title: The output of my graph from rrdtool is blank. Why?
body: <p>I'm wanting to graph the memory of certain processes in windows using rrdtool which I can then show in a simple webpage.</p>
  <p>So I got this far.  Not quite sure I understand how it works after following some tutorials I get blank output.</p>
  <pre><code>rrdtool create psrvr-mem.rrd --start 1023654125 --step 300 DS:mem:GAUGE:600:0:U RRA:AVERAGE:0.5:12:24 RRA:AVERAGE:0.5:288:31
  </code></pre>
  <p>Update script.</p>
  <pre><code>@ECHO OFF
  
  :LOOP
  FOR /F &quot;tokens=*&quot; %%g IN ('powershell &quot;get-process psrvr | select -ExpandProperty PrivateMemorySize&quot;') do (SET mem_usage=%%g)
  
  rrdtool update psrvr-mem.rrd N:%mem_usage%
  TIMEOUT /t 300
  GOTO LOOP
  </code></pre>
  <p>And finally the graph</p>
  <pre><code>rrdtool graph memory.png --start -1800 -a PNG -t &quot;Memory&quot; --vertical-label &quot;&quot; -w 1260 -h 400 -r DEF:mem=psrvr-mem.rrd:mem:AVERAGE  AREA:mem#FF0000
  </code></pre>
  <p>Unfortunately, the result is an empty graph.  Not sure why.  And not quite understanding if the start time is particularly critical or not.</p>
  <p>-- edit --
  Still not creating lines on the graph.
  However, well I found one problem is there were no labels on any axis.  Because the font file was missing.  Turns out the pre-compiled binaries downloaded from rrdtool website are 15 years out of date for windows.  I found a newer binary but if I get this going then I'll probably try and compile it with the latest revision.  For now, I'll settle with something that seems to be working better from 2013.</p>
  <p>After more messing about this is my attempt at creating a 5 minute average.
  rrdtool create psrvr-mem.rrd --start 1592774026 --step 60 DS:mem:GAUGE:120:0:U RRA:AVERAGE:0.5:1:5</p>
  <p>Then fill with some values using the update script above.</p>
  <p>And then try to graph it again.
  rrdtool graph memory.png --start=now-300  -a PNG -t &quot;Memory&quot; --vertical-label &quot;Bytes&quot; -w 800 -h 300 -r DEF:mem=psrvr.rrd:mem:AVERAGE LINE:mem#FF0000</p>
  <p>The output is a graph where the line isn't moving. It might be zero all the way.</p>
  <p><a href="https://i.stack.imgur.com/FJl3q.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/FJl3q.png" alt="enter image description here" /></a></p>