Question

9

How to prevent from CronJob run process twice?

rated 0 times [ 9] [ 0] / answers: 1 / hits: 7527 / 2 Years ago, fri, december 3, 2021, 4:37:49

I have a Cron Job scripts which runs every 4 minutes.
In rare cases the script is not finished within 4 minutes.
This causes problems.

How can I perform a check that if there the previous script is not finished then skip the current run

Expected behavior:

10:00 : Script A starts

10:04 : Script A2 starts - it finds that script A was not finish so this script aborts. Simply finish without doing nothing.

10:06 : Script A finish 

10:08 : Script A3 starts - no other scripts running so it continue

Notice: A, A2, A3 are the same script (just in different times)! It shouldn't consider other scripts that might be running also

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1 Year ago

answered 2 Years ago pantkie · Accepted Answer

There are two main approaches:

make the script exit if it detects another instance of itself running. Just add these lines to the beginning of your script:
```
if [ $(pgrep -c "${0##*/}") -gt 1 ]; then

     echo "Another instance of the script is running. Aborting."

     exit

fi
```
$0 is the name of the script, and ${0##*/} is the name of the script with everything until the last / removed (so, /path/to/script.sh becomes script.sh). This means that if you have another, unrelated script with the same name running, it will still be detected. on the other hand, it also means that it will work even if you call the script from a symlink. Which one you prefer depends on your use case.

Use a lock file and exit the script if the file exists:

#!/bin/bash



if [ -e "/tmp/i.am.running" ]; then

    echo "Another instance of the script is running. Aborting."

    exit

fi

else

    touch  "/tmp/i.am.running"

fi



## The rest of the script goes here



rm "/tmp/i.am.running"