title: jmap tool works only as root and output columns are not clear
body: <p>Using jmap on Ubuntu Mate 18.04-64bits with Oracle JDK 10.0.1-64bits, the tool works only when running both the target and the tool as root, but using the same normal user for running both gives the following error:</p>
  
  <pre><code>Exception in thread "main" com.sun.tools.attach.AttachNotSupportedException: Unable to open socket file /proc/13538/cwd/.attach_pid13538: target process 13538 doesn't respond within 10500ms or HotSpot VM not loaded
  at jdk.attach/sun.tools.attach.VirtualMachineImpl.&lt;init&gt;(VirtualMachineImpl.java:103)
  at jdk.attach/sun.tools.attach.AttachProviderImpl.attachVirtualMachine(AttachProviderImpl.java:58)
  at jdk.attach/com.sun.tools.attach.VirtualMachine.attach(VirtualMachine.java:207)
  at jdk.jcmd/sun.tools.jmap.JMap.executeCommandForPid(JMap.java:124)
  at jdk.jcmd/sun.tools.jmap.JMap.main(JMap.java:114)
  </code></pre>
  
  <p>When using root user to run the following command</p>
  
  <pre><code>jmap -clstats &lt;pid&gt;
  </code></pre>
  
  <p>everything works fine but I found some difficulties to understand the meaning of the output columns:
  <a href="https://i.stack.imgur.com/3SNt8.png" rel="noreferrer"><img src="https://i.stack.imgur.com/3SNt8.png" alt="enter image description here"></a>
  Is there any official documentation that explains the meaning of each column ?</p>