JAR does not exist or is not a normal file
I faced the same problem and problem was with the version number in file. For example, in the installation instructions, the command was:
bin/hadoop jar share/hadoop/mapreduce/hadoop-mapreduce-examples-3.2.1.jar grep input output 'dfs[a-z.]+'
While the version I'm working with was 3.1.3 so what worked for me was:
bin/hadoop jar share/hadoop/mapreduce/hadoop-mapreduce-examples-3.1.3.jar grep input output 'dfs[a-z.]+'