Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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linux
1.. _kernelparameters:
2
3The kernel's command-line parameters
4====================================
5
6The following is a consolidated list of the kernel parameters as implemented
7by the __setup(), early_param(), core_param() and module_param() macros
8and sorted into English Dictionary order (defined as ignoring all
9punctuation and sorting digits before letters in a case insensitive
10manner), and with descriptions where known.
11
12The kernel parses parameters from the kernel command line up to "``--``";
13if it doesn't recognize a parameter and it doesn't contain a '.', the
14parameter gets passed to init: parameters with '=' go into init's
15environment, others are passed as command line arguments to init.
16Everything after "``--``" is passed as an argument to init.
17
18Module parameters can be specified in two ways: via the kernel command
19line with a module name prefix, or via modprobe, e.g.::
20
21 (kernel command line) usbcore.blinkenlights=1
22 (modprobe command line) modprobe usbcore blinkenlights=1
23
24Parameters for modules which are built into the kernel need to be
25specified on the kernel command line. modprobe looks through the
26kernel command line (/proc/cmdline) and collects module parameters
27when it loads a module, so the kernel command line can be used for
28loadable modules too.
29
30Hyphens (dashes) and underscores are equivalent in parameter names, so::
31
32 log_buf_len=1M print-fatal-signals=1
33
34can also be entered as::
35
36 log-buf-len=1M print_fatal_signals=1
37
38Double-quotes can be used to protect spaces in values, e.g.::
39
40 param="spaces in here"
41
42cpu lists:
43----------
44
45Some kernel parameters take a list of CPUs as a value, e.g. isolcpus,
46nohz_full, irqaffinity, rcu_nocbs. The format of this list is:
47
48 <cpu number>,...,<cpu number>
49
50or
51
52 <cpu number>-<cpu number>
53 (must be a positive range in ascending order)
54
55or a mixture
56
57<cpu number>,...,<cpu number>-<cpu number>
58
59Note that for the special case of a range one can split the range into equal
60sized groups and for each group use some amount from the beginning of that
61group:
62
63 <cpu number>-<cpu number>:<used size>/<group size>
64
65For example one can add to the command line following parameter:
66
67 isolcpus=1,2,10-20,100-2000:2/25
68
69where the final item represents CPUs 100,101,125,126,150,151,...
70
71The value "N" can be used to represent the numerically last CPU on the system,
72i.e "foo_cpus=16-N" would be equivalent to "16-31" on a 32 core system.
73
74Keep in mind that "N" is dynamic, so if system changes cause the bitmap width
75to change, such as less cores in the CPU list, then N and any ranges using N
76will also change. Use the same on a small 4 core system, and "16-N" becomes
77"16-3" and now the same boot input will be flagged as invalid (start > end).
78
79
80This document may not be entirely up to date and comprehensive. The command
81"modinfo -p ${modulename}" shows a current list of all parameters of a loadable
82module. Loadable modules, after being loaded into the running kernel, also
83reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
84parameters may be changed at runtime by the command
85``echo -n ${value} > /sys/module/${modulename}/parameters/${parm}``.
86
87The parameters listed below are only valid if certain kernel build options were
88enabled and if respective hardware is present. The text in square brackets at
89the beginning of each description states the restrictions within which a
90parameter is applicable::
91
92 ACPI ACPI support is enabled.
93 AGP AGP (Accelerated Graphics Port) is enabled.
94 ALSA ALSA sound support is enabled.
95 APIC APIC support is enabled.
96 APM Advanced Power Management support is enabled.
97 ARM ARM architecture is enabled.
98 ARM64 ARM64 architecture is enabled.
99 AX25 Appropriate AX.25 support is enabled.
100 CLK Common clock infrastructure is enabled.
101 CMA Contiguous Memory Area support is enabled.
102 DRM Direct Rendering Management support is enabled.
103 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
104 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
105 EFI EFI Partitioning (GPT) is enabled
106 EIDE EIDE/ATAPI support is enabled.
107 EVM Extended Verification Module
108 FB The frame buffer device is enabled.
109 FTRACE Function tracing enabled.
110 GCOV GCOV profiling is enabled.
111 HW Appropriate hardware is enabled.
112 IA-64 IA-64 architecture is enabled.
113 IMA Integrity measurement architecture is enabled.
114 IOSCHED More than one I/O scheduler is enabled.
115 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
116 IPV6 IPv6 support is enabled.
117 ISAPNP ISA PnP code is enabled.
118 ISDN Appropriate ISDN support is enabled.
119 ISOL CPU Isolation is enabled.
120 JOY Appropriate joystick support is enabled.
121 KGDB Kernel debugger support is enabled.
122 KVM Kernel Virtual Machine support is enabled.
123 LIBATA Libata driver is enabled
124 LP Printer support is enabled.
125 LOOP Loopback device support is enabled.
126 M68k M68k architecture is enabled.
127 These options have more detailed description inside of
128 Documentation/m68k/kernel-options.rst.
129 MDA MDA console support is enabled.
130 MIPS MIPS architecture is enabled.
131 MOUSE Appropriate mouse support is enabled.
132 MSI Message Signaled Interrupts (PCI).
133 MTD MTD (Memory Technology Device) support is enabled.
134 NET Appropriate network support is enabled.
135 NUMA NUMA support is enabled.
136 NFS Appropriate NFS support is enabled.
137 OF Devicetree is enabled.
138 OSS OSS sound support is enabled.
139 PV_OPS A paravirtualized kernel is enabled.
140 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
141 PARISC The PA-RISC architecture is enabled.
142 PCI PCI bus support is enabled.
143 PCIE PCI Express support is enabled.
144 PCMCIA The PCMCIA subsystem is enabled.
145 PNP Plug & Play support is enabled.
146 PPC PowerPC architecture is enabled.
147 PPT Parallel port support is enabled.
148 PS2 Appropriate PS/2 support is enabled.
149 RAM RAM disk support is enabled.
150 RISCV RISCV architecture is enabled.
151 RDT Intel Resource Director Technology.
152 S390 S390 architecture is enabled.
153 SCSI Appropriate SCSI support is enabled.
154 A lot of drivers have their options described inside
155 the Documentation/scsi/ sub-directory.
156 SECURITY Different security models are enabled.
157 SELINUX SELinux support is enabled.
158 APPARMOR AppArmor support is enabled.
159 SERIAL Serial support is enabled.
160 SH SuperH architecture is enabled.
161 SMP The kernel is an SMP kernel.
162 SPARC Sparc architecture is enabled.
163 SWSUSP Software suspend (hibernation) is enabled.
164 SUSPEND System suspend states are enabled.
165 TPM TPM drivers are enabled.
166 TS Appropriate touchscreen support is enabled.
167 UMS USB Mass Storage support is enabled.
168 USB USB support is enabled.
169 USBHID USB Human Interface Device support is enabled.
170 V4L Video For Linux support is enabled.
171 VMMIO Driver for memory mapped virtio devices is enabled.
172 VGA The VGA console has been enabled.
173 VT Virtual terminal support is enabled.
174 WDT Watchdog support is enabled.
175 XT IBM PC/XT MFM hard disk support is enabled.
176 X86-32 X86-32, aka i386 architecture is enabled.
177 X86-64 X86-64 architecture is enabled.
178 More X86-64 boot options can be found in
179 Documentation/x86/x86_64/boot-options.rst.
180 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
181 X86_UV SGI UV support is enabled.
182 XEN Xen support is enabled
183 XTENSA xtensa architecture is enabled.
184
185In addition, the following text indicates that the option::
186
187 BUGS= Relates to possible processor bugs on the said processor.
188 KNL Is a kernel start-up parameter.
189 BOOT Is a boot loader parameter.
190
191Parameters denoted with BOOT are actually interpreted by the boot
192loader, and have no meaning to the kernel directly.
193Do not modify the syntax of boot loader parameters without extreme
194need or coordination with <Documentation/x86/boot.rst>.
195
196There are also arch-specific kernel-parameters not documented here.
197See for example <Documentation/x86/x86_64/boot-options.rst>.
198
199Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
200a trailing = on the name of any parameter states that that parameter will
201be entered as an environment variable, whereas its absence indicates that
202it will appear as a kernel argument readable via /proc/cmdline by programs
203running once the system is up.
204
205The number of kernel parameters is not limited, but the length of the
206complete command line (parameters including spaces etc.) is limited to
207a fixed number of characters. This limit depends on the architecture
208and is between 256 and 4096 characters. It is defined in the file
209./include/asm/setup.h as COMMAND_LINE_SIZE.
210
211Finally, the [KMG] suffix is commonly described after a number of kernel
212parameter values. These 'K', 'M', and 'G' letters represent the _binary_
213multipliers 'Kilo', 'Mega', and 'Giga', equaling 2^10, 2^20, and 2^30
214bytes respectively. Such letter suffixes can also be entirely omitted:
215
216.. include:: kernel-parameters.txt
217 :literal:
218
219Todo
220----
221
222 Add more DRM drivers.