[mysql] Job for mysqld.service failed See "systemctl status mysqld.service"

I met this problem today, and fix it with bellowed steps.

1, Check the log file /var/log/mysqld.log

tail -f /var/log/mysqld.log

 2017-03-14T07:06:53.374603Z 0 [ERROR] /usr/sbin/mysqld: Can't create/write to file '/var/run/mysqld/mysqld.pid' (Errcode: 2 - No such file or directory)
 2017-03-14T07:06:53.374614Z 0 [ERROR] Can't start server: can't create PID file: No such file or directory

The log says that there isn't a file or directory /var/run/mysqld/mysqld.pid

2, Create the directory /var/run/mysqld

mkdir -p /var/run/mysqld/

3, Start the mysqld again service mysqld start, but still fail, check the log again /var/log/mysqld.log

2017-03-14T07:14:22.967667Z 0 [ERROR] /usr/sbin/mysqld: Can't create/write to file '/var/run/mysqld/mysqld.pid' (Errcode: 13 - Permission denied)
2017-03-14T07:14:22.967678Z 0 [ERROR] Can't start server: can't create PID file: Permission denied

It saids permission denied.

4, Grant the permission to mysql chown mysql.mysql /var/run/mysqld/

5, Restart the mysqld

# service mysqld restart
Restarting mysqld (via systemctl):                         [  OK  ]