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From: mouse@thunder.mcrcim.mcgill.edu (der Mouse)
Newsgroups: comp.unix.questions
Subject: Re: tty blocked in background job
Message-ID: <1991Jun1.195940.25681@thunder.mcrcim.mcgill.edu>
Date: 1 Jun 91 19:59:40 GMT
References: <1991May29.054939.11898@csc.canberra.edu.au>
Organization: McGill Research Centre for Intelligent Machines
Lines: 29

In article <1991May29.054939.11898@csc.canberra.edu.au>, rvp@softserver.canberra.edu.au (Rey Paulo) writes:

> Whenever a job is run int the background and the job happens to write
> to the tty from which it was run, the message "tty blocked" occurs.

Odd, which system and shell is this?  I don't know that message.

> This causes the job to be suspended.  Is there any way that a
> background job's access to the tty not blocked?

You don't say what your system is.  I'll describe BSD, simply because
that's the original breeding ground of background jobs and SIGTTOU....

There is a bit in the tty settings that controls this.  At the user
level, this is controlled with "stty tostop" and "stty -tostop".  At
the ioctl level, this is the LTOSTOP bit in the local mode word (the
thing manipulated with TIOCL{BIS,BIC,SET,GET}).

There are also some special cases, which may or may not be implemented
the same way in your system: if the process has SIGTTOU (the generated
signal) blocked or ignored, or if the process is a child process
running in its parent's memory during a vfork(), the output is
permitted and no SIGTTOU is generated.

					der Mouse

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