Oracle Listener doesn't starts after DB instance installation

During the installation of Netweaver 7.3 on Oracle 19, we faced a scenario where the SWPM stopped while installing the primary application server at the stage where it tends to restart the SAP instance. Further investigation led to the log which suggested that the application host was unable to connect to the database

"R3trans -d" was failing

On checking further it was revealed that the Listener was not running and when an attempt was made to start the listener, it failed

<hostname>:<sid>adm $ lsnrctl start [LISTENER_NAME]

LSNRCTL for LINUX: Version 19.0.0.0.0 - Production on 35-SEP-2024 11:06:29

Copyright (c) 1991, 2024, Oracle.  All rights reserved.

Starting /oracle/<SID>/19/bin/tnslsnr: please wait...

TNSLSNR for <OS>: Version 19.0.0.0.0 - Production

System parameter file is /oracle/<SID>/19/network/admin/listener.ora

Log messages written to /oracle/<SID>/19/network/log/listener.log

Error listening on: (ADDRESS=(PROTOCOL=IPC)(KEY=<SID>.WORLD))

TNS-12555: TNS:permission denied

TNS-12560: TNS:protocol adapter error

  TNS-00525: Insufficient privilege for operation

   <OS> Error: 1: Not owner

Cause of the error: As visible in the error log it points to a permission issue but all the files and folders inside /oracle filesystem were created with the right owner and permission.

Digging further into this issue it was observed that in this case, it was caused by a lack of permissions in the socket files.

These files are present inside the .oracle folder created under /var/tmp

Even though the user used in the installation was ora<sid> still the permission was set to root as owner. 

Resolution: The ownership needs to be changed to ora<sid> or oracle depending on which user is responsible for the installation/operations.

After this change was made the listener was able to start without any issues.

<sid>adm user was able to connect to the database

As a result of which the installation was completed successfully.