.. _kernelparameters:
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The kernel's command-line parameters
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====================================
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The following is a consolidated list of the kernel parameters as
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implemented by the __setup(), core_param() and module_param() macros
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and sorted into English Dictionary order (defined as ignoring all
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punctuation and sorting digits before letters in a case insensitive
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manner), and with descriptions where known.
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The kernel parses parameters from the kernel command line up to "``--``";
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if it doesn't recognize a parameter and it doesn't contain a '.', the
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parameter gets passed to init: parameters with '=' go into init's
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environment, others are passed as command line arguments to init.
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Everything after "``--``" is passed as an argument to init.
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Module parameters can be specified in two ways: via the kernel command
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line with a module name prefix, or via modprobe, e.g.::
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(kernel command line) usbcore.blinkenlights=1
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(modprobe command line) modprobe usbcore blinkenlights=1
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Parameters for modules which are built into the kernel need to be
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specified on the kernel command line. modprobe looks through the
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kernel command line (/proc/cmdline) and collects module parameters
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when it loads a module, so the kernel command line can be used for
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loadable modules too.
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Hyphens (dashes) and underscores are equivalent in parameter names, so::
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log_buf_len=1M print-fatal-signals=1
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can also be entered as::
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log-buf-len=1M print_fatal_signals=1
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Double-quotes can be used to protect spaces in values, e.g.::
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param="spaces in here"
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cpu lists:
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----------
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Some kernel parameters take a list of CPUs as a value, e.g. isolcpus,
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nohz_full, irqaffinity, rcu_nocbs. The format of this list is:
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<cpu number>,...,<cpu number>
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or
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<cpu number>-<cpu number>
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(must be a positive range in ascending order)
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or a mixture
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<cpu number>,...,<cpu number>-<cpu number>
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Note that for the special case of a range one can split the range into equal
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sized groups and for each group use some amount from the beginning of that
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group:
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<cpu number>-cpu number>:<used size>/<group size>
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For example one can add to the command line following parameter:
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isolcpus=1,2,10-20,100-2000:2/25
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where the final item represents CPUs 100,101,125,126,150,151,...
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This document may not be entirely up to date and comprehensive. The command
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"modinfo -p ${modulename}" shows a current list of all parameters of a loadable
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module. Loadable modules, after being loaded into the running kernel, also
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reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
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parameters may be changed at runtime by the command
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``echo -n ${value} > /sys/module/${modulename}/parameters/${parm}``.
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The parameters listed below are only valid if certain kernel build options were
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enabled and if respective hardware is present. The text in square brackets at
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the beginning of each description states the restrictions within which a
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parameter is applicable::
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ACPI ACPI support is enabled.
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AGP AGP (Accelerated Graphics Port) is enabled.
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ALSA ALSA sound support is enabled.
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APIC APIC support is enabled.
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APM Advanced Power Management support is enabled.
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ARM ARM architecture is enabled.
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ARM64 ARM64 architecture is enabled.
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AX25 Appropriate AX.25 support is enabled.
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CLK Common clock infrastructure is enabled.
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CMA Contiguous Memory Area support is enabled.
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DRM Direct Rendering Management support is enabled.
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DYNAMIC_DEBUG Build in debug messages and enable them at runtime
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EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
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EFI EFI Partitioning (GPT) is enabled
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EIDE EIDE/ATAPI support is enabled.
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EVM Extended Verification Module
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FB The frame buffer device is enabled.
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FTRACE Function tracing enabled.
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GCOV GCOV profiling is enabled.
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HW Appropriate hardware is enabled.
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IA-64 IA-64 architecture is enabled.
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IMA Integrity measurement architecture is enabled.
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IOSCHED More than one I/O scheduler is enabled.
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IP_PNP IP DHCP, BOOTP, or RARP is enabled.
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IPV6 IPv6 support is enabled.
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ISAPNP ISA PnP code is enabled.
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ISDN Appropriate ISDN support is enabled.
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ISOL CPU Isolation is enabled.
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JOY Appropriate joystick support is enabled.
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KGDB Kernel debugger support is enabled.
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KVM Kernel Virtual Machine support is enabled.
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LIBATA Libata driver is enabled
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LP Printer support is enabled.
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LOOP Loopback device support is enabled.
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M68k M68k architecture is enabled.
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These options have more detailed description inside of
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Documentation/m68k/kernel-options.rst.
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MDA MDA console support is enabled.
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MIPS MIPS architecture is enabled.
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MOUSE Appropriate mouse support is enabled.
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MSI Message Signaled Interrupts (PCI).
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MTD MTD (Memory Technology Device) support is enabled.
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NET Appropriate network support is enabled.
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NUMA NUMA support is enabled.
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NFS Appropriate NFS support is enabled.
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OF Devicetree is enabled.
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OSS OSS sound support is enabled.
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PV_OPS A paravirtualized kernel is enabled.
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PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
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PARISC The PA-RISC architecture is enabled.
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PCI PCI bus support is enabled.
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PCIE PCI Express support is enabled.
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PCMCIA The PCMCIA subsystem is enabled.
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PNP Plug & Play support is enabled.
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PPC PowerPC architecture is enabled.
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PPT Parallel port support is enabled.
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PS2 Appropriate PS/2 support is enabled.
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RAM RAM disk support is enabled.
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RDT Intel Resource Director Technology.
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S390 S390 architecture is enabled.
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SCSI Appropriate SCSI support is enabled.
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A lot of drivers have their options described inside
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the Documentation/scsi/ sub-directory.
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SECURITY Different security models are enabled.
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SELINUX SELinux support is enabled.
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APPARMOR AppArmor support is enabled.
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SERIAL Serial support is enabled.
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SH SuperH architecture is enabled.
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SMP The kernel is an SMP kernel.
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SPARC Sparc architecture is enabled.
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SWSUSP Software suspend (hibernation) is enabled.
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SUSPEND System suspend states are enabled.
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TPM TPM drivers are enabled.
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TS Appropriate touchscreen support is enabled.
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UMS USB Mass Storage support is enabled.
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USB USB support is enabled.
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USBHID USB Human Interface Device support is enabled.
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V4L Video For Linux support is enabled.
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VMMIO Driver for memory mapped virtio devices is enabled.
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VGA The VGA console has been enabled.
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VT Virtual terminal support is enabled.
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WDT Watchdog support is enabled.
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XT IBM PC/XT MFM hard disk support is enabled.
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X86-32 X86-32, aka i386 architecture is enabled.
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X86-64 X86-64 architecture is enabled.
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More X86-64 boot options can be found in
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Documentation/x86/x86_64/boot-options.rst.
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X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
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X86_UV SGI UV support is enabled.
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XEN Xen support is enabled
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In addition, the following text indicates that the option::
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BUGS= Relates to possible processor bugs on the said processor.
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KNL Is a kernel start-up parameter.
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BOOT Is a boot loader parameter.
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Parameters denoted with BOOT are actually interpreted by the boot
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loader, and have no meaning to the kernel directly.
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Do not modify the syntax of boot loader parameters without extreme
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need or coordination with <Documentation/x86/boot.rst>.
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There are also arch-specific kernel-parameters not documented here.
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See for example <Documentation/x86/x86_64/boot-options.rst>.
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Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
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a trailing = on the name of any parameter states that that parameter will
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be entered as an environment variable, whereas its absence indicates that
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it will appear as a kernel argument readable via /proc/cmdline by programs
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running once the system is up.
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The number of kernel parameters is not limited, but the length of the
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complete command line (parameters including spaces etc.) is limited to
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a fixed number of characters. This limit depends on the architecture
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and is between 256 and 4096 characters. It is defined in the file
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./include/asm/setup.h as COMMAND_LINE_SIZE.
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Finally, the [KMG] suffix is commonly described after a number of kernel
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parameter values. These 'K', 'M', and 'G' letters represent the _binary_
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multipliers 'Kilo', 'Mega', and 'Giga', equaling 2^10, 2^20, and 2^30
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bytes respectively. Such letter suffixes can also be entirely omitted:
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.. include:: kernel-parameters.txt
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:literal:
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Todo
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----
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Add more DRM drivers.
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