Log a message in Magento 2.

magento2-logger.php

<?php

$om = \Magento\Framework\App\ObjectManager::getInstance();
$logger = $om->get(\Psr\Log\LoggerInterface::class);

$logger->emergency('message');
$logger->alert('message');
$logger->critical('message');
$logger->error('message');
$logger->warning('message');
$logger->notice('message');
$logger->info('message');
$logger->debug('message');

/**
 * Psr\Log\LogLevel::EMERGENCY
 * Psr\Log\LogLevel::ALERT
 * Psr\Log\LogLevel::CRITICAL
 * Psr\Log\LogLevel::ERROR
 * Psr\Log\LogLevel::WARNING
 * Psr\Log\LogLevel::NOTICE
 * Psr\Log\LogLevel::INFO
 * Psr\Log\LogLevel::DEBUG
 */
$logger->log(Psr\Log\LogLevel::DEBUG, 'message');