[Bug 1747927] Re: when net booting servers with MAAS, grub should never wait for user input to reboot

[Steve Langasek]

On Wed, Feb 07, 2018 at 06:19:16PM -0000, Jason Hobbs wrote:
> Steve,

> Sorry, I missed comment #65 on the original bug.

> I think this is a bit different question than what to do when it can't
> find the file.

> In that bug, grub has been instructed to fall back to
> grub.cfg-default-amd64 if it can't find the file. In some cases it
> does, but in others it displays the error message linked above and
> hangs up.

The intent of this grub.cfg is to fall back if grub.cfg-<mac> *does not
exist*.  The current situation is that it's falling back to
grub.cfg-default-amd64 not because the file does not exist, but because of a
server error.

It is not unambiguously correct to fall back to grub.cfg-default-amd64 in
that case.  The current error messages in this scenario do point to a grub
bug.  I just don't know that fixing that bug is going to result in the
desired behavior.  Booting from local disk (which is what
grub.cfg-default-amd64 does) doesn't seem to me to be sensible error
handling for maas failing to serve the per-host file, and at a high level I
don't see why anyone would want that instead of halting or powering off the
machine.  In all cases, for a MAAS-managed system, the solution is the same
- shoot the node in the head, and power it back on to try again.

> In the case of not being able to find the file, or of an error, I
> think it should go back to UEFI and let UEFI handle it as a failed
> boot/can't boot from that device, and let UEFI handle that however it
> handles it.

I quite agree with this - it matches what I suggested to Andres would be a
sensible error handling in the case of maas not being able to serve the
correct grub.cfg-<mac> within the time limit.  But I think this is a
domain-specific policy, not something that grub should have as built-in
behavior in the event of all failed config file reads, and therefore is best
achieved by having the maas rack controller itself detect that it's having
problems with the db, and serving a straight 'exit' as the full contents of
grub.cfg-<mac> in place of the real config.

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https://bugs.launchpad.net/bugs/1747927

Title:
  when net booting servers with MAAS, grub should never wait for user
  input to reboot

Status in grub2 package in Ubuntu:
  New

Bug description:
  In bug 1743249, grub sometimes would hang waiting for user input on
  the keyboard.  This is never an appropriate action for a net booting
  server, at least not one booting under MAAS direction. It may be
  appropriate to pause for 30 seconds or something so someone can see
  the error, but to just hang is wrong.

  
  https://imgur.com/a/as8Sx

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