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.rst, 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.rst 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/admin-guide/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/admin-guide/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 Note: to get most of debug_pagealloc error reports, it's
813 useful to also enable the page_owner functionality.
814 on: enable the feature
816 debugpat [X86] Enable PAT debugging
818 decnet.addr= [HW,NET]
819 Format: <area>[,<node>]
820 See also Documentation/networking/decnet.txt.
823 [same as hugepagesz=] The size of the default
824 HugeTLB page size. This is the size represented by
825 the legacy /proc/ hugepages APIs, used for SHM, and
826 default size when mounting hugetlbfs filesystems.
827 Defaults to the default architecture's huge page size
830 deferred_probe_timeout=
831 [KNL] Debugging option to set a timeout in seconds for
832 deferred probe to give up waiting on dependencies to
833 probe. Only specific dependencies (subsystems or
834 drivers) that have opted in will be ignored. A timeout of 0
835 will timeout at the end of initcalls. This option will also
836 dump out devices still on the deferred probe list after
840 Set number of hash buckets for dentry cache.
842 disable_1tb_segments [PPC]
843 Disables the use of 1TB hash page table segments. This
844 causes the kernel to fall back to 256MB segments which
845 can be useful when debugging issues that require an SLB
849 See Documentation/networking/ipv6.txt.
852 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
853 hardening is enabled for this boot. Hardened
854 usercopy checking is used to protect the kernel
855 from reading or writing beyond known memory
856 allocation boundaries as a proactive defense
857 against bounds-checking flaws in the kernel's
858 copy_to_user()/copy_from_user() interface.
859 on Perform hardened usercopy checks (default).
860 off Disable hardened usercopy checks.
863 Disable RADIX MMU mode on POWER9
866 Disable TLBIE instruction. Currently does not work
867 with KVM, with HASH MMU, or with coherent accelerators.
869 disable_cpu_apicid= [X86,APIC,SMP]
871 The number of initial APIC ID for the
872 corresponding CPU to be disabled at boot,
873 mostly used for the kdump 2nd kernel to
874 disable BSP to wake up multiple CPUs without
875 causing system reset or hang due to sending
878 perf_v4_pmi= [X86,INTEL]
880 Disable Intel PMU counter freezing feature.
881 The feature only exists starting from
882 Arch Perfmon v4 (Skylake and newer).
884 disable_ddw [PPC/PSERIES]
885 Disable Dynamic DMA Window support. Use this if
886 to workaround buggy firmware.
889 See Documentation/networking/ipv6.txt.
891 disable_mtrr_cleanup [X86]
892 The kernel tries to adjust MTRR layout from continuous
893 to discrete, to make X server driver able to add WB
894 entry later. This parameter disables that.
896 disable_mtrr_trim [X86, Intel and AMD only]
897 By default the kernel will trim any uncacheable
898 memory out of your available memory pool based on
899 MTRR settings. This parameter disables that behavior,
900 possibly causing your machine to run very slowly.
902 disable_timer_pin_1 [X86]
903 Disable PIN 1 of APIC timer
904 Can be useful to work around chipset bugs.
906 dis_ucode_ldr [X86] Disable the microcode loader.
908 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
909 this option disables the debugging code at boot.
911 dma_debug_entries=<number>
912 This option allows to tune the number of preallocated
913 entries for DMA-API debugging code. One entry is
914 required per DMA-API allocation. Use this if the
915 DMA-API debugging code disables itself because the
916 architectural default is too low.
918 dma_debug_driver=<driver_name>
919 With this option the DMA-API debugging driver
920 filter feature can be enabled at boot time. Just
921 pass the driver to filter for as the parameter.
922 The filter can be disabled or changed to another
923 driver later using sysfs.
925 driver_async_probe= [KNL]
926 List of driver names to be probed asynchronously.
927 Format: <driver_name1>,<driver_name2>...
929 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
930 Broken monitors, graphic adapters, KVMs and EDIDless
931 panels may send no or incorrect EDID data sets.
932 This parameter allows to specify an EDID data sets
933 in the /lib/firmware directory that are used instead.
934 Generic built-in EDID data sets are used, if one of
935 edid/1024x768.bin, edid/1280x1024.bin,
936 edid/1680x1050.bin, or edid/1920x1080.bin is given
937 and no file with the same name exists. Details and
938 instructions how to build your own EDID data are
939 available in Documentation/driver-api/edid.rst. An EDID
940 data set will only be used for a particular connector,
941 if its name and a colon are prepended to the EDID
942 name. Each connector may use a unique EDID data
943 set by separating the files with a comma. An EDID
944 data set with no connector name will be used for
945 any connectors not explicitly specified.
950 Format: {"off" | "known"}
951 Control how the dt_cpu_ftrs device-tree binding is
952 used for CPU feature discovery and setup (if it
954 off: Do not use it, fall back to legacy cpu table.
955 known: Do not pass through unknown features to guests
956 or userspace, only those that the kernel is aware of.
958 dump_apple_properties [X86]
959 Dump name and content of EFI device properties on
960 x86 Macs. Useful for driver authors to determine
961 what data is available or for reverse-engineering.
963 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
964 module.dyndbg[="val"]
965 Enable debug messages at boot time. See
966 Documentation/admin-guide/dynamic-debug-howto.rst
969 nompx [X86] Disables Intel Memory Protection Extensions.
970 See Documentation/x86/intel_mpx.rst for more
971 information about the feature.
973 nopku [X86] Disable Memory Protection Keys CPU feature found
976 module.async_probe [KNL]
977 Enable asynchronous probe on this module.
979 early_ioremap_debug [KNL]
980 Enable debug messages in early_ioremap support. This
981 is useful for tracking down temporary early mappings
982 which are not unmapped.
984 earlycon= [KNL] Output early console device and options.
986 [ARM64] The early console is determined by the
987 stdout-path property in device tree's chosen node,
988 or determined by the ACPI SPCR table.
990 [X86] When used with no options the early console is
991 determined by the ACPI SPCR table.
993 cdns,<addr>[,options]
994 Start an early, polled-mode console on a Cadence
995 (xuartps) serial port at the specified address. Only
996 supported option is baud rate. If baud rate is not
997 specified, the serial port must already be setup and
1000 uart[8250],io,<addr>[,options]
1001 uart[8250],mmio,<addr>[,options]
1002 uart[8250],mmio32,<addr>[,options]
1003 uart[8250],mmio32be,<addr>[,options]
1004 uart[8250],0x<addr>[,options]
1005 Start an early, polled-mode console on the 8250/16550
1006 UART at the specified I/O port or MMIO address.
1007 MMIO inter-register address stride is either 8-bit
1008 (mmio) or 32-bit (mmio32 or mmio32be).
1009 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1010 to be equivalent to 'mmio'. 'options' are specified
1011 in the same format described for "console=ttyS<n>"; if
1012 unspecified, the h/w is not initialized.
1016 Start an early, polled-mode console on a pl011 serial
1017 port at the specified address. The pl011 serial port
1018 must already be setup and configured. Options are not
1019 yet supported. If 'mmio32' is specified, then only
1020 the driver will use only 32-bit accessors to read/write
1021 the device registers.
1024 Start an early, polled-mode console on a meson serial
1025 port at the specified address. The serial port must
1026 already be setup and configured. Options are not yet
1030 Start an early, polled-mode console on an msm serial
1031 port at the specified address. The serial port
1032 must already be setup and configured. Options are not
1035 msm_serial_dm,<addr>
1036 Start an early, polled-mode console on an msm serial
1037 dm port at the specified address. The serial port
1038 must already be setup and configured. Options are not
1042 Start an early, polled-mode console on a serial port
1043 of an Actions Semi SoC, such as S500 or S900, at the
1044 specified address. The serial port must already be
1045 setup and configured. Options are not yet supported.
1048 Start an early, polled-mode console on a serial port
1049 of an RDA Micro SoC, such as RDA8810PL, at the
1050 specified address. The serial port must already be
1051 setup and configured. Options are not yet supported.
1054 Use RISC-V SBI (Supervisor Binary Interface) for early
1057 smh Use ARM semihosting calls for early console.
1065 Use early console provided by serial driver available
1066 on Samsung SoCs, requires selecting proper type and
1067 a correct base address of the selected UART port. The
1068 serial port must already be setup and configured.
1069 Options are not yet supported.
1072 Start an early, polled-mode console on a lantiq serial
1073 (lqasc) port at the specified address. The serial port
1074 must already be setup and configured. Options are not
1079 Use early console provided by Freescale LP UART driver
1080 found on Freescale Vybrid and QorIQ LS1021A processors.
1081 A valid base address must be provided, and the serial
1082 port must already be setup and configured.
1085 Start an early, polled-mode console on the
1086 Armada 3700 serial port at the specified
1087 address. The serial port must already be setup
1088 and configured. Options are not yet supported.
1091 Start an early, polled-mode console on a Qualcomm
1092 Generic Interface (GENI) based serial port at the
1093 specified address. The serial port must already be
1094 setup and configured. Options are not yet supported.
1097 Start an early, unaccelerated console on the EFI
1098 memory mapped framebuffer (if available). On cache
1099 coherent non-x86 systems that use system memory for
1100 the framebuffer, pass the 'ram' option so that it is
1101 mapped with the correct attributes.
1104 Use early console provided by Freescale LinFlex UART
1105 serial driver for NXP S32V234 SoCs. A valid base
1106 address must be provided, and the serial port must
1107 already be setup and configured.
1109 earlyprintk= [X86,SH,ARM,M68k,S390]
1113 earlyprintk=serial[,ttySn[,baudrate]]
1114 earlyprintk=serial[,0x...[,baudrate]]
1115 earlyprintk=ttySn[,baudrate]
1116 earlyprintk=dbgp[debugController#]
1117 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1118 earlyprintk=xdbc[xhciController#]
1120 earlyprintk is useful when the kernel crashes before
1121 the normal console is initialized. It is not enabled by
1122 default because it has some cosmetic problems.
1124 Append ",keep" to not disable it when the real console
1127 Only one of vga, efi, serial, or usb debug port can
1130 Currently only ttyS0 and ttyS1 may be specified by
1131 name. Other I/O ports may be explicitly specified
1132 on some architectures (x86 and arm at least) by
1133 replacing ttySn with an I/O port address, like this:
1134 earlyprintk=serial,0x1008,115200
1135 You can find the port for a given device in
1136 /proc/tty/driver/serial:
1137 2: uart:ST16650V2 port:00001008 irq:18 ...
1139 Interaction with the standard serial driver is not
1142 The VGA and EFI output is eventually overwritten by
1145 The xen output can only be used by Xen PV guests.
1147 The sclp output can only be used on s390.
1149 The optional "force" to "pciserial" enables use of a
1150 PCI device even when its classcode is not of the
1153 edac_report= [HW,EDAC] Control how to report EDAC event
1154 Format: {"on" | "off" | "force"}
1155 on: enable EDAC to report H/W event. May be overridden
1156 by other higher priority error reporting module.
1157 off: disable H/W event reporting through EDAC.
1158 force: enforce the use of EDAC to report H/W event.
1161 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1164 This is designed to be used in conjunction with
1165 the boot argument: earlyprintk=vga
1168 Format: {"off" | "on" | "skip[mbr]"}
1171 Format: { "old_map", "nochunk", "noruntime", "debug" }
1172 old_map [X86-64]: switch to the old ioremap-based EFI
1173 runtime services mapping. 32-bit still uses this one by
1175 nochunk: disable reading files in "chunks" in the EFI
1176 boot stub, as chunking can cause problems with some
1177 firmware implementations.
1178 noruntime : disable EFI runtime services support
1179 debug: enable misc debug output
1181 efi_no_storage_paranoia [EFI; X86]
1182 Using this parameter you can use more than 50% of
1183 your efi variable storage. Use this parameter only if
1184 you are really sure that your UEFI does sane gc and
1185 fulfills the spec otherwise your board may brick.
1187 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1188 Add arbitrary attribute to specific memory range by
1189 updating original EFI memory map.
1190 Region of memory which aa attribute is added to is
1192 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1193 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1194 attribute is added to range 0x100000000-0x180000000 and
1195 0x10a0000000-0x1120000000.
1197 Using this parameter you can do debugging of EFI memmap
1198 related feature. For example, you can do debugging of
1199 Address Range Mirroring feature even if your box
1202 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1203 that is to be dynamically loaded by Linux. If there are
1204 multiple variables with the same name but with different
1205 vendor GUIDs, all of them will be loaded. See
1206 Documentation/admin-guide/acpi/ssdt-overlays.rst for details.
1209 eisa_irq_edge= [PARISC,HW]
1210 See header of drivers/parisc/eisa.c.
1213 See comment before function elanfreq_setup() in
1214 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1216 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1217 Specifies physical address of start of kernel core
1218 image elf header and optionally the size. Generally
1219 kexec loader will pass this option to capture kernel.
1220 See Documentation/admin-guide/kdump/kdump.rst for details.
1222 enable_mtrr_cleanup [X86]
1223 The kernel tries to adjust MTRR layout from continuous
1224 to discrete, to make X server driver able to add WB
1225 entry later. This parameter enables that.
1227 enable_timer_pin_1 [X86]
1228 Enable PIN 1 of APIC timer
1229 Can be useful to work around chipset bugs
1230 (in particular on some ATI chipsets).
1231 The kernel tries to set a reasonable default.
1233 enforcing [SELINUX] Set initial enforcing status.
1235 See security/selinux/Kconfig help text.
1236 0 -- permissive (log only, no denials).
1237 1 -- enforcing (deny and log).
1239 Value can be changed at runtime via /selinux/enforce.
1242 Disable Error Record Serialization Table (ERST)
1245 ether= [HW,NET] Ethernet cards parameters
1246 This option is obsoleted by the "netdev=" option, which
1247 has equivalent usage. See its documentation for details.
1251 Permit 'security.evm' to be updated regardless of
1252 current integrity status.
1256 fail_make_request=[KNL]
1257 General fault injection mechanism.
1258 Format: <interval>,<probability>,<space>,<times>
1259 See also Documentation/fault-injection/.
1262 See Documentation/admin-guide/blockdev/floppy.rst.
1264 force_pal_cache_flush
1265 [IA-64] Avoid check_sal_cache_flush which may hang on
1266 buggy SAL_CACHE_FLUSH implementations. Using this
1267 parameter will force ia64_sal_cache_flush to call
1268 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1271 Forcefully enable Physical Address Extension (PAE).
1272 Many Pentium M systems disable PAE but may have a
1273 functionally usable PAE implementation.
1274 Warning: use of this parameter will taint the kernel
1275 and may cause unknown problems.
1278 [FTRACE] will set and start the specified tracer
1279 as early as possible in order to facilitate early
1282 ftrace_dump_on_oops[=orig_cpu]
1283 [FTRACE] will dump the trace buffers on oops.
1284 If no parameter is passed, ftrace will dump
1285 buffers of all CPUs, but if you pass orig_cpu, it will
1286 dump only the buffer of the CPU that triggered the
1289 ftrace_filter=[function-list]
1290 [FTRACE] Limit the functions traced by the function
1291 tracer at boot up. function-list is a comma separated
1292 list of functions. This list can be changed at run
1293 time by the set_ftrace_filter file in the debugfs
1296 ftrace_notrace=[function-list]
1297 [FTRACE] Do not trace the functions specified in
1298 function-list. This list can be changed at run time
1299 by the set_ftrace_notrace file in the debugfs
1302 ftrace_graph_filter=[function-list]
1303 [FTRACE] Limit the top level callers functions traced
1304 by the function graph tracer at boot up.
1305 function-list is a comma separated list of functions
1306 that can be changed at run time by the
1307 set_graph_function file in the debugfs tracing directory.
1309 ftrace_graph_notrace=[function-list]
1310 [FTRACE] Do not trace from the functions specified in
1311 function-list. This list is a comma separated list of
1312 functions that can be changed at run time by the
1313 set_graph_notrace file in the debugfs tracing directory.
1315 ftrace_graph_max_depth=<uint>
1316 [FTRACE] Used with the function graph tracer. This is
1317 the max depth it will trace into a function. This value
1318 can be changed at run time by the max_graph_depth file
1319 in the tracefs tracing directory. default: 0 (no limit)
1322 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1323 support via parallel port (up to 5 devices per port)
1324 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1325 See also Documentation/input/devices/joystick-parport.rst
1329 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1333 gcov_persist= [GCOV] When non-zero (default), profiling data for
1334 kernel modules is saved and remains accessible via
1335 debugfs, even when the module is unloaded/reloaded.
1336 When zero, profiling data is discarded and associated
1337 debugfs files are removed at module unload time.
1339 goldfish [X86] Enable the goldfish android emulator platform.
1340 Don't use this when you are not running on the
1343 gpt [EFI] Forces disk with valid GPT signature but
1344 invalid Protective MBR to be treated as GPT. If the
1345 primary GPT is corrupted, it enables the backup/alternate
1346 GPT to be used instead.
1348 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1349 the "Enable 0" bit of the configuration register.
1352 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1353 the "Enable 0" bit of the configuration register.
1356 grcan.select= [HW] Select which physical interface to use.
1359 grcan.txsize= [HW] Sets the size of the tx buffer.
1360 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1362 grcan.rxsize= [HW] Sets the size of the rx buffer.
1363 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1366 gpio-mockup.gpio_mockup_ranges
1367 [HW] Sets the ranges of gpiochip of for this device.
1368 Format: <start1>,<end1>,<start2>,<end2>...
1370 hardlockup_all_cpu_backtrace=
1371 [KNL] Should the hard-lockup detector generate
1372 backtraces on all cpus.
1375 hashdist= [KNL,NUMA] Large hashes allocated during boot
1376 are distributed across NUMA nodes. Defaults on
1377 for 64-bit NUMA, off otherwise.
1378 Format: 0 | 1 (for off | on)
1380 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1382 hd= [EIDE] (E)IDE hard drive subsystem geometry
1383 Format: <cyl>,<head>,<sect>
1386 Disable Hardware Error Source Table (HEST) support;
1387 corresponding firmware-first mode error processing
1388 logic will be disabled.
1390 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1391 size of <nn>. This works even on boxes that have no
1392 highmem otherwise. This also works to reduce highmem
1393 size on bigger boxes.
1395 highres= [KNL] Enable/disable high resolution timer mode.
1396 Valid parameters: "on", "off"
1401 hpet= [X86-32,HPET] option to control HPET usage
1402 Format: { enable (default) | disable | force |
1404 disable: disable HPET and use PIT instead
1405 force: allow force enabled of undocumented chips (ICH4,
1407 verbose: show contents of HPET registers during setup
1409 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1410 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1412 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1413 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1414 On x86-64 and powerpc, this option can be specified
1415 multiple times interleaved with hugepages= to reserve
1416 huge pages of different sizes. Valid pages sizes on
1417 x86-64 are 2M (when the CPU supports "pse") and 1G
1418 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1421 [KNL] Should the hung task detector generate panics.
1424 A nonzero value instructs the kernel to panic when a
1425 hung task is detected. The default value is controlled
1426 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1427 option. The value selected by this boot parameter can
1428 be changed later by the kernel.hung_task_panic sysctl.
1430 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1431 terminal devices. Valid values: 0..8
1432 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1433 If specified, z/VM IUCV HVC accepts connections
1434 from listed z/VM user IDs only.
1436 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations
1437 which allow the hypervisor to 'idle' the
1438 guest on lock contention.
1441 Do not unregister boot console at start. This is only
1442 useful for debugging when something happens in the window
1443 between unregistering the boot console and initializing
1446 i2c_bus= [HW] Override the default board specific I2C bus speed
1447 or register an additional I2C bus that is not
1448 registered from board initialization code.
1452 i8042.debug [HW] Toggle i8042 debug mode
1453 i8042.unmask_kbd_data
1454 [HW] Enable printing of interrupt data from the KBD port
1455 (disabled by default, and as a pre-condition
1456 requires that i8042.debug=1 be enabled)
1457 i8042.direct [HW] Put keyboard port into non-translated mode
1458 i8042.dumbkbd [HW] Pretend that controller can only read data from
1459 keyboard and cannot control its state
1460 (Don't attempt to blink the leds)
1461 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1462 i8042.nokbd [HW] Don't check/create keyboard port
1463 i8042.noloop [HW] Disable the AUX Loopback command while probing
1465 i8042.nomux [HW] Don't check presence of an active multiplexing
1467 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1469 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1470 i8042.reset [HW] Reset the controller during init, cleanup and
1471 suspend-to-ram transitions, only during s2r
1472 transitions, or never reset
1473 Format: { 1 | Y | y | 0 | N | n }
1474 1, Y, y: always reset controller
1475 0, N, n: don't ever reset controller
1476 Default: only on s2r transitions on x86; most other
1477 architectures force reset to be always executed
1478 i8042.unlock [HW] Unlock (ignore) the keylock
1479 i8042.kbdreset [HW] Reset device connected to KBD port
1483 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1484 indicates that the driver is running on unsupported
1486 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1487 does not match list of supported models.
1489 [HW] Report power status in /proc/i8k
1490 (disabled by default)
1491 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1494 i915.invert_brightness=
1495 [DRM] Invert the sense of the variable that is used to
1496 set the brightness of the panel backlight. Normally a
1497 brightness value of 0 indicates backlight switched off,
1498 and the maximum of the brightness value sets the backlight
1499 to maximum brightness. If this parameter is set to 0
1500 (default) and the machine requires it, or this parameter
1501 is set to 1, a brightness value of 0 sets the backlight
1502 to maximum brightness, and the maximum of the brightness
1503 value switches the backlight off.
1504 -1 -- never invert brightness
1505 0 -- machine default
1506 1 -- force brightness inversion
1509 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1511 ide-core.nodma= [HW] (E)IDE subsystem
1512 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1513 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1514 .cdrom .chs .ignore_cable are additional options
1515 See Documentation/ide/ide.rst.
1517 ide-generic.probe-mask= [HW] (E)IDE subsystem
1519 Probe mask for legacy ISA IDE ports. Depending on
1520 platform up to 6 ports are supported, enabled by
1521 setting corresponding bits in the mask to 1. The
1522 default value is 0x0, which has a special meaning.
1523 On systems that have PCI, it triggers scanning the
1524 PCI bus for the first and the second port, which
1525 are then probed. On systems without PCI the value
1526 of 0x0 enables probing the two first ports as if it
1529 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1530 Claim all unknown PCI IDE storage controllers.
1533 Format: idle=poll, idle=halt, idle=nomwait
1534 Poll forces a polling idle loop that can slightly
1535 improve the performance of waking up a idle CPU, but
1536 will use a lot of power and make the system run hot.
1538 idle=halt: Halt is forced to be used for CPU idle.
1539 In such case C2/C3 won't be used again.
1540 idle=nomwait: Disable mwait for CPU C-states
1542 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1543 Format: { strict | legacy | 2008 | relaxed }
1546 Choose which programs will be accepted for execution
1547 based on the IEEE 754 NaN encoding(s) supported by
1548 the FPU and the NaN encoding requested with the value
1549 of an ELF file header flag individually set by each
1550 binary. Hardware implementations are permitted to
1551 support either or both of the legacy and the 2008 NaN
1554 Available settings are as follows:
1555 strict accept binaries that request a NaN encoding
1556 supported by the FPU
1557 legacy only accept legacy-NaN binaries, if supported
1559 2008 only accept 2008-NaN binaries, if supported
1561 relaxed accept any binaries regardless of whether
1562 supported by the FPU
1564 The FPU emulator is always able to support both NaN
1565 encodings, so if no FPU hardware is present or it has
1566 been disabled with 'nofpu', then the settings of
1567 'legacy' and '2008' strap the emulator accordingly,
1568 'relaxed' straps the emulator for both legacy-NaN and
1569 2008-NaN, whereas 'strict' enables legacy-NaN only on
1570 legacy processors and both NaN encodings on MIPS32 or
1573 The setting for ABS.fmt/NEG.fmt instruction execution
1574 mode generally follows that for the NaN encoding,
1575 except where unsupported by hardware.
1577 ignore_loglevel [KNL]
1578 Ignore loglevel setting - this will print /all/
1579 kernel messages to the console. Useful for debugging.
1580 We also add it as printk module parameter, so users
1581 could change it dynamically, usually by
1582 /sys/module/printk/parameters/ignore_loglevel.
1585 Ignore RLIMIT_DATA setting for data mappings,
1586 print warning at first misuse. Can be changed via
1587 /sys/module/kernel/parameters/ignore_rlimit_data.
1589 ihash_entries= [KNL]
1590 Set number of hash buckets for inode cache.
1592 ima_appraise= [IMA] appraise integrity measurements
1593 Format: { "off" | "enforce" | "fix" | "log" }
1596 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead.
1597 The builtin appraise policy appraises all files
1600 ima_canonical_fmt [IMA]
1601 Use the canonical format for the binary runtime
1602 measurements, instead of host native format.
1605 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1609 The list of supported hash algorithms is defined
1610 in crypto/hash_info.h.
1613 The builtin policies to load during IMA setup.
1614 Format: "tcb | appraise_tcb | secure_boot |
1617 The "tcb" policy measures all programs exec'd, files
1618 mmap'd for exec, and all files opened with the read
1619 mode bit set by either the effective uid (euid=0) or
1622 The "appraise_tcb" policy appraises the integrity of
1623 all files owned by root.
1625 The "secure_boot" policy appraises the integrity
1626 of files (eg. kexec kernel image, kernel modules,
1627 firmware, policy, etc) based on file signatures.
1629 The "fail_securely" policy forces file signature
1630 verification failure also on privileged mounted
1631 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1634 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1635 Load a policy which meets the needs of the Trusted
1636 Computing Base. This means IMA will measure all
1637 programs exec'd, files mmap'd for exec, and all files
1638 opened for read by uid=0.
1641 Select one of defined IMA measurements template formats.
1642 Formats: { "ima" | "ima-ng" | "ima-sig" }
1646 [IMA] Define a custom template format.
1647 Format: { "field1|...|fieldN" }
1649 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1650 Format: <min_file_size>
1651 Set the minimal file size for using asynchronous hash.
1652 If left unspecified, ahash usage is disabled.
1654 ahash performance varies for different data sizes on
1655 different crypto accelerators. This option can be used
1656 to achieve the best performance for a particular HW.
1658 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1660 Set hashing buffer size. Default: 4k.
1662 ahash performance varies for different chunk sizes on
1663 different crypto accelerators. This option can be used
1664 to achieve best performance for particular HW.
1668 Run specified binary instead of /sbin/init as init
1671 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1672 for working out where the kernel is dying during
1675 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1676 initcall functions. Useful for debugging built-in
1677 modules and initcalls.
1679 initrd= [BOOT] Specify the location of the initial ramdisk
1681 init_on_alloc= [MM] Fill newly allocated pages and heap objects with
1684 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
1686 init_on_free= [MM] Fill freed pages and heap objects with zeroes.
1688 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.
1690 init_pkru= [x86] Specify the default memory protection keys rights
1691 register contents for all processes. 0x55555554 by
1692 default (disallow access to all but pkey 0). Can
1693 override in debugfs after boot.
1695 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1698 int_pln_enable [x86] Enable power limit notification interrupt
1700 integrity_audit=[IMA]
1701 Format: { "0" | "1" }
1702 0 -- basic integrity auditing messages. (Default)
1703 1 -- additional integrity auditing messages.
1705 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1707 Enable intel iommu driver.
1709 Disable intel iommu driver.
1710 igfx_off [Default Off]
1711 By default, gfx is mapped as normal device. If a gfx
1712 device has a dedicated DMAR unit, the DMAR unit is
1713 bypassed by not enabling DMAR with this option. In
1714 this case, gfx device will use physical address for
1717 With this option iommu will not optimize to look
1718 for io virtual address below 32-bit forcing dual
1719 address cycle on pci bus for cards supporting greater
1720 than 32-bit addressing. The default is to look
1721 for translation below 32-bit and if not available
1722 then look in the higher range.
1723 strict [Default Off]
1724 With this option on every unmap_single operation will
1725 result in a hardware IOTLB flush operation as opposed
1726 to batching them for performance.
1727 sp_off [Default Off]
1728 By default, super page will be supported if Intel IOMMU
1729 has the capability. With this option, super page will
1732 By default, scalable mode will be disabled even if the
1733 hardware advertises that it has support for the scalable
1734 mode translation. With this option set, scalable mode
1735 will be used on hardware which claims to support it.
1736 tboot_noforce [Default Off]
1737 Do not force the Intel IOMMU enabled under tboot.
1738 By default, tboot will force Intel IOMMU on, which
1739 could harm performance of some high-throughput
1740 devices like 40GBit network cards, even if identity
1742 Note that using this option lowers the security
1743 provided by tboot because it makes the system
1744 vulnerable to DMA attacks.
1745 nobounce [Default off]
1746 Disable bounce buffer for unstrusted devices such as
1747 the Thunderbolt devices. This will treat the untrusted
1748 devices as the trusted ones, hence might expose security
1749 risks of DMA attacks.
1751 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1752 0 disables intel_idle and fall back on acpi_idle.
1753 1 to 9 specify maximum depth of C-state.
1757 Do not enable intel_pstate as the default
1758 scaling driver for the supported processors
1760 Use intel_pstate as a scaling driver, but configure it
1761 to work with generic cpufreq governors (instead of
1762 enabling its internal governor). This mode cannot be
1763 used along with the hardware-managed P-states (HWP)
1766 Enable intel_pstate on systems that prohibit it by default
1767 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1768 instead of acpi-cpufreq may disable platform features, such
1769 as thermal controls and power capping, that rely on ACPI
1770 P-States information being indicated to OSPM and therefore
1771 should be used with caution. This option does not work with
1772 processors that aren't supported by the intel_pstate driver
1773 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1775 Do not enable hardware P state control (HWP)
1778 Only load intel_pstate on systems which support
1779 hardware P state control (HWP) if available.
1781 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1782 Description Table, specifies preferred power management
1783 profile as "Enterprise Server" or "Performance Server",
1784 then this feature is turned on by default.
1786 Allow per-logical-CPU P-State performance control limits using
1787 cpufreq sysfs interface
1789 intremap= [X86-64, Intel-IOMMU]
1790 on enable Interrupt Remapping (default)
1791 off disable Interrupt Remapping
1792 nosid disable Source ID checking
1794 BIOS x2APIC opt-out request will be ignored
1795 nopost disable Interrupt Posting
1797 iomem= Disable strict checking of access to MMIO memory
1798 strict regions from userspace.
1813 nobypass [PPC/POWERNV]
1814 Disable IOMMU bypass, using IOMMU for PCI devices.
1816 iommu.strict= [ARM64] Configure TLB invalidation behaviour
1817 Format: { "0" | "1" }
1819 Request that DMA unmap operations use deferred
1820 invalidation of hardware TLBs, for increased
1821 throughput at the cost of reduced device isolation.
1822 Will fall back to strict mode if not supported by
1823 the relevant IOMMU driver.
1824 1 - Strict mode (default).
1825 DMA unmap operations invalidate IOMMU hardware TLBs
1829 [ARM64, X86] Configure DMA to bypass the IOMMU by default.
1830 Format: { "0" | "1" }
1831 0 - Use IOMMU translation for DMA.
1832 1 - Bypass the IOMMU for DMA.
1833 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
1835 io7= [HW] IO7 for Marvel based alpha systems
1836 See comment before marvel_specify_io7 in
1837 arch/alpha/kernel/core_marvel.c.
1839 io_delay= [X86] I/O delay method
1841 Standard port 0x80 based delay
1843 Alternate port 0xed based delay (needed on some systems)
1845 Simple two microseconds delay
1850 See Documentation/filesystems/nfs/nfsroot.txt.
1852 ipcmni_extend [KNL] Extend the maximum number of unique System V
1853 IPC identifiers from 32,768 to 16,777,216.
1855 irqaffinity= [SMP] Set the default irq affinity mask
1856 The argument is a cpu list, as described above.
1858 irqchip.gicv2_force_probe=
1861 Force the kernel to look for the second 4kB page
1862 of a GICv2 controller even if the memory range
1863 exposed by the device tree is too small.
1865 irqchip.gicv3_nolpi=
1867 Force the kernel to ignore the availability of
1868 LPIs (and by consequence ITSs). Intended for system
1869 that use the kernel as a bootloader, and thus want
1870 to let secondary kernels in charge of setting up
1873 irqchip.gicv3_pseudo_nmi= [ARM64]
1874 Enables support for pseudo-NMIs in the kernel. This
1875 requires the kernel to be built with
1876 CONFIG_ARM64_PSEUDO_NMI.
1879 When an interrupt is not handled search all handlers
1880 for it. Intended to get systems with badly broken
1884 When an interrupt is not handled search all handlers
1885 for it. Also check all handlers each timer
1886 interrupt. Intended to get systems with badly broken
1890 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1892 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1893 [Deprecated - use cpusets instead]
1894 Format: [flag-list,]<cpu-list>
1896 Specify one or more CPUs to isolate from disturbances
1897 specified in the flag list (default: domain):
1900 Disable the tick when a single task runs.
1902 A residual 1Hz tick is offloaded to workqueues, which you
1903 need to affine to housekeeping through the global
1904 workqueue's affinity configured via the
1905 /sys/devices/virtual/workqueue/cpumask sysfs file, or
1906 by using the 'domain' flag described below.
1908 NOTE: by default the global workqueue runs on all CPUs,
1909 so to protect individual CPUs the 'cpumask' file has to
1910 be configured manually after bootup.
1913 Isolate from the general SMP balancing and scheduling
1914 algorithms. Note that performing domain isolation this way
1915 is irreversible: it's not possible to bring back a CPU to
1916 the domains once isolated through isolcpus. It's strongly
1917 advised to use cpusets instead to disable scheduler load
1918 balancing through the "cpuset.sched_load_balance" file.
1919 It offers a much more flexible interface where CPUs can
1920 move in and out of an isolated set anytime.
1922 You can move a process onto or off an "isolated" CPU via
1923 the CPU affinity syscalls or cpuset.
1924 <cpu number> begins at 0 and the maximum value is
1925 "number of CPUs in system - 1".
1927 The format of <cpu-list> is described above.
1933 ivrs_ioapic [HW,X86_64]
1934 Provide an override to the IOAPIC-ID<->DEVICE-ID
1935 mapping provided in the IVRS ACPI table. For
1936 example, to map IOAPIC-ID decimal 10 to
1937 PCI device 00:14.0 write the parameter as:
1938 ivrs_ioapic[10]=00:14.0
1940 ivrs_hpet [HW,X86_64]
1941 Provide an override to the HPET-ID<->DEVICE-ID
1942 mapping provided in the IVRS ACPI table. For
1943 example, to map HPET-ID decimal 0 to
1944 PCI device 00:14.0 write the parameter as:
1945 ivrs_hpet[0]=00:14.0
1947 ivrs_acpihid [HW,X86_64]
1948 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1949 mapping provided in the IVRS ACPI table. For
1950 example, to map UART-HID:UID AMD0020:0 to
1951 PCI device 00:14.5 write the parameter as:
1952 ivrs_acpihid[00:14.5]=AMD0020:0
1954 js= [HW,JOY] Analog joystick
1955 See Documentation/input/joydev/joystick.rst.
1958 When CONFIG_RANDOMIZE_BASE is set, this disables
1959 kernel and module base offset ASLR (Address Space
1960 Layout Randomization).
1963 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1964 report on every invalid memory access. Without this
1965 parameter KASAN will print report only for the first
1970 kernelcore= [KNL,X86,IA-64,PPC]
1971 Format: nn[KMGTPE] | nn% | "mirror"
1972 This parameter specifies the amount of memory usable by
1973 the kernel for non-movable allocations. The requested
1974 amount is spread evenly throughout all nodes in the
1975 system as ZONE_NORMAL. The remaining memory is used for
1976 movable memory in its own zone, ZONE_MOVABLE. In the
1977 event, a node is too small to have both ZONE_NORMAL and
1978 ZONE_MOVABLE, kernelcore memory will take priority and
1979 other nodes will have a larger ZONE_MOVABLE.
1981 ZONE_MOVABLE is used for the allocation of pages that
1982 may be reclaimed or moved by the page migration
1983 subsystem. Note that allocations like PTEs-from-HighMem
1984 still use the HighMem zone if it exists, and the Normal
1985 zone if it does not.
1987 It is possible to specify the exact amount of memory in
1988 the form of "nn[KMGTPE]", a percentage of total system
1989 memory in the form of "nn%", or "mirror". If "mirror"
1990 option is specified, mirrored (reliable) memory is used
1991 for non-movable allocations and remaining memory is used
1992 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
1993 are exclusive, so you cannot specify multiple forms.
1995 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1996 Format: <Controller#>[,poll interval]
1997 The controller # is the number of the ehci usb debug
1998 port as it is probed via PCI. The poll interval is
1999 optional and is the number seconds in between
2000 each poll cycle to the debug port in case you need
2001 the functionality for interrupting the kernel with
2002 gdb or control-c on the dbgp connection. When
2003 not using this parameter you use sysrq-g to break into
2004 the kernel debugger.
2006 kgdboc= [KGDB,HW] kgdb over consoles.
2007 Requires a tty driver that supports console polling,
2008 or a supported polling keyboard driver (non-usb).
2009 Serial only format: <serial_device>[,baud]
2010 keyboard only format: kbd
2011 keyboard and serial format: kbd,<serial_device>[,baud]
2012 Optional Kernel mode setting:
2013 kms, kbd format: kms,kbd
2014 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
2016 kgdbwait [KGDB] Stop kernel execution and enter the
2017 kernel debugger at the earliest opportunity.
2019 kmac= [MIPS] korina ethernet MAC address.
2020 Configure the RouterBoard 532 series on-chip
2021 Ethernet adapter MAC address.
2023 kmemleak= [KNL] Boot-time kmemleak enable/disable
2024 Valid arguments: on, off
2026 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
2029 kprobe_event=[probe-list]
2030 [FTRACE] Add kprobe events and enable at boot time.
2031 The probe-list is a semicolon delimited list of probe
2032 definitions. Each definition is same as kprobe_events
2033 interface, but the parameters are comma delimited.
2034 For example, to add a kprobe event on vfs_read with
2035 arg1 and arg2, add to the command line;
2037 kprobe_event=p,vfs_read,$arg1,$arg2
2039 See also Documentation/trace/kprobetrace.rst "Kernel
2040 Boot Parameter" section.
2042 kpti= [ARM64] Control page table isolation of user
2043 and kernel address spaces.
2044 Default: enabled on cores which need mitigation.
2048 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
2049 Default is 0 (don't ignore, but inject #GP)
2051 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
2052 Default is false (don't support).
2054 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
2059 [KVM] Controls the software workaround for the
2060 X86_BUG_ITLB_MULTIHIT bug.
2061 force : Always deploy workaround.
2062 off : Never deploy workaround.
2063 auto : Deploy workaround based on the presence of
2064 X86_BUG_ITLB_MULTIHIT.
2068 If the software workaround is enabled for the host,
2069 guests do need not to enable it for nested guests.
2071 kvm.nx_huge_pages_recovery_ratio=
2072 [KVM] Controls how many 4KiB pages are periodically zapped
2073 back to huge pages. 0 disables the recovery, otherwise if
2074 the value is N KVM will zap 1/Nth of the 4KiB pages every
2075 minute. The default is 60.
2077 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
2078 Default is 1 (enabled)
2080 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
2082 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
2084 kvm-arm.vgic_v3_group0_trap=
2085 [KVM,ARM] Trap guest accesses to GICv3 group-0
2088 kvm-arm.vgic_v3_group1_trap=
2089 [KVM,ARM] Trap guest accesses to GICv3 group-1
2092 kvm-arm.vgic_v3_common_trap=
2093 [KVM,ARM] Trap guest accesses to GICv3 common
2096 kvm-arm.vgic_v4_enable=
2097 [KVM,ARM] Allow use of GICv4 for direct injection of
2100 kvm-intel.ept= [KVM,Intel] Disable extended page tables
2101 (virtualized MMU) support on capable Intel chips.
2102 Default is 1 (enabled)
2104 kvm-intel.emulate_invalid_guest_state=
2105 [KVM,Intel] Enable emulation of invalid guest states
2106 Default is 0 (disabled)
2108 kvm-intel.flexpriority=
2109 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
2110 Default is 1 (enabled)
2113 [KVM,Intel] Enable VMX nesting (nVMX).
2114 Default is 0 (disabled)
2116 kvm-intel.unrestricted_guest=
2117 [KVM,Intel] Disable unrestricted guest feature
2118 (virtualized real and unpaged mode) on capable
2119 Intel chips. Default is 1 (enabled)
2121 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2124 Valid arguments: never, cond, always
2126 always: L1D cache flush on every VMENTER.
2127 cond: Flush L1D on VMENTER only when the code between
2128 VMEXIT and VMENTER can leak host memory.
2129 never: Disables the mitigation
2131 Default is cond (do L1 cache flush in specific instances)
2133 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2134 feature (tagged TLBs) on capable Intel chips.
2135 Default is 1 (enabled)
2137 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2140 The kernel PTE inversion protection is unconditionally
2141 enabled and cannot be disabled.
2144 Provides all available mitigations for the
2145 L1TF vulnerability. Disables SMT and
2146 enables all mitigations in the
2147 hypervisors, i.e. unconditional L1D flush.
2149 SMT control and L1D flush control via the
2150 sysfs interface is still possible after
2151 boot. Hypervisors will issue a warning
2152 when the first VM is started in a
2153 potentially insecure configuration,
2154 i.e. SMT enabled or L1D flush disabled.
2157 Same as 'full', but disables SMT and L1D
2158 flush runtime control. Implies the
2159 'nosmt=force' command line option.
2160 (i.e. sysfs control of SMT is disabled.)
2163 Leaves SMT enabled and enables the default
2164 hypervisor mitigation, i.e. conditional
2167 SMT control and L1D flush control via the
2168 sysfs interface is still possible after
2169 boot. Hypervisors will issue a warning
2170 when the first VM is started in a
2171 potentially insecure configuration,
2172 i.e. SMT enabled or L1D flush disabled.
2176 Disables SMT and enables the default
2177 hypervisor mitigation.
2179 SMT control and L1D flush control via the
2180 sysfs interface is still possible after
2181 boot. Hypervisors will issue a warning
2182 when the first VM is started in a
2183 potentially insecure configuration,
2184 i.e. SMT enabled or L1D flush disabled.
2187 Same as 'flush', but hypervisors will not
2188 warn when a VM is started in a potentially
2189 insecure configuration.
2192 Disables hypervisor mitigations and doesn't
2194 It also drops the swap size and available
2195 RAM limit restriction on both hypervisor and
2200 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
2206 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2209 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2210 value for LAPIC timer one-shot implementation. Default
2211 back to the programmable timer unit in the LAPIC.
2213 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2216 libata.dma= [LIBATA] DMA control
2217 libata.dma=0 Disable all PATA and SATA DMA
2218 libata.dma=1 PATA and SATA Disk DMA only
2219 libata.dma=2 ATAPI (CDROM) DMA only
2220 libata.dma=4 Compact Flash DMA only
2221 Combinations also work, so libata.dma=3 enables DMA
2222 for disks and CDROMs, but not CFs.
2224 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2225 libata.ignore_hpa=0 keep BIOS limits (default)
2226 libata.ignore_hpa=1 ignore limits, using full disk
2228 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2232 libata.force= [LIBATA] Force configurations. The format is comma
2233 separated list of "[ID:]VAL" where ID is
2234 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2235 matching port, link or device. Basically, it matches
2236 the ATA ID string printed on console by libata. If
2237 the whole ID part is omitted, the last PORT and DEVICE
2238 values are used. If ID hasn't been specified yet, the
2239 configuration applies to all ports, links and devices.
2241 If only DEVICE is omitted, the parameter applies to
2242 the port and all links and devices behind it. DEVICE
2243 number of 0 either selects the first device or the
2244 first fan-out link behind PMP device. It does not
2245 select the host link. DEVICE number of 15 selects the
2246 host link and device attached to it.
2248 The VAL specifies the configuration to force. As long
2249 as there's no ambiguity shortcut notation is allowed.
2250 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2251 The following configurations can be forced.
2253 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2254 Any ID with matching PORT is used.
2256 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2258 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2259 udma[/][16,25,33,44,66,100,133] notation is also
2262 * [no]ncq: Turn on or off NCQ.
2264 * [no]ncqtrim: Turn off queued DSM TRIM.
2266 * nohrst, nosrst, norst: suppress hard, soft
2269 * rstonce: only attempt one reset during
2270 hot-unplug link recovery
2272 * dump_id: dump IDENTIFY data.
2274 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2276 * disable: Disable this device.
2278 If there are multiple matching configurations changing
2279 the same attribute, the last one is used.
2281 memblock=debug [KNL] Enable memblock debug messages.
2283 load_ramdisk= [RAM] List of ramdisks to load from floppy
2284 See Documentation/admin-guide/blockdev/ramdisk.rst.
2286 lockd.nlm_grace_period=P [NFS] Assign grace period.
2289 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2292 lockd.nlm_timeout=T [NFS] Assign timeout value.
2295 lockd.nlm_udpport=M [NFS] Assign UDP port.
2298 lockdown= [SECURITY]
2299 { integrity | confidentiality }
2300 Enable the kernel lockdown feature. If set to
2301 integrity, kernel features that allow userland to
2302 modify the running kernel are disabled. If set to
2303 confidentiality, kernel features that allow userland
2304 to extract confidential information from the kernel
2307 locktorture.nreaders_stress= [KNL]
2308 Set the number of locking read-acquisition kthreads.
2309 Defaults to being automatically set based on the
2310 number of online CPUs.
2312 locktorture.nwriters_stress= [KNL]
2313 Set the number of locking write-acquisition kthreads.
2315 locktorture.onoff_holdoff= [KNL]
2316 Set time (s) after boot for CPU-hotplug testing.
2318 locktorture.onoff_interval= [KNL]
2319 Set time (s) between CPU-hotplug operations, or
2320 zero to disable CPU-hotplug testing.
2322 locktorture.shuffle_interval= [KNL]
2323 Set task-shuffle interval (jiffies). Shuffling
2324 tasks allows some CPUs to go into dyntick-idle
2325 mode during the locktorture test.
2327 locktorture.shutdown_secs= [KNL]
2328 Set time (s) after boot system shutdown. This
2329 is useful for hands-off automated testing.
2331 locktorture.stat_interval= [KNL]
2332 Time (s) between statistics printk()s.
2334 locktorture.stutter= [KNL]
2335 Time (s) to stutter testing, for example,
2336 specifying five seconds causes the test to run for
2337 five seconds, wait for five seconds, and so on.
2338 This tests the locking primitive's ability to
2339 transition abruptly to and from idle.
2341 locktorture.torture_type= [KNL]
2342 Specify the locking implementation to test.
2344 locktorture.verbose= [KNL]
2345 Enable additional printk() statements.
2347 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2350 loglevel= All Kernel Messages with a loglevel smaller than the
2351 console loglevel will be printed to the console. It can
2352 also be changed with klogd or other programs. The
2353 loglevels are defined as follows:
2355 0 (KERN_EMERG) system is unusable
2356 1 (KERN_ALERT) action must be taken immediately
2357 2 (KERN_CRIT) critical conditions
2358 3 (KERN_ERR) error conditions
2359 4 (KERN_WARNING) warning conditions
2360 5 (KERN_NOTICE) normal but significant condition
2361 6 (KERN_INFO) informational
2362 7 (KERN_DEBUG) debug-level messages
2364 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2365 in bytes. n must be a power of two and greater
2366 than the minimal size. The minimal size is defined
2367 by LOG_BUF_SHIFT kernel config parameter. There is
2368 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2369 that allows to increase the default size depending on
2370 the number of CPUs. See init/Kconfig for more details.
2372 logo.nologo [FB] Disables display of the built-in Linux logo.
2373 This may be used to provide more screen space for
2374 kernel log messages and is useful when debugging
2375 kernel boot problems.
2377 lp=0 [LP] Specify parallel ports to use, e.g,
2378 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2379 lp=reset first parallel port). 'lp=0' disables the
2380 lp=auto printer driver. 'lp=reset' (which can be
2381 specified in addition to the ports) causes
2382 attached printers to be reset. Using
2383 lp=port1,port2,... specifies the parallel ports
2384 to associate lp devices with, starting with
2385 lp0. A port specification may be 'none' to skip
2386 that lp device, or a parport name such as
2387 'parport0'. Specifying 'lp=auto' instead of a
2388 port specification list means that device IDs
2389 from each port should be examined, to see if
2390 an IEEE 1284-compliant printer is attached; if
2391 so, the driver will manage that printer.
2392 See also header of drivers/char/lp.c.
2395 Sets loops_per_jiffy to given constant, thus avoiding
2396 time-consuming boot-time autodetection (up to 250 ms per
2397 CPU). 0 enables autodetection (default). To determine
2398 the correct value for your kernel, boot with normal
2399 autodetection and see what value is printed. Note that
2400 on SMP systems the preset will be applied to all CPUs,
2401 which is likely to cause problems if your CPUs need
2402 significantly divergent settings. An incorrect value
2403 will cause delays in the kernel to be wrong, leading to
2404 unpredictable I/O errors and other breakage. Although
2405 unlikely, in the extreme case this might damage your
2409 Format: <io>,<irq>,<dma>
2411 lsm.debug [SECURITY] Enable LSM initialization debugging output.
2414 [SECURITY] Choose order of LSM initialization. This
2415 overrides CONFIG_LSM, and the "security=" parameter.
2417 machvec= [IA-64] Force the use of a particular machine-vector
2418 (machvec) in a generic kernel.
2419 Example: machvec=hpzx1
2421 machtype= [Loongson] Share the same kernel image file between different
2423 Example: machtype=lemote-yeeloong-2f-7inch
2425 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2426 than or equal to this physical address is ignored.
2428 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2429 will bring up during bootup. maxcpus=n : n >= 0 limits
2430 the kernel to bring up 'n' processors. Surely after
2431 bootup you can bring up the other plugged cpu by executing
2432 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2433 only takes effect during system bootup.
2434 While n=0 is a special case, it is equivalent to "nosmp",
2435 which also disables the IO APIC.
2437 max_loop= [LOOP] The number of loop block devices that get
2438 (loop.max_loop) unconditionally pre-created at init time. The default
2439 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2440 of statically allocating a predefined number, loop
2441 devices can be requested on-demand with the
2442 /dev/loop-control interface.
2444 mce [X86-32] Machine Check Exception
2446 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst
2448 md= [HW] RAID subsystems devices and level
2449 See Documentation/admin-guide/md.rst.
2452 Format: <first>,<last>
2453 Specifies range of consoles to be captured by the MDA.
2456 Control mitigation for the Micro-architectural Data
2457 Sampling (MDS) vulnerability.
2459 Certain CPUs are vulnerable to an exploit against CPU
2460 internal buffers which can forward information to a
2461 disclosure gadget under certain conditions.
2463 In vulnerable processors, the speculatively
2464 forwarded data can be used in a cache side channel
2465 attack, to access data to which the attacker does
2466 not have direct access.
2468 This parameter controls the MDS mitigation. The
2471 full - Enable MDS mitigation on vulnerable CPUs
2472 full,nosmt - Enable MDS mitigation and disable
2473 SMT on vulnerable CPUs
2474 off - Unconditionally disable MDS mitigation
2476 On TAA-affected machines, mds=off can be prevented by
2477 an active TAA mitigation as both vulnerabilities are
2478 mitigated with the same mechanism so in order to disable
2479 this mitigation, you need to specify tsx_async_abort=off
2482 Not specifying this option is equivalent to
2485 For details see: Documentation/admin-guide/hw-vuln/mds.rst
2487 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2488 Amount of memory to be used when the kernel is not able
2489 to see the whole system memory or for test.
2490 [X86] Work as limiting max address. Use together
2491 with memmap= to avoid physical address space collisions.
2492 Without memmap= PCI devices could be placed at addresses
2493 belonging to unused RAM.
2495 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2499 [KNL,SH] Allow user to override the default size for
2500 per-device physically contiguous DMA buffers.
2502 memhp_default_state=online/offline
2503 [KNL] Set the initial state for the memory hotplug
2504 onlining policy. If not specified, the default value is
2505 set according to the
2506 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2508 See Documentation/admin-guide/mm/memory-hotplug.rst.
2510 memmap=exactmap [KNL,X86] Enable setting of an exact
2511 E820 memory map, as specified by the user.
2512 Such memmap=exactmap lines can be constructed based on
2513 BIOS output or other requirements. See the memmap=nn@ss
2516 memmap=nn[KMG]@ss[KMG]
2517 [KNL] Force usage of a specific region of memory.
2518 Region of memory to be used is from ss to ss+nn.
2519 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2520 which limits max address to nn[KMG].
2521 Multiple different regions can be specified,
2524 memmap=100M@2G,100M#3G,1G!1024G
2526 memmap=nn[KMG]#ss[KMG]
2527 [KNL,ACPI] Mark specific memory as ACPI data.
2528 Region of memory to be marked is from ss to ss+nn.
2530 memmap=nn[KMG]$ss[KMG]
2531 [KNL,ACPI] Mark specific memory as reserved.
2532 Region of memory to be reserved is from ss to ss+nn.
2533 Example: Exclude memory from 0x18690000-0x1869ffff
2534 memmap=64K$0x18690000
2536 memmap=0x10000$0x18690000
2537 Some bootloaders may need an escape character before '$',
2538 like Grub2, otherwise '$' and the following number
2541 memmap=nn[KMG]!ss[KMG]
2542 [KNL,X86] Mark specific memory as protected.
2543 Region of memory to be used, from ss to ss+nn.
2544 The memory region may be marked as e820 type 12 (0xc)
2545 and is NVDIMM or ADR memory.
2547 memmap=<size>%<offset>-<oldtype>+<newtype>
2548 [KNL,ACPI] Convert memory within the specified region
2549 from <oldtype> to <newtype>. If "-<oldtype>" is left
2550 out, the whole region will be marked as <newtype>,
2551 even if previously unavailable. If "+<newtype>" is left
2552 out, matching memory will be removed. Types are
2553 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2554 3 = ACPI, 12 = PRAM.
2556 memory_corruption_check=0/1 [X86]
2557 Some BIOSes seem to corrupt the first 64k of
2558 memory when doing things like suspend/resume.
2559 Setting this option will scan the memory
2560 looking for corruption. Enabling this will
2561 both detect corruption and prevent the kernel
2562 from using the memory being corrupted.
2563 However, its intended as a diagnostic tool; if
2564 repeatable BIOS-originated corruption always
2565 affects the same memory, you can use memmap=
2566 to prevent the kernel from using that memory.
2568 memory_corruption_check_size=size [X86]
2569 By default it checks for corruption in the low
2570 64k, making this memory unavailable for normal
2571 use. Use this parameter to scan for
2572 corruption in more or less memory.
2574 memory_corruption_check_period=seconds [X86]
2575 By default it checks for corruption every 60
2576 seconds. Use this parameter to check at some
2577 other rate. 0 disables periodic checking.
2579 memtest= [KNL,X86,ARM,PPC] Enable memtest
2581 default : 0 <disable>
2582 Specifies the number of memtest passes to be
2583 performed. Each pass selects another test
2584 pattern from a given set of patterns. Memtest
2585 fills the memory with this pattern, validates
2586 memory contents and reserves bad memory
2587 regions that are detected.
2589 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2590 Valid arguments: on, off
2591 Default (depends on kernel configuration option):
2592 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2593 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2594 mem_encrypt=on: Activate SME
2595 mem_encrypt=off: Do not activate SME
2597 Refer to Documentation/virt/kvm/amd-memory-encryption.rst
2598 for details on when memory encryption can be activated.
2600 mem_sleep_default= [SUSPEND] Default system suspend mode:
2601 s2idle - Suspend-To-Idle
2602 shallow - Power-On Suspend or equivalent (if supported)
2603 deep - Suspend-To-RAM or equivalent (if supported)
2604 See Documentation/admin-guide/pm/sleep-states.rst.
2606 meye.*= [HW] Set MotionEye Camera parameters
2607 See Documentation/media/v4l-drivers/meye.rst.
2609 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2610 Multi-Function General Purpose Timers on AMD Geode
2613 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2614 the BIOS has incorrectly applied a workaround. TinyBIOS
2615 version 0.98 is known to be affected, 0.99 fixes the
2616 problem by letting the user disable the workaround.
2620 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2621 physical address is ignored.
2623 mini2440= [ARM,HW,KNL]
2624 Format:[0..2][b][c][t]
2626 MINI2440 configuration specification:
2627 0 - The attached screen is the 3.5" TFT
2628 1 - The attached screen is the 7" TFT
2629 2 - The VGA Shield is attached (1024x768)
2630 Leaving out the screen size parameter will not load
2631 the TFT driver, and the framebuffer will be left
2633 b - Enable backlight. The TFT backlight pin will be
2634 linked to the kernel VESA blanking code and a GPIO
2635 LED. This parameter is not necessary when using the
2637 c - Enable the s3c camera interface.
2638 t - Reserved for enabling touchscreen support. The
2639 touchscreen support is not enabled in the mainstream
2640 kernel as of 2.6.30, a preliminary port can be found
2641 in the "bleeding edge" mini2440 support kernel at
2642 http://repo.or.cz/w/linux-2.6/mini2440.git
2645 [X86,PPC,S390,ARM64] Control optional mitigations for
2646 CPU vulnerabilities. This is a set of curated,
2647 arch-independent options, each of which is an
2648 aggregation of existing arch-specific options.
2651 Disable all optional CPU mitigations. This
2652 improves system performance, but it may also
2653 expose users to several CPU vulnerabilities.
2654 Equivalent to: nopti [X86,PPC]
2656 nospectre_v1 [X86,PPC]
2658 nospectre_v2 [X86,PPC,S390,ARM64]
2659 spectre_v2_user=off [X86]
2660 spec_store_bypass_disable=off [X86,PPC]
2661 ssbd=force-off [ARM64]
2664 tsx_async_abort=off [X86]
2665 kvm.nx_huge_pages=off [X86]
2668 This does not have any effect on
2669 kvm.nx_huge_pages when
2670 kvm.nx_huge_pages=force.
2673 Mitigate all CPU vulnerabilities, but leave SMT
2674 enabled, even if it's vulnerable. This is for
2675 users who don't want to be surprised by SMT
2676 getting disabled across kernel upgrades, or who
2677 have other ways of avoiding SMT-based attacks.
2678 Equivalent to: (default behavior)
2681 Mitigate all CPU vulnerabilities, disabling SMT
2682 if needed. This is for users who always want to
2683 be fully mitigated, even if it means losing SMT.
2684 Equivalent to: l1tf=flush,nosmt [X86]
2685 mds=full,nosmt [X86]
2686 tsx_async_abort=full,nosmt [X86]
2689 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2690 parameter allows control of the logging verbosity for
2691 the additional memory initialisation checks. A value
2692 of 0 disables mminit logging and a level of 4 will
2693 log everything. Information is printed at KERN_DEBUG
2694 so loglevel=8 may also need to be specified.
2697 [KNL] When CONFIG_MODULE_SIG is set, this means that
2698 modules without (valid) signatures will fail to load.
2699 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2700 is always true, so this option does nothing.
2702 module_blacklist= [KNL] Do not load a comma-separated list of
2703 modules. Useful for debugging problem modules.
2706 [MOUSE] Maximum time between finger touching and
2707 leaving touchpad surface for touch to be considered
2708 a tap and be reported as a left button click (for
2709 touchpads working in absolute mode only).
2711 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2712 reporting absolute coordinates, such as tablets
2713 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2714 reporting absolute coordinates, such as tablets
2716 movablecore= [KNL,X86,IA-64,PPC]
2717 Format: nn[KMGTPE] | nn%
2718 This parameter is the complement to kernelcore=, it
2719 specifies the amount of memory used for migratable
2720 allocations. If both kernelcore and movablecore is
2721 specified, then kernelcore will be at *least* the
2722 specified value but may be more. If movablecore on its
2723 own is specified, the administrator must be careful
2724 that the amount of memory usable for all allocations
2727 movable_node [KNL] Boot-time switch to make hotplugable memory
2728 NUMA nodes to be movable. This means that the memory
2729 of such nodes will be usable only for movable
2730 allocations which rules out almost all kernel
2731 allocations. Use with caution!
2733 MTD_Partition= [MTD]
2734 Format: <name>,<region-number>,<size>,<offset>
2736 MTD_Region= [MTD] Format:
2737 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2740 See drivers/mtd/cmdlinepart.c.
2742 multitce=off [PPC] This parameter disables the use of the pSeries
2743 firmware feature for updating multiple TCE entries
2746 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2748 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2750 boundary - index of last SLC block on Flex-OneNAND.
2751 The remaining blocks are configured as MLC blocks.
2752 lock - Configure if Flex-OneNAND boundary should be locked.
2753 Once locked, the boundary cannot be changed.
2754 1 indicates lock status, 0 indicates unlock status.
2757 ARM/S3C2412 JIVE boot control
2759 See arch/arm/mach-s3c2412/mach-jive.c
2761 mtouchusb.raw_coordinates=
2762 [HW] Make the MicroTouch USB driver use raw coordinates
2763 ('y', default) or cooked coordinates ('n')
2765 mtrr_chunk_size=nn[KMG] [X86]
2766 used for mtrr cleanup. It is largest continuous chunk
2767 that could hold holes aka. UC entries.
2769 mtrr_gran_size=nn[KMG] [X86]
2770 Used for mtrr cleanup. It is granularity of mtrr block.
2772 Large value could prevent small alignment from
2775 mtrr_spare_reg_nr=n [X86]
2777 Range: 0,7 : spare reg number
2779 Used for mtrr cleanup. It is spare mtrr entries number.
2780 Set to 2 or more if your graphical card needs more.
2782 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2784 netdev= [NET] Network devices parameters
2785 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2786 Note that mem_start is often overloaded to mean
2787 something different and driver-specific.
2788 This usage is only documented in each driver source
2792 [NETFILTER] Enable connection tracking flow accounting
2793 0 to disable accounting
2794 1 to enable accounting
2797 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2798 See Documentation/filesystems/nfs/nfsroot.txt.
2800 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2801 See Documentation/filesystems/nfs/nfsroot.txt.
2803 nfsrootdebug [NFS] enable nfsroot debugging messages.
2804 See Documentation/filesystems/nfs/nfsroot.txt.
2806 nfs.callback_nr_threads=
2807 [NFSv4] set the total number of threads that the
2808 NFS client will assign to service NFSv4 callback
2811 nfs.callback_tcpport=
2812 [NFS] set the TCP port on which the NFSv4 callback
2813 channel should listen.
2816 [NFS] sets the pathname to the program which is used
2817 to update the NFS client cache entries.
2819 nfs.cache_getent_timeout=
2820 [NFS] sets the timeout after which an attempt to
2821 update a cache entry is deemed to have failed.
2823 nfs.idmap_cache_timeout=
2824 [NFS] set the maximum lifetime for idmapper cache
2828 [NFS] enable 64-bit inode numbers.
2829 If zero, the NFS client will fake up a 32-bit inode
2830 number for the readdir() and stat() syscalls instead
2831 of returning the full 64-bit number.
2832 The default is to return 64-bit inode numbers.
2834 nfs.max_session_cb_slots=
2835 [NFSv4.1] Sets the maximum number of session
2836 slots the client will assign to the callback
2837 channel. This determines the maximum number of
2838 callbacks the client will process in parallel for
2839 a particular server.
2841 nfs.max_session_slots=
2842 [NFSv4.1] Sets the maximum number of session slots
2843 the client will attempt to negotiate with the server.
2844 This limits the number of simultaneous RPC requests
2845 that the client can send to the NFSv4.1 server.
2846 Note that there is little point in setting this
2847 value higher than the max_tcp_slot_table_limit.
2849 nfs.nfs4_disable_idmapping=
2850 [NFSv4] When set to the default of '1', this option
2851 ensures that both the RPC level authentication
2852 scheme and the NFS level operations agree to use
2853 numeric uids/gids if the mount is using the
2854 'sec=sys' security flavour. In effect it is
2855 disabling idmapping, which can make migration from
2856 legacy NFSv2/v3 systems to NFSv4 easier.
2857 Servers that do not support this mode of operation
2858 will be autodetected by the client, and it will fall
2859 back to using the idmapper.
2860 To turn off this behaviour, set the value to '0'.
2862 [NFS4] Specify an additional fixed unique ident-
2863 ification string that NFSv4 clients can insert into
2864 their nfs_client_id4 string. This is typically a
2865 UUID that is generated at system install time.
2867 nfs.send_implementation_id =
2868 [NFSv4.1] Send client implementation identification
2869 information in exchange_id requests.
2870 If zero, no implementation identification information
2872 The default is to send the implementation identification
2875 nfs.recover_lost_locks =
2876 [NFSv4] Attempt to recover locks that were lost due
2877 to a lease timeout on the server. Please note that
2878 doing this risks data corruption, since there are
2879 no guarantees that the file will remain unchanged
2880 after the locks are lost.
2881 If you want to enable the kernel legacy behaviour of
2882 attempting to recover these locks, then set this
2884 The default parameter value of '0' causes the kernel
2885 not to attempt recovery of lost locks.
2887 nfs4.layoutstats_timer =
2888 [NFSv4.2] Change the rate at which the kernel sends
2889 layoutstats to the pNFS metadata server.
2891 Setting this to value to 0 causes the kernel to use
2892 whatever value is the default set by the layout
2893 driver. A non-zero value sets the minimum interval
2894 in seconds between layoutstats transmissions.
2896 nfsd.nfs4_disable_idmapping=
2897 [NFSv4] When set to the default of '1', the NFSv4
2898 server will return only numeric uids and gids to
2899 clients using auth_sys, and will accept numeric uids
2900 and gids from such clients. This is intended to ease
2901 migration from NFSv2/v3.
2903 nmi_debug= [KNL,SH] Specify one or more actions to take
2904 when a NMI is triggered.
2905 Format: [state][,regs][,debounce][,die]
2907 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2908 Format: [panic,][nopanic,][num]
2910 0 - turn hardlockup detector in nmi_watchdog off
2911 1 - turn hardlockup detector in nmi_watchdog on
2912 When panic is specified, panic when an NMI watchdog
2913 timeout occurs (or 'nopanic' to not panic on an NMI
2914 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set)
2915 To disable both hard and soft lockup detectors,
2916 please see 'nowatchdog'.
2917 This is useful when you use a panic=... timeout and
2918 need the box quickly up again.
2920 These settings can be accessed at runtime via
2921 the nmi_watchdog and hardlockup_panic sysctls.
2923 netpoll.carrier_timeout=
2924 [NET] Specifies amount of time (in seconds) that
2925 netpoll should wait for a carrier. By default netpoll
2928 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2929 emulation library even if a 387 maths coprocessor
2932 no5lvl [X86-64] Disable 5-level paging mode. Forces
2933 kernel to use 4-level paging instead.
2936 [HW] Never suspend the console
2937 Disable suspending of consoles during suspend and
2938 hibernate operations. Once disabled, debugging
2939 messages can reach various consoles while the rest
2940 of the system is being put to sleep (ie, while
2941 debugging driver suspend/resume hooks). This may
2942 not work reliably with all consoles, but is known
2943 to work with serial and VGA consoles.
2944 To facilitate more flexible debugging, we also add
2945 console_suspend, a printk module parameter to control
2946 it. Users could use console_suspend (usually
2947 /sys/module/printk/parameters/console_suspend) to
2948 turn on/off it dynamically.
2950 novmcoredd [KNL,KDUMP]
2951 Disable device dump. Device dump allows drivers to
2952 append dump data to vmcore so you can collect driver
2953 specified debug info. Drivers can append the data
2954 without any limit and this data is stored in memory,
2955 so this may cause significant memory stress. Disabling
2956 device dump can help save memory but the driver debug
2957 data will be no longer available. This parameter
2958 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP
2961 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2962 caches in the slab allocator. Saves per-node memory,
2963 but will impact performance.
2967 noaltinstr [S390] Disables alternative instructions patching
2968 (CPU alternatives feature).
2970 noapic [SMP,APIC] Tells the kernel to not make use of any
2971 IOAPICs that may be present in the system.
2973 noautogroup Disable scheduler automatic task group creation.
2975 nobats [PPC] Do not use BATs for mapping kernel lowmem
2976 on "Classic" PPC cores.
2980 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2982 nodelayacct [KNL] Disable per-task delay accounting
2984 nodsp [SH] Disable hardware DSP at boot time.
2986 noefi Disable EFI runtime services support.
2991 On X86-32 available only on PAE configured kernels.
2992 noexec=on: enable non-executable mappings (default)
2993 noexec=off: disable non-executable mappings
2996 Disable SMAP (Supervisor Mode Access Prevention)
2997 even if it is supported by processor.
3000 Disable SMEP (Supervisor Mode Execution Prevention)
3001 even if it is supported by processor.
3004 This affects only 32-bit executables.
3005 noexec32=on: enable non-executable mappings (default)
3006 read doesn't imply executable mappings
3007 noexec32=off: disable non-executable mappings
3008 read implies executable mappings
3010 nofpu [MIPS,SH] Disable hardware FPU at boot time.
3012 nofxsr [BUGS=X86-32] Disables x86 floating point extended
3013 register save and restore. The kernel will only save
3014 legacy floating-point registers on task switch.
3016 nohugeiomap [KNL,x86,PPC] Disable kernel huge I/O mappings.
3018 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
3019 Equivalent to smt=1.
3021 [KNL,x86] Disable symmetric multithreading (SMT).
3022 nosmt=force: Force disable SMT, cannot be undone
3023 via the sysfs control file.
3025 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1
3026 (bounds check bypass). With this option data leaks are
3027 possible in the system.
3029 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for
3030 the Spectre variant 2 (indirect branch prediction)
3031 vulnerability. System may allow data leaks with this
3034 nospec_store_bypass_disable
3035 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
3037 noxsave [BUGS=X86] Disables x86 extended register state save
3038 and restore using xsave. The kernel will fallback to
3039 enabling legacy floating-point and sse state.
3041 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
3042 register states. The kernel will fall back to use
3043 xsave to save the states. By using this parameter,
3044 performance of saving the states is degraded because
3045 xsave doesn't support modified optimization while
3046 xsaveopt supports it on xsaveopt enabled systems.
3048 noxsaves [X86] Disables xsaves and xrstors used in saving and
3049 restoring x86 extended register state in compacted
3050 form of xsave area. The kernel will fall back to use
3051 xsaveopt and xrstor to save and restore the states
3052 in standard form of xsave area. By using this
3053 parameter, xsave area per process might occupy more
3054 memory on xsaves enabled systems.
3056 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
3057 wfi(ARM) instruction doesn't work correctly and not to
3058 use it. This is also useful when using JTAG debugger.
3060 no_file_caps Tells the kernel not to honor file capabilities. The
3061 only way then for a file to be executed with privilege
3062 is to be setuid root or executed by root.
3064 nohalt [IA-64] Tells the kernel not to use the power saving
3065 function PAL_HALT_LIGHT when idle. This increases
3066 power-consumption. On the positive side, it reduces
3067 interrupt wake-up latency, which may improve performance
3068 in certain environments such as networked servers or
3071 nohibernate [HIBERNATION] Disable hibernation and resume.
3073 nohz= [KNL] Boottime enable/disable dynamic ticks
3074 Valid arguments: on, off
3077 nohz_full= [KNL,BOOT,SMP,ISOL]
3078 The argument is a cpu list, as described above.
3079 In kernels built with CONFIG_NO_HZ_FULL=y, set
3080 the specified list of CPUs whose tick will be stopped
3081 whenever possible. The boot CPU will be forced outside
3082 the range to maintain the timekeeping. Any CPUs
3083 in this list will have their RCU callbacks offloaded,
3084 just as if they had also been called out in the
3085 rcu_nocbs= boot parameter.
3087 noiotrap [SH] Disables trapped I/O port accesses.
3089 noirqdebug [X86-32] Disables the code which attempts to detect and
3090 disable unhandled interrupt sources.
3092 no_timer_check [X86,APIC] Disables the code which tests for
3093 broken timer IRQ sources.
3095 noisapnp [ISAPNP] Disables ISA PnP code.
3097 noinitrd [RAM] Tells the kernel not to load any configured
3100 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
3102 [Deprecated - use intremap=off]
3106 noinvpcid [X86] Disable the INVPCID cpu feature.
3108 nojitter [IA-64] Disables jitter checking for ITC timers.
3110 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
3112 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
3116 [X86,PV_OPS] Disable paravirtualized VMware scheduler
3117 clock and use the default one.
3119 no-steal-acc [X86,KVM,ARM64] Disable paravirtualized steal time
3120 accounting. steal time is computed, but won't
3121 influence scheduler behaviour
3123 nolapic [X86-32,APIC] Do not enable or use the local APIC.
3125 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
3127 noltlbs [PPC] Do not use large page/tlb entries for kernel
3128 lowmem mapping on PPC40x and PPC8xx
3130 nomca [IA-64] Disable machine check abort handling
3132 nomce [X86-32] Disable Machine Check Exception
3134 nomfgpt [X86-32] Disable Multi-Function General Purpose
3135 Timer usage (for AMD Geode machines).
3137 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
3138 shutdown the other cpus. Instead use the REBOOT_VECTOR
3141 nomodule Disable module load
3143 nopat [X86] Disable PAT (page attribute table extension of
3144 pagetables) support.
3146 nopcid [X86-64] Disable the PCID cpu feature.
3148 norandmaps Don't use address space randomization. Equivalent to
3149 echo 0 > /proc/sys/kernel/randomize_va_space
3151 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
3152 with UP alternatives
3154 nordrand [X86] Disable kernel use of the RDRAND and
3155 RDSEED instructions even if they are supported
3156 by the processor. RDRAND and RDSEED are still
3157 available to user space applications.
3159 noresume [SWSUSP] Disables resume and restores original swap
3162 no-scroll [VGA] Disables scrollback.
3163 This is required for the Braillex ib80-piezo Braille
3164 reader made by F.H. Papenmeier (Germany).
3168 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
3170 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
3171 and disable the IO APIC. legacy for "maxcpus=0".
3173 nosoftlockup [KNL] Disable the soft-lockup detector.
3175 nosync [HW,M68K] Disables sync negotiation for all devices.
3177 nowatchdog [KNL] Disable both lockup detectors, i.e.
3178 soft-lockup and NMI watchdog (hard-lockup).
3182 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
3184 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
3185 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
3186 Some features depend on CPU0. Known dependencies are:
3187 1. Resume from suspend/hibernate depends on CPU0.
3188 Suspend/hibernate will fail if CPU0 is offline and you
3189 need to online CPU0 before suspend/hibernate.
3190 2. PIC interrupts also depend on CPU0. CPU0 can't be
3191 removed if a PIC interrupt is detected.
3192 It's said poweroff/reboot may depend on CPU0 on some
3193 machines although I haven't seen such issues so far
3194 after CPU0 is offline on a few tested machines.
3195 If the dependencies are under your control, you can
3196 turn on cpu0_hotplug.
3198 nps_mtm_hs_ctr= [KNL,ARC]
3199 This parameter sets the maximum duration, in
3200 cycles, each HW thread of the CTOP can run
3201 without interruptions, before HW switches it.
3202 The actual maximum duration is 16 times this
3204 Format: integer between 1 and 255
3207 nptcg= [IA-64] Override max number of concurrent global TLB
3208 purges which is reported from either PAL_VM_SUMMARY or
3211 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
3212 could support. nr_cpus=n : n >= 1 limits the kernel to
3213 support 'n' processors. It could be larger than the
3214 number of already plugged CPU during bootup, later in
3215 runtime you can physically add extra cpu until it reaches
3216 n. So during boot up some boot time memory for per-cpu
3217 variables need be pre-allocated for later physical cpu
3220 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3222 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
3223 Allowed values are enable and disable
3225 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3226 'node', 'default' can be specified
3227 This can be set from sysctl after boot.
3228 See Documentation/admin-guide/sysctl/vm.rst for details.
3230 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3231 See Documentation/debugging-via-ohci1394.txt for more
3234 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3235 Rather than timing out after 20 ms if an EC
3236 command is not properly ACKed, override the length
3237 of the timeout. We have interrupts disabled while
3238 waiting for the ACK, so if this is set too high
3239 interrupts *may* be lost!
3241 omap_mux= [OMAP] Override bootloader pin multiplexing.
3242 Format: <mux_mode0.mode_name=value>...
3243 For example, to override I2C bus2:
3244 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3246 oprofile.timer= [HW]
3247 Use timer interrupt instead of performance counters
3249 oprofile.cpu_type= Force an oprofile cpu type
3250 This might be useful if you have an older oprofile
3251 userland or if you want common events.
3252 Format: { arch_perfmon }
3253 arch_perfmon: [X86] Force use of architectural
3254 perfmon on Intel CPUs instead of the
3255 CPU specific event set.
3256 timer: [X86] Force use of architectural NMI
3257 timer mode (see also oprofile.timer
3258 for generic hr timer mode)
3260 oops=panic Always panic on oopses. Default is to just kill the
3261 process, but there is a small probability of
3262 deadlocking the machine.
3263 This will also cause panics on machine check exceptions.
3264 Useful together with panic=30 to trigger a reboot.
3267 [KNL] Boolean flag to control whether the page allocator
3268 should randomize its free lists. The randomization may
3269 be automatically enabled if the kernel detects it is
3270 running on a platform with a direct-mapped memory-side
3271 cache, and this parameter can be used to
3272 override/disable that behavior. The state of the flag
3273 can be read from sysfs at:
3274 /sys/module/page_alloc/parameters/shuffle.
3276 page_owner= [KNL] Boot-time page_owner enabling option.
3277 Storage of the information about who allocated
3278 each page is disabled in default. With this switch,
3280 on: enable the feature
3282 page_poison= [KNL] Boot-time parameter changing the state of
3283 poisoning on the buddy allocator, available with
3284 CONFIG_PAGE_POISONING=y.
3285 off: turn off poisoning (default)
3286 on: turn on poisoning
3288 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3289 timeout > 0: seconds before rebooting
3290 timeout = 0: wait forever
3291 timeout < 0: reboot immediately
3294 panic_print= Bitmask for printing system info when panic happens.
3295 User can chose combination of the following bits:
3296 bit 0: print all tasks info
3297 bit 1: print system memory info
3298 bit 2: print timer info
3299 bit 3: print locks info if CONFIG_LOCKDEP is on
3300 bit 4: print ftrace buffer
3301 bit 5: print all printk messages in buffer
3303 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3306 crash_kexec_post_notifiers
3307 Run kdump after running panic-notifiers and dumping
3308 kmsg. This only for the users who doubt kdump always
3309 succeeds in any situation.
3310 Note that this also increases risks of kdump failure,
3311 because some panic notifiers can make the crashed
3312 kernel more unstable.
3314 parkbd.port= [HW] Parallel port number the keyboard adapter is
3315 connected to, default is 0.
3317 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3318 0 for XT, 1 for AT (default is AT).
3321 parport= [HW,PPT] Specify parallel ports. 0 disables.
3322 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3323 Use 'auto' to force the driver to use any
3324 IRQ/DMA settings detected (the default is to
3325 ignore detected IRQ/DMA settings because of
3326 possible conflicts). You can specify the base
3327 address, IRQ, and DMA settings; IRQ and DMA
3328 should be numbers, or 'auto' (for using detected
3329 settings on that particular port), or 'nofifo'
3330 (to avoid using a FIFO even if it is detected).
3331 Parallel ports are assigned in the order they
3332 are specified on the command line, starting
3335 parport_init_mode= [HW,PPT]
3336 Configure VIA parallel port to operate in
3337 a specific mode. This is necessary on Pegasos
3338 computer where firmware has no options for setting
3339 up parallel port mode and sets it to spp.
3340 Currently this function knows 686a and 8231 chips.
3341 Format: [spp|ps2|epp|ecp|ecpepp]
3344 Halt all CPUs after the first oops has been printed for
3345 the specified number of seconds. This is to be used if
3346 your oopses keep scrolling off the screen.
3351 See header of drivers/block/paride/pcd.c.
3352 See also Documentation/admin-guide/blockdev/paride.rst.
3354 pci=option[,option...] [PCI] various PCI subsystem options.
3356 Some options herein operate on a specific device
3357 or a set of devices (<pci_dev>). These are
3358 specified in one of the following formats:
3360 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
3361 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
3363 Note: the first format specifies a PCI
3364 bus/device/function address which may change
3365 if new hardware is inserted, if motherboard
3366 firmware changes, or due to changes caused
3367 by other kernel parameters. If the
3368 domain is left unspecified, it is
3369 taken to be zero. Optionally, a path
3370 to a device through multiple device/function
3371 addresses can be specified after the base
3372 address (this is more robust against
3373 renumbering issues). The second format
3374 selects devices using IDs from the
3375 configuration space which may match multiple
3376 devices in the system.
3378 earlydump dump PCI config space before the kernel
3380 off [X86] don't probe for the PCI bus
3381 bios [X86-32] force use of PCI BIOS, don't access
3382 the hardware directly. Use this if your machine
3383 has a non-standard PCI host bridge.
3384 nobios [X86-32] disallow use of PCI BIOS, only direct
3385 hardware access methods are allowed. Use this
3386 if you experience crashes upon bootup and you
3387 suspect they are caused by the BIOS.
3388 conf1 [X86] Force use of PCI Configuration Access
3389 Mechanism 1 (config address in IO port 0xCF8,
3390 data in IO port 0xCFC, both 32-bit).
3391 conf2 [X86] Force use of PCI Configuration Access
3392 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3393 the function, IO port 0xCFA, also 8-bit, sets
3394 bus number. The config space is then accessed
3395 through ports 0xC000-0xCFFF).
3396 See http://wiki.osdev.org/PCI for more info
3397 on the configuration access mechanisms.
3398 noaer [PCIE] If the PCIEAER kernel config parameter is
3399 enabled, this kernel boot option can be used to
3400 disable the use of PCIE advanced error reporting.
3401 nodomains [PCI] Disable support for multiple PCI
3402 root domains (aka PCI segments, in ACPI-speak).
3403 nommconf [X86] Disable use of MMCONFIG for PCI
3405 check_enable_amd_mmconf [X86] check for and enable
3406 properly configured MMIO access to PCI
3407 config space on AMD family 10h CPU
3408 nomsi [MSI] If the PCI_MSI kernel config parameter is
3409 enabled, this kernel boot option can be used to
3410 disable the use of MSI interrupts system-wide.
3411 noioapicquirk [APIC] Disable all boot interrupt quirks.
3412 Safety option to keep boot IRQs enabled. This
3413 should never be necessary.
3414 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3415 primary IO-APIC for bridges that cannot disable
3416 boot IRQs. This fixes a source of spurious IRQs
3417 when the system masks IRQs.
3418 noioapicreroute [APIC] Disable workaround that uses the
3419 boot IRQ equivalent of an IRQ that connects to
3420 a chipset where boot IRQs cannot be disabled.
3421 The opposite of ioapicreroute.
3422 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3423 routing table. These calls are known to be buggy
3424 on several machines and they hang the machine
3425 when used, but on other computers it's the only
3426 way to get the interrupt routing table. Try
3427 this option if the kernel is unable to allocate
3428 IRQs or discover secondary PCI buses on your
3430 rom [X86] Assign address space to expansion ROMs.
3431 Use with caution as certain devices share
3432 address decoders between ROMs and other
3434 norom [X86] Do not assign address space to
3435 expansion ROMs that do not already have
3436 BIOS assigned address ranges.
3437 nobar [X86] Do not assign address space to the
3438 BARs that weren't assigned by the BIOS.
3439 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3440 assigned automatically to PCI devices. You can
3441 make the kernel exclude IRQs of your ISA cards
3443 pirqaddr=0xAAAAA [X86] Specify the physical address
3444 of the PIRQ table (normally generated
3445 by the BIOS) if it is outside the
3446 F0000h-100000h range.
3447 lastbus=N [X86] Scan all buses thru bus #N. Can be
3448 useful if the kernel is unable to find your
3449 secondary buses and you want to tell it
3450 explicitly which ones they are.
3451 assign-busses [X86] Always assign all PCI bus
3452 numbers ourselves, overriding
3453 whatever the firmware may have done.
3454 usepirqmask [X86] Honor the possible IRQ mask stored
3455 in the BIOS $PIR table. This is needed on
3456 some systems with broken BIOSes, notably
3457 some HP Pavilion N5400 and Omnibook XE3
3458 notebooks. This will have no effect if ACPI
3459 IRQ routing is enabled.
3460 noacpi [X86] Do not use ACPI for IRQ routing
3461 or for PCI scanning.
3462 use_crs [X86] Use PCI host bridge window information
3463 from ACPI. On BIOSes from 2008 or later, this
3464 is enabled by default. If you need to use this,
3465 please report a bug.
3466 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3467 If you need to use this, please report a bug.
3468 routeirq Do IRQ routing for all PCI devices.
3469 This is normally done in pci_enable_device(),
3470 so this option is a temporary workaround
3471 for broken drivers that don't call it.
3472 skip_isa_align [X86] do not align io start addr, so can
3473 handle more pci cards
3474 noearly [X86] Don't do any early type 1 scanning.
3475 This might help on some broken boards which
3476 machine check when some devices' config space
3477 is read. But various workarounds are disabled
3478 and some IOMMU drivers will not work.
3479 bfsort Sort PCI devices into breadth-first order.
3480 This sorting is done to get a device
3481 order compatible with older (<= 2.4) kernels.
3482 nobfsort Don't sort PCI devices into breadth-first order.
3483 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3484 tuning and use the BIOS-configured MPS defaults.
3485 pcie_bus_safe Set every device's MPS to the largest value
3486 supported by all devices below the root complex.
3487 pcie_bus_perf Set device MPS to the largest allowable MPS
3488 based on its parent bus. Also set MRRS (Max
3489 Read Request Size) to the largest supported
3490 value (no larger than the MPS that the device
3491 or bus can support) for best performance.
3492 pcie_bus_peer2peer Set every device's MPS to 128B, which
3493 every device is guaranteed to support. This
3494 configuration allows peer-to-peer DMA between
3495 any pair of devices, possibly at the cost of
3496 reduced performance. This also guarantees
3497 that hot-added devices will work.
3498 cbiosize=nn[KMG] The fixed amount of bus space which is
3499 reserved for the CardBus bridge's IO window.
3500 The default value is 256 bytes.
3501 cbmemsize=nn[KMG] The fixed amount of bus space which is
3502 reserved for the CardBus bridge's memory
3503 window. The default value is 64 megabytes.
3506 [<order of align>@]<pci_dev>[; ...]
3507 Specifies alignment and device to reassign
3508 aligned memory resources. How to
3509 specify the device is described above.
3510 If <order of align> is not specified,
3511 PAGE_SIZE is used as alignment.
3512 A PCI-PCI bridge can be specified if resource
3513 windows need to be expanded.
3514 To specify the alignment for several
3515 instances of a device, the PCI vendor,
3516 device, subvendor, and subdevice may be
3517 specified, e.g., 12@pci:8086:9c22:103c:198f
3518 for 4096-byte alignment.
3519 ecrc= Enable/disable PCIe ECRC (transaction layer
3520 end-to-end CRC checking).
3521 bios: Use BIOS/firmware settings. This is the
3525 hpiosize=nn[KMG] The fixed amount of bus space which is
3526 reserved for hotplug bridge's IO window.
3527 Default size is 256 bytes.
3528 hpmemsize=nn[KMG] The fixed amount of bus space which is
3529 reserved for hotplug bridge's memory window.
3530 Default size is 2 megabytes.
3531 hpbussize=nn The minimum amount of additional bus numbers
3532 reserved for buses below a hotplug bridge.
3534 realloc= Enable/disable reallocating PCI bridge resources
3535 if allocations done by BIOS are too small to
3536 accommodate resources required by all child
3538 off: Turn realloc off
3540 realloc same as realloc=on
3541 noari do not use PCIe ARI.
3542 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
3543 do not use PCIe ATS (and IOMMU device IOTLB).
3544 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3545 only look for one device below a PCIe downstream
3547 big_root_window Try to add a big 64bit memory window to the PCIe
3548 root complex on AMD CPUs. Some GFX hardware
3549 can resize a BAR to allow access to all VRAM.
3550 Adding the window is slightly risky (it may
3551 conflict with unreported devices), so this
3553 disable_acs_redir=<pci_dev>[; ...]
3554 Specify one or more PCI devices (in the format
3555 specified above) separated by semicolons.
3556 Each device specified will have the PCI ACS
3557 redirect capabilities forced off which will
3558 allow P2P traffic between devices through
3559 bridges without forcing it upstream. Note:
3560 this removes isolation between devices and
3561 may put more devices in an IOMMU group.
3562 force_floating [S390] Force usage of floating interrupts.
3563 nomio [S390] Do not use MIO instructions.
3565 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3568 force Enable ASPM even on devices that claim not to support it.
3569 WARNING: Forcing ASPM on may cause system lockups.
3571 pcie_ports= [PCIE] PCIe port services handling:
3572 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
3573 even if the platform doesn't give the OS permission to
3574 use them. This may cause conflicts if the platform
3575 also tries to use these services.
3576 compat Disable native PCIe services (PME, AER, DPC, PCIe
3579 pcie_port_pm= [PCIE] PCIe port power management handling:
3580 off Disable power management of all PCIe ports
3581 force Forcibly enable power management of all PCIe ports
3583 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3584 nomsi Do not use MSI for native PCIe PME signaling (this makes
3585 all PCIe root ports use INTx for all services).
3587 pcmv= [HW,PCMCIA] BadgePAD 4
3591 Keep all power-domains already enabled by bootloader on,
3592 even if no driver has claimed them. This is useful
3593 for debug and development, but should not be
3594 needed on a platform with proper driver support.
3597 See Documentation/admin-guide/blockdev/paride.rst.
3599 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3602 See arch/parisc/kernel/pdc_chassis.c
3604 percpu_alloc= Select which percpu first chunk allocator to use.
3605 Currently supported values are "embed" and "page".
3606 Archs may support subset or none of the selections.
3607 See comments in mm/percpu.c for details on each
3608 allocator. This parameter is primarily for debugging
3609 and performance comparison.
3612 See Documentation/admin-guide/blockdev/paride.rst.
3615 See Documentation/admin-guide/blockdev/paride.rst.
3617 pirq= [SMP,APIC] Manual mp-table setup
3618 See Documentation/x86/i386/IO-APIC.rst.
3620 plip= [PPT,NET] Parallel port network link
3621 Format: { parport<nr> | timid | 0 }
3622 See also Documentation/admin-guide/parport.rst.
3624 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3625 Override pmtimer IOPort with a hex value.
3629 Enable PNP debug messages (depends on the
3630 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3631 via /sys/module/pnp/parameters/debug. We always show
3632 current resource usage; turning this on also shows
3633 possible settings and some assignment information.
3639 { on | off | curr | res | no-curr | no-res }
3642 [ISAPNP] Exclude IRQs for the autoconfiguration
3645 [ISAPNP] Exclude DMAs for the autoconfiguration
3647 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3648 Ranges are in pairs (I/O port base and size).
3651 [ISAPNP] Exclude memory regions for the
3653 Ranges are in pairs (memory base and size).
3655 ports= [IP_VS_FTP] IPVS ftp helper module
3657 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3659 Format: <port>,<port>....
3661 powersave=off [PPC] This option disables power saving features.
3662 It specifically disables cpuidle and sets the
3663 platform machine description specific power_save
3664 function to NULL. On Idle the CPU just reduces
3667 ppc_strict_facility_enable
3668 [PPC] This option catches any kernel floating point,
3669 Altivec, VSX and SPE outside of regions specifically
3670 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3671 There is some performance impact when enabling this.
3675 Disable Hardware Transactional Memory
3677 print-fatal-signals=
3678 [KNL] debug: print fatal signals
3680 If enabled, warn about various signal handling
3681 related application anomalies: too many signals,
3682 too many POSIX.1 timers, fatal signals causing a
3685 If you hit the warning due to signal overflow,
3686 you might want to try "ulimit -i unlimited".
3690 printk.always_kmsg_dump=
3691 Trigger kmsg_dump for cases other than kernel oops or
3693 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3696 printk.devkmsg={on,off,ratelimit}
3697 Control writing to /dev/kmsg.
3698 on - unlimited logging to /dev/kmsg from userspace
3699 off - logging to /dev/kmsg disabled
3700 ratelimit - ratelimit the logging
3703 printk.time= Show timing data prefixed to each printk message line
3704 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3706 processor.max_cstate= [HW,ACPI]
3707 Limit processor to maximum C-state
3708 max_cstate=9 overrides any DMI blacklist limit.
3710 processor.nocst [HW,ACPI]
3711 Ignore the _CST method to determine C-states,
3712 instead using the legacy FADT method
3714 profile= [KNL] Enable kernel profiling via /proc/profile
3715 Format: [<profiletype>,]<number>
3716 Param: <profiletype>: "schedule", "sleep", or "kvm"
3717 [defaults to kernel profiling]
3718 Param: "schedule" - profile schedule points.
3719 Param: "sleep" - profile D-state sleeping (millisecs).
3720 Requires CONFIG_SCHEDSTATS
3721 Param: "kvm" - profile VM exits.
3722 Param: <number> - step/bucket size as a power of 2 for
3723 statistical time based profiling.
3725 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3727 See Documentation/admin-guide/blockdev/ramdisk.rst.
3729 psi= [KNL] Enable or disable pressure stall information
3733 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3734 probe for; one of (bare|imps|exps|lifebook|any).
3735 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3737 psmouse.resetafter= [HW,MOUSE]
3738 Try to reset the device after so many bad packets
3741 [HW,MOUSE] Set desired mouse resolution, in dpi.
3742 psmouse.smartscroll=
3743 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3744 0 = disabled, 1 = enabled (default).
3746 pstore.backend= Specify the name of the pstore backend to use
3749 See Documentation/admin-guide/blockdev/paride.rst.
3751 pti= [X86_64] Control Page Table Isolation of user and
3752 kernel address spaces. Disabling this feature
3753 removes hardening, but improves performance of
3754 system calls and interrupts.
3756 on - unconditionally enable
3757 off - unconditionally disable
3758 auto - kernel detects whether your CPU model is
3759 vulnerable to issues that PTI mitigates
3761 Not specifying this option is equivalent to pti=auto.
3764 Equivalent to pti=off
3767 [KNL] Number of legacy pty's. Overwrites compiled-in
3770 quiet [KNL] Disable most log messages
3775 See Documentation/admin-guide/md.rst.
3777 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3778 See Documentation/admin-guide/blockdev/ramdisk.rst.
3780 random.trust_cpu={on,off}
3781 [KNL] Enable or disable trusting the use of the
3782 CPU's random number generator (if available) to
3783 fully seed the kernel's CRNG. Default is controlled
3784 by CONFIG_RANDOM_TRUST_CPU.
3786 ras=option[,option,...] [KNL] RAS-specific options
3789 Disable the Correctable Errors Collector,
3790 see CONFIG_RAS_CEC help text.
3793 The argument is a cpu list, as described above,
3794 except that the string "all" can be used to
3795 specify every CPU on the system.
3797 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3798 the specified list of CPUs to be no-callback CPUs.
3799 Invocation of these CPUs' RCU callbacks will be
3800 offloaded to "rcuox/N" kthreads created for that
3801 purpose, where "x" is "p" for RCU-preempt, and
3802 "s" for RCU-sched, and "N" is the CPU number.
3803 This reduces OS jitter on the offloaded CPUs,
3804 which can be useful for HPC and real-time
3805 workloads. It can also improve energy efficiency
3806 for asymmetric multiprocessors.
3809 Rather than requiring that offloaded CPUs
3810 (specified by rcu_nocbs= above) explicitly
3811 awaken the corresponding "rcuoN" kthreads,
3812 make these kthreads poll for callbacks.
3813 This improves the real-time response for the
3814 offloaded CPUs by relieving them of the need to
3815 wake up the corresponding kthread, but degrades
3816 energy efficiency by requiring that the kthreads
3817 periodically wake up to do the polling.
3819 rcutree.blimit= [KNL]
3820 Set maximum number of finished RCU callbacks to
3821 process in one batch.
3823 rcutree.dump_tree= [KNL]
3824 Dump the structure of the rcu_node combining tree
3825 out at early boot. This is used for diagnostic
3826 purposes, to verify correct tree setup.
3828 rcutree.gp_cleanup_delay= [KNL]
3829 Set the number of jiffies to delay each step of
3830 RCU grace-period cleanup.
3832 rcutree.gp_init_delay= [KNL]
3833 Set the number of jiffies to delay each step of
3834 RCU grace-period initialization.
3836 rcutree.gp_preinit_delay= [KNL]
3837 Set the number of jiffies to delay each step of
3838 RCU grace-period pre-initialization, that is,
3839 the propagation of recent CPU-hotplug changes up
3840 the rcu_node combining tree.
3842 rcutree.use_softirq= [KNL]
3843 If set to zero, move all RCU_SOFTIRQ processing to
3844 per-CPU rcuc kthreads. Defaults to a non-zero
3845 value, meaning that RCU_SOFTIRQ is used by default.
3846 Specify rcutree.use_softirq=0 to use rcuc kthreads.
3848 rcutree.rcu_fanout_exact= [KNL]
3849 Disable autobalancing of the rcu_node combining
3850 tree. This is used by rcutorture, and might
3851 possibly be useful for architectures having high
3852 cache-to-cache transfer latencies.
3854 rcutree.rcu_fanout_leaf= [KNL]
3855 Change the number of CPUs assigned to each
3856 leaf rcu_node structure. Useful for very
3857 large systems, which will choose the value 64,
3858 and for NUMA systems with large remote-access
3859 latencies, which will choose a value aligned
3860 with the appropriate hardware boundaries.
3862 rcutree.jiffies_till_first_fqs= [KNL]
3863 Set delay from grace-period initialization to
3864 first attempt to force quiescent states.
3865 Units are jiffies, minimum value is zero,
3866 and maximum value is HZ.
3868 rcutree.jiffies_till_next_fqs= [KNL]
3869 Set delay between subsequent attempts to force
3870 quiescent states. Units are jiffies, minimum
3871 value is one, and maximum value is HZ.
3873 rcutree.jiffies_till_sched_qs= [KNL]
3874 Set required age in jiffies for a
3875 given grace period before RCU starts
3876 soliciting quiescent-state help from
3877 rcu_note_context_switch() and cond_resched().
3878 If not specified, the kernel will calculate
3879 a value based on the most recent settings
3880 of rcutree.jiffies_till_first_fqs
3881 and rcutree.jiffies_till_next_fqs.
3882 This calculated value may be viewed in
3883 rcutree.jiffies_to_sched_qs. Any attempt to set
3884 rcutree.jiffies_to_sched_qs will be cheerfully
3887 rcutree.kthread_prio= [KNL,BOOT]
3888 Set the SCHED_FIFO priority of the RCU per-CPU
3889 kthreads (rcuc/N). This value is also used for
3890 the priority of the RCU boost threads (rcub/N)
3891 and for the RCU grace-period kthreads (rcu_bh,
3892 rcu_preempt, and rcu_sched). If RCU_BOOST is
3893 set, valid values are 1-99 and the default is 1
3894 (the least-favored priority). Otherwise, when
3895 RCU_BOOST is not set, valid values are 0-99 and
3896 the default is zero (non-realtime operation).
3898 rcutree.rcu_nocb_gp_stride= [KNL]
3899 Set the number of NOCB callback kthreads in
3900 each group, which defaults to the square root
3901 of the number of CPUs. Larger numbers reduce
3902 the wakeup overhead on the global grace-period
3903 kthread, but increases that same overhead on
3904 each group's NOCB grace-period kthread.
3906 rcutree.qhimark= [KNL]
3907 Set threshold of queued RCU callbacks beyond which
3908 batch limiting is disabled.
3910 rcutree.qlowmark= [KNL]
3911 Set threshold of queued RCU callbacks below which
3912 batch limiting is re-enabled.
3914 rcutree.rcu_idle_gp_delay= [KNL]
3915 Set wakeup interval for idle CPUs that have
3916 RCU callbacks (RCU_FAST_NO_HZ=y).
3918 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3919 Set wakeup interval for idle CPUs that have
3920 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3921 Lazy RCU callbacks are those which RCU can
3922 prove do nothing more than free memory.
3924 rcutree.rcu_kick_kthreads= [KNL]
3925 Cause the grace-period kthread to get an extra
3926 wake_up() if it sleeps three times longer than
3927 it should at force-quiescent-state time.
3928 This wake_up() will be accompanied by a
3929 WARN_ONCE() splat and an ftrace_dump().
3931 rcutree.sysrq_rcu= [KNL]
3932 Commandeer a sysrq key to dump out Tree RCU's
3933 rcu_node tree with an eye towards determining
3934 why a new grace period has not yet started.
3936 rcuperf.gp_async= [KNL]
3937 Measure performance of asynchronous
3938 grace-period primitives such as call_rcu().
3940 rcuperf.gp_async_max= [KNL]
3941 Specify the maximum number of outstanding
3942 callbacks per writer thread. When a writer
3943 thread exceeds this limit, it invokes the
3944 corresponding flavor of rcu_barrier() to allow
3945 previously posted callbacks to drain.
3947 rcuperf.gp_exp= [KNL]
3948 Measure performance of expedited synchronous
3949 grace-period primitives.
3951 rcuperf.holdoff= [KNL]
3952 Set test-start holdoff period. The purpose of
3953 this parameter is to delay the start of the
3954 test until boot completes in order to avoid
3957 rcuperf.nreaders= [KNL]
3958 Set number of RCU readers. The value -1 selects
3959 N, where N is the number of CPUs. A value
3960 "n" less than -1 selects N-n+1, where N is again
3961 the number of CPUs. For example, -2 selects N
3962 (the number of CPUs), -3 selects N+1, and so on.
3963 A value of "n" less than or equal to -N selects
3966 rcuperf.nwriters= [KNL]
3967 Set number of RCU writers. The values operate
3968 the same as for rcuperf.nreaders.
3969 N, where N is the number of CPUs
3971 rcuperf.perf_type= [KNL]
3972 Specify the RCU implementation to test.
3974 rcuperf.shutdown= [KNL]
3975 Shut the system down after performance tests
3976 complete. This is useful for hands-off automated
3979 rcuperf.verbose= [KNL]
3980 Enable additional printk() statements.
3982 rcuperf.writer_holdoff= [KNL]
3983 Write-side holdoff between grace periods,
3984 in microseconds. The default of zero says
3987 rcutorture.fqs_duration= [KNL]
3988 Set duration of force_quiescent_state bursts
3991 rcutorture.fqs_holdoff= [KNL]
3992 Set holdoff time within force_quiescent_state bursts
3995 rcutorture.fqs_stutter= [KNL]
3996 Set wait time between force_quiescent_state bursts
3999 rcutorture.fwd_progress= [KNL]
4000 Enable RCU grace-period forward-progress testing
4001 for the types of RCU supporting this notion.
4003 rcutorture.fwd_progress_div= [KNL]
4004 Specify the fraction of a CPU-stall-warning
4005 period to do tight-loop forward-progress testing.
4007 rcutorture.fwd_progress_holdoff= [KNL]
4008 Number of seconds to wait between successive
4009 forward-progress tests.
4011 rcutorture.fwd_progress_need_resched= [KNL]
4012 Enclose cond_resched() calls within checks for
4013 need_resched() during tight-loop forward-progress
4016 rcutorture.gp_cond= [KNL]
4017 Use conditional/asynchronous update-side
4018 primitives, if available.
4020 rcutorture.gp_exp= [KNL]
4021 Use expedited update-side primitives, if available.
4023 rcutorture.gp_normal= [KNL]
4024 Use normal (non-expedited) asynchronous
4025 update-side primitives, if available.
4027 rcutorture.gp_sync= [KNL]
4028 Use normal (non-expedited) synchronous
4029 update-side primitives, if available. If all
4030 of rcutorture.gp_cond=, rcutorture.gp_exp=,
4031 rcutorture.gp_normal=, and rcutorture.gp_sync=
4032 are zero, rcutorture acts as if is interpreted
4033 they are all non-zero.
4035 rcutorture.n_barrier_cbs= [KNL]
4036 Set callbacks/threads for rcu_barrier() testing.
4038 rcutorture.nfakewriters= [KNL]
4039 Set number of concurrent RCU writers. These just
4040 stress RCU, they don't participate in the actual
4041 test, hence the "fake".
4043 rcutorture.nreaders= [KNL]
4044 Set number of RCU readers. The value -1 selects
4045 N-1, where N is the number of CPUs. A value
4046 "n" less than -1 selects N-n-2, where N is again
4047 the number of CPUs. For example, -2 selects N
4048 (the number of CPUs), -3 selects N+1, and so on.
4050 rcutorture.object_debug= [KNL]
4051 Enable debug-object double-call_rcu() testing.
4053 rcutorture.onoff_holdoff= [KNL]
4054 Set time (s) after boot for CPU-hotplug testing.
4056 rcutorture.onoff_interval= [KNL]
4057 Set time (jiffies) between CPU-hotplug operations,
4058 or zero to disable CPU-hotplug testing.
4060 rcutorture.shuffle_interval= [KNL]
4061 Set task-shuffle interval (s). Shuffling tasks
4062 allows some CPUs to go into dyntick-idle mode
4063 during the rcutorture test.
4065 rcutorture.shutdown_secs= [KNL]
4066 Set time (s) after boot system shutdown. This
4067 is useful for hands-off automated testing.
4069 rcutorture.stall_cpu= [KNL]
4070 Duration of CPU stall (s) to test RCU CPU stall
4071 warnings, zero to disable.
4073 rcutorture.stall_cpu_holdoff= [KNL]
4074 Time to wait (s) after boot before inducing stall.
4076 rcutorture.stall_cpu_irqsoff= [KNL]
4077 Disable interrupts while stalling if set.
4079 rcutorture.stat_interval= [KNL]
4080 Time (s) between statistics printk()s.
4082 rcutorture.stutter= [KNL]
4083 Time (s) to stutter testing, for example, specifying
4084 five seconds causes the test to run for five seconds,
4085 wait for five seconds, and so on. This tests RCU's
4086 ability to transition abruptly to and from idle.
4088 rcutorture.test_boost= [KNL]
4089 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
4090 "Maybe" means test if the RCU implementation
4091 under test support RCU priority boosting.
4093 rcutorture.test_boost_duration= [KNL]
4094 Duration (s) of each individual boost test.
4096 rcutorture.test_boost_interval= [KNL]
4097 Interval (s) between each boost test.
4099 rcutorture.test_no_idle_hz= [KNL]
4100 Test RCU's dyntick-idle handling. See also the
4101 rcutorture.shuffle_interval parameter.
4103 rcutorture.torture_type= [KNL]
4104 Specify the RCU implementation to test.
4106 rcutorture.verbose= [KNL]
4107 Enable additional printk() statements.
4109 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL]
4110 Dump ftrace buffer after reporting RCU CPU
4113 rcupdate.rcu_cpu_stall_suppress= [KNL]
4114 Suppress RCU CPU stall warning messages.
4116 rcupdate.rcu_cpu_stall_timeout= [KNL]
4117 Set timeout for RCU CPU stall warning messages.
4119 rcupdate.rcu_expedited= [KNL]
4120 Use expedited grace-period primitives, for
4121 example, synchronize_rcu_expedited() instead
4122 of synchronize_rcu(). This reduces latency,
4123 but can increase CPU utilization, degrade
4124 real-time latency, and degrade energy efficiency.
4125 No effect on CONFIG_TINY_RCU kernels.
4127 rcupdate.rcu_normal= [KNL]
4128 Use only normal grace-period primitives,
4129 for example, synchronize_rcu() instead of
4130 synchronize_rcu_expedited(). This improves
4131 real-time latency, CPU utilization, and
4132 energy efficiency, but can expose users to
4133 increased grace-period latency. This parameter
4134 overrides rcupdate.rcu_expedited. No effect on
4135 CONFIG_TINY_RCU kernels.
4137 rcupdate.rcu_normal_after_boot= [KNL]
4138 Once boot has completed (that is, after
4139 rcu_end_inkernel_boot() has been invoked), use
4140 only normal grace-period primitives. No effect
4141 on CONFIG_TINY_RCU kernels.
4143 rcupdate.rcu_task_stall_timeout= [KNL]
4144 Set timeout in jiffies for RCU task stall warning
4145 messages. Disable with a value less than or equal
4148 rcupdate.rcu_self_test= [KNL]
4149 Run the RCU early boot self tests
4153 Run specified binary instead of /init from the ramdisk,
4154 used for early userspace startup. See initrd.
4157 force - Override the decision by the kernel to hide the
4158 advertisement of RDRAND support (this affects
4159 certain AMD processors because of buggy BIOS
4160 support, specifically around the suspend/resume
4164 Turn on/off individual RDT features. List is:
4165 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
4167 E.g. to turn on cmt and turn off mba use:
4171 Format (x86 or x86_64):
4172 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
4174 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
4176 Where reboot_mode is one of warm (soft) or cold (hard) or gpio
4177 (prefix with 'panic_' to set mode for panic
4179 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
4180 reboot_force is either force or not specified,
4181 reboot_cpu is s[mp]#### with #### being the processor
4182 to be used for rebooting.
4185 [KNL, SMP] Set scheduler's default relax_domain_level.
4186 See Documentation/admin-guide/cgroup-v1/cpusets.rst.
4188 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
4189 Format: <base1>,<size1>[,<base2>,<size2>,...]
4190 Reserve I/O ports or memory so the kernel won't use
4191 them. If <base> is less than 0x10000, the region
4192 is assumed to be I/O ports; otherwise it is memory.
4194 reservetop= [X86-32]
4196 Reserves a hole at the top of the kernel virtual
4201 Set the amount of memory to reserve for BIOS at
4202 the bottom of the address space.
4204 reset_devices [KNL] Force drivers to reset the underlying device
4205 during initialization.
4208 Specify the partition device for software suspend
4210 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
4212 resume_offset= [SWSUSP]
4213 Specify the offset from the beginning of the partition
4214 given by "resume=" at which the swap header is located,
4215 in <PAGE_SIZE> units (needed only for swap files).
4216 See Documentation/power/swsusp-and-swap-files.rst
4218 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
4219 read the resume files
4221 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
4222 Useful for devices that are detected asynchronously
4223 (e.g. USB and MMC devices).
4225 hibernate= [HIBERNATION]
4226 noresume Don't check if there's a hibernation image
4227 present during boot.
4228 nocompress Don't compress/decompress hibernation images.
4229 no Disable hibernation and resume.
4230 protect_image Turn on image protection during restoration
4231 (that will set all pages holding image data
4232 during restoration read-only).
4234 retain_initrd [RAM] Keep initrd memory after extraction
4236 rfkill.default_state=
4237 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
4238 etc. communication is blocked by default.
4241 rfkill.master_switch_mode=
4242 0 The "airplane mode" button does nothing.
4243 1 The "airplane mode" button toggles between everything
4244 blocked and the previous configuration.
4245 2 The "airplane mode" button toggles between everything
4246 blocked and everything unblocked.
4248 rhash_entries= [KNL,NET]
4249 Set number of hash buckets for route cache
4252 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
4255 ro [KNL] Mount root device read-only on boot
4258 on Mark read-only kernel memory as read-only (default).
4259 off Leave read-only kernel memory writable for debugging.
4262 Enable the uart passthrough on the designated usb port
4263 on Rockchip SoCs. When active, the signals of the
4264 debug-uart get routed to the D+ and D- pins of the usb
4265 port and the regular usb controller gets disabled.
4267 root= [KNL] Root filesystem
4268 See name_to_dev_t comment in init/do_mounts.c.
4270 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
4271 mount the root filesystem
4273 rootflags= [KNL] Set root filesystem mount option string
4275 rootfstype= [KNL] Set root filesystem type
4277 rootwait [KNL] Wait (indefinitely) for root device to show up.
4278 Useful for devices that are detected asynchronously
4279 (e.g. USB and MMC devices).
4281 rproc_mem=nn[KMG][@address]
4282 [KNL,ARM,CMA] Remoteproc physical memory block.
4283 Memory area to be used by remote processor image,
4286 rw [KNL] Mount root device read-write on boot
4288 S [KNL] Run init in single mode
4290 s390_iommu= [HW,S390]
4291 Set s390 IOTLB flushing mode
4293 With strict flushing every unmap operation will result in
4294 an IOTLB flush. Default is lazy flushing before reuse,
4298 See drivers/net/irda/sa1100_ir.c.
4300 sbni= [NET] Granch SBNI12 leased line adapter
4302 sched_debug [KNL] Enables verbose scheduler debug messages.
4304 schedstats= [KNL,X86] Enable or disable scheduled statistics.
4305 Allowed values are enable and disable. This feature
4306 incurs a small amount of overhead in the scheduler
4307 but is useful for debugging and performance tuning.
4309 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
4310 xtime_lock contention on larger systems, and/or RCU lock
4311 contention on all systems with CONFIG_MAXSMP set.
4312 Format: { "0" | "1" }
4313 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
4315 Note: increases power consumption, thus should only be
4316 enabled if running jitter sensitive (HPC/RT) workloads.
4318 security= [SECURITY] Choose a legacy "major" security module to
4319 enable at boot. This has been deprecated by the
4322 selinux= [SELINUX] Disable or enable SELinux at boot time.
4323 Format: { "0" | "1" }
4324 See security/selinux/Kconfig help text.
4327 Default value is set via kernel config option.
4328 If enabled at boot time, /selinux/disable can be used
4329 later to disable prior to initial policy load.
4331 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
4332 Format: { "0" | "1" }
4333 See security/apparmor/Kconfig help text
4336 Default value is set via kernel config option.
4338 serialnumber [BUGS=X86-32]
4341 Maximal number of shapers.
4349 Disable merging of slabs with similar size. May be
4350 necessary if there is some reason to distinguish
4351 allocs to different slabs, especially in hardened
4352 environments where the risk of heap overflows and
4353 layout control by attackers can usually be
4354 frustrated by disabling merging. This will reduce
4355 most of the exposure of a heap attack to a single
4356 cache (risks via metadata attacks are mostly
4357 unchanged). Debug options disable merging on their
4359 For more information see Documentation/vm/slub.rst.
4361 slab_max_order= [MM, SLAB]
4362 Determines the maximum allowed order for slabs.
4363 A high setting may cause OOMs due to memory
4364 fragmentation. Defaults to 1 for systems with
4365 more than 32MB of RAM, 0 otherwise.
4367 slub_debug[=options[,slabs]] [MM, SLUB]
4368 Enabling slub_debug allows one to determine the
4369 culprit if slab objects become corrupted. Enabling
4370 slub_debug can create guard zones around objects and
4371 may poison objects when not in use. Also tracks the
4372 last alloc / free. For more information see
4373 Documentation/vm/slub.rst.
4375 slub_memcg_sysfs= [MM, SLUB]
4376 Determines whether to enable sysfs directories for
4377 memory cgroup sub-caches. 1 to enable, 0 to disable.
4378 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
4379 Enabling this can lead to a very high number of debug
4380 directories and files being created under
4383 slub_max_order= [MM, SLUB]
4384 Determines the maximum allowed order for slabs.
4385 A high setting may cause OOMs due to memory
4386 fragmentation. For more information see
4387 Documentation/vm/slub.rst.
4389 slub_min_objects= [MM, SLUB]
4390 The minimum number of objects per slab. SLUB will
4391 increase the slab order up to slub_max_order to
4392 generate a sufficiently large slab able to contain
4393 the number of objects indicated. The higher the number
4394 of objects the smaller the overhead of tracking slabs
4395 and the less frequently locks need to be acquired.
4396 For more information see Documentation/vm/slub.rst.
4398 slub_min_order= [MM, SLUB]
4399 Determines the minimum page order for slabs. Must be
4400 lower than slub_max_order.
4401 For more information see Documentation/vm/slub.rst.
4403 slub_nomerge [MM, SLUB]
4404 Same with slab_nomerge. This is supported for legacy.
4405 See slab_nomerge for more information.
4408 Format: <io1>[,<io2>[,...,<io8>]]
4410 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4411 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4412 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4413 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4414 smsc-ircc2.ircc_irq= [HW] IRQ line
4415 smsc-ircc2.ircc_dma= [HW] DMA channel
4416 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4417 0: Toshiba Satellite 1800 (GP data pin select)
4418 1: Fast pin select (default)
4421 smt [KNL,S390] Set the maximum number of threads (logical
4422 CPUs) to use per physical CPU on systems capable of
4423 symmetric multithreading (SMT). Will be capped to the
4424 actual hardware limit.
4426 Default: -1 (no limit)
4429 [KNL] Should the soft-lockup detector generate panics.
4432 A nonzero value instructs the soft-lockup detector
4433 to panic the machine when a soft-lockup occurs. This
4434 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
4435 which is the respective build-time switch to that
4438 softlockup_all_cpu_backtrace=
4439 [KNL] Should the soft-lockup detector generate
4440 backtraces on all cpus.
4443 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4444 See Documentation/admin-guide/laptops/sonypi.rst
4446 spectre_v2= [X86] Control mitigation of Spectre variant 2
4447 (indirect branch speculation) vulnerability.
4448 The default operation protects the kernel from
4451 on - unconditionally enable, implies
4453 off - unconditionally disable, implies
4455 auto - kernel detects whether your CPU model is
4458 Selecting 'on' will, and 'auto' may, choose a
4459 mitigation method at run time according to the
4460 CPU, the available microcode, the setting of the
4461 CONFIG_RETPOLINE configuration option, and the
4462 compiler with which the kernel was built.
4464 Selecting 'on' will also enable the mitigation
4465 against user space to user space task attacks.
4467 Selecting 'off' will disable both the kernel and
4468 the user space protections.
4470 Specific mitigations can also be selected manually:
4472 retpoline - replace indirect branches
4473 retpoline,generic - google's original retpoline
4474 retpoline,amd - AMD-specific minimal thunk
4476 Not specifying this option is equivalent to
4480 [X86] Control mitigation of Spectre variant 2
4481 (indirect branch speculation) vulnerability between
4484 on - Unconditionally enable mitigations. Is
4485 enforced by spectre_v2=on
4487 off - Unconditionally disable mitigations. Is
4488 enforced by spectre_v2=off
4490 prctl - Indirect branch speculation is enabled,
4491 but mitigation can be enabled via prctl
4492 per thread. The mitigation control state
4493 is inherited on fork.
4496 - Like "prctl" above, but only STIBP is
4497 controlled per thread. IBPB is issued
4498 always when switching between different user
4502 - Same as "prctl" above, but all seccomp
4503 threads will enable the mitigation unless
4504 they explicitly opt out.
4507 - Like "seccomp" above, but only STIBP is
4508 controlled per thread. IBPB is issued
4509 always when switching between different
4510 user space processes.
4512 auto - Kernel selects the mitigation depending on
4513 the available CPU features and vulnerability.
4516 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
4518 Not specifying this option is equivalent to
4519 spectre_v2_user=auto.
4521 spec_store_bypass_disable=
4522 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4523 (Speculative Store Bypass vulnerability)
4525 Certain CPUs are vulnerable to an exploit against a
4526 a common industry wide performance optimization known
4527 as "Speculative Store Bypass" in which recent stores
4528 to the same memory location may not be observed by
4529 later loads during speculative execution. The idea
4530 is that such stores are unlikely and that they can
4531 be detected prior to instruction retirement at the
4532 end of a particular speculation execution window.
4534 In vulnerable processors, the speculatively forwarded
4535 store can be used in a cache side channel attack, for
4536 example to read memory to which the attacker does not
4537 directly have access (e.g. inside sandboxed code).
4539 This parameter controls whether the Speculative Store
4540 Bypass optimization is used.
4542 On x86 the options are:
4544 on - Unconditionally disable Speculative Store Bypass
4545 off - Unconditionally enable Speculative Store Bypass
4546 auto - Kernel detects whether the CPU model contains an
4547 implementation of Speculative Store Bypass and
4548 picks the most appropriate mitigation. If the
4549 CPU is not vulnerable, "off" is selected. If the
4550 CPU is vulnerable the default mitigation is
4551 architecture and Kconfig dependent. See below.
4552 prctl - Control Speculative Store Bypass per thread
4553 via prctl. Speculative Store Bypass is enabled
4554 for a process by default. The state of the control
4555 is inherited on fork.
4556 seccomp - Same as "prctl" above, but all seccomp threads
4557 will disable SSB unless they explicitly opt out.
4559 Default mitigations:
4560 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4562 On powerpc the options are:
4564 on,auto - On Power8 and Power9 insert a store-forwarding
4565 barrier on kernel entry and exit. On Power7
4566 perform a software flush on kernel entry and
4570 Not specifying this option is equivalent to
4571 spec_store_bypass_disable=auto.
4573 spia_io_base= [HW,MTD]
4578 srcutree.counter_wrap_check [KNL]
4579 Specifies how frequently to check for
4580 grace-period sequence counter wrap for the
4581 srcu_data structure's ->srcu_gp_seq_needed field.
4582 The greater the number of bits set in this kernel
4583 parameter, the less frequently counter wrap will
4584 be checked for. Note that the bottom two bits
4587 srcutree.exp_holdoff [KNL]
4588 Specifies how many nanoseconds must elapse
4589 since the end of the last SRCU grace period for
4590 a given srcu_struct until the next normal SRCU
4591 grace period will be considered for automatic
4592 expediting. Set to zero to disable automatic
4596 Speculative Store Bypass Disable control
4598 On CPUs that are vulnerable to the Speculative
4599 Store Bypass vulnerability and offer a
4600 firmware based mitigation, this parameter
4601 indicates how the mitigation should be used:
4603 force-on: Unconditionally enable mitigation for
4604 for both kernel and userspace
4605 force-off: Unconditionally disable mitigation for
4606 for both kernel and userspace
4607 kernel: Always enable mitigation in the
4608 kernel, and offer a prctl interface
4609 to allow userspace to register its
4610 interest in being mitigated too.
4612 stack_guard_gap= [MM]
4613 override the default stack gap protection. The value
4614 is in page units and it defines how many pages prior
4615 to (for stacks growing down) resp. after (for stacks
4616 growing up) the main stack are reserved for no other
4617 mapping. Default value is 256 pages.
4620 Enabled the stack tracer on boot up.
4622 stacktrace_filter=[function-list]
4623 [FTRACE] Limit the functions that the stack tracer
4624 will trace at boot up. function-list is a comma separated
4625 list of functions. This list can be changed at run
4626 time by the stack_trace_filter file in the debugfs
4627 tracing directory. Note, this enables stack tracing
4628 and the stacktrace above is not needed.
4632 Set the STI (builtin display/keyboard on the HP-PARISC
4633 machines) console (graphic card) which should be used
4634 as the initial boot-console.
4635 See also comment in drivers/video/console/sticore.c.
4638 See comment in drivers/video/console/sticore.c.
4641 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4643 sunrpc.min_resvport=
4644 sunrpc.max_resvport=
4646 SunRPC servers often require that client requests
4647 originate from a privileged port (i.e. a port in the
4648 range 0 < portnr < 1024).
4649 An administrator who wishes to reserve some of these
4650 ports for other uses may adjust the range that the
4651 kernel's sunrpc client considers to be privileged
4652 using these two parameters to set the minimum and
4653 maximum port values.
4655 sunrpc.svc_rpc_per_connection_limit=
4657 Limit the number of requests that the server will
4658 process in parallel from a single connection.
4659 The default value is 0 (no limit).
4663 Control how the NFS server code allocates CPUs to
4664 service thread pools. Depending on how many NICs
4665 you have and where their interrupts are bound, this
4666 option will affect which CPUs will do NFS serving.
4667 Note: this parameter cannot be changed while the
4668 NFS server is running.
4670 auto the server chooses an appropriate mode
4671 automatically using heuristics
4672 global a single global pool contains all CPUs
4673 percpu one pool for each CPU
4674 pernode one pool for each NUMA node (equivalent
4675 to global on non-NUMA machines)
4677 sunrpc.tcp_slot_table_entries=
4678 sunrpc.udp_slot_table_entries=
4680 Sets the upper limit on the number of simultaneous
4681 RPC calls that can be sent from the client to a
4682 server. Increasing these values may allow you to
4683 improve throughput, but will also increase the
4684 amount of memory reserved for use by the client.
4686 suspend.pm_test_delay=
4688 Sets the number of seconds to remain in a suspend test
4689 mode before resuming the system (see
4690 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4691 is set. Default value is 5.
4694 Format: { on | off | y | n | 1 | 0 }
4695 This parameter controls use of the Protected
4696 Execution Facility on pSeries.
4699 [KNL] Enable accounting of swap in memory resource
4700 controller if no parameter or 1 is given or disable
4701 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst)
4703 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4704 Format: { <int> | force | noforce }
4705 <int> -- Number of I/O TLB slabs
4706 force -- force using of bounce buffers even if they
4707 wouldn't be automatically used by the kernel
4708 noforce -- Never use bounce buffers (for debugging)
4712 sysfs.deprecated=0|1 [KNL]
4713 Enable/disable old style sysfs layout for old udev
4714 on older distributions. When this option is enabled
4715 very new udev will not work anymore. When this option
4716 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4717 in older udev will not work anymore.
4718 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4719 the kernel configuration.
4721 sysrq_always_enabled
4723 Ignore sysrq setting - this boot parameter will
4724 neutralize any effect of /proc/sys/kernel/sysrq.
4725 Useful for debugging.
4727 tcpmhash_entries= [KNL,NET]
4728 Set the number of tcp_metrics_hash slots.
4729 Default value is 8192 or 16384 depending on total
4730 ram pages. This is used to specify the TCP metrics
4731 cache size. See Documentation/networking/ip-sysctl.txt
4732 "tcp_no_metrics_save" section for more details.
4736 test_suspend= [SUSPEND][,N]
4737 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4738 standby suspend) or "freeze" (for suspend type freeze)
4739 as the system sleep state during system startup with
4740 the optional capability to repeat N number of times.
4741 The system is woken from this state using a
4742 wakeup-capable RTC alarm.
4744 thash_entries= [KNL,NET]
4745 Set number of hash buckets for TCP connection
4747 thermal.act= [HW,ACPI]
4748 -1: disable all active trip points in all thermal zones
4749 <degrees C>: override all lowest active trip points
4751 thermal.crt= [HW,ACPI]
4752 -1: disable all critical trip points in all thermal zones
4753 <degrees C>: override all critical trip points
4755 thermal.nocrt= [HW,ACPI]
4756 Set to disable actions on ACPI thermal zone
4757 critical and hot trip points.
4759 thermal.off= [HW,ACPI]
4760 1: disable ACPI thermal control
4762 thermal.psv= [HW,ACPI]
4763 -1: disable all passive trip points
4764 <degrees C>: override all passive trip points to this
4767 thermal.tzp= [HW,ACPI]
4768 Specify global default ACPI thermal zone polling rate
4769 <deci-seconds>: poll all this frequency
4770 0: no polling (default)
4773 Force threading of all interrupt handlers except those
4774 marked explicitly IRQF_NO_THREAD.
4778 Specify if the kernel should make use of the cpu
4779 topology information if the hardware supports this.
4780 The scheduler will make use of this information and
4781 e.g. base its process migration decisions on it.
4784 topology_updates= [KNL, PPC, NUMA]
4786 Specify if the kernel should ignore (off)
4787 topology updates sent by the hypervisor to this
4792 tpm_suspend_pcr=[HW,TPM]
4793 Format: integer pcr id
4794 Specify that at suspend time, the tpm driver
4795 should extend the specified pcr with zeros,
4796 as a workaround for some chips which fail to
4797 flush the last written pcr on TPM_SaveState.
4798 This will guarantee that all the other pcrs
4801 trace_buf_size=nn[KMG]
4802 [FTRACE] will set tracing buffer size on each cpu.
4804 trace_event=[event-list]
4805 [FTRACE] Set and start specified trace events in order
4806 to facilitate early boot debugging. The event-list is a
4807 comma separated list of trace events to enable. See
4808 also Documentation/trace/events.rst
4810 trace_options=[option-list]
4811 [FTRACE] Enable or disable tracer options at boot.
4812 The option-list is a comma delimited list of options
4813 that can be enabled or disabled just as if you were
4814 to echo the option name into
4816 /sys/kernel/debug/tracing/trace_options
4818 For example, to enable stacktrace option (to dump the
4819 stack trace of each event), add to the command line:
4821 trace_options=stacktrace
4823 See also Documentation/trace/ftrace.rst "trace options"
4827 Have the tracepoints sent to printk as well as the
4828 tracing ring buffer. This is useful for early boot up
4829 where the system hangs or reboots and does not give the
4830 option for reading the tracing buffer or performing a
4831 ftrace_dump_on_oops.
4833 To turn off having tracepoints sent to printk,
4834 echo 0 > /proc/sys/kernel/tracepoint_printk
4835 Note, echoing 1 into this file without the
4836 tracepoint_printk kernel cmdline option has no effect.
4840 Having tracepoints sent to printk() and activating high
4841 frequency tracepoints such as irq or sched, can cause
4842 the system to live lock.
4845 [FTRACE] enable this option to disable tracing when a
4846 warning is hit. This turns off "tracing_on". Tracing can
4847 be enabled again by echoing '1' into the "tracing_on"
4848 file located in /sys/kernel/debug/tracing/
4850 This option is useful, as it disables the trace before
4851 the WARNING dump is called, which prevents the trace to
4852 be filled with content caused by the warning output.
4854 This option can also be set at run time via the sysctl
4855 option: kernel/traceoff_on_warning
4857 transparent_hugepage=
4859 Format: [always|madvise|never]
4860 Can be used to control the default behavior of the system
4861 with respect to transparent hugepages.
4862 See Documentation/admin-guide/mm/transhuge.rst
4865 tsc= Disable clocksource stability checks for TSC.
4867 [x86] reliable: mark tsc clocksource as reliable, this
4868 disables clocksource verification at runtime, as well
4869 as the stability checks done at bootup. Used to enable
4870 high-resolution timer mode on older hardware, and in
4871 virtualized environment.
4872 [x86] noirqtime: Do not use TSC to do irq accounting.
4873 Used to run time disable IRQ_TIME_ACCOUNTING on any
4874 platforms where RDTSC is slow and this accounting
4876 [x86] unstable: mark the TSC clocksource as unstable, this
4877 marks the TSC unconditionally unstable at bootup and
4878 avoids any further wobbles once the TSC watchdog notices.
4879 [x86] nowatchdog: disable clocksource watchdog. Used
4880 in situations with strict latency requirements (where
4881 interruptions from clocksource watchdog are not
4884 tsx= [X86] Control Transactional Synchronization
4885 Extensions (TSX) feature in Intel processors that
4886 support TSX control.
4888 This parameter controls the TSX feature. The options are:
4890 on - Enable TSX on the system. Although there are
4891 mitigations for all known security vulnerabilities,
4892 TSX has been known to be an accelerator for
4893 several previous speculation-related CVEs, and
4894 so there may be unknown security risks associated
4895 with leaving it enabled.
4897 off - Disable TSX on the system. (Note that this
4898 option takes effect only on newer CPUs which are
4899 not vulnerable to MDS, i.e., have
4900 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
4901 the new IA32_TSX_CTRL MSR through a microcode
4902 update. This new MSR allows for the reliable
4903 deactivation of the TSX functionality.)
4905 auto - Disable TSX if X86_BUG_TAA is present,
4906 otherwise enable TSX on the system.
4908 Not specifying this option is equivalent to tsx=off.
4910 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
4913 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async
4914 Abort (TAA) vulnerability.
4916 Similar to Micro-architectural Data Sampling (MDS)
4917 certain CPUs that support Transactional
4918 Synchronization Extensions (TSX) are vulnerable to an
4919 exploit against CPU internal buffers which can forward
4920 information to a disclosure gadget under certain
4923 In vulnerable processors, the speculatively forwarded
4924 data can be used in a cache side channel attack, to
4925 access data to which the attacker does not have direct
4928 This parameter controls the TAA mitigation. The
4931 full - Enable TAA mitigation on vulnerable CPUs
4934 full,nosmt - Enable TAA mitigation and disable SMT on
4935 vulnerable CPUs. If TSX is disabled, SMT
4936 is not disabled because CPU is not
4937 vulnerable to cross-thread TAA attacks.
4938 off - Unconditionally disable TAA mitigation
4940 On MDS-affected machines, tsx_async_abort=off can be
4941 prevented by an active MDS mitigation as both vulnerabilities
4942 are mitigated with the same mechanism so in order to disable
4943 this mitigation, you need to specify mds=off too.
4945 Not specifying this option is equivalent to
4946 tsx_async_abort=full. On CPUs which are MDS affected
4947 and deploy MDS mitigation, TAA mitigation is not
4948 required and doesn't provide any additional
4952 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
4954 turbografx.map[2|3]= [HW,JOY]
4955 TurboGraFX parallel port interface
4957 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4958 See also Documentation/input/devices/joystick-parport.rst
4960 udbg-immortal [PPC] When debugging early kernel crashes that
4961 happen after console_init() and before a proper
4962 console driver takes over, this boot options might
4963 help "seeing" what's going on.
4965 uhash_entries= [KNL,NET]
4966 Set number of hash buckets for UDP/UDP-Lite connections
4969 [USB] Ignore overcurrent events (default N).
4970 Some badly-designed motherboards generate lots of
4971 bogus events, for ports that aren't wired to
4972 anything. Set this parameter to avoid log spamming.
4973 Note that genuine overcurrent events won't be
4977 [X86] Cause panic on unknown NMI.
4979 usbcore.authorized_default=
4980 [USB] Default USB device authorization:
4981 (default -1 = authorized except for wireless USB,
4982 0 = not authorized, 1 = authorized, 2 = authorized
4983 if device connected to internal port)
4985 usbcore.autosuspend=
4986 [USB] The autosuspend time delay (in seconds) used
4987 for newly-detected USB devices (default 2). This
4988 is the time required before an idle device will be
4989 autosuspended. Devices for which the delay is set
4990 to a negative value won't be autosuspended at all.
4992 usbcore.usbfs_snoop=
4993 [USB] Set to log all usbfs traffic (default 0 = off).
4995 usbcore.usbfs_snoop_max=
4996 [USB] Maximum number of bytes to snoop in each URB
4999 usbcore.blinkenlights=
5000 [USB] Set to cycle leds on hubs (default 0 = off).
5002 usbcore.old_scheme_first=
5003 [USB] Start with the old device initialization
5004 scheme, applies only to low and full-speed devices
5007 usbcore.usbfs_memory_mb=
5008 [USB] Memory limit (in MB) for buffers allocated by
5009 usbfs (default = 16, 0 = max = 2047).
5011 usbcore.use_both_schemes=
5012 [USB] Try the other device initialization scheme
5013 if the first one fails (default 1 = enabled).
5015 usbcore.initial_descriptor_timeout=
5016 [USB] Specifies timeout for the initial 64-byte
5017 USB_REQ_GET_DESCRIPTOR request in milliseconds
5018 (default 5000 = 5.0 seconds).
5020 usbcore.nousb [USB] Disable the USB subsystem
5023 [USB] A list of quirk entries to augment the built-in
5024 usb core quirk list. List entries are separated by
5025 commas. Each entry has the form
5026 VendorID:ProductID:Flags. The IDs are 4-digit hex
5027 numbers and Flags is a set of letters. Each letter
5028 will change the built-in quirk; setting it if it is
5029 clear and clearing it if it is set. The letters have
5030 the following meanings:
5031 a = USB_QUIRK_STRING_FETCH_255 (string
5032 descriptors must not be fetched using
5034 b = USB_QUIRK_RESET_RESUME (device can't resume
5035 correctly so reset it instead);
5036 c = USB_QUIRK_NO_SET_INTF (device can't handle
5037 Set-Interface requests);
5038 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
5039 handle its Configuration or Interface
5041 e = USB_QUIRK_RESET (device can't be reset
5042 (e.g morph devices), don't use reset);
5043 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
5044 more interface descriptions than the
5045 bNumInterfaces count, and can't handle
5046 talking to these interfaces);
5047 g = USB_QUIRK_DELAY_INIT (device needs a pause
5048 during initialization, after we read
5049 the device descriptor);
5050 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
5051 high speed and super speed interrupt
5052 endpoints, the USB 2.0 and USB 3.0 spec
5053 require the interval in microframes (1
5054 microframe = 125 microseconds) to be
5055 calculated as interval = 2 ^
5057 Devices with this quirk report their
5058 bInterval as the result of this
5059 calculation instead of the exponent
5060 variable used in the calculation);
5061 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
5062 handle device_qualifier descriptor
5064 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
5065 generates spurious wakeup, ignore
5066 remote wakeup capability);
5067 k = USB_QUIRK_NO_LPM (device can't handle Link
5069 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
5070 (Device reports its bInterval as linear
5071 frames instead of the USB 2.0
5073 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
5074 to be disconnected before suspend to
5075 prevent spurious wakeup);
5076 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
5077 pause after every control message);
5078 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
5079 delay after resetting its port);
5080 Example: quirks=0781:5580:bk,0a5c:5834:gij
5083 [USBHID] The interval which mice are to be polled at.
5086 [USBHID] The interval which joysticks are to be polled at.
5089 [USBHID] The interval which keyboards are to be polled at.
5091 usb-storage.delay_use=
5092 [UMS] The delay in seconds before a new device is
5093 scanned for Logical Units (default 1).
5096 [UMS] A list of quirks entries to supplement or
5097 override the built-in unusual_devs list. List
5098 entries are separated by commas. Each entry has
5099 the form VID:PID:Flags where VID and PID are Vendor
5100 and Product ID values (4-digit hex numbers) and
5101 Flags is a set of characters, each corresponding
5102 to a common usb-storage quirk flag as follows:
5103 a = SANE_SENSE (collect more than 18 bytes
5105 b = BAD_SENSE (don't collect more than 18
5106 bytes of sense data);
5107 c = FIX_CAPACITY (decrease the reported
5108 device capacity by one sector);
5109 d = NO_READ_DISC_INFO (don't use
5110 READ_DISC_INFO command);
5111 e = NO_READ_CAPACITY_16 (don't use
5112 READ_CAPACITY_16 command);
5113 f = NO_REPORT_OPCODES (don't use report opcodes
5115 g = MAX_SECTORS_240 (don't transfer more than
5116 240 sectors at a time, uas only);
5117 h = CAPACITY_HEURISTICS (decrease the
5118 reported device capacity by one
5119 sector if the number is odd);
5120 i = IGNORE_DEVICE (don't bind to this
5122 j = NO_REPORT_LUNS (don't use report luns
5124 l = NOT_LOCKABLE (don't try to lock and
5125 unlock ejectable media);
5126 m = MAX_SECTORS_64 (don't transfer more
5127 than 64 sectors = 32 KB at a time);
5128 n = INITIAL_READ10 (force a retry of the
5129 initial READ(10) command);
5130 o = CAPACITY_OK (accept the capacity
5131 reported by the device);
5132 p = WRITE_CACHE (the device cache is ON
5134 r = IGNORE_RESIDUE (the device reports
5135 bogus residue values);
5136 s = SINGLE_LUN (the device has only one
5138 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
5139 commands, uas only);
5140 u = IGNORE_UAS (don't bind to the uas driver);
5141 w = NO_WP_DETECT (don't test whether the
5142 medium is write-protected).
5143 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
5144 even if the device claims no cache)
5145 Example: quirks=0419:aaf5:rl,0421:0433:rc
5147 user_debug= [KNL,ARM]
5149 See arch/arm/Kconfig.debug help text.
5150 1 - undefined instruction events
5152 4 - invalid data aborts
5155 Example: user_debug=31
5158 [X86] Flags controlling user PTE allocations.
5160 nohigh = do not allocate PTE pages in
5161 HIGHMEM regardless of setting
5165 On X86_32, this is an alias for vdso32=. Otherwise:
5167 vdso=1: enable VDSO (the default)
5168 vdso=0: disable VDSO mapping
5170 vdso32= [X86] Control the 32-bit vDSO
5171 vdso32=1: enable 32-bit VDSO
5172 vdso32=0 or vdso32=2: disable 32-bit VDSO
5174 See the help text for CONFIG_COMPAT_VDSO for more
5175 details. If CONFIG_COMPAT_VDSO is set, the default is
5176 vdso32=0; otherwise, the default is vdso32=1.
5178 For compatibility with older kernels, vdso32=2 is an
5181 Try vdso32=0 if you encounter an error that says:
5182 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
5185 vector=percpu: enable percpu vector domain
5187 video= [FB] Frame buffer configuration
5188 See Documentation/fb/modedb.rst.
5190 video.brightness_switch_enabled= [0,1]
5191 If set to 1, on receiving an ACPI notify event
5192 generated by hotkey, video driver will adjust brightness
5193 level and then send out the event to user space through
5194 the allocated input device; If set to 0, video driver
5195 will only send out the event without touching backlight
5200 [VMMIO] Memory mapped virtio (platform) device.
5202 <size>@<baseaddr>:<irq>[:<id>]
5204 <size> := size (can use standard suffixes
5206 <baseaddr> := physical base address
5207 <irq> := interrupt number (as passed to
5209 <id> := (optional) platform device id
5211 virtio_mmio.device=1K@0x100b0000:48:7
5213 Can be used multiple times for multiple devices.
5215 vga= [BOOT,X86-32] Select a particular video mode
5216 See Documentation/x86/boot.rst and
5217 Documentation/admin-guide/svga.rst.
5218 Use vga=ask for menu.
5219 This is actually a boot loader parameter; the value is
5220 passed to the kernel using a special protocol.
5222 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
5223 May slow down system boot speed, especially when
5224 enabled on systems with a large amount of memory.
5225 All options are enabled by default, and this
5226 interface is meant to allow for selectively
5227 enabling or disabling specific virtual memory
5230 Available options are:
5231 P Enable page structure init time poisoning
5232 - Disable all of the above options
5234 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
5235 size of <nn>. This can be used to increase the
5236 minimum size (128MB on x86). It can also be used to
5237 decrease the size and leave more room for directly
5240 vmcp_cma=nn[MG] [KNL,S390]
5241 Sets the memory size reserved for contiguous memory
5242 allocations for the vmcp device driver.
5244 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
5247 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
5250 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
5254 Controls the behavior of vsyscalls (i.e. calls to
5255 fixed addresses of 0xffffffffff600x00 from legacy
5256 code). Most statically-linked binaries and older
5257 versions of glibc use these calls. Because these
5258 functions are at fixed addresses, they make nice
5259 targets for exploits that can control RIP.
5261 emulate [default] Vsyscalls turn into traps and are
5262 emulated reasonably safely. The vsyscall
5265 xonly Vsyscalls turn into traps and are
5266 emulated reasonably safely. The vsyscall
5267 page is not readable.
5269 none Vsyscalls don't work at all. This makes
5270 them quite hard to use for exploits but
5271 might break your system.
5273 vt.color= [VT] Default text color.
5274 Format: 0xYX, X = foreground, Y = background.
5275 Default: 0x07 = light gray on black.
5277 vt.cur_default= [VT] Default cursor shape.
5278 Format: 0xCCBBAA, where AA, BB, and CC are the same as
5279 the parameters of the <Esc>[?A;B;Cc escape sequence;
5280 see VGA-softcursor.txt. Default: 2 = underline.
5282 vt.default_blu= [VT]
5283 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
5284 Change the default blue palette of the console.
5285 This is a 16-member array composed of values
5288 vt.default_grn= [VT]
5289 Format: <green0>,<green1>,<green2>,...,<green15>
5290 Change the default green palette of the console.
5291 This is a 16-member array composed of values
5294 vt.default_red= [VT]
5295 Format: <red0>,<red1>,<red2>,...,<red15>
5296 Change the default red palette of the console.
5297 This is a 16-member array composed of values
5303 Set system-wide default UTF-8 mode for all tty's.
5304 Default is 1, i.e. UTF-8 mode is enabled for all
5305 newly opened terminals.
5307 vt.global_cursor_default=
5310 Set system-wide default for whether a cursor
5311 is shown on new VTs. Default is -1,
5312 i.e. cursors will be created by default unless
5313 overridden by individual drivers. 0 will hide
5314 cursors, 1 will display them.
5316 vt.italic= [VT] Default color for italic text; 0-15.
5319 vt.underline= [VT] Default color for underlined text; 0-15.
5322 watchdog timers [HW,WDT] For information on watchdog timers,
5323 see Documentation/watchdog/watchdog-parameters.rst
5324 or other driver-specific files in the
5325 Documentation/watchdog/ directory.
5329 Set the hard lockup detector stall duration
5330 threshold in seconds. The soft lockup detector
5331 threshold is set to twice the value. A value of 0
5332 disables both lockup detectors. Default is 10
5335 workqueue.watchdog_thresh=
5336 If CONFIG_WQ_WATCHDOG is configured, workqueue can
5337 warn stall conditions and dump internal state to
5338 help debugging. 0 disables workqueue stall
5339 detection; otherwise, it's the stall threshold
5340 duration in seconds. The default value is 30 and
5341 it can be updated at runtime by writing to the
5342 corresponding sysfs file.
5344 workqueue.disable_numa
5345 By default, all work items queued to unbound
5346 workqueues are affine to the NUMA nodes they're
5347 issued on, which results in better behavior in
5348 general. If NUMA affinity needs to be disabled for
5349 whatever reason, this option can be used. Note
5350 that this also can be controlled per-workqueue for
5351 workqueues visible under /sys/bus/workqueue/.
5353 workqueue.power_efficient
5354 Per-cpu workqueues are generally preferred because
5355 they show better performance thanks to cache
5356 locality; unfortunately, per-cpu workqueues tend to
5357 be more power hungry than unbound workqueues.
5359 Enabling this makes the per-cpu workqueues which
5360 were observed to contribute significantly to power
5361 consumption unbound, leading to measurably lower
5362 power usage at the cost of small performance
5365 The default value of this parameter is determined by
5366 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
5368 workqueue.debug_force_rr_cpu
5369 Workqueue used to implicitly guarantee that work
5370 items queued without explicit CPU specified are put
5371 on the local CPU. This guarantee is no longer true
5372 and while local CPU is still preferred work items
5373 may be put on foreign CPUs. This debug option
5374 forces round-robin CPU selection to flush out
5375 usages which depend on the now broken guarantee.
5376 When enabled, memory and cache locality will be
5379 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
5380 default x2apic cluster mode on platforms
5383 x86_intel_mid_timer= [X86-32,APBT]
5384 Choose timer option for x86 Intel MID platform.
5385 Two valid options are apbt timer only and lapic timer
5386 plus one apbt timer for broadcast timer.
5387 x86_intel_mid_timer=apbt_only | lapic_and_apbt
5389 xen_512gb_limit [KNL,X86-64,XEN]
5390 Restricts the kernel running paravirtualized under Xen
5391 to use only up to 512 GB of RAM. The reason to do so is
5392 crash analysis tools and Xen tools for doing domain
5393 save/restore/migration must be enabled to handle larger
5396 xen_emul_unplug= [HW,X86,XEN]
5397 Unplug Xen emulated devices
5398 Format: [unplug0,][unplug1]
5399 ide-disks -- unplug primary master IDE devices
5400 aux-ide-disks -- unplug non-primary-master IDE devices
5401 nics -- unplug network devices
5402 all -- unplug all emulated devices (NICs and IDE disks)
5403 unnecessary -- unplugging emulated devices is
5404 unnecessary even if the host did not respond to
5406 never -- do not unplug even if version check succeeds
5408 xen_legacy_crash [X86,XEN]
5409 Crash from Xen panic notifier, without executing late
5410 panic() code such as dumping handler.
5412 xen_nopvspin [X86,XEN]
5413 Disables the ticketlock slowpath using Xen PV
5417 Disables the PV optimizations forcing the HVM guest to
5418 run as generic HVM guest with no PV drivers.
5419 This option is obsoleted by the "nopv" option, which
5420 has equivalent effect for XEN platform.
5422 xen_scrub_pages= [XEN]
5423 Boolean option to control scrubbing pages before giving them back
5424 to Xen, for use by other domains. Can be also changed at runtime
5425 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
5426 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
5428 xen_timer_slop= [X86-64,XEN]
5429 Set the timer slop (in nanoseconds) for the virtual Xen
5430 timers (default is 100000). This adjusts the minimum
5431 delta of virtualized Xen timers, where lower values
5432 improve timer resolution at the expense of processing
5433 more timer interrupts.
5435 nopv= [X86,XEN,KVM,HYPER_V,VMWARE]
5436 Disables the PV optimizations forcing the guest to run
5437 as generic guest with no PV drivers. Currently support
5438 XEN HVM, KVM, HYPER_V and VMWARE guest.
5440 xirc2ps_cs= [NET,PCMCIA]
5442 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
5445 By default on POWER9 and above, the kernel will
5446 natively use the XIVE interrupt controller. This option
5447 allows the fallback firmware mode to be used:
5449 off Fallback to firmware control of XIVE interrupt
5450 controller on both pseries and powernv
5451 platforms. Only useful on POWER9 and above.
5453 xhci-hcd.quirks [USB,KNL]
5454 A hex value specifying bitmask with supplemental xhci
5455 host controller quirks. Meaning of each bit can be
5456 consulted in header drivers/usb/host/xhci.h.
5459 Format: { early | on | rw | ro | off }
5460 Controls if xmon debugger is enabled. Default is off.
5461 Passing only "xmon" is equivalent to "xmon=early".
5462 early Call xmon as early as possible on boot; xmon
5463 debugger is called from setup_arch().
5464 on xmon debugger hooks will be installed so xmon
5465 is only called on a kernel crash. Default mode,
5466 i.e. either "ro" or "rw" mode, is controlled
5467 with CONFIG_XMON_DEFAULT_RO_MODE.
5468 rw xmon debugger hooks will be installed so xmon
5469 is called only on a kernel crash, mode is write,
5470 meaning SPR registers, memory and, other data
5471 can be written using xmon commands.
5472 ro same as "rw" option above but SPR registers,
5473 memory, and other data can't be written using
5475 off xmon is disabled.
projects / linux-2.6-block.git / blob