> 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
>>> 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...?
> 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 


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