default: 0
acpi_backlight= [HW,ACPI]
- acpi_backlight=vendor
- acpi_backlight=video
- If set to vendor, prefer vendor specific driver
+ { vendor | video | native | none }
+ If set to vendor, prefer vendor-specific driver
(e.g. thinkpad_acpi, sony_acpi, etc.) instead
of the ACPI video.ko driver.
+ If set to video, use the ACPI video.ko driver.
+ If set to native, use the device's native backlight mode.
+ If set to none, disable the ACPI backlight interface.
acpi_force_32bit_fadt_addr
force FADT to use 32 bit addresses rather than the
dynamic table installation which will install SSDT
tables to /sys/firmware/acpi/tables/dynamic.
+ acpi_no_watchdog [HW,ACPI,WDT]
+ Ignore the ACPI-based watchdog interface (WDAT) and let
+ a native driver control the watchdog device instead.
+
acpi_rsdp= [ACPI,EFI,KEXEC]
Pass the RSDP address to the kernel, mostly used
on machines running EFI runtime service to boot the
bert_disable [ACPI]
Disable BERT OS support on buggy BIOSes.
+ bgrt_disable [ACPI][X86]
+ Disable BGRT to avoid flickering OEM logo.
+
bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
bttv.radio= Most important insmod options are available as
kernel args too.
Default value is set via a kernel config option.
Value can be changed at runtime via
/sys/fs/selinux/checkreqprot.
+ Setting checkreqprot to 1 is deprecated.
cio_ignore= [S390]
See Documentation/s390/common_io.rst for details.
coredump_filter=
[KNL] Change the default value for
/proc/<pid>/coredump_filter.
- See also Documentation/filesystems/proc.txt.
+ See also Documentation/filesystems/proc.rst.
coresight_cpu_debug.enable
[ARM,ARM64]
edid/1680x1050.bin, or edid/1920x1080.bin is given
and no file with the same name exists. Details and
instructions how to build your own EDID data are
- available in Documentation/driver-api/edid.rst. An EDID
+ available in Documentation/admin-guide/edid.rst. An EDID
data set will only be used for a particular connector,
if its name and a colon are prepended to the EDID
name. Each connector may use a unique EDID data
Documentation/admin-guide/dynamic-debug-howto.rst
for details.
- nompx [X86] Disables Intel Memory Protection Extensions.
- See Documentation/x86/intel_mpx.rst for more
- information about the feature.
-
nopku [X86] Disable Memory Protection Keys CPU feature found
in some Intel CPUs.
A valid base address must be provided, and the serial
port must already be setup and configured.
+ ec_imx21,<addr>
+ ec_imx6q,<addr>
+ Start an early, polled-mode, output-only console on the
+ Freescale i.MX UART at the specified address. The UART
+ must already be setup and configured.
+
ar3700_uart,<addr>
Start an early, polled-mode console on the
Armada 3700 serial port at the specified
can be changed at run time by the max_graph_depth file
in the tracefs tracing directory. default: 0 (no limit)
+ fw_devlink= [KNL] Create device links between consumer and supplier
+ devices by scanning the firmware to infer the
+ consumer/supplier relationships. This feature is
+ especially useful when drivers are loaded as modules as
+ it ensures proper ordering of tasks like device probing
+ (suppliers first, then consumers), supplier boot state
+ clean up (only after all consumers have probed),
+ suspend/resume & runtime PM (consumers first, then
+ suppliers).
+ Format: { off | permissive | on | rpm }
+ off -- Don't create device links from firmware info.
+ permissive -- Create device links from firmware info
+ but use it only for ordering boot state clean
+ up (sync_state() calls).
+ on -- Create device links from firmware info and use it
+ to enforce probe and suspend/resume ordering.
+ rpm -- Like "on", but also use to order runtime PM.
+
gamecon.map[2|3]=
[HW,JOY] Multisystem joystick and NES/SNES/PSX pad
support via parallel port (up to 5 devices per port)
provided by tboot because it makes the system
vulnerable to DMA attacks.
nobounce [Default off]
- Disable bounce buffer for unstrusted devices such as
+ Disable bounce buffer for untrusted devices such as
the Thunderbolt devices. This will treat the untrusted
devices as the trusted ones, hence might expose security
risks of DMA attacks.
No delay
ip= [IP_PNP]
- See Documentation/filesystems/nfs/nfsroot.txt.
+ See Documentation/admin-guide/nfs/nfsroot.rst.
ipcmni_extend [KNL] Extend the maximum number of unique System V
IPC identifiers from 32,768 to 16,777,216.
For details see: Documentation/admin-guide/hw-vuln/mds.rst
mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
- Amount of memory to be used when the kernel is not able
- to see the whole system memory or for test.
+ Amount of memory to be used in cases as follows:
+
+ 1 for test;
+ 2 when the kernel is not able to see the whole system memory;
+ 3 memory that lies after 'mem=' boundary is excluded from
+ the hypervisor, then assigned to KVM guests.
+
[X86] Work as limiting max address. Use together
with memmap= to avoid physical address space collisions.
Without memmap= PCI devices could be placed at addresses
belonging to unused RAM.
+ Note that this only takes effects during boot time since
+ in above case 3, memory may need be hot added after boot
+ if system memory of hypervisor is not sufficient.
+
mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
memory.
<name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
mtdparts= [MTD]
- See drivers/mtd/cmdlinepart.c.
+ See drivers/mtd/parsers/cmdlinepart.c
multitce=off [PPC] This parameter disables the use of the pSeries
firmware feature for updating multiple TCE entries
Default value is 0.
nfsaddrs= [NFS] Deprecated. Use ip= instead.
- See Documentation/filesystems/nfs/nfsroot.txt.
+ See Documentation/admin-guide/nfs/nfsroot.rst.
nfsroot= [NFS] nfs root filesystem for disk-less boxes.
- See Documentation/filesystems/nfs/nfsroot.txt.
+ See Documentation/admin-guide/nfs/nfsroot.rst.
nfsrootdebug [NFS] enable nfsroot debugging messages.
- See Documentation/filesystems/nfs/nfsroot.txt.
+ See Documentation/admin-guide/nfs/nfsroot.rst.
nfs.callback_nr_threads=
[NFSv4] set the total number of threads that the
[X86,PV_OPS] Disable paravirtualized VMware scheduler
clock and use the default one.
- no-steal-acc [X86,KVM,ARM64] Disable paravirtualized steal time
+ no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time
accounting. steal time is computed, but won't
influence scheduler behaviour
This can be set from sysctl after boot.
See Documentation/admin-guide/sysctl/vm.rst for details.
- of_devlink [OF, KNL] Create device links between consumer and
- supplier devices by scanning the devictree to infer the
- consumer/supplier relationships. A consumer device
- will not be probed until all the supplier devices have
- probed successfully.
-
ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
See Documentation/debugging-via-ohci1394.txt for more
info.
Override pmtimer IOPort with a hex value.
e.g. pmtmr=0x508
+ pm_debug_messages [SUSPEND,KNL]
+ Enable suspend/resume debug messages during boot up.
+
pnp.debug=1 [PNP]
Enable PNP debug messages (depends on the
CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
before loading.
See Documentation/admin-guide/blockdev/ramdisk.rst.
+ prot_virt= [S390] enable hosting protected virtual machines
+ isolated from the hypervisor (if hardware supports
+ that).
+ Format: <bool>
+
psi= [KNL] Enable or disable pressure stall information
tracking.
Format: <bool>
Set threshold of queued RCU callbacks below which
batch limiting is re-enabled.
+ rcutree.qovld= [KNL]
+ Set threshold of queued RCU callbacks beyond which
+ RCU's force-quiescent-state scan will aggressively
+ enlist help from cond_resched() and sched IPIs to
+ help CPUs more quickly reach quiescent states.
+ Set to less than zero to make this be set based
+ on rcutree.qhimark at boot time and to zero to
+ disable more aggressive help enlistment.
+
rcutree.rcu_idle_gp_delay= [KNL]
Set wakeup interval for idle CPUs that have
RCU callbacks (RCU_FAST_NO_HZ=y).
rcupdate.rcu_cpu_stall_suppress= [KNL]
Suppress RCU CPU stall warning messages.
+ rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL]
+ Suppress RCU CPU stall warning messages and
+ rcutorture writer stall warnings that occur
+ during early boot, that is, during the time
+ before the init task is spawned.
+
rcupdate.rcu_cpu_stall_timeout= [KNL]
Set timeout for RCU CPU stall warning messages.
incurs a small amount of overhead in the scheduler
but is useful for debugging and performance tuning.
+ sched_thermal_decay_shift=
+ [KNL, SMP] Set a decay shift for scheduler thermal
+ pressure signal. Thermal pressure signal follows the
+ default decay period of other scheduler pelt
+ signals(usually 32 ms but configurable). Setting
+ sched_thermal_decay_shift will left shift the decay
+ period for the thermal pressure signal by the shift
+ value.
+ i.e. with the default pelt decay period of 32 ms
+ sched_thermal_decay_shift thermal pressure decay pr
+ 1 64 ms
+ 2 128 ms
+ and so on.
+ Format: integer between 0 and 10
+ Default is 0.
+
skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
xtime_lock contention on larger systems, and/or RCU lock
contention on all systems with CONFIG_MAXSMP set.
Format: <integer>
A nonzero value instructs the soft-lockup detector
- to panic the machine when a soft-lockup occurs. This
- is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
- which is the respective build-time switch to that
- functionality.
+ to panic the machine when a soft-lockup occurs. It is
+ also controlled by the kernel.softlockup_panic sysctl
+ and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the
+ respective build-time switch to that functionality.
softlockup_all_cpu_backtrace=
[KNL] Should the soft-lockup detector generate
spia_pedr=
spia_peddr=
+ split_lock_detect=
+ [X86] Enable split lock detection
+
+ When enabled (and if hardware support is present), atomic
+ instructions that access data across cache line
+ boundaries will result in an alignment check exception.
+
+ off - not enabled
+
+ warn - the kernel will emit rate limited warnings
+ about applications triggering the #AC
+ exception. This mode is the default on CPUs
+ that supports split lock detection.
+
+ fatal - the kernel will send SIGBUS to applications
+ that trigger the #AC exception.
+
+ If an #AC exception is hit in the kernel or in
+ firmware (i.e. not while executing in user mode)
+ the kernel will oops in either "warn" or "fatal"
+ mode.
+
srcutree.counter_wrap_check [KNL]
Specifies how frequently to check for
grace-period sequence counter wrap for the
topology updates sent by the hypervisor to this
LPAR.
+ torture.disable_onoff_at_boot= [KNL]
+ Prevent the CPU-hotplug component of torturing
+ until after init has spawned.
+
tp720= [HW,PS2]
tpm_suspend_pcr=[HW,TPM]
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