Linux for DevOps: What to Learn and What to Skip

Why Linux comes first

Almost everything later on this roadmap runs on Linux. Docker containers use Linux features. Kubernetes nodes and most cloud servers usually run it too. When any of those break, you end up at a Linux command line, reading logs.

It also gives you fast feedback. You type a command and see what happens. That makes it a better first step than a large tool like Kubernetes, where one error can have many causes.

What to learn, in order

1. Move around in the terminal. Learn ls, cd, cat, less, grep, and pipes (|, which send one command's output into another). Every later step uses these.
2. Connect with SSH. SSH is how you log in to a remote server. Set up a key pair, because many servers turn off password login.
3. Users and permissions. Learn chmod, chown and sudo. Permission errors are among the most common failures you will meet.
4. Processes. Learn ps, top and kill, so you can see what is running and stop it.
5. Services with systemd. systemd is the program that starts and watches services on most Linux servers. Learn systemctl and how to write a small unit file (the config file for a service).
6. Logs. Learn journalctl and /var/log. Most troubleshooting starts here.
7. Disk and memory. Learn df, du and free. A full disk is a classic cause of outages.
8. Packages. Learn apt on Ubuntu, so you can install and update software.

What to skip for now

• Kernel tuning and compiling your own kernel.
• Deep disk topics such as LVM (a way to manage disks) beyond knowing that it exists.
• Linux certifications such as RHCSA.
• Trying lots of distros or customizing your desktop.

None of these will help you pass the test on this page. Some may matter later on the job.

Common mistakes

• Using chmod 777 to make an error go away. It gives everyone full access to the file. Find out which user needs access, then give access only to that user.
• Restarting before reading the logs. A restart can hide the cause. Read the logs first, so you know what you are fixing.
• Only watching videos. You do not learn this by watching. Type every command on a machine you can break.

Your project

Create a virtual machine. Set up a user, SSH, and one service. Write down each step as a runbook (a list of steps someone else could follow). Then delete the machine and rebuild it from your notes, twice. Keep the runbook, because you will put it in Git at step 3.