InnoDB: Unable to lock ./ib_logfile0, error: 11

One of our MySQL servers got restarted and after restart MySQL instance was not coming online.

I see below error message in mysqld.log

InnoDB: Unable to lock ./ib_logfile0, error: 11
InnoDB: Check that you do not already have another mysqld process
InnoDB: using the same InnoDB data or log files.
InnoDB: Error in opening ./ib_logfile0
160712 19:16:34 [ERROR] Plugin 'InnoDB' init function returned error.
160712 19:16:34 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed.
160712 19:16:34 [ERROR] Unknown/unsupported storage engine: InnoDB
160712 19:16:34 [ERROR] Aborting
160712 19:16:34 [Note] /u01/mysql/5.5.22/bin/mysqld: Shutdown complete
I receive below error message when trying to access the database from command line

# mysql -u root -p
Enter password:
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/u01/mysql/5.5.22/mysqld.sock' (2) 

It looks like the sudden server crash didn’t update the logfile or datafile header properly and not able to lock to bring the instance up.

After research I was able to fix this error by following below steps

1. Go to the data directory and backup the ./ib_logfile0 and copy a new one
$ mv ib_logfile0 ib_logfile0.bak
$ cp -a ib_logfile0.bak ib_logfile0

2. Restart the mySQL database

Thanks,
Satishbabu Gunukula, Oracle ACE
http://www.oracleracexpert.com