unable to open '/dev/dm-0'
unable to open '/dev/dm-4'
unable to open '/dev/sda'
unable to open '/dev/sdb'
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... [f27299bf7a81ecc20545311be3ff8545-2]
Scanning disc for index files...
Found 2 package indexes, 0 source indexes, 0 translation indexes and 1 signatures
Found label 'Ubuntu 16.04.3 LTS _Xenial Xerus_ - Release amd64 (20170801)'
This disc is called: 
'Ubuntu 16.04.3 LTS _Xenial Xerus_ - Release amd64 (20170801)'
Copying package lists...gpgv: Signature made Tue Aug  1 11:51:24 2017 UTC using RSA key ID EFE21092
gpgv: Good signature from "Ubuntu CD Image Automatic Signing Key (2012) <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 16.04.3 LTS _Xenial Xerus_ - Release amd64 (20170801)]/ xenial main restricted
Repeat this process for the rest of the CDs in your set.