I have a pretty new install of Slackware 10.2 and I found I couldn't run graphical programs (well, Emacs was the only one I tried) as root, getting error messages like this:

Xlib: connection to ":0.0" refused by server
Xlib: No protocol specified

emacs: Cannot connect to X server :0.
Check the DISPLAY environment variable or use `-d'.
Also use the `xhost' program to verify that it is set to permit
connections from your machine.

I found numerous threads saying to run "xhost +localhost" and this seems to fix the problem temporarily. If I reboot, then I get the same error and have to run xhost again.

How do I make the "xhost +localhost" setting permanent?

Thanks!

You could try adding "xhost +localhost" to your .profile (~/.profile).

That seems to work, thanks! I had to create the file, as it didn't exist.