sshd

Identity

• Unit: sshd.service (or ssh.service on some Debian systems)
• Config: /etc/ssh/sshd_config, /etc/ssh/sshd_config.d/ (drop-in dir)
• Logs: journalctl -u sshd / journalctl -u ssh, /var/log/auth.log (Debian), /var/log/secure (RHEL)
• User: runs as root (drops privs per session)
• Install: pre-installed on most distros; apt install openssh-server / dnf install openssh-server

Key Operations

• Validate config: sudo sshd -t
• Reload (without dropping connections): sudo systemctl reload sshd
• Restart (drops active sessions!): sudo systemctl restart sshd
• Test connection: ssh -v user@host (verbose, shows auth methods tried)
• Check effective config: sudo sshd -T (shows full parsed config with defaults)
• Test config for specific user: sudo sshd -T -C user=myuser,host=1.2.3.4

Expected Ports

• 22/tcp (default); commonly changed to reduce noise
• Verify: ss -tlnp | grep sshd