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| {{Installing Moodle}} | | {{Installing Moodle}} |
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| | The Moodle 'cron' process is a PHP script (part of the standard Moodle installation) that must be run regularly in the background. The Moodle cron script runs different tasks at differently scheduled intervals. |
| 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.
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| 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.
| | '''IMPORTANT: Do not skip setting up the cron process on your server for your Moodle. Your site will not work properly without it.''' |
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| ==Overview of cron==
| | It is recommended that ''the cron is run every minute'', as required for asynchronous activity deletion when using the [[Recycle bin|recycle bin]]. |
| ===Script overview===
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| The cron.php script looks at specific Moodle database tables and uses this information to look the Moodle code to perform actions on a regular basis.
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| The cron.php script looks through the mdl_modules table (assuming the default table prefix is mdl_) in the Moodle database for modules scheduled to have their cron functions run. It then looks in each such module directory for a function called module-name_cron in the lib.php file and runs it.
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| Cron.php also looks through the mdl_block table for blocks scheduled 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.
| | The cron program (that runs the Moodle script) is a core part of Unix based systems (including Linux and OSX) being used to run all manner of time-dependent services. On Windows the simplest solution is to create a task in the Windows Task Scheduler and set it to run at regular intervals. On shared hosting, you should find the documentation (or ask support) how cron is configured. |
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| 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.
| | Essentially, the task involves adding a single command to the list of cron activities on your system. On Unix based systems this list is a file called a 'crontab' which all users have. |
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| ===Starting cron=== | | == General discussion == |
| 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.
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| ''Site administeration >Security > Site Policies'' See the image below.
| | See the later sections for your server type; this section contains some general background information. |
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| The cronclionly setting will stop the browser URL trigger. This sets Moodle so that cron.php cannot be invoked by the Moodle URL.
| | There are essentially two steps to implementing cron: |
| | # identifying the correct command to run |
| | # finding the right place on your system to put the command |
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| The cron process can be protected by a password with the cronremotepassword setting.
| | === Working out the Moodle cron command === |
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| [[Image:Moodelcronadmin.png]]
| | Moodle has two different ways to deploy cron which use different scripts within the Moodle install. These are as follows... |
| | # The CLI (command line interpreter) script. This will be at the path <pre>/path/to/moodle/admin/cli/cron.php</pre> If in doubt, this is the correct script to use. This needs to be run by a 'PHP CLI' program on your computer. So the final command may look something like <pre>/usr/bin/php /path/to/moodle/admin/cli/cron.php</pre> You can (and should) try this on your command line to see if it works. '''WARNING: Check your command-line PHP version is compatible with your chosen version of Moodle. The command-line PHP program is different to the one running your web site and is not always the same version.''' |
| | # If, for some reason, you cannot run the CLI script there is the web based script. Note that this is now deprecated and may be removed in future versions. This needs to be run from a web browser and will be accessed via a web url something like '''http://your.moodle.site/admin/cron.php'''. You can find command line based web browser (e.g. wget) so the final command may look like <pre>/usr/bin/wget http://your.moodle.site/admin/cron.php</pre> This has the advantage that it can be run from *anywhere*. If you can't get cron to work on your machine it can be run somewhere else. |
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| :''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. | | ===The web based Moodle cron command=== |
| | * If you have a choice, do not use the web based cron. It is likely to be removed in a future Moodle version. |
| | * From Moodle 2.9 onwards, the cron job can no longer be run from web by default. You will get an error message: |
| | !!! Sorry, internet access to this page has been disabled by the administrator. !!! |
| | * You can change this in ' Dashboard ► Site administration ► Security ► Site policies ' by deselecting 'Cron execution via command line only'. |
| | ** You will be warned that 'Running the cron from a web browser can expose privileged information to anonymous users. Thus it is recommended to only run the cron from the command line or set a cron password for remote access.' |
| | ** You can then write a 'Cron password for remote access'. If this field is left empty, no password is required. |
| | ** This means that the cron.php script cannot be run from a web browser without supplying the password using the following form of URL: |
| | http://site.example.com/admin/cron.php?password=opensesame |
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| ===Cron service location and timing=== | | === Finding the right place to put the command === |
| 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.
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| 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.
| | This really does depend on the system you are using and you should find and read the documentation for your platform or hosting. In most cases getting the Moodle cron to run consists of establishing the correct command (above) and then adding it, and the time to run the command, to some sort of file. This might be either through a specific user interface or by editing the file directly. |
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| ===Testing cron and manual trigger===
| | If using the CLI version you also need to make sure that the cron process is run as the correct user. This is not an issue with the web version. |
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| First, test that the script works by running it directly from your browser: ''<nowiki>http://example.com/moodle/admin/cron.php</nowiki>''
| | Example... installing cron on Ubuntu/Debian Linux. Assuming logged in as root.. |
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| 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.
| | ''use the crontab command to open a crontab editor window for the www-data user. This is the user that Apache (the web server) runs as on Debian based systems'' |
| | <pre> |
| | $ crontab -u www-data -e |
| | </pre> |
| | ''This will open an editor window. To run the cli cron script every 1 minute, add the line:'' |
| | <pre> |
| | */1 * * * * /usr/bin/php /path/to/moodle/admin/cli/cron.php >/dev/null |
| | </pre> |
| | NOTE: the final '''>/dev/null''' sends all the output to the 'bin' and stops you getting an email every 1 minute. |
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| Now, you need to set up some of way of running the script automatically and regularly.
| | == Setting up cron on your system == |
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| | Choose the information for your server type: |
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| ==Managing Cron on Windows systems==
| | *[[Cron with Unix or Linux]]- Cron services on various UNIX and Linux flavored operating systems. |
| | *[[Cron with Windows OS]] - Cron services in Windows |
| | *''Apple OSX'' - use the built-in 'crontab' service which is exactly the same as [[Cron with Unix or Linux]]. However, you might want to do it the 'Apple way' using launchd - see [[Cron with MAC OS X]] |
| | *[[Cron with web hosting services]]- Cron services in various web hosting examples. |
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| There are two different ways for setting-up Moodle cron.php on Windows systems:
| | Here are some more instructions for specific hosts (please check that these are up to date): |
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| *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! :-) | | *[[Cron on 1and1 shared servers]] |
| *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:
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| ** Choose either the '''php.exe/php-win.exe (command line binary)''' or '''wget'''
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| ::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.
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| ::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).
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| :* Setup a '''Scheduled Task'''.
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| :: - Go to Start >> Control Panel >> Scheduled Tasks >> Add Scheduled Task.
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| :: - Click "Next" to start the wizard:
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| :: - Click in the "Browse..." button and browse to c:\php\php.exe or c:\windows\wget.exe and click "Open"
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| :: - Type "Moodle Cron" as the name of the task and select "Daily" as the schedule. Click "Next".
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| :: - Select "12:00 AM" as the start time, perform the task "Every Day" and choose today's date as the starting date. Click "Next".
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| :: - 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".
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| :: - Mark the checkbox titled "Open advanced properties for this task when I click Finish" and click "Finish".
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| :: - 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>
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| :: - Click on the "Schedule" tab and there in the "Advanced..." button.
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| :: - Mark the "Repeat task" checkbox and set "Every:" to 5 minutes, and set "Until:" to "Duration" and type "23" hours and "59" minutes.
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| :: - Click "OK" and you are done.
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| * '''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.
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| * '''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:
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| <pre>c:\php\php.exe -f c:\moodle\admin\cron.php > c:\moodle\admin\cron.log</pre>
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| 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.
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| '''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 third party cron service == |
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| | Besides using cron hosted on your own server, you may use third party cron service (usually called webcron): |
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| ==Managing the cron job on Mac OS X with launchd==
| | *[https://cron-job.org/ cron-job.org] is a free service. (1Minute cron is possible) |
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| 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.
| | *[https://www.easycron.com EasyCron] - A webcron service provider that eliminates the need of crontab or other task schedulers to set cron job. |
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| 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.
| | === Cron settings in Moodle === |
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| 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.
| | An admin can set cron execution via command line only or a cron password for remote access in ''Administration > Site administration > Security > Site policies''. |
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| ===Use the graphical way=== | | ===Remote cron=== |
| 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/
| | Using the 'web based' version of cron it is perfectly ok to place the cron process on a different machine to the Moodle server. For example, the cron service on a Unix server can invoke the cron web 'page' on a Windows based Moodle server. |
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| [[Image:macosx-lingon.png]] | | ==Scheduling tasks== |
| | An administrator can schedule cron tasks very precisely from Administration > Site administration > Server > Scheduled tasks, see [[Scheduled tasks]] |
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| ===Use a text editor=== | | ==Running cron for several Moodle servers== |
| 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!
| | * Tasks can run in parallel and processes use locking to prevent tasks from running at the same time which allows cron to be triggered from multiple web servers that serve the same Moodle instance. |
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| <?xml version="1.0" encoding="UTF-8"?>
| | * If you are running different Moodle instances on the same server, then each Moodle instance needs a cron job. (Even a single Apache web server can run different Moodle instances on different domains by using its virtual hosts capability [https://httpd.apache.org/docs/2.2/vhosts/index.html https://httpd.apache.org/docs/2.2/vhosts/index.html].) |
| <!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN"
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| "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
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| <plist version="1.0">
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| <dict>
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| <key>KeepAlive</key><false/>
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| <key>Label</key><string>moodle4mac.cron</string>
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| <key>ProgramArguments</key>
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| <array>
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| <string>curl</string>
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| <string>-s</string>
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| <string>http://your-server-address/moodle19/admin/cron.php</string>
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| </array>
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| <key>RunAtLoad</key><true />
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| <key>StartInterval</key><integer>300</integer>
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| <key>StandardErrorPath</key><string>/dev/null</string>
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| <key>StandardOutPath</key><string>/dev/null</string>
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| </dict>
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| </plist>
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| 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>`.
| | == Debugging Scheduled Tasks == |
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| That's all, really!
| | Sometimes, a particular cron task may not be working correctly. In Moodle versions before 2.7 - any cron task that was throwing exceptions would prevent the rest of cron from running. The only way to monitor if cron was completing each time, was to add some automated checking of the output of running cron (e.g. searching for the string "Cron completed at "). |
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| ===How to start and stop the cron service===
| | In Moodle 2.7 and later, a single failing scheduled task will not prevent the remaining tasks from completing. When any single scheduled task fails, it is marked as a failure, and scheduled to be reattempted. If the task keeps failing, the next scheduled time will be backed off until it is attempted at most once every 24 hours. But checking the [[Scheduled tasks]] admin page, you can see if any task is currently failing (it will have a non-zero fail delay - which is the number of seconds to wait before reattempting a failed task). A simple way to debug a failing task, is to run it immediately using the [[Administration via command line#Scheduled_tasks|cli scheduled task runner]] and monitor the output. |
| You can start the new cron service in the Terminal.
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| sudo launchctl load /Library/LaunchDaemons/moodle4mac.cron.plist
| | ==See also== |
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| 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.
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| sudo launchctl unload /Library/LaunchDaemons/moodle4mac.cron.plist
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| ===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.
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| <nowiki>curl -s http://your-server-address/moodle[19-20]/admin/cron.php</nowiki>
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| 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!!
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| 192.168.0.220 - - [30/Jul/2009:22:10:56 +0200] "GET /moodle19/admin/cron.php HTTP/1.1" 200 1136
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| 192.168.0.220 - - [30/Jul/2009:22:10:57 +0200] "GET /moodle20/admin/cron.php HTTP/1.1" 200 1403
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| 192.168.0.220 - - [30/Jul/2009:22:11:18 +0200] "OPTIONS * HTTP/1.0" 200 -
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| 192.168.0.220 - - [30/Jul/2009:22:15:56 +0200] "GET /moodle19/admin/cron.php HTTP/1.1" 200 735
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| 192.168.0.220 - - [30/Jul/2009:22:15:57 +0200] "GET /moodle20/admin/cron.php HTTP/1.1" 200 964
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| 192.168.0.220 - - [30/Jul/2009:22:20:56 +0200] "GET /moodle19/admin/cron.php HTTP/1.1" 200 1136
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| 192.168.0.220 - - [30/Jul/2009:22:20:57 +0200] "GET /moodle20/admin/cron.php HTTP/1.1" 200 1365
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| ==Managing cron on web hosting services==
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| Your web-based control panel may have a web page that allows you to set up a cron service process.
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| ===CPanel cron service===
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| 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.
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| Email address for output: emailaddress@mydomain.con
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| Minute:*/30
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| Hour:*
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| Day:*
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| Month:*
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| Weekday:*
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| <nowiki>Command: wget -q -O /dev/null http://www.mydomain.com/moodle/admin/cron.php</nowiki>
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| Click Commit Changes. Check your email for the output.
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| [[Image:Cpanel-cron-setup.JPG]]
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| ===Other systems cron service===
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| For other systems, look for a button called "Cron jobs". In there you can put the same sort of Unix commands as listed below.
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| If you don't have permissions to run the 'wget' command on the server, you can use this php command:
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| /usr/local/bin/php -q /real/path/to/script/admin/cron.php
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| For example:
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| /usr/local/bin/php -q /home/username/public_html/moodle/admin/cron.php
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| If you don't know what is the real path of your Moodle folder you can use the PHP command realpath.
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| Another alternative, if you do not have permission to run the 'wget' command, may be to use a curl command.
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| For example:
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| curl --silent --compressed http://mydomain.com/moodle/admin/cron.php
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| '''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'''
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| ==Using a cron command line in Unix==
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| 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.
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| '''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.
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| For example, you can use a Unix utility like 'wget':
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| wget -q -O /dev/null <nowiki>http://example.com/moodle/admin/cron.php</nowiki>
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| Note in this example that the output is thrown away (to /dev/null).
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| 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:
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| php <nowiki>http://example.com/moodle/admin/cron.php</nowiki>
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| The same thing using lynx:
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| lynx -dump <nowiki>http://example.com/moodle/admin/cron.php</nowiki> > /dev/null
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| Note in this example that the output is thrown away (to /dev/null).
| | * [[Scheduled tasks]] |
| | | * [http://en.wikipedia.org/wiki/Cron Wikipedia article on cron function] |
| 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.
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| /opt/bin/php /web/moodle/admin/cli/cron.php
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| Example command to run at lower priority:
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| ionice -c3 -p$$;nice -n 10 /usr/bin/php /moodle/admin/cli/cron.php > /dev/null
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| '''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'''
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| ===Using the crontab program on Unix===
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| 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:
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| crontab -e
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| and then adding one of the above commands like:
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| */30 * * * * wget -q -O /dev/null <nowiki>http://example.com/moodle/admin/cron.php</nowiki>
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| 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 (*).
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| 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.
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| * [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] | |
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| 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.
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| 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.
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| ==See also==
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| Using Moodle forum discussions:
| | Forum discussions: |
| *[http://moodle.org/mod/forum/discuss.php?d=41827 Cron - can someone give me a quick confirmation of function?]
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| *[http://moodle.org/mod/forum/discuss.php?d=97684 Cronjob Question]
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| *[http://moodle.org/mod/forum/discuss.php?d=97457 Slow cron : avoiding simultaneous cron]
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| *[http://moodle.org/mod/forum/discuss.php?d=117168 Visibility of cron.php]
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| *[http://moodle.org/mod/forum/discuss.php?d=139263#p609060 How to log the output of a Scheduled Task on Windows] - this discussion explains a nice trick that can be very useful when you are experiencing problems with your Windows Scheduled Task and you need to log the output of the Scheduled Task to a log file. | | *[http://moodle.org/mod/forum/discuss.php?d=139263#p609060 How to log the output of a Scheduled Task on Windows] - this discussion explains a nice trick that can be very useful when you are experiencing problems with your Windows Scheduled Task and you need to log the output of the Scheduled Task to a log file. |
| | *[https://moodle.org/mod/forum/discuss.php?d=324443 Cron Lock] |
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| | [[de:Cron-Job]] |
The Moodle 'cron' process is a PHP script (part of the standard Moodle installation) that must be run regularly in the background. The Moodle cron script runs different tasks at differently scheduled intervals.
IMPORTANT: Do not skip setting up the cron process on your server for your Moodle. Your site will not work properly without it.
It is recommended that the cron is run every minute, as required for asynchronous activity deletion when using the recycle bin.
The cron program (that runs the Moodle script) is a core part of Unix based systems (including Linux and OSX) being used to run all manner of time-dependent services. On Windows the simplest solution is to create a task in the Windows Task Scheduler and set it to run at regular intervals. On shared hosting, you should find the documentation (or ask support) how cron is configured.
Essentially, the task involves adding a single command to the list of cron activities on your system. On Unix based systems this list is a file called a 'crontab' which all users have.
General discussion
See the later sections for your server type; this section contains some general background information.
There are essentially two steps to implementing cron:
- identifying the correct command to run
- finding the right place on your system to put the command
Working out the Moodle cron command
Moodle has two different ways to deploy cron which use different scripts within the Moodle install. These are as follows...
- The CLI (command line interpreter) script. This will be at the path
/path/to/moodle/admin/cli/cron.php
If in doubt, this is the correct script to use. This needs to be run by a 'PHP CLI' program on your computer. So the final command may look something like /usr/bin/php /path/to/moodle/admin/cli/cron.php
You can (and should) try this on your command line to see if it works. WARNING: Check your command-line PHP version is compatible with your chosen version of Moodle. The command-line PHP program is different to the one running your web site and is not always the same version.
- If, for some reason, you cannot run the CLI script there is the web based script. Note that this is now deprecated and may be removed in future versions. This needs to be run from a web browser and will be accessed via a web url something like http://your.moodle.site/admin/cron.php. You can find command line based web browser (e.g. wget) so the final command may look like
/usr/bin/wget http://your.moodle.site/admin/cron.php
This has the advantage that it can be run from *anywhere*. If you can't get cron to work on your machine it can be run somewhere else.
The web based Moodle cron command
- If you have a choice, do not use the web based cron. It is likely to be removed in a future Moodle version.
- From Moodle 2.9 onwards, the cron job can no longer be run from web by default. You will get an error message:
!!! Sorry, internet access to this page has been disabled by the administrator. !!!
- You can change this in ' Dashboard ► Site administration ► Security ► Site policies ' by deselecting 'Cron execution via command line only'.
- You will be warned that 'Running the cron from a web browser can expose privileged information to anonymous users. Thus it is recommended to only run the cron from the command line or set a cron password for remote access.'
- You can then write a 'Cron password for remote access'. If this field is left empty, no password is required.
- This means that the cron.php script cannot be run from a web browser without supplying the password using the following form of URL:
http://site.example.com/admin/cron.php?password=opensesame
Finding the right place to put the command
This really does depend on the system you are using and you should find and read the documentation for your platform or hosting. In most cases getting the Moodle cron to run consists of establishing the correct command (above) and then adding it, and the time to run the command, to some sort of file. This might be either through a specific user interface or by editing the file directly.
If using the CLI version you also need to make sure that the cron process is run as the correct user. This is not an issue with the web version.
Example... installing cron on Ubuntu/Debian Linux. Assuming logged in as root..
use the crontab command to open a crontab editor window for the www-data user. This is the user that Apache (the web server) runs as on Debian based systems
$ crontab -u www-data -e
This will open an editor window. To run the cli cron script every 1 minute, add the line:
*/1 * * * * /usr/bin/php /path/to/moodle/admin/cli/cron.php >/dev/null
NOTE: the final >/dev/null sends all the output to the 'bin' and stops you getting an email every 1 minute.
Setting up cron on your system
Choose the information for your server type:
Here are some more instructions for specific hosts (please check that these are up to date):
Using third party cron service
Besides using cron hosted on your own server, you may use third party cron service (usually called webcron):
- EasyCron - A webcron service provider that eliminates the need of crontab or other task schedulers to set cron job.
Cron settings in Moodle
An admin can set cron execution via command line only or a cron password for remote access in Administration > Site administration > Security > Site policies.
Remote cron
Using the 'web based' version of cron it is perfectly ok to place the cron process on a different machine to the Moodle server. For example, the cron service on a Unix server can invoke the cron web 'page' on a Windows based Moodle server.
Scheduling tasks
An administrator can schedule cron tasks very precisely from Administration > Site administration > Server > Scheduled tasks, see Scheduled tasks
Running cron for several Moodle servers
- Tasks can run in parallel and processes use locking to prevent tasks from running at the same time which allows cron to be triggered from multiple web servers that serve the same Moodle instance.
- If you are running different Moodle instances on the same server, then each Moodle instance needs a cron job. (Even a single Apache web server can run different Moodle instances on different domains by using its virtual hosts capability https://httpd.apache.org/docs/2.2/vhosts/index.html.)
Debugging Scheduled Tasks
Sometimes, a particular cron task may not be working correctly. In Moodle versions before 2.7 - any cron task that was throwing exceptions would prevent the rest of cron from running. The only way to monitor if cron was completing each time, was to add some automated checking of the output of running cron (e.g. searching for the string "Cron completed at ").
In Moodle 2.7 and later, a single failing scheduled task will not prevent the remaining tasks from completing. When any single scheduled task fails, it is marked as a failure, and scheduled to be reattempted. If the task keeps failing, the next scheduled time will be backed off until it is attempted at most once every 24 hours. But checking the Scheduled tasks admin page, you can see if any task is currently failing (it will have a non-zero fail delay - which is the number of seconds to wait before reattempting a failed task). A simple way to debug a failing task, is to run it immediately using the cli scheduled task runner and monitor the output.
See also
Forum discussions:
