If you happen to see a message like this
seg fault or similar nasty error detected in the parent process
when reloading Apache2, and if you’re using PHP5 through mod_php5, then it may be related to having an extension loaded via php.ini and not really present on the system. It was my case with a redis extension (redis.so) and I banged my head a day before finding it.
The eternal fight between admins and computers 