In Ubuntu package zabbix-server-mysql 1:4.2.6-1+bionic, zabbix-server.service is missing mariadb.service dependency, which may cause mariadb.service shutdown before zabbix-server.service shutdown by systemd shutting down the system. As a result zabbix-server.service will hang indefinitely reporting "a stop job is running for Zabbix Server (no limit)", thus preventing system shutdown.