[Bug 1959971] Re: increase /boot partition size

[Michael Mikowski]

@sil2100 @brian-murray: Thank you for your work and consideration on
this. We addressed this issue Kubuntu Focus OEM ISO
(https://kfocus.org/try) by increasing the /boot partition size and
providing an app that monitors and removes unused kernels
(https://kfocus.org/wf/tools#kclean). We want to share our findings
upstream for the benefit of everyone that uses client Ubuntu with FDE.
In summary, an additional 1.2G of disk space is a very small price to
pay to avoid the expense of guiding non-expert users to recover from an
over-full partition.

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https://bugs.launchpad.net/bugs/1959971

Title:
  increase /boot partition size

Status in partman-auto package in Ubuntu:
  Triaged
Status in ubiquity package in Ubuntu:
  Confirmed
Status in partman-auto source package in Focal:
  Fix Committed
Status in ubiquity source package in Focal:
  Fix Committed
Status in partman-auto source package in Jammy:
  Triaged
Status in ubiquity source package in Jammy:
  Confirmed

Bug description:
  [Impact]
  All new installs of 20.04.

  [Test case]
  1) Install Ubuntu 20.04 with encryption (this'll create a separate /boot partition) on a system
  2) Validate that the size of the /boot partition is greater than or equal to 768MB; should be somewhere between 768MB and 1536GB.

  [Regression potential]This may adversely affect installs on tiny disks, by taking up more space for the /boot partition than was previously taken, at the cost of / or /home. As such, failures to install due to insufficient space on a partition, or failure to partition a disk that was previously working should be investigated as possible regressions.
  This is a corner case in general since there is no requirement to allocate a separate partition for /boot in the default configuration, and if you are using a non-default configuration where /boot must be a separate partition, you probably also don't have a disk so small that an additional 256MB of disk usage is a problem.

  ---
  The kernel in Jammy is a bit larger than the one in Focal and our previous /boot partition size calculation (LP: #1716999) likely didn't take into account adding modules like nvidia to the initramfs. Subsequently, we need to revisit the size calculations for Focal.

  I'm utilizing cryptsetup and nvidia modules and have a 164M initrd
  when using lz4 (the default in Focal) compression. Using the same
  formula we previously did we end up with this:

  2* (3*11 + 4*164 + 11) = 1400

  So modifying the maximum size to 1536 seems reasonable, the current
  minimum is 512 which is actually a bit too small for an initrd with
  less modules e.g.:

  2* (3*11 + 4*62 + 11) = 584

  So the minimum should also be increased to 768.

  The default compression level for Jammy is currently being discussed
  and until that is decided we shouldn't make changes to partman-auto
  for Jammy.

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