[Bug 1968154] Re: Only keep 2 kernels

[Launchpad Bug Tracker]

This bug was fixed in the package apt - 1.6.17

---------------
apt (1.6.17) bionic; urgency=medium

  * Bump cache minor version for kernel collection.
    The previous update introduced the new kernel autoremoval code which
    collects kernels in the cache as providers of a $kernel package.
    We need to bump the cache minor version for this as otherwise the
    $kernel package might not exist and all kernels end up autoremovable
    until a package got installed or sources updated.

apt (1.6.16) bionic; urgency=medium

  * postinst: Do not run removed kernel postinst.d script (LP: #1974456)

apt (1.6.15) bionic; urgency=medium

  * Revert "Protect currently running kernel at run-time"
  * Backport Determine autoremovable kernels at run-time (LP: #1615381) as of
    2.4.5; including the change to only protect two kernels, not last installed
    one (LP: #1968154)

 -- Julian Andres Klode <juliank at ubuntu.com>  Fri, 12 Aug 2022 12:38:33
+0200

** Changed in: apt (Ubuntu Bionic)
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/1968154

Title:
  Only keep 2 kernels

Status in apt package in Ubuntu:
  Fix Released
Status in apt source package in Bionic:
  Fix Released
Status in apt source package in Focal:
  Fix Released
Status in apt source package in Impish:
  Fix Released

Bug description:
  [Impact]
  APT currently keeps 3 kernels or even 4 in some releases. Our boot partition is sized for a steady state of 2 kernels + 1 new one being unpacked, hence users run out of space and new kernels fail to install, upgrade runs might abort in the middle. It's not nice.

  [Test plan]
  1. Have two kernels installed (let's call them version 3, 2)
  2. Check that both kernels are not autoremovable
  3. Install an old kernel (let's call it 1), and mark it automatic
  4. Check that 1 will be autoremovable (apt autoremove -s)
  5. Reboot into 1, check that 2 is autoremovable (apt autoremove -s)
  6. Actually remove 2
  7. Reboot into 3 and check that both 1 and 3 are now not autoremovable

  [Where problems could occur]
  We could keep the wrong kernels installed that the user did not expect.

  We remove the requirement to keep the most recently installed version,
  previously recorded in APT::LastInstalledKernel, to achieve this, as
  we had 3 hard requirements so far:

  1. keep booted kernel
  2. keep highest version
  3. keep most recently installed

  1 can't be removed as it would break running systems, 2 is what you
  definitely want to keep.

  During normal system lifetime, the most recently installed kernel is
  the same as the highest version, so 2==3, and there are no changes to
  behavior.

  Likewise, if you most recently installed an older kernel manually for
  debugging, it would be manually installed and not subject to removal,
  even if the rule is dropped.

  The behavior really only changes if you install an older kernel, and
  then mark it auto - that older kernel becomes automatically removable
  immediately after it is marked as auto.

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