I have a Vagrant running Linux and I\'m trying to install Symfony.
After the command composer create-project symfony/framework-standard-edition ./ \"2.5.*\"
This has something do to with the synchronization of the folders between host and guest OSes, the folder might be simply temporarily locked from your host machine.
The solution is simply to delete the offending .git folder from your host OS or reboot the machine and launch composer install again.
Ideally each OS has its own dependencies and different binaries, therefore you should isolate your /vendor folder out from the rsync/vagrant folder share, likewise you would do the same with /node_modules on a Nodejs project.