Linux file system and directory structure

Everything in Linux can be reduced to a file. Partitions are associated with files such as /dev/hda1. Hardware components are associated with files such as /dev/modem. Detected devices are documented as files in the /proc directory. The Filesystem Hierarchy Standard (FHS) is the official way to organize files in Unix and Linux directories.

Linux file system and directory structure

Several major directories are associated with all modern Unix/Linux operating systems. These directories organize user files, drivers, kernels, logs, programs, utilities, and more into different categories. The standardization of the FHS makes it easier for users of other Unix-based operating systems to understand the basics of Linux. Every FHS starts with the root directory, also known by its label, the single forward slash (/). All of the other directories shown in Table are subdirectories of the root directory. Unless they are mounted separately, you can also find their files on the same partition as the root directory.

/	The root directory, the top-level directory in the FHS. All other directories are subdirectories of root, which is always mounted on some partition. All directories that are not mounted on a separate partition are included in the root directory?s partition.
/bin	Essential command line utilities. Should not be mounted separately; otherwise, it could be difficult to get to these utilities when using a rescue disk.
/boot	Includes Linux startup files, including the Linux kernel. Can be small; 16MB is usually adequate for a typical modular kernel. If you use multiple kernels, such as for testing a kernel upgrade, increase the size of this partition accordingly.
/etc	Most basic configuration files.
/dev	Hardware and software device drivers for everything from floppy drives to terminals. Do not mount this directory on a separate partition.
/home	Home directories for almost every user.
/lib	Program libraries for the kernel and various command line utilities. Do not mount this directory on a separate partition.
/mnt	The mount point for removable media, including floppy drives, CD-ROMs, and Zip disks.
/opt	Applications such as WordPerfect or StarOffice.
/proc	Currently running kernel-related processes, including device assignments such as IRQ ports, I/O addresses, and DMA channels.
/root	The home directory of the root user.
/sbin	System administration commands. Don't mount this directory separately.
/tmp	Temporary files. By default, Red Hat Linux deletes all files in this directory periodically.
/usr	Small programs accessible to all users. Includes many system administration commands and utilities.
/var	Variable data, including log files and printer spools.

Have you wondered why certain programs are located under /bin, or /sbin, or /usr/bin, or /usr/sbin?

For example, less command is located under /usr/bin directory. Why not /bin, or /sbin, or /usr/sbin? What is the different between all these directories?

In this article, let us review the Linux filesystem structures and understand the meaning of individual high-level directories.

1. / – Root

• Every single file and directory starts from the root directory.
• Only root user has write privilege under this directory.
• Please note that /root is root user’s home directory, which is not same as /.

2. /bin – User Binaries

• 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.
• For example: ps, ls, ping, grep, cp.

3. /sbin – System Binaries

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

4. /etc – Configuration Files

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

5. /dev – Device Files

• Contains device files.
• These include terminal devices, usb, or any device attached to the system.
• For example: /dev/tty1, /dev/usbmon0

6. /proc – Process Information

• 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

7. /var – Variable Files

• var stands for variable files.
• Content of the files that are expected to grow can be found under this directory.
• This includes — system log files (/var/log); packages and database files (/var/lib); emails (/var/mail); print queues (/var/spool); lock files (/var/lock); temp files needed across reboots (/var/tmp);

8. /tmp – Temporary Files

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

9. /usr – User Programs

• 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

10. /home – Home Directories

• Home directories for all users to store their personal files.
• For example: /home/john, /home/nikita

11. /boot – Boot Loader Files

• Contains boot loader related files.
• Kernel initrd, vmlinux, grub files are located under /boot
• For example: initrd.img-2.6.32-24-generic, vmlinuz-2.6.32-24-generic

12. /lib – System Libraries

• Contains library files that supports the binaries located under /bin and /sbin
• Library filenames are either ld* or lib*.so.*
• For example: ld-2.11.1.so, libncurses.so.5.7

13. /opt – Optional add-on Applications

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

14. /mnt – Mount Directory

• Temporary mount directory where sysadmins can mount filesystems.

15. /media – Removable Media Devices

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

16. /srv – Service Data

• srv stands for service.
• Contains server specific services related data.
• For example, /srv/cvs contains CVS related data.