title: Docker: How to add backports to sources.list via Dockerfile?
body: <p>I need to install <code>ffmeg</code> on debian jessie via Dockerfile.</p>
  
  <p>Debian recommends to use backports. But how do I do this in my Dockerfile?</p>
  
  <p>Add</p>
  
  <pre><code>deb http://httpredir.debian.org/debian jessie-backports main non-free
  deb-src http://httpredir.debian.org/debian jessie-backports main non-free
  </code></pre>
  
  <p>to</p>
  
  <pre><code>/etc/apt/sources.list
  </code></pre>
  
  <p>This is how my Dockerfile looks like:</p>
  
  <pre><code>FROM node:4.8-slim
  
  COPY . /
  
  ## How to add backports to list ???
  
  RUN apt-get update &amp;&amp; apt-get install ffmpeg &amp;&amp; ffmpeg -i
  
  RUN (cd programs/server &amp;&amp; npm install --silent)
  CMD ["node", "main.js"]
  </code></pre>