Online Linux lab: practice real commands in your browser

15 Linux practice exercises

Click a command to have it typed into the terminal, or type it yourself, which sticks better. Under each one is what you should see.

1. Navigate

   Where am I and what is here?

   pwd prints the folder you are in; ls -la lists everything in it, including hidden files, which start with a dot.

   pwd && ls -la

   You should see: /home/estudiante and a listing with .bashrc, .profile, bienvenida.txt, Documentos and proyectos, each with its permissions, owner and size.

2. Navigate

   Go into a folder and come back

   cd changes folders and cat prints a file. Watch the prompt change. The ~ sign is your home folder.

   cd ~/proyectos/nube-volcan && cat README.mdcd ~ && pwd

   You should see: The README contents ("# Nube Volcán"), the prompt showing ~/proyectos/nube-volcan and, after the second command, back in /home/estudiante.

3. Create files

   A folder and a file with text

   mkdir -p creates the folder; echo with > writes the text into a new file (or replaces it if it exists); cat reads it back.

   mkdir -p ~/practica && echo "hola linux" > ~/practica/notas.txt && cat ~/practica/notas.txt

   You should see: hola linux

4. Create files

   Copy, move and rename

   cp copies and leaves the original in place. mv moves, and when the target is a new name in the same folder, it renames.

   cp ~/bienvenida.txt ~/Documentos/ && ls ~/Documentosmv ~/Documentos/bienvenida.txt ~/Documentos/leame.txt && ls -l ~/Documentos

   You should see: First bienvenida.txt inside Documentos; then leame.txt in its place.

5. Permissions

   A file only you can read

   chmod 600 leaves read and write for the owner and nothing for anyone else: 6 = read (4) + write (2).

   touch ~/secreto.txt && chmod 600 ~/secreto.txt && ls -l ~/secreto.txt

   You should see: -rw------- 1 estudiante estudiante 0 … /home/estudiante/secreto.txt

6. Permissions

   Your first executable script

   Without the x permission, Linux will not run a file even if it contains commands. chmod +x adds it.

   echo 'echo Hola desde mi script' > ~/saludo.sh && chmod +x ~/saludo.sh && ~/saludo.sh

   You should see: Hola desde mi script

7. Users

   Who am I and which groups am I in?

   whoami prints your user; id prints your user number (uid) and your groups. Being in the sudo group is what lets you administer the server.

   whoami && id

   You should see: estudiante, then uid=1000(estudiante) gid=1000(estudiante) with the adm and sudo groups.

8. Users

   Create a user and add a group

   useradd -m creates the user with a home folder. usermod -aG adds a group without removing the ones she already had (without -a, it removes them).

   sudo useradd -m ana && id anasudo usermod -aG sudo ana && groups ana

   You should see: uid=1001(ana) gid=1001(ana), then ana : ana sudo.

9. grep and pipes

   Find a line in a file

   grep prints only the lines that contain the text you are looking for. /etc/passwd has one line per user, with fields separated by colons.

   grep estudiante /etc/passwd

   You should see: estudiante:x:1000:1000:Estudiante de la Academia:/home/estudiante:/bin/bash

10. grep and pipes

    Chain commands with |

    The | pipe hands one command’s output to the next. The second example counts failed SSH logins grouped by IP address, the first thing you check during an incident.

    cut -d: -f1 /etc/passwd | sort | head -5grep "Failed password" /var/log/auth.log | grep -o "from [0-9.]*" | sort | uniq -c

    You should see: Five user names in alphabetical order, then how many failed attempts came from 198.51.100.7 and from 203.0.113.45.

11. Processes

    See which programs are running

    ps aux lists every process on the system; grep keeps the ones you care about. The second column is the PID, the number you use to control each process.

    ps aux | grep sshd

    You should see: The sshd lines (the SSH server) running as root, with their PID.

12. Processes

    A background process

    The trailing & keeps the command running and gives you the prompt back. jobs lists what is in the background and kill %1 stops job number 1.

    sleep 300 &jobskill %1

    You should see: [1] and a PID; then the job listed as running (Ejecutando) and, at the end, terminated (Terminado).

13. Services

    Check and restart a service

    systemctl controls services: status tells you whether it is running, restart restarts it. journalctl -u shows that service’s log.

    systemctl status sshsudo systemctl restart ssh && journalctl -u ssh -n 5

    You should see: active (running) in green; after the restart, the Stopping…, Starting… and Started ssh.service lines.

14. Disks

    See the disks and free space

    lsblk draws the disks and their partitions; df -h tells you how much space is left on each mounted file system.

    lsblkdf -h

    You should see: sda with partitions sda1 and sda2 plus three unused disks (sdb, sdc, sdd); then the root / at 39G and 24% used.

15. Network

    Addresses, ports and connectivity

    ip -br a sums up the interfaces and their addresses; ss -tln shows the ports waiting for connections; ping -c 2 checks that you can reach the internet.

    ip -br ass -tlnping -c 2 203.0.113.10

    You should see: enp0s3 UP with 10.0.2.15/24; port 22 (SSH) in LISTEN; and two replies from 203.0.113.10 with 0% packet loss.