see blog post: http://tpokorra.blogspot.de/2013/07/notify-all-users-logged-in-over-x2go-on.html

_jiffybox.php

<?php
// get from here: https://github.com/tfnet/jiffy-api-php-client/blob/master/JiffyBoxApi.class.php
require "JiffyBoxApi.class.php";
$token = "INSERT YOUR TOKEN HERE";
$id=INSERT YOU jiffybox id HERE;
$planid=20;
$hours=2;

if (!empty($argc) && strstr($argv[0], basename(__FILE__)))
{
    if (!file_exists("refresh.txt"))
    {
        die();
        die("no server running");
    }
    $jb = new JiffyBox ($token, $id);
    if ($jb->getStatus () == "")
    {
        die("problems connecting to jiffybox");
    }
    if ($argv[1] == "freeze")
    {
        echo freeze($jb);
    }
    else
    {
        # check how old the last request is
        # freeze or start
        $timestamp = file_get_contents("refresh.txt");
        if ((time()-$timestamp)<60*60*$hours)
        {
            refresh($jb, $planid);
        }
        else
        {
            freeze($jb);
            unlink("refresh.txt");
        }
    }
    die("command line");
}
else if ($_GET["operation"] == "refresh")
{
    $jb = new JiffyBox ($token, $id);
    if ($jb->getStatus () == "")
    {
        die("problems connecting to jiffybox");
    }

    # save to file current timestamp
    file_put_contents("refresh.txt", time());

    refresh($jb, $planid);
    $shutdowntime= date('Y-m-d H:i e', strtotime('+'.$hours.' hours'));
    die("machine will run until ".$shutdowntime." if it is not refreshed again"                                                                              );
}
die ("exit");
?><pre><?

#echo "status: ".($jb->getStatus ())."<br/>";
#echo "public IP: ".$jb->getInfo()->ips->public[0]."<br/>";
#print_r($jb->getInfo());
#print_r($jb->start());
#print_r($jb->stop());
#print_r($jb->freeze());
#print_r($jb->thaw($planid));
#print_r($jb->getPlans());

?></pre><?
#echo freeze($jb);
# status: READY FROZEN STOPPING UPDATING
function freeze($jb)
{
    echo "stopping...";
    $jb->stop();
    while ($jb->getStatus () != "READY")
    {
        sleep(20);
    }
    echo "freezing...";
    $jb->freeze();
    while ($jb->getStatus () != "FROZEN")
    {
        sleep(20);
    }
    return $jb->getStatus ();
}

function refresh($jb, $planid)
{
    if ($jb->getStatus () == "FROZEN")
    {
        $msg=$jb->thaw($planid);
        while ($jb->getStatus () != "READY")
        {
            echo "waiting";
            sleep(20);
        }
        echo $jb->getStatus ();
    }
    if ($jb->getStatus () == "READY")
    {
        $jb->start();
    }
}
?>

zenity.sh

message="Server will shutdown soon, please refresh if you still need it by visiting http://jb.solidcharity.com"
wall $message
for display in `ps xaf | grep x2goagent | grep -v grep | awk '{ print ( $(NF) ) }'`
do
  user=`ps xaf | grep x2goagent | grep -v grep | grep "$display$" | awk ' { print ( $(NF-5) ) }' | awk ' { print ( $3 ) }' FS='/'`
  echo "$user $display"
  su - $user -c "zenity --info --display=$display --text='$message'&"

done