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From: lwa%mit-csr@sri-unix.UUCP
Newsgroups: net.unix
Subject: Re: Attaching a printer to a 68000 UNIX system
Message-ID: <14499@sri-arpa.UUCP>
Date: Sat, 10-Dec-83 13:29:00 EST
Article-I.D.: sri-arpa.14499
Posted: Sat Dec 10 13:29:00 1983
Date-Received: Wed, 14-Dec-83 00:57:46 EST
Lines: 37

The problem here lies in your supplier's use of the term 'on-line'.
The first character of each line in the /etc/ttys file actually indicates
whether that terminal line is to be available for login.  Thus for each
line in the /etc/ttys file which begins with '1', a program (/etc/getty,
as I recall) is started at bootstrap time; this program prints out the
"login:" message on the terminal and proceeds to wait for some user to
type his login id.  If the line in the /etc/ttys file begins with '0',
the /etc/getty program is not run on that line.  Printer ports, or
ports used for communication with other computers, etc. should have the
first character '0'.

The second character is interpreted in a non-standardized way by 
/etc/getty to determine the characteristics of the terminal line:
its terminal type, baud rate, number of stop bits, and so forth.
There is no standard assignment of characters to terminal characteristics;
in fact, most systems that I've seen don't even have documentation on
the local meanings.  This is one of the most poorly documented areas in
UNIX.  Probably the only way to find out what the particular characters
in your /etc/ttys file mean is to look at the source of /etc/getty
(or ask your supplier).

Now the /etc/ttys file is normally only read at system startup, by the
/etc/init program.  This means that changes to the /etc/ttys file will
normally only take effect after rebooting the system.  Some versions of
UNIX, however, permit reinitialization of the terminals without the
need to reboot; this is performed by sending a SIGHUP signal to the
/etc/init program, by using the command 'kill -1 1'.  Unfortunately,
this doesn't work on all versions of UNIX.  It's not really that
important, though, as on most systems the terminal configuration
doesn't change all that often.

Some of this stuff should be documented in section 5 of the UNIX manual;
this is the section which describes file formats.  Try looking for
ttys(5) in the manual.  Another possibility is that your manual may
have a page for /etc/getty; this will probably be in getty(8).
					-Larry Allen
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