Cron with Unix or Linux

On Unix and Linux use the built in cron program which is standard on nearly all systems. You are required to add a command to the 'crontab' (the table that holds cron commands) for the web server user.

There are two different methods that can be used to invoke the Moodle cron process:

NOTE: The commands shown need to be added to the crontab to function (described in a moment). However, you can - and should - run them on the command line to check they work first.

The command line (cli) cron

If you have the PHP CLI version installed then this is the recommended method of invoking cron. The correct command is as follows...

/usr/bin/php /path/to/moodle/admin/cli/cron.php

(substitute the correct path to moodle and for php as required)

Web based cron

NOTE: In order to use the web based cron script you must first check Cron settings to make sure this method is enabled.

The idea is to call the following web page (you can try this from your browser):

http://url.of.your/moodle/admin/cron.php

A command line (text based) browser is needed to run this from the server. Possibilities are as follows...

wget -q -O /dev/null/ http://url.of.your/moodle/admin/cron.php

(no output is displayed - remove the -O /dev/null/ to test)

...OR...

curl http://url.of.your/moodle/admin/cron.php -o /dev/null/ -silent

(no output is displayed - remove the -o /dev/null/ -silent to test)

php

A number of users of Moodle have found that 'wget' sometimes fails. Especially if you have trouble with email digests not being sent on a daily basis to all users, an alternative command that solves the problem is:

php http://example.com/moodle/admin/cron.php

The same thing using lynx:

lynx -dump http://example.com/moodle/admin/cron.php > /dev/null

Note in this example that the output is thrown away (to /dev/null).

Alternatively, you can use a standalone version of PHP, compiled to be run on the command line. The disadvantage is that you need to have access to a command-line version of php. The advantage is that your web server logs aren't filled with constant requests to cron.php and you can run at a lower I/O and CPU priority.

/opt/bin/php /web/moodle/admin/cli/cron.php

Example command to run at lower priority:

 ionice -c3 -p$$;nice -n 10 /usr/bin/php /moodle/admin/cli/cron.php > /dev/null

Note: In version 2.0 and later the path for running cron.php from the commandline has changed. Use c:\moodle\admin\cli\cron.php

Using the crontab program on Unix

All that Cpanel does is provide a web interface to a Unix utility known as crontab. If you have a command line, you can set up crontab yourself using the command:

crontab -e

and then adding one of the above commands like:

*/30 * * * * wget -q -O /dev/null http://example.com/moodle/admin/cron.php

The first five entries are the times to run values, followed by the command to run. The asterisk is a wildcard, indicating any time. The above example means run the command wget -q -O /dev/null... every 30 minutes (*/30), every hour (*), every day of the month (*), every month (*), every day of the week (*).

The "O" of "-O" is the capital letter not zero, and refers the output file destination, in this case "/dev/null" which is a black hole and discards the output. If you want to see the output of your cron.php then enter its url in your browser.

• A basic crontab tutorial
• Online version of the man page

For beginners, "EDITOR=nano crontab -e" will allow you to edit the crontab using the nano editor. Ubuntu defaults to using the nano editor.

Usually, the "crontab -e" command will put you into the 'vi' editor. You enter "insert mode" by pressing "i", then type in the line as above, then exit insert mode by pressing ESC. You save and exit by typing ":wq", or quit without saving using ":q!" (without the quotes). Here is an intro to the 'vi' editor.