I have a server that needs to begin as root to open a socket, but after that I want it to run as a non-privileged entity. But I cannot seem to set the gid. 
#!/usr/bin/perl -w  
use strict;

$>=$<=48; # uid
$)=$(=48; # gid
setpgrp $$,48;

open(FH,">/tmp/new.txt");
close(FH);

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The uid changes, but the gid does not. The point with the open() is that it must write files as "apache.apache". But because the gid does not change, they end up "apache.root". Then if I try system("chown ...") it is, predictably, denied permission.

How can I change the process group? Or failing that, how can I set the ownership of a created file in this situation?

In reply to set gid by halfcountplus

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