Tag: sysadmin

One syntax error in /etc/sudoers locks everyone out of root. Use visudo, read the syntax properly, avoid the common mistakes, and know what NOPASSWD gives.

Certificates expire silently and take the site with them. Check expiry with openssl, automate the check with cron or Uptime Kuma, and audit every cert.

Environment variables live in five places on Linux: /etc/environment, ~/.bashrc, ~/.profile, systemd Environment=, and the shell. When to use each one.

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 rather than competing. Exec form vs shell form, the full behavior matrix, the combo pattern, and the debug override.

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

systemctl status packs a lot into 12 lines. What Loaded, Active, Invocation, Main PID, Tasks, and the CGroup tree each tell you when a service misbehaves.

Default mount options and journald settings burn SSD write endurance. Check health with smartctl, mount noatime, move logs to tmpfs, find the real writer.

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.