Comment 5 for bug 1700611

There seems to be a difference in behavior in apt. Precise's apt-cache, for example, doesn't seem to care:

ubuntu@precise-esm:~$ l /etc/apt/sources.list.d/staging-ubuntu-esm-precise.list
-rw------- 1 root root 200 Jun 7 18:35 /etc/apt/sources.list.d/staging-ubuntu-esm-precise.list

ubuntu@precise-esm:~$ apt-cache policy landscape-client
landscape-client:
  Installed: (none)
  Candidate: 14.12-0ubuntu0.12.04
  Version table:
     14.12-0ubuntu0.12.04 0
        500 http://br.archive.ubuntu.com/ubuntu/ precise-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     12.04.3-0ubuntu1 0
        500 http://br.archive.ubuntu.com/ubuntu/ precise/main amd64 Packages

ubuntu@precise-esm:~$ sudo apt-cache policy landscape-client
landscape-client:
  Installed: (none)
  Candidate: 14.12-0ubuntu5.12.04
  Version table:
     14.12-0ubuntu5.12.04 0
        500 https://extended.security.staging.ubuntu.com/ubuntu/ precise/main amd64 Packages
     14.12-0ubuntu0.12.04 0
        500 http://br.archive.ubuntu.com/ubuntu/ precise-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     12.04.3-0ubuntu1 0
        500 http://br.archive.ubuntu.com/ubuntu/ precise/main amd64 Packages

So I would be OK for this change on precise, and also trusty (just tested) where it has the same behavior as precise. But from xenial onwards it breaks apt-cache as a whole for non-root users:

ubuntu@xenial-test:~$ apt-cache search juju
E: Opening /etc/apt/sources.list.d/juju-ubuntu-stable-xenial.list - ifstream::ifstream (13: Permission denied)
E: The list of sources could not be read.
ubuntu@xenial-test:~$