libc-bin "cycle found while processing triggers"

[Peter Silva]

dunno... bit of a guess, but it looks like it is getting messed up because
you need a mail-transfer-agent, but the MTA does not need to be postfix.

https://packages.ubuntu.com/bionic/mail-transport-agent

I would try:

apt --simulate install nullmailer

so that should make postfix removable without losing the
mail-transfer-agent target, and thus without triggering libc armageddon.


I don't recommend removing libc... that is never going to end well...
better off re-installing from scratch. You could upgrade to a different
version, but removing will likely leave the userland unusable.


On Mon, Jun 15, 2020 at 10:20 PM Gary Aitken <ubuntu at dreamchaser.org> wrote:

> 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
>
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