EM Configuration issue. $ORACLE_HOME/rhel.localdomain.net_orcl not found.

Problem:

Recently I installed RHEL 5 and Oracle Database 11gR2 (11.2.0.3) on a machine. After that I installed OEM12c R2 (12.1.0.2) without any issues.

Right after the Oracle installation, without having made any changes, I typed:
cd $OMS_HOME/bin
$ ./emctl stop oms -all
 
and received the following error:

EM Configuration issue. /u01/app/oracle/product/11.2.0/db_1/rhel.localdomain.net_orcl not found.

I was able to correct the problem by doing the following:

cd $ORACLE_HOME
ln -s localhost_orcl rhel.localdomain.net_orcl
cd $ORACLE_HOME/oc4j/j2ee
ln -s OC4J_DBConsole_localhost_orcl OC4J_DBConsole_rhel.localdomain.net_orcl

Note: If the folder localhost_orcl doesn't lie in ORACLE_HOME location, you can simply create the folder with user who owns the database.

I can now use emctl to start and stop the OMS without trouble.

But the strange question is why did the Oracle installer use 'localhost_orcl' instead of 'rhel.localdomain.net_orcl'.
The service name I specified at the 'Desktop Class' installation in the OUI was 'rhel.localdomain.net' - it was printed already.
 I definitely did not change the host or domain name or made any changes to the hosts file, or any other changes at all

I tried to stop database and listner, than start database and listner and retest issue but still the issue persisted.

Solution:
So I would recommend in environment variable file set  ORACLE_HOSTNAME variable before invoking the OUI or when you run OUI environment variable, you can specify this hostname to avoid any problem.

./runInstaller -ORACLE_HOSTNAME=myhostname.mydomain

Note:Please be sure DO NOT SET ORACLE_HOME or ORACLE_SID before starting EM12c installation.
Now you should not see this issue.

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OC4J Configuration issue. /u01/app/oracle/product/11.2.0/db_1/oc4j/j2ee/OC4J_DBConsole_rhel.localdomain.net_orcl not found

For this error please try below command:

./emca -config dbcontrol db << it will ask u some questions liks sys user pass, lsnr port etc. please give correct value and retest issue
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Hope this helps..!!