需要apt_preferences澄清

Question

问题是：

# apt-get install libssl-dev
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 libssl-dev : Depends: libssl1.0.0 (= 1.0.1t-1+deb8u6) but 1.0.2k-1~bpo8+1 is to be installed
              Recommends: libssl-doc but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

这项研究：

# apt-cache policy libssl-dev
libssl-dev:
  Installed: (none)
  Candidate: 1.0.1t-1+deb8u6
  Version table:
     1.0.2k-1~bpo8+1 0
        400 http://httpredir.debian.org/debian/ jessie-backports/main amd64 Packages
     1.0.1t-1+deb8u6 0
        900 http://security.debian.org/ jessie/updates/main amd64 Packages
     1.0.1t-1+deb8u5 0
        900 http://httpredir.debian.org/debian/ jessie/main amd64 Packages

100 <= P< 500导致安装一个版本，除非有一个属于其他发行版的可用版本，或者已安装的版本是最近的，500 <= P< 990将导致安装一个版本，除非有一个属于目标发行版的可用版本，或者已安装的版本是最新版本。

详细信息：

# lsb_release -a
No LSB modules are available.
Distributor ID: Debian
Description:    Debian GNU/Linux 8.7 (jessie)
Release:    8.7
Codename:   jessie

# cat /etc/apt/preferences
Package: *
Pin: release a=stable
Pin-Priority: 900

Package: *
Pin: release a=jessie-backports
Pin-Priority: 400

尽管apt-get试图从jessie-backorts安装版本，但我的优先级似乎是正确的。为什么？

编辑

# apt-cache policy libssl1.0.0
libssl1.0.0:
  Installed: 1.0.2k-1~bpo8+1
  Candidate: 1.0.2k-1~bpo8+1
  Version table:
 *** 1.0.2k-1~bpo8+1 0
        100 /var/lib/dpkg/status
     1.0.1t-1+deb8u6 0
        990 http://security.debian.org/ jessie/updates/main amd64 Packages
     1.0.1t-1+deb8u5 0
        990 http://httpredir.debian.org/debian/ jessie/main amd64 Packages

我想我现在明白了问题的所在。

Answer 1

您不应该将backports套件固定在一起；默认情况下，它被配置为只用于具有明确目标的安装，或用于升级支持版本。我建议您完全删除/etc/apt/preferences文件。

无论如何，您的错误与钉扎无关，而是由从后端安装的libssl1.0.0版本引起的。注意apt-cache policy libssl-dev给出的候选版本:这表明apt-get更喜欢稳定的版本，而不是支持的版本。你得到的错误信息是

The following packages have unmet dependencies:
 libssl-dev : Depends: libssl1.0.0 (= 1.0.1t-1+deb8u6) but 1.0.2k-1~bpo8+1 is to be installed
              Recommends: libssl-doc but it is not going to be installed

这表明apt-get正在尝试安装libssl-dev 1.0.1t-1+deb8u6 8u 6(因此依赖于具有相同版本的libssl1.0.0 )，但考虑的libssl1.0.0版本是1.0.2k-1~bpo8+1，因为已经安装了.