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Old 11-10-2004, 08:15 AM   #1
Vikinghat
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FC3: Media test pass - but MD5SUM is wrong


Have just downloaded the Fedora Core 3 cd iso files - ran MD5SUM and they all pass.
I then burnt the first ISO file as an image to CD using K3b - it calculated the MD5SUM before burning and this was correct as before. Then on completion of the burn K3b checked and reported the checksum had failed (but does not tell you the value of the failing checksum). Fair enough coasters happen, but out of curiosity I tried booting the PC off the CD - it booted and proceeded to the media test, which when run passed!!!! Which makes me wonder what the media test does! I've since rebooted back to Mandrake 10 and run MD5SUM on /dev/cdrom, which produces a checksum that does not match the expected value - so I can but assume K3b correctly reported the CD checksum fails.

So what is going on with FC3 media check?
 
Old 11-10-2004, 08:23 AM   #2
b0uncer
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dunno, but I can tell that several people have noticed this - the md5sum of the iso does not match the md5sum of the burned disc, though nothing seems to be different or damaged...

so, my thoughts on this are that the burning process changes the md5sum (so the data is ok, but something in the whole process of burning data to disc creates or removes something that has nothing to do with data itself, so the md5sum is different) so it doesn't match. the other option is, that a lot of people can't get their isos burned well, though they seem to work which sounds a bit odd...

I'm not sure but I could imagine that the md5sum of the disc includes the burned data And something else (well, I'm not a pro on how a cd is actually, bit by bit, burned, but..) like something concerning the fs, so the final "output" is not exactly the same as the iso is. there is always the difference that iso resides in your HD but the data on a cd, which needs a filesystem too, and is a bit different than HD. I'm not sure but might have something to do with this fact...

so, if the media test passed, you should be ok even though the md5sums don't match.

Last edited by b0uncer; 11-10-2004 at 08:32 AM.
 
Old 11-10-2004, 10:06 AM   #3
marghorp
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you have the md5sum for ISO, not files

Try creating an ISO with mkisofs form the cdrom and run md5sum on that. See if it differs

I believe this is a k3b bug, I have experienced some problems with k3b before. Some data was unreadable, for some reason, I don't know.
 
Old 11-10-2004, 10:53 AM   #4
Vikinghat
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Thank you for the advice. I'm still mystified. I've now used Nero to burn another CD from the original downloaded ISO image. This produces the same MD5SUM as the previously burnt CD. Which is at least consistent. A search on Google has shown this appears to be a recurring issue, see http://twiki.org/cgi-bin/view/Wikile...msAfterBurning

Which suggests the changes in MD5SUM results can be due to padding zeroes added by the writing software. Unfortunately the alternate ways of checking the CD suggested there do not produce pass results on my CD copies.

As for using mkisofs - I've had a go but the options used with it affect the resulting extracted iso file size and hence MD5sum - and none of them match the original downloaded ISO.

Note I've also used dd to extract the ISO and this also does not match up to the original downloaded file - but does match the MD5sum of the cd obtained with md5sum /dev/cdrom.

The only other thing I'm planning to do is try burning at a slow speed.
 
Old 11-11-2004, 01:28 AM   #5
Vikinghat
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Victory - though not by a route I like, as it puts me firmly into windows for writing CD's (and CD writing is the one activity that is keeping windows going on my PC).

Further to my last post - I didn't write another CD, as I remembered I had Isobuster installed under windows. Which when I checked, can calculate the MD5sum that would result if an image were to be extracted from the burnt cd. Hey presto this MD5SUM matches the original downloaded MD5SUM.

So until I can find a simple way to calculate this properly under linux I'm going to avoid burning CD's under linux. It can't be that simple as I note Nero does not offer to verify a written image file (admittedly the version I'm using is old).
 
Old 10-24-2006, 03:23 AM   #6
squir
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Md5sum

Can somebody explain how to use MD5SUM.
Thanks
 
Old 10-24-2006, 03:45 AM   #7
marghorp
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Using MD5SUM

Go to this link and read about the usage in windows.

http://etree.org/md5com.html

The easiest way to md5sum your media is through wxisting windows installation. Or if you already have linux installed, md5sum is part of the installation. )

Have fun!

 
Old 10-24-2006, 04:02 AM   #8
squir
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Md5sum

I have winxp OS. Where do I find MD5SUM?
 
Old 10-24-2006, 04:17 AM   #9
marghorp
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Read please

You really need to read man

If you are not willing to read (no hard feelings intended), then you can leave linux now and stick to windows.

The link I provided in the previous post explains, that you have to download md5sum.exe and copy it to a folder in the systems PATH variable. one of those is C:\WINDOWS\SYSTEM32

Then you can run it from the command line as the examples shown in the site demonstrate.

Enjoy linux!
 
Old 10-24-2006, 04:58 AM   #10
squir
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yes, I found how to use MD5SUM.

Thanks the link is useful
 
  


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