Job for mysqld.service failed in Centos 7

Check below things to fix the issue

Check the permission of mysql data dir using below command. The ownership should be mysql:mysql and the directory permission should be 700
```
ls -ld /var/lib/mysql/
```
Check the permission of databases inside mysql data dir using below command. The ownership should be mysql:mysql for all the files inside that directory
```
ls -lh /var/lib/mysql/
```
Check the listening network tcp ports using below command
```
netstat -ntlp
```
Check the mysql log files for any error using below command.
```
cat /var/log/mysql/mysqld.log
```
Try to start mysql using below command
```
mysqld_safe --defaults-file=/etc/my.cf
```

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