1 acpi= [HW,ACPI,X86,ARM64]
2 Advanced Configuration and Power Interface
3 Format: { force | on | off | strict | noirq | rsdt |
5 force -- enable ACPI if default was off
6 on -- enable ACPI but allow fallback to DT [arm64]
7 off -- disable ACPI if default was on
8 noirq -- do not use ACPI for IRQ routing
9 strict -- Be less tolerant of platforms that are not
10 strictly ACPI specification compliant.
11 rsdt -- prefer RSDT over (default) XSDT
12 copy_dsdt -- copy DSDT to memory
13 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"
16 See also Documentation/power/runtime_pm.txt, pci=noacpi
18 acpi_apic_instance= [ACPI, IOAPIC]
20 2: use 2nd APIC table, if available
21 1,0: use 1st APIC table
24 acpi_backlight= [HW,ACPI]
27 If set to vendor, prefer vendor specific driver
28 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
29 of the ACPI video.ko driver.
31 acpi_force_32bit_fadt_addr
32 force FADT to use 32 bit addresses rather than the
33 64 bit X_* addresses. Some firmware have broken 64
34 bit addresses for force ACPI ignore these and use
35 the older legacy 32 bit addresses.
37 acpica_no_return_repair [HW, ACPI]
38 Disable AML predefined validation mechanism
39 This mechanism can repair the evaluation result to make
40 the return objects more ACPI specification compliant.
41 This option is useful for developers to identify the
42 root cause of an AML interpreter issue when the issue
43 has something to do with the repair mechanism.
45 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
46 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
48 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
49 debug output. Bits in debug_layer correspond to a
50 _COMPONENT in an ACPI source file, e.g.,
51 #define _COMPONENT ACPI_PCI_COMPONENT
52 Bits in debug_level correspond to a level in
53 ACPI_DEBUG_PRINT statements, e.g.,
54 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
55 The debug_level mask defaults to "info". See
56 Documentation/acpi/debug.txt for more information about
57 debug layers and levels.
59 Enable processor driver info messages:
60 acpi.debug_layer=0x20000000
61 Enable PCI/PCI interrupt routing info messages:
62 acpi.debug_layer=0x400000
63 Enable AML "Debug" output, i.e., stores to the Debug
64 object while interpreting AML:
65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
66 Enable all messages related to ACPI hardware:
67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
69 Some values produce so much output that the system is
70 unusable. The "log_buf_len" parameter may be useful
71 if you need to capture more output.
73 acpi_enforce_resources= [ACPI]
75 Check for resource conflicts between native drivers
76 and ACPI OperationRegions (SystemIO and SystemMemory
77 only). IO ports and memory declared in ACPI might be
78 used by the ACPI subsystem in arbitrary AML code and
79 can interfere with legacy drivers.
80 strict (default): access to resources claimed by ACPI
81 is denied; legacy drivers trying to access reserved
82 resources will fail to bind to device using them.
83 lax: access to resources claimed by ACPI is allowed;
84 legacy drivers trying to access reserved resources
85 will bind successfully but a warning message is logged.
86 no: ACPI OperationRegions are not marked as reserved,
87 no further checks are performed.
89 acpi_force_table_verification [HW,ACPI]
90 Enable table checksum verification during early stage.
91 By default, this is disabled due to x86 early mapping
94 acpi_irq_balance [HW,ACPI]
95 ACPI will balance active IRQs
98 acpi_irq_nobalance [HW,ACPI]
99 ACPI will not move active IRQs (default)
102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
103 Format: <irq>,<irq>...
105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
107 Format: <irq>,<irq>...
109 acpi_mask_gpe= [HW,ACPI]
110 Due to the existence of _Lxx/_Exx, some GPEs triggered
111 by unsupported hardware/firmware features can result in
112 GPE floodings that cannot be automatically disabled by
114 This facility can be used to prevent such uncontrolled
118 acpi_no_auto_serialize [HW,ACPI]
119 Disable auto-serialization of AML methods
120 AML control methods that contain the opcodes to create
121 named objects will be marked as "Serialized" by the
122 auto-serialization feature.
123 This feature is enabled by default.
124 This option allows to turn off the feature.
126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
129 acpi_no_static_ssdt [HW,ACPI]
130 Disable installation of static SSDTs at early boot time
131 By default, SSDTs contained in the RSDT/XSDT will be
132 installed automatically and they will appear under
133 /sys/firmware/acpi/tables.
134 This option turns off this feature.
135 Note that specifying this option does not affect
136 dynamic table installation which will install SSDT
137 tables to /sys/firmware/acpi/tables/dynamic.
139 acpi_rsdp= [ACPI,EFI,KEXEC]
140 Pass the RSDP address to the kernel, mostly used
141 on machines running EFI runtime service to boot the
142 second kernel for kdump.
144 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
145 Format: To spoof as Windows 98: ="Microsoft Windows"
147 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
148 of 2 which is mandated by ACPI 6) as the supported ACPI
149 specification revision (when using this switch, it may
150 be necessary to carry out a cold reboot _twice_ in a
151 row to make it take effect on the platform firmware).
153 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
154 acpi_osi="string1" # add string1
155 acpi_osi="!string2" # remove string2
156 acpi_osi=!* # remove all strings
157 acpi_osi=! # disable all built-in OS vendor
159 acpi_osi=!! # enable all built-in OS vendor
161 acpi_osi= # disable all strings
163 'acpi_osi=!' can be used in combination with single or
164 multiple 'acpi_osi="string1"' to support specific OS
165 vendor string(s). Note that such command can only
166 affect the default state of the OS vendor strings, thus
167 it cannot affect the default state of the feature group
168 strings and the current state of the OS vendor strings,
169 specifying it multiple times through kernel command line
170 is meaningless. This command is useful when one do not
171 care about the state of the feature group strings which
172 should be controlled by the OSPM.
174 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
175 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
176 can make '_OSI("Windows 2000")' TRUE.
178 'acpi_osi=' cannot be used in combination with other
179 'acpi_osi=' command lines, the _OSI method will not
180 exist in the ACPI namespace. NOTE that such command can
181 only affect the _OSI support state, thus specifying it
182 multiple times through kernel command line is also
185 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
188 'acpi_osi=!*' can be used in combination with single or
189 multiple 'acpi_osi="string1"' to support specific
190 string(s). Note that such command can affect the
191 current state of both the OS vendor strings and the
192 feature group strings, thus specifying it multiple times
193 through kernel command line is meaningful. But it may
194 still not able to affect the final state of a string if
195 there are quirks related to this string. This command
196 is useful when one want to control the state of the
197 feature group strings to debug BIOS issues related to
200 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
201 '_OSI("Module Device")' FALSE.
202 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
203 '_OSI("Module Device")' TRUE.
204 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
206 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
208 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
209 they all will make '_OSI("Windows 2000")' TRUE.
212 Override the pmtimer bug detection: force the kernel
213 to assume that this machine's pmtimer latches its value
214 and always returns good values.
216 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
217 Format: { level | edge | high | low }
219 acpi_skip_timer_override [HW,ACPI]
220 Recognize and ignore IRQ0/pin2 Interrupt Override.
221 For broken nForce2 BIOS resulting in XT-PIC timer.
223 acpi_sleep= [HW,ACPI] Sleep options
224 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
225 old_ordering, nonvs, sci_force_enable, nobl }
226 See Documentation/power/video.txt for information on
228 s3_beep is for debugging; it makes the PC's speaker beep
229 as soon as the kernel's real-mode entry point is called.
230 s4_nohwsig prevents ACPI hardware signature from being
231 used during resume from hibernation.
232 old_ordering causes the ACPI 1.0 ordering of the _PTS
233 control method, with respect to putting devices into
234 low power states, to be enforced (the ACPI 2.0 ordering
235 of _PTS is used by default).
236 nonvs prevents the kernel from saving/restoring the
237 ACPI NVS memory during suspend/hibernation and resume.
238 sci_force_enable causes the kernel to set SCI_EN directly
239 on resume from S1/S3 (which is against the ACPI spec,
240 but some broken systems don't work without it).
241 nobl causes the internal blacklist of systems known to
242 behave incorrectly in some ways with respect to system
243 suspend and resume to be ignored (use wisely).
245 acpi_use_timer_override [HW,ACPI]
246 Use timer override. For some broken Nvidia NF5 boards
247 that require a timer override, but don't have HPET
249 add_efi_memmap [EFI; X86] Include EFI memory map in
250 kernel's map of available physical RAM.
253 { off | try_unsupported }
254 off: disable AGP support
255 try_unsupported: try to drive unsupported chipsets
256 (may crash computer or cause data corruption)
259 See Documentation/sound/alsa-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 whilst booting
335 Format: { quiet (default) | verbose | debug }
336 Change the amount of debugging information output
337 when initialising the APIC and IO-APIC components.
338 For X86-32, this can also be used to specify an APIC
340 Format: apic=driver_name
341 Examples: apic=bigsmp
343 apic_extnmi= [APIC,X86] External NMI delivery setting
344 Format: { bsp (default) | all | none }
345 bsp: External NMI is delivered only to CPU 0
346 all: External NMIs are broadcast to all CPUs as a
348 none: External NMI is masked for all CPUs. This is
349 useful so that a dump capture kernel won't be
353 See Documentation/networking/ipv6.txt.
355 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
356 Limit apic dumping. The parameter defines the maximal
357 number of local apics being dumped. Also it is possible
358 to set it to "all" by meaning -- no limit here.
359 Format: { 1 (default) | 2 | ... | all }.
360 The parameter valid if only apic=debug or
361 apic=verbose is specified.
362 Example: apic=debug show_lapic=all
364 apm= [APM] Advanced Power Management
365 See header of arch/x86/kernel/apm_32.c.
367 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
368 Format: <io>,<irq>,<nodeID>
372 atarimouse= [HW,MOUSE] Atari Mouse
374 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
375 EzKey and similar keyboards
377 atkbd.reset= [HW] Reset keyboard during initialization
379 atkbd.set= [HW] Select keyboard code set
380 Format: <int> (2 = AT (default), 3 = PS/2)
382 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
385 atkbd.softraw= [HW] Choose between synthetic and real raw mode
386 Format: <bool> (0 = real, 1 = synthetic (default))
388 atkbd.softrepeat= [HW]
389 Use software keyboard repeat
391 audit= [KNL] Enable the audit sub-system
392 Format: { "0" | "1" | "off" | "on" }
393 0 | off - kernel audit is disabled and can not be
394 enabled until the next reboot
395 unset - kernel audit is initialized but disabled and
396 will be fully enabled by the userspace auditd.
397 1 | on - kernel audit is initialized and partially
398 enabled, storing at most audit_backlog_limit
399 messages in RAM until it is fully enabled by the
403 audit_backlog_limit= [KNL] Set the audit queue size limit.
404 Format: <int> (must be >=0)
407 bau= [X86_UV] Enable the BAU on SGI UV. The default
408 behavior is to disable the BAU (i.e. bau=0).
409 Format: { "0" | "1" }
412 unset - Disable the BAU.
414 baycom_epp= [HW,AX25]
417 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
419 See header of drivers/net/hamradio/baycom_par.c.
421 baycom_ser_fdx= [HW,AX25]
422 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
423 Format: <io>,<irq>,<mode>[,<baud>]
424 See header of drivers/net/hamradio/baycom_ser_fdx.c.
426 baycom_ser_hdx= [HW,AX25]
427 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
428 Format: <io>,<irq>,<mode>
429 See header of drivers/net/hamradio/baycom_ser_hdx.c.
431 blkdevparts= Manual partition parsing of block device(s) for
432 embedded devices based on command line input.
433 See Documentation/block/cmdline-partition.txt
435 boot_delay= Milliseconds to delay each printk during boot.
436 Values larger than 10 seconds (10000) are changed to
440 bootmem_debug [KNL] Enable bootmem allocator debug messages.
443 Disable BERT OS support on buggy BIOSes.
445 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
446 bttv.radio= Most important insmod options are available as
448 bttv.pll= See Documentation/media/v4l-drivers/bttv.rst
451 bulk_remove=off [PPC] This parameter disables the use of the pSeries
452 firmware feature for flushing multiple hpte entries
455 c101= [NET] Moxa C101 synchronous serial card
457 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
458 Sometimes CPU hardware bugs make them report the cache
459 size incorrectly. The kernel will attempt work arounds
460 to fix known problems, but for some CPUs it is not
461 possible to determine what the correct size should be.
462 This option provides an override for these situations.
464 ca_keys= [KEYS] This parameter identifies a specific key(s) on
465 the system trusted keyring to be used for certificate
467 format: { id:<keyid> | builtin }
469 cca= [MIPS] Override the kernel pages' cache coherency
470 algorithm. Accepted values range from 0 to 7
471 inclusive. See arch/mips/include/asm/pgtable-bits.h
472 for platform specific values (SB1, Loongson3 and
475 ccw_timeout_log [S390]
476 See Documentation/s390/CommonIO for details.
478 cgroup_disable= [KNL] Disable a particular controller
479 Format: {name of the controller(s) to disable}
480 The effects of cgroup_disable=foo are:
481 - foo isn't auto-mounted if you mount all cgroups in
483 - foo isn't visible as an individually mountable
485 {Currently only "memory" controller deal with this and
486 cut the overhead, others just disable the usage. So
487 only cgroup_disable=memory is actually worthy}
489 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
490 Format: { controller[,controller...] | "all" }
491 Like cgroup_disable, but only applies to cgroup v1;
492 the blacklisted controllers remain available in cgroup2.
494 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
496 nosocket -- Disable socket memory accounting.
497 nokmem -- Disable kernel memory accounting.
499 checkreqprot [SELINUX] Set initial checkreqprot flag value.
500 Format: { "0" | "1" }
501 See security/selinux/Kconfig help text.
502 0 -- check protection applied by kernel (includes
503 any implied execute protection).
504 1 -- check protection requested by application.
505 Default value is set via a kernel config option.
506 Value can be changed at runtime via
507 /selinux/checkreqprot.
510 See Documentation/s390/CommonIO for details.
513 Prevents the clock framework from automatically gating
514 clocks that have not been explicitly enabled by a Linux
515 device driver but are enabled in hardware at reset or
516 by the bootloader/firmware. Note that this does not
517 force such clocks to be always-on nor does it reserve
518 those clocks in any way. This parameter is useful for
519 debug and development, but should not be needed on a
520 platform with proper driver support. For more
521 information, see Documentation/driver-api/clk.rst.
523 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
525 Forces specified clocksource (if available) to be used
526 when calculating gettimeofday(). If specified
527 clocksource is not available, it defaults to PIT.
528 Format: { pit | tsc | cyclone | pmtmr }
530 clocksource= Override the default clocksource
532 Override the default clocksource and use the clocksource
533 with the name specified.
534 Some clocksource names to choose from, depending on
536 [all] jiffies (this is the base, fallback clocksource)
538 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
539 pxa_timer,timer3,32k_counter,timer0_1
540 [X86-32] pit,hpet,tsc;
541 scx200_hrt on Geode; cyclone on IBM x440
549 clocksource.arm_arch_timer.evtstrm=
552 Enable/disable the eventstream feature of the ARM
553 architected timer so that code using WFE-based polling
554 loops can be debugged more effectively on production
557 clearcpuid=BITNUM [X86]
558 Disable CPUID feature X for the kernel. See
559 arch/x86/include/asm/cpufeatures.h for the valid bit
560 numbers. Note the Linux specific bits are not necessarily
561 stable over kernel options, but the vendor specific
563 Also note that user programs calling CPUID directly
564 or using the feature without checking anything
565 will still see it. This just prevents it from
566 being used by the kernel or shown in /proc/cpuinfo.
567 Also note the kernel might malfunction if you disable
570 cma=nn[MG]@[start[MG][-end[MG]]]
572 Sets the size of kernel global memory area for
573 contiguous memory allocations and optionally the
574 placement constraint by the physical address range of
575 memory allocations. A value of 0 disables CMA
576 altogether. For more information, see
577 include/linux/dma-contiguous.h
579 cmo_free_hint= [PPC] Format: { yes | no }
580 Specify whether pages are marked as being inactive
581 when they are freed. This is used in CMO environments
582 to determine OS memory pressure for page stealing by
586 coherent_pool=nn[KMG] [ARM,KNL]
587 Sets the size of memory pool for coherent, atomic dma
588 allocations, by default set to 256K.
590 com20020= [HW,NET] ARCnet - COM20020 chipset
592 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
594 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
598 ARCnet - COM90xx chipset (memory-mapped buffers)
599 Format: <io>[,<irq>[,<memstart>]]
601 condev= [HW,S390] console device
604 console= [KNL] Output console device and options.
606 tty<n> Use the virtual console device <n>.
610 Use the specified serial port. The options are of
611 the form "bbbbpnf", where "bbbb" is the baud rate,
612 "p" is parity ("n", "o", or "e"), "n" is number of
613 bits, and "f" is flow control ("r" for RTS or
614 omit it). Default is "9600n8".
616 See Documentation/admin-guide/serial-console.rst for more
618 Documentation/networking/netconsole.txt for an
621 uart[8250],io,<addr>[,options]
622 uart[8250],mmio,<addr>[,options]
623 uart[8250],mmio16,<addr>[,options]
624 uart[8250],mmio32,<addr>[,options]
625 uart[8250],0x<addr>[,options]
626 Start an early, polled-mode console on the 8250/16550
627 UART at the specified I/O port or MMIO address,
628 switching to the matching ttyS device later.
629 MMIO inter-register address stride is either 8-bit
630 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
631 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
632 to be equivalent to 'mmio'. 'options' are specified in
633 the same format described for ttyS above; if unspecified,
634 the h/w is not re-initialized.
636 hvc<n> Use the hypervisor console device <n>. This is for
637 both Xen and PowerPC hypervisors.
639 If the device connected to the port is not a TTY but a braille
640 device, prepend "brl," before the device type, for instance
642 For now, only VisioBraille is supported.
645 [KNL] Change console messages format
647 By default we print messages on consoles in
648 "[time stamp] text\n" format (time stamp may not be
649 printed, depending on CONFIG_PRINTK_TIME or
650 `printk_time' param).
652 Switch to syslog format: "<%u>[time stamp] text\n"
653 IOW, each message will have a facility and loglevel
654 prefix. The format is similar to one used by syslog()
655 syscall, or to executing "dmesg -S --raw" or to reading
658 consoleblank= [KNL] The console blank (screen saver) timeout in
659 seconds. A value of 0 disables the blank timer.
663 [KNL] Change the default value for
664 /proc/<pid>/coredump_filter.
665 See also Documentation/filesystems/proc.txt.
667 coresight_cpu_debug.enable
670 Enable/disable the CPU sampling based debugging.
671 0: default value, disable debugging
672 1: enable debugging at boot time
674 cpuidle.off=1 [CPU_IDLE]
675 disable the cpuidle sub-system
677 cpufreq.off=1 [CPU_FREQ]
678 disable the cpufreq sub-system
681 [X86] Delay for N microsec between assert and de-assert
682 of APIC INIT to start processors. This delay occurs
683 on every CPU online, such as boot, and resume from suspend.
686 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
688 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
690 crashkernel=size[KMG][@offset[KMG]]
691 [KNL] Using kexec, Linux can switch to a 'crash kernel'
692 upon panic. This parameter reserves the physical
693 memory region [offset, offset + size] for that kernel
694 image. If '@offset' is omitted, then a suitable offset
695 is selected automatically. Check
696 Documentation/kdump/kdump.txt for further details.
698 crashkernel=range1:size1[,range2:size2,...][@offset]
699 [KNL] Same as above, but depends on the memory
700 in the running system. The syntax of range is
701 start-[end] where start and end are both
702 a memory unit (amount[KMG]). See also
703 Documentation/kdump/kdump.txt for an example.
705 crashkernel=size[KMG],high
706 [KNL, x86_64] range could be above 4G. Allow kernel
707 to allocate physical memory region from top, so could
708 be above 4G if system have more than 4G ram installed.
709 Otherwise memory region will be allocated below 4G, if
711 It will be ignored if crashkernel=X is specified.
712 crashkernel=size[KMG],low
713 [KNL, x86_64] range under 4G. When crashkernel=X,high
714 is passed, kernel could allocate physical memory region
715 above 4G, that cause second kernel crash on system
716 that require some amount of low memory, e.g. swiotlb
717 requires at least 64M+32K low memory, also enough extra
718 low memory is needed to make sure DMA buffers for 32-bit
719 devices won't run out. Kernel would try to allocate at
720 at least 256M below 4G automatically.
721 This one let user to specify own low range under 4G
722 for second kernel instead.
723 0: to disable low allocation.
724 It will be ignored when crashkernel=X,high is not used
725 or memory reserved is below 4G.
728 [KNL] Disable crypto self-tests
733 cs89x0_media= [HW,NET]
734 Format: { rj45 | aui | bnc }
737 See header of drivers/s390/block/dasd_devmap.c.
739 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
740 (one device per port)
741 Format: <port#>,<type>
742 See also Documentation/input/devices/joystick-parport.rst
744 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
746 Documentation/admin-guide/dynamic-debug-howto.rst for
747 details. Deprecated, see dyndbg.
749 debug [KNL] Enable kernel debugging (events log level).
752 [KNL] Enable printing [hashed] pointers early in the
753 boot sequence. If enabled, we use a weak hash instead
754 of siphash to hash pointers. Use this option if you are
755 seeing instances of '(___ptrval___)') and need to see a
756 value (hashed pointer) instead. Cryptographically
757 insecure, please do not use on production kernels.
760 [KNL] verbose self-tests
762 Print debugging info while doing the locking API
764 We default to 0 (no extra messages), setting it to
765 1 will print _a lot_ more information - normally
766 only useful to kernel developers.
768 debug_objects [KNL] Enable object debugging
771 [KNL] Disable object debugging
773 debug_guardpage_minorder=
774 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
775 parameter allows control of the order of pages that will
776 be intentionally kept free (and hence protected) by the
777 buddy allocator. Bigger value increase the probability
778 of catching random memory corruption, but reduce the
779 amount of memory for normal system use. The maximum
780 possible value is MAX_ORDER/2. Setting this parameter
781 to 1 or 2 should be enough to identify most random
782 memory corruption problems caused by bugs in kernel or
783 driver code when a CPU writes to (or reads from) a
784 random memory location. Note that there exists a class
785 of memory corruptions problems caused by buggy H/W or
786 F/W or by drivers badly programing DMA (basically when
787 memory is written at bus level and the CPU MMU is
788 bypassed) which are not detectable by
789 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
790 tracking down these problems.
793 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
794 parameter enables the feature at boot time. In
795 default, it is disabled. We can avoid allocating huge
796 chunk of memory for debug pagealloc if we don't enable
797 it at boot time and the system will work mostly same
798 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
799 on: enable the feature
801 debugpat [X86] Enable PAT debugging
803 decnet.addr= [HW,NET]
804 Format: <area>[,<node>]
805 See also Documentation/networking/decnet.txt.
808 [same as hugepagesz=] The size of the default
809 HugeTLB page size. This is the size represented by
810 the legacy /proc/ hugepages APIs, used for SHM, and
811 default size when mounting hugetlbfs filesystems.
812 Defaults to the default architecture's huge page size
815 deferred_probe_timeout=
816 [KNL] Debugging option to set a timeout in seconds for
817 deferred probe to give up waiting on dependencies to
818 probe. Only specific dependencies (subsystems or
819 drivers) that have opted in will be ignored. A timeout of 0
820 will timeout at the end of initcalls. This option will also
821 dump out devices still on the deferred probe list after
825 Set number of hash buckets for dentry cache.
827 disable_1tb_segments [PPC]
828 Disables the use of 1TB hash page table segments. This
829 causes the kernel to fall back to 256MB segments which
830 can be useful when debugging issues that require an SLB
834 See Documentation/networking/ipv6.txt.
837 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
838 hardening is enabled for this boot. Hardened
839 usercopy checking is used to protect the kernel
840 from reading or writing beyond known memory
841 allocation boundaries as a proactive defense
842 against bounds-checking flaws in the kernel's
843 copy_to_user()/copy_from_user() interface.
844 on Perform hardened usercopy checks (default).
845 off Disable hardened usercopy checks.
848 Disable RADIX MMU mode on POWER9
850 disable_cpu_apicid= [X86,APIC,SMP]
852 The number of initial APIC ID for the
853 corresponding CPU to be disabled at boot,
854 mostly used for the kdump 2nd kernel to
855 disable BSP to wake up multiple CPUs without
856 causing system reset or hang due to sending
859 disable_ddw [PPC/PSERIES]
860 Disable Dynamic DMA Window support. Use this if
861 to workaround buggy firmware.
864 See Documentation/networking/ipv6.txt.
866 disable_mtrr_cleanup [X86]
867 The kernel tries to adjust MTRR layout from continuous
868 to discrete, to make X server driver able to add WB
869 entry later. This parameter disables that.
871 disable_mtrr_trim [X86, Intel and AMD only]
872 By default the kernel will trim any uncacheable
873 memory out of your available memory pool based on
874 MTRR settings. This parameter disables that behavior,
875 possibly causing your machine to run very slowly.
877 disable_timer_pin_1 [X86]
878 Disable PIN 1 of APIC timer
879 Can be useful to work around chipset bugs.
881 dis_ucode_ldr [X86] Disable the microcode loader.
883 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
884 this option disables the debugging code at boot.
886 dma_debug_entries=<number>
887 This option allows to tune the number of preallocated
888 entries for DMA-API debugging code. One entry is
889 required per DMA-API allocation. Use this if the
890 DMA-API debugging code disables itself because the
891 architectural default is too low.
893 dma_debug_driver=<driver_name>
894 With this option the DMA-API debugging driver
895 filter feature can be enabled at boot time. Just
896 pass the driver to filter for as the parameter.
897 The filter can be disabled or changed to another
898 driver later using sysfs.
900 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
901 Broken monitors, graphic adapters, KVMs and EDIDless
902 panels may send no or incorrect EDID data sets.
903 This parameter allows to specify an EDID data sets
904 in the /lib/firmware directory that are used instead.
905 Generic built-in EDID data sets are used, if one of
906 edid/1024x768.bin, edid/1280x1024.bin,
907 edid/1680x1050.bin, or edid/1920x1080.bin is given
908 and no file with the same name exists. Details and
909 instructions how to build your own EDID data are
910 available in Documentation/EDID/HOWTO.txt. An EDID
911 data set will only be used for a particular connector,
912 if its name and a colon are prepended to the EDID
913 name. Each connector may use a unique EDID data
914 set by separating the files with a comma. An EDID
915 data set with no connector name will be used for
916 any connectors not explicitly specified.
921 Format: {"off" | "known"}
922 Control how the dt_cpu_ftrs device-tree binding is
923 used for CPU feature discovery and setup (if it
925 off: Do not use it, fall back to legacy cpu table.
926 known: Do not pass through unknown features to guests
927 or userspace, only those that the kernel is aware of.
929 dump_apple_properties [X86]
930 Dump name and content of EFI device properties on
931 x86 Macs. Useful for driver authors to determine
932 what data is available or for reverse-engineering.
934 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
935 module.dyndbg[="val"]
936 Enable debug messages at boot time. See
937 Documentation/admin-guide/dynamic-debug-howto.rst
940 nompx [X86] Disables Intel Memory Protection Extensions.
941 See Documentation/x86/intel_mpx.txt for more
942 information about the feature.
944 nopku [X86] Disable Memory Protection Keys CPU feature found
947 module.async_probe [KNL]
948 Enable asynchronous probe on this module.
950 early_ioremap_debug [KNL]
951 Enable debug messages in early_ioremap support. This
952 is useful for tracking down temporary early mappings
953 which are not unmapped.
955 earlycon= [KNL] Output early console device and options.
957 [ARM64] The early console is determined by the
958 stdout-path property in device tree's chosen node,
959 or determined by the ACPI SPCR table.
961 [X86] When used with no options the early console is
962 determined by the ACPI SPCR table.
964 cdns,<addr>[,options]
965 Start an early, polled-mode console on a Cadence
966 (xuartps) serial port at the specified address. Only
967 supported option is baud rate. If baud rate is not
968 specified, the serial port must already be setup and
971 uart[8250],io,<addr>[,options]
972 uart[8250],mmio,<addr>[,options]
973 uart[8250],mmio32,<addr>[,options]
974 uart[8250],mmio32be,<addr>[,options]
975 uart[8250],0x<addr>[,options]
976 Start an early, polled-mode console on the 8250/16550
977 UART at the specified I/O port or MMIO address.
978 MMIO inter-register address stride is either 8-bit
979 (mmio) or 32-bit (mmio32 or mmio32be).
980 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
981 to be equivalent to 'mmio'. 'options' are specified
982 in the same format described for "console=ttyS<n>"; if
983 unspecified, the h/w is not initialized.
987 Start an early, polled-mode console on a pl011 serial
988 port at the specified address. The pl011 serial port
989 must already be setup and configured. Options are not
990 yet supported. If 'mmio32' is specified, then only
991 the driver will use only 32-bit accessors to read/write
992 the device registers.
995 Start an early, polled-mode console on a meson serial
996 port at the specified address. The serial port must
997 already be setup and configured. Options are not yet
1001 Start an early, polled-mode console on an msm serial
1002 port at the specified address. The serial port
1003 must already be setup and configured. Options are not
1006 msm_serial_dm,<addr>
1007 Start an early, polled-mode console on an msm serial
1008 dm port at the specified address. The serial port
1009 must already be setup and configured. Options are not
1013 Start an early, polled-mode console on a serial port
1014 of an Actions Semi SoC, such as S500 or S900, at the
1015 specified address. The serial port must already be
1016 setup and configured. Options are not yet supported.
1018 smh Use ARM semihosting calls for early console.
1026 Use early console provided by serial driver available
1027 on Samsung SoCs, requires selecting proper type and
1028 a correct base address of the selected UART port. The
1029 serial port must already be setup and configured.
1030 Options are not yet supported.
1033 Start an early, polled-mode console on a lantiq serial
1034 (lqasc) port at the specified address. The serial port
1035 must already be setup and configured. Options are not
1040 Use early console provided by Freescale LP UART driver
1041 found on Freescale Vybrid and QorIQ LS1021A processors.
1042 A valid base address must be provided, and the serial
1043 port must already be setup and configured.
1046 Start an early, polled-mode console on the
1047 Armada 3700 serial port at the specified
1048 address. The serial port must already be setup
1049 and configured. Options are not yet supported.
1052 Start an early, polled-mode console on a Qualcomm
1053 Generic Interface (GENI) based serial port at the
1054 specified address. The serial port must already be
1055 setup and configured. Options are not yet supported.
1057 earlyprintk= [X86,SH,ARM,M68k,S390]
1062 earlyprintk=serial[,ttySn[,baudrate]]
1063 earlyprintk=serial[,0x...[,baudrate]]
1064 earlyprintk=ttySn[,baudrate]
1065 earlyprintk=dbgp[debugController#]
1066 earlyprintk=pciserial,bus:device.function[,baudrate]
1067 earlyprintk=xdbc[xhciController#]
1069 earlyprintk is useful when the kernel crashes before
1070 the normal console is initialized. It is not enabled by
1071 default because it has some cosmetic problems.
1073 Append ",keep" to not disable it when the real console
1076 Only one of vga, efi, serial, or usb debug port can
1079 Currently only ttyS0 and ttyS1 may be specified by
1080 name. Other I/O ports may be explicitly specified
1081 on some architectures (x86 and arm at least) by
1082 replacing ttySn with an I/O port address, like this:
1083 earlyprintk=serial,0x1008,115200
1084 You can find the port for a given device in
1085 /proc/tty/driver/serial:
1086 2: uart:ST16650V2 port:00001008 irq:18 ...
1088 Interaction with the standard serial driver is not
1091 The VGA and EFI output is eventually overwritten by
1094 The xen output can only be used by Xen PV guests.
1096 The sclp output can only be used on s390.
1098 edac_report= [HW,EDAC] Control how to report EDAC event
1099 Format: {"on" | "off" | "force"}
1100 on: enable EDAC to report H/W event. May be overridden
1101 by other higher priority error reporting module.
1102 off: disable H/W event reporting through EDAC.
1103 force: enforce the use of EDAC to report H/W event.
1106 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1109 This is designed to be used in conjunction with
1110 the boot argument: earlyprintk=vga
1113 Format: {"off" | "on" | "skip[mbr]"}
1116 Format: { "old_map", "nochunk", "noruntime", "debug" }
1117 old_map [X86-64]: switch to the old ioremap-based EFI
1118 runtime services mapping. 32-bit still uses this one by
1120 nochunk: disable reading files in "chunks" in the EFI
1121 boot stub, as chunking can cause problems with some
1122 firmware implementations.
1123 noruntime : disable EFI runtime services support
1124 debug: enable misc debug output
1126 efi_no_storage_paranoia [EFI; X86]
1127 Using this parameter you can use more than 50% of
1128 your efi variable storage. Use this parameter only if
1129 you are really sure that your UEFI does sane gc and
1130 fulfills the spec otherwise your board may brick.
1132 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1133 Add arbitrary attribute to specific memory range by
1134 updating original EFI memory map.
1135 Region of memory which aa attribute is added to is
1137 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1138 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1139 attribute is added to range 0x100000000-0x180000000 and
1140 0x10a0000000-0x1120000000.
1142 Using this parameter you can do debugging of EFI memmap
1143 related feature. For example, you can do debugging of
1144 Address Range Mirroring feature even if your box
1147 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1148 that is to be dynamically loaded by Linux. If there are
1149 multiple variables with the same name but with different
1150 vendor GUIDs, all of them will be loaded. See
1151 Documentation/acpi/ssdt-overlays.txt for details.
1154 eisa_irq_edge= [PARISC,HW]
1155 See header of drivers/parisc/eisa.c.
1158 See comment before function elanfreq_setup() in
1159 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1162 Format: {"cfq" | "deadline" | "noop"}
1163 See Documentation/block/cfq-iosched.txt and
1164 Documentation/block/deadline-iosched.txt for details.
1166 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1167 Specifies physical address of start of kernel core
1168 image elf header and optionally the size. Generally
1169 kexec loader will pass this option to capture kernel.
1170 See Documentation/kdump/kdump.txt for details.
1172 enable_mtrr_cleanup [X86]
1173 The kernel tries to adjust MTRR layout from continuous
1174 to discrete, to make X server driver able to add WB
1175 entry later. This parameter enables that.
1177 enable_timer_pin_1 [X86]
1178 Enable PIN 1 of APIC timer
1179 Can be useful to work around chipset bugs
1180 (in particular on some ATI chipsets).
1181 The kernel tries to set a reasonable default.
1183 enforcing [SELINUX] Set initial enforcing status.
1185 See security/selinux/Kconfig help text.
1186 0 -- permissive (log only, no denials).
1187 1 -- enforcing (deny and log).
1189 Value can be changed at runtime via /selinux/enforce.
1192 Disable Error Record Serialization Table (ERST)
1195 ether= [HW,NET] Ethernet cards parameters
1196 This option is obsoleted by the "netdev=" option, which
1197 has equivalent usage. See its documentation for details.
1201 Permit 'security.evm' to be updated regardless of
1202 current integrity status.
1206 fail_make_request=[KNL]
1207 General fault injection mechanism.
1208 Format: <interval>,<probability>,<space>,<times>
1209 See also Documentation/fault-injection/.
1212 See Documentation/blockdev/floppy.txt.
1214 force_pal_cache_flush
1215 [IA-64] Avoid check_sal_cache_flush which may hang on
1216 buggy SAL_CACHE_FLUSH implementations. Using this
1217 parameter will force ia64_sal_cache_flush to call
1218 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1221 Forcefully enable Physical Address Extension (PAE).
1222 Many Pentium M systems disable PAE but may have a
1223 functionally usable PAE implementation.
1224 Warning: use of this parameter will taint the kernel
1225 and may cause unknown problems.
1228 [FTRACE] will set and start the specified tracer
1229 as early as possible in order to facilitate early
1232 ftrace_dump_on_oops[=orig_cpu]
1233 [FTRACE] will dump the trace buffers on oops.
1234 If no parameter is passed, ftrace will dump
1235 buffers of all CPUs, but if you pass orig_cpu, it will
1236 dump only the buffer of the CPU that triggered the
1239 ftrace_filter=[function-list]
1240 [FTRACE] Limit the functions traced by the function
1241 tracer at boot up. function-list is a comma separated
1242 list of functions. This list can be changed at run
1243 time by the set_ftrace_filter file in the debugfs
1246 ftrace_notrace=[function-list]
1247 [FTRACE] Do not trace the functions specified in
1248 function-list. This list can be changed at run time
1249 by the set_ftrace_notrace file in the debugfs
1252 ftrace_graph_filter=[function-list]
1253 [FTRACE] Limit the top level callers functions traced
1254 by the function graph tracer at boot up.
1255 function-list is a comma separated list of functions
1256 that can be changed at run time by the
1257 set_graph_function file in the debugfs tracing directory.
1259 ftrace_graph_notrace=[function-list]
1260 [FTRACE] Do not trace from the functions specified in
1261 function-list. This list is a comma separated list of
1262 functions that can be changed at run time by the
1263 set_graph_notrace file in the debugfs tracing directory.
1265 ftrace_graph_max_depth=<uint>
1266 [FTRACE] Used with the function graph tracer. This is
1267 the max depth it will trace into a function. This value
1268 can be changed at run time by the max_graph_depth file
1269 in the tracefs tracing directory. default: 0 (no limit)
1272 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1273 support via parallel port (up to 5 devices per port)
1274 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1275 See also Documentation/input/devices/joystick-parport.rst
1279 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1283 gcov_persist= [GCOV] When non-zero (default), profiling data for
1284 kernel modules is saved and remains accessible via
1285 debugfs, even when the module is unloaded/reloaded.
1286 When zero, profiling data is discarded and associated
1287 debugfs files are removed at module unload time.
1289 goldfish [X86] Enable the goldfish android emulator platform.
1290 Don't use this when you are not running on the
1293 gpt [EFI] Forces disk with valid GPT signature but
1294 invalid Protective MBR to be treated as GPT. If the
1295 primary GPT is corrupted, it enables the backup/alternate
1296 GPT to be used instead.
1298 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1299 the "Enable 0" bit of the configuration register.
1302 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1303 the "Enable 0" bit of the configuration register.
1306 grcan.select= [HW] Select which physical interface to use.
1309 grcan.txsize= [HW] Sets the size of the tx buffer.
1310 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1312 grcan.rxsize= [HW] Sets the size of the rx buffer.
1313 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1316 gpio-mockup.gpio_mockup_ranges
1317 [HW] Sets the ranges of gpiochip of for this device.
1318 Format: <start1>,<end1>,<start2>,<end2>...
1320 hardlockup_all_cpu_backtrace=
1321 [KNL] Should the hard-lockup detector generate
1322 backtraces on all cpus.
1325 hashdist= [KNL,NUMA] Large hashes allocated during boot
1326 are distributed across NUMA nodes. Defaults on
1327 for 64-bit NUMA, off otherwise.
1328 Format: 0 | 1 (for off | on)
1330 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1332 hd= [EIDE] (E)IDE hard drive subsystem geometry
1333 Format: <cyl>,<head>,<sect>
1336 Disable Hardware Error Source Table (HEST) support;
1337 corresponding firmware-first mode error processing
1338 logic will be disabled.
1340 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1341 size of <nn>. This works even on boxes that have no
1342 highmem otherwise. This also works to reduce highmem
1343 size on bigger boxes.
1345 highres= [KNL] Enable/disable high resolution timer mode.
1346 Valid parameters: "on", "off"
1350 See Documentation/isdn/README.HiSax.
1354 hpet= [X86-32,HPET] option to control HPET usage
1355 Format: { enable (default) | disable | force |
1357 disable: disable HPET and use PIT instead
1358 force: allow force enabled of undocumented chips (ICH4,
1360 verbose: show contents of HPET registers during setup
1362 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1363 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1365 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1366 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1367 On x86-64 and powerpc, this option can be specified
1368 multiple times interleaved with hugepages= to reserve
1369 huge pages of different sizes. Valid pages sizes on
1370 x86-64 are 2M (when the CPU supports "pse") and 1G
1371 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1374 [KNL] Should the hung task detector generate panics.
1377 A nonzero value instructs the kernel to panic when a
1378 hung task is detected. The default value is controlled
1379 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1380 option. The value selected by this boot parameter can
1381 be changed later by the kernel.hung_task_panic sysctl.
1383 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1384 terminal devices. Valid values: 0..8
1385 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1386 If specified, z/VM IUCV HVC accepts connections
1387 from listed z/VM user IDs only.
1389 Do not unregister boot console at start. This is only
1390 useful for debugging when something happens in the window
1391 between unregistering the boot console and initializing
1394 i2c_bus= [HW] Override the default board specific I2C bus speed
1395 or register an additional I2C bus that is not
1396 registered from board initialization code.
1400 i8042.debug [HW] Toggle i8042 debug mode
1401 i8042.unmask_kbd_data
1402 [HW] Enable printing of interrupt data from the KBD port
1403 (disabled by default, and as a pre-condition
1404 requires that i8042.debug=1 be enabled)
1405 i8042.direct [HW] Put keyboard port into non-translated mode
1406 i8042.dumbkbd [HW] Pretend that controller can only read data from
1407 keyboard and cannot control its state
1408 (Don't attempt to blink the leds)
1409 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1410 i8042.nokbd [HW] Don't check/create keyboard port
1411 i8042.noloop [HW] Disable the AUX Loopback command while probing
1413 i8042.nomux [HW] Don't check presence of an active multiplexing
1415 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1417 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1418 i8042.reset [HW] Reset the controller during init, cleanup and
1419 suspend-to-ram transitions, only during s2r
1420 transitions, or never reset
1421 Format: { 1 | Y | y | 0 | N | n }
1422 1, Y, y: always reset controller
1423 0, N, n: don't ever reset controller
1424 Default: only on s2r transitions on x86; most other
1425 architectures force reset to be always executed
1426 i8042.unlock [HW] Unlock (ignore) the keylock
1427 i8042.kbdreset [HW] Reset device connected to KBD port
1431 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1432 indicates that the driver is running on unsupported
1434 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1435 does not match list of supported models.
1437 [HW] Report power status in /proc/i8k
1438 (disabled by default)
1439 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1442 i915.invert_brightness=
1443 [DRM] Invert the sense of the variable that is used to
1444 set the brightness of the panel backlight. Normally a
1445 brightness value of 0 indicates backlight switched off,
1446 and the maximum of the brightness value sets the backlight
1447 to maximum brightness. If this parameter is set to 0
1448 (default) and the machine requires it, or this parameter
1449 is set to 1, a brightness value of 0 sets the backlight
1450 to maximum brightness, and the maximum of the brightness
1451 value switches the backlight off.
1452 -1 -- never invert brightness
1453 0 -- machine default
1454 1 -- force brightness inversion
1457 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1459 ide-core.nodma= [HW] (E)IDE subsystem
1460 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1461 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1462 .cdrom .chs .ignore_cable are additional options
1463 See Documentation/ide/ide.txt.
1465 ide-generic.probe-mask= [HW] (E)IDE subsystem
1467 Probe mask for legacy ISA IDE ports. Depending on
1468 platform up to 6 ports are supported, enabled by
1469 setting corresponding bits in the mask to 1. The
1470 default value is 0x0, which has a special meaning.
1471 On systems that have PCI, it triggers scanning the
1472 PCI bus for the first and the second port, which
1473 are then probed. On systems without PCI the value
1474 of 0x0 enables probing the two first ports as if it
1477 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1478 Claim all unknown PCI IDE storage controllers.
1481 Format: idle=poll, idle=halt, idle=nomwait
1482 Poll forces a polling idle loop that can slightly
1483 improve the performance of waking up a idle CPU, but
1484 will use a lot of power and make the system run hot.
1486 idle=halt: Halt is forced to be used for CPU idle.
1487 In such case C2/C3 won't be used again.
1488 idle=nomwait: Disable mwait for CPU C-states
1490 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1491 Format: { strict | legacy | 2008 | relaxed }
1494 Choose which programs will be accepted for execution
1495 based on the IEEE 754 NaN encoding(s) supported by
1496 the FPU and the NaN encoding requested with the value
1497 of an ELF file header flag individually set by each
1498 binary. Hardware implementations are permitted to
1499 support either or both of the legacy and the 2008 NaN
1502 Available settings are as follows:
1503 strict accept binaries that request a NaN encoding
1504 supported by the FPU
1505 legacy only accept legacy-NaN binaries, if supported
1507 2008 only accept 2008-NaN binaries, if supported
1509 relaxed accept any binaries regardless of whether
1510 supported by the FPU
1512 The FPU emulator is always able to support both NaN
1513 encodings, so if no FPU hardware is present or it has
1514 been disabled with 'nofpu', then the settings of
1515 'legacy' and '2008' strap the emulator accordingly,
1516 'relaxed' straps the emulator for both legacy-NaN and
1517 2008-NaN, whereas 'strict' enables legacy-NaN only on
1518 legacy processors and both NaN encodings on MIPS32 or
1521 The setting for ABS.fmt/NEG.fmt instruction execution
1522 mode generally follows that for the NaN encoding,
1523 except where unsupported by hardware.
1525 ignore_loglevel [KNL]
1526 Ignore loglevel setting - this will print /all/
1527 kernel messages to the console. Useful for debugging.
1528 We also add it as printk module parameter, so users
1529 could change it dynamically, usually by
1530 /sys/module/printk/parameters/ignore_loglevel.
1533 Ignore RLIMIT_DATA setting for data mappings,
1534 print warning at first misuse. Can be changed via
1535 /sys/module/kernel/parameters/ignore_rlimit_data.
1537 ihash_entries= [KNL]
1538 Set number of hash buckets for inode cache.
1540 ima_appraise= [IMA] appraise integrity measurements
1541 Format: { "off" | "enforce" | "fix" | "log" }
1544 ima_appraise_tcb [IMA]
1545 The builtin appraise policy appraises all files
1548 ima_canonical_fmt [IMA]
1549 Use the canonical format for the binary runtime
1550 measurements, instead of host native format.
1553 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1557 The list of supported hash algorithms is defined
1558 in crypto/hash_info.h.
1561 The builtin policies to load during IMA setup.
1562 Format: "tcb | appraise_tcb | secure_boot |
1565 The "tcb" policy measures all programs exec'd, files
1566 mmap'd for exec, and all files opened with the read
1567 mode bit set by either the effective uid (euid=0) or
1570 The "appraise_tcb" policy appraises the integrity of
1571 all files owned by root. (This is the equivalent
1572 of ima_appraise_tcb.)
1574 The "secure_boot" policy appraises the integrity
1575 of files (eg. kexec kernel image, kernel modules,
1576 firmware, policy, etc) based on file signatures.
1578 The "fail_securely" policy forces file signature
1579 verification failure also on privileged mounted
1580 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1583 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1584 Load a policy which meets the needs of the Trusted
1585 Computing Base. This means IMA will measure all
1586 programs exec'd, files mmap'd for exec, and all files
1587 opened for read by uid=0.
1590 Select one of defined IMA measurements template formats.
1591 Formats: { "ima" | "ima-ng" | "ima-sig" }
1595 [IMA] Define a custom template format.
1596 Format: { "field1|...|fieldN" }
1598 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1599 Format: <min_file_size>
1600 Set the minimal file size for using asynchronous hash.
1601 If left unspecified, ahash usage is disabled.
1603 ahash performance varies for different data sizes on
1604 different crypto accelerators. This option can be used
1605 to achieve the best performance for a particular HW.
1607 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1609 Set hashing buffer size. Default: 4k.
1611 ahash performance varies for different chunk sizes on
1612 different crypto accelerators. This option can be used
1613 to achieve best performance for particular HW.
1617 Run specified binary instead of /sbin/init as init
1620 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1621 for working out where the kernel is dying during
1624 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1625 initcall functions. Useful for debugging built-in
1626 modules and initcalls.
1628 initrd= [BOOT] Specify the location of the initial ramdisk
1630 init_pkru= [x86] Specify the default memory protection keys rights
1631 register contents for all processes. 0x55555554 by
1632 default (disallow access to all but pkey 0). Can
1633 override in debugfs after boot.
1635 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1638 int_pln_enable [x86] Enable power limit notification interrupt
1640 integrity_audit=[IMA]
1641 Format: { "0" | "1" }
1642 0 -- basic integrity auditing messages. (Default)
1643 1 -- additional integrity auditing messages.
1645 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1647 Enable intel iommu driver.
1649 Disable intel iommu driver.
1650 igfx_off [Default Off]
1651 By default, gfx is mapped as normal device. If a gfx
1652 device has a dedicated DMAR unit, the DMAR unit is
1653 bypassed by not enabling DMAR with this option. In
1654 this case, gfx device will use physical address for
1657 With this option iommu will not optimize to look
1658 for io virtual address below 32-bit forcing dual
1659 address cycle on pci bus for cards supporting greater
1660 than 32-bit addressing. The default is to look
1661 for translation below 32-bit and if not available
1662 then look in the higher range.
1663 strict [Default Off]
1664 With this option on every unmap_single operation will
1665 result in a hardware IOTLB flush operation as opposed
1666 to batching them for performance.
1667 sp_off [Default Off]
1668 By default, super page will be supported if Intel IOMMU
1669 has the capability. With this option, super page will
1671 ecs_off [Default Off]
1672 By default, extended context tables will be supported if
1673 the hardware advertises that it has support both for the
1674 extended tables themselves, and also PASID support. With
1675 this option set, extended tables will not be used even
1676 on hardware which claims to support them.
1677 tboot_noforce [Default Off]
1678 Do not force the Intel IOMMU enabled under tboot.
1679 By default, tboot will force Intel IOMMU on, which
1680 could harm performance of some high-throughput
1681 devices like 40GBit network cards, even if identity
1683 Note that using this option lowers the security
1684 provided by tboot because it makes the system
1685 vulnerable to DMA attacks.
1687 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1688 0 disables intel_idle and fall back on acpi_idle.
1689 1 to 9 specify maximum depth of C-state.
1693 Do not enable intel_pstate as the default
1694 scaling driver for the supported processors
1696 Use intel_pstate as a scaling driver, but configure it
1697 to work with generic cpufreq governors (instead of
1698 enabling its internal governor). This mode cannot be
1699 used along with the hardware-managed P-states (HWP)
1702 Enable intel_pstate on systems that prohibit it by default
1703 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1704 instead of acpi-cpufreq may disable platform features, such
1705 as thermal controls and power capping, that rely on ACPI
1706 P-States information being indicated to OSPM and therefore
1707 should be used with caution. This option does not work with
1708 processors that aren't supported by the intel_pstate driver
1709 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1711 Do not enable hardware P state control (HWP)
1714 Only load intel_pstate on systems which support
1715 hardware P state control (HWP) if available.
1717 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1718 Description Table, specifies preferred power management
1719 profile as "Enterprise Server" or "Performance Server",
1720 then this feature is turned on by default.
1722 Allow per-logical-CPU P-State performance control limits using
1723 cpufreq sysfs interface
1725 intremap= [X86-64, Intel-IOMMU]
1726 on enable Interrupt Remapping (default)
1727 off disable Interrupt Remapping
1728 nosid disable Source ID checking
1730 BIOS x2APIC opt-out request will be ignored
1731 nopost disable Interrupt Posting
1733 iomem= Disable strict checking of access to MMIO memory
1734 strict regions from userspace.
1748 nobypass [PPC/POWERNV]
1749 Disable IOMMU bypass, using IOMMU for PCI devices.
1752 [ARM64] Configure DMA to bypass the IOMMU by default.
1753 Format: { "0" | "1" }
1754 0 - Use IOMMU translation for DMA.
1755 1 - Bypass the IOMMU for DMA.
1756 unset - Use IOMMU translation for DMA.
1758 io7= [HW] IO7 for Marvel based alpha systems
1759 See comment before marvel_specify_io7 in
1760 arch/alpha/kernel/core_marvel.c.
1762 io_delay= [X86] I/O delay method
1764 Standard port 0x80 based delay
1766 Alternate port 0xed based delay (needed on some systems)
1768 Simple two microseconds delay
1773 See Documentation/filesystems/nfs/nfsroot.txt.
1775 irqaffinity= [SMP] Set the default irq affinity mask
1776 The argument is a cpu list, as described above.
1778 irqchip.gicv2_force_probe=
1781 Force the kernel to look for the second 4kB page
1782 of a GICv2 controller even if the memory range
1783 exposed by the device tree is too small.
1785 irqchip.gicv3_nolpi=
1787 Force the kernel to ignore the availability of
1788 LPIs (and by consequence ITSs). Intended for system
1789 that use the kernel as a bootloader, and thus want
1790 to let secondary kernels in charge of setting up
1794 When an interrupt is not handled search all handlers
1795 for it. Intended to get systems with badly broken
1799 When an interrupt is not handled search all handlers
1800 for it. Also check all handlers each timer
1801 interrupt. Intended to get systems with badly broken
1805 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1807 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1808 [Deprecated - use cpusets instead]
1809 Format: [flag-list,]<cpu-list>
1811 Specify one or more CPUs to isolate from disturbances
1812 specified in the flag list (default: domain):
1815 Disable the tick when a single task runs.
1817 A residual 1Hz tick is offloaded to workqueues, which you
1818 need to affine to housekeeping through the global
1819 workqueue's affinity configured via the
1820 /sys/devices/virtual/workqueue/cpumask sysfs file, or
1821 by using the 'domain' flag described below.
1823 NOTE: by default the global workqueue runs on all CPUs,
1824 so to protect individual CPUs the 'cpumask' file has to
1825 be configured manually after bootup.
1828 Isolate from the general SMP balancing and scheduling
1829 algorithms. Note that performing domain isolation this way
1830 is irreversible: it's not possible to bring back a CPU to
1831 the domains once isolated through isolcpus. It's strongly
1832 advised to use cpusets instead to disable scheduler load
1833 balancing through the "cpuset.sched_load_balance" file.
1834 It offers a much more flexible interface where CPUs can
1835 move in and out of an isolated set anytime.
1837 You can move a process onto or off an "isolated" CPU via
1838 the CPU affinity syscalls or cpuset.
1839 <cpu number> begins at 0 and the maximum value is
1840 "number of CPUs in system - 1".
1842 The format of <cpu-list> is described above.
1848 ivrs_ioapic [HW,X86_64]
1849 Provide an override to the IOAPIC-ID<->DEVICE-ID
1850 mapping provided in the IVRS ACPI table. For
1851 example, to map IOAPIC-ID decimal 10 to
1852 PCI device 00:14.0 write the parameter as:
1853 ivrs_ioapic[10]=00:14.0
1855 ivrs_hpet [HW,X86_64]
1856 Provide an override to the HPET-ID<->DEVICE-ID
1857 mapping provided in the IVRS ACPI table. For
1858 example, to map HPET-ID decimal 0 to
1859 PCI device 00:14.0 write the parameter as:
1860 ivrs_hpet[0]=00:14.0
1862 ivrs_acpihid [HW,X86_64]
1863 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1864 mapping provided in the IVRS ACPI table. For
1865 example, to map UART-HID:UID AMD0020:0 to
1866 PCI device 00:14.5 write the parameter as:
1867 ivrs_acpihid[00:14.5]=AMD0020:0
1869 js= [HW,JOY] Analog joystick
1870 See Documentation/input/joydev/joystick.rst.
1873 When CONFIG_RANDOMIZE_BASE is set, this disables
1874 kernel and module base offset ASLR (Address Space
1875 Layout Randomization).
1878 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1879 report on every invalid memory access. Without this
1880 parameter KASAN will print report only for the first
1885 kernelcore= [KNL,X86,IA-64,PPC]
1886 Format: nn[KMGTPE] | nn% | "mirror"
1887 This parameter specifies the amount of memory usable by
1888 the kernel for non-movable allocations. The requested
1889 amount is spread evenly throughout all nodes in the
1890 system as ZONE_NORMAL. The remaining memory is used for
1891 movable memory in its own zone, ZONE_MOVABLE. In the
1892 event, a node is too small to have both ZONE_NORMAL and
1893 ZONE_MOVABLE, kernelcore memory will take priority and
1894 other nodes will have a larger ZONE_MOVABLE.
1896 ZONE_MOVABLE is used for the allocation of pages that
1897 may be reclaimed or moved by the page migration
1898 subsystem. Note that allocations like PTEs-from-HighMem
1899 still use the HighMem zone if it exists, and the Normal
1900 zone if it does not.
1902 It is possible to specify the exact amount of memory in
1903 the form of "nn[KMGTPE]", a percentage of total system
1904 memory in the form of "nn%", or "mirror". If "mirror"
1905 option is specified, mirrored (reliable) memory is used
1906 for non-movable allocations and remaining memory is used
1907 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
1908 are exclusive, so you cannot specify multiple forms.
1910 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1911 Format: <Controller#>[,poll interval]
1912 The controller # is the number of the ehci usb debug
1913 port as it is probed via PCI. The poll interval is
1914 optional and is the number seconds in between
1915 each poll cycle to the debug port in case you need
1916 the functionality for interrupting the kernel with
1917 gdb or control-c on the dbgp connection. When
1918 not using this parameter you use sysrq-g to break into
1919 the kernel debugger.
1921 kgdboc= [KGDB,HW] kgdb over consoles.
1922 Requires a tty driver that supports console polling,
1923 or a supported polling keyboard driver (non-usb).
1924 Serial only format: <serial_device>[,baud]
1925 keyboard only format: kbd
1926 keyboard and serial format: kbd,<serial_device>[,baud]
1927 Optional Kernel mode setting:
1928 kms, kbd format: kms,kbd
1929 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1931 kgdbwait [KGDB] Stop kernel execution and enter the
1932 kernel debugger at the earliest opportunity.
1934 kmac= [MIPS] korina ethernet MAC address.
1935 Configure the RouterBoard 532 series on-chip
1936 Ethernet adapter MAC address.
1938 kmemleak= [KNL] Boot-time kmemleak enable/disable
1939 Valid arguments: on, off
1941 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1944 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1945 Default is 0 (don't ignore, but inject #GP)
1947 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
1948 Default is false (don't support).
1950 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1954 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1955 Default is 1 (enabled)
1957 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1959 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1961 kvm-arm.vgic_v3_group0_trap=
1962 [KVM,ARM] Trap guest accesses to GICv3 group-0
1965 kvm-arm.vgic_v3_group1_trap=
1966 [KVM,ARM] Trap guest accesses to GICv3 group-1
1969 kvm-arm.vgic_v3_common_trap=
1970 [KVM,ARM] Trap guest accesses to GICv3 common
1973 kvm-arm.vgic_v4_enable=
1974 [KVM,ARM] Allow use of GICv4 for direct injection of
1977 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1978 (virtualized MMU) support on capable Intel chips.
1979 Default is 1 (enabled)
1981 kvm-intel.emulate_invalid_guest_state=
1982 [KVM,Intel] Enable emulation of invalid guest states
1983 Default is 0 (disabled)
1985 kvm-intel.flexpriority=
1986 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1987 Default is 1 (enabled)
1990 [KVM,Intel] Enable VMX nesting (nVMX).
1991 Default is 0 (disabled)
1993 kvm-intel.unrestricted_guest=
1994 [KVM,Intel] Disable unrestricted guest feature
1995 (virtualized real and unpaged mode) on capable
1996 Intel chips. Default is 1 (enabled)
1998 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2001 Valid arguments: never, cond, always
2003 always: L1D cache flush on every VMENTER.
2004 cond: Flush L1D on VMENTER only when the code between
2005 VMEXIT and VMENTER can leak host memory.
2006 never: Disables the mitigation
2008 Default is cond (do L1 cache flush in specific instances)
2010 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2011 feature (tagged TLBs) on capable Intel chips.
2012 Default is 1 (enabled)
2014 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2017 The kernel PTE inversion protection is unconditionally
2018 enabled and cannot be disabled.
2021 Provides all available mitigations for the
2022 L1TF vulnerability. Disables SMT and
2023 enables all mitigations in the
2024 hypervisors, i.e. unconditional L1D flush.
2026 SMT control and L1D flush control via the
2027 sysfs interface is still possible after
2028 boot. Hypervisors will issue a warning
2029 when the first VM is started in a
2030 potentially insecure configuration,
2031 i.e. SMT enabled or L1D flush disabled.
2034 Same as 'full', but disables SMT and L1D
2035 flush runtime control. Implies the
2036 'nosmt=force' command line option.
2037 (i.e. sysfs control of SMT is disabled.)
2040 Leaves SMT enabled and enables the default
2041 hypervisor mitigation, i.e. conditional
2044 SMT control and L1D flush control via the
2045 sysfs interface is still possible after
2046 boot. Hypervisors will issue a warning
2047 when the first VM is started in a
2048 potentially insecure configuration,
2049 i.e. SMT enabled or L1D flush disabled.
2053 Disables SMT and enables the default
2054 hypervisor mitigation.
2056 SMT control and L1D flush control via the
2057 sysfs interface is still possible after
2058 boot. Hypervisors will issue a warning
2059 when the first VM is started in a
2060 potentially insecure configuration,
2061 i.e. SMT enabled or L1D flush disabled.
2064 Same as 'flush', but hypervisors will not
2065 warn when a VM is started in a potentially
2066 insecure configuration.
2069 Disables hypervisor mitigations and doesn't
2074 For details see: Documentation/admin-guide/l1tf.rst
2080 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2083 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2084 value for LAPIC timer one-shot implementation. Default
2085 back to the programmable timer unit in the LAPIC.
2087 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2090 libata.dma= [LIBATA] DMA control
2091 libata.dma=0 Disable all PATA and SATA DMA
2092 libata.dma=1 PATA and SATA Disk DMA only
2093 libata.dma=2 ATAPI (CDROM) DMA only
2094 libata.dma=4 Compact Flash DMA only
2095 Combinations also work, so libata.dma=3 enables DMA
2096 for disks and CDROMs, but not CFs.
2098 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2099 libata.ignore_hpa=0 keep BIOS limits (default)
2100 libata.ignore_hpa=1 ignore limits, using full disk
2102 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2106 libata.force= [LIBATA] Force configurations. The format is comma
2107 separated list of "[ID:]VAL" where ID is
2108 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2109 matching port, link or device. Basically, it matches
2110 the ATA ID string printed on console by libata. If
2111 the whole ID part is omitted, the last PORT and DEVICE
2112 values are used. If ID hasn't been specified yet, the
2113 configuration applies to all ports, links and devices.
2115 If only DEVICE is omitted, the parameter applies to
2116 the port and all links and devices behind it. DEVICE
2117 number of 0 either selects the first device or the
2118 first fan-out link behind PMP device. It does not
2119 select the host link. DEVICE number of 15 selects the
2120 host link and device attached to it.
2122 The VAL specifies the configuration to force. As long
2123 as there's no ambiguity shortcut notation is allowed.
2124 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2125 The following configurations can be forced.
2127 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2128 Any ID with matching PORT is used.
2130 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2132 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2133 udma[/][16,25,33,44,66,100,133] notation is also
2136 * [no]ncq: Turn on or off NCQ.
2138 * [no]ncqtrim: Turn off queued DSM TRIM.
2140 * nohrst, nosrst, norst: suppress hard, soft
2143 * rstonce: only attempt one reset during
2144 hot-unplug link recovery
2146 * dump_id: dump IDENTIFY data.
2148 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2150 * disable: Disable this device.
2152 If there are multiple matching configurations changing
2153 the same attribute, the last one is used.
2155 memblock=debug [KNL] Enable memblock debug messages.
2157 load_ramdisk= [RAM] List of ramdisks to load from floppy
2158 See Documentation/blockdev/ramdisk.txt.
2160 lockd.nlm_grace_period=P [NFS] Assign grace period.
2163 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2166 lockd.nlm_timeout=T [NFS] Assign timeout value.
2169 lockd.nlm_udpport=M [NFS] Assign UDP port.
2172 locktorture.nreaders_stress= [KNL]
2173 Set the number of locking read-acquisition kthreads.
2174 Defaults to being automatically set based on the
2175 number of online CPUs.
2177 locktorture.nwriters_stress= [KNL]
2178 Set the number of locking write-acquisition kthreads.
2180 locktorture.onoff_holdoff= [KNL]
2181 Set time (s) after boot for CPU-hotplug testing.
2183 locktorture.onoff_interval= [KNL]
2184 Set time (s) between CPU-hotplug operations, or
2185 zero to disable CPU-hotplug testing.
2187 locktorture.shuffle_interval= [KNL]
2188 Set task-shuffle interval (jiffies). Shuffling
2189 tasks allows some CPUs to go into dyntick-idle
2190 mode during the locktorture test.
2192 locktorture.shutdown_secs= [KNL]
2193 Set time (s) after boot system shutdown. This
2194 is useful for hands-off automated testing.
2196 locktorture.stat_interval= [KNL]
2197 Time (s) between statistics printk()s.
2199 locktorture.stutter= [KNL]
2200 Time (s) to stutter testing, for example,
2201 specifying five seconds causes the test to run for
2202 five seconds, wait for five seconds, and so on.
2203 This tests the locking primitive's ability to
2204 transition abruptly to and from idle.
2206 locktorture.torture_type= [KNL]
2207 Specify the locking implementation to test.
2209 locktorture.verbose= [KNL]
2210 Enable additional printk() statements.
2212 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2215 loglevel= All Kernel Messages with a loglevel smaller than the
2216 console loglevel will be printed to the console. It can
2217 also be changed with klogd or other programs. The
2218 loglevels are defined as follows:
2220 0 (KERN_EMERG) system is unusable
2221 1 (KERN_ALERT) action must be taken immediately
2222 2 (KERN_CRIT) critical conditions
2223 3 (KERN_ERR) error conditions
2224 4 (KERN_WARNING) warning conditions
2225 5 (KERN_NOTICE) normal but significant condition
2226 6 (KERN_INFO) informational
2227 7 (KERN_DEBUG) debug-level messages
2229 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2230 in bytes. n must be a power of two and greater
2231 than the minimal size. The minimal size is defined
2232 by LOG_BUF_SHIFT kernel config parameter. There is
2233 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2234 that allows to increase the default size depending on
2235 the number of CPUs. See init/Kconfig for more details.
2237 logo.nologo [FB] Disables display of the built-in Linux logo.
2238 This may be used to provide more screen space for
2239 kernel log messages and is useful when debugging
2240 kernel boot problems.
2242 lp=0 [LP] Specify parallel ports to use, e.g,
2243 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2244 lp=reset first parallel port). 'lp=0' disables the
2245 lp=auto printer driver. 'lp=reset' (which can be
2246 specified in addition to the ports) causes
2247 attached printers to be reset. Using
2248 lp=port1,port2,... specifies the parallel ports
2249 to associate lp devices with, starting with
2250 lp0. A port specification may be 'none' to skip
2251 that lp device, or a parport name such as
2252 'parport0'. Specifying 'lp=auto' instead of a
2253 port specification list means that device IDs
2254 from each port should be examined, to see if
2255 an IEEE 1284-compliant printer is attached; if
2256 so, the driver will manage that printer.
2257 See also header of drivers/char/lp.c.
2260 Sets loops_per_jiffy to given constant, thus avoiding
2261 time-consuming boot-time autodetection (up to 250 ms per
2262 CPU). 0 enables autodetection (default). To determine
2263 the correct value for your kernel, boot with normal
2264 autodetection and see what value is printed. Note that
2265 on SMP systems the preset will be applied to all CPUs,
2266 which is likely to cause problems if your CPUs need
2267 significantly divergent settings. An incorrect value
2268 will cause delays in the kernel to be wrong, leading to
2269 unpredictable I/O errors and other breakage. Although
2270 unlikely, in the extreme case this might damage your
2274 Format: <io>,<irq>,<dma>
2276 machvec= [IA-64] Force the use of a particular machine-vector
2277 (machvec) in a generic kernel.
2278 Example: machvec=hpzx1_swiotlb
2280 machtype= [Loongson] Share the same kernel image file between different
2282 Example: machtype=lemote-yeeloong-2f-7inch
2284 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2285 than or equal to this physical address is ignored.
2287 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2288 will bring up during bootup. maxcpus=n : n >= 0 limits
2289 the kernel to bring up 'n' processors. Surely after
2290 bootup you can bring up the other plugged cpu by executing
2291 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2292 only takes effect during system bootup.
2293 While n=0 is a special case, it is equivalent to "nosmp",
2294 which also disables the IO APIC.
2296 max_loop= [LOOP] The number of loop block devices that get
2297 (loop.max_loop) unconditionally pre-created at init time. The default
2298 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2299 of statically allocating a predefined number, loop
2300 devices can be requested on-demand with the
2301 /dev/loop-control interface.
2303 mce [X86-32] Machine Check Exception
2305 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2307 md= [HW] RAID subsystems devices and level
2308 See Documentation/admin-guide/md.rst.
2311 Format: <first>,<last>
2312 Specifies range of consoles to be captured by the MDA.
2314 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2315 Amount of memory to be used when the kernel is not able
2316 to see the whole system memory or for test.
2317 [X86] Work as limiting max address. Use together
2318 with memmap= to avoid physical address space collisions.
2319 Without memmap= PCI devices could be placed at addresses
2320 belonging to unused RAM.
2322 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2326 [KNL,SH] Allow user to override the default size for
2327 per-device physically contiguous DMA buffers.
2329 memhp_default_state=online/offline
2330 [KNL] Set the initial state for the memory hotplug
2331 onlining policy. If not specified, the default value is
2332 set according to the
2333 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2335 See Documentation/memory-hotplug.txt.
2337 memmap=exactmap [KNL,X86] Enable setting of an exact
2338 E820 memory map, as specified by the user.
2339 Such memmap=exactmap lines can be constructed based on
2340 BIOS output or other requirements. See the memmap=nn@ss
2343 memmap=nn[KMG]@ss[KMG]
2344 [KNL] Force usage of a specific region of memory.
2345 Region of memory to be used is from ss to ss+nn.
2346 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2347 which limits max address to nn[KMG].
2348 Multiple different regions can be specified,
2351 memmap=100M@2G,100M#3G,1G!1024G
2353 memmap=nn[KMG]#ss[KMG]
2354 [KNL,ACPI] Mark specific memory as ACPI data.
2355 Region of memory to be marked is from ss to ss+nn.
2357 memmap=nn[KMG]$ss[KMG]
2358 [KNL,ACPI] Mark specific memory as reserved.
2359 Region of memory to be reserved is from ss to ss+nn.
2360 Example: Exclude memory from 0x18690000-0x1869ffff
2361 memmap=64K$0x18690000
2363 memmap=0x10000$0x18690000
2364 Some bootloaders may need an escape character before '$',
2365 like Grub2, otherwise '$' and the following number
2368 memmap=nn[KMG]!ss[KMG]
2369 [KNL,X86] Mark specific memory as protected.
2370 Region of memory to be used, from ss to ss+nn.
2371 The memory region may be marked as e820 type 12 (0xc)
2372 and is NVDIMM or ADR memory.
2374 memmap=<size>%<offset>-<oldtype>+<newtype>
2375 [KNL,ACPI] Convert memory within the specified region
2376 from <oldtype> to <newtype>. If "-<oldtype>" is left
2377 out, the whole region will be marked as <newtype>,
2378 even if previously unavailable. If "+<newtype>" is left
2379 out, matching memory will be removed. Types are
2380 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2381 3 = ACPI, 12 = PRAM.
2383 memory_corruption_check=0/1 [X86]
2384 Some BIOSes seem to corrupt the first 64k of
2385 memory when doing things like suspend/resume.
2386 Setting this option will scan the memory
2387 looking for corruption. Enabling this will
2388 both detect corruption and prevent the kernel
2389 from using the memory being corrupted.
2390 However, its intended as a diagnostic tool; if
2391 repeatable BIOS-originated corruption always
2392 affects the same memory, you can use memmap=
2393 to prevent the kernel from using that memory.
2395 memory_corruption_check_size=size [X86]
2396 By default it checks for corruption in the low
2397 64k, making this memory unavailable for normal
2398 use. Use this parameter to scan for
2399 corruption in more or less memory.
2401 memory_corruption_check_period=seconds [X86]
2402 By default it checks for corruption every 60
2403 seconds. Use this parameter to check at some
2404 other rate. 0 disables periodic checking.
2406 memtest= [KNL,X86,ARM] Enable memtest
2408 default : 0 <disable>
2409 Specifies the number of memtest passes to be
2410 performed. Each pass selects another test
2411 pattern from a given set of patterns. Memtest
2412 fills the memory with this pattern, validates
2413 memory contents and reserves bad memory
2414 regions that are detected.
2416 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2417 Valid arguments: on, off
2418 Default (depends on kernel configuration option):
2419 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2420 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2421 mem_encrypt=on: Activate SME
2422 mem_encrypt=off: Do not activate SME
2424 Refer to Documentation/x86/amd-memory-encryption.txt
2425 for details on when memory encryption can be activated.
2427 mem_sleep_default= [SUSPEND] Default system suspend mode:
2428 s2idle - Suspend-To-Idle
2429 shallow - Power-On Suspend or equivalent (if supported)
2430 deep - Suspend-To-RAM or equivalent (if supported)
2431 See Documentation/admin-guide/pm/sleep-states.rst.
2433 meye.*= [HW] Set MotionEye Camera parameters
2434 See Documentation/media/v4l-drivers/meye.rst.
2436 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2437 Multi-Function General Purpose Timers on AMD Geode
2440 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2441 the BIOS has incorrectly applied a workaround. TinyBIOS
2442 version 0.98 is known to be affected, 0.99 fixes the
2443 problem by letting the user disable the workaround.
2447 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2448 physical address is ignored.
2450 mini2440= [ARM,HW,KNL]
2451 Format:[0..2][b][c][t]
2453 MINI2440 configuration specification:
2454 0 - The attached screen is the 3.5" TFT
2455 1 - The attached screen is the 7" TFT
2456 2 - The VGA Shield is attached (1024x768)
2457 Leaving out the screen size parameter will not load
2458 the TFT driver, and the framebuffer will be left
2460 b - Enable backlight. The TFT backlight pin will be
2461 linked to the kernel VESA blanking code and a GPIO
2462 LED. This parameter is not necessary when using the
2464 c - Enable the s3c camera interface.
2465 t - Reserved for enabling touchscreen support. The
2466 touchscreen support is not enabled in the mainstream
2467 kernel as of 2.6.30, a preliminary port can be found
2468 in the "bleeding edge" mini2440 support kernel at
2469 http://repo.or.cz/w/linux-2.6/mini2440.git
2472 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2473 parameter allows control of the logging verbosity for
2474 the additional memory initialisation checks. A value
2475 of 0 disables mminit logging and a level of 4 will
2476 log everything. Information is printed at KERN_DEBUG
2477 so loglevel=8 may also need to be specified.
2480 [KNL] When CONFIG_MODULE_SIG is set, this means that
2481 modules without (valid) signatures will fail to load.
2482 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2483 is always true, so this option does nothing.
2485 module_blacklist= [KNL] Do not load a comma-separated list of
2486 modules. Useful for debugging problem modules.
2489 [MOUSE] Maximum time between finger touching and
2490 leaving touchpad surface for touch to be considered
2491 a tap and be reported as a left button click (for
2492 touchpads working in absolute mode only).
2494 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2495 reporting absolute coordinates, such as tablets
2496 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2497 reporting absolute coordinates, such as tablets
2499 movablecore= [KNL,X86,IA-64,PPC]
2500 Format: nn[KMGTPE] | nn%
2501 This parameter is the complement to kernelcore=, it
2502 specifies the amount of memory used for migratable
2503 allocations. If both kernelcore and movablecore is
2504 specified, then kernelcore will be at *least* the
2505 specified value but may be more. If movablecore on its
2506 own is specified, the administrator must be careful
2507 that the amount of memory usable for all allocations
2510 movable_node [KNL] Boot-time switch to make hotplugable memory
2511 NUMA nodes to be movable. This means that the memory
2512 of such nodes will be usable only for movable
2513 allocations which rules out almost all kernel
2514 allocations. Use with caution!
2516 MTD_Partition= [MTD]
2517 Format: <name>,<region-number>,<size>,<offset>
2519 MTD_Region= [MTD] Format:
2520 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2523 See drivers/mtd/cmdlinepart.c.
2525 multitce=off [PPC] This parameter disables the use of the pSeries
2526 firmware feature for updating multiple TCE entries
2529 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2531 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2533 boundary - index of last SLC block on Flex-OneNAND.
2534 The remaining blocks are configured as MLC blocks.
2535 lock - Configure if Flex-OneNAND boundary should be locked.
2536 Once locked, the boundary cannot be changed.
2537 1 indicates lock status, 0 indicates unlock status.
2540 ARM/S3C2412 JIVE boot control
2542 See arch/arm/mach-s3c2412/mach-jive.c
2544 mtouchusb.raw_coordinates=
2545 [HW] Make the MicroTouch USB driver use raw coordinates
2546 ('y', default) or cooked coordinates ('n')
2548 mtrr_chunk_size=nn[KMG] [X86]
2549 used for mtrr cleanup. It is largest continuous chunk
2550 that could hold holes aka. UC entries.
2552 mtrr_gran_size=nn[KMG] [X86]
2553 Used for mtrr cleanup. It is granularity of mtrr block.
2555 Large value could prevent small alignment from
2558 mtrr_spare_reg_nr=n [X86]
2560 Range: 0,7 : spare reg number
2562 Used for mtrr cleanup. It is spare mtrr entries number.
2563 Set to 2 or more if your graphical card needs more.
2565 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2567 netdev= [NET] Network devices parameters
2568 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2569 Note that mem_start is often overloaded to mean
2570 something different and driver-specific.
2571 This usage is only documented in each driver source
2575 [NETFILTER] Enable connection tracking flow accounting
2576 0 to disable accounting
2577 1 to enable accounting
2580 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2581 See Documentation/filesystems/nfs/nfsroot.txt.
2583 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2584 See Documentation/filesystems/nfs/nfsroot.txt.
2586 nfsrootdebug [NFS] enable nfsroot debugging messages.
2587 See Documentation/filesystems/nfs/nfsroot.txt.
2589 nfs.callback_nr_threads=
2590 [NFSv4] set the total number of threads that the
2591 NFS client will assign to service NFSv4 callback
2594 nfs.callback_tcpport=
2595 [NFS] set the TCP port on which the NFSv4 callback
2596 channel should listen.
2599 [NFS] sets the pathname to the program which is used
2600 to update the NFS client cache entries.
2602 nfs.cache_getent_timeout=
2603 [NFS] sets the timeout after which an attempt to
2604 update a cache entry is deemed to have failed.
2606 nfs.idmap_cache_timeout=
2607 [NFS] set the maximum lifetime for idmapper cache
2611 [NFS] enable 64-bit inode numbers.
2612 If zero, the NFS client will fake up a 32-bit inode
2613 number for the readdir() and stat() syscalls instead
2614 of returning the full 64-bit number.
2615 The default is to return 64-bit inode numbers.
2617 nfs.max_session_cb_slots=
2618 [NFSv4.1] Sets the maximum number of session
2619 slots the client will assign to the callback
2620 channel. This determines the maximum number of
2621 callbacks the client will process in parallel for
2622 a particular server.
2624 nfs.max_session_slots=
2625 [NFSv4.1] Sets the maximum number of session slots
2626 the client will attempt to negotiate with the server.
2627 This limits the number of simultaneous RPC requests
2628 that the client can send to the NFSv4.1 server.
2629 Note that there is little point in setting this
2630 value higher than the max_tcp_slot_table_limit.
2632 nfs.nfs4_disable_idmapping=
2633 [NFSv4] When set to the default of '1', this option
2634 ensures that both the RPC level authentication
2635 scheme and the NFS level operations agree to use
2636 numeric uids/gids if the mount is using the
2637 'sec=sys' security flavour. In effect it is
2638 disabling idmapping, which can make migration from
2639 legacy NFSv2/v3 systems to NFSv4 easier.
2640 Servers that do not support this mode of operation
2641 will be autodetected by the client, and it will fall
2642 back to using the idmapper.
2643 To turn off this behaviour, set the value to '0'.
2645 [NFS4] Specify an additional fixed unique ident-
2646 ification string that NFSv4 clients can insert into
2647 their nfs_client_id4 string. This is typically a
2648 UUID that is generated at system install time.
2650 nfs.send_implementation_id =
2651 [NFSv4.1] Send client implementation identification
2652 information in exchange_id requests.
2653 If zero, no implementation identification information
2655 The default is to send the implementation identification
2658 nfs.recover_lost_locks =
2659 [NFSv4] Attempt to recover locks that were lost due
2660 to a lease timeout on the server. Please note that
2661 doing this risks data corruption, since there are
2662 no guarantees that the file will remain unchanged
2663 after the locks are lost.
2664 If you want to enable the kernel legacy behaviour of
2665 attempting to recover these locks, then set this
2667 The default parameter value of '0' causes the kernel
2668 not to attempt recovery of lost locks.
2670 nfs4.layoutstats_timer =
2671 [NFSv4.2] Change the rate at which the kernel sends
2672 layoutstats to the pNFS metadata server.
2674 Setting this to value to 0 causes the kernel to use
2675 whatever value is the default set by the layout
2676 driver. A non-zero value sets the minimum interval
2677 in seconds between layoutstats transmissions.
2679 nfsd.nfs4_disable_idmapping=
2680 [NFSv4] When set to the default of '1', the NFSv4
2681 server will return only numeric uids and gids to
2682 clients using auth_sys, and will accept numeric uids
2683 and gids from such clients. This is intended to ease
2684 migration from NFSv2/v3.
2686 nmi_debug= [KNL,SH] Specify one or more actions to take
2687 when a NMI is triggered.
2688 Format: [state][,regs][,debounce][,die]
2690 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2691 Format: [panic,][nopanic,][num]
2693 0 - turn hardlockup detector in nmi_watchdog off
2694 1 - turn hardlockup detector in nmi_watchdog on
2695 When panic is specified, panic when an NMI watchdog
2696 timeout occurs (or 'nopanic' to override the opposite
2697 default). To disable both hard and soft lockup detectors,
2698 please see 'nowatchdog'.
2699 This is useful when you use a panic=... timeout and
2700 need the box quickly up again.
2702 These settings can be accessed at runtime via
2703 the nmi_watchdog and hardlockup_panic sysctls.
2705 netpoll.carrier_timeout=
2706 [NET] Specifies amount of time (in seconds) that
2707 netpoll should wait for a carrier. By default netpoll
2710 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2711 emulation library even if a 387 maths coprocessor
2714 no5lvl [X86-64] Disable 5-level paging mode. Forces
2715 kernel to use 4-level paging instead.
2718 [HW] Never suspend the console
2719 Disable suspending of consoles during suspend and
2720 hibernate operations. Once disabled, debugging
2721 messages can reach various consoles while the rest
2722 of the system is being put to sleep (ie, while
2723 debugging driver suspend/resume hooks). This may
2724 not work reliably with all consoles, but is known
2725 to work with serial and VGA consoles.
2726 To facilitate more flexible debugging, we also add
2727 console_suspend, a printk module parameter to control
2728 it. Users could use console_suspend (usually
2729 /sys/module/printk/parameters/console_suspend) to
2730 turn on/off it dynamically.
2732 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2733 caches in the slab allocator. Saves per-node memory,
2734 but will impact performance.
2738 noaltinstr [S390] Disables alternative instructions patching
2739 (CPU alternatives feature).
2741 noapic [SMP,APIC] Tells the kernel to not make use of any
2742 IOAPICs that may be present in the system.
2744 noautogroup Disable scheduler automatic task group creation.
2746 nobats [PPC] Do not use BATs for mapping kernel lowmem
2747 on "Classic" PPC cores.
2751 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2753 nodelayacct [KNL] Disable per-task delay accounting
2755 nodsp [SH] Disable hardware DSP at boot time.
2757 noefi Disable EFI runtime services support.
2762 On X86-32 available only on PAE configured kernels.
2763 noexec=on: enable non-executable mappings (default)
2764 noexec=off: disable non-executable mappings
2767 Disable SMAP (Supervisor Mode Access Prevention)
2768 even if it is supported by processor.
2771 Disable SMEP (Supervisor Mode Execution Prevention)
2772 even if it is supported by processor.
2775 This affects only 32-bit executables.
2776 noexec32=on: enable non-executable mappings (default)
2777 read doesn't imply executable mappings
2778 noexec32=off: disable non-executable mappings
2779 read implies executable mappings
2781 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2783 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2784 register save and restore. The kernel will only save
2785 legacy floating-point registers on task switch.
2787 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2789 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2790 Equivalent to smt=1.
2792 [KNL,x86] Disable symmetric multithreading (SMT).
2793 nosmt=force: Force disable SMT, cannot be undone
2794 via the sysfs control file.
2796 nospectre_v1 [PPC] Disable mitigations for Spectre Variant 1 (bounds
2797 check bypass). With this option data leaks are possible
2800 nospectre_v2 [X86] Disable all mitigations for the Spectre variant 2
2801 (indirect branch prediction) vulnerability. System may
2802 allow data leaks with this option, which is equivalent
2805 nospec_store_bypass_disable
2806 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
2808 noxsave [BUGS=X86] Disables x86 extended register state save
2809 and restore using xsave. The kernel will fallback to
2810 enabling legacy floating-point and sse state.
2812 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2813 register states. The kernel will fall back to use
2814 xsave to save the states. By using this parameter,
2815 performance of saving the states is degraded because
2816 xsave doesn't support modified optimization while
2817 xsaveopt supports it on xsaveopt enabled systems.
2819 noxsaves [X86] Disables xsaves and xrstors used in saving and
2820 restoring x86 extended register state in compacted
2821 form of xsave area. The kernel will fall back to use
2822 xsaveopt and xrstor to save and restore the states
2823 in standard form of xsave area. By using this
2824 parameter, xsave area per process might occupy more
2825 memory on xsaves enabled systems.
2827 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2828 wfi(ARM) instruction doesn't work correctly and not to
2829 use it. This is also useful when using JTAG debugger.
2831 no_file_caps Tells the kernel not to honor file capabilities. The
2832 only way then for a file to be executed with privilege
2833 is to be setuid root or executed by root.
2835 nohalt [IA-64] Tells the kernel not to use the power saving
2836 function PAL_HALT_LIGHT when idle. This increases
2837 power-consumption. On the positive side, it reduces
2838 interrupt wake-up latency, which may improve performance
2839 in certain environments such as networked servers or
2842 nohibernate [HIBERNATION] Disable hibernation and resume.
2844 nohz= [KNL] Boottime enable/disable dynamic ticks
2845 Valid arguments: on, off
2848 nohz_full= [KNL,BOOT,SMP,ISOL]
2849 The argument is a cpu list, as described above.
2850 In kernels built with CONFIG_NO_HZ_FULL=y, set
2851 the specified list of CPUs whose tick will be stopped
2852 whenever possible. The boot CPU will be forced outside
2853 the range to maintain the timekeeping. Any CPUs
2854 in this list will have their RCU callbacks offloaded,
2855 just as if they had also been called out in the
2856 rcu_nocbs= boot parameter.
2858 noiotrap [SH] Disables trapped I/O port accesses.
2860 noirqdebug [X86-32] Disables the code which attempts to detect and
2861 disable unhandled interrupt sources.
2863 no_timer_check [X86,APIC] Disables the code which tests for
2864 broken timer IRQ sources.
2866 noisapnp [ISAPNP] Disables ISA PnP code.
2868 noinitrd [RAM] Tells the kernel not to load any configured
2871 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2873 [Deprecated - use intremap=off]
2877 noinvpcid [X86] Disable the INVPCID cpu feature.
2879 nojitter [IA-64] Disables jitter checking for ITC timers.
2881 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2883 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2887 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2888 clock and use the default one.
2890 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2891 steal time is computed, but won't influence scheduler
2894 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2896 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2898 noltlbs [PPC] Do not use large page/tlb entries for kernel
2899 lowmem mapping on PPC40x and PPC8xx
2901 nomca [IA-64] Disable machine check abort handling
2903 nomce [X86-32] Disable Machine Check Exception
2905 nomfgpt [X86-32] Disable Multi-Function General Purpose
2906 Timer usage (for AMD Geode machines).
2908 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2909 shutdown the other cpus. Instead use the REBOOT_VECTOR
2912 nomodule Disable module load
2914 nopat [X86] Disable PAT (page attribute table extension of
2915 pagetables) support.
2917 nopcid [X86-64] Disable the PCID cpu feature.
2919 norandmaps Don't use address space randomization. Equivalent to
2920 echo 0 > /proc/sys/kernel/randomize_va_space
2922 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2923 with UP alternatives
2925 nordrand [X86] Disable kernel use of the RDRAND and
2926 RDSEED instructions even if they are supported
2927 by the processor. RDRAND and RDSEED are still
2928 available to user space applications.
2930 noresume [SWSUSP] Disables resume and restores original swap
2933 no-scroll [VGA] Disables scrollback.
2934 This is required for the Braillex ib80-piezo Braille
2935 reader made by F.H. Papenmeier (Germany).
2939 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2941 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2942 and disable the IO APIC. legacy for "maxcpus=0".
2944 nosoftlockup [KNL] Disable the soft-lockup detector.
2946 nosync [HW,M68K] Disables sync negotiation for all devices.
2948 nowatchdog [KNL] Disable both lockup detectors, i.e.
2949 soft-lockup and NMI watchdog (hard-lockup).
2953 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2955 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2956 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2957 Some features depend on CPU0. Known dependencies are:
2958 1. Resume from suspend/hibernate depends on CPU0.
2959 Suspend/hibernate will fail if CPU0 is offline and you
2960 need to online CPU0 before suspend/hibernate.
2961 2. PIC interrupts also depend on CPU0. CPU0 can't be
2962 removed if a PIC interrupt is detected.
2963 It's said poweroff/reboot may depend on CPU0 on some
2964 machines although I haven't seen such issues so far
2965 after CPU0 is offline on a few tested machines.
2966 If the dependencies are under your control, you can
2967 turn on cpu0_hotplug.
2969 nps_mtm_hs_ctr= [KNL,ARC]
2970 This parameter sets the maximum duration, in
2971 cycles, each HW thread of the CTOP can run
2972 without interruptions, before HW switches it.
2973 The actual maximum duration is 16 times this
2975 Format: integer between 1 and 255
2978 nptcg= [IA-64] Override max number of concurrent global TLB
2979 purges which is reported from either PAL_VM_SUMMARY or
2982 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2983 could support. nr_cpus=n : n >= 1 limits the kernel to
2984 support 'n' processors. It could be larger than the
2985 number of already plugged CPU during bootup, later in
2986 runtime you can physically add extra cpu until it reaches
2987 n. So during boot up some boot time memory for per-cpu
2988 variables need be pre-allocated for later physical cpu
2991 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2993 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2994 Allowed values are enable and disable
2996 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2997 'node', 'default' can be specified
2998 This can be set from sysctl after boot.
2999 See Documentation/sysctl/vm.txt for details.
3001 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3002 See Documentation/debugging-via-ohci1394.txt for more
3005 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3006 Rather than timing out after 20 ms if an EC
3007 command is not properly ACKed, override the length
3008 of the timeout. We have interrupts disabled while
3009 waiting for the ACK, so if this is set too high
3010 interrupts *may* be lost!
3012 omap_mux= [OMAP] Override bootloader pin multiplexing.
3013 Format: <mux_mode0.mode_name=value>...
3014 For example, to override I2C bus2:
3015 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3017 oprofile.timer= [HW]
3018 Use timer interrupt instead of performance counters
3020 oprofile.cpu_type= Force an oprofile cpu type
3021 This might be useful if you have an older oprofile
3022 userland or if you want common events.
3023 Format: { arch_perfmon }
3024 arch_perfmon: [X86] Force use of architectural
3025 perfmon on Intel CPUs instead of the
3026 CPU specific event set.
3027 timer: [X86] Force use of architectural NMI
3028 timer mode (see also oprofile.timer
3029 for generic hr timer mode)
3031 oops=panic Always panic on oopses. Default is to just kill the
3032 process, but there is a small probability of
3033 deadlocking the machine.
3034 This will also cause panics on machine check exceptions.
3035 Useful together with panic=30 to trigger a reboot.
3037 page_owner= [KNL] Boot-time page_owner enabling option.
3038 Storage of the information about who allocated
3039 each page is disabled in default. With this switch,
3041 on: enable the feature
3043 page_poison= [KNL] Boot-time parameter changing the state of
3044 poisoning on the buddy allocator.
3045 off: turn off poisoning
3046 on: turn on poisoning
3048 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3049 timeout > 0: seconds before rebooting
3050 timeout = 0: wait forever
3051 timeout < 0: reboot immediately
3054 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3057 crash_kexec_post_notifiers
3058 Run kdump after running panic-notifiers and dumping
3059 kmsg. This only for the users who doubt kdump always
3060 succeeds in any situation.
3061 Note that this also increases risks of kdump failure,
3062 because some panic notifiers can make the crashed
3063 kernel more unstable.
3065 parkbd.port= [HW] Parallel port number the keyboard adapter is
3066 connected to, default is 0.
3068 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3069 0 for XT, 1 for AT (default is AT).
3072 parport= [HW,PPT] Specify parallel ports. 0 disables.
3073 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3074 Use 'auto' to force the driver to use any
3075 IRQ/DMA settings detected (the default is to
3076 ignore detected IRQ/DMA settings because of
3077 possible conflicts). You can specify the base
3078 address, IRQ, and DMA settings; IRQ and DMA
3079 should be numbers, or 'auto' (for using detected
3080 settings on that particular port), or 'nofifo'
3081 (to avoid using a FIFO even if it is detected).
3082 Parallel ports are assigned in the order they
3083 are specified on the command line, starting
3086 parport_init_mode= [HW,PPT]
3087 Configure VIA parallel port to operate in
3088 a specific mode. This is necessary on Pegasos
3089 computer where firmware has no options for setting
3090 up parallel port mode and sets it to spp.
3091 Currently this function knows 686a and 8231 chips.
3092 Format: [spp|ps2|epp|ecp|ecpepp]
3095 Halt all CPUs after the first oops has been printed for
3096 the specified number of seconds. This is to be used if
3097 your oopses keep scrolling off the screen.
3102 See header of drivers/block/paride/pcd.c.
3103 See also Documentation/blockdev/paride.txt.
3105 pci=option[,option...] [PCI] various PCI subsystem options.
3107 Some options herein operate on a specific device
3108 or a set of devices (<pci_dev>). These are
3109 specified in one of the following formats:
3111 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
3112 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
3114 Note: the first format specifies a PCI
3115 bus/device/function address which may change
3116 if new hardware is inserted, if motherboard
3117 firmware changes, or due to changes caused
3118 by other kernel parameters. If the
3119 domain is left unspecified, it is
3120 taken to be zero. Optionally, a path
3121 to a device through multiple device/function
3122 addresses can be specified after the base
3123 address (this is more robust against
3124 renumbering issues). The second format
3125 selects devices using IDs from the
3126 configuration space which may match multiple
3127 devices in the system.
3129 earlydump dump PCI config space before the kernel
3131 off [X86] don't probe for the PCI bus
3132 bios [X86-32] force use of PCI BIOS, don't access
3133 the hardware directly. Use this if your machine
3134 has a non-standard PCI host bridge.
3135 nobios [X86-32] disallow use of PCI BIOS, only direct
3136 hardware access methods are allowed. Use this
3137 if you experience crashes upon bootup and you
3138 suspect they are caused by the BIOS.
3139 conf1 [X86] Force use of PCI Configuration Access
3140 Mechanism 1 (config address in IO port 0xCF8,
3141 data in IO port 0xCFC, both 32-bit).
3142 conf2 [X86] Force use of PCI Configuration Access
3143 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3144 the function, IO port 0xCFA, also 8-bit, sets
3145 bus number. The config space is then accessed
3146 through ports 0xC000-0xCFFF).
3147 See http://wiki.osdev.org/PCI for more info
3148 on the configuration access mechanisms.
3149 noaer [PCIE] If the PCIEAER kernel config parameter is
3150 enabled, this kernel boot option can be used to
3151 disable the use of PCIE advanced error reporting.
3152 nodomains [PCI] Disable support for multiple PCI
3153 root domains (aka PCI segments, in ACPI-speak).
3154 nommconf [X86] Disable use of MMCONFIG for PCI
3156 check_enable_amd_mmconf [X86] check for and enable
3157 properly configured MMIO access to PCI
3158 config space on AMD family 10h CPU
3159 nomsi [MSI] If the PCI_MSI kernel config parameter is
3160 enabled, this kernel boot option can be used to
3161 disable the use of MSI interrupts system-wide.
3162 noioapicquirk [APIC] Disable all boot interrupt quirks.
3163 Safety option to keep boot IRQs enabled. This
3164 should never be necessary.
3165 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3166 primary IO-APIC for bridges that cannot disable
3167 boot IRQs. This fixes a source of spurious IRQs
3168 when the system masks IRQs.
3169 noioapicreroute [APIC] Disable workaround that uses the
3170 boot IRQ equivalent of an IRQ that connects to
3171 a chipset where boot IRQs cannot be disabled.
3172 The opposite of ioapicreroute.
3173 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3174 routing table. These calls are known to be buggy
3175 on several machines and they hang the machine
3176 when used, but on other computers it's the only
3177 way to get the interrupt routing table. Try
3178 this option if the kernel is unable to allocate
3179 IRQs or discover secondary PCI buses on your
3181 rom [X86] Assign address space to expansion ROMs.
3182 Use with caution as certain devices share
3183 address decoders between ROMs and other
3185 norom [X86] Do not assign address space to
3186 expansion ROMs that do not already have
3187 BIOS assigned address ranges.
3188 nobar [X86] Do not assign address space to the
3189 BARs that weren't assigned by the BIOS.
3190 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3191 assigned automatically to PCI devices. You can
3192 make the kernel exclude IRQs of your ISA cards
3194 pirqaddr=0xAAAAA [X86] Specify the physical address
3195 of the PIRQ table (normally generated
3196 by the BIOS) if it is outside the
3197 F0000h-100000h range.
3198 lastbus=N [X86] Scan all buses thru bus #N. Can be
3199 useful if the kernel is unable to find your
3200 secondary buses and you want to tell it
3201 explicitly which ones they are.
3202 assign-busses [X86] Always assign all PCI bus
3203 numbers ourselves, overriding
3204 whatever the firmware may have done.
3205 usepirqmask [X86] Honor the possible IRQ mask stored
3206 in the BIOS $PIR table. This is needed on
3207 some systems with broken BIOSes, notably
3208 some HP Pavilion N5400 and Omnibook XE3
3209 notebooks. This will have no effect if ACPI
3210 IRQ routing is enabled.
3211 noacpi [X86] Do not use ACPI for IRQ routing
3212 or for PCI scanning.
3213 use_crs [X86] Use PCI host bridge window information
3214 from ACPI. On BIOSes from 2008 or later, this
3215 is enabled by default. If you need to use this,
3216 please report a bug.
3217 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3218 If you need to use this, please report a bug.
3219 routeirq Do IRQ routing for all PCI devices.
3220 This is normally done in pci_enable_device(),
3221 so this option is a temporary workaround
3222 for broken drivers that don't call it.
3223 skip_isa_align [X86] do not align io start addr, so can
3224 handle more pci cards
3225 noearly [X86] Don't do any early type 1 scanning.
3226 This might help on some broken boards which
3227 machine check when some devices' config space
3228 is read. But various workarounds are disabled
3229 and some IOMMU drivers will not work.
3230 bfsort Sort PCI devices into breadth-first order.
3231 This sorting is done to get a device
3232 order compatible with older (<= 2.4) kernels.
3233 nobfsort Don't sort PCI devices into breadth-first order.
3234 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3235 tuning and use the BIOS-configured MPS defaults.
3236 pcie_bus_safe Set every device's MPS to the largest value
3237 supported by all devices below the root complex.
3238 pcie_bus_perf Set device MPS to the largest allowable MPS
3239 based on its parent bus. Also set MRRS (Max
3240 Read Request Size) to the largest supported
3241 value (no larger than the MPS that the device
3242 or bus can support) for best performance.
3243 pcie_bus_peer2peer Set every device's MPS to 128B, which
3244 every device is guaranteed to support. This
3245 configuration allows peer-to-peer DMA between
3246 any pair of devices, possibly at the cost of
3247 reduced performance. This also guarantees
3248 that hot-added devices will work.
3249 cbiosize=nn[KMG] The fixed amount of bus space which is
3250 reserved for the CardBus bridge's IO window.
3251 The default value is 256 bytes.
3252 cbmemsize=nn[KMG] The fixed amount of bus space which is
3253 reserved for the CardBus bridge's memory
3254 window. The default value is 64 megabytes.
3257 [<order of align>@]<pci_dev>[; ...]
3258 Specifies alignment and device to reassign
3259 aligned memory resources. How to
3260 specify the device is described above.
3261 If <order of align> is not specified,
3262 PAGE_SIZE is used as alignment.
3263 PCI-PCI bridge can be specified, if resource
3264 windows need to be expanded.
3265 To specify the alignment for several
3266 instances of a device, the PCI vendor,
3267 device, subvendor, and subdevice may be
3268 specified, e.g., 4096@pci:8086:9c22:103c:198f
3269 ecrc= Enable/disable PCIe ECRC (transaction layer
3270 end-to-end CRC checking).
3271 bios: Use BIOS/firmware settings. This is the
3275 hpiosize=nn[KMG] The fixed amount of bus space which is
3276 reserved for hotplug bridge's IO window.
3277 Default size is 256 bytes.
3278 hpmemsize=nn[KMG] The fixed amount of bus space which is
3279 reserved for hotplug bridge's memory window.
3280 Default size is 2 megabytes.
3281 hpbussize=nn The minimum amount of additional bus numbers
3282 reserved for buses below a hotplug bridge.
3284 realloc= Enable/disable reallocating PCI bridge resources
3285 if allocations done by BIOS are too small to
3286 accommodate resources required by all child
3288 off: Turn realloc off
3290 realloc same as realloc=on
3291 noari do not use PCIe ARI.
3292 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
3293 do not use PCIe ATS (and IOMMU device IOTLB).
3294 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3295 only look for one device below a PCIe downstream
3297 big_root_window Try to add a big 64bit memory window to the PCIe
3298 root complex on AMD CPUs. Some GFX hardware
3299 can resize a BAR to allow access to all VRAM.
3300 Adding the window is slightly risky (it may
3301 conflict with unreported devices), so this
3303 disable_acs_redir=<pci_dev>[; ...]
3304 Specify one or more PCI devices (in the format
3305 specified above) separated by semicolons.
3306 Each device specified will have the PCI ACS
3307 redirect capabilities forced off which will
3308 allow P2P traffic between devices through
3309 bridges without forcing it upstream. Note:
3310 this removes isolation between devices and
3311 may put more devices in an IOMMU group.
3313 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3316 force Enable ASPM even on devices that claim not to support it.
3317 WARNING: Forcing ASPM on may cause system lockups.
3319 pcie_ports= [PCIE] PCIe port services handling:
3320 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
3321 even if the platform doesn't give the OS permission to
3322 use them. This may cause conflicts if the platform
3323 also tries to use these services.
3324 compat Disable native PCIe services (PME, AER, DPC, PCIe
3327 pcie_port_pm= [PCIE] PCIe port power management handling:
3328 off Disable power management of all PCIe ports
3329 force Forcibly enable power management of all PCIe ports
3331 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3332 nomsi Do not use MSI for native PCIe PME signaling (this makes
3333 all PCIe root ports use INTx for all services).
3335 pcmv= [HW,PCMCIA] BadgePAD 4
3339 Keep all power-domains already enabled by bootloader on,
3340 even if no driver has claimed them. This is useful
3341 for debug and development, but should not be
3342 needed on a platform with proper driver support.
3345 See Documentation/blockdev/paride.txt.
3347 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3350 See arch/parisc/kernel/pdc_chassis.c
3352 percpu_alloc= Select which percpu first chunk allocator to use.
3353 Currently supported values are "embed" and "page".
3354 Archs may support subset or none of the selections.
3355 See comments in mm/percpu.c for details on each
3356 allocator. This parameter is primarily for debugging
3357 and performance comparison.
3360 See Documentation/blockdev/paride.txt.
3363 See Documentation/blockdev/paride.txt.
3365 pirq= [SMP,APIC] Manual mp-table setup
3366 See Documentation/x86/i386/IO-APIC.txt.
3368 plip= [PPT,NET] Parallel port network link
3369 Format: { parport<nr> | timid | 0 }
3370 See also Documentation/admin-guide/parport.rst.
3372 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3373 Override pmtimer IOPort with a hex value.
3377 Enable PNP debug messages (depends on the
3378 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3379 via /sys/module/pnp/parameters/debug. We always show
3380 current resource usage; turning this on also shows
3381 possible settings and some assignment information.
3387 { on | off | curr | res | no-curr | no-res }
3390 [ISAPNP] Exclude IRQs for the autoconfiguration
3393 [ISAPNP] Exclude DMAs for the autoconfiguration
3395 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3396 Ranges are in pairs (I/O port base and size).
3399 [ISAPNP] Exclude memory regions for the
3401 Ranges are in pairs (memory base and size).
3403 ports= [IP_VS_FTP] IPVS ftp helper module
3405 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3407 Format: <port>,<port>....
3409 powersave=off [PPC] This option disables power saving features.
3410 It specifically disables cpuidle and sets the
3411 platform machine description specific power_save
3412 function to NULL. On Idle the CPU just reduces
3415 ppc_strict_facility_enable
3416 [PPC] This option catches any kernel floating point,
3417 Altivec, VSX and SPE outside of regions specifically
3418 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3419 There is some performance impact when enabling this.
3423 Disable Hardware Transactional Memory
3425 print-fatal-signals=
3426 [KNL] debug: print fatal signals
3428 If enabled, warn about various signal handling
3429 related application anomalies: too many signals,
3430 too many POSIX.1 timers, fatal signals causing a
3433 If you hit the warning due to signal overflow,
3434 you might want to try "ulimit -i unlimited".
3438 printk.always_kmsg_dump=
3439 Trigger kmsg_dump for cases other than kernel oops or
3441 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3444 printk.devkmsg={on,off,ratelimit}
3445 Control writing to /dev/kmsg.
3446 on - unlimited logging to /dev/kmsg from userspace
3447 off - logging to /dev/kmsg disabled
3448 ratelimit - ratelimit the logging
3451 printk.time= Show timing data prefixed to each printk message line
3452 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3454 processor.max_cstate= [HW,ACPI]
3455 Limit processor to maximum C-state
3456 max_cstate=9 overrides any DMI blacklist limit.
3458 processor.nocst [HW,ACPI]
3459 Ignore the _CST method to determine C-states,
3460 instead using the legacy FADT method
3462 profile= [KNL] Enable kernel profiling via /proc/profile
3463 Format: [<profiletype>,]<number>
3464 Param: <profiletype>: "schedule", "sleep", or "kvm"
3465 [defaults to kernel profiling]
3466 Param: "schedule" - profile schedule points.
3467 Param: "sleep" - profile D-state sleeping (millisecs).
3468 Requires CONFIG_SCHEDSTATS
3469 Param: "kvm" - profile VM exits.
3470 Param: <number> - step/bucket size as a power of 2 for
3471 statistical time based profiling.
3473 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3475 See Documentation/blockdev/ramdisk.txt.
3477 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3478 probe for; one of (bare|imps|exps|lifebook|any).
3479 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3481 psmouse.resetafter= [HW,MOUSE]
3482 Try to reset the device after so many bad packets
3485 [HW,MOUSE] Set desired mouse resolution, in dpi.
3486 psmouse.smartscroll=
3487 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3488 0 = disabled, 1 = enabled (default).
3490 pstore.backend= Specify the name of the pstore backend to use
3493 See Documentation/blockdev/paride.txt.
3495 pti= [X86_64] Control Page Table Isolation of user and
3496 kernel address spaces. Disabling this feature
3497 removes hardening, but improves performance of
3498 system calls and interrupts.
3500 on - unconditionally enable
3501 off - unconditionally disable
3502 auto - kernel detects whether your CPU model is
3503 vulnerable to issues that PTI mitigates
3505 Not specifying this option is equivalent to pti=auto.
3508 Equivalent to pti=off
3511 [KNL] Number of legacy pty's. Overwrites compiled-in
3514 quiet [KNL] Disable most log messages
3519 See Documentation/admin-guide/md.rst.
3521 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3522 See Documentation/blockdev/ramdisk.txt.
3524 ras=option[,option,...] [KNL] RAS-specific options
3527 Disable the Correctable Errors Collector,
3528 see CONFIG_RAS_CEC help text.
3531 The argument is a cpu list, as described above.
3533 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3534 the specified list of CPUs to be no-callback CPUs.
3535 Invocation of these CPUs' RCU callbacks will
3536 be offloaded to "rcuox/N" kthreads created for
3537 that purpose, where "x" is "b" for RCU-bh, "p"
3538 for RCU-preempt, and "s" for RCU-sched, and "N"
3539 is the CPU number. This reduces OS jitter on the
3540 offloaded CPUs, which can be useful for HPC and
3541 real-time workloads. It can also improve energy
3542 efficiency for asymmetric multiprocessors.
3545 Rather than requiring that offloaded CPUs
3546 (specified by rcu_nocbs= above) explicitly
3547 awaken the corresponding "rcuoN" kthreads,
3548 make these kthreads poll for callbacks.
3549 This improves the real-time response for the
3550 offloaded CPUs by relieving them of the need to
3551 wake up the corresponding kthread, but degrades
3552 energy efficiency by requiring that the kthreads
3553 periodically wake up to do the polling.
3555 rcutree.blimit= [KNL]
3556 Set maximum number of finished RCU callbacks to
3557 process in one batch.
3559 rcutree.dump_tree= [KNL]
3560 Dump the structure of the rcu_node combining tree
3561 out at early boot. This is used for diagnostic
3562 purposes, to verify correct tree setup.
3564 rcutree.gp_cleanup_delay= [KNL]
3565 Set the number of jiffies to delay each step of
3566 RCU grace-period cleanup.
3568 rcutree.gp_init_delay= [KNL]
3569 Set the number of jiffies to delay each step of
3570 RCU grace-period initialization.
3572 rcutree.gp_preinit_delay= [KNL]
3573 Set the number of jiffies to delay each step of
3574 RCU grace-period pre-initialization, that is,
3575 the propagation of recent CPU-hotplug changes up
3576 the rcu_node combining tree.
3578 rcutree.rcu_fanout_exact= [KNL]
3579 Disable autobalancing of the rcu_node combining
3580 tree. This is used by rcutorture, and might
3581 possibly be useful for architectures having high
3582 cache-to-cache transfer latencies.
3584 rcutree.rcu_fanout_leaf= [KNL]
3585 Change the number of CPUs assigned to each
3586 leaf rcu_node structure. Useful for very
3587 large systems, which will choose the value 64,
3588 and for NUMA systems with large remote-access
3589 latencies, which will choose a value aligned
3590 with the appropriate hardware boundaries.
3592 rcutree.jiffies_till_sched_qs= [KNL]
3593 Set required age in jiffies for a
3594 given grace period before RCU starts
3595 soliciting quiescent-state help from
3596 rcu_note_context_switch().
3598 rcutree.jiffies_till_first_fqs= [KNL]
3599 Set delay from grace-period initialization to
3600 first attempt to force quiescent states.
3601 Units are jiffies, minimum value is zero,
3602 and maximum value is HZ.
3604 rcutree.jiffies_till_next_fqs= [KNL]
3605 Set delay between subsequent attempts to force
3606 quiescent states. Units are jiffies, minimum
3607 value is one, and maximum value is HZ.
3609 rcutree.kthread_prio= [KNL,BOOT]
3610 Set the SCHED_FIFO priority of the RCU per-CPU
3611 kthreads (rcuc/N). This value is also used for
3612 the priority of the RCU boost threads (rcub/N)
3613 and for the RCU grace-period kthreads (rcu_bh,
3614 rcu_preempt, and rcu_sched). If RCU_BOOST is
3615 set, valid values are 1-99 and the default is 1
3616 (the least-favored priority). Otherwise, when
3617 RCU_BOOST is not set, valid values are 0-99 and
3618 the default is zero (non-realtime operation).
3620 rcutree.rcu_nocb_leader_stride= [KNL]
3621 Set the number of NOCB kthread groups, which
3622 defaults to the square root of the number of
3623 CPUs. Larger numbers reduces the wakeup overhead
3624 on the per-CPU grace-period kthreads, but increases
3625 that same overhead on each group's leader.
3627 rcutree.qhimark= [KNL]
3628 Set threshold of queued RCU callbacks beyond which
3629 batch limiting is disabled.
3631 rcutree.qlowmark= [KNL]
3632 Set threshold of queued RCU callbacks below which
3633 batch limiting is re-enabled.
3635 rcutree.rcu_idle_gp_delay= [KNL]
3636 Set wakeup interval for idle CPUs that have
3637 RCU callbacks (RCU_FAST_NO_HZ=y).
3639 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3640 Set wakeup interval for idle CPUs that have
3641 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3642 Lazy RCU callbacks are those which RCU can
3643 prove do nothing more than free memory.
3645 rcutree.rcu_kick_kthreads= [KNL]
3646 Cause the grace-period kthread to get an extra
3647 wake_up() if it sleeps three times longer than
3648 it should at force-quiescent-state time.
3649 This wake_up() will be accompanied by a
3650 WARN_ONCE() splat and an ftrace_dump().
3652 rcuperf.gp_async= [KNL]
3653 Measure performance of asynchronous
3654 grace-period primitives such as call_rcu().
3656 rcuperf.gp_async_max= [KNL]
3657 Specify the maximum number of outstanding
3658 callbacks per writer thread. When a writer
3659 thread exceeds this limit, it invokes the
3660 corresponding flavor of rcu_barrier() to allow
3661 previously posted callbacks to drain.
3663 rcuperf.gp_exp= [KNL]
3664 Measure performance of expedited synchronous
3665 grace-period primitives.
3667 rcuperf.holdoff= [KNL]
3668 Set test-start holdoff period. The purpose of
3669 this parameter is to delay the start of the
3670 test until boot completes in order to avoid
3673 rcuperf.nreaders= [KNL]
3674 Set number of RCU readers. The value -1 selects
3675 N, where N is the number of CPUs. A value
3676 "n" less than -1 selects N-n+1, where N is again
3677 the number of CPUs. For example, -2 selects N
3678 (the number of CPUs), -3 selects N+1, and so on.
3679 A value of "n" less than or equal to -N selects
3682 rcuperf.nwriters= [KNL]
3683 Set number of RCU writers. The values operate
3684 the same as for rcuperf.nreaders.
3685 N, where N is the number of CPUs
3687 rcuperf.perf_type= [KNL]
3688 Specify the RCU implementation to test.
3690 rcuperf.shutdown= [KNL]
3691 Shut the system down after performance tests
3692 complete. This is useful for hands-off automated
3695 rcuperf.verbose= [KNL]
3696 Enable additional printk() statements.
3698 rcuperf.writer_holdoff= [KNL]
3699 Write-side holdoff between grace periods,
3700 in microseconds. The default of zero says
3703 rcutorture.cbflood_inter_holdoff= [KNL]
3704 Set holdoff time (jiffies) between successive
3705 callback-flood tests.
3707 rcutorture.cbflood_intra_holdoff= [KNL]
3708 Set holdoff time (jiffies) between successive
3709 bursts of callbacks within a given callback-flood
3712 rcutorture.cbflood_n_burst= [KNL]
3713 Set the number of bursts making up a given
3714 callback-flood test. Set this to zero to
3715 disable callback-flood testing.
3717 rcutorture.cbflood_n_per_burst= [KNL]
3718 Set the number of callbacks to be registered
3719 in a given burst of a callback-flood test.
3721 rcutorture.fqs_duration= [KNL]
3722 Set duration of force_quiescent_state bursts
3725 rcutorture.fqs_holdoff= [KNL]
3726 Set holdoff time within force_quiescent_state bursts
3729 rcutorture.fqs_stutter= [KNL]
3730 Set wait time between force_quiescent_state bursts
3733 rcutorture.gp_cond= [KNL]
3734 Use conditional/asynchronous update-side
3735 primitives, if available.
3737 rcutorture.gp_exp= [KNL]
3738 Use expedited update-side primitives, if available.
3740 rcutorture.gp_normal= [KNL]
3741 Use normal (non-expedited) asynchronous
3742 update-side primitives, if available.
3744 rcutorture.gp_sync= [KNL]
3745 Use normal (non-expedited) synchronous
3746 update-side primitives, if available. If all
3747 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3748 rcutorture.gp_normal=, and rcutorture.gp_sync=
3749 are zero, rcutorture acts as if is interpreted
3750 they are all non-zero.
3752 rcutorture.n_barrier_cbs= [KNL]
3753 Set callbacks/threads for rcu_barrier() testing.
3755 rcutorture.nfakewriters= [KNL]
3756 Set number of concurrent RCU writers. These just
3757 stress RCU, they don't participate in the actual
3758 test, hence the "fake".
3760 rcutorture.nreaders= [KNL]
3761 Set number of RCU readers. The value -1 selects
3762 N-1, where N is the number of CPUs. A value
3763 "n" less than -1 selects N-n-2, where N is again
3764 the number of CPUs. For example, -2 selects N
3765 (the number of CPUs), -3 selects N+1, and so on.
3767 rcutorture.object_debug= [KNL]
3768 Enable debug-object double-call_rcu() testing.
3770 rcutorture.onoff_holdoff= [KNL]
3771 Set time (s) after boot for CPU-hotplug testing.
3773 rcutorture.onoff_interval= [KNL]
3774 Set time (jiffies) between CPU-hotplug operations,
3775 or zero to disable CPU-hotplug testing.
3777 rcutorture.shuffle_interval= [KNL]
3778 Set task-shuffle interval (s). Shuffling tasks
3779 allows some CPUs to go into dyntick-idle mode
3780 during the rcutorture test.
3782 rcutorture.shutdown_secs= [KNL]
3783 Set time (s) after boot system shutdown. This
3784 is useful for hands-off automated testing.
3786 rcutorture.stall_cpu= [KNL]
3787 Duration of CPU stall (s) to test RCU CPU stall
3788 warnings, zero to disable.
3790 rcutorture.stall_cpu_holdoff= [KNL]
3791 Time to wait (s) after boot before inducing stall.
3793 rcutorture.stall_cpu_irqsoff= [KNL]
3794 Disable interrupts while stalling if set.
3796 rcutorture.stat_interval= [KNL]
3797 Time (s) between statistics printk()s.
3799 rcutorture.stutter= [KNL]
3800 Time (s) to stutter testing, for example, specifying
3801 five seconds causes the test to run for five seconds,
3802 wait for five seconds, and so on. This tests RCU's
3803 ability to transition abruptly to and from idle.
3805 rcutorture.test_boost= [KNL]
3806 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3807 "Maybe" means test if the RCU implementation
3808 under test support RCU priority boosting.
3810 rcutorture.test_boost_duration= [KNL]
3811 Duration (s) of each individual boost test.
3813 rcutorture.test_boost_interval= [KNL]
3814 Interval (s) between each boost test.
3816 rcutorture.test_no_idle_hz= [KNL]
3817 Test RCU's dyntick-idle handling. See also the
3818 rcutorture.shuffle_interval parameter.
3820 rcutorture.torture_type= [KNL]
3821 Specify the RCU implementation to test.
3823 rcutorture.verbose= [KNL]
3824 Enable additional printk() statements.
3826 rcupdate.rcu_cpu_stall_suppress= [KNL]
3827 Suppress RCU CPU stall warning messages.
3829 rcupdate.rcu_cpu_stall_timeout= [KNL]
3830 Set timeout for RCU CPU stall warning messages.
3832 rcupdate.rcu_expedited= [KNL]
3833 Use expedited grace-period primitives, for
3834 example, synchronize_rcu_expedited() instead
3835 of synchronize_rcu(). This reduces latency,
3836 but can increase CPU utilization, degrade
3837 real-time latency, and degrade energy efficiency.
3838 No effect on CONFIG_TINY_RCU kernels.
3840 rcupdate.rcu_normal= [KNL]
3841 Use only normal grace-period primitives,
3842 for example, synchronize_rcu() instead of
3843 synchronize_rcu_expedited(). This improves
3844 real-time latency, CPU utilization, and
3845 energy efficiency, but can expose users to
3846 increased grace-period latency. This parameter
3847 overrides rcupdate.rcu_expedited. No effect on
3848 CONFIG_TINY_RCU kernels.
3850 rcupdate.rcu_normal_after_boot= [KNL]
3851 Once boot has completed (that is, after
3852 rcu_end_inkernel_boot() has been invoked), use
3853 only normal grace-period primitives. No effect
3854 on CONFIG_TINY_RCU kernels.
3856 rcupdate.rcu_task_stall_timeout= [KNL]
3857 Set timeout in jiffies for RCU task stall warning
3858 messages. Disable with a value less than or equal
3861 rcupdate.rcu_self_test= [KNL]
3862 Run the RCU early boot self tests
3864 rcupdate.rcu_self_test_bh= [KNL]
3865 Run the RCU bh early boot self tests
3867 rcupdate.rcu_self_test_sched= [KNL]
3868 Run the RCU sched early boot self tests
3872 Run specified binary instead of /init from the ramdisk,
3873 used for early userspace startup. See initrd.
3876 Turn on/off individual RDT features. List is:
3877 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
3879 E.g. to turn on cmt and turn off mba use:
3883 Format (x86 or x86_64):
3884 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3886 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3888 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3889 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3890 reboot_force is either force or not specified,
3891 reboot_cpu is s[mp]#### with #### being the processor
3892 to be used for rebooting.
3895 [KNL, SMP] Set scheduler's default relax_domain_level.
3896 See Documentation/cgroup-v1/cpusets.txt.
3898 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
3899 Format: <base1>,<size1>[,<base2>,<size2>,...]
3900 Reserve I/O ports or memory so the kernel won't use
3901 them. If <base> is less than 0x10000, the region
3902 is assumed to be I/O ports; otherwise it is memory.
3904 reservetop= [X86-32]
3906 Reserves a hole at the top of the kernel virtual
3911 Set the amount of memory to reserve for BIOS at
3912 the bottom of the address space.
3914 reset_devices [KNL] Force drivers to reset the underlying device
3915 during initialization.
3918 Specify the partition device for software suspend
3920 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3922 resume_offset= [SWSUSP]
3923 Specify the offset from the beginning of the partition
3924 given by "resume=" at which the swap header is located,
3925 in <PAGE_SIZE> units (needed only for swap files).
3926 See Documentation/power/swsusp-and-swap-files.txt
3928 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3929 read the resume files
3931 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3932 Useful for devices that are detected asynchronously
3933 (e.g. USB and MMC devices).
3935 hibernate= [HIBERNATION]
3936 noresume Don't check if there's a hibernation image
3937 present during boot.
3938 nocompress Don't compress/decompress hibernation images.
3939 no Disable hibernation and resume.
3940 protect_image Turn on image protection during restoration
3941 (that will set all pages holding image data
3942 during restoration read-only).
3944 retain_initrd [RAM] Keep initrd memory after extraction
3946 rfkill.default_state=
3947 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3948 etc. communication is blocked by default.
3951 rfkill.master_switch_mode=
3952 0 The "airplane mode" button does nothing.
3953 1 The "airplane mode" button toggles between everything
3954 blocked and the previous configuration.
3955 2 The "airplane mode" button toggles between everything
3956 blocked and everything unblocked.
3958 rhash_entries= [KNL,NET]
3959 Set number of hash buckets for route cache
3962 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
3965 ro [KNL] Mount root device read-only on boot
3968 on Mark read-only kernel memory as read-only (default).
3969 off Leave read-only kernel memory writable for debugging.
3972 Enable the uart passthrough on the designated usb port
3973 on Rockchip SoCs. When active, the signals of the
3974 debug-uart get routed to the D+ and D- pins of the usb
3975 port and the regular usb controller gets disabled.
3977 root= [KNL] Root filesystem
3978 See name_to_dev_t comment in init/do_mounts.c.
3980 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3981 mount the root filesystem
3983 rootflags= [KNL] Set root filesystem mount option string
3985 rootfstype= [KNL] Set root filesystem type
3987 rootwait [KNL] Wait (indefinitely) for root device to show up.
3988 Useful for devices that are detected asynchronously
3989 (e.g. USB and MMC devices).
3991 rproc_mem=nn[KMG][@address]
3992 [KNL,ARM,CMA] Remoteproc physical memory block.
3993 Memory area to be used by remote processor image,
3996 rw [KNL] Mount root device read-write on boot
3998 S [KNL] Run init in single mode
4000 s390_iommu= [HW,S390]
4001 Set s390 IOTLB flushing mode
4003 With strict flushing every unmap operation will result in
4004 an IOTLB flush. Default is lazy flushing before reuse,
4008 See drivers/net/irda/sa1100_ir.c.
4010 sbni= [NET] Granch SBNI12 leased line adapter
4012 sched_debug [KNL] Enables verbose scheduler debug messages.
4014 schedstats= [KNL,X86] Enable or disable scheduled statistics.
4015 Allowed values are enable and disable. This feature
4016 incurs a small amount of overhead in the scheduler
4017 but is useful for debugging and performance tuning.
4019 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
4020 xtime_lock contention on larger systems, and/or RCU lock
4021 contention on all systems with CONFIG_MAXSMP set.
4022 Format: { "0" | "1" }
4023 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
4025 Note: increases power consumption, thus should only be
4026 enabled if running jitter sensitive (HPC/RT) workloads.
4028 security= [SECURITY] Choose a security module to enable at boot.
4029 If this boot parameter is not specified, only the first
4030 security module asking for security registration will be
4031 loaded. An invalid security module name will be treated
4032 as if no module has been chosen.
4034 selinux= [SELINUX] Disable or enable SELinux at boot time.
4035 Format: { "0" | "1" }
4036 See security/selinux/Kconfig help text.
4039 Default value is set via kernel config option.
4040 If enabled at boot time, /selinux/disable can be used
4041 later to disable prior to initial policy load.
4043 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
4044 Format: { "0" | "1" }
4045 See security/apparmor/Kconfig help text
4048 Default value is set via kernel config option.
4050 serialnumber [BUGS=X86-32]
4053 Maximal number of shapers.
4061 Disable merging of slabs with similar size. May be
4062 necessary if there is some reason to distinguish
4063 allocs to different slabs, especially in hardened
4064 environments where the risk of heap overflows and
4065 layout control by attackers can usually be
4066 frustrated by disabling merging. This will reduce
4067 most of the exposure of a heap attack to a single
4068 cache (risks via metadata attacks are mostly
4069 unchanged). Debug options disable merging on their
4071 For more information see Documentation/vm/slub.rst.
4073 slab_max_order= [MM, SLAB]
4074 Determines the maximum allowed order for slabs.
4075 A high setting may cause OOMs due to memory
4076 fragmentation. Defaults to 1 for systems with
4077 more than 32MB of RAM, 0 otherwise.
4079 slub_debug[=options[,slabs]] [MM, SLUB]
4080 Enabling slub_debug allows one to determine the
4081 culprit if slab objects become corrupted. Enabling
4082 slub_debug can create guard zones around objects and
4083 may poison objects when not in use. Also tracks the
4084 last alloc / free. For more information see
4085 Documentation/vm/slub.rst.
4087 slub_memcg_sysfs= [MM, SLUB]
4088 Determines whether to enable sysfs directories for
4089 memory cgroup sub-caches. 1 to enable, 0 to disable.
4090 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
4091 Enabling this can lead to a very high number of debug
4092 directories and files being created under
4095 slub_max_order= [MM, SLUB]
4096 Determines the maximum allowed order for slabs.
4097 A high setting may cause OOMs due to memory
4098 fragmentation. For more information see
4099 Documentation/vm/slub.rst.
4101 slub_min_objects= [MM, SLUB]
4102 The minimum number of objects per slab. SLUB will
4103 increase the slab order up to slub_max_order to
4104 generate a sufficiently large slab able to contain
4105 the number of objects indicated. The higher the number
4106 of objects the smaller the overhead of tracking slabs
4107 and the less frequently locks need to be acquired.
4108 For more information see Documentation/vm/slub.rst.
4110 slub_min_order= [MM, SLUB]
4111 Determines the minimum page order for slabs. Must be
4112 lower than slub_max_order.
4113 For more information see Documentation/vm/slub.rst.
4115 slub_nomerge [MM, SLUB]
4116 Same with slab_nomerge. This is supported for legacy.
4117 See slab_nomerge for more information.
4120 Format: <io1>[,<io2>[,...,<io8>]]
4122 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4123 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4124 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4125 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4126 smsc-ircc2.ircc_irq= [HW] IRQ line
4127 smsc-ircc2.ircc_dma= [HW] DMA channel
4128 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4129 0: Toshiba Satellite 1800 (GP data pin select)
4130 1: Fast pin select (default)
4133 smt [KNL,S390] Set the maximum number of threads (logical
4134 CPUs) to use per physical CPU on systems capable of
4135 symmetric multithreading (SMT). Will be capped to the
4136 actual hardware limit.
4138 Default: -1 (no limit)
4141 [KNL] Should the soft-lockup detector generate panics.
4144 A nonzero value instructs the soft-lockup detector
4145 to panic the machine when a soft-lockup occurs. This
4146 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
4147 which is the respective build-time switch to that
4150 softlockup_all_cpu_backtrace=
4151 [KNL] Should the soft-lockup detector generate
4152 backtraces on all cpus.
4155 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4156 See Documentation/laptops/sonypi.txt
4158 spectre_v2= [X86] Control mitigation of Spectre variant 2
4159 (indirect branch speculation) vulnerability.
4161 on - unconditionally enable
4162 off - unconditionally disable
4163 auto - kernel detects whether your CPU model is
4166 Selecting 'on' will, and 'auto' may, choose a
4167 mitigation method at run time according to the
4168 CPU, the available microcode, the setting of the
4169 CONFIG_RETPOLINE configuration option, and the
4170 compiler with which the kernel was built.
4172 Specific mitigations can also be selected manually:
4174 retpoline - replace indirect branches
4175 retpoline,generic - google's original retpoline
4176 retpoline,amd - AMD-specific minimal thunk
4178 Not specifying this option is equivalent to
4181 spec_store_bypass_disable=
4182 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4183 (Speculative Store Bypass vulnerability)
4185 Certain CPUs are vulnerable to an exploit against a
4186 a common industry wide performance optimization known
4187 as "Speculative Store Bypass" in which recent stores
4188 to the same memory location may not be observed by
4189 later loads during speculative execution. The idea
4190 is that such stores are unlikely and that they can
4191 be detected prior to instruction retirement at the
4192 end of a particular speculation execution window.
4194 In vulnerable processors, the speculatively forwarded
4195 store can be used in a cache side channel attack, for
4196 example to read memory to which the attacker does not
4197 directly have access (e.g. inside sandboxed code).
4199 This parameter controls whether the Speculative Store
4200 Bypass optimization is used.
4202 On x86 the options are:
4204 on - Unconditionally disable Speculative Store Bypass
4205 off - Unconditionally enable Speculative Store Bypass
4206 auto - Kernel detects whether the CPU model contains an
4207 implementation of Speculative Store Bypass and
4208 picks the most appropriate mitigation. If the
4209 CPU is not vulnerable, "off" is selected. If the
4210 CPU is vulnerable the default mitigation is
4211 architecture and Kconfig dependent. See below.
4212 prctl - Control Speculative Store Bypass per thread
4213 via prctl. Speculative Store Bypass is enabled
4214 for a process by default. The state of the control
4215 is inherited on fork.
4216 seccomp - Same as "prctl" above, but all seccomp threads
4217 will disable SSB unless they explicitly opt out.
4219 Default mitigations:
4220 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4222 On powerpc the options are:
4224 on,auto - On Power8 and Power9 insert a store-forwarding
4225 barrier on kernel entry and exit. On Power7
4226 perform a software flush on kernel entry and
4230 Not specifying this option is equivalent to
4231 spec_store_bypass_disable=auto.
4233 spia_io_base= [HW,MTD]
4238 srcutree.counter_wrap_check [KNL]
4239 Specifies how frequently to check for
4240 grace-period sequence counter wrap for the
4241 srcu_data structure's ->srcu_gp_seq_needed field.
4242 The greater the number of bits set in this kernel
4243 parameter, the less frequently counter wrap will
4244 be checked for. Note that the bottom two bits
4247 srcutree.exp_holdoff [KNL]
4248 Specifies how many nanoseconds must elapse
4249 since the end of the last SRCU grace period for
4250 a given srcu_struct until the next normal SRCU
4251 grace period will be considered for automatic
4252 expediting. Set to zero to disable automatic
4256 Speculative Store Bypass Disable control
4258 On CPUs that are vulnerable to the Speculative
4259 Store Bypass vulnerability and offer a
4260 firmware based mitigation, this parameter
4261 indicates how the mitigation should be used:
4263 force-on: Unconditionally enable mitigation for
4264 for both kernel and userspace
4265 force-off: Unconditionally disable mitigation for
4266 for both kernel and userspace
4267 kernel: Always enable mitigation in the
4268 kernel, and offer a prctl interface
4269 to allow userspace to register its
4270 interest in being mitigated too.
4272 stack_guard_gap= [MM]
4273 override the default stack gap protection. The value
4274 is in page units and it defines how many pages prior
4275 to (for stacks growing down) resp. after (for stacks
4276 growing up) the main stack are reserved for no other
4277 mapping. Default value is 256 pages.
4280 Enabled the stack tracer on boot up.
4282 stacktrace_filter=[function-list]
4283 [FTRACE] Limit the functions that the stack tracer
4284 will trace at boot up. function-list is a comma separated
4285 list of functions. This list can be changed at run
4286 time by the stack_trace_filter file in the debugfs
4287 tracing directory. Note, this enables stack tracing
4288 and the stacktrace above is not needed.
4292 Set the STI (builtin display/keyboard on the HP-PARISC
4293 machines) console (graphic card) which should be used
4294 as the initial boot-console.
4295 See also comment in drivers/video/console/sticore.c.
4298 See comment in drivers/video/console/sticore.c.
4301 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4303 sunrpc.min_resvport=
4304 sunrpc.max_resvport=
4306 SunRPC servers often require that client requests
4307 originate from a privileged port (i.e. a port in the
4308 range 0 < portnr < 1024).
4309 An administrator who wishes to reserve some of these
4310 ports for other uses may adjust the range that the
4311 kernel's sunrpc client considers to be privileged
4312 using these two parameters to set the minimum and
4313 maximum port values.
4315 sunrpc.svc_rpc_per_connection_limit=
4317 Limit the number of requests that the server will
4318 process in parallel from a single connection.
4319 The default value is 0 (no limit).
4323 Control how the NFS server code allocates CPUs to
4324 service thread pools. Depending on how many NICs
4325 you have and where their interrupts are bound, this
4326 option will affect which CPUs will do NFS serving.
4327 Note: this parameter cannot be changed while the
4328 NFS server is running.
4330 auto the server chooses an appropriate mode
4331 automatically using heuristics
4332 global a single global pool contains all CPUs
4333 percpu one pool for each CPU
4334 pernode one pool for each NUMA node (equivalent
4335 to global on non-NUMA machines)
4337 sunrpc.tcp_slot_table_entries=
4338 sunrpc.udp_slot_table_entries=
4340 Sets the upper limit on the number of simultaneous
4341 RPC calls that can be sent from the client to a
4342 server. Increasing these values may allow you to
4343 improve throughput, but will also increase the
4344 amount of memory reserved for use by the client.
4346 suspend.pm_test_delay=
4348 Sets the number of seconds to remain in a suspend test
4349 mode before resuming the system (see
4350 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4351 is set. Default value is 5.
4354 [KNL] Enable accounting of swap in memory resource
4355 controller if no parameter or 1 is given or disable
4356 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4358 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4359 Format: { <int> | force | noforce }
4360 <int> -- Number of I/O TLB slabs
4361 force -- force using of bounce buffers even if they
4362 wouldn't be automatically used by the kernel
4363 noforce -- Never use bounce buffers (for debugging)
4367 sysfs.deprecated=0|1 [KNL]
4368 Enable/disable old style sysfs layout for old udev
4369 on older distributions. When this option is enabled
4370 very new udev will not work anymore. When this option
4371 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4372 in older udev will not work anymore.
4373 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4374 the kernel configuration.
4376 sysrq_always_enabled
4378 Ignore sysrq setting - this boot parameter will
4379 neutralize any effect of /proc/sys/kernel/sysrq.
4380 Useful for debugging.
4382 tcpmhash_entries= [KNL,NET]
4383 Set the number of tcp_metrics_hash slots.
4384 Default value is 8192 or 16384 depending on total
4385 ram pages. This is used to specify the TCP metrics
4386 cache size. See Documentation/networking/ip-sysctl.txt
4387 "tcp_no_metrics_save" section for more details.
4391 test_suspend= [SUSPEND][,N]
4392 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4393 standby suspend) or "freeze" (for suspend type freeze)
4394 as the system sleep state during system startup with
4395 the optional capability to repeat N number of times.
4396 The system is woken from this state using a
4397 wakeup-capable RTC alarm.
4399 thash_entries= [KNL,NET]
4400 Set number of hash buckets for TCP connection
4402 thermal.act= [HW,ACPI]
4403 -1: disable all active trip points in all thermal zones
4404 <degrees C>: override all lowest active trip points
4406 thermal.crt= [HW,ACPI]
4407 -1: disable all critical trip points in all thermal zones
4408 <degrees C>: override all critical trip points
4410 thermal.nocrt= [HW,ACPI]
4411 Set to disable actions on ACPI thermal zone
4412 critical and hot trip points.
4414 thermal.off= [HW,ACPI]
4415 1: disable ACPI thermal control
4417 thermal.psv= [HW,ACPI]
4418 -1: disable all passive trip points
4419 <degrees C>: override all passive trip points to this
4422 thermal.tzp= [HW,ACPI]
4423 Specify global default ACPI thermal zone polling rate
4424 <deci-seconds>: poll all this frequency
4425 0: no polling (default)
4428 Force threading of all interrupt handlers except those
4429 marked explicitly IRQF_NO_THREAD.
4432 Enable the Transcendent memory driver if built-in.
4434 tmem.cleancache=0|1 [KNL, XEN]
4435 Default is on (1). Disable the usage of the cleancache
4436 API to send anonymous pages to the hypervisor.
4438 tmem.frontswap=0|1 [KNL, XEN]
4439 Default is on (1). Disable the usage of the frontswap
4440 API to send swap pages to the hypervisor. If disabled
4441 the selfballooning and selfshrinking are force disabled.
4443 tmem.selfballooning=0|1 [KNL, XEN]
4444 Default is on (1). Disable the driving of swap pages
4447 tmem.selfshrinking=0|1 [KNL, XEN]
4448 Default is on (1). Partial swapoff that immediately
4449 transfers pages from Xen hypervisor back to the
4450 kernel based on different criteria.
4454 Specify if the kernel should make use of the cpu
4455 topology information if the hardware supports this.
4456 The scheduler will make use of this information and
4457 e.g. base its process migration decisions on it.
4460 topology_updates= [KNL, PPC, NUMA]
4462 Specify if the kernel should ignore (off)
4463 topology updates sent by the hypervisor to this
4468 tpm_suspend_pcr=[HW,TPM]
4469 Format: integer pcr id
4470 Specify that at suspend time, the tpm driver
4471 should extend the specified pcr with zeros,
4472 as a workaround for some chips which fail to
4473 flush the last written pcr on TPM_SaveState.
4474 This will guarantee that all the other pcrs
4477 trace_buf_size=nn[KMG]
4478 [FTRACE] will set tracing buffer size on each cpu.
4480 trace_event=[event-list]
4481 [FTRACE] Set and start specified trace events in order
4482 to facilitate early boot debugging. The event-list is a
4483 comma separated list of trace events to enable. See
4484 also Documentation/trace/events.rst
4486 trace_options=[option-list]
4487 [FTRACE] Enable or disable tracer options at boot.
4488 The option-list is a comma delimited list of options
4489 that can be enabled or disabled just as if you were
4490 to echo the option name into
4492 /sys/kernel/debug/tracing/trace_options
4494 For example, to enable stacktrace option (to dump the
4495 stack trace of each event), add to the command line:
4497 trace_options=stacktrace
4499 See also Documentation/trace/ftrace.rst "trace options"
4503 Have the tracepoints sent to printk as well as the
4504 tracing ring buffer. This is useful for early boot up
4505 where the system hangs or reboots and does not give the
4506 option for reading the tracing buffer or performing a
4507 ftrace_dump_on_oops.
4509 To turn off having tracepoints sent to printk,
4510 echo 0 > /proc/sys/kernel/tracepoint_printk
4511 Note, echoing 1 into this file without the
4512 tracepoint_printk kernel cmdline option has no effect.
4516 Having tracepoints sent to printk() and activating high
4517 frequency tracepoints such as irq or sched, can cause
4518 the system to live lock.
4521 [FTRACE] enable this option to disable tracing when a
4522 warning is hit. This turns off "tracing_on". Tracing can
4523 be enabled again by echoing '1' into the "tracing_on"
4524 file located in /sys/kernel/debug/tracing/
4526 This option is useful, as it disables the trace before
4527 the WARNING dump is called, which prevents the trace to
4528 be filled with content caused by the warning output.
4530 This option can also be set at run time via the sysctl
4531 option: kernel/traceoff_on_warning
4533 transparent_hugepage=
4535 Format: [always|madvise|never]
4536 Can be used to control the default behavior of the system
4537 with respect to transparent hugepages.
4538 See Documentation/admin-guide/mm/transhuge.rst
4541 tsc= Disable clocksource stability checks for TSC.
4543 [x86] reliable: mark tsc clocksource as reliable, this
4544 disables clocksource verification at runtime, as well
4545 as the stability checks done at bootup. Used to enable
4546 high-resolution timer mode on older hardware, and in
4547 virtualized environment.
4548 [x86] noirqtime: Do not use TSC to do irq accounting.
4549 Used to run time disable IRQ_TIME_ACCOUNTING on any
4550 platforms where RDTSC is slow and this accounting
4552 [x86] unstable: mark the TSC clocksource as unstable, this
4553 marks the TSC unconditionally unstable at bootup and
4554 avoids any further wobbles once the TSC watchdog notices.
4556 turbografx.map[2|3]= [HW,JOY]
4557 TurboGraFX parallel port interface
4559 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4560 See also Documentation/input/devices/joystick-parport.rst
4562 udbg-immortal [PPC] When debugging early kernel crashes that
4563 happen after console_init() and before a proper
4564 console driver takes over, this boot options might
4565 help "seeing" what's going on.
4567 uhash_entries= [KNL,NET]
4568 Set number of hash buckets for UDP/UDP-Lite connections
4571 [USB] Ignore overcurrent events (default N).
4572 Some badly-designed motherboards generate lots of
4573 bogus events, for ports that aren't wired to
4574 anything. Set this parameter to avoid log spamming.
4575 Note that genuine overcurrent events won't be
4579 [X86] Cause panic on unknown NMI.
4581 usbcore.authorized_default=
4582 [USB] Default USB device authorization:
4583 (default -1 = authorized except for wireless USB,
4584 0 = not authorized, 1 = authorized)
4586 usbcore.autosuspend=
4587 [USB] The autosuspend time delay (in seconds) used
4588 for newly-detected USB devices (default 2). This
4589 is the time required before an idle device will be
4590 autosuspended. Devices for which the delay is set
4591 to a negative value won't be autosuspended at all.
4593 usbcore.usbfs_snoop=
4594 [USB] Set to log all usbfs traffic (default 0 = off).
4596 usbcore.usbfs_snoop_max=
4597 [USB] Maximum number of bytes to snoop in each URB
4600 usbcore.blinkenlights=
4601 [USB] Set to cycle leds on hubs (default 0 = off).
4603 usbcore.old_scheme_first=
4604 [USB] Start with the old device initialization
4605 scheme (default 0 = off).
4607 usbcore.usbfs_memory_mb=
4608 [USB] Memory limit (in MB) for buffers allocated by
4609 usbfs (default = 16, 0 = max = 2047).
4611 usbcore.use_both_schemes=
4612 [USB] Try the other device initialization scheme
4613 if the first one fails (default 1 = enabled).
4615 usbcore.initial_descriptor_timeout=
4616 [USB] Specifies timeout for the initial 64-byte
4617 USB_REQ_GET_DESCRIPTOR request in milliseconds
4618 (default 5000 = 5.0 seconds).
4620 usbcore.nousb [USB] Disable the USB subsystem
4623 [USB] A list of quirk entries to augment the built-in
4624 usb core quirk list. List entries are separated by
4625 commas. Each entry has the form
4626 VendorID:ProductID:Flags. The IDs are 4-digit hex
4627 numbers and Flags is a set of letters. Each letter
4628 will change the built-in quirk; setting it if it is
4629 clear and clearing it if it is set. The letters have
4630 the following meanings:
4631 a = USB_QUIRK_STRING_FETCH_255 (string
4632 descriptors must not be fetched using
4634 b = USB_QUIRK_RESET_RESUME (device can't resume
4635 correctly so reset it instead);
4636 c = USB_QUIRK_NO_SET_INTF (device can't handle
4637 Set-Interface requests);
4638 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
4639 handle its Configuration or Interface
4641 e = USB_QUIRK_RESET (device can't be reset
4642 (e.g morph devices), don't use reset);
4643 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
4644 more interface descriptions than the
4645 bNumInterfaces count, and can't handle
4646 talking to these interfaces);
4647 g = USB_QUIRK_DELAY_INIT (device needs a pause
4648 during initialization, after we read
4649 the device descriptor);
4650 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
4651 high speed and super speed interrupt
4652 endpoints, the USB 2.0 and USB 3.0 spec
4653 require the interval in microframes (1
4654 microframe = 125 microseconds) to be
4655 calculated as interval = 2 ^
4657 Devices with this quirk report their
4658 bInterval as the result of this
4659 calculation instead of the exponent
4660 variable used in the calculation);
4661 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
4662 handle device_qualifier descriptor
4664 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
4665 generates spurious wakeup, ignore
4666 remote wakeup capability);
4667 k = USB_QUIRK_NO_LPM (device can't handle Link
4669 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
4670 (Device reports its bInterval as linear
4671 frames instead of the USB 2.0
4673 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
4674 to be disconnected before suspend to
4675 prevent spurious wakeup);
4676 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
4677 pause after every control message);
4678 Example: quirks=0781:5580:bk,0a5c:5834:gij
4681 [USBHID] The interval which mice are to be polled at.
4684 [USBHID] The interval which joysticks are to be polled at.
4687 [USBHID] The interval which keyboards are to be polled at.
4689 usb-storage.delay_use=
4690 [UMS] The delay in seconds before a new device is
4691 scanned for Logical Units (default 1).
4694 [UMS] A list of quirks entries to supplement or
4695 override the built-in unusual_devs list. List
4696 entries are separated by commas. Each entry has
4697 the form VID:PID:Flags where VID and PID are Vendor
4698 and Product ID values (4-digit hex numbers) and
4699 Flags is a set of characters, each corresponding
4700 to a common usb-storage quirk flag as follows:
4701 a = SANE_SENSE (collect more than 18 bytes
4703 b = BAD_SENSE (don't collect more than 18
4704 bytes of sense data);
4705 c = FIX_CAPACITY (decrease the reported
4706 device capacity by one sector);
4707 d = NO_READ_DISC_INFO (don't use
4708 READ_DISC_INFO command);
4709 e = NO_READ_CAPACITY_16 (don't use
4710 READ_CAPACITY_16 command);
4711 f = NO_REPORT_OPCODES (don't use report opcodes
4713 g = MAX_SECTORS_240 (don't transfer more than
4714 240 sectors at a time, uas only);
4715 h = CAPACITY_HEURISTICS (decrease the
4716 reported device capacity by one
4717 sector if the number is odd);
4718 i = IGNORE_DEVICE (don't bind to this
4720 j = NO_REPORT_LUNS (don't use report luns
4722 l = NOT_LOCKABLE (don't try to lock and
4723 unlock ejectable media);
4724 m = MAX_SECTORS_64 (don't transfer more
4725 than 64 sectors = 32 KB at a time);
4726 n = INITIAL_READ10 (force a retry of the
4727 initial READ(10) command);
4728 o = CAPACITY_OK (accept the capacity
4729 reported by the device);
4730 p = WRITE_CACHE (the device cache is ON
4732 r = IGNORE_RESIDUE (the device reports
4733 bogus residue values);
4734 s = SINGLE_LUN (the device has only one
4736 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4737 commands, uas only);
4738 u = IGNORE_UAS (don't bind to the uas driver);
4739 w = NO_WP_DETECT (don't test whether the
4740 medium is write-protected).
4741 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4742 even if the device claims no cache)
4743 Example: quirks=0419:aaf5:rl,0421:0433:rc
4745 user_debug= [KNL,ARM]
4747 See arch/arm/Kconfig.debug help text.
4748 1 - undefined instruction events
4750 4 - invalid data aborts
4753 Example: user_debug=31
4756 [X86] Flags controlling user PTE allocations.
4758 nohigh = do not allocate PTE pages in
4759 HIGHMEM regardless of setting
4763 On X86_32, this is an alias for vdso32=. Otherwise:
4765 vdso=1: enable VDSO (the default)
4766 vdso=0: disable VDSO mapping
4768 vdso32= [X86] Control the 32-bit vDSO
4769 vdso32=1: enable 32-bit VDSO
4770 vdso32=0 or vdso32=2: disable 32-bit VDSO
4772 See the help text for CONFIG_COMPAT_VDSO for more
4773 details. If CONFIG_COMPAT_VDSO is set, the default is
4774 vdso32=0; otherwise, the default is vdso32=1.
4776 For compatibility with older kernels, vdso32=2 is an
4779 Try vdso32=0 if you encounter an error that says:
4780 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4783 vector=percpu: enable percpu vector domain
4785 video= [FB] Frame buffer configuration
4786 See Documentation/fb/modedb.txt.
4788 video.brightness_switch_enabled= [0,1]
4789 If set to 1, on receiving an ACPI notify event
4790 generated by hotkey, video driver will adjust brightness
4791 level and then send out the event to user space through
4792 the allocated input device; If set to 0, video driver
4793 will only send out the event without touching backlight
4798 [VMMIO] Memory mapped virtio (platform) device.
4800 <size>@<baseaddr>:<irq>[:<id>]
4802 <size> := size (can use standard suffixes
4804 <baseaddr> := physical base address
4805 <irq> := interrupt number (as passed to
4807 <id> := (optional) platform device id
4809 virtio_mmio.device=1K@0x100b0000:48:7
4811 Can be used multiple times for multiple devices.
4813 vga= [BOOT,X86-32] Select a particular video mode
4814 See Documentation/x86/boot.txt and
4815 Documentation/svga.txt.
4816 Use vga=ask for menu.
4817 This is actually a boot loader parameter; the value is
4818 passed to the kernel using a special protocol.
4820 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4821 size of <nn>. This can be used to increase the
4822 minimum size (128MB on x86). It can also be used to
4823 decrease the size and leave more room for directly
4826 vmcp_cma=nn[MG] [KNL,S390]
4827 Sets the memory size reserved for contiguous memory
4828 allocations for the vmcp device driver.
4830 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4833 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4836 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4840 Controls the behavior of vsyscalls (i.e. calls to
4841 fixed addresses of 0xffffffffff600x00 from legacy
4842 code). Most statically-linked binaries and older
4843 versions of glibc use these calls. Because these
4844 functions are at fixed addresses, they make nice
4845 targets for exploits that can control RIP.
4847 emulate [default] Vsyscalls turn into traps and are
4848 emulated reasonably safely.
4850 native Vsyscalls are native syscall instructions.
4851 This is a little bit faster than trapping
4852 and makes a few dynamic recompilers work
4853 better than they would in emulation mode.
4854 It also makes exploits much easier to write.
4856 none Vsyscalls don't work at all. This makes
4857 them quite hard to use for exploits but
4858 might break your system.
4860 vt.color= [VT] Default text color.
4861 Format: 0xYX, X = foreground, Y = background.
4862 Default: 0x07 = light gray on black.
4864 vt.cur_default= [VT] Default cursor shape.
4865 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4866 the parameters of the <Esc>[?A;B;Cc escape sequence;
4867 see VGA-softcursor.txt. Default: 2 = underline.
4869 vt.default_blu= [VT]
4870 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4871 Change the default blue palette of the console.
4872 This is a 16-member array composed of values
4875 vt.default_grn= [VT]
4876 Format: <green0>,<green1>,<green2>,...,<green15>
4877 Change the default green palette of the console.
4878 This is a 16-member array composed of values
4881 vt.default_red= [VT]
4882 Format: <red0>,<red1>,<red2>,...,<red15>
4883 Change the default red palette of the console.
4884 This is a 16-member array composed of values
4890 Set system-wide default UTF-8 mode for all tty's.
4891 Default is 1, i.e. UTF-8 mode is enabled for all
4892 newly opened terminals.
4894 vt.global_cursor_default=
4897 Set system-wide default for whether a cursor
4898 is shown on new VTs. Default is -1,
4899 i.e. cursors will be created by default unless
4900 overridden by individual drivers. 0 will hide
4901 cursors, 1 will display them.
4903 vt.italic= [VT] Default color for italic text; 0-15.
4906 vt.underline= [VT] Default color for underlined text; 0-15.
4909 watchdog timers [HW,WDT] For information on watchdog timers,
4910 see Documentation/watchdog/watchdog-parameters.txt
4911 or other driver-specific files in the
4912 Documentation/watchdog/ directory.
4914 workqueue.watchdog_thresh=
4915 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4916 warn stall conditions and dump internal state to
4917 help debugging. 0 disables workqueue stall
4918 detection; otherwise, it's the stall threshold
4919 duration in seconds. The default value is 30 and
4920 it can be updated at runtime by writing to the
4921 corresponding sysfs file.
4923 workqueue.disable_numa
4924 By default, all work items queued to unbound
4925 workqueues are affine to the NUMA nodes they're
4926 issued on, which results in better behavior in
4927 general. If NUMA affinity needs to be disabled for
4928 whatever reason, this option can be used. Note
4929 that this also can be controlled per-workqueue for
4930 workqueues visible under /sys/bus/workqueue/.
4932 workqueue.power_efficient
4933 Per-cpu workqueues are generally preferred because
4934 they show better performance thanks to cache
4935 locality; unfortunately, per-cpu workqueues tend to
4936 be more power hungry than unbound workqueues.
4938 Enabling this makes the per-cpu workqueues which
4939 were observed to contribute significantly to power
4940 consumption unbound, leading to measurably lower
4941 power usage at the cost of small performance
4944 The default value of this parameter is determined by
4945 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4947 workqueue.debug_force_rr_cpu
4948 Workqueue used to implicitly guarantee that work
4949 items queued without explicit CPU specified are put
4950 on the local CPU. This guarantee is no longer true
4951 and while local CPU is still preferred work items
4952 may be put on foreign CPUs. This debug option
4953 forces round-robin CPU selection to flush out
4954 usages which depend on the now broken guarantee.
4955 When enabled, memory and cache locality will be
4958 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4959 default x2apic cluster mode on platforms
4962 x86_intel_mid_timer= [X86-32,APBT]
4963 Choose timer option for x86 Intel MID platform.
4964 Two valid options are apbt timer only and lapic timer
4965 plus one apbt timer for broadcast timer.
4966 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4968 xen_512gb_limit [KNL,X86-64,XEN]
4969 Restricts the kernel running paravirtualized under Xen
4970 to use only up to 512 GB of RAM. The reason to do so is
4971 crash analysis tools and Xen tools for doing domain
4972 save/restore/migration must be enabled to handle larger
4975 xen_emul_unplug= [HW,X86,XEN]
4976 Unplug Xen emulated devices
4977 Format: [unplug0,][unplug1]
4978 ide-disks -- unplug primary master IDE devices
4979 aux-ide-disks -- unplug non-primary-master IDE devices
4980 nics -- unplug network devices
4981 all -- unplug all emulated devices (NICs and IDE disks)
4982 unnecessary -- unplugging emulated devices is
4983 unnecessary even if the host did not respond to
4985 never -- do not unplug even if version check succeeds
4987 xen_nopvspin [X86,XEN]
4988 Disables the ticketlock slowpath using Xen PV
4992 Disables the PV optimizations forcing the HVM guest to
4993 run as generic HVM guest with no PV drivers.
4995 xirc2ps_cs= [NET,PCMCIA]
4997 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4999 xhci-hcd.quirks [USB,KNL]
5000 A hex value specifying bitmask with supplemental xhci
5001 host controller quirks. Meaning of each bit can be
5002 consulted in header drivers/usb/host/xhci.h.
git.samba.org / sfrench / cifs-2.6.git / blob