Data Collector fails to start: "Expected exactly 1 stage lib jar but found X with name lib_name "

Issue:

Data Collector fails to start with the following exception:

MAIN CLASS : com.streamsets.datacollector.main.DataCollectorMain 
Exception in thread "main" java.lang.ExceptionInInitializerError: Expected exactly 1 stage lib jar but found X with name <lib_name> 

Solution:

This exception can happen if there are multiple lib jars under a directory.  A common scenario where this may happen is when performing an RPM upgrade and forgetting to uninstall the stage libraries from the previous version. 

Check the jars under the library path, e.g. for streamsets-datacollector-dev-lib:

ls -al /opt/streamsets-datacollector/streamsets-libs/streamsets-datacollector-dev-lib/lib

If there are older version jars, please make sure to move them out.

For the RPM upgrade, please make sure that you uninstall stage libraries from the previous version as documented here.