ubuntu – 升级系统时与PAM配置文件冲突

我有一个运行Ubuntu 14.04.4 LTS的VPS;它是由OVH的Plesk整体安装的.我juste进行了apt-get升级,并且在某些时候我收到了关于PAM的消息.该系统是法语,但基本上它说：

At least one file of /etc/pam.d/common-{auth,account,password,session} was modified locally. Please indicate if local changes should be discarded and stick with the standard configuration. Otherwise you will have to configure the authentication system by yourself.

我决定保留当地的变化,APT也报告说：

pam-auth-update: Local modifications to /etc/pam.d/common-*,not updating.
pam-auth-update: Run pam-auth-update --force to override.

我想知道本地更改与更新要设置的文件之间的区别.我怎样才能做到这一点？

因为我不想改变系统上PAM的实时配置,所以我最终使用chroot jail来设置默认的PAM配置,以便我可以查看差异：

# lsb_release --codename
Codename:       trusty
# debootstrap trusty /tmp/foo
I: Retrieving Release 
I: Retrieving Release.gpg 
  ...

查看差异：

for f in common-{account,auth,session,session-noninteractive}; do
  echo ==== $f ====
  diff --unified /etc/pam.d/$f /tmp/foo/etc/pam.d/$f
done