Playing with utmp(5).

utmp-test.pl

#!/usr/bin/perl -w
use strict;
use diagnostics;
use POSIX;
use User::Utmp qw(:constants);

my $idle_threshold = 1800; # seconds

while (my $utent = User::Utmp::getutent()){
        # Skip irrelevant utmp entries that are not interactive sessions
	my $uttype = $utent->{'ut_type'};
	next unless (USER_PROCESS == $uttype);

	my $utline = $utent->{'ut_line'};
	my $utuser = $utent->{'ut_user'};
	my $utpid  = $utent->{'ut_pid'};
	my $utipad = $utent->{'ut_addr'};

	# Procedure from procps/w.c to get idle time:
	# 1) Get atime from terminal device node
	# 2) Substract from current time
	# 3) ???
	# 4) Profit!
	my $tty       = sprintf("/dev/%s", $utline);
	my $atime     = (stat($tty))[8];
	my $idle      = time() - $atime;
	my $treatment = 'left_alone';
	if ($idle > $idle_threshold){
		kill SIGKILL, $utpid;
		$treatment = 'killed';
	}
	printf "tty=%s, pid=%s, user=%s, host=%s, idle=%s, treatment=$treatment\n", 
		$utline, $utpid, $utuser, join('.',unpack('C4', $utipad)), $idle, $treatment;
}