Setup

For those more bare-bones distros that don't ship with a cron daemon, I like to install cronie. This will install the binary crontab with which you can edit your user's crontab with the usual crontab -e and list it with crontab -l.

This method generates an empty crontab file, in which I like to add the following:

# +--------------------------- Minute (0-59)
# |    +---------------------- Hour   (0-23)
# |    |     +---------------- Day    (1-31)
# |    |     |   +------------ Month  (1-12)
# |    |     |   |   +-------- Day of week (0-6, 0=Sunday)
# |    |     |   |   |    +--- Command to be run
# |    |     |   |   |    |
# v    v     v   v   v    v
#====================================================================
# Uncomment for testing
# *   *   *   *   *    $HOME/cron/showcron

Most of us don't have the entire cron syntax memorized, and this little helper comment is always helpful!

Troubleshooting

If you're having trouble with a cronjob, and the script works when running it as your user, the problem is usually the environment / environment variables.

You can save this little script (which is also included in the above helper comment as the "testing" script - $HOME/cron/showcron):

#!/bin/bash

tag=${0##*/}
exec > /tmp/$tag.$$

echo "Generated by $tag on $(date)

Environment:"

/bin/env | /bin/sort
echo
echo '----------------------------------------------'
echo Shell settings:
set
exit 0

This will generate some output under /tmp/showcron.xyz in which you can inspect the env variables available to your cron scripts at runtime.