Is it a normal behaviour that you can change the UID of a single thread in perl without effecting the whole process? I've run a perl test program, the main thread creates a new thread which then changes its UID with the subroutine below. I added everywhere a sleep and executed this script as root. Then I saw this process running as root and a new perl thread (thread=process under linux 'top'?) running under the user spezified. This is what I wanted, but I expected that it shouldn't work. But why does it work? 
sub change_uid {
    my $user = shift or die "no user defined";
    my ($uid,$gid) = (getpwnam( $user ))[2,3];
    die "user not found" unless defined $uid;
    $( = $gid;
    $) = $gid;
    $< = $uid;
    $> = $uid;
}

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In reply to Change UID for threads? by mbalex

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