What does this warning mean? I got it when executing following command using root at amazon ec2 Ubuntu 14.04 LTS instance:
$ pip install https://github.com/troeger/opensubmit/archive/0.6.2.tar.gz
The directory '/home/ubuntu/.cache/pip/http' or its parent directory is not owned by the current user and the cache has been disabled. Please check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.
The directory '/home/ubuntu/.cache/pip' or its parent directory is not owned by the current user and caching wheels has been disabled. check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.