[Bug 1087501] Re: Unable to boot unsigned kernel, boot freezes in shim call

[Stéphane Graber]

Forgot to comment there (only did it in private on IRC). The binary
above doesn't print anything to screen in my case, it's as if grub was
somehow preventing the shim to render anything on screen.

My suggestion is to use a nvram variable accessible from the booted system and use that to store the debug output.
However be careful to only log a very minimal amount of data as my mention suffers from the UEFI garbage collection bug that bricks machines when more than 50% of the nvram variable space is used.

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Title:
  Unable to boot unsigned kernel, boot freezes in shim call

Status in “shim” package in Ubuntu:
  Incomplete

Bug description:
  On a Lenovo x230 with secureboot enabled, I can only boot signed
  kernel.

  Initially this was thought to be a grub2 issue but after investigation
  (added debug code in grub and running with debug=all), it was
  determined that the last thing grub does before the freeze is call a
  shim hook.

  The current workaround is to either disable secureboot or use a signed
  kernel.

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