Linux Ubuntu 18. MariaDB 10.3.
MariaDB service fails to start throwing a systemd error. The reason seems to be that the userid contains a dot (.).

`systemd[1]: Invalid user/group name or numeric ID: myuser.withdot`

Configuration:

The service file from MariaDB is /etc/systemd/system/mariadb.service.d/migrated.conf, and it contains:

```
[Service]
User=myuser.withdot

```