How can I specify a display?

Question

When I run some programs over SSH, such as firefox &, I get an error

Error: no display specified 

I would like to open ma

Answer 1

I ran into a similar issue, so maybe this answer will help someone.

The reason for the Error: no display specified error is that Firefox is being launched, but there is no X server (GUI) running on the remote host. You can use X11 forwarding to run Firefox on the remote host, but display it on your local host. On Mac OS X, you will need to download XQuartz in order to use X11 forwarding. Without it, you won't have a $DISPLAY variable set, so if you try and echo $DISPLAY, it will be blank.

Answer 2

The way that X works is the same as the way any network program works. You have a server of some description (in this case, the X display server) which runs on a specific machine, and you have X clients (like firefox) that try to connect to that server to get their information displayed.

Often (on "home" machines), the client and server run on the same box and there's only one server, but X is powerful enough that this doesn't need to happen. It was built with the server/client separation built in from the start.

This allows you to do such wondrous things such as log on to your box (in text mode) halfway around the planet, tell it that the display server is the box you're currently on and, voila, the windows suddenly start appearing locally.

In order for a client to interact with a user, it needs to know how to find the server. There are a number of ways to do this. Many clients allow the -display or --displayoption to specify it:

xeyes -display paxbox1.paxco.com:0.0

Many will use the DISPLAY environment variable if a display isn't specifically given. You can set this variable like any other:

DISPLAY=paxbox1.paxco.com:0.0; export DISPLAY # in .profile
export DISPLAY=paxbox1.paxco.com:0.0 # in your shell
DISPLAY=paxbox1.paxco.com:0.0 firefox & # for that command (shell permitting)

The first part of the DISPLAY variable is just the address of the display server machine. It follows the same rule as any other IP address; it can be a resolvable DNS name (including localhost) or a specific IP address (such as 192.168.10.55).

The second part is X-specific. It gives the X "display" (X server) number and screen number to use. The first (display number) generally refers to a group of devices containing one or more screens but with a single keyboard and mouse (i.e., one input stream). The screen number generally gives the specific screen within that group.

An example would be:

+----------------------------------------+
|paxbox1.paxco.com|                      |
+-----------------+                      |
|                                        |
|  +----------+----+  +----------+----+  |
|  |Display :0|    |  |Display :1|    |  |
|  +----------+    |  +----------+    |  |
|  |               |  |               |  |
|  | +-----------+ |  |               |  |
|  | |Screen :0.0| |  |               |  |
|  | +-----------+ |  |               |  |
|  | +-----------+ |  |               |  |
|  | |Screen :0.1| |  |               |  |
|  | +-----------+ |  |               |  |
|  | +-----------+ |  | +-----------+ |  |
|  | |Screen :0.2| |  | |Screen :1.0| |  |
|  | +-----------+ |  | +-----------+ |  |
|  | +-----------+ |  | +-----------+ |  |
|  | |Screen :0.3| |  | |Screen :1.1| |  |
|  | +-----------+ |  | +-----------+ |  |
|  | +-----------+ |  | +-----------+ |  |
|  | | Keyboard  | |  | |  Keyboard | |  |
|  | +-----------+ |  | +-----------+ |  |
|  | +-----------+ |  | +-----------+ |  |
|  | |   Mouse   | |  | |   Mouse   | |  |
|  | +-----------+ |  | +-----------+ |  |
|  +---------------+  +---------------+  |
|                                        |
+----------------------------------------+

Here you have a single machine (paxbox1.paxco.com) with two display servers. The first has four screens and the second has two. The possibilities are then:

DISPLAY=paxbox1.paxco.com:0.0
DISPLAY=paxbox1.paxco.com:0.1
DISPLAY=paxbox1.paxco.com:0.2
DISPLAY=paxbox1.paxco.com:0.3
DISPLAY=paxbox1.paxco.com:1.0
DISPLAY=paxbox1.paxco.com:1.1

depending on where you want your actual windows to appear and which input devices you want to use.

Answer 3

I faced similar problem today. So, here's a simple solution: While doing SSH to the machine, just add Ctrl - Y.

ssh user@ip_address -Y

After login, type firefox &. And you are good to go.

Answer 4

When you are connecting to another machine over SSH, you can enable X-Forwarding in SSH, so that X windows are forwarded encrypted through the SSH tunnel back to your machine. You can enable X forwarding by appending -X to the ssh command line or setting ForwardX11 yes in your SSH config file.

To check if the X-Forwarding was set up successfully (the server might not allow it), just try if echo $DISPLAY outputs something like localhost:10.0.

Answer 5

login to your server via

ssh -X root@yourIP

edit /etc/ssh/sshd_config file, and add this line to it.

X11UseLocalhost no

Restart sshd. for CentOS (check your distribution)

/sbin/service sshd restart

check your DISPLAY

echo $DISPLAY

you should see this

yourIP:10.0

Enjoy

firefox

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