[colug-432] Centos ISO Padding Curiosity

[jep200404 at columbus.rr.com]

Some distros pad their ISO(-9660) images. In the past this might 
have been to help some lame burning programs or drives that 
would quit too early. Within a distro, some ISO files might be 
padded and others would not. In the past, whenever I inspected 
the padding, the padding was always zeros. With that knowledge, 
I could reconcile sums.

A Centos image has non-zero padding. That is interesting.

    knoppix at Microknoppix:/.../CentOS-7.0-1406-x86_64-DVD$ ll
    total 4051076
    -rw-r--r-- 1 knoppix knoppix 4148166656 Feb 18 20:34 CentOS-7.0-1406-x86_64-DVD.iso
    -rw-r--r-- 1 knoppix knoppix        609 Feb 18 16:07 sha256sum.txt
    -rw-r--r-- 1 knoppix knoppix       1485 Feb 18 16:07 sha256sum.txt.asc
    knoppix at Microknoppix:/.../CentOS-7.0-1406-x86_64-DVD$ echo 'scale=10;4148166656/2048' | bc
    2025472.0000000000
    knoppix at Microknoppix:/.../CentOS-7.0-1406-x86_64-DVD$ isoinfo -d -i CentOS-7.0-1406-x86_64-DVD.iso | grep "^Volume size is:"
    Volume size is: 2025430
    knoppix at Microknoppix:/.../CentOS-7.0-1406-x86_64-DVD$ isoinfo -d -i CentOS-7.0-1406-x86_64-DVD.iso | grep "^Logical block size is:"
    Logical block size is: 2048
    knoppix at Microknoppix:/.../CentOS-7.0-1406-x86_64-DVD$ echo 'scale=10;2025472-2025430' | bc
    42
    knoppix at Microknoppix:/.../CentOS-7.0-1406-x86_64-DVD$ dd if=CentOS-7.0-1406-x86_64-DVD.iso bs=2k skip=2025430 | xxd -a -g 1 -u
    0000000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    42+0 records in
    42+0 records out
    86016 bytes (86 kB) copied, 0.00287602 s, 29.9 MB/s
    *
    0010c00: A2 A0 D0 EB E5 B9 33 44 87 C0 68 B6 B7 26 99 C7  ......3D..h..&..
    0010c10: 4D FC 0E A0 08 12 EC 44 B5 8E 53 6C 22 2E 41 21  M......D..Sl".A!
    0010c20: 00 00 00 00 00 00 00 00 58 9F 7B 00 00 00 00 00  ........X.{.....
    0010c30: 00 00 00 00 00 00 00 00 49 53 4F 48 79 62 72 69  ........ISOHybri
    0010c40: 64 20 49 53 4F 00 49 53 4F 48 79 62 72 69 64 00  d ISO.ISOHybrid.
    0010c50: 41 70 70 6C 00 00 00 00 00 00 00 00 00 00 00 00  Appl............
    0010c60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    0010c70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    0010c80: A2 A0 D0 EB E5 B9 33 44 87 C0 68 B6 B7 26 99 C7  ......3D..h..&..
    0010c90: D3 5A BD EC 2D 14 F7 41 B4 5E FC A4 BE F1 B5 94  .Z..-..A.^......
    0010ca0: 4C 08 00 00 00 00 00 00 6F 39 00 00 00 00 00 00  L.......o9......
    0010cb0: 00 00 00 00 00 00 00 00 49 53 4F 48 79 62 72 69  ........ISOHybri
    0010cc0: 64 00 41 70 70 6C 65 00 41 70 70 6C 00 00 00 00  d.Apple.Appl....
    0010cd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    *
    0014c00: 45 46 49 20 50 41 52 54 00 00 01 00 5C 00 00 00  EFI PART....\...
    0014c10: 19 59 BB 03 00 00 00 00 FE 9F 7B 00 00 00 00 00  .Y........{.....
    0014c20: 01 00 00 00 00 00 00 00 22 00 00 00 00 00 00 00  ........".......
    0014c30: DE 9F 7B 00 00 00 00 00 48 61 35 42 F0 B6 3A 42  ..{.....Ha5B..:B
    0014c40: 8B 58 E8 46 75 21 FC F9 DE 9F 7B 00 00 00 00 00  .X.Fu!....{.....
    0014c50: 80 00 00 00 80 00 00 00 6E D5 88 2A 00 00 00 00  ........n..*....
    0014c60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    *
    0014ff0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    knoppix at Microknoppix:/.../CentOS-7.0-1406-x86_64-DVD$