private function verifyCommand() {
        $process = new Process('which cracklib-check');
        $process->setTimeout(10);
        $process->run();

        if ($process->isSuccessful()) {
            return trim($process->getOutput() );
        }

        $process = new Process('whereis cracklib-check');
        $process->setTimeout(10);
        $process->run();

        if ($process->isSuccessful()) {
            return preg_replace('/cracklib-check: ([^ ]*) .*/', '$1', trim($process->getOutput() ) );
        }

        throw new RuntimeException('Unable to find cracklib-check command, please install cracklib-check');
    }