You can also try using getmypid() instead.
(PHP 4, PHP 5)
posix_getpid — Restituisce l'ID per il processo corrente
Restituisce l'ID per il processo corrente.
In order to use posix_getpid on Fedeora 11 and up you have to install php-process
# yum install php-process
Since upgrading fedora 10 to 12, I discovered that posix_getpid() disappeared and not compiled in by default, as it specifies here.
It turns out that it had been moved into package php-process.
Just do "yum install php-process", and all should be sweet again.
Hope this saves someone half an hour of research.