The /etc directory

The /etc  directory contains a lot of files. Some of them are described below. For others, you should determine which program they belong to and read the manual page for that program. Many networking configuration files are in /etc  as well, and are described in the Networking Administrators' Guide.

/etc/rc  or /etc/rc.d  or /etc/rc?.d 

Scripts or directories of scripts to run at startup or when changing the run level. See the chapter on init  for further information.

/etc/passwd 

The user database, with fields giving the username, real name, home directory, encrypted password, and other information about each user. The format is documented in the passwd  manual page.

/etc/fdprm 

Floppy disk parameter table. Describes what different floppy disk formats look like. Used by setfdprm . See the setfdprm  manual page for more information.

/etc/fstab 

Lists the filesystems mounted automatically at startup by the mount -a command (in /etc/rc  or equivalent startup file). Under Linux, also contains information about swap areas used automatically by swapon -a. See section 3.8.5 and the mount  manual page for more information.

/etc/group 

Similar to /etc/passwd , but describes groups instead of users. See the group  manual page for more information.

/etc/inittab 

Configuration file for init .

/etc/issue 

Output by getty  before the login prompt. Usually contains a short description or welcoming message to the system. The contents are up to the system administrator.

/etc/magic 

The configuration file for file . Contains the descriptions of various file formats based on which file  guesses the type of the file. See the magic  and file  manual pages for more information.

/etc/motd 

The message of the day, automatically output after a successful login. Contents are up to the system administrator. Often used for getting information to every user, such as warnings about planned downtimes.

/etc/mtab 

List of currently mounted filesystems. Initially set up by the scripts, and updated automatically by the mount  command. Used when a list of mounted filesystems is needed, e.g., by the df  command.

/etc/shadow 

Shadow password file on systems with shadow password software installed. Shadow passwords move the encrypted password from /etc/passwd  into /etc/shadow ; the latter is not readable by anyone except root. This makes it harder to crack passwords.

/etc/login.defs 

Configuration file for the login  command.

/etc/printcap 

Like /etc/termcap , but intended for printers. Different syntax.

/etc/profile , /etc/csh.login , /etc/csh.cshrc 

Files executed at login or startup time by the Bourne or C shells. These allow the system administrator to set global defaults for all users. See the manual pages for the respective shells.

/etc/securetty 

Identifies secure terminals, i.e., the terminals from which root is allowed to log in. Typically only the virtual consoles are listed, so that it becomes impossible (or at least harder) to gain superuser privileges by breaking into a system over a modem or a network.

/etc/shells 

Lists trusted shells. The chsh  command allows users to change their login shell only to shells listed in this file. ftpd , the server process that provides FTP services for a machine, will check that the user's shell is listed in /etc/shells  and will not let people log in unles the shell is listed there.

/etc/termcap 

The terminal capability database. Describes by what ``escape sequences'' various terminals can be controlled. Programs are written so that instead of directly outputting an escape sequence that only works on a particular brand of terminal, they look up the correct sequence to do whatever it is they want to do in /etc/termcap . As a result most programs work with most kinds of terminals. See the termcap , curs_termcap , and terminfo  manual pages for more information.