On 2018-07-09 12:45, Giles Orr wrote:
This link: https://www.computerhope.com/issues/ch000474.htm suggests the problem is lower level than I thought (BIOS rather than OS, which may negate what I've written below). You could take a look and see if their suggestions help. Doesn't look like a fun problem to tackle, sorry. As they suggest, start reseating or better, disconnecting internal components one at a time in the hope the problem goes away on one of them.
This link was useful to me because it explains the problem better than I did in my original post. In addition, I see why I could not find it using a google search. I searched using the same words as the title of this thread plus 'linux'. If I had used as my search text 'Verifying DMI Pool Data ...' I would have found the link. It shows that when using search engines you have to choose the right search words -- often difficult to do.
I use Knoppix ( http://www.knopper.net/knoppix-mirrors/index-en.html ) almost exclusively for rescue - I would give it a try. I'm inclined to suspect a hardware problem, and if you get the same error after burning Knoppix to a USB stick and booting, that would be ... well, a partial confirmation. Only partial because Knoppix is still, at its core (I think ...), Debian.
So I downloaded Knoppix 8.2, burned it to a DVD. It did indeed boot the offending computer. I was able to access my /home directory. I then tried again to boot the computer from the hard drives which have Jessie installed. (There are two hard drives which form a RAID1 device.) This time the boot completed, no more 99s! During subsequent bootings from these drives however, using both the installed Jessie and the Knoppix, after the message 'Verifying DMI Pool Data ...' was displayed it was a long time before they were detected. So it is possible that those drives, or perhaps one of them, are close to failing. They have been in use since 2011. Testing them is consequently next on my troubleshooting my agenda. Thanks for the info. Regards, Ken