Right now, we have the following configuration scopes:

• ~/.spack/linux
• ~/.spack
• etc/spack/linux
• etc/spack

I may be biased because I only manage Linux clusters, but I don't find these configuration scopes very useful. I would find the following much more useful:

• ~/.spack/linux-centos7-x86_64
• ~/.spack
• etc/spack/linux-centos7-x86_64
• etc/spack

I manage 2 clusters, one is CentOS 6 and the other is CentOS 7. These clusters provide different versions of the system installed packages. At the moment, it is impossible to use external packages on 2 different OSes without lying. I've tried:

packages:
  libtool:
    paths:
      libtool@2.4.2 arch=linux-centos7-x86_64: /usr
      libtool@2.2.6b arch=linux-centos6-x86_64: /usr
    buildable: False

but this doesn't work (see #3508). I could lie and say that they are both the same version, but this won't work for packages that require a specific version, or if the packages are in different locations. Having more specific configuration scopes would make life much easier. We can still keep ~/.spack/linux and etc/spack/linux if people really want them.