CONFIG(5) FreeBSD File Formats Manual CONFIG(5)
NAME
config - kernel configuration file format
DESCRIPTION
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).
Lexical Structure
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.
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.
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).
Obsolete Directives
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).
FILES
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.
SEE ALSO
kenv(1), make(1), device.hints(5), loader.conf(5), config(8), kldload(8),
loader(8)
Samuel J. Leffler and Michael J. Karels, Building 4.4BSD Kernels with
Config.
HISTORY
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.
FreeBSD 13.1-RELEASE-p6 October 28, 2021 FreeBSD 13.1-RELEASE-p6
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