How to prevent duplicate cron jobs from running?

Sometimes you may find that duplicate cronjobs are running at the same time. This may happen when the cronjob takes longer to complete than its execution interval. Here is a simple way to prevent this from happening ever again.

Use flock

Flock is a very simple and easy-to-use utility found in most Linux systems.

Its functionality goes like this. It takes two parameters - a lock file and a command (or shell script).

It locks the lock file at the start of the execution of the command and unlocks it at the end. Then if the same cronjob is started it checks if the lock file is still locked. If the lock file is locked, it means that the previous cronjob isn't finished yet and the flock will prevent from starting a new one.

*   *  *   *   *  /usr/bin/flock -n /home/myfolder/file.lockfile /bin/backup.sh

This will create a cronjob that runs the /bin/backup.sh script and prevent duplicate cronjobs from running using /home/myfolder/file.lockfile lock file.

Got an article suggestion? Let us know

Explore more

Cron

How to run cron jobs every 5, 10, 15 or 30 minutes?

Every minute cron goes through all the crontabs and looks for the jobs that should be executed. The exact time of the execution can be specified using the cron syntax. Whenever the parameter matches the current date and time cron job is executed.

Questions

How to set up a cron job for a specific time and date?

In this quick tutorial, we will take a look at how to set up a cron job to run at a specific time.

Questions

How to run a cronjob as a specific user?

One of the features of Cron is the ability to run Cron jobs as a specific user. Sometimes you may even want to create a special user with limited privileges just to run Cron jobs. There are two methods how to run cronjob as a specific user.

Questions

How to view and read cron logs on Ubuntu, Debian and CentOS?

Cron can generate logs, which are very useful in troubleshooting your cron jobs. In this quick tutorial, we will take a look at cron logs – how to find them and how to read them.

Questions

This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.