libc-bin "cycle found while processing triggers"

[Gary Aitken]

Hi all,

I'm attempting to manage a google-compute system running ubuntu;
I normally run a freebsd system so I'm out of my element here and web
searches haven't helped:

81~16.04.1-Ubuntu SMP Mon May 11 14:56:45 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

When originally built, the system had a screwed-up postfix installation;
in attempting to solve this problem, I wanted to uninstall postfix and
reinstall it.  However, I don't think I should do that because the postfix
installation has an issue:

$ aptitude why postfix
i   automysqlbackup Depends  bsd-mailx | mailx
i A bsd-mailx       Depends  default-mta | mail-transport-agent
i A postfix         Provides mail-transport-agent

$ dpkg --simulate --remove postfix
dpkg: could not open log '/var/log/dpkg.log': Permission denied
dpkg: dependency problems prevent removal of postfix:
  bsd-mailx depends on default-mta | mail-transport-agent; however:
   Package default-mta is not installed.
   Package postfix which provides default-mta is to be removed.
   Package mail-transport-agent is not installed.
   Package postfix which provides mail-transport-agent is to be removed.
  bsd-mailx depends on default-mta | mail-transport-agent; however:
   Package default-mta is not installed.
   Package postfix which provides default-mta is to be removed.
   Package mail-transport-agent is not installed.
   Package postfix which provides mail-transport-agent is to be removed.

dpkg: error processing package postfix (--remove):
  dependency problems - not removing
Processing triggers for libc-bin (2.23-0ubuntu10) ...
dpkg: cycle found while processing triggers:
  chain of packages whose triggers are or may be responsible:
   libc-bin -> libc-bin
  packages' pending triggers which are or may be unresolvable:
   libc-bin: ldconfig
dpkg: error processing package libc-bin (--remove):
  triggers looping, abandoned
Errors were encountered while processing:
  postfix
  libc-bin

If I consider removing libc-bin so I can re-install it and correct the
dependency loop, I am unable to do so:

$ dpkg --simulate --remove libc-bin
dpkg: could not open log '/var/log/dpkg.log': Permission denied
dpkg: error processing package libc-bin (--remove):
  this is an essential package; it should not be removed
Processing triggers for libc-bin (2.23-0ubuntu10) ...
dpkg: cycle found while processing triggers:
  chain of packages whose triggers are or may be responsible:
   libc-bin -> libc-bin
  packages' pending triggers which are or may be unresolvable:
   libc-bin: ldconfig
dpkg: error processing package libc-bin (--remove):
  triggers looping, abandoned
Errors were encountered while processing:
  libc-bin
  libc-bin

I then considered forcing removal of postfix by ignoring dependencies, but
that has the same libc-bin loop issue:

$ dpkg --simulate --ignore-depends bsd-mailx --purge postfix
dpkg: could not open log '/var/log/dpkg.log': Permission denied
(Reading database ... 171222 files and directories currently installed.)
Would remove or purge postfix (3.1.0-3ubuntu0.3) ...
Processing triggers for libc-bin (2.23-0ubuntu10) ...
dpkg: cycle found while processing triggers:
  chain of packages whose triggers are or may be responsible:
   libc-bin -> libc-bin
  packages' pending triggers which are or may be unresolvable:
   libc-bin: ldconfig
dpkg: error processing package libc-bin (--purge):
  triggers looping, abandoned
Errors were encountered while processing:
  libc-bin

Can anyone give me some clues on how to resolve this (i.e. get rid of the
libc-bin self-reference?
The main goal is to uninstall postfix and re-install it, without uninstalling
the automysqlbackup as this is a production system and the autobackup is
working properly.  I believe the postfix dependency is for cases where the
auto-backup fails; it's also preventing mail from being delivered for failing
cron jobs.

Sorry for the naivete of this; I'm new to linux.
BTW, I know I can't actually run these commands unprivileged if I drop the
--simulate.

Thanks,

Gary