Kernel Parameters
~~~~~~~~~~~~~~~~~
-The following is a consolidated list of the kernel parameters as implemented
-(mostly) by the __setup() macro and sorted into English Dictionary order
-(defined as ignoring all punctuation and sorting digits before letters in a
-case insensitive manner), and with descriptions where known.
-
-Module parameters for loadable modules are specified only as the
-parameter name with optional '=' and value as appropriate, such as:
-
- modprobe usbcore blinkenlights=1
-
-Module parameters for modules that are built into the kernel image
-are specified on the kernel command line with the module name plus
-'.' plus parameter name, with '=' and value if appropriate, such as:
-
- usbcore.blinkenlights=1
+The following is a consolidated list of the kernel parameters as
+implemented by the __setup(), core_param() and module_param() macros
+and sorted into English Dictionary order (defined as ignoring all
+punctuation and sorting digits before letters in a case insensitive
+manner), and with descriptions where known.
+
+The kernel parses parameters from the kernel command line up to "--";
+if it doesn't recognize a parameter and it doesn't contain a '.', the
+parameter gets passed to init: parameters with '=' go into init's
+environment, others are passed as command line arguments to init.
+Everything after "--" is passed as an argument to init.
+
+Module parameters can be specified in two ways: via the kernel command
+line with a module name prefix, or via modprobe, e.g.:
+
+ (kernel command line) usbcore.blinkenlights=1
+ (modprobe command line) modprobe usbcore blinkenlights=1
+
+Parameters for modules which are built into the kernel need to be
+specified on the kernel command line. modprobe looks through the
+kernel command line (/proc/cmdline) and collects module parameters
+when it loads a module, so the kernel command line can be used for
+loadable modules too.
Hyphens (dashes) and underscores are equivalent in parameter names, so
log_buf_len=1M print-fatal-signals=1
can also be entered as
log-buf-len=1M print_fatal_signals=1
+Double-quotes can be used to protect spaces in values, e.g.:
+ param="spaces in here"
This document may not be entirely up to date and comprehensive. The command
"modinfo -p ${modulename}" shows a current list of all parameters of a loadable
unusable. The "log_buf_len" parameter may be useful
if you need to capture more output.
+ acpi_force_table_verification [HW,ACPI]
+ Enable table checksum verification during early stage.
+ By default, this is disabled due to x86 early mapping
+ size limitation.
+
acpi_irq_balance [HW,ACPI]
ACPI will balance active IRQs
default in APIC mode
This feature is enabled by default.
This option allows to turn off the feature.
- acpi_no_auto_ssdt [HW,ACPI] Disable automatic loading of SSDT
+ acpi_no_static_ssdt [HW,ACPI]
+ Disable installation of static SSDTs at early boot time
+ By default, SSDTs contained in the RSDT/XSDT will be
+ installed automatically and they will appear under
+ /sys/firmware/acpi/tables.
+ This option turns off this feature.
+ Note that specifying this option does not affect
+ dynamic table installation which will install SSDT
+ tables to /sys/firmware/acpi/tables/dynamic.
acpica_no_return_repair [HW, ACPI]
Disable AML predefined validation mechanism
Also note the kernel might malfunction if you disable
some critical bits.
- cma=nn[MG] [ARM,KNL]
- Sets the size of kernel global memory area for contiguous
+ cma=nn[MG]@[start[MG][-end[MG]]]
+ [ARM,X86,KNL]
+ Sets the size of kernel global memory area for
+ contiguous memory allocations and optionally the
+ placement constraint by the physical address range of
memory allocations. For more information, see
include/linux/dma-contiguous.h
which are not unmapped.
earlycon= [KNL] Output early console device and options.
+
uart[8250],io,<addr>[,options]
uart[8250],mmio,<addr>[,options]
uart[8250],mmio32,<addr>[,options]
(mmio) or 32-bit (mmio32).
The options are the same as for ttyS, above.
- earlyprintk= [X86,SH,BLACKFIN,ARM]
+ pl011,<addr>
+ Start an early, polled-mode console on a pl011 serial
+ port at the specified address. The pl011 serial port
+ must already be setup and configured. Options are not
+ yet supported.
+
+ smh Use ARM semihosting calls for early console.
+
+ earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
earlyprintk=vga
earlyprintk=efi
earlyprintk=xen
for working out where the kernel is dying during
startup.
+ initcall_blacklist= [KNL] Do not execute a comma-separated list of
+ initcall functions. Useful for debugging built-in
+ modules and initcalls.
+
initrd= [BOOT] Specify the location of the initial ramdisk
inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
timeout < 0: reboot immediately
Format: <timeout>
+ crash_kexec_post_notifiers
+ Run kdump after running panic-notifiers and dumping
+ kmsg. This only for the users who doubt kdump always
+ succeeds in any situation.
+ Note that this also increases risks of kdump failure,
+ because some panic notifiers can make the crashed
+ kernel more unstable.
+
parkbd.port= [HW] Parallel port number the keyboard adapter is
connected to, default is 0.
Format: <parport#>
[KNL, SMP] Set scheduler's default relax_domain_level.
See Documentation/cgroups/cpusets.txt.
+ relative_sleep_states=
+ [SUSPEND] Use sleep state labeling where the deepest
+ state available other than hibernation is always "mem".
+ Format: { "0" | "1" }
+ 0 -- Traditional sleep state labels.
+ 1 -- Relative sleep state labels.
+
reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
reservetop= [X86-32]
the allocated input device; If set to 0, video driver
will only send out the event without touching backlight
brightness level.
- default: 1
+ default: 0
virtio_mmio.device=
[VMMIO] Memory mapped virtio (platform) device.
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