The Linux Root Directory Explained

Written by Nick Otter.

Contents

Introduction

Let’s take a look at the Linux / directory and it’s subdirectories.

The Contents Of /

This is a fresh install of RHEL 8. Let’s take a look.

[minikube@control-plane ~]$ cd /

[minikube@control-plane /]$ ls
bin   dev  home  lib64  mnt  proc  run   src  sys  usr
boot  etc  lib   media  opt  root  sbin  srv  tmp  var

So, we have some directories. But what are they? The Linux Foundation describes them as part of the Filesystem Hierarchy Standard. Most Linux distributions follow the Filesystem Hierarchy Standard and declare it their own policy to maintain FHS compliance. The latest version of the FHS is 3.0 and was released on 3 June 2015.

I normally use the FHS wiki as it is a great condense of the docs. You can view the wiki here and the complete docs at linuxfoundation.org.

So, here goes… I’m going to go through the table documented on the wiki and add any additional notes too.

Here lies a description of all the subdirectories in the root directory, and any further directories of note.

Directory Description
/ 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, including to bring up the system or repair it;[3] for all users, e.g., cat, ls, cp.
/boot Boot loader files, e.g., kernels, initrd.
/dev Device files, e.g., /dev/null, /dev/disk0, /dev/sda1, /dev/tty, /dev/random.
/etc Host-specific system-wide configuration files.
/etc/opt Configuration files for add-on packages that are stored in /opt.
/etc/xml Configuration files, such as catalogs, for software that processes XML.
/home Directories users login to. User directories populated by all contents of/etc/skel directory.
/lib Libraries essential for the binaries in /bin and /sbin.
/lib64 Alternate format essential libraries. E.g. 64 bit or 32 bit depending on install format.
/media Mount points for removable media such as USB.
/mnt Temporarily mounted filesystems. Persistent mounts are configured in /etc/fstab.
/opt Optional application software packages. Not required by the system to function, and normally installed additionally by the user.
/proc VFS providing process and kernel information as files. Corresponds to procfs mount. Generally automatically generated and populated by the system, on the fly.
/root Home dir for the root user.
/run Run-time variable data: information about the running system since last boot e.g. cron, mount, docker, rsyslog. Files under this directory must be either removed or truncated at the begining of the boot process, but this is not necessary on systems that provide this directory as a tmpfs.
/sbin Essential system binaries e.g. fsck, init, mkfs.
/srv An old school directory. Out of use some of the time now. Data directory. For data such as data and scripts for web servers, data offered by FTP servers (FTP is (hopefully) a thing of the past.)
/sys Contains information about devices, drivers and some kernel features.
/tmp Directory for temporary files (see also /var/tmp). Often not preserved between system reboots and may be severely size-restricted.
/usr Secondary hierarchy for read-only user data; contains the majority of (multi-)user utilities and applications. Should be shareable and read-only.
  /usr/bin Non-essential command binaries (not needed in single-user mode); for all users.
  /usr/include Header files. Read more here.
  /usr/lib Libraries for the binaries in /usr/bin and /usr/sbin.
  /usr/lib<qual> Alt-format libraries, e.g. /usr/lib32 for 32-bit libriaries on a 64-bit machine.
  /usr/local Tertiary hierarchy for local data, specific to the host. Normally has further subdirectories e.g. bin, lib.
  /usr/sbin Non-essential system binaries e.g. daemons for various network services.
  /usr/share Architecture-independent (shared) data.
  /usr/src Source code e.g. the kernel source code with its header files.
/var Variable files: files whose content is expected to continually change during the normal operation of the system, such as logs and spool files.
  /var/cache Application cache data. Such data are locally generated as a result of time-consuming I/O or calculation. The application must be able to regenerate or restore the data. The cached files can be deleted without loss of data.
  /var/lib State information. Persistent data modified by programs as they run. Normally containing directories named after applications but no persistent data.
  /var/lock Lock files. Files keeping track of resources currently in use.
  /var/log Log files. Various logs. Log files here might be generated by the rsyslog daemon.
  /var/mail Mailbox files. In some distributions, these files may be located in the deprecated /var/spool/mail.
  /var/opt Variable data from add-on packagaes that are stored in /opt.
  /var/run Run-time variable data. This directory contains system information data describing the system since it was booted. In FHS 3.0, /var/run is replaced by /run; a system should either continue to provide a /var/run directory or provide a sym link from /var/run to /run for backwards compatibility.
  /var/spool Spool for tasks waiting to be processed, e.g. print queues and outgoing mail queue.
    /var/spool/mail Deprecated location for users’ mailboxes.
   /var/tmp Temporary files to be preserved between reboots.

— Thanks. This article was written by Nick Otter.