Path: utzoo!utgpu!water!watmath!clyde!cbosgd!mandrill!hal!ncoast!allbery
From: allbery@ncoast.UUCP (Brandon Allbery)
Newsgroups: comp.unix.wizards
Subject: Re: /dev/tty doesn't exist?
Message-ID: <6955@ncoast.UUCP>
Date: 6 Jan 88 00:40:30 GMT
References: <445@minya.UUCP> <243@jc3b21.UUCP>
Reply-To: allbery@ncoast.UUCP (Brandon Allbery)
Followup-To: comp.unix.wizards
Organization: Cleveland Public Access UN*X, Cleveland, Oh
Lines: 26

As quoted from <243@jc3b21.UUCP> by jra@jc3b21.UUCP (Jay R. Ashworth):
+---------------
| In article <445@minya.UUCP>, jc@minya.UUCP (John Chambers) says:
| > Some hints:  This is a rather generic Unix Sys/V.2, so the problem should
| > be similar to most ATT Unices.  The most unusual thing about how X is run
| > is that it isn't being started by a login shell; it is started as a daemon
| > by init, and in some cases, decides to grab a terminal (whose name is on
| Aha.  As I understand the way these things work, and I'm sure someone
| will clarify what I'm about to say :-), /dev/tty is set by the kernel
| to point to the control terminal of a process group.  Background
| process, those running as daemons, have no control terminal.  Look at
+---------------

/dev/tty is more of an alias than a device.  A function call on /dev/tty
looks up in the user block of the process to determine the controlling
terminal, then repeats the function call on that terminal.  If there is
no controlling terminal, an open on /dev/tty will fail because the /dev/tty
open routine can't figure out what tty's open routine to call.

In particular, /dev/tty does not work at all like the /dev/window device on
the 3B1, which searches for the first UNUSED window device rather than the
current one.
-- 
	      Brandon S. Allbery, Moderator of comp.sources.misc
 {hoptoad,harvard!necntc,cbosgd,sun!mandrill!hal,uunet!hnsurg3}!ncoast!allbery
PS/2:  Half a computer.    OS/2:  Half an operating system for half a computer.