Difference between revisions of "Cron entry"

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Revision as of 11:48, 8 July 2011

PythonIcon.png Skill level: Medium
The instructions on this page require a basic knowledge of linux.


How to automatically run a command periodically with Cron daemon.

Custom template

This is the preferred method on SME Server, see documentation. Custom templates survive updates and are included in a regular backup.

Make directory for custom template

mkdir -p /etc/e-smith/templates-custom/etc/crontab

Create and open a file with the text editor nano:

nano /etc/e-smith/templates-custom/etc/crontab/your_file_name

Add your cron entries, example for running a script daily at 16,00:

# Run custom script with cron
00 16 * * * root /root/cronjobs/external_ip.sh

Syntax: (0-59) (0-23) (1-31) (1-12 or Jan-Dec) (0-6 or Sun-Sat) (user) (command)

Save and exit.

Regenerate the template:

expand-template /etc/crontab

Verify your new entry in the regenerated crontab:

more /etc/crontab

Restart the cron daemon:

service crond restart

Cron directorys

This method is simple, but will not be included in a regular backup and might have problems with updates and upgrades.

There are four directorys in /etc/: cron.hourly, cron.daily, cron.weekly and cron.monthly.

Any executable script dropped in these will be executed automatically each period (indicated by the directory name).


Cron jobs are executed by the user admin (which is an alias for root).

Cron job results are usually sent by email to the administrator.

A script fired by a cron entry must be executable.


Forum post 1

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Developers Manual on Configuration file templates

Crontab Manager