On RHEL 7 and CentOS7 systems, if the Rhythmyx server fails to start it may be due to a lack of a static hostname.  This can be temporarily resolved by using the hostname command, but that will not persist when the system reboots.

In order to persist a static hostname change, you will need to modify the /etc/hostname file to have the desired hostname for the instance,  additionally you will need to modify the /etc/hosts file to have localhost aliased to your new hostname.

Example /etc/hosts

127.0 . 0.1 my_custom_hostname localhost.localdomain localhost

You will need to ensure that the /etc/sysconfig/network file has the HOSTNAME property set to the hostname you used in the previous files.  

For additional information on changing sysconfig settings

Finally, the instance will require to be rebooted to pick up the new hostname.  After it has finished rebooting, confirm the new hostname by using the hostname command again.