If you get this error
Jul 14 13:00:20 mariadb systemd[1]: Starting MariaDB 10.3.15 database server... Jul 14 13:00:21 mariadb systemd[1296]: mariadb.service: Failed to set up mount namespacing: Permission denied Jul 14 13:00:21 mariadb systemd[1296]: mariadb.service: Failed at step NAMESPACE spawning /usr/sbin/mysqld: Permission denied Jul 14 13:00:21 mariadb systemd[1]: mariadb.service: Main process exited, code=exited, status=226/NAMESPACE Jul 14 13:00:21 mariadb systemd[1]: mariadb.service: Failed with result 'exit-code'. Jul 14 13:00:21 mariadb systemd[1]: Failed to start MariaDB 10.3.15 database server.
The workaround is to override the mariadb.service file
cat <<EOF >/etc/systemd/system/mariadb.service.d/override.conf [Service] ProtectSystem=off PrivateDevices=false ProtectHome=false EOF
If running a container in Proxmox you can also enable Nesting from web gui container > Options > Edit > Features > Nesting
If starting with systemctl start mariadb times out, try checking if the instance is part of Galera cluster. It might be that other instances need to be started as well.