Logging

The main logging mechanism in Drupal is a database log through which client code can use an API to save messages into the watchdog table. The messages in there are cleared after they reach a certain number, but meanwhile, they can be viewed in the browser via a handy interface (at admin/reports/dblog):

Figure 3.1: Viewing Recent log messages

Alternatively, a core module that is disabled by default, Syslog, can be used to complement/replace this logging mechanism with the Syslog of the server the site is running on. For the purposes of this book, we will focus on how logging works with any mechanism, but we will also take a look at how we can implement our own logging system.

Drupal 7 developers are very familiar with the watchdog() function, which they use for logging their messages. This is a procedural API for logging that exposes a simple function that takes some parameters:

• $type – the category of the message
• $message –...