$ Linux One Liners

long-form guides

Troubleshoot Linux problems step by step.

Use these guides when a single command is not enough. Each guide starts with safe inspection, links to focused commands, and points to scenario drills.

Review commands Drills Cert practice

10 guides

Guide library

8 min read 2 drills

Find Large Files on Linux Without Making the Problem Worse

Use read-only ranking commands to find candidates, then decide whether each file should be rotated, compressed, archived, truncated, or left alone.

find /var -xdev -type f -printf '%s %p\n' | sort -nr | head -20
10 min read 4 drills

Nginx Site Down: A Practical Triage Path

Work from the outside in: DNS answer, TCP listener, Nginx config, service logs, then upstream application behavior.

dig +short example.com
9 min read 2 drills

DNS Changed but Not Working: What to Check

DNS troubleshooting works best when you separate authoritative records, resolver cache, local cache, and the web server response path.

dig +short example.com
9 min read 2 drills

Linux Permissions Troubleshooting Before chmod

Permission failures are usually path problems, ownership problems, service-user problems, or mode problems. Inspect all four before changing anything.

namei -l /var/www/example/index.html
8 min read 1 drills

Rsync Dry Run: Preview Copy and Delete Changes

A dry run turns a risky sync into reviewable output. That matters most when `--delete`, backups, or deployment targets are involved.

rsync -avhn --delete ./source/ ./backup/
8 min read 2 drills

Open Ports on Linux: Find What Is Listening

A port problem starts with socket evidence: address, port, protocol, process, and whether it is bound to localhost or a public interface.

sudo ss -tulpn
9 min read 3 drills

systemd Service Failed: What to Check First

Use systemd's failed-unit state, then inspect one unit with status and journal output before deciding whether restart, config repair, or dependency work is needed.

systemctl --failed --no-pager