buildroot/package/mariadb/mysqld.service

[Unit]
Description=MySQL database server

[Service]
ExecStartPre=/bin/sh -c 'test "`ls -1 /var/lib/mysql | wc -l`" != "0" || mysql_install_db --basedir=/usr --datadir=/var/lib/mysql'
ExecStart=/usr/bin/mysqld_safe
Restart=always
User=mysql
RuntimeDirectory=mysql
RuntimeDirectoryMode=0755

[Install]
WantedBy=multi-user.target