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grab_vcsa(1)		  Linux	console	vcsa grabber		  grab_vcsa(1)

       grab_vcsa - Linux console vcsa grabber


       The  Linux  console allows text mode video buffer access^. For each tty
       device (/dev/tty0..31) there  exist  two	 devices  (/dev/vcs0..31)  and
       (/dev/vcsa0..31).   These  devices are two different representations of
       the content of the console.

       When you	login on the Linux console, your tty device is	changed	 owner
       to you, so you can read/write it. When you logout it is takes from you.
       This does not happen with the vcs and vcsa devices, i.e.	you cannot ac-
       cess the	video buffer of	your own tty.

       Unfortunately  there is a lot of	reason to use the text mode video buf-
       fer. For	instance, it is	not possible to	get access  to	the  full  256
       characters  the	VGA  adapter  can  display without using the text mode
       video buffer (Linux emulates the	vt100 character	 set  which  does  not
       have  all  VGA  characters). This annoyance severely limits the porting
       possibilities to	Linux of software that was written with	a VGA  charac-
       ter set in mind.

       grab_vcsa  is  a	 setuid	root program that, when	called will change the
       owner of	the vcs	and vcsa devices to you, after a  series  of  security
       checks have been	performed.

       It is not necessary to change the permissions back again	(this would be
       pointless since a user could kill a imaginary release_vcsa program  be-
       fore it can do its work). The permissions are automatically reverted on

       grab_vcsa is used by the	Free Pascal video unit.	The video unit	allows
       programmers  to	develop	 portable programs across Dos, Linux, FreeBSD,
       Windows,	OS/2 and other operating systems while they can	 still	assume
       being able to use the full VGA character	set.

       grab_vcsa has the following return codes:

       0      Success

       1      You are not running on the Linux console

       2      Error while statting tty.

       3      Error while executing chown.

       4      Error while executing chmod.

       4      You do not own your own tty.

       Daniel Mantione <>

Free Pascal			  22 jan 2006			  grab_vcsa(1)


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