Fix bad display error for xauth

When xauth shows the error message: "bad display name "xxxxx:0" in "add" command because of "unknown host" error", you can try to ping xxxxx and then you will get the "unknown host" error.

In order to fix this error, we have to edit the file "/etc/hosts" and add the IP address for the xxxxx. For example,
127.0.0.1   xxxxx

Then the problem should be fixed.