Sysadmin

Service Management

• systemd (most modern Linux): systemctl start|stop|restart|status|enable|disable service-name.
• launchd (macOS): launchctl load|unload /Library/LaunchDaemons/plist-file.
• Always check service status and logs after making changes.
• Use systemctl list-units --failed to find broken services.

Security Hardening

• Disable root SSH login. Use key-based authentication only.
• Configure ufw or iptables/nftables to allow only necessary ports.
• Keep systems updated: apt update && apt upgrade, yum update, brew upgrade.
• Use fail2ban to protect against brute-force attacks.
• Audit running services with ss -tlnp and disable anything unnecessary.

Pitfalls to Avoid

• Never run chmod -R 777 — it is a security disaster. Use the minimum permissions needed.
• Never edit /etc/sudoers directly — always use visudo.
• Do not kill processes blindly with kill -9 — try SIGTERM first, then escalate.
• Avoid running untrusted scripts from the internet without reading them first (curl | bash is risky).
• Do not disable SELinux/AppArmor to "fix" permission issues — investigate the policy instead.