CRON

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(Restarting Cron)
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# | | | | day of the week (0-6 with 0=Sunday). # | | | | day of the week (0-6 with 0=Sunday).
# | | | | | commands # | | | | | commands
 +
 +== External links ==
 +* [http://www.math-linux.com/spip.php?article45 Crontab : Scheduling Tasks]

Revision as of 10:15, 27 June 2006

The crontab command, found in Unix and Unix-like operating systems, is used to schedule commands to be executed periodically. Dreamhost crontab wiki has a good explanation of how crontab works. A more official explanaton can be found here.


Contents

Pre-requisites

In order for cron to function properly, you must have the date and time set correctly. You can check this in the GUI by going to -> Status -> Router tab -> Current Time. You can also check the time in the command line by using the 'date' command.

You must also enable crontab in DD-WRT before you can use it. You can enable crontab in the GUI by going to -> Administration -> Management -> Cron, and set it to enable.


File Locations

Cron can be set in two locations on dd-wrt:

1. Either by putting your command in the /tmp/crontab file

echo '  *      *       *       *       *       root /bin/date > /tmp/test.txt' >> /tmp/crontab

which will look like this:

  *      *       *       *       *       root /bin/date > /tmp/test.txt

2. Or by putting a file in the /tmp/cron.d/ folder (eg. /tmp/cron.d/dosomething) that holds your command

echo '* * * * * root /bin/date > /tmp/test.txt' > /tmp/cron.d/date

which will look like this:

* * * * * root /bin/date > /tmp/test.txt


Restarting Crond

After you modify/add the appropriate command you will need to restart cron in order for your changes to take effect. You can restart crond with the following command:

killall -9 crond; crond

Since end of June cron changed to crond!!!

Extras

You may wish to add this to your startup script, before any jobs are added. It will add clarity to your crontab file:

echo '# minute (0-59),' >> /tmp/crontab
echo '# |      hour (0-23),' >> /tmp/crontab
echo '# |      |       day of the month (1-31),' >> /tmp/crontab
echo '# |      |       |       month of the year (1-12),' >> /tmp/crontab
echo '# |      |       |       |       day of the week (0-6 with 0=Sunday).' >> /tmp/crontab
echo '# |      |       |       |       |       commands' >> /tmp/crontab

If you add this to your startup script, you will see this in your crontab file:

# minute (0-59),
# |      hour (0-23),
# |      |       day of the month (1-31),
# |      |       |       month of the year (1-12),
# |      |       |       |       day of the week (0-6 with 0=Sunday).
# |      |       |       |       |       commands

External links