Inside /etc ( Plain text configuration file)

The /etc directory

The /etc maintains 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

/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 Section 2.3.1 for further information.

/etc/passwd

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

/etc/shadow

/etc/shadow is an encrypted file the holds user passwords.

/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.

/etc/group

Similar to /etc/passwd, but describes groups instead of users.

/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/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 bootup scripts, and updated automatically by the mount command. Used when a list of mounted filesystems is needed, e.g., by the df command.

etc/login.defs

Configuration file for the login command.

/etc/profile, /etc/bash.rc, /etc/csh.cshrc

Files executed at login or startup time by the Bourne, BASH , or C shells. These allow the system

administrator to set global defaults for all users. Users can also create individual copies of these in their home directory to personalize their environment. See the manual pages for the respective shells.

/etc/shells

Lists trusted shells. The chsh command allows users to change their login shell only to shells listed in this file. ftpd, is 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 unless the shell is listed there.