unable to open '/dev/sdb'
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... [2f1a2eb39cd04de4f50719ecc696513e-2]
Scanning disc for index files...
Found 2 package indexes, 0 source indexes, 0 translation indexes and 1 signatures
Found label 'Ubuntu 14.04.3 LTS _Trusty Tahr_ - Beta amd64 (20150805)'
This disc is called: 
'Ubuntu 14.04.3 LTS _Trusty Tahr_ - Beta amd64 (20150805)'
Copying package lists...gpgv: Signature made Wed Aug  5 05:37:55 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 14.04.3 LTS _Trusty Tahr_ - Beta amd64 (20150805)]/ trusty main restricted
Repeat this process for the rest of the CDs in your set.