<?php

namespace Oro\Bundle\DistributionBundle\DependencyInjection;

use Symfony\Component\Config\Definition\Builder\TreeBuilder;
use Symfony\Component\Config\Definition\ConfigurationInterface;

class Configuration implements ConfigurationInterface
{
    /**
     * {@inheritDoc}
     */
    public function getConfigTreeBuilder()
    {
        $treeBuilder = new TreeBuilder();
        $treeBuilder->root('oro_distribution')
            ->children()
                ->scalarNode('entry_point')
                    ->beforeNormalization()
                        ->ifNull()
                        ->then(
                            function () {
                                return 'install.php';
                            }
                        )
                    ->end()
                ->end()
            ->end();

        return $treeBuilder;
    }
}

<?php

namespace Oro\Bundle\DistributionBundle\DependencyInjection;

use Symfony\Component\Config\Definition\Builder\TreeBuilder;
use Symfony\Component\Config\Definition\ConfigurationInterface;

class Configuration implements ConfigurationInterface
{
    /**
     * {@inheritDoc}
     */
    public function getConfigTreeBuilder()
    {
        $treeBuilder = new TreeBuilder();
        $treeBuilder->root('oro_distribution')
            ->children()
                ->scalarNode('entry_point')
                    ->beforeNormalization()
                        ->ifNull()
                        ->then(
                            function () {
                                return '/install.php';
                            }
                        )
                    ->end()
                ->end()
            ->end();

        return $treeBuilder;
    }
}

--- 
+++ 
@@ -20,7 +20,7 @@
                         ->ifNull()
                         ->then(
                             function () {
-                                return '/install.php';
+                                return 'install.php';
                             }
                         )
                     ->end()
BAP-3835: Package Manager does not take in account root folder
