Linux Directory Structure

The Linux directory structure is like a tree. The base of the Linux file system hierarchy begins at the root, or trunk, and directories branch off from there. Each one of these directories, called folders on other operating systems, can and often do contain other directories. The directories on a Linux system are separated by a forward slash.

Common Top-Level Directories

What follows is a list of some of the most important top-level directories. Of course, all of the directories on a Linux system have a purpose, but understanding what these particular directories are for is rather important as a user of a Linux system. These top-level directories will be the ones that you interact with most often.

/   The Root Directory

Every file and directory on a Linux system resides under the / directory. This directory is referred to as the root directory or sometimes "slash," a shorthand way of saying forward slash.

Even additional physical or virtual storage devices that are attached to a Linux system live somewhere underneath the / directory. The C:\ drive on a Windows system is analogous to / on Linux. When another storage device is attached to a Windows system, it is assigned a new drive letter such as D:\. On a Linux system, storage devices are attached, or mounted, to a directory such as /mnt or /media/external.

/bin   Binaries

The /bin directory houses essential user binaries and other executable programs. The most basic and fundamental command line utilities reside in /bin. For example, some of the commands in /bin are used to list, copy, move, and view files. Other non-essential binaries are located in /usr/bin. You will find graphical applications such as web browsers and mail readers there, as well as various other command line utilities.

/etc   System Configuration Files

Configuration files that control how applications or the operating system behave are located in the /etc directory. For example, there is a configuration file in /etc that tells the operating system whether to boot into a text mode or a graphical mode.

/home   Home Directories

Each user on a Linux system has a subdirectory dedicated to his or her account in the /home directory. For example, my user account is "jason" and thus my home directory is /home/jason. Since all users have their own home directory, they have the option of keeping their data private, sharing it with other users on the system, or a combination of the two.

Typical home directory contents include files created by the user, text documents, vacation pictures, music, etc. Additionally, user-specific configurations are stored in the home directory. These configuration files can control the behavior of the user's graphical or text environment, for example.

/opt   Optional or Third-Party Software

Optional or third-party software resides in the /opt directory. The /opt directory is for software that is not bundled with the operating system. For example, the Google Chrome web browser is not part of the standard Linux operating system and installs in /opt/google/chrome.

/tmp   Temporary Space

Temporary space is available in /tmp. This directory can be used by applications or by individual users on the system. The contents of /tmp are typically cleared at boot time, so do not store anything in /tmp that you can't live without or that you want to store long-term.

/usr   User-Related Data, Read-Only

The /usr directory is where user-related programs and read-only data reside. The contents of /usr are meant to be used by actual users of the system as opposed to the operating system itself. A whole directory hierarchy exists in /usr. For example, the /usr/bin directory contains binary files and applications, while /usr/share/doc contains documentation related to those applications.

/var   Variable Data

Variable data, the most notable being log files, is stored in the /var directory. Several log files exist in the /var/log directory or a subdirectory thereof.

Comprehensive Listing of Top-Level Directories

In addition to the directories previously covered, there are additional top-level directories you may encounter on a Linux system. Many of these directories will be of little concern to you in your day-to-day use of the operating system; however, they are an essential part of a functioning Linux system. This may be used as a quick reference to help you understand the general purpose of each of these top-level directories. Some subdirectories are included in this list to help clearly define the purpose of the top-level directory.

/   The starting point of the Linux file system hierarchy, called the root directory.

/bin   Binaries and other executable programs.

/boot   Files required to boot the operating system.

/cdrom   Where CD-ROMs are attached or mounted.

/cgroup   Control groups hierarchy.

/dev   Device files, typically controlled by the operating system and the system administrators.

/etc   System configuration files.

/home   User home directories.

/lib   System libraries.

/lib64   System libraries, 64-bit.

/lost+found   Used by the file system to store recovered files after a file system check has been performed.

/media   Used to mount removable media like USB drives.

/mnt   Used to mount external file systems.

/opt   Optional or third-party software.

/proc   Process information virtual file system.

/root   The home directory for the root (superuser) account.

/sbin   System administration binaries.

/selinux   Virtual file system used to display information about SELinux.

/srv   Contains data which is served by the system.

/srv/www   Web server files.

/srv/ftp   FTP files.

/sys   Virtual file system used to display and sometimes configure the devices and buses known to the Linux kernel.

/tmp   Temporary space, typically cleared on reboot.

/usr   User-related programs, libraries, and documentation.

/usr/bin   Binaries and other executable programs.

/usr/lib   Libraries.

/usr/local   Locally installed software that is not part of the base operating system.

/usr/sbin   System administration binaries.

/var   Variable data, most notably log files.

/var/log   Log files.

If you encounter other top-level directories that have not been listed here, those were more than likely created by the system administrator.

Application Directory Structures

Application directory structures can be patterned after the operating system. Here is a sample directory structure of an application named apache installed in /usr/local.

/usr/local/apache/bin   The application's binaries and other executable programs.

/usr/local/apache/etc   Configuration files for the application.

/usr/local/apache/lib   Application libraries.

/usr/local/apache/logs   Application log files.

If apache were to be installed in /opt it would look like this:

/opt/apache/bin   The application's binaries and other executable programs.

/opt/apache/etc   Configuration files for the application.

/opt/apache/lib   Application libraries.

/opt/apache/logs   Application log files.

Another common application directory structure pattern includes moving the configuration and variable data outside of /opt. Instead of placing all of the application components in /opt/app-name, /etc/opt/app-name is used for configuration files and /var/opt/app-name is used for logs. Continuing with the apache application example, here is a demonstration of this method:

/etc/opt/apache   Configuration files for the application.

/opt/apache/bin   The application's binaries and other executable programs.

/opt/apache/lib   Application libraries.

/var/opt/apache   Application log files.

Not only can applications be segregated into their own directories, they can share a common directory structure with other applications that are not part of the standard operating system. For example, apache can be directly installed into /usr/local. In this case, the binaries would reside in /usr/local/bin, while the configuration would reside in /usr/local/etc. Since apache may not be the only locally installed application, it could share that space with the other programs.

Organizational Directory Structures

Directory structures can be based on an organization such as a company, group, or team. For example, if you work for the Widget corporation, you may find a directory named /opt/widget or /usr/local/widget on the company's Linux servers. In some cases, this base directory is treated much like an application directory. It will contain common subdirectories like /etc and /bin. Here is an example:

/opt/widget   The top-level directory for the Widget company.

/opt/widget/bin   Binaries and programs installed or created by the Widget company.

/opt/widget/etc   Configuration files for the programs installed or created by the Widget company.

Further subdivisions can be made within this organizational directory structure. For instance, each application may receive its own subdirectory as follows:

/opt/widget   The top-level directory for the Widget company.

/opt/widget/apache   The top-level directory for the Widget company's installation of apache.

/opt/widget/apache/bin   The apache binaries.

/opt/widget/apache/bin   The apache configuration files.

Here are variations on the same theme, but based on a team within the company.

/opt/sysadmin   The system administrator team's top-level directory.

/opt/widget/sysadmin   The system administrator team's top-level directory.

/usr/local/widget/sysadmin   The system administrator team's top-level directory.