Logging
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Read the updated version of this page for Symfony 7.1 (the current stable version).
Symfony comes with a minimalist PSR-3 logger: Logger.
In conformance with the twelve-factor app methodology, it sends messages starting from the
WARNING
level to stderr.
The minimal log level can be changed by setting the SHELL_VERBOSITY
environment variable:
SHELL_VERBOSITY value |
Minimum log level |
---|---|
-1 |
ERROR |
1 |
NOTICE |
2 |
INFO |
3 |
DEBUG |
The minimum log level, the default output and the log format can also be changed by passing the appropriate arguments to the constructor of Logger. To do so, override the "logger" service definition.
Logging a Message
To log a message, inject the default logger in your controller:
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use Psr\Log\LoggerInterface;
public function indexAction(LoggerInterface $logger)
{
// alternative way of getting the logger
// $logger = $this->get('logger');
$logger->info('I just got the logger');
$logger->error('An error occurred');
$logger->critical('I left the oven on!', [
// include extra "context" info in your logs
'cause' => 'in_hurry',
]);
// ...
}
The logger
service has different methods for different logging levels/priorities.
See LoggerInterface for a list of all of the methods on the logger.
Monolog
Symfony integrates seamlessly with Monolog, the most popular PHP logging library, to create and store log messages in a variety of different places and trigger various actions.
For instance, using Monolog you can configure the logger to do different things based on the level of a message (e.g. send an email when an error occurs).
Run this command to install the Monolog based logger before using it:
1
$ composer require symfony/monolog-bundle
The following sections assume that Monolog is installed.
Where Logs are Stored
The configuration for where logs are stored lives in the specific
environment configuration files: config_dev.yml
and config_prod.yml
.
By default, log entries are written to the var/logs/dev.log
file when you're in
the dev
environment. In the prod
environment, logs are written to var/logs/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.
Handlers: Writing Logs to different Locations
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 How to Log Messages to different Files.
Symfony pre-configures some basic handlers in the config_dev.yml
and config_prod.yml
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 syslog function:
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# app/config/config.yml
monolog:
handlers:
# this "file_log" key could be anything
file_log:
type: stream
# log to var/logs/(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
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<!-- app/config/config.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
https://symfony.com/schema/dic/services/services-1.0.xsd
http://symfony.com/schema/dic/monolog
https://symfony.com/schema/dic/monolog/monolog-1.0.xsd">
<monolog:config>
<!-- this "file_log" key could be anything -->
<monolog:handler name="file_log"
type="stream"
path="%kernel.logs_dir%/%kernel.environment%.log"
level="debug"/><!-- log *all* messages (debug is lowest level) -->
<monolog:handler name="syslog_handler"
type="syslog"
level="error"/><!-- log error-level messages and higher -->
</monolog:config>
</container>
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// app/config/config.php
$container->loadFromExtension('monolog', [
'handlers' => [
// this "file_log" key could be anything
'file_log' => [
'type' => 'stream',
// log to var/logs/(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',
],
],
]);
This defines a stack of handlers and each handler is called in the order that it's defined.
Handlers that Modify Log Entries
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:
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# app/config/config.yml
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
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<!-- app/config/config.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
https://symfony.com/schema/dic/services/services-1.0.xsd
http://symfony.com/schema/dic/monolog
https://symfony.com/schema/dic/monolog/monolog-1.0.xsd">
<monolog:config>
<!-- if *one* log is error or higher, pass *all* to file_log -->
<monolog:handler name="filter_for_errors"
type="fingers_crossed"
action-level="error"
handler="file_log"
/>
<!-- now passed *all* logs, but only if one log is error or higher -->
<monolog:handler name="file_log"
type="stream"
path="%kernel.logs_dir%/%kernel.environment%.log"
level="debug"
/>
<!-- still passed *all* logs, and still only logs error or higher -->
<monolog:handler name="syslog_handler"
type="syslog"
level="error"
/>
</monolog:config>
</container>
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// app/config/config.php
$container->loadFromExtension('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',
'level' => 'debug',
],
// still passed *all* logs, and still only logs error or higher
'syslog_handler' => [
'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.
All Built-in Handlers
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.
How to Rotate your Log Files
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
:
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# app/config/config_dev.yml
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
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<!-- app/config/config_dev.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
https://symfony.com/schema/dic/services/services-1.0.xsd
http://symfony.com/schema/dic/monolog
https://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>
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// app/config/config_dev.php
$container->loadFromExtension('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,
],
],
]);
Using a Logger inside a Service
To use a logger in your own services, add the @logger
service as an argument
of those services. If you want to use 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
Dependency Injection reference.
Adding extra Data to each Log (e.g. a unique request token)
Monolog also supports processors: functions that can dynamically add extra information to your log entries.
See How to Add extra Data to Log Messages via a Processor for details.
Learn more
- How to Log Messages to different Files
- How to Disable Microseconds Precision (for a Performance Boost)
- How to Define a Custom Logging Formatter
- How to Configure Monolog to Display Console Messages
- How to Configure Monolog to Email Errors
- How to Configure Monolog to Exclude 404 Errors from the Log
- How to Add extra Data to Log Messages via a Processor