RDBMS Error Traching

If you are getting the

ALTER SYSTEM SET EVENT='942 trace name errorstack forever, level 4' SCOPE=spfile;

If you have set multiple events, your statement should look like this:
ALTER SYSTEM SET EVENT='942 trace name errorstack forever, level 4'
, '1000 trace name context forever, level 1' SCOPE=spfile;

You can reset events lateron with:
alter system reset event scope=SPFILE sid='*';