[plug] Redhat 7.3 install (argh!!!!)

[Russell Keith-Magee]

> > I decided to bite the bullet and upgrade my work Linux box to Redhat
> > 7.3. All was going fine until it asked me to insert redhat 7.3 cd
> > number 3. I inserted the disk with the correct number on it (wasn't too
> > hard there were only 3 disks) and then got an error message telling me
> > that I have inserted the wrong disk. After many re-inserts and many
> > rechecks I can confirm that I have inserted the correct disk even
> > though the install program would like to tell me otherwise. I suspect I
> > have a bad CD but I am not too sure on how to check this - any hints
> > anyone?
>
> I don't know how you would check the CD; unless you did something like a
> du -s, or a df on it, and compared the figures with a known good CD. The
> only thing of which I can think, is to do a byte count (or as near as
> possible), on your CD #3, and compare it with a known good CD #3.

du and df are not really good indicators of CD image quality. Single bit
flips/corruptions and errors caused by buffer overwrites during burning are
not revealed by such a check.

The generally accepted method is to use an MD5 checksum. This essentially
adds up the value of all the data on the disk, and computes the result MOD
some value (the actual algorithm is a little more complicated than this, but
you get the idea). This reduces the 650MB CD image to a string of
approximately 50 characters, which are very sensitive to single bit changes.
This technique can be applied to CD images, files, directories, entire
disks, whatever.

Redhat 7.3 CDs have MD5 checksums embedded in them; the installer knows how
to check and validate the CDs. When you start the installer, and are
presented with the "boot:" menu, type
"linux mediacheck" (ordinarily you would just press enter to get a graphical
install, or type "text" to get the text mode install).

For other distros (including earlier versions of redhat), run md5sum over
the drive with the cd in it: e.g.,

md5sum /dev/cdrom

This will spit out a long string (about 50 chars IIRC). This string can then
be compared with the md5sum that is usually provided along side any large
file download.

Russ %-)

********************************************
Dr Russell Keith-Magee
Software Engineer
Calytrix Technologies
Unit 9, EIR Building, Technology Park
PO Box 1173, BENTLEY 6982, Western Australia