Generating locales (this might take a while)...
Generation complete.
pwconv: failed to change the mode of /etc/passwd- to 0600
Using CD-ROM mount point /cdrom/
Identifying... [a1be0e719738dfa0ef6a3f1cc9eb0fed-2]
Scanning disc for index files...
Found 4 package indexes, 0 source indexes, 0 translation indexes and 1 signatures
Found label 'Ubuntu-GNOME 16.04 LTS _Xenial Xerus_ - Release amd64 (20160421)'
This disc is called: 
'Ubuntu-GNOME 16.04 LTS _Xenial Xerus_ - Release amd64 (20160421)'
Copying package lists...gpgv: Signature made Thu Apr 21 06:53:28 2016 UTC using DSA key ID FBB75451
gpgv: Good signature from "Ubuntu CD Image Automatic Signing Key <cdimage@ubuntu.com>"

Reading Package Indexes... 0%

Reading Package Indexes... Done
Writing new source list
Source list entries for this disc are:
deb cdrom:[Ubuntu-GNOME 16.04 LTS _Xenial Xerus_ - Release amd64 (20160421)]/ xenial main multiverse restricted universe
Repeat this process for the rest of the CDs in your set.