The most common one happens with MySQL 5.5 and older when the InnoDB log file size (innodb_log_file_size) was set to an new value which is not compatible with the old value. To avoid this problem shut-down MySQL properly (mysqladmin --user=root shutdown). Then backup and after remove the logfiles, configure the my.cnf with the new log file size. Start MySQL again and check the error.log.
innodb_log_file_size
Hello Oli,
this can have several different reasons.
The most common one happens with MySQL 5.5 and older when the InnoDB log file size (innodb_log_file_size) was set to an new value which is not compatible with the old value. To avoid this problem shut-down MySQL properly (mysqladmin --user=root shutdown). Then backup and after remove the logfiles, configure the my.cnf with the new log file size. Start MySQL again and check the error.log.