HADOOP-12271. Hadoop Jar Error Should Be More Explanatory. Contributed by Josh Elser.

(cherry picked from commit 2087eaf684d9fb14b5390e21bf17e93ac8fea7f8)

hadoop-common-project/hadoop-common/CHANGES.txt

@@ -30,6 +30,9 @@ Release 2.8.0 - UNRELEASED
 
   IMPROVEMENTS
 
+    HADOOP-12271. Hadoop Jar Error Should Be More Explanatory
+    (Josh Elser via harsh)
+
     HADOOP-6842. "hadoop fs -text" does not give a useful text representation
     of MapWritable objects (Akira Ajisaka via bobby)
 

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/RunJar.java

@@ -148,7 +148,8 @@ public class RunJar {
     String fileName = args[firstArg++];
     File file = new File(fileName);
     if (!file.exists() || !file.isFile()) {
-      System.err.println("Not a valid JAR: " + file.getCanonicalPath());
+      System.err.println("JAR does not exist or is not a normal file: " +
+          file.getCanonicalPath());
       System.exit(-1);
     }
     String mainClassName = null;