Screen capturing:

Screen capturing:

[Luke Davis]

Ok, I'm running a few consoles, and a terminal . . .

cp /dev/tty0 /dev/ttyS0

Will copy what ever I type on tty0, to the screen of ttyS0.
Fine, but that's not what I wanted . . .

What I want, is to be able to copy what's already on the console/terminal
screen, to a terminal/file/console.

Can that be done?

Thanks

Luke J. Davis
-------------
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Re: Screen capturing:

[Nikhil Nair]

On Sat, 30 Nov 1996, Luke Davis wrote:

> Ok, I'm running a few consoles, and a terminal . . .
> [...]
> Fine, but that's not what I wanted . . .
> 
> What I want, is to be able to copy what's already on the console/terminal
> screen, to a terminal/file/console.
> 
> Can that be done?

Yes.  Unfortunately, it's very operating system dependent.  What follows
works only on Linux, and requires kernel 1.1.92 or later.

There are some devices called /dev/vcs* and /dev/vcsa*.  The numbers after
those prefices are 0 or none for current VC, or any other number for that
number VC, i.e. /dev/vcsa or /dev/vcsa0 uses the current VC, /dev/vcsa3
uses VC 3.

the vcs versions are the simplest.  If you don't have them, then as root
you could type:

mknod -m o= /dev/vcs$n c 7 $n
chown root.tty /dev/vcs$n
chmod 660 /dev/vcs$n

where $n is between 0 and 63.

The vcs devices contain one character per screen position, going in the
order you'd expect (left to right then top to bottom).

WARNING: these devices may not use the character set you expect!  BEcause
of a quirk in Linux, chances are you won't be able to recover accent signs
correctly, without some manual translation, anyway.

The vcsa devices are more powerful, in that they give screen size, cursor
position and attribute information.  They also take more interpreting, of
course.

To create them, simply add 128 to the minor device number of the
corresponding vcs device, i.e.

mknod -m o= /dev/vcsa$n c 7 $[n+128]
chown root.tty /dev/vcsa$n
chmod 660 /dev/vcsa$n

If you want to know about the file format, and if you can't find the
documentation, ask me.  For some sample code using it, you could look at
the LiveScreen class in scrdev.cc from brltty-1.0.2:
   ftp://sunsite.unc.edu/pub/Linux/system/Access/brltty-1.0.2.tar.gz

I didn't know about setterm until just now, but remember that, unless the
last octal digit of your umask is 7 (which it wouldn't normally be), using
this is a potential security hole, as other users could read the contents
of the console through the contents of that file.  Use that with care!

Hope this helps,

Nikhil.

--
Nikhil Nair
Trinity College, Cambridge, England
Tel.: +44 1223 368353
Email: nn201@cus.cam.ac.uk
       nnair@debian.org

Re: Screen capturing:

[AARON HOWELL]

On Sat, 30 Nov 1996, Nikhil Nair wrote:
[]
> I didn't know about setterm until just now, but remember that, unless the
> last octal digit of your umask is 7 (which it wouldn't normally be), using
> this is a potential security hole, as other users could read the contents
> of the console through the contents of that file.  Use that with care!
Err. Yes. that's why ioctl(dump) Which is the kernel function which is
used to get the info off the console is only available to processes
running as root. Naturally, the normal cautions with doing anything as
root apply to  this as well.
Aaron
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Re: Screen capturing:

[Peter Nilsson]

On Sat, 30 Nov 1996, Luke Davis wrote:

> What I want, is to be able to copy what's already on the console/terminal
> screen, to a terminal/file/console.
> 

The contents on the virtual consoles can be read via the device files
vcs* (see man vcs). The vcs<n> where n>0 contains the _text_ on the
virtual console n. vcs0 has the contents on the currently displayed vc.
The vcsa* give you the same, but also contain the cursor position, screen
size and attributes.

I don't think there is a way to get the contents of the screen of a tty
other than the vc:s, but I'm not sure.


 -- 
HaDe/P

Re: Screen capturing:

[Jim Van Zandt]

In message <Pine.LNX.3.95.961130090634.3141A-100000@amasis.trin.cam.ac.uk>, Nik
hil Nair writes:
>There are some devices called /dev/vcs* and /dev/vcsa*.  The numbers after
>those prefices are 0 or none for current VC, or any other number for that
>number VC, i.e. /dev/vcsa or /dev/vcsa0 uses the current VC, /dev/vcsa3
>uses VC 3.
>
>If you want to know about the file format, and if you can't find the
>documentation, ask me.

You can also do "man vcs".  If you don't have that man page, then you
need to install a new set of man pages.  If you find it confusing or
incorrect, please let me know.  As it happens, I wrote that man page
:-).

                             - Jim Van Zandt