LOG_DEBUG debug messages are not printed

None of the LOG_DEBUG messages are getting printed
I put these two lines in the chan_zap.c below line 6033 and compiled it.

ast_log(LOG_WARNING, "just for test \n "); ast_log(LOG_DEBUG, "just for test \n ");

after running asterisk (-vvvvgcd), the first line gets printed on the screen and in /var/log/asterisk/messages but the second line doesn’t get printed.

Could anyone tell me whats wrong.

Abhijeet Mhatre