Linux Configuration Files and their explanations

Profile		System wide environment and startup script program.
/dev/MAKEDEV		The /dev/MAKEDEV file is a script written by the system administrator that creates local only device files or links such as device files for a non-standard device driver.
/etc/aliases		Where the user's name is matched to a nickname for e-mail.
/etc/bootptab		The configuration for the BOOTP server daemon.
/etc/crontab		Lists commands and times to run them for the cron deamon.
/etc/dhcpd.conf		The configuration file for the DHCP server daemon.
/etc/ethers		File for RARP mapping from hardware addresses to IP addresses. See the man page ethers(5).
/etc/exports		The file describing exported filesystems for NFS services.
/etc/fdprm		The floppy disk parameter table. Describes the formats of different floppy disks. Used by setfdprm.
/etc/filesystems		Can be used to set the filesystem probe order when filesystems are mounted with the auto option. The nodev parameter is specified for filesystems that are not really locally mounted systems such as proc, devpts, and nfs systems.
/etc/fstab		Lists the filesystems mounted automatically at startup by the mount -a command (in /etc/rc or equivalent startup file).
/etc/group		Similar to /etc/passwd but for groups rather than users.
/etc/groups		May contain passwords that let a user join a group.
/etc/gshadow		Used to hold the group password and group administrator password information for shadow passwords.
/etc/host.conf		Specifies how host names are resolved.
/etc/hosts		List hosts for name lookup use that are locally required.
/etc/HOSTNAME		Shows the host name of this host. Used for support of older programs since the hostname is stored in the /etc/sysconfig/network file.
/etc/inittab		Configuration file for init, controls startup run levels, determines scripts to start with.
/etc/inetd.conf		Sets up the services that run under the inetd daemon.
/etc/issue		Output by getty before the login prompt. Description or welcoming message.
/etc/issue.net		Output for network logins with LINUX version
/etc/ld.so.conf		Configuration file for ld.so, the run time linker.
/etc/lilo.conf		Configuration file for LILO.
/etc/limits		Limits users resources when a system has shadow passwords installed.
/etc/localtime		In Debian the system time zone is determined by this link.
/etc/login.defs		Sets user login features on systems with shadow passwords.
/etc/logrotate.conf		Configures the logrotate program used for managing logfiles.
/etc/magic		The configuration file for file types. Contains the descriptions of various file formats for the file command.
/etc/motd		The message of the day, automatically output by a successful login.
/etc/mtab		A list of currently mounted file systems. Setup by boot scripts and updated by the mount command.
/etc/named.conf		Used for domain name servers.
/etc/networks		Lists names and addresses of your own and other networks, used by the route command.
/etc/nologin		If this file exists, non-root logins are disabled. Typically it is created when the system is shutting down.
/etc/nsswitch.conf		Name service switch configuration file.
/etc/passwd		The user database with fields giving the username, real name, home directory, encrypted password and other information about each user.
/etc/printcap		A configuration file for printers.
/etc/profile, /etc/cshlogin, /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.
/etc/protocols		Describes DARPA internet protocols available from the TCP/IP subsystem. Maps protocol ID numbers to protocol names.
/etc/rc or /etc/rc.d or /etc/rc?.d		Scripts or directories of scripts to run at startup or when changing run level.
/etc/rc.d/rc0.d		Contains files used to control run level 0. Usually these files are softlink files.
/etc/rc.d/rc1.d		Contains files to control run level 1. Scripts beginning with an S are for start, K for kill.
/etc/rc.d/rc.sysinit		Init runs this when it starts.
/etc/resolv.conf		Configures the name resolver, specifying the address of your name server and your domain name.
/etc/securetty		Identifies secure terminals from which root is allowed to log in.
/etc/services		Lists the network services that the system supports.
/etc/shadow		Shadow password file on systems with shadow password software installed. Shadow passwords move the encrypted password files from /etc/passwd to /etc/shadow which can only be read by root.
/etc/shadow.group		Systems with shadow passwords may have this file.
/etc/shells		Lists trusted shells. The chsh command allows users to change their login shell to shells listed only in this file.
/etc/skel/.profile		Can be used by administrator to set the editor environment variable to some editor that is friendly to new users.
/etc/sudoers		A list of users with special privileges along with the commands they can execute.
/etc/smb.conf		The configuration file for setting up Samba services.
/etc/sysconfig/amd		Used to configure the auto mount daemon.
/etc/sysconfig/clock		Used to configure the system clock to Universal or local time and set some other clock parameters.
/etc/sysconfig/i18n		Controls the system font settings.
/etc/sysconfig/init		This file is used to set some terminal characteristics and environment variables.
/etc/sysconfig/keyboard		Used to configure the keyboard.
/etc/sysconfig/mouse		This file is used to configure the mouse.
/etc/sysconfig/network-scripts/ifcfg-interface		Defines a network interface.
/etc/sysconfig/pcmcia		Used to configure pcmcia network cards.
/etc/sysconfig//routed		Sets up dynamic routing policies.
/etc/sysconfig/static-routes		Configures static routes on a network.
/etc/sysconfig/tape		Used for backup tape device configuration.
/etc/X11/XF86Config		The configuration file for the X server.
/etc/syslog.conf		Configuration file for the syslogd daemon.
/etc/termcap		The terminal capability database. Describes by what "escape sequences" various terminals can be controlled. See terminfo, termcap, curs_termcap man pages.
/etc/terminfo		Details for terminal I/O.
/etc/usertty		This file is used to impose special access restrictions on users.
$HOME/.bashrc		User aliases, path modifier, and functions.
$HOME/.bash_profile		Users environment stuff and startup programs.
$HOME/.bash_logout		User actions to be done at logout.
$HOME/.hushlogin		When this file exists in the user's home directory, it will prevent check for mail, printing of the last login time, and the message of the day when the user logs in.
$HOME/.inputrc		Contains keybindings and other bits.
$HOME/Xrootenv.0		Has networking and environment info.
/proc/cpuinfo		Information about the processor such as its type, make and performance.
/proc/devices		A list of devices configured into the currently running kernel.
/proc/dma		Shows which DMA channels are being used at the moment.
/proc/filesystems		Filesystems that are configured into the kernel. The file used to detect filesystems if the /etc/filesystems does not exist.
/proc/ioports		Shows which I/O ports are in use at the moment.
/proc/interrupts		Shows which interrupts are in use and how many of each there have been.
/proc/kcore		An image of the physical memory of the system.
/proc/kmsg		Messages output by the kernel. These are also routed to syslog.
/proc/ksyms		Symbol table for the kernel.
/proc/loadavg		The load average of the system.
/proc/meminfo		Information about memory usage, both physical and swap.
/proc/modules		Which kernel modules are currently loaded.
/proc/mounts		Contains information on filesystems currently mounted, similar to /etc/mtab
/proc/net		Contains status information about network protocols.
/proc/self		A symbolic link to the process directory of the program that is looking at /proc. When 2 process look at proc, they get different links.
/proc/stat		Various statistics about the system such as the number of page faults since the system was booted.
/proc/uptime		The time the system has been up.
/proc/version		The kernel version.
/tmp/fvwmrca01339		FVWM-M4 defines. Contains networking, Xwindows, other setup info.
/usr/lib/zoneinfo		Time zone datafiles are stored here on the Debian system
/var/log/lastlog		Used by finger to tell when a user was last logged in.
/var/log/wtmp		Binary info on users that have been logged on. The last command uses this info.
/var/run/utmp		Contains information about users currently logged in. Who and w commands use this file.
/var/named/root.hints		Used for domain name server. Placed here optionally, but this is the normal location.
/var/named/*		Files used by domain name server. Placed here optionally, but this is the normal location.
/var/log/btmp		Used to store information about failed logins. This file must be first created to activate it.
/var/log/lastlog		Contains information about the last time a login was done on the system. Works with lastb(1).
/var/log/maillog		The normal system mail log file.
/var/log/messages		The main system message log file.
var/log/secure		System tracking of user logins. Check this file periodically.
/var/spool/mail		Where mailboxes are usually stored.