Linux. Oracle. Connection failed Error: -999

“Connection failed   Error:  -999” error message appears while connecting to Oracle database on Linux OS.
First add or edit the value of the following environment variable
in the $LYCIA_DIR/etc/inet.env file, save it, restart an application and check if
$QUERIX_BASE/apache-tomcat/logs/lycia-web.log file contains these lines:
u SqlError : Error number -999 (21561)
e SqlError : ORA-21561: OID generation failed

If “ORA-21561: OID generation failed” error message is found then
it means that an entry for the host is missing in the /etc/hosts file
and host name cannot be resolved via DNS request.
Whether correct DNS record for the host or add host entry into /etc/hosts file.
For example:
host name is
At least the following line must present in the /etc/hosts file: host