[Bug 1878541] Re: Grub fails to load kernel from squashfs if mem < 1500mb

[Dimitri John Ledkov]

Starting uc20 in a virsh domain, whilst controlling for peak memory
usage, and modifying command line to boot to "rdinit=/bin/sh" => meaning
boot to unpacked initrd and start busybox shell without doing anything
else.

The rss memory achieved to get to that point was 744684, out of 2033104
available (i'm not sure which units virsh is using here, but it is
~740MB out of 2048MB).

Note on any other platform or mode, we do not loop mount xz compressed
snap. And we have stopped using lzma/xz for kernel image or modules
compression throughout Ubuntu.

Next steps is to try booting with kernel.snap without compression, or
unpacked.

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https://bugs.launchpad.net/bugs/1878541

Title:
  Grub fails to load kernel from squashfs if mem < 1500mb

Status in snapd:
  New
Status in grub2 package in Ubuntu:
  New

Bug description:
  Booting a uc20 system fails early currently. The image used was:
  http://cdimage.ubuntu.com/ubuntu-core/20/beta/20200513.2/

  Attached is a screenshot of the debug output.

  This appears to be some sort of regression with grub in 20.04 or with
  UEFI grub - this used to work in uc18.

  Note that there is memory < 1500mb

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