On 12/4/17 2:09 pm, Toomas Soome wrote:
On 12. apr 2017, at 9:04, Julian Elischer <jul...@freebsd.org> wrote:

On 12/4/17 12:34 pm, Colin Percival wrote:
[CCing freebsd-cloud, which is the right place for discussions of FreeBSD/EC2]

On 04/11/17 21:03, Julian Elischer wrote:
In Amazon ec2 they have no console access (though I heard rumors that it was
available I have not seen any sign of it) so I'd like to put a "recovery
partition" into an AMI.
The trick is how to convince it to boot to that instead of the regular action.
Can you get what you want via gptboot's support for selecting the partition
to boot via "bootonce" and "bootme" flags?
not if you can't get onto to the machine.
When I talk about a recovery partition I mean it in the same way that apple 
means it..
"system won't boot? press the power button and hold down the 'option' key.
it will give you the option to boot to a recovery mode"
(* actually I can't remember the keys but you get the idea..)

in our case we would like to be able to recover a customer's AMI by giving a 
simple set of instructions over the phone.
We can assume they know how to get into the amazon menus, but we would like to 
not have to assume much more.

The ideal thing would be if there was  way to 'influence' one of the smbios
values in some way, and have the boot code see it, but I'm open to any
I really need only 1 bit of information to get through.

Possibilties include "changing the VM to have only 2G of ram" (we'd never do
that in a real machine).
or maybe temporarily removing all the disks other than the root drive? Almost
anything I could do to signal the boot code to behave differently.
I don't think adding/removing disks will be useful, since the extra disks will
be Xen blkfront devices; AFAIK the boot loader doesn't know anything about
these.  (The boot device is also a blkfront device but gets ATA emulation for
the benefit of boot loaders.)

Maybe you can repurpose some of the logic used for booting over NFS?  I've
never heard of people booting over NFS when the initial bootstrap comes from
disk rather than PXE, but I assume it's possible...?
Oh I've done it, in the past but you still have the same issue..
how do you signal the boot code to do this?

(does an AMI have a bios capable of doing network operations?) I was thinking
about whether we could add a really simple xn driver into the bootcode to allow
us to have an console of sorts (accessible from an adjacent machine only??)

basically you want what zfsbootcfg does but in reverse — with fallback to 
that is also a possibility  N failed boots in a row..


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