When developing you might just need to clear your Apache error log files from time to time. There is a brillant answer to this problem on Serverfault.
Assuming you are logging to the default error.log:
#Debian based: Ubuntu etc.. sudo su echo > /var/log/apache2/error.log
#RHL based : CentOS, Fedora etc... sudo su echo > /var/log/httpd/error.log
That truncates the file without closing any open file handles. Note that you need to be
root user, a simple
sudo might still throw permission errors.