ORA-12547 TNS lost contact

Issue / Oracle error

sqlplus scott/tiger
SQL*Plus: Release 10.2.0.5.0 - Production on Wed May 18 09:32:35 2011
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ERROR:
ORA-12547: TNS :lost contact when try to connect to Oracle.

Issue description

I saw that TNS connection issue along with ORA-12547 Oracle error several times, usually when trying to connect to Oracle database server on Unix / Linux host with an OS user that does not belong to oinstall group (Oracle binaries owner group).  In this case, interesting enough that local TNS connection to database (when using tnsnames alias) works fine:

sqlplus scott/tiger@orcl

and only local BEQ protocol connection through an Oracle error ORA-12547:

sqlplus scott/tiger
ERROR:
ORA-12547: TNS:lost contact

There can be different reasons of this issue, but usually the problem is in wrong privileges/ownership of some Oracle binaries located in $ORACLE_HOME/bin directory. Perhaps, Oracle database binaries were installed / linked not correctly or something or somebody has changed the files’ ownership.

Solution

1. Ensure the DB is up and running and you can connect locally AS SYSDBA to the database using Oracle binaries owner (usually oracle:oinstall Unix / Linux user). If it does not work, probably you encounter a different problem.
2. Check privileges of an Oracle file on Unix / Linux host where database is running:
cd $ORACLE_HOME/bin
ls -ltr oracle
-rwxr-xr-x    1 oracle   oinstall       136803483 Mar 16 20:32 oracle
3. Change permissions as below:
chmod 6751 oracle
ls -ltr oracle
-rwsr-s--x    1 oracle   oinstall       136803483 Mar 16 20:32 oracle
4. Usually the above operation should fix the issue but I suggest continue investigating privileges of other files to avoid further possible problems.  As the matter of fact these special rights of Oracle binaries are set by $ORACLE_HOME/root.sh script on Unix / Linux after the Oracle installation. You can run the script again as root user, if you see more files have wrong permissions or ownership (make backup before, just in case). For that I provide as an example 2 lists of oracle binary files in $ORACLE_HOME/bin directory with correct rights below.