Troubleshooting

Set up smartd on Debian 13 to catch failing SATA and NVMe drives: read smartctl output, schedule self-tests, and prove that alert mail actually arrives.

Fix MariaDB ERROR 2002 on Debian 13: tell a stopped server from a socket path mismatch or unix_socket root auth, with diagnostics for MariaDB 11.8.

Fix Postfix Relay access denied, deferred port 25 timeouts, Domain not found and SASL failures on Debian 13, with diagnostic commands and an open-relay test.

Fix nginx 502 Bad Gateway with PHP-FPM 8.4 on Debian 13: map errno 13, 2, 111 and 110 in error.log to their cause, with namei, ss and cgi-fcgi checks.

Fix SSH Permission denied (publickey) on Debian 13 by reading sshd's journal reason: StrictModes, key types, AllowUsers, drop-ins and ssh.socket.

No space left on device but df shows free space? Debug exhausted inodes, deleted files held open by processes and a bloated systemd journal on Debian 13.

GRUB not showing Windows or other Linux installs? Set GRUB_DISABLE_OS_PROBER=false in /etc/default/grub, run update-grub and the entries come back.