Running Oracle 19c gridSetup.sh or runInstaller on Linux 8, the following errors occur:
[INS-08101] Unexpected error while executing the action at state: ‘supportedOSCheck’

SOLUTION
Set the following variable:
$ export CV_ASSUME_DISTID=OEL7.8
OR
Edit the file cvu_config which is located in $ORACLE_HOME/cv/admin, change the line from
# Fallback to this distribution id
#CV_ASSUME_DISTID=OEL5
to
# Fallback to this distribution id
CV_ASSUME_DISTID=OEL7.8