Tag: sysadmin

Never edit /etc/sudoers directly. One syntax error locks everyone out. Use visudo, understand NOPASSWD risks.

Certs expire silently. Check expiry with openssl, automate renewal checks with cron, get alerts before disaster.

Navigate /etc/environment, ~/.bashrc, ~/.profile, and systemd Environment=. When to use each.

Understand sticky bit, setuid, and setgid: what they do, how to set them, security implications, and real-world use cases.

Verify fail2ban is protecting you: check jails, test bans, monitor logs, common misconfiguration, and unban IPs when needed.

Your Linux box takes forever to boot? systemd-analyze shows exactly which services drag it down. Read blame, critical-chain, plot, and fix the slow ones.

CMD and ENTRYPOINT work together. Learn the difference, exec vs shell form, and when to use the combo pattern.

SSHFS mounts remote filesystems over SSH so you can browse and edit files locally, faster than scp for interactive work.

Decode systemctl status: Active state, CGroup processes, recent logs, loaded/enabled state. What each field tells you.

Check SSD health, find excessive write patterns, use noatime, move logs to tmpfs to extend lifespan.

Essential journalctl commands: -u, -f, --since, -p, -k, -b, --no-pager, JSON output. The queries you need on a broken server at 2 AM.

Fix SSH timeouts: ServerAliveInterval, ServerAliveCountMax, ClientAliveInterval. Understand NAT, firewalls, and TCP keepalive.