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.
- In the FHS, all files and directories appear under the root directory /, even if they are stored on different physical or virtual devices.
- Some of these directories only exist on a particular system if certain subsystems, such as the X Window System, are installed.
- Most of these directories exist in all UNIX operating systems and are generally used in much the same way; however, the descriptions here are those used specifically for the FHS, and are not considered authoritative for platforms other than Linux.
1. / (Root) : Primary hierarchy root and root directory of the entire file system hierarchy.
- Every single file and directory starts from the root directory
- Only root user has the right to write under this directory
- /root is root user’s home directory, which is not same as /
2. /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
3. /boot : Boot loader files, e.g., kernels, initrd.
- Kernel initrd, vmlinux, grub files are located under /boot
- Example: initrd.img-2.6.32-24-generic, vmlinuz-2.6.32-24-generic
4. /dev : Essential device files, e.g., /dev/null.
- These include terminal devices, usb, or any device attached to the system.
- Example: /dev/tty1, /dev/usbmon0
5. /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.
6. /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
7. /lib : Libraries essential for the binaries in /bin/ and /sbin/.
- Library filenames are either ld* or lib*.so.*
- Example: ld-2.11.1.so, libncurses.so.5.7
8. /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
9. /mnt : Temporarily mounted filesystems.
- Temporary mount directory where sysadmins can mount filesystems.
10. /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.
11. /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
12. /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.
- Example, /srv/cvs contains CVS related data.
13. /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.
14. /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
- /usr/local contains users programs that you install from source. For example, when you install apache from source, it goes under /usr/local/apache2
- /usr/src holds the Linux kernel sources, header-files and documentation.
15. /proc : Virtual filesystem providing process and kernel information as files. In Linux, corresponds to a procfs mount. Generally automatically generated and populated by the system, on the fly.
- Contains information about system process.
- This is a pseudo filesystem contains information about running process. For example: /proc/{pid} directory contains information about the process with that particular pid.
- This is a virtual filesystem with text information about system resources. For example: /proc/uptime
