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.

1. Generic Hierarchical File System Software Download

• 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.

What a Hierarchical File System Is All About. In a nutshell, a hierarchy is a system organized by graded categorization. A familiar example is the organizational structure of a company, where workers report to supervisors and supervisors report to middle managers. With simple generic data entry, following a hierarchical structure, the system should automatically generate the configuration file required by the system software. Knowledge Organization, Concepts, Signs A Semeiotic Framework. / (Root): Primary hierarchy root and root directory of the entire file system hierarchy. /bin: Essential command binaries that need to be available in single user mode; for all users, e.g., cat, ls, cp. Common linux commands you need to use in single-user modes are located under this directory.

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 aministrator, 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.

Generic Hierarchical File System Software Download

• 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

Modern Linux distributions include a /run directory as a temporary filesystem (tmpfs) which stores volatile runtime data, following the FHS version 3.0. According to the FHS version 2.3, such data were stored in /var/run but this was a problem in some cases because this directory is not always available at early boot. As a result, these programs have had to resort to trickery, such as using /dev/.udev, /dev/.mdadm, /dev/.systemd or /dev/.mount directories, even though the device directory isn’t intended for such data.Among other advantages, this makes the system easier to use normally with the root filesystem mounted read-only. For example, below are the changes Debian made in its 2013 Wheezy release:

• /dev/.* ? /run/*
• /dev/shm ? /run/shm
• /dev/shm/* ? /run/*
• /etc/* (writeable files) ? /run/*
• /lib/init/rw ? /run
• /var/lock ? /run/lock
• /var/run ? /run
• /tmp ? /run/tmp

Reference : Wikipedia – Filesystem Hierarchy Standard

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