The system environment:
Centos7
Mysql5.6

Background:
1. No system and mysql deployment and operation manual leave, and I do not familiar with mysql less dba experience,
2. Make the mysql a boot startup (see it in the chkconfig),
3. One day the operating system restart, but found no up mysql (no mysqld process, no port 3306),

Processing after:
D/directory to perform in the/etc/init.
Service mysqld start to quote the following error:
Starting MYSQL. The server quit without updating The PID file (XXXXX. PID). (FAILED)

Other auxiliary description:
1. After start up, had the rm command manually deleted data/mysql - bin. 0000 x files,
2. According to some articles in baidu delete mysql - XXXX. The index file, has been deleted, (XXX is a pronoun)
3. 2 place was found in the system (with directory generation refers to A directory and B) there are data data, in the/etc/my CNF file configuration datadir is pointing to A directory, but look from the data file timestamp, B directory data file is the latest, don't know which catalog data is valid, the problem also go to the insufficient basis (mysql)

Conclusion, after some simple try, implementing mysql start, just above the fault, don't know from which aspects to investigate and deal with, send this post for help,