Unit mysqld.service failed to load: No such file or directory.
1，刚安装完 mysqld，/etc/init.d/mysqld 启动失败：
Starting mysqld (via systemctl): mysqld.serviceFailed to start mysqld.service: Unit mysqld.service failed to load: No such file or directory.
2，解决方法：重启系统 或 执行以下命令：
systemctl disable mysqld.service