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

6       grab_vcsa - Linux console vcsa grabber
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SYNOPSIS

10       grab_vcsa
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DESCRIPTION

14       The  Linux  console allows text mode video buffer access^. For each tty
15       device (/dev/tty0..31) there  exist  two  devices  (/dev/vcs0..31)  and
16       (/dev/vcsa0..31).   These  devices are two different representations of
17       the content of the console.
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19       When you login on the Linux console, your tty device is  changed  owner
20       to you, so you can read/write it. When you logout it is takes from you.
21       This does not happen with the vcs and vcsa  devices,  i.e.  you  cannot
22       access the video buffer of your own tty.
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24       Unfortunately  there is a lot of reason to use the text mode video buf‐
25       fer. For instance, it is not possible to get access  to  the  full  256
26       characters  the  VGA  adapter  can  display without using the text mode
27       video buffer (Linux emulates the vt100 character  set  which  does  not
28       have  all  VGA  characters). This annoyance severely limits the porting
29       possibilities to Linux of software that was written with a VGA  charac‐
30       ter set in mind.
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32       grab_vcsa  is  a  setuid root program that, when called will change the
33       owner of the vcs and vcsa devices to you, after a  series  of  security
34       checks have been performed.
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36       It is not necessary to change the permissions back again (this would be
37       pointless since a user could  kill  a  imaginary  release_vcsa  program
38       before  it can do its work). The permissions are automatically reverted
39       on logout.
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41       grab_vcsa is used by the Free Pascal video unit. The video unit  allows
42       programmers  to  develop  portable programs across Dos, Linux, FreeBSD,
43       Windows, OS/2 and other operating systems while they can  still  assume
44       being able to use the full VGA character set.
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RETURN CODES

48       grab_vcsa has the following return codes:
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50       0      Success
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52       1      You are not running on the Linux console
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54       2      Error while statting tty.
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56       3      Error while executing chown.
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58       4      Error while executing chmod.
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60       4      You do not own your own tty.
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AUTHOR

64       Daniel Mantione <daniel.mantione@freepascal.org>
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68Free Pascal                       22 jan 2006                     grab_vcsa(1)