How to Prevent the Cron Job Execution, If It Is Already Running

How to prevent the cron job execution, if it is already running

Advisory locking is made for exactly this purpose.

You can accomplish advisory locking with flock(). Simply apply the function to a previously opened lock file to determine if another script has a lock on it.

$f = fopen('lock', 'w') or die ('Cannot create lock file');
if (flock($f, LOCK_EX | LOCK_NB)) {
    // yay
}

In this case I'm adding LOCK_NB to prevent the next script from waiting until the first has finished. Since you're using cron there will always be a next script.

If the current script prematurely terminates, any file locks will get released by the OS.

Run cron job only if it isn't already running

I do this for a print spooler program that I wrote, it's just a shell script:

#!/bin/sh
if ps -ef | grep -v grep | grep doctype.php ; then
        exit 0
else
        /home/user/bin/doctype.php >> /home/user/bin/spooler.log &
        #mailing program
        /home/user/bin/simplemail.php "Print spooler was not running...  Restarted." 
        exit 0
fi

It runs every two minutes and is quite effective. I have it email me with special information if for some reason the process is not running.

Stop an already running cron job

http://unix.derkeiler.com/Newsgroups/comp.unix.admin/2006-09/msg00132.html

http://unix.ittoolbox.com/groups/technical-functional/shellscript-l/how-to-kill-the-cronjob-which-is-running-currently-477250

You need to get the PID of your running cron job and then perform simple kill command.

Stop cron job from starting while it's already running (even across servers)

A PID file over a shared folder?

Schedule cron entries to run script only when not already running

An easy way would be to have your Cron start a bashfile that checks if such a process exist.

cron:

 */10 * * * * /path/to/bashscript.sh

(Make sure it has the correct user and is executable)

The pgrep command looks for a process with a the given name, and returns the processID when such a process is found.

#!/bin/bash
# bashscript.sh    

pID=$(pgrep -n "yourjarfile") 

# Check if jarfile is running
if $pID > /dev/null
then       
    #log something to syslog 
    logger  $pID "already running. not restarting." 
else
    # start jar file 
    /usr/bin/java -jar /path/to/yourjarfile.jar
fi

--EDIT--

Inspired by F. Hauri's answer (which works fine btw), I came up with a shorter version :

 */10 * * * *  pgrep -n "yourjarfile." || /usr/bin/java -jar /path/to/yourjarfile.jar

How to prevent a Cronjob execution in Kubernetes if there is already a job running

CronJob resource has a property called concurrencyPolicy, here an example:

apiVersion: batch/v1beta1
kind: CronJob
metadata:
  name: your-cron
spec:
  schedule: "*/40 8-18 * * 1-6"
  concurrencyPolicy: Forbid
  jobTemplate:
    spec:
      template:
        metadata:
          labels:
            app: your-periodic-job
        spec:
          containers:
          - name: your_container
            image: your_image
            imagePullPolicy: IfNotPresent
          restartPolicy: OnFailure

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