Steps to reproduce:

1. Execute apt update && apt upgrade -y while background processes (e.g., unattended-upgrades) or debconf hold active locks on /var/cache/debconf/config.dat.

1. Package configuration stalls, causing needrestart / systemd triggers to attempt restarting zabbix-server or database services prematurely.

1. The database socket (/var/run/mysqld/mysqld.sock) is closed or deleted during the stalled upgrade, resulting in a system deadlock during service stop/restart (systemctl restart zabbix-server).

1. Attempting to access the Zabbix Web UI via browser triggers the database connection error.

Result:

• Web UI throws Database error: No such file or directory.

• systemctl restart zabbix-server hangs indefinitely waiting for process locks/DB sockets.

• OS reboot stalls on systemd service stop timeout (TimeoutStopSec), forcing a hard reboot or Rescue Mode intervention.

Expected:

• Packages upgrade cleanly without debconf resource lock exceptions.

• Database sockets remain active or regenerate cleanly upon service restart.

• Zabbix Web UI reconnects successfully post-upgrade.