a X window trouble

When I connected from localhost to an instance of ubuntu in lxc, I encountered following message upon login via ssh.

X11 forwarding request failed on channel 0

That is, I connected to this host with -X option for the purpose of X forwarding. (so as to use gvim)

$ ssh -X -l ubuntu <lxc_instance_IP>

Let us dig into further by adding verbose option, -v as argument of ssh.

$ ssh -X -v -l ubuntu <lxc_instance_IP>

Then I found following debug message, which states that relevant xauth application does not exist.

debug1: Remote: No xauth program; cannot forward with spoofing.

Ok, let us install xauth on target host side.

$ sudo apt-get install xauth

After installation of xauth, this message never comes up. And I am able to forward X sessions to host without any problem.