The default implementation of the \Psr\Log\LoggerInterface is \Magento\Framework\Logger\Monolog

[dmitrii_fediuk]

https://github.com/magento/magento2/blob/8fd3e8/app/etc/di.xml#L9-L9

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https://github.com/magento/magento2/blob/8fd3e8/lib/internal/Magento/Framework/Logger/Monolog.php#L7-L11

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https://github.com/magento/magento2/blob/8fd3e8/composer.json#L38-L38

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https://github.com/Seldaek/monolog/blob/1.16.0/composer.json#L17-L17

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https://github.com/Seldaek/monolog/blob/1.16.0/src/Monolog/Logger.php#L19-L27

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https://github.com/php-fig/log/blob/1.0.0/Psr/Log/LoggerInterface.php#L3-L20

[dmitrii_fediuk]

See also:

• How does \Magento\Framework\Logger\Monolog::critical() work?
• How does \Magento\Framework\Logger\Monolog::addRecord() work?
• The exceptions are loggged into the var/log/exception.log file
• The non-exceptional messages are loggged into the var/log/system.log file
• The debug messages are logged into the var/log/debug.log file
• How to write a message to a log file?