我的 Kubuntu 14.4 上的 muon 不见了。如果我尝试使用
sudo apt-get install muon
我明白了
The following packages have unresolved dependencies:
muon : Depends on: apt-xapian-index but shall not be installed
E: Problems can not be corrected, you have retained defect packages.
（译成英文）
执行命令包裹系统坏了。该如何修复？以各种顺序多次（正如答案所暗示的那样）都没有帮助。
所以我当时做的是
sudo apt-get install apt-xapian-index
答案是
The following packages have unresolved dependencies:
apt-xapian-index : Depends on: python-xapian (>= 1.0.2) but shall not be installed.
Depends on: python-apt (>= 0.7.93.2) but shall not be installed.
Depends on: python-debian (>= 0.1.14) but shall not be installed.
Depends on: python:any (>= 2.7.1-0ubuntu2) but shall not be installed.
E: Problems can not be corrected, you have retained defect packages.
（译成英文）
就在那时我才想起来，我试图在我的 ubuntu 14.04 上安装 python 2.7.10（它本身只有 python 2.7.6）。但是，我删除了和PATH中的扩展，因此~/.profile~/.bashrc
$ python --version
Python 2.7.6
回来了。我仍然有 python 2.7.10，/opt/python并没有改变我的
$ ln -s /opt/python/bin/python2.7 /usr/local/bin/python2.7.10
我该怎么办？
答案1
解决方案是明确允许 apt 降级软件包：
sudo su -
sudo echo 'Package: *
Pin: release o=Ubuntu
Pin-Priority: 1001
' >> /etc/apt/preferences.d/allow-downgrade
apt-get update
apt-get upgrade
apt-get -f install
apt-get update
mv /etc/apt/preferences.d/allow-downgrade > /etc/apt/preferences.d/allow-downgrade_old
sudo apt-get install muon
exit