-bash-4.2# service mysqld restart
Redirecting to /bin/systemctl restart mysqld.service
Failed to restart mysqld.service: Unit not found.
并不存在 mysqld 的服务，
-bash-4.2# -bash-4.2# chkconfig -list -list: unknown option -bash-4.2# chkconfig --list Note: This output shows SysV services only and does not include native systemd services. SysV configuration data might be overridden by native systemd configuration. If you want to list systemd services use 'systemctl list-unit-files'. To see services enabled on particular target use 'systemctl list-dependencies [target]'. aegis 0:off 1:off 2:on 3:on 4:on 5:on 6:off agentwatch 0:off 1:off 2:on 3:on 4:on 5:on 6:off iprdump 0:off 1:off 2:on 3:on 4:on 5:on 6:off iprinit 0:off 1:off 2:on 3:on 4:on 5:on 6:off iprupdate 0:off 1:off 2:on 3:on 4:on 5:on 6:off jexec 0:off 1:on 2:on 3:on 4:on 5:on 6:off mysql.server 0:off 1:off 2:on 3:on 4:on 5:on 6:off netconsole 0:off 1:off 2:off 3:off 4:off 5:off 6:off network 0:off 1:off 2:on 3:on 4:on 5:on 6:off
可见，服务名不是mysqld 而是 mysql.server
于是：
-bash-4.2# service mysql.server restart
Shutting down MySQL....[ OK ]
Starting MySQL.[ OK ]