Mastering Linux Filesystem Hierarchy: A Complete Guide to FHS Directories

Introduction

Understanding the Linux filesystem hierarchy is essential for any Linux learner. The root (/) is the top of the tree, and the Filesystem Hierarchy Standard (FHS) defines the purpose of each directory.

Four Types of Directories

FHS classifies directories as shareable/static, unshareable/static, shareable/variable, and unshareable/variable. Key examples include:

/usr – software location (shareable, static)

/etc – configuration files (unshareable, static)

/opt – third‑party software (shareable, static)

/boot – boot files (unshareable, static)

/var/mail – user mailboxes (shareable, variable)

/var/run – runtime data (unshareable, variable)

/var/spool/news – news groups (shareable, variable)

/var/lock – lock files (unshareable, variable)

Key Top‑Level Directories

/ (root) – entry point of the filesystem, contains essential files for booting and system recovery. It should reside on a small partition.

/usr – “Unix Software Resource”, holds shareable and static data such as installed software. Subdirectories include /usr/bin, /usr/lib, /usr/include, /usr/local, /usr/share, etc.

/var – variable data that grows during system operation, such as logs, caches, mail, and lock files. Subdirectories include /var/log, /var/lib, /var/spool, /var/cache, and more.

Other Important Directories

/bin, /sbin, /lib, /dev, /home, /media, /mnt, /opt, /root, /tmp, /proc, and /sys each serve specific purposes, from essential binaries to device files, user homes, removable media, temporary files, and virtual filesystems.

Path Types

Absolute paths start with “/” (e.g., /var/log), while relative paths are based on the current directory (e.g., ./run.sh, ../var/spool).

Examples

Changing directories using absolute and relative paths:

<code>cd /var/spool/mail
cd ../cron</code>

Running a script in the current directory requires the “./” prefix:

<code>./run.sh</code>