title: Where can I find a list of 'os' and 'dist' options for Travis-CI / Multi OS Build Matrix
body: <p><a href="https://docs.travis-ci.com/user/multi-os/" rel="noreferrer">Per the Travis-CI documentation</a> you can run tests on different operating systems and distributions amongst them. </p>
  
  <p>A the time of writing, a Google search doesn't turn up a list of <strong>all</strong> the possible os and dist options. All one has to go from is the <a href="https://docs.travis-ci.com/user/multi-os/#Example-Multi-OS-Build-Matrix" rel="noreferrer">following example</a> which provides the following under the <strong><em>build matrix</em></strong> sub heading:</p>
  
  <blockquote>
    <p>There are many options available and using the <code>matrix.include</code> key is
    essential to include any specific entries. For example, this matrix
    would route builds to the Trusty beta build environment and to an OS X
    image using Xcode 7.2:</p>
    
    <p><code>matrix:
      include:
        - os: linux
          dist: trusty
          sudo: required
        - os: osx
          osx_image: xcode7.2</code></p>
  </blockquote>
  
  <p>Yet there's no guidance on what options are available for the <code>os</code>, <code>dist</code>, or <code>osx_image</code> keys. Does anyone know where to find these values?</p>