1 acpi= [HW,ACPI,X86,ARM64]
2 Advanced Configuration and Power Interface
3 Format: { force | on | off | strict | noirq | rsdt |
5 force -- enable ACPI if default was off
6 on -- enable ACPI but allow fallback to DT [arm64]
7 off -- disable ACPI if default was on
8 noirq -- do not use ACPI for IRQ routing
9 strict -- Be less tolerant of platforms that are not
10 strictly ACPI specification compliant.
11 rsdt -- prefer RSDT over (default) XSDT
12 copy_dsdt -- copy DSDT to memory
13 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"
16 See also Documentation/power/runtime_pm.txt, pci=noacpi
18 acpi_apic_instance= [ACPI, IOAPIC]
20 2: use 2nd APIC table, if available
21 1,0: use 1st APIC table
24 acpi_backlight= [HW,ACPI]
27 If set to vendor, prefer vendor specific driver
28 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
29 of the ACPI video.ko driver.
31 acpi_force_32bit_fadt_addr
32 force FADT to use 32 bit addresses rather than the
33 64 bit X_* addresses. Some firmware have broken 64
34 bit addresses for force ACPI ignore these and use
35 the older legacy 32 bit addresses.
37 acpica_no_return_repair [HW, ACPI]
38 Disable AML predefined validation mechanism
39 This mechanism can repair the evaluation result to make
40 the return objects more ACPI specification compliant.
41 This option is useful for developers to identify the
42 root cause of an AML interpreter issue when the issue
43 has something to do with the repair mechanism.
45 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
46 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
48 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
49 debug output. Bits in debug_layer correspond to a
50 _COMPONENT in an ACPI source file, e.g.,
51 #define _COMPONENT ACPI_PCI_COMPONENT
52 Bits in debug_level correspond to a level in
53 ACPI_DEBUG_PRINT statements, e.g.,
54 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
55 The debug_level mask defaults to "info". See
56 Documentation/acpi/debug.txt for more information about
57 debug layers and levels.
59 Enable processor driver info messages:
60 acpi.debug_layer=0x20000000
61 Enable PCI/PCI interrupt routing info messages:
62 acpi.debug_layer=0x400000
63 Enable AML "Debug" output, i.e., stores to the Debug
64 object while interpreting AML:
65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
66 Enable all messages related to ACPI hardware:
67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
69 Some values produce so much output that the system is
70 unusable. The "log_buf_len" parameter may be useful
71 if you need to capture more output.
73 acpi_enforce_resources= [ACPI]
75 Check for resource conflicts between native drivers
76 and ACPI OperationRegions (SystemIO and SystemMemory
77 only). IO ports and memory declared in ACPI might be
78 used by the ACPI subsystem in arbitrary AML code and
79 can interfere with legacy drivers.
80 strict (default): access to resources claimed by ACPI
81 is denied; legacy drivers trying to access reserved
82 resources will fail to bind to device using them.
83 lax: access to resources claimed by ACPI is allowed;
84 legacy drivers trying to access reserved resources
85 will bind successfully but a warning message is logged.
86 no: ACPI OperationRegions are not marked as reserved,
87 no further checks are performed.
89 acpi_force_table_verification [HW,ACPI]
90 Enable table checksum verification during early stage.
91 By default, this is disabled due to x86 early mapping
94 acpi_irq_balance [HW,ACPI]
95 ACPI will balance active IRQs
98 acpi_irq_nobalance [HW,ACPI]
99 ACPI will not move active IRQs (default)
102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
103 Format: <irq>,<irq>...
105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
107 Format: <irq>,<irq>...
109 acpi_mask_gpe= [HW,ACPI]
110 Due to the existence of _Lxx/_Exx, some GPEs triggered
111 by unsupported hardware/firmware features can result in
112 GPE floodings that cannot be automatically disabled by
114 This facility can be used to prevent such uncontrolled
118 acpi_no_auto_serialize [HW,ACPI]
119 Disable auto-serialization of AML methods
120 AML control methods that contain the opcodes to create
121 named objects will be marked as "Serialized" by the
122 auto-serialization feature.
123 This feature is enabled by default.
124 This option allows to turn off the feature.
126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
129 acpi_no_static_ssdt [HW,ACPI]
130 Disable installation of static SSDTs at early boot time
131 By default, SSDTs contained in the RSDT/XSDT will be
132 installed automatically and they will appear under
133 /sys/firmware/acpi/tables.
134 This option turns off this feature.
135 Note that specifying this option does not affect
136 dynamic table installation which will install SSDT
137 tables to /sys/firmware/acpi/tables/dynamic.
139 acpi_rsdp= [ACPI,EFI,KEXEC]
140 Pass the RSDP address to the kernel, mostly used
141 on machines running EFI runtime service to boot the
142 second kernel for kdump.
144 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
145 Format: To spoof as Windows 98: ="Microsoft Windows"
147 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
148 of 2 which is mandated by ACPI 6) as the supported ACPI
149 specification revision (when using this switch, it may
150 be necessary to carry out a cold reboot _twice_ in a
151 row to make it take effect on the platform firmware).
153 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
154 acpi_osi="string1" # add string1
155 acpi_osi="!string2" # remove string2
156 acpi_osi=!* # remove all strings
157 acpi_osi=! # disable all built-in OS vendor
159 acpi_osi=!! # enable all built-in OS vendor
161 acpi_osi= # disable all strings
163 'acpi_osi=!' can be used in combination with single or
164 multiple 'acpi_osi="string1"' to support specific OS
165 vendor string(s). Note that such command can only
166 affect the default state of the OS vendor strings, thus
167 it cannot affect the default state of the feature group
168 strings and the current state of the OS vendor strings,
169 specifying it multiple times through kernel command line
170 is meaningless. This command is useful when one do not
171 care about the state of the feature group strings which
172 should be controlled by the OSPM.
174 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
175 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
176 can make '_OSI("Windows 2000")' TRUE.
178 'acpi_osi=' cannot be used in combination with other
179 'acpi_osi=' command lines, the _OSI method will not
180 exist in the ACPI namespace. NOTE that such command can
181 only affect the _OSI support state, thus specifying it
182 multiple times through kernel command line is also
185 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
188 'acpi_osi=!*' can be used in combination with single or
189 multiple 'acpi_osi="string1"' to support specific
190 string(s). Note that such command can affect the
191 current state of both the OS vendor strings and the
192 feature group strings, thus specifying it multiple times
193 through kernel command line is meaningful. But it may
194 still not able to affect the final state of a string if
195 there are quirks related to this string. This command
196 is useful when one want to control the state of the
197 feature group strings to debug BIOS issues related to
200 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
201 '_OSI("Module Device")' FALSE.
202 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
203 '_OSI("Module Device")' TRUE.
204 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
206 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
208 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
209 they all will make '_OSI("Windows 2000")' TRUE.
212 Override the pmtimer bug detection: force the kernel
213 to assume that this machine's pmtimer latches its value
214 and always returns good values.
216 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
217 Format: { level | edge | high | low }
219 acpi_skip_timer_override [HW,ACPI]
220 Recognize and ignore IRQ0/pin2 Interrupt Override.
221 For broken nForce2 BIOS resulting in XT-PIC timer.
223 acpi_sleep= [HW,ACPI] Sleep options
224 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
225 old_ordering, nonvs, sci_force_enable, nobl }
226 See Documentation/power/video.txt for information on
228 s3_beep is for debugging; it makes the PC's speaker beep
229 as soon as the kernel's real-mode entry point is called.
230 s4_nohwsig prevents ACPI hardware signature from being
231 used during resume from hibernation.
232 old_ordering causes the ACPI 1.0 ordering of the _PTS
233 control method, with respect to putting devices into
234 low power states, to be enforced (the ACPI 2.0 ordering
235 of _PTS is used by default).
236 nonvs prevents the kernel from saving/restoring the
237 ACPI NVS memory during suspend/hibernation and resume.
238 sci_force_enable causes the kernel to set SCI_EN directly
239 on resume from S1/S3 (which is against the ACPI spec,
240 but some broken systems don't work without it).
241 nobl causes the internal blacklist of systems known to
242 behave incorrectly in some ways with respect to system
243 suspend and resume to be ignored (use wisely).
245 acpi_use_timer_override [HW,ACPI]
246 Use timer override. For some broken Nvidia NF5 boards
247 that require a timer override, but don't have HPET
249 add_efi_memmap [EFI; X86] Include EFI memory map in
250 kernel's map of available physical RAM.
253 { off | try_unsupported }
254 off: disable AGP support
255 try_unsupported: try to drive unsupported chipsets
256 (may crash computer or cause data corruption)
259 See Documentation/sound/alsa-configuration.rst
262 Allow the default userspace alignment fault handler
263 behaviour to be specified. Bit 0 enables warnings,
264 bit 1 enables fixups, and bit 2 sends a segfault.
266 align_va_addr= [X86-64]
267 Align virtual addresses by clearing slice [14:12] when
268 allocating a VMA at process creation time. This option
269 gives you up to 3% performance improvement on AMD F15h
270 machines (where it is enabled by default) for a
271 CPU-intensive style benchmark, and it can vary highly in
272 a microbenchmark depending on workload and compiler.
274 32: only for 32-bit processes
275 64: only for 64-bit processes
276 on: enable for both 32- and 64-bit processes
277 off: disable for both 32- and 64-bit processes
279 alloc_snapshot [FTRACE]
280 Allocate the ftrace snapshot buffer on boot up when the
281 main buffer is allocated. This is handy if debugging
282 and you need to use tracing_snapshot() on boot up, and
283 do not want to use tracing_snapshot_alloc() as it needs
284 to be done where GFP_KERNEL allocations are allowed.
286 amd_iommu= [HW,X86-64]
287 Pass parameters to the AMD IOMMU driver in the system.
289 fullflush - enable flushing of IO/TLB entries when
290 they are unmapped. Otherwise they are
291 flushed before they will be reused, which
293 off - do not initialize any AMD IOMMU found in
295 force_isolation - Force device isolation for all
296 devices. The IOMMU driver is not
297 allowed anymore to lift isolation
298 requirements as needed. This option
299 does not override iommu=pt
301 amd_iommu_dump= [HW,X86-64]
302 Enable AMD IOMMU driver option to dump the ACPI table
303 for AMD IOMMU. With this option enabled, AMD IOMMU
304 driver will print ACPI tables for AMD IOMMU during
305 IOMMU initialization.
307 amd_iommu_intr= [HW,X86-64]
308 Specifies one of the following AMD IOMMU interrupt
310 legacy - Use legacy interrupt remapping mode.
311 vapic - Use virtual APIC mode, which allows IOMMU
312 to inject interrupts directly into guest.
313 This mode requires kvm-amd.avic=1.
314 (Default when IOMMU HW support is present.)
316 amijoy.map= [HW,JOY] Amiga joystick support
317 Map of devices attached to JOY0DAT and JOY1DAT
319 See also Documentation/input/joydev/joystick.rst
321 analog.map= [HW,JOY] Analog joystick and gamepad support
322 Specifies type or capabilities of an analog joystick
323 connected to one of 16 gameports
324 Format: <type1>,<type2>,..<type16>
327 Power management functions (SPARCstation-4/5 + deriv.)
329 Disable APC CPU standby support. SPARCstation-Fox does
330 not play well with APC CPU idle - disable it if you have
331 APC and your system crashes randomly.
333 apic= [APIC,X86] Advanced Programmable Interrupt Controller
334 Change the output verbosity whilst booting
335 Format: { quiet (default) | verbose | debug }
336 Change the amount of debugging information output
337 when initialising the APIC and IO-APIC components.
338 For X86-32, this can also be used to specify an APIC
340 Format: apic=driver_name
341 Examples: apic=bigsmp
343 apic_extnmi= [APIC,X86] External NMI delivery setting
344 Format: { bsp (default) | all | none }
345 bsp: External NMI is delivered only to CPU 0
346 all: External NMIs are broadcast to all CPUs as a
348 none: External NMI is masked for all CPUs. This is
349 useful so that a dump capture kernel won't be
353 See Documentation/networking/ipv6.txt.
355 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
356 Limit apic dumping. The parameter defines the maximal
357 number of local apics being dumped. Also it is possible
358 to set it to "all" by meaning -- no limit here.
359 Format: { 1 (default) | 2 | ... | all }.
360 The parameter valid if only apic=debug or
361 apic=verbose is specified.
362 Example: apic=debug show_lapic=all
364 apm= [APM] Advanced Power Management
365 See header of arch/x86/kernel/apm_32.c.
367 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
368 Format: <io>,<irq>,<nodeID>
372 atarimouse= [HW,MOUSE] Atari Mouse
374 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
375 EzKey and similar keyboards
377 atkbd.reset= [HW] Reset keyboard during initialization
379 atkbd.set= [HW] Select keyboard code set
380 Format: <int> (2 = AT (default), 3 = PS/2)
382 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
385 atkbd.softraw= [HW] Choose between synthetic and real raw mode
386 Format: <bool> (0 = real, 1 = synthetic (default))
388 atkbd.softrepeat= [HW]
389 Use software keyboard repeat
391 audit= [KNL] Enable the audit sub-system
392 Format: { "0" | "1" | "off" | "on" }
393 0 | off - kernel audit is disabled and can not be
394 enabled until the next reboot
395 unset - kernel audit is initialized but disabled and
396 will be fully enabled by the userspace auditd.
397 1 | on - kernel audit is initialized and partially
398 enabled, storing at most audit_backlog_limit
399 messages in RAM until it is fully enabled by the
403 audit_backlog_limit= [KNL] Set the audit queue size limit.
404 Format: <int> (must be >=0)
407 bau= [X86_UV] Enable the BAU on SGI UV. The default
408 behavior is to disable the BAU (i.e. bau=0).
409 Format: { "0" | "1" }
412 unset - Disable the BAU.
414 baycom_epp= [HW,AX25]
417 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
419 See header of drivers/net/hamradio/baycom_par.c.
421 baycom_ser_fdx= [HW,AX25]
422 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
423 Format: <io>,<irq>,<mode>[,<baud>]
424 See header of drivers/net/hamradio/baycom_ser_fdx.c.
426 baycom_ser_hdx= [HW,AX25]
427 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
428 Format: <io>,<irq>,<mode>
429 See header of drivers/net/hamradio/baycom_ser_hdx.c.
431 blkdevparts= Manual partition parsing of block device(s) for
432 embedded devices based on command line input.
433 See Documentation/block/cmdline-partition.txt
435 boot_delay= Milliseconds to delay each printk during boot.
436 Values larger than 10 seconds (10000) are changed to
440 bootmem_debug [KNL] Enable bootmem allocator debug messages.
443 Disable BERT OS support on buggy BIOSes.
445 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
446 bttv.radio= Most important insmod options are available as
448 bttv.pll= See Documentation/media/v4l-drivers/bttv.rst
451 bulk_remove=off [PPC] This parameter disables the use of the pSeries
452 firmware feature for flushing multiple hpte entries
455 c101= [NET] Moxa C101 synchronous serial card
457 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
458 Sometimes CPU hardware bugs make them report the cache
459 size incorrectly. The kernel will attempt work arounds
460 to fix known problems, but for some CPUs it is not
461 possible to determine what the correct size should be.
462 This option provides an override for these situations.
464 ca_keys= [KEYS] This parameter identifies a specific key(s) on
465 the system trusted keyring to be used for certificate
467 format: { id:<keyid> | builtin }
469 cca= [MIPS] Override the kernel pages' cache coherency
470 algorithm. Accepted values range from 0 to 7
471 inclusive. See arch/mips/include/asm/pgtable-bits.h
472 for platform specific values (SB1, Loongson3 and
475 ccw_timeout_log [S390]
476 See Documentation/s390/CommonIO for details.
478 cgroup_disable= [KNL] Disable a particular controller
479 Format: {name of the controller(s) to disable}
480 The effects of cgroup_disable=foo are:
481 - foo isn't auto-mounted if you mount all cgroups in
483 - foo isn't visible as an individually mountable
485 {Currently only "memory" controller deal with this and
486 cut the overhead, others just disable the usage. So
487 only cgroup_disable=memory is actually worthy}
489 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
490 Format: { controller[,controller...] | "all" }
491 Like cgroup_disable, but only applies to cgroup v1;
492 the blacklisted controllers remain available in cgroup2.
494 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
496 nosocket -- Disable socket memory accounting.
497 nokmem -- Disable kernel memory accounting.
499 checkreqprot [SELINUX] Set initial checkreqprot flag value.
500 Format: { "0" | "1" }
501 See security/selinux/Kconfig help text.
502 0 -- check protection applied by kernel (includes
503 any implied execute protection).
504 1 -- check protection requested by application.
505 Default value is set via a kernel config option.
506 Value can be changed at runtime via
507 /selinux/checkreqprot.
510 See Documentation/s390/CommonIO for details.
513 Prevents the clock framework from automatically gating
514 clocks that have not been explicitly enabled by a Linux
515 device driver but are enabled in hardware at reset or
516 by the bootloader/firmware. Note that this does not
517 force such clocks to be always-on nor does it reserve
518 those clocks in any way. This parameter is useful for
519 debug and development, but should not be needed on a
520 platform with proper driver support. For more
521 information, see Documentation/driver-api/clk.rst.
523 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
525 Forces specified clocksource (if available) to be used
526 when calculating gettimeofday(). If specified
527 clocksource is not available, it defaults to PIT.
528 Format: { pit | tsc | cyclone | pmtmr }
530 clocksource= Override the default clocksource
532 Override the default clocksource and use the clocksource
533 with the name specified.
534 Some clocksource names to choose from, depending on
536 [all] jiffies (this is the base, fallback clocksource)
538 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
539 pxa_timer,timer3,32k_counter,timer0_1
540 [X86-32] pit,hpet,tsc;
541 scx200_hrt on Geode; cyclone on IBM x440
549 clocksource.arm_arch_timer.evtstrm=
552 Enable/disable the eventstream feature of the ARM
553 architected timer so that code using WFE-based polling
554 loops can be debugged more effectively on production
557 clearcpuid=BITNUM [X86]
558 Disable CPUID feature X for the kernel. See
559 arch/x86/include/asm/cpufeatures.h for the valid bit
560 numbers. Note the Linux specific bits are not necessarily
561 stable over kernel options, but the vendor specific
563 Also note that user programs calling CPUID directly
564 or using the feature without checking anything
565 will still see it. This just prevents it from
566 being used by the kernel or shown in /proc/cpuinfo.
567 Also note the kernel might malfunction if you disable
570 cma=nn[MG]@[start[MG][-end[MG]]]
572 Sets the size of kernel global memory area for
573 contiguous memory allocations and optionally the
574 placement constraint by the physical address range of
575 memory allocations. A value of 0 disables CMA
576 altogether. For more information, see
577 include/linux/dma-contiguous.h
579 cmo_free_hint= [PPC] Format: { yes | no }
580 Specify whether pages are marked as being inactive
581 when they are freed. This is used in CMO environments
582 to determine OS memory pressure for page stealing by
586 coherent_pool=nn[KMG] [ARM,KNL]
587 Sets the size of memory pool for coherent, atomic dma
588 allocations, by default set to 256K.
590 com20020= [HW,NET] ARCnet - COM20020 chipset
592 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
594 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
598 ARCnet - COM90xx chipset (memory-mapped buffers)
599 Format: <io>[,<irq>[,<memstart>]]
601 condev= [HW,S390] console device
604 console= [KNL] Output console device and options.
606 tty<n> Use the virtual console device <n>.
610 Use the specified serial port. The options are of
611 the form "bbbbpnf", where "bbbb" is the baud rate,
612 "p" is parity ("n", "o", or "e"), "n" is number of
613 bits, and "f" is flow control ("r" for RTS or
614 omit it). Default is "9600n8".
616 See Documentation/admin-guide/serial-console.rst for more
618 Documentation/networking/netconsole.txt for an
621 uart[8250],io,<addr>[,options]
622 uart[8250],mmio,<addr>[,options]
623 uart[8250],mmio16,<addr>[,options]
624 uart[8250],mmio32,<addr>[,options]
625 uart[8250],0x<addr>[,options]
626 Start an early, polled-mode console on the 8250/16550
627 UART at the specified I/O port or MMIO address,
628 switching to the matching ttyS device later.
629 MMIO inter-register address stride is either 8-bit
630 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
631 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
632 to be equivalent to 'mmio'. 'options' are specified in
633 the same format described for ttyS above; if unspecified,
634 the h/w is not re-initialized.
636 hvc<n> Use the hypervisor console device <n>. This is for
637 both Xen and PowerPC hypervisors.
639 If the device connected to the port is not a TTY but a braille
640 device, prepend "brl," before the device type, for instance
642 For now, only VisioBraille is supported.
645 [KNL] Change console messages format
647 By default we print messages on consoles in
648 "[time stamp] text\n" format (time stamp may not be
649 printed, depending on CONFIG_PRINTK_TIME or
650 `printk_time' param).
652 Switch to syslog format: "<%u>[time stamp] text\n"
653 IOW, each message will have a facility and loglevel
654 prefix. The format is similar to one used by syslog()
655 syscall, or to executing "dmesg -S --raw" or to reading
658 consoleblank= [KNL] The console blank (screen saver) timeout in
659 seconds. A value of 0 disables the blank timer.
663 [KNL] Change the default value for
664 /proc/<pid>/coredump_filter.
665 See also Documentation/filesystems/proc.txt.
667 coresight_cpu_debug.enable
670 Enable/disable the CPU sampling based debugging.
671 0: default value, disable debugging
672 1: enable debugging at boot time
674 cpuidle.off=1 [CPU_IDLE]
675 disable the cpuidle sub-system
677 cpufreq.off=1 [CPU_FREQ]
678 disable the cpufreq sub-system
681 [X86] Delay for N microsec between assert and de-assert
682 of APIC INIT to start processors. This delay occurs
683 on every CPU online, such as boot, and resume from suspend.
686 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
688 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
690 crashkernel=size[KMG][@offset[KMG]]
691 [KNL] Using kexec, Linux can switch to a 'crash kernel'
692 upon panic. This parameter reserves the physical
693 memory region [offset, offset + size] for that kernel
694 image. If '@offset' is omitted, then a suitable offset
695 is selected automatically. Check
696 Documentation/kdump/kdump.txt for further details.
698 crashkernel=range1:size1[,range2:size2,...][@offset]
699 [KNL] Same as above, but depends on the memory
700 in the running system. The syntax of range is
701 start-[end] where start and end are both
702 a memory unit (amount[KMG]). See also
703 Documentation/kdump/kdump.txt for an example.
705 crashkernel=size[KMG],high
706 [KNL, x86_64] range could be above 4G. Allow kernel
707 to allocate physical memory region from top, so could
708 be above 4G if system have more than 4G ram installed.
709 Otherwise memory region will be allocated below 4G, if
711 It will be ignored if crashkernel=X is specified.
712 crashkernel=size[KMG],low
713 [KNL, x86_64] range under 4G. When crashkernel=X,high
714 is passed, kernel could allocate physical memory region
715 above 4G, that cause second kernel crash on system
716 that require some amount of low memory, e.g. swiotlb
717 requires at least 64M+32K low memory, also enough extra
718 low memory is needed to make sure DMA buffers for 32-bit
719 devices won't run out. Kernel would try to allocate at
720 at least 256M below 4G automatically.
721 This one let user to specify own low range under 4G
722 for second kernel instead.
723 0: to disable low allocation.
724 It will be ignored when crashkernel=X,high is not used
725 or memory reserved is below 4G.
728 [KNL] Disable crypto self-tests
733 cs89x0_media= [HW,NET]
734 Format: { rj45 | aui | bnc }
737 See header of drivers/s390/block/dasd_devmap.c.
739 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
740 (one device per port)
741 Format: <port#>,<type>
742 See also Documentation/input/devices/joystick-parport.rst
744 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
746 Documentation/admin-guide/dynamic-debug-howto.rst for
747 details. Deprecated, see dyndbg.
749 debug [KNL] Enable kernel debugging (events log level).
752 [KNL] Enable printing [hashed] pointers early in the
753 boot sequence. If enabled, we use a weak hash instead
754 of siphash to hash pointers. Use this option if you are
755 seeing instances of '(___ptrval___)') and need to see a
756 value (hashed pointer) instead. Cryptographically
757 insecure, please do not use on production kernels.
760 [KNL] verbose self-tests
762 Print debugging info while doing the locking API
764 We default to 0 (no extra messages), setting it to
765 1 will print _a lot_ more information - normally
766 only useful to kernel developers.
768 debug_objects [KNL] Enable object debugging
771 [KNL] Disable object debugging
773 debug_guardpage_minorder=
774 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
775 parameter allows control of the order of pages that will
776 be intentionally kept free (and hence protected) by the
777 buddy allocator. Bigger value increase the probability
778 of catching random memory corruption, but reduce the
779 amount of memory for normal system use. The maximum
780 possible value is MAX_ORDER/2. Setting this parameter
781 to 1 or 2 should be enough to identify most random
782 memory corruption problems caused by bugs in kernel or
783 driver code when a CPU writes to (or reads from) a
784 random memory location. Note that there exists a class
785 of memory corruptions problems caused by buggy H/W or
786 F/W or by drivers badly programing DMA (basically when
787 memory is written at bus level and the CPU MMU is
788 bypassed) which are not detectable by
789 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
790 tracking down these problems.
793 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
794 parameter enables the feature at boot time. In
795 default, it is disabled. We can avoid allocating huge
796 chunk of memory for debug pagealloc if we don't enable
797 it at boot time and the system will work mostly same
798 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
799 on: enable the feature
801 debugpat [X86] Enable PAT debugging
803 decnet.addr= [HW,NET]
804 Format: <area>[,<node>]
805 See also Documentation/networking/decnet.txt.
808 [same as hugepagesz=] The size of the default
809 HugeTLB page size. This is the size represented by
810 the legacy /proc/ hugepages APIs, used for SHM, and
811 default size when mounting hugetlbfs filesystems.
812 Defaults to the default architecture's huge page size
815 deferred_probe_timeout=
816 [KNL] Debugging option to set a timeout in seconds for
817 deferred probe to give up waiting on dependencies to
818 probe. Only specific dependencies (subsystems or
819 drivers) that have opted in will be ignored. A timeout of 0
820 will timeout at the end of initcalls. This option will also
821 dump out devices still on the deferred probe list after
825 Set number of hash buckets for dentry cache.
827 disable_1tb_segments [PPC]
828 Disables the use of 1TB hash page table segments. This
829 causes the kernel to fall back to 256MB segments which
830 can be useful when debugging issues that require an SLB
834 See Documentation/networking/ipv6.txt.
837 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
838 hardening is enabled for this boot. Hardened
839 usercopy checking is used to protect the kernel
840 from reading or writing beyond known memory
841 allocation boundaries as a proactive defense
842 against bounds-checking flaws in the kernel's
843 copy_to_user()/copy_from_user() interface.
844 on Perform hardened usercopy checks (default).
845 off Disable hardened usercopy checks.
848 Disable RADIX MMU mode on POWER9
850 disable_cpu_apicid= [X86,APIC,SMP]
852 The number of initial APIC ID for the
853 corresponding CPU to be disabled at boot,
854 mostly used for the kdump 2nd kernel to
855 disable BSP to wake up multiple CPUs without
856 causing system reset or hang due to sending
859 disable_counter_freezing [HW]
860 Disable Intel PMU counter freezing feature.
861 The feature only exists starting from
862 Arch Perfmon v4 (Skylake and newer).
864 disable_ddw [PPC/PSERIES]
865 Disable Dynamic DMA Window support. Use this if
866 to workaround buggy firmware.
869 See Documentation/networking/ipv6.txt.
871 disable_mtrr_cleanup [X86]
872 The kernel tries to adjust MTRR layout from continuous
873 to discrete, to make X server driver able to add WB
874 entry later. This parameter disables that.
876 disable_mtrr_trim [X86, Intel and AMD only]
877 By default the kernel will trim any uncacheable
878 memory out of your available memory pool based on
879 MTRR settings. This parameter disables that behavior,
880 possibly causing your machine to run very slowly.
882 disable_timer_pin_1 [X86]
883 Disable PIN 1 of APIC timer
884 Can be useful to work around chipset bugs.
886 dis_ucode_ldr [X86] Disable the microcode loader.
888 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
889 this option disables the debugging code at boot.
891 dma_debug_entries=<number>
892 This option allows to tune the number of preallocated
893 entries for DMA-API debugging code. One entry is
894 required per DMA-API allocation. Use this if the
895 DMA-API debugging code disables itself because the
896 architectural default is too low.
898 dma_debug_driver=<driver_name>
899 With this option the DMA-API debugging driver
900 filter feature can be enabled at boot time. Just
901 pass the driver to filter for as the parameter.
902 The filter can be disabled or changed to another
903 driver later using sysfs.
905 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
906 Broken monitors, graphic adapters, KVMs and EDIDless
907 panels may send no or incorrect EDID data sets.
908 This parameter allows to specify an EDID data sets
909 in the /lib/firmware directory that are used instead.
910 Generic built-in EDID data sets are used, if one of
911 edid/1024x768.bin, edid/1280x1024.bin,
912 edid/1680x1050.bin, or edid/1920x1080.bin is given
913 and no file with the same name exists. Details and
914 instructions how to build your own EDID data are
915 available in Documentation/EDID/HOWTO.txt. An EDID
916 data set will only be used for a particular connector,
917 if its name and a colon are prepended to the EDID
918 name. Each connector may use a unique EDID data
919 set by separating the files with a comma. An EDID
920 data set with no connector name will be used for
921 any connectors not explicitly specified.
926 Format: {"off" | "known"}
927 Control how the dt_cpu_ftrs device-tree binding is
928 used for CPU feature discovery and setup (if it
930 off: Do not use it, fall back to legacy cpu table.
931 known: Do not pass through unknown features to guests
932 or userspace, only those that the kernel is aware of.
934 dump_apple_properties [X86]
935 Dump name and content of EFI device properties on
936 x86 Macs. Useful for driver authors to determine
937 what data is available or for reverse-engineering.
939 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
940 module.dyndbg[="val"]
941 Enable debug messages at boot time. See
942 Documentation/admin-guide/dynamic-debug-howto.rst
945 nompx [X86] Disables Intel Memory Protection Extensions.
946 See Documentation/x86/intel_mpx.txt for more
947 information about the feature.
949 nopku [X86] Disable Memory Protection Keys CPU feature found
952 module.async_probe [KNL]
953 Enable asynchronous probe on this module.
955 early_ioremap_debug [KNL]
956 Enable debug messages in early_ioremap support. This
957 is useful for tracking down temporary early mappings
958 which are not unmapped.
960 earlycon= [KNL] Output early console device and options.
962 [ARM64] The early console is determined by the
963 stdout-path property in device tree's chosen node,
964 or determined by the ACPI SPCR table.
966 [X86] When used with no options the early console is
967 determined by the ACPI SPCR table.
969 cdns,<addr>[,options]
970 Start an early, polled-mode console on a Cadence
971 (xuartps) serial port at the specified address. Only
972 supported option is baud rate. If baud rate is not
973 specified, the serial port must already be setup and
976 uart[8250],io,<addr>[,options]
977 uart[8250],mmio,<addr>[,options]
978 uart[8250],mmio32,<addr>[,options]
979 uart[8250],mmio32be,<addr>[,options]
980 uart[8250],0x<addr>[,options]
981 Start an early, polled-mode console on the 8250/16550
982 UART at the specified I/O port or MMIO address.
983 MMIO inter-register address stride is either 8-bit
984 (mmio) or 32-bit (mmio32 or mmio32be).
985 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
986 to be equivalent to 'mmio'. 'options' are specified
987 in the same format described for "console=ttyS<n>"; if
988 unspecified, the h/w is not initialized.
992 Start an early, polled-mode console on a pl011 serial
993 port at the specified address. The pl011 serial port
994 must already be setup and configured. Options are not
995 yet supported. If 'mmio32' is specified, then only
996 the driver will use only 32-bit accessors to read/write
997 the device registers.
1000 Start an early, polled-mode console on a meson serial
1001 port at the specified address. The serial port must
1002 already be setup and configured. Options are not yet
1006 Start an early, polled-mode console on an msm serial
1007 port at the specified address. The serial port
1008 must already be setup and configured. Options are not
1011 msm_serial_dm,<addr>
1012 Start an early, polled-mode console on an msm serial
1013 dm port at the specified address. The serial port
1014 must already be setup and configured. Options are not
1018 Start an early, polled-mode console on a serial port
1019 of an Actions Semi SoC, such as S500 or S900, at the
1020 specified address. The serial port must already be
1021 setup and configured. Options are not yet supported.
1023 smh Use ARM semihosting calls for early console.
1031 Use early console provided by serial driver available
1032 on Samsung SoCs, requires selecting proper type and
1033 a correct base address of the selected UART port. The
1034 serial port must already be setup and configured.
1035 Options are not yet supported.
1038 Start an early, polled-mode console on a lantiq serial
1039 (lqasc) port at the specified address. The serial port
1040 must already be setup and configured. Options are not
1045 Use early console provided by Freescale LP UART driver
1046 found on Freescale Vybrid and QorIQ LS1021A processors.
1047 A valid base address must be provided, and the serial
1048 port must already be setup and configured.
1051 Start an early, polled-mode console on the
1052 Armada 3700 serial port at the specified
1053 address. The serial port must already be setup
1054 and configured. Options are not yet supported.
1057 Start an early, polled-mode console on a Qualcomm
1058 Generic Interface (GENI) based serial port at the
1059 specified address. The serial port must already be
1060 setup and configured. Options are not yet supported.
1062 earlyprintk= [X86,SH,ARM,M68k,S390]
1067 earlyprintk=serial[,ttySn[,baudrate]]
1068 earlyprintk=serial[,0x...[,baudrate]]
1069 earlyprintk=ttySn[,baudrate]
1070 earlyprintk=dbgp[debugController#]
1071 earlyprintk=pciserial,bus:device.function[,baudrate]
1072 earlyprintk=xdbc[xhciController#]
1074 earlyprintk is useful when the kernel crashes before
1075 the normal console is initialized. It is not enabled by
1076 default because it has some cosmetic problems.
1078 Append ",keep" to not disable it when the real console
1081 Only one of vga, efi, serial, or usb debug port can
1084 Currently only ttyS0 and ttyS1 may be specified by
1085 name. Other I/O ports may be explicitly specified
1086 on some architectures (x86 and arm at least) by
1087 replacing ttySn with an I/O port address, like this:
1088 earlyprintk=serial,0x1008,115200
1089 You can find the port for a given device in
1090 /proc/tty/driver/serial:
1091 2: uart:ST16650V2 port:00001008 irq:18 ...
1093 Interaction with the standard serial driver is not
1096 The VGA and EFI output is eventually overwritten by
1099 The xen output can only be used by Xen PV guests.
1101 The sclp output can only be used on s390.
1103 edac_report= [HW,EDAC] Control how to report EDAC event
1104 Format: {"on" | "off" | "force"}
1105 on: enable EDAC to report H/W event. May be overridden
1106 by other higher priority error reporting module.
1107 off: disable H/W event reporting through EDAC.
1108 force: enforce the use of EDAC to report H/W event.
1111 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1114 This is designed to be used in conjunction with
1115 the boot argument: earlyprintk=vga
1118 Format: {"off" | "on" | "skip[mbr]"}
1121 Format: { "old_map", "nochunk", "noruntime", "debug" }
1122 old_map [X86-64]: switch to the old ioremap-based EFI
1123 runtime services mapping. 32-bit still uses this one by
1125 nochunk: disable reading files in "chunks" in the EFI
1126 boot stub, as chunking can cause problems with some
1127 firmware implementations.
1128 noruntime : disable EFI runtime services support
1129 debug: enable misc debug output
1131 efi_no_storage_paranoia [EFI; X86]
1132 Using this parameter you can use more than 50% of
1133 your efi variable storage. Use this parameter only if
1134 you are really sure that your UEFI does sane gc and
1135 fulfills the spec otherwise your board may brick.
1137 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1138 Add arbitrary attribute to specific memory range by
1139 updating original EFI memory map.
1140 Region of memory which aa attribute is added to is
1142 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1143 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1144 attribute is added to range 0x100000000-0x180000000 and
1145 0x10a0000000-0x1120000000.
1147 Using this parameter you can do debugging of EFI memmap
1148 related feature. For example, you can do debugging of
1149 Address Range Mirroring feature even if your box
1152 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1153 that is to be dynamically loaded by Linux. If there are
1154 multiple variables with the same name but with different
1155 vendor GUIDs, all of them will be loaded. See
1156 Documentation/acpi/ssdt-overlays.txt for details.
1159 eisa_irq_edge= [PARISC,HW]
1160 See header of drivers/parisc/eisa.c.
1163 See comment before function elanfreq_setup() in
1164 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1167 Format: {"cfq" | "deadline" | "noop"}
1168 See Documentation/block/cfq-iosched.txt and
1169 Documentation/block/deadline-iosched.txt for details.
1171 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1172 Specifies physical address of start of kernel core
1173 image elf header and optionally the size. Generally
1174 kexec loader will pass this option to capture kernel.
1175 See Documentation/kdump/kdump.txt for details.
1177 enable_mtrr_cleanup [X86]
1178 The kernel tries to adjust MTRR layout from continuous
1179 to discrete, to make X server driver able to add WB
1180 entry later. This parameter enables that.
1182 enable_timer_pin_1 [X86]
1183 Enable PIN 1 of APIC timer
1184 Can be useful to work around chipset bugs
1185 (in particular on some ATI chipsets).
1186 The kernel tries to set a reasonable default.
1188 enforcing [SELINUX] Set initial enforcing status.
1190 See security/selinux/Kconfig help text.
1191 0 -- permissive (log only, no denials).
1192 1 -- enforcing (deny and log).
1194 Value can be changed at runtime via /selinux/enforce.
1197 Disable Error Record Serialization Table (ERST)
1200 ether= [HW,NET] Ethernet cards parameters
1201 This option is obsoleted by the "netdev=" option, which
1202 has equivalent usage. See its documentation for details.
1206 Permit 'security.evm' to be updated regardless of
1207 current integrity status.
1211 fail_make_request=[KNL]
1212 General fault injection mechanism.
1213 Format: <interval>,<probability>,<space>,<times>
1214 See also Documentation/fault-injection/.
1217 See Documentation/blockdev/floppy.txt.
1219 force_pal_cache_flush
1220 [IA-64] Avoid check_sal_cache_flush which may hang on
1221 buggy SAL_CACHE_FLUSH implementations. Using this
1222 parameter will force ia64_sal_cache_flush to call
1223 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1226 Forcefully enable Physical Address Extension (PAE).
1227 Many Pentium M systems disable PAE but may have a
1228 functionally usable PAE implementation.
1229 Warning: use of this parameter will taint the kernel
1230 and may cause unknown problems.
1233 [FTRACE] will set and start the specified tracer
1234 as early as possible in order to facilitate early
1237 ftrace_dump_on_oops[=orig_cpu]
1238 [FTRACE] will dump the trace buffers on oops.
1239 If no parameter is passed, ftrace will dump
1240 buffers of all CPUs, but if you pass orig_cpu, it will
1241 dump only the buffer of the CPU that triggered the
1244 ftrace_filter=[function-list]
1245 [FTRACE] Limit the functions traced by the function
1246 tracer at boot up. function-list is a comma separated
1247 list of functions. This list can be changed at run
1248 time by the set_ftrace_filter file in the debugfs
1251 ftrace_notrace=[function-list]
1252 [FTRACE] Do not trace the functions specified in
1253 function-list. This list can be changed at run time
1254 by the set_ftrace_notrace file in the debugfs
1257 ftrace_graph_filter=[function-list]
1258 [FTRACE] Limit the top level callers functions traced
1259 by the function graph tracer at boot up.
1260 function-list is a comma separated list of functions
1261 that can be changed at run time by the
1262 set_graph_function file in the debugfs tracing directory.
1264 ftrace_graph_notrace=[function-list]
1265 [FTRACE] Do not trace from the functions specified in
1266 function-list. This list is a comma separated list of
1267 functions that can be changed at run time by the
1268 set_graph_notrace file in the debugfs tracing directory.
1270 ftrace_graph_max_depth=<uint>
1271 [FTRACE] Used with the function graph tracer. This is
1272 the max depth it will trace into a function. This value
1273 can be changed at run time by the max_graph_depth file
1274 in the tracefs tracing directory. default: 0 (no limit)
1277 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1278 support via parallel port (up to 5 devices per port)
1279 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1280 See also Documentation/input/devices/joystick-parport.rst
1284 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1288 gcov_persist= [GCOV] When non-zero (default), profiling data for
1289 kernel modules is saved and remains accessible via
1290 debugfs, even when the module is unloaded/reloaded.
1291 When zero, profiling data is discarded and associated
1292 debugfs files are removed at module unload time.
1294 goldfish [X86] Enable the goldfish android emulator platform.
1295 Don't use this when you are not running on the
1298 gpt [EFI] Forces disk with valid GPT signature but
1299 invalid Protective MBR to be treated as GPT. If the
1300 primary GPT is corrupted, it enables the backup/alternate
1301 GPT to be used instead.
1303 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1304 the "Enable 0" bit of the configuration register.
1307 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1308 the "Enable 0" bit of the configuration register.
1311 grcan.select= [HW] Select which physical interface to use.
1314 grcan.txsize= [HW] Sets the size of the tx buffer.
1315 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1317 grcan.rxsize= [HW] Sets the size of the rx buffer.
1318 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1321 gpio-mockup.gpio_mockup_ranges
1322 [HW] Sets the ranges of gpiochip of for this device.
1323 Format: <start1>,<end1>,<start2>,<end2>...
1325 hardlockup_all_cpu_backtrace=
1326 [KNL] Should the hard-lockup detector generate
1327 backtraces on all cpus.
1330 hashdist= [KNL,NUMA] Large hashes allocated during boot
1331 are distributed across NUMA nodes. Defaults on
1332 for 64-bit NUMA, off otherwise.
1333 Format: 0 | 1 (for off | on)
1335 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1337 hd= [EIDE] (E)IDE hard drive subsystem geometry
1338 Format: <cyl>,<head>,<sect>
1341 Disable Hardware Error Source Table (HEST) support;
1342 corresponding firmware-first mode error processing
1343 logic will be disabled.
1345 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1346 size of <nn>. This works even on boxes that have no
1347 highmem otherwise. This also works to reduce highmem
1348 size on bigger boxes.
1350 highres= [KNL] Enable/disable high resolution timer mode.
1351 Valid parameters: "on", "off"
1355 See Documentation/isdn/README.HiSax.
1359 hpet= [X86-32,HPET] option to control HPET usage
1360 Format: { enable (default) | disable | force |
1362 disable: disable HPET and use PIT instead
1363 force: allow force enabled of undocumented chips (ICH4,
1365 verbose: show contents of HPET registers during setup
1367 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1368 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1370 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1371 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1372 On x86-64 and powerpc, this option can be specified
1373 multiple times interleaved with hugepages= to reserve
1374 huge pages of different sizes. Valid pages sizes on
1375 x86-64 are 2M (when the CPU supports "pse") and 1G
1376 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1379 [KNL] Should the hung task detector generate panics.
1382 A nonzero value instructs the kernel to panic when a
1383 hung task is detected. The default value is controlled
1384 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1385 option. The value selected by this boot parameter can
1386 be changed later by the kernel.hung_task_panic sysctl.
1388 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1389 terminal devices. Valid values: 0..8
1390 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1391 If specified, z/VM IUCV HVC accepts connections
1392 from listed z/VM user IDs only.
1394 Do not unregister boot console at start. This is only
1395 useful for debugging when something happens in the window
1396 between unregistering the boot console and initializing
1399 i2c_bus= [HW] Override the default board specific I2C bus speed
1400 or register an additional I2C bus that is not
1401 registered from board initialization code.
1405 i8042.debug [HW] Toggle i8042 debug mode
1406 i8042.unmask_kbd_data
1407 [HW] Enable printing of interrupt data from the KBD port
1408 (disabled by default, and as a pre-condition
1409 requires that i8042.debug=1 be enabled)
1410 i8042.direct [HW] Put keyboard port into non-translated mode
1411 i8042.dumbkbd [HW] Pretend that controller can only read data from
1412 keyboard and cannot control its state
1413 (Don't attempt to blink the leds)
1414 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1415 i8042.nokbd [HW] Don't check/create keyboard port
1416 i8042.noloop [HW] Disable the AUX Loopback command while probing
1418 i8042.nomux [HW] Don't check presence of an active multiplexing
1420 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1422 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1423 i8042.reset [HW] Reset the controller during init, cleanup and
1424 suspend-to-ram transitions, only during s2r
1425 transitions, or never reset
1426 Format: { 1 | Y | y | 0 | N | n }
1427 1, Y, y: always reset controller
1428 0, N, n: don't ever reset controller
1429 Default: only on s2r transitions on x86; most other
1430 architectures force reset to be always executed
1431 i8042.unlock [HW] Unlock (ignore) the keylock
1432 i8042.kbdreset [HW] Reset device connected to KBD port
1436 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1437 indicates that the driver is running on unsupported
1439 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1440 does not match list of supported models.
1442 [HW] Report power status in /proc/i8k
1443 (disabled by default)
1444 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1447 i915.invert_brightness=
1448 [DRM] Invert the sense of the variable that is used to
1449 set the brightness of the panel backlight. Normally a
1450 brightness value of 0 indicates backlight switched off,
1451 and the maximum of the brightness value sets the backlight
1452 to maximum brightness. If this parameter is set to 0
1453 (default) and the machine requires it, or this parameter
1454 is set to 1, a brightness value of 0 sets the backlight
1455 to maximum brightness, and the maximum of the brightness
1456 value switches the backlight off.
1457 -1 -- never invert brightness
1458 0 -- machine default
1459 1 -- force brightness inversion
1462 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1464 ide-core.nodma= [HW] (E)IDE subsystem
1465 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1466 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1467 .cdrom .chs .ignore_cable are additional options
1468 See Documentation/ide/ide.txt.
1470 ide-generic.probe-mask= [HW] (E)IDE subsystem
1472 Probe mask for legacy ISA IDE ports. Depending on
1473 platform up to 6 ports are supported, enabled by
1474 setting corresponding bits in the mask to 1. The
1475 default value is 0x0, which has a special meaning.
1476 On systems that have PCI, it triggers scanning the
1477 PCI bus for the first and the second port, which
1478 are then probed. On systems without PCI the value
1479 of 0x0 enables probing the two first ports as if it
1482 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1483 Claim all unknown PCI IDE storage controllers.
1486 Format: idle=poll, idle=halt, idle=nomwait
1487 Poll forces a polling idle loop that can slightly
1488 improve the performance of waking up a idle CPU, but
1489 will use a lot of power and make the system run hot.
1491 idle=halt: Halt is forced to be used for CPU idle.
1492 In such case C2/C3 won't be used again.
1493 idle=nomwait: Disable mwait for CPU C-states
1495 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1496 Format: { strict | legacy | 2008 | relaxed }
1499 Choose which programs will be accepted for execution
1500 based on the IEEE 754 NaN encoding(s) supported by
1501 the FPU and the NaN encoding requested with the value
1502 of an ELF file header flag individually set by each
1503 binary. Hardware implementations are permitted to
1504 support either or both of the legacy and the 2008 NaN
1507 Available settings are as follows:
1508 strict accept binaries that request a NaN encoding
1509 supported by the FPU
1510 legacy only accept legacy-NaN binaries, if supported
1512 2008 only accept 2008-NaN binaries, if supported
1514 relaxed accept any binaries regardless of whether
1515 supported by the FPU
1517 The FPU emulator is always able to support both NaN
1518 encodings, so if no FPU hardware is present or it has
1519 been disabled with 'nofpu', then the settings of
1520 'legacy' and '2008' strap the emulator accordingly,
1521 'relaxed' straps the emulator for both legacy-NaN and
1522 2008-NaN, whereas 'strict' enables legacy-NaN only on
1523 legacy processors and both NaN encodings on MIPS32 or
1526 The setting for ABS.fmt/NEG.fmt instruction execution
1527 mode generally follows that for the NaN encoding,
1528 except where unsupported by hardware.
1530 ignore_loglevel [KNL]
1531 Ignore loglevel setting - this will print /all/
1532 kernel messages to the console. Useful for debugging.
1533 We also add it as printk module parameter, so users
1534 could change it dynamically, usually by
1535 /sys/module/printk/parameters/ignore_loglevel.
1538 Ignore RLIMIT_DATA setting for data mappings,
1539 print warning at first misuse. Can be changed via
1540 /sys/module/kernel/parameters/ignore_rlimit_data.
1542 ihash_entries= [KNL]
1543 Set number of hash buckets for inode cache.
1545 ima_appraise= [IMA] appraise integrity measurements
1546 Format: { "off" | "enforce" | "fix" | "log" }
1549 ima_appraise_tcb [IMA]
1550 The builtin appraise policy appraises all files
1553 ima_canonical_fmt [IMA]
1554 Use the canonical format for the binary runtime
1555 measurements, instead of host native format.
1558 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1562 The list of supported hash algorithms is defined
1563 in crypto/hash_info.h.
1566 The builtin policies to load during IMA setup.
1567 Format: "tcb | appraise_tcb | secure_boot |
1570 The "tcb" policy measures all programs exec'd, files
1571 mmap'd for exec, and all files opened with the read
1572 mode bit set by either the effective uid (euid=0) or
1575 The "appraise_tcb" policy appraises the integrity of
1576 all files owned by root. (This is the equivalent
1577 of ima_appraise_tcb.)
1579 The "secure_boot" policy appraises the integrity
1580 of files (eg. kexec kernel image, kernel modules,
1581 firmware, policy, etc) based on file signatures.
1583 The "fail_securely" policy forces file signature
1584 verification failure also on privileged mounted
1585 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1588 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1589 Load a policy which meets the needs of the Trusted
1590 Computing Base. This means IMA will measure all
1591 programs exec'd, files mmap'd for exec, and all files
1592 opened for read by uid=0.
1595 Select one of defined IMA measurements template formats.
1596 Formats: { "ima" | "ima-ng" | "ima-sig" }
1600 [IMA] Define a custom template format.
1601 Format: { "field1|...|fieldN" }
1603 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1604 Format: <min_file_size>
1605 Set the minimal file size for using asynchronous hash.
1606 If left unspecified, ahash usage is disabled.
1608 ahash performance varies for different data sizes on
1609 different crypto accelerators. This option can be used
1610 to achieve the best performance for a particular HW.
1612 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1614 Set hashing buffer size. Default: 4k.
1616 ahash performance varies for different chunk sizes on
1617 different crypto accelerators. This option can be used
1618 to achieve best performance for particular HW.
1622 Run specified binary instead of /sbin/init as init
1625 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1626 for working out where the kernel is dying during
1629 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1630 initcall functions. Useful for debugging built-in
1631 modules and initcalls.
1633 initrd= [BOOT] Specify the location of the initial ramdisk
1635 init_pkru= [x86] Specify the default memory protection keys rights
1636 register contents for all processes. 0x55555554 by
1637 default (disallow access to all but pkey 0). Can
1638 override in debugfs after boot.
1640 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1643 int_pln_enable [x86] Enable power limit notification interrupt
1645 integrity_audit=[IMA]
1646 Format: { "0" | "1" }
1647 0 -- basic integrity auditing messages. (Default)
1648 1 -- additional integrity auditing messages.
1650 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1652 Enable intel iommu driver.
1654 Disable intel iommu driver.
1655 igfx_off [Default Off]
1656 By default, gfx is mapped as normal device. If a gfx
1657 device has a dedicated DMAR unit, the DMAR unit is
1658 bypassed by not enabling DMAR with this option. In
1659 this case, gfx device will use physical address for
1662 With this option iommu will not optimize to look
1663 for io virtual address below 32-bit forcing dual
1664 address cycle on pci bus for cards supporting greater
1665 than 32-bit addressing. The default is to look
1666 for translation below 32-bit and if not available
1667 then look in the higher range.
1668 strict [Default Off]
1669 With this option on every unmap_single operation will
1670 result in a hardware IOTLB flush operation as opposed
1671 to batching them for performance.
1672 sp_off [Default Off]
1673 By default, super page will be supported if Intel IOMMU
1674 has the capability. With this option, super page will
1676 ecs_off [Default Off]
1677 By default, extended context tables will be supported if
1678 the hardware advertises that it has support both for the
1679 extended tables themselves, and also PASID support. With
1680 this option set, extended tables will not be used even
1681 on hardware which claims to support them.
1682 tboot_noforce [Default Off]
1683 Do not force the Intel IOMMU enabled under tboot.
1684 By default, tboot will force Intel IOMMU on, which
1685 could harm performance of some high-throughput
1686 devices like 40GBit network cards, even if identity
1688 Note that using this option lowers the security
1689 provided by tboot because it makes the system
1690 vulnerable to DMA attacks.
1692 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1693 0 disables intel_idle and fall back on acpi_idle.
1694 1 to 9 specify maximum depth of C-state.
1698 Do not enable intel_pstate as the default
1699 scaling driver for the supported processors
1701 Use intel_pstate as a scaling driver, but configure it
1702 to work with generic cpufreq governors (instead of
1703 enabling its internal governor). This mode cannot be
1704 used along with the hardware-managed P-states (HWP)
1707 Enable intel_pstate on systems that prohibit it by default
1708 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1709 instead of acpi-cpufreq may disable platform features, such
1710 as thermal controls and power capping, that rely on ACPI
1711 P-States information being indicated to OSPM and therefore
1712 should be used with caution. This option does not work with
1713 processors that aren't supported by the intel_pstate driver
1714 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1716 Do not enable hardware P state control (HWP)
1719 Only load intel_pstate on systems which support
1720 hardware P state control (HWP) if available.
1722 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1723 Description Table, specifies preferred power management
1724 profile as "Enterprise Server" or "Performance Server",
1725 then this feature is turned on by default.
1727 Allow per-logical-CPU P-State performance control limits using
1728 cpufreq sysfs interface
1730 intremap= [X86-64, Intel-IOMMU]
1731 on enable Interrupt Remapping (default)
1732 off disable Interrupt Remapping
1733 nosid disable Source ID checking
1735 BIOS x2APIC opt-out request will be ignored
1736 nopost disable Interrupt Posting
1738 iomem= Disable strict checking of access to MMIO memory
1739 strict regions from userspace.
1754 nobypass [PPC/POWERNV]
1755 Disable IOMMU bypass, using IOMMU for PCI devices.
1758 [ARM64] Configure DMA to bypass the IOMMU by default.
1759 Format: { "0" | "1" }
1760 0 - Use IOMMU translation for DMA.
1761 1 - Bypass the IOMMU for DMA.
1762 unset - Use IOMMU translation for DMA.
1764 io7= [HW] IO7 for Marvel based alpha systems
1765 See comment before marvel_specify_io7 in
1766 arch/alpha/kernel/core_marvel.c.
1768 io_delay= [X86] I/O delay method
1770 Standard port 0x80 based delay
1772 Alternate port 0xed based delay (needed on some systems)
1774 Simple two microseconds delay
1779 See Documentation/filesystems/nfs/nfsroot.txt.
1781 irqaffinity= [SMP] Set the default irq affinity mask
1782 The argument is a cpu list, as described above.
1784 irqchip.gicv2_force_probe=
1787 Force the kernel to look for the second 4kB page
1788 of a GICv2 controller even if the memory range
1789 exposed by the device tree is too small.
1791 irqchip.gicv3_nolpi=
1793 Force the kernel to ignore the availability of
1794 LPIs (and by consequence ITSs). Intended for system
1795 that use the kernel as a bootloader, and thus want
1796 to let secondary kernels in charge of setting up
1800 When an interrupt is not handled search all handlers
1801 for it. Intended to get systems with badly broken
1805 When an interrupt is not handled search all handlers
1806 for it. Also check all handlers each timer
1807 interrupt. Intended to get systems with badly broken
1811 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1813 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1814 [Deprecated - use cpusets instead]
1815 Format: [flag-list,]<cpu-list>
1817 Specify one or more CPUs to isolate from disturbances
1818 specified in the flag list (default: domain):
1821 Disable the tick when a single task runs.
1823 A residual 1Hz tick is offloaded to workqueues, which you
1824 need to affine to housekeeping through the global
1825 workqueue's affinity configured via the
1826 /sys/devices/virtual/workqueue/cpumask sysfs file, or
1827 by using the 'domain' flag described below.
1829 NOTE: by default the global workqueue runs on all CPUs,
1830 so to protect individual CPUs the 'cpumask' file has to
1831 be configured manually after bootup.
1834 Isolate from the general SMP balancing and scheduling
1835 algorithms. Note that performing domain isolation this way
1836 is irreversible: it's not possible to bring back a CPU to
1837 the domains once isolated through isolcpus. It's strongly
1838 advised to use cpusets instead to disable scheduler load
1839 balancing through the "cpuset.sched_load_balance" file.
1840 It offers a much more flexible interface where CPUs can
1841 move in and out of an isolated set anytime.
1843 You can move a process onto or off an "isolated" CPU via
1844 the CPU affinity syscalls or cpuset.
1845 <cpu number> begins at 0 and the maximum value is
1846 "number of CPUs in system - 1".
1848 The format of <cpu-list> is described above.
1854 ivrs_ioapic [HW,X86_64]
1855 Provide an override to the IOAPIC-ID<->DEVICE-ID
1856 mapping provided in the IVRS ACPI table. For
1857 example, to map IOAPIC-ID decimal 10 to
1858 PCI device 00:14.0 write the parameter as:
1859 ivrs_ioapic[10]=00:14.0
1861 ivrs_hpet [HW,X86_64]
1862 Provide an override to the HPET-ID<->DEVICE-ID
1863 mapping provided in the IVRS ACPI table. For
1864 example, to map HPET-ID decimal 0 to
1865 PCI device 00:14.0 write the parameter as:
1866 ivrs_hpet[0]=00:14.0
1868 ivrs_acpihid [HW,X86_64]
1869 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1870 mapping provided in the IVRS ACPI table. For
1871 example, to map UART-HID:UID AMD0020:0 to
1872 PCI device 00:14.5 write the parameter as:
1873 ivrs_acpihid[00:14.5]=AMD0020:0
1875 js= [HW,JOY] Analog joystick
1876 See Documentation/input/joydev/joystick.rst.
1879 When CONFIG_RANDOMIZE_BASE is set, this disables
1880 kernel and module base offset ASLR (Address Space
1881 Layout Randomization).
1884 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1885 report on every invalid memory access. Without this
1886 parameter KASAN will print report only for the first
1891 kernelcore= [KNL,X86,IA-64,PPC]
1892 Format: nn[KMGTPE] | nn% | "mirror"
1893 This parameter specifies the amount of memory usable by
1894 the kernel for non-movable allocations. The requested
1895 amount is spread evenly throughout all nodes in the
1896 system as ZONE_NORMAL. The remaining memory is used for
1897 movable memory in its own zone, ZONE_MOVABLE. In the
1898 event, a node is too small to have both ZONE_NORMAL and
1899 ZONE_MOVABLE, kernelcore memory will take priority and
1900 other nodes will have a larger ZONE_MOVABLE.
1902 ZONE_MOVABLE is used for the allocation of pages that
1903 may be reclaimed or moved by the page migration
1904 subsystem. Note that allocations like PTEs-from-HighMem
1905 still use the HighMem zone if it exists, and the Normal
1906 zone if it does not.
1908 It is possible to specify the exact amount of memory in
1909 the form of "nn[KMGTPE]", a percentage of total system
1910 memory in the form of "nn%", or "mirror". If "mirror"
1911 option is specified, mirrored (reliable) memory is used
1912 for non-movable allocations and remaining memory is used
1913 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
1914 are exclusive, so you cannot specify multiple forms.
1916 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1917 Format: <Controller#>[,poll interval]
1918 The controller # is the number of the ehci usb debug
1919 port as it is probed via PCI. The poll interval is
1920 optional and is the number seconds in between
1921 each poll cycle to the debug port in case you need
1922 the functionality for interrupting the kernel with
1923 gdb or control-c on the dbgp connection. When
1924 not using this parameter you use sysrq-g to break into
1925 the kernel debugger.
1927 kgdboc= [KGDB,HW] kgdb over consoles.
1928 Requires a tty driver that supports console polling,
1929 or a supported polling keyboard driver (non-usb).
1930 Serial only format: <serial_device>[,baud]
1931 keyboard only format: kbd
1932 keyboard and serial format: kbd,<serial_device>[,baud]
1933 Optional Kernel mode setting:
1934 kms, kbd format: kms,kbd
1935 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1937 kgdbwait [KGDB] Stop kernel execution and enter the
1938 kernel debugger at the earliest opportunity.
1940 kmac= [MIPS] korina ethernet MAC address.
1941 Configure the RouterBoard 532 series on-chip
1942 Ethernet adapter MAC address.
1944 kmemleak= [KNL] Boot-time kmemleak enable/disable
1945 Valid arguments: on, off
1947 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1950 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1951 Default is 0 (don't ignore, but inject #GP)
1953 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
1954 Default is false (don't support).
1956 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1960 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1961 Default is 1 (enabled)
1963 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1965 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1967 kvm-arm.vgic_v3_group0_trap=
1968 [KVM,ARM] Trap guest accesses to GICv3 group-0
1971 kvm-arm.vgic_v3_group1_trap=
1972 [KVM,ARM] Trap guest accesses to GICv3 group-1
1975 kvm-arm.vgic_v3_common_trap=
1976 [KVM,ARM] Trap guest accesses to GICv3 common
1979 kvm-arm.vgic_v4_enable=
1980 [KVM,ARM] Allow use of GICv4 for direct injection of
1983 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1984 (virtualized MMU) support on capable Intel chips.
1985 Default is 1 (enabled)
1987 kvm-intel.emulate_invalid_guest_state=
1988 [KVM,Intel] Enable emulation of invalid guest states
1989 Default is 0 (disabled)
1991 kvm-intel.flexpriority=
1992 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1993 Default is 1 (enabled)
1996 [KVM,Intel] Enable VMX nesting (nVMX).
1997 Default is 0 (disabled)
1999 kvm-intel.unrestricted_guest=
2000 [KVM,Intel] Disable unrestricted guest feature
2001 (virtualized real and unpaged mode) on capable
2002 Intel chips. Default is 1 (enabled)
2004 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2007 Valid arguments: never, cond, always
2009 always: L1D cache flush on every VMENTER.
2010 cond: Flush L1D on VMENTER only when the code between
2011 VMEXIT and VMENTER can leak host memory.
2012 never: Disables the mitigation
2014 Default is cond (do L1 cache flush in specific instances)
2016 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2017 feature (tagged TLBs) on capable Intel chips.
2018 Default is 1 (enabled)
2020 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2023 The kernel PTE inversion protection is unconditionally
2024 enabled and cannot be disabled.
2027 Provides all available mitigations for the
2028 L1TF vulnerability. Disables SMT and
2029 enables all mitigations in the
2030 hypervisors, i.e. unconditional L1D flush.
2032 SMT control and L1D flush control via the
2033 sysfs interface is still possible after
2034 boot. Hypervisors will issue a warning
2035 when the first VM is started in a
2036 potentially insecure configuration,
2037 i.e. SMT enabled or L1D flush disabled.
2040 Same as 'full', but disables SMT and L1D
2041 flush runtime control. Implies the
2042 'nosmt=force' command line option.
2043 (i.e. sysfs control of SMT is disabled.)
2046 Leaves SMT enabled and enables the default
2047 hypervisor mitigation, i.e. conditional
2050 SMT control and L1D flush control via the
2051 sysfs interface is still possible after
2052 boot. Hypervisors will issue a warning
2053 when the first VM is started in a
2054 potentially insecure configuration,
2055 i.e. SMT enabled or L1D flush disabled.
2059 Disables SMT and enables the default
2060 hypervisor mitigation.
2062 SMT control and L1D flush control via the
2063 sysfs interface is still possible after
2064 boot. Hypervisors will issue a warning
2065 when the first VM is started in a
2066 potentially insecure configuration,
2067 i.e. SMT enabled or L1D flush disabled.
2070 Same as 'flush', but hypervisors will not
2071 warn when a VM is started in a potentially
2072 insecure configuration.
2075 Disables hypervisor mitigations and doesn't
2080 For details see: Documentation/admin-guide/l1tf.rst
2086 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2089 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2090 value for LAPIC timer one-shot implementation. Default
2091 back to the programmable timer unit in the LAPIC.
2093 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2096 libata.dma= [LIBATA] DMA control
2097 libata.dma=0 Disable all PATA and SATA DMA
2098 libata.dma=1 PATA and SATA Disk DMA only
2099 libata.dma=2 ATAPI (CDROM) DMA only
2100 libata.dma=4 Compact Flash DMA only
2101 Combinations also work, so libata.dma=3 enables DMA
2102 for disks and CDROMs, but not CFs.
2104 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2105 libata.ignore_hpa=0 keep BIOS limits (default)
2106 libata.ignore_hpa=1 ignore limits, using full disk
2108 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2112 libata.force= [LIBATA] Force configurations. The format is comma
2113 separated list of "[ID:]VAL" where ID is
2114 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2115 matching port, link or device. Basically, it matches
2116 the ATA ID string printed on console by libata. If
2117 the whole ID part is omitted, the last PORT and DEVICE
2118 values are used. If ID hasn't been specified yet, the
2119 configuration applies to all ports, links and devices.
2121 If only DEVICE is omitted, the parameter applies to
2122 the port and all links and devices behind it. DEVICE
2123 number of 0 either selects the first device or the
2124 first fan-out link behind PMP device. It does not
2125 select the host link. DEVICE number of 15 selects the
2126 host link and device attached to it.
2128 The VAL specifies the configuration to force. As long
2129 as there's no ambiguity shortcut notation is allowed.
2130 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2131 The following configurations can be forced.
2133 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2134 Any ID with matching PORT is used.
2136 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2138 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2139 udma[/][16,25,33,44,66,100,133] notation is also
2142 * [no]ncq: Turn on or off NCQ.
2144 * [no]ncqtrim: Turn off queued DSM TRIM.
2146 * nohrst, nosrst, norst: suppress hard, soft
2149 * rstonce: only attempt one reset during
2150 hot-unplug link recovery
2152 * dump_id: dump IDENTIFY data.
2154 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2156 * disable: Disable this device.
2158 If there are multiple matching configurations changing
2159 the same attribute, the last one is used.
2161 memblock=debug [KNL] Enable memblock debug messages.
2163 load_ramdisk= [RAM] List of ramdisks to load from floppy
2164 See Documentation/blockdev/ramdisk.txt.
2166 lockd.nlm_grace_period=P [NFS] Assign grace period.
2169 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2172 lockd.nlm_timeout=T [NFS] Assign timeout value.
2175 lockd.nlm_udpport=M [NFS] Assign UDP port.
2178 locktorture.nreaders_stress= [KNL]
2179 Set the number of locking read-acquisition kthreads.
2180 Defaults to being automatically set based on the
2181 number of online CPUs.
2183 locktorture.nwriters_stress= [KNL]
2184 Set the number of locking write-acquisition kthreads.
2186 locktorture.onoff_holdoff= [KNL]
2187 Set time (s) after boot for CPU-hotplug testing.
2189 locktorture.onoff_interval= [KNL]
2190 Set time (s) between CPU-hotplug operations, or
2191 zero to disable CPU-hotplug testing.
2193 locktorture.shuffle_interval= [KNL]
2194 Set task-shuffle interval (jiffies). Shuffling
2195 tasks allows some CPUs to go into dyntick-idle
2196 mode during the locktorture test.
2198 locktorture.shutdown_secs= [KNL]
2199 Set time (s) after boot system shutdown. This
2200 is useful for hands-off automated testing.
2202 locktorture.stat_interval= [KNL]
2203 Time (s) between statistics printk()s.
2205 locktorture.stutter= [KNL]
2206 Time (s) to stutter testing, for example,
2207 specifying five seconds causes the test to run for
2208 five seconds, wait for five seconds, and so on.
2209 This tests the locking primitive's ability to
2210 transition abruptly to and from idle.
2212 locktorture.torture_type= [KNL]
2213 Specify the locking implementation to test.
2215 locktorture.verbose= [KNL]
2216 Enable additional printk() statements.
2218 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2221 loglevel= All Kernel Messages with a loglevel smaller than the
2222 console loglevel will be printed to the console. It can
2223 also be changed with klogd or other programs. The
2224 loglevels are defined as follows:
2226 0 (KERN_EMERG) system is unusable
2227 1 (KERN_ALERT) action must be taken immediately
2228 2 (KERN_CRIT) critical conditions
2229 3 (KERN_ERR) error conditions
2230 4 (KERN_WARNING) warning conditions
2231 5 (KERN_NOTICE) normal but significant condition
2232 6 (KERN_INFO) informational
2233 7 (KERN_DEBUG) debug-level messages
2235 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2236 in bytes. n must be a power of two and greater
2237 than the minimal size. The minimal size is defined
2238 by LOG_BUF_SHIFT kernel config parameter. There is
2239 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2240 that allows to increase the default size depending on
2241 the number of CPUs. See init/Kconfig for more details.
2243 logo.nologo [FB] Disables display of the built-in Linux logo.
2244 This may be used to provide more screen space for
2245 kernel log messages and is useful when debugging
2246 kernel boot problems.
2248 lp=0 [LP] Specify parallel ports to use, e.g,
2249 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2250 lp=reset first parallel port). 'lp=0' disables the
2251 lp=auto printer driver. 'lp=reset' (which can be
2252 specified in addition to the ports) causes
2253 attached printers to be reset. Using
2254 lp=port1,port2,... specifies the parallel ports
2255 to associate lp devices with, starting with
2256 lp0. A port specification may be 'none' to skip
2257 that lp device, or a parport name such as
2258 'parport0'. Specifying 'lp=auto' instead of a
2259 port specification list means that device IDs
2260 from each port should be examined, to see if
2261 an IEEE 1284-compliant printer is attached; if
2262 so, the driver will manage that printer.
2263 See also header of drivers/char/lp.c.
2266 Sets loops_per_jiffy to given constant, thus avoiding
2267 time-consuming boot-time autodetection (up to 250 ms per
2268 CPU). 0 enables autodetection (default). To determine
2269 the correct value for your kernel, boot with normal
2270 autodetection and see what value is printed. Note that
2271 on SMP systems the preset will be applied to all CPUs,
2272 which is likely to cause problems if your CPUs need
2273 significantly divergent settings. An incorrect value
2274 will cause delays in the kernel to be wrong, leading to
2275 unpredictable I/O errors and other breakage. Although
2276 unlikely, in the extreme case this might damage your
2280 Format: <io>,<irq>,<dma>
2282 machvec= [IA-64] Force the use of a particular machine-vector
2283 (machvec) in a generic kernel.
2284 Example: machvec=hpzx1_swiotlb
2286 machtype= [Loongson] Share the same kernel image file between different
2288 Example: machtype=lemote-yeeloong-2f-7inch
2290 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2291 than or equal to this physical address is ignored.
2293 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2294 will bring up during bootup. maxcpus=n : n >= 0 limits
2295 the kernel to bring up 'n' processors. Surely after
2296 bootup you can bring up the other plugged cpu by executing
2297 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2298 only takes effect during system bootup.
2299 While n=0 is a special case, it is equivalent to "nosmp",
2300 which also disables the IO APIC.
2302 max_loop= [LOOP] The number of loop block devices that get
2303 (loop.max_loop) unconditionally pre-created at init time. The default
2304 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2305 of statically allocating a predefined number, loop
2306 devices can be requested on-demand with the
2307 /dev/loop-control interface.
2309 mce [X86-32] Machine Check Exception
2311 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2313 md= [HW] RAID subsystems devices and level
2314 See Documentation/admin-guide/md.rst.
2317 Format: <first>,<last>
2318 Specifies range of consoles to be captured by the MDA.
2320 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2321 Amount of memory to be used when the kernel is not able
2322 to see the whole system memory or for test.
2323 [X86] Work as limiting max address. Use together
2324 with memmap= to avoid physical address space collisions.
2325 Without memmap= PCI devices could be placed at addresses
2326 belonging to unused RAM.
2328 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2332 [KNL,SH] Allow user to override the default size for
2333 per-device physically contiguous DMA buffers.
2335 memhp_default_state=online/offline
2336 [KNL] Set the initial state for the memory hotplug
2337 onlining policy. If not specified, the default value is
2338 set according to the
2339 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2341 See Documentation/memory-hotplug.txt.
2343 memmap=exactmap [KNL,X86] Enable setting of an exact
2344 E820 memory map, as specified by the user.
2345 Such memmap=exactmap lines can be constructed based on
2346 BIOS output or other requirements. See the memmap=nn@ss
2349 memmap=nn[KMG]@ss[KMG]
2350 [KNL] Force usage of a specific region of memory.
2351 Region of memory to be used is from ss to ss+nn.
2352 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2353 which limits max address to nn[KMG].
2354 Multiple different regions can be specified,
2357 memmap=100M@2G,100M#3G,1G!1024G
2359 memmap=nn[KMG]#ss[KMG]
2360 [KNL,ACPI] Mark specific memory as ACPI data.
2361 Region of memory to be marked is from ss to ss+nn.
2363 memmap=nn[KMG]$ss[KMG]
2364 [KNL,ACPI] Mark specific memory as reserved.
2365 Region of memory to be reserved is from ss to ss+nn.
2366 Example: Exclude memory from 0x18690000-0x1869ffff
2367 memmap=64K$0x18690000
2369 memmap=0x10000$0x18690000
2370 Some bootloaders may need an escape character before '$',
2371 like Grub2, otherwise '$' and the following number
2374 memmap=nn[KMG]!ss[KMG]
2375 [KNL,X86] Mark specific memory as protected.
2376 Region of memory to be used, from ss to ss+nn.
2377 The memory region may be marked as e820 type 12 (0xc)
2378 and is NVDIMM or ADR memory.
2380 memmap=<size>%<offset>-<oldtype>+<newtype>
2381 [KNL,ACPI] Convert memory within the specified region
2382 from <oldtype> to <newtype>. If "-<oldtype>" is left
2383 out, the whole region will be marked as <newtype>,
2384 even if previously unavailable. If "+<newtype>" is left
2385 out, matching memory will be removed. Types are
2386 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2387 3 = ACPI, 12 = PRAM.
2389 memory_corruption_check=0/1 [X86]
2390 Some BIOSes seem to corrupt the first 64k of
2391 memory when doing things like suspend/resume.
2392 Setting this option will scan the memory
2393 looking for corruption. Enabling this will
2394 both detect corruption and prevent the kernel
2395 from using the memory being corrupted.
2396 However, its intended as a diagnostic tool; if
2397 repeatable BIOS-originated corruption always
2398 affects the same memory, you can use memmap=
2399 to prevent the kernel from using that memory.
2401 memory_corruption_check_size=size [X86]
2402 By default it checks for corruption in the low
2403 64k, making this memory unavailable for normal
2404 use. Use this parameter to scan for
2405 corruption in more or less memory.
2407 memory_corruption_check_period=seconds [X86]
2408 By default it checks for corruption every 60
2409 seconds. Use this parameter to check at some
2410 other rate. 0 disables periodic checking.
2412 memtest= [KNL,X86,ARM] Enable memtest
2414 default : 0 <disable>
2415 Specifies the number of memtest passes to be
2416 performed. Each pass selects another test
2417 pattern from a given set of patterns. Memtest
2418 fills the memory with this pattern, validates
2419 memory contents and reserves bad memory
2420 regions that are detected.
2422 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2423 Valid arguments: on, off
2424 Default (depends on kernel configuration option):
2425 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2426 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2427 mem_encrypt=on: Activate SME
2428 mem_encrypt=off: Do not activate SME
2430 Refer to Documentation/x86/amd-memory-encryption.txt
2431 for details on when memory encryption can be activated.
2433 mem_sleep_default= [SUSPEND] Default system suspend mode:
2434 s2idle - Suspend-To-Idle
2435 shallow - Power-On Suspend or equivalent (if supported)
2436 deep - Suspend-To-RAM or equivalent (if supported)
2437 See Documentation/admin-guide/pm/sleep-states.rst.
2439 meye.*= [HW] Set MotionEye Camera parameters
2440 See Documentation/media/v4l-drivers/meye.rst.
2442 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2443 Multi-Function General Purpose Timers on AMD Geode
2446 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2447 the BIOS has incorrectly applied a workaround. TinyBIOS
2448 version 0.98 is known to be affected, 0.99 fixes the
2449 problem by letting the user disable the workaround.
2453 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2454 physical address is ignored.
2456 mini2440= [ARM,HW,KNL]
2457 Format:[0..2][b][c][t]
2459 MINI2440 configuration specification:
2460 0 - The attached screen is the 3.5" TFT
2461 1 - The attached screen is the 7" TFT
2462 2 - The VGA Shield is attached (1024x768)
2463 Leaving out the screen size parameter will not load
2464 the TFT driver, and the framebuffer will be left
2466 b - Enable backlight. The TFT backlight pin will be
2467 linked to the kernel VESA blanking code and a GPIO
2468 LED. This parameter is not necessary when using the
2470 c - Enable the s3c camera interface.
2471 t - Reserved for enabling touchscreen support. The
2472 touchscreen support is not enabled in the mainstream
2473 kernel as of 2.6.30, a preliminary port can be found
2474 in the "bleeding edge" mini2440 support kernel at
2475 http://repo.or.cz/w/linux-2.6/mini2440.git
2478 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2479 parameter allows control of the logging verbosity for
2480 the additional memory initialisation checks. A value
2481 of 0 disables mminit logging and a level of 4 will
2482 log everything. Information is printed at KERN_DEBUG
2483 so loglevel=8 may also need to be specified.
2486 [KNL] When CONFIG_MODULE_SIG is set, this means that
2487 modules without (valid) signatures will fail to load.
2488 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2489 is always true, so this option does nothing.
2491 module_blacklist= [KNL] Do not load a comma-separated list of
2492 modules. Useful for debugging problem modules.
2495 [MOUSE] Maximum time between finger touching and
2496 leaving touchpad surface for touch to be considered
2497 a tap and be reported as a left button click (for
2498 touchpads working in absolute mode only).
2500 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2501 reporting absolute coordinates, such as tablets
2502 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2503 reporting absolute coordinates, such as tablets
2505 movablecore= [KNL,X86,IA-64,PPC]
2506 Format: nn[KMGTPE] | nn%
2507 This parameter is the complement to kernelcore=, it
2508 specifies the amount of memory used for migratable
2509 allocations. If both kernelcore and movablecore is
2510 specified, then kernelcore will be at *least* the
2511 specified value but may be more. If movablecore on its
2512 own is specified, the administrator must be careful
2513 that the amount of memory usable for all allocations
2516 movable_node [KNL] Boot-time switch to make hotplugable memory
2517 NUMA nodes to be movable. This means that the memory
2518 of such nodes will be usable only for movable
2519 allocations which rules out almost all kernel
2520 allocations. Use with caution!
2522 MTD_Partition= [MTD]
2523 Format: <name>,<region-number>,<size>,<offset>
2525 MTD_Region= [MTD] Format:
2526 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2529 See drivers/mtd/cmdlinepart.c.
2531 multitce=off [PPC] This parameter disables the use of the pSeries
2532 firmware feature for updating multiple TCE entries
2535 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2537 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2539 boundary - index of last SLC block on Flex-OneNAND.
2540 The remaining blocks are configured as MLC blocks.
2541 lock - Configure if Flex-OneNAND boundary should be locked.
2542 Once locked, the boundary cannot be changed.
2543 1 indicates lock status, 0 indicates unlock status.
2546 ARM/S3C2412 JIVE boot control
2548 See arch/arm/mach-s3c2412/mach-jive.c
2550 mtouchusb.raw_coordinates=
2551 [HW] Make the MicroTouch USB driver use raw coordinates
2552 ('y', default) or cooked coordinates ('n')
2554 mtrr_chunk_size=nn[KMG] [X86]
2555 used for mtrr cleanup. It is largest continuous chunk
2556 that could hold holes aka. UC entries.
2558 mtrr_gran_size=nn[KMG] [X86]
2559 Used for mtrr cleanup. It is granularity of mtrr block.
2561 Large value could prevent small alignment from
2564 mtrr_spare_reg_nr=n [X86]
2566 Range: 0,7 : spare reg number
2568 Used for mtrr cleanup. It is spare mtrr entries number.
2569 Set to 2 or more if your graphical card needs more.
2571 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2573 netdev= [NET] Network devices parameters
2574 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2575 Note that mem_start is often overloaded to mean
2576 something different and driver-specific.
2577 This usage is only documented in each driver source
2581 [NETFILTER] Enable connection tracking flow accounting
2582 0 to disable accounting
2583 1 to enable accounting
2586 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2587 See Documentation/filesystems/nfs/nfsroot.txt.
2589 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2590 See Documentation/filesystems/nfs/nfsroot.txt.
2592 nfsrootdebug [NFS] enable nfsroot debugging messages.
2593 See Documentation/filesystems/nfs/nfsroot.txt.
2595 nfs.callback_nr_threads=
2596 [NFSv4] set the total number of threads that the
2597 NFS client will assign to service NFSv4 callback
2600 nfs.callback_tcpport=
2601 [NFS] set the TCP port on which the NFSv4 callback
2602 channel should listen.
2605 [NFS] sets the pathname to the program which is used
2606 to update the NFS client cache entries.
2608 nfs.cache_getent_timeout=
2609 [NFS] sets the timeout after which an attempt to
2610 update a cache entry is deemed to have failed.
2612 nfs.idmap_cache_timeout=
2613 [NFS] set the maximum lifetime for idmapper cache
2617 [NFS] enable 64-bit inode numbers.
2618 If zero, the NFS client will fake up a 32-bit inode
2619 number for the readdir() and stat() syscalls instead
2620 of returning the full 64-bit number.
2621 The default is to return 64-bit inode numbers.
2623 nfs.max_session_cb_slots=
2624 [NFSv4.1] Sets the maximum number of session
2625 slots the client will assign to the callback
2626 channel. This determines the maximum number of
2627 callbacks the client will process in parallel for
2628 a particular server.
2630 nfs.max_session_slots=
2631 [NFSv4.1] Sets the maximum number of session slots
2632 the client will attempt to negotiate with the server.
2633 This limits the number of simultaneous RPC requests
2634 that the client can send to the NFSv4.1 server.
2635 Note that there is little point in setting this
2636 value higher than the max_tcp_slot_table_limit.
2638 nfs.nfs4_disable_idmapping=
2639 [NFSv4] When set to the default of '1', this option
2640 ensures that both the RPC level authentication
2641 scheme and the NFS level operations agree to use
2642 numeric uids/gids if the mount is using the
2643 'sec=sys' security flavour. In effect it is
2644 disabling idmapping, which can make migration from
2645 legacy NFSv2/v3 systems to NFSv4 easier.
2646 Servers that do not support this mode of operation
2647 will be autodetected by the client, and it will fall
2648 back to using the idmapper.
2649 To turn off this behaviour, set the value to '0'.
2651 [NFS4] Specify an additional fixed unique ident-
2652 ification string that NFSv4 clients can insert into
2653 their nfs_client_id4 string. This is typically a
2654 UUID that is generated at system install time.
2656 nfs.send_implementation_id =
2657 [NFSv4.1] Send client implementation identification
2658 information in exchange_id requests.
2659 If zero, no implementation identification information
2661 The default is to send the implementation identification
2664 nfs.recover_lost_locks =
2665 [NFSv4] Attempt to recover locks that were lost due
2666 to a lease timeout on the server. Please note that
2667 doing this risks data corruption, since there are
2668 no guarantees that the file will remain unchanged
2669 after the locks are lost.
2670 If you want to enable the kernel legacy behaviour of
2671 attempting to recover these locks, then set this
2673 The default parameter value of '0' causes the kernel
2674 not to attempt recovery of lost locks.
2676 nfs4.layoutstats_timer =
2677 [NFSv4.2] Change the rate at which the kernel sends
2678 layoutstats to the pNFS metadata server.
2680 Setting this to value to 0 causes the kernel to use
2681 whatever value is the default set by the layout
2682 driver. A non-zero value sets the minimum interval
2683 in seconds between layoutstats transmissions.
2685 nfsd.nfs4_disable_idmapping=
2686 [NFSv4] When set to the default of '1', the NFSv4
2687 server will return only numeric uids and gids to
2688 clients using auth_sys, and will accept numeric uids
2689 and gids from such clients. This is intended to ease
2690 migration from NFSv2/v3.
2692 nmi_debug= [KNL,SH] Specify one or more actions to take
2693 when a NMI is triggered.
2694 Format: [state][,regs][,debounce][,die]
2696 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2697 Format: [panic,][nopanic,][num]
2699 0 - turn hardlockup detector in nmi_watchdog off
2700 1 - turn hardlockup detector in nmi_watchdog on
2701 When panic is specified, panic when an NMI watchdog
2702 timeout occurs (or 'nopanic' to override the opposite
2703 default). To disable both hard and soft lockup detectors,
2704 please see 'nowatchdog'.
2705 This is useful when you use a panic=... timeout and
2706 need the box quickly up again.
2708 These settings can be accessed at runtime via
2709 the nmi_watchdog and hardlockup_panic sysctls.
2711 netpoll.carrier_timeout=
2712 [NET] Specifies amount of time (in seconds) that
2713 netpoll should wait for a carrier. By default netpoll
2716 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2717 emulation library even if a 387 maths coprocessor
2720 no5lvl [X86-64] Disable 5-level paging mode. Forces
2721 kernel to use 4-level paging instead.
2724 [HW] Never suspend the console
2725 Disable suspending of consoles during suspend and
2726 hibernate operations. Once disabled, debugging
2727 messages can reach various consoles while the rest
2728 of the system is being put to sleep (ie, while
2729 debugging driver suspend/resume hooks). This may
2730 not work reliably with all consoles, but is known
2731 to work with serial and VGA consoles.
2732 To facilitate more flexible debugging, we also add
2733 console_suspend, a printk module parameter to control
2734 it. Users could use console_suspend (usually
2735 /sys/module/printk/parameters/console_suspend) to
2736 turn on/off it dynamically.
2738 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2739 caches in the slab allocator. Saves per-node memory,
2740 but will impact performance.
2744 noaltinstr [S390] Disables alternative instructions patching
2745 (CPU alternatives feature).
2747 noapic [SMP,APIC] Tells the kernel to not make use of any
2748 IOAPICs that may be present in the system.
2750 noautogroup Disable scheduler automatic task group creation.
2752 nobats [PPC] Do not use BATs for mapping kernel lowmem
2753 on "Classic" PPC cores.
2757 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2759 nodelayacct [KNL] Disable per-task delay accounting
2761 nodsp [SH] Disable hardware DSP at boot time.
2763 noefi Disable EFI runtime services support.
2768 On X86-32 available only on PAE configured kernels.
2769 noexec=on: enable non-executable mappings (default)
2770 noexec=off: disable non-executable mappings
2773 Disable SMAP (Supervisor Mode Access Prevention)
2774 even if it is supported by processor.
2777 Disable SMEP (Supervisor Mode Execution Prevention)
2778 even if it is supported by processor.
2781 This affects only 32-bit executables.
2782 noexec32=on: enable non-executable mappings (default)
2783 read doesn't imply executable mappings
2784 noexec32=off: disable non-executable mappings
2785 read implies executable mappings
2787 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2789 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2790 register save and restore. The kernel will only save
2791 legacy floating-point registers on task switch.
2793 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2795 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2796 Equivalent to smt=1.
2798 [KNL,x86] Disable symmetric multithreading (SMT).
2799 nosmt=force: Force disable SMT, cannot be undone
2800 via the sysfs control file.
2802 nospectre_v1 [PPC] Disable mitigations for Spectre Variant 1 (bounds
2803 check bypass). With this option data leaks are possible
2806 nospectre_v2 [X86] Disable all mitigations for the Spectre variant 2
2807 (indirect branch prediction) vulnerability. System may
2808 allow data leaks with this option, which is equivalent
2811 nospec_store_bypass_disable
2812 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
2814 noxsave [BUGS=X86] Disables x86 extended register state save
2815 and restore using xsave. The kernel will fallback to
2816 enabling legacy floating-point and sse state.
2818 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2819 register states. The kernel will fall back to use
2820 xsave to save the states. By using this parameter,
2821 performance of saving the states is degraded because
2822 xsave doesn't support modified optimization while
2823 xsaveopt supports it on xsaveopt enabled systems.
2825 noxsaves [X86] Disables xsaves and xrstors used in saving and
2826 restoring x86 extended register state in compacted
2827 form of xsave area. The kernel will fall back to use
2828 xsaveopt and xrstor to save and restore the states
2829 in standard form of xsave area. By using this
2830 parameter, xsave area per process might occupy more
2831 memory on xsaves enabled systems.
2833 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2834 wfi(ARM) instruction doesn't work correctly and not to
2835 use it. This is also useful when using JTAG debugger.
2837 no_file_caps Tells the kernel not to honor file capabilities. The
2838 only way then for a file to be executed with privilege
2839 is to be setuid root or executed by root.
2841 nohalt [IA-64] Tells the kernel not to use the power saving
2842 function PAL_HALT_LIGHT when idle. This increases
2843 power-consumption. On the positive side, it reduces
2844 interrupt wake-up latency, which may improve performance
2845 in certain environments such as networked servers or
2848 nohibernate [HIBERNATION] Disable hibernation and resume.
2850 nohz= [KNL] Boottime enable/disable dynamic ticks
2851 Valid arguments: on, off
2854 nohz_full= [KNL,BOOT,SMP,ISOL]
2855 The argument is a cpu list, as described above.
2856 In kernels built with CONFIG_NO_HZ_FULL=y, set
2857 the specified list of CPUs whose tick will be stopped
2858 whenever possible. The boot CPU will be forced outside
2859 the range to maintain the timekeeping. Any CPUs
2860 in this list will have their RCU callbacks offloaded,
2861 just as if they had also been called out in the
2862 rcu_nocbs= boot parameter.
2864 noiotrap [SH] Disables trapped I/O port accesses.
2866 noirqdebug [X86-32] Disables the code which attempts to detect and
2867 disable unhandled interrupt sources.
2869 no_timer_check [X86,APIC] Disables the code which tests for
2870 broken timer IRQ sources.
2872 noisapnp [ISAPNP] Disables ISA PnP code.
2874 noinitrd [RAM] Tells the kernel not to load any configured
2877 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2879 [Deprecated - use intremap=off]
2883 noinvpcid [X86] Disable the INVPCID cpu feature.
2885 nojitter [IA-64] Disables jitter checking for ITC timers.
2887 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2889 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2893 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2894 clock and use the default one.
2896 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2897 steal time is computed, but won't influence scheduler
2900 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2902 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2904 noltlbs [PPC] Do not use large page/tlb entries for kernel
2905 lowmem mapping on PPC40x and PPC8xx
2907 nomca [IA-64] Disable machine check abort handling
2909 nomce [X86-32] Disable Machine Check Exception
2911 nomfgpt [X86-32] Disable Multi-Function General Purpose
2912 Timer usage (for AMD Geode machines).
2914 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2915 shutdown the other cpus. Instead use the REBOOT_VECTOR
2918 nomodule Disable module load
2920 nopat [X86] Disable PAT (page attribute table extension of
2921 pagetables) support.
2923 nopcid [X86-64] Disable the PCID cpu feature.
2925 norandmaps Don't use address space randomization. Equivalent to
2926 echo 0 > /proc/sys/kernel/randomize_va_space
2928 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2929 with UP alternatives
2931 nordrand [X86] Disable kernel use of the RDRAND and
2932 RDSEED instructions even if they are supported
2933 by the processor. RDRAND and RDSEED are still
2934 available to user space applications.
2936 noresume [SWSUSP] Disables resume and restores original swap
2939 no-scroll [VGA] Disables scrollback.
2940 This is required for the Braillex ib80-piezo Braille
2941 reader made by F.H. Papenmeier (Germany).
2945 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2947 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2948 and disable the IO APIC. legacy for "maxcpus=0".
2950 nosoftlockup [KNL] Disable the soft-lockup detector.
2952 nosync [HW,M68K] Disables sync negotiation for all devices.
2954 nowatchdog [KNL] Disable both lockup detectors, i.e.
2955 soft-lockup and NMI watchdog (hard-lockup).
2959 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2961 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2962 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2963 Some features depend on CPU0. Known dependencies are:
2964 1. Resume from suspend/hibernate depends on CPU0.
2965 Suspend/hibernate will fail if CPU0 is offline and you
2966 need to online CPU0 before suspend/hibernate.
2967 2. PIC interrupts also depend on CPU0. CPU0 can't be
2968 removed if a PIC interrupt is detected.
2969 It's said poweroff/reboot may depend on CPU0 on some
2970 machines although I haven't seen such issues so far
2971 after CPU0 is offline on a few tested machines.
2972 If the dependencies are under your control, you can
2973 turn on cpu0_hotplug.
2975 nps_mtm_hs_ctr= [KNL,ARC]
2976 This parameter sets the maximum duration, in
2977 cycles, each HW thread of the CTOP can run
2978 without interruptions, before HW switches it.
2979 The actual maximum duration is 16 times this
2981 Format: integer between 1 and 255
2984 nptcg= [IA-64] Override max number of concurrent global TLB
2985 purges which is reported from either PAL_VM_SUMMARY or
2988 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2989 could support. nr_cpus=n : n >= 1 limits the kernel to
2990 support 'n' processors. It could be larger than the
2991 number of already plugged CPU during bootup, later in
2992 runtime you can physically add extra cpu until it reaches
2993 n. So during boot up some boot time memory for per-cpu
2994 variables need be pre-allocated for later physical cpu
2997 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2999 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
3000 Allowed values are enable and disable
3002 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3003 'node', 'default' can be specified
3004 This can be set from sysctl after boot.
3005 See Documentation/sysctl/vm.txt for details.
3007 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3008 See Documentation/debugging-via-ohci1394.txt for more
3011 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3012 Rather than timing out after 20 ms if an EC
3013 command is not properly ACKed, override the length
3014 of the timeout. We have interrupts disabled while
3015 waiting for the ACK, so if this is set too high
3016 interrupts *may* be lost!
3018 omap_mux= [OMAP] Override bootloader pin multiplexing.
3019 Format: <mux_mode0.mode_name=value>...
3020 For example, to override I2C bus2:
3021 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3023 oprofile.timer= [HW]
3024 Use timer interrupt instead of performance counters
3026 oprofile.cpu_type= Force an oprofile cpu type
3027 This might be useful if you have an older oprofile
3028 userland or if you want common events.
3029 Format: { arch_perfmon }
3030 arch_perfmon: [X86] Force use of architectural
3031 perfmon on Intel CPUs instead of the
3032 CPU specific event set.
3033 timer: [X86] Force use of architectural NMI
3034 timer mode (see also oprofile.timer
3035 for generic hr timer mode)
3037 oops=panic Always panic on oopses. Default is to just kill the
3038 process, but there is a small probability of
3039 deadlocking the machine.
3040 This will also cause panics on machine check exceptions.
3041 Useful together with panic=30 to trigger a reboot.
3043 page_owner= [KNL] Boot-time page_owner enabling option.
3044 Storage of the information about who allocated
3045 each page is disabled in default. With this switch,
3047 on: enable the feature
3049 page_poison= [KNL] Boot-time parameter changing the state of
3050 poisoning on the buddy allocator, available with
3051 CONFIG_PAGE_POISONING=y.
3052 off: turn off poisoning (default)
3053 on: turn on poisoning
3055 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3056 timeout > 0: seconds before rebooting
3057 timeout = 0: wait forever
3058 timeout < 0: reboot immediately
3061 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3064 crash_kexec_post_notifiers
3065 Run kdump after running panic-notifiers and dumping
3066 kmsg. This only for the users who doubt kdump always
3067 succeeds in any situation.
3068 Note that this also increases risks of kdump failure,
3069 because some panic notifiers can make the crashed
3070 kernel more unstable.
3072 parkbd.port= [HW] Parallel port number the keyboard adapter is
3073 connected to, default is 0.
3075 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3076 0 for XT, 1 for AT (default is AT).
3079 parport= [HW,PPT] Specify parallel ports. 0 disables.
3080 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3081 Use 'auto' to force the driver to use any
3082 IRQ/DMA settings detected (the default is to
3083 ignore detected IRQ/DMA settings because of
3084 possible conflicts). You can specify the base
3085 address, IRQ, and DMA settings; IRQ and DMA
3086 should be numbers, or 'auto' (for using detected
3087 settings on that particular port), or 'nofifo'
3088 (to avoid using a FIFO even if it is detected).
3089 Parallel ports are assigned in the order they
3090 are specified on the command line, starting
3093 parport_init_mode= [HW,PPT]
3094 Configure VIA parallel port to operate in
3095 a specific mode. This is necessary on Pegasos
3096 computer where firmware has no options for setting
3097 up parallel port mode and sets it to spp.
3098 Currently this function knows 686a and 8231 chips.
3099 Format: [spp|ps2|epp|ecp|ecpepp]
3102 Halt all CPUs after the first oops has been printed for
3103 the specified number of seconds. This is to be used if
3104 your oopses keep scrolling off the screen.
3109 See header of drivers/block/paride/pcd.c.
3110 See also Documentation/blockdev/paride.txt.
3112 pci=option[,option...] [PCI] various PCI subsystem options.
3114 Some options herein operate on a specific device
3115 or a set of devices (<pci_dev>). These are
3116 specified in one of the following formats:
3118 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
3119 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
3121 Note: the first format specifies a PCI
3122 bus/device/function address which may change
3123 if new hardware is inserted, if motherboard
3124 firmware changes, or due to changes caused
3125 by other kernel parameters. If the
3126 domain is left unspecified, it is
3127 taken to be zero. Optionally, a path
3128 to a device through multiple device/function
3129 addresses can be specified after the base
3130 address (this is more robust against
3131 renumbering issues). The second format
3132 selects devices using IDs from the
3133 configuration space which may match multiple
3134 devices in the system.
3136 earlydump dump PCI config space before the kernel
3138 off [X86] don't probe for the PCI bus
3139 bios [X86-32] force use of PCI BIOS, don't access
3140 the hardware directly. Use this if your machine
3141 has a non-standard PCI host bridge.
3142 nobios [X86-32] disallow use of PCI BIOS, only direct
3143 hardware access methods are allowed. Use this
3144 if you experience crashes upon bootup and you
3145 suspect they are caused by the BIOS.
3146 conf1 [X86] Force use of PCI Configuration Access
3147 Mechanism 1 (config address in IO port 0xCF8,
3148 data in IO port 0xCFC, both 32-bit).
3149 conf2 [X86] Force use of PCI Configuration Access
3150 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3151 the function, IO port 0xCFA, also 8-bit, sets
3152 bus number. The config space is then accessed
3153 through ports 0xC000-0xCFFF).
3154 See http://wiki.osdev.org/PCI for more info
3155 on the configuration access mechanisms.
3156 noaer [PCIE] If the PCIEAER kernel config parameter is
3157 enabled, this kernel boot option can be used to
3158 disable the use of PCIE advanced error reporting.
3159 nodomains [PCI] Disable support for multiple PCI
3160 root domains (aka PCI segments, in ACPI-speak).
3161 nommconf [X86] Disable use of MMCONFIG for PCI
3163 check_enable_amd_mmconf [X86] check for and enable
3164 properly configured MMIO access to PCI
3165 config space on AMD family 10h CPU
3166 nomsi [MSI] If the PCI_MSI kernel config parameter is
3167 enabled, this kernel boot option can be used to
3168 disable the use of MSI interrupts system-wide.
3169 noioapicquirk [APIC] Disable all boot interrupt quirks.
3170 Safety option to keep boot IRQs enabled. This
3171 should never be necessary.
3172 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3173 primary IO-APIC for bridges that cannot disable
3174 boot IRQs. This fixes a source of spurious IRQs
3175 when the system masks IRQs.
3176 noioapicreroute [APIC] Disable workaround that uses the
3177 boot IRQ equivalent of an IRQ that connects to
3178 a chipset where boot IRQs cannot be disabled.
3179 The opposite of ioapicreroute.
3180 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3181 routing table. These calls are known to be buggy
3182 on several machines and they hang the machine
3183 when used, but on other computers it's the only
3184 way to get the interrupt routing table. Try
3185 this option if the kernel is unable to allocate
3186 IRQs or discover secondary PCI buses on your
3188 rom [X86] Assign address space to expansion ROMs.
3189 Use with caution as certain devices share
3190 address decoders between ROMs and other
3192 norom [X86] Do not assign address space to
3193 expansion ROMs that do not already have
3194 BIOS assigned address ranges.
3195 nobar [X86] Do not assign address space to the
3196 BARs that weren't assigned by the BIOS.
3197 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3198 assigned automatically to PCI devices. You can
3199 make the kernel exclude IRQs of your ISA cards
3201 pirqaddr=0xAAAAA [X86] Specify the physical address
3202 of the PIRQ table (normally generated
3203 by the BIOS) if it is outside the
3204 F0000h-100000h range.
3205 lastbus=N [X86] Scan all buses thru bus #N. Can be
3206 useful if the kernel is unable to find your
3207 secondary buses and you want to tell it
3208 explicitly which ones they are.
3209 assign-busses [X86] Always assign all PCI bus
3210 numbers ourselves, overriding
3211 whatever the firmware may have done.
3212 usepirqmask [X86] Honor the possible IRQ mask stored
3213 in the BIOS $PIR table. This is needed on
3214 some systems with broken BIOSes, notably
3215 some HP Pavilion N5400 and Omnibook XE3
3216 notebooks. This will have no effect if ACPI
3217 IRQ routing is enabled.
3218 noacpi [X86] Do not use ACPI for IRQ routing
3219 or for PCI scanning.
3220 use_crs [X86] Use PCI host bridge window information
3221 from ACPI. On BIOSes from 2008 or later, this
3222 is enabled by default. If you need to use this,
3223 please report a bug.
3224 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3225 If you need to use this, please report a bug.
3226 routeirq Do IRQ routing for all PCI devices.
3227 This is normally done in pci_enable_device(),
3228 so this option is a temporary workaround
3229 for broken drivers that don't call it.
3230 skip_isa_align [X86] do not align io start addr, so can
3231 handle more pci cards
3232 noearly [X86] Don't do any early type 1 scanning.
3233 This might help on some broken boards which
3234 machine check when some devices' config space
3235 is read. But various workarounds are disabled
3236 and some IOMMU drivers will not work.
3237 bfsort Sort PCI devices into breadth-first order.
3238 This sorting is done to get a device
3239 order compatible with older (<= 2.4) kernels.
3240 nobfsort Don't sort PCI devices into breadth-first order.
3241 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3242 tuning and use the BIOS-configured MPS defaults.
3243 pcie_bus_safe Set every device's MPS to the largest value
3244 supported by all devices below the root complex.
3245 pcie_bus_perf Set device MPS to the largest allowable MPS
3246 based on its parent bus. Also set MRRS (Max
3247 Read Request Size) to the largest supported
3248 value (no larger than the MPS that the device
3249 or bus can support) for best performance.
3250 pcie_bus_peer2peer Set every device's MPS to 128B, which
3251 every device is guaranteed to support. This
3252 configuration allows peer-to-peer DMA between
3253 any pair of devices, possibly at the cost of
3254 reduced performance. This also guarantees
3255 that hot-added devices will work.
3256 cbiosize=nn[KMG] The fixed amount of bus space which is
3257 reserved for the CardBus bridge's IO window.
3258 The default value is 256 bytes.
3259 cbmemsize=nn[KMG] The fixed amount of bus space which is
3260 reserved for the CardBus bridge's memory
3261 window. The default value is 64 megabytes.
3264 [<order of align>@]<pci_dev>[; ...]
3265 Specifies alignment and device to reassign
3266 aligned memory resources. How to
3267 specify the device is described above.
3268 If <order of align> is not specified,
3269 PAGE_SIZE is used as alignment.
3270 PCI-PCI bridge can be specified, if resource
3271 windows need to be expanded.
3272 To specify the alignment for several
3273 instances of a device, the PCI vendor,
3274 device, subvendor, and subdevice may be
3275 specified, e.g., 4096@pci:8086:9c22:103c:198f
3276 ecrc= Enable/disable PCIe ECRC (transaction layer
3277 end-to-end CRC checking).
3278 bios: Use BIOS/firmware settings. This is the
3282 hpiosize=nn[KMG] The fixed amount of bus space which is
3283 reserved for hotplug bridge's IO window.
3284 Default size is 256 bytes.
3285 hpmemsize=nn[KMG] The fixed amount of bus space which is
3286 reserved for hotplug bridge's memory window.
3287 Default size is 2 megabytes.
3288 hpbussize=nn The minimum amount of additional bus numbers
3289 reserved for buses below a hotplug bridge.
3291 realloc= Enable/disable reallocating PCI bridge resources
3292 if allocations done by BIOS are too small to
3293 accommodate resources required by all child
3295 off: Turn realloc off
3297 realloc same as realloc=on
3298 noari do not use PCIe ARI.
3299 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
3300 do not use PCIe ATS (and IOMMU device IOTLB).
3301 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3302 only look for one device below a PCIe downstream
3304 big_root_window Try to add a big 64bit memory window to the PCIe
3305 root complex on AMD CPUs. Some GFX hardware
3306 can resize a BAR to allow access to all VRAM.
3307 Adding the window is slightly risky (it may
3308 conflict with unreported devices), so this
3310 disable_acs_redir=<pci_dev>[; ...]
3311 Specify one or more PCI devices (in the format
3312 specified above) separated by semicolons.
3313 Each device specified will have the PCI ACS
3314 redirect capabilities forced off which will
3315 allow P2P traffic between devices through
3316 bridges without forcing it upstream. Note:
3317 this removes isolation between devices and
3318 may put more devices in an IOMMU group.
3320 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3323 force Enable ASPM even on devices that claim not to support it.
3324 WARNING: Forcing ASPM on may cause system lockups.
3326 pcie_ports= [PCIE] PCIe port services handling:
3327 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
3328 even if the platform doesn't give the OS permission to
3329 use them. This may cause conflicts if the platform
3330 also tries to use these services.
3331 compat Disable native PCIe services (PME, AER, DPC, PCIe
3334 pcie_port_pm= [PCIE] PCIe port power management handling:
3335 off Disable power management of all PCIe ports
3336 force Forcibly enable power management of all PCIe ports
3338 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3339 nomsi Do not use MSI for native PCIe PME signaling (this makes
3340 all PCIe root ports use INTx for all services).
3342 pcmv= [HW,PCMCIA] BadgePAD 4
3346 Keep all power-domains already enabled by bootloader on,
3347 even if no driver has claimed them. This is useful
3348 for debug and development, but should not be
3349 needed on a platform with proper driver support.
3352 See Documentation/blockdev/paride.txt.
3354 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3357 See arch/parisc/kernel/pdc_chassis.c
3359 percpu_alloc= Select which percpu first chunk allocator to use.
3360 Currently supported values are "embed" and "page".
3361 Archs may support subset or none of the selections.
3362 See comments in mm/percpu.c for details on each
3363 allocator. This parameter is primarily for debugging
3364 and performance comparison.
3367 See Documentation/blockdev/paride.txt.
3370 See Documentation/blockdev/paride.txt.
3372 pirq= [SMP,APIC] Manual mp-table setup
3373 See Documentation/x86/i386/IO-APIC.txt.
3375 plip= [PPT,NET] Parallel port network link
3376 Format: { parport<nr> | timid | 0 }
3377 See also Documentation/admin-guide/parport.rst.
3379 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3380 Override pmtimer IOPort with a hex value.
3384 Enable PNP debug messages (depends on the
3385 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3386 via /sys/module/pnp/parameters/debug. We always show
3387 current resource usage; turning this on also shows
3388 possible settings and some assignment information.
3394 { on | off | curr | res | no-curr | no-res }
3397 [ISAPNP] Exclude IRQs for the autoconfiguration
3400 [ISAPNP] Exclude DMAs for the autoconfiguration
3402 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3403 Ranges are in pairs (I/O port base and size).
3406 [ISAPNP] Exclude memory regions for the
3408 Ranges are in pairs (memory base and size).
3410 ports= [IP_VS_FTP] IPVS ftp helper module
3412 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3414 Format: <port>,<port>....
3416 powersave=off [PPC] This option disables power saving features.
3417 It specifically disables cpuidle and sets the
3418 platform machine description specific power_save
3419 function to NULL. On Idle the CPU just reduces
3422 ppc_strict_facility_enable
3423 [PPC] This option catches any kernel floating point,
3424 Altivec, VSX and SPE outside of regions specifically
3425 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3426 There is some performance impact when enabling this.
3430 Disable Hardware Transactional Memory
3432 print-fatal-signals=
3433 [KNL] debug: print fatal signals
3435 If enabled, warn about various signal handling
3436 related application anomalies: too many signals,
3437 too many POSIX.1 timers, fatal signals causing a
3440 If you hit the warning due to signal overflow,
3441 you might want to try "ulimit -i unlimited".
3445 printk.always_kmsg_dump=
3446 Trigger kmsg_dump for cases other than kernel oops or
3448 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3451 printk.devkmsg={on,off,ratelimit}
3452 Control writing to /dev/kmsg.
3453 on - unlimited logging to /dev/kmsg from userspace
3454 off - logging to /dev/kmsg disabled
3455 ratelimit - ratelimit the logging
3458 printk.time= Show timing data prefixed to each printk message line
3459 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3461 processor.max_cstate= [HW,ACPI]
3462 Limit processor to maximum C-state
3463 max_cstate=9 overrides any DMI blacklist limit.
3465 processor.nocst [HW,ACPI]
3466 Ignore the _CST method to determine C-states,
3467 instead using the legacy FADT method
3469 profile= [KNL] Enable kernel profiling via /proc/profile
3470 Format: [<profiletype>,]<number>
3471 Param: <profiletype>: "schedule", "sleep", or "kvm"
3472 [defaults to kernel profiling]
3473 Param: "schedule" - profile schedule points.
3474 Param: "sleep" - profile D-state sleeping (millisecs).
3475 Requires CONFIG_SCHEDSTATS
3476 Param: "kvm" - profile VM exits.
3477 Param: <number> - step/bucket size as a power of 2 for
3478 statistical time based profiling.
3480 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3482 See Documentation/blockdev/ramdisk.txt.
3484 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3485 probe for; one of (bare|imps|exps|lifebook|any).
3486 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3488 psmouse.resetafter= [HW,MOUSE]
3489 Try to reset the device after so many bad packets
3492 [HW,MOUSE] Set desired mouse resolution, in dpi.
3493 psmouse.smartscroll=
3494 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3495 0 = disabled, 1 = enabled (default).
3497 pstore.backend= Specify the name of the pstore backend to use
3500 See Documentation/blockdev/paride.txt.
3502 pti= [X86_64] Control Page Table Isolation of user and
3503 kernel address spaces. Disabling this feature
3504 removes hardening, but improves performance of
3505 system calls and interrupts.
3507 on - unconditionally enable
3508 off - unconditionally disable
3509 auto - kernel detects whether your CPU model is
3510 vulnerable to issues that PTI mitigates
3512 Not specifying this option is equivalent to pti=auto.
3515 Equivalent to pti=off
3518 [KNL] Number of legacy pty's. Overwrites compiled-in
3521 quiet [KNL] Disable most log messages
3526 See Documentation/admin-guide/md.rst.
3528 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3529 See Documentation/blockdev/ramdisk.txt.
3531 random.trust_cpu={on,off}
3532 [KNL] Enable or disable trusting the use of the
3533 CPU's random number generator (if available) to
3534 fully seed the kernel's CRNG. Default is controlled
3535 by CONFIG_RANDOM_TRUST_CPU.
3537 ras=option[,option,...] [KNL] RAS-specific options
3540 Disable the Correctable Errors Collector,
3541 see CONFIG_RAS_CEC help text.
3544 The argument is a cpu list, as described above.
3546 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3547 the specified list of CPUs to be no-callback CPUs.
3548 Invocation of these CPUs' RCU callbacks will be
3549 offloaded to "rcuox/N" kthreads created for that
3550 purpose, where "x" is "p" for RCU-preempt, and
3551 "s" for RCU-sched, and "N" is the CPU number.
3552 This reduces OS jitter on the offloaded CPUs,
3553 which can be useful for HPC and real-time
3554 workloads. It can also improve energy efficiency
3555 for asymmetric multiprocessors.
3558 Rather than requiring that offloaded CPUs
3559 (specified by rcu_nocbs= above) explicitly
3560 awaken the corresponding "rcuoN" kthreads,
3561 make these kthreads poll for callbacks.
3562 This improves the real-time response for the
3563 offloaded CPUs by relieving them of the need to
3564 wake up the corresponding kthread, but degrades
3565 energy efficiency by requiring that the kthreads
3566 periodically wake up to do the polling.
3568 rcutree.blimit= [KNL]
3569 Set maximum number of finished RCU callbacks to
3570 process in one batch.
3572 rcutree.dump_tree= [KNL]
3573 Dump the structure of the rcu_node combining tree
3574 out at early boot. This is used for diagnostic
3575 purposes, to verify correct tree setup.
3577 rcutree.gp_cleanup_delay= [KNL]
3578 Set the number of jiffies to delay each step of
3579 RCU grace-period cleanup.
3581 rcutree.gp_init_delay= [KNL]
3582 Set the number of jiffies to delay each step of
3583 RCU grace-period initialization.
3585 rcutree.gp_preinit_delay= [KNL]
3586 Set the number of jiffies to delay each step of
3587 RCU grace-period pre-initialization, that is,
3588 the propagation of recent CPU-hotplug changes up
3589 the rcu_node combining tree.
3591 rcutree.rcu_fanout_exact= [KNL]
3592 Disable autobalancing of the rcu_node combining
3593 tree. This is used by rcutorture, and might
3594 possibly be useful for architectures having high
3595 cache-to-cache transfer latencies.
3597 rcutree.rcu_fanout_leaf= [KNL]
3598 Change the number of CPUs assigned to each
3599 leaf rcu_node structure. Useful for very
3600 large systems, which will choose the value 64,
3601 and for NUMA systems with large remote-access
3602 latencies, which will choose a value aligned
3603 with the appropriate hardware boundaries.
3605 rcutree.jiffies_till_sched_qs= [KNL]
3606 Set required age in jiffies for a
3607 given grace period before RCU starts
3608 soliciting quiescent-state help from
3609 rcu_note_context_switch(). If not specified, the
3610 kernel will calculate a value based on the most
3611 recent settings of rcutree.jiffies_till_first_fqs
3612 and rcutree.jiffies_till_next_fqs.
3613 This calculated value may be viewed in
3614 rcutree.jiffies_to_sched_qs. Any attempt to
3615 set rcutree.jiffies_to_sched_qs will be
3616 cheerfully overwritten.
3618 rcutree.jiffies_till_first_fqs= [KNL]
3619 Set delay from grace-period initialization to
3620 first attempt to force quiescent states.
3621 Units are jiffies, minimum value is zero,
3622 and maximum value is HZ.
3624 rcutree.jiffies_till_next_fqs= [KNL]
3625 Set delay between subsequent attempts to force
3626 quiescent states. Units are jiffies, minimum
3627 value is one, and maximum value is HZ.
3629 rcutree.kthread_prio= [KNL,BOOT]
3630 Set the SCHED_FIFO priority of the RCU per-CPU
3631 kthreads (rcuc/N). This value is also used for
3632 the priority of the RCU boost threads (rcub/N)
3633 and for the RCU grace-period kthreads (rcu_bh,
3634 rcu_preempt, and rcu_sched). If RCU_BOOST is
3635 set, valid values are 1-99 and the default is 1
3636 (the least-favored priority). Otherwise, when
3637 RCU_BOOST is not set, valid values are 0-99 and
3638 the default is zero (non-realtime operation).
3640 rcutree.rcu_nocb_leader_stride= [KNL]
3641 Set the number of NOCB kthread groups, which
3642 defaults to the square root of the number of
3643 CPUs. Larger numbers reduces the wakeup overhead
3644 on the per-CPU grace-period kthreads, but increases
3645 that same overhead on each group's leader.
3647 rcutree.qhimark= [KNL]
3648 Set threshold of queued RCU callbacks beyond which
3649 batch limiting is disabled.
3651 rcutree.qlowmark= [KNL]
3652 Set threshold of queued RCU callbacks below which
3653 batch limiting is re-enabled.
3655 rcutree.rcu_idle_gp_delay= [KNL]
3656 Set wakeup interval for idle CPUs that have
3657 RCU callbacks (RCU_FAST_NO_HZ=y).
3659 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3660 Set wakeup interval for idle CPUs that have
3661 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3662 Lazy RCU callbacks are those which RCU can
3663 prove do nothing more than free memory.
3665 rcutree.rcu_kick_kthreads= [KNL]
3666 Cause the grace-period kthread to get an extra
3667 wake_up() if it sleeps three times longer than
3668 it should at force-quiescent-state time.
3669 This wake_up() will be accompanied by a
3670 WARN_ONCE() splat and an ftrace_dump().
3672 rcuperf.gp_async= [KNL]
3673 Measure performance of asynchronous
3674 grace-period primitives such as call_rcu().
3676 rcuperf.gp_async_max= [KNL]
3677 Specify the maximum number of outstanding
3678 callbacks per writer thread. When a writer
3679 thread exceeds this limit, it invokes the
3680 corresponding flavor of rcu_barrier() to allow
3681 previously posted callbacks to drain.
3683 rcuperf.gp_exp= [KNL]
3684 Measure performance of expedited synchronous
3685 grace-period primitives.
3687 rcuperf.holdoff= [KNL]
3688 Set test-start holdoff period. The purpose of
3689 this parameter is to delay the start of the
3690 test until boot completes in order to avoid
3693 rcuperf.nreaders= [KNL]
3694 Set number of RCU readers. The value -1 selects
3695 N, where N is the number of CPUs. A value
3696 "n" less than -1 selects N-n+1, where N is again
3697 the number of CPUs. For example, -2 selects N
3698 (the number of CPUs), -3 selects N+1, and so on.
3699 A value of "n" less than or equal to -N selects
3702 rcuperf.nwriters= [KNL]
3703 Set number of RCU writers. The values operate
3704 the same as for rcuperf.nreaders.
3705 N, where N is the number of CPUs
3707 rcuperf.perf_type= [KNL]
3708 Specify the RCU implementation to test.
3710 rcuperf.shutdown= [KNL]
3711 Shut the system down after performance tests
3712 complete. This is useful for hands-off automated
3715 rcuperf.verbose= [KNL]
3716 Enable additional printk() statements.
3718 rcuperf.writer_holdoff= [KNL]
3719 Write-side holdoff between grace periods,
3720 in microseconds. The default of zero says
3723 rcutorture.cbflood_inter_holdoff= [KNL]
3724 Set holdoff time (jiffies) between successive
3725 callback-flood tests.
3727 rcutorture.cbflood_intra_holdoff= [KNL]
3728 Set holdoff time (jiffies) between successive
3729 bursts of callbacks within a given callback-flood
3732 rcutorture.cbflood_n_burst= [KNL]
3733 Set the number of bursts making up a given
3734 callback-flood test. Set this to zero to
3735 disable callback-flood testing.
3737 rcutorture.cbflood_n_per_burst= [KNL]
3738 Set the number of callbacks to be registered
3739 in a given burst of a callback-flood test.
3741 rcutorture.fqs_duration= [KNL]
3742 Set duration of force_quiescent_state bursts
3745 rcutorture.fqs_holdoff= [KNL]
3746 Set holdoff time within force_quiescent_state bursts
3749 rcutorture.fqs_stutter= [KNL]
3750 Set wait time between force_quiescent_state bursts
3753 rcutorture.gp_cond= [KNL]
3754 Use conditional/asynchronous update-side
3755 primitives, if available.
3757 rcutorture.gp_exp= [KNL]
3758 Use expedited update-side primitives, if available.
3760 rcutorture.gp_normal= [KNL]
3761 Use normal (non-expedited) asynchronous
3762 update-side primitives, if available.
3764 rcutorture.gp_sync= [KNL]
3765 Use normal (non-expedited) synchronous
3766 update-side primitives, if available. If all
3767 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3768 rcutorture.gp_normal=, and rcutorture.gp_sync=
3769 are zero, rcutorture acts as if is interpreted
3770 they are all non-zero.
3772 rcutorture.n_barrier_cbs= [KNL]
3773 Set callbacks/threads for rcu_barrier() testing.
3775 rcutorture.nfakewriters= [KNL]
3776 Set number of concurrent RCU writers. These just
3777 stress RCU, they don't participate in the actual
3778 test, hence the "fake".
3780 rcutorture.nreaders= [KNL]
3781 Set number of RCU readers. The value -1 selects
3782 N-1, where N is the number of CPUs. A value
3783 "n" less than -1 selects N-n-2, where N is again
3784 the number of CPUs. For example, -2 selects N
3785 (the number of CPUs), -3 selects N+1, and so on.
3787 rcutorture.object_debug= [KNL]
3788 Enable debug-object double-call_rcu() testing.
3790 rcutorture.onoff_holdoff= [KNL]
3791 Set time (s) after boot for CPU-hotplug testing.
3793 rcutorture.onoff_interval= [KNL]
3794 Set time (jiffies) between CPU-hotplug operations,
3795 or zero to disable CPU-hotplug testing.
3797 rcutorture.shuffle_interval= [KNL]
3798 Set task-shuffle interval (s). Shuffling tasks
3799 allows some CPUs to go into dyntick-idle mode
3800 during the rcutorture test.
3802 rcutorture.shutdown_secs= [KNL]
3803 Set time (s) after boot system shutdown. This
3804 is useful for hands-off automated testing.
3806 rcutorture.stall_cpu= [KNL]
3807 Duration of CPU stall (s) to test RCU CPU stall
3808 warnings, zero to disable.
3810 rcutorture.stall_cpu_holdoff= [KNL]
3811 Time to wait (s) after boot before inducing stall.
3813 rcutorture.stall_cpu_irqsoff= [KNL]
3814 Disable interrupts while stalling if set.
3816 rcutorture.stat_interval= [KNL]
3817 Time (s) between statistics printk()s.
3819 rcutorture.stutter= [KNL]
3820 Time (s) to stutter testing, for example, specifying
3821 five seconds causes the test to run for five seconds,
3822 wait for five seconds, and so on. This tests RCU's
3823 ability to transition abruptly to and from idle.
3825 rcutorture.test_boost= [KNL]
3826 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3827 "Maybe" means test if the RCU implementation
3828 under test support RCU priority boosting.
3830 rcutorture.test_boost_duration= [KNL]
3831 Duration (s) of each individual boost test.
3833 rcutorture.test_boost_interval= [KNL]
3834 Interval (s) between each boost test.
3836 rcutorture.test_no_idle_hz= [KNL]
3837 Test RCU's dyntick-idle handling. See also the
3838 rcutorture.shuffle_interval parameter.
3840 rcutorture.torture_type= [KNL]
3841 Specify the RCU implementation to test.
3843 rcutorture.verbose= [KNL]
3844 Enable additional printk() statements.
3846 rcupdate.rcu_cpu_stall_suppress= [KNL]
3847 Suppress RCU CPU stall warning messages.
3849 rcupdate.rcu_cpu_stall_timeout= [KNL]
3850 Set timeout for RCU CPU stall warning messages.
3852 rcupdate.rcu_expedited= [KNL]
3853 Use expedited grace-period primitives, for
3854 example, synchronize_rcu_expedited() instead
3855 of synchronize_rcu(). This reduces latency,
3856 but can increase CPU utilization, degrade
3857 real-time latency, and degrade energy efficiency.
3858 No effect on CONFIG_TINY_RCU kernels.
3860 rcupdate.rcu_normal= [KNL]
3861 Use only normal grace-period primitives,
3862 for example, synchronize_rcu() instead of
3863 synchronize_rcu_expedited(). This improves
3864 real-time latency, CPU utilization, and
3865 energy efficiency, but can expose users to
3866 increased grace-period latency. This parameter
3867 overrides rcupdate.rcu_expedited. No effect on
3868 CONFIG_TINY_RCU kernels.
3870 rcupdate.rcu_normal_after_boot= [KNL]
3871 Once boot has completed (that is, after
3872 rcu_end_inkernel_boot() has been invoked), use
3873 only normal grace-period primitives. No effect
3874 on CONFIG_TINY_RCU kernels.
3876 rcupdate.rcu_task_stall_timeout= [KNL]
3877 Set timeout in jiffies for RCU task stall warning
3878 messages. Disable with a value less than or equal
3881 rcupdate.rcu_self_test= [KNL]
3882 Run the RCU early boot self tests
3886 Run specified binary instead of /init from the ramdisk,
3887 used for early userspace startup. See initrd.
3890 Turn on/off individual RDT features. List is:
3891 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
3893 E.g. to turn on cmt and turn off mba use:
3897 Format (x86 or x86_64):
3898 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3900 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3902 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3903 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3904 reboot_force is either force or not specified,
3905 reboot_cpu is s[mp]#### with #### being the processor
3906 to be used for rebooting.
3909 [KNL, SMP] Set scheduler's default relax_domain_level.
3910 See Documentation/cgroup-v1/cpusets.txt.
3912 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
3913 Format: <base1>,<size1>[,<base2>,<size2>,...]
3914 Reserve I/O ports or memory so the kernel won't use
3915 them. If <base> is less than 0x10000, the region
3916 is assumed to be I/O ports; otherwise it is memory.
3918 reservetop= [X86-32]
3920 Reserves a hole at the top of the kernel virtual
3925 Set the amount of memory to reserve for BIOS at
3926 the bottom of the address space.
3928 reset_devices [KNL] Force drivers to reset the underlying device
3929 during initialization.
3932 Specify the partition device for software suspend
3934 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3936 resume_offset= [SWSUSP]
3937 Specify the offset from the beginning of the partition
3938 given by "resume=" at which the swap header is located,
3939 in <PAGE_SIZE> units (needed only for swap files).
3940 See Documentation/power/swsusp-and-swap-files.txt
3942 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3943 read the resume files
3945 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3946 Useful for devices that are detected asynchronously
3947 (e.g. USB and MMC devices).
3949 hibernate= [HIBERNATION]
3950 noresume Don't check if there's a hibernation image
3951 present during boot.
3952 nocompress Don't compress/decompress hibernation images.
3953 no Disable hibernation and resume.
3954 protect_image Turn on image protection during restoration
3955 (that will set all pages holding image data
3956 during restoration read-only).
3958 retain_initrd [RAM] Keep initrd memory after extraction
3960 rfkill.default_state=
3961 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3962 etc. communication is blocked by default.
3965 rfkill.master_switch_mode=
3966 0 The "airplane mode" button does nothing.
3967 1 The "airplane mode" button toggles between everything
3968 blocked and the previous configuration.
3969 2 The "airplane mode" button toggles between everything
3970 blocked and everything unblocked.
3972 rhash_entries= [KNL,NET]
3973 Set number of hash buckets for route cache
3976 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
3979 ro [KNL] Mount root device read-only on boot
3982 on Mark read-only kernel memory as read-only (default).
3983 off Leave read-only kernel memory writable for debugging.
3986 Enable the uart passthrough on the designated usb port
3987 on Rockchip SoCs. When active, the signals of the
3988 debug-uart get routed to the D+ and D- pins of the usb
3989 port and the regular usb controller gets disabled.
3991 root= [KNL] Root filesystem
3992 See name_to_dev_t comment in init/do_mounts.c.
3994 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3995 mount the root filesystem
3997 rootflags= [KNL] Set root filesystem mount option string
3999 rootfstype= [KNL] Set root filesystem type
4001 rootwait [KNL] Wait (indefinitely) for root device to show up.
4002 Useful for devices that are detected asynchronously
4003 (e.g. USB and MMC devices).
4005 rproc_mem=nn[KMG][@address]
4006 [KNL,ARM,CMA] Remoteproc physical memory block.
4007 Memory area to be used by remote processor image,
4010 rw [KNL] Mount root device read-write on boot
4012 S [KNL] Run init in single mode
4014 s390_iommu= [HW,S390]
4015 Set s390 IOTLB flushing mode
4017 With strict flushing every unmap operation will result in
4018 an IOTLB flush. Default is lazy flushing before reuse,
4022 See drivers/net/irda/sa1100_ir.c.
4024 sbni= [NET] Granch SBNI12 leased line adapter
4026 sched_debug [KNL] Enables verbose scheduler debug messages.
4028 schedstats= [KNL,X86] Enable or disable scheduled statistics.
4029 Allowed values are enable and disable. This feature
4030 incurs a small amount of overhead in the scheduler
4031 but is useful for debugging and performance tuning.
4033 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
4034 xtime_lock contention on larger systems, and/or RCU lock
4035 contention on all systems with CONFIG_MAXSMP set.
4036 Format: { "0" | "1" }
4037 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
4039 Note: increases power consumption, thus should only be
4040 enabled if running jitter sensitive (HPC/RT) workloads.
4042 security= [SECURITY] Choose a security module to enable at boot.
4043 If this boot parameter is not specified, only the first
4044 security module asking for security registration will be
4045 loaded. An invalid security module name will be treated
4046 as if no module has been chosen.
4048 selinux= [SELINUX] Disable or enable SELinux at boot time.
4049 Format: { "0" | "1" }
4050 See security/selinux/Kconfig help text.
4053 Default value is set via kernel config option.
4054 If enabled at boot time, /selinux/disable can be used
4055 later to disable prior to initial policy load.
4057 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
4058 Format: { "0" | "1" }
4059 See security/apparmor/Kconfig help text
4062 Default value is set via kernel config option.
4064 serialnumber [BUGS=X86-32]
4067 Maximal number of shapers.
4075 Disable merging of slabs with similar size. May be
4076 necessary if there is some reason to distinguish
4077 allocs to different slabs, especially in hardened
4078 environments where the risk of heap overflows and
4079 layout control by attackers can usually be
4080 frustrated by disabling merging. This will reduce
4081 most of the exposure of a heap attack to a single
4082 cache (risks via metadata attacks are mostly
4083 unchanged). Debug options disable merging on their
4085 For more information see Documentation/vm/slub.rst.
4087 slab_max_order= [MM, SLAB]
4088 Determines the maximum allowed order for slabs.
4089 A high setting may cause OOMs due to memory
4090 fragmentation. Defaults to 1 for systems with
4091 more than 32MB of RAM, 0 otherwise.
4093 slub_debug[=options[,slabs]] [MM, SLUB]
4094 Enabling slub_debug allows one to determine the
4095 culprit if slab objects become corrupted. Enabling
4096 slub_debug can create guard zones around objects and
4097 may poison objects when not in use. Also tracks the
4098 last alloc / free. For more information see
4099 Documentation/vm/slub.rst.
4101 slub_memcg_sysfs= [MM, SLUB]
4102 Determines whether to enable sysfs directories for
4103 memory cgroup sub-caches. 1 to enable, 0 to disable.
4104 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
4105 Enabling this can lead to a very high number of debug
4106 directories and files being created under
4109 slub_max_order= [MM, SLUB]
4110 Determines the maximum allowed order for slabs.
4111 A high setting may cause OOMs due to memory
4112 fragmentation. For more information see
4113 Documentation/vm/slub.rst.
4115 slub_min_objects= [MM, SLUB]
4116 The minimum number of objects per slab. SLUB will
4117 increase the slab order up to slub_max_order to
4118 generate a sufficiently large slab able to contain
4119 the number of objects indicated. The higher the number
4120 of objects the smaller the overhead of tracking slabs
4121 and the less frequently locks need to be acquired.
4122 For more information see Documentation/vm/slub.rst.
4124 slub_min_order= [MM, SLUB]
4125 Determines the minimum page order for slabs. Must be
4126 lower than slub_max_order.
4127 For more information see Documentation/vm/slub.rst.
4129 slub_nomerge [MM, SLUB]
4130 Same with slab_nomerge. This is supported for legacy.
4131 See slab_nomerge for more information.
4134 Format: <io1>[,<io2>[,...,<io8>]]
4136 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4137 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4138 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4139 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4140 smsc-ircc2.ircc_irq= [HW] IRQ line
4141 smsc-ircc2.ircc_dma= [HW] DMA channel
4142 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4143 0: Toshiba Satellite 1800 (GP data pin select)
4144 1: Fast pin select (default)
4147 smt [KNL,S390] Set the maximum number of threads (logical
4148 CPUs) to use per physical CPU on systems capable of
4149 symmetric multithreading (SMT). Will be capped to the
4150 actual hardware limit.
4152 Default: -1 (no limit)
4155 [KNL] Should the soft-lockup detector generate panics.
4158 A nonzero value instructs the soft-lockup detector
4159 to panic the machine when a soft-lockup occurs. This
4160 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
4161 which is the respective build-time switch to that
4164 softlockup_all_cpu_backtrace=
4165 [KNL] Should the soft-lockup detector generate
4166 backtraces on all cpus.
4169 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4170 See Documentation/laptops/sonypi.txt
4172 spectre_v2= [X86] Control mitigation of Spectre variant 2
4173 (indirect branch speculation) vulnerability.
4175 on - unconditionally enable
4176 off - unconditionally disable
4177 auto - kernel detects whether your CPU model is
4180 Selecting 'on' will, and 'auto' may, choose a
4181 mitigation method at run time according to the
4182 CPU, the available microcode, the setting of the
4183 CONFIG_RETPOLINE configuration option, and the
4184 compiler with which the kernel was built.
4186 Specific mitigations can also be selected manually:
4188 retpoline - replace indirect branches
4189 retpoline,generic - google's original retpoline
4190 retpoline,amd - AMD-specific minimal thunk
4192 Not specifying this option is equivalent to
4195 spec_store_bypass_disable=
4196 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4197 (Speculative Store Bypass vulnerability)
4199 Certain CPUs are vulnerable to an exploit against a
4200 a common industry wide performance optimization known
4201 as "Speculative Store Bypass" in which recent stores
4202 to the same memory location may not be observed by
4203 later loads during speculative execution. The idea
4204 is that such stores are unlikely and that they can
4205 be detected prior to instruction retirement at the
4206 end of a particular speculation execution window.
4208 In vulnerable processors, the speculatively forwarded
4209 store can be used in a cache side channel attack, for
4210 example to read memory to which the attacker does not
4211 directly have access (e.g. inside sandboxed code).
4213 This parameter controls whether the Speculative Store
4214 Bypass optimization is used.
4216 On x86 the options are:
4218 on - Unconditionally disable Speculative Store Bypass
4219 off - Unconditionally enable Speculative Store Bypass
4220 auto - Kernel detects whether the CPU model contains an
4221 implementation of Speculative Store Bypass and
4222 picks the most appropriate mitigation. If the
4223 CPU is not vulnerable, "off" is selected. If the
4224 CPU is vulnerable the default mitigation is
4225 architecture and Kconfig dependent. See below.
4226 prctl - Control Speculative Store Bypass per thread
4227 via prctl. Speculative Store Bypass is enabled
4228 for a process by default. The state of the control
4229 is inherited on fork.
4230 seccomp - Same as "prctl" above, but all seccomp threads
4231 will disable SSB unless they explicitly opt out.
4233 Default mitigations:
4234 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4236 On powerpc the options are:
4238 on,auto - On Power8 and Power9 insert a store-forwarding
4239 barrier on kernel entry and exit. On Power7
4240 perform a software flush on kernel entry and
4244 Not specifying this option is equivalent to
4245 spec_store_bypass_disable=auto.
4247 spia_io_base= [HW,MTD]
4252 srcutree.counter_wrap_check [KNL]
4253 Specifies how frequently to check for
4254 grace-period sequence counter wrap for the
4255 srcu_data structure's ->srcu_gp_seq_needed field.
4256 The greater the number of bits set in this kernel
4257 parameter, the less frequently counter wrap will
4258 be checked for. Note that the bottom two bits
4261 srcutree.exp_holdoff [KNL]
4262 Specifies how many nanoseconds must elapse
4263 since the end of the last SRCU grace period for
4264 a given srcu_struct until the next normal SRCU
4265 grace period will be considered for automatic
4266 expediting. Set to zero to disable automatic
4270 Speculative Store Bypass Disable control
4272 On CPUs that are vulnerable to the Speculative
4273 Store Bypass vulnerability and offer a
4274 firmware based mitigation, this parameter
4275 indicates how the mitigation should be used:
4277 force-on: Unconditionally enable mitigation for
4278 for both kernel and userspace
4279 force-off: Unconditionally disable mitigation for
4280 for both kernel and userspace
4281 kernel: Always enable mitigation in the
4282 kernel, and offer a prctl interface
4283 to allow userspace to register its
4284 interest in being mitigated too.
4286 stack_guard_gap= [MM]
4287 override the default stack gap protection. The value
4288 is in page units and it defines how many pages prior
4289 to (for stacks growing down) resp. after (for stacks
4290 growing up) the main stack are reserved for no other
4291 mapping. Default value is 256 pages.
4294 Enabled the stack tracer on boot up.
4296 stacktrace_filter=[function-list]
4297 [FTRACE] Limit the functions that the stack tracer
4298 will trace at boot up. function-list is a comma separated
4299 list of functions. This list can be changed at run
4300 time by the stack_trace_filter file in the debugfs
4301 tracing directory. Note, this enables stack tracing
4302 and the stacktrace above is not needed.
4306 Set the STI (builtin display/keyboard on the HP-PARISC
4307 machines) console (graphic card) which should be used
4308 as the initial boot-console.
4309 See also comment in drivers/video/console/sticore.c.
4312 See comment in drivers/video/console/sticore.c.
4315 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4317 sunrpc.min_resvport=
4318 sunrpc.max_resvport=
4320 SunRPC servers often require that client requests
4321 originate from a privileged port (i.e. a port in the
4322 range 0 < portnr < 1024).
4323 An administrator who wishes to reserve some of these
4324 ports for other uses may adjust the range that the
4325 kernel's sunrpc client considers to be privileged
4326 using these two parameters to set the minimum and
4327 maximum port values.
4329 sunrpc.svc_rpc_per_connection_limit=
4331 Limit the number of requests that the server will
4332 process in parallel from a single connection.
4333 The default value is 0 (no limit).
4337 Control how the NFS server code allocates CPUs to
4338 service thread pools. Depending on how many NICs
4339 you have and where their interrupts are bound, this
4340 option will affect which CPUs will do NFS serving.
4341 Note: this parameter cannot be changed while the
4342 NFS server is running.
4344 auto the server chooses an appropriate mode
4345 automatically using heuristics
4346 global a single global pool contains all CPUs
4347 percpu one pool for each CPU
4348 pernode one pool for each NUMA node (equivalent
4349 to global on non-NUMA machines)
4351 sunrpc.tcp_slot_table_entries=
4352 sunrpc.udp_slot_table_entries=
4354 Sets the upper limit on the number of simultaneous
4355 RPC calls that can be sent from the client to a
4356 server. Increasing these values may allow you to
4357 improve throughput, but will also increase the
4358 amount of memory reserved for use by the client.
4360 suspend.pm_test_delay=
4362 Sets the number of seconds to remain in a suspend test
4363 mode before resuming the system (see
4364 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4365 is set. Default value is 5.
4368 [KNL] Enable accounting of swap in memory resource
4369 controller if no parameter or 1 is given or disable
4370 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4372 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4373 Format: { <int> | force | noforce }
4374 <int> -- Number of I/O TLB slabs
4375 force -- force using of bounce buffers even if they
4376 wouldn't be automatically used by the kernel
4377 noforce -- Never use bounce buffers (for debugging)
4381 sysfs.deprecated=0|1 [KNL]
4382 Enable/disable old style sysfs layout for old udev
4383 on older distributions. When this option is enabled
4384 very new udev will not work anymore. When this option
4385 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4386 in older udev will not work anymore.
4387 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4388 the kernel configuration.
4390 sysrq_always_enabled
4392 Ignore sysrq setting - this boot parameter will
4393 neutralize any effect of /proc/sys/kernel/sysrq.
4394 Useful for debugging.
4396 tcpmhash_entries= [KNL,NET]
4397 Set the number of tcp_metrics_hash slots.
4398 Default value is 8192 or 16384 depending on total
4399 ram pages. This is used to specify the TCP metrics
4400 cache size. See Documentation/networking/ip-sysctl.txt
4401 "tcp_no_metrics_save" section for more details.
4405 test_suspend= [SUSPEND][,N]
4406 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4407 standby suspend) or "freeze" (for suspend type freeze)
4408 as the system sleep state during system startup with
4409 the optional capability to repeat N number of times.
4410 The system is woken from this state using a
4411 wakeup-capable RTC alarm.
4413 thash_entries= [KNL,NET]
4414 Set number of hash buckets for TCP connection
4416 thermal.act= [HW,ACPI]
4417 -1: disable all active trip points in all thermal zones
4418 <degrees C>: override all lowest active trip points
4420 thermal.crt= [HW,ACPI]
4421 -1: disable all critical trip points in all thermal zones
4422 <degrees C>: override all critical trip points
4424 thermal.nocrt= [HW,ACPI]
4425 Set to disable actions on ACPI thermal zone
4426 critical and hot trip points.
4428 thermal.off= [HW,ACPI]
4429 1: disable ACPI thermal control
4431 thermal.psv= [HW,ACPI]
4432 -1: disable all passive trip points
4433 <degrees C>: override all passive trip points to this
4436 thermal.tzp= [HW,ACPI]
4437 Specify global default ACPI thermal zone polling rate
4438 <deci-seconds>: poll all this frequency
4439 0: no polling (default)
4442 Force threading of all interrupt handlers except those
4443 marked explicitly IRQF_NO_THREAD.
4446 Enable the Transcendent memory driver if built-in.
4448 tmem.cleancache=0|1 [KNL, XEN]
4449 Default is on (1). Disable the usage of the cleancache
4450 API to send anonymous pages to the hypervisor.
4452 tmem.frontswap=0|1 [KNL, XEN]
4453 Default is on (1). Disable the usage of the frontswap
4454 API to send swap pages to the hypervisor. If disabled
4455 the selfballooning and selfshrinking are force disabled.
4457 tmem.selfballooning=0|1 [KNL, XEN]
4458 Default is on (1). Disable the driving of swap pages
4461 tmem.selfshrinking=0|1 [KNL, XEN]
4462 Default is on (1). Partial swapoff that immediately
4463 transfers pages from Xen hypervisor back to the
4464 kernel based on different criteria.
4468 Specify if the kernel should make use of the cpu
4469 topology information if the hardware supports this.
4470 The scheduler will make use of this information and
4471 e.g. base its process migration decisions on it.
4474 topology_updates= [KNL, PPC, NUMA]
4476 Specify if the kernel should ignore (off)
4477 topology updates sent by the hypervisor to this
4482 tpm_suspend_pcr=[HW,TPM]
4483 Format: integer pcr id
4484 Specify that at suspend time, the tpm driver
4485 should extend the specified pcr with zeros,
4486 as a workaround for some chips which fail to
4487 flush the last written pcr on TPM_SaveState.
4488 This will guarantee that all the other pcrs
4491 trace_buf_size=nn[KMG]
4492 [FTRACE] will set tracing buffer size on each cpu.
4494 trace_event=[event-list]
4495 [FTRACE] Set and start specified trace events in order
4496 to facilitate early boot debugging. The event-list is a
4497 comma separated list of trace events to enable. See
4498 also Documentation/trace/events.rst
4500 trace_options=[option-list]
4501 [FTRACE] Enable or disable tracer options at boot.
4502 The option-list is a comma delimited list of options
4503 that can be enabled or disabled just as if you were
4504 to echo the option name into
4506 /sys/kernel/debug/tracing/trace_options
4508 For example, to enable stacktrace option (to dump the
4509 stack trace of each event), add to the command line:
4511 trace_options=stacktrace
4513 See also Documentation/trace/ftrace.rst "trace options"
4517 Have the tracepoints sent to printk as well as the
4518 tracing ring buffer. This is useful for early boot up
4519 where the system hangs or reboots and does not give the
4520 option for reading the tracing buffer or performing a
4521 ftrace_dump_on_oops.
4523 To turn off having tracepoints sent to printk,
4524 echo 0 > /proc/sys/kernel/tracepoint_printk
4525 Note, echoing 1 into this file without the
4526 tracepoint_printk kernel cmdline option has no effect.
4530 Having tracepoints sent to printk() and activating high
4531 frequency tracepoints such as irq or sched, can cause
4532 the system to live lock.
4535 [FTRACE] enable this option to disable tracing when a
4536 warning is hit. This turns off "tracing_on". Tracing can
4537 be enabled again by echoing '1' into the "tracing_on"
4538 file located in /sys/kernel/debug/tracing/
4540 This option is useful, as it disables the trace before
4541 the WARNING dump is called, which prevents the trace to
4542 be filled with content caused by the warning output.
4544 This option can also be set at run time via the sysctl
4545 option: kernel/traceoff_on_warning
4547 transparent_hugepage=
4549 Format: [always|madvise|never]
4550 Can be used to control the default behavior of the system
4551 with respect to transparent hugepages.
4552 See Documentation/admin-guide/mm/transhuge.rst
4555 tsc= Disable clocksource stability checks for TSC.
4557 [x86] reliable: mark tsc clocksource as reliable, this
4558 disables clocksource verification at runtime, as well
4559 as the stability checks done at bootup. Used to enable
4560 high-resolution timer mode on older hardware, and in
4561 virtualized environment.
4562 [x86] noirqtime: Do not use TSC to do irq accounting.
4563 Used to run time disable IRQ_TIME_ACCOUNTING on any
4564 platforms where RDTSC is slow and this accounting
4566 [x86] unstable: mark the TSC clocksource as unstable, this
4567 marks the TSC unconditionally unstable at bootup and
4568 avoids any further wobbles once the TSC watchdog notices.
4570 turbografx.map[2|3]= [HW,JOY]
4571 TurboGraFX parallel port interface
4573 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4574 See also Documentation/input/devices/joystick-parport.rst
4576 udbg-immortal [PPC] When debugging early kernel crashes that
4577 happen after console_init() and before a proper
4578 console driver takes over, this boot options might
4579 help "seeing" what's going on.
4581 uhash_entries= [KNL,NET]
4582 Set number of hash buckets for UDP/UDP-Lite connections
4585 [USB] Ignore overcurrent events (default N).
4586 Some badly-designed motherboards generate lots of
4587 bogus events, for ports that aren't wired to
4588 anything. Set this parameter to avoid log spamming.
4589 Note that genuine overcurrent events won't be
4593 [X86] Cause panic on unknown NMI.
4595 usbcore.authorized_default=
4596 [USB] Default USB device authorization:
4597 (default -1 = authorized except for wireless USB,
4598 0 = not authorized, 1 = authorized)
4600 usbcore.autosuspend=
4601 [USB] The autosuspend time delay (in seconds) used
4602 for newly-detected USB devices (default 2). This
4603 is the time required before an idle device will be
4604 autosuspended. Devices for which the delay is set
4605 to a negative value won't be autosuspended at all.
4607 usbcore.usbfs_snoop=
4608 [USB] Set to log all usbfs traffic (default 0 = off).
4610 usbcore.usbfs_snoop_max=
4611 [USB] Maximum number of bytes to snoop in each URB
4614 usbcore.blinkenlights=
4615 [USB] Set to cycle leds on hubs (default 0 = off).
4617 usbcore.old_scheme_first=
4618 [USB] Start with the old device initialization
4619 scheme (default 0 = off).
4621 usbcore.usbfs_memory_mb=
4622 [USB] Memory limit (in MB) for buffers allocated by
4623 usbfs (default = 16, 0 = max = 2047).
4625 usbcore.use_both_schemes=
4626 [USB] Try the other device initialization scheme
4627 if the first one fails (default 1 = enabled).
4629 usbcore.initial_descriptor_timeout=
4630 [USB] Specifies timeout for the initial 64-byte
4631 USB_REQ_GET_DESCRIPTOR request in milliseconds
4632 (default 5000 = 5.0 seconds).
4634 usbcore.nousb [USB] Disable the USB subsystem
4637 [USB] A list of quirk entries to augment the built-in
4638 usb core quirk list. List entries are separated by
4639 commas. Each entry has the form
4640 VendorID:ProductID:Flags. The IDs are 4-digit hex
4641 numbers and Flags is a set of letters. Each letter
4642 will change the built-in quirk; setting it if it is
4643 clear and clearing it if it is set. The letters have
4644 the following meanings:
4645 a = USB_QUIRK_STRING_FETCH_255 (string
4646 descriptors must not be fetched using
4648 b = USB_QUIRK_RESET_RESUME (device can't resume
4649 correctly so reset it instead);
4650 c = USB_QUIRK_NO_SET_INTF (device can't handle
4651 Set-Interface requests);
4652 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
4653 handle its Configuration or Interface
4655 e = USB_QUIRK_RESET (device can't be reset
4656 (e.g morph devices), don't use reset);
4657 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
4658 more interface descriptions than the
4659 bNumInterfaces count, and can't handle
4660 talking to these interfaces);
4661 g = USB_QUIRK_DELAY_INIT (device needs a pause
4662 during initialization, after we read
4663 the device descriptor);
4664 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
4665 high speed and super speed interrupt
4666 endpoints, the USB 2.0 and USB 3.0 spec
4667 require the interval in microframes (1
4668 microframe = 125 microseconds) to be
4669 calculated as interval = 2 ^
4671 Devices with this quirk report their
4672 bInterval as the result of this
4673 calculation instead of the exponent
4674 variable used in the calculation);
4675 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
4676 handle device_qualifier descriptor
4678 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
4679 generates spurious wakeup, ignore
4680 remote wakeup capability);
4681 k = USB_QUIRK_NO_LPM (device can't handle Link
4683 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
4684 (Device reports its bInterval as linear
4685 frames instead of the USB 2.0
4687 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
4688 to be disconnected before suspend to
4689 prevent spurious wakeup);
4690 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
4691 pause after every control message);
4692 Example: quirks=0781:5580:bk,0a5c:5834:gij
4695 [USBHID] The interval which mice are to be polled at.
4698 [USBHID] The interval which joysticks are to be polled at.
4701 [USBHID] The interval which keyboards are to be polled at.
4703 usb-storage.delay_use=
4704 [UMS] The delay in seconds before a new device is
4705 scanned for Logical Units (default 1).
4708 [UMS] A list of quirks entries to supplement or
4709 override the built-in unusual_devs list. List
4710 entries are separated by commas. Each entry has
4711 the form VID:PID:Flags where VID and PID are Vendor
4712 and Product ID values (4-digit hex numbers) and
4713 Flags is a set of characters, each corresponding
4714 to a common usb-storage quirk flag as follows:
4715 a = SANE_SENSE (collect more than 18 bytes
4717 b = BAD_SENSE (don't collect more than 18
4718 bytes of sense data);
4719 c = FIX_CAPACITY (decrease the reported
4720 device capacity by one sector);
4721 d = NO_READ_DISC_INFO (don't use
4722 READ_DISC_INFO command);
4723 e = NO_READ_CAPACITY_16 (don't use
4724 READ_CAPACITY_16 command);
4725 f = NO_REPORT_OPCODES (don't use report opcodes
4727 g = MAX_SECTORS_240 (don't transfer more than
4728 240 sectors at a time, uas only);
4729 h = CAPACITY_HEURISTICS (decrease the
4730 reported device capacity by one
4731 sector if the number is odd);
4732 i = IGNORE_DEVICE (don't bind to this
4734 j = NO_REPORT_LUNS (don't use report luns
4736 l = NOT_LOCKABLE (don't try to lock and
4737 unlock ejectable media);
4738 m = MAX_SECTORS_64 (don't transfer more
4739 than 64 sectors = 32 KB at a time);
4740 n = INITIAL_READ10 (force a retry of the
4741 initial READ(10) command);
4742 o = CAPACITY_OK (accept the capacity
4743 reported by the device);
4744 p = WRITE_CACHE (the device cache is ON
4746 r = IGNORE_RESIDUE (the device reports
4747 bogus residue values);
4748 s = SINGLE_LUN (the device has only one
4750 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4751 commands, uas only);
4752 u = IGNORE_UAS (don't bind to the uas driver);
4753 w = NO_WP_DETECT (don't test whether the
4754 medium is write-protected).
4755 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4756 even if the device claims no cache)
4757 Example: quirks=0419:aaf5:rl,0421:0433:rc
4759 user_debug= [KNL,ARM]
4761 See arch/arm/Kconfig.debug help text.
4762 1 - undefined instruction events
4764 4 - invalid data aborts
4767 Example: user_debug=31
4770 [X86] Flags controlling user PTE allocations.
4772 nohigh = do not allocate PTE pages in
4773 HIGHMEM regardless of setting
4777 On X86_32, this is an alias for vdso32=. Otherwise:
4779 vdso=1: enable VDSO (the default)
4780 vdso=0: disable VDSO mapping
4782 vdso32= [X86] Control the 32-bit vDSO
4783 vdso32=1: enable 32-bit VDSO
4784 vdso32=0 or vdso32=2: disable 32-bit VDSO
4786 See the help text for CONFIG_COMPAT_VDSO for more
4787 details. If CONFIG_COMPAT_VDSO is set, the default is
4788 vdso32=0; otherwise, the default is vdso32=1.
4790 For compatibility with older kernels, vdso32=2 is an
4793 Try vdso32=0 if you encounter an error that says:
4794 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4797 vector=percpu: enable percpu vector domain
4799 video= [FB] Frame buffer configuration
4800 See Documentation/fb/modedb.txt.
4802 video.brightness_switch_enabled= [0,1]
4803 If set to 1, on receiving an ACPI notify event
4804 generated by hotkey, video driver will adjust brightness
4805 level and then send out the event to user space through
4806 the allocated input device; If set to 0, video driver
4807 will only send out the event without touching backlight
4812 [VMMIO] Memory mapped virtio (platform) device.
4814 <size>@<baseaddr>:<irq>[:<id>]
4816 <size> := size (can use standard suffixes
4818 <baseaddr> := physical base address
4819 <irq> := interrupt number (as passed to
4821 <id> := (optional) platform device id
4823 virtio_mmio.device=1K@0x100b0000:48:7
4825 Can be used multiple times for multiple devices.
4827 vga= [BOOT,X86-32] Select a particular video mode
4828 See Documentation/x86/boot.txt and
4829 Documentation/svga.txt.
4830 Use vga=ask for menu.
4831 This is actually a boot loader parameter; the value is
4832 passed to the kernel using a special protocol.
4834 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4835 size of <nn>. This can be used to increase the
4836 minimum size (128MB on x86). It can also be used to
4837 decrease the size and leave more room for directly
4840 vmcp_cma=nn[MG] [KNL,S390]
4841 Sets the memory size reserved for contiguous memory
4842 allocations for the vmcp device driver.
4844 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4847 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4850 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4854 Controls the behavior of vsyscalls (i.e. calls to
4855 fixed addresses of 0xffffffffff600x00 from legacy
4856 code). Most statically-linked binaries and older
4857 versions of glibc use these calls. Because these
4858 functions are at fixed addresses, they make nice
4859 targets for exploits that can control RIP.
4861 emulate [default] Vsyscalls turn into traps and are
4862 emulated reasonably safely.
4864 native Vsyscalls are native syscall instructions.
4865 This is a little bit faster than trapping
4866 and makes a few dynamic recompilers work
4867 better than they would in emulation mode.
4868 It also makes exploits much easier to write.
4870 none Vsyscalls don't work at all. This makes
4871 them quite hard to use for exploits but
4872 might break your system.
4874 vt.color= [VT] Default text color.
4875 Format: 0xYX, X = foreground, Y = background.
4876 Default: 0x07 = light gray on black.
4878 vt.cur_default= [VT] Default cursor shape.
4879 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4880 the parameters of the <Esc>[?A;B;Cc escape sequence;
4881 see VGA-softcursor.txt. Default: 2 = underline.
4883 vt.default_blu= [VT]
4884 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4885 Change the default blue palette of the console.
4886 This is a 16-member array composed of values
4889 vt.default_grn= [VT]
4890 Format: <green0>,<green1>,<green2>,...,<green15>
4891 Change the default green palette of the console.
4892 This is a 16-member array composed of values
4895 vt.default_red= [VT]
4896 Format: <red0>,<red1>,<red2>,...,<red15>
4897 Change the default red palette of the console.
4898 This is a 16-member array composed of values
4904 Set system-wide default UTF-8 mode for all tty's.
4905 Default is 1, i.e. UTF-8 mode is enabled for all
4906 newly opened terminals.
4908 vt.global_cursor_default=
4911 Set system-wide default for whether a cursor
4912 is shown on new VTs. Default is -1,
4913 i.e. cursors will be created by default unless
4914 overridden by individual drivers. 0 will hide
4915 cursors, 1 will display them.
4917 vt.italic= [VT] Default color for italic text; 0-15.
4920 vt.underline= [VT] Default color for underlined text; 0-15.
4923 watchdog timers [HW,WDT] For information on watchdog timers,
4924 see Documentation/watchdog/watchdog-parameters.txt
4925 or other driver-specific files in the
4926 Documentation/watchdog/ directory.
4928 workqueue.watchdog_thresh=
4929 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4930 warn stall conditions and dump internal state to
4931 help debugging. 0 disables workqueue stall
4932 detection; otherwise, it's the stall threshold
4933 duration in seconds. The default value is 30 and
4934 it can be updated at runtime by writing to the
4935 corresponding sysfs file.
4937 workqueue.disable_numa
4938 By default, all work items queued to unbound
4939 workqueues are affine to the NUMA nodes they're
4940 issued on, which results in better behavior in
4941 general. If NUMA affinity needs to be disabled for
4942 whatever reason, this option can be used. Note
4943 that this also can be controlled per-workqueue for
4944 workqueues visible under /sys/bus/workqueue/.
4946 workqueue.power_efficient
4947 Per-cpu workqueues are generally preferred because
4948 they show better performance thanks to cache
4949 locality; unfortunately, per-cpu workqueues tend to
4950 be more power hungry than unbound workqueues.
4952 Enabling this makes the per-cpu workqueues which
4953 were observed to contribute significantly to power
4954 consumption unbound, leading to measurably lower
4955 power usage at the cost of small performance
4958 The default value of this parameter is determined by
4959 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4961 workqueue.debug_force_rr_cpu
4962 Workqueue used to implicitly guarantee that work
4963 items queued without explicit CPU specified are put
4964 on the local CPU. This guarantee is no longer true
4965 and while local CPU is still preferred work items
4966 may be put on foreign CPUs. This debug option
4967 forces round-robin CPU selection to flush out
4968 usages which depend on the now broken guarantee.
4969 When enabled, memory and cache locality will be
4972 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4973 default x2apic cluster mode on platforms
4976 x86_intel_mid_timer= [X86-32,APBT]
4977 Choose timer option for x86 Intel MID platform.
4978 Two valid options are apbt timer only and lapic timer
4979 plus one apbt timer for broadcast timer.
4980 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4982 xen_512gb_limit [KNL,X86-64,XEN]
4983 Restricts the kernel running paravirtualized under Xen
4984 to use only up to 512 GB of RAM. The reason to do so is
4985 crash analysis tools and Xen tools for doing domain
4986 save/restore/migration must be enabled to handle larger
4989 xen_emul_unplug= [HW,X86,XEN]
4990 Unplug Xen emulated devices
4991 Format: [unplug0,][unplug1]
4992 ide-disks -- unplug primary master IDE devices
4993 aux-ide-disks -- unplug non-primary-master IDE devices
4994 nics -- unplug network devices
4995 all -- unplug all emulated devices (NICs and IDE disks)
4996 unnecessary -- unplugging emulated devices is
4997 unnecessary even if the host did not respond to
4999 never -- do not unplug even if version check succeeds
5001 xen_nopvspin [X86,XEN]
5002 Disables the ticketlock slowpath using Xen PV
5006 Disables the PV optimizations forcing the HVM guest to
5007 run as generic HVM guest with no PV drivers.
5009 xen_scrub_pages= [XEN]
5010 Boolean option to control scrubbing pages before giving them back
5011 to Xen, for use by other domains. Can be also changed at runtime
5012 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
5013 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
5015 xirc2ps_cs= [NET,PCMCIA]
5017 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
5019 xhci-hcd.quirks [USB,KNL]
5020 A hex value specifying bitmask with supplemental xhci
5021 host controller quirks. Meaning of each bit can be
5022 consulted in header drivers/usb/host/xhci.h.
git.samba.org / sfrench / cifs-2.6.git / blob