How to debug "IO Error: End of TNS data channel" errors? I am seeing sporadic reports of an application failing certain queries with an "End of TNS data channel" error from the Oracle (10g) server.  Are there any queries I can run (e.g., with SQL*Plus or other tool) to ask the Oracle server what was the cause of such failures?  What logs should I look for?
You could check the alert log, as described in the Stack Overflow Q &amp; A:

How to find and tail the Oracle alert log

...where the question author tardate says:


  I posted some bash and Perl scripts to find and tail the alert log on my blog some time back, and I'm surprised to see that post still getting lots of hits.
  The technique used is to lookup background_dump_dest from v$parameter.


The accepted answer by cagcowboy adds:


  If the background_dump_dest parameter isn't set, the alert.log will be put in $ORACLE_HOME/RDBMS/trace.