I was getting Cacti set up and was having trouble with PHP. Specifically, it appeared that enabling the Cacti cron job caused a PHP segfault. I looked in /etc/cron.d/cacti to see what was being run:
cat /etc/cron.d/cacti
#*/5 * * * * cacti /usr/bin/php /usr/share/cacti/poller.php > /dev/null 2>&1
Then I ran it from the command line myself: