CiviCRM relies on a number of scheduled jobs that are run on a regular basis to keep data up to date and to perform certain tasks. These jobs must be triggered by a cron that runs regularly on your web hosting server.
Examples of scheduled jobs include:
Some jobs need to be run very frequently, for example the email send task tends to be run once every 5 or 10 minutes. Others need to be run less frequency, for example the membership update script may be run just once a day.
There are two ways of configuring scheduled jobs:
These methods are discussed below.
Cron (think "cronology" or "cronograph") is a time-based automatic scheduler that triggers certain programs to run on your web server. Generally speaking, cron (also known as 'a cronjob') can be setup in your web hosting control panel or configured by the server administrator in charge of your web hosting. We recommend choosing web hosting that offers cron as a free service.
Before scheduled jobs configured via the user interface will actually work you will need to configure a web server CRON job. There are CRON configuration examples found in the Running Command-line Scripts via URL wiki page.
The user interface for scheduled tasks is designed to make it easy for people to set up scheduled jobs, and avoid having to create or edit a cron job each time you want to make a change to a scheduled job. Most smaller installations should be fine configuring and running scheduled jobs via the user interface. Larger sites should consider creating cron jobs in the normal way for each task. That requires some system administration skills.
The Scheduled Jobs page (Administer> System Settings > Scheduled Jobs) is designed to make it easy to set up scheduled jobs and to monitor when they were last run. It shows a list of all scheduled jobs and you can edit each one and set its frequency (hourly, daily or every time the scheduled job is run - typically this is set as every 5-10 minutes) and also any relevant parameters.
You can find an up to date list of all scheduled jobs and the parameters that can be sent to them on Managing Scheduled Jobs wiki page.
Some jobs perform special data update tasks and are not designed to be run automatically or repeatedly. These are: "Update Greetings and Addressees" and "Set Renewal Reminder Dates". Details about when to run them are provided on the Managing Scheduled Jobs wiki page.
The scheduled jobs page can also be used to run scheduled jobs on a one off basis. This is useful for some of the scheduled jobs that are designed to be run on a less regular basis, including the geo-coding job and the greetings and addressees job. Execute a job manually by clicking the More > Execute Now link for the given job at Administer > System Settings > Scheduled Jobs.
System administrators more commonly talk about scheduled jobs as cron jobs. If you run a lot of scheduled jobs on large data sets you may wish to consider getting an experienced system administrator to set these up using cron. This will allow more granular control over when and how these jobs are executed, which may be useful if these processes put significant load on your server.
Note scheduled jobs that were run via an individual cron job directly do not automatically appear here. They need to be configured to do so. Details on triggering specific jobs via command-line, URL, Drush and other methods can be found in the Managing Scheduled Jobs wiki page.