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Author Topic: Your Boot Menu Integrity Check may be a little shakey.  (Read 689 times)

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Offline utu

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Your Boot Menu Integrity Check may be a little shakey.
« on: July 23, 2016, 09:18:01 pm »
The 'Integrity Check' is a little flawed for most Ubuntu 10.04-derivative
systems. Not much, but a little. The check goes through around 360 md5sums
and determines OK or Fail for each. What is happening is a proper md5sum
test for the files in the downloaded iso. If you've made a proper LiveUSB
and apply this 'proper md5sum' test, several files are quite likely to fail
since they were modified in the transformation of the iso into a working
system. I don't know for sure, but I suspect that only if the basic squash
file fails will there be any disruption of continuing to boot-up.

In my case, making a LiveUSB from a LiveCD iso, I usually modify the boot
menu to make it look more like a LiveUSB, not a mere Installer menu. Also,
with my Broadcom wifi, there are two other chances for things to get changed:
one is an initramfs operation for the default b43 driver install; another
is a second initramfs operation when I remove the b43 and replace it with
the new and better wl model 271 wifi driver replacement.

In my case, eight md5sums fail, 352 pass, including the squash file.
On close inspection each one of the eight files in question has a later
origination date than md5sum.txt used in the test. Evidence enough to
suspect the md5sum test is likely flawed itself.

If I weren't so lazy, I'd calculate some correct md5sums and replace the
impostors. As it is, I just thought you ought to be a little suspicious of
the Integrity test. It is a really good idea, just a trifle flawed in its
execution.

I can demonstrate these ideas using a small bash program, check.md5s, to show
for my LiveUSB, which works just fine, thanks:
Code: [Select]
Checking 360 lines in md5sum.txt:
 -- Please wait for squashfs test to complete --
./isolinux/isolinux.cfg: FAILED
./isolinux/txt.cfg: FAILED
./isolinux/vesamenu.c32: FAILED
./isolinux/menu.cfg: FAILED
./md5sum.txt: FAILED
./boot/grub/grub.cfg: FAILED
./boot/grub/loopback.cfg: FAILED
./casper/initrd.lz: FAILED
md5sum: WARNING: 8 computed checksums did NOT match
peppermint@peppermint ~ $

Offline PCNetSpec

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Re: Your Boot Menu Integrity Check may be a little shakey.
« Reply #1 on: July 24, 2016, 02:37:21 pm »
Am I missing something here .. you (or a LiveUSB creator) modify the boot menu, then you're surprised that menu fails the md5sum :-\
« Last Edit: July 24, 2016, 02:50:59 pm by PCNetSpec »
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Offline utu

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Re: Your Boot Menu Integrity Check may be a little shakey.
« Reply #2 on: July 24, 2016, 04:42:50 pm »
Thanks for your comment.

I am pointing out that the 'integrity check' menu choice checks 360 md5sums
but merely ignores failed md5sum checks. My guess is it certainly must do
something more significant if the squash file fails. Some Ubuntu 10.04
derivatives whiz through all the md5s and don't even call out failed md5s,
if any.

I would think some users might wonder why some of these md5sums may be wrong.
Six or seven of my md5sum fails are caused by initramfs ops in getting my wifi
driver shifted over to something better than the default. That might not be so
obvious to some users.