tty swtch key

tty swtch key

[Phillip Susi]

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I could have sworn that I used the tty swtch feature once many years
ago and that it sent a special signal to the shell, causing it to be
suspended and return you to the parent shell, as if you had entered
the suspend command.  I can't find the signal in the man pages now,
and using stty to set a swtch key and hitting it does nothing.  Is
this unimplemented on linux, and if so, shouldn't the man page be
updated to reflect that?

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Re: tty swtch key

[Mantas Mikulėnas]

On 2014-03-26 20:47, Phillip Susi wrote:
> I could have sworn that I used the tty swtch feature once many years
> ago and that it sent a special signal to the shell, causing it to be
> suspended and return you to the parent shell, as if you had entered
> the suspend command.  I can't find the signal in the man pages now,
> and using stty to set a swtch key and hitting it does nothing.  Is
> this unimplemented on linux, and if so, shouldn't the man page be
> updated to reflect that?

AFAIK, Linux never had this feature built-in. I'm not quite old enough
to have actually used it, but I've read and saved a few Usenet posts
that say `shl` ("shell layers") only existed in very old Unix versions
like SVR3, to compete with BSD-style job control.

(Looks like Google Groups removed find-by-Message-ID, unfortunately. I
guess I could just attach all of the posts...)

On the other hand, there _is_ a reimplementation of shl for Linux and
Solaris, as part of heirloom-toolchest
<http://heirloom.sourceforge.net/tools.html> and
<http://heirloom.sourceforge.net/man/shl.1.html>.

-- 
Mantas Mikulėnas <grawity@gmail.com>

Re: tty swtch key

[Phillip Susi]

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On 3/27/2014 2:40 PM, Mantas Mikulėnas wrote:

> On the other hand, there _is_ a reimplementation of shl for Linux
> and Solaris, as part of heirloom-toolchest 
> <http://heirloom.sourceforge.net/tools.html> and 
> <http://heirloom.sourceforge.net/man/shl.1.html>.

How so?  It has to be implemented in the kernel tty layer.


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Re: tty swtch key

[Mantas Mikulėnas]

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On 2014-03-27 21:22, Phillip Susi wrote:
> On 3/27/2014 2:40 PM, Mantas Mikulėnas wrote:
> 
>> On the other hand, there _is_ a reimplementation of shl for Linux
>> and Solaris, as part of heirloom-toolchest
>> <http://heirloom.sourceforge.net/tools.html> and
>> <http://heirloom.sourceforge.net/man/shl.1.html>.
> 
> How so?  It has to be implemented in the kernel tty layer.

Not necessarily – remember that `screen` and `tmux` and `dtach` were
implemented entirely in user space. Similarly, heirloom's shl appears to
be built on top of ptys, probably just intercepting the "switch" key and
relaying the rest.

Actually it sounds quite similar to the descriptions of how the old shl
worked... (see Message-ID: <cjs1ka$e25@harn.ceas.rochester.edu>)

-- 
Mantas Mikulėnas <grawity@gmail.com>

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Re: tty swtch key

[Phillip Susi]

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On 3/27/2014 4:12 PM, Mantas Mikulėnas wrote:
> Actually it sounds quite similar to the descriptions of how the old
> shl worked... (see Message-ID:
> <cjs1ka$e25@harn.ceas.rochester.edu>)

See that message id where?


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Re: tty swtch key

[Phillip Susi]

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On 03/27/2014 07:28 PM, Mantas Mikulėnas wrote:
> On 2014-03-27 22:48, Phillip Susi wrote:
>> On 3/27/2014 4:12 PM, Mantas Mikulėnas wrote:
>>> Actually it sounds quite similar to the descriptions of how the
>>> old shl worked... (see Message-ID: 
>>> <cjs1ka$e25@harn.ceas.rochester.edu>)
>> 
>> See that message id where?
> 
> The mbox folder attached to the previous message, unless it got
> lost.

Thanks, I didn't notice the attachment.  So it sounds like maybe this
should be removed from both stty and the kernel then, since it was
never implemented and won't ever be?



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Re: tty swtch key

[Samuel Thibault]

Mantas Mikulėnas, le Thu 27 Mar 2014 22:12:41 +0200, a écrit :
> On 2014-03-27 21:22, Phillip Susi wrote:
> > On 3/27/2014 2:40 PM, Mantas Mikulėnas wrote:
> > 
> >> On the other hand, there _is_ a reimplementation of shl for Linux
> >> and Solaris, as part of heirloom-toolchest
> >> <http://heirloom.sourceforge.net/tools.html> and
> >> <http://heirloom.sourceforge.net/man/shl.1.html>.
> > 
> > How so?  It has to be implemented in the kernel tty layer.
> 
> Not necessarily – remember that `screen` and `tmux` and `dtach` were
> implemented entirely in user space.

Err, no, they have to depend on some kernel features. For instance, you
want to be able to ^C a program running in a sudo shell. Only the kernel
can do that.

Samuel

Re: tty swtch key

[Dale R. Worley]

> From: Mantas Mikulėnas <grawity@gmail.com>

> (Looks like Google Groups removed find-by-Message-ID, unfortunately. I
> guess I could just attach all of the posts...)

It looks like you can fake that.
https://groups.google.com/forum/#!topic/news.software.readers/IdRY8FQh8xE
reports:

    Also, you can use Google Groups to point to an article, like this:

      https://groups.google.com/forum/#!original/alt.free.newsservers/I6gEnVSP8eI/0Eg5aLNbi0UJ

    Which is a link to the source, header and all, unformatted.

    ⋅AND⋅, when you hit the big "Back Arrow" button,
    it places you on the proper article, in the thread/topic,
    properly formatted, on the proper page of the thread/topic ! !

Dale