K3B verifies, CLI method gives wrong checksum [Solved]

[ReemZ]

I've downloaded and burnt several ISO's last couple of weeks and all seem to show the same behaviour.
K3B burns them without any problems, set to verify after burn and returns 'success', but checking the integrity of the burnt disks the oldschool way I get an md5 hash different from the one on the mirror. md5sum'ing the downloaded ISOs gives the correct ones, so downloads were all successful. Tried on different media (some dvd, some cd, all different brands, both cheap ones and top brand) but the results are the same.
Burnt on two different machines (32-bit desky and 64-bit lappy) so not a hardware problem.
The ISOs I've tried are Forensic spin, 32-bit KDE and LXDE versions and 64-bit Awesome version.
I've not tried booting them yet, apart from the KDE and LXDE ones on my girlfriend's lappy, which booted slowly but successfully in QEMU.
Is this a false OK in K3B or could it be something else? Can I trust the burnt disks or can I use them as coasters?

[Fitzcarraldo]

If K3b is telling you the burn is good then I'd be inclined to believe it. I'm 5,000 km from home at the moment and have no time or way of checking either K3b or the 'old school way' (to quote you) but it's possible something has changed since I wrote that procedure four years ago. Out of interest, how do the checksums compare if you use the following command on the LiveCD or LiveDVD?:

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md5sum /dev/sr0

or:

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md5sum /dev/cdrom

or:

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md5sum /dev/dvd

or:

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md5sum /dev/dvdrw

(I'm not sure what your optical device is called, but one of the above should cover it. If not, have a look in the /dev directory for the optical device and use the relevant name.)

[ReemZ]

I'll be...that worked!

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reemz@Sm0kerZ-T0shiba ~ $ md5sum /dev/cdrom && cat Linux\ ISOs/SL\ 7\ Awesome\ x86_64/Sabayon_Linux_7_amd64_Awesome.iso.md5
576b0b3efcc3c779330c605e0eb5d600  /dev/cdrom
576b0b3efcc3c779330c605e0eb5d600  Sabayon_Linux_7_amd64_Awesome.iso
reemz@Sm0kerZ-T0shiba ~ $

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reemz@Sm0kerZ-T0shiba ~ $ md5sum /dev/cdrom && cat Sabayon_Linux_DAILY_x86_ForensicsXfce.iso.md5
0d9a891d1dbbaf2ba1d0973dd7942c65  /dev/cdrom
0d9a891d1dbbaf2ba1d0973dd7942c65  Sabayon_Linux_DAILY_x86_ForensicsXfce.iso
reemz@Sm0kerZ-T0shiba ~ $

Tried on the live-usb too out of curiosity but I already expected that not to work:

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reemz@Sm0kerZ-T0shiba ~ $ mount | grep sd
/dev/sda3 on /boot type ext4 (rw,commit=0)
/dev/sdb1 on /media/SL7GNOME64 type vfat (rw,nosuid,nodev,uhelper=udisks,uid=1000,gid=1001,shortname=mixed,dmask=0077,utf8=1,showexec)
reemz@Sm0kerZ-T0shiba ~ $ md5sum /dev/sdb1 && cat Linux\ ISOs/SL\ 7\ Gnome\ x86_64/Sabayon_Linux_7_amd64_G.iso.md5
md5sum: /dev/sdb1: Permission denied
reemz@Sm0kerZ-T0shiba ~ $

(Yup, decided I'd at least go see what G3 looks like, but I've never deemed Gnome worthy of wasting a dvd on )