amazon/xen... any way at all to pass a message/signal/semaphoere/morse-code to the boot loader?

[Leif Pedersen]

I keep an extra EBS volume handy that has a simple recovery image. If I get
stuck into a trouble, I change the normal boot disk to sdb, and attach my
recovery volume as sda1. Essentially, the extra volume is my "recovery
partition". To make it cheaper, keep only a snapshot of it.

Same idea on Google Compute Engine.




On Apr 11, 2017 11:34 PM, "Colin Percival" <cperciva at tarsnap.com> 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?
>
> > 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
> > suggestions.
> > 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...?
>
> --
> Colin Percival
> Security Officer Emeritus, FreeBSD | The power to serve
> Founder, Tarsnap | www.tarsnap.com | Online backups for the truly paranoid
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