[wellylug] Screens

[Daniel Pittman]

"E.Chalaron" <e.chalaron at xtra.co.nz> writes:

> As usual my contribution to the list will be a question.
> I am using Cinelerra for controling my movie transfers (colors etc ...)
>
> Having one video monitor to control the output I need to share it
> among several machines.
>
> For now it is on machine A.  Machines B, C and D having Cinelerra as
> well. all of them Ubuntu or Debian
>
> There is an option in Cinelerra where I can indicate the video driver
> and the display. I did a bit of RTFM but the manual is somehow not
> complete some guys have been using : localhost:0.1
>
> I guessed it was the numbers related to the PCI on the host

No.  It has absolutely *nothing* to do with the hardware.

What you are looking at there (localhost:0.1) is an X-Windows "display"
specification -- the address of the X server to communicate with.

That particular specification reads something like this:

  We connect via TCP/IP  (because we gave a hostname)
  The server runs on localhost 
  We are talking to X server 0
  We are talking to the second screen (1) on that server.

[...]

> In my case it should be something like
> machineA.chalaron.org:5.0

Well, assuming that you have only one X server running on that machine
and only one display connected to it, the address would be:

   DISPLAY=machineA.chalaron.org:0  # or 0.0; the .0 is the default. :)

Note: this will not work out of the box.  Specifically, without making
other arrangements the X security settings will not permit a remote
display connection like that.

You can address that in one of three ways:

You can tunnel X to that machine over some secure protocol; ssh can do X
forwarding.  That allows a user on machineA to run the software on
machineB and display it locally -- not quite what you want.[1]


You can transfer your "magic cookie" from machineA to machineB.  One
easy way is to share your home directory, in which your .Xauthority file
resides, over the network.

You can also do this with some xauth magic.  This is, however, also
hard.


Finally, *if* you trust the local network[2] you can simply permit
*anyone* on machineB to connect to the display on machineA, but running
this command *on machine A*:

    xhost +machineB.chalaron.org

This has two problems: first, it permits any user on machineB to connect
to the X server on machineA.  They can run any software there --
including software that will sniff out every keystroke and mouse
movement and record it, if they wish.

Second, performance for video playback may not be quite what you hope
for.  That is hardly unique to this option, though. :)

Regards,
        Daniel

Footnotes: 
[1]  You can also forward X using normal X11 port forwarding, but that
     is hard(tm) because you need to handle the magic cookie yourself.

[2]  Which you probably do, even if this is bad security advice.  
     I can offer it, though, because I am a professional or something. ;)

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