Replace mysql with mysqld for RedHat-based platforms.

Ubuntu 16.10 and later, RedHat/CentOS 7 and later, fedora and other platform with systemd

sudo systemctl restart mysql.service

Older platforms with System V init scripts

sudo /etc/init.d/mysql restart

Platforms with service command. Normally a wrapper to System V init scripts or systemd commands.

sudo sudo service mysql restart