Importanf files and its descriptions.

* /boot/vmlinuz - the typical location and name of the Linux kernel. In the Slackware distribution, the kernel is located at /vmlinuz.

* /dev/fd0 - first floppy disk drive

* /dev/fd0H1440 - driver for the first floppy drive in high density mode. Generally, this is invoked when formatting a floppy drive for a particular density. Slackware comes with drivers that allow for formatting a 3.5" diskette with up to 1.7MB of space. Red Hat and Mandrake do not contain these device driver files by default.

* /dev/fd1 - second floppy disk drive

* /dev/hda - first IDE hard drive

* /dev/hdc - on many machines, the IDE cdrom drive. Most often, there is a symbolic link called /dev/cdrom which is just a link to the true cdrom driver file.

* /dev/null - used when you want to send output into oblivion

* /etc/aliases - file containing aliases used by sendmail and other MTAs (mail transport agents). After updating this file, it is necessary to run the newaliases utility for the changes to be passed to sendmail.

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

* /etc/conf.modules - aliases and options for configurable modules

* /etc/crontab - shell script to run different commands periodically (hourly, daily, weekly, monthly, etc.)

* /etc/DIR_COLORS - used to store colors for different file types when using ls command. The dircolors command uses this file when there is not a .dir_colors file in the user's home directory. Used in conjunction with the eval command (see below).

* /etc/exports - specifies hosts to which file systems can be exported using NFS. Man exports contains information on how to set up this file for remote users.

* /etc/fstab - contains information on partitions and file systems used by system to mount different partitions and devices on the directory tree

* /etc/HOSTNAME - stores the name of the host computer

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

* /etc/hosts.allow - hosts allowed (by the tcpd daemon) to access Internet services

* /etc/hosts.deny - hosts forbidden (by the tcpd daemon) to access Internet services

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

* /etc/inetd.conf - configures the inetd daemon to tell it what TCP/IP services to provide (which daemons to load at boot time). A good start to securing a Linux box is to turn off these services unless they are necessary.

* /etc/inittab - runs different programs and processes on startup. This is typically the program which is responsible for, among other things, setting the default runlevel, running the rc.sysinit script contained in /etc/rc.d, setting up virtual login terminals, bringing down the system in an orderly fashion in response to [Ctrl][Alt][Del], running the rc script in /etc/rc.d, and running xdm for a graphical login prompt (only if the default runlevel is set for a graphical login).

* /etc/issue - pre-login message. This is often overwitten by the /etc/rc.d/rc.S script (in Slackware) or by the /etc/rc.d/rc.local script (in Mandrake and Red Hat, and perhaps other rpm-based distributions). The relevant lines should be commented out (or changed) in these scripts if a custom pre-login message is desired.

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

* /etc/motd - message of the day file, printed immediately after login. This is often overwritten by /etc/rc.d/rc.S (Slackware) or /etc/rc.d/rc.local (Mandrake/Red Hat) on startup. See the remarks in connection with /etc/issue.

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

* /etc/passwd - contains passwords and other information concerning users who are registered to use the system. For obvious security reasons, this is readable only by root. 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/printcap - shows the setup of printers

* /etc/profile - sets system-wide defaults for bash shell. It is this file in Slackware that sets up the DIR_COLORS environment variable for the color ls command. Also sets up other system-wide environment variables.

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

* /etc/securetty - contains a list of terminals on which root can login. For security reasons, this should not include dialup terminals.

* /etc/termcap - ASCII database defining the capabilities and characteristics of different consoles, terminals, and printers

* /etc/X11/XF86Config - X configuration file. The location in Slackware is /etc/XF86Config.

* /proc/cpuinfo - cpu information

* /proc/filesystems - prints filesystems currently in use

* /proc/interrupts - prints interrupts currently in use

* /proc/ioports - contains a list of the i/o addresses used by various devices connected to the computer

* /proc/kcore - The command ls -l /proc/kcore will give the amount of RAM on the computer. It's also possible to use the free command to get the same information (and more).

* /proc/version - prints Linux version and other info

* /var/log/messages - used by syslog daemon to store kernel boot-time messages

* /var/log/lastlog - used by system to store information about last boot

* /var/log/wtmp - contains binary data indicating login times and duration for each user on system.