----- Original Message -----
From: "Pat Welch" <patubb@inreach.com>
Newsgroups: comp.unix.sco.misc
To: <distro@jpr.com>
Sent: Sunday, March 16, 2008 8:43 PM
Subject: Re: Remote Control a terminal or the console.


> Nico Kadel-Garcia wrote:
>> Brian K. White wrote:
>>> Note: sco has a built in program very similar to screen called mscreen.
>>> But I don't think either one provides shared sessions.
>>>
>>> SCO made a TLS package that had a facility called spyfs that was
>>> supposed to allow one user to watch anothers tty. I never tried it
>>> myself. It didn't saound from the instructions to be good enough for
>>> what I need. I have used dv a lot on sco, and used to use ttysnoop
>>> (free) on linux, but haven't used ttysnoop lately because we have to
>>> use FacetWin for our terminal emulator, and ttysnoop can't work with
>>> FacetWin because FacetWin does not call an external login program. DV
>>> would work because it works at the kernel level, but dv is practically
>>> useless on linux because of the way they tie in to specific kernels
>>> and won't work with any other version or build. There is another
>>> product that works like ttysnoop but isn't free called peek. I haven't
>>> tried that myself because, if I could use peek, then I could use
>>> ttysnoop.
>>>
>>> For our support needs we've basically been living without any
>>> replacement for DV since switching off of SCO. For training and sales
>>> demos we use a web based full desktop thing via
>>> http://www.beamyourscreen.com/US/Welcome.aspx
>>>
>>> Not nearly as convenient or fast, but, for demos and training it is
>>> useful to be able to show the whole desktop since several parts of the
>>> app cause things to happen outside the terminal emulator window, like
>>> scanning and printing and printing to pdf/email/fax etc..
>>>
>>> If I could find a windows programmer to pay to finish my few remaining
>>> hacks to Putty, and port my existing hacks up to the current putty,
>>> then I could finally escape facetwin and get dv-like functionality
>>> back in the form of ttysnoop. *sigh*...
>>>
>>
>> Hop over to comp.security.ssh: a number of the Putty programmers work
>> there, and I've been active on that group for years. Good people.
>>
>> I take it you don't like VNC for this?
>
> I think you are misunderstanding the primary purpose behind this thread
> - It's not to access the server per se, it's the ability to attach to a
> specific users pty or tty *AFTER* they've already logged in and are
> actively running the application you are trying to fix/debug.

Then I'm not misunderstanding anything.
That is exactly what I was talking about.
That is exactly what all of dv, ttysnoop, peek, and spyfs provide, and what screen & mscreen do not provide.

> How you get to the server is immaterial - telnet, ssh, VPN, VNC, modem
> or whatever.

What? Of course how you connect to the server could (and as it happens, does) matter to how and whether a tty multiplexer works.

How you get to the server matters a great deal, if the tty multiplexer happens to work by replacing /bin/login and sitting between you and the kernel all during your session.
That is how ttysnoop and peek both work. What happens is, during login, THEY actually become the top level process for that tty instead of your shell, but then they launch your shell and connect it to the tty, so from your point of view it's like any other normal login, but, really there is an application in the background (ttysnoop or peek) that all of the tty data for your entire session is passing through, and so it's possible for that application to multiplex that data with any other sessions which that application is also managing. If all users everywhere have logged in this way, then any tty may be connected to any other tty.

But FacetWin does not call an external login program, nor can it be configured to do so, nor can you trick it by replacing the real /bin/login with a wrapper, because it just plain doesn't call any external program.

And so, ttysnoop and peek do both provide exactly the function you describe, and, happen to not be useable if you are logging in via FacetWin.
They can't be used with openssh either by default, but openssh can be configured to call a login program of your choice, and/or you can replace the real /bin/login with a wrapper.

DV on the other hand, and spyfs too I beleive, works similarly in that it inserts itself between you and the real tty's, but it does so at a lower level, right in the kernel (in the form of a driver module), and takes the place of, or sits in front of, the kernel level tty api's which any and all userspace tty-granting/tty-using code must talk to, including FacetWin and openssh in it's normal mode and anything/everything else. Therefor, dv and spyfs also provide the same functionality, but in their case it doesn't matter what facility you used to log in and get a tty.

xterms/xterm-alikes probably fall in the FacetWin category of things that create tty's without calling some external program like /bin/login, however, in that case the xterm binary itself could probably be replaced with a wrapper script that calls ttysnoop or peek. I don't think you can do that with FacetWin's vtpd which is called from inetd (xinetd on linux). I don't remember if I ever tried that... hm...

Brian K. White brian@aljex.com http://www.myspace.com/KEYofR
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