[Bug 1778817] Re: release upgrade from xenial to bionic desktop: screen locks itself, password to unlock fails

[Steve Langasek]

The failure is because pam_unix depends on libcrypt, and libcrypt is
part of glibc, and compiz doesn't otherwise have libcrypt loaded into
memory, and libcrypt has a tight versioned dependency on the
corresponding version of libc itself (requires symbol GLIBC_2.25).  So
when dlopen() tries to load libcrypt from disk, because compiz is doing
it wrong, it can't find the symbols.

** Also affects: ubuntu-release-upgrader (Ubuntu Bionic)
   Importance: Undecided
       Status: New

** Also affects: compiz (Ubuntu)
   Importance: Undecided
       Status: New

** Changed in: compiz (Ubuntu)
   Importance: Undecided => Critical

** Changed in: ubuntu-release-upgrader (Ubuntu Bionic)
   Importance: Undecided => Critical

** Changed in: compiz (Ubuntu Bionic)
   Importance: Undecided => Critical

** Changed in: ubuntu-release-upgrader (Ubuntu Bionic)
       Status: New => Triaged

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https://bugs.launchpad.net/bugs/1778817

Title:
  release upgrade from xenial to bionic desktop: screen locks itself,
  password to unlock fails

Status in compiz package in Ubuntu:
  New
Status in ubuntu-release-upgrader package in Ubuntu:
  Triaged
Status in compiz source package in Bionic:
  New
Status in ubuntu-release-upgrader source package in Bionic:
  Triaged

Bug description:
  During a release upgrade, the screen should not be locked because the
  upgrade of underlying libraries may leave the system in an
  inconsistent state where the process locking the screen may not be
  able to unlock it again.

  There is code in the ubuntu-release-upgrader to handle this
  (DistUpgrade/DistUpgradeQuirks.py:DistUpgradeQuirks._inhibitIdle).

  I have just started a release upgrade of an Ubuntu desktop from xenial
  to bionic with update-manager -d.  After leaving it unattended for a
  while, I came back to find the screen was locked.

  /var/log/auth.log includes messages such as:

  Jun 26 16:00:45 epona compiz: PAM unable to dlopen(pam_unix.so):
  /lib/security/pam_unix.so: cannot open shared object file: No such
  file or directory

  This indicates a problem dlopen()ing the PAM modules (actual path:
  /lib/x86_64-linux-gnu/security/pam_unix.so) because some ABI has
  changed in the system libraries, and the copy loaded into the running
  compiz process does not have the symbols required in order to run this
  module.

  This is the exact reason the screensaver is supposed to be inhibited
  on upgrade.

  This is also why every sensible screensaver spawns a fresh helper
  process to handle the authentication through PAM.  compiz (unity),
  apparently, does not.

  I do not yet know what symbols have changed to cause this failure.
  I'm still investigating that.

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