source
Cron is a daemon that executes commands at specified intervals. These
commands are called "cron jobs." Cron is available on Unix, Linux and
Mac servers. Windows servers use a Scheduled Task to execute commands.
For a modest personal site, you might set up this cron job to run once a day. For a more active site you might want to run that job more often—perhaps every few hours or every hour. This regular visit will tell Drupal to perform its periodic tasks, and this will help keep your system running smoothly.
There is a video, How To: Setting up Drupal's Cron that talks about cron and shows various ways of configuring it.
In the above sample, the
The rest of the line basically tells the server to request the url http://www.example.com/cron.php, so that the server executes the cron.php script. NOTE: The -O is "dash capital letter O", not "dash zero". Yes, the capital O is important. Lowercase o won't work
In Drupal 7, a secure private URL is generated to run the cron job. This URL is available in the Administration > Reports > Status page in the cron maintenance tasks.
The URL is something like:
http://www.example.com/cron.php?cron_key=y85HnNQxjdqM-deRXj2Xrp2MJumqe1H...
Replace any reference to http://www.example.com/cron.php with your secure private URL if you use Drupal 7.
Here is a diagram of the general crontab syntax, for illustration:
Thus, the cron command example above means "ping http://www.example.com/cron.php at the zero minute on every hour of every day of every month of every day of the week."
For instance, if your site were www.example.com, loading the URL http://www.example.com/cron.php in your browser would run the maintenance.
This page is automatically set up when you install Drupal. Simply loading the URL will run the maintenance. Nothing more is required.
In order to schedule your cron job in Plesk for Linux, go to Settings > Scheduled Tasks in the General Group. Select the system user account on whose behalf the task will be executed (usually the domain ftp user). Click "Schedule New Task". Specify when to run your command. You can schedule the time using the UNIX crontab entry form as specified in this article. Then, specify which command to run, using the same format as specified in this article. Then, Click OK.
Otherwise, check with your hosting company for detailed instructions if you are using a web-based control panel.
To edit a crontab through the command line, type:
If this fails, see the Troubleshooting Cron section below.
Add ONE of the following lines:
This would have a lynx, wget, or curl visit your cron page 45 minutes after every hour.
Three options are provided in case either wget, lynx or curl are not installed on the server. Any will do the job well.
Learn more about the crontab file syntax here to set up the cron job to run more or less often.
There are many ways to configure a cron job. If you have full access to crontab features, you should be able to simply paste in one of the above example commands – be sure to replace "example.com" with your own web domain or docroot.
If you're on shared hosting, you should be able to find cron job configuration somewhere in your hosting control panel. Some hosts even have cron "wizards" that walk you through the cron configuration, making it much easier if cron is new to you. On a Windows system you can accomplish the same thing with scheduled tasks to launch Internet Explorer pointed to the URL.
Some hosting companies do not permit local loopback, so using wget, curl or lynx will not work. If this is the case, and they run PHP as a CGI (check with your hosting company to see if this is the case), the following will run the cron locally:-
If you receive a permission denied error after starting crontab -e, you may need to use sudo:
You may need to adjust the path to wget, lynx or curl in your crontab. For example, the cron example listed above contains the line:
However, Lynx may be in a different location on your server, or not installed at all. To find out where Lynx is installed, enter:
or
If it is not located at /usr/bin/lynx, adjust the path as needed. The same applies for wget and curl. If none are installed, ask a server administrator for help.
It may be necessary to change http://example.com/cron.php to the location of your Drupal installation. For example, if you have Drupal installed in a subdirectory, it might be http://www.example.com/drupal/cron.php).
Note that the scripts will need to be updated with the path to your directory and URL.
You should set up crontab to run your cron tasks as the same user that runs the web server; for example, if you run your webserver as the user www-data:
More info http://drush.ws/docs/cron.html
Note that http://default/cron.php is NOT shown as an example, it should be used as is, without changes.
Taking this approach allows cron.php to be blocked to prevent remote access.
To block remote access to cron.php, in the server's .htaccess file or vhost configuration file add this section:
If you take this approach and use drupal.sh to call cron.php, it is
probably best not to use the root user to run the cron job. A
non-privileged user account, or the Apache account user, for example
http-service or www-data, is a better choice. To do so, call crontab -e
when logged in as a non-privileged user, or for the Apache account on a
Debian server, for example, you can add a user parameter:
The downside to this method is that any URLs generated by cron jobs using this method will not be properly formed, starting with "http://default/".
Then place multiple individual files into the /etc/cron.5min directory, one for each site. The files can be named "site1", "site2", etc. -- note that run-parts may fail to detect files which contain a dot (.) in their name. To make sure that all of your files are visible to cron, type this at a shell prompt:
and make sure that all of your files are listed.
Each of the files in /etc/cron.5min should contain one line:
or, alternatively, one of the curl or wget commands specified above.
If this doesn't work, try putting another line at the start of each file:
and make sure that the files are executable by doing
For more information about using cron in a multisite configuration, see the Multisite Cron section of this guide.
For a modest personal site, you might set up this cron job to run once a day. For a more active site you might want to run that job more often—perhaps every few hours or every hour. This regular visit will tell Drupal to perform its periodic tasks, and this will help keep your system running smoothly.
There is a video, How To: Setting up Drupal's Cron that talks about cron and shows various ways of configuring it.
The cron command
In the following example, the crontab command shown below will activate the cron tasks automatically on the hour:0 * * * * wget -O - -q -t 1 http://www.example.com/cron.phpIn the above sample, the
0 * * * * represents when the
task should happen. The first figure represents minutes – in this case,
on the "zero" minute, or top of the hour. (If the number were, say, 10,
then the action would take place at 10 minutes past the hour.) The other
figures represent, respectively, hour, day, month and day of the week. A
* is a wildcard, meaning "every time."The rest of the line basically tells the server to request the url http://www.example.com/cron.php, so that the server executes the cron.php script. NOTE: The -O is "dash capital letter O", not "dash zero". Yes, the capital O is important. Lowercase o won't work
In Drupal 7, a secure private URL is generated to run the cron job. This URL is available in the Administration > Reports > Status page in the cron maintenance tasks.
The URL is something like:
http://www.example.com/cron.php?cron_key=y85HnNQxjdqM-deRXj2Xrp2MJumqe1H...
Replace any reference to http://www.example.com/cron.php with your secure private URL if you use Drupal 7.
Here is a diagram of the general crontab syntax, for illustration:
# +---------------- minute (0 - 59)
# | +------------- hour (0 - 23)
# | | +---------- day of month (1 - 31)
# | | | +------- month (1 - 12)
# | | | | +---- day of week (0 - 7) (Sunday=0 or 7)
# | | | | |
* * * * * command to be executedHow Drupal uses cron
Every Drupal install requires regular actions to handle maintenance tasks such as cleaning up log files and checking for updates. Cron.php is the file that Drupal uses to run the maintenance process.For instance, if your site were www.example.com, loading the URL http://www.example.com/cron.php in your browser would run the maintenance.
This page is automatically set up when you install Drupal. Simply loading the URL will run the maintenance. Nothing more is required.
How to set up a cron job
Cron jobs are scheduled by setting up a "crontab." A crontab is a text file that contains the commands to be run. This file can be created and edited either through the command line interface, or, if you manage your website through a web-based control panel such as cpanel or Plesk, you will use the web interface.In order to schedule your cron job in Plesk for Linux, go to Settings > Scheduled Tasks in the General Group. Select the system user account on whose behalf the task will be executed (usually the domain ftp user). Click "Schedule New Task". Specify when to run your command. You can schedule the time using the UNIX crontab entry form as specified in this article. Then, specify which command to run, using the same format as specified in this article. Then, Click OK.
Otherwise, check with your hosting company for detailed instructions if you are using a web-based control panel.
To edit a crontab through the command line, type:
crontab -eIf this fails, see the Troubleshooting Cron section below.
Add ONE of the following lines:
45 * * * * /usr/bin/lynx -source http://example.com/cron.php
45 * * * * /usr/bin/wget -O - -q -t 1 http://www.example.com/cron.php
45 * * * * curl --silent --compressed http://example.com/cron.php Three options are provided in case either wget, lynx or curl are not installed on the server. Any will do the job well.
Learn more about the crontab file syntax here to set up the cron job to run more or less often.
There are many ways to configure a cron job. If you have full access to crontab features, you should be able to simply paste in one of the above example commands – be sure to replace "example.com" with your own web domain or docroot.
If you're on shared hosting, you should be able to find cron job configuration somewhere in your hosting control panel. Some hosts even have cron "wizards" that walk you through the cron configuration, making it much easier if cron is new to you. On a Windows system you can accomplish the same thing with scheduled tasks to launch Internet Explorer pointed to the URL.
Some hosting companies do not permit local loopback, so using wget, curl or lynx will not work. If this is the case, and they run PHP as a CGI (check with your hosting company to see if this is the case), the following will run the cron locally:-
/usr/bin/php /home/sites/example.com/public_html/cron.phpSome hosting companies don’t allow access to cron
If your hosting company restricts access to cron, you have many options.- Ask the company to give you access, or to set up a cron job for you
- Ask someone else with access to a server to set up a cron job for you. Any Unix, Linux, or Mac server with access to the internet can have a cron job to regularly visit your site. There are also some companies that offer cron services.
- Use the Poor Man's Cron module.
- Find an online cron service. Many are free but with restrictions.
Troubleshooting cron jobs
Make sure your web site is not in maintenance mode.If you receive a permission denied error after starting crontab -e, you may need to use sudo:
sudo crontab -eYou may need to adjust the path to wget, lynx or curl in your crontab. For example, the cron example listed above contains the line:
45 * * * * /usr/bin/lynx -source http://example.com/cron.php However, Lynx may be in a different location on your server, or not installed at all. To find out where Lynx is installed, enter:
whereis lynxor
which lynxIf it is not located at /usr/bin/lynx, adjust the path as needed. The same applies for wget and curl. If none are installed, ask a server administrator for help.
It may be necessary to change http://example.com/cron.php to the location of your Drupal installation. For example, if you have Drupal installed in a subdirectory, it might be http://www.example.com/drupal/cron.php).
Example scripts
Drupal ships with two example scripts in the scripts directory, cron-curl.sh and cron-lynx.sh. You can call these scripts from cron as well:45 * * * * /home/www/drupal/scripts/cron-lynx.shNote that the scripts will need to be updated with the path to your directory and URL.
Running cron as an authenticated user
#!/bin/sh
# Reference http://drupal.org/node/479948#comment-1673488 by pearlbear
SITE=https://dev.example.com/
USERNAME=user.name
PASS=ChangeMe!!12
COOKIES=/tmp/cron-cookies.txt
WGETPARAMS="--quiet -O /dev/null --no-check-certificate --save-cookies $COOKIES --keep-session-cookies --load-cookies $COOKIES"
# if you run drupal in a default language different than English you need to modify this
LOGIN="Log%20in"
wget $WGETPARAMS "${SITE}user"
wget $WGETPARAMS --post-data="name=$USERNAME&pass=$PASS&op=$LOGIN&form_id=user_login" "${SITE}user"
wget $WGETPARAMS " ${SITE}cron.php"Running Drupal cron tasks from Drush
If you just want to get started quickly, here is a crontab entry that will run cron once every hour at ten minutes after the hour:10
* * * * /usr/bin/env
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
COLUMNS=72 /usr/local/drush/drush --root=/path/to/your/drupalroot
--uri=your.drupalsite.org --quiet cron You should set up crontab to run your cron tasks as the same user that runs the web server; for example, if you run your webserver as the user www-data:
sudo -u www-data crontab -e More info http://drush.ws/docs/cron.html
Security notes
It is possible to run cron.php directly via scripts/drupal.sh with Drupal 6. Drupal.sh allows a Drupal page to be executed from a shell script. To do so, add the following cron job to run as the Apache user:/full/path/to/drupal.sh --root /full/path/to/site/root/ http://default/cron.phpNote that http://default/cron.php is NOT shown as an example, it should be used as is, without changes.
Taking this approach allows cron.php to be blocked to prevent remote access.
To block remote access to cron.php, in the server's .htaccess file or vhost configuration file add this section:
<Files cron.php>
Order Deny,Allow
Deny from all
Allow from localhost
Allow from 127.0.0.1
Allow from xx.xx.xx.xx <-- your IP address
</Files>sudo crontab -e -u www-dataThe downside to this method is that any URLs generated by cron jobs using this method will not be properly formed, starting with "http://default/".
Multiple sites
If you run many sites, you can use this tip to make managing your cron jobs easier. To minimize the clutter, create an /etc/cron.5min directory and have crontab read this directory every five minutes.*/5 * * * * root run-parts /etc/cron.5minThen place multiple individual files into the /etc/cron.5min directory, one for each site. The files can be named "site1", "site2", etc. -- note that run-parts may fail to detect files which contain a dot (.) in their name. To make sure that all of your files are visible to cron, type this at a shell prompt:
$ sudo run-parts --test /etc/cron.5minand make sure that all of your files are listed.
Each of the files in /etc/cron.5min should contain one line:
/usr/bin/lynx -source http://(full site URL)/cron.php > /dev/null 2>&1or, alternatively, one of the curl or wget commands specified above.
If this doesn't work, try putting another line at the start of each file:
#!/bin/shand make sure that the files are executable by doing
$ sudo chmod u+x /etc/cron.5min/*
For more information about using cron in a multisite configuration, see the Multisite Cron section of this guide.
SSL
When using SSL, add one additional argument when calling wget: --no-check-certificate. Do not put “--no-check-certificate” between the -0 and the -.45 * * * * /usr/bin/wget --no-check-certificate --quiet -O - https://example.com/cron.phpConfiguring an editor for cron
You can specify which text editor (emacs, vi, nano, etc.) you want to use to edit the crontab. To tell the system which editor you want to use, type:export EDITOR=nano
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