SHELL DEFAULTS

/etc/bashrc 
- system-wide default functions and aliases for the bash shell

/etc/profile 
- system-wide defaults for bash shell, including system-wide environment variables. 


ADMINISTRATIVE SETTINGS

/etc/passwd 
- contains passwords and other information concerning users 
who are registered to use the system. 
It can be modified by root directly, but it is preferable to use a configuration utility 
such as passwd to make the changes. 
A corrupt /etc/passwd file can easily render a Linux box unusable.

/etc/shadow 
- contains "shadow" information for the passwd file, i.e., 
the information pieces which "the world" does not have permission to read.

/etc/group 
- similar to /etc/passwd but for groups.

/etc/crontab 
- setup for "cron", which runs commands periodically (hourly, daily, weekly, monthly, etc.).

/etc/inittab 
- runs different programs and processes on startup.

/etc/issue 
- message that accompanies login prompt. This is often overwitten by the rc.local script.

/etc/issue.net 
- same as above, but used when login is attempted over the network.

/etc/motd 
- "message of the day" file, displayed after a user logs in.

/etc/rc.d/rc.local 
- the last script to execute on the system bootup. I put the commands which customize 
my local machine at the end of this file. It works like DOS "autoexec.bat". 


NETWORK CONFIGURATION

/etc/hosts 
- contains a list of host names and absolute IP addresses.

/etc/hosts.allow 
- hosts allowed to access Internet services

/etc/hosts.deny 
- hosts forbidden to access Internet services

/etc/resolv.conf 
- setups for a list of domain name servers used by the local machine

/etc/inetd.conf 
- configures the inetd daemon to tell it what TCP/IP services your machine should run.

/etc/exports 
- specifies hosts to which file systems can be exported using NFS (network file system). 
man exports contains information on how to set up this file for remote users. 


HARDWARE CONFIGURATION

/etc/conf.modules 
- setup for the linux kernel modules. Modules are like "device drivers" under MS Windows or DOS.

/etc/fstab 
- contains information on partitions and filesystems used by system to mount different partitions 
and devices on the directory tree.

/etc/mtab 
- shows currently mounted devices and partitions and their status.

/etc/lilo.conf 
- configuration file for lilo boot loader.

/boot/grub/grub.conf - configuration file for grub boot loader.

/etc/printcap 
- setup for printers.

/etc/termcap 
- ASCII database defining the capabilities and characteristics of different consoles, 
terminals, and printers. You typically don't want to change these.

/etc/X11/XF86Config 
- X configuration file. For XFree version 4.xx, the file is /etc/X11/XF86Config-4 
(if it does not exist, then XF86Config is tried).