If Spack is configured with a packages.yaml that includes external packages, these packages may appear installed even if they are not. The cause of that is how we compute the installed property:

which returns True if the prefix is there (without any check of the DB).

Expected Result

Starting with this packages.yaml:

packages:
  openssl:
    buildable: False
    paths:
      openssl@system: /usr/lib

and Spack at 231664e:

$ spack find
==> 0 installed packages.

I would expect the following:

$ spack-python
Spack version 0.11.2
Python 2.7.15rc1, Linux x86_64
>>> import spack.spec
>>> s = spack.spec.Spec('openssl')
>>> s.concretize()
>>> s.package.installed
False

Actual Result

What we obtain instead is that openssl appears to be installed:

$ spack-python
Spack version 0.11.2
Python 2.7.15rc1, Linux x86_64
>>> import spack.spec
>>> s = spack.spec.Spec('openssl')
>>> s.concretize()
>>> s.package.installed
True

Information on your system

The only relevant part should be the packages.yaml above