--- old/src/share/classes/jdk/jfr/internal/dcmd/DCmdStart.java	2019-09-27 13:25:31.541578641 +0800
+++ new/src/share/classes/jdk/jfr/internal/dcmd/DCmdStart.java	2019-09-27 13:25:31.427574654 +0800
@@ -24,6 +24,7 @@
  */
 package jdk.jfr.internal.dcmd;
 
+import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.nio.file.Files;
 import java.nio.file.InvalidPathException;
@@ -105,8 +106,9 @@
         if (duration == null && Boolean.FALSE.equals(dumpOnExit) && path != null) {
             throw new DCmdException("Filename can only be set for a time bound recording or if dumponexit=true. Set duration/dumponexit or omit filename.");
         }
-
-
+        if (settings.length == 1 && settings[0].length() == 0) {
+            throw new DCmdException("No settings specified. Use settings=none to start without any settings");
+        }
         Map<String, String> s = new HashMap<>();
 
         if (settings == null || settings.length == 0) {
@@ -116,8 +118,10 @@
         for (String configName : settings) {
             try {
                 s.putAll(JFC.createKnown(configName).getSettings());
+            } catch(FileNotFoundException e) {
+                throw new DCmdException("Could not find settings file'" + configName + "'", e);
             } catch (IOException | ParseException e) {
-                throw new DCmdException("Could not parse setting " + settings[0], e);
+                throw new DCmdException("Could not parse settings file '" + settings[0] + "'", e);
             }
         }