/home/

In here users home directories are located

It may be mounted on a different partition (to avoid losing data, specially in multi-user systems)

/root is the home directory of the super user

/bin and /sbin

The /bin directory contains executable binaries, essential commands used to boot the system or in single-user mode, and essential commands required by all system users, such as cat, cp, ls, mv, ps, and rm.

sbin also contains binaries but for system administration like fsck and ip

/usr/bin and /usr/sbin also exist and were different in the past. Nowadays, they are symbolically linked with /bin and /sbin

/proc

In this directory, a pseudo-filesystem is mounted (Pseudo because it has no permanent presence anywhere on the disk)

The /proc filesystem contains virtual files (files that exist only in memory) that show constantly changing kernel data.

/proc contains files and directories that mimic kernel structures and configuration information. It does not contain real files, but runtime system information. Some examples are

• /proc/cpuinfo
• /proc/interrupts
• /proc/meminfo
• /proc/mounts
• /proc/partitions
• /proc/version

It also has sub-folders like /proc/<Process-ID-#> or /proc/sys. the information it reports is gathered only as needed and never needs storage on the disk.

/dev

Contains “device nodes”. These are files representing almost every HW and SW device (except for NW devices).

The directory is initially empty, when not mounted. udev which manages devices in linux, then creates entries dynamically when devices are found.

Some examples

• sda is a hard disk
• sda1 the first partition of the disk
• lp1 second printer
• random Random number generator

/var

The /var directory contains files that are expected to change in size and content as the system is running. Some examples are

• System log files: /var/log
• Packages and database files: /var/lib
• Print queues: /var/spool
• Temporary files: /var/tmp

It maybe mounted in a different partition to avoid that a size overflow will damage the entire system.

/etc

This directory contains configuration files and executable scripts for system-wide configuration.

For example:

• /etc/resolv.conf tells the system where to go on the network to obtain host name to IP address mappings (DNS).
• Files like passwd, shadow and group for managing user accounts are also found.
• environment allows for configuration of environment variables

/boot

• This directory contains the file necessary to boot the OS.
• This includes files for each Kernel installed in the system (compressed kernel, files for debugging/logging)
• GRUB files are also here

/lib

Contains libraries (common code shared by executables and needed for them to run) for the essential programs in /bin and /sbin. Some distros include /lib64 for 64bit libraries (and lib has 32 bits) In newer distros, /usr/lib is symbolically linked with /lib/

/mnt, /media and /run

These directories are used for mounting external filesystems (Removable media or other) Traditionally mnt is used for mounting NW Filesystems, and others. media (and more recently run) are used to automatically mount USB drives, or any other removable filesystem when connected to the machine.

/usr

This directory contains non essential binaries, and has its own tree. Is is the user’s application space. Not for applications used by the system

• /usr/include Header files used to compile applications
• /usr/lib Libraries for programs in /usr/bin and /usr/sbin
• /usr/lib64 64-bit libraries for 64-bit programs in /usr/bin and /usr/sbin
• /usr/sbin Non-essential system binaries, such as system daemons
• /usr/share Shared data used by applications, generally architecture-independent
• /usr/src Source code, usually for the Linux kernel
• /usr/local Data and programs specific to the local machine. Subdirectories include bin, sbin, lib, share, include, etc.
• /usr/bin This is the primary directory of executable commands on the system