Cron

Source: https://www.cyberciti.biz/faq/how-do-i-add-jobs-to-cron-under-linux-or-unix-oses/

Open file to edit

crontab -e

Format

a b c d e /path/command

• a: Minute (0-59)
• b: Hours (0-23)
• c: Day (0-31)
• d: Month (0-12 [12 == December])
• e: Day of the week(0-7 [7 or 0 == sunday])
• /path/command – Script or command name to schedule

Options other than number

Source: https://crontab.guru/every-5-minutes

• * : any value
• , : value list separator
• - : range of values
• / : step values

Example every 5 minutes

*/5 * * * * date >> ~/date.txt

Special @ shortcuts

Source: https://www.linode.com/docs/guides/schedule-tasks-with-cron/#special-cron-syntaxes

• @reboot statement runs the specified command once, at start up.
• @yearly and @annually both run the specified task every year at 12:00am on the 1st of January. This is equivalent to specifying 0 0 1 1 * in the crontab line.
• @daily and @midnight both run the cronjob every day at 12:00am. This is equivalent to the following cron syntax: 0 0 * * *.
• @monthly runs the job once a month, on the 1st, at 12:00am. In standard cron syntax this is equivalent to: 0 0 1 * *.
• @weekly runs the job once a week at 12:00am on Sunday. This is the same as specifying 0 0 * * 0 on the crontab line.
• @hourly runs the job at the top of every hour. In standard cron syntax this is equivalent to: 0 * * * *.

Example Usage

@reboot date >> ~/test_cron.txt

Test Cron

Simple Test

Open Crontab

crontab -e

Add line to bottom and save (Ensure there is a new line at the end of the line)

* * * * * date >> ~/date.txt

Wait one minute and confirm that it works

More involved test that uses a script

Overview: Create test script and set cron to run script

Create temp folder

mkdir ~/tmp

Create test script

echo 'date >> ~/tmp/cron_result.txt' > ~/tmp/cron_test.sh
chmod 700 ~/tmp/cron_test.sh
ls -l ~/tmp

Open Crontab

crontab -e

Add line to bottom and save (Ensure there is a new line at the end of the line)

* * * * * ~/tmp/cron_test.sh

Wait one minute and confirm that it works

cat ~/tmp/cron_result.txt