libc-bin "cycle found while processing triggers"

[Gary Aitken]

On 6/15/20 9:24 PM, Peter Silva wrote:
> 
> 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.

Thank you!
The complete sequence was:
   apt install nullmailer
   apt purge postfix
   apt install postfix
I believe the install of nullmailer cleared the libc-bin trigger loop.

> 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.

It seemed like a bit harsh on the surface.

Thank you again,

Gary

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