CUPS service on RHEL7 is configured to support on demand start using systemd unit cups.socket. However it's only configure to start on demand by accessing a UNIX socket and not the CUPS web interface socket on TCP port 631. This makes our check fails which just tries to connect to localhost:631. We should add an additional check if /var/run/cups/cups.sock exists (owned by systemd) to provide better out of the box experience. Workaround is to manually enable cups.service.
Fixed in r29408.
Tested using ThinLinc build 4505, works as expected with cups.service stopped and cups.socket running.
(In reply to comment #2) > Tested using ThinLinc build 4505, works as expected with cups.service stopped > and cups.socket running. Also tested with cups.service enabled and running which also works as expected.