Very interesting. I tried to make a fresh (reduced) install of Slack 10.0 in
an old machine, not installing X, but installing, however, all libraries
("L") and console applications ("a" and "ap"), and, of course, some servers
("n") - it is supposed to be a server in which I obviously don't intend to
run any X application/window managers, and in which I wanted to save as
much harddisk space as reasonable.

Tried configuring cups through the browser at console ("links
localhost:631"), and the "parport" with the "hp840c" printer would not
appear in the list... Actually, the parport, parport_pc and lp modules were
not being loaded at startup (even with the hotplug).

Ok, changed permissions to /dev/lp0, restarted cups and back to the browser.
Nothing changed.

Ok, "modprobe lp", restarted cups and again back to the browser. And there
it was, so I finished configuring. Tried a test page and... still not
working... tried "lpr-cups XXXx.txt" and still nothing... and worse, in the
job list, got many of the weird messages "job aborted" (???). Tried the
"restart", and... client-error...

So, set cups error log in debug mode (in cupsd.conf) and tried to print
something again. Examining the log, noticed there was a message about an
"error closing renderer". Looking more carefully, i noticed that the
failure was when the "gs" command/application was invoked, and what was
being missed was an X runtime library to work (at least in this system
configuration): libXt.so.6 !!!

What a sh***, I thought, an X library!!!

Installed X and... it works now... So, it seems that in order to have cups
working in this configuration (a non postscript printer), it will use gs
(ESPgs, I think), and gs seems to need some X in there. Actually, making
"ldd gs" at /usr/bin/ shows at least five runtime-libraries especifically
at the /usr/X11R6/lib/ path: libXt.so.6, libXext.so.6, libX11.so.6,
libSM.so.6 and libICE.so.6 .

It is interesting, because gs can be used under X (to view ps files, for
example) as well as in the printing system, but I thought the part was
quite independent from "X" itself...

Well, hope this to be usefull to someone (took me hours to discover, hope to
avoid others having the same headache).

Regards!

Paulo