Important Directories in Linux File System

Directory	Description
/	The root directory where the file system begins. In most cases the root directory only contains subdirectories.
/boot	This is where the Linux kernel and boot loader files are kept. The kernel is a file called vmlinuz.
/etc	The /etc directory contains the configuration files for the system. All of the files in /etc should be text files. Points of interest: /etc/passwd The passwd file contains the essential information for each user. It is here that users are defined. /etc/fstab The fstab file contains a table of devices that get mounted when your system boots. This file defines your disk drives. /etc/hosts This file lists the network host names and IP addresses that are intrinsically known to the system. /etc/init.d This directory contains the scripts that start various system services typically at boot time.
/bin, /usr/bin	These two directories contain most of the programs for the system. The /bin directory has the essential programs that the system requires to operate, while /usr/bin contains applications for the system's users.
/sbin, /usr/sbin	The sbin directories contain programs for system administration, mostly for use by the superuser.
/usr	The /usr directory contains a variety of things that support user applications. Some highlights: /usr/share/X11 Support files for the X Window system /usr/share/dict Dictionaries for the spelling checker. Bet you didn't know that Linux had a spelling checker. See look and aspell. /usr/share/doc Various documentation files in a variety of formats. /usr/share/man The man pages are kept here. /usr/src Source code files. If you installed the kernel source code package, you will find the entire Linux kernel source code here.
/usr/local	/usr/local and its subdirectories are used for the installation of software and other files for use on the local machine. What this really means is that software that is not part of the official distribution (which usually goes in /usr/bin) goes here. When you find interesting programs to install on your system, they should be installed in one of the /usr/local directories. Most often, the directory of choice is /usr/local/bin.
/var	The /var directory contains files that change as the system is running. This includes: /var/log Directory that contains log files. These are updated as the system runs. You should view the files in this directory from time to time, to monitor the health of your system. /var/spool This directory is used to hold files that are queued for some process, such as mail messages and print jobs. When a user's mail first arrives on the local system (assuming you have local mail), the messages are first stored in /var/spool/mail
/lib	The shared libraries (similar to DLLs in that other operating system) are kept here.
/home	/home is where users keep their personal work. In general, this is the only place users are allowed to write files. This keeps things nice and clean :-)
/root	This is the superuser's home directory.
/tmp	/tmp is a directory in which programs can write their temporary files.
/dev	The /dev directory is a special directory, since it does not really contain files in the usual sense. Rather, it contains devices that are available to the system. In Linux (like Unix), devices are treated like files. You can read and write devices as though they were files. For example /dev/fd0 is the first floppy disk drive, /dev/sda (/dev/hda on older systems) is the first hard drive. All the devices that the kernel understands are represented here.
/proc	The /proc directory is also special. This directory does not contain files. In fact, this directory does not really exist at all. It is entirely virtual. The /proc directory contains little peep holes into the kernel itself. There are a group of numbered entries in this directory that correspond to all the processes running on the system. In addition, there are a number of named entries that permit access to the current configuration of the system. Many of these entries can be viewed. Try viewing /proc/cpuinfo. This entry will tell you what the kernel thinks of your CPU.
/media,/mnt	Finally, we come to /media, a normal directory which is used in a special way. The /media directory is used for mount points.Different physical storage devices (like hard disk drives) are attached to the file system tree in various places. This process of attaching a device to the tree is called mounting. For a device to be available, it must first be mounted. When your system boots, it reads a list of mounting instructions in the file /etc/fstab, which describes which device is mounted at which mount point in the directory tree. This takes care of the hard drives, but you may also have devices that are considered temporary, such as CD-ROMs, thumb drives, and floppy disks. Since these are removable, they do not stay mounted all the time. The /media directory is used by the automatic device mounting mechanisms found in modern desktop oriented Linux distributions. On systems that require manual mounting of removable devices, the /mnt directory provides a convenient place for mounting these temporary devices. You will often see the directories /mnt/floppy and /mnt/cdrom. To see what devices and mount points are used, type mount.