance for a particular HW.
1648 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1650 Set hashing buffer size. Default: 4k.
1652 ahash performance varies for different chunk sizes on
1653 different crypto accelerators. This option can be used
1654 to achieve best performance for particular HW.
1658 Run specified binary instead of /sbin/init as init
1661 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1662 for working out where the kernel is dying during
1665 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1666 initcall functions. Useful for debugging built-in
1667 modules and initcalls.
1669 initrd= [BOOT] Specify the location of the initial ramdisk
1671 init_on_alloc= [MM] Fill newly allocated pages and heap objects with
1674 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
1676 init_on_free= [MM] Fill freed pages and heap objects with zeroes.
1678 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.
1680 init_pkru= [x86] Specify the default memory protection keys rights
1681 register contents for all processes. 0x55555554 by
1682 default (disallow access to all but pkey 0). Can
1683 override in debugfs after boot.
1685 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1688 int_pln_enable [x86] Enable power limit notification interrupt
1690 integrity_audit=[IMA]
1691 Format: { "0" | "1" }
1692 0 -- basic integrity auditing messages. (Default)
1693 1 -- additional integrity auditing messages.
1695 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1697 Enable intel iommu driver.
1699 Disable intel iommu driver.
1700 igfx_off [Default Off]
1701 By default, gfx is mapped as normal device. If a gfx
1702 device has a dedicated DMAR unit, the DMAR unit is
1703 bypassed by not enabling DMAR with this option. In
1704 this case, gfx device will use physical address for
1707 With this option iommu will not optimize to look
1708 for io virtual address below 32-bit forcing dual
1709 address cycle on pci bus for cards supporting greater
1710 than 32-bit addressing. The default is to look
1711 for translation below 32-bit and if not available
1712 then look in the higher range.
1713 strict [Default Off]
1714 With this option on every unmap_single operation will
1715 result in a hardware IOTLB flush operation as opposed
1716 to batching them for performance.
1717 sp_off [Default Off]
1718 By default, super page will be supported if Intel IOMMU
1719 has the capability. With this option, super page will
1722 By default, scalable mode will be disabled even if the
1723 hardware advertises that it has support for the scalable
1724 mode translation. With this option set, scalable mode
1725 will be used on hardware which claims to support it.
1726 tboot_noforce [Default Off]
1727 Do not force the Intel IOMMU enabled under tboot.
1728 By default, tboot will force Intel IOMMU on, which
1729 could harm performance of some high-throughput
1730 devices like 40GBit network cards, even if identity
1732 Note that using this option lowers the security
1733 provided by tboot because it makes the system
1734 vulnerable to DMA attacks.
1736 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1737 0 disables intel_idle and fall back on acpi_idle.
1738 1 to 9 specify maximum depth of C-state.
1742 Do not enable intel_pstate as the default
1743 scaling driver for the supported processors
1745 Use intel_pstate as a scaling driver, but configure it
1746 to work with generic cpufreq governors (instead of
1747 enabling its internal governor). This mode cannot be
1748 used along with the hardware-managed P-states (HWP)
1751 Enable intel_pstate on systems that prohibit it by default
1752 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1753 instead of acpi-cpufreq may disable platform features, such
1754 as thermal controls and power capping, that rely on ACPI
1755 P-States information being indicated to OSPM and therefore
1756 should be used with caution. This option does not work with
1757 processors that aren't supported by the intel_pstate driver
1758 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1760 Do not enable hardware P state control (HWP)
1763 Only load intel_pstate on systems which support
1764 hardware P state control (HWP) if available.
1766 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1767 Description Table, specifies preferred power management
1768 profile as "Enterprise Server" or "Performance Server",
1769 then this feature is turned on by default.
1771 Allow per-logical-CPU P-State performance control limits using
1772 cpufreq sysfs interface
1774 intremap= [X86-64, Intel-IOMMU]
1775 on enable Interrupt Remapping (default)
1776 off disable Interrupt Remapping
1777 nosid disable Source ID checking
1779 BIOS x2APIC opt-out request will be ignored
1780 nopost disable Interrupt Posting
1782 iomem= Disable strict checking of access to MMIO memory
1783 strict regions from userspace.
1798 nobypass [PPC/POWERNV]
1799 Disable IOMMU bypass, using IOMMU for PCI devices.
1801 iommu.strict= [ARM64] Configure TLB invalidation behaviour
1802 Format: { "0" | "1" }
1804 Request that DMA unmap operations use deferred
1805 invalidation of hardware TLBs, for increased
1806 throughput at the cost of reduced device isolation.
1807 Will fall back to strict mode if not supported by
1808 the relevant IOMMU driver.
1809 1 - Strict mode (default).
1810 DMA unmap operations invalidate IOMMU hardware TLBs
1814 [ARM64] Configure DMA to bypass the IOMMU by default.
1815 Format: { "0" | "1" }
1816 0 - Use IOMMU translation for DMA.
1817 1 - Bypass the IOMMU for DMA.
1818 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
1820 io7= [HW] IO7 for Marvel based alpha systems
1821 See comment before marvel_specify_io7 in
1822 arch/alpha/kernel/core_marvel.c.
1824 io_delay= [X86] I/O delay method
1826 Standard port 0x80 based delay
1828 Alternate port 0xed based delay (needed on some systems)
1830 Simple two microseconds delay
1835 See Documentation/filesystems/nfs/nfsroot.txt.
1837 ipcmni_extend [KNL] Extend the maximum number of unique System V
1838 IPC identifiers from 32,768 to 16,777,216.
1840 irqaffinity= [SMP] Set the default irq affinity mask
1841 The argument is a cpu list, as described above.
1843 irqchip.gicv2_force_probe=
1846 Force the kernel to look for the second 4kB page
1847 of a GICv2 controller even if the memory range
1848 exposed by the device tree is too small.
1850 irqchip.gicv3_nolpi=
1852 Force the kernel to ignore the availability of
1853 LPIs (and by consequence ITSs). Intended for system
1854 that use the kernel as a bootloader, and thus want
1855 to let secondary kernels in charge of setting up
1858 irqchip.gicv3_pseudo_nmi= [ARM64]
1859 Enables support for pseudo-NMIs in the kernel. This
1860 requires the kernel to be built with
1861 CONFIG_ARM64_PSEUDO_NMI.
1864 When an interrupt is not handled search all handlers
1865 for it. Intended to get systems with badly broken
1869 When an interrupt is not handled search all handlers
1870 for it. Also check all handlers each timer
1871 interrupt. Intended to get systems with badly broken
1875 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1877 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1878 [Deprecated - use cpusets instead]
1879 Format: [flag-list,]<cpu-list>
1881 Specify one or more CPUs to isolate from disturbances
1882 specified in the flag list (default: domain):
1885 Disable the tick when a single task runs.
1887 A residual 1Hz tick is offloaded to workqueues, which you
1888 need to affine to housekeeping through the global
1889 workqueue's affinity configured via the
1890 /sys/devices/virtual/workqueue/cpumask sysfs file, or
1891 by using the 'domain' flag described below.
1893 NOTE: by default the global workqueue runs on all CPUs,
1894 so to protect individual CPUs the 'cpumask' file has to
1895 be configured manually after bootup.
1898 Isolate from the general SMP balancing and scheduling
1899 algorithms. Note that performing domain isolation this way
1900 is irreversible: it's not possible to bring back a CPU to
1901 the domains once isolated through isolcpus. It's strongly
1902 advised to use cpusets instead to disable scheduler load
1903 balancing through the "cpuset.sched_load_balance" file.
1904 It offers a much more flexible interface where CPUs can
1905 move in and out of an isolated set anytime.
1907 You can move a process onto or off an "isolated" CPU via
1908 the CPU affinity syscalls or cpuset.
1909 <cpu number> begins at 0 and the maximum value is
1910 "number of CPUs in system - 1".
1912 The format of <cpu-list> is described above.
1918 ivrs_ioapic [HW,X86_64]
1919 Provide an override to the IOAPIC-ID<->DEVICE-ID
1920 mapping provided in the IVRS ACPI table. For
1921 example, to map IOAPIC-ID decimal 10 to
1922 PCI device 00:14.0 write the parameter as:
1923 ivrs_ioapic[10]=00:14.0
1925 ivrs_hpet [HW,X86_64]
1926 Provide an override to the HPET-ID<->DEVICE-ID
1927 mapping provided in the IVRS ACPI table. For
1928 example, to map HPET-ID decimal 0 to
1929 PCI device 00:14.0 write the parameter as:
1930 ivrs_hpet[0]=00:14.0
1932 ivrs_acpihid [HW,X86_64]
1933 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1934 mapping provided in the IVRS ACPI table. For
1935 example, to map UART-HID:UID AMD0020:0 to
1936 PCI device 00:14.5 write the parameter as:
1937 ivrs_acpihid[00:14.5]=AMD0020:0
1939 js= [HW,JOY] Analog joystick
1940 See Documentation/input/joydev/joystick.rst.
1943 When CONFIG_RANDOMIZE_BASE is set, this disables
1944 kernel and module base offset ASLR (Address Space
1945 Layout Randomization).
1948 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1949 report on every invalid memory access. Without this
1950 parameter KASAN will print report only for the first
1955 kernelcore= [KNL,X86,IA-64,PPC]
1956 Format: nn[KMGTPE] | nn% | "mirror"
1957 This parameter specifies the amount of memory usable by
1958 the kernel for non-movable allocations. The requested
1959 amount is spread evenly throughout all nodes in the
1960 system as ZONE_NORMAL. The remaining memory is used for
1961 movable memory in its own zone, ZONE_MOVABLE. In the
1962 event, a node is too small to have both ZONE_NORMAL and
1963 ZONE_MOVABLE, kernelcore memory will take priority and
1964 other nodes will have a larger ZONE_MOVABLE.
1966 ZONE_MOVABLE is used for the allocation of pages that
1967 may be reclaimed or moved by the page migration
1968 subsystem. Note that allocations like PTEs-from-HighMem
1969 still use the HighMem zone if it exists, and the Normal
1970 zone if it does not.
1972 It is possible to specify the exact amount of memory in
1973 the form of "nn[KMGTPE]", a percentage of total system
1974 memory in the form of "nn%", or "mirror". If "mirror"
1975 option is specified, mirrored (reliable) memory is used
1976 for non-movable allocations and remaining memory is used
1977 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
1978 are exclusive, so you cannot specify multiple forms.
1980 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1981 Format: <Controller#>[,poll interval]
1982 The controller # is the number of the ehci usb debug
1983 port as it is probed via PCI. The poll interval is
1984 optional and is the number seconds in between
1985 each poll cycle to the debug port in case you need
1986 the functionality for interrupting the kernel with
1987 gdb or control-c on the dbgp connection. When
1988 not using this parameter you use sysrq-g to break into
1989 the kernel debugger.
1991 kgdboc= [KGDB,HW] kgdb over consoles.
1992 Requires a tty driver that supports console polling,
1993 or a supported polling keyboard driver (non-usb).
1994 Serial only format: <serial_device>[,baud]
1995 keyboard only format: kbd
1996 keyboard and serial format: kbd,<serial_device>[,baud]
1997 Optional Kernel mode setting:
1998 kms, kbd format: kms,kbd
1999 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
2001 kgdbwait [KGDB] Stop kernel execution and enter the
2002 kernel debugger at the earliest opportunity.
2004 kmac= [MIPS] korina ethernet MAC address.
2005 Configure the RouterBoard 532 series on-chip
2006 Ethernet adapter MAC address.
2008 kmemleak= [KNL] Boot-time kmemleak enable/disable
2009 Valid arguments: on, off
2011 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
2014 kpti= [ARM64] Control page table isolation of user
2015 and kernel address spaces.
2016 Default: enabled on cores which need mitigation.
2020 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
2021 Default is 0 (don't ignore, but inject #GP)
2023 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
2024 Default is false (don't support).
2026 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
2030 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
2031 Default is 1 (enabled)
2033 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
2035 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
2037 kvm-arm.vgic_v3_group0_trap=
2038 [KVM,ARM] Trap guest accesses to GICv3 group-0
2041 kvm-arm.vgic_v3_group1_trap=
2042 [KVM,ARM] Trap guest accesses to GICv3 group-1
2045 kvm-arm.vgic_v3_common_trap=
2046 [KVM,ARM] Trap guest accesses to GICv3 common
2049 kvm-arm.vgic_v4_enable=
2050 [KVM,ARM] Allow use of GICv4 for direct injection of
2053 kvm-intel.ept= [KVM,Intel] Disable extended page tables
2054 (virtualized MMU) support on capable Intel chips.
2055 Default is 1 (enabled)
2057 kvm-intel.emulate_invalid_guest_state=
2058 [KVM,Intel] Enable emulation of invalid guest states
2059 Default is 0 (disabled)
2061 kvm-intel.flexpriority=
2062 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
2063 Default is 1 (enabled)
2066 [KVM,Intel] Enable VMX nesting (nVMX).
2067 Default is 0 (disabled)
2069 kvm-intel.unrestricted_guest=
2070 [KVM,Intel] Disable unrestricted guest feature
2071 (virtualized real and unpaged mode) on capable
2072 Intel chips. Default is 1 (enabled)
2074 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2077 Valid arguments: never, cond, always
2079 always: L1D cache flush on every VMENTER.
2080 cond: Flush L1D on VMENTER only when the code between
2081 VMEXIT and VMENTER can leak host memory.
2082 never: Disables the mitigation
2084 Default is cond (do L1 cache flush in specific instances)
2086 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2087 feature (tagged TLBs) on capable Intel chips.
2088 Default is 1 (enabled)
2090 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2093 The kernel PTE inversion protection is unconditionally
2094 enabled and cannot be disabled.
2097 Provides all available mitigations for the
2098 L1TF vulnerability. Disables SMT and
2099 enables all mitigations in the
2100 hypervisors, i.e. unconditional L1D flush.
2102 SMT control and L1D flush control via the
2103 sysfs interface is still possible after
2104 boot. Hypervisors will issue a warning
2105 when the first VM is started in a
2106 potentially insecure configuration,
2107 i.e. SMT enabled or L1D flush disabled.
2110 Same as 'full', but disables SMT and L1D
2111 flush runtime control. Implies the
2112 'nosmt=force' command line option.
2113 (i.e. sysfs control of SMT is disabled.)
2116 Leaves SMT enabled and enables the default
2117 hypervisor mitigation, i.e. conditional
2120 SMT control and L1D flush control via the
2121 sysfs interface is still possible after
2122 boot. Hypervisors will issue a warning
2123 when the first VM is started in a
2124 potentially insecure configuration,
2125 i.e. SMT enabled or L1D flush disabled.
2129 Disables SMT and enables the default
2130 hypervisor mitigation.
2132 SMT control and L1D flush control via the
2133 sysfs interface is still possible after
2134 boot. Hypervisors will issue a warning
2135 when the first VM is started in a
2136 potentially insecure configuration,
2137 i.e. SMT enabled or L1D flush disabled.
2140 Same as 'flush', but hypervisors will not
2141 warn when a VM is started in a potentially
2142 insecure configuration.
2145 Disables hypervisor mitigations and doesn't
2147 It also drops the swap size and available
2148 RAM limit restriction on both hypervisor and
2153 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
2159 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2162 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2163 value for LAPIC timer one-shot implementation. Default
2164 back to the programmable timer unit in the LAPIC.
2166 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2169 libata.dma= [LIBATA] DMA control
2170 libata.dma=0 Disable all PATA and SATA DMA
2171 libata.dma=1 PATA and SATA Disk DMA only
2172 libata.dma=2 ATAPI (CDROM) DMA only
2173 libata.dma=4 Compact Flash DMA only
2174 Combinations also work, so libata.dma=3 enables DMA
2175 for disks and CDROMs, but not CFs.
2177 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2178 libata.ignore_hpa=0 keep BIOS limits (default)
2179 libata.ignore_hpa=1 ignore limits, using full disk
2181 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2185 libata.force= [LIBATA] Force configurations. The format is comma
2186 separated list of "[ID:]VAL" where ID is
2187 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2188 matching port, link or device. Basically, it matches
2189 the ATA ID string printed on console by libata. If
2190 the whole ID part is omitted, the last PORT and DEVICE
2191 values are used. If ID hasn't been specified yet, the
2192 configuration applies to all ports, links and devices.
2194 If only DEVICE is omitted, the parameter applies to
2195 the port and all links and devices behind it. DEVICE
2196 number of 0 either selects the first device or the
2197 first fan-out link behind PMP device. It does not
2198 select the host link. DEVICE number of 15 selects the
2199 host link and device attached to it.
2201 The VAL specifies the configuration to force. As long
2202 as there's no ambiguity shortcut notation is allowed.
2203 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2204 The following configurations can be forced.
2206 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2207 Any ID with matching PORT is used.
2209 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2211 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2212 udma[/][16,25,33,44,66,100,133] notation is also
2215 * [no]ncq: Turn on or off NCQ.
2217 * [no]ncqtrim: Turn off queued DSM TRIM.
2219 * nohrst, nosrst, norst: suppress hard, soft
2222 * rstonce: only attempt one reset during
2223 hot-unplug link recovery
2225 * dump_id: dump IDENTIFY data.
2227 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2229 * disable: Disable this device.
2231 If there are multiple matching configurations changing
2232 the same attribute, the last one is used.
2234 memblock=debug [KNL] Enable memblock debug messages.
2236 load_ramdisk= [RAM] List of ramdisks to load from floppy
2237 See Documentation/blockdev/ramdisk.rst.
2239 lockd.nlm_grace_period=P [NFS] Assign grace period.
2242 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2245 lockd.nlm_timeout=T [NFS] Assign timeout value.
2248 lockd.nlm_udpport=M [NFS] Assign UDP port.
2251 locktorture.nreaders_stress= [KNL]
2252 Set the number of locking read-acquisition kthreads.
2253 Defaults to being automatically set based on the
2254 number of online CPUs.
2256 locktorture.nwriters_stress= [KNL]
2257 Set the number of locking write-acquisition kthreads.
2259 locktorture.onoff_holdoff= [KNL]
2260 Set time (s) after boot for CPU-hotplug testing.
2262 locktorture.onoff_interval= [KNL]
2263 Set time (s) between CPU-hotplug operations, or
2264 zero to disable CPU-hotplug testing.
2266 locktorture.shuffle_interval= [KNL]
2267 Set task-shuffle interval (jiffies). Shuffling
2268 tasks allows some CPUs to go into dyntick-idle
2269 mode during the locktorture test.
2271 locktorture.shutdown_secs= [KNL]
2272 Set time (s) after boot system shutdown. This
2273 is useful for hands-off automated testing.
2275 locktorture.stat_interval= [KNL]
2276 Time (s) between statistics printk()s.
2278 locktorture.stutter= [KNL]
2279 Time (s) to stutter testing, for example,
2280 specifying five seconds causes the test to run for
2281 five seconds, wait for five seconds, and so on.
2282 This tests the locking primitive's ability to
2283 transition abruptly to and from idle.
2285 locktorture.torture_type= [KNL]
2286 Specify the locking implementation to test.
2288 locktorture.verbose= [KNL]
2289 Enable additional printk() statements.
2291 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2294 loglevel= All Kernel Messages with a loglevel smaller than the
2295 console loglevel will be printed to the console. It can
2296 also be changed with klogd or other programs. The
2297 loglevels are defined as follows:
2299 0 (KERN_EMERG) system is unusable
2300 1 (KERN_ALERT) action must be taken immediately
2301 2 (KERN_CRIT) critical conditions
2302 3 (KERN_ERR) error conditions
2303 4 (KERN_WARNING) warning conditions
2304 5 (KERN_NOTICE) normal but significant condition
2305 6 (KERN_INFO) informational
2306 7 (KERN_DEBUG) debug-level messages
2308 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2309 in bytes. n must be a power of two and greater
2310 than the minimal size. The minimal size is defined
2311 by LOG_BUF_SHIFT kernel config parameter. There is
2312 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2313 that allows to increase the default size depending on
2314 the number of CPUs. See init/Kconfig for more details.
2316 logo.nologo [FB] Disables display of the built-in Linux logo.
2317 This may be used to provide more screen space for
2318 kernel log messages and is useful when debugging
2319 kernel boot problems.
2321 lp=0 [LP] Specify parallel ports to use, e.g,
2322 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2323 lp=reset first parallel port). 'lp=0' disables the
2324 lp=auto printer driver. 'lp=reset' (which can be
2325 specified in addition to the ports) causes
2326 attached printers to be reset. Using
2327 lp=port1,port2,... specifies the parallel ports
2328 to associate lp devices with, starting with
2329 lp0. A port specification may be 'none' to skip
2330 that lp device, or a parport name such as
2331 'parport0'. Specifying 'lp=auto' instead of a
2332 port specification list means that device IDs
2333 from each port should be examined, to see if
2334 an IEEE 1284-compliant printer is attached; if
2335 so, the driver will manage that printer.
2336 See also header of drivers/char/lp.c.
2339 Sets loops_per_jiffy to given constant, thus avoiding
2340 time-consuming boot-time autodetection (up to 250 ms per
2341 CPU). 0 enables autodetection (default). To determine
2342 the correct value for your kernel, boot with normal
2343 autodetection and see what value is printed. Note that
2344 on SMP systems the preset will be applied to all CPUs,
2345 which is likely to cause problems if your CPUs need
2346 significantly divergent settings. An incorrect value
2347 will cause delays in the kernel to be wrong, leading to
2348 unpredictable I/O errors and other breakage. Although
2349 unlikely, in the extreme case this might damage your
2353 Format: <io>,<irq>,<dma>
2355 lsm.debug [SECURITY] Enable LSM initialization debugging output.
2358 [SECURITY] Choose order of LSM initialization. This
2359 overrides CONFIG_LSM, and the "security=" parameter.
2361 machvec= [IA-64] Force the use of a particular machine-vector
2362 (machvec) in a generic kernel.
2363 Example: machvec=hpzx1_swiotlb
2365 machtype= [Loongson] Share the same kernel image file between different
2367 Example: machtype=lemote-yeeloong-2f-7inch
2369 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2370 than or equal to this physical address is ignored.
2372 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2373 will bring up during bootup. maxcpus=n : n >= 0 limits
2374 the kernel to bring up 'n' processors. Surely after
2375 bootup you can bring up the other plugged cpu by executing
2376 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2377 only takes effect during system bootup.
2378 While n=0 is a special case, it is equivalent to "nosmp",
2379 which also disables the IO APIC.
2381 max_loop= [LOOP] The number of loop block devices that get
2382 (loop.max_loop) unconditionally pre-created at init time. The default
2383 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2384 of statically allocating a predefined number, loop
2385 devices can be requested on-demand with the
2386 /dev/loop-control interface.
2388 mce [X86-32] Machine Check Exception
2390 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst
2392 md= [HW] RAID subsystems devices and level
2393 See Documentation/admin-guide/md.rst.
2396 Format: <first>,<last>
2397 Specifies range of consoles to be captured by the MDA.
2400 Control mitigation for the Micro-architectural Data
2401 Sampling (MDS) vulnerability.
2403 Certain CPUs are vulnerable to an exploit against CPU
2404 internal buffers which can forward information to a
2405 disclosure gadget under certain conditions.
2407 In vulnerable processors, the speculatively
2408 forwarded data can be used in a cache side channel
2409 attack, to access data to which the attacker does
2410 not have direct access.
2412 This parameter controls the MDS mitigation. The
2415 full - Enable MDS mitigation on vulnerable CPUs
2416 full,nosmt - Enable MDS mitigation and disable
2417 SMT on vulnerable CPUs
2418 off - Unconditionally disable MDS mitigation
2420 Not specifying this option is equivalent to
2423 For details see: Documentation/admin-guide/hw-vuln/mds.rst
2425 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2426 Amount of memory to be used when the kernel is not able
2427 to see the whole system memory or for test.
2428 [X86] Work as limiting max address. Use together
2429 with memmap= to avoid physical address space collisions.
2430 Without memmap= PCI devices could be placed at addresses
2431 belonging to unused RAM.
2433 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2437 [KNL,SH] Allow user to override the default size for
2438 per-device physically contiguous DMA buffers.
2440 memhp_default_state=online/offline
2441 [KNL] Set the initial state for the memory hotplug
2442 onlining policy. If not specified, the default value is
2443 set according to the
2444 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2446 See Documentation/admin-guide/mm/memory-hotplug.rst.
2448 memmap=exactmap [KNL,X86] Enable setting of an exact
2449 E820 memory map, as specified by the user.
2450 Such memmap=exactmap lines can be constructed based on
2451 BIOS output or other requirements. See the memmap=nn@ss
2454 memmap=nn[KMG]@ss[KMG]
2455 [KNL] Force usage of a specific region of memory.
2456 Region of memory to be used is from ss to ss+nn.
2457 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2458 which limits max address to nn[KMG].
2459 Multiple different regions can be specified,
2462 memmap=100M@2G,100M#3G,1G!1024G
2464 memmap=nn[KMG]#ss[KMG]
2465 [KNL,ACPI] Mark specific memory as ACPI data.
2466 Region of memory to be marked is from ss to ss+nn.
2468 memmap=nn[KMG]$ss[KMG]
2469 [KNL,ACPI] Mark specific memory as reserved.
2470 Region of memory to be reserved is from ss to ss+nn.
2471 Example: Exclude memory from 0x18690000-0x1869ffff
2472 memmap=64K$0x18690000
2474 memmap=0x10000$0x18690000
2475 Some bootloaders may need an escape character before '$',
2476 like Grub2, otherwise '$' and the following number
2479 memmap=nn[KMG]!ss[KMG]
2480 [KNL,X86] Mark specific memory as protected.
2481 Region of memory to be used, from ss to ss+nn.
2482 The memory region may be marked as e820 type 12 (0xc)
2483 and is NVDIMM or ADR memory.
2485 memmap=<size>%<offset>-<oldtype>+<newtype>
2486 [KNL,ACPI] Convert memory within the specified region
2487 from <oldtype> to <newtype>. If "-<oldtype>" is left
2488 out, the whole region will be marked as <newtype>,
2489 even if previously unavailable. If "+<newtype>" is left
2490 out, matching memory will be removed. Types are
2491 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2492 3 = ACPI, 12 = PRAM.
2494 memory_corruption_check=0/1 [X86]
2495 Some BIOSes seem to corrupt the first 64k of
2496 memory when doing things like suspend/resume.
2497 Setting this option will scan the memory
2498 looking for corruption. Enabling this will
2499 both detect corruption and prevent the kernel
2500 from using the memory being corrupted.
2501 However, its intended as a diagnostic tool; if
2502 repeatable BIOS-originated corruption always
2503 affects the same memory, you can use memmap=
2504 to prevent the kernel from using that memory.
2506 memory_corruption_check_size=size [X86]
2507 By default it checks for corruption in the low
2508 64k, making this memory unavailable for normal
2509 use. Use this parameter to scan for
2510 corruption in more or less memory.
2512 memory_corruption_check_period=seconds [X86]
2513 By default it checks for corruption every 60
2514 seconds. Use this parameter to check at some
2515 other rate. 0 disables periodic checking.
2517 memtest= [KNL,X86,ARM,PPC] Enable memtest
2519 default : 0 <disable>
2520 Specifies the number of memtest passes to be
2521 performed. Each pass selects another test
2522 pattern from a given set of patterns. Memtest
2523 fills the memory with this pattern, validates
2524 memory contents and reserves bad memory
2525 regions that are detected.
2527 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2528 Valid arguments: on, off
2529 Default (depends on kernel configuration option):
2530 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2531 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2532 mem_encrypt=on: Activate SME
2533 mem_encrypt=off: Do not activate SME
2535 Refer to Documentation/virtual/kvm/amd-memory-encryption.rst
2536 for details on when memory encryption can be activated.
2538 mem_sleep_default= [SUSPEND] Default system suspend mode:
2539 s2idle - Suspend-To-Idle
2540 shallow - Power-On Suspend or equivalent (if supported)
2541 deep - Suspend-To-RAM or equivalent (if supported)
2542 See Documentation/admin-guide/pm/sleep-states.rst.
2544 meye.*= [HW] Set MotionEye Camera parameters
2545 See Documentation/media/v4l-drivers/meye.rst.
2547 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2548 Multi-Function General Purpose Timers on AMD Geode
2551 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2552 the BIOS has incorrectly applied a workaround. TinyBIOS
2553 version 0.98 is known to be affected, 0.99 fixes the
2554 problem by letting the user disable the workaround.
2558 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2559 physical address is ignored.
2561 mini2440= [ARM,HW,KNL]
2562 Format:[0..2][b][c][t]
2564 MINI2440 configuration specification:
2565 0 - The attached screen is the 3.5" TFT
2566 1 - The attached screen is the 7" TFT
2567 2 - The VGA Shield is attached (1024x768)
2568 Leaving out the screen size parameter will not load
2569 the TFT driver, and the framebuffer will be left
2571 b - Enable backlight. The TFT backlight pin will be
2572 linked to the kernel VESA blanking code and a GPIO
2573 LED. This parameter is not necessary when using the
2575 c - Enable the s3c camera interface.
2576 t - Reserved for enabling touchscreen support. The
2577 touchscreen support is not enabled in the mainstream
2578 kernel as of 2.6.30, a preliminary port can be found
2579 in the "bleeding edge" mini2440 support kernel at
2580 http://repo.or.cz/w/linux-2.6/mini2440.git
2583 [X86,PPC,S390,ARM64] Control optional mitigations for
2584 CPU vulnerabilities. This is a set of curated,
2585 arch-independent options, each of which is an
2586 aggregation of existing arch-specific options.
2589 Disable all optional CPU mitigations. This
2590 improves system performance, but it may also
2591 expose users to several CPU vulnerabilities.
2592 Equivalent to: nopti [X86,PPC]
2596 nospectre_v2 [X86,PPC,S390,ARM64]
2597 spectre_v2_user=off [X86]
2598 spec_store_bypass_disable=off [X86,PPC]
2599 ssbd=force-off [ARM64]
2604 Mitigate all CPU vulnerabilities, but leave SMT
2605 enabled, even if it's vulnerable. This is for
2606 users who don't want to be surprised by SMT
2607 getting disabled across kernel upgrades, or who
2608 have other ways of avoiding SMT-based attacks.
2609 Equivalent to: (default behavior)
2612 Mitigate all CPU vulnerabilities, disabling SMT
2613 if needed. This is for users who always want to
2614 be fully mitigated, even if it means losing SMT.
2615 Equivalent to: l1tf=flush,nosmt [X86]
2616 mds=full,nosmt [X86]
2619 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2620 parameter allows control of the logging verbosity for
2621 the additional memory initialisation checks. A value
2622 of 0 disables mminit logging and a level of 4 will
2623 log everything. Information is printed at KERN_DEBUG
2624 so loglevel=8 may also need to be specified.
2627 [KNL] When CONFIG_MODULE_SIG is set, this means that
2628 modules without (valid) signatures will fail to load.
2629 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2630 is always true, so this option does nothing.
2632 module_blacklist= [KNL] Do not load a comma-separated list of
2633 modules. Useful for debugging problem modules.
2636 [MOUSE] Maximum time between finger touching and
2637 leaving touchpad surface for touch to be considered
2638 a tap and be reported as a left button click (for
2639 touchpads working in absolute mode only).
2641 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2642 reporting absolute coordinates, such as tablets
2643 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2644 reporting absolute coordinates, such as tablets
2646 movablecore= [KNL,X86,IA-64,PPC]
2647 Format: nn[KMGTPE] | nn%
2648 This parameter is the complement to kernelcore=, it
2649 specifies the amount of memory used for migratable
2650 allocations. If both kernelcore and movablecore is
2651 specified, then kernelcore will be at *least* the
2652 specified value but may be more. If movablecore on its
2653 own is specified, the administrator must be careful
2654 that the amount of memory usable for all allocations
2657 movable_node [KNL] Boot-time switch to make hotplugable memory
2658 NUMA nodes to be movable. This means that the memory
2659 of such nodes will be usable only for movable
2660 allocations which rules out almost all kernel
2661 allocations. Use with caution!
2663 MTD_Partition= [MTD]
2664 Format: <name>,<region-number>,<size>,<offset>
2666 MTD_Region= [MTD] Format:
2667 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2670 See drivers/mtd/cmdlinepart.c.
2672 multitce=off [PPC] This parameter disables the use of the pSeries
2673 firmware feature for updating multiple TCE entries
2676 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2678 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2680 boundary - index of last SLC block on Flex-OneNAND.
2681 The remaining blocks are configured as MLC blocks.
2682 lock - Configure if Flex-OneNAND boundary should be locked.
2683 Once locked, the boundary cannot be changed.
2684 1 indicates lock status, 0 indicates unlock status.
2687 ARM/S3C2412 JIVE boot control
2689 See arch/arm/mach-s3c2412/mach-jive.c
2691 mtouchusb.raw_coordinates=
2692 [HW] Make the MicroTouch USB driver use raw coordinates
2693 ('y', default) or cooked coordinates ('n')
2695 mtrr_chunk_size=nn[KMG] [X86]
2696 used for mtrr cleanup. It is largest continuous chunk
2697 that could hold holes aka. UC entries.
2699 mtrr_gran_size=nn[KMG] [X86]
2700 Used for mtrr cleanup. It is granularity of mtrr block.
2702 Large value could prevent small alignment from
2705 mtrr_spare_reg_nr=n [X86]
2707 Range: 0,7 : spare reg number
2709 Used for mtrr cleanup. It is spare mtrr entries number.
2710 Set to 2 or more if your graphical card needs more.
2712 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2714 netdev= [NET] Network devices parameters
2715 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2716 Note that mem_start is often overloaded to mean
2717 something different and driver-specific.
2718 This usage is only documented in each driver source
2722 [NETFILTER] Enable connection tracking flow accounting
2723 0 to disable accounting
2724 1 to enable accounting
2727 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2728 See Documentation/filesystems/nfs/nfsroot.txt.
2730 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2731 See Documentation/filesystems/nfs/nfsroot.txt.
2733 nfsrootdebug [NFS] enable nfsroot debugging messages.
2734 See Documentation/filesystems/nfs/nfsroot.txt.
2736 nfs.callback_nr_threads=
2737 [NFSv4] set the total number of threads that the
2738 NFS client will assign to service NFSv4 callback
2741 nfs.callback_tcpport=
2742 [NFS] set the TCP port on which the NFSv4 callback
2743 channel should listen.
2746 [NFS] sets the pathname to the program which is used
2747 to update the NFS client cache entries.
2749 nfs.cache_getent_timeout=
2750 [NFS] sets the timeout after which an attempt to
2751 update a cache entry is deemed to have failed.
2753 nfs.idmap_cache_timeout=
2754 [NFS] set the maximum lifetime for idmapper cache
2758 [NFS] enable 64-bit inode numbers.
2759 If zero, the NFS client will fake up a 32-bit inode
2760 number for the readdir() and stat() syscalls instead
2761 of returning the full 64-bit number.
2762 The default is to return 64-bit inode numbers.
2764 nfs.max_session_cb_slots=
2765 [NFSv4.1] Sets the maximum number of session
2766 slots the client will assign to the callback
2767 channel. This determines the maximum number of
2768 callbacks the client will process in parallel for
2769 a particular server.
2771 nfs.max_session_slots=
2772 [NFSv4.1] Sets the maximum number of session slots
2773 the client will attempt to negotiate with the server.
2774 This limits the number of simultaneous RPC requests
2775 that the client can send to the NFSv4.1 server.
2776 Note that there is little point in setting this
2777 value higher than the max_tcp_slot_table_limit.
2779 nfs.nfs4_disable_idmapping=
2780 [NFSv4] When set to the default of '1', this option
2781 ensures that both the RPC level authentication
2782 scheme and the NFS level operations agree to use
2783 numeric uids/gids if the mount is using the
2784 'sec=sys' security flavour. In effect it is
2785 disabling idmapping, which can make migration from
2786 legacy NFSv2/v3 systems to NFSv4 easier.
2787 Servers that do not support this mode of operation
2788 will be autodetected by the client, and it will fall
2789 back to using the idmapper.
2790 To turn off this behaviour, set the value to '0'.
2792 [NFS4] Specify an additional fixed unique ident-
2793 ification string that NFSv4 clients can insert into
2794 their nfs_client_id4 string. This is typically a
2795 UUID that is generated at system install time.
2797 nfs.send_implementation_id =
2798 [NFSv4.1] Send client implementation identification
2799 information in exchange_id requests.
2800 If zero, no implementation identification information
2802 The default is to send the implementation identification
2805 nfs.recover_lost_locks =
2806 [NFSv4] Attempt to recover locks that were lost due
2807 to a lease timeout on the server. Please note that
2808 doing this risks data corruption, since there are
2809 no guarantees that the file will remain unchanged
2810 after the locks are lost.
2811 If you want to enable the kernel legacy behaviour of
2812 attempting to recover these locks, then set this
2814 The default parameter value of '0' causes the kernel
2815 not to attempt recovery of lost locks.
2817 nfs4.layoutstats_timer =
2818 [NFSv4.2] Change the rate at which the kernel sends
2819 layoutstats to the pNFS metadata server.
2821 Setting this to value to 0 causes the kernel to use
2822 whatever value is the default set by the layout
2823 driver. A non-zero value sets the minimum interval
2824 in seconds between layoutstats transmissions.
2826 nfsd.nfs4_disable_idmapping=
2827 [NFSv4] When set to the default of '1', the NFSv4
2828 server will return only numeric uids and gids to
2829 clients using auth_sys, and will accept numeric uids
2830 and gids from such clients. This is intended to ease
2831 migration from NFSv2/v3.
2833 nmi_debug= [KNL,SH] Specify one or more actions to take
2834 when a NMI is triggered.
2835 Format: [state][,regs][,debounce][,die]
2837 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2838 Format: [panic,][nopanic,][num]
2840 0 - turn hardlockup detector in nmi_watchdog off
2841 1 - turn hardlockup detector in nmi_watchdog on
2842 When panic is specified, panic when an NMI watchdog
2843 timeout occurs (or 'nopanic' to not panic on an NMI
2844 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set)
2845 To disable both hard and soft lockup detectors,
2846 please see 'nowatchdog'.
2847 This is useful when you use a panic=... timeout and
2848 need the box quickly up again.
2850 These settings can be accessed at runtime via
2851 the nmi_watchdog and hardlockup_panic sysctls.
2853 netpoll.carrier_timeout=
2854 [NET] Specifies amount of time (in seconds) that
2855 netpoll should wait for a carrier. By default netpoll
2858 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2859 emulation library even if a 387 maths coprocessor
2862 no5lvl [X86-64] Disable 5-level paging mode. Forces
2863 kernel to use 4-level paging instead.
2866 [HW] Never suspend the console
2867 Disable suspending of consoles during suspend and
2868 hibernate operations. Once disabled, debugging
2869 messages can reach various consoles while the rest
2870 of the system is being put to sleep (ie, while
2871 debugging driver suspend/resume hooks). This may
2872 not work reliably with all consoles, but is known
2873 to work with serial and VGA consoles.
2874 To facilitate more flexible debugging, we also add
2875 console_suspend, a printk module parameter to control
2876 it. Users could use console_suspend (usually
2877 /sys/module/printk/parameters/console_suspend) to
2878 turn on/off it dynamically.
2880 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2881 caches in the slab allocator. Saves per-node memory,
2882 but will impact performance.
2886 noaltinstr [S390] Disables alternative instructions patching
2887 (CPU alternatives feature).
2889 noapic [SMP,APIC] Tells the kernel to not make use of any
2890 IOAPICs that may be present in the system.
2892 noautogroup Disable scheduler automatic task group creation.
2894 nobats [PPC] Do not use BATs for mapping kernel lowmem
2895 on "Classic" PPC cores.
2899 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2901 nodelayacct [KNL] Disable per-task delay accounting
2903 nodsp [SH] Disable hardware DSP at boot time.
2905 noefi Disable EFI runtime services support.
2910 On X86-32 available only on PAE configured kernels.
2911 noexec=on: enable non-executable mappings (default)
2912 noexec=off: disable non-executable mappings
2915 Disable SMAP (Supervisor Mode Access Prevention)
2916 even if it is supported by processor.
2919 Disable SMEP (Supervisor Mode Execution Prevention)
2920 even if it is supported by processor.
2923 This affects only 32-bit executables.
2924 noexec32=on: enable non-executable mappings (default)
2925 read doesn't imply executable mappings
2926 noexec32=off: disable non-executable mappings
2927 read implies executable mappings
2929 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2931 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2932 register save and restore. The kernel will only save
2933 legacy floating-point registers on task switch.
2935 nohugeiomap [KNL,x86,PPC] Disable kernel huge I/O mappings.
2937 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2938 Equivalent to smt=1.
2940 [KNL,x86] Disable symmetric multithreading (SMT).
2941 nosmt=force: Force disable SMT, cannot be undone
2942 via the sysfs control file.
2944 nospectre_v1 [PPC] Disable mitigations for Spectre Variant 1 (bounds
2945 check bypass). With this option data leaks are possible
2948 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for
2949 the Spectre variant 2 (indirect branch prediction)
2950 vulnerability. System may allow data leaks with this
2953 nospec_store_bypass_disable
2954 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
2956 noxsave [BUGS=X86] Disables x86 extended register state save
2957 and restore using xsave. The kernel will fallback to
2958 enabling legacy floating-point and sse state.
2960 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2961 register states. The kernel will fall back to use
2962 xsave to save the states. By using this parameter,
2963 performance of saving the states is degraded because
2964 xsave doesn't support modified optimization while
2965 xsaveopt supports it on xsaveopt enabled systems.
2967 noxsaves [X86] Disables xsaves and xrstors used in saving and
2968 restoring x86 extended register state in compacted
2969 form of xsave area. The kernel will fall back to use
2970 xsaveopt and xrstor to save and restore the states
2971 in standard form of xsave area. By using this
2972 parameter, xsave area per process might occupy more
2973 memory on xsaves enabled systems.
2975 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2976 wfi(ARM) instruction doesn't work correctly and not to
2977 use it. This is also useful when using JTAG debugger.
2979 no_file_caps Tells the kernel not to honor file capabilities. The
2980 only way then for a file to be executed with privilege
2981 is to be setuid root or executed by root.
2983 nohalt [IA-64] Tells the kernel not to use the power saving
2984 function PAL_HALT_LIGHT when idle. This increases
2985 power-consumption. On the positive side, it reduces
2986 interrupt wake-up latency, which may improve performance
2987 in certain environments such as networked servers or
2990 nohibernate [HIBERNATION] Disable hibernation and resume.
2992 nohz= [KNL] Boottime enable/disable dynamic ticks
2993 Valid arguments: on, off
2996 nohz_full= [KNL,BOOT,SMP,ISOL]
2997 The argument is a cpu list, as described above.
2998 In kernels built with CONFIG_NO_HZ_FULL=y, set
2999 the specified list of CPUs whose tick will be stopped
3000 whenever possible. The boot CPU will be forced outside
3001 the range to maintain the timekeeping. Any CPUs
3002 in this list will have their RCU callbacks offloaded,
3003 just as if they had also been called out in the
3004 rcu_nocbs= boot parameter.
3006 noiotrap [SH] Disables trapped I/O port accesses.
3008 noirqdebug [X86-32] Disables the code which attempts to detect and
3009 disable unhandled interrupt sources.
3011 no_timer_check [X86,APIC] Disables the code which tests for
3012 broken timer IRQ sources.
3014 noisapnp [ISAPNP] Disables ISA PnP code.
3016 noinitrd [RAM] Tells the kernel not to load any configured
3019 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
3021 [Deprecated - use intremap=off]
3025 noinvpcid [X86] Disable the INVPCID cpu feature.
3027 nojitter [IA-64] Disables jitter checking for ITC timers.
3029 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
3031 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
3035 [X86,PV_OPS] Disable paravirtualized VMware scheduler
3036 clock and use the default one.
3038 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
3039 steal time is computed, but won't influence scheduler
3042 nolapic [X86-32,APIC] Do not enable or use the local APIC.
3044 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
3046 noltlbs [PPC] Do not use large page/tlb entries for kernel
3047 lowmem mapping on PPC40x and PPC8xx
3049 nomca [IA-64] Disable machine check abort handling
3051 nomce [X86-32] Disable Machine Check Exception
3053 nomfgpt [X86-32] Disable Multi-Function General Purpose
3054 Timer usage (for AMD Geode machines).
3056 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
3057 shutdown the other cpus. Instead use the REBOOT_VECTOR
3060 nomodule Disable module load
3062 nopat [X86] Disable PAT (page attribute table extension of
3063 pagetables) support.
3065 nopcid [X86-64] Disable the PCID cpu feature.
3067 norandmaps Don't use address space randomization. Equivalent to
3068 echo 0 > /proc/sys/kernel/randomize_va_space
3070 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
3071 with UP alternatives
3073 nordrand [X86] Disable kernel use of the RDRAND and
3074 RDSEED instructions even if they are supported
3075 by the processor. RDRAND and RDSEED are still
3076 available to user space applications.
3078 noresume [SWSUSP] Disables resume and restores original swap
3081 no-scroll [VGA] Disables scrollback.
3082 This is required for the Braillex ib80-piezo Braille
3083 reader made by F.H. Papenmeier (Germany).
3087 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
3089 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
3090 and disable the IO APIC. legacy for "maxcpus=0".
3092 nosoftlockup [KNL] Disable the soft-lockup detector.
3094 nosync [HW,M68K] Disables sync negotiation for all devices.
3096 nowatchdog [KNL] Disable both lockup detectors, i.e.
3097 soft-lockup and NMI watchdog (hard-lockup).
3101 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
3103 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
3104 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
3105 Some features depend on CPU0. Known dependencies are:
3106 1. Resume from suspend/hibernate depends on CPU0.
3107 Suspend/hibernate will fail if CPU0 is offline and you
3108 need to online CPU0 before suspend/hibernate.
3109 2. PIC interrupts also depend on CPU0. CPU0 can't be
3110 removed if a PIC interrupt is detected.
3111 It's said poweroff/reboot may depend on CPU0 on some
3112 machines although I haven't seen such issues so far
3113 after CPU0 is offline on a few tested machines.
3114 If the dependencies are under your control, you can
3115 turn on cpu0_hotplug.
3117 nps_mtm_hs_ctr= [KNL,ARC]
3118 This parameter sets the maximum duration, in
3119 cycles, each HW thread of the CTOP can run
3120 without interruptions, before HW switches it.
3121 The actual maximum duration is 16 times this
3123 Format: integer between 1 and 255
3126 nptcg= [IA-64] Override max number of concurrent global TLB
3127 purges which is reported from either PAL_VM_SUMMARY or
3130 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
3131 could support. nr_cpus=n : n >= 1 limits the kernel to
3132 support 'n' processors. It could be larger than the
3133 number of already plugged CPU during bootup, later in
3134 runtime you can physically add extra cpu until it reaches
3135 n. So during boot up some boot time memory for per-cpu
3136 variables need be pre-allocated for later physical cpu
3139 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3141 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
3142 Allowed values are enable and disable
3144 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3145 'node', 'default' can be specified
3146 This can be set from sysctl after boot.
3147 See Documentation/admin-guide/sysctl/vm.rst for details.
3149 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3150 See Documentation/debugging-via-ohci1394.txt for more
3153 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3154 Rather than timing out after 20 ms if an EC
3155 command is not properly ACKed, override the length
3156 of the timeout. We have interrupts disabled while
3157 waiting for the ACK, so if this is set too high
3158 interrupts *may* be lost!
3160 omap_mux= [OMAP] Override bootloader pin multiplexing.
3161 Format: <mux_mode0.mode_name=value>...
3162 For example, to override I2C bus2:
3163 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3165 oprofile.timer= [HW]
3166 Use timer interrupt instead of performance counters
3168 oprofile.cpu_type= Force an oprofile cpu type
3169 This might be useful if you have an older oprofile
3170 userland or if you want common events.
3171 Format: { arch_perfmon }
3172 arch_perfmon: [X86] Force use of architectural
3173 perfmon on Intel CPUs instead of the
3174 CPU specific event set.
3175 timer: [X86] Force use of architectural NMI
3176 timer mode (see also oprofile.timer
3177 for generic hr timer mode)
3179 oops=panic Always panic on oopses. Default is to just kill the
3180 process, but there is a small probability of
3181 deadlocking the machine.
3182 This will also cause panics on machine check exceptions.
3183 Useful together with panic=30 to trigger a reboot.
3186 [KNL] Boolean flag to control whether the page allocator
3187 should randomize its free lists. The randomization may
3188 be automatically enabled if the kernel detects it is
3189 running on a platform with a direct-mapped memory-side
3190 cache, and this parameter can be used to
3191 override/disable that behavior. The state of the flag
3192 can be read from sysfs at:
3193 /sys/module/page_alloc/parameters/shuffle.
3195 page_owner= [KNL] Boot-time page_owner enabling option.
3196 Storage of the information about who allocated
3197 each page is disabled in default. With this switch,
3199 on: enable the feature
3201 page_poison= [KNL] Boot-time parameter changing the state of
3202 poisoning on the buddy allocator, available with
3203 CONFIG_PAGE_POISONING=y.
3204 off: turn off poisoning (default)
3205 on: turn on poisoning
3207 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3208 timeout > 0: seconds before rebooting
3209 timeout = 0: wait forever
3210 timeout < 0: reboot immediately
3213 panic_print= Bitmask for printing system info when panic happens.
3214 User can chose combination of the following bits:
3215 bit 0: print all tasks info
3216 bit 1: print system memory info
3217 bit 2: print timer info
3218 bit 3: print locks info if CONFIG_LOCKDEP is on
3219 bit 4: print ftrace buffer
3220 bit 5: print all printk messages in buffer
3222 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3225 crash_kexec_post_notifiers
3226 Run kdump after running panic-notifiers and dumping
3227 kmsg. This only for the users who doubt kdump always
3228 succeeds in any situation.
3229 Note that this also increases risks of kdump failure,
3230 because some panic notifiers can make the crashed
3231 kernel more unstable.
3233 parkbd.port= [HW] Parallel port number the keyboard adapter is
3234 connected to, default is 0.
3236 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3237 0 for XT, 1 for AT (default is AT).
3240 parport= [HW,PPT] Specify parallel ports. 0 disables.
3241 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3242 Use 'auto' to force the driver to use any
3243 IRQ/DMA settings detected (the default is to
3244 ignore detected IRQ/DMA settings because of
3245 possible conflicts). You can specify the base
3246 address, IRQ, and DMA settings; IRQ and DMA
3247 should be numbers, or 'auto' (for using detected
3248 settings on that particular port), or 'nofifo'
3249 (to avoid using a FIFO even if it is detected).
3250 Parallel ports are assigned in the order they
3251 are specified on the command line, starting
3254 parport_init_mode= [HW,PPT]
3255 Configure VIA parallel port to operate in
3256 a specific mode. This is necessary on Pegasos
3257 computer where firmware has no options for setting
3258 up parallel port mode and sets it to spp.
3259 Currently this function knows 686a and 8231 chips.
3260 Format: [spp|ps2|epp|ecp|ecpepp]
3263 Halt all CPUs after the first oops has been printed for
3264 the specified number of seconds. This is to be used if
3265 your oopses keep scrolling off the screen.
3270 See header of drivers/block/paride/pcd.c.
3271 See also Documentation/blockdev/paride.rst.
3273 pci=option[,option...] [PCI] various PCI subsystem options.
3275 Some options herein operate on a specific device
3276 or a set of devices (<pci_dev>). These are
3277 specified in one of the following formats:
3279 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
3280 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
3282 Note: the first format specifies a PCI
3283 bus/device/function address which may change
3284 if new hardware is inserted, if motherboard
3285 firmware changes, or due to changes caused
3286 by other kernel parameters. If the
3287 domain is left unspecified, it is
3288 taken to be zero. Optionally, a path
3289 to a device through multiple device/function
3290 addresses can be specified after the base
3291 address (this is more robust against
3292 renumbering issues). The second format
3293 selects devices using IDs from the
3294 configuration space which may match multiple
3295 devices in the system.
3297 earlydump dump PCI config space before the kernel
3299 off [X86] don't probe for the PCI bus
3300 bios [X86-32] force use of PCI BIOS, don't access
3301 the hardware directly. Use this if your machine
3302 has a non-standard PCI host bridge.
3303 nobios [X86-32] disallow use of PCI BIOS, only direct
3304 hardware access methods are allowed. Use this
3305 if you experience crashes upon bootup and you
3306 suspect they are caused by the BIOS.
3307 conf1 [X86] Force use of PCI Configuration Access
3308 Mechanism 1 (config address in IO port 0xCF8,
3309 data in IO port 0xCFC, both 32-bit).
3310 conf2 [X86] Force use of PCI Configuration Access
3311 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3312 the function, IO port 0xCFA, also 8-bit, sets
3313 bus number. The config space is then accessed
3314 through ports 0xC000-0xCFFF).
3315 See http://wiki.osdev.org/PCI for more info
3316 on the configuration access mechanisms.
3317 noaer [PCIE] If the PCIEAER kernel config parameter is
3318 enabled, this kernel boot option can be used to
3319 disable the use of PCIE advanced error reporting.
3320 nodomains [PCI] Disable support for multiple PCI
3321 root domains (aka PCI segments, in ACPI-speak).
3322 nommconf [X86] Disable use of MMCONFIG for PCI
3324 check_enable_amd_mmconf [X86] check for and enable
3325 properly configured MMIO access to PCI
3326 config space on AMD family 10h CPU
3327 nomsi [MSI] If the PCI_MSI kernel config parameter is
3328 enabled, this kernel boot option can be used to
3329 disable the use of MSI interrupts system-wide.
3330 noioapicquirk [APIC] Disable all boot interrupt quirks.
3331 Safety option to keep boot IRQs enabled. This
3332 should never be necessary.
3333 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3334 primary IO-APIC for bridges that cannot disable
3335 boot IRQs. This fixes a source of spurious IRQs
3336 when the system masks IRQs.
3337 noioapicreroute [APIC] Disable workaround that uses the
3338 boot IRQ equivalent of an IRQ that connects to
3339 a chipset where boot IRQs cannot be disabled.
3340 The opposite of ioapicreroute.
3341 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3342 routing table. These calls are known to be buggy
3343 on several machines and they hang the machine
3344 when used, but on other computers it's the only
3345 way to get the interrupt routing table. Try
3346 this option if the kernel is unable to allocate
3347 IRQs or discover secondary PCI buses on your
3349 rom [X86] Assign address space to expansion ROMs.
3350 Use with caution as certain devices share
3351 address decoders between ROMs and other
3353 norom [X86] Do not assign address space to
3354 expansion ROMs that do not already have
3355 BIOS assigned address ranges.
3356 nobar [X86] Do not assign address space to the
3357 BARs that weren't assigned by the BIOS.
3358 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3359 assigned automatically to PCI devices. You can
3360 make the kernel exclude IRQs of your ISA cards
3362 pirqaddr=0xAAAAA [X86] Specify the physical address
3363 of the PIRQ table (normally generated
3364 by the BIOS) if it is outside the
3365 F0000h-100000h range.
3366 lastbus=N [X86] Scan all buses thru bus #N. Can be
3367 useful if the kernel is unable to find your
3368 secondary buses and you want to tell it
3369 explicitly which ones they are.
3370 assign-busses [X86] Always assign all PCI bus
3371 numbers ourselves, overriding
3372 whatever the firmware may have done.
3373 usepirqmask [X86] Honor the possible IRQ mask stored
3374 in the BIOS $PIR table. This is needed on
3375 some systems with broken BIOSes, notably
3376 some HP Pavilion N5400 and Omnibook XE3
3377 notebooks. This will have no effect if ACPI
3378 IRQ routing is enabled.
3379 noacpi [X86] Do not use ACPI for IRQ routing
3380 or for PCI scanning.
3381 use_crs [X86] Use PCI host bridge window information
3382 from ACPI. On BIOSes from 2008 or later, this
3383 is enabled by default. If you need to use this,
3384 please report a bug.
3385 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3386 If you need to use this, please report a bug.
3387 routeirq Do IRQ routing for all PCI devices.
3388 This is normally done in pci_enable_device(),
3389 so this option is a temporary workaround
3390 for broken drivers that don't call it.
3391 skip_isa_align [X86] do not align io start addr, so can
3392 handle more pci cards
3393 noearly [X86] Don't do any early type 1 scanning.
3394 This might help on some broken boards which
3395 machine check when some devices' config space
3396 is read. But various workarounds are disabled
3397 and some IOMMU drivers will not work.
3398 bfsort Sort PCI devices into breadth-first order.
3399 This sorting is done to get a device
3400 order compatible with older (<= 2.4) kernels.
3401 nobfsort Don't sort PCI devices into breadth-first order.
3402 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3403 tuning and use the BIOS-configured MPS defaults.
3404 pcie_bus_safe Set every device's MPS to the largest value
3405 supported by all devices below the root complex.
3406 pcie_bus_perf Set device MPS to the largest allowable MPS
3407 based on its parent bus. Also set MRRS (Max
3408 Read Request Size) to the largest supported
3409 value (no larger than the MPS that the device
3410 or bus can support) for best performance.
3411 pcie_bus_peer2peer Set every device's MPS to 128B, which
3412 every device is guaranteed to support. This
3413 configuration allows peer-to-peer DMA between
3414 any pair of devices, possibly at the cost of
3415 reduced performance. This also guarantees
3416 that hot-added devices will work.
3417 cbiosize=nn[KMG] The fixed amount of bus space which is
3418 reserved for the CardBus bridge's IO window.
3419 The default value is 256 bytes.
3420 cbmemsize=nn[KMG] The fixed amount of bus space which is
3421 reserved for the CardBus bridge's memory
3422 window. The default value is 64 megabytes.
3425 [<order of align>@]<pci_dev>[; ...]
3426 Specifies alignment and device to reassign
3427 aligned memory resources. How to
3428 specify the device is described above.
3429 If <order of align> is not specified,
3430 PAGE_SIZE is used as alignment.
3431 PCI-PCI bridge can be specified, if resource
3432 windows need to be expanded.
3433 To specify the alignment for several
3434 instances of a device, the PCI vendor,
3435 device, subvendor, and subdevice may be
3436 specified, e.g., 4096@pci:8086:9c22:103c:198f
3437 ecrc= Enable/disable PCIe ECRC (transaction layer
3438 end-to-end CRC checking).
3439 bios: Use BIOS/firmware settings. This is the
3443 hpiosize=nn[KMG] The fixed amount of bus space which is
3444 reserved for hotplug bridge's IO window.
3445 Default size is 256 bytes.
3446 hpmemsize=nn[KMG] The fixed amount of bus space which is
3447 reserved for hotplug bridge's memory window.
3448 Default size is 2 megabytes.
3449 hpbussize=nn The minimum amount of additional bus numbers
3450 reserved for buses below a hotplug bridge.
3452 realloc= Enable/disable reallocating PCI bridge resources
3453 if allocations done by BIOS are too small to
3454 accommodate resources required by all child
3456 off: Turn realloc off
3458 realloc same as realloc=on
3459 noari do not use PCIe ARI.
3460 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
3461 do not use PCIe ATS (and IOMMU device IOTLB).
3462 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3463 only look for one device below a PCIe downstream
3465 big_root_window Try to add a big 64bit memory window to the PCIe
3466 root complex on AMD CPUs. Some GFX hardware
3467 can resize a BAR to allow access to all VRAM.
3468 Adding the window is slightly risky (it may
3469 conflict with unreported devices), so this
3471 disable_acs_redir=<pci_dev>[; ...]
3472 Specify one or more PCI devices (in the format
3473 specified above) separated by semicolons.
3474 Each device specified will have the PCI ACS
3475 redirect capabilities forced off which will
3476 allow P2P traffic between devices through
3477 bridges without forcing it upstream. Note:
3478 this removes isolation between devices and
3479 may put more devices in an IOMMU group.
3480 force_floating [S390] Force usage of floating interrupts.
3481 nomio [S390] Do not use MIO instructions.
3483 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3486 force Enable ASPM even on devices that claim not to support it.
3487 WARNING: Forcing ASPM on may cause system lockups.
3489 pcie_ports= [PCIE] PCIe port services handling:
3490 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
3491 even if the platform doesn't give the OS permission to
3492 use them. This may cause conflicts if the platform
3493 also tries to use these services.
3494 compat Disable native PCIe services (PME, AER, DPC, PCIe
3497 pcie_port_pm= [PCIE] PCIe port power management handling:
3498 off Disable power management of all PCIe ports
3499 force Forcibly enable power management of all PCIe ports
3501 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3502 nomsi Do not use MSI for native PCIe PME signaling (this makes
3503 all PCIe root ports use INTx for all services).
3505 pcmv= [HW,PCMCIA] BadgePAD 4
3509 Keep all power-domains already enabled by bootloader on,
3510 even if no driver has claimed them. This is useful
3511 for debug and development, but should not be
3512 needed on a platform with proper driver support.
3515 See Documentation/blockdev/paride.rst.
3517 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3520 See arch/parisc/kernel/pdc_chassis.c
3522 percpu_alloc= Select which percpu first chunk allocator to use.
3523 Currently supported values are "embed" and "page".
3524 Archs may support subset or none of the selections.
3525 See comments in mm/percpu.c for details on each
3526 allocator. This parameter is primarily for debugging
3527 and performance comparison.
3530 See Documentation/blockdev/paride.rst.
3533 See Documentation/blockdev/paride.rst.
3535 pirq= [SMP,APIC] Manual mp-table setup
3536 See Documentation/x86/i386/IO-APIC.rst.
3538 plip= [PPT,NET] Parallel port network link
3539 Format: { parport<nr> | timid | 0 }
3540 See also Documentation/admin-guide/parport.rst.
3542 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3543 Override pmtimer IOPort with a hex value.
3547 Enable PNP debug messages (depends on the
3548 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3549 via /sys/module/pnp/parameters/debug. We always show
3550 current resource usage; turning this on also shows
3551 possible settings and some assignment information.
3557 { on | off | curr | res | no-curr | no-res }
3560 [ISAPNP] Exclude IRQs for the autoconfiguration
3563 [ISAPNP] Exclude DMAs for the autoconfiguration
3565 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3566 Ranges are in pairs (I/O port base and size).
3569 [ISAPNP] Exclude memory regions for the
3571 Ranges are in pairs (memory base and size).
3573 ports= [IP_VS_FTP] IPVS ftp helper module
3575 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3577 Format: <port>,<port>....
3579 powersave=off [PPC] This option disables power saving features.
3580 It specifically disables cpuidle and sets the
3581 platform machine description specific power_save
3582 function to NULL. On Idle the CPU just reduces
3585 ppc_strict_facility_enable
3586 [PPC] This option catches any kernel floating point,
3587 Altivec, VSX and SPE outside of regions specifically
3588 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3589 There is some performance impact when enabling this.
3593 Disable Hardware Transactional Memory
3595 print-fatal-signals=
3596 [KNL] debug: print fatal signals
3598 If enabled, warn about various signal handling
3599 related application anomalies: too many signals,
3600 too many POSIX.1 timers, fatal signals causing a
3603 If you hit the warning due to signal overflow,
3604 you might want to try "ulimit -i unlimited".
3608 printk.always_kmsg_dump=
3609 Trigger kmsg_dump for cases other than kernel oops or
3611 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3614 printk.devkmsg={on,off,ratelimit}
3615 Control writing to /dev/kmsg.
3616 on - unlimited logging to /dev/kmsg from userspace
3617 off - logging to /dev/kmsg disabled
3618 ratelimit - ratelimit the logging
3621 printk.time= Show timing data prefixed to each printk message line
3622 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3624 processor.max_cstate= [HW,ACPI]
3625 Limit processor to maximum C-state
3626 max_cstate=9 overrides any DMI blacklist limit.
3628 processor.nocst [HW,ACPI]
3629 Ignore the _CST method to determine C-states,
3630 instead using the legacy FADT method
3632 profile= [KNL] Enable kernel profiling via /proc/profile
3633 Format: [<profiletype>,]<number>
3634 Param: <profiletype>: "schedule", "sleep", or "kvm"
3635 [defaults to kernel profiling]
3636 Param: "schedule" - profile schedule points.
3637 Param: "sleep" - profile D-state sleeping (millisecs).
3638 Requires CONFIG_SCHEDSTATS
3639 Param: "kvm" - profile VM exits.
3640 Param: <number> - step/bucket size as a power of 2 for
3641 statistical time based profiling.
3643 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3645 See Documentation/blockdev/ramdisk.rst.
3647 psi= [KNL] Enable or disable pressure stall information
3651 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3652 probe for; one of (bare|imps|exps|lifebook|any).
3653 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3655 psmouse.resetafter= [HW,MOUSE]
3656 Try to reset the device after so many bad packets
3659 [HW,MOUSE] Set desired mouse resolution, in dpi.
3660 psmouse.smartscroll=
3661 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3662 0 = disabled, 1 = enabled (default).
3664 pstore.backend= Specify the name of the pstore backend to use
3667 See Documentation/blockdev/paride.rst.
3669 pti= [X86_64] Control Page Table Isolation of user and
3670 kernel address spaces. Disabling this feature
3671 removes hardening, but improves performance of
3672 system calls and interrupts.
3674 on - unconditionally enable
3675 off - unconditionally disable
3676 auto - kernel detects whether your CPU model is
3677 vulnerable to issues that PTI mitigates
3679 Not specifying this option is equivalent to pti=auto.
3682 Equivalent to pti=off
3685 [KNL] Number of legacy pty's. Overwrites compiled-in
3688 quiet [KNL] Disable most log messages
3693 See Documentation/admin-guide/md.rst.
3695 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3696 See Documentation/blockdev/ramdisk.rst.
3698 random.trust_cpu={on,off}
3699 [KNL] Enable or disable trusting the use of the
3700 CPU's random number generator (if available) to
3701 fully seed the kernel's CRNG. Default is controlled
3702 by CONFIG_RANDOM_TRUST_CPU.
3704 ras=option[,option,...] [KNL] RAS-specific options
3707 Disable the Correctable Errors Collector,
3708 see CONFIG_RAS_CEC help text.
3711 The argument is a cpu list, as described above,
3712 except that the string "all" can be used to
3713 specify every CPU on the system.
3715 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3716 the specified list of CPUs to be no-callback CPUs.
3717 Invocation of these CPUs' RCU callbacks will be
3718 offloaded to "rcuox/N" kthreads created for that
3719 purpose, where "x" is "p" for RCU-preempt, and
3720 "s" for RCU-sched, and "N" is the CPU number.
3721 This reduces OS jitter on the offloaded CPUs,
3722 which can be useful for HPC and real-time
3723 workloads. It can also improve energy efficiency
3724 for asymmetric multiprocessors.
3727 Rather than requiring that offloaded CPUs
3728 (specified by rcu_nocbs= above) explicitly
3729 awaken the corresponding "rcuoN" kthreads,
3730 make these kthreads poll for callbacks.
3731 This improves the real-time response for the
3732 offloaded CPUs by relieving them of the need to
3733 wake up the corresponding kthread, but degrades
3734 energy efficiency by requiring that the kthreads
3735 periodically wake up to do the polling.
3737 rcutree.blimit= [KNL]
3738 Set maximum number of finished RCU callbacks to
3739 process in one batch.
3741 rcutree.dump_tree= [KNL]
3742 Dump the structure of the rcu_node combining tree
3743 out at early boot. This is used for diagnostic
3744 purposes, to verify correct tree setup.
3746 rcutree.gp_cleanup_delay= [KNL]
3747 Set the number of jiffies to delay each step of
3748 RCU grace-period cleanup.
3750 rcutree.gp_init_delay= [KNL]
3751 Set the number of jiffies to delay each step of
3752 RCU grace-period initialization.
3754 rcutree.gp_preinit_delay= [KNL]
3755 Set the number of jiffies to delay each step of
3756 RCU grace-period pre-initialization, that is,
3757 the propagation of recent CPU-hotplug changes up
3758 the rcu_node combining tree.
3760 rcutree.use_softirq= [KNL]
3761 If set to zero, move all RCU_SOFTIRQ processing to
3762 per-CPU rcuc kthreads. Defaults to a non-zero
3763 value, meaning that RCU_SOFTIRQ is used by default.
3764 Specify rcutree.use_softirq=0 to use rcuc kthreads.
3766 rcutree.rcu_fanout_exact= [KNL]
3767 Disable autobalancing of the rcu_node combining
3768 tree. This is used by rcutorture, and might
3769 possibly be useful for architectures having high
3770 cache-to-cache transfer latencies.
3772 rcutree.rcu_fanout_leaf= [KNL]
3773 Change the number of CPUs assigned to each
3774 leaf rcu_node structure. Useful for very
3775 large systems, which will choose the value 64,
3776 and for NUMA systems with large remote-access
3777 latencies, which will choose a value aligned
3778 with the appropriate hardware boundaries.
3780 rcutree.jiffies_till_first_fqs= [KNL]
3781 Set delay from grace-period initialization to
3782 first attempt to force quiescent states.
3783 Units are jiffies, minimum value is zero,
3784 and maximum value is HZ.
3786 rcutree.jiffies_till_next_fqs= [KNL]
3787 Set delay between subsequent attempts to force
3788 quiescent states. Units are jiffies, minimum
3789 value is one, and maximum value is HZ.
3791 rcutree.jiffies_till_sched_qs= [KNL]
3792 Set required age in jiffies for a
3793 given grace period before RCU starts
3794 soliciting quiescent-state help from
3795 rcu_note_context_switch() and cond_resched().
3796 If not specified, the kernel will calculate
3797 a value based on the most recent settings
3798 of rcutree.jiffies_till_first_fqs
3799 and rcutree.jiffies_till_next_fqs.
3800 This calculated value may be viewed in
3801 rcutree.jiffies_to_sched_qs. Any attempt to set
3802 rcutree.jiffies_to_sched_qs will be cheerfully
3805 rcutree.kthread_prio= [KNL,BOOT]
3806 Set the SCHED_FIFO priority of the RCU per-CPU
3807 kthreads (rcuc/N). This value is also used for
3808 the priority of the RCU boost threads (rcub/N)
3809 and for the RCU grace-period kthreads (rcu_bh,
3810 rcu_preempt, and rcu_sched). If RCU_BOOST is
3811 set, valid values are 1-99 and the default is 1
3812 (the least-favored priority). Otherwise, when
3813 RCU_BOOST is not set, valid values are 0-99 and
3814 the default is zero (non-realtime operation).
3816 rcutree.rcu_nocb_leader_stride= [KNL]
3817 Set the number of NOCB kthread groups, which
3818 defaults to the square root of the number of
3819 CPUs. Larger numbers reduces the wakeup overhead
3820 on the per-CPU grace-period kthreads, but increases
3821 that same overhead on each group's leader.
3823 rcutree.qhimark= [KNL]
3824 Set threshold of queued RCU callbacks beyond which
3825 batch limiting is disabled.
3827 rcutree.qlowmark= [KNL]
3828 Set threshold of queued RCU callbacks below which
3829 batch limiting is re-enabled.
3831 rcutree.rcu_idle_gp_delay= [KNL]
3832 Set wakeup interval for idle CPUs that have
3833 RCU callbacks (RCU_FAST_NO_HZ=y).
3835 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3836 Set wakeup interval for idle CPUs that have
3837 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3838 Lazy RCU callbacks are those which RCU can
3839 prove do nothing more than free memory.
3841 rcutree.rcu_kick_kthreads= [KNL]
3842 Cause the grace-period kthread to get an extra
3843 wake_up() if it sleeps three times longer than
3844 it should at force-quiescent-state time.
3845 This wake_up() will be accompanied by a
3846 WARN_ONCE() splat and an ftrace_dump().
3848 rcutree.sysrq_rcu= [KNL]
3849 Commandeer a sysrq key to dump out Tree RCU's
3850 rcu_node tree with an eye towards determining
3851 why a new grace period has not yet started.
3853 rcuperf.gp_async= [KNL]
3854 Measure performance of asynchronous
3855 grace-period primitives such as call_rcu().
3857 rcuperf.gp_async_max= [KNL]
3858 Specify the maximum number of outstanding
3859 callbacks per writer thread. When a writer
3860 thread exceeds this limit, it invokes the
3861 corresponding flavor of rcu_barrier() to allow
3862 previously posted callbacks to drain.
3864 rcuperf.gp_exp= [KNL]
3865 Measure performance of expedited synchronous
3866 grace-period primitives.
3868 rcuperf.holdoff= [KNL]
3869 Set test-start holdoff period. The purpose of
3870 this parameter is to delay the start of the
3871 test until boot completes in order to avoid
3874 rcuperf.nreaders= [KNL]
3875 Set number of RCU readers. The value -1 selects
3876 N, where N is the number of CPUs. A value
3877 "n" less than -1 selects N-n+1, where N is again
3878 the number of CPUs. For example, -2 selects N
3879 (the number of CPUs), -3 selects N+1, and so on.
3880 A value of "n" less than or equal to -N selects
3883 rcuperf.nwriters= [KNL]
3884 Set number of RCU writers. The values operate
3885 the same as for rcuperf.nreaders.
3886 N, where N is the number of CPUs
3888 rcuperf.perf_type= [KNL]
3889 Specify the RCU implementation to test.
3891 rcuperf.shutdown= [KNL]
3892 Shut the system down after performance tests
3893 complete. This is useful for hands-off automated
3896 rcuperf.verbose= [KNL]
3897 Enable additional printk() statements.
3899 rcuperf.writer_holdoff= [KNL]
3900 Write-side holdoff between grace periods,
3901 in microseconds. The default of zero says
3904 rcutorture.fqs_duration= [KNL]
3905 Set duration of force_quiescent_state bursts
3908 rcutorture.fqs_holdoff= [KNL]
3909 Set holdoff time within force_quiescent_state bursts
3912 rcutorture.fqs_stutter= [KNL]
3913 Set wait time between force_quiescent_state bursts
3916 rcutorture.fwd_progress= [KNL]
3917 Enable RCU grace-period forward-progress testing
3918 for the types of RCU supporting this notion.
3920 rcutorture.fwd_progress_div= [KNL]
3921 Specify the fraction of a CPU-stall-warning
3922 period to do tight-loop forward-progress testing.
3924 rcutorture.fwd_progress_holdoff= [KNL]
3925 Number of seconds to wait between successive
3926 forward-progress tests.
3928 rcutorture.fwd_progress_need_resched= [KNL]
3929 Enclose cond_resched() calls within checks for
3930 need_resched() during tight-loop forward-progress
3933 rcutorture.gp_cond= [KNL]
3934 Use conditional/asynchronous update-side
3935 primitives, if available.
3937 rcutorture.gp_exp= [KNL]
3938 Use expedited update-side primitives, if available.
3940 rcutorture.gp_normal= [KNL]
3941 Use normal (non-expedited) asynchronous
3942 update-side primitives, if available.
3944 rcutorture.gp_sync= [KNL]
3945 Use normal (non-expedited) synchronous
3946 update-side primitives, if available. If all
3947 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3948 rcutorture.gp_normal=, and rcutorture.gp_sync=
3949 are zero, rcutorture acts as if is interpreted
3950 they are all non-zero.
3952 rcutorture.n_barrier_cbs= [KNL]
3953 Set callbacks/threads for rcu_barrier() testing.
3955 rcutorture.nfakewriters= [KNL]
3956 Set number of concurrent RCU writers. These just
3957 stress RCU, they don't participate in the actual
3958 test, hence the "fake".
3960 rcutorture.nreaders= [KNL]
3961 Set number of RCU readers. The value -1 selects
3962 N-1, where N is the number of CPUs. A value
3963 "n" less than -1 selects N-n-2, where N is again
3964 the number of CPUs. For example, -2 selects N
3965 (the number of CPUs), -3 selects N+1, and so on.
3967 rcutorture.object_debug= [KNL]
3968 Enable debug-object double-call_rcu() testing.
3970 rcutorture.onoff_holdoff= [KNL]
3971 Set time (s) after boot for CPU-hotplug testing.
3973 rcutorture.onoff_interval= [KNL]
3974 Set time (jiffies) between CPU-hotplug operations,
3975 or zero to disable CPU-hotplug testing.
3977 rcutorture.shuffle_interval= [KNL]
3978 Set task-shuffle interval (s). Shuffling tasks
3979 allows some CPUs to go into dyntick-idle mode
3980 during the rcutorture test.
3982 rcutorture.shutdown_secs= [KNL]
3983 Set time (s) after boot system shutdown. This
3984 is useful for hands-off automated testing.
3986 rcutorture.stall_cpu= [KNL]
3987 Duration of CPU stall (s) to test RCU CPU stall
3988 warnings, zero to disable.
3990 rcutorture.stall_cpu_holdoff= [KNL]
3991 Time to wait (s) after boot before inducing stall.
3993 rcutorture.stall_cpu_irqsoff= [KNL]
3994 Disable interrupts while stalling if set.
3996 rcutorture.stat_interval= [KNL]
3997 Time (s) between statistics printk()s.
3999 rcutorture.stutter= [KNL]
4000 Time (s) to stutter testing, for example, specifying
4001 five seconds causes the test to run for five seconds,
4002 wait for five seconds, and so on. This tests RCU's
4003 ability to transition abruptly to and from idle.
4005 rcutorture.test_boost= [KNL]
4006 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
4007 "Maybe" means test if the RCU implementation
4008 under test support RCU priority boosting.
4010 rcutorture.test_boost_duration= [KNL]
4011 Duration (s) of each individual boost test.
4013 rcutorture.test_boost_interval= [KNL]
4014 Interval (s) between each boost test.
4016 rcutorture.test_no_idle_hz= [KNL]
4017 Test RCU's dyntick-idle handling. See also the
4018 rcutorture.shuffle_interval parameter.
4020 rcutorture.torture_type= [KNL]
4021 Specify the RCU implementation to test.
4023 rcutorture.verbose= [KNL]
4024 Enable additional printk() statements.
4026 rcupdate.rcu_cpu_stall_suppress= [KNL]
4027 Suppress RCU CPU stall warning messages.
4029 rcupdate.rcu_cpu_stall_timeout= [KNL]
4030 Set timeout for RCU CPU stall warning messages.
4032 rcupdate.rcu_expedited= [KNL]
4033 Use expedited grace-period primitives, for
4034 example, synchronize_rcu_expedited() instead
4035 of synchronize_rcu(). This reduces latency,
4036 but can increase CPU utilization, degrade
4037 real-time latency, and degrade energy efficiency.
4038 No effect on CONFIG_TINY_RCU kernels.
4040 rcupdate.rcu_normal= [KNL]
4041 Use only normal grace-period primitives,
4042 for example, synchronize_rcu() instead of
4043 synchronize_rcu_expedited(). This improves
4044 real-time latency, CPU utilization, and
4045 energy efficiency, but can expose users to
4046 increased grace-period latency. This parameter
4047 overrides rcupdate.rcu_expedited. No effect on
4048 CONFIG_TINY_RCU kernels.
4050 rcupdate.rcu_normal_after_boot= [KNL]
4051 Once boot has completed (that is, after
4052 rcu_end_inkernel_boot() has been invoked), use
4053 only normal grace-period primitives. No effect
4054 on CONFIG_TINY_RCU kernels.
4056 rcupdate.rcu_task_stall_timeout= [KNL]
4057 Set timeout in jiffies for RCU task stall warning
4058 messages. Disable with a value less than or equal
4061 rcupdate.rcu_self_test= [KNL]
4062 Run the RCU early boot self tests
4066 Run specified binary instead of /init from the ramdisk,
4067 used for early userspace startup. See initrd.
4070 Turn on/off individual RDT features. List is:
4071 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
4073 E.g. to turn on cmt and turn off mba use:
4077 Format (x86 or x86_64):
4078 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
4080 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
4082 Where reboot_mode is one of warm (soft) or cold (hard) or gpio
4083 (prefix with 'panic_' to set mode for panic
4085 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
4086 reboot_force is either force or not specified,
4087 reboot_cpu is s[mp]#### with #### being the processor
4088 to be used for rebooting.
4091 [KNL, SMP] Set scheduler's default relax_domain_level.
4092 See Documentation/cgroup-v1/cpusets.rst.
4094 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
4095 Format: <base1>,<size1>[,<base2>,<size2>,...]
4096 Reserve I/O ports or memory so the kernel won't use
4097 them. If <base> is less than 0x10000, the region
4098 is assumed to be I/O ports; otherwise it is memory.
4100 reservetop= [X86-32]
4102 Reserves a hole at the top of the kernel virtual
4107 Set the amount of memory to reserve for BIOS at
4108 the bottom of the address space.
4110 reset_devices [KNL] Force drivers to reset the underlying device
4111 during initialization.
4114 Specify the partition device for software suspend
4116 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
4118 resume_offset= [SWSUSP]
4119 Specify the offset from the beginning of the partition
4120 given by "resume=" at which the swap header is located,
4121 in <PAGE_SIZE> units (needed only for swap files).
4122 See Documentation/power/swsusp-and-swap-files.txt
4124 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
4125 read the resume files
4127 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
4128 Useful for devices that are detected asynchronously
4129 (e.g. USB and MMC devices).
4131 hibernate= [HIBERNATION]
4132 noresume Don't check if there's a hibernation image
4133 present during boot.
4134 nocompress Don't compress/decompress hibernation images.
4135 no Disable hibernation and resume.
4136 protect_image Turn on image protection during restoration
4137 (that will set all pages holding image data
4138 during restoration read-only).
4140 retain_initrd [RAM] Keep initrd memory after extraction
4142 rfkill.default_state=
4143 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
4144 etc. communication is blocked by default.
4147 rfkill.master_switch_mode=
4148 0 The "airplane mode" button does nothing.
4149 1 The "airplane mode" button toggles between everything
4150 blocked and the previous configuration.
4151 2 The "airplane mode" button toggles between everything
4152 blocked and everything unblocked.
4154 rhash_entries= [KNL,NET]
4155 Set number of hash buckets for route cache
4158 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
4161 ro [KNL] Mount root device read-only on boot
4164 on Mark read-only kernel memory as read-only (default).
4165 off Leave read-only kernel memory writable for debugging.
4168 Enable the uart passthrough on the designated usb port
4169 on Rockchip SoCs. When active, the signals of the
4170 debug-uart get routed to the D+ and D- pins of the usb
4171 port and the regular usb controller gets disabled.
4173 root= [KNL] Root filesystem
4174 See name_to_dev_t comment in init/do_mounts.c.
4176 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
4177 mount the root filesystem
4179 rootflags= [KNL] Set root filesystem mount option string
4181 rootfstype= [KNL] Set root filesystem type
4183 rootwait [KNL] Wait (indefinitely) for root device to show up.
4184 Useful for devices that are detected asynchronously
4185 (e.g. USB and MMC devices).
4187 rproc_mem=nn[KMG][@address]
4188 [KNL,ARM,CMA] Remoteproc physical memory block.
4189 Memory area to be used by remote processor image,
4192 rw [KNL] Mount root device read-write on boot
4194 S [KNL] Run init in single mode
4196 s390_iommu= [HW,S390]
4197 Set s390 IOTLB flushing mode
4199 With strict flushing every unmap operation will result in
4200 an IOTLB flush. Default is lazy flushing before reuse,
4204 See drivers/net/irda/sa1100_ir.c.
4206 sbni= [NET] Granch SBNI12 leased line adapter
4208 sched_debug [KNL] Enables verbose scheduler debug messages.
4210 schedstats= [KNL,X86] Enable or disable scheduled statistics.
4211 Allowed values are enable and disable. This feature
4212 incurs a small amount of overhead in the scheduler
4213 but is useful for debugging and performance tuning.
4215 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
4216 xtime_lock contention on larger systems, and/or RCU lock
4217 contention on all systems with CONFIG_MAXSMP set.
4218 Format: { "0" | "1" }
4219 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
4221 Note: increases power consumption, thus should only be
4222 enabled if running jitter sensitive (HPC/RT) workloads.
4224 security= [SECURITY] Choose a legacy "major" security module to
4225 enable at boot. This has been deprecated by the
4228 selinux= [SELINUX] Disable or enable SELinux at boot time.
4229 Format: { "0" | "1" }
4230 See security/selinux/Kconfig help text.
4233 Default value is set via kernel config option.
4234 If enabled at boot time, /selinux/disable can be used
4235 later to disable prior to initial policy load.
4237 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
4238 Format: { "0" | "1" }
4239 See security/apparmor/Kconfig help text
4242 Default value is set via kernel config option.
4244 serialnumber [BUGS=X86-32]
4247 Maximal number of shapers.
4255 Disable merging of slabs with similar size. May be
4256 necessary if there is some reason to distinguish
4257 allocs to different slabs, especially in hardened
4258 environments where the risk of heap overflows and
4259 layout control by attackers can usually be
4260 frustrated by disabling merging. This will reduce
4261 most of the exposure of a heap attack to a single
4262 cache (risks via metadata attacks are mostly
4263 unchanged). Debug options disable merging on their
4265 For more information see Documentation/vm/slub.rst.
4267 slab_max_order= [MM, SLAB]
4268 Determines the maximum allowed order for slabs.
4269 A high setting may cause OOMs due to memory
4270 fragmentation. Defaults to 1 for systems with
4271 more than 32MB of RAM, 0 otherwise.
4273 slub_debug[=options[,slabs]] [MM, SLUB]
4274 Enabling slub_debug allows one to determine the
4275 culprit if slab objects become corrupted. Enabling
4276 slub_debug can create guard zones around objects and
4277 may poison objects when not in use. Also tracks the
4278 last alloc / free. For more information see
4279 Documentation/vm/slub.rst.
4281 slub_memcg_sysfs= [MM, SLUB]
4282 Determines whether to enable sysfs directories for
4283 memory cgroup sub-caches. 1 to enable, 0 to disable.
4284 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
4285 Enabling this can lead to a very high number of debug
4286 directories and files being created under
4289 slub_max_order= [MM, SLUB]
4290 Determines the maximum allowed order for slabs.
4291 A high setting may cause OOMs due to memory
4292 fragmentation. For more information see
4293 Documentation/vm/slub.rst.
4295 slub_min_objects= [MM, SLUB]
4296 The minimum number of objects per slab. SLUB will
4297 increase the slab order up to slub_max_order to
4298 generate a sufficiently large slab able to contain
4299 the number of objects indicated. The higher the number
4300 of objects the smaller the overhead of tracking slabs
4301 and the less frequently locks need to be acquired.
4302 For more information see Documentation/vm/slub.rst.
4304 slub_min_order= [MM, SLUB]
4305 Determines the minimum page order for slabs. Must be
4306 lower than slub_max_order.
4307 For more information see Documentation/vm/slub.rst.
4309 slub_nomerge [MM, SLUB]
4310 Same with slab_nomerge. This is supported for legacy.
4311 See slab_nomerge for more information.
4314 Format: <io1>[,<io2>[,...,<io8>]]
4316 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4317 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4318 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4319 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4320 smsc-ircc2.ircc_irq= [HW] IRQ line
4321 smsc-ircc2.ircc_dma= [HW] DMA channel
4322 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4323 0: Toshiba Satellite 1800 (GP data pin select)
4324 1: Fast pin select (default)
4327 smt [KNL,S390] Set the maximum number of threads (logical
4328 CPUs) to use per physical CPU on systems capable of
4329 symmetric multithreading (SMT). Will be capped to the
4330 actual hardware limit.
4332 Default: -1 (no limit)
4335 [KNL] Should the soft-lockup detector generate panics.
4338 A nonzero value instructs the soft-lockup detector
4339 to panic the machine when a soft-lockup occurs. This
4340 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
4341 which is the respective build-time switch to that
4344 softlockup_all_cpu_backtrace=
4345 [KNL] Should the soft-lockup detector generate
4346 backtraces on all cpus.
4349 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4350 See Documentation/laptops/sonypi.rst
4352 spectre_v2= [X86] Control mitigation of Spectre variant 2
4353 (indirect branch speculation) vulnerability.
4354 The default operation protects the kernel from
4357 on - unconditionally enable, implies
4359 off - unconditionally disable, implies
4361 auto - kernel detects whether your CPU model is
4364 Selecting 'on' will, and 'auto' may, choose a
4365 mitigation method at run time according to the
4366 CPU, the available microcode, the setting of the
4367 CONFIG_RETPOLINE configuration option, and the
4368 compiler with which the kernel was built.
4370 Selecting 'on' will also enable the mitigation
4371 against user space to user space task attacks.
4373 Selecting 'off' will disable both the kernel and
4374 the user space protections.
4376 Specific mitigations can also be selected manually:
4378 retpoline - replace indirect branches
4379 retpoline,generic - google's original retpoline
4380 retpoline,amd - AMD-specific minimal thunk
4382 Not specifying this option is equivalent to
4386 [X86] Control mitigation of Spectre variant 2
4387 (indirect branch speculation) vulnerability between
4390 on - Unconditionally enable mitigations. Is
4391 enforced by spectre_v2=on
4393 off - Unconditionally disable mitigations. Is
4394 enforced by spectre_v2=off
4396 prctl - Indirect branch speculation is enabled,
4397 but mitigation can be enabled via prctl
4398 per thread. The mitigation control state
4399 is inherited on fork.
4402 - Like "prctl" above, but only STIBP is
4403 controlled per thread. IBPB is issued
4404 always when switching between different user
4408 - Same as "prctl" above, but all seccomp
4409 threads will enable the mitigation unless
4410 they explicitly opt out.
4413 - Like "seccomp" above, but only STIBP is
4414 controlled per thread. IBPB is issued
4415 always when switching between different
4416 user space processes.
4418 auto - Kernel selects the mitigation depending on
4419 the available CPU features and vulnerability.
4422 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
4424 Not specifying this option is equivalent to
4425 spectre_v2_user=auto.
4427 spec_store_bypass_disable=
4428 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4429 (Speculative Store Bypass vulnerability)
4431 Certain CPUs are vulnerable to an exploit against a
4432 a common industry wide performance optimization known
4433 as "Speculative Store Bypass" in which recent stores
4434 to the same memory location may not be observed by
4435 later loads during speculative execution. The idea
4436 is that such stores are unlikely and that they can
4437 be detected prior to instruction retirement at the
4438 end of a particular speculation execution window.
4440 In vulnerable processors, the speculatively forwarded
4441 store can be used in a cache side channel attack, for
4442 example to read memory to which the attacker does not
4443 directly have access (e.g. inside sandboxed code).
4445 This parameter controls whether the Speculative Store
4446 Bypass optimization is used.
4448 On x86 the options are:
4450 on - Unconditionally disable Speculative Store Bypass
4451 off - Unconditionally enable Speculative Store Bypass
4452 auto - Kernel detects whether the CPU model contains an
4453 implementation of Speculative Store Bypass and
4454 picks the most appropriate mitigation. If the
4455 CPU is not vulnerable, "off" is selected. If the
4456 CPU is vulnerable the default mitigation is
4457 architecture and Kconfig dependent. See below.
4458 prctl - Control Speculative Store Bypass per thread
4459 via prctl. Speculative Store Bypass is enabled
4460 for a process by default. The state of the control
4461 is inherited on fork.
4462 seccomp - Same as "prctl" above, but all seccomp threads
4463 will disable SSB unless they explicitly opt out.
4465 Default mitigations:
4466 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4468 On powerpc the options are:
4470 on,auto - On Power8 and Power9 insert a store-forwarding
4471 barrier on kernel entry and exit. On Power7
4472 perform a software flush on kernel entry and
4476 Not specifying this option is equivalent to
4477 spec_store_bypass_disable=auto.
4479 spia_io_base= [HW,MTD]
4484 srcutree.counter_wrap_check [KNL]
4485 Specifies how frequently to check for
4486 grace-period sequence counter wrap for the
4487 srcu_data structure's ->srcu_gp_seq_needed field.
4488 The greater the number of bits set in this kernel
4489 parameter, the less frequently counter wrap will
4490 be checked for. Note that the bottom two bits
4493 srcutree.exp_holdoff [KNL]
4494 Specifies how many nanoseconds must elapse
4495 since the end of the last SRCU grace period for
4496 a given srcu_struct until the next normal SRCU
4497 grace period will be considered for automatic
4498 expediting. Set to zero to disable automatic
4502 Speculative Store Bypass Disable control
4504 On CPUs that are vulnerable to the Speculative
4505 Store Bypass vulnerability and offer a
4506 firmware based mitigation, this parameter
4507 indicates how the mitigation should be used:
4509 force-on: Unconditionally enable mitigation for
4510 for both kernel and userspace
4511 force-off: Unconditionally disable mitigation for
4512 for both kernel and userspace
4513 kernel: Always enable mitigation in the
4514 kernel, and offer a prctl interface
4515 to allow userspace to register its
4516 interest in being mitigated too.
4518 stack_guard_gap= [MM]
4519 override the default stack gap protection. The value
4520 is in page units and it defines how many pages prior
4521 to (for stacks growing down) resp. after (for stacks
4522 growing up) the main stack are reserved for no other
4523 mapping. Default value is 256 pages.
4526 Enabled the stack tracer on boot up.
4528 stacktrace_filter=[function-list]
4529 [FTRACE] Limit the functions that the stack tracer
4530 will trace at boot up. function-list is a comma separated
4531 list of functions. This list can be changed at run
4532 time by the stack_trace_filter file in the debugfs
4533 tracing directory. Note, this enables stack tracing
4534 and the stacktrace above is not needed.
4538 Set the STI (builtin display/keyboard on the HP-PARISC
4539 machines) console (graphic card) which should be used
4540 as the initial boot-console.
4541 See also comment in drivers/video/console/sticore.c.
4544 See comment in drivers/video/console/sticore.c.
4547 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4549 sunrpc.min_resvport=
4550 sunrpc.max_resvport=
4552 SunRPC servers often require that client requests
4553 originate from a privileged port (i.e. a port in the
4554 range 0 < portnr < 1024).
4555 An administrator who wishes to reserve some of these
4556 ports for other uses may adjust the range that the
4557 kernel's sunrpc client considers to be privileged
4558 using these two parameters to set the minimum and
4559 maximum port values.
4561 sunrpc.svc_rpc_per_connection_limit=
4563 Limit the number of requests that the server will
4564 process in parallel from a single connection.
4565 The default value is 0 (no limit).
4569 Control how the NFS server code allocates CPUs to
4570 service thread pools. Depending on how many NICs
4571 you have and where their interrupts are bound, this
4572 option will affect which CPUs will do NFS serving.
4573 Note: this parameter cannot be changed while the
4574 NFS server is running.
4576 auto the server chooses an appropriate mode
4577 automatically using heuristics
4578 global a single global pool contains all CPUs
4579 percpu one pool for each CPU
4580 pernode one pool for each NUMA node (equivalent
4581 to global on non-NUMA machines)
4583 sunrpc.tcp_slot_table_entries=
4584 sunrpc.udp_slot_table_entries=
4586 Sets the upper limit on the number of simultaneous
4587 RPC calls that can be sent from the client to a
4588 server. Increasing these values may allow you to
4589 improve throughput, but will also increase the
4590 amount of memory reserved for use by the client.
4592 suspend.pm_test_delay=
4594 Sets the number of seconds to remain in a suspend test
4595 mode before resuming the system (see
4596 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4597 is set. Default value is 5.
4600 [KNL] Enable accounting of swap in memory resource
4601 controller if no parameter or 1 is given or disable
4602 it if 0 is given (See Documentation/cgroup-v1/memory.rst)
4604 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4605 Format: { <int> | force | noforce }
4606 <int> -- Number of I/O TLB slabs
4607 force -- force using of bounce buffers even if they
4608 wouldn't be automatically used by the kernel
4609 noforce -- Never use bounce buffers (for debugging)
4613 sysfs.deprecated=0|1 [KNL]
4614 Enable/disable old style sysfs layout for old udev
4615 on older distributions. When this option is enabled
4616 very new udev will not work anymore. When this option
4617 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4618 in older udev will not work anymore.
4619 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4620 the kernel configuration.
4622 sysrq_always_enabled
4624 Ignore sysrq setting - this boot parameter will
4625 neutralize any effect of /proc/sys/kernel/sysrq.
4626 Useful for debugging.
4628 tcpmhash_entries= [KNL,NET]
4629 Set the number of tcp_metrics_hash slots.
4630 Default value is 8192 or 16384 depending on total
4631 ram pages. This is used to specify the TCP metrics
4632 cache size. See Documentation/networking/ip-sysctl.txt
4633 "tcp_no_metrics_save" section for more details.
4637 test_suspend= [SUSPEND][,N]
4638 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4639 standby suspend) or "freeze" (for suspend type freeze)
4640 as the system sleep state during system startup with
4641 the optional capability to repeat N number of times.
4642 The system is woken from this state using a
4643 wakeup-capable RTC alarm.
4645 thash_entries= [KNL,NET]
4646 Set number of hash buckets for TCP connection
4648 thermal.act= [HW,ACPI]
4649 -1: disable all active trip points in all thermal zones
4650 <degrees C>: override all lowest active trip points
4652 thermal.crt= [HW,ACPI]
4653 -1: disable all critical trip points in all thermal zones
4654 <degrees C>: override all critical trip points
4656 thermal.nocrt= [HW,ACPI]
4657 Set to disable actions on ACPI thermal zone
4658 critical and hot trip points.
4660 thermal.off= [HW,ACPI]
4661 1: disable ACPI thermal control
4663 thermal.psv= [HW,ACPI]
4664 -1: disable all passive trip points
4665 <degrees C>: override all passive trip points to this
4668 thermal.tzp= [HW,ACPI]
4669 Specify global default ACPI thermal zone polling rate
4670 <deci-seconds>: poll all this frequency
4671 0: no polling (default)
4674 Force threading of all interrupt handlers except those
4675 marked explicitly IRQF_NO_THREAD.
4678 Enable the Transcendent memory driver if built-in.
4680 tmem.cleancache=0|1 [KNL, XEN]
4681 Default is on (1). Disable the usage of the cleancache
4682 API to send anonymous pages to the hypervisor.
4684 tmem.frontswap=0|1 [KNL, XEN]
4685 Default is on (1). Disable the usage of the frontswap
4686 API to send swap pages to the hypervisor. If disabled
4687 the selfballooning and selfshrinking are force disabled.
4689 tmem.selfballooning=0|1 [KNL, XEN]
4690 Default is on (1). Disable the driving of swap pages
4693 tmem.selfshrinking=0|1 [KNL, XEN]
4694 Default is on (1). Partial swapoff that immediately
4695 transfers pages from Xen hypervisor back to the
4696 kernel based on different criteria.
4700 Specify if the kernel should make use of the cpu
4701 topology information if the hardware supports this.
4702 The scheduler will make use of this information and
4703 e.g. base its process migration decisions on it.
4706 topology_updates= [KNL, PPC, NUMA]
4708 Specify if the kernel should ignore (off)
4709 topology updates sent by the hypervisor to this
4714 tpm_suspend_pcr=[HW,TPM]
4715 Format: integer pcr id
4716 Specify that at suspend time, the tpm driver
4717 should extend the specified pcr with zeros,
4718 as a workaround for some chips which fail to
4719 flush the last written pcr on TPM_SaveState.
4720 This will guarantee that all the other pcrs
4723 trace_buf_size=nn[KMG]
4724 [FTRACE] will set tracing buffer size on each cpu.
4726 trace_event=[event-list]
4727 [FTRACE] Set and start specified trace events in order
4728 to facilitate early boot debugging. The event-list is a
4729 comma separated list of trace events to enable. See
4730 also Documentation/trace/events.rst
4732 trace_options=[option-list]
4733 [FTRACE] Enable or disable tracer options at boot.
4734 The option-list is a comma delimited list of options
4735 that can be enabled or disabled just as if you were
4736 to echo the option name into
4738 /sys/kernel/debug/tracing/trace_options
4740 For example, to enable stacktrace option (to dump the
4741 stack trace of each event), add to the command line:
4743 trace_options=stacktrace
4745 See also Documentation/trace/ftrace.rst "trace options"
4749 Have the tracepoints sent to printk as well as the
4750 tracing ring buffer. This is useful for early boot up
4751 where the system hangs or reboots and does not give the
4752 option for reading the tracing buffer or performing a
4753 ftrace_dump_on_oops.
4755 To turn off having tracepoints sent to printk,
4756 echo 0 > /proc/sys/kernel/tracepoint_printk
4757 Note, echoing 1 into this file without the
4758 tracepoint_printk kernel cmdline option has no effect.
4762 Having tracepoints sent to printk() and activating high
4763 frequency tracepoints such as irq or sched, can cause
4764 the system to live lock.
4767 [FTRACE] enable this option to disable tracing when a
4768 warning is hit. This turns off "tracing_on". Tracing can
4769 be enabled again by echoing '1' into the "tracing_on"
4770 file located in /sys/kernel/debug/tracing/
4772 This option is useful, as it disables the trace before
4773 the WARNING dump is called, which prevents the trace to
4774 be filled with content caused by the warning output.
4776 This option can also be set at run time via the sysctl
4777 option: kernel/traceoff_on_warning
4779 transparent_hugepage=
4781 Format: [always|madvise|never]
4782 Can be used to control the default behavior of the system
4783 with respect to transparent hugepages.
4784 See Documentation/admin-guide/mm/transhuge.rst
4787 tsc= Disable clocksource stability checks for TSC.
4789 [x86] reliable: mark tsc clocksource as reliable, this
4790 disables clocksource verification at runtime, as well
4791 as the stability checks done at bootup. Used to enable
4792 high-resolution timer mode on older hardware, and in
4793 virtualized environment.
4794 [x86] noirqtime: Do not use TSC to do irq accounting.
4795 Used to run time disable IRQ_TIME_ACCOUNTING on any
4796 platforms where RDTSC is slow and this accounting
4798 [x86] unstable: mark the TSC clocksource as unstable, this
4799 marks the TSC unconditionally unstable at bootup and
4800 avoids any further wobbles once the TSC watchdog notices.
4801 [x86] nowatchdog: disable clocksource watchdog. Used
4802 in situations with strict latency requirements (where
4803 interruptions from clocksource watchdog are not
4806 turbografx.map[2|3]= [HW,JOY]
4807 TurboGraFX parallel port interface
4809 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4810 See also Documentation/input/devices/joystick-parport.rst
4812 udbg-immortal [PPC] When debugging early kernel crashes that
4813 happen after console_init() and before a proper
4814 console driver takes over, this boot options might
4815 help "seeing" what's going on.
4817 uhash_entries= [KNL,NET]
4818 Set number of hash buckets for UDP/UDP-Lite connections
4821 [USB] Ignore overcurrent events (default N).
4822 Some badly-designed motherboards generate lots of
4823 bogus events, for ports that aren't wired to
4824 anything. Set this parameter to avoid log spamming.
4825 Note that genuine overcurrent events won't be
4829 [X86] Cause panic on unknown NMI.
4831 usbcore.authorized_default=
4832 [USB] Default USB device authorization:
4833 (default -1 = authorized except for wireless USB,
4834 0 = not authorized, 1 = authorized, 2 = authorized
4835 if device connected to internal port)
4837 usbcore.autosuspend=
4838 [USB] The autosuspend time delay (in seconds) used
4839 for newly-detected USB devices (default 2). This
4840 is the time required before an idle device will be
4841 autosuspended. Devices for which the delay is set
4842 to a negative value won't be autosuspended at all.
4844 usbcore.usbfs_snoop=
4845 [USB] Set to log all usbfs traffic (default 0 = off).
4847 usbcore.usbfs_snoop_max=
4848 [USB] Maximum number of bytes to snoop in each URB
4851 usbcore.blinkenlights=
4852 [USB] Set to cycle leds on hubs (default 0 = off).
4854 usbcore.old_scheme_first=
4855 [USB] Start with the old device initialization
4856 scheme, applies only to low and full-speed devices
4859 usbcore.usbfs_memory_mb=
4860 [USB] Memory limit (in MB) for buffers allocated by
4861 usbfs (default = 16, 0 = max = 2047).
4863 usbcore.use_both_schemes=
4864 [USB] Try the other device initialization scheme
4865 if the first one fails (default 1 = enabled).
4867 usbcore.initial_descriptor_timeout=
4868 [USB] Specifies timeout for the initial 64-byte
4869 USB_REQ_GET_DESCRIPTOR request in milliseconds
4870 (default 5000 = 5.0 seconds).
4872 usbcore.nousb [USB] Disable the USB subsystem
4875 [USB] A list of quirk entries to augment the built-in
4876 usb core quirk list. List entries are separated by
4877 commas. Each entry has the form
4878 VendorID:ProductID:Flags. The IDs are 4-digit hex
4879 numbers and Flags is a set of letters. Each letter
4880 will change the built-in quirk; setting it if it is
4881 clear and clearing it if it is set. The letters have
4882 the following meanings:
4883 a = USB_QUIRK_STRING_FETCH_255 (string
4884 descriptors must not be fetched using
4886 b = USB_QUIRK_RESET_RESUME (device can't resume
4887 correctly so reset it instead);
4888 c = USB_QUIRK_NO_SET_INTF (device can't handle
4889 Set-Interface requests);
4890 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
4891 handle its Configuration or Interface
4893 e = USB_QUIRK_RESET (device can't be reset
4894 (e.g morph devices), don't use reset);
4895 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
4896 more interface descriptions than the
4897 bNumInterfaces count, and can't handle
4898 talking to these interfaces);
4899 g = USB_QUIRK_DELAY_INIT (device needs a pause
4900 during initialization, after we read
4901 the device descriptor);
4902 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
4903 high speed and super speed interrupt
4904 endpoints, the USB 2.0 and USB 3.0 spec
4905 require the interval in microframes (1
4906 microframe = 125 microseconds) to be
4907 calculated as interval = 2 ^
4909 Devices with this quirk report their
4910 bInterval as the result of this
4911 calculation instead of the exponent
4912 variable used in the calculation);
4913 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
4914 handle device_qualifier descriptor
4916 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
4917 generates spurious wakeup, ignore
4918 remote wakeup capability);
4919 k = USB_QUIRK_NO_LPM (device can't handle Link
4921 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
4922 (Device reports its bInterval as linear
4923 frames instead of the USB 2.0
4925 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
4926 to be disconnected before suspend to
4927 prevent spurious wakeup);
4928 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
4929 pause after every control message);
4930 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
4931 delay after resetting its port);
4932 Example: quirks=0781:5580:bk,0a5c:5834:gij
4935 [USBHID] The interval which mice are to be polled at.
4938 [USBHID] The interval which joysticks are to be polled at.
4941 [USBHID] The interval which keyboards are to be polled at.
4943 usb-storage.delay_use=
4944 [UMS] The delay in seconds before a new device is
4945 scanned for Logical Units (default 1).
4948 [UMS] A list of quirks entries to supplement or
4949 override the built-in unusual_devs list. List
4950 entries are separated by commas. Each entry has
4951 the form VID:PID:Flags where VID and PID are Vendor
4952 and Product ID values (4-digit hex numbers) and
4953 Flags is a set of characters, each corresponding
4954 to a common usb-storage quirk flag as follows:
4955 a = SANE_SENSE (collect more than 18 bytes
4957 b = BAD_SENSE (don't collect more than 18
4958 bytes of sense data);
4959 c = FIX_CAPACITY (decrease the reported
4960 device capacity by one sector);
4961 d = NO_READ_DISC_INFO (don't use
4962 READ_DISC_INFO command);
4963 e = NO_READ_CAPACITY_16 (don't use
4964 READ_CAPACITY_16 command);
4965 f = NO_REPORT_OPCODES (don't use report opcodes
4967 g = MAX_SECTORS_240 (don't transfer more than
4968 240 sectors at a time, uas only);
4969 h = CAPACITY_HEURISTICS (decrease the
4970 reported device capacity by one
4971 sector if the number is odd);
4972 i = IGNORE_DEVICE (don't bind to this
4974 j = NO_REPORT_LUNS (don't use report luns
4976 l = NOT_LOCKABLE (don't try to lock and
4977 unlock ejectable media);
4978 m = MAX_SECTORS_64 (don't transfer more
4979 than 64 sectors = 32 KB at a time);
4980 n = INITIAL_READ10 (force a retry of the
4981 initial READ(10) command);
4982 o = CAPACITY_OK (accept the capacity
4983 reported by the device);
4984 p = WRITE_CACHE (the device cache is ON
4986 r = IGNORE_RESIDUE (the device reports
4987 bogus residue values);
4988 s = SINGLE_LUN (the device has only one
4990 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4991 commands, uas only);
4992 u = IGNORE_UAS (don't bind to the uas driver);
4993 w = NO_WP_DETECT (don't test whether the
4994 medium is write-protected).
4995 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4996 even if the device claims no cache)
4997 Example: quirks=0419:aaf5:rl,0421:0433:rc
4999 user_debug= [KNL,ARM]
5001 See arch/arm/Kconfig.debug help text.
5002 1 - undefined instruction events
5004 4 - invalid data aborts
5007 Example: user_debug=31
5010 [X86] Flags controlling user PTE allocations.
5012 nohigh = do not allocate PTE pages in
5013 HIGHMEM regardless of setting
5017 On X86_32, this is an alias for vdso32=. Otherwise:
5019 vdso=1: enable VDSO (the default)
5020 vdso=0: disable VDSO mapping
5022 vdso32= [X86] Control the 32-bit vDSO
5023 vdso32=1: enable 32-bit VDSO
5024 vdso32=0 or vdso32=2: disable 32-bit VDSO
5026 See the help text for CONFIG_COMPAT_VDSO for more
5027 details. If CONFIG_COMPAT_VDSO is set, the default is
5028 vdso32=0; otherwise, the default is vdso32=1.
5030 For compatibility with older kernels, vdso32=2 is an
5033 Try vdso32=0 if you encounter an error that says:
5034 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
5037 vector=percpu: enable percpu vector domain
5039 video= [FB] Frame buffer configuration
5040 See Documentation/fb/modedb.rst.
5042 video.brightness_switch_enabled= [0,1]
5043 If set to 1, on receiving an ACPI notify event
5044 generated by hotkey, video driver will adjust brightness
5045 level and then send out the event to user space through
5046 the allocated input device; If set to 0, video driver
5047 will only send out the event without touching backlight
5052 [VMMIO] Memory mapped virtio (platform) device.
5054 <size>@<baseaddr>:<irq>[:<id>]
5056 <size> := size (can use standard suffixes
5058 <baseaddr> := physical base address
5059 <irq> := interrupt number (as passed to
5061 <id> := (optional) platform device id
5063 virtio_mmio.device=1K@0x100b0000:48:7
5065 Can be used multiple times for multiple devices.
5067 vga= [BOOT,X86-32] Select a particular video mode
5068 See Documentation/x86/boot.rst and
5069 Documentation/svga.txt.
5070 Use vga=ask for menu.
5071 This is actually a boot loader parameter; the value is
5072 passed to the kernel using a special protocol.
5074 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
5075 May slow down system boot speed, especially when
5076 enabled on systems with a large amount of memory.
5077 All options are enabled by default, and this
5078 interface is meant to allow for selectively
5079 enabling or disabling specific virtual memory
5082 Available options are:
5083 P Enable page structure init time poisoning
5084 - Disable all of the above options
5086 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
5087 size of <nn>. This can be used to increase the
5088 minimum size (128MB on x86). It can also be used to
5089 decrease the size and leave more room for directly
5092 vmcp_cma=nn[MG] [KNL,S390]
5093 Sets the memory size reserved for contiguous memory
5094 allocations for the vmcp device driver.
5096 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
5099 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
5102 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
5106 Controls the behavior of vsyscalls (i.e. calls to
5107 fixed addresses of 0xffffffffff600x00 from legacy
5108 code). Most statically-linked binaries and older
5109 versions of glibc use these calls. Because these
5110 functions are at fixed addresses, they make nice
5111 targets for exploits that can control RIP.
5113 emulate [default] Vsyscalls turn into traps and are
5114 emulated reasonably safely. The vsyscall
5117 xonly Vsyscalls turn into traps and are
5118 emulated reasonably safely. The vsyscall
5119 page is not readable.
5121 none Vsyscalls don't work at all. This makes
5122 them quite hard to use for exploits but
5123 might break your system.
5125 vt.color= [VT] Default text color.
5126 Format: 0xYX, X = foreground, Y = background.
5127 Default: 0x07 = light gray on black.
5129 vt.cur_default= [VT] Default cursor shape.
5130 Format: 0xCCBBAA, where AA, BB, and CC are the same as
5131 the parameters of the <Esc>[?A;B;Cc escape sequence;
5132 see VGA-softcursor.txt. Default: 2 = underline.
5134 vt.default_blu= [VT]
5135 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
5136 Change the default blue palette of the console.
5137 This is a 16-member array composed of values
5140 vt.default_grn= [VT]
5141 Format: <green0>,<green1>,<green2>,...,<green15>
5142 Change the default green palette of the console.
5143 This is a 16-member array composed of values
5146 vt.default_red= [VT]
5147 Format: <red0>,<red1>,<red2>,...,<red15>
5148 Change the default red palette of the console.
5149 This is a 16-member array composed of values
5155 Set system-wide default UTF-8 mode for all tty's.
5156 Default is 1, i.e. UTF-8 mode is enabled for all
5157 newly opened terminals.
5159 vt.global_cursor_default=
5162 Set system-wide default for whether a cursor
5163 is shown on new VTs. Default is -1,
5164 i.e. cursors will be created by default unless
5165 overridden by individual drivers. 0 will hide
5166 cursors, 1 will display them.
5168 vt.italic= [VT] Default color for italic text; 0-15.
5171 vt.underline= [VT] Default color for underlined text; 0-15.
5174 watchdog timers [HW,WDT] For information on watchdog timers,
5175 see Documentation/watchdog/watchdog-parameters.rst
5176 or other driver-specific files in the
5177 Documentation/watchdog/ directory.
5181 Set the hard lockup detector stall duration
5182 threshold in seconds. The soft lockup detector
5183 threshold is set to twice the value. A value of 0
5184 disables both lockup detectors. Default is 10
5187 workqueue.watchdog_thresh=
5188 If CONFIG_WQ_WATCHDOG is configured, workqueue can
5189 warn stall conditions and dump internal state to
5190 help debugging. 0 disables workqueue stall
5191 detection; otherwise, it's the stall threshold
5192 duration in seconds. The default value is 30 and
5193 it can be updated at runtime by writing to the
5194 corresponding sysfs file.
5196 workqueue.disable_numa
5197 By default, all work items queued to unbound
5198 workqueues are affine to the NUMA nodes they're
5199 issued on, which results in better behavior in
5200 general. If NUMA affinity needs to be disabled for
5201 whatever reason, this option can be used. Note
5202 that this also can be controlled per-workqueue for
5203 workqueues visible under /sys/bus/workqueue/.
5205 workqueue.power_efficient
5206 Per-cpu workqueues are generally preferred because
5207 they show better performance thanks to cache
5208 locality; unfortunately, per-cpu workqueues tend to
5209 be more power hungry than unbound workqueues.
5211 Enabling this makes the per-cpu workqueues which
5212 were observed to contribute significantly to power
5213 consumption unbound, leading to measurably lower
5214 power usage at the cost of small performance
5217 The default value of this parameter is determined by
5218 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
5220 workqueue.debug_force_rr_cpu
5221 Workqueue used to implicitly guarantee that work
5222 items queued without explicit CPU specified are put
5223 on the local CPU. This guarantee is no longer true
5224 and while local CPU is still preferred work items
5225 may be put on foreign CPUs. This debug option
5226 forces round-robin CPU selection to flush out
5227 usages which depend on the now broken guarantee.
5228 When enabled, memory and cache locality will be
5231 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
5232 default x2apic cluster mode on platforms
5235 x86_intel_mid_timer= [X86-32,APBT]
5236 Choose timer option for x86 Intel MID platform.
5237 Two valid options are apbt timer only and lapic timer
5238 plus one apbt timer for broadcast timer.
5239 x86_intel_mid_timer=apbt_only | lapic_and_apbt
5241 xen_512gb_limit [KNL,X86-64,XEN]
5242 Restricts the kernel running paravirtualized under Xen
5243 to use only up to 512 GB of RAM. The reason to do so is
5244 crash analysis tools and Xen tools for doing domain
5245 save/restore/migration must be enabled to handle larger
5248 xen_emul_unplug= [HW,X86,XEN]
5249 Unplug Xen emulated devices
5250 Format: [unplug0,][unplug1]
5251 ide-disks -- unplug primary master IDE devices
5252 aux-ide-disks -- unplug non-primary-master IDE devices
5253 nics -- unplug network devices
5254 all -- unplug all emulated devices (NICs and IDE disks)
5255 unnecessary -- unplugging emulated devices is
5256 unnecessary even if the host did not respond to
5258 never -- do not unplug even if version check succeeds
5260 xen_nopvspin [X86,XEN]
5261 Disables the ticketlock slowpath using Xen PV
5265 Disables the PV optimizations forcing the HVM guest to
5266 run as generic HVM guest with no PV drivers.
5268 xen_scrub_pages= [XEN]
5269 Boolean option to control scrubbing pages before giving them back
5270 to Xen, for use by other domains. Can be also changed at runtime
5271 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
5272 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
5274 xen_timer_slop= [X86-64,XEN]
5275 Set the timer slop (in nanoseconds) for the virtual Xen
5276 timers (default is 100000). This adjusts the minimum
5277 delta of virtualized Xen timers, where lower values
5278 improve timer resolution at the expense of processing
5279 more timer interrupts.
5281 xirc2ps_cs= [NET,PCMCIA]
5283 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
5286 By default on POWER9 and above, the kernel will
5287 natively use the XIVE interrupt controller. This option
5288 allows the fallback firmware mode to be used:
5290 off Fallback to firmware control of XIVE interrupt
5291 controller on both pseries and powernv
5292 platforms. Only useful on POWER9 and above.
5294 xhci-hcd.quirks [USB,KNL]
5295 A hex value specifying bitmask with supplemental xhci
5296 host controller quirks. Meaning of each bit can be
5297 consulted in header drivers/usb/host/xhci.h.
git.samba.org / sfrench / cifs-2.6.git / blob