Undefined function: posix_getegid?

I just discovered PmWiki, very nice! I tried a couple of other packages 
(TWiki, PHPWiki, Tiki) but they were all either overly complex or too 
simple. So far PmWiki looks just right. ;)

I have run into one problem so far. PmWiki runs fine on my laptop (RH9) 
and on the sourceforge servers. When I try to install it on my own host 
(www.modwest.com, running Linux, Apache, and PHP 4.3.1) I get the 
message "Fatal error: Call to undefined function: posix_getegid() in 
/htdocs/www/pmwiki/pmwiki.php on line 270" when I try to run pmwiki.php 
for the first time. Can anyone give me an idea what could be wrong? I am 
not sure where I should be looking to fix this problem.

Thanks!

Jason
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