drills
Work through 12 scenario-driven drills for unofficial Linux certification practice. Each drill starts with inspection, expected output, and the mistake to avoid before changing a live system.
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12 drills
A VPS starts returning write errors and an app cannot create new uploads. You need to decide whether the root filesystem, a mounted data volume, or inode exhaustion is the real problem before deleting anything.
3 related command replays available.
df -h && df -i
The root filesystem is nearly full and /var looks suspicious. You need a read-only way to find the biggest files without crossing into other mounted filesystems.
2 related command replays available.
find /var -xdev -type f -printf '%s %p\n' | sort -nr | head -20
A service restarted during deploy and is now unhealthy. You need the recent unit logs, not every log line on the machine.
2 related command replays available.
journalctl -u nginx --since '30 minutes ago' --no-pager
A teammate changed a server block and wants to reload nginx. You need to prove the configuration parses before touching the running service.
2 related command replays available.
sudo nginx -t
Port 8080 is already in use and a new service will not start. You need to identify the listener before killing or reconfiguring anything.
2 related command replays available.
sudo ss -ltnp 'sport = :8080'
Users say a site is down, but the server may still be answering. You need to compare public DNS with a forced request to the expected IP.
2 related command replays available.
dig +short example.com && curl -I https://example.com/
An app cannot read a file and someone suggests chmod 777. You need to inspect the path, owner, group, and mode before changing permissions.
2 related command replays available.
namei -l /srv/app/current/.env
You need to mirror a release directory to a backup target, but stale files on the target should be removed. Before running the real sync, you must preview deletions.
2 related command replays available.
rsync -ani --delete /srv/app/releases/current/ /backup/app/current/
After a reboot, a host is reachable but something feels broken. You need a quick inventory of failed units before digging into individual logs.
2 related command replays available.
systemctl --failed --no-pager
A Debian or Ubuntu server may be missing important updates. You need to list pending upgrades without installing anything.
2 related command replays available.
apt list --upgradable
A server is slow and someone wants to restart the app. You need to see whether RAM, swap, or a specific process is the likely cause.
2 related command replays available.
free -h && ps aux --sort=-%mem | head
A public VPS has SSH exposed and you need to see whether failed login attempts are normal background noise or focused guessing against real usernames.
2 related command replays available.
journalctl -u ssh --since today --no-pager | grep 'Failed password'