every minute like that: byteli/mqtt/heartbeat 19:40:01 up 6 days, 4:42, 1 user, load average: 0.00, 0.00, 0.00

mqttHeartbeat.py

import os, time, mosquitto, subprocess

# cronjon
# */2       *      *      *       *       /usr/bin/python /root/mqttHeartbeat.py 2>&1 > /dev/null

pidFile = '/var/run/mqttHeartbeatPid'

def on_connect(userdata, flags, rc):
        print "connected..."

def isRunning(pid):
  try:
    pid = int(pid)
    os.kill(pid, 0)
    return True
  except (OSError, ValueError):
    return False

mqttClient = mosquitto.Mosquitto("python-heartbeat-"+str(os.getpid()));

#define the callbacks
mqttClient.on_connect = on_connect

try:
  f = open(pidFile,'r')
  runningPid = f.read()
  f.close()
  pidFileExists = True
except IOError:
  pidFileExists = False

if (not pidFileExists or not isRunning(runningPid)):
  #not allready running
  mqttClient.connect("127.0.0.1", 1883, 62, True)
  # create pid file
  f = open(pidFile,'w')
  f.write(str(os.getpid()))
  f.close()
else:
  print "not supposed to run, allready running here: " + runningPid
  raise SystemExit(0)

def publishHeartbeat():
    process = subprocess.Popen("uptime", shell=True, stdout=subprocess.PIPE)
    process.wait()
    uptime =  process.stdout.read().rstrip()
    mqttClient.publish("byteli/mqtt/heartbeat", uptime , 1)

try:
  while True:
    mqttClient.loop()
    time.sleep(60)
    publishHeartbeat()

except (KeyboardInterrupt):
  print "Time to die ... disconnecting and deleting pidFile"
  mqttClient.disconnect()
  # remove pid file
  os.remove(pidFile)