where is the oracle 12c logfile? I am getting all of the following error first:


  ORA-12162: TNS:net service name is incorrectly specified


When I export the ORACLE_SID , I can run any command and I get the following error:


  connected to an idle instance


Where is the ALERTLOG file in 12C?

I can't see any file in ORACLE_HOME/log folder. I am using ubuntu 14.04 BTW.
The alert log never has been under ORACLE_HOME/log. 

It is in $ORACLE_BASE/diag/rdbms/&lt;sid&gt;/&lt;sid&gt;/trace and is named alert_&lt;sid&gt;.log 

If you don't have $ORACLE_BASE, this typically is equivalent to $ORACLE_HOME/../../..

This is no different in 12c than it was in 11g (or 10g if I recall correctly).

You can also use the ADRCI tool: http://docs.oracle.com/database/121/SUTIL/adrci.htm#SUTIL1474