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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 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 ARM ARM architecture is enabled.
103 ARM64 ARM64 architecture is enabled.
104 AX25 Appropriate AX.25 support is enabled.
105 CLK Common clock infrastructure is enabled.
106 CMA Contiguous Memory Area support is enabled.
107 DRM Direct Rendering Management support is enabled.
108 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
109 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
110 EFI EFI Partitioning (GPT) is enabled
111 EIDE EIDE/ATAPI support 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 HW Appropriate hardware is enabled.
117 IA-64 IA-64 architecture is enabled.
118 IMA Integrity measurement architecture is enabled.
119 IOSCHED More than one I/O scheduler is enabled.
120 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
121 IPV6 IPv6 support is enabled.
122 ISAPNP ISA PnP code is enabled.
123 ISDN Appropriate ISDN support is enabled.
124 ISOL CPU Isolation is enabled.
125 JOY Appropriate joystick support is enabled.
126 KGDB Kernel debugger support is enabled.
127 KVM Kernel Virtual Machine support is enabled.
128 LIBATA Libata driver is enabled
129 LP Printer support is enabled.
130 LOOP Loopback device support is enabled.
131 M68k M68k architecture is enabled.
132 These options have more detailed description inside of
133 Documentation/m68k/kernel-options.rst.
134 MDA MDA console support is enabled.
135 MIPS MIPS architecture is enabled.
136 MOUSE Appropriate mouse support is enabled.
137 MSI Message Signaled Interrupts (PCI).
138 MTD MTD (Memory Technology Device) support is enabled.
139 NET Appropriate network support is enabled.
140 NUMA NUMA support is enabled.
141 NFS Appropriate NFS support is enabled.
142 OF Devicetree is enabled.
143 OSS OSS sound support 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 APPARMOR AppArmor support is enabled.
164 SERIAL Serial support is enabled.
165 SH SuperH architecture is enabled.
166 SMP The kernel is an SMP kernel.
167 SPARC Sparc architecture is enabled.
168 SWSUSP Software suspend (hibernation) is enabled.
169 SUSPEND System suspend states are enabled.
170 TPM TPM drivers are enabled.
171 TS Appropriate touchscreen support is enabled.
172 UMS USB Mass Storage support is enabled.
173 USB USB support is enabled.
174 USBHID USB Human Interface Device support is enabled.
175 V4L Video For Linux support is enabled.
176 VMMIO Driver for memory mapped virtio devices is enabled.
177 VGA The VGA console has been enabled.
178 VT Virtual terminal support is enabled.
179 WDT Watchdog support is enabled.
180 XT IBM PC/XT MFM hard disk support is enabled.
181 X86-32 X86-32, aka i386 architecture is enabled.
182 X86-64 X86-64 architecture is enabled.
183 More X86-64 boot options can be found in
184 Documentation/x86/x86_64/boot-options.rst.
185 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
186 X86_UV SGI UV support is enabled.
187 XEN Xen support is enabled
188 XTENSA xtensa architecture is enabled.
189
190In addition, the following text indicates that the option::
191
192 BUGS= Relates to possible processor bugs on the said processor.
193 KNL Is a kernel start-up parameter.
194 BOOT Is a boot loader parameter.
195
196Parameters denoted with BOOT are actually interpreted by the boot
197loader, and have no meaning to the kernel directly.
198Do not modify the syntax of boot loader parameters without extreme
199need or coordination with <Documentation/x86/boot.rst>.
200
201There are also arch-specific kernel-parameters not documented here.
202See for example <Documentation/x86/x86_64/boot-options.rst>.
203
204Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
205a trailing = on the name of any parameter states that that parameter will
206be entered as an environment variable, whereas its absence indicates that
207it will appear as a kernel argument readable via /proc/cmdline by programs
208running once the system is up.
209
210The number of kernel parameters is not limited, but the length of the
211complete command line (parameters including spaces etc.) is limited to
212a fixed number of characters. This limit depends on the architecture
213and is between 256 and 4096 characters. It is defined in the file
214./include/asm/setup.h as COMMAND_LINE_SIZE.
215
216Finally, the [KMG] suffix is commonly described after a number of kernel
217parameter values. These 'K', 'M', and 'G' letters represent the _binary_
218multipliers 'Kilo', 'Mega', and 'Giga', equaling 2^10, 2^20, and 2^30
219bytes respectively. Such letter suffixes can also be entirely omitted:
220
221.. include:: kernel-parameters.txt
222 :literal:
223
224Todo
225----
226
227 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
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 ARM64 ARM64 architecture is enabled.
92 AX25 Appropriate AX.25 support is enabled.
93 CLK Common clock infrastructure is enabled.
94 CMA Contiguous Memory Area support is enabled.
95 DRM Direct Rendering Management support is enabled.
96 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
97 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
98 EFI EFI Partitioning (GPT) is enabled
99 EIDE EIDE/ATAPI support is enabled.
100 EVM Extended Verification Module
101 FB The frame buffer device is enabled.
102 FTRACE Function tracing enabled.
103 GCOV GCOV profiling is enabled.
104 HW Appropriate hardware is enabled.
105 IA-64 IA-64 architecture is enabled.
106 IMA Integrity measurement architecture is enabled.
107 IOSCHED More than one I/O scheduler is enabled.
108 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
109 IPV6 IPv6 support is enabled.
110 ISAPNP ISA PnP code is enabled.
111 ISDN Appropriate ISDN support is enabled.
112 ISOL CPU Isolation is enabled.
113 JOY Appropriate joystick support is enabled.
114 KGDB Kernel debugger support is enabled.
115 KVM Kernel Virtual Machine support is enabled.
116 LIBATA Libata driver is enabled
117 LP Printer support is enabled.
118 LOOP Loopback device support is enabled.
119 M68k M68k architecture is enabled.
120 These options have more detailed description inside of
121 Documentation/m68k/kernel-options.rst.
122 MDA MDA console support is enabled.
123 MIPS MIPS architecture is enabled.
124 MOUSE Appropriate mouse support is enabled.
125 MSI Message Signaled Interrupts (PCI).
126 MTD MTD (Memory Technology Device) support is enabled.
127 NET Appropriate network support is enabled.
128 NUMA NUMA support is enabled.
129 NFS Appropriate NFS support is enabled.
130 OF Devicetree is enabled.
131 OSS OSS sound support is enabled.
132 PV_OPS A paravirtualized kernel is enabled.
133 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
134 PARISC The PA-RISC architecture is enabled.
135 PCI PCI bus support is enabled.
136 PCIE PCI Express support is enabled.
137 PCMCIA The PCMCIA subsystem is enabled.
138 PNP Plug & Play support is enabled.
139 PPC PowerPC architecture is enabled.
140 PPT Parallel port support is enabled.
141 PS2 Appropriate PS/2 support is enabled.
142 RAM RAM disk support is enabled.
143 RDT Intel Resource Director Technology.
144 S390 S390 architecture is enabled.
145 SCSI Appropriate SCSI support is enabled.
146 A lot of drivers have their options described inside
147 the Documentation/scsi/ sub-directory.
148 SECURITY Different security models are enabled.
149 SELINUX SELinux support is enabled.
150 APPARMOR AppArmor support is enabled.
151 SERIAL Serial support is enabled.
152 SH SuperH architecture is enabled.
153 SMP The kernel is an SMP kernel.
154 SPARC Sparc architecture is enabled.
155 SWSUSP Software suspend (hibernation) is enabled.
156 SUSPEND System suspend states are enabled.
157 TPM TPM drivers are enabled.
158 TS Appropriate touchscreen support is enabled.
159 UMS USB Mass Storage support is enabled.
160 USB USB support is enabled.
161 USBHID USB Human Interface Device support is enabled.
162 V4L Video For Linux support is enabled.
163 VMMIO Driver for memory mapped virtio devices is enabled.
164 VGA The VGA console has been enabled.
165 VT Virtual terminal support is enabled.
166 WDT Watchdog support is enabled.
167 XT IBM PC/XT MFM hard disk support is enabled.
168 X86-32 X86-32, aka i386 architecture is enabled.
169 X86-64 X86-64 architecture is enabled.
170 More X86-64 boot options can be found in
171 Documentation/x86/x86_64/boot-options.rst.
172 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
173 X86_UV SGI UV support is enabled.
174 XEN Xen support is enabled
175
176In addition, the following text indicates that the option::
177
178 BUGS= Relates to possible processor bugs on the said processor.
179 KNL Is a kernel start-up parameter.
180 BOOT Is a boot loader parameter.
181
182Parameters denoted with BOOT are actually interpreted by the boot
183loader, and have no meaning to the kernel directly.
184Do not modify the syntax of boot loader parameters without extreme
185need or coordination with <Documentation/x86/boot.rst>.
186
187There are also arch-specific kernel-parameters not documented here.
188See for example <Documentation/x86/x86_64/boot-options.rst>.
189
190Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
191a trailing = on the name of any parameter states that that parameter will
192be entered as an environment variable, whereas its absence indicates that
193it will appear as a kernel argument readable via /proc/cmdline by programs
194running once the system is up.
195
196The number of kernel parameters is not limited, but the length of the
197complete command line (parameters including spaces etc.) is limited to
198a fixed number of characters. This limit depends on the architecture
199and is between 256 and 4096 characters. It is defined in the file
200./include/asm/setup.h as COMMAND_LINE_SIZE.
201
202Finally, the [KMG] suffix is commonly described after a number of kernel
203parameter values. These 'K', 'M', and 'G' letters represent the _binary_
204multipliers 'Kilo', 'Mega', and 'Giga', equaling 2^10, 2^20, and 2^30
205bytes respectively. Such letter suffixes can also be entirely omitted:
206
207.. include:: kernel-parameters.txt
208 :literal:
209
210Todo
211----
212
213 Add more DRM drivers.