Before you start

This course is about looking after a Linux server: a computer, often with no screen, that runs programs for other people, like a website or a database. It builds on the three earlier Linux courses, and this lesson gathers what it uses from them.

In the examples, $ is the prompt: type what follows it. sudo in front of a command runs it as root, the administrator account that may change anything; most of this course needs it. Settings are text files, mostly under /etc, and you change them with an editor: sudo nano /etc/hosts, then Ctrl+O to save and Ctrl+X to exit. Logs, a program's running record of what it did, live under /var/log.

Permissions say who may read (r = 4), write (w = 2) and execute (x = 1) a file, for the owner, the group and everyone else. Added up per set, they give the numbers you'll see: 700 means only the owner can do anything, and 600 means only the owner can read and write.

Joining commands: a | b feeds a's output to b, > file saves output to a file and >> file adds to the end. Errors travel separately, and 2>&1 sends them to the same place as the output. $(cmd) drops a command's output into another command, so $(date +%F) becomes today's date. PATH is the list of folders the shell searches for programs, which is why scripts sometimes need full paths like /usr/bin/tar.

$ echo "started $(date +%F)" >> run.log
$ tail -n 1 run.log
started 2026-10-21

The kernel is the core of Linux that runs the hardware and every program; booting is the computer starting up, and the kernel is loaded first. A distribution (Ubuntu, Debian, Fedora and so on) is the kernel plus a chosen set of programs and tools.

Networking words: every machine has an IP address, like 203.0.113.20, that others use to reach it. A port is a number that picks which program on the machine gets the traffic, like 22 for SSH logins and 443 for secure websites. DNS turns names like example.com into IP addresses. A firewall blocks traffic to ports you haven't allowed. Encrypted means scrambled so only the two ends can read it.