Configuring in the Kernel

Some configuration can be done on the kernel class itself (located by default at src/Kernel.php). You can do this by overriding specific methods in the parent Kernel class.

Configuration

In previous Symfony versions there was another configuration option to define the “kernel name”, which is only important when using applications with multiple kernels. If you need a unique ID for your kernels use the kernel.container_class parameter or the Kernel::getContainerClass() method.

Charset

type: string default: UTF-8

This option defines the charset that is used in the application. This value is exposed via the kernel.charset configuration parameter and the getCharset() method.

To change this value, override the getCharset() method and return another charset:

// src/Kernel.php
use Symfony\Component\HttpKernel\Kernel as BaseKernel;
// ...

class Kernel extends BaseKernel
{
    public function getCharset()
    {
        return 'ISO-8859-1';
    }
}

Project Directory

type: string default: the directory of the project composer.json

This returns the absolute path of the root directory of your Symfony project, which is used by applications to perform operations with file paths relative to the project’s root directory.

By default, its value is calculated automatically as the directory where the main composer.json file is stored. This value is exposed via the kernel.project_dir configuration parameter and the getProjectDir() method.

If you don’t use Composer, or have moved the composer.json file location or have deleted it entirely (for example in the production servers), you can override the getProjectDir() method to return the right project directory:

// src/Kernel.php
use Symfony\Component\HttpKernel\Kernel as BaseKernel;
// ...

class Kernel extends BaseKernel
{
    // ...

    public function getProjectDir(): string
    {
        return \dirname(__DIR__);
    }
}

Cache Directory

type: string default: $this->getProjectDir()/var/cache/$this->environment

This returns the absolute path of the cache directory of your Symfony project. It’s calculated automatically based on the current environment.

This value is exposed via the kernel.cache_dir configuration parameter and the getCacheDir() method. To change this setting, override the getCacheDir() method to return the right cache directory.

Log Directory

type: string default: $this->getProjectDir()/var/log

This returns the absolute path of the log directory of your Symfony project. It’s calculated automatically based on the current environment.

This value is exposed via the kernel.logs_dir configuration parameter and the getLogDir() method. To change this setting, override the getLogDir() method to return the right log directory.

Container Build Time

type: string default: the result of executing time()

Symfony follows the reproducible builds philosophy, which ensures that the result of compiling the exact same source code doesn’t produce different results. This helps checking that a given binary or executable code was compiled from some trusted source code.

In practice, the compiled service container of your application will always be the same if you don’t change its source code. This is exposed via these configuration parameters:

  • container.build_hash, a hash of the contents of all your source files;
  • container.build_time, a timestamp of the moment when the container was built (the result of executing PHP’s time function);
  • container.build_id, the result of merging the two previous parameters and encoding the result using CRC32.

Since the container.build_time value will change every time you compile the application, the build will not be strictly reproducible. If you care about this, the solution is to use another configuration parameter called kernel.container_build_time and set it to a non-changing build time to achieve a strict reproducible build:

  • YAML
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    # config/services.yaml
parameters:
    # ...
    kernel.container_build_time: '1234567890'
  • XML
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    <!-- config/services.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://symfony.com/schema/dic/services https://symfony.com/schema/dic/services/services-1.0.xsd">

    <parameters>
        <!-- ... -->
        <parameter key="kernel.container_build_time">1234567890</parameter>
    </parameters>
</container>
  • PHP
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    // config/services.php

// ...
$container->setParameter('kernel.container_build_time', '1234567890');