1The kernel's command-line parameters 2==================================== 3 4The following is a consolidated list of the kernel parameters as 5implemented by the __setup(), core_param() and module_param() macros 6and sorted into English Dictionary order (defined as ignoring all 7punctuation and sorting digits before letters in a case insensitive 8manner), and with descriptions where known. 9 10The kernel parses parameters from the kernel command line up to "--"; 11if it doesn't recognize a parameter and it doesn't contain a '.', the 12parameter gets passed to init: parameters with '=' go into init's 13environment, others are passed as command line arguments to init. 14Everything after "--" is passed as an argument to init. 15 16Module parameters can be specified in two ways: via the kernel command 17line with a module name prefix, or via modprobe, e.g.:: 18 19 (kernel command line) usbcore.blinkenlights=1 20 (modprobe command line) modprobe usbcore blinkenlights=1 21 22Parameters for modules which are built into the kernel need to be 23specified on the kernel command line. modprobe looks through the 24kernel command line (/proc/cmdline) and collects module parameters 25when it loads a module, so the kernel command line can be used for 26loadable modules too. 27 28Hyphens (dashes) and underscores are equivalent in parameter names, so:: 29 30 log_buf_len=1M print-fatal-signals=1 31 32can also be entered as:: 33 34 log-buf-len=1M print_fatal_signals=1 35 36Double-quotes can be used to protect spaces in values, e.g.:: 37 38 param="spaces in here" 39 40cpu lists: 41---------- 42 43Some kernel parameters take a list of CPUs as a value, e.g. isolcpus, 44nohz_full, irqaffinity, rcu_nocbs. The format of this list is: 45 46 <cpu number>,...,<cpu number> 47 48or 49 50 <cpu number>-<cpu number> 51 (must be a positive range in ascending order) 52 53or a mixture 54 55<cpu number>,...,<cpu number>-<cpu number> 56 57Note that for the special case of a range one can split the range into equal 58sized groups and for each group use some amount from the beginning of that 59group: 60 61 <cpu number>-cpu number>:<used size>/<group size> 62 63For example one can add to the command line following parameter: 64 65 isolcpus=1,2,10-20,100-2000:2/25 66 67where the final item represents CPUs 100,101,125,126,150,151,... 68 69 70 71This document may not be entirely up to date and comprehensive. The command 72"modinfo -p ${modulename}" shows a current list of all parameters of a loadable 73module. Loadable modules, after being loaded into the running kernel, also 74reveal their parameters in /sys/module/${modulename}/parameters/. Some of these 75parameters may be changed at runtime by the command 76``echo -n ${value} > /sys/module/${modulename}/parameters/${parm}``. 77 78The parameters listed below are only valid if certain kernel build options were 79enabled and if respective hardware is present. The text in square brackets at 80the beginning of each description states the restrictions within which a 81parameter is applicable:: 82 83 ACPI ACPI support is enabled. 84 AGP AGP (Accelerated Graphics Port) is enabled. 85 ALSA ALSA sound support is enabled. 86 APIC APIC support is enabled. 87 APM Advanced Power Management support is enabled. 88 ARM ARM architecture is enabled. 89 AVR32 AVR32 architecture is enabled. 90 AX25 Appropriate AX.25 support is enabled. 91 BLACKFIN Blackfin architecture is enabled. 92 CLK Common clock infrastructure is enabled. 93 CMA Contiguous Memory Area support is enabled. 94 DRM Direct Rendering Management support is enabled. 95 DYNAMIC_DEBUG Build in debug messages and enable them at runtime 96 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled 97 EFI EFI Partitioning (GPT) is enabled 98 EIDE EIDE/ATAPI support is enabled. 99 EVM Extended Verification Module 100 FB The frame buffer device is enabled. 101 FTRACE Function tracing enabled. 102 GCOV GCOV profiling is enabled. 103 HW Appropriate hardware is enabled. 104 IA-64 IA-64 architecture is enabled. 105 IMA Integrity measurement architecture is enabled. 106 IOSCHED More than one I/O scheduler is enabled. 107 IP_PNP IP DHCP, BOOTP, or RARP is enabled. 108 IPV6 IPv6 support is enabled. 109 ISAPNP ISA PnP code is enabled. 110 ISDN Appropriate ISDN support is enabled. 111 JOY Appropriate joystick support is enabled. 112 KGDB Kernel debugger support is enabled. 113 KVM Kernel Virtual Machine support is enabled. 114 LIBATA Libata driver is enabled 115 LP Printer support is enabled. 116 LOOP Loopback device support is enabled. 117 M68k M68k architecture is enabled. 118 These options have more detailed description inside of 119 Documentation/m68k/kernel-options.txt. 120 MDA MDA console support is enabled. 121 MIPS MIPS architecture is enabled. 122 MOUSE Appropriate mouse support is enabled. 123 MSI Message Signaled Interrupts (PCI). 124 MTD MTD (Memory Technology Device) support is enabled. 125 NET Appropriate network support is enabled. 126 NUMA NUMA support is enabled. 127 NFS Appropriate NFS support is enabled. 128 OSS OSS sound support is enabled. 129 PV_OPS A paravirtualized kernel is enabled. 130 PARIDE The ParIDE (parallel port IDE) subsystem is enabled. 131 PARISC The PA-RISC architecture is enabled. 132 PCI PCI bus support is enabled. 133 PCIE PCI Express support is enabled. 134 PCMCIA The PCMCIA subsystem is enabled. 135 PNP Plug & Play support is enabled. 136 PPC PowerPC architecture is enabled. 137 PPT Parallel port support is enabled. 138 PS2 Appropriate PS/2 support is enabled. 139 RAM RAM disk support is enabled. 140 S390 S390 architecture is enabled. 141 SCSI Appropriate SCSI support is enabled. 142 A lot of drivers have their options described inside 143 the Documentation/scsi/ sub-directory. 144 SECURITY Different security models are enabled. 145 SELINUX SELinux support is enabled. 146 APPARMOR AppArmor support is enabled. 147 SERIAL Serial support is enabled. 148 SH SuperH architecture is enabled. 149 SMP The kernel is an SMP kernel. 150 SPARC Sparc architecture is enabled. 151 SWSUSP Software suspend (hibernation) is enabled. 152 SUSPEND System suspend states are enabled. 153 TPM TPM drivers are enabled. 154 TS Appropriate touchscreen support is enabled. 155 UMS USB Mass Storage support is enabled. 156 USB USB support is enabled. 157 USBHID USB Human Interface Device support is enabled. 158 V4L Video For Linux support is enabled. 159 VMMIO Driver for memory mapped virtio devices is enabled. 160 VGA The VGA console has been enabled. 161 VT Virtual terminal support is enabled. 162 WDT Watchdog support is enabled. 163 XT IBM PC/XT MFM hard disk support is enabled. 164 X86-32 X86-32, aka i386 architecture is enabled. 165 X86-64 X86-64 architecture is enabled. 166 More X86-64 boot options can be found in 167 Documentation/x86/x86_64/boot-options.txt . 168 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64) 169 X86_UV SGI UV support is enabled. 170 XEN Xen support is enabled 171 172In addition, the following text indicates that the option:: 173 174 BUGS= Relates to possible processor bugs on the said processor. 175 KNL Is a kernel start-up parameter. 176 BOOT Is a boot loader parameter. 177 178Parameters denoted with BOOT are actually interpreted by the boot 179loader, and have no meaning to the kernel directly. 180Do not modify the syntax of boot loader parameters without extreme 181need or coordination with <Documentation/x86/boot.txt>. 182 183There are also arch-specific kernel-parameters not documented here. 184See for example <Documentation/x86/x86_64/boot-options.txt>. 185 186Note that ALL kernel parameters listed below are CASE SENSITIVE, and that 187a trailing = on the name of any parameter states that that parameter will 188be entered as an environment variable, whereas its absence indicates that 189it will appear as a kernel argument readable via /proc/cmdline by programs 190running once the system is up. 191 192The number of kernel parameters is not limited, but the length of the 193complete command line (parameters including spaces etc.) is limited to 194a fixed number of characters. This limit depends on the architecture 195and is between 256 and 4096 characters. It is defined in the file 196./include/asm/setup.h as COMMAND_LINE_SIZE. 197 198Finally, the [KMG] suffix is commonly described after a number of kernel 199parameter values. These 'K', 'M', and 'G' letters represent the _binary_ 200multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30 201bytes respectively. Such letter suffixes can also be entirely omitted: 202 203.. include:: kernel-parameters.txt 204 :literal: 205 206Todo 207---- 208 209 Add more DRM drivers. 210