apt-cache policy linux-headers-generic
linux-headers-generic:
  Installed: 4.4.0.47.50
  Candidate: 4.4.0.47.50
  Version table:
 *** 4.4.0.47.50 100
        100 /var/lib/dpkg/status
     4.4.0.21.22 500
        500 http://archive.ubuntu.com/ubuntu xenial/main amd64 Packages