Linux File Hierarchy

The Linux File Hierarchy Structure or the Filesystem Hierarchy Standard (FHS) defines the directory structure and directory contents in Unix-like operating systems. It is maintained by the Linux Foundation.

/ (Root)

Primary hierarchy root and root directory of the entire file system hierarchy. 

• Every single file and directory starts from the root directory
• The only root user has the right to write under this directory
• /root is the root user’s home directory, which is not the same as /

/bin

Essential command binaries that need to be available in single-user mode; for all users, e.g., cat, ls, cp. 

•  Contains binary executables
• Common linux commands you need to use in single-user modes are located under this directory.
• Commands used by all the users of the system are located here e.g. ps, ls, ping, grep, cp

/boot

Boot loader files, e.g., kernels, initrd. 

• Kernel initrd, vmlinux, grub files are located under /boot

/dev

Essential device files, e.g., /dev/null. 

• These include terminal devices, usb, or any device attached to the system.

/etc

Host-specific system-wide configuration files.

• Contains configuration files required by all programs.
• This also contains startup and shutdown shell scripts used to start/stop individual programs.
• Example: /etc/resolv.conf, /etc/logrotate.conf.

 /home

Users’ home directories, containing saved files, personal settings, etc.

• Home directories for all users to store their personal files.
• example: /home/kishlay, /home/kv

/lib

Libraries essential for the binaries in /bin/ and /sbin/.

• Library filenames are either ld* or lib*.so.*

 /media

Mount points for removable media such as CD-ROMs (appeared in FHS-2.3).

• Temporary mount directory for removable devices.
• Examples, /media/cdrom for CD-ROM; /media/floppy for floppy drives; /media/cdrecorder for CD writer

/mnt

Temporarily mounted filesystems.

• Temporary mount directory where sysadmins can mount filesystems.

/sbin

Essential system binaries, e.g., fsck, init, route.

• Just like /bin, /sbin also contains binary executables.
• The linux commands located under this directory are used typically by system administrator, for system maintenance purpose.
• Example: iptables, reboot, fdisk, ifconfig, swapon

/proc

Virtual filesystem providing process and kernel information as files. In Linux, corresponds to a procs mount. Generally automatically generated and populated by the system, on the fly.

• Contains information about system process.

 /srv

Site-specific data served by this system, such as data and scripts for web servers, data offered by FTP servers, and repositories for version control systems.

• srv stands for service.
• Contains server specific services related data.

/tmp

Temporary files. Often not preserved between system reboots, and may be severely size restricted.

• Directory that contains temporary files created by system and users.
• Files under this directory are deleted when system is rebooted.

 /opt

Optional application software packages.

• Contains add-on applications from individual vendors.
• Add-on applications should be installed under either /opt/ or /opt/ sub-directory.

/usr

Secondary hierarchy for read-only user data; contains the majority of (multi-)user utilities and applications. 

Contains binaries, libraries, documentation, and source-code for second level programs.

• /usr/bin contains binary files for user programs. If you can’t find a user binary under /bin, look under /usr/bin. For example: at, awk, cc, less, scp
• /usr/sbin contains binary files for system administrators. If you can’t find a system binary under /sbin, look under /usr/sbin. For example: atd, cron, sshd, useradd, userdel
• /usr/lib contains libraries for /usr/bin and /usr/sbin