Understanding the Linux Filesystem: A Beginner's Guide

What is the Linux filesystem?

As a DevOps engineer, understanding the Linux filesystem is one of the first foundational skills you need. When you SSH into a Linux server to investigate a failed deployment, check application logs, modify a service configuration, or troubleshoot disk space, you are interacting with the Linux filesystem.

Linux powers a large portion of modern infrastructure, and even when you're working with technologies such as AWS, Azure, Docker, Kubernetes, or CI/CD tools, Linux is often running underneath these technologies.

The Linux filesystem is how Linux organises files, directories, configurations, applications, logs, and other resources. Once you understand where these things live, navigating a server and troubleshooting problems becomes much easier.

In this article, we'll explore some of the most important Linux directories, what they contain, and why they matter to a DevOps engineer.

Linux filesystem hierarchy

Core filesystem

• The /root directory

The root directory is the top-level directory of a Linux filesystem. It is represented by the symbol /. It can also be described as the starting point of all files and directories in Linux.

/
├── etc
├── home
├── opt
├── tmp
├── usr
└── var

Unlike Windows, where you may be familiar with drives such as C:\ and directories such as C:\Users or C:\Program Files, Linux uses a single directory tree. Everything starts from a directory called the **root directory**, represented by /.

From /, other directories branch out to form a hierarchical, tree-like structure.

It's important to note that the root directory / is different from the root user, which is the Linux superuser.

• The /home directory

The /home directory is directly under the root directory / and it contains personal files and folders for users. This is where users would typically store their documents, projects, downloaded files, etc.

If your Linux username is mary, your home directory would be

/home/mary

This is important as each user would typically have their own home directory, which provides a separate space for their personal files and projects.

• The /etc directory

The /etc directory contains system-wide configuration files and configuration files for many installed applications.

For example, if Nginx is installed on a server, you may find its configuration under:

/etc/nginx/

You may also come across files such as:

/etc/hosts
/etc/ssh/sshd_config

The /etc/hosts file can be used to manually map hostnames to IP addresses, while SSH configuration files control how the SSH server behaves.

As a DevOps engineer, you'll frequently work with /etc when configuring servers and applications, managing services, troubleshooting networking issues, or modifying system settings.

When you know where an application's configuration lives, you know where to look when something isn't working as expected.

• The /var directory

The /var directory contains files that change frequently while the system and applications are running. There are several important subdirectories, including:

/var
├── log       → system and application logs
├── cache     → cached application/package data
├── lib       → persistent application/system data
└── tmp       → temporary files

One of the most important is the /var/log directory. This contains the system and application logs.

Imagine Nginx suddenly stops serving requests. You check the configuration under /etc/nginx, but the configuration looks correct. Your next step might be to inspect /var/log/nginx/ for errors.

Learning to read logs is one of the most useful Linux troubleshooting skills a DevOps engineer needs to have in their stack.

• The /usr directory

This directory contains most of the programs, libraries, and other resources used by users and applications. It generally contains software managed as part of the operating system.

/usr
├── bin      → user commands and executable programs
├── lib      → libraries used by programs
├── local    → software installed locally by the administrator
└── share    → architecture-independent data such as documentation

You will frequently encounter /usr/bin when working with Linux commands. For example, a command such as ls may be located at /usr/bin/ls