Debugging custom libraries hive update logging to console.
When launch Hive cli change logging set root logging or your library logging to DEBUG or INFO and print to console-
hive --hiveconf hive.root.logger=<info>,console
</info>
Check Mapreduce jobs logs-
http://jobtracker:<job tracker port e.g.>/jobdetails.jsp?jobid=<job id> then go to map or reduce and browse logs</job></job>