Provided by: fp-utils-3.0.4_3.0.4+dfsg-18_amd64 bug


       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 access the video buffer of your own tty.

       Unfortunately there is a lot of reason to use the text mode video buffer. 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 character 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  before  it  can  do its work). The
       permissions are automatically reverted on logout.

       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 <>