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Linux Basics

By Lint8590 Level 1

You installed Ubuntu Server. Now what? The terminal is your desktop. Every command you run happens over SSH. No mouse. No context menu. Just a prompt and a blinking cursor.

This guide covers the commands you’ll use every day. Not everything Linux can do. The 20% that gets you 80% of the way.

Method 1: Getting Around

The File System

Linux has no C: drive. Everything starts at /.

/          - root. top of everything
/home      - your files live here (/home/youruser)
/etc       - config files (/etc/nginx, /etc/ssh)
/var       - data that changes (logs in /var/log, databases in /var/lib)
/tmp       - temp files. deleted on reboot.
/opt       - optional software. Docker volumes often go here.

Your home directory is /home/youruser. That’s ~ for short. You spend most of your time here.

pwd                      # where am I?
ls                       # what's in this directory?
ls -la                   # same, but show hidden files and details
cd /etc/nginx            # go to a directory
cd ~                     # go home
cd ..                    # go up one level

ls -la is the most useful command you’ll learn. The -l flag shows permissions, owner, size, date. The -a flag shows hidden files (they start with a dot).

Reading Files

cat file.txt             # print the whole file
less file.txt            # scroll through it (q to quit)
head -n 20 file.txt      # first 20 lines
tail -n 20 file.txt      # last 20 lines
tail -f file.txt         # watch new lines appear (Ctrl+C to stop)

tail -f is how you watch logs in real time. When something is broken, this is your first stop.

Editing Files

You need a text editor. Nano is already installed and works over SSH:

nano /etc/nginx/nginx.conf

Arrow keys to move. Type to edit. Ctrl+O to save. Ctrl+X to exit.

That’s enough for now. If you find yourself editing configs daily, learn Vim. If not, stick with Nano.

File Operations

cp source.txt dest.txt    # copy
mv old.txt new.txt        # rename or move
rm file.txt               # delete (no trash bin)
rm -rf directory/         # delete a directory and everything in it
mkdir newdir              # create a directory
mkdir -p a/b/c            # create nested directories

rm -rf is dangerous. Triple check before you run it. There is no undo.

Permissions

Every file has an owner and a permission set:

-rw-r--r--  1 root root  1234 Apr 15 10:00 config.yml

The first character is type (- = file, d = directory). Then three groups of three: owner, group, everyone.

rw- means read and write. r-- means read only. --- means nothing.

Common permission commands:

chmod 600 file           # owner can read+write, nobody else
chmod 755 file           # owner can do everything, others can read+execute
chown user:group file    # change owner and group

For config files that contain passwords:

chmod 600 ~/docker-services/.env

Getting Help

command --help           # quick reference
man command              # full manual (q to quit)

Run man ls and you get the complete documentation for ls. Press q to exit the manual.

Method 2: Managing Services

systemd

Ubuntu uses systemd to manage services. When you install something like Nginx or Docker, systemd keeps it running.

systemctl status nginx          # is it running?
systemctl start nginx           # start it
systemctl stop nginx            # stop it
systemctl restart nginx         # restart (after config change)
systemctl enable nginx          # start on boot
systemctl disable nginx         # don't start on boot

Check if a service is running with status. If it shows “active (running)”, you’re good. If “failed”, something is wrong.

journalctl -u nginx             # see the service's logs
journalctl -u nginx --since "1 hour ago"

Processes

ps aux                       # all running processes
top                          # live view of processes (q to quit)
htop                         # nicer version of top (install with apt)

ps aux | grep docker shows you all processes with “docker” in the name. The pipe (|) sends output from one command to another. grep filters for matching lines.

Disk

df -h                        # disk space (human readable)
du -sh ~/docker-services/    # size of a directory

Run df -h weekly or put it in your head. A full disk causes more failures than any other single issue.

Network

ip addr show                 # your IP addresses
ip link show                 # network interfaces
ping 8.8.8.8                 # can you reach the internet?
ss -tulpn                   # what ports are listening?

ss -tulpn shows every service accepting connections. Run it when a port doesn’t work and you’ll see whether the service is listening at all.

Package Management

Ubuntu uses apt:

sudo apt update               # refresh package list
sudo apt install htop         # install something
sudo apt remove htop          # uninstall
sudo apt upgrade              # update everything
sudo apt autoremove           # clean up unused packages

Run sudo apt update && sudo apt upgrade regularly. Security patches come through here.

Docker-Specific

docker ps                     # running containers
docker ps -a                  # all containers
docker logs -f container-name # watch container logs
docker restart container-name # restart a container
docker system df              # how much disk Docker is using

Docker containers restart with docker compose restart or docker restart <name>. Docker itself restarts with sudo systemctl restart docker.

Your Daily Routine

SSH into your server:

ssh youruser@192.168.1.100

Check what’s running:

htop

Check disk space:

df -h

Check Docker:

docker ps

Check for updates:

sudo apt update && sudo apt upgrade

That’s five commands. Takes 30 seconds. You now know the health of your server.

When something breaks, start here:

  1. systemctl status <service> - is it running?
  2. journalctl -u <service> --since "10 min ago" - what does the log say?
  3. tail -f /var/log/syslog - what is the system doing right now?
  4. df -h - is the disk full?

9 times out of 10, those four commands tell you the problem.

Next Steps

You can navigate, edit files, and manage services. That’s most of what Linux asks of you. Next: monitor your new skills with Setting Up Monitoring.

Next Steps