An eBook

The technique mentioned by Nathan De Hert below is rather insecure -- you should never leave a password lying around in a file readable by the apache user.

If you need this sort of functionality on *nix systems, have a look at the /etc/sudo file (edited with the command 'visudo'). The tag NOPASSWD allows specified commands to be run as root by another user, without needing to specify a password. It's a little extra configuration, but much more secure.