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CONFIG(5) |
FreeBSD File Formats Manual |
CONFIG(5) |
config —
kernel configuration file format
A kernel configuration file specifies the configuration of a
FreeBSD kernel. It is processed by
config(8)
to create a build environment where a kernel may be built using
make(1).
A kernel configuration file comprises a sequence of specification directives.
A specification directive starts with a keyword at the beginning
of the line and is followed by additional parameters.
A specification directive may be terminated by a semicolon
‘; ’ 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.
Case is significant,
“machine ” and
“MACHINE ” are different tokens.
A double quote character
‘" ’ starts a quoted string. All
characters up to the next quote character form the value of the quoted
string. A ‘" ’ character may be
inserted into a quoted string by using the sequence
‘\" ’.
Numbers are specified using C-style syntax.
A ‘# ’ character starts a
comment; all characters from the ‘# ’
character till the end of the current line are ignored.
Whitespace between tokens is ignored, except inside quoted
strings. Whitespace following a comment line is ignored.
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.
The list of keywords and their meanings are as follows:
cpu
cputype
- Specify the CPU this kernel will run on. There can be more than one
cpu directive in a configuration file. The allowed
list of CPU names is architecture specific and is defined in the file
sys/conf/options.⟨arch⟩.
device
name [, name [...]]
-
devices
name [, name [...]]
- Configures the specified devices for inclusion into the kernel image.
Devices that are common to all architectures are defined in the file
sys/conf/files. Devices that are specific to
architecture arch are defined in the file
sys/conf/files.⟨arch⟩.
env
filename
- Specifies a filename containing a kernel environment definition.
The kernel will augment this compiled-in environment with the
environment prepared for it at boot time by
loader(8).
Environment variables specified in the
loader(8)
environment will take precedence over environment variables specified in
filename, and environment variables specified in
the dynamic environment take precedence over both of these.
loader_env.disabled=1 may be specified
in the static environment to disable the
loader(8)
environment. Disabling the
loader(8)
should be done with caution and due consideration for whether or not it
supplies environment variables needed for properly booting the
system.
static_env.disabled=1 may be specified
in the
loader(8)
environment to disable use of the static environment. This option has no
effect if specified in any environment after the
loader(8)
environment is processed. This option is not usable in conjunction with
loader_env.disabled.
This directive is useful for setting kernel tunables in
embedded environments that do not start from
loader(8).
All env and
envvar directives will be processed and added to
the static environment in reversed order of appearance so that later
specified variables properly override earlier specified variables. Note
that within filename, the first appearance of a
given variable will be the first one seen by the kernel, effectively
shadowing any later appearances of the same variable within
filename.
envvar
setting
- Specifies an individual environment setting to be added to the kernel's
compiled-in environment. setting must be of the form
“name=value”. Optional quotes are
supported in both name and value.
All env and
envvar directives will be processed and added to
the static environment in reversed order of appearance so that later
specified variables properly override earlier specified variables.
files
filename
- Specifies a file containing a list of files specific to that kernel
configuration file (a la
files.⟨arch⟩).
hints
filename
- Specifies a file to load a static device configuration specification from.
From FreeBSD 5.0 onwards, the kernel reads the
system's device configuration at boot time (see
device.hints(5)).
This directive configures the kernel to use the static device
configuration listed in filename.
Hints provided in this static device configuration will be
overwritten in the order in which they're encountered. Hints in the
compiled-in environment takes precedence over compiled-in hints, and
hints in the environment prepared for the kernel by
loader(8)
takes precedence over hints in the compiled-in environment.
Once the dynamic environment becomes available, all
compiled-in hints will be added to the dynamic environment if they do
not already have an override in the dynamic environment. The dynamic
environment will then be used for all searches of hints.
static_hints.disabled=1 may be specified
in either a compiled-in environment or the
loader(8)
environment to disable use of these hints files. This option has no
effect if specified in any environment after the
loader(8)
environment is processed.
The file filename must conform to the
syntax specified by
device.hints(5).
Multiple hints lines are allowed. The resulting hints will be the files
concatenated in reverse order of appearance so that hints in later files
properly override hints in earlier files.
ident
name
- Set the kernel name to name. At least one
ident directive is required.
include
filename
- Read subsequent text from file filename and return
to the current file after filename is successfully
processed.
machine
arch [cpuarch]
- Specifies the architecture of the machine the kernel is being compiled
for. Legal values for arch include:
arm64
- The 64-bit ARM application architecture.
arm
- The ARM architecture
amd64
- The AMD x86-64 architecture.
i386
- The Intel x86 based PC architecture.
mips
- The MIPS architecture.
powerpc
- The IBM PowerPC architecture.
riscv
- The RISC-V architecture.
If argument cpuarch is specified, it
points
config(8)
to the cpu architecture of the machine. When
cpuarch is not specified, it is assumed to be the
same as arch. arch
corresponds to MACHINE. cpuarch corresponds to
MACHINE_ARCH.
A kernel configuration file may have only one
machine directive, unless the second one matches
the machine argument in the first one exactly.
makeoption
options
-
makeoptions
options
- Add options to the generated makefile.
The options argument is a comma
separated list of one or more option specifications. Each option
specification has the form
MakeVariableName[=Value]
MakeVariableName+=Value
and results in the appropriate
make(1)
variable definition being inserted into the generated makefile. If only
the name of the
make(1)
variable is specified, value is assumed to be the
empty string.
Example:
makeoptions MYMAKEOPTION="foo"
makeoptions MYMAKEOPTION+="bar"
makeoptions MYNULLMAKEOPTION
maxusers
number
- This optional directive is used to configure the size of some kernel data
structures. The parameter 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 for 32-bit
systems, or scale the value higher based on available memory for 64-bit
systems.
As explained in
tuning(7),
this tunable can also be set at boot time using
loader(8).
nocpu
cputype
- Remove the specified CPU from the list of previously selected CPUs. This
directive can be used to cancel the effect of
cpu
directives in files included using include .
nodevice
name [, name [...]]
-
nodevices
name [, name [...]]
- Remove the specified devices from the list of previously selected devices.
This directive can be used to cancel the effects of
device or devices
directives in files included using include .
nomakeoption
name
-
nomakeoptions
name
- Removes previously defined
make(1)
option name from the kernel build. This directive
can be used to cancel the effects of
makeoption
directives in files included using include .
nooption
name [, name [...]]
-
nooptions
name [, name [...]]
- Remove the specified kernel options from the list of previously defined
options. This directive can be used to cancel the effects of
option or options
directives in files included using include .
option
optionspec [, optionspec
[...]]
-
options
optionspec [, optionspec
[...]]
- Add compile time kernel options to the kernel build. Each option
specification has the form
name[=value]
If value is not specified, it is assumed
to be NULL . Options common to all architectures
are specified in the file sys/conf/options.
Options specific to architecture arch are
specified in the file
sys/conf/options.⟨arch⟩.
profile
number
- Enables kernel profiling if number is non-zero. If
number is 2 or greater, the kernel is configured for
high-resolution profiling. Kernels can also be built for profiling using
the
-p option to
config(8).
The following kernel configuration directives are obsolete.
config
- This directive was used to specify the device to be used for the root file
system. From FreeBSD 4.0 onwards, this information
is passed to a booting kernel by
loader(8).
- sys/compile/NAME
- Compile directory created from a kernel configuration.
- sys/conf/Makefile.arch
- Makefile fragments for architecture
arch.
- sys/conf/files
- Devices common to all architectures.
- sys/conf/files.arch
- Devices for architecture arch.
- sys/conf/options
- Options common to all architectures.
- sys/conf/options.arch
- Options for architecture arch.
The
config(8)
utility first appeared in 4.1BSD, and was subsequently
revised in 4.4BSD.
The kernel configuration mechanism changed further in
FreeBSD 4.0 and FreeBSD 5.0,
moving toward an architecture supporting dynamic kernel configuration.
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