Log to record activity against a database
You can enable general log by adding this line in my.cnf/my.ini file:
http://dev.mysql.com/doc/refman/5.1/en/server-system-variables.html#sysvar_general_log

[mysqld]
general_log=1
also You can set General log output by changing your my.cnf/my.ini file (MySQL configuration file) to either TABLE or FILE if TABLE is choosen then server will log all queries in general_log table of mysql schema otherwise in FILE option it will log in a file path mentioned. 
http://dev.mysql.com/doc/refman/5.1/en/server-system-variables.html#sysvar_log_output