Collect Info

Checking System Version

$ uname -a
Linux gentoo 2.6.12-*** #3 Mon Feb 13 22:58:28 CET 2006 i686 Pentium III (Coppermine) GNU/Linux

Checking gcc/glibc Version

$ gcc -v
Reading specs from /usr/lib/gcc/i686-pc-linux-gnu/3.4.5/specs
Configured with: ...............
Thread model: posix
gcc version 3.4.5 (Gentoo 3.4.5-r1, ssp-3.4.5-1.0, pie-8.7.9)

You may check from php-cli or php-cgi:

Checking version with php cli or cgi

$ php -v
PHP 5.2.0-dev (cli) (built: May  8 2006 18:26:52) (DEBUG)
Copyright (c) 1997-2006 The PHP Group
Zend Engine v2.1.0, Copyright (c) 1998-2006 Zend Technologies

$ php-cgi -v
PHP 4.4.3-dev (cgi-fcgi) (built: Mar 10 2006 18:46:02)
Copyright (c) 1997-2006 The PHP Group
Zend Engine v1.3.0, Copyright (c) 1998-2004 Zend Technologies
    with XCache v1.0, Copyright (c) 2005-2006, by mOo

But are you sure which one you use in webserver? it may not be the same version as cli/cgi, so try

Check with phpinfo

<?php phpinfo(); ?>