root@ubuntu:/var/lib# apt-get policy postgresql-9.1
E: Invalid operation policy
root@ubuntu:/var/lib# apt-cache policy postgresql-9.1
postgresql-9.1:
  Installed: 9.1.11-0ubuntu0.13.10
  Candidate: 9.1.11-0ubuntu0.13.10
  Version table:
 *** 9.1.11-0ubuntu0.13.10 0
        500 http://us.archive.ubuntu.com/ubuntu/ saucy-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     9.1.10-1 0
        500 http://us.archive.ubuntu.com/ubuntu/ saucy/main amd64 Packages
root@ubuntu:/var/lib# apt-cache policy postgresql-common
postgresql-common:
  Installed: 148
  Candidate: 148
  Version table:
 *** 148 0
        500 http://us.archive.ubuntu.com/ubuntu/ saucy/main amd64 Packages
        100 /var/lib/dpkg/status