CentOS-6-64bit ./install_amp fails at line 728

This is a NEW installation of CentOS-6-64bit on a core2quad using Digium TDM410 analog cards. Asterisk version 1.8.7.1 and Dahdi version 2.5.0.2 both are compiled and believed to be correctly installed. After downloading FreePBX 2.8.1 (and running in the /usr/src/freepbx-2.8.1 directory) the following command:
./install_amp --username=asteriskuser --password=PASSWORD2

The following error message appears (additionally, i have tried running the above command without any arguements, and the result is the same failure below)

Checking for PEAR DB…OK
Checking for PEAR Console::Getopt…OK
Checking user…PHP Fatal error: Call to undefined function posix_getpwuid() in /usr/src/freepbx-2.8.1/install_amp on line 728

ANY help on this new install is GREATLY appreciated.
thank you…

Please ensure you have php-process install and let me know if you have any additional issue.