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1.. _kernelparameters:
2
3The kernel's command-line parameters
4====================================
5
6The following is a consolidated list of the kernel parameters as
7implemented by the __setup(), 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
71
72
73This document may not be entirely up to date and comprehensive. The command
74"modinfo -p ${modulename}" shows a current list of all parameters of a loadable
75module. Loadable modules, after being loaded into the running kernel, also
76reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
77parameters may be changed at runtime by the command
78``echo -n ${value} > /sys/module/${modulename}/parameters/${parm}``.
79
80The parameters listed below are only valid if certain kernel build options were
81enabled and if respective hardware is present. The text in square brackets at
82the beginning of each description states the restrictions within which a
83parameter is applicable::
84
85 ACPI ACPI support is enabled.
86 AGP AGP (Accelerated Graphics Port) is enabled.
87 ALSA ALSA sound support is enabled.
88 APIC APIC support is enabled.
89 APM Advanced Power Management support is enabled.
90 ARM ARM architecture is enabled.
91 AX25 Appropriate AX.25 support 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 ISOL CPU Isolation is enabled.
112 JOY Appropriate joystick support is enabled.
113 KGDB Kernel debugger support is enabled.
114 KVM Kernel Virtual Machine support is enabled.
115 LIBATA Libata driver is enabled
116 LP Printer support is enabled.
117 LOOP Loopback device support is enabled.
118 M68k M68k architecture is enabled.
119 These options have more detailed description inside of
120 Documentation/m68k/kernel-options.txt.
121 MDA MDA console support is enabled.
122 MIPS MIPS architecture is enabled.
123 MOUSE Appropriate mouse support is enabled.
124 MSI Message Signaled Interrupts (PCI).
125 MTD MTD (Memory Technology Device) support is enabled.
126 NET Appropriate network support is enabled.
127 NUMA NUMA support is enabled.
128 NFS Appropriate NFS support is enabled.
129 OSS OSS sound support is enabled.
130 PV_OPS A paravirtualized kernel is enabled.
131 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
132 PARISC The PA-RISC architecture is enabled.
133 PCI PCI bus support is enabled.
134 PCIE PCI Express support is enabled.
135 PCMCIA The PCMCIA subsystem is enabled.
136 PNP Plug & Play support is enabled.
137 PPC PowerPC architecture is enabled.
138 PPT Parallel port support is enabled.
139 PS2 Appropriate PS/2 support is enabled.
140 RAM RAM disk support is enabled.
141 RDT Intel Resource Director Technology.
142 S390 S390 architecture is enabled.
143 SCSI Appropriate SCSI support is enabled.
144 A lot of drivers have their options described inside
145 the Documentation/scsi/ sub-directory.
146 SECURITY Different security models are enabled.
147 SELINUX SELinux support is enabled.
148 APPARMOR AppArmor support is enabled.
149 SERIAL Serial support is enabled.
150 SH SuperH architecture is enabled.
151 SMP The kernel is an SMP kernel.
152 SPARC Sparc architecture is enabled.
153 SWSUSP Software suspend (hibernation) is enabled.
154 SUSPEND System suspend states are enabled.
155 TPM TPM drivers are enabled.
156 TS Appropriate touchscreen support is enabled.
157 UMS USB Mass Storage support is enabled.
158 USB USB support is enabled.
159 USBHID USB Human Interface Device support is enabled.
160 V4L Video For Linux support is enabled.
161 VMMIO Driver for memory mapped virtio devices is enabled.
162 VGA The VGA console has been enabled.
163 VT Virtual terminal support is enabled.
164 WDT Watchdog support is enabled.
165 XT IBM PC/XT MFM hard disk support is enabled.
166 X86-32 X86-32, aka i386 architecture is enabled.
167 X86-64 X86-64 architecture is enabled.
168 More X86-64 boot options can be found in
169 Documentation/x86/x86_64/boot-options.txt .
170 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
171 X86_UV SGI UV support is enabled.
172 XEN Xen support is enabled
173
174In addition, the following text indicates that the option::
175
176 BUGS= Relates to possible processor bugs on the said processor.
177 KNL Is a kernel start-up parameter.
178 BOOT Is a boot loader parameter.
179
180Parameters denoted with BOOT are actually interpreted by the boot
181loader, and have no meaning to the kernel directly.
182Do not modify the syntax of boot loader parameters without extreme
183need or coordination with <Documentation/x86/boot.txt>.
184
185There are also arch-specific kernel-parameters not documented here.
186See for example <Documentation/x86/x86_64/boot-options.txt>.
187
188Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
189a trailing = on the name of any parameter states that that parameter will
190be entered as an environment variable, whereas its absence indicates that
191it will appear as a kernel argument readable via /proc/cmdline by programs
192running once the system is up.
193
194The number of kernel parameters is not limited, but the length of the
195complete command line (parameters including spaces etc.) is limited to
196a fixed number of characters. This limit depends on the architecture
197and is between 256 and 4096 characters. It is defined in the file
198./include/asm/setup.h as COMMAND_LINE_SIZE.
199
200Finally, the [KMG] suffix is commonly described after a number of kernel
201parameter values. These 'K', 'M', and 'G' letters represent the _binary_
202multipliers 'Kilo', 'Mega', and 'Giga', equaling 2^10, 2^20, and 2^30
203bytes respectively. Such letter suffixes can also be entirely omitted:
204
205.. include:: kernel-parameters.txt
206 :literal:
207
208Todo
209----
210
211 Add more DRM drivers.
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
79The special case-tolerant group name "all" has a meaning of selecting all CPUs,
80so that "nohz_full=all" is the equivalent of "nohz_full=0-N".
81
82The semantics of "N" and "all" is supported on a level of bitmaps and holds for
83all users of bitmap_parse().
84
85This document may not be entirely up to date and comprehensive. The command
86"modinfo -p ${modulename}" shows a current list of all parameters of a loadable
87module. Loadable modules, after being loaded into the running kernel, also
88reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
89parameters may be changed at runtime by the command
90``echo -n ${value} > /sys/module/${modulename}/parameters/${parm}``.
91
92The parameters listed below are only valid if certain kernel build options were
93enabled and if respective hardware is present. The text in square brackets at
94the beginning of each description states the restrictions within which a
95parameter is applicable::
96
97 ACPI ACPI support is enabled.
98 AGP AGP (Accelerated Graphics Port) is enabled.
99 ALSA ALSA sound support is enabled.
100 APIC APIC support is enabled.
101 APM Advanced Power Management support is enabled.
102 APPARMOR AppArmor support is enabled.
103 ARM ARM architecture is enabled.
104 ARM64 ARM64 architecture is enabled.
105 AX25 Appropriate AX.25 support is enabled.
106 CLK Common clock infrastructure is enabled.
107 CMA Contiguous Memory Area support is enabled.
108 DRM Direct Rendering Management support is enabled.
109 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
110 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
111 EFI EFI Partitioning (GPT) is enabled
112 EVM Extended Verification Module
113 FB The frame buffer device is enabled.
114 FTRACE Function tracing enabled.
115 GCOV GCOV profiling is enabled.
116 HIBERNATION HIBERNATION is enabled.
117 HW Appropriate hardware is enabled.
118 HYPER_V HYPERV support is enabled.
119 IA-64 IA-64 architecture is enabled.
120 IMA Integrity measurement architecture is enabled.
121 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
122 IPV6 IPv6 support is enabled.
123 ISAPNP ISA PnP code is enabled.
124 ISDN Appropriate ISDN support is enabled.
125 ISOL CPU Isolation is enabled.
126 JOY Appropriate joystick support is enabled.
127 KGDB Kernel debugger support is enabled.
128 KVM Kernel Virtual Machine support is enabled.
129 LIBATA Libata driver is enabled
130 LP Printer support is enabled.
131 LOOP Loopback device support is enabled.
132 M68k M68k architecture is enabled.
133 These options have more detailed description inside of
134 Documentation/m68k/kernel-options.rst.
135 MDA MDA console support is enabled.
136 MIPS MIPS architecture is enabled.
137 MOUSE Appropriate mouse support is enabled.
138 MSI Message Signaled Interrupts (PCI).
139 MTD MTD (Memory Technology Device) support is enabled.
140 NET Appropriate network support is enabled.
141 NUMA NUMA support is enabled.
142 NFS Appropriate NFS support is enabled.
143 OF Devicetree is enabled.
144 PV_OPS A paravirtualized kernel is enabled.
145 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
146 PARISC The PA-RISC architecture is enabled.
147 PCI PCI bus support is enabled.
148 PCIE PCI Express support is enabled.
149 PCMCIA The PCMCIA subsystem is enabled.
150 PNP Plug & Play support is enabled.
151 PPC PowerPC architecture is enabled.
152 PPT Parallel port support is enabled.
153 PS2 Appropriate PS/2 support is enabled.
154 RAM RAM disk support is enabled.
155 RISCV RISCV architecture is enabled.
156 RDT Intel Resource Director Technology.
157 S390 S390 architecture is enabled.
158 SCSI Appropriate SCSI support is enabled.
159 A lot of drivers have their options described inside
160 the Documentation/scsi/ sub-directory.
161 SECURITY Different security models are enabled.
162 SELINUX SELinux support is enabled.
163 SERIAL Serial support is enabled.
164 SH SuperH architecture is enabled.
165 SMP The kernel is an SMP kernel.
166 SPARC Sparc architecture is enabled.
167 SWSUSP Software suspend (hibernation) is enabled.
168 SUSPEND System suspend states are enabled.
169 TPM TPM drivers are enabled.
170 UMS USB Mass Storage support is enabled.
171 USB USB support is enabled.
172 USBHID USB Human Interface Device support is enabled.
173 V4L Video For Linux support is enabled.
174 VMMIO Driver for memory mapped virtio devices is enabled.
175 VGA The VGA console has been enabled.
176 VT Virtual terminal support is enabled.
177 WDT Watchdog support is enabled.
178 X86-32 X86-32, aka i386 architecture is enabled.
179 X86-64 X86-64 architecture is enabled.
180 More X86-64 boot options can be found in
181 Documentation/x86/x86_64/boot-options.rst.
182 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
183 X86_UV SGI UV support is enabled.
184 XEN Xen support is enabled
185 XTENSA xtensa architecture is enabled.
186
187In addition, the following text indicates that the option::
188
189 BUGS= Relates to possible processor bugs on the said processor.
190 KNL Is a kernel start-up parameter.
191 BOOT Is a boot loader parameter.
192
193Parameters denoted with BOOT are actually interpreted by the boot
194loader, and have no meaning to the kernel directly.
195Do not modify the syntax of boot loader parameters without extreme
196need or coordination with <Documentation/x86/boot.rst>.
197
198There are also arch-specific kernel-parameters not documented here.
199See for example <Documentation/x86/x86_64/boot-options.rst>.
200
201Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
202a trailing = on the name of any parameter states that that parameter will
203be entered as an environment variable, whereas its absence indicates that
204it will appear as a kernel argument readable via /proc/cmdline by programs
205running once the system is up.
206
207The number of kernel parameters is not limited, but the length of the
208complete command line (parameters including spaces etc.) is limited to
209a fixed number of characters. This limit depends on the architecture
210and is between 256 and 4096 characters. It is defined in the file
211./include/uapi/asm-generic/setup.h as COMMAND_LINE_SIZE.
212
213Finally, the [KMG] suffix is commonly described after a number of kernel
214parameter values. These 'K', 'M', and 'G' letters represent the _binary_
215multipliers 'Kilo', 'Mega', and 'Giga', equaling 2^10, 2^20, and 2^30
216bytes respectively. Such letter suffixes can also be entirely omitted:
217
218.. include:: kernel-parameters.txt
219 :literal:
220
221Todo
222----
223
224 Add more DRM drivers.