Linux Terminal Playground

What is this?

A Linux shell that runs entirely in your browser. It emulates a small server — with a home directory, logs, nginx and SSH configuration — in two flavours: Ubuntu 24.04 (Debian family) and Rocky Linux 9 (RHEL-compatible: RHEL, Rocky, AlmaLinux). Switch between them to see where they differ: /var/log/auth.log vs /var/log/secure, sudo vs wheel, sites-available vs conf.d. You can practice commands without a VM, a cloud account, or the fear of breaking something. Nothing is sent to a server, and Reset brings the machine back to its starting state.

What you can do

• Navigate and manage files: ls -la, cd, tree, mkdir -p, cp -r, mv, rm -r, symbolic links with ln -s and readlink
• Read and search: cat, head, tail, grep -rn, find (with -L and -type l for links), sed, wc, xargs
• Combine commands with pipes, redirections and command substitution: grep error app.log | sort | uniq -c > summary.txt, sudo chown $(id -u):$(id -g) file
• Work with permissions: chmod 640, chmod u+x, chown, sudo, sudo -i
• Manage services and read their logs: systemctl status, systemctl restart, systemctl list-unit-files (to find a service’s name on each distribution), journalctl -u nginx, journalctl -k, dmesg
• Check ports and test services: ss -tlnp, lsof -i :80, curl -I http://localhost, nginx -t, pg_isready
• Use git in the scenarios that have a repository: git status, add, commit, log, diff, stash, pull, push, switch, .gitignore rules with check-ignore and rm --cached, safe.directory and more, with a simulated GitHub as the remote
• Use Docker in the scenarios that have it: docker ps, run (with --memory and --platform), start, stop, kill, rm, logs --tail, pull, inspect -f, image inspect, stats --no-stream, with the docker service in systemctl and the docker group (usermod -aG, newgrp, groups); a container over its memory limit is killed with exit code 137, an image built for another CPU fails with exec format error, and a program the image doesn’t have (bash on Alpine) with executable file not found in $PATH; Docker Compose reads compose.yaml (up -d, down [-v], ps, ls, logs, config, exec, -p NAME, healthchecks and depends_on), with its YAML errors, container name conflicts, ports held by another project, and a PostgreSQL database in a named volume that keeps the password it was created with and lacks a POSTGRES_DB added later (psql -c inside the container)
• Use kubectl in the scenarios that have a Kubernetes cluster: kubectl get, describe pod, logs --previous, rollout status|restart|undo, set image, set env, create secret, apply -f, config view and more. Pods follow the clock (image pulls, restarts and back-off), the scheduler places them by what they request (describe node, top, set resources, scale), RBAC decides what --as may do (auth can-i, Roles and RoleBindings), the kubelet checks runAsNonRoot against the image (patch, exec … -- id) and evicts pods from a node under pressure, and a Service only gets the ready pods its selector matches (get endpointslices, describe svc|ingress, set selector). kubectl reads its config from ~/.kube/config or $KUBECONFIG, as the real one does
• Reach the other machines of a scenario: ssh app01 (and exit to come back), curl http://app01:8080, nc -zv app01 8080, ssh -G, ssh-add -l — with ~/.ssh/config, keys and the ssh-agent
• Open and close ports in the firewall: ufw on Ubuntu, firewall-cmd on Rocky Linux — and see the difference from outside: a dropped packet times out, a rejected one says “No route to host”
• Check disks and mounts: df -h, du -sh, lsblk -f, blkid, findmnt, mount (a partition on a folder, or mount -a from /etc/fstab), umount, fsck, free -h
• On Rocky Linux: SELinux with getenforce, getsebool and setsebool

Type help inside the terminal for the full list, and man <command> for the options each one supports.

Scenarios

Many OhSudo articles come with a scenario: the terminal opens with the files, services and logs of a real problem — nginx that won’t start, a disk that went read-only, a 502 Bad Gateway — so you can find the cause and fix it step by step. Look for the “Practice this in the terminal” box at the end of an article, or the “Try it in the terminal” links under code blocks.

FAQ

Is it safe to try rm -rf here?

Yes. Everything happens in a pretend filesystem in your browser tab. Try sudo rm -rf /var/log and see what happens — then hit Reset. (It’s still a terrible idea on a real server.)

Why do some commands say “Permission denied”?

Just like on a real server, you’re logged in as a normal user, guest. Files like /etc/shadow or /var/log/auth.log need root: put sudo in front of the command, or run sudo -i to get a root shell (exit to leave it).

Will my files still be there tomorrow?

Not yet — the machine starts fresh every time you open the page. Saving your progress is planned.

Is there a guided way to learn this?

Yes: the Terminal Lessons take you through it step by step, and check your work as you go.