freebsd/usr.sbin/config/config.5

.\" Copyright (c) 2003 Joseph Koshy
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.Dd July 3, 2003
.Dt CONFIG 5
.Os
.Sh NAME
.Nm config
.Nd kernel configuration file format
.Sh DESCRIPTION
A kernel configuration file specifies the configuration of a
.Fx
kernel.
It is processed by
.Xr config 8
to create a build environment where a kernel may be built using
.Xr make 1 .
.Ss Lexical Structure
A kernel configuration file comprises a sequence of specification
directives.
.Pp
A specification directive starts with a keyword at the beginning
of the line and is followed by additional parameters.
.Pp
A specification directive may be terminated by a semicolon
.Ql \&;
or by a newline.
Long input lines may be broken into shorter lines by starting the
second and subsequent lines with a white space character.
.Pp
Case is significant,
.Dq Li machine
and
.Dq Li MACHINE
are different tokens.
.Pp
A double quote character
.Ql \[dq]
starts a quoted string.
All characters up to the next quote character form the value
of the quoted string.
A
.Ql \[dq]
character may be inserted into a quoted string by
using the sequence
.Ql \e\[dq] .
.Pp
Numbers are specified using
.Tn C Ns -style
syntax.
.Pp
A
.Ql #
character starts a comment; all characters from the
.Ql #
character till the end of the current line are ignored.
.Pp
Whitespace between tokens is ignored, except inside quoted strings.
Whitespace following a comment line is ignored.
.Ss Configuration Directives
Kernel configuration directives may appear in any order
in a kernel configuration file.
Directives are processed in order of appearance with subsequent
directive lines overriding the effect of prior ones.
.Pp
The list of keywords and their meanings are as follows:
.Bl -tag -width indent
.\" -------- CPU --------
.It Ic cpu Ar cputype
Specify the CPU this kernel will run on.
There can be more than one
.Ic cpu
directive in a configuration file.
The allowed list of CPU names is architecture specific and is
defined in the file
.Pa sys/conf/options. Ns Aq Ar arch .
.\" -------- DEVICE --------
.It Ic device Ar name Op Ar count
Configures device
.Ar name
for inclusion into the kernel image.
If
.Ar count
is specified, the device is configured for
.Ar count
instances.
Devices that are common to all architectures are
defined in the file
.Pa sys/conf/files .
Devices that are specific to architecture
.Ar arch
are defined in the file
.Pa sys/conf/files. Ns Aq Ar arch .
.\" -------- ENV --------
.It Ic env Ar filename
Specifies a filename containing a kernel environment definition.
The kernel normally uses an environment prepared for it at boot time
by
.Xr loader 8 .
This directive makes the kernel ignore the boot environment and use
the compiled-in environment instead.
.Pp
This directive is useful for setting kernel tunables in
embedded environments that do not start from
.Xr loader 8 .
.\" -------- HINTS --------
.It Ic hints Ar filename
Specifies a file to load a static device configuration specification
from.
From
.Fx 5.0
onwards, the kernel reads the system's device configuration at boot
time (see
.Xr device.hints 5 ) .
This directive configures the kernel to use the static device configuration
listed in
.Ar filename .
The file
.Ar filename
must conform to the syntax specified by
.Xr device.hints 5 .
.\" -------- IDENT --------
.It Ic ident Ar name
Set the kernel name to
.Ar name .
At least one
.Ic ident
directive is required.
.\" -------- INCLUDE --------
.It Ic include Ar filename
Read subsequent text from file
.Ar filename
and return to the current file after
.Ar filename
is successfully processed.
.\" -------- MACHINE --------
.It Ic machine Ar arch
Specifies the architecture of the machine the kernel is being
compiled for.
Legal values for
.Ar arch
include:
.Pp
.Bl -tag -width ".Cm powerpc" -compact
.It Cm alpha
The DEC Alpha architecture.
.It Cm amd64
The AMD x86-64 architecture.
.It Cm i386
The Intel x86 based PC architecture.
.It Cm ia64
The Intel IA64 architecture.
.It Cm pc98
The PC98 architecture.
.It Cm powerpc
The IBM PowerPC architecture.
.It Cm sparc64
The Sun Sparc64 architecture.
.El
.Pp
A kernel configuration file may have only one
.Ic machine
directive.
.\" -------- MAKEOPTION --------
.It Ic makeoptions Ar options
Add
.Ar options
to the generated makefile.
.Pp
The
.Ar options
argument is a comma separated list of one or more option
specifications.
Each option specification has the form
.Pp
.D1 Ar MakeVariableName Ns Op = Ns Ar Value
.Pp
and results in the appropriate
.Xr make 1
variable definition being inserted into the generated makefile.
If only the name of the
.Xr make 1
variable is specified,
.Ar value
is assumed to be the empty string.
.Pp
Example:
.Bd -literal -offset indent -compact
makeoptions MYMAKEOPTION="foobar"
makeoptions MYNULLMAKEOPTION
.Ed
.\" -------- MAXUSERS --------
.It Ic maxusers Ar number
This optional directive is used to configure the size
of some kernel data structures.
The parameter
.Ar number
can be 0 (the default) or an integer greater than or equal to 2.
A value of 0 indicates that the kernel should configure
its data structures according to the size of available
physical memory.
If auto configuration is requested, the kernel will set
this tunable to a value between 32 and 384.
.Pp
As explained in
.Xr tuning 7 ,
this tunable can also be set at boot time using
.Xr loader 8 .
.\" -------- NOMAKEOPTION --------
.It Ic nomakeoption Ar name
Removes previously defined
.Xr make 1
option
.Ar name
from the kernel build.
This directive can be used to cancel the effects of
.Ic makeoption
directives in files included using
.Ic include .
.\" -------- NOOPTION --------
.It Ic nooption Ar kerneloptionname
Remove kernel option
.Ar kerneloptionname
from the list of previously defined options.
This directive can be used to cancel the effects of
.Ic options
directives in files included using
.Ic include .
.\" -------- OPTIONS --------
.It Ic options Ar optionspecs
Add compile time kernel options to the kernel build.
The argument
.Ar optionspecs
is a comma separated list of option specifications.
Each option specification has the form
.Pp
.D1 Ar KernelOptionName Ns Op = Ns Ar OptionValue
.Pp
If
.Ar OptionValue
is not specified, it is assumed to be
.Dv NULL .
Options common to all architectures are specified in
the file
.Pa sys/conf/options .
Options specific to architecture
.Ar arch
are specified in the file
.Pa sys/conf/options. Ns Aq Ar arch .
.\" -------- PROFILE --------
.It Ic profile Ar number
Enables kernel profiling if
.Ar number
is non-zero.
If
.Ar number
is 2 or greater, the kernel is configured for
high-resolution profiling.
Kernels can also be built for profiling using the
.Fl p
option to
.Xr config 8 .
.El
.Ss Obsolete Directives
The following kernel configuration directives are obsolete.
.Bl -tag -width indent
.\" -------- CONFIG --------
.It Ic config
This directive was used to specify the device to be used for the root
file system.
From
.Fx 4.0
onwards, this information is passed to a booting kernel by
.Xr loader 8 .
.El
.Sh FILES
.Bl -tag -width ".Pa sys/conf/Makefile. Ns Ar arch" -compact
.It Pa sys/compile/ Ns Ar NAME
Compile directory created from a kernel configuration.
.It Pa sys/conf/Makefile. Ns Ar arch
.Pa Makefile
fragments for architecture
.Ar arch .
.It Pa sys/conf/files
Devices common to all architectures.
.It Pa sys/conf/files. Ns Ar arch
Devices for architecture
.Ar arch .
.It Pa sys/conf/options
Options common to all architectures.
.It Pa sys/conf/options. Ns Ar arch
Options for architecture
.Ar arch .
.El
.Sh SEE ALSO
.Xr kenv 1 ,
.Xr make 1 ,
.Xr device.hints 5 ,
.Xr loader.conf 5 ,
.Xr config 8 ,
.Xr kldload 8 ,
.Xr loader 8
.Rs
.%T "Building 4.4BSD Kernels with Config"
.%A "Samuel J. Leffler"
.%A "Michael J. Karels"
.Re
.Sh HISTORY
The
.Xr config 8
utility first appeared in
.Bx 4.1 ,
and was subsequently revised in
.Bx 4.4 .
.Pp
The kernel configuration mechanism changed further in
.Fx 4.0
and
.Fx 5.0 ,
moving toward an architecture supporting dynamic kernel
configuration.