1 .\" Copyright (c) 2003 Joseph Koshy
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31 .Nd kernel configuration file format
33 A kernel configuration file specifies the configuration of a
38 to create a build environment where a kernel may be built using
41 A kernel configuration file comprises a sequence of specification
44 A specification directive starts with a keyword at the beginning
45 of the line and is followed by additional parameters.
47 A specification directive may be terminated by a semicolon
50 Long input lines may be broken into shorter lines by starting the
51 second and subsequent lines with a white space character.
59 A double quote character
61 starts a quoted string.
62 All characters up to the next quote character form the value
66 character may be inserted into a quoted string by
70 Numbers are specified using
76 character starts a comment; all characters from the
78 character till the end of the current line are ignored.
80 Whitespace between tokens is ignored, except inside quoted strings.
81 Whitespace following a comment line is ignored.
82 .Ss Configuration Directives
83 Kernel configuration directives may appear in any order
84 in a kernel configuration file.
85 Directives are processed in order of appearance with subsequent
86 directive lines overriding the effect of prior ones.
88 The list of keywords and their meanings are as follows:
90 .Bl -tag -width indent -compact
91 .\" -------- CPU --------
93 Specify the CPU this kernel will run on.
94 There can be more than one
96 directive in a configuration file.
97 The allowed list of CPU names is architecture specific and is
99 .Pa sys/conf/options. Ns Aq Ar arch .
100 .\" -------- DEVICE --------
102 .It Ic device Ar name Op , Ar name Op ...
103 .It Ic devices Ar name Op , Ar name Op ...
104 Configures the specified devices
105 for inclusion into the kernel image.
106 Devices that are common to all architectures are
109 Devices that are specific to architecture
111 are defined in the file
112 .Pa sys/conf/files. Ns Aq Ar arch .
113 .\" -------- ENV --------
115 .It Ic env Ar filename
116 Specifies a filename containing a kernel environment definition.
117 The kernel normally uses an environment prepared for it at boot time
120 This directive makes the kernel ignore the boot environment and use
121 the compiled-in environment instead.
123 This directive is useful for setting kernel tunables in
124 embedded environments that do not start from
126 .\" -------- FILES --------
128 .It Ic files Ar filename
129 Specifies a file containing a list of files specific to that kernel
130 configuration file (a la
131 .Pa files. Ns Aq Ar arch ) .
132 .\" -------- HINTS --------
134 .It Ic hints Ar filename
135 Specifies a file to load a static device configuration specification
139 onwards, the kernel reads the system's device configuration at boot
141 .Xr device.hints 5 ) .
142 This directive configures the kernel to use the static device configuration
147 must conform to the syntax specified by
149 Multiple hints lines are allowed.
150 The resulting hints will be the files concatenated in the order of appearance.
151 .\" -------- IDENT --------
154 Set the kernel name to
158 directive is required.
159 .\" -------- INCLUDE --------
161 .It Ic include Ar filename
162 Read subsequent text from file
164 and return to the current file after
166 is successfully processed.
167 .\" -------- MACHINE --------
169 .It Ic machine Ar arch Op Ar cpuarch
170 Specifies the architecture of the machine the kernel is being
176 .Bl -tag -width ".Cm powerpc" -compact
178 The DEC Alpha architecture.
180 The ARM architecture.
182 The AMD x86-64 architecture.
184 The Intel x86 based PC architecture.
186 The MIPS architecture.
188 The PC98 architecture.
190 The IBM PowerPC architecture.
192 The Sun Sparc64 architecture.
197 is specified, it points
199 to the cpu architecture of the machine.
202 architecture requires its cpu architecture
207 is not specified, it is assumed to be the same as
210 corresponds to MACHINE.
212 corresponds to MACHINE_ARCH.
214 A kernel configuration file may have only one
217 .\" -------- MAKEOPTION --------
219 .It Ic makeoption Ar options
220 .It Ic makeoptions Ar options
223 to the generated makefile.
227 argument is a comma separated list of one or more option
229 Each option specification has the form
231 .D1 Ar MakeVariableName Ns Op = Ns Ar Value
232 .D1 Ar MakeVariableName Ns += Ns Ar Value
234 and results in the appropriate
236 variable definition being inserted into the generated makefile.
237 If only the name of the
239 variable is specified,
241 is assumed to be the empty string.
244 .Bd -literal -offset indent -compact
245 makeoptions MYMAKEOPTION="foo"
246 makeoptions MYMAKEOPTION+="bar"
247 makeoptions MYNULLMAKEOPTION
249 .\" -------- MAXUSERS --------
251 .It Ic maxusers Ar number
252 This optional directive is used to configure the size
253 of some kernel data structures.
256 can be 0 (the default) or an integer greater than or equal to 2.
257 A value of 0 indicates that the kernel should configure
258 its data structures according to the size of available
260 If auto configuration is requested, the kernel will set
261 this tunable to a value between 32 and 384.
265 this tunable can also be set at boot time using
267 .\" -------- NOCPU --------
269 .It Ic nocpu Ar cputype
270 Remove the specified CPU
271 from the list of previously selected CPUs.
272 This directive can be used to cancel the effect of
274 directives in files included using
276 .\" -------- NODEVICE --------
278 .It Ic nodevice Ar name Op , Ar name Op ...
279 .It Ic nodevices Ar name Op , Ar name Op ...
280 Remove the specified devices
281 from the list of previously selected devices.
282 This directive can be used to cancel the effects of
286 directives in files included using
288 .\" -------- NOMAKEOPTION --------
290 .It Ic nomakeoption Ar name
291 .It Ic nomakeoptions Ar name
292 Removes previously defined
296 from the kernel build.
297 This directive can be used to cancel the effects of
299 directives in files included using
301 .\" -------- NOOPTION --------
303 .It Ic nooption Ar name Op , Ar name Op ...
304 .It Ic nooptions Ar name Op , Ar name Op ...
305 Remove the specified kernel options
306 from the list of previously defined options.
307 This directive can be used to cancel the effects of
311 directives in files included using
313 .\" -------- OPTIONS --------
315 .It Ic option Ar optionspec Op , Ar optionspec Op ...
316 .It Ic options Ar optionspec Op , Ar optionspec Op ...
317 Add compile time kernel options to the kernel build.
318 Each option specification has the form
320 .D1 Ar name Ns Op = Ns Ar value
324 is not specified, it is assumed to be
326 Options common to all architectures are specified in
328 .Pa sys/conf/options .
329 Options specific to architecture
331 are specified in the file
332 .Pa sys/conf/options. Ns Aq Ar arch .
333 .\" -------- PROFILE --------
335 .It Ic profile Ar number
336 Enables kernel profiling if
341 is 2 or greater, the kernel is configured for
342 high-resolution profiling.
343 Kernels can also be built for profiling using the
348 .Ss Obsolete Directives
349 The following kernel configuration directives are obsolete.
350 .Bl -tag -width indent
351 .\" -------- CONFIG --------
353 This directive was used to specify the device to be used for the root
357 onwards, this information is passed to a booting kernel by
361 .Bl -tag -width ".Pa sys/conf/Makefile. Ns Ar arch" -compact
362 .It Pa sys/compile/ Ns Ar NAME
363 Compile directory created from a kernel configuration.
364 .It Pa sys/conf/Makefile. Ns Ar arch
366 fragments for architecture
368 .It Pa sys/conf/files
369 Devices common to all architectures.
370 .It Pa sys/conf/files. Ns Ar arch
371 Devices for architecture
373 .It Pa sys/conf/options
374 Options common to all architectures.
375 .It Pa sys/conf/options. Ns Ar arch
376 Options for architecture
388 .%T "Building 4.4BSD Kernels with Config"
389 .%A "Samuel J. Leffler"
390 .%A "Michael J. Karels"
395 utility first appeared in
397 and was subsequently revised in
400 The kernel configuration mechanism changed further in
404 moving toward an architecture supporting dynamic kernel