title: Have cron wait for job to finish before re-launching
body: <p>I have a cronjob that executes every second minute that usually runs in seconds, but sometimes for several minutes. </p>
  
  <p>I need cron to not execute the command if it's already running when the next minute comes.</p>
  
  <p>The line looks like this
  */1 * * * * cmd</p>
  
  <p>I have tried with this
  * * * * * ID=job1 FREQ=1m AFTER=job1 cmd </p>
  
  <p>but to no success.</p>
  
  <p>Is it possible to solve with cron or do I have to implement locking?</p>