Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!rutgers!apple!bloom-beacon!mit-eddie!killer!dcs!wnp
From: wnp@dcs.UUCP (Wolf N. Paul)
Newsgroups: comp.unix.xenix
Subject: Re: /usr/lib/uucp/uucico ignores LCK.. files
Message-ID: <216@dcs.UUCP>
Date: 11 Oct 88 11:47:54 GMT
References: <171@libove.UUCP>
Reply-To: wnp@dcs.UUCP (Wolf N. Paul)
Organization: DCS, Dallas, Texas
Lines: 33

In article <171@libove.UUCP> root@libove.UUCP (Jay M. Libove) writes:
>I have a SCO Xenix 80286 v2.2.1 system, and it has one modem, which I
>use for manual dial out as well as automatic dial out for UUCP connections.
>While I am using it manually, if a cron job comes up that calls 
>/usr/lib/uucp/uucico, the LCK.. file in /usr/spool/uucp/ will be ignored
>and I will get the modem commands being fired out on the line while I
>am connected over it! As yet, this has beena nuisance, but I suppose it
>stands to be damaging eventually.

There are two schemes used by different versions of uucp to determine
if a lockfile is still valid or can be safely ignored.

Older versions of uucp looked at the update time of the lockfile; the
uucp software itself would keep touching the its lockfiles while they were
valid, and if it found a "foreign" lockfile, it would delete it only
if it had not been touched in a certain period of time. Don't know
what that time period is, though.

The newer version of uucp (and I don't know whether the Xenix TB version
belongs here) looks at the lockfile's content to determine the PID
of the process which created it. If that process is still active (determined
by system call "kill(PID, 0)"), the lockfile is honored; if the process
is no longer active, the lockfile gets deleted.

My recollection of kermit's implementation of lockfiles is that it is 
very rudimentary: it does not touch its lockfiles regularly, and it does
not put its PID into them, either in the old binary format, or in the
newer "fprintf(lfp,"%10d\n", PID)" format. Therefore neither version of uucp,
in my experience, KNOWS HOW TO honor kermit lockfiles.
-- 
Wolf N. Paul * 3387 Sam Rayburn Run * Carrollton TX 75007 * (214) 306-9101
UUCP:     killer!dcs!wnp                 ESL: 62832882
DOMAIN:   dcs!wnp@killer.dallas.tx.us    TLX: 910-380-0585 EES PLANO UD