A /dev/null equivilent for DISPLAY when the display is just noise

Question

I'm running a java app which creates a visual display of some of the things it is doing, while it is doing it. However, I'm want to run this in a script that won't have a display to attach to. In the current environment, there isn't even a DISPLAY environment variable set. I tried to simply set my DISPLAY to :0.0. But that doesn't exist. I don't really care about the display. I just want the app to process the files silently.

Since I can't just turn the display off(not my app), I'm left with trying to get around the need for display.

Is there a black hole that I can send the DISPLAY to? an equivalent to /dev/null?

I searched around for a bit on the web, but the words I could think of to use: "display" "null" "disregard" etc are all two generic to get me to an answer.

This is the middle of a larger script, so I want the rest of the output to stdout to be available.

Answer 1

There's a headless X server called Xvfb. It's basically what you need since it accepts X clients but basically does nothing with the data from them. From that linked page (slightly paraphrased):

Xvfb, the X virtual framebuffer, is a display server implementing the X11 display server protocol.

In contrast to other display servers, Xvfb performs all graphical operations in memory without showing any screen output.

From the point of view of the client, it acts exactly like any other X display server, serving requests and sending events and errors as appropriate. However, no output is shown.

This virtual server does not require the computer it is running on to have a screen or any input device. Only a network layer is necessary.

If you can't find that, then another possibility would be to use a spare PC with a full CygWin install. CygWin comes with a full-blown X server which you could connect your application to (and just ignore it). You could even set it up as the corporate /dev/null DISPLAY.

But I'd look into Xvfb first.

Answer 2

If it's a java program you can use the headless mode to run the application.

Try to run it with -Djava.awt.headless=true parameter, like this if it's a jar file:

java -Djava.awt.headless=true -jar jarfile.jar

More about headless mode...

Answer 3

You can use Xvfb, as noted above. That way, you will never see the output (you can use a tool to take screenshots, though).

http://en.wikipedia.org/wiki/Xvfb http://packages.debian.org/sid/xvfb

Or you could set up a VNC server. Under Linux, a VNC server is implemented as a special X server that can be accessed via VNC, insstead of displaying on a local monitor. That gives you a headless X server, with the added bonus that you can connect to it via VNC just in case you do need to see what's going on.

http://www.tightvnc.com/vncserver.1.html

vncserver is a nice wrapper script for (tight)VNC, which makes starting a VNC server a breeze. Most distros should install it by default.

Answer 4

Short answer, use:

xvfb-run JAVA_COMMAND_LINE

Depending on your version and flavor of Linux, there may be one line you have to change in xvfb-run to get everything to run.

Answer 5

Can you run a VM on the target machine? Then you could set your DISPLAY to that. Or you could try vnc (currently on a machine which doesn't allow this or I'd try it...).