Common Configuration files of Linux

Configuration files and their information

File	Information/service
aliases	Mail aliases file for use with the Sendmail and Postfix mail server. Running a mail server on each and every system has long been common use in the UNIX world, and almost every Linux distribution still comes with a Sendmail package. In this file local user names are matched with real names as they occur in E-mail addresses, or with other local addresses.
apache	Config files for the Apache web server.
bashrc	The system-wide configuration file for the Bourne Again SHell. Defines functions and aliases for all users. Other shells may have their own system-wide config files, like cshrc.
crontab and the cron.* directories	Configuration of tasks that need to be executed periodically - backups, updates of the system databases, cleaning of the system, rotating logs etc.
default	Default options for certain commands, such as useradd.
filesystems	Known file systems: ext3, vfat, iso9660 etc.
fstab	Lists partitions and their mount points.
ftp*	Configuration of the ftp-server: who can connect, what parts of the system are accessible etc.
group	Configuration file for user groups. Use the shadow utilities groupadd, groupmod and groupdel to edit this file. Edit manually only if you really know what you are doing.
hosts	A list of machines that can be contacted using the network, but without the need for a domain name service. This has nothing to do with the system's network configuration, which is done in /etc/sysconfig.
inittab	Information for booting: mode, number of text consoles etc.
issue	Information about the distribution (release version and/or kernel info).
ld.so.conf	Locations of library files.
lilo.conf, silo.conf, aboot.conf etc.	Boot information for the LInux LOader, the system for booting that is now gradually being replaced with GRUB.
logrotate.*	Rotation of the logs, a system preventing the collection of huge amounts of log files.
mail	Directory containing instructions for the behavior of the mail server.
modules.conf	Configuration of modules that enable special features (drivers).
motd	Message Of The Day: Shown to everyone who connects to the system (in text mode), may be used by the system admin to announce system services/maintenance etc.
mtab	Currently mounted file systems. It is advised to never edit this file.
nsswitch.conf	Order in which to contact the name resolvers when a process demands resolving of a host name.
pam.d	Configuration of authentication modules.
passwd	Lists local users. Use the shadow utilities useradd, usermod and userdel to edit this file. Edit manually only when you really know what you are doing.
printcap	Outdated but still frequently used printer configuration file. Don't edit this manually unless you really know what you are doing.
profile	System wide configuration of the shell environment: variables, default properties of new files, limitation of resources etc.
rc*	Directories defining active services for each run level.
resolv.conf	Order in which to contact DNS servers (Domain Name Servers only).
sendmail.cf	Main config file for the Sendmail server.
services	Connections accepted by this machine (open ports).
sndconfig or sound	Configuration of the sound card and sound events.
ssh	Directory containing the config files for secure shell client and server.
sysconfig	Directory containing the system configuration files: mouse, keyboard, network, desktop, system clock, power management etc. (specific to RedHat)
X11	Settings for the graphical server, X. RedHat uses XFree, which is reflected in the name of the main configuration file, XFree86Config. Also contains the general directions for the window managers available on the system, for example gdm, fvwm, twm, etc.
xinetd.* or inetd.conf	Configuration files for Internet services that are run from the system's (extended) Internet services daemon (servers that don't run an independent daemon).