1 .. _kernelparameters:
2 
3 The kernel's command-line parameters
4 ====================================
5 
6 The following is a consolidated list of the kernel parameters as implemented
7 by the __setup(), early_param(), core_param() and module_param() macros
8 and sorted into English Dictionary order (defined as ignoring all
9 punctuation and sorting digits before letters in a case insensitive
10 manner), and with descriptions where known.
11 
12 The kernel parses parameters from the kernel command line up to "``--``";
13 if it doesn't recognize a parameter and it doesn't contain a '.', the
14 parameter gets passed to init: parameters with '=' go into init's
15 environment, others are passed as command line arguments to init.
16 Everything after "``--``" is passed as an argument to init.
17 
18 Module parameters can be specified in two ways: via the kernel command
19 line 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 
24 Parameters for modules which are built into the kernel need to be
25 specified on the kernel command line.  modprobe looks through the
26 kernel command line (/proc/cmdline) and collects module parameters
27 when it loads a module, so the kernel command line can be used for
28 loadable modules too.
29 
30 Hyphens (dashes) and underscores are equivalent in parameter names, so::
31 
32 	log_buf_len=1M print-fatal-signals=1
33 
34 can also be entered as::
35 
36 	log-buf-len=1M print_fatal_signals=1
37 
38 Double-quotes can be used to protect spaces in values, e.g.::
39 
40 	param="spaces in here"
41 
42 cpu lists:
43 ----------
44 
45 Some kernel parameters take a list of CPUs as a value, e.g.  isolcpus,
46 nohz_full, irqaffinity, rcu_nocbs.  The format of this list is:
47 
48 	<cpu number>,...,<cpu number>
49 
50 or
51 
52 	<cpu number>-<cpu number>
53 	(must be a positive range in ascending order)
54 
55 or a mixture
56 
57 <cpu number>,...,<cpu number>-<cpu number>
58 
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 amount from the beginning of that
61 group:
62 
63 	<cpu number>-<cpu number>:<used size>/<group size>
64 
65 For example one can add to the command line following parameter:
66 
67 	isolcpus=1,2,10-20,100-2000:2/25
68 
69 where the final item represents CPUs 100,101,125,126,150,151,...
70 
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 "16-31" on a 32 core system.
73 
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, then N and any ranges using N
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 flagged as invalid (start > end).
78 
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 "nohz_full=0-N".
81 
82 The semantics of "N" and "all" is supported on a level of bitmaps and holds for
83 all users of bitmap_parselist().
84 
85 This document may not be entirely up to date and comprehensive. The command
86 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
87 module. Loadable modules, after being loaded into the running kernel, also
88 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
89 parameters may be changed at runtime by the command
90 ``echo -n ${value} > /sys/module/${modulename}/parameters/${parm}``.
91 
92 The parameters listed below are only valid if certain kernel build options
93 were enabled and if respective hardware is present. This list should be kept
94 in alphabetical order. The text in square brackets at the beginning
95 of each description states the restrictions within which a parameter
96 is applicable::
97 
98 	ACPI	ACPI support is enabled.
99 	AGP	AGP (Accelerated Graphics Port) is enabled.
100 	ALSA	ALSA sound support is enabled.
101 	APIC	APIC support is enabled.
102 	APM	Advanced Power Management support is enabled.
103 	APPARMOR AppArmor support is enabled.
104 	ARM	ARM architecture is enabled.
105 	ARM64	ARM64 architecture is enabled.
106 	AX25	Appropriate AX.25 support is enabled.
107 	CLK	Common clock infrastructure is enabled.
108 	CMA	Contiguous Memory Area support is enabled.
109 	DRM	Direct Rendering Management support is enabled.
110 	DYNAMIC_DEBUG Build in debug messages and enable them at runtime
111 	EARLY	Parameter processed too early to be embedded in initrd.
112 	EDD	BIOS Enhanced Disk Drive Services (EDD) is enabled
113 	EFI	EFI Partitioning (GPT) is enabled
114 	EVM	Extended Verification Module
115 	FB	The frame buffer device is enabled.
116 	FTRACE	Function tracing enabled.
117 	GCOV	GCOV profiling is enabled.
118 	HIBERNATION HIBERNATION is enabled.
119 	HW	Appropriate hardware is enabled.
120 	HYPER_V HYPERV support is enabled.
121 	IMA     Integrity measurement architecture is enabled.
122 	IP_PNP	IP DHCP, BOOTP, or RARP is enabled.
123 	IPV6	IPv6 support is enabled.
124 	ISAPNP	ISA PnP code is enabled.
125 	ISDN	Appropriate ISDN support is enabled.
126 	ISOL	CPU Isolation is enabled.
127 	JOY	Appropriate joystick support is enabled.
128 	KGDB	Kernel debugger support is enabled.
129 	KVM	Kernel Virtual Machine support is enabled.
130 	LIBATA  Libata driver is enabled
131 	LOONGARCH LoongArch architecture is enabled.
132 	LOOP	Loopback device support is enabled.
133 	LP	Printer support is enabled.
134 	M68k	M68k architecture is enabled.
135 			These options have more detailed description inside of
136 			Documentation/arch/m68k/kernel-options.rst.
137 	MDA	MDA console support is enabled.
138 	MIPS	MIPS architecture is enabled.
139 	MOUSE	Appropriate mouse support is enabled.
140 	MSI	Message Signaled Interrupts (PCI).
141 	MTD	MTD (Memory Technology Device) support is enabled.
142 	NET	Appropriate network support is enabled.
143 	NFS	Appropriate NFS support is enabled.
144 	NUMA	NUMA support is enabled.
145 	OF	Devicetree 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 	PV_OPS	A paravirtualized kernel is enabled.
155 	RAM	RAM disk support is enabled.
156 	RDT	Intel Resource Director Technology.
157 	RISCV	RISCV architecture is enabled.
158 	S390	S390 architecture is enabled.
159 	SCSI	Appropriate SCSI support is enabled.
160 			A lot of drivers have their options described inside
161 			the Documentation/scsi/ sub-directory.
162 	SECURITY Different security models are enabled.
163 	SELINUX SELinux 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 	SUSPEND	System suspend states are enabled.
169 	SWSUSP	Software suspend (hibernation) is enabled.
170 	TPM	TPM drivers are enabled.
171 	UMS	USB Mass Storage support is enabled.
172 	USB	USB support is enabled.
173 	USBHID	USB Human Interface Device support is enabled.
174 	V4L	Video For Linux support is enabled.
175 	VGA	The VGA console has been enabled.
176 	VMMIO   Driver for memory mapped virtio devices is enabled.
177 	VT	Virtual terminal support is enabled.
178 	WDT	Watchdog support is enabled.
179 	X86-32	X86-32, aka i386 architecture is enabled.
180 	X86-64	X86-64 architecture is enabled.
181 			More X86-64 boot options can be found in
182 			Documentation/arch/x86/x86_64/boot-options.rst.
183 	X86	Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
184 	X86_UV	SGI UV support is enabled.
185 	XEN	Xen support is enabled
186 	XTENSA	xtensa architecture is enabled.
187 
188 In addition, the following text indicates that the option::
189 
190 	BOOT	Is a boot loader parameter.
191 	BUGS=	Relates to possible processor bugs on the said processor.
192 	KNL	Is a kernel start-up parameter.
193 
194 Parameters denoted with BOOT are actually interpreted by the boot
195 loader, and have no meaning to the kernel directly.
196 Do not modify the syntax of boot loader parameters without extreme
197 need or coordination with <Documentation/arch/x86/boot.rst>.
198 
199 There are also arch-specific kernel-parameters not documented here.
200 See for example <Documentation/arch/x86/x86_64/boot-options.rst>.
201 
202 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
203 a trailing = on the name of any parameter states that that parameter will
204 be entered as an environment variable, whereas its absence indicates that
205 it will appear as a kernel argument readable via /proc/cmdline by programs
206 running once the system is up.
207 
208 The number of kernel parameters is not limited, but the length of the
209 complete command line (parameters including spaces etc.) is limited to
210 a fixed number of characters. This limit depends on the architecture
211 and is between 256 and 4096 characters. It is defined in the file
212 ./include/uapi/asm-generic/setup.h as COMMAND_LINE_SIZE.
213 
214 Finally, the [KMG] suffix is commonly described after a number of kernel
215 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
216 multipliers 'Kilo', 'Mega', and 'Giga', equaling 2^10, 2^20, and 2^30
217 bytes respectively. Such letter suffixes can also be entirely omitted:
218 
219 .. include:: kernel-parameters.txt
220    :literal:
221