8. Cron Jobs

Lesson Content

Although we have been talking about resource utilization, I think this would be a good point to mention a neat tool in Linux that is used to schedule tasks using cron. There is a service that runs programs for you at whatever time you schedule. This is a really useful if you have a script you want to run once a day that needs to execute something for you.

For example, let’s say I have a script located in /home/pete/scripts/change_wallpaper. I use this script every morning to change the picture I use for my wallpaper, but each morning I have to manually execute this script. Instead what I can do is create a cron job that executes my script through cron. I can specify the time I want this cron job to run and execute my script.

30 08 * * * /home/pete/scripts/change_wallpaper

The fields are as follows from left to right:

Minute - (0-59)
Hour - (0-23)
Day of the month - (1-31)
Month - (1-12)
Day of the week - (0-7). 0 and 7 are denoted as Sunday

The asterisk in the field means to match every value. So in my above example, I want this to run every day in every month at 8:30am.

To create a cronjob, just edit the crontab file:

crontab -e

Exercise

Create a cronjob that you want to run at a scheduled time.

Quiz Question

# What is the command to edit your cronjobs? > The cron command-line utility is a job scheduler on Unix-like operating systems. Users who set up and maintain software environments use cron to schedule jobs, also known as cron jobs, to run periodically at fixed times, dates, or intervals. 1. [ ] cron 2. [ ] cronjob -e 3. [ ] cron -e 4. [x] crontab -e