posix_setegid
    (PHP 4 >= 4.0.2)
posix_setegid --       Set the effective GID of the current process     
Description
bool 
posix_setegid ( int gid)
     Set the effective group ID of the current process. This is a      privileged function and you need appropriate privileges (usually      root) on your system to be able to perform this function.     
     Returns TRUE on success, FALSE otherwise.