The Filesystem Hierarchy Standard (FHS) is a set of directories that should exist in every Linux distribution. The reason for having the Filesystem Hierarchy Standard is so that regardless of the distribution being used, the structure of the filesystem will be the same. The Filesystem Hierarchy Standard has the following directories under the / (root) directory.

/bin

The /bin (binary) directory contains binary files, such as /bin/ls and /bin/pwd. The binary files are commands that can be run by anyone - these commands do not require elevated privilege to be execute.

/boot

The /boot directory contains files related to booting the computer, such as the GRUB configuration file and the initrd image.

/dev

The /dev (devices) directory contains files for both physcial and virtual devices, such as /dev/ha1 (hard disk drive), /dev/sda1 (solid state drive), and /dev/tty1 (first virtual console).

/home

The /home drectory contains each users personal files and folders.

/lib

The /lib (library) directory contains shared library files used by programs and kernel modules.

/media

The /media directory is typically used to mount devices such as USB flash drives, CDROM drives, and smart phones.

/mnt

The /mnt (mount) directory is typically used to mount remote shares, such as Samba or NFS share.

/opt

The /opt directory contains files and folders for software, such as a package installed on the PC.

/proc

The /proc (processes) directory contains files for each process, such as /proc/meminfo and /proc/cpuinfo.

/sbin

The /sbin (super user binary) directory contains binary files, such as /sbin/shutdown and /sbin/ifdown. The binary files are commands that require elevated privilege to be executed.

/sys

The /sys (system) directory contains files for drivers to talk to applications.

/tmp

The /temp (temporary) directory contains temporary files.

/usr

The /usr directory contains most of the system programs and libraries, such as /usr/bin, /usr/lib, and /usr/local.

/var

The /var (variable) directory contains files that can change, such as log files (/var/log/messages) and website files (/var/www/html).