Subject: X11 forwarding fails without /tmp/.X11-unix directory

From: myglc2 <[email-masked]>
Date: Sun, 06 Mar 2016 20:10:33 -0500

Example: using guix commit 59a4dd5 with openssh xauth & emacs in the
user profile (c02glc.scm) and a minimal system profile (c02system.scm),
after a reboot we see ...

nemo:~ $ ssh g1
glc@g1's password:
X11 forwarding request failed on channel 0

... and in /var/log/messages ...

Mar  6 19:23:35 localhost lshd[372]: lshd: Failed to cd to `/tmp/.X11-unix' (errno = 2): No such file or directory 
Mar  6 19:23:35 localhost lshd[372]: lshd: Updating utmp for login failed (errno = 2): No such file or directory 

If we do ...

mkdir /tmp/.X11-unix

... logout and login, forwarding works, emacs runs in X, and
/var/log/messages is clean. If we reboot, X11 forwarding again fails.