Does anyone know if a burned installation disc can only be verified while using the operating system it was downloaded/burned on?
It doesn't matter which OS you use, because the disc's contents are not subjective.
Verified md5sum at the time.
As of 2010, the CMU Software Engineering Institute considers MD5 "cryptographically broken and unsuitable for further use", and most U.S. government applications now require the SHA-2 family of hash functions.
I would suggest using SHA-256 over MD5 when possible as MD5 has known collisions. As a former standard, it is still widely provided, as is SHA-1, but SHA-2 is the new standard, in particular SHA-256. Personally I tend to use SHA-512, but people rarely ever provide SHA-512 checksums so I end up using SHA-256 alot. I would like to start using SHA-3, but none of the tools I currently use support it.
got "input/output" error messages
I suspect you were hashing a device that didn't exist. You can use blkid to determine which device your DVD drive is. It will output a list, and the labels should help you figure out which one is the DVD. For example, my Ubuntu disc has the label "Ubuntu 14.04 LTS amd64", and using that I know my DVD device is "/dev/sr0".
1. In terminal type:
2. Look through blkid output to determine which device is the DVD drive (eg: /dev/sr0).
I'm 99% sure I finalized the Ubuntu RW Disc
Keep in mind that some burning tools add padding, and if you finalize a disc you've essentially done the same, which means you must hash only part of the disc, or the padding will cause you to get a different checksum than expected. You can accomplish this by determing the size of the original ISO used to create the disc.
1. In terminal type:
wc -c /directory/file.iso
Substitute "/directory/file.iso" with the path to and filename of the ISO you are hashing. This will tell you the size of the ISO. You need to know this so you know how much of the device to hash.
2. In terminal type:
head -c SIZEOFISO /dev/sr# | sha256sum
Substitute "/dev/sr#" for your DVD drive. Substitute "SIZEOFISO" for the size of the ISO. This will hash only the part of the DVD expected to match the ISO.
it strikes me odd that a DVD-RW would be considered "not a good idea" for installation media.
I wouldn't describe re-writable discs as unsafe. I use DVD+RW quite often. I only use DVD-R for discs I intend to keep long term. DVD-R is the safest DVD media, because once you burn it, and finalize it you've got a DVD-ROM (Read Only Media). Using read-only media adds a level of physical protection against malware, and user-error. For that reason I would recommend using DVD-R over any other type of DVD when planning to use portable distros (eg: Puppy Linux, Knoppix, etc) or when using distros like Ubuntu in try-mode for the same purpose. But I don't think it matters that much. Re-writable DVD media are still safer than using a flashdrive. Not that I would describe flashdrives as unsafe either. All boils down to how much the user cares I think.
Edited by hollowface, 03 April 2016 - 03:27 PM.