config -- kernel configuration file format
A kernel configuration file specifies the configuration of a FreeBSD ker- nel. 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 direc- tives. 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 con- figuration 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 [count] Configures device name for inclusion into the kernel image. If count is specified, the device is configured for count instances. 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 normally uses an environment prepared for it at boot nel configuration file (a la files.<arch>). hints filename Specifies a file to load a static device configuration specifica- tion from. From FreeBSD 5.0 onwards, the kernel reads the sys- tem's device configuration at boot time (see device.hints(5)). This directive configures the kernel to use the static device configuration listed in filename. The file filename must conform to the syntax specified by device.hints(5). 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 Specifies the architecture of the machine the kernel is being compiled for. Legal values for arch include: alpha The DEC Alpha architecture. amd64 The AMD x86-64 architecture. i386 The Intel x86 based PC architecture. ia64 The Intel IA64 architecture. pc98 The PC98 architecture. powerpc The IBM PowerPC architecture. sparc64 The Sun Sparc64 architecture. A kernel configuration file may have only one machine directive. 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] 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="foobar" 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 con- figuration is requested, the kernel will set this tunable to a value between 32 and 384. nooption kerneloptionname Remove kernel option kerneloptionname from the list of previously defined options. This directive can be used to cancel the effects of options directives in files included using include. options optionspecs Add compile time kernel options to the kernel build. The argu- ment optionspecs is a comma separated list of option specifica- tions. Each option specification has the form KernelOptionName[=OptionValue] If OptionValue 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 profil- ing. 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).
sys/compile/NAME Compile directory created from a kernel configu- ration. 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.
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.
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 con- figuration. FreeBSD 5.4 May 13, 2004 FreeBSD 5.4
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