I was getting below mysql error log:-
[Note] Plugin 'FEDERATED' is disabled. InnoDB: The InnoDB memory heap is disabled InnoDB: Mutexes and rw_locks use GCC atomic builtins InnoDB: Compressed tables use zlib 1.2.3 InnoDB: Using Linux native AIO InnoDB: Initializing buffer pool, size = 128.0M InnoDB: mmap(137363456 bytes) failed; errno 12 InnoDB: Completed initialization of buffer pool InnoDB: Fatal error: cannot allocate memory for the buffer pool [ERROR] Plugin 'InnoDB' init function returned error. [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed. [ERROR] Unknown/unsupported storage engine: InnoDB [ERROR] Aborting [Note] /usr/libexec/mysqld: Shutdown complete
I found out there are two solutions which are:-
1)Set innodb_log_file_size equal to the actual size of the existing InnoDB log files. To see what size of innoDB log allocated, login mysql and enter following cmd:-
SHOW GLOBAL VARIABLES LIKE 'innodb_log_file_size';
Expected result example:- 5242880
After that, insert that value in my.cnf:- vi /etc/my.cnf
2)Rename or move both the ./ib_logfile0 and ./ib_logfile1 files, and then start the MySQL server.This normally will be located at /var/lib/mysql. After start mysql, it create new innoDB log file and restore possible half-written data from the file of .ibd.
The expexted mysql log example:-
InnoDB: Database physically writes the file full: wait... 161216 9:58:54 InnoDB: Log file ./ib_logfile1 did not exist: new to be created InnoDB: Setting log file ./ib_logfile1 size to 5 MB InnoDB: Database physically writes the file full: wait... 161216 9:58:54 InnoDB: highest supported file format is Barracuda. InnoDB: The log sequence number in ibdata files does not match InnoDB: the log sequence number in the ib_logfiles! 161216 9:58:54 InnoDB: Database was not shut down normally! InnoDB: Starting crash recovery. InnoDB: Reading tablespace information from the .ibd files... InnoDB: Restoring possible half-written data pages from the doublewrite InnoDB: buffer... 161216 9:58:54 InnoDB: Waiting for the background threads to start 161216 9:58:55 InnoDB: 5.5.50 started; log sequence number 1589772 161216 9:58:55 [Note] Server hostname (bind-address): '0.0.0.0'; port: 3306 161216 9:58:55 [Note] - '0.0.0.0' resolves to '0.0.0.0'; 161216 9:58:55 [Note] Server socket created on IP: '0.0.0.0'. 161216 9:58:55 [Note] Event Scheduler: Loaded 0 events 161216 9:58:55 [Note] /usr/libexec/mysqld: ready for connections. Version: '5.5.50' socket: '/var/lib/mysql/mysql.sock' port: 3306 MySQL Community Server (GPL) by Remi
References:- JUSTIN KULESZA (2011). MySQL: Failed Registration of InnoDB as a Storage Engine. Available at: https://spin.atomicobject.com/2011/05/09/mysql-failed-registration-of-innodb-as-a-storage-engine/.
RolandoMySQLDBA (2014). MySQL my.cnf: innodb_log_file_size is missing. Available at: http://dba.stackexchange.com/questions/75688/mysql-my-cnf-innodb-log-file-size-is-missing/158325#158325
Changing the Number or Size of InnoDB Redo Log Files. Available at: http://dev.mysql.com/doc/refman/5.7/en/innodb-data-log-reconfiguration.html