Unix configuration files are a unique type of plain file. As the name implies, configuration files contain information about the structure or arrangement of specific parts of the system. They are kept in the /etc directory.
These files are not necessarily of any direct use to users, although they do affect the way a system functions. An example of this is /etc/fstab .This is the filesystem configuration file that lists all the disk partitions and the purpose of each partition. For regular partitions, the conventional mount point may also be listed. The /etc/fstab file is used by mount and other such commands. It is what allows filesystems to be mounted automatically at boot time rather than having to mount them all by hand, one at a time.
System administration tasks frequently necessitate modifying these files. For instance, every time a new user is added, the /etc/passwd and /etc/group configuration files must be modified.
/etc/passwd is a password file. Each line in the file holds all the information on a single user. A line consists of seven fields, separated by a colon.
Userid's (UID's) are mapped to the names in this file. Every time a new user is added their information must be added to this file.
/etc/group contains the names of valid groups and the usernames of their members. This file is owned by root and only root may modify it. When a new user is added information on what groups they are a member of must be added here. Groupid's (GID's) are mapped to the group names kept in this file.
Other configuration files include: /etc/inetd.config, /etc/hosts, /etc/inittab, /etc/hosts.equiv, /etc/export, and /etc/mtab.
/etc/inetd.config is the Internet daemon file. It holds the instructions used by /etc/inetd to manage the network service daemons.
/etc/hosts is a TCP/IP network configuration file. It is accessed by all commands that use the network. The file contains a list of IP addresses, hostnames and hostname aliases.
/etc/inittab is a system configuration file that helps regulate the operation of serial interfaces.
/etc/hosts.equiv contains a list of TCP/IP "trusted" hosts. If machine A is a trusted host of machine B, then all users on machine A may rlogin to machine B without supplying a password.
/etc/export lists all the filesystems that are available to other machines via NFS.
/etc/mtab holds information on all mounted filesystems.
Terms used: mount, mount point, partition, boot, root, Internet, daemon, network, hostname, TCP/IP, IP address, NFS.