Cron

Inačica od 08:04, 31. kolovoza 2010. koju je unio/unijela Helen Foster (razgovor | doprinosi)

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Some of Moodle's modules require continual checks to perform tasks. For example, Moodle needs to check the discussion forums so it can mail out copies of posts to people who have subscribed.

The script that does all this is located in the admin directory, and is called cron.php. However, it can not run itself, so you need to set up a mechanism where this script is run regularly (eg every five or ten minutes). This provides a "heartbeat" so that the script can perform functions at periods defined by each module. This kind of regular mechanism is known as a cron service.

The cron.php script looks through all the module directories for cron.php files and runs them. These files can contain cleanup functions, email functions or anything that needs to be run on a regular basis. For example, cron will trigger the system to create the backups of courses at the time specified in the administration settings. It also triggers any messaging module or forum email notifications, but not all functions are called each time the cron runs. Some functions, such as unenrolling students who have not logged in or deleting old copies of log files, are only run occasionally. The cron.php file has a section which will randomly call these core tasks approximately 1 in 5 times the cron runs.

Note that the machine performing the cron does not need to be the same machine that is running Moodle. For example, if you have a limited web hosting service that does not have a cron service, then you can might choose to run cron on another server or on your home computer. All that matters is that the cron.php file is called regularly.

The load of this script is not very high, so 5 minutes is usually reasonable, but if you're worried about it you can reduce the time period to something like 15 minutes or even 30 minutes. It's best not to make the time period too long, as delaying mail-outs can slow down activity within the course. Remember that mail-outs also wait for the editing time to expire before being queued for sending.

First, test that the script works by running it directly from your browser: http://example.com/moodle/admin/cron.php

If cron is called from the command line by any user logged in to your Moodle it will create a temporary admin environment in order to run and then log the user out. You can disable command line running of cron by disabling the appropriate section in the cron.php file.

Now, you need to set up some of way of running the script automatically and regularly.

On Windows systems

The simplest way is to use this little package MoodleCron-Setup.exe which makes this whole thing very easy by installing a small Windows service. Run it and forget about it! :-)

On the other hand, if you are having trouble with moodle-cron-for-windows package, you can use wget for windows and setup a scheduled task. Just follow these steps:

  1. Download a compiled version of wget for windows from Heiko Herold's wget for windows page (http://xoomer.virgilio.it/hherold/) or Bart Puype's wget for windows page (http://users.ugent.be/~bpuype/wget/). If you use Heiko Herold's package, copy all of the .DLL files to your C:\Windows\system32 directory.
  2. Copy the wget.exe file to c:\windows (this makes sure wget is always in the search path).
  3. Go to Start >> Control Panel >> Scheduled Tasks >> Add Scheduled Task.
    1. Click "Next" to start the wizard:
    2. Click in the "Browse..." button and browse to C:\windows\wget.exe and click "Open"
    3. Type "Moodle Cron" as the name of the task and select "Daily" as the schedule. Click "Next".
    4. Select "12:00 AM" as the start time, perform the task "Every Day" and choose today's date as the starting date. Click "Next".
    5. Enter the username and password of the user the task will run under (it doesn't have to be a priviledged account at all). Make sure you type the password correctly :-). Click "Next".
    6. Mark the checkbox titled "Open advanced properties for this task when I click Finish" and click "Finish".
    7. In the new dialog box, type the following in the "Run:" text box:
C:\windows\wget.exe -q -O NUL http://my.moodle.site/moodle/admin/cron.php
    1. Click on the "Schedule" tab and there in the "Advanced..." button.
    2. Mark the "Repeat task" checkbox and set "Every:" to 5 minutes, and set "Until:" to "Duration" and type "23" hours and "59" minutes.
    3. Click "OK" and you are done.

You can test that your task can run successfully by clicking it with the right button and chosing "Run". If everything is correctly setup, you will briefly see a DOS command window while wget executes and fetches the cron page and then it disappears.

If you refresh the scheduled tasks folder, you will see the Last Run Time column (in detailed folder view) reflects the current time, and that the Last Result column displays "0x0" (everything went OK). If either of these is different, then you should recheck your setup.

On web hosting services

Your web-based control panel may have a web page that allows you to set up this cron process. For example, on Cpanel system, look for a button called "Cron jobs". In there you can put the same sort of Unix commands as listed below.

Using the command line on Unix

There are different command line programs you can use to call the page from the command line. Not all of them may be available on a given server.

For example, you can use a Unix utility like 'wget':

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

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

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 could use a standalone version of PHP, compiled to be run on the command line. The advantage with doing this is that your web server logs aren't filled with constant requests to cron.php. The disadvantage is that you need to have access to a command-line version of php.

/opt/bin/php /web/moodle/admin/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:

*/5 * * * * wget -q -O /dev/null http://example.com/moodle/admin/cron.php

Usually, the "crontab" 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).

See also