title: Can I ensure that every CentOS 7 has /etc/os-release file?
body: <p>I made a script, and it checks OS version in the beginning.<br>
  It reads /etc/os-release file, and checks whether the os is CentOS 7 or not.<br>
  But I'm not sure whether I can ensure that every CentOS 7 has that file.<br>
  Other OSs don't matter, but CentOS 7 matters.<br>
  Can I ensure this?<br>
  Is there any document about this?<br>
  Thanks :)</p>