Debian / Ubuntu using System V init scripts:

• service mysql restart

Debian / Ubuntu using systemd:

• systemctl enable mysql.service
• systemctl restart mysql.service

Devuan:

• service mysql restart

CentOS 7:

• systemctl enable mariadb.service
• systemctl start mariadb.service

CentOS 8 and later or Rocky Linux:

• systemctl enable mysqld.service
• systemctl start mysqld.service

CentOS 6 and earlier, Fedora, and Redhat:

• chkconfig mysqld on
• service mysqld start