root@localhost:/data/mysqldata/log# /etc/init.d/mysqld start
[....] Starting mysqld (via systemctl): mysqld.serviceFailed to start mysqld.service: Unit mysqld.service not fou
failed!
解决：
cp /root/mysql-5.7.15/support-files/mysql.server /usr/lib/systemd/
cp /root/mysql-5.7.15/support-files/mysql.server /usr/lib/systemd/user/
systemctl daemon-reload