---
name: "config"
section: "8"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["freebsd", "openbsd"]
url: "https://new.carta.tech/config/8"
---

# config(8)

build system configuration files

## NAME

**config** – build system configuration files

## SYNOPSIS

**config** \[**-CVgpv**\] \[**-I** *path*\] \[**-d** *destdir*\] \[**-s** *srcdir*\] *SYSTEM\_NAME*

**config** \[**-x** *kernel*\]

## DESCRIPTION

The **config** utility builds a set of system configuration files from the file *SYSTEM\_NAME* which describes the system to configure. A second file tells **config** what files are needed to generate a system and can be augmented by configuration specific set of files that give alternate files for a specific machine (see the FILES section below).

Available options and operands:

- **-V**

  Print the **config** version number.

- **-C**

  If the INCLUDE\_CONFIG\_FILE is present in a configuration file, kernel image will contain full configuration files included literally (preserving comments). This flag is kept for backward compatibility.

- **-I** *path*

  Search in *path* for any file included by the **include** directive. This option may be specified more than once.

- **-d** *destdir*

  Use *destdir* as the output directory, instead of the default one. Note that **config** does not append *SYSTEM\_NAME* to the directory given.

- **-s** *srcdir*

  Use *srcdir* as the source directory, instead of the default one.

- **-m**

  Print the MACHINE and MACHINE\_ARCH values for this kernel and exit.

- **-g**

  Configure a system for debugging.

- **-x** *kernel*

  Print kernel configuration file embedded into a kernel file. This option makes sense only if **options INCLUDE\_CONFIG\_FILE** entry was present in your configuration file.

- **-v**

  Turns on verbose output.

- *SYSTEM\_NAME*

  Specify the name of the system configuration file containing device specifications, configuration options and other system parameters for one system configuration.

The **config** utility should be run from the *conf* subdirectory of the system source (usually */sys/**ARCH**/conf*), where *ARCH* represents one of the architectures supported by FreeBSD. The **config** utility creates the directory *../compile/**SYSTEM\_NAME* or the one given with the **-d** option as necessary and places all output files there. The output of **config** consists of a number of files; for the i386, they are: *Makefile*, used by [make(1)](/make/1.md) in building the system; header files, definitions of the number of various devices that will be compiled into the system.

The **config** utility looks for kernel sources in the directory *../..* or the one given with the **-s** option.

After running **config**, it is necessary to run “make depend” in the directory where the new makefile was created. The **config** utility prints a reminder of this when it completes.

If any other error messages are produced by **config**, the problems in the configuration file should be corrected and **config** should be run again. Attempts to compile a system that had configuration errors are likely to fail.

## DEBUG KERNELS

Traditional BSD kernels are compiled without symbols due to the heavy load on the system when compiling a “debug” kernel. A debug kernel contains complete symbols for all the source files, and enables an experienced kernel programmer to analyse the cause of a problem. The debuggers available prior to 4.4BSD-Lite were able to find some information from a normal kernel; [gdb(1)](/gdb/1.md) (*ports/devel/gdb*) provides very little support for normal kernels, and a debug kernel is needed for any meaningful analysis.

For reasons of history, time and space, building a debug kernel is not the default with FreeBSD: a debug kernel takes up to 30% longer to build and requires about 30 MB of disk storage in the build directory, compared to about 6 MB for a non-debug kernel. A debug kernel is about 11 MB in size, compared to about 2 MB for a non-debug kernel. This space is used both in the root file system and at run time in memory. Use the **-g** option to build a debug kernel. With this option, **config** causes two kernel files to be built in the kernel build directory:

- *kernel.debug* is the complete debug kernel.

- *kernel* is a copy of the kernel with the debug symbols stripped off. This is equivalent to the normal non-debug kernel.

There is currently little sense in installing and booting from a debug kernel, since the only tools available which use the symbols do not run on-line. There are therefore two options for installing a debug kernel:

- “make install” installs *kernel* in the root file system.

- “make install.debug” installs *kernel.debug* in the root file system.

## FILES

- */sys/conf/files*

  list of common files system is built from

- */sys/conf/Makefile*.*ARCH*

  generic makefile for the *ARCH*

- */sys/conf/files*.*ARCH*

  list of *ARCH* specific files

- */sys/**ARCH**/compile/**SYSTEM\_NAME*

  default kernel build directory for system *SYSTEM\_NAME* on *ARCH*.

## SEE ALSO

[config(5)](/config/5.md)

The SYNOPSIS portion of each device in section 4. S. J. Leffler and M. J. Karels, “Building 4.3 BSD UNIX System with Config”, *4.4BSD System Manager's Manual (SMM)*.

## HISTORY

The **config** utility appeared in 4.1BSD.

Before support for **-x** was introduced, **options INCLUDE\_CONFIG\_FILE** included entire configuration file that used to be embedded in the new kernel. This meant that [strings(1)](/strings/1.md) could be used to extract it from a kernel: to extract the configuration information, you had to use the command:

```
strings -n 3 kernel | sed -n 's/^___//p'
```

## BUGS

The line numbers reported in error messages are usually off by one.