A simple example of executing a background process with php.

gistfile1.php

<?php

    exec(
        sprintf(
            'cd "%s" && %s "%s" install > "%s" 2>&1 & echo $! >> "%s"',
            __DIR__,
            '/usr/bin/php',
            __DIR__ . '/bin/composer.phar',
            __DIR__ . '/var/log/composer-' . date('dmY-His') . '.log',
            __DIR__ . '/var/run/composer.pid'
        )
    );