dpkg“处理触发器时发现循环”libc-bin

Question

在debian/ubuntu 16.04.01系统(gcloud-compute)上，我试图删除并重新安装一个搞砸了的postfix包，而不是删除依赖它的包(automysqlbackup)，并在一开始就强制安装它。因为这是一个正在运行的系统，所以我尽量不要打扰太多。尝试看看会发生什么：

$ dpkg --simulate --purge 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.

由于通向postfix的邮件器链是ok的，所以我想把它放在原处：

$ 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

我不是很精通这一点，我正在使用一个我没有创建的系统，所以任何帮助/指示都会非常感谢。libc-bin循环问题看起来像是搞砸了，需要在处理postfix问题之前修复。如何继续？

Answer 1

解决方案是安装nullmailer，它删除了postfix，但仍然满足default-mta和mail-transport-agent依赖关系。然后清除postfix，然后安装postfix：

  apt install nullmailer
  apt purge postfix
  apt install postfix

非常感谢ubuntu用户组的Peter Silva提出了这个方法。