MySQL: Adding innodb_log_file_size in my.cnf causes not starting MySQL service
To change innodb_log_file_size do following


Stop MySQL gracefully. Check the error log and make sure it was "Normal shutdown", no crashes, no errors etc.
Move existing ib_logfile* to safe place. You will need them if you want to roll back
Change innodb_log_file_size in my.cnf to the new value
Start MySQL. InnoDB will notice there are no ib_logfile* and will create new ones