/bin : All the executable binary programs (file) required during booting, repairing, files required to run into single-user-mode, and other important, basic commands viz. , cat, du, df, tar, rpm, wc, history, etc.
/boot : Holds important files during boot-up process, including Linux Kernel .
/dev : Contains device files for all the hardware devices on the machine like cdrom, CPU .
/etc : Directory is reserved for configuration files that are local to the machine. It should contain no binaries;
/home : Home directory of the users. Every time a new user is created, a directory in the name of user is created within home directory which contains other directories like Desktop , Downloads, Documents, etc.
/lib : directory should only contain libraries needed to execute the binaries in /bin/ and /sbin/. These shared library images are used to boot the system or execute commands within the root file system.
/lost+found : This Directory is installed during installation of Linux , useful for recovering files which may be broken due to unexpected shut-down .
/media : Temporary mount directory is created for removable devices like media/cdrom .
/mnt : directory is reserved for temporarily mounted file systems, such as NFS file system mounts.
/opt : directory is normally reserved for software and add-on packages that are not part of the default installation.
/proc : directory contains special files that either extract information from the kernel or send information to it. Examples of such information include system memory, CPU information, and hardware configuration.
/root : This is the home directory of root user and should never be confused with ‘/ ‘ .
/run : This directory is the only clean solution for early runtime-dir problem.
/sbin : directory stores binaries essential for booting, restoring, recovering, or repairing the system. The binaries in /sbin/ require root privileges to use. In addition, /sbin/ contains binaries used by the system before the /usr/ directory is mounted; any system utilities used after /usr/ is mounted are typically placed in /usr/sbin/.
/srv : Service is abbreviated as ‘srv ‘. This directory contains server specific and service related files.
/sys : Modern Linux distributions include a /sys directory as a virtual filesystem , which stores and allows modification of the devices connected to the system.
/tmp :System’s Temporary Directory, Accessible by users and root. Stores temporary files for user and system, till next boot.
/usr : Contains executable binaries , documentation , source code , libraries for second level program.
/var : is for variable data, which includes spool directories and files, logging data, transient and temporary files.