Folks,
I have been using Debian 9 in a multi-boot setup for quite some time with a great deal of satisfaction. The basic set up was:
Windows 7 (for the infrequent use by other family members)
Debian 9 (living on /dev/sda5; used very often by me for work)
Siduction (living on /dev/sda8; mainly for goofing off and experimentation)
Note: /home is on a separate partition for some of the obvious reasons.
I was able to multi-boot between these very nicely with a minimum of fuss.
Recently I figured that I should move across to Debian 10 and take advantage of updates and other progress-like stuff. I decided to install Debian 10 onto /dev/sda8 (stomp over Siduction) and transition to it gradually from Debian 9 - in my mind a fairly reasonable plan.
The installation went fairly steadily, as I would have expected based on past experience. The installer reached the point where the other operating system were detected (a good sign to me); interestingly the displayed information said that grub would set up one other OS along with the current installed system Debian 10. I went ahead and completed the installation and got Debian 10 to boot successfully.
However (don't you hate the word?), when trying out the other multi-boot options I found that the pre-existing Debian 9 would not boot - the Windows 7 booted OK. The choice for selecting and booting from Debian 9 was being presented but when selected there is just a blank screen and a flashing cursor.
I'm guessing that Grub might have chosen to ignore Debian 9 (a generous excuse) or something else has gone astray. I have attached the grub.cfg files from the Debian 9 and Debian 10 installations; I don't have the background (or time and willingness to become a grub expert) to examine these for meaningful differences. I'm hoping that they may be more enlightening to you folk.
What I would appreciate very much:
1. Some simple and straightforward instruction on how to enable the grub booting mechanism to allow me to boot Debian 9. If it was doable before, it should be doable now.
2. Not to expend an excessive amount of time going to and fro trying out poorly conceived suggestions.
3. I would hope that this might inform you of a possible malfunction in the structure of the Debian installer and that it can be remedied successfully - as said before, this wasn't an issue in the past.
This was something of an unexpected and 'bummer' outcome; I have enjoyed using Debian in the past and look forward to using it in the future. So far my enthusiasm for Debian/Linux is not dented.
Cheers
Paul D.