title: Using a non existing UID for a docker container - what is the meaning or implications?
body: <p>I read a lot about running a docker container with different users (i.e different than root).
  I was wondering, since its possible to run a docker container with a UID that does not exist on the host, what is the meaning of this? what should I expect?
  for example, assume the following Dockerfile:</p>
  <pre><code>FROM scratch
  COPY my-app /app/
  WORKDIR /app
  USER 110011:110011
  CMD [&quot;/app/my-app&quot;]
  </code></pre>
  <p>Assuming my-app doesn't require any special permissions, this works.
  So I was wondering, what does this mean in term of the host and its user.
  I know its nameless, but is it really a non existing user? and what does this mean?</p>
  <p>I assume that I should expect no permissions on the file system in the container.
  anything else I should be wary about?</p>
  <p>any thoughts would be welcome.</p>
  <p>Thanks!</p>