Applying PSU 11.2.0.2.4 on Oracle 11.2.0.2.0 is often a breezing experience. But sometimes you get a mild jolt kind of thing when at the last step, after a beautifully successful patching session you get following error, while trying to restart the listener:

/u01/app/oracle> lsnrctl start
lsnrctl: symbol lookup error: lsnrctl: undefined symbol: nlgh


If you panic and start getting bad impressions, you are so human.

But don't worry, just relink all the binaries and try again. But before that, you must shutdown all the databases and there should be no Oracle binary running.

After making sure that nothing Oracle is  running, relink:

/u01/app/oracle/product/11.2.0/db_1/bin> ./relink all
writing relink log to: /u01/app/oracle/product/11.2.0/db_1/install/relink.log
/u01/app/oracle/product/11.2.0/db_1/bin> lsnrctl start

And listener should start.