Symfony2, composer, your PHP version (5.6.18) overriden by "config.platform.php" version (5.3.9) does not satisfy requirement

Somewhere in your composer.json you have

"config": {   "preferred-install": "dist",   "platform": {       "php": "5.3.9"   }}

That block overrides your current PHP version as described in composer doc.

In your composer.json, remove the following lines :

// ..."config": {    "platform": {        "php": "5.3.9"    }},// ...

See platform config in composer.

I use doctrine migrations with Symfony 2.7

In my composer.json I have, I noticed you don't, you could try adding it

"doctrine/doctrine-migrations-bundle": "^1.0"

I manually installed migrations following Symfony2 docs, you can read it here.

This is my whole 2.7 Symfony composer:

"require": {    "php": ">=5.3.9",    "symfony/symfony": "2.7.*",    "doctrine/orm": "~2.2,>=2.2.3,<2.5",    "doctrine/dbal": "<2.5",    "doctrine/doctrine-bundle": "~1.4",    "symfony/assetic-bundle": "~2.3",    "symfony/swiftmailer-bundle": "~2.3",    "symfony/monolog-bundle": "~2.4",    "sensio/distribution-bundle": "~4.0",    "sensio/framework-extra-bundle": "~3.0,>=3.0.2",    "incenteev/composer-parameter-handler": "~2.0",    "friendsofsymfony/user-bundle": "1.3.*@dev",    "ircmaxell/password-compat": "^1.0",    "sonata-project/block-bundle": "2.3.*@dev",    "sonata-project/easy-extends-bundle": "^2.1",    "sonata-project/datagrid-bundle": "~2.2@dev",    "sonata-project/admin-bundle": "~2.3@dev",    "sonata-project/doctrine-orm-admin-bundle": "~2.3@dev",    "sonata-project/user-bundle": "~2.3@dev",    "doctrine/doctrine-migrations-bundle": "^1.0"},