I am following the guide on symblog: http://tutorial.symblog.co.uk/docs/doctrine-2-the-blog-model.html
I am trying to run:
$ php composer.phar update
Failed to remove file
An error occurred when executing the "'cache:clear --no-warmup'" command.
This is a common problem with Symfony2 you should run your commands under the apache2 user in most cases this is the www-data user.
You can switch to the www-data user with
su www-data -s /bin/bash
then you should set 755 to the cache folder that the www-data has enough permissions. There is a goof explanation in the Symfony2 documentation about that.
Here in the documentation is a section "Setting up Permissions" there you can see how you can configure ACLs and other user permissions.