Composer update creates a lack of memory

While using Symfony 2 it’s common that you have to run the command composer update. Sometimes we’re graced with the error: The following exception is caused by a lack of memory and not having swap configured PHP Fatal error: Uncaught exception 'ErrorException' with message 'proc_open(): fork failed - Cannot allocate memory' in phar:///usr/local/bin/composer/vendor/symfony/console/Application.php:954 Stack trace: