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#1 2008-05-05 17:01:52

icrave
Member
Registered: 2006-04-11
Posts: 193

[SOLVED] md5sum never works

Hi,

I'm trying to verify a cd with md5sum, but it doesn't work. I don't know why, but after many tries it seems to resists...
The steps that i follow are:

# Create .iso of files to burn:
mkisofs -pad -J -r -o imagen.iso /directory/to/burn/

# Create md5 checksum:
md5sum imagen.iso > imagen.iso.md5

# Burn iso image to CD:
cdrecord -v -eject dev=/dev/scd0 -data imagen.iso

# With the burned cd and isoinfo, i get volume size and block size:
volume size = isoinfo -d -i /dev/scd0 | grep "^Volume size is:" | cut -d " " -f 4
block size = isoinfo -d -i /dev/scd0 | grep "^Logical block size is:" | cut -d " " -f 5

# Create iso image from CD:
dd if=/dev/scd0 of=imagen.iso bs=(block size) co=(volume size)

# Check md5sum:
md5sum -c imagen.iso.md5

Someone knows what I'm doing wrong?

Last edited by icrave (2008-05-06 10:09:21)

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#2 2008-05-05 19:58:29

ghostHack
Member
From: Bristol UK
Registered: 2008-02-29
Posts: 261

Re: [SOLVED] md5sum never works

When getting the md5sum of a burned CD I have found that I have to point md5sum at the device entry, e.g

md5sum /dev/cdrom

I don't know if that is the 'correct' method but its the only way I found of getting an md5sum from a CD.

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#3 2008-05-05 21:28:58

icrave
Member
Registered: 2006-04-11
Posts: 193

Re: [SOLVED] md5sum never works

Your command to generate md5 directly from /dev/cdrom doesn't work (input/output error).

Now, I'm trying another method to create image from cd:

dd if=/dev/cdrom | head -c 188160000 | md5sum

Where 188160000 is the exact size on bytes of image (used stat to get it)... but off course, It doesn't work mad.

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#4 2008-05-05 21:35:07

ghostHack
Member
From: Bristol UK
Registered: 2008-02-29
Posts: 261

Re: [SOLVED] md5sum never works

hmm, /dev/cdrom is actually a link to /dev/sr0 on my system, try to find out the proper device that your cdrom maps to and use that instead

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#5 2008-05-05 21:46:24

icrave
Member
Registered: 2006-04-11
Posts: 193

Re: [SOLVED] md5sum never works

I think that the problem isn't /dev/cdrom, because i can do "cat /dev/cdrom | md5sum" (yes, the md5sum are incorrect).
Using the original dev (in my case /dev/sr0, too), i have the same error.

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#6 2008-05-05 21:51:58

_Marco_
Member
Registered: 2008-04-21
Posts: 242

Re: [SOLVED] md5sum never works

but are you sure that the cdrom md5sum should be equal to the .iso one?
because to close the session the cd recorder writes some (I'm not a technician so I don't know which) bits...
I think it is normal the md5sum results incorrect, am I wrong?

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#7 2008-05-05 21:59:14

icrave
Member
Registered: 2006-04-11
Posts: 193

Re: [SOLVED] md5sum never works

Just for this, I use head or isoinfo to read only the exact number of bytes with dd.

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#8 2008-05-05 22:03:44

_Marco_
Member
Registered: 2008-04-21
Posts: 242

Re: [SOLVED] md5sum never works

ah.. thanks for your explanation..  ^^"

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#9 2008-05-05 22:15:34

ghostHack
Member
From: Bristol UK
Registered: 2008-02-29
Posts: 261

Re: [SOLVED] md5sum never works

icrave, What speed did you burn the disc at?  I've just done a test on an old sidux disc I have and I get the same results from the CD as the iso on my hard disk

$ md5sum /data/media/Downloads/distro_downloads/sidux64-2007-04-200711210257-eros-kde-full.iso 
1ef35f3aad9682e85ebb5f706b11a856  /data/media/Downloads/distro_downloads/sidux64-2007-04-200711210257-eros-kde-full.iso

$ md5sum /dev/cdrom
1ef35f3aad9682e85ebb5f706b11a856  /dev/cdrom

If you are still seeing differences then it might be that you actually do have a bad burn.

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#10 2008-05-06 10:02:18

icrave
Member
Registered: 2006-04-11
Posts: 193

Re: [SOLVED] md5sum never works

To verify if I have a bad burn, I check md5sum of files separately and the result is... checksums corrects.
So, I'm not sure where is the problem.

I will keep trying...

EDIT:
AHA! Finally I got it. The problem seems to be in mkisofs and it's resolved adding -pad to the make-image-to-burn command. Before, I only added -pad to make-image-to-check command

EDIT2:
The problem maybe was in use -follow-links in mkisofs, too.

EDIT3:
Forget -pad and -follow-links... the error was more simple... I create image(1) and i burn it. I create image(2) and I check burned cd with it. Checksums of image(1) and image(2) are not the same...

Last edited by icrave (2008-05-06 10:30:33)

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