/etc : Host-specific system configuration
Purpose
The /etc hierarchy contains configuration files. A "configuration file" is a local file used to control the operation of a program; it must be static and cannot be an executable binary. [4]
Requirements
No binaries may be located under /etc. [5]
The following directories, or symbolic links to directories are required in /etc:
Specific Options
The following directories, or symbolic links to directories must be in /etc, if the corresponding subsystem is installed:
The following files, or symbolic links to files, must be in /etc if the corresponding subsystem is installed: [6]
| File | Description |
|---|---|
| csh.login | Systemwide initialization file for C shell logins (optional) |
| exports | NFS filesystem access control list (optional) |
| fstab | Static information about filesystems (optional) |
| ftpusers | FTP daemon user access control list (optional) |
| gateways | File which lists gateways for routed (optional) |
| gettydefs | Speed and terminal settings used by getty (optional) |
| group | User group file (optional) |
| host.conf | Resolver configuration file (optional) |
| hosts | Static information about host names (optional) |
| hosts.allow | Host access file for TCP wrappers (optional) |
| hosts.deny | Host access file for TCP wrappers (optional) |
| hosts.equiv | List of trusted hosts for rlogin, rsh, rcp (optional) |
| hosts.lpd | List of trusted hosts for lpd (optional) |
| inetd.conf | Configuration file for inetd (optional) |
| inittab | Configuration file for init (optional) |
| issue | Pre-login message and identification file (optional) |
| ld.so.conf | List of extra directories to search for shared libraries (optional) |
| motd | Post-login message of the day file (optional) |
| mtab | Dynamic information about filesystems (optional) |
| mtools.conf | Configuration file for mtools (optional) |
| networks | Static information about network names (optional) |
| passwd | The password file (optional) |
| printcap | The lpd printer capability database (optional) |
| profile | Systemwide initialization file for sh shell logins (optional) |
| protocols | IP protocol listing (optional) |
| resolv.conf | Resolver configuration file (optional) |
| rpc | RPC protocol listing (optional) |
| securetty | TTY access control for root login (optional) |
| services | Port names for network services (optional) |
| shells | Pathnames of valid login shells (optional) |
| syslog.conf | Configuration file for syslogd (optional) |
mtab does not fit the static nature of /etc: it is excepted for historical reasons. [7]
/etc/opt : Configuration files for /opt
Purpose
Host-specific configuration files for add-on application software packages must be installed within the directory /etc/opt/<subdir>, where <subdir> is the name of the subtree in /opt where the static data from that package is stored.
Requirements
No structure is imposed on the internal arrangement of /etc/opt/<subdir>.
If a configuration file must reside in a different location in order for the package or system to function properly, it may be placed in a location other than /etc/opt/<subdir>.
Refer to the rationale for /opt.
/etc/X11 : Configuration for the X Window System (optional)
Purpose
/etc/X11 is the location for all X11 host-specific configuration. This directory is necessary to allow local control if /usr is mounted read only.
Specific Options
The following files, or symbolic links to files, must be in /etc/X11 if the corresponding subsystem is installed:
| File | Description |
|---|---|
| Xconfig | The configuration file for early versions of XFree86 (optional) |
| XF86Config | The configuration file for XFree86 versions 3 and 4 (optional) |
| Xmodmap | Global X11 keyboard modification file (optional) |
Subdirectories of /etc/X11 may include those for xdm and for any other programs (some window managers, for example) that need them. [8] We recommend that window managers with only one configuration file which is a default .*wmrc file must name it system.*wmrc (unless there is a widely-accepted alternative name) and not use a subdirectory. Any window manager subdirectories must be identically named to the actual window manager binary.
/etc/sgml : Configuration files for SGML (optional)
Purpose
Generic configuration files defining high-level parameters of the SGML systems are installed here. Files with names *.conf indicate generic configuration files. File with names *.cat are the DTD-specific centralized catalogs, containing references to all other catalogs needed to use the given DTD. The super catalog file catalog references all the centralized catalogs.
/etc/xml : Configuration files for XML (optional)
Purpose
Generic configuration files defining high-level parameters of the XML systems are installed here. Files with names *.conf indicate generic configuration files. The super catalog file catalog references all the centralized catalogs.