1 .. _kernelparameters: 1 .. _kernelparameters:
2 2
3 The kernel's command-line parameters 3 The kernel's command-line parameters
4 ==================================== 4 ====================================
5 5
6 The following is a consolidated list of the ke 6 The following is a consolidated list of the kernel parameters as implemented
7 by the __setup(), early_param(), core_param() 7 by the __setup(), early_param(), core_param() and module_param() macros
8 and sorted into English Dictionary order (defi 8 and sorted into English Dictionary order (defined as ignoring all
9 punctuation and sorting digits before letters 9 punctuation and sorting digits before letters in a case insensitive
10 manner), and with descriptions where known. 10 manner), and with descriptions where known.
11 11
12 The kernel parses parameters from the kernel c 12 The kernel parses parameters from the kernel command line up to "``--``";
13 if it doesn't recognize a parameter and it doe 13 if it doesn't recognize a parameter and it doesn't contain a '.', the
14 parameter gets passed to init: parameters with 14 parameter gets passed to init: parameters with '=' go into init's
15 environment, others are passed as command line 15 environment, others are passed as command line arguments to init.
16 Everything after "``--``" is passed as an argu 16 Everything after "``--``" is passed as an argument to init.
17 17
18 Module parameters can be specified in two ways 18 Module parameters can be specified in two ways: via the kernel command
19 line with a module name prefix, or via modprob 19 line with a module name prefix, or via modprobe, e.g.::
20 20
21 (kernel command line) usbcore.blinkenl 21 (kernel command line) usbcore.blinkenlights=1
22 (modprobe command line) modprobe usbco 22 (modprobe command line) modprobe usbcore blinkenlights=1
23 23
24 Parameters for modules which are built into th 24 Parameters for modules which are built into the kernel need to be
25 specified on the kernel command line. modprob 25 specified on the kernel command line. modprobe looks through the
26 kernel command line (/proc/cmdline) and collec 26 kernel command line (/proc/cmdline) and collects module parameters
27 when it loads a module, so the kernel command 27 when it loads a module, so the kernel command line can be used for
28 loadable modules too. 28 loadable modules too.
29 29
30 Hyphens (dashes) and underscores are equivalen 30 Hyphens (dashes) and underscores are equivalent in parameter names, so::
31 31
32 log_buf_len=1M print-fatal-signals=1 32 log_buf_len=1M print-fatal-signals=1
33 33
34 can also be entered as:: 34 can also be entered as::
35 35
36 log-buf-len=1M print_fatal_signals=1 36 log-buf-len=1M print_fatal_signals=1
37 37
38 Double-quotes can be used to protect spaces in 38 Double-quotes can be used to protect spaces in values, e.g.::
39 39
40 param="spaces in here" 40 param="spaces in here"
41 41
42 cpu lists: 42 cpu lists:
43 ---------- 43 ----------
44 44
45 Some kernel parameters take a list of CPUs as 45 Some kernel parameters take a list of CPUs as a value, e.g. isolcpus,
46 nohz_full, irqaffinity, rcu_nocbs. The format 46 nohz_full, irqaffinity, rcu_nocbs. The format of this list is:
47 47
48 <cpu number>,...,<cpu number> 48 <cpu number>,...,<cpu number>
49 49
50 or 50 or
51 51
52 <cpu number>-<cpu number> 52 <cpu number>-<cpu number>
53 (must be a positive range in ascending 53 (must be a positive range in ascending order)
54 54
55 or a mixture 55 or a mixture
56 56
57 <cpu number>,...,<cpu number>-<cpu number> 57 <cpu number>,...,<cpu number>-<cpu number>
58 58
59 Note that for the special case of a range one 59 Note that for the special case of a range one can split the range into equal
60 sized groups and for each group use some amoun 60 sized groups and for each group use some amount from the beginning of that
61 group: 61 group:
62 62
63 <cpu number>-<cpu number>:<used size>/ 63 <cpu number>-<cpu number>:<used size>/<group size>
64 64
65 For example one can add to the command line fo 65 For example one can add to the command line following parameter:
66 66
67 isolcpus=1,2,10-20,100-2000:2/25 67 isolcpus=1,2,10-20,100-2000:2/25
68 68
69 where the final item represents CPUs 100,101,1 69 where the final item represents CPUs 100,101,125,126,150,151,...
70 70
71 The value "N" can be used to represent the num 71 The value "N" can be used to represent the numerically last CPU on the system,
72 i.e "foo_cpus=16-N" would be equivalent to "16 72 i.e "foo_cpus=16-N" would be equivalent to "16-31" on a 32 core system.
73 73
74 Keep in mind that "N" is dynamic, so if system 74 Keep in mind that "N" is dynamic, so if system changes cause the bitmap width
75 to change, such as less cores in the CPU list, 75 to change, such as less cores in the CPU list, then N and any ranges using N
76 will also change. Use the same on a small 4 c 76 will 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 fla 77 "16-3" and now the same boot input will be flagged as invalid (start > end).
78 78
79 The special case-tolerant group name "all" has 79 The special case-tolerant group name "all" has a meaning of selecting all CPUs,
80 so that "nohz_full=all" is the equivalent of " 80 so that "nohz_full=all" is the equivalent of "nohz_full=0-N".
81 81
82 The semantics of "N" and "all" is supported on 82 The semantics of "N" and "all" is supported on a level of bitmaps and holds for
83 all users of bitmap_parselist(). 83 all users of bitmap_parselist().
84 84
85 This document may not be entirely up to date a 85 This document may not be entirely up to date and comprehensive. The command
86 "modinfo -p ${modulename}" shows a current lis 86 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
87 module. Loadable modules, after being loaded i 87 module. Loadable modules, after being loaded into the running kernel, also
88 reveal their parameters in /sys/module/${modul 88 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
89 parameters may be changed at runtime by the co 89 parameters may be changed at runtime by the command
90 ``echo -n ${value} > /sys/module/${modulename} 90 ``echo -n ${value} > /sys/module/${modulename}/parameters/${parm}``.
91 91
92 The parameters listed below are only valid if 92 The parameters listed below are only valid if certain kernel build options
93 were enabled and if respective hardware is pre 93 were enabled and if respective hardware is present. This list should be kept
94 in alphabetical order. The text in square brac 94 in alphabetical order. The text in square brackets at the beginning
95 of each description states the restrictions wi 95 of each description states the restrictions within which a parameter
96 is applicable:: 96 is applicable::
97 97
98 ACPI ACPI support is enabled. 98 ACPI ACPI support is enabled.
99 AGP AGP (Accelerated Graphics Port 99 AGP AGP (Accelerated Graphics Port) is enabled.
100 ALSA ALSA sound support is enabled. 100 ALSA ALSA sound support is enabled.
101 APIC APIC support is enabled. 101 APIC APIC support is enabled.
102 APM Advanced Power Management supp 102 APM Advanced Power Management support is enabled.
103 APPARMOR AppArmor support is enabled. 103 APPARMOR AppArmor support is enabled.
104 ARM ARM architecture is enabled. 104 ARM ARM architecture is enabled.
105 ARM64 ARM64 architecture is enabled. 105 ARM64 ARM64 architecture is enabled.
106 AX25 Appropriate AX.25 support is e 106 AX25 Appropriate AX.25 support is enabled.
107 CLK Common clock infrastructure is 107 CLK Common clock infrastructure is enabled.
108 CMA Contiguous Memory Area support 108 CMA Contiguous Memory Area support is enabled.
109 DRM Direct Rendering Management su 109 DRM Direct Rendering Management support is enabled.
110 DYNAMIC_DEBUG Build in debug messages 110 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
111 EARLY Parameter processed too early 111 EARLY Parameter processed too early to be embedded in initrd.
112 EDD BIOS Enhanced Disk Drive Servi 112 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
113 EFI EFI Partitioning (GPT) is enab 113 EFI EFI Partitioning (GPT) is enabled
114 EVM Extended Verification Module 114 EVM Extended Verification Module
115 FB The frame buffer device is ena 115 FB The frame buffer device is enabled.
116 FTRACE Function tracing enabled. 116 FTRACE Function tracing enabled.
117 GCOV GCOV profiling is enabled. 117 GCOV GCOV profiling is enabled.
118 HIBERNATION HIBERNATION is enabled. 118 HIBERNATION HIBERNATION is enabled.
119 HW Appropriate hardware is enable 119 HW Appropriate hardware is enabled.
120 HYPER_V HYPERV support is enabled. 120 HYPER_V HYPERV support is enabled.
121 IMA Integrity measurement architec 121 IMA Integrity measurement architecture is enabled.
122 IP_PNP IP DHCP, BOOTP, or RARP is ena 122 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
123 IPV6 IPv6 support is enabled. 123 IPV6 IPv6 support is enabled.
124 ISAPNP ISA PnP code is enabled. 124 ISAPNP ISA PnP code is enabled.
125 ISDN Appropriate ISDN support is en 125 ISDN Appropriate ISDN support is enabled.
126 ISOL CPU Isolation is enabled. 126 ISOL CPU Isolation is enabled.
127 JOY Appropriate joystick support i 127 JOY Appropriate joystick support is enabled.
128 KGDB Kernel debugger support is ena 128 KGDB Kernel debugger support is enabled.
129 KVM Kernel Virtual Machine support 129 KVM Kernel Virtual Machine support is enabled.
130 LIBATA Libata driver is enabled 130 LIBATA Libata driver is enabled
131 LOONGARCH LoongArch architecture is en 131 LOONGARCH LoongArch architecture is enabled.
132 LOOP Loopback device support is ena 132 LOOP Loopback device support is enabled.
133 LP Printer support is enabled. 133 LP Printer support is enabled.
134 M68k M68k architecture is enabled. 134 M68k M68k architecture is enabled.
135 These options have mor 135 These options have more detailed description inside of
136 Documentation/arch/m68 136 Documentation/arch/m68k/kernel-options.rst.
137 MDA MDA console support is enabled 137 MDA MDA console support is enabled.
138 MIPS MIPS architecture is enabled. 138 MIPS MIPS architecture is enabled.
139 MOUSE Appropriate mouse support is e 139 MOUSE Appropriate mouse support is enabled.
140 MSI Message Signaled Interrupts (P 140 MSI Message Signaled Interrupts (PCI).
141 MTD MTD (Memory Technology Device) 141 MTD MTD (Memory Technology Device) support is enabled.
142 NET Appropriate network support is 142 NET Appropriate network support is enabled.
143 NFS Appropriate NFS support is ena 143 NFS Appropriate NFS support is enabled.
144 NUMA NUMA support is enabled. 144 NUMA NUMA support is enabled.
145 OF Devicetree is enabled. 145 OF Devicetree is enabled.
146 PARISC The PA-RISC architecture is en 146 PARISC The PA-RISC architecture is enabled.
147 PCI PCI bus support is enabled. 147 PCI PCI bus support is enabled.
148 PCIE PCI Express support is enabled 148 PCIE PCI Express support is enabled.
149 PCMCIA The PCMCIA subsystem is enable 149 PCMCIA The PCMCIA subsystem is enabled.
150 PNP Plug & Play support is enabled 150 PNP Plug & Play support is enabled.
151 PPC PowerPC architecture is enable 151 PPC PowerPC architecture is enabled.
152 PPT Parallel port support is enabl 152 PPT Parallel port support is enabled.
153 PS2 Appropriate PS/2 support is en 153 PS2 Appropriate PS/2 support is enabled.
154 PV_OPS A paravirtualized kernel is en 154 PV_OPS A paravirtualized kernel is enabled.
155 RAM RAM disk support is enabled. 155 RAM RAM disk support is enabled.
156 RDT Intel Resource Director Techno 156 RDT Intel Resource Director Technology.
157 RISCV RISCV architecture is enabled. 157 RISCV RISCV architecture is enabled.
158 S390 S390 architecture is enabled. 158 S390 S390 architecture is enabled.
159 SCSI Appropriate SCSI support is en 159 SCSI Appropriate SCSI support is enabled.
160 A lot of drivers have 160 A lot of drivers have their options described inside
161 the Documentation/scsi 161 the Documentation/scsi/ sub-directory.
162 SECURITY Different security models are 162 SECURITY Different security models are enabled.
163 SELINUX SELinux support is enabled. 163 SELINUX SELinux support is enabled.
164 SERIAL Serial support is enabled. 164 SERIAL Serial support is enabled.
165 SH SuperH architecture is enabled 165 SH SuperH architecture is enabled.
166 SMP The kernel is an SMP kernel. 166 SMP The kernel is an SMP kernel.
167 SPARC Sparc architecture is enabled. 167 SPARC Sparc architecture is enabled.
168 SUSPEND System suspend states are enab 168 SUSPEND System suspend states are enabled.
169 SWSUSP Software suspend (hibernation) 169 SWSUSP Software suspend (hibernation) is enabled.
170 TPM TPM drivers are enabled. 170 TPM TPM drivers are enabled.
171 UMS USB Mass Storage support is en 171 UMS USB Mass Storage support is enabled.
172 USB USB support is enabled. 172 USB USB support is enabled.
173 USBHID USB Human Interface Device sup 173 USBHID USB Human Interface Device support is enabled.
174 V4L Video For Linux support is ena 174 V4L Video For Linux support is enabled.
175 VGA The VGA console has been enabl 175 VGA The VGA console has been enabled.
176 VMMIO Driver for memory mapped virti 176 VMMIO Driver for memory mapped virtio devices is enabled.
177 VT Virtual terminal support is en 177 VT Virtual terminal support is enabled.
178 WDT Watchdog support is enabled. 178 WDT Watchdog support is enabled.
179 X86-32 X86-32, aka i386 architecture 179 X86-32 X86-32, aka i386 architecture is enabled.
180 X86-64 X86-64 architecture is enabled 180 X86-64 X86-64 architecture is enabled.
181 More X86-64 boot optio 181 More X86-64 boot options can be found in
182 Documentation/arch/x86 182 Documentation/arch/x86/x86_64/boot-options.rst.
183 X86 Either 32-bit or 64-bit x86 (s 183 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
184 X86_UV SGI UV support is enabled. 184 X86_UV SGI UV support is enabled.
185 XEN Xen support is enabled 185 XEN Xen support is enabled
186 XTENSA xtensa architecture is enabled 186 XTENSA xtensa architecture is enabled.
187 187
188 In addition, the following text indicates that 188 In addition, the following text indicates that the option::
189 189
190 BOOT Is a boot loader parameter. 190 BOOT Is a boot loader parameter.
191 BUGS= Relates to possible processor 191 BUGS= Relates to possible processor bugs on the said processor.
192 KNL Is a kernel start-up parameter 192 KNL Is a kernel start-up parameter.
193 193
194 Parameters denoted with BOOT are actually inte 194 Parameters denoted with BOOT are actually interpreted by the boot
195 loader, and have no meaning to the kernel dire 195 loader, and have no meaning to the kernel directly.
196 Do not modify the syntax of boot loader parame 196 Do not modify the syntax of boot loader parameters without extreme
197 need or coordination with <Documentation/arch/ 197 need or coordination with <Documentation/arch/x86/boot.rst>.
198 198
199 There are also arch-specific kernel-parameters 199 There are also arch-specific kernel-parameters not documented here.
200 See for example <Documentation/arch/x86/x86_64 200 See for example <Documentation/arch/x86/x86_64/boot-options.rst>.
201 201
202 Note that ALL kernel parameters listed below a 202 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
203 a trailing = on the name of any parameter stat 203 a trailing = on the name of any parameter states that that parameter will
204 be entered as an environment variable, whereas 204 be entered as an environment variable, whereas its absence indicates that
205 it will appear as a kernel argument readable v 205 it will appear as a kernel argument readable via /proc/cmdline by programs
206 running once the system is up. 206 running once the system is up.
207 207
208 The number of kernel parameters is not limited 208 The number of kernel parameters is not limited, but the length of the
209 complete command line (parameters including sp 209 complete command line (parameters including spaces etc.) is limited to
210 a fixed number of characters. This limit depen 210 a fixed number of characters. This limit depends on the architecture
211 and is between 256 and 4096 characters. It is 211 and is between 256 and 4096 characters. It is defined in the file
212 ./include/uapi/asm-generic/setup.h as COMMAND_ 212 ./include/uapi/asm-generic/setup.h as COMMAND_LINE_SIZE.
213 213
214 Finally, the [KMG] suffix is commonly describe 214 Finally, the [KMG] suffix is commonly described after a number of kernel
215 parameter values. These 'K', 'M', and 'G' lett 215 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
216 multipliers 'Kilo', 'Mega', and 'Giga', equali 216 multipliers 'Kilo', 'Mega', and 'Giga', equaling 2^10, 2^20, and 2^30
217 bytes respectively. Such letter suffixes can a 217 bytes respectively. Such letter suffixes can also be entirely omitted:
218 218
219 .. include:: kernel-parameters.txt 219 .. include:: kernel-parameters.txt
220 :literal: 220 :literal:
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