Why pcntl_fork() not defined in Laravel Controller?

I have Controller:

class HomeController extends Controller
{
    /**
     * Create a new controller instance.
     *
     * @return void
     */
    public function __construct(){}

    public function index()
    {
        pcntl_fork();
    }
}

Then I call index() by HTTP request, And I get:

Symfony \ Component \ Debug \ Exception \ FatalThrowableError (E_ERROR)
Call to undefined function App\Http\Controllers\pcntl_fork()

Then I try this:

class CodeSheet extends Command
{
    /**
     * The name and signature of the console command.
     *
     * @var string
     */
    protected $signature = 'code_sheet';

    /**
     * The console command description.
     *
     * @var string
     */
    protected $description = 'Command description';

    /**
     * Create a new command instance.
     *
     * @return void
     */
    public function __construct()
    {
        parent::__construct();
    }

    /**
     * Execute the console command.
     *
     * @return mixed
     */
    public function handle()
    {
        pcntl_fork();
        echo "1\n";
    }
}

Then I call this command:

vagrant@homestead:~$ php artisan code_sheet
1
1

So my question is, Why I can call pcntl_fork() in command, but can't in HTTP request?

The PCNTL extension is disabled in web environments (it probably even only compiles for the CLI SAPI), this has nothing to do with Laravel.

The reason for that is simple - the web server itself (or PHP-FPM) is in control of process management, so using this extension would create a conflict with it.

It's also not available under Windows as it's a UNIX-specific thing.