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I have a local machine A, and a server B.

from A, I got:

#ps -ef
root      3161  3160  0 09:07 tty1     00:03:04 /usr/bin/Xorg :0 -nr -verbose -auth /var/run/gdm/auth-for-gdm-dJExDH/database vt1

#netstat -nltu
tcp        0      0      *                   LISTEN      - 

#xhost +
access control disabled, clients can connect from any host

A's ip address is

From B, I trid:

#export DISPLAY=
Xlib: connection to "" refused by server
Xlib: No protocol specified

Error: Can't open display:

I have another desktop C, if I change the DISPLAY to C's IP address, xclock will work. Any suggestion on what to check in A?

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migrated from serverfault.com Jan 13 '12 at 7:42

This question came from our site for system and network administrators.

Are you using SSH to connect to both? If so, make sure you use the -Y switch to enable trusted X forwarding. – user13742 Jan 13 '12 at 13:00
no, I'm not using SSH, thanks – valpa Jan 16 '12 at 0:41

Looks as if xclock tries to connect to the x-server using a tcp connection while the x server is not listening to tcp.

In ubuntu that can be changed by:

sudo gedit /etc/gdm/gdm.schemas



change from true to false:


and then restart gdm.

share|improve this answer
#netstat -nltu tcp 0 0* LISTEN - X server already listen on 6000 – valpa Jan 16 '12 at 0:42
firewall that does rejects instead of drops? – Folkert van Heusden Jan 17 '12 at 0:53

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