The Cron Job/Crontab
To have your task run at this frequency, use the following cron:
20 */4 * * *
This cron command translates to the following (in Human-Readable format):
“Every 4 hours at 20 minutes past the hour.”
What is a Cron Job & Crontab?
A cron job is a task that is scheduled to run at a specific time or interval. Cron is a Linux utility that allows tasks to be automatically run in the background at regular intervals. These tasks are often called “cron jobs.”
A crontab is a table or list of commands that are scheduled to run at specified times. The commands in a crontab file (also called a “cron table”) are normally executed by the cron daemon, which runs in the background and executes these commands automatically.
Every cron job uses five fields. Here is an explanation of what each field does in this cron, which runs “every 4 hours at 20 minutes past the hour“:
FUN FACT: When editing your crontab, it is important to use a text editor that supports Unix-style line endings (LF), as opposed to Windows-style line endings (CRLF)..
You might want to set up a crontab or cron job to run every 4 hours at 20 minutes past the hour for several reasons, including:
- Automatically backing up a database
- Generating reports
- Sending out email notifications
- Updating data from an external source
Similar Cron Jobs
You might also want to run a crontab:
- every 7 hours
- every 12 hours
- every 2 hours
- every 10 hours
- every 3 hours
- every hour between 5:00 am and 10:00 am
- every hour between 6:00 am and 10:00 pm
FUN FACT: If you need to delete a cron job, simply remove the corresponding line from the crontab file and save your changes..
In this article, you learned how to set up a cron job that runs every 4 hours at 20 minutes past the hour. Please share this page with friends and colleagues if you find it useful.
If you have any questions, please don’t hesitate to comment below.
If you are looking for cron jobs that run at certain minutes, hours, days, weekdays, or months, or if you are looking for miscellaneous cron jobs, then check out our relevant sections, or visit our crontab cheat sheet for a list of hundreds of popular cron jobs.