Stage 8 of 8 · 9 lessons · ~3 weeks

SSH, servers and debugging

Log into remote machines with SSH keys, set up and secure a small Linux server, keep work running with tmux, and debug problems with logs and networking tools.

Start: Logging in with SSH

Lessons· one lesson for each topic, in this order

Do this

Create a small VPS or free-tier instance and set a billing alert.
Create a sudo user, copy your key with `ssh-copy-id`, then disable root and password login.
Enable ufw allowing only SSH and the ports you need.
Add the server to `~/.ssh/config` and deploy a folder with `rsync --dry-run`, then for real.
Run a long job inside tmux, disconnect and reattach.
Serve a simple site or API, check it with `curl -i`, and read its logs with journalctl.
Find which process holds a port with `ss` or `lsof`.
Write a one-page runbook and delete the server when you no longer need it.

Start with· follow one of these

GuideFree
Initial Server Setup with Ubuntu (DigitalOcean)
DigitalOcean · Beginner
A clear, widely used checklist for a new user, sudo, SSH access and a firewall on Ubuntu
CourseFree
The Missing Semester of Your CS Education
MIT · Beginner
The command-line environment lecture covers SSH, tmux, job control and dotfiles

Practise

Linux Upskill Challenge
A free month of daily sysadmin tasks on your own server, from SSH to logs and scheduling
OverTheWire: Bandit
Its later levels need SSH keys, ports and network tools to move on

Keep handy

Everything curl
The free book on curl by its creator, for every option you will need
VS Code Remote Development
Edit files on your server (or in WSL) from VS Code over SSH

Also worth your time

roadmap.sh: LinuxGo deeper
The server, networking and troubleshooting branches of the Linux map

Before moving on: A small Linux server you set up yourself: a sudo user with key-only SSH, root and password login disabled, a firewall, a simple site or API served and checked with curl, your cron script running on it, and a one-page runbook covering how to log in, read logs, restart the service and what to check when it fails.

Tauseef's advice

A cheap server you can break and rebuild teaches you more than any course, as long as you set a billing alert first and delete it when you are done. Keep a runbook as you go. When something breaks, read the logs before you search the error; the answer is usually right there.