This is more of a Unix question rather than a Perl one, but still...

I'm looking for a way to stop my daemon, but I don't want to terminate an innocent bystander process. I came up with idea that PID file is created after the process has been spawned. Therefore, it's not older then the process, so the following code was written which seems to work correctly on my Ubuntu:

    open (my $fd, "<", $conf->{pidfile})
        or die "Failed to read pidfile $conf->{pidfile}: $!";

    my $pid = <$fd>;
    chomp $pid;
    die "Broken pid file $conf->{pidfile}"
        unless $pid =~ /^\d+$/;

    # detect stale pid
    if ([stat $fd]->[9] >= ([stat "/proc/$pid"]->[9] || 9**9**9)) {
        print "Killing pid $pid...\n";
        kill INT => $pid;
    };

[download]

Of course, it can still be tricked by touching the pid file, but then it's also possible to write rubbish into the pid file anyway.

Now I would like to ask what is the proper way of avoiding sending signal to a wrong process? CPAN has a multitude of modules for PID file handling, I was unable to choose one.

Thank you!

In reply to Detecting stale pid file under *nix by Dallaylaen

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