Linux Directory Structure and Functions

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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 file-systems.

  • Temporary mount directory where sysadmins can mount file-systems.

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 file-system 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 file-system contains information about running process. For example: /proc/{pid} directory contains information about the process with that particular pid.
  • This is a virtual file-system with text information about system resources. For example: /proc/uptime
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