When starting Oracle Listener gets an error TNS-00525: Insufficient privilege for operation

Symptoms:
When trying to start the Oracle Listener, it returns an error regarding permission but not clear on the logs what it is:

TNSLSNR for Linux: Version 19.0.0.0.0 - Production
System parameter file is /u01/ora19c/product/19.3.0/network/admin/listener.ora
Log messages written to /u01/ora19c/diag/tnslsnr/sandbox19js/listener/alert/log.xml
Listening on: (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=sandbox19js)(PORT=1521)))
Error listening on: (DESCRIPTION=(ADDRESS=(PROTOCOL=IPC)(KEY=EXTPROC1521)))
TNS-12555: TNS:permission denied
 TNS-12560: TNS:protocol adapter error
  TNS-00525: Insufficient privilege for operation
   Linux Error: 1: Operation not permitted

Cause:
In the directory /var/tmp/.oracle there exist some socket files which do not belong to UNIX user oracle and group dba, but to another user.
When the Listener process starts, it tries to create the following socket files:
  /var/tmp/.oracle/s#<pid>.1
  /var/tmp/.oracle/s#<pid>.2
  /var/tmp/.oracle/sREGISTER
where <pid> is the ID of the operating system process for the Listener.

Solution:
As UNIX user root, delete all socket files from directory /var/tmp/.oracle
Then as oracle owner UNIX user, starts the Listener by executing the command "lsnrctl start".