Comment 8 for bug 1598300

First, xinetd is not needed. systemd handles running services on-demand well.

Important to know is that there are two access methods for CUPS:

1. The domain socket file /var/run/cups/cups.sock

2. IP Port 631

CUPS can be configured to use one of these methods or both.

Both methods can be used and the applications printing via CUPS and correctly implemented (usually using libcups) automatically choose a suitable method.

As web browsers can only access network locations, the CUPS web interface is only available via port 631, for example under the URI http://localhost:631/. This means that a CUPS only configured for the domain socket cannot use the web interface at all.

When I look at the systemd files which describe how to automatically start CUPS, I see only a /lib/systemd/system/cups.socket which starts CUPS by traffic on the domain socket and /lib/systemd/system/cups.service which starts CUPS on boot. I do not see some systemd instruction file making CUPS triggered via port 631. This seems to be the problem.

By the way, Mike Sweet, author of CUPS, tells that the web interface should work with on-demand CUPS daemon. See https://github.com/apple/cups/issues/4874.