无法启动 mysql 服务器：“找不到单元 mysqld.service”“mysql.service 作业失败”

Question

当我输入此命令时，启动 MySQL 服务器时出现问题

service mysqld status

我得到这个输出：

Unit mysqld.service could not be found

还：

$ sudo service mysql start
Job for mysql.service failed because the control process exited with error code. See "systemctl status mysql.service" and "journalctl -xe" for details

和

$ sudo mysql -u root -p
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)