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From: roy@phri.UUCP (Roy Smith)
Newsgroups: comp.unix.wizards
Subject: Re: distributed /etc/printcap
Message-ID: <2902@phri.UUCP>
Date: Sun, 20-Sep-87 22:13:44 EDT
Article-I.D.: phri.2902
Posted: Sun Sep 20 22:13:44 1987
Date-Received: Mon, 21-Sep-87 04:31:21 EDT
References: <81900001@sfu_cmpt>
Reply-To: roy@phri.UUCP (Roy Smith)
Organization: Public Health Research Inst. (NY, NY)
Lines: 66
Summary: Use the Yellow Pages (achk, gag!)

In article <81900001@sfu_cmpt> stevec@sfu_cmpt.cs.sfu describes how some
of his 50-odd Suns have private /etc/printcaps, and some share a common
/etc/printcap via NFS, and the problems therein.

	We took a different approach.  We (actually I had little to do with
it; phri!nomi did all the hard work) hacked up lpr to use the Yellow Pages.
BTW, printcap seems like such a natural for YP that I'm really surprised
that Sun doesn't ship systems with it already set up.  All of the lpr suite
of programs now know to look in the local /etc/printcap first to resolve a
printer name and then to query the YP.  Thus, we list all our printers in
the YP and for each host which actually has a printer, we put an entry in
the local /etc/printcap for the printer.  Most hosts don't have local
printers so they don't have /etc/printcaps at all (or zero-length ones) For
example, our YP has the following entry:

laser9|ps9: \
	:lp=:rm=adenine:rp=laser9:\
	:sd=/usr/spool/laser9:lf=/usr/spool/laser9/log:

but adenine's /etc/printcap looks like:

laser9|ps9:\
	:lp=:rm=phri:rp=laser10:\
	:sd=/usr/spool/laser9:\
	:lf=/usr/spool/laser9/log:
	
#laser9|ps9|postscript|PostScript:\
#	:lp=/dev/ttya:sd=/usr/spool/laser9:\
#	:lf=/usr/spool/laser9/log:af=/usr/adm/laser9.acct:\
#	:br#9600:rw:fc#0000374:fs#0000003:xc#0:xs#0040040:mx#0:sf:sb:\
#	:if=/usr/local/lib/ps/psif:\
#	:of=/usr/local/lib/ps/psof:gf=/usr/local/lib/ps/psgf:\
#	:nf=/usr/local/lib/ps/psnf:tf=/usr/local/lib/ps/pstf:\
#	:rf=/usr/local/lib/ps/psrf:vf=/usr/local/lib/ps/psvf:\
#	:cf=/usr/local/lib/ps/pscf:df=/usr/local/lib/ps/psdf:

	Actually, I happened to pick an example which is a bit more
interesting than I intended, but illustrates something worth talking about.
Usually, adenine's /etc/printcap is just the commented out entry.  It just
so happens that laser9 is down for a few days right now so we're rerouting
jobs sent there to laser10, which is on host "phri".

	It's not very efficient (the jobs get sent to adenine, which then
turns them around and ships them to phri), but it's only for a few days and
we're willing to put up with the extra network traffic for a while in
return for the administrative convenience.  The efficient alternative would
have been to change the YP entry for laser9 to point to phri:laser10, but
then I would have had to change the local entry on adenine as well.

	One minor wart in this approach.  We use /etc/printcap on our
master YP server as the source for the YP printcap map.  Since a machine
with a local printer needs a printcap entry for that printer different from
what's in the YP map, this only works as long as we don't have a printer on
our master YP server.  If we ever do that, we'll have to switch over to
keeping the map source file someplace other than /etc/printcap.

	Please do not construe my advocacy of YP in this situation to mean
that I think YP is any more than an ugly hack.  The idea is nice, but the
implementation is disgusting.  I've seen YP programs fail in all sorts of
strange and wonderful (and decidedly non-intuitive) ways.  For example,
"getpwuid (getuid)" can fail (with errno set to all sorts of
non-informative things) if you don't have things set up properly.
-- 
Roy Smith, {allegra,cmcl2,philabs}!phri!roy
System Administrator, Public Health Research Institute
455 First Avenue, New York, NY 10016