Docker:无法纠正问题，您已持有损坏的包

Question

我有一个Dockerfile，我已经使用了很多次，没有出现任何问题。现在我需要向其中添加一些包(ssmtp和sendmail)，当我添加它们时，构建会失败，并显示以下错误：

Sending build context to Docker daemon 645.3 MB
Sending build context to Docker daemon 
Step 0 : FROM debian:jessie
 ---> 736e5442e772
Step 1 : MAINTAINER Larry Martell <larry.martell@foo.com>
 ---> Using cache
 ---> bd272aa26940
Step 2 : ENV HOME /opt/django/CAPgraph/
 ---> Using cache
 ---> 1c540ed91808
Step 3 : RUN echo "deb http://http.debian.net/debian jessie-backports main" >> /etc/apt/sources.list
 ---> Using cache
 ---> 8788d48e625d
Step 4 : RUN (apt-get update && DEBIAN_FRONTEND=noninteractive apt-get install -y build-essential git python python-dev python-setuptools nginx sqlite3 supervisor mysql-server libmysqlclient-dev vim cron unzip software-properties-common python-software-properties openjdk-8-jre xvfb wkhtmltopdf ssmtp sendmail)
 ---> Running in 8986bca93fdb
Get:1 http://security.debian.org jessie/updates InRelease [63.1 kB]
Get:2 http://security.debian.org jessie/updates/main amd64 Packages [436 kB]
Get:3 http://http.debian.net jessie-backports InRelease [166 kB]
Get:4 http://httpredir.debian.org jessie-updates InRelease [145 kB]
Get:5 http://http.debian.net jessie-backports/main amd64 Packages [1031 kB]
Get:6 http://httpredir.debian.org jessie-updates/main amd64 Packages [17.6 kB]
Ign http://httpredir.debian.org jessie InRelease
Get:7 http://httpredir.debian.org jessie Release.gpg [2373 B]
Get:8 http://httpredir.debian.org jessie Release [148 kB]
Get:9 http://httpredir.debian.org jessie/main amd64 Packages [9049 kB]
Fetched 11.1 MB in 9s (1211 kB/s)
Reading package lists...
Reading package lists...
Building dependency tree...
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:
 sendmail : Depends: sendmail-bin but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
The command '/bin/sh -c (apt-get update && DEBIAN_FRONTEND=noninteractive apt-get install -y build-essential git python python-dev python-setuptools nginx sqlite3 supervisor mysql-server libmysqlclient-dev vim cron unzip software-properties-common python-software-properties openjdk-8-jre xvfb wkhtmltopdf ssmtp sendmail)' returned a non-zero code: 100

如果我将这些包添加到列表中，我就会抱怨其他包。这个“持有损坏的包”消息是什么意思?我该如何修复它？

这是我的Dockerfile的第一部分：

FROM debian:jessie ENV HOME /opt/django/CAPgraph/ 
RUN echo "deb http://http.debian.net/debian jessie-backports main" >> /etc/apt/sources.list 
RUN (apt-get update && DEBIAN_FRONTEND=noninteractive apt-get install -y build-essential git python python-dev python-setuptools nginx sqlite3 supervisor mysql-server libmysqlclient-dev vim cron unzip software-properties-common python-software-properties openjdk-8-jre xvfb wkhtmltopdf sendmail ssmtp)

我尝试添加sendmail-bin，但失败了，出现以下错误：

The following packages have unmet dependencies:
 sendmail-bin : Conflicts: mail-transport-agent
 ssmtp : Conflicts: mail-transport-agent
E: Unable to correct problems, you have held broken packages.

然后，我添加了mail-transport-agent，失败的原因是：

Package mail-transport-agent is a virtual package provided by:
  opensmtpd 5.7.3p2-1~bpo8+1
  ssmtp 2.64-8
  sendmail-bin 8.14.4-8+deb8u1
  qmail-run 2.0.2+nmu1
  postfix 2.11.3-1
  nullmailer 1:1.13-1+deb8u1
  msmtp-mta 1.4.32-2
  masqmail 0.2.30-1
  lsb-invalid-mta 4.1+Debian13+nmu1
  exim4-daemon-light 4.84.2-2+deb8u3
  exim4-daemon-heavy 4.84.2-2+deb8u3
  esmtp-run 1.2-12
  dma 0.9-1
  courier-mta 0.73.1-1.6
  citadel-mta 8.24-1+b3

E: Package 'mail-transport-agent' has no installation candidate

Answer 1

Debian被设置为只允许一个邮件传输代理，而您的安装命令试图包含两个代理: ssmtp和sendmail/sendmail-bin。由于它们相互冲突，您需要从安装命令中删除其中一个。

Answer 2

如果sendmail依赖是为了让您的Python应用程序能够通过MTA二进制文件发送电子邮件，那么只需安装ssmtp并将其配置为使用外部sendmail即可。

不建议尝试在Docker容器中运行sendmail