listener.log is very big ....How to truncate listener.log ?

truncate listener.log
listener.log not been updated

lsnrctl help show

LSNRCTL>set current_listener (if not using default LISTENER) 

LSNRCTL>set LOG_STATUS off 

LSNRCTL>save_config 

If you're trying to disable listener logging temporarily, do not issue SAVE_CONFIG. Once listener logging is disabled, you can now safely delete or archive the existing listener log. To restore logging again and/or to create a new listener log, simply enable logging as follows: 

LSNRCTL>set current_listener (if not using default LISTENER) 

LSNRCTL>set LOG_STATUS on 

After one year I found the listener.log on my server became so large (4GB). 

Execute the following commands to delete the listener.log file:

lsnrctl set log_status off

on system 

rm listener.log 

lsnrctl set log_status on