The Playground

A pretend Linux server that runs in your browser. Switch between Rocky and Ubuntu in the title bar. You can't break anything, and Reset gives you a fresh machine.

Challenges

Find the treasure hidden in games/maze
Install cowsay on both families (each one has a catch)
Launch a website and curl localhost to see it
Lock yourself out with ufw on Ubuntu, then work out why
Type sl after installing it 🚂
Find which log file records logins on each family
Find the kernel file in /boot and the CPU model in /proc/cpuinfo
Make a service account with --system on both families and compare the UIDs and shells
Make your own command in /usr/local/bin, then try it with sudo on both families
Schedule a job with crontab -e, then timewarp 10m
Create a user, a group and a shared folder
Write a script, chmod +x it and run it
Back up Documents with tar and restore it
Make a symlink to /var/log in your home, then find it with find ~ -type l
Count the accounts that can log in: grep bash /etc/passwd | wc -l. Is it the same on both?
Make a self-signed certificate with openssl and check when it expires
Start a tmux session, detach with Ctrl+B D, and get back in
Switch the server to your time zone with timedatectl
Visit Alpine: podman run -it docker.io/library/alpine:3.22 (install podman first), then find out whose kernel it's using
Turn your home folder's Documents into a git repository and make three commits
Write a script that says “use dnf” on Rocky and “use apt” on Ubuntu, using case
Count to 10 with a while loop, then with for i in $(seq 10)
Make a #!/bin/sh script that uses <( ). Run it on Ubuntu, then on Rocky. What changes?
SRE: install sysstat and run the 60-second checklist (uptime, vmstat 1 5, mpstat -P ALL 1 3, iostat -xz 1 3…). Is this quiet server healthy?
SRE: install Apache, then load-test it with ab -n 2000 -c N http://localhost/ for N = 1, 10, 100, 500. Where's the knee?
SRE: seq 1000 | awk '{t[NR]=$1} END {print t[int(NR*0.99)]}', then work out p50 and p95 the same way
DevOps: write your own Containerfile (FROM alpine, busybox-extras, httpd -f), podman build it, run it with -p 8080:8080 and curl localhost:8080
DevOps: install jq and pull the name out of echo '{"user":{"name":"ada"}}'. Then try -r.
DevOps: put a password in a .env file, chmod 600 it, and make git ignore it

Handy

help: what the playground knows
explain CMD: plain-English tutor
man CMD: the manual
Tab completes, ↑ repeats
timewarp 1h: skip time (playground only)
sudo password: linux

This is a simulation. It copies real output and error messages closely, but it isn't a real Linux machine.