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So I'd like to checksum my Debian 9.0 installation DVD to be able to compare it to the respective .iso file's hashes and the published hashes to be able to verify my installation's integrity.

I burned the Debian installation .iso to DVD under Ubuntu. There it had a problem verifying the DVD's checksum as it didn't proceed anymore at around 50% with the time remaining only rising and rising. However this may due to the fact that I accidentally executed sha512 (it had an error and didn't seem to have modified the .iso) instead of sha512sum on the .iso file during burning or checksumming. (The sha512 hash of the .iso was correct.)

I'd like to use sha512 and it seems I need the blocksize in bytes of my DVD first.

These 2 questions help but do not solve this issue for me:

Edit: Related question / finding of mine

mYnDstrEAm
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    if you still have the iso: https://unix.stackexchange.com/a/146221/30851 – frostschutz Jun 24 '17 at 12:36
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    and if not, this: https://unix.stackexchange.com/a/3795/30851 (you need to know the size in bytes, as the DVD might include padding which changes the hash sums) – frostschutz Jun 24 '17 at 12:38
  • @frostschutz Thank you. I'd like to compare the hashes myself so I'd really like to get a hash of the CD/DVD. The latter answer does not include a way to get the size in bytes. – mYnDstrEAm Jun 24 '17 at 12:40
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    `ls -l file.iso` shows the size in bytes, otherwise it should be mentioned on one of the download locations or shown by `wget` as you start downloading it. – frostschutz Jun 24 '17 at 12:48
  • @frostschutz When I run `dd if=/media/cdrom0 bs=1 count=3804708864 | md5sum` I get `dd: error reading '/media/cdrom0': Is a directory 0+0 records in 0+0 records out d41d8cd98f00b204e9800998ecf8427e`. I used `debian-9.0.0-amd64-DVD-1.iso`. – mYnDstrEAm Jun 24 '17 at 13:28
  • why `/media/cdrom`, it's `/dev/...` – frostschutz Jun 24 '17 at 14:08
  • Install K3b, it will show an md5 of the disk when it starts *or when asked to). –  Jun 25 '17 at 03:00

2 Answers2

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Install the package genisoimage like this:

apt-get install genisoimage

It will install a program isoinfo which will report the number of sectors in the disk (assuming the CD device is sr0):

$ isoinfo dev=/dev/sr0 -d
CD-ROM is in ISO 9660 format
System id: C@-RTKS C@-BRIDCE
Volume id: antartica
Volume set id:
Publisher id:
Data preparer id:
Application id: CAUAF File System - Adaptec
Copyright File id:
Abstract File id:
Bibliographic File id:
Volume set size is: 1
Volume set sequence number is: 1
Logical block size is: 2048
Volume size is: 297247
NO Joliet present
NO Rock Ridge present

And, if that command is succesful, you will get some details about the disk.
Read the "Logical block size" (usually 2048) and the "Volume size" And execute the commands below:

$ a=2048                # Block size read above.
$ b=297247              # Volume size. Near 300.000 for a 600Mega disk
$ dd if=/dev/sr0 bs="$a" count="$b" | md5sum

That will give you the MD5 hash. If you need a sha512 hash, use:

$ dd if=/dev/sr0 bs="$a" count="$b" | sha512sum

Reading a whole disk will take some time, be patient.

  • Great; there's just 2 things I have an issue with: why are people saying it's /dev/ and not /media/? I couldn't find anything under /dev/ or open /dev/sr0 while I could open /media/cdrom0 (that's also selected by default). The second issue is that my CD drive doesn't detect the DVD most of the time - sometimes it worked at first try without a problem but it hasn't worked since quite a number of restarts and tries per each now. My drive is probably getting old but do you maybe know any ways to check for CD drive issues or to manually scan for CDs in it (e.g. with a longer scan time)? – mYnDstrEAm Jun 25 '17 at 20:47
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    Because `/dev/sro` is (usually) the block device and `/media/cdrom` (when it exist) is the filesystem where you "see" the files contained in the physical disk. Both are related but never the same. In `/dev` the name of the cdrom device may be `/dev/cdrom`, `/dev/cdrw`, `/dev/dvd`, or/and`/dev/dvdrw`. If none of those exist in your system it may be because someone erased them. They could be re-created if needed. –  Jun 25 '17 at 23:14
  • If the device doesn't read the disk, maybe the disk was written to a low quality/too old re-grabable media, that usually happens. No I don't have the expertise to scan and analize what could be wrong with the hardware of your dvd reader. The scan provided in my answer does a full scan of the contents of the laser disk. Scanning of the device itself deserve some other question. –  Jun 25 '17 at 23:17
  • @mYnDstrEAm Have you tried K3b ? –  Jun 25 '17 at 23:18
  • When I run `isoinfo dev=/dev/sr0 -d` (as root) I get `Error trying to open /dev/sr0 exclusively (Device or resource busy)... giving up. WARNING: /dev/sr0 seems to be mounted! isoinfo: Device or resource busy. Cannot open '/dev/sr0'. Cannot open SCSI driver.` Where can I find the MD5 in K3b? I only see info on the sector length (`1857775 1857776 (412:50:26)`). Also for my CD drive: it may have gotten too hot - I restarted this morning and it worked at first try again. – mYnDstrEAm Jun 26 '17 at 09:13
  • Then, as root, execute: `umount /dev/sr0` (or, maybe, `umount /media/cdrom` and try again. About K3b: start the program and, while the program is running, insert the disk. It should detect the new disk and calculate the md5 sum automatically. –  Jun 26 '17 at 09:31
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    It's probably better to use cksum for speed assuming you're only worried about accidental defects (which if you're using md5 has to be the case because md5 isn't secure anymore) – 0x777C Sep 03 '21 at 20:00
  • This seems like a useful answer: it demonstrates how to get the sha512 hashsum and retrieve the blocksize using a tool that's not mentioned in any other answer. – Jeff Schaller May 20 '22 at 13:03
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There would be far easier burning new DVD with checksummed image then doing a checksum of burned image cause that will take a long time.

Also @arrow gave you the best option if you really need to check the status of your burned ISO.

Today people are more often doing dd to the USB drive and installing from there. There are a lot of laptops without internal CD/DVD drive and NAND memory is harder to corrupt, you can't really scratch it like the DVD.

Stephen Rauch
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MarkoShiva
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