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Cron is the name of a Unix program that runs predefined tasks on a computer at regular intervals. The cron process in Moodle assists some modules to perform tasks on a scheduled basis. For example, the cron process might tell Moodle to check all discussion forums so it can mail out copies of new posts to people who have subscribed to that forum.  
Cron is the name of a Unix program that runs predefined tasks on a computer at regular intervals. It assists some of Moodle's modules to perform tasks on a scheduled basis. For example, the cron process might tell Moodle to check all discussion forums so it can mail out copies of new posts to people who have subscribed to that forum.  


The primary Moodle script that does all this is located in the admin directory, and is called cron.php. However, it can not tell itself to run, 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 service can be part of a webhost or can be something run from a different server or computer.
The Moodle cron process can not tell itself to run.  It is a best practice to set up a cron service either on the hosting web server, another server or on another computer that will tell the Moodle cron process to run.  
*[[Cron reports]] - Examples of reports shown after admin/cron.php was triggered
*[[Cron settings]] - Moodle cron process password and CLI settings
*[[Cron with Windows OS]] - Cron services in Windows
*[[Cron with MAC OS X]]- Cron services in a MAC environment
*[[Cron with web hosting services]]- Cron services in various web hosting examples.
*[[Cron with UNIX]]- Cron services on various UNIX and Linux flavored operating systems.


==Overview of cron==
:Note: Asking a human to use their browser to run the Moodle cron process every five or ten minutes,or when anybody on the site thinks it needs to be run is not a best practice.   The outside cron service provides a "heartbeat" so that the Moodle cron process can perform functions at periods defined for each module that needs it.
===Script overview===
The cron.php script basically finds and determines if certain functions need to run. These functions are defined in code associated with specific activities and processes. Usually the function looks for new activity that has occurred since cron was last run. Some of the functions may use a timestamp to determine if they should look for new activity. A few functions are run on a random basis.


==Starting cron==
There are a number of way to invoke Moodle cron process. Cron can be started from the address bar in a browser (For example http:demo.moodle.net/admin/cron.php), via a [[Daemon]], or wq1et, curl or some other form of a cron service.
===Cron service location and timing===
Note that the machine providing the cron service  '''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 might choose to run cron on another server or on your home computer. All that matters is that the Moodle cron process is run on a regular basis.
The load of the Moodle cron process on the Moodle server is not very high, so 5 minutes is usually reasonable.  However 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.  For example delaying mail-outs can slow down activity within the course and create a large mail outbox to process.  Or student want to see their activity and course completions updated quickly. 
===Testing cron and manual trigger===
On a new Moodle install or upgrade, it is a good idea to test the Moodle cron process directly from your browser: ''<nowiki>http://example.com/moodle/admin/cron.php</nowiki>''  (See [[Cron settings]] if this does not work).
Next, you need to set up a way to manage an automatic scheduled process to run the script on a regular basis. This will depend upon the operating system and program you select.
:Note: When the Moodle cron process is called from cron service, 'the command line' trigger creates a temporary admin environment (similar to a login) in order to run and then deletes that environment. You can disable command line running of cron by disabling the appropriate section in the cron.php file.
==Moodle cron process ==
The Moodle cron process basically finds and determines if certain functions need to run. These functions are defined in code associated with specific activities and processes. Usually the function looks for new activity that has occurred since cron was last run.  Some of the functions may use a timestamp to determine if they should look for new activity. A few functions are run on a random basis. 
===Examples of Moodle cron processes===
Moodle's cron processes include:
Moodle's cron processes include:
*updating reports such as quiz, admin, gradebook  
*updating reports such as quiz, admin, gradebook  
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*create the backups of courses at the time specified in the administration settings.  
*create the backups of courses at the time specified in the administration settings.  
*updating messaging module or forum email notifications.
*updating messaging module or forum email notifications.
*unenroll students - this is done on a random basis about 20% of the time Moodle's cron process is triggered.
*unenrol students - this is done on a random basis about 20% of the time Moodle's cron process is triggered.
*deleting users who have not filled out their profile via the 20% random trigger
*deleting users who have not filled out their profile via the 20% random trigger
*deleting old logs are also checked 20% of the time via the 20% random trigger
*deleting old logs are also checked 20% of the time via the 20% random trigger
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*updates registrations
*updates registrations


The code in lib/cronlib.php shows the places that are being checked when the admin/cron.php is run and the report which is displayed on the screen after it has run.
The code in lib/cronlib.php shows the places that are being checked when the admin/cron.php is run and the report which is displayed on the screen after it has run.  As mentioned elsewhere admin/cli/cron.php is the file which outside cron services run to trigger the Moodle cron process.
 
===Starting cron===
There are a number of way to invoke cron.php. Cron can be started from the address bar in a browser (URL usually ending in admin/cron.php), via a [[Daemon]], or wq1et, curl or some other code.
 
''Site administeration >Security > Site Policies'' See the image below.
 
The cronclionly setting will stop the browser URL trigger.  This sets Moodle so that cron.php cannot be invoked by the Moodle URL.
 
The cron process can be protected by a password with the cronremotepassword setting.
 
[[Image:Moodelcronadmin.png]]
 
:''TIP:'' While this is identified as CLI (command line interface) this is a bit misleading in that it does not mean that you have to be sitting at a shell account entering the command. If you enable this switch you can invoke cron.php through any set of batch or script files you wish,  but it must be invoked via its correct location in the operating systems file structure.  This can be especially frustrating for those not used to scripting in that environment is not typically provided.
 
===Cron service location and timing===
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 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.
 
===Testing cron and manual trigger===
 
First, test that the script works by running it directly from your browser: ''<nowiki>http://example.com/moodle/admin/cron.php</nowiki>''
 
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.
 
Next, you need to set up a way to manage an automatic scheduled process to run the script on a regular basis. This will depend upon the operating system and program you select.
 
==Managing Cron on Windows systems==
 
There are two different ways for setting-up Moodle cron.php on Windows systems:
 
*Use the '''Moodle Cron package'''. The simplest way is to use this little package [http://download.moodle.org/download.php/windows/MoodleCron-Setup.exe MoodleCron-Setup.exe], which makes this whole thing very easy by installing a small Windows service. Run it and forget about it! :-)
*Use a '''Scheduled Task'''. If you prefer to use the built-in Windows Scheduler or are having trouble with moodle-cron-for-windows package, you can use wget for windows or php from the command line and setup a scheduled task. Just follow these steps:
** Choose either the '''php.exe/php-win.exe (command line binary)''' or '''wget'''
::The php.exe or php-win.exe binary (for PHP version 5 or later) is installed in your php folder (e.g. c:\php) will give you better performance when running the cron script.
::If you want to use wget, download a compiled version of wget for windows from the native GNU Win32 ports (http://unxutils.sourceforge.net/), 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. Copy the wget.exe file to c:\windows (this makes sure wget is always in the search path).
:* Setup a '''Scheduled Task'''.
:: - Go to Start >> Control Panel >> Scheduled Tasks >> Add Scheduled Task.
:: - Click "Next" to start the wizard:
:: - Click in the "Browse..." button and browse to c:\php\php.exe or c:\windows\wget.exe and click "Open"
:: - Type "Moodle Cron" as the name of the task and select "Daily" as the schedule. Click "Next".
:: - Select "12:00 AM" as the start time, perform the task "Every Day" and choose today's date as the starting date. Click "Next".
:: - 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".
:: - Mark the checkbox titled "Open advanced properties for this task when I click Finish" and click "Finish".
:: - In the new dialog box, type the following in the "Run:" text box: <pre>c:\windows\wget.exe -q -O NUL http://my.moodle.site/moodle/admin/cron.php</pre> or <pre>c:\php\php-win.exe -f c:\moodle\admin\cron.php</pre> Replace "c:\moodle" with the path to your moodle directory or "my.moode.site" with the name of your site.<br><br>
:: - Click on the "Schedule" tab and there in the "Advanced..." button.
:: - Mark the "Repeat task" checkbox and set "Every:" to 5 minutes, and set "Until:" to "Duration" and type "23" hours and "59" minutes.
:: - Click "OK" and you are done.
* '''Test your scheduled task'''. You can test that your scheduled 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/php 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.
* '''Logging cron output'''. You may want to log the output of the cron script as it executes, in case you see the job is producing errors, backups are not being completed or users are experiencing delays in receiving forum emails. To do this, adjust the command so that it uses the php.exe and stores the output in a file called (for example c:\moodle\admin\cron.log). Here is an example of the php.exe command:
<pre>c:\php\php.exe -f c:\moodle\admin\cron.php > c:\moodle\admin\cron.log</pre>
If you experience problems logging the output of cron.php to a text file using the above command then read [http://moodle.org/mod/forum/discuss.php?d=139263#p609060 this] message by Iñaki Arenaza for an alternative way to log the output of Cron.
 
'''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'''
 
==Managing the cron job on Mac OS X with launchd==
 
It's really important to start the cron job every 5 minutes. The cron job assists most of Moodle's modules to perform tasks on a scheduled basis. For example, the discussion forums can only mail out copies of new posts to all subscribers if the cron job tells Moodle to do this.
 
In Mac OS X 10.5 you will find the system daemon ''launchd'' for this service. This daemon offers a standardized interface to any user and all programs started automatically by the system. Please look at http://developer.apple.com/macosx/launchd.html for more informations about the configurations and all parameters.
 
In our case the service should get the web page http://your-server-address/moodle19/admin/cron.php every 5 minutes. The configuration will be done by the file named ''moodle4mac.cron.plist'' which must be placed in the system folder ''/Library/LaunchDaemons/'' ... surely you can use any other file name but it should say something about the function of the service. The extension must be ''.plist''. After any reboot of your Mac server the cron service will start automaticly because the file is placed in the correct system folder.
 
===Use the graphical way===
You can use Lingon to add a new daemon plist or to edit one. It produces the same text as you can write in your text editor. http://sourceforge.net/projects/lingon/files/
 
[[Image:macosx-lingon.png]]
 
===Use a text editor===
Please use a text editor to write the needed file. You can open the Terminal and use the system editors vi or pico. But you can also write the text file with any GUI text editor ... I mostly use TextWrangler ... but do NOT take an editor for formatted texts like Microsoft Word or OpenOffice Writer. You must get pure text!
 
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN"
      "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>KeepAlive</key><false/>
<key>Label</key><string>moodle4mac.cron</string>
<key>ProgramArguments</key>
<array>
      <string>curl</string>
      <string>-s</string>
      <string>http://your-server-address/moodle19/admin/cron.php</string>
</array>
<key>RunAtLoad</key><true />
<key>StartInterval</key><integer>300</integer>
<key>StandardErrorPath</key><string>/dev/null</string>
<key>StandardOutPath</key><string>/dev/null</string>
</dict>
</plist>
 
The label string must be the same as the file name is but without the extension ''.plist''. Save the text file ''/Library/LaunchDaemons/moodle4mac.cron.plist''. The owner of the file must be set to the system user ''root''.  If you use a site with SSL (ie: it has an http'''s''':// protocol) you either need to have your SSL certificates listed for use by the CURL utility ([http://curl.haxx.se/docs/sslcerts.html see these docs] for more details) OR you must use the '-k' switch in addition to the '-s' switch used above; your arguments line would then read: `<string>-s -k</string>`.
 
That's all, really!
 
===How to start and stop the cron service===
You can start the new cron service in the Terminal.
 
sudo launchctl load /Library/LaunchDaemons/moodle4mac.cron.plist
 
The following command would stop the service. If you want to activate changes in the cron service you need to ''unload'' and then to ''load'' the daemon again.
 
sudo launchctl unload /Library/LaunchDaemons/moodle4mac.cron.plist
 
===Only one service for two servers?===
For my server I needed to have a cron service for to instances ''moodle19'' and ''moodle20'' ... no problem ... with the typo ''moodle[19-20]'' I will get a cron service for both.
 
<nowiki>curl -s http://your-server-address/moodle[19-20]/admin/cron.php</nowiki>
 
To see if the cron service works correctly you should look at the ''access.log'' of your web server. The cron.php should be accessed every 5 minutes ... on my server for both Moodle instances ''moodle19'' and ''moodle20'' ... oh yes, it works!!
 
192.168.0.220 - - [30/Jul/2009:22:10:56 +0200] "GET /moodle19/admin/cron.php HTTP/1.1" 200 1136
192.168.0.220 - - [30/Jul/2009:22:10:57 +0200] "GET /moodle20/admin/cron.php HTTP/1.1" 200 1403
192.168.0.220 - - [30/Jul/2009:22:11:18 +0200] "OPTIONS * HTTP/1.0" 200 -
192.168.0.220 - - [30/Jul/2009:22:15:56 +0200] "GET /moodle19/admin/cron.php HTTP/1.1" 200 735
192.168.0.220 - - [30/Jul/2009:22:15:57 +0200] "GET /moodle20/admin/cron.php HTTP/1.1" 200 964
192.168.0.220 - - [30/Jul/2009:22:20:56 +0200] "GET /moodle19/admin/cron.php HTTP/1.1" 200 1136
192.168.0.220 - - [30/Jul/2009:22:20:57 +0200] "GET /moodle20/admin/cron.php HTTP/1.1" 200 1365
 
==Managing cron on web hosting services==
 
Your web-based control panel may have a web page that allows you to set up a cron service process.
 
===CPanel cron service===
If you are using CPanel, login then look for "Advanced" category towards the bottom of the page. Click on Cron Jobs -> Advanced (Unix style). Enter the following for the cron to run every 30 minutes.
 
Email address for output: emailaddress@mydomain.con
Minute:*/30
Hour:*
Day:*
Month:*
Weekday:*
<nowiki>Command: wget -q -O /dev/null http://www.mydomain.com/moodle/admin/cron.php</nowiki>
 
Click Commit Changes. Check your email for the output.
 
[[Image:Cpanel-cron-setup.JPG]]
 
===Other systems cron service===
For other systems, look for a button called "Cron jobs". In there you can put the same sort of Unix commands as listed below.
 
 
If you don't have permissions to run the 'wget' command on the server, you can use this php command:
 
/usr/local/bin/php -q /real/path/to/script/admin/cron.php
 
For example:
 
/usr/local/bin/php -q /home/username/public_html/moodle/admin/cron.php
 
If you don't know what is the real path of your Moodle folder you can use the PHP command realpath.
 
Another alternative, if you do not have permission to run the 'wget' command, may be to use a curl command.
 
For example:
 
curl --silent --compressed http://mydomain.com/moodle/admin/cron.php
 
'''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 a cron command line in 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.
 
'''Note:''' The examples with wget, lynx, and similar are '''not''' the same as the "CLI only" cron checkbox, mentioned above (the configuration variable "cronclionly"). wget, lynx, and other similar utilities are Unix command-line HTTP clients, and thus running cron.php in this way is the same as running it in a browser, from Moodle's point of view.
 
For example, you can use a Unix utility like 'wget':
 
wget -q -O /dev/null <nowiki>http://example.com/moodle/admin/cron.php</nowiki>
 
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 <nowiki>http://example.com/moodle/admin/cron.php</nowiki>
 
The same thing using lynx:
 
lynx -dump <nowiki>http://example.com/moodle/admin/cron.php</nowiki> > /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 <nowiki>http://example.com/moodle/admin/cron.php</nowiki>
 
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.
 
* [http://linuxweblog.com/node/24 A basic crontab tutorial]
* [http://www.freebsd.org/cgi/man.cgi?query=crontab&apropos=0&sektion=5&manpath=FreeBSD+6.0-RELEASE+and+Ports&format=html Online version of the man page]
 
For '''beginners''', "EDITOR=nano crontab -e" will allow you to edit the crontab using the [http://www.nano-editor.org/dist/v1.2/faq.html 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 [http://www.unix-manuals.com/tutorials/vi/vi-in-10-1.html intro] to the 'vi' editor.


==See also==
==See also==
Using Moodle forum discussions:
Using Moodle forum discussions:
*[http://moodle.org/mod/forum/discuss.php?d=41827 Cron - can someone give me a quick confirmation of function?]
*[http://moodle.org/mod/forum/discuss.php?d=41827 Cron - can someone give me a quick confirmation of function?]

Revision as of 11:53, 22 November 2011

Cron is the name of a Unix program that runs predefined tasks on a computer at regular intervals. The cron process in Moodle assists some modules to perform tasks on a scheduled basis. For example, the cron process might tell Moodle to check all discussion forums so it can mail out copies of new posts to people who have subscribed to that forum.

The Moodle cron process can not tell itself to run. It is a best practice to set up a cron service either on the hosting web server, another server or on another computer that will tell the Moodle cron process to run.

Note: Asking a human to use their browser to run the Moodle cron process every five or ten minutes,or when anybody on the site thinks it needs to be run is not a best practice. The outside cron service provides a "heartbeat" so that the Moodle cron process can perform functions at periods defined for each module that needs it.

Starting cron

There are a number of way to invoke Moodle cron process. Cron can be started from the address bar in a browser (For example http:demo.moodle.net/admin/cron.php), via a Daemon, or wq1et, curl or some other form of a cron service.

Cron service location and timing

Note that the machine providing the cron service 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 might choose to run cron on another server or on your home computer. All that matters is that the Moodle cron process is run on a regular basis.

The load of the Moodle cron process on the Moodle server is not very high, so 5 minutes is usually reasonable. However 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. For example delaying mail-outs can slow down activity within the course and create a large mail outbox to process. Or student want to see their activity and course completions updated quickly.

Testing cron and manual trigger

On a new Moodle install or upgrade, it is a good idea to test the Moodle cron process directly from your browser: http://example.com/moodle/admin/cron.php (See Cron settings if this does not work).

Next, you need to set up a way to manage an automatic scheduled process to run the script on a regular basis. This will depend upon the operating system and program you select.

Note: When the Moodle cron process is called from cron service, 'the command line' trigger creates a temporary admin environment (similar to a login) in order to run and then deletes that environment. You can disable command line running of cron by disabling the appropriate section in the cron.php file.

Moodle cron process

The Moodle cron process basically finds and determines if certain functions need to run. These functions are defined in code associated with specific activities and processes. Usually the function looks for new activity that has occurred since cron was last run. Some of the functions may use a timestamp to determine if they should look for new activity. A few functions are run on a random basis.

Examples of Moodle cron processes

Moodle's cron processes include:

  • updating reports such as quiz, admin, gradebook
  • updating course and activity completion (if enabled in advanced settings)
  • updating portfolio
  • plagiarism checks
  • updates activity modules. It looks through the mod directory for lib.php files that contain the function activity-name_cron and will call it. In a standard install this includes assignment, chat, forum, and SCROM.
  • updates blocks. It looks for blocks for their cron methods (object functions) to be run. It then, for each such block, runs the cron method for a new object associated with that block (for more details read admin/cron.php). These files (the lib.php files and the files where the block classes are defined) can contain cleanup functions, email functions or anything that needs to be run on a regular basis.
  • create the backups of courses at the time specified in the administration settings.
  • updating messaging module or forum email notifications.
  • unenrol students - this is done on a random basis about 20% of the time Moodle's cron process is triggered.
  • deleting users who have not filled out their profile via the 20% random trigger
  • deleting old logs are also checked 20% of the time via the 20% random trigger
  • deletes old cached text
  • generates new passwords for new users and notifies users
  • runs authentication enrolments processes
  • updates stats if enabled.
  • runs blog cleanups
  • updates registrations

The code in lib/cronlib.php shows the places that are being checked when the admin/cron.php is run and the report which is displayed on the screen after it has run. As mentioned elsewhere admin/cli/cron.php is the file which outside cron services run to trigger the Moodle cron process.

See also

Using Moodle forum discussions:

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