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Magento logging in more detail

Monolog

Magento 2 complies with the PSR-3 standard. By default, Magento uses Monolog. Monolog implemented as a preference for Psr\Log\LoggerInterface in the Magento application di.xml.

Monolog is a popular PHP logging solution with a wide range of handlers that enable you to build advanced logging strategies. Following is a summary of how Monolog works.

A Monolog logger is a channel that has its own set of handlers. Monolog has a large number of handlers, including:

  • Log to files and syslog
  • Send alerts and e-mails
  • Log specific servers and networked logging
  • Logging in development (integration with FireBug and Chrome Logger, among others)
  • Log to the database

Each handler can either process the input message and stop propagation or pass the control to the next handler in a chain.

Log messages can be processed in many different ways. For example, you can store all debug information into a file on disk, put the messages with higher log levels into a database, and finally send messages with log level “critical” by e-mail.

Other channels can have a different set of handlers and logic.

Get started with logging

To start working with a logger, you must create an instance of \Psr\Log\LoggerInterface. With this interface, you can call the following functions to write data to log files:

One way to do that is illustrated in the database logging example.

Another way follows:

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class SomeModel
 {
     private $logger;

     public function __construct(\Psr\Log\LoggerInterface $logger)
     {
         $this->logger = $logger;
     }

     public function doSomething()
     {
         try {
             //do something
         } catch (\Exception $e) {
             $this->logger->critical('Error message', ['exception' => $e]);
         }
     }
 }

The preceding example shows that SomeModel receives a \Psr\Log\LoggerInterface object using constructor injection. In a method doSomething, if some error occurred, it is logged to a method critical ($this->logger->critical($e);).

RFC 5424 defines eight log levels (debug, info, notice, warning, error, critical, alert, and emergency).

Next step

Example—logging database activity