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