title: Docker error: Unable to locate package git
body: <p>I'm using an image <code>nginx</code> which is based on <code>dockerfile/ubuntu</code>. On attaching to the docker container's shell</p>
  
  <pre><code>docker exec -it &lt;container_id&gt; /bin/bash
  </code></pre>
  
  <p>I want to do a <code>git pull</code> so I tried installing <code>git</code> but <code>apt</code> is unable to find the package:</p>
  
  <pre><code>root@a71e45d5cd40:/# apt-get install git
  Reading package lists... Done
  Building dependency tree       
  Reading state information... Done
  E: Unable to locate package git
  </code></pre>
  
  <p>How can we install <code>git</code> from that image and why is it missing?</p>
  
  <hr>
  
  <p><strong>cat /etc/apt/sources.list</strong></p>
  
  <pre><code>deb http://httpredir.debian.org/debian wheezy main
  deb http://httpredir.debian.org/debian wheezy-updates main
  deb http://security.debian.org wheezy/updates main
  deb http://nginx.org/packages/mainline/debian/ wheezy nginx
  </code></pre>
  
  <p><strong>cat /etc/apt/sources.list.d/*</strong></p>
  
  <pre><code>cat: /etc/apt/sources.list.d/*: No such file or directory
  </code></pre>
  
  <p><strong>apt-cache madison git</strong></p>
  
  <pre><code>N: Unable to locate package git
  </code></pre>