unable to export DISPLAY to Xming desktop after becoming root

[Rob White]

Security requirements dictate that I ssh into a Linux or Unix host with my user ID using a key card. After doing this (using putty), I am able to run X apps and have them display on my PC which is running Xming. So I know putty is configured correctly.

To become root we must use sudo (i.e. $ sudo su - root).
When I do this, I loose the ability to display X apps on my PC.

When I fist log into a host: DISPLAY is localhost:10.0
When I sudo to root DISPLAY is also localhstt:10.0 ;however when I run xclock I get the following error.
# xclock
Xlib: connection to "localhost:10.0" refused by server
Xlib: PuTTY X11 proxy: MIT-MAGIC-COOKIE-1 data did not match
Error: Can't open display: localhost:10.0
If I set DISPLAY to the IP of my PC (export DISPLAY=xx.xx.36.53:0.0)
#first octets not shown for security reasons
I get a different error:
Xlib: connection to "xx.xx.36.53:0.0" refused by server
Xlib: No protocol specified
Error: Can't open display: xx.xx.36.53:0

[Lusotec]

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First a warning, run as root only what can't be run as a normal user. This
is especially true for X clients because of the way X clients can interact
with each other.

Now for your particular issue. You need to get the MIT-MAGIC-COOKIE-1 value
from the normal remote user with access to the X server and add it to the
root's authorization file (.Xauthority).

First to get the MIT-MAGIC-COOKIE-1 value from the normal remote user. Open
a ssh to the normal user account and run the following command.

xauth extract - $DISPLAY > /tmp/xauth.bin

This command will write the X authorization information for the current X
display to /tmp/xauth.bin

Now, open a terminal for the root (probably using the command "su -") and
run the following command.

xauth -v merge - < /tmp/xauth.bin

You should see output similar to the following.

# xauth -v merge - < /tmp/xauth.bin
Using authority file /home/artur/.Xauthority
1 entries read in: 0 new, 1 replacement
Writing authority file /home/artur/.Xauthority

Now try running a X client (e.g. xclock).

Regards.
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[Bill Marcum]

You might also need to export the variable XAUTHORITY. Connecting to the
ip address doesn't work because the X server isn't listening on the
network interface, only through the ssh tunnel.

[Philippe Weill]

perhaps trying sudo -E

2nd solution

modify your sshd server configuration

X11UseLocalhost no
( and read about security when doing this)