title: Mount Docker container's root filesystem as read only
body: <p>I want to mount a container's root filesystem as read-only when I run the following command:</p>
  <pre class="lang-sh prettyprint-override"><code>docker ps --quiet --all | \
    xargs docker inspect \
      --format '{{ .Id }}: ReadonlyRootfs={{ .HostConfig.ReadonlyRootfs }}'
  </code></pre>
  <p>If the above command returns <code>true</code>, it means the root filesystem is mounted read-only. If the above command returns <code>false</code>, it means the root filesystem is writable.</p>
  <p>When I run the command, <code>ReadonlyRootfs=false</code> is being shown.  How do I make it show <code>true</code>?</p>