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 while booting
335 Format: { quiet (default) | verbose | debug }
336 Change the amount of debugging information output
337 when initialising the APIC and IO-APIC components.
338 For X86-32, this can also be used to specify an APIC
340 Format: apic=driver_name
341 Examples: apic=bigsmp
343 apic_extnmi= [APIC,X86] External NMI delivery setting
344 Format: { bsp (default) | all | none }
345 bsp: External NMI is delivered only to CPU 0
346 all: External NMIs are broadcast to all CPUs as a
348 none: External NMI is masked for all CPUs. This is
349 useful so that a dump capture kernel won't be
353 See Documentation/networking/ipv6.txt.
355 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
356 Limit apic dumping. The parameter defines the maximal
357 number of local apics being dumped. Also it is possible
358 to set it to "all" by meaning -- no limit here.
359 Format: { 1 (default) | 2 | ... | all }.
360 The parameter valid if only apic=debug or
361 apic=verbose is specified.
362 Example: apic=debug show_lapic=all
364 apm= [APM] Advanced Power Management
365 See header of arch/x86/kernel/apm_32.c.
367 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
368 Format: <io>,<irq>,<nodeID>
372 atarimouse= [HW,MOUSE] Atari Mouse
374 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
375 EzKey and similar keyboards
377 atkbd.reset= [HW] Reset keyboard during initialization
379 atkbd.set= [HW] Select keyboard code set
380 Format: <int> (2 = AT (default), 3 = PS/2)
382 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
385 atkbd.softraw= [HW] Choose between synthetic and real raw mode
386 Format: <bool> (0 = real, 1 = synthetic (default))
388 atkbd.softrepeat= [HW]
389 Use software keyboard repeat
391 audit= [KNL] Enable the audit sub-system
392 Format: { "0" | "1" | "off" | "on" }
393 0 | off - kernel audit is disabled and can not be
394 enabled until the next reboot
395 unset - kernel audit is initialized but disabled and
396 will be fully enabled by the userspace auditd.
397 1 | on - kernel audit is initialized and partially
398 enabled, storing at most audit_backlog_limit
399 messages in RAM until it is fully enabled by the
403 audit_backlog_limit= [KNL] Set the audit queue size limit.
404 Format: <int> (must be >=0)
407 bau= [X86_UV] Enable the BAU on SGI UV. The default
408 behavior is to disable the BAU (i.e. bau=0).
409 Format: { "0" | "1" }
412 unset - Disable the BAU.
414 baycom_epp= [HW,AX25]
417 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
419 See header of drivers/net/hamradio/baycom_par.c.
421 baycom_ser_fdx= [HW,AX25]
422 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
423 Format: <io>,<irq>,<mode>[,<baud>]
424 See header of drivers/net/hamradio/baycom_ser_fdx.c.
426 baycom_ser_hdx= [HW,AX25]
427 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
428 Format: <io>,<irq>,<mode>
429 See header of drivers/net/hamradio/baycom_ser_hdx.c.
431 blkdevparts= Manual partition parsing of block device(s) for
432 embedded devices based on command line input.
433 See Documentation/block/cmdline-partition.txt
435 boot_delay= Milliseconds to delay each printk during boot.
436 Values larger than 10 seconds (10000) are changed to
440 bootmem_debug [KNL] Enable bootmem allocator debug messages.
443 Disable BERT OS support on buggy BIOSes.
445 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
446 bttv.radio= Most important insmod options are available as
448 bttv.pll= See Documentation/media/v4l-drivers/bttv.rst
451 bulk_remove=off [PPC] This parameter disables the use of the pSeries
452 firmware feature for flushing multiple hpte entries
455 c101= [NET] Moxa C101 synchronous serial card
457 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
458 Sometimes CPU hardware bugs make them report the cache
459 size incorrectly. The kernel will attempt work arounds
460 to fix known problems, but for some CPUs it is not
461 possible to determine what the correct size should be.
462 This option provides an override for these situations.
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 cgroup controllers and named hierarchies in v1
490 Format: { { controller | "all" | "named" }
491 [,{ controller | "all" | "named" }...] }
492 Like cgroup_disable, but only applies to cgroup v1;
493 the blacklisted controllers remain available in cgroup2.
494 "all" blacklists all controllers and "named" disables
495 named mounts. Specifying both "all" and "named" disables
498 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
500 nosocket -- Disable socket memory accounting.
501 nokmem -- Disable kernel memory accounting.
503 checkreqprot [SELINUX] Set initial checkreqprot flag value.
504 Format: { "0" | "1" }
505 See security/selinux/Kconfig help text.
506 0 -- check protection applied by kernel (includes
507 any implied execute protection).
508 1 -- check protection requested by application.
509 Default value is set via a kernel config option.
510 Value can be changed at runtime via
511 /selinux/checkreqprot.
514 See Documentation/s390/CommonIO for details.
517 Prevents the clock framework from automatically gating
518 clocks that have not been explicitly enabled by a Linux
519 device driver but are enabled in hardware at reset or
520 by the bootloader/firmware. Note that this does not
521 force such clocks to be always-on nor does it reserve
522 those clocks in any way. This parameter is useful for
523 debug and development, but should not be needed on a
524 platform with proper driver support. For more
525 information, see Documentation/driver-api/clk.rst.
527 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
529 Forces specified clocksource (if available) to be used
530 when calculating gettimeofday(). If specified
531 clocksource is not available, it defaults to PIT.
532 Format: { pit | tsc | cyclone | pmtmr }
534 clocksource= Override the default clocksource
536 Override the default clocksource and use the clocksource
537 with the name specified.
538 Some clocksource names to choose from, depending on
540 [all] jiffies (this is the base, fallback clocksource)
542 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
543 pxa_timer,timer3,32k_counter,timer0_1
544 [X86-32] pit,hpet,tsc;
545 scx200_hrt on Geode; cyclone on IBM x440
553 clocksource.arm_arch_timer.evtstrm=
556 Enable/disable the eventstream feature of the ARM
557 architected timer so that code using WFE-based polling
558 loops can be debugged more effectively on production
561 clearcpuid=BITNUM [X86]
562 Disable CPUID feature X for the kernel. See
563 arch/x86/include/asm/cpufeatures.h for the valid bit
564 numbers. Note the Linux specific bits are not necessarily
565 stable over kernel options, but the vendor specific
567 Also note that user programs calling CPUID directly
568 or using the feature without checking anything
569 will still see it. This just prevents it from
570 being used by the kernel or shown in /proc/cpuinfo.
571 Also note the kernel might malfunction if you disable
574 cma=nn[MG]@[start[MG][-end[MG]]]
576 Sets the size of kernel global memory area for
577 contiguous memory allocations and optionally the
578 placement constraint by the physical address range of
579 memory allocations. A value of 0 disables CMA
580 altogether. For more information, see
581 include/linux/dma-contiguous.h
583 cmo_free_hint= [PPC] Format: { yes | no }
584 Specify whether pages are marked as being inactive
585 when they are freed. This is used in CMO environments
586 to determine OS memory pressure for page stealing by
590 coherent_pool=nn[KMG] [ARM,KNL]
591 Sets the size of memory pool for coherent, atomic dma
592 allocations, by default set to 256K.
594 com20020= [HW,NET] ARCnet - COM20020 chipset
596 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
598 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
602 ARCnet - COM90xx chipset (memory-mapped buffers)
603 Format: <io>[,<irq>[,<memstart>]]
605 condev= [HW,S390] console device
608 console= [KNL] Output console device and options.
610 tty<n> Use the virtual console device <n>.
614 Use the specified serial port. The options are of
615 the form "bbbbpnf", where "bbbb" is the baud rate,
616 "p" is parity ("n", "o", or "e"), "n" is number of
617 bits, and "f" is flow control ("r" for RTS or
618 omit it). Default is "9600n8".
620 See Documentation/admin-guide/serial-console.rst for more
622 Documentation/networking/netconsole.txt for an
625 uart[8250],io,<addr>[,options]
626 uart[8250],mmio,<addr>[,options]
627 uart[8250],mmio16,<addr>[,options]
628 uart[8250],mmio32,<addr>[,options]
629 uart[8250],0x<addr>[,options]
630 Start an early, polled-mode console on the 8250/16550
631 UART at the specified I/O port or MMIO address,
632 switching to the matching ttyS device later.
633 MMIO inter-register address stride is either 8-bit
634 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
635 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
636 to be equivalent to 'mmio'. 'options' are specified in
637 the same format described for ttyS above; if unspecified,
638 the h/w is not re-initialized.
640 hvc<n> Use the hypervisor console device <n>. This is for
641 both Xen and PowerPC hypervisors.
643 If the device connected to the port is not a TTY but a braille
644 device, prepend "brl," before the device type, for instance
646 For now, only VisioBraille is supported.
649 [KNL] Change console messages format
651 By default we print messages on consoles in
652 "[time stamp] text\n" format (time stamp may not be
653 printed, depending on CONFIG_PRINTK_TIME or
654 `printk_time' param).
656 Switch to syslog format: "<%u>[time stamp] text\n"
657 IOW, each message will have a facility and loglevel
658 prefix. The format is similar to one used by syslog()
659 syscall, or to executing "dmesg -S --raw" or to reading
662 consoleblank= [KNL] The console blank (screen saver) timeout in
663 seconds. A value of 0 disables the blank timer.
667 [KNL] Change the default value for
668 /proc/<pid>/coredump_filter.
669 See also Documentation/filesystems/proc.txt.
671 coresight_cpu_debug.enable
674 Enable/disable the CPU sampling based debugging.
675 0: default value, disable debugging
676 1: enable debugging at boot time
678 cpuidle.off=1 [CPU_IDLE]
679 disable the cpuidle sub-system
682 [CPU_IDLE] Name of the cpuidle governor to use.
684 cpufreq.off=1 [CPU_FREQ]
685 disable the cpufreq sub-system
688 [X86] Delay for N microsec between assert and de-assert
689 of APIC INIT to start processors. This delay occurs
690 on every CPU online, such as boot, and resume from suspend.
693 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
695 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
697 crashkernel=size[KMG][@offset[KMG]]
698 [KNL] Using kexec, Linux can switch to a 'crash kernel'
699 upon panic. This parameter reserves the physical
700 memory region [offset, offset + size] for that kernel
701 image. If '@offset' is omitted, then a suitable offset
702 is selected automatically. Check
703 Documentation/kdump/kdump.txt for further details.
705 crashkernel=range1:size1[,range2:size2,...][@offset]
706 [KNL] Same as above, but depends on the memory
707 in the running system. The syntax of range is
708 start-[end] where start and end are both
709 a memory unit (amount[KMG]). See also
710 Documentation/kdump/kdump.txt for an example.
712 crashkernel=size[KMG],high
713 [KNL, x86_64] range could be above 4G. Allow kernel
714 to allocate physical memory region from top, so could
715 be above 4G if system have more than 4G ram installed.
716 Otherwise memory region will be allocated below 4G, if
718 It will be ignored if crashkernel=X is specified.
719 crashkernel=size[KMG],low
720 [KNL, x86_64] range under 4G. When crashkernel=X,high
721 is passed, kernel could allocate physical memory region
722 above 4G, that cause second kernel crash on system
723 that require some amount of low memory, e.g. swiotlb
724 requires at least 64M+32K low memory, also enough extra
725 low memory is needed to make sure DMA buffers for 32-bit
726 devices won't run out. Kernel would try to allocate at
727 at least 256M below 4G automatically.
728 This one let user to specify own low range under 4G
729 for second kernel instead.
730 0: to disable low allocation.
731 It will be ignored when crashkernel=X,high is not used
732 or memory reserved is below 4G.
735 [KNL] Disable crypto self-tests
740 cs89x0_media= [HW,NET]
741 Format: { rj45 | aui | bnc }
744 See header of drivers/s390/block/dasd_devmap.c.
746 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
747 (one device per port)
748 Format: <port#>,<type>
749 See also Documentation/input/devices/joystick-parport.rst
751 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
753 Documentation/admin-guide/dynamic-debug-howto.rst for
754 details. Deprecated, see dyndbg.
756 debug [KNL] Enable kernel debugging (events log level).
759 [KNL] Enable printing [hashed] pointers early in the
760 boot sequence. If enabled, we use a weak hash instead
761 of siphash to hash pointers. Use this option if you are
762 seeing instances of '(___ptrval___)') and need to see a
763 value (hashed pointer) instead. Cryptographically
764 insecure, please do not use on production kernels.
767 [KNL] verbose self-tests
769 Print debugging info while doing the locking API
771 We default to 0 (no extra messages), setting it to
772 1 will print _a lot_ more information - normally
773 only useful to kernel developers.
775 debug_objects [KNL] Enable object debugging
778 [KNL] Disable object debugging
780 debug_guardpage_minorder=
781 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
782 parameter allows control of the order of pages that will
783 be intentionally kept free (and hence protected) by the
784 buddy allocator. Bigger value increase the probability
785 of catching random memory corruption, but reduce the
786 amount of memory for normal system use. The maximum
787 possible value is MAX_ORDER/2. Setting this parameter
788 to 1 or 2 should be enough to identify most random
789 memory corruption problems caused by bugs in kernel or
790 driver code when a CPU writes to (or reads from) a
791 random memory location. Note that there exists a class
792 of memory corruptions problems caused by buggy H/W or
793 F/W or by drivers badly programing DMA (basically when
794 memory is written at bus level and the CPU MMU is
795 bypassed) which are not detectable by
796 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
797 tracking down these problems.
800 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
801 parameter enables the feature at boot time. In
802 default, it is disabled. We can avoid allocating huge
803 chunk of memory for debug pagealloc if we don't enable
804 it at boot time and the system will work mostly same
805 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
806 on: enable the feature
808 debugpat [X86] Enable PAT debugging
810 decnet.addr= [HW,NET]
811 Format: <area>[,<node>]
812 See also Documentation/networking/decnet.txt.
815 [same as hugepagesz=] The size of the default
816 HugeTLB page size. This is the size represented by
817 the legacy /proc/ hugepages APIs, used for SHM, and
818 default size when mounting hugetlbfs filesystems.
819 Defaults to the default architecture's huge page size
822 deferred_probe_timeout=
823 [KNL] Debugging option to set a timeout in seconds for
824 deferred probe to give up waiting on dependencies to
825 probe. Only specific dependencies (subsystems or
826 drivers) that have opted in will be ignored. A timeout of 0
827 will timeout at the end of initcalls. This option will also
828 dump out devices still on the deferred probe list after
832 Set number of hash buckets for dentry cache.
834 disable_1tb_segments [PPC]
835 Disables the use of 1TB hash page table segments. This
836 causes the kernel to fall back to 256MB segments which
837 can be useful when debugging issues that require an SLB
841 See Documentation/networking/ipv6.txt.
844 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
845 hardening is enabled for this boot. Hardened
846 usercopy checking is used to protect the kernel
847 from reading or writing beyond known memory
848 allocation boundaries as a proactive defense
849 against bounds-checking flaws in the kernel's
850 copy_to_user()/copy_from_user() interface.
851 on Perform hardened usercopy checks (default).
852 off Disable hardened usercopy checks.
855 Disable RADIX MMU mode on POWER9
857 disable_cpu_apicid= [X86,APIC,SMP]
859 The number of initial APIC ID for the
860 corresponding CPU to be disabled at boot,
861 mostly used for the kdump 2nd kernel to
862 disable BSP to wake up multiple CPUs without
863 causing system reset or hang due to sending
866 perf_v4_pmi= [X86,INTEL]
868 Disable Intel PMU counter freezing feature.
869 The feature only exists starting from
870 Arch Perfmon v4 (Skylake and newer).
872 disable_ddw [PPC/PSERIES]
873 Disable Dynamic DMA Window support. Use this if
874 to workaround buggy firmware.
877 See Documentation/networking/ipv6.txt.
879 disable_mtrr_cleanup [X86]
880 The kernel tries to adjust MTRR layout from continuous
881 to discrete, to make X server driver able to add WB
882 entry later. This parameter disables that.
884 disable_mtrr_trim [X86, Intel and AMD only]
885 By default the kernel will trim any uncacheable
886 memory out of your available memory pool based on
887 MTRR settings. This parameter disables that behavior,
888 possibly causing your machine to run very slowly.
890 disable_timer_pin_1 [X86]
891 Disable PIN 1 of APIC timer
892 Can be useful to work around chipset bugs.
894 dis_ucode_ldr [X86] Disable the microcode loader.
896 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
897 this option disables the debugging code at boot.
899 dma_debug_entries=<number>
900 This option allows to tune the number of preallocated
901 entries for DMA-API debugging code. One entry is
902 required per DMA-API allocation. Use this if the
903 DMA-API debugging code disables itself because the
904 architectural default is too low.
906 dma_debug_driver=<driver_name>
907 With this option the DMA-API debugging driver
908 filter feature can be enabled at boot time. Just
909 pass the driver to filter for as the parameter.
910 The filter can be disabled or changed to another
911 driver later using sysfs.
913 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
914 Broken monitors, graphic adapters, KVMs and EDIDless
915 panels may send no or incorrect EDID data sets.
916 This parameter allows to specify an EDID data sets
917 in the /lib/firmware directory that are used instead.
918 Generic built-in EDID data sets are used, if one of
919 edid/1024x768.bin, edid/1280x1024.bin,
920 edid/1680x1050.bin, or edid/1920x1080.bin is given
921 and no file with the same name exists. Details and
922 instructions how to build your own EDID data are
923 available in Documentation/EDID/HOWTO.txt. An EDID
924 data set will only be used for a particular connector,
925 if its name and a colon are prepended to the EDID
926 name. Each connector may use a unique EDID data
927 set by separating the files with a comma. An EDID
928 data set with no connector name will be used for
929 any connectors not explicitly specified.
934 Format: {"off" | "known"}
935 Control how the dt_cpu_ftrs device-tree binding is
936 used for CPU feature discovery and setup (if it
938 off: Do not use it, fall back to legacy cpu table.
939 known: Do not pass through unknown features to guests
940 or userspace, only those that the kernel is aware of.
942 dump_apple_properties [X86]
943 Dump name and content of EFI device properties on
944 x86 Macs. Useful for driver authors to determine
945 what data is available or for reverse-engineering.
947 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
948 module.dyndbg[="val"]
949 Enable debug messages at boot time. See
950 Documentation/admin-guide/dynamic-debug-howto.rst
953 nompx [X86] Disables Intel Memory Protection Extensions.
954 See Documentation/x86/intel_mpx.txt for more
955 information about the feature.
957 nopku [X86] Disable Memory Protection Keys CPU feature found
960 module.async_probe [KNL]
961 Enable asynchronous probe on this module.
963 early_ioremap_debug [KNL]
964 Enable debug messages in early_ioremap support. This
965 is useful for tracking down temporary early mappings
966 which are not unmapped.
968 earlycon= [KNL] Output early console device and options.
970 [ARM64] The early console is determined by the
971 stdout-path property in device tree's chosen node,
972 or determined by the ACPI SPCR table.
974 [X86] When used with no options the early console is
975 determined by the ACPI SPCR table.
977 cdns,<addr>[,options]
978 Start an early, polled-mode console on a Cadence
979 (xuartps) serial port at the specified address. Only
980 supported option is baud rate. If baud rate is not
981 specified, the serial port must already be setup and
984 uart[8250],io,<addr>[,options]
985 uart[8250],mmio,<addr>[,options]
986 uart[8250],mmio32,<addr>[,options]
987 uart[8250],mmio32be,<addr>[,options]
988 uart[8250],0x<addr>[,options]
989 Start an early, polled-mode console on the 8250/16550
990 UART at the specified I/O port or MMIO address.
991 MMIO inter-register address stride is either 8-bit
992 (mmio) or 32-bit (mmio32 or mmio32be).
993 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
994 to be equivalent to 'mmio'. 'options' are specified
995 in the same format described for "console=ttyS<n>"; if
996 unspecified, the h/w is not initialized.
1000 Start an early, polled-mode console on a pl011 serial
1001 port at the specified address. The pl011 serial port
1002 must already be setup and configured. Options are not
1003 yet supported. If 'mmio32' is specified, then only
1004 the driver will use only 32-bit accessors to read/write
1005 the device registers.
1008 Start an early, polled-mode console on a meson serial
1009 port at the specified address. The serial port must
1010 already be setup and configured. Options are not yet
1014 Start an early, polled-mode console on an msm serial
1015 port at the specified address. The serial port
1016 must already be setup and configured. Options are not
1019 msm_serial_dm,<addr>
1020 Start an early, polled-mode console on an msm serial
1021 dm port at the specified address. The serial port
1022 must already be setup and configured. Options are not
1026 Start an early, polled-mode console on a serial port
1027 of an Actions Semi SoC, such as S500 or S900, at the
1028 specified address. The serial port must already be
1029 setup and configured. Options are not yet supported.
1031 smh Use ARM semihosting calls for early console.
1039 Use early console provided by serial driver available
1040 on Samsung SoCs, requires selecting proper type and
1041 a correct base address of the selected UART port. The
1042 serial port must already be setup and configured.
1043 Options are not yet supported.
1046 Start an early, polled-mode console on a lantiq serial
1047 (lqasc) port at the specified address. The serial port
1048 must already be setup and configured. Options are not
1053 Use early console provided by Freescale LP UART driver
1054 found on Freescale Vybrid and QorIQ LS1021A processors.
1055 A valid base address must be provided, and the serial
1056 port must already be setup and configured.
1059 Start an early, polled-mode console on the
1060 Armada 3700 serial port at the specified
1061 address. The serial port must already be setup
1062 and configured. Options are not yet supported.
1065 Start an early, polled-mode console on a Qualcomm
1066 Generic Interface (GENI) based serial port at the
1067 specified address. The serial port must already be
1068 setup and configured. Options are not yet supported.
1070 earlyprintk= [X86,SH,ARM,M68k,S390]
1075 earlyprintk=serial[,ttySn[,baudrate]]
1076 earlyprintk=serial[,0x...[,baudrate]]
1077 earlyprintk=ttySn[,baudrate]
1078 earlyprintk=dbgp[debugController#]
1079 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1080 earlyprintk=xdbc[xhciController#]
1082 earlyprintk is useful when the kernel crashes before
1083 the normal console is initialized. It is not enabled by
1084 default because it has some cosmetic problems.
1086 Append ",keep" to not disable it when the real console
1089 Only one of vga, efi, serial, or usb debug port can
1092 Currently only ttyS0 and ttyS1 may be specified by
1093 name. Other I/O ports may be explicitly specified
1094 on some architectures (x86 and arm at least) by
1095 replacing ttySn with an I/O port address, like this:
1096 earlyprintk=serial,0x1008,115200
1097 You can find the port for a given device in
1098 /proc/tty/driver/serial:
1099 2: uart:ST16650V2 port:00001008 irq:18 ...
1101 Interaction with the standard serial driver is not
1104 The VGA and EFI output is eventually overwritten by
1107 The xen output can only be used by Xen PV guests.
1109 The sclp output can only be used on s390.
1111 The optional "force" to "pciserial" enables use of a
1112 PCI device even when its classcode is not of the
1115 edac_report= [HW,EDAC] Control how to report EDAC event
1116 Format: {"on" | "off" | "force"}
1117 on: enable EDAC to report H/W event. May be overridden
1118 by other higher priority error reporting module.
1119 off: disable H/W event reporting through EDAC.
1120 force: enforce the use of EDAC to report H/W event.
1123 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1126 This is designed to be used in conjunction with
1127 the boot argument: earlyprintk=vga
1130 Format: {"off" | "on" | "skip[mbr]"}
1133 Format: { "old_map", "nochunk", "noruntime", "debug" }
1134 old_map [X86-64]: switch to the old ioremap-based EFI
1135 runtime services mapping. 32-bit still uses this one by
1137 nochunk: disable reading files in "chunks" in the EFI
1138 boot stub, as chunking can cause problems with some
1139 firmware implementations.
1140 noruntime : disable EFI runtime services support
1141 debug: enable misc debug output
1143 efi_no_storage_paranoia [EFI; X86]
1144 Using this parameter you can use more than 50% of
1145 your efi variable storage. Use this parameter only if
1146 you are really sure that your UEFI does sane gc and
1147 fulfills the spec otherwise your board may brick.
1149 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1150 Add arbitrary attribute to specific memory range by
1151 updating original EFI memory map.
1152 Region of memory which aa attribute is added to is
1154 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1155 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1156 attribute is added to range 0x100000000-0x180000000 and
1157 0x10a0000000-0x1120000000.
1159 Using this parameter you can do debugging of EFI memmap
1160 related feature. For example, you can do debugging of
1161 Address Range Mirroring feature even if your box
1164 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1165 that is to be dynamically loaded by Linux. If there are
1166 multiple variables with the same name but with different
1167 vendor GUIDs, all of them will be loaded. See
1168 Documentation/acpi/ssdt-overlays.txt for details.
1171 eisa_irq_edge= [PARISC,HW]
1172 See header of drivers/parisc/eisa.c.
1175 See comment before function elanfreq_setup() in
1176 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1179 Format: {"cfq" | "deadline" | "noop"}
1180 See Documentation/block/cfq-iosched.txt and
1181 Documentation/block/deadline-iosched.txt for details.
1183 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1184 Specifies physical address of start of kernel core
1185 image elf header and optionally the size. Generally
1186 kexec loader will pass this option to capture kernel.
1187 See Documentation/kdump/kdump.txt for details.
1189 enable_mtrr_cleanup [X86]
1190 The kernel tries to adjust MTRR layout from continuous
1191 to discrete, to make X server driver able to add WB
1192 entry later. This parameter enables that.
1194 enable_timer_pin_1 [X86]
1195 Enable PIN 1 of APIC timer
1196 Can be useful to work around chipset bugs
1197 (in particular on some ATI chipsets).
1198 The kernel tries to set a reasonable default.
1200 enforcing [SELINUX] Set initial enforcing status.
1202 See security/selinux/Kconfig help text.
1203 0 -- permissive (log only, no denials).
1204 1 -- enforcing (deny and log).
1206 Value can be changed at runtime via /selinux/enforce.
1209 Disable Error Record Serialization Table (ERST)
1212 ether= [HW,NET] Ethernet cards parameters
1213 This option is obsoleted by the "netdev=" option, which
1214 has equivalent usage. See its documentation for details.
1218 Permit 'security.evm' to be updated regardless of
1219 current integrity status.
1223 fail_make_request=[KNL]
1224 General fault injection mechanism.
1225 Format: <interval>,<probability>,<space>,<times>
1226 See also Documentation/fault-injection/.
1229 See Documentation/blockdev/floppy.txt.
1231 force_pal_cache_flush
1232 [IA-64] Avoid check_sal_cache_flush which may hang on
1233 buggy SAL_CACHE_FLUSH implementations. Using this
1234 parameter will force ia64_sal_cache_flush to call
1235 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1238 Forcefully enable Physical Address Extension (PAE).
1239 Many Pentium M systems disable PAE but may have a
1240 functionally usable PAE implementation.
1241 Warning: use of this parameter will taint the kernel
1242 and may cause unknown problems.
1245 [FTRACE] will set and start the specified tracer
1246 as early as possible in order to facilitate early
1249 ftrace_dump_on_oops[=orig_cpu]
1250 [FTRACE] will dump the trace buffers on oops.
1251 If no parameter is passed, ftrace will dump
1252 buffers of all CPUs, but if you pass orig_cpu, it will
1253 dump only the buffer of the CPU that triggered the
1256 ftrace_filter=[function-list]
1257 [FTRACE] Limit the functions traced by the function
1258 tracer at boot up. function-list is a comma separated
1259 list of functions. This list can be changed at run
1260 time by the set_ftrace_filter file in the debugfs
1263 ftrace_notrace=[function-list]
1264 [FTRACE] Do not trace the functions specified in
1265 function-list. This list can be changed at run time
1266 by the set_ftrace_notrace file in the debugfs
1269 ftrace_graph_filter=[function-list]
1270 [FTRACE] Limit the top level callers functions traced
1271 by the function graph tracer at boot up.
1272 function-list is a comma separated list of functions
1273 that can be changed at run time by the
1274 set_graph_function file in the debugfs tracing directory.
1276 ftrace_graph_notrace=[function-list]
1277 [FTRACE] Do not trace from the functions specified in
1278 function-list. This list is a comma separated list of
1279 functions that can be changed at run time by the
1280 set_graph_notrace file in the debugfs tracing directory.
1282 ftrace_graph_max_depth=<uint>
1283 [FTRACE] Used with the function graph tracer. This is
1284 the max depth it will trace into a function. This value
1285 can be changed at run time by the max_graph_depth file
1286 in the tracefs tracing directory. default: 0 (no limit)
1289 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1290 support via parallel port (up to 5 devices per port)
1291 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1292 See also Documentation/input/devices/joystick-parport.rst
1296 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1300 gcov_persist= [GCOV] When non-zero (default), profiling data for
1301 kernel modules is saved and remains accessible via
1302 debugfs, even when the module is unloaded/reloaded.
1303 When zero, profiling data is discarded and associated
1304 debugfs files are removed at module unload time.
1306 goldfish [X86] Enable the goldfish android emulator platform.
1307 Don't use this when you are not running on the
1310 gpt [EFI] Forces disk with valid GPT signature but
1311 invalid Protective MBR to be treated as GPT. If the
1312 primary GPT is corrupted, it enables the backup/alternate
1313 GPT to be used instead.
1315 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1316 the "Enable 0" bit of the configuration register.
1319 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1320 the "Enable 0" bit of the configuration register.
1323 grcan.select= [HW] Select which physical interface to use.
1326 grcan.txsize= [HW] Sets the size of the tx buffer.
1327 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1329 grcan.rxsize= [HW] Sets the size of the rx buffer.
1330 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1333 gpio-mockup.gpio_mockup_ranges
1334 [HW] Sets the ranges of gpiochip of for this device.
1335 Format: <start1>,<end1>,<start2>,<end2>...
1337 hardlockup_all_cpu_backtrace=
1338 [KNL] Should the hard-lockup detector generate
1339 backtraces on all cpus.
1342 hashdist= [KNL,NUMA] Large hashes allocated during boot
1343 are distributed across NUMA nodes. Defaults on
1344 for 64-bit NUMA, off otherwise.
1345 Format: 0 | 1 (for off | on)
1347 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1349 hd= [EIDE] (E)IDE hard drive subsystem geometry
1350 Format: <cyl>,<head>,<sect>
1353 Disable Hardware Error Source Table (HEST) support;
1354 corresponding firmware-first mode error processing
1355 logic will be disabled.
1357 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1358 size of <nn>. This works even on boxes that have no
1359 highmem otherwise. This also works to reduce highmem
1360 size on bigger boxes.
1362 highres= [KNL] Enable/disable high resolution timer mode.
1363 Valid parameters: "on", "off"
1367 See Documentation/isdn/README.HiSax.
1371 hpet= [X86-32,HPET] option to control HPET usage
1372 Format: { enable (default) | disable | force |
1374 disable: disable HPET and use PIT instead
1375 force: allow force enabled of undocumented chips (ICH4,
1377 verbose: show contents of HPET registers during setup
1379 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1380 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1382 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1383 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1384 On x86-64 and powerpc, this option can be specified
1385 multiple times interleaved with hugepages= to reserve
1386 huge pages of different sizes. Valid pages sizes on
1387 x86-64 are 2M (when the CPU supports "pse") and 1G
1388 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1391 [KNL] Should the hung task detector generate panics.
1394 A nonzero value instructs the kernel to panic when a
1395 hung task is detected. The default value is controlled
1396 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1397 option. The value selected by this boot parameter can
1398 be changed later by the kernel.hung_task_panic sysctl.
1400 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1401 terminal devices. Valid values: 0..8
1402 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1403 If specified, z/VM IUCV HVC accepts connections
1404 from listed z/VM user IDs only.
1406 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations
1407 which allow the hypervisor to 'idle' the
1408 guest on lock contention.
1411 Do not unregister boot console at start. This is only
1412 useful for debugging when something happens in the window
1413 between unregistering the boot console and initializing
1416 i2c_bus= [HW] Override the default board specific I2C bus speed
1417 or register an additional I2C bus that is not
1418 registered from board initialization code.
1422 i8042.debug [HW] Toggle i8042 debug mode
1423 i8042.unmask_kbd_data
1424 [HW] Enable printing of interrupt data from the KBD port
1425 (disabled by default, and as a pre-condition
1426 requires that i8042.debug=1 be enabled)
1427 i8042.direct [HW] Put keyboard port into non-translated mode
1428 i8042.dumbkbd [HW] Pretend that controller can only read data from
1429 keyboard and cannot control its state
1430 (Don't attempt to blink the leds)
1431 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1432 i8042.nokbd [HW] Don't check/create keyboard port
1433 i8042.noloop [HW] Disable the AUX Loopback command while probing
1435 i8042.nomux [HW] Don't check presence of an active multiplexing
1437 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1439 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1440 i8042.reset [HW] Reset the controller during init, cleanup and
1441 suspend-to-ram transitions, only during s2r
1442 transitions, or never reset
1443 Format: { 1 | Y | y | 0 | N | n }
1444 1, Y, y: always reset controller
1445 0, N, n: don't ever reset controller
1446 Default: only on s2r transitions on x86; most other
1447 architectures force reset to be always executed
1448 i8042.unlock [HW] Unlock (ignore) the keylock
1449 i8042.kbdreset [HW] Reset device connected to KBD port
1453 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1454 indicates that the driver is running on unsupported
1456 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1457 does not match list of supported models.
1459 [HW] Report power status in /proc/i8k
1460 (disabled by default)
1461 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1464 i915.invert_brightness=
1465 [DRM] Invert the sense of the variable that is used to
1466 set the brightness of the panel backlight. Normally a
1467 brightness value of 0 indicates backlight switched off,
1468 and the maximum of the brightness value sets the backlight
1469 to maximum brightness. If this parameter is set to 0
1470 (default) and the machine requires it, or this parameter
1471 is set to 1, a brightness value of 0 sets the backlight
1472 to maximum brightness, and the maximum of the brightness
1473 value switches the backlight off.
1474 -1 -- never invert brightness
1475 0 -- machine default
1476 1 -- force brightness inversion
1479 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1481 ide-core.nodma= [HW] (E)IDE subsystem
1482 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1483 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1484 .cdrom .chs .ignore_cable are additional options
1485 See Documentation/ide/ide.txt.
1487 ide-generic.probe-mask= [HW] (E)IDE subsystem
1489 Probe mask for legacy ISA IDE ports. Depending on
1490 platform up to 6 ports are supported, enabled by
1491 setting corresponding bits in the mask to 1. The
1492 default value is 0x0, which has a special meaning.
1493 On systems that have PCI, it triggers scanning the
1494 PCI bus for the first and the second port, which
1495 are then probed. On systems without PCI the value
1496 of 0x0 enables probing the two first ports as if it
1499 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1500 Claim all unknown PCI IDE storage controllers.
1503 Format: idle=poll, idle=halt, idle=nomwait
1504 Poll forces a polling idle loop that can slightly
1505 improve the performance of waking up a idle CPU, but
1506 will use a lot of power and make the system run hot.
1508 idle=halt: Halt is forced to be used for CPU idle.
1509 In such case C2/C3 won't be used again.
1510 idle=nomwait: Disable mwait for CPU C-states
1512 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1513 Format: { strict | legacy | 2008 | relaxed }
1516 Choose which programs will be accepted for execution
1517 based on the IEEE 754 NaN encoding(s) supported by
1518 the FPU and the NaN encoding requested with the value
1519 of an ELF file header flag individually set by each
1520 binary. Hardware implementations are permitted to
1521 support either or both of the legacy and the 2008 NaN
1524 Available settings are as follows:
1525 strict accept binaries that request a NaN encoding
1526 supported by the FPU
1527 legacy only accept legacy-NaN binaries, if supported
1529 2008 only accept 2008-NaN binaries, if supported
1531 relaxed accept any binaries regardless of whether
1532 supported by the FPU
1534 The FPU emulator is always able to support both NaN
1535 encodings, so if no FPU hardware is present or it has
1536 been disabled with 'nofpu', then the settings of
1537 'legacy' and '2008' strap the emulator accordingly,
1538 'relaxed' straps the emulator for both legacy-NaN and
1539 2008-NaN, whereas 'strict' enables legacy-NaN only on
1540 legacy processors and both NaN encodings on MIPS32 or
1543 The setting for ABS.fmt/NEG.fmt instruction execution
1544 mode generally follows that for the NaN encoding,
1545 except where unsupported by hardware.
1547 ignore_loglevel [KNL]
1548 Ignore loglevel setting - this will print /all/
1549 kernel messages to the console. Useful for debugging.
1550 We also add it as printk module parameter, so users
1551 could change it dynamically, usually by
1552 /sys/module/printk/parameters/ignore_loglevel.
1555 Ignore RLIMIT_DATA setting for data mappings,
1556 print warning at first misuse. Can be changed via
1557 /sys/module/kernel/parameters/ignore_rlimit_data.
1559 ihash_entries= [KNL]
1560 Set number of hash buckets for inode cache.
1562 ima_appraise= [IMA] appraise integrity measurements
1563 Format: { "off" | "enforce" | "fix" | "log" }
1566 ima_appraise_tcb [IMA]
1567 The builtin appraise policy appraises all files
1570 ima_canonical_fmt [IMA]
1571 Use the canonical format for the binary runtime
1572 measurements, instead of host native format.
1575 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1579 The list of supported hash algorithms is defined
1580 in crypto/hash_info.h.
1583 The builtin policies to load during IMA setup.
1584 Format: "tcb | appraise_tcb | secure_boot |
1587 The "tcb" policy measures all programs exec'd, files
1588 mmap'd for exec, and all files opened with the read
1589 mode bit set by either the effective uid (euid=0) or
1592 The "appraise_tcb" policy appraises the integrity of
1593 all files owned by root. (This is the equivalent
1594 of ima_appraise_tcb.)
1596 The "secure_boot" policy appraises the integrity
1597 of files (eg. kexec kernel image, kernel modules,
1598 firmware, policy, etc) based on file signatures.
1600 The "fail_securely" policy forces file signature
1601 verification failure also on privileged mounted
1602 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1605 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1606 Load a policy which meets the needs of the Trusted
1607 Computing Base. This means IMA will measure all
1608 programs exec'd, files mmap'd for exec, and all files
1609 opened for read by uid=0.
1612 Select one of defined IMA measurements template formats.
1613 Formats: { "ima" | "ima-ng" | "ima-sig" }
1617 [IMA] Define a custom template format.
1618 Format: { "field1|...|fieldN" }
1620 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1621 Format: <min_file_size>
1622 Set the minimal file size for using asynchronous hash.
1623 If left unspecified, ahash usage is disabled.
1625 ahash performance varies for different data sizes on
1626 different crypto accelerators. This option can be used
1627 to achieve the best performance for a particular HW.
1629 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1631 Set hashing buffer size. Default: 4k.
1633 ahash performance varies for different chunk sizes on
1634 different crypto accelerators. This option can be used
1635 to achieve best performance for particular HW.
1639 Run specified binary instead of /sbin/init as init
1642 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1643 for working out where the kernel is dying during
1646 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1647 initcall functions. Useful for debugging built-in
1648 modules and initcalls.
1650 initrd= [BOOT] Specify the location of the initial ramdisk
1652 init_pkru= [x86] Specify the default memory protection keys rights
1653 register contents for all processes. 0x55555554 by
1654 default (disallow access to all but pkey 0). Can
1655 override in debugfs after boot.
1657 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1660 int_pln_enable [x86] Enable power limit notification interrupt
1662 integrity_audit=[IMA]
1663 Format: { "0" | "1" }
1664 0 -- basic integrity auditing messages. (Default)
1665 1 -- additional integrity auditing messages.
1667 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1669 Enable intel iommu driver.
1671 Disable intel iommu driver.
1672 igfx_off [Default Off]
1673 By default, gfx is mapped as normal device. If a gfx
1674 device has a dedicated DMAR unit, the DMAR unit is
1675 bypassed by not enabling DMAR with this option. In
1676 this case, gfx device will use physical address for
1679 With this option iommu will not optimize to look
1680 for io virtual address below 32-bit forcing dual
1681 address cycle on pci bus for cards supporting greater
1682 than 32-bit addressing. The default is to look
1683 for translation below 32-bit and if not available
1684 then look in the higher range.
1685 strict [Default Off]
1686 With this option on every unmap_single operation will
1687 result in a hardware IOTLB flush operation as opposed
1688 to batching them for performance.
1689 sp_off [Default Off]
1690 By default, super page will be supported if Intel IOMMU
1691 has the capability. With this option, super page will
1693 ecs_off [Default Off]
1694 By default, extended context tables will be supported if
1695 the hardware advertises that it has support both for the
1696 extended tables themselves, and also PASID support. With
1697 this option set, extended tables will not be used even
1698 on hardware which claims to support them.
1699 tboot_noforce [Default Off]
1700 Do not force the Intel IOMMU enabled under tboot.
1701 By default, tboot will force Intel IOMMU on, which
1702 could harm performance of some high-throughput
1703 devices like 40GBit network cards, even if identity
1705 Note that using this option lowers the security
1706 provided by tboot because it makes the system
1707 vulnerable to DMA attacks.
1709 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1710 0 disables intel_idle and fall back on acpi_idle.
1711 1 to 9 specify maximum depth of C-state.
1715 Do not enable intel_pstate as the default
1716 scaling driver for the supported processors
1718 Use intel_pstate as a scaling driver, but configure it
1719 to work with generic cpufreq governors (instead of
1720 enabling its internal governor). This mode cannot be
1721 used along with the hardware-managed P-states (HWP)
1724 Enable intel_pstate on systems that prohibit it by default
1725 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1726 instead of acpi-cpufreq may disable platform features, such
1727 as thermal controls and power capping, that rely on ACPI
1728 P-States information being indicated to OSPM and therefore
1729 should be used with caution. This option does not work with
1730 processors that aren't supported by the intel_pstate driver
1731 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1733 Do not enable hardware P state control (HWP)
1736 Only load intel_pstate on systems which support
1737 hardware P state control (HWP) if available.
1739 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1740 Description Table, specifies preferred power management
1741 profile as "Enterprise Server" or "Performance Server",
1742 then this feature is turned on by default.
1744 Allow per-logical-CPU P-State performance control limits using
1745 cpufreq sysfs interface
1747 intremap= [X86-64, Intel-IOMMU]
1748 on enable Interrupt Remapping (default)
1749 off disable Interrupt Remapping
1750 nosid disable Source ID checking
1752 BIOS x2APIC opt-out request will be ignored
1753 nopost disable Interrupt Posting
1755 iomem= Disable strict checking of access to MMIO memory
1756 strict regions from userspace.
1771 nobypass [PPC/POWERNV]
1772 Disable IOMMU bypass, using IOMMU for PCI devices.
1774 iommu.strict= [ARM64] Configure TLB invalidation behaviour
1775 Format: { "0" | "1" }
1777 Request that DMA unmap operations use deferred
1778 invalidation of hardware TLBs, for increased
1779 throughput at the cost of reduced device isolation.
1780 Will fall back to strict mode if not supported by
1781 the relevant IOMMU driver.
1782 1 - Strict mode (default).
1783 DMA unmap operations invalidate IOMMU hardware TLBs
1787 [ARM64] Configure DMA to bypass the IOMMU by default.
1788 Format: { "0" | "1" }
1789 0 - Use IOMMU translation for DMA.
1790 1 - Bypass the IOMMU for DMA.
1791 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
1793 io7= [HW] IO7 for Marvel based alpha systems
1794 See comment before marvel_specify_io7 in
1795 arch/alpha/kernel/core_marvel.c.
1797 io_delay= [X86] I/O delay method
1799 Standard port 0x80 based delay
1801 Alternate port 0xed based delay (needed on some systems)
1803 Simple two microseconds delay
1808 See Documentation/filesystems/nfs/nfsroot.txt.
1810 irqaffinity= [SMP] Set the default irq affinity mask
1811 The argument is a cpu list, as described above.
1813 irqchip.gicv2_force_probe=
1816 Force the kernel to look for the second 4kB page
1817 of a GICv2 controller even if the memory range
1818 exposed by the device tree is too small.
1820 irqchip.gicv3_nolpi=
1822 Force the kernel to ignore the availability of
1823 LPIs (and by consequence ITSs). Intended for system
1824 that use the kernel as a bootloader, and thus want
1825 to let secondary kernels in charge of setting up
1829 When an interrupt is not handled search all handlers
1830 for it. Intended to get systems with badly broken
1834 When an interrupt is not handled search all handlers
1835 for it. Also check all handlers each timer
1836 interrupt. Intended to get systems with badly broken
1840 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1842 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1843 [Deprecated - use cpusets instead]
1844 Format: [flag-list,]<cpu-list>
1846 Specify one or more CPUs to isolate from disturbances
1847 specified in the flag list (default: domain):
1850 Disable the tick when a single task runs.
1852 A residual 1Hz tick is offloaded to workqueues, which you
1853 need to affine to housekeeping through the global
1854 workqueue's affinity configured via the
1855 /sys/devices/virtual/workqueue/cpumask sysfs file, or
1856 by using the 'domain' flag described below.
1858 NOTE: by default the global workqueue runs on all CPUs,
1859 so to protect individual CPUs the 'cpumask' file has to
1860 be configured manually after bootup.
1863 Isolate from the general SMP balancing and scheduling
1864 algorithms. Note that performing domain isolation this way
1865 is irreversible: it's not possible to bring back a CPU to
1866 the domains once isolated through isolcpus. It's strongly
1867 advised to use cpusets instead to disable scheduler load
1868 balancing through the "cpuset.sched_load_balance" file.
1869 It offers a much more flexible interface where CPUs can
1870 move in and out of an isolated set anytime.
1872 You can move a process onto or off an "isolated" CPU via
1873 the CPU affinity syscalls or cpuset.
1874 <cpu number> begins at 0 and the maximum value is
1875 "number of CPUs in system - 1".
1877 The format of <cpu-list> is described above.
1883 ivrs_ioapic [HW,X86_64]
1884 Provide an override to the IOAPIC-ID<->DEVICE-ID
1885 mapping provided in the IVRS ACPI table. For
1886 example, to map IOAPIC-ID decimal 10 to
1887 PCI device 00:14.0 write the parameter as:
1888 ivrs_ioapic[10]=00:14.0
1890 ivrs_hpet [HW,X86_64]
1891 Provide an override to the HPET-ID<->DEVICE-ID
1892 mapping provided in the IVRS ACPI table. For
1893 example, to map HPET-ID decimal 0 to
1894 PCI device 00:14.0 write the parameter as:
1895 ivrs_hpet[0]=00:14.0
1897 ivrs_acpihid [HW,X86_64]
1898 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1899 mapping provided in the IVRS ACPI table. For
1900 example, to map UART-HID:UID AMD0020:0 to
1901 PCI device 00:14.5 write the parameter as:
1902 ivrs_acpihid[00:14.5]=AMD0020:0
1904 js= [HW,JOY] Analog joystick
1905 See Documentation/input/joydev/joystick.rst.
1908 When CONFIG_RANDOMIZE_BASE is set, this disables
1909 kernel and module base offset ASLR (Address Space
1910 Layout Randomization).
1913 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1914 report on every invalid memory access. Without this
1915 parameter KASAN will print report only for the first
1920 kernelcore= [KNL,X86,IA-64,PPC]
1921 Format: nn[KMGTPE] | nn% | "mirror"
1922 This parameter specifies the amount of memory usable by
1923 the kernel for non-movable allocations. The requested
1924 amount is spread evenly throughout all nodes in the
1925 system as ZONE_NORMAL. The remaining memory is used for
1926 movable memory in its own zone, ZONE_MOVABLE. In the
1927 event, a node is too small to have both ZONE_NORMAL and
1928 ZONE_MOVABLE, kernelcore memory will take priority and
1929 other nodes will have a larger ZONE_MOVABLE.
1931 ZONE_MOVABLE is used for the allocation of pages that
1932 may be reclaimed or moved by the page migration
1933 subsystem. Note that allocations like PTEs-from-HighMem
1934 still use the HighMem zone if it exists, and the Normal
1935 zone if it does not.
1937 It is possible to specify the exact amount of memory in
1938 the form of "nn[KMGTPE]", a percentage of total system
1939 memory in the form of "nn%", or "mirror". If "mirror"
1940 option is specified, mirrored (reliable) memory is used
1941 for non-movable allocations and remaining memory is used
1942 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
1943 are exclusive, so you cannot specify multiple forms.
1945 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1946 Format: <Controller#>[,poll interval]
1947 The controller # is the number of the ehci usb debug
1948 port as it is probed via PCI. The poll interval is
1949 optional and is the number seconds in between
1950 each poll cycle to the debug port in case you need
1951 the functionality for interrupting the kernel with
1952 gdb or control-c on the dbgp connection. When
1953 not using this parameter you use sysrq-g to break into
1954 the kernel debugger.
1956 kgdboc= [KGDB,HW] kgdb over consoles.
1957 Requires a tty driver that supports console polling,
1958 or a supported polling keyboard driver (non-usb).
1959 Serial only format: <serial_device>[,baud]
1960 keyboard only format: kbd
1961 keyboard and serial format: kbd,<serial_device>[,baud]
1962 Optional Kernel mode setting:
1963 kms, kbd format: kms,kbd
1964 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1966 kgdbwait [KGDB] Stop kernel execution and enter the
1967 kernel debugger at the earliest opportunity.
1969 kmac= [MIPS] korina ethernet MAC address.
1970 Configure the RouterBoard 532 series on-chip
1971 Ethernet adapter MAC address.
1973 kmemleak= [KNL] Boot-time kmemleak enable/disable
1974 Valid arguments: on, off
1976 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1979 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1980 Default is 0 (don't ignore, but inject #GP)
1982 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
1983 Default is false (don't support).
1985 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1989 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1990 Default is 1 (enabled)
1992 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1994 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1996 kvm-arm.vgic_v3_group0_trap=
1997 [KVM,ARM] Trap guest accesses to GICv3 group-0
2000 kvm-arm.vgic_v3_group1_trap=
2001 [KVM,ARM] Trap guest accesses to GICv3 group-1
2004 kvm-arm.vgic_v3_common_trap=
2005 [KVM,ARM] Trap guest accesses to GICv3 common
2008 kvm-arm.vgic_v4_enable=
2009 [KVM,ARM] Allow use of GICv4 for direct injection of
2012 kvm-intel.ept= [KVM,Intel] Disable extended page tables
2013 (virtualized MMU) support on capable Intel chips.
2014 Default is 1 (enabled)
2016 kvm-intel.emulate_invalid_guest_state=
2017 [KVM,Intel] Enable emulation of invalid guest states
2018 Default is 0 (disabled)
2020 kvm-intel.flexpriority=
2021 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
2022 Default is 1 (enabled)
2025 [KVM,Intel] Enable VMX nesting (nVMX).
2026 Default is 0 (disabled)
2028 kvm-intel.unrestricted_guest=
2029 [KVM,Intel] Disable unrestricted guest feature
2030 (virtualized real and unpaged mode) on capable
2031 Intel chips. Default is 1 (enabled)
2033 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2036 Valid arguments: never, cond, always
2038 always: L1D cache flush on every VMENTER.
2039 cond: Flush L1D on VMENTER only when the code between
2040 VMEXIT and VMENTER can leak host memory.
2041 never: Disables the mitigation
2043 Default is cond (do L1 cache flush in specific instances)
2045 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2046 feature (tagged TLBs) on capable Intel chips.
2047 Default is 1 (enabled)
2049 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2052 The kernel PTE inversion protection is unconditionally
2053 enabled and cannot be disabled.
2056 Provides all available mitigations for the
2057 L1TF vulnerability. Disables SMT and
2058 enables all mitigations in the
2059 hypervisors, i.e. unconditional L1D flush.
2061 SMT control and L1D flush control via the
2062 sysfs interface is still possible after
2063 boot. Hypervisors will issue a warning
2064 when the first VM is started in a
2065 potentially insecure configuration,
2066 i.e. SMT enabled or L1D flush disabled.
2069 Same as 'full', but disables SMT and L1D
2070 flush runtime control. Implies the
2071 'nosmt=force' command line option.
2072 (i.e. sysfs control of SMT is disabled.)
2075 Leaves SMT enabled and enables the default
2076 hypervisor mitigation, i.e. conditional
2079 SMT control and L1D flush control via the
2080 sysfs interface is still possible after
2081 boot. Hypervisors will issue a warning
2082 when the first VM is started in a
2083 potentially insecure configuration,
2084 i.e. SMT enabled or L1D flush disabled.
2088 Disables SMT and enables the default
2089 hypervisor mitigation.
2091 SMT control and L1D flush control via the
2092 sysfs interface is still possible after
2093 boot. Hypervisors will issue a warning
2094 when the first VM is started in a
2095 potentially insecure configuration,
2096 i.e. SMT enabled or L1D flush disabled.
2099 Same as 'flush', but hypervisors will not
2100 warn when a VM is started in a potentially
2101 insecure configuration.
2104 Disables hypervisor mitigations and doesn't
2106 It also drops the swap size and available
2107 RAM limit restriction on both hypervisor and
2112 For details see: Documentation/admin-guide/l1tf.rst
2118 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2121 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2122 value for LAPIC timer one-shot implementation. Default
2123 back to the programmable timer unit in the LAPIC.
2125 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2128 libata.dma= [LIBATA] DMA control
2129 libata.dma=0 Disable all PATA and SATA DMA
2130 libata.dma=1 PATA and SATA Disk DMA only
2131 libata.dma=2 ATAPI (CDROM) DMA only
2132 libata.dma=4 Compact Flash DMA only
2133 Combinations also work, so libata.dma=3 enables DMA
2134 for disks and CDROMs, but not CFs.
2136 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2137 libata.ignore_hpa=0 keep BIOS limits (default)
2138 libata.ignore_hpa=1 ignore limits, using full disk
2140 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2144 libata.force= [LIBATA] Force configurations. The format is comma
2145 separated list of "[ID:]VAL" where ID is
2146 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2147 matching port, link or device. Basically, it matches
2148 the ATA ID string printed on console by libata. If
2149 the whole ID part is omitted, the last PORT and DEVICE
2150 values are used. If ID hasn't been specified yet, the
2151 configuration applies to all ports, links and devices.
2153 If only DEVICE is omitted, the parameter applies to
2154 the port and all links and devices behind it. DEVICE
2155 number of 0 either selects the first device or the
2156 first fan-out link behind PMP device. It does not
2157 select the host link. DEVICE number of 15 selects the
2158 host link and device attached to it.
2160 The VAL specifies the configuration to force. As long
2161 as there's no ambiguity shortcut notation is allowed.
2162 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2163 The following configurations can be forced.
2165 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2166 Any ID with matching PORT is used.
2168 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2170 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2171 udma[/][16,25,33,44,66,100,133] notation is also
2174 * [no]ncq: Turn on or off NCQ.
2176 * [no]ncqtrim: Turn off queued DSM TRIM.
2178 * nohrst, nosrst, norst: suppress hard, soft
2181 * rstonce: only attempt one reset during
2182 hot-unplug link recovery
2184 * dump_id: dump IDENTIFY data.
2186 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2188 * disable: Disable this device.
2190 If there are multiple matching configurations changing
2191 the same attribute, the last one is used.
2193 memblock=debug [KNL] Enable memblock debug messages.
2195 load_ramdisk= [RAM] List of ramdisks to load from floppy
2196 See Documentation/blockdev/ramdisk.txt.
2198 lockd.nlm_grace_period=P [NFS] Assign grace period.
2201 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2204 lockd.nlm_timeout=T [NFS] Assign timeout value.
2207 lockd.nlm_udpport=M [NFS] Assign UDP port.
2210 locktorture.nreaders_stress= [KNL]
2211 Set the number of locking read-acquisition kthreads.
2212 Defaults to being automatically set based on the
2213 number of online CPUs.
2215 locktorture.nwriters_stress= [KNL]
2216 Set the number of locking write-acquisition kthreads.
2218 locktorture.onoff_holdoff= [KNL]
2219 Set time (s) after boot for CPU-hotplug testing.
2221 locktorture.onoff_interval= [KNL]
2222 Set time (s) between CPU-hotplug operations, or
2223 zero to disable CPU-hotplug testing.
2225 locktorture.shuffle_interval= [KNL]
2226 Set task-shuffle interval (jiffies). Shuffling
2227 tasks allows some CPUs to go into dyntick-idle
2228 mode during the locktorture test.
2230 locktorture.shutdown_secs= [KNL]
2231 Set time (s) after boot system shutdown. This
2232 is useful for hands-off automated testing.
2234 locktorture.stat_interval= [KNL]
2235 Time (s) between statistics printk()s.
2237 locktorture.stutter= [KNL]
2238 Time (s) to stutter testing, for example,
2239 specifying five seconds causes the test to run for
2240 five seconds, wait for five seconds, and so on.
2241 This tests the locking primitive's ability to
2242 transition abruptly to and from idle.
2244 locktorture.torture_type= [KNL]
2245 Specify the locking implementation to test.
2247 locktorture.verbose= [KNL]
2248 Enable additional printk() statements.
2250 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2253 loglevel= All Kernel Messages with a loglevel smaller than the
2254 console loglevel will be printed to the console. It can
2255 also be changed with klogd or other programs. The
2256 loglevels are defined as follows:
2258 0 (KERN_EMERG) system is unusable
2259 1 (KERN_ALERT) action must be taken immediately
2260 2 (KERN_CRIT) critical conditions
2261 3 (KERN_ERR) error conditions
2262 4 (KERN_WARNING) warning conditions
2263 5 (KERN_NOTICE) normal but significant condition
2264 6 (KERN_INFO) informational
2265 7 (KERN_DEBUG) debug-level messages
2267 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2268 in bytes. n must be a power of two and greater
2269 than the minimal size. The minimal size is defined
2270 by LOG_BUF_SHIFT kernel config parameter. There is
2271 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2272 that allows to increase the default size depending on
2273 the number of CPUs. See init/Kconfig for more details.
2275 logo.nologo [FB] Disables display of the built-in Linux logo.
2276 This may be used to provide more screen space for
2277 kernel log messages and is useful when debugging
2278 kernel boot problems.
2280 lp=0 [LP] Specify parallel ports to use, e.g,
2281 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2282 lp=reset first parallel port). 'lp=0' disables the
2283 lp=auto printer driver. 'lp=reset' (which can be
2284 specified in addition to the ports) causes
2285 attached printers to be reset. Using
2286 lp=port1,port2,... specifies the parallel ports
2287 to associate lp devices with, starting with
2288 lp0. A port specification may be 'none' to skip
2289 that lp device, or a parport name such as
2290 'parport0'. Specifying 'lp=auto' instead of a
2291 port specification list means that device IDs
2292 from each port should be examined, to see if
2293 an IEEE 1284-compliant printer is attached; if
2294 so, the driver will manage that printer.
2295 See also header of drivers/char/lp.c.
2298 Sets loops_per_jiffy to given constant, thus avoiding
2299 time-consuming boot-time autodetection (up to 250 ms per
2300 CPU). 0 enables autodetection (default). To determine
2301 the correct value for your kernel, boot with normal
2302 autodetection and see what value is printed. Note that
2303 on SMP systems the preset will be applied to all CPUs,
2304 which is likely to cause problems if your CPUs need
2305 significantly divergent settings. An incorrect value
2306 will cause delays in the kernel to be wrong, leading to
2307 unpredictable I/O errors and other breakage. Although
2308 unlikely, in the extreme case this might damage your
2312 Format: <io>,<irq>,<dma>
2314 lsm.debug [SECURITY] Enable LSM initialization debugging output.
2316 machvec= [IA-64] Force the use of a particular machine-vector
2317 (machvec) in a generic kernel.
2318 Example: machvec=hpzx1_swiotlb
2320 machtype= [Loongson] Share the same kernel image file between different
2322 Example: machtype=lemote-yeeloong-2f-7inch
2324 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2325 than or equal to this physical address is ignored.
2327 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2328 will bring up during bootup. maxcpus=n : n >= 0 limits
2329 the kernel to bring up 'n' processors. Surely after
2330 bootup you can bring up the other plugged cpu by executing
2331 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2332 only takes effect during system bootup.
2333 While n=0 is a special case, it is equivalent to "nosmp",
2334 which also disables the IO APIC.
2336 max_loop= [LOOP] The number of loop block devices that get
2337 (loop.max_loop) unconditionally pre-created at init time. The default
2338 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2339 of statically allocating a predefined number, loop
2340 devices can be requested on-demand with the
2341 /dev/loop-control interface.
2343 mce [X86-32] Machine Check Exception
2345 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2347 md= [HW] RAID subsystems devices and level
2348 See Documentation/admin-guide/md.rst.
2351 Format: <first>,<last>
2352 Specifies range of consoles to be captured by the MDA.
2354 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2355 Amount of memory to be used when the kernel is not able
2356 to see the whole system memory or for test.
2357 [X86] Work as limiting max address. Use together
2358 with memmap= to avoid physical address space collisions.
2359 Without memmap= PCI devices could be placed at addresses
2360 belonging to unused RAM.
2362 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2366 [KNL,SH] Allow user to override the default size for
2367 per-device physically contiguous DMA buffers.
2369 memhp_default_state=online/offline
2370 [KNL] Set the initial state for the memory hotplug
2371 onlining policy. If not specified, the default value is
2372 set according to the
2373 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2375 See Documentation/memory-hotplug.txt.
2377 memmap=exactmap [KNL,X86] Enable setting of an exact
2378 E820 memory map, as specified by the user.
2379 Such memmap=exactmap lines can be constructed based on
2380 BIOS output or other requirements. See the memmap=nn@ss
2383 memmap=nn[KMG]@ss[KMG]
2384 [KNL] Force usage of a specific region of memory.
2385 Region of memory to be used is from ss to ss+nn.
2386 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2387 which limits max address to nn[KMG].
2388 Multiple different regions can be specified,
2391 memmap=100M@2G,100M#3G,1G!1024G
2393 memmap=nn[KMG]#ss[KMG]
2394 [KNL,ACPI] Mark specific memory as ACPI data.
2395 Region of memory to be marked is from ss to ss+nn.
2397 memmap=nn[KMG]$ss[KMG]
2398 [KNL,ACPI] Mark specific memory as reserved.
2399 Region of memory to be reserved is from ss to ss+nn.
2400 Example: Exclude memory from 0x18690000-0x1869ffff
2401 memmap=64K$0x18690000
2403 memmap=0x10000$0x18690000
2404 Some bootloaders may need an escape character before '$',
2405 like Grub2, otherwise '$' and the following number
2408 memmap=nn[KMG]!ss[KMG]
2409 [KNL,X86] Mark specific memory as protected.
2410 Region of memory to be used, from ss to ss+nn.
2411 The memory region may be marked as e820 type 12 (0xc)
2412 and is NVDIMM or ADR memory.
2414 memmap=<size>%<offset>-<oldtype>+<newtype>
2415 [KNL,ACPI] Convert memory within the specified region
2416 from <oldtype> to <newtype>. If "-<oldtype>" is left
2417 out, the whole region will be marked as <newtype>,
2418 even if previously unavailable. If "+<newtype>" is left
2419 out, matching memory will be removed. Types are
2420 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2421 3 = ACPI, 12 = PRAM.
2423 memory_corruption_check=0/1 [X86]
2424 Some BIOSes seem to corrupt the first 64k of
2425 memory when doing things like suspend/resume.
2426 Setting this option will scan the memory
2427 looking for corruption. Enabling this will
2428 both detect corruption and prevent the kernel
2429 from using the memory being corrupted.
2430 However, its intended as a diagnostic tool; if
2431 repeatable BIOS-originated corruption always
2432 affects the same memory, you can use memmap=
2433 to prevent the kernel from using that memory.
2435 memory_corruption_check_size=size [X86]
2436 By default it checks for corruption in the low
2437 64k, making this memory unavailable for normal
2438 use. Use this parameter to scan for
2439 corruption in more or less memory.
2441 memory_corruption_check_period=seconds [X86]
2442 By default it checks for corruption every 60
2443 seconds. Use this parameter to check at some
2444 other rate. 0 disables periodic checking.
2446 memtest= [KNL,X86,ARM,PPC] Enable memtest
2448 default : 0 <disable>
2449 Specifies the number of memtest passes to be
2450 performed. Each pass selects another test
2451 pattern from a given set of patterns. Memtest
2452 fills the memory with this pattern, validates
2453 memory contents and reserves bad memory
2454 regions that are detected.
2456 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2457 Valid arguments: on, off
2458 Default (depends on kernel configuration option):
2459 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2460 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2461 mem_encrypt=on: Activate SME
2462 mem_encrypt=off: Do not activate SME
2464 Refer to Documentation/x86/amd-memory-encryption.txt
2465 for details on when memory encryption can be activated.
2467 mem_sleep_default= [SUSPEND] Default system suspend mode:
2468 s2idle - Suspend-To-Idle
2469 shallow - Power-On Suspend or equivalent (if supported)
2470 deep - Suspend-To-RAM or equivalent (if supported)
2471 See Documentation/admin-guide/pm/sleep-states.rst.
2473 meye.*= [HW] Set MotionEye Camera parameters
2474 See Documentation/media/v4l-drivers/meye.rst.
2476 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2477 Multi-Function General Purpose Timers on AMD Geode
2480 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2481 the BIOS has incorrectly applied a workaround. TinyBIOS
2482 version 0.98 is known to be affected, 0.99 fixes the
2483 problem by letting the user disable the workaround.
2487 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2488 physical address is ignored.
2490 mini2440= [ARM,HW,KNL]
2491 Format:[0..2][b][c][t]
2493 MINI2440 configuration specification:
2494 0 - The attached screen is the 3.5" TFT
2495 1 - The attached screen is the 7" TFT
2496 2 - The VGA Shield is attached (1024x768)
2497 Leaving out the screen size parameter will not load
2498 the TFT driver, and the framebuffer will be left
2500 b - Enable backlight. The TFT backlight pin will be
2501 linked to the kernel VESA blanking code and a GPIO
2502 LED. This parameter is not necessary when using the
2504 c - Enable the s3c camera interface.
2505 t - Reserved for enabling touchscreen support. The
2506 touchscreen support is not enabled in the mainstream
2507 kernel as of 2.6.30, a preliminary port can be found
2508 in the "bleeding edge" mini2440 support kernel at
2509 http://repo.or.cz/w/linux-2.6/mini2440.git
2512 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2513 parameter allows control of the logging verbosity for
2514 the additional memory initialisation checks. A value
2515 of 0 disables mminit logging and a level of 4 will
2516 log everything. Information is printed at KERN_DEBUG
2517 so loglevel=8 may also need to be specified.
2520 [KNL] When CONFIG_MODULE_SIG is set, this means that
2521 modules without (valid) signatures will fail to load.
2522 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2523 is always true, so this option does nothing.
2525 module_blacklist= [KNL] Do not load a comma-separated list of
2526 modules. Useful for debugging problem modules.
2529 [MOUSE] Maximum time between finger touching and
2530 leaving touchpad surface for touch to be considered
2531 a tap and be reported as a left button click (for
2532 touchpads working in absolute mode only).
2534 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2535 reporting absolute coordinates, such as tablets
2536 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2537 reporting absolute coordinates, such as tablets
2539 movablecore= [KNL,X86,IA-64,PPC]
2540 Format: nn[KMGTPE] | nn%
2541 This parameter is the complement to kernelcore=, it
2542 specifies the amount of memory used for migratable
2543 allocations. If both kernelcore and movablecore is
2544 specified, then kernelcore will be at *least* the
2545 specified value but may be more. If movablecore on its
2546 own is specified, the administrator must be careful
2547 that the amount of memory usable for all allocations
2550 movable_node [KNL] Boot-time switch to make hotplugable memory
2551 NUMA nodes to be movable. This means that the memory
2552 of such nodes will be usable only for movable
2553 allocations which rules out almost all kernel
2554 allocations. Use with caution!
2556 MTD_Partition= [MTD]
2557 Format: <name>,<region-number>,<size>,<offset>
2559 MTD_Region= [MTD] Format:
2560 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2563 See drivers/mtd/cmdlinepart.c.
2565 multitce=off [PPC] This parameter disables the use of the pSeries
2566 firmware feature for updating multiple TCE entries
2569 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2571 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2573 boundary - index of last SLC block on Flex-OneNAND.
2574 The remaining blocks are configured as MLC blocks.
2575 lock - Configure if Flex-OneNAND boundary should be locked.
2576 Once locked, the boundary cannot be changed.
2577 1 indicates lock status, 0 indicates unlock status.
2580 ARM/S3C2412 JIVE boot control
2582 See arch/arm/mach-s3c2412/mach-jive.c
2584 mtouchusb.raw_coordinates=
2585 [HW] Make the MicroTouch USB driver use raw coordinates
2586 ('y', default) or cooked coordinates ('n')
2588 mtrr_chunk_size=nn[KMG] [X86]
2589 used for mtrr cleanup. It is largest continuous chunk
2590 that could hold holes aka. UC entries.
2592 mtrr_gran_size=nn[KMG] [X86]
2593 Used for mtrr cleanup. It is granularity of mtrr block.
2595 Large value could prevent small alignment from
2598 mtrr_spare_reg_nr=n [X86]
2600 Range: 0,7 : spare reg number
2602 Used for mtrr cleanup. It is spare mtrr entries number.
2603 Set to 2 or more if your graphical card needs more.
2605 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2607 netdev= [NET] Network devices parameters
2608 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2609 Note that mem_start is often overloaded to mean
2610 something different and driver-specific.
2611 This usage is only documented in each driver source
2615 [NETFILTER] Enable connection tracking flow accounting
2616 0 to disable accounting
2617 1 to enable accounting
2620 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2621 See Documentation/filesystems/nfs/nfsroot.txt.
2623 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2624 See Documentation/filesystems/nfs/nfsroot.txt.
2626 nfsrootdebug [NFS] enable nfsroot debugging messages.
2627 See Documentation/filesystems/nfs/nfsroot.txt.
2629 nfs.callback_nr_threads=
2630 [NFSv4] set the total number of threads that the
2631 NFS client will assign to service NFSv4 callback
2634 nfs.callback_tcpport=
2635 [NFS] set the TCP port on which the NFSv4 callback
2636 channel should listen.
2639 [NFS] sets the pathname to the program which is used
2640 to update the NFS client cache entries.
2642 nfs.cache_getent_timeout=
2643 [NFS] sets the timeout after which an attempt to
2644 update a cache entry is deemed to have failed.
2646 nfs.idmap_cache_timeout=
2647 [NFS] set the maximum lifetime for idmapper cache
2651 [NFS] enable 64-bit inode numbers.
2652 If zero, the NFS client will fake up a 32-bit inode
2653 number for the readdir() and stat() syscalls instead
2654 of returning the full 64-bit number.
2655 The default is to return 64-bit inode numbers.
2657 nfs.max_session_cb_slots=
2658 [NFSv4.1] Sets the maximum number of session
2659 slots the client will assign to the callback
2660 channel. This determines the maximum number of
2661 callbacks the client will process in parallel for
2662 a particular server.
2664 nfs.max_session_slots=
2665 [NFSv4.1] Sets the maximum number of session slots
2666 the client will attempt to negotiate with the server.
2667 This limits the number of simultaneous RPC requests
2668 that the client can send to the NFSv4.1 server.
2669 Note that there is little point in setting this
2670 value higher than the max_tcp_slot_table_limit.
2672 nfs.nfs4_disable_idmapping=
2673 [NFSv4] When set to the default of '1', this option
2674 ensures that both the RPC level authentication
2675 scheme and the NFS level operations agree to use
2676 numeric uids/gids if the mount is using the
2677 'sec=sys' security flavour. In effect it is
2678 disabling idmapping, which can make migration from
2679 legacy NFSv2/v3 systems to NFSv4 easier.
2680 Servers that do not support this mode of operation
2681 will be autodetected by the client, and it will fall
2682 back to using the idmapper.
2683 To turn off this behaviour, set the value to '0'.
2685 [NFS4] Specify an additional fixed unique ident-
2686 ification string that NFSv4 clients can insert into
2687 their nfs_client_id4 string. This is typically a
2688 UUID that is generated at system install time.
2690 nfs.send_implementation_id =
2691 [NFSv4.1] Send client implementation identification
2692 information in exchange_id requests.
2693 If zero, no implementation identification information
2695 The default is to send the implementation identification
2698 nfs.recover_lost_locks =
2699 [NFSv4] Attempt to recover locks that were lost due
2700 to a lease timeout on the server. Please note that
2701 doing this risks data corruption, since there are
2702 no guarantees that the file will remain unchanged
2703 after the locks are lost.
2704 If you want to enable the kernel legacy behaviour of
2705 attempting to recover these locks, then set this
2707 The default parameter value of '0' causes the kernel
2708 not to attempt recovery of lost locks.
2710 nfs4.layoutstats_timer =
2711 [NFSv4.2] Change the rate at which the kernel sends
2712 layoutstats to the pNFS metadata server.
2714 Setting this to value to 0 causes the kernel to use
2715 whatever value is the default set by the layout
2716 driver. A non-zero value sets the minimum interval
2717 in seconds between layoutstats transmissions.
2719 nfsd.nfs4_disable_idmapping=
2720 [NFSv4] When set to the default of '1', the NFSv4
2721 server will return only numeric uids and gids to
2722 clients using auth_sys, and will accept numeric uids
2723 and gids from such clients. This is intended to ease
2724 migration from NFSv2/v3.
2726 nmi_debug= [KNL,SH] Specify one or more actions to take
2727 when a NMI is triggered.
2728 Format: [state][,regs][,debounce][,die]
2730 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2731 Format: [panic,][nopanic,][num]
2733 0 - turn hardlockup detector in nmi_watchdog off
2734 1 - turn hardlockup detector in nmi_watchdog on
2735 When panic is specified, panic when an NMI watchdog
2736 timeout occurs (or 'nopanic' to override the opposite
2737 default). To disable both hard and soft lockup detectors,
2738 please see 'nowatchdog'.
2739 This is useful when you use a panic=... timeout and
2740 need the box quickly up again.
2742 These settings can be accessed at runtime via
2743 the nmi_watchdog and hardlockup_panic sysctls.
2745 netpoll.carrier_timeout=
2746 [NET] Specifies amount of time (in seconds) that
2747 netpoll should wait for a carrier. By default netpoll
2750 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2751 emulation library even if a 387 maths coprocessor
2754 no5lvl [X86-64] Disable 5-level paging mode. Forces
2755 kernel to use 4-level paging instead.
2758 [HW] Never suspend the console
2759 Disable suspending of consoles during suspend and
2760 hibernate operations. Once disabled, debugging
2761 messages can reach various consoles while the rest
2762 of the system is being put to sleep (ie, while
2763 debugging driver suspend/resume hooks). This may
2764 not work reliably with all consoles, but is known
2765 to work with serial and VGA consoles.
2766 To facilitate more flexible debugging, we also add
2767 console_suspend, a printk module parameter to control
2768 it. Users could use console_suspend (usually
2769 /sys/module/printk/parameters/console_suspend) to
2770 turn on/off it dynamically.
2772 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2773 caches in the slab allocator. Saves per-node memory,
2774 but will impact performance.
2778 noaltinstr [S390] Disables alternative instructions patching
2779 (CPU alternatives feature).
2781 noapic [SMP,APIC] Tells the kernel to not make use of any
2782 IOAPICs that may be present in the system.
2784 noautogroup Disable scheduler automatic task group creation.
2786 nobats [PPC] Do not use BATs for mapping kernel lowmem
2787 on "Classic" PPC cores.
2791 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2793 nodelayacct [KNL] Disable per-task delay accounting
2795 nodsp [SH] Disable hardware DSP at boot time.
2797 noefi Disable EFI runtime services support.
2802 On X86-32 available only on PAE configured kernels.
2803 noexec=on: enable non-executable mappings (default)
2804 noexec=off: disable non-executable mappings
2807 Disable SMAP (Supervisor Mode Access Prevention)
2808 even if it is supported by processor.
2811 Disable SMEP (Supervisor Mode Execution Prevention)
2812 even if it is supported by processor.
2815 This affects only 32-bit executables.
2816 noexec32=on: enable non-executable mappings (default)
2817 read doesn't imply executable mappings
2818 noexec32=off: disable non-executable mappings
2819 read implies executable mappings
2821 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2823 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2824 register save and restore. The kernel will only save
2825 legacy floating-point registers on task switch.
2827 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2829 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2830 Equivalent to smt=1.
2832 [KNL,x86] Disable symmetric multithreading (SMT).
2833 nosmt=force: Force disable SMT, cannot be undone
2834 via the sysfs control file.
2836 nospectre_v1 [PPC] Disable mitigations for Spectre Variant 1 (bounds
2837 check bypass). With this option data leaks are possible
2840 nospectre_v2 [X86,PPC_FSL_BOOK3E] Disable all mitigations for the Spectre variant 2
2841 (indirect branch prediction) vulnerability. System may
2842 allow data leaks with this option, which is equivalent
2845 nospec_store_bypass_disable
2846 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
2848 noxsave [BUGS=X86] Disables x86 extended register state save
2849 and restore using xsave. The kernel will fallback to
2850 enabling legacy floating-point and sse state.
2852 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2853 register states. The kernel will fall back to use
2854 xsave to save the states. By using this parameter,
2855 performance of saving the states is degraded because
2856 xsave doesn't support modified optimization while
2857 xsaveopt supports it on xsaveopt enabled systems.
2859 noxsaves [X86] Disables xsaves and xrstors used in saving and
2860 restoring x86 extended register state in compacted
2861 form of xsave area. The kernel will fall back to use
2862 xsaveopt and xrstor to save and restore the states
2863 in standard form of xsave area. By using this
2864 parameter, xsave area per process might occupy more
2865 memory on xsaves enabled systems.
2867 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2868 wfi(ARM) instruction doesn't work correctly and not to
2869 use it. This is also useful when using JTAG debugger.
2871 no_file_caps Tells the kernel not to honor file capabilities. The
2872 only way then for a file to be executed with privilege
2873 is to be setuid root or executed by root.
2875 nohalt [IA-64] Tells the kernel not to use the power saving
2876 function PAL_HALT_LIGHT when idle. This increases
2877 power-consumption. On the positive side, it reduces
2878 interrupt wake-up latency, which may improve performance
2879 in certain environments such as networked servers or
2882 nohibernate [HIBERNATION] Disable hibernation and resume.
2884 nohz= [KNL] Boottime enable/disable dynamic ticks
2885 Valid arguments: on, off
2888 nohz_full= [KNL,BOOT,SMP,ISOL]
2889 The argument is a cpu list, as described above.
2890 In kernels built with CONFIG_NO_HZ_FULL=y, set
2891 the specified list of CPUs whose tick will be stopped
2892 whenever possible. The boot CPU will be forced outside
2893 the range to maintain the timekeeping. Any CPUs
2894 in this list will have their RCU callbacks offloaded,
2895 just as if they had also been called out in the
2896 rcu_nocbs= boot parameter.
2898 noiotrap [SH] Disables trapped I/O port accesses.
2900 noirqdebug [X86-32] Disables the code which attempts to detect and
2901 disable unhandled interrupt sources.
2903 no_timer_check [X86,APIC] Disables the code which tests for
2904 broken timer IRQ sources.
2906 noisapnp [ISAPNP] Disables ISA PnP code.
2908 noinitrd [RAM] Tells the kernel not to load any configured
2911 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2913 [Deprecated - use intremap=off]
2917 noinvpcid [X86] Disable the INVPCID cpu feature.
2919 nojitter [IA-64] Disables jitter checking for ITC timers.
2921 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2923 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2927 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2928 clock and use the default one.
2930 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2931 steal time is computed, but won't influence scheduler
2934 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2936 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2938 noltlbs [PPC] Do not use large page/tlb entries for kernel
2939 lowmem mapping on PPC40x and PPC8xx
2941 nomca [IA-64] Disable machine check abort handling
2943 nomce [X86-32] Disable Machine Check Exception
2945 nomfgpt [X86-32] Disable Multi-Function General Purpose
2946 Timer usage (for AMD Geode machines).
2948 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2949 shutdown the other cpus. Instead use the REBOOT_VECTOR
2952 nomodule Disable module load
2954 nopat [X86] Disable PAT (page attribute table extension of
2955 pagetables) support.
2957 nopcid [X86-64] Disable the PCID cpu feature.
2959 norandmaps Don't use address space randomization. Equivalent to
2960 echo 0 > /proc/sys/kernel/randomize_va_space
2962 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2963 with UP alternatives
2965 nordrand [X86] Disable kernel use of the RDRAND and
2966 RDSEED instructions even if they are supported
2967 by the processor. RDRAND and RDSEED are still
2968 available to user space applications.
2970 noresume [SWSUSP] Disables resume and restores original swap
2973 no-scroll [VGA] Disables scrollback.
2974 This is required for the Braillex ib80-piezo Braille
2975 reader made by F.H. Papenmeier (Germany).
2979 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2981 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2982 and disable the IO APIC. legacy for "maxcpus=0".
2984 nosoftlockup [KNL] Disable the soft-lockup detector.
2986 nosync [HW,M68K] Disables sync negotiation for all devices.
2988 nowatchdog [KNL] Disable both lockup detectors, i.e.
2989 soft-lockup and NMI watchdog (hard-lockup).
2993 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2995 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2996 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2997 Some features depend on CPU0. Known dependencies are:
2998 1. Resume from suspend/hibernate depends on CPU0.
2999 Suspend/hibernate will fail if CPU0 is offline and you
3000 need to online CPU0 before suspend/hibernate.
3001 2. PIC interrupts also depend on CPU0. CPU0 can't be
3002 removed if a PIC interrupt is detected.
3003 It's said poweroff/reboot may depend on CPU0 on some
3004 machines although I haven't seen such issues so far
3005 after CPU0 is offline on a few tested machines.
3006 If the dependencies are under your control, you can
3007 turn on cpu0_hotplug.
3009 nps_mtm_hs_ctr= [KNL,ARC]
3010 This parameter sets the maximum duration, in
3011 cycles, each HW thread of the CTOP can run
3012 without interruptions, before HW switches it.
3013 The actual maximum duration is 16 times this
3015 Format: integer between 1 and 255
3018 nptcg= [IA-64] Override max number of concurrent global TLB
3019 purges which is reported from either PAL_VM_SUMMARY or
3022 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
3023 could support. nr_cpus=n : n >= 1 limits the kernel to
3024 support 'n' processors. It could be larger than the
3025 number of already plugged CPU during bootup, later in
3026 runtime you can physically add extra cpu until it reaches
3027 n. So during boot up some boot time memory for per-cpu
3028 variables need be pre-allocated for later physical cpu
3031 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3033 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
3034 Allowed values are enable and disable
3036 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3037 'node', 'default' can be specified
3038 This can be set from sysctl after boot.
3039 See Documentation/sysctl/vm.txt for details.
3041 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3042 See Documentation/debugging-via-ohci1394.txt for more
3045 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3046 Rather than timing out after 20 ms if an EC
3047 command is not properly ACKed, override the length
3048 of the timeout. We have interrupts disabled while
3049 waiting for the ACK, so if this is set too high
3050 interrupts *may* be lost!
3052 omap_mux= [OMAP] Override bootloader pin multiplexing.
3053 Format: <mux_mode0.mode_name=value>...
3054 For example, to override I2C bus2:
3055 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3057 oprofile.timer= [HW]
3058 Use timer interrupt instead of performance counters
3060 oprofile.cpu_type= Force an oprofile cpu type
3061 This might be useful if you have an older oprofile
3062 userland or if you want common events.
3063 Format: { arch_perfmon }
3064 arch_perfmon: [X86] Force use of architectural
3065 perfmon on Intel CPUs instead of the
3066 CPU specific event set.
3067 timer: [X86] Force use of architectural NMI
3068 timer mode (see also oprofile.timer
3069 for generic hr timer mode)
3071 oops=panic Always panic on oopses. Default is to just kill the
3072 process, but there is a small probability of
3073 deadlocking the machine.
3074 This will also cause panics on machine check exceptions.
3075 Useful together with panic=30 to trigger a reboot.
3077 page_owner= [KNL] Boot-time page_owner enabling option.
3078 Storage of the information about who allocated
3079 each page is disabled in default. With this switch,
3081 on: enable the feature
3083 page_poison= [KNL] Boot-time parameter changing the state of
3084 poisoning on the buddy allocator, available with
3085 CONFIG_PAGE_POISONING=y.
3086 off: turn off poisoning (default)
3087 on: turn on poisoning
3089 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3090 timeout > 0: seconds before rebooting
3091 timeout = 0: wait forever
3092 timeout < 0: reboot immediately
3095 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3098 crash_kexec_post_notifiers
3099 Run kdump after running panic-notifiers and dumping
3100 kmsg. This only for the users who doubt kdump always
3101 succeeds in any situation.
3102 Note that this also increases risks of kdump failure,
3103 because some panic notifiers can make the crashed
3104 kernel more unstable.
3106 parkbd.port= [HW] Parallel port number the keyboard adapter is
3107 connected to, default is 0.
3109 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3110 0 for XT, 1 for AT (default is AT).
3113 parport= [HW,PPT] Specify parallel ports. 0 disables.
3114 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3115 Use 'auto' to force the driver to use any
3116 IRQ/DMA settings detected (the default is to
3117 ignore detected IRQ/DMA settings because of
3118 possible conflicts). You can specify the base
3119 address, IRQ, and DMA settings; IRQ and DMA
3120 should be numbers, or 'auto' (for using detected
3121 settings on that particular port), or 'nofifo'
3122 (to avoid using a FIFO even if it is detected).
3123 Parallel ports are assigned in the order they
3124 are specified on the command line, starting
3127 parport_init_mode= [HW,PPT]
3128 Configure VIA parallel port to operate in
3129 a specific mode. This is necessary on Pegasos
3130 computer where firmware has no options for setting
3131 up parallel port mode and sets it to spp.
3132 Currently this function knows 686a and 8231 chips.
3133 Format: [spp|ps2|epp|ecp|ecpepp]
3136 Halt all CPUs after the first oops has been printed for
3137 the specified number of seconds. This is to be used if
3138 your oopses keep scrolling off the screen.
3143 See header of drivers/block/paride/pcd.c.
3144 See also Documentation/blockdev/paride.txt.
3146 pci=option[,option...] [PCI] various PCI subsystem options.
3148 Some options herein operate on a specific device
3149 or a set of devices (<pci_dev>). These are
3150 specified in one of the following formats:
3152 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
3153 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
3155 Note: the first format specifies a PCI
3156 bus/device/function address which may change
3157 if new hardware is inserted, if motherboard
3158 firmware changes, or due to changes caused
3159 by other kernel parameters. If the
3160 domain is left unspecified, it is
3161 taken to be zero. Optionally, a path
3162 to a device through multiple device/function
3163 addresses can be specified after the base
3164 address (this is more robust against
3165 renumbering issues). The second format
3166 selects devices using IDs from the
3167 configuration space which may match multiple
3168 devices in the system.
3170 earlydump dump PCI config space before the kernel
3172 off [X86] don't probe for the PCI bus
3173 bios [X86-32] force use of PCI BIOS, don't access
3174 the hardware directly. Use this if your machine
3175 has a non-standard PCI host bridge.
3176 nobios [X86-32] disallow use of PCI BIOS, only direct
3177 hardware access methods are allowed. Use this
3178 if you experience crashes upon bootup and you
3179 suspect they are caused by the BIOS.
3180 conf1 [X86] Force use of PCI Configuration Access
3181 Mechanism 1 (config address in IO port 0xCF8,
3182 data in IO port 0xCFC, both 32-bit).
3183 conf2 [X86] Force use of PCI Configuration Access
3184 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3185 the function, IO port 0xCFA, also 8-bit, sets
3186 bus number. The config space is then accessed
3187 through ports 0xC000-0xCFFF).
3188 See http://wiki.osdev.org/PCI for more info
3189 on the configuration access mechanisms.
3190 noaer [PCIE] If the PCIEAER kernel config parameter is
3191 enabled, this kernel boot option can be used to
3192 disable the use of PCIE advanced error reporting.
3193 nodomains [PCI] Disable support for multiple PCI
3194 root domains (aka PCI segments, in ACPI-speak).
3195 nommconf [X86] Disable use of MMCONFIG for PCI
3197 check_enable_amd_mmconf [X86] check for and enable
3198 properly configured MMIO access to PCI
3199 config space on AMD family 10h CPU
3200 nomsi [MSI] If the PCI_MSI kernel config parameter is
3201 enabled, this kernel boot option can be used to
3202 disable the use of MSI interrupts system-wide.
3203 noioapicquirk [APIC] Disable all boot interrupt quirks.
3204 Safety option to keep boot IRQs enabled. This
3205 should never be necessary.
3206 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3207 primary IO-APIC for bridges that cannot disable
3208 boot IRQs. This fixes a source of spurious IRQs
3209 when the system masks IRQs.
3210 noioapicreroute [APIC] Disable workaround that uses the
3211 boot IRQ equivalent of an IRQ that connects to
3212 a chipset where boot IRQs cannot be disabled.
3213 The opposite of ioapicreroute.
3214 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3215 routing table. These calls are known to be buggy
3216 on several machines and they hang the machine
3217 when used, but on other computers it's the only
3218 way to get the interrupt routing table. Try
3219 this option if the kernel is unable to allocate
3220 IRQs or discover secondary PCI buses on your
3222 rom [X86] Assign address space to expansion ROMs.
3223 Use with caution as certain devices share
3224 address decoders between ROMs and other
3226 norom [X86] Do not assign address space to
3227 expansion ROMs that do not already have
3228 BIOS assigned address ranges.
3229 nobar [X86] Do not assign address space to the
3230 BARs that weren't assigned by the BIOS.
3231 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3232 assigned automatically to PCI devices. You can
3233 make the kernel exclude IRQs of your ISA cards
3235 pirqaddr=0xAAAAA [X86] Specify the physical address
3236 of the PIRQ table (normally generated
3237 by the BIOS) if it is outside the
3238 F0000h-100000h range.
3239 lastbus=N [X86] Scan all buses thru bus #N. Can be
3240 useful if the kernel is unable to find your
3241 secondary buses and you want to tell it
3242 explicitly which ones they are.
3243 assign-busses [X86] Always assign all PCI bus
3244 numbers ourselves, overriding
3245 whatever the firmware may have done.
3246 usepirqmask [X86] Honor the possible IRQ mask stored
3247 in the BIOS $PIR table. This is needed on
3248 some systems with broken BIOSes, notably
3249 some HP Pavilion N5400 and Omnibook XE3
3250 notebooks. This will have no effect if ACPI
3251 IRQ routing is enabled.
3252 noacpi [X86] Do not use ACPI for IRQ routing
3253 or for PCI scanning.
3254 use_crs [X86] Use PCI host bridge window information
3255 from ACPI. On BIOSes from 2008 or later, this
3256 is enabled by default. If you need to use this,
3257 please report a bug.
3258 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3259 If you need to use this, please report a bug.
3260 routeirq Do IRQ routing for all PCI devices.
3261 This is normally done in pci_enable_device(),
3262 so this option is a temporary workaround
3263 for broken drivers that don't call it.
3264 skip_isa_align [X86] do not align io start addr, so can
3265 handle more pci cards
3266 noearly [X86] Don't do any early type 1 scanning.
3267 This might help on some broken boards which
3268 machine check when some devices' config space
3269 is read. But various workarounds are disabled
3270 and some IOMMU drivers will not work.
3271 bfsort Sort PCI devices into breadth-first order.
3272 This sorting is done to get a device
3273 order compatible with older (<= 2.4) kernels.
3274 nobfsort Don't sort PCI devices into breadth-first order.
3275 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3276 tuning and use the BIOS-configured MPS defaults.
3277 pcie_bus_safe Set every device's MPS to the largest value
3278 supported by all devices below the root complex.
3279 pcie_bus_perf Set device MPS to the largest allowable MPS
3280 based on its parent bus. Also set MRRS (Max
3281 Read Request Size) to the largest supported
3282 value (no larger than the MPS that the device
3283 or bus can support) for best performance.
3284 pcie_bus_peer2peer Set every device's MPS to 128B, which
3285 every device is guaranteed to support. This
3286 configuration allows peer-to-peer DMA between
3287 any pair of devices, possibly at the cost of
3288 reduced performance. This also guarantees
3289 that hot-added devices will work.
3290 cbiosize=nn[KMG] The fixed amount of bus space which is
3291 reserved for the CardBus bridge's IO window.
3292 The default value is 256 bytes.
3293 cbmemsize=nn[KMG] The fixed amount of bus space which is
3294 reserved for the CardBus bridge's memory
3295 window. The default value is 64 megabytes.
3298 [<order of align>@]<pci_dev>[; ...]
3299 Specifies alignment and device to reassign
3300 aligned memory resources. How to
3301 specify the device is described above.
3302 If <order of align> is not specified,
3303 PAGE_SIZE is used as alignment.
3304 PCI-PCI bridge can be specified, if resource
3305 windows need to be expanded.
3306 To specify the alignment for several
3307 instances of a device, the PCI vendor,
3308 device, subvendor, and subdevice may be
3309 specified, e.g., 4096@pci:8086:9c22:103c:198f
3310 ecrc= Enable/disable PCIe ECRC (transaction layer
3311 end-to-end CRC checking).
3312 bios: Use BIOS/firmware settings. This is the
3316 hpiosize=nn[KMG] The fixed amount of bus space which is
3317 reserved for hotplug bridge's IO window.
3318 Default size is 256 bytes.
3319 hpmemsize=nn[KMG] The fixed amount of bus space which is
3320 reserved for hotplug bridge's memory window.
3321 Default size is 2 megabytes.
3322 hpbussize=nn The minimum amount of additional bus numbers
3323 reserved for buses below a hotplug bridge.
3325 realloc= Enable/disable reallocating PCI bridge resources
3326 if allocations done by BIOS are too small to
3327 accommodate resources required by all child
3329 off: Turn realloc off
3331 realloc same as realloc=on
3332 noari do not use PCIe ARI.
3333 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
3334 do not use PCIe ATS (and IOMMU device IOTLB).
3335 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3336 only look for one device below a PCIe downstream
3338 big_root_window Try to add a big 64bit memory window to the PCIe
3339 root complex on AMD CPUs. Some GFX hardware
3340 can resize a BAR to allow access to all VRAM.
3341 Adding the window is slightly risky (it may
3342 conflict with unreported devices), so this
3344 disable_acs_redir=<pci_dev>[; ...]
3345 Specify one or more PCI devices (in the format
3346 specified above) separated by semicolons.
3347 Each device specified will have the PCI ACS
3348 redirect capabilities forced off which will
3349 allow P2P traffic between devices through
3350 bridges without forcing it upstream. Note:
3351 this removes isolation between devices and
3352 may put more devices in an IOMMU group.
3354 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3357 force Enable ASPM even on devices that claim not to support it.
3358 WARNING: Forcing ASPM on may cause system lockups.
3360 pcie_ports= [PCIE] PCIe port services handling:
3361 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
3362 even if the platform doesn't give the OS permission to
3363 use them. This may cause conflicts if the platform
3364 also tries to use these services.
3365 compat Disable native PCIe services (PME, AER, DPC, PCIe
3368 pcie_port_pm= [PCIE] PCIe port power management handling:
3369 off Disable power management of all PCIe ports
3370 force Forcibly enable power management of all PCIe ports
3372 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3373 nomsi Do not use MSI for native PCIe PME signaling (this makes
3374 all PCIe root ports use INTx for all services).
3376 pcmv= [HW,PCMCIA] BadgePAD 4
3380 Keep all power-domains already enabled by bootloader on,
3381 even if no driver has claimed them. This is useful
3382 for debug and development, but should not be
3383 needed on a platform with proper driver support.
3386 See Documentation/blockdev/paride.txt.
3388 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3391 See arch/parisc/kernel/pdc_chassis.c
3393 percpu_alloc= Select which percpu first chunk allocator to use.
3394 Currently supported values are "embed" and "page".
3395 Archs may support subset or none of the selections.
3396 See comments in mm/percpu.c for details on each
3397 allocator. This parameter is primarily for debugging
3398 and performance comparison.
3401 See Documentation/blockdev/paride.txt.
3404 See Documentation/blockdev/paride.txt.
3406 pirq= [SMP,APIC] Manual mp-table setup
3407 See Documentation/x86/i386/IO-APIC.txt.
3409 plip= [PPT,NET] Parallel port network link
3410 Format: { parport<nr> | timid | 0 }
3411 See also Documentation/admin-guide/parport.rst.
3413 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3414 Override pmtimer IOPort with a hex value.
3418 Enable PNP debug messages (depends on the
3419 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3420 via /sys/module/pnp/parameters/debug. We always show
3421 current resource usage; turning this on also shows
3422 possible settings and some assignment information.
3428 { on | off | curr | res | no-curr | no-res }
3431 [ISAPNP] Exclude IRQs for the autoconfiguration
3434 [ISAPNP] Exclude DMAs for the autoconfiguration
3436 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3437 Ranges are in pairs (I/O port base and size).
3440 [ISAPNP] Exclude memory regions for the
3442 Ranges are in pairs (memory base and size).
3444 ports= [IP_VS_FTP] IPVS ftp helper module
3446 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3448 Format: <port>,<port>....
3450 powersave=off [PPC] This option disables power saving features.
3451 It specifically disables cpuidle and sets the
3452 platform machine description specific power_save
3453 function to NULL. On Idle the CPU just reduces
3456 ppc_strict_facility_enable
3457 [PPC] This option catches any kernel floating point,
3458 Altivec, VSX and SPE outside of regions specifically
3459 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3460 There is some performance impact when enabling this.
3464 Disable Hardware Transactional Memory
3466 print-fatal-signals=
3467 [KNL] debug: print fatal signals
3469 If enabled, warn about various signal handling
3470 related application anomalies: too many signals,
3471 too many POSIX.1 timers, fatal signals causing a
3474 If you hit the warning due to signal overflow,
3475 you might want to try "ulimit -i unlimited".
3479 printk.always_kmsg_dump=
3480 Trigger kmsg_dump for cases other than kernel oops or
3482 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3485 printk.devkmsg={on,off,ratelimit}
3486 Control writing to /dev/kmsg.
3487 on - unlimited logging to /dev/kmsg from userspace
3488 off - logging to /dev/kmsg disabled
3489 ratelimit - ratelimit the logging
3492 printk.time= Show timing data prefixed to each printk message line
3493 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3495 processor.max_cstate= [HW,ACPI]
3496 Limit processor to maximum C-state
3497 max_cstate=9 overrides any DMI blacklist limit.
3499 processor.nocst [HW,ACPI]
3500 Ignore the _CST method to determine C-states,
3501 instead using the legacy FADT method
3503 profile= [KNL] Enable kernel profiling via /proc/profile
3504 Format: [<profiletype>,]<number>
3505 Param: <profiletype>: "schedule", "sleep", or "kvm"
3506 [defaults to kernel profiling]
3507 Param: "schedule" - profile schedule points.
3508 Param: "sleep" - profile D-state sleeping (millisecs).
3509 Requires CONFIG_SCHEDSTATS
3510 Param: "kvm" - profile VM exits.
3511 Param: <number> - step/bucket size as a power of 2 for
3512 statistical time based profiling.
3514 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3516 See Documentation/blockdev/ramdisk.txt.
3518 psi= [KNL] Enable or disable pressure stall information
3522 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3523 probe for; one of (bare|imps|exps|lifebook|any).
3524 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3526 psmouse.resetafter= [HW,MOUSE]
3527 Try to reset the device after so many bad packets
3530 [HW,MOUSE] Set desired mouse resolution, in dpi.
3531 psmouse.smartscroll=
3532 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3533 0 = disabled, 1 = enabled (default).
3535 pstore.backend= Specify the name of the pstore backend to use
3538 See Documentation/blockdev/paride.txt.
3540 pti= [X86_64] Control Page Table Isolation of user and
3541 kernel address spaces. Disabling this feature
3542 removes hardening, but improves performance of
3543 system calls and interrupts.
3545 on - unconditionally enable
3546 off - unconditionally disable
3547 auto - kernel detects whether your CPU model is
3548 vulnerable to issues that PTI mitigates
3550 Not specifying this option is equivalent to pti=auto.
3553 Equivalent to pti=off
3556 [KNL] Number of legacy pty's. Overwrites compiled-in
3559 quiet [KNL] Disable most log messages
3564 See Documentation/admin-guide/md.rst.
3566 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3567 See Documentation/blockdev/ramdisk.txt.
3569 random.trust_cpu={on,off}
3570 [KNL] Enable or disable trusting the use of the
3571 CPU's random number generator (if available) to
3572 fully seed the kernel's CRNG. Default is controlled
3573 by CONFIG_RANDOM_TRUST_CPU.
3575 ras=option[,option,...] [KNL] RAS-specific options
3578 Disable the Correctable Errors Collector,
3579 see CONFIG_RAS_CEC help text.
3582 The argument is a cpu list, as described above.
3584 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3585 the specified list of CPUs to be no-callback CPUs.
3586 Invocation of these CPUs' RCU callbacks will be
3587 offloaded to "rcuox/N" kthreads created for that
3588 purpose, where "x" is "p" for RCU-preempt, and
3589 "s" for RCU-sched, and "N" is the CPU number.
3590 This reduces OS jitter on the offloaded CPUs,
3591 which can be useful for HPC and real-time
3592 workloads. It can also improve energy efficiency
3593 for asymmetric multiprocessors.
3596 Rather than requiring that offloaded CPUs
3597 (specified by rcu_nocbs= above) explicitly
3598 awaken the corresponding "rcuoN" kthreads,
3599 make these kthreads poll for callbacks.
3600 This improves the real-time response for the
3601 offloaded CPUs by relieving them of the need to
3602 wake up the corresponding kthread, but degrades
3603 energy efficiency by requiring that the kthreads
3604 periodically wake up to do the polling.
3606 rcutree.blimit= [KNL]
3607 Set maximum number of finished RCU callbacks to
3608 process in one batch.
3610 rcutree.dump_tree= [KNL]
3611 Dump the structure of the rcu_node combining tree
3612 out at early boot. This is used for diagnostic
3613 purposes, to verify correct tree setup.
3615 rcutree.gp_cleanup_delay= [KNL]
3616 Set the number of jiffies to delay each step of
3617 RCU grace-period cleanup.
3619 rcutree.gp_init_delay= [KNL]
3620 Set the number of jiffies to delay each step of
3621 RCU grace-period initialization.
3623 rcutree.gp_preinit_delay= [KNL]
3624 Set the number of jiffies to delay each step of
3625 RCU grace-period pre-initialization, that is,
3626 the propagation of recent CPU-hotplug changes up
3627 the rcu_node combining tree.
3629 rcutree.rcu_fanout_exact= [KNL]
3630 Disable autobalancing of the rcu_node combining
3631 tree. This is used by rcutorture, and might
3632 possibly be useful for architectures having high
3633 cache-to-cache transfer latencies.
3635 rcutree.rcu_fanout_leaf= [KNL]
3636 Change the number of CPUs assigned to each
3637 leaf rcu_node structure. Useful for very
3638 large systems, which will choose the value 64,
3639 and for NUMA systems with large remote-access
3640 latencies, which will choose a value aligned
3641 with the appropriate hardware boundaries.
3643 rcutree.jiffies_till_sched_qs= [KNL]
3644 Set required age in jiffies for a
3645 given grace period before RCU starts
3646 soliciting quiescent-state help from
3647 rcu_note_context_switch(). If not specified, the
3648 kernel will calculate a value based on the most
3649 recent settings of rcutree.jiffies_till_first_fqs
3650 and rcutree.jiffies_till_next_fqs.
3651 This calculated value may be viewed in
3652 rcutree.jiffies_to_sched_qs. Any attempt to
3653 set rcutree.jiffies_to_sched_qs will be
3654 cheerfully overwritten.
3656 rcutree.jiffies_till_first_fqs= [KNL]
3657 Set delay from grace-period initialization to
3658 first attempt to force quiescent states.
3659 Units are jiffies, minimum value is zero,
3660 and maximum value is HZ.
3662 rcutree.jiffies_till_next_fqs= [KNL]
3663 Set delay between subsequent attempts to force
3664 quiescent states. Units are jiffies, minimum
3665 value is one, and maximum value is HZ.
3667 rcutree.kthread_prio= [KNL,BOOT]
3668 Set the SCHED_FIFO priority of the RCU per-CPU
3669 kthreads (rcuc/N). This value is also used for
3670 the priority of the RCU boost threads (rcub/N)
3671 and for the RCU grace-period kthreads (rcu_bh,
3672 rcu_preempt, and rcu_sched). If RCU_BOOST is
3673 set, valid values are 1-99 and the default is 1
3674 (the least-favored priority). Otherwise, when
3675 RCU_BOOST is not set, valid values are 0-99 and
3676 the default is zero (non-realtime operation).
3678 rcutree.rcu_nocb_leader_stride= [KNL]
3679 Set the number of NOCB kthread groups, which
3680 defaults to the square root of the number of
3681 CPUs. Larger numbers reduces the wakeup overhead
3682 on the per-CPU grace-period kthreads, but increases
3683 that same overhead on each group's leader.
3685 rcutree.qhimark= [KNL]
3686 Set threshold of queued RCU callbacks beyond which
3687 batch limiting is disabled.
3689 rcutree.qlowmark= [KNL]
3690 Set threshold of queued RCU callbacks below which
3691 batch limiting is re-enabled.
3693 rcutree.rcu_idle_gp_delay= [KNL]
3694 Set wakeup interval for idle CPUs that have
3695 RCU callbacks (RCU_FAST_NO_HZ=y).
3697 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3698 Set wakeup interval for idle CPUs that have
3699 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3700 Lazy RCU callbacks are those which RCU can
3701 prove do nothing more than free memory.
3703 rcutree.rcu_kick_kthreads= [KNL]
3704 Cause the grace-period kthread to get an extra
3705 wake_up() if it sleeps three times longer than
3706 it should at force-quiescent-state time.
3707 This wake_up() will be accompanied by a
3708 WARN_ONCE() splat and an ftrace_dump().
3710 rcuperf.gp_async= [KNL]
3711 Measure performance of asynchronous
3712 grace-period primitives such as call_rcu().
3714 rcuperf.gp_async_max= [KNL]
3715 Specify the maximum number of outstanding
3716 callbacks per writer thread. When a writer
3717 thread exceeds this limit, it invokes the
3718 corresponding flavor of rcu_barrier() to allow
3719 previously posted callbacks to drain.
3721 rcuperf.gp_exp= [KNL]
3722 Measure performance of expedited synchronous
3723 grace-period primitives.
3725 rcuperf.holdoff= [KNL]
3726 Set test-start holdoff period. The purpose of
3727 this parameter is to delay the start of the
3728 test until boot completes in order to avoid
3731 rcuperf.nreaders= [KNL]
3732 Set number of RCU readers. The value -1 selects
3733 N, where N is the number of CPUs. A value
3734 "n" less than -1 selects N-n+1, where N is again
3735 the number of CPUs. For example, -2 selects N
3736 (the number of CPUs), -3 selects N+1, and so on.
3737 A value of "n" less than or equal to -N selects
3740 rcuperf.nwriters= [KNL]
3741 Set number of RCU writers. The values operate
3742 the same as for rcuperf.nreaders.
3743 N, where N is the number of CPUs
3745 rcuperf.perf_type= [KNL]
3746 Specify the RCU implementation to test.
3748 rcuperf.shutdown= [KNL]
3749 Shut the system down after performance tests
3750 complete. This is useful for hands-off automated
3753 rcuperf.verbose= [KNL]
3754 Enable additional printk() statements.
3756 rcuperf.writer_holdoff= [KNL]
3757 Write-side holdoff between grace periods,
3758 in microseconds. The default of zero says
3761 rcutorture.fqs_duration= [KNL]
3762 Set duration of force_quiescent_state bursts
3765 rcutorture.fqs_holdoff= [KNL]
3766 Set holdoff time within force_quiescent_state bursts
3769 rcutorture.fqs_stutter= [KNL]
3770 Set wait time between force_quiescent_state bursts
3773 rcutorture.fwd_progress= [KNL]
3774 Enable RCU grace-period forward-progress testing
3775 for the types of RCU supporting this notion.
3777 rcutorture.fwd_progress_div= [KNL]
3778 Specify the fraction of a CPU-stall-warning
3779 period to do tight-loop forward-progress testing.
3781 rcutorture.fwd_progress_holdoff= [KNL]
3782 Number of seconds to wait between successive
3783 forward-progress tests.
3785 rcutorture.fwd_progress_need_resched= [KNL]
3786 Enclose cond_resched() calls within checks for
3787 need_resched() during tight-loop forward-progress
3790 rcutorture.gp_cond= [KNL]
3791 Use conditional/asynchronous update-side
3792 primitives, if available.
3794 rcutorture.gp_exp= [KNL]
3795 Use expedited update-side primitives, if available.
3797 rcutorture.gp_normal= [KNL]
3798 Use normal (non-expedited) asynchronous
3799 update-side primitives, if available.
3801 rcutorture.gp_sync= [KNL]
3802 Use normal (non-expedited) synchronous
3803 update-side primitives, if available. If all
3804 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3805 rcutorture.gp_normal=, and rcutorture.gp_sync=
3806 are zero, rcutorture acts as if is interpreted
3807 they are all non-zero.
3809 rcutorture.n_barrier_cbs= [KNL]
3810 Set callbacks/threads for rcu_barrier() testing.
3812 rcutorture.nfakewriters= [KNL]
3813 Set number of concurrent RCU writers. These just
3814 stress RCU, they don't participate in the actual
3815 test, hence the "fake".
3817 rcutorture.nreaders= [KNL]
3818 Set number of RCU readers. The value -1 selects
3819 N-1, where N is the number of CPUs. A value
3820 "n" less than -1 selects N-n-2, where N is again
3821 the number of CPUs. For example, -2 selects N
3822 (the number of CPUs), -3 selects N+1, and so on.
3824 rcutorture.object_debug= [KNL]
3825 Enable debug-object double-call_rcu() testing.
3827 rcutorture.onoff_holdoff= [KNL]
3828 Set time (s) after boot for CPU-hotplug testing.
3830 rcutorture.onoff_interval= [KNL]
3831 Set time (jiffies) between CPU-hotplug operations,
3832 or zero to disable CPU-hotplug testing.
3834 rcutorture.shuffle_interval= [KNL]
3835 Set task-shuffle interval (s). Shuffling tasks
3836 allows some CPUs to go into dyntick-idle mode
3837 during the rcutorture test.
3839 rcutorture.shutdown_secs= [KNL]
3840 Set time (s) after boot system shutdown. This
3841 is useful for hands-off automated testing.
3843 rcutorture.stall_cpu= [KNL]
3844 Duration of CPU stall (s) to test RCU CPU stall
3845 warnings, zero to disable.
3847 rcutorture.stall_cpu_holdoff= [KNL]
3848 Time to wait (s) after boot before inducing stall.
3850 rcutorture.stall_cpu_irqsoff= [KNL]
3851 Disable interrupts while stalling if set.
3853 rcutorture.stat_interval= [KNL]
3854 Time (s) between statistics printk()s.
3856 rcutorture.stutter= [KNL]
3857 Time (s) to stutter testing, for example, specifying
3858 five seconds causes the test to run for five seconds,
3859 wait for five seconds, and so on. This tests RCU's
3860 ability to transition abruptly to and from idle.
3862 rcutorture.test_boost= [KNL]
3863 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3864 "Maybe" means test if the RCU implementation
3865 under test support RCU priority boosting.
3867 rcutorture.test_boost_duration= [KNL]
3868 Duration (s) of each individual boost test.
3870 rcutorture.test_boost_interval= [KNL]
3871 Interval (s) between each boost test.
3873 rcutorture.test_no_idle_hz= [KNL]
3874 Test RCU's dyntick-idle handling. See also the
3875 rcutorture.shuffle_interval parameter.
3877 rcutorture.torture_type= [KNL]
3878 Specify the RCU implementation to test.
3880 rcutorture.verbose= [KNL]
3881 Enable additional printk() statements.
3883 rcupdate.rcu_cpu_stall_suppress= [KNL]
3884 Suppress RCU CPU stall warning messages.
3886 rcupdate.rcu_cpu_stall_timeout= [KNL]
3887 Set timeout for RCU CPU stall warning messages.
3889 rcupdate.rcu_expedited= [KNL]
3890 Use expedited grace-period primitives, for
3891 example, synchronize_rcu_expedited() instead
3892 of synchronize_rcu(). This reduces latency,
3893 but can increase CPU utilization, degrade
3894 real-time latency, and degrade energy efficiency.
3895 No effect on CONFIG_TINY_RCU kernels.
3897 rcupdate.rcu_normal= [KNL]
3898 Use only normal grace-period primitives,
3899 for example, synchronize_rcu() instead of
3900 synchronize_rcu_expedited(). This improves
3901 real-time latency, CPU utilization, and
3902 energy efficiency, but can expose users to
3903 increased grace-period latency. This parameter
3904 overrides rcupdate.rcu_expedited. No effect on
3905 CONFIG_TINY_RCU kernels.
3907 rcupdate.rcu_normal_after_boot= [KNL]
3908 Once boot has completed (that is, after
3909 rcu_end_inkernel_boot() has been invoked), use
3910 only normal grace-period primitives. No effect
3911 on CONFIG_TINY_RCU kernels.
3913 rcupdate.rcu_task_stall_timeout= [KNL]
3914 Set timeout in jiffies for RCU task stall warning
3915 messages. Disable with a value less than or equal
3918 rcupdate.rcu_self_test= [KNL]
3919 Run the RCU early boot self tests
3923 Run specified binary instead of /init from the ramdisk,
3924 used for early userspace startup. See initrd.
3927 Turn on/off individual RDT features. List is:
3928 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
3930 E.g. to turn on cmt and turn off mba use:
3934 Format (x86 or x86_64):
3935 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3937 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3939 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3940 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3941 reboot_force is either force or not specified,
3942 reboot_cpu is s[mp]#### with #### being the processor
3943 to be used for rebooting.
3946 [KNL, SMP] Set scheduler's default relax_domain_level.
3947 See Documentation/cgroup-v1/cpusets.txt.
3949 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
3950 Format: <base1>,<size1>[,<base2>,<size2>,...]
3951 Reserve I/O ports or memory so the kernel won't use
3952 them. If <base> is less than 0x10000, the region
3953 is assumed to be I/O ports; otherwise it is memory.
3955 reservetop= [X86-32]
3957 Reserves a hole at the top of the kernel virtual
3962 Set the amount of memory to reserve for BIOS at
3963 the bottom of the address space.
3965 reset_devices [KNL] Force drivers to reset the underlying device
3966 during initialization.
3969 Specify the partition device for software suspend
3971 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3973 resume_offset= [SWSUSP]
3974 Specify the offset from the beginning of the partition
3975 given by "resume=" at which the swap header is located,
3976 in <PAGE_SIZE> units (needed only for swap files).
3977 See Documentation/power/swsusp-and-swap-files.txt
3979 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3980 read the resume files
3982 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3983 Useful for devices that are detected asynchronously
3984 (e.g. USB and MMC devices).
3986 hibernate= [HIBERNATION]
3987 noresume Don't check if there's a hibernation image
3988 present during boot.
3989 nocompress Don't compress/decompress hibernation images.
3990 no Disable hibernation and resume.
3991 protect_image Turn on image protection during restoration
3992 (that will set all pages holding image data
3993 during restoration read-only).
3995 retain_initrd [RAM] Keep initrd memory after extraction
3997 rfkill.default_state=
3998 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3999 etc. communication is blocked by default.
4002 rfkill.master_switch_mode=
4003 0 The "airplane mode" button does nothing.
4004 1 The "airplane mode" button toggles between everything
4005 blocked and the previous configuration.
4006 2 The "airplane mode" button toggles between everything
4007 blocked and everything unblocked.
4009 rhash_entries= [KNL,NET]
4010 Set number of hash buckets for route cache
4013 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
4016 ro [KNL] Mount root device read-only on boot
4019 on Mark read-only kernel memory as read-only (default).
4020 off Leave read-only kernel memory writable for debugging.
4023 Enable the uart passthrough on the designated usb port
4024 on Rockchip SoCs. When active, the signals of the
4025 debug-uart get routed to the D+ and D- pins of the usb
4026 port and the regular usb controller gets disabled.
4028 root= [KNL] Root filesystem
4029 See name_to_dev_t comment in init/do_mounts.c.
4031 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
4032 mount the root filesystem
4034 rootflags= [KNL] Set root filesystem mount option string
4036 rootfstype= [KNL] Set root filesystem type
4038 rootwait [KNL] Wait (indefinitely) for root device to show up.
4039 Useful for devices that are detected asynchronously
4040 (e.g. USB and MMC devices).
4042 rproc_mem=nn[KMG][@address]
4043 [KNL,ARM,CMA] Remoteproc physical memory block.
4044 Memory area to be used by remote processor image,
4047 rw [KNL] Mount root device read-write on boot
4049 S [KNL] Run init in single mode
4051 s390_iommu= [HW,S390]
4052 Set s390 IOTLB flushing mode
4054 With strict flushing every unmap operation will result in
4055 an IOTLB flush. Default is lazy flushing before reuse,
4059 See drivers/net/irda/sa1100_ir.c.
4061 sbni= [NET] Granch SBNI12 leased line adapter
4063 sched_debug [KNL] Enables verbose scheduler debug messages.
4065 schedstats= [KNL,X86] Enable or disable scheduled statistics.
4066 Allowed values are enable and disable. This feature
4067 incurs a small amount of overhead in the scheduler
4068 but is useful for debugging and performance tuning.
4070 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
4071 xtime_lock contention on larger systems, and/or RCU lock
4072 contention on all systems with CONFIG_MAXSMP set.
4073 Format: { "0" | "1" }
4074 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
4076 Note: increases power consumption, thus should only be
4077 enabled if running jitter sensitive (HPC/RT) workloads.
4079 security= [SECURITY] Choose a security module to enable at boot.
4080 If this boot parameter is not specified, only the first
4081 security module asking for security registration will be
4082 loaded. An invalid security module name will be treated
4083 as if no module has been chosen.
4085 selinux= [SELINUX] Disable or enable SELinux at boot time.
4086 Format: { "0" | "1" }
4087 See security/selinux/Kconfig help text.
4090 Default value is set via kernel config option.
4091 If enabled at boot time, /selinux/disable can be used
4092 later to disable prior to initial policy load.
4094 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
4095 Format: { "0" | "1" }
4096 See security/apparmor/Kconfig help text
4099 Default value is set via kernel config option.
4101 serialnumber [BUGS=X86-32]
4104 Maximal number of shapers.
4112 Disable merging of slabs with similar size. May be
4113 necessary if there is some reason to distinguish
4114 allocs to different slabs, especially in hardened
4115 environments where the risk of heap overflows and
4116 layout control by attackers can usually be
4117 frustrated by disabling merging. This will reduce
4118 most of the exposure of a heap attack to a single
4119 cache (risks via metadata attacks are mostly
4120 unchanged). Debug options disable merging on their
4122 For more information see Documentation/vm/slub.rst.
4124 slab_max_order= [MM, SLAB]
4125 Determines the maximum allowed order for slabs.
4126 A high setting may cause OOMs due to memory
4127 fragmentation. Defaults to 1 for systems with
4128 more than 32MB of RAM, 0 otherwise.
4130 slub_debug[=options[,slabs]] [MM, SLUB]
4131 Enabling slub_debug allows one to determine the
4132 culprit if slab objects become corrupted. Enabling
4133 slub_debug can create guard zones around objects and
4134 may poison objects when not in use. Also tracks the
4135 last alloc / free. For more information see
4136 Documentation/vm/slub.rst.
4138 slub_memcg_sysfs= [MM, SLUB]
4139 Determines whether to enable sysfs directories for
4140 memory cgroup sub-caches. 1 to enable, 0 to disable.
4141 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
4142 Enabling this can lead to a very high number of debug
4143 directories and files being created under
4146 slub_max_order= [MM, SLUB]
4147 Determines the maximum allowed order for slabs.
4148 A high setting may cause OOMs due to memory
4149 fragmentation. For more information see
4150 Documentation/vm/slub.rst.
4152 slub_min_objects= [MM, SLUB]
4153 The minimum number of objects per slab. SLUB will
4154 increase the slab order up to slub_max_order to
4155 generate a sufficiently large slab able to contain
4156 the number of objects indicated. The higher the number
4157 of objects the smaller the overhead of tracking slabs
4158 and the less frequently locks need to be acquired.
4159 For more information see Documentation/vm/slub.rst.
4161 slub_min_order= [MM, SLUB]
4162 Determines the minimum page order for slabs. Must be
4163 lower than slub_max_order.
4164 For more information see Documentation/vm/slub.rst.
4166 slub_nomerge [MM, SLUB]
4167 Same with slab_nomerge. This is supported for legacy.
4168 See slab_nomerge for more information.
4171 Format: <io1>[,<io2>[,...,<io8>]]
4173 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4174 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4175 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4176 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4177 smsc-ircc2.ircc_irq= [HW] IRQ line
4178 smsc-ircc2.ircc_dma= [HW] DMA channel
4179 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4180 0: Toshiba Satellite 1800 (GP data pin select)
4181 1: Fast pin select (default)
4184 smt [KNL,S390] Set the maximum number of threads (logical
4185 CPUs) to use per physical CPU on systems capable of
4186 symmetric multithreading (SMT). Will be capped to the
4187 actual hardware limit.
4189 Default: -1 (no limit)
4192 [KNL] Should the soft-lockup detector generate panics.
4195 A nonzero value instructs the soft-lockup detector
4196 to panic the machine when a soft-lockup occurs. This
4197 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
4198 which is the respective build-time switch to that
4201 softlockup_all_cpu_backtrace=
4202 [KNL] Should the soft-lockup detector generate
4203 backtraces on all cpus.
4206 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4207 See Documentation/laptops/sonypi.txt
4209 spectre_v2= [X86] Control mitigation of Spectre variant 2
4210 (indirect branch speculation) vulnerability.
4211 The default operation protects the kernel from
4214 on - unconditionally enable, implies
4216 off - unconditionally disable, implies
4218 auto - kernel detects whether your CPU model is
4221 Selecting 'on' will, and 'auto' may, choose a
4222 mitigation method at run time according to the
4223 CPU, the available microcode, the setting of the
4224 CONFIG_RETPOLINE configuration option, and the
4225 compiler with which the kernel was built.
4227 Selecting 'on' will also enable the mitigation
4228 against user space to user space task attacks.
4230 Selecting 'off' will disable both the kernel and
4231 the user space protections.
4233 Specific mitigations can also be selected manually:
4235 retpoline - replace indirect branches
4236 retpoline,generic - google's original retpoline
4237 retpoline,amd - AMD-specific minimal thunk
4239 Not specifying this option is equivalent to
4243 [X86] Control mitigation of Spectre variant 2
4244 (indirect branch speculation) vulnerability between
4247 on - Unconditionally enable mitigations. Is
4248 enforced by spectre_v2=on
4250 off - Unconditionally disable mitigations. Is
4251 enforced by spectre_v2=off
4253 prctl - Indirect branch speculation is enabled,
4254 but mitigation can be enabled via prctl
4255 per thread. The mitigation control state
4256 is inherited on fork.
4259 - Like "prctl" above, but only STIBP is
4260 controlled per thread. IBPB is issued
4261 always when switching between different user
4265 - Same as "prctl" above, but all seccomp
4266 threads will enable the mitigation unless
4267 they explicitly opt out.
4270 - Like "seccomp" above, but only STIBP is
4271 controlled per thread. IBPB is issued
4272 always when switching between different
4273 user space processes.
4275 auto - Kernel selects the mitigation depending on
4276 the available CPU features and vulnerability.
4279 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
4281 Not specifying this option is equivalent to
4282 spectre_v2_user=auto.
4284 spec_store_bypass_disable=
4285 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4286 (Speculative Store Bypass vulnerability)
4288 Certain CPUs are vulnerable to an exploit against a
4289 a common industry wide performance optimization known
4290 as "Speculative Store Bypass" in which recent stores
4291 to the same memory location may not be observed by
4292 later loads during speculative execution. The idea
4293 is that such stores are unlikely and that they can
4294 be detected prior to instruction retirement at the
4295 end of a particular speculation execution window.
4297 In vulnerable processors, the speculatively forwarded
4298 store can be used in a cache side channel attack, for
4299 example to read memory to which the attacker does not
4300 directly have access (e.g. inside sandboxed code).
4302 This parameter controls whether the Speculative Store
4303 Bypass optimization is used.
4305 On x86 the options are:
4307 on - Unconditionally disable Speculative Store Bypass
4308 off - Unconditionally enable Speculative Store Bypass
4309 auto - Kernel detects whether the CPU model contains an
4310 implementation of Speculative Store Bypass and
4311 picks the most appropriate mitigation. If the
4312 CPU is not vulnerable, "off" is selected. If the
4313 CPU is vulnerable the default mitigation is
4314 architecture and Kconfig dependent. See below.
4315 prctl - Control Speculative Store Bypass per thread
4316 via prctl. Speculative Store Bypass is enabled
4317 for a process by default. The state of the control
4318 is inherited on fork.
4319 seccomp - Same as "prctl" above, but all seccomp threads
4320 will disable SSB unless they explicitly opt out.
4322 Default mitigations:
4323 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4325 On powerpc the options are:
4327 on,auto - On Power8 and Power9 insert a store-forwarding
4328 barrier on kernel entry and exit. On Power7
4329 perform a software flush on kernel entry and
4333 Not specifying this option is equivalent to
4334 spec_store_bypass_disable=auto.
4336 spia_io_base= [HW,MTD]
4341 srcutree.counter_wrap_check [KNL]
4342 Specifies how frequently to check for
4343 grace-period sequence counter wrap for the
4344 srcu_data structure's ->srcu_gp_seq_needed field.
4345 The greater the number of bits set in this kernel
4346 parameter, the less frequently counter wrap will
4347 be checked for. Note that the bottom two bits
4350 srcutree.exp_holdoff [KNL]
4351 Specifies how many nanoseconds must elapse
4352 since the end of the last SRCU grace period for
4353 a given srcu_struct until the next normal SRCU
4354 grace period will be considered for automatic
4355 expediting. Set to zero to disable automatic
4359 Speculative Store Bypass Disable control
4361 On CPUs that are vulnerable to the Speculative
4362 Store Bypass vulnerability and offer a
4363 firmware based mitigation, this parameter
4364 indicates how the mitigation should be used:
4366 force-on: Unconditionally enable mitigation for
4367 for both kernel and userspace
4368 force-off: Unconditionally disable mitigation for
4369 for both kernel and userspace
4370 kernel: Always enable mitigation in the
4371 kernel, and offer a prctl interface
4372 to allow userspace to register its
4373 interest in being mitigated too.
4375 stack_guard_gap= [MM]
4376 override the default stack gap protection. The value
4377 is in page units and it defines how many pages prior
4378 to (for stacks growing down) resp. after (for stacks
4379 growing up) the main stack are reserved for no other
4380 mapping. Default value is 256 pages.
4383 Enabled the stack tracer on boot up.
4385 stacktrace_filter=[function-list]
4386 [FTRACE] Limit the functions that the stack tracer
4387 will trace at boot up. function-list is a comma separated
4388 list of functions. This list can be changed at run
4389 time by the stack_trace_filter file in the debugfs
4390 tracing directory. Note, this enables stack tracing
4391 and the stacktrace above is not needed.
4395 Set the STI (builtin display/keyboard on the HP-PARISC
4396 machines) console (graphic card) which should be used
4397 as the initial boot-console.
4398 See also comment in drivers/video/console/sticore.c.
4401 See comment in drivers/video/console/sticore.c.
4404 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4406 sunrpc.min_resvport=
4407 sunrpc.max_resvport=
4409 SunRPC servers often require that client requests
4410 originate from a privileged port (i.e. a port in the
4411 range 0 < portnr < 1024).
4412 An administrator who wishes to reserve some of these
4413 ports for other uses may adjust the range that the
4414 kernel's sunrpc client considers to be privileged
4415 using these two parameters to set the minimum and
4416 maximum port values.
4418 sunrpc.svc_rpc_per_connection_limit=
4420 Limit the number of requests that the server will
4421 process in parallel from a single connection.
4422 The default value is 0 (no limit).
4426 Control how the NFS server code allocates CPUs to
4427 service thread pools. Depending on how many NICs
4428 you have and where their interrupts are bound, this
4429 option will affect which CPUs will do NFS serving.
4430 Note: this parameter cannot be changed while the
4431 NFS server is running.
4433 auto the server chooses an appropriate mode
4434 automatically using heuristics
4435 global a single global pool contains all CPUs
4436 percpu one pool for each CPU
4437 pernode one pool for each NUMA node (equivalent
4438 to global on non-NUMA machines)
4440 sunrpc.tcp_slot_table_entries=
4441 sunrpc.udp_slot_table_entries=
4443 Sets the upper limit on the number of simultaneous
4444 RPC calls that can be sent from the client to a
4445 server. Increasing these values may allow you to
4446 improve throughput, but will also increase the
4447 amount of memory reserved for use by the client.
4449 suspend.pm_test_delay=
4451 Sets the number of seconds to remain in a suspend test
4452 mode before resuming the system (see
4453 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4454 is set. Default value is 5.
4457 [KNL] Enable accounting of swap in memory resource
4458 controller if no parameter or 1 is given or disable
4459 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4461 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4462 Format: { <int> | force | noforce }
4463 <int> -- Number of I/O TLB slabs
4464 force -- force using of bounce buffers even if they
4465 wouldn't be automatically used by the kernel
4466 noforce -- Never use bounce buffers (for debugging)
4470 sysfs.deprecated=0|1 [KNL]
4471 Enable/disable old style sysfs layout for old udev
4472 on older distributions. When this option is enabled
4473 very new udev will not work anymore. When this option
4474 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4475 in older udev will not work anymore.
4476 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4477 the kernel configuration.
4479 sysrq_always_enabled
4481 Ignore sysrq setting - this boot parameter will
4482 neutralize any effect of /proc/sys/kernel/sysrq.
4483 Useful for debugging.
4485 tcpmhash_entries= [KNL,NET]
4486 Set the number of tcp_metrics_hash slots.
4487 Default value is 8192 or 16384 depending on total
4488 ram pages. This is used to specify the TCP metrics
4489 cache size. See Documentation/networking/ip-sysctl.txt
4490 "tcp_no_metrics_save" section for more details.
4494 test_suspend= [SUSPEND][,N]
4495 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4496 standby suspend) or "freeze" (for suspend type freeze)
4497 as the system sleep state during system startup with
4498 the optional capability to repeat N number of times.
4499 The system is woken from this state using a
4500 wakeup-capable RTC alarm.
4502 thash_entries= [KNL,NET]
4503 Set number of hash buckets for TCP connection
4505 thermal.act= [HW,ACPI]
4506 -1: disable all active trip points in all thermal zones
4507 <degrees C>: override all lowest active trip points
4509 thermal.crt= [HW,ACPI]
4510 -1: disable all critical trip points in all thermal zones
4511 <degrees C>: override all critical trip points
4513 thermal.nocrt= [HW,ACPI]
4514 Set to disable actions on ACPI thermal zone
4515 critical and hot trip points.
4517 thermal.off= [HW,ACPI]
4518 1: disable ACPI thermal control
4520 thermal.psv= [HW,ACPI]
4521 -1: disable all passive trip points
4522 <degrees C>: override all passive trip points to this
4525 thermal.tzp= [HW,ACPI]
4526 Specify global default ACPI thermal zone polling rate
4527 <deci-seconds>: poll all this frequency
4528 0: no polling (default)
4531 Force threading of all interrupt handlers except those
4532 marked explicitly IRQF_NO_THREAD.
4535 Enable the Transcendent memory driver if built-in.
4537 tmem.cleancache=0|1 [KNL, XEN]
4538 Default is on (1). Disable the usage of the cleancache
4539 API to send anonymous pages to the hypervisor.
4541 tmem.frontswap=0|1 [KNL, XEN]
4542 Default is on (1). Disable the usage of the frontswap
4543 API to send swap pages to the hypervisor. If disabled
4544 the selfballooning and selfshrinking are force disabled.
4546 tmem.selfballooning=0|1 [KNL, XEN]
4547 Default is on (1). Disable the driving of swap pages
4550 tmem.selfshrinking=0|1 [KNL, XEN]
4551 Default is on (1). Partial swapoff that immediately
4552 transfers pages from Xen hypervisor back to the
4553 kernel based on different criteria.
4557 Specify if the kernel should make use of the cpu
4558 topology information if the hardware supports this.
4559 The scheduler will make use of this information and
4560 e.g. base its process migration decisions on it.
4563 topology_updates= [KNL, PPC, NUMA]
4565 Specify if the kernel should ignore (off)
4566 topology updates sent by the hypervisor to this
4571 tpm_suspend_pcr=[HW,TPM]
4572 Format: integer pcr id
4573 Specify that at suspend time, the tpm driver
4574 should extend the specified pcr with zeros,
4575 as a workaround for some chips which fail to
4576 flush the last written pcr on TPM_SaveState.
4577 This will guarantee that all the other pcrs
4580 trace_buf_size=nn[KMG]
4581 [FTRACE] will set tracing buffer size on each cpu.
4583 trace_event=[event-list]
4584 [FTRACE] Set and start specified trace events in order
4585 to facilitate early boot debugging. The event-list is a
4586 comma separated list of trace events to enable. See
4587 also Documentation/trace/events.rst
4589 trace_options=[option-list]
4590 [FTRACE] Enable or disable tracer options at boot.
4591 The option-list is a comma delimited list of options
4592 that can be enabled or disabled just as if you were
4593 to echo the option name into
4595 /sys/kernel/debug/tracing/trace_options
4597 For example, to enable stacktrace option (to dump the
4598 stack trace of each event), add to the command line:
4600 trace_options=stacktrace
4602 See also Documentation/trace/ftrace.rst "trace options"
4606 Have the tracepoints sent to printk as well as the
4607 tracing ring buffer. This is useful for early boot up
4608 where the system hangs or reboots and does not give the
4609 option for reading the tracing buffer or performing a
4610 ftrace_dump_on_oops.
4612 To turn off having tracepoints sent to printk,
4613 echo 0 > /proc/sys/kernel/tracepoint_printk
4614 Note, echoing 1 into this file without the
4615 tracepoint_printk kernel cmdline option has no effect.
4619 Having tracepoints sent to printk() and activating high
4620 frequency tracepoints such as irq or sched, can cause
4621 the system to live lock.
4624 [FTRACE] enable this option to disable tracing when a
4625 warning is hit. This turns off "tracing_on". Tracing can
4626 be enabled again by echoing '1' into the "tracing_on"
4627 file located in /sys/kernel/debug/tracing/
4629 This option is useful, as it disables the trace before
4630 the WARNING dump is called, which prevents the trace to
4631 be filled with content caused by the warning output.
4633 This option can also be set at run time via the sysctl
4634 option: kernel/traceoff_on_warning
4636 transparent_hugepage=
4638 Format: [always|madvise|never]
4639 Can be used to control the default behavior of the system
4640 with respect to transparent hugepages.
4641 See Documentation/admin-guide/mm/transhuge.rst
4644 tsc= Disable clocksource stability checks for TSC.
4646 [x86] reliable: mark tsc clocksource as reliable, this
4647 disables clocksource verification at runtime, as well
4648 as the stability checks done at bootup. Used to enable
4649 high-resolution timer mode on older hardware, and in
4650 virtualized environment.
4651 [x86] noirqtime: Do not use TSC to do irq accounting.
4652 Used to run time disable IRQ_TIME_ACCOUNTING on any
4653 platforms where RDTSC is slow and this accounting
4655 [x86] unstable: mark the TSC clocksource as unstable, this
4656 marks the TSC unconditionally unstable at bootup and
4657 avoids any further wobbles once the TSC watchdog notices.
4659 turbografx.map[2|3]= [HW,JOY]
4660 TurboGraFX parallel port interface
4662 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4663 See also Documentation/input/devices/joystick-parport.rst
4665 udbg-immortal [PPC] When debugging early kernel crashes that
4666 happen after console_init() and before a proper
4667 console driver takes over, this boot options might
4668 help "seeing" what's going on.
4670 uhash_entries= [KNL,NET]
4671 Set number of hash buckets for UDP/UDP-Lite connections
4674 [USB] Ignore overcurrent events (default N).
4675 Some badly-designed motherboards generate lots of
4676 bogus events, for ports that aren't wired to
4677 anything. Set this parameter to avoid log spamming.
4678 Note that genuine overcurrent events won't be
4682 [X86] Cause panic on unknown NMI.
4684 usbcore.authorized_default=
4685 [USB] Default USB device authorization:
4686 (default -1 = authorized except for wireless USB,
4687 0 = not authorized, 1 = authorized)
4689 usbcore.autosuspend=
4690 [USB] The autosuspend time delay (in seconds) used
4691 for newly-detected USB devices (default 2). This
4692 is the time required before an idle device will be
4693 autosuspended. Devices for which the delay is set
4694 to a negative value won't be autosuspended at all.
4696 usbcore.usbfs_snoop=
4697 [USB] Set to log all usbfs traffic (default 0 = off).
4699 usbcore.usbfs_snoop_max=
4700 [USB] Maximum number of bytes to snoop in each URB
4703 usbcore.blinkenlights=
4704 [USB] Set to cycle leds on hubs (default 0 = off).
4706 usbcore.old_scheme_first=
4707 [USB] Start with the old device initialization
4708 scheme, applies only to low and full-speed devices
4711 usbcore.usbfs_memory_mb=
4712 [USB] Memory limit (in MB) for buffers allocated by
4713 usbfs (default = 16, 0 = max = 2047).
4715 usbcore.use_both_schemes=
4716 [USB] Try the other device initialization scheme
4717 if the first one fails (default 1 = enabled).
4719 usbcore.initial_descriptor_timeout=
4720 [USB] Specifies timeout for the initial 64-byte
4721 USB_REQ_GET_DESCRIPTOR request in milliseconds
4722 (default 5000 = 5.0 seconds).
4724 usbcore.nousb [USB] Disable the USB subsystem
4727 [USB] A list of quirk entries to augment the built-in
4728 usb core quirk list. List entries are separated by
4729 commas. Each entry has the form
4730 VendorID:ProductID:Flags. The IDs are 4-digit hex
4731 numbers and Flags is a set of letters. Each letter
4732 will change the built-in quirk; setting it if it is
4733 clear and clearing it if it is set. The letters have
4734 the following meanings:
4735 a = USB_QUIRK_STRING_FETCH_255 (string
4736 descriptors must not be fetched using
4738 b = USB_QUIRK_RESET_RESUME (device can't resume
4739 correctly so reset it instead);
4740 c = USB_QUIRK_NO_SET_INTF (device can't handle
4741 Set-Interface requests);
4742 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
4743 handle its Configuration or Interface
4745 e = USB_QUIRK_RESET (device can't be reset
4746 (e.g morph devices), don't use reset);
4747 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
4748 more interface descriptions than the
4749 bNumInterfaces count, and can't handle
4750 talking to these interfaces);
4751 g = USB_QUIRK_DELAY_INIT (device needs a pause
4752 during initialization, after we read
4753 the device descriptor);
4754 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
4755 high speed and super speed interrupt
4756 endpoints, the USB 2.0 and USB 3.0 spec
4757 require the interval in microframes (1
4758 microframe = 125 microseconds) to be
4759 calculated as interval = 2 ^
4761 Devices with this quirk report their
4762 bInterval as the result of this
4763 calculation instead of the exponent
4764 variable used in the calculation);
4765 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
4766 handle device_qualifier descriptor
4768 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
4769 generates spurious wakeup, ignore
4770 remote wakeup capability);
4771 k = USB_QUIRK_NO_LPM (device can't handle Link
4773 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
4774 (Device reports its bInterval as linear
4775 frames instead of the USB 2.0
4777 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
4778 to be disconnected before suspend to
4779 prevent spurious wakeup);
4780 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
4781 pause after every control message);
4782 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
4783 delay after resetting its port);
4784 Example: quirks=0781:5580:bk,0a5c:5834:gij
4787 [USBHID] The interval which mice are to be polled at.
4790 [USBHID] The interval which joysticks are to be polled at.
4793 [USBHID] The interval which keyboards are to be polled at.
4795 usb-storage.delay_use=
4796 [UMS] The delay in seconds before a new device is
4797 scanned for Logical Units (default 1).
4800 [UMS] A list of quirks entries to supplement or
4801 override the built-in unusual_devs list. List
4802 entries are separated by commas. Each entry has
4803 the form VID:PID:Flags where VID and PID are Vendor
4804 and Product ID values (4-digit hex numbers) and
4805 Flags is a set of characters, each corresponding
4806 to a common usb-storage quirk flag as follows:
4807 a = SANE_SENSE (collect more than 18 bytes
4809 b = BAD_SENSE (don't collect more than 18
4810 bytes of sense data);
4811 c = FIX_CAPACITY (decrease the reported
4812 device capacity by one sector);
4813 d = NO_READ_DISC_INFO (don't use
4814 READ_DISC_INFO command);
4815 e = NO_READ_CAPACITY_16 (don't use
4816 READ_CAPACITY_16 command);
4817 f = NO_REPORT_OPCODES (don't use report opcodes
4819 g = MAX_SECTORS_240 (don't transfer more than
4820 240 sectors at a time, uas only);
4821 h = CAPACITY_HEURISTICS (decrease the
4822 reported device capacity by one
4823 sector if the number is odd);
4824 i = IGNORE_DEVICE (don't bind to this
4826 j = NO_REPORT_LUNS (don't use report luns
4828 l = NOT_LOCKABLE (don't try to lock and
4829 unlock ejectable media);
4830 m = MAX_SECTORS_64 (don't transfer more
4831 than 64 sectors = 32 KB at a time);
4832 n = INITIAL_READ10 (force a retry of the
4833 initial READ(10) command);
4834 o = CAPACITY_OK (accept the capacity
4835 reported by the device);
4836 p = WRITE_CACHE (the device cache is ON
4838 r = IGNORE_RESIDUE (the device reports
4839 bogus residue values);
4840 s = SINGLE_LUN (the device has only one
4842 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4843 commands, uas only);
4844 u = IGNORE_UAS (don't bind to the uas driver);
4845 w = NO_WP_DETECT (don't test whether the
4846 medium is write-protected).
4847 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4848 even if the device claims no cache)
4849 Example: quirks=0419:aaf5:rl,0421:0433:rc
4851 user_debug= [KNL,ARM]
4853 See arch/arm/Kconfig.debug help text.
4854 1 - undefined instruction events
4856 4 - invalid data aborts
4859 Example: user_debug=31
4862 [X86] Flags controlling user PTE allocations.
4864 nohigh = do not allocate PTE pages in
4865 HIGHMEM regardless of setting
4869 On X86_32, this is an alias for vdso32=. Otherwise:
4871 vdso=1: enable VDSO (the default)
4872 vdso=0: disable VDSO mapping
4874 vdso32= [X86] Control the 32-bit vDSO
4875 vdso32=1: enable 32-bit VDSO
4876 vdso32=0 or vdso32=2: disable 32-bit VDSO
4878 See the help text for CONFIG_COMPAT_VDSO for more
4879 details. If CONFIG_COMPAT_VDSO is set, the default is
4880 vdso32=0; otherwise, the default is vdso32=1.
4882 For compatibility with older kernels, vdso32=2 is an
4885 Try vdso32=0 if you encounter an error that says:
4886 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4889 vector=percpu: enable percpu vector domain
4891 video= [FB] Frame buffer configuration
4892 See Documentation/fb/modedb.txt.
4894 video.brightness_switch_enabled= [0,1]
4895 If set to 1, on receiving an ACPI notify event
4896 generated by hotkey, video driver will adjust brightness
4897 level and then send out the event to user space through
4898 the allocated input device; If set to 0, video driver
4899 will only send out the event without touching backlight
4904 [VMMIO] Memory mapped virtio (platform) device.
4906 <size>@<baseaddr>:<irq>[:<id>]
4908 <size> := size (can use standard suffixes
4910 <baseaddr> := physical base address
4911 <irq> := interrupt number (as passed to
4913 <id> := (optional) platform device id
4915 virtio_mmio.device=1K@0x100b0000:48:7
4917 Can be used multiple times for multiple devices.
4919 vga= [BOOT,X86-32] Select a particular video mode
4920 See Documentation/x86/boot.txt and
4921 Documentation/svga.txt.
4922 Use vga=ask for menu.
4923 This is actually a boot loader parameter; the value is
4924 passed to the kernel using a special protocol.
4926 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
4927 May slow down system boot speed, especially when
4928 enabled on systems with a large amount of memory.
4929 All options are enabled by default, and this
4930 interface is meant to allow for selectively
4931 enabling or disabling specific virtual memory
4934 Available options are:
4935 P Enable page structure init time poisoning
4936 - Disable all of the above options
4938 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4939 size of <nn>. This can be used to increase the
4940 minimum size (128MB on x86). It can also be used to
4941 decrease the size and leave more room for directly
4944 vmcp_cma=nn[MG] [KNL,S390]
4945 Sets the memory size reserved for contiguous memory
4946 allocations for the vmcp device driver.
4948 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4951 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4954 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4958 Controls the behavior of vsyscalls (i.e. calls to
4959 fixed addresses of 0xffffffffff600x00 from legacy
4960 code). Most statically-linked binaries and older
4961 versions of glibc use these calls. Because these
4962 functions are at fixed addresses, they make nice
4963 targets for exploits that can control RIP.
4965 emulate [default] Vsyscalls turn into traps and are
4966 emulated reasonably safely.
4968 native Vsyscalls are native syscall instructions.
4969 This is a little bit faster than trapping
4970 and makes a few dynamic recompilers work
4971 better than they would in emulation mode.
4972 It also makes exploits much easier to write.
4974 none Vsyscalls don't work at all. This makes
4975 them quite hard to use for exploits but
4976 might break your system.
4978 vt.color= [VT] Default text color.
4979 Format: 0xYX, X = foreground, Y = background.
4980 Default: 0x07 = light gray on black.
4982 vt.cur_default= [VT] Default cursor shape.
4983 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4984 the parameters of the <Esc>[?A;B;Cc escape sequence;
4985 see VGA-softcursor.txt. Default: 2 = underline.
4987 vt.default_blu= [VT]
4988 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4989 Change the default blue palette of the console.
4990 This is a 16-member array composed of values
4993 vt.default_grn= [VT]
4994 Format: <green0>,<green1>,<green2>,...,<green15>
4995 Change the default green palette of the console.
4996 This is a 16-member array composed of values
4999 vt.default_red= [VT]
5000 Format: <red0>,<red1>,<red2>,...,<red15>
5001 Change the default red palette of the console.
5002 This is a 16-member array composed of values
5008 Set system-wide default UTF-8 mode for all tty's.
5009 Default is 1, i.e. UTF-8 mode is enabled for all
5010 newly opened terminals.
5012 vt.global_cursor_default=
5015 Set system-wide default for whether a cursor
5016 is shown on new VTs. Default is -1,
5017 i.e. cursors will be created by default unless
5018 overridden by individual drivers. 0 will hide
5019 cursors, 1 will display them.
5021 vt.italic= [VT] Default color for italic text; 0-15.
5024 vt.underline= [VT] Default color for underlined text; 0-15.
5027 watchdog timers [HW,WDT] For information on watchdog timers,
5028 see Documentation/watchdog/watchdog-parameters.txt
5029 or other driver-specific files in the
5030 Documentation/watchdog/ directory.
5032 workqueue.watchdog_thresh=
5033 If CONFIG_WQ_WATCHDOG is configured, workqueue can
5034 warn stall conditions and dump internal state to
5035 help debugging. 0 disables workqueue stall
5036 detection; otherwise, it's the stall threshold
5037 duration in seconds. The default value is 30 and
5038 it can be updated at runtime by writing to the
5039 corresponding sysfs file.
5041 workqueue.disable_numa
5042 By default, all work items queued to unbound
5043 workqueues are affine to the NUMA nodes they're
5044 issued on, which results in better behavior in
5045 general. If NUMA affinity needs to be disabled for
5046 whatever reason, this option can be used. Note
5047 that this also can be controlled per-workqueue for
5048 workqueues visible under /sys/bus/workqueue/.
5050 workqueue.power_efficient
5051 Per-cpu workqueues are generally preferred because
5052 they show better performance thanks to cache
5053 locality; unfortunately, per-cpu workqueues tend to
5054 be more power hungry than unbound workqueues.
5056 Enabling this makes the per-cpu workqueues which
5057 were observed to contribute significantly to power
5058 consumption unbound, leading to measurably lower
5059 power usage at the cost of small performance
5062 The default value of this parameter is determined by
5063 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
5065 workqueue.debug_force_rr_cpu
5066 Workqueue used to implicitly guarantee that work
5067 items queued without explicit CPU specified are put
5068 on the local CPU. This guarantee is no longer true
5069 and while local CPU is still preferred work items
5070 may be put on foreign CPUs. This debug option
5071 forces round-robin CPU selection to flush out
5072 usages which depend on the now broken guarantee.
5073 When enabled, memory and cache locality will be
5076 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
5077 default x2apic cluster mode on platforms
5080 x86_intel_mid_timer= [X86-32,APBT]
5081 Choose timer option for x86 Intel MID platform.
5082 Two valid options are apbt timer only and lapic timer
5083 plus one apbt timer for broadcast timer.
5084 x86_intel_mid_timer=apbt_only | lapic_and_apbt
5086 xen_512gb_limit [KNL,X86-64,XEN]
5087 Restricts the kernel running paravirtualized under Xen
5088 to use only up to 512 GB of RAM. The reason to do so is
5089 crash analysis tools and Xen tools for doing domain
5090 save/restore/migration must be enabled to handle larger
5093 xen_emul_unplug= [HW,X86,XEN]
5094 Unplug Xen emulated devices
5095 Format: [unplug0,][unplug1]
5096 ide-disks -- unplug primary master IDE devices
5097 aux-ide-disks -- unplug non-primary-master IDE devices
5098 nics -- unplug network devices
5099 all -- unplug all emulated devices (NICs and IDE disks)
5100 unnecessary -- unplugging emulated devices is
5101 unnecessary even if the host did not respond to
5103 never -- do not unplug even if version check succeeds
5105 xen_nopvspin [X86,XEN]
5106 Disables the ticketlock slowpath using Xen PV
5110 Disables the PV optimizations forcing the HVM guest to
5111 run as generic HVM guest with no PV drivers.
5113 xen_scrub_pages= [XEN]
5114 Boolean option to control scrubbing pages before giving them back
5115 to Xen, for use by other domains. Can be also changed at runtime
5116 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
5117 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
5119 xirc2ps_cs= [NET,PCMCIA]
5121 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
5123 xhci-hcd.quirks [USB,KNL]
5124 A hex value specifying bitmask with supplemental xhci
5125 host controller quirks. Meaning of each bit can be
5126 consulted in header drivers/usb/host/xhci.h.
projects / linux-2.6-microblaze.git / blob