Q:

Symfony2 post-update-cmd gives "An error occurred when generating the bootstrap file"

I am currently on Symfony2 2.3.7.
When I run the composer update command. In the post-update-cmd a script is run to update symfony2. But it fails:
Script Sensio\Bundle\DistributionBundle\Composer\ScriptHandler::buildBootstrap handling the post-update-cmd event terminated with an exception

  [RuntimeException]                                     
  An error occurred when generating the bootstrap file.  

update [--prefer-source] [--prefer-dist] [--dry-run] [--dev] [--no-dev] [--lock] [--no-plugins] [--no-custom-installers] [--no-scripts] [--no-progress] [--with-dependencies] [-v|vv|vvv|--verbose] [-o|--optimize-autoloader] [packages1] ... [packagesN]

Any idea why this is happening?
I tried to run:
composer update --no-scripts 

.. and that runs fine. The following is also working fine:
php vendor/sensio/distribution-bundle/Sensio/Bundle/DistributionBundle/Resources/bin/build_bootstrap.php

But everytime I try the normal composer update the post script fails.
Running the update with --verbose gives the following:
Script Sensio\Bundle\DistributionBundle\Composer\ScriptHandler::buildBootstrap handling the post-update-cmd event terminated with an exception

  [RuntimeException]                                     
  An error occurred when generating the bootstrap file.                                                      

Exception trace:
 () at C:\xampp\htdocs\forvaltning\vendor\sensio\distribution-bundle\Sensio\Bundle\DistributionBundle\Composer\ScriptHandler.php:203
 Sensio\Bundle\DistributionBundle\Composer\ScriptHandler::executeBuildBootstrap() at C:\xampp\htdocs\forvaltning\vendor\sensio\distribution-bundle\Sensio\Bundle\DistributionBundle\Composer\ScriptHandler.php:43
 Sensio\Bundle\DistributionBundle\Composer\ScriptHandler::buildBootstrap() at phar://C:/ProgramData/Composer/bin/composer.phar/src/Composer/EventDispatcher/EventDispatcher.php:165
 Composer\EventDispatcher\EventDispatcher->executeEventPhpScript() at phar://C:/ProgramData/Composer/bin/composer.phar/src/Composer/EventDispatcher/EventDispatcher.php:138
 Composer\EventDispatcher\EventDispatcher->doDispatch() at phar://C:/ProgramData/Composer/bin/composer.phar/src/Composer/EventDispatcher/EventDispatcher.php:107
 Composer\EventDispatcher\EventDispatcher->dispatchCommandEvent() at phar://C:/ProgramData/Composer/bin/composer.phar/src/Composer/Installer.php:289
 Composer\Installer->run() at phar://C:/ProgramData/Composer/bin/composer.phar/src/Composer/Command/UpdateCommand.php:118
 Composer\Command\UpdateCommand->execute() at phar://C:/ProgramData/Composer/bin/composer.phar/vendor/symfony/console/Symfony/Component/Console/Command/Command.php:244
 Symfony\Component\Console\Command\Command->run() at phar://C:/ProgramData/Composer/bin/composer.phar/vendor/symfony/console/Symfony/Component/Console/Application.php:897
 Symfony\Component\Console\Application->doRunCommand() at phar://C:/ProgramData/Composer/bin/composer.phar/vendor/symfony/console/Symfony/Component/Console/Application.php:191
 Symfony\Component\Console\Application->doRun() at phar://C:/ProgramData/Composer/bin/composer.phar/src/Composer/Console/Application.php:117
 Composer\Console\Application->doRun() at phar://C:/ProgramData/Composer/bin/composer.phar/vendor/symfony/console/Symfony/Component/Console/Application.php:121
 Symfony\Component\Console\Application->run() at phar://C:/ProgramData/Composer/bin/composer.phar/src/Composer/Console/Application.php:83
 Composer\Console\Application->run() at phar://C:/ProgramData/Composer/bin/composer.phar/bin/composer:43
 require() at C:\ProgramData\Composer\bin\composer.phar:15

update [--prefer-source] [--prefer-dist] [--dry-run] [--dev] [--no-dev] [--lock] [--no-plugins] [--no-custom-installers] [--no-scripts] [--no-progress] [--with-dependencies] [-v|vv|vvv|--verbose] [-o|--optimize-autoloader] [packages1] ... [packagesN]

The composer.json contains:
{
"name": "symfony/framework-standard-edition",
"license": "MIT",
"type": "project",
"description": "The \"Symfony Standard Edition\" distribution",
"autoload": {
    "psr-0": { "": "src/" }
},
"repositories": [
    {
        "type": "package",
        "package": {
            "name": "jquery/jquery",
            "version": "1.9.1",
            "dist": {
                "url": "http://code.jquery.com/jquery-1.9.1.js",
                "type": "file"
            }
        }
    }
],
"require": {
    "php": ">=5.3.3",
    "symfony/symfony": "2.3.*",
    "twig/extensions": "1.0.*",
    "symfony/assetic-bundle": "2.3.*",
    "symfony/swiftmailer-bundle": "2.3.*",
    "symfony/monolog-bundle": "2.3.*",
    "sensio/distribution-bundle": "2.3.*",
    "sensio/framework-extra-bundle": "2.3.*",
    "sensio/generator-bundle": "2.3.*",
    "knplabs/knp-menu": "2.0.*@dev",
    "leafo/lessphp": "0.4.*@dev",
    "knplabs/knp-menu-bundle": "2.0.*@dev",
    "incenteev/composer-parameter-handler": "~2.0",
    "twbs/bootstrap": "2.3.*",
    "jquery/jquery": "1.9.*",
    "FortAwesome/Font-Awesome": "3.2.1",
    "egeloen/ckeditor-bundle": "2.*"
},
"require-dev": {
    "phpunit/phpunit": "3.7.*"
},
"scripts": {
    "post-install-cmd": [
        "Incenteev\\ParameterHandler\\ScriptHandler::buildParameters",
        "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::buildBootstrap",
        "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::clearCache",
        "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installAssets",
        "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installRequirementsFile"
    ],
    "post-update-cmd": [
        "Incenteev\\ParameterHandler\\ScriptHandler::buildParameters",
        "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::buildBootstrap",
        "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::clearCache",
        "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installAssets",
        "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installRequirementsFile"
    ]
},
"config": {
    "bin-dir": "bin"
},
"minimum-stability": "stable",
"extra": {
    "symfony-app-dir": "app",
    "symfony-web-dir": "web",
    "incenteev-parameters": {
        "file": "app/config/parameters.yml"
    },
    "branch-alias": {
        "dev-master": "2.3-dev"
    }
}

}

A:

How to solve install/update Symfony 2 issues
One important Symfony requirement is that the app/cache and app/logs directories must be writable both by the web server and the command line user.
On Linux and macOS systems, if your web server user is different from your command line user, you need to configure permissions properly to avoid issues. There are several ways to achieve that:
The most common solution :
In a terminal execute following commands :
rm -rf bin
rm -rf vendor
composer install
# or if your didn't install composer
php composer.phar install

It should work now! For more informations see Symfony installation.
If you still have this error : «An error occurred when generating the bootstrap file»
It means that you have file permission issue.See below procedure for solve the problem ↓
Setting up or Fixing File Permissions :
In a terminal execute following commands :
rm -rf app/cache/*
rm -rf app/logs/*

On macOS systems, the chmod command supports the +a flag to define an ACL. Use the following script to determine your web server user and grant the needed permissions:
HTTPDUSER=$(ps axo user,comm | grep -E '[a]pache|[h]ttpd|[_]www|[w]ww-data|[n]ginx' | grep -v root | head -1 | cut -d\  -f1)
sudo chmod +a "$HTTPDUSER allow delete,write,append,file_inherit,directory_inherit" app/cache app/logs
sudo chmod +a "$(whoami) allow delete,write,append,file_inherit,directory_inherit" app/cache app/logs

On most Linux and BSD distributions don't support chmod +a, but do support another utility called setfacl. You may need to install setfacl and enable ACL support on your disk partition before using it. Then, use the following script to determine your web server user and grant the needed permissions:
HTTPDUSER=$(ps axo user,comm | grep -E '[a]pache|[h]ttpd|[_]www|[w]ww-data|[n]ginx' | grep -v root | head -1 | cut -d\  -f1)
# if this doesn't work, try adding `-n` option
sudo setfacl -dR -m u:"$HTTPDUSER":rwX -m u:$(whoami):rwX app/cache app/logs
sudo setfacl -R -m u:"$HTTPDUSER":rwX -m u:$(whoami):rwX app/cache app/logs

If none of the previous methods work for you
Change the umask so that the cache and log directories are group-writable or world-writable (depending if the web server user and the command line user are in the same group or not). To achieve this, put the following line at the beginning of the app/console, web/app.php and web/app_dev.php files:
umask(0002); // This will let the permissions be 0775
// or
umask(0000); // This will let the permissions be 0777

Note : Changing the umask is not thread-safe, so the ACL methods are recommended when they are available.

For more information see official documentation : Symfony file permissions

