Symfony integrates seamlessly with Monolog, the most popular PHP logging library, to create and store log messages in a variety of different places.
In applications using :doc:`Symfony Flex </setup/flex>`, run this command to install the Monolog based logger before using it:
$ composer require symfony/monolog-bundle
If the application uses the :ref:`default services.yaml configuration <service-container-services-load-example>`,
you can get the logger service injecting the LoggerInterface class:
use Psr\Log\LoggerInterface;
public function index(LoggerInterface $logger)
{
$logger->info('I just got the logger');
$logger->error('An error occurred');
$logger->critical('I left the oven on!', array(
// include extra "context" info in your logs
'cause' => 'in_hurry',
));
// ...
}
The logger service has different methods for different logging levels/priorities. You can configure the logger to do different things based on the level of a message (e.g. :doc:`send an email when an error occurs </logging/monolog_email>`).
See LoggerInterface for a list of all of the methods on the logger.
By default, log entries are written to the var/log/dev.log file when you're in
the dev environment. In the prod environment, logs are written to var/log/prod.log,
but only during a request where an error or high-priority log entry was made
(i.e. error() , critical(), alert() or emergency()).
To control this, you'll configure different handlers that handle log entries, sometimes modify them, and ultimately store them.
The logger has a stack of handlers, and each can be used to write the log entries to different locations (e.g. files, database, Slack, etc).
Tip
You can also configure logging "channels", which are like categories. Each channel can have its own handlers, which means you can store different log messages in different places. See :doc:`/logging/channels_handlers`.
Symfony pre-configures some basic handlers in the default monolog.yaml
config files. Check these out for some real-world examples.
This example uses two handlers: stream (to write to a file) and syslog
to write logs using the :phpfunction:`syslog` function:
.. configuration-block::
.. code-block:: yaml
# config/packages/prod/monolog.yaml
monolog:
handlers:
# this "file_log" key could be anything
file_log:
type: stream
# log to var/log/(environment).log
path: "%kernel.logs_dir%/%kernel.environment%.log"
# log *all* messages (debug is lowest level)
level: debug
syslog_handler:
type: syslog
# log error-level messages and higher
level: error
.. code-block:: xml
<!-- config/packages/prod/monolog.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:monolog="http://symfony.com/schema/dic/monolog"
xsi:schemaLocation="http://symfony.com/schema/dic/services
http://symfony.com/schema/dic/services/services-1.0.xsd
http://symfony.com/schema/dic/monolog
http://symfony.com/schema/dic/monolog/monolog-1.0.xsd">
<monolog:config>
<monolog:handler
name="file_log"
type="stream"
path="%kernel.logs_dir%/%kernel.environment%.log"
level="debug"
/>
<monolog:handler
name="syslog_handler"
type="syslog"
level="error"
/>
</monolog:config>
</container>
.. code-block:: php
// config/packages/prod/monolog.php
$container->loadFromExtension('monolog', array(
'handlers' => array(
'file_log' => array(
'type' => 'stream',
'path' => '%kernel.logs_dir%/%kernel.environment%.log',
'level' => 'debug',
),
'syslog_handler' => array(
'type' => 'syslog',
'level' => 'error',
),
),
));
This defines a stack of handlers and each handler is called in the order that it's defined.
Instead of writing log files somewhere, some handlers are used to filter or modify
log entries before sending them to other handlers. One powerful, built-in handler
called fingers_crossed is used in the prod environment by default. It stores
all log messages during a request but only passes them to a second handler if
one of the messages reaches an action_level. Take this example:
.. configuration-block::
.. code-block:: yaml
# config/packages/prod/monolog.yaml
monolog:
handlers:
filter_for_errors:
type: fingers_crossed
# if *one* log is error or higher, pass *all* to file_log
action_level: error
handler: file_log
# now passed *all* logs, but only if one log is error or higher
file_log:
type: stream
path: "%kernel.logs_dir%/%kernel.environment%.log"
# still passed *all* logs, and still only logs error or higher
syslog_handler:
type: syslog
level: error
.. code-block:: xml
<!-- config/packages/prod/monolog.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:monolog="http://symfony.com/schema/dic/monolog"
xsi:schemaLocation="http://symfony.com/schema/dic/services
http://symfony.com/schema/dic/services/services-1.0.xsd
http://symfony.com/schema/dic/monolog
http://symfony.com/schema/dic/monolog/monolog-1.0.xsd">
<monolog:config>
<monolog:handler
name="filter_for_errors"
type="fingers_crossed"
action-level="error"
handler="file_log"
/>
<monolog:handler
name="file_log"
type="stream"
path="%kernel.logs_dir%/%kernel.environment%.log"
level="debug"
/>
<monolog:handler
name="syslog_handler"
type="syslog"
level="error"
/>
</monolog:config>
</container>
.. code-block:: php
// config/packages/prod/monolog.php
$container->loadFromExtension('monolog', array(
'handlers' => array(
'filter_for_errors' => array(
'type' => 'fingers_crossed',
'action_level' => 'error',
'handler' => 'file_log',
),
'file_log' => array(
'type' => 'stream',
'path' => '%kernel.logs_dir%/%kernel.environment%.log',
'level' => 'debug',
),
'syslog_handler' => array(
'type' => 'syslog',
'level' => 'error',
),
),
));
Now, if even one log entry has an error level or higher, then all log entries
for that request are saved to a file via the file_log handler. That means that
your log file will contain all the details about the problematic request - making
debugging much easier!
Tip
The handler named "file_log" will not be included in the stack itself as
it is used as a nested handler of the fingers_crossed handler.
Note
If you want to override the monolog configuration via another config
file, you will need to redefine the entire handlers stack. The configuration
from the two files cannot be merged because the order matters and a merge does
not allow to control the order.
Monolog comes with many built-in handlers for emailing logs, sending them to Loggly, or notifying you in Slack. These are documented inside of MonologBundle itself. For a full list, see Monolog Configuration.
Over time, log files can grow to be huge, both while developing and on production. One best-practice solution is to use a tool like the logrotate Linux command to rotate log files before they become too large.
Another option is to have Monolog rotate the files for you by using the
rotating_file handler. This handler creates a new log file every day
and can also remove old files automatically. To use it, just set the type
option of your handler to rotating_file:
.. configuration-block::
.. code-block:: yaml
# config/packages/prod/monolog.yaml
monolog:
handlers:
main:
type: rotating_file
path: '%kernel.logs_dir%/%kernel.environment%.log'
level: debug
# max number of log files to keep
# defaults to zero, which means infinite files
max_files: 10
.. code-block:: xml
<!-- config/packages/prod/monolog.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:monolog="http://symfony.com/schema/dic/monolog"
xsi:schemaLocation="http://symfony.com/schema/dic/services
http://symfony.com/schema/dic/services/services-1.0.xsd
http://symfony.com/schema/dic/monolog
http://symfony.com/schema/dic/monolog/monolog-1.0.xsd">
<monolog:config>
<!-- "max_files": max number of log files to keep
defaults to zero, which means infinite files -->
<monolog:handler name="main"
type="rotating_file"
path="%kernel.logs_dir%/%kernel.environment%.log"
level="debug"
max-files="10"
/>
</monolog:config>
</container>
.. code-block:: php
// config/packages/prod/monolog.php
$container->loadFromExtension('monolog', array(
'handlers' => array(
'main' => array(
'type' => 'rotating_file',
'path' => '%kernel.logs_dir%/%kernel.environment%.log',
'level' => 'debug',
// max number of log files to keep
// defaults to zero, which means infinite files
'max_files' => 10,
),
),
));
If you want to use in your own services a pre-configured logger which uses a
specific channel (app by default), use the monolog.logger tag with the
channel property as explained in the
:ref:`Dependency Injection reference <dic_tags-monolog>`.
Monolog also supports processors: functions that can dynamically add extra information to your log entries.
See :doc:`/logging/processors` for details.
.. toctree::
:maxdepth: 1
logging/monolog_email
logging/channels_handlers
logging/formatter
logging/processors
logging/monolog_exclude_http_codes
logging/monolog_console
.. toctree::
:hidden:
logging/monolog_regex_based_excludes