Debugging Cron on Ubuntu

Basics

Create a crontab by defining it in a text file and then hand it over to cron with this command:

crontab my_text_file.txt

List your cron jobs with

crontab -l

Edit your cron jobs with

crontab -e

Remove all your cron jobs with

crontab -r

Debugging

If you’ve scheduled a cron job but it doesn’t seem to be running, here are a few things to remember.

% characters in your crontab need to be escaped

Your crontab needs to have a newline at the end.

All cron events are logged to /var/log/syslog.

Check there for information.

By default, the output of each cron run is emailed to the user that it runs as.

This is your unix mail. So, check your unix login account mail for messages. These will be very helpful.

I use mutt to read unix mail.

sudo apt-get install mutt; mutt

Wrap Up

That should be enough to allow you to figure out what’s preventing cron from behaving as you think it should.