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 AX25 Appropriate AX.25 support is enabled. 90 BLACKFIN Blackfin architecture is enabled. 91 CLK Common clock infrastructure is enabled. 92 CMA Contiguous Memory Area support is enabled. 93 DRM Direct Rendering Management support is enabled. 94 DYNAMIC_DEBUG Build in debug messages and enable them at runtime 95 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled 96 EFI EFI Partitioning (GPT) is enabled 97 EIDE EIDE/ATAPI support is enabled. 98 EVM Extended Verification Module 99 FB The frame buffer device is enabled. 100 FTRACE Function tracing enabled. 101 GCOV GCOV profiling is enabled. 102 HW Appropriate hardware is enabled. 103 IA-64 IA-64 architecture is enabled. 104 IMA Integrity measurement architecture is enabled. 105 IOSCHED More than one I/O scheduler is enabled. 106 IP_PNP IP DHCP, BOOTP, or RARP is enabled. 107 IPV6 IPv6 support is enabled. 108 ISAPNP ISA PnP code is enabled. 109 ISDN Appropriate ISDN support is enabled. 110 JOY Appropriate joystick support is enabled. 111 KGDB Kernel debugger support is enabled. 112 KVM Kernel Virtual Machine support is enabled. 113 LIBATA Libata driver is enabled 114 LP Printer support is enabled. 115 LOOP Loopback device support is enabled. 116 M68k M68k architecture is enabled. 117 These options have more detailed description inside of 118 Documentation/m68k/kernel-options.txt. 119 MDA MDA console support is enabled. 120 MIPS MIPS architecture is enabled. 121 MOUSE Appropriate mouse support is enabled. 122 MSI Message Signaled Interrupts (PCI). 123 MTD MTD (Memory Technology Device) support is enabled. 124 NET Appropriate network support is enabled. 125 NUMA NUMA support is enabled. 126 NFS Appropriate NFS support is enabled. 127 OSS OSS sound support is enabled. 128 PV_OPS A paravirtualized kernel is enabled. 129 PARIDE The ParIDE (parallel port IDE) subsystem is enabled. 130 PARISC The PA-RISC architecture is enabled. 131 PCI PCI bus support is enabled. 132 PCIE PCI Express support is enabled. 133 PCMCIA The PCMCIA subsystem is enabled. 134 PNP Plug & Play support is enabled. 135 PPC PowerPC architecture is enabled. 136 PPT Parallel port support is enabled. 137 PS2 Appropriate PS/2 support is enabled. 138 RAM RAM disk support is enabled. 139 S390 S390 architecture is enabled. 140 SCSI Appropriate SCSI support is enabled. 141 A lot of drivers have their options described inside 142 the Documentation/scsi/ sub-directory. 143 SECURITY Different security models are enabled. 144 SELINUX SELinux support is enabled. 145 APPARMOR AppArmor support is enabled. 146 SERIAL Serial support is enabled. 147 SH SuperH architecture is enabled. 148 SMP The kernel is an SMP kernel. 149 SPARC Sparc architecture is enabled. 150 SWSUSP Software suspend (hibernation) is enabled. 151 SUSPEND System suspend states are enabled. 152 TPM TPM drivers are enabled. 153 TS Appropriate touchscreen support is enabled. 154 UMS USB Mass Storage support is enabled. 155 USB USB support is enabled. 156 USBHID USB Human Interface Device support is enabled. 157 V4L Video For Linux support is enabled. 158 VMMIO Driver for memory mapped virtio devices is enabled. 159 VGA The VGA console has been enabled. 160 VT Virtual terminal support is enabled. 161 WDT Watchdog support is enabled. 162 XT IBM PC/XT MFM hard disk support is enabled. 163 X86-32 X86-32, aka i386 architecture is enabled. 164 X86-64 X86-64 architecture is enabled. 165 More X86-64 boot options can be found in 166 Documentation/x86/x86_64/boot-options.txt . 167 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64) 168 X86_UV SGI UV support is enabled. 169 XEN Xen support is enabled 170 171In addition, the following text indicates that the option:: 172 173 BUGS= Relates to possible processor bugs on the said processor. 174 KNL Is a kernel start-up parameter. 175 BOOT Is a boot loader parameter. 176 177Parameters denoted with BOOT are actually interpreted by the boot 178loader, and have no meaning to the kernel directly. 179Do not modify the syntax of boot loader parameters without extreme 180need or coordination with <Documentation/x86/boot.txt>. 181 182There are also arch-specific kernel-parameters not documented here. 183See for example <Documentation/x86/x86_64/boot-options.txt>. 184 185Note that ALL kernel parameters listed below are CASE SENSITIVE, and that 186a trailing = on the name of any parameter states that that parameter will 187be entered as an environment variable, whereas its absence indicates that 188it will appear as a kernel argument readable via /proc/cmdline by programs 189running once the system is up. 190 191The number of kernel parameters is not limited, but the length of the 192complete command line (parameters including spaces etc.) is limited to 193a fixed number of characters. This limit depends on the architecture 194and is between 256 and 4096 characters. It is defined in the file 195./include/asm/setup.h as COMMAND_LINE_SIZE. 196 197Finally, the [KMG] suffix is commonly described after a number of kernel 198parameter values. These 'K', 'M', and 'G' letters represent the _binary_ 199multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30 200bytes respectively. Such letter suffixes can also be entirely omitted: 201 202.. include:: kernel-parameters.txt 203 :literal: 204 205Todo 206---- 207 208 Add more DRM drivers. 209