Derick Rethans has a new post to his blog showing how you can, using a few simple unix tools, figure out what PHP is doing when your scripts are executing.
Sometimes when you have a long running PHP script, you might wonder what the hell it is doing at the moment. There are a few tools that can help you to find out, without having to stop the script. Some of these work only on Linux.
He shows you how to use the following commands to track down exactly what your process is working on: strace, ltrace and gdb (a handy debugger that will probably give you more information than you're looking for). He includes some sample output for the commands and gives an example of a PHP script-to-gdb output relationship.