php+nginx+vagrant - php fails to write

I have figured out the problem.

I have forgot to give PHP the correct user-privileges and permissions to write to the folder. Basically, my PHP user/user-group was www-data/www-data however, vagrant has its own user/group (vagrant/vagrant) which mounts the folder /local/.

Since I did not want to mess with my vagrant mounting behaviour, I just simply changed my php config to start PHP with the user/group - vagrant/vagrant.