开启Gii

config/web.php:

$config = [ ... ];

if (YII_ENV_DEV) {
    $config['bootstrap'][] = 'gii';
    $config['modules']['gii'] = 'yii\gii\Module';
}

在web/index.php中设置YII_ENV_DEV:

defined('YII_ENV') or define('YII_ENV', 'dev');

如果是从非localhost访问需要在配置文件中作如下设置:

'gii' => [
    'class' => 'yii\gii\Module',
    'allowedIPs' => ['127.0.0.1', '::1', '192.168.0.*', '192.168.178.20'] // adjust this to your needs
],

测试:

http://hostname/index.php?r=gii