Add following line in .htaccess
These commands are for centOS which might work on other Linux versions but you will have to check the path if it doesn’t work.
Check Apache Status /etc/init.d/httpd status
Restart Apache in /sbin/service httpd restart
Start Apache in /sbin/service httpd start
Stop Apache /sbin/service httpd stop
This will allow logs to be archived once they exceed the threshold.
From WHM >> Service Configuration >> Apache Configuration >> Log Rotation you can specify which logs to be archived.
The threshold settings can be changed from WHM >> Server Configuration >> Tweak Settings
search for rotatelogs_size_threshhold_in_megabytes variable
By default this value is 300MB.
By default Apache restarts every 2 hours (or so) and every 24 hours. This is done automatically in order for Apache to grab new file handles for logs.
The auto restart can be disabled by enabling piped logging from WHP->Apache Configuration->Enable Piped Apache Logs
More details on this thread http://forums.cpanel.net/f5/why-apache-restarting-every-two-hours-254022.html