Generating locales...
  en_US.UTF-8... done
Generation complete.
pwconv: failed to change the mode of /etc/passwd- to 0600
Using CD-ROM mount point /cdrom/
Identifying... [68998c743b086348f9feda50f9a3eefa-2]
Scanning disc for index files...
Found 2 package indexes, 0 source indexes, 0 translation indexes and 1 signatures
Found label 'Ubuntu 15.04 _Vivid Vervet_ - Release amd64 (20150422)'
This disc is called: 
'Ubuntu 15.04 _Vivid Vervet_ - Release amd64 (20150422)'
Copying package lists...gpgv: Signature made Wed Apr 22 12:30:00 2015 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 15.04 _Vivid Vervet_ - Release amd64 (20150422)]/ vivid main restricted
Repeat this process for the rest of the CDs in your set.