title: How get correct DPI information on linux?
body: <p>system: Ubuntu 20.04.3 LTS</p>
  <p>The default Resolution is 1280x720, the DPI is 96.</p>
  <p>When adjust the 'fractional scaling' is 125%, I have two options to get the DPI:</p>
  <p>Use the command: <code>xrdb -query |grep dpi</code></p>
  <p>the DPI is <code>192</code> ??!</p>
  <pre><code>Xft.dpi:    192
  </code></pre>
  <p>Use the command: <code>xdpyinfo</code>, the DPI is <code>120</code>.</p>
  <pre><code>screen #0:
    dimensions:    2048x1152 pixels (433x244 millimeters)
    resolution:    120x120 dots per inch
  </code></pre>
  <p>Why the two commands return different DPI ?</p>
  <p>When scaling to 125%, Why the dimensions is 2048x1152 ? (2048/1280 = 1.6, 1152/720 = 1.6)</p>
  <p>Is the X11 API is wrong or other problem?
  Thanks.</p>