Grub legacy has a very nice feature called fallback(savedefault) that allows one to tell grub to modify the next boot entry number everytime it boots.
This is obviously very useful (in combination with some other kernel/init measures)
when doing a remote kernel update, since you can ask grub to boot back to the old kernel should the new one fail to come up no matter what the failure was (as long as grub itself is not misconfigured of course).
It would be nice to have this in grub2 as well, if for no other reason but to achieve feature parity with grub-legacy and lilo so that people can migrate to grub2 from those bootloaders without a regression.
Unfortunately, there have been quite a few problems with savedefault in grub-legacy (debian and ubuntu bugzillas have the relevant details), so I 'd like to start the discussion on how to port this feature in a way that most people are happy about it (it may be that
just a little bit more documentation on limitations/pitfalls is enough).
The main problem is that to implement fallback, grub must be able to write the next default boot entry *some* location, before it brings up the kernel. This location could be
* the MBR (if there is room, lilo does it this way I think) * whatever is the replacement of the old stage2 file (fedora's grub-legacy uses the stage2) * an auxilliary file in /boot (latest upstream grub-legacy uses /boot/grub/default - a text file)
No matter which of the above is chosen, there *will* be pitfalls and limitations. I can see no perfect, 100% foolproof solution. On the other hand, this feature is such a life saver and I hope it can be implemented so that most people who really need this feature can
at least use it and all the rest just have it out of their way and don't have to think about it.
So, what do you think? Which write location would you prefer? Would you like me to try and elaborate on the pros and cons of each approach?