bug#22930: X11 forwarding fails without /tmp/.X11-unix directory

bug#22930: X11 forwarding fails without /tmp/.X11-unix directory

[myglc2]

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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.


[-- Attachment #2: c02glc.scm --]
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(use-package-modules
 gettext
 ghostscript ;; gs-fonts
 fonts ;; font-dejavu font-gnu-freefont-ttf
 base
 ssh rsync wget screen
 version-control
 emacs
 curl
 xorg certs
 graphviz
 ) 
(packages->manifest
 (list
  ;;  gnu-gettext
  gs-fonts font-dejavu font-gnu-freefont-ttf
  gnu-make
  openssh nss-certs xauth rsync wget git git-manpages
  emacs magit screen 
  curl ;; lpaste
  graphviz
  ))

[-- Attachment #3: c02system.scm --]
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(use-modules (gnu))
(use-service-modules networking ssh)
(use-package-modules admin
		     disk
		     ;;		     gcc databases gnupg autotools pkg-config gettext graphviz man ;; guix		     
		     )
(operating-system
  (host-name "g1")
  (timezone "America/New_York")
  (locale "en_US.utf8")
  (bootloader (grub-configuration (device "/dev/sda")))
  (file-systems (cons (file-system
                        (device "g1sd")
                        (title 'label)
                        (mount-point "/")
                        (type "ext4"))
                      %base-file-systems))
  (users (cons* (user-account
		 (name "glc")
		 (comment "g l c")
		 (group "users")
		 (supplementary-groups '("wheel"))
		 (home-directory "/home/glc"))
		(user-account
		 (name "glc2")
		 (comment "glc2")
		 (group "users")
		 (supplementary-groups '("wheel"))
		 (home-directory "/home/glc2"))
		(user-account
		 (name "glc3")
		 (comment "glc3")
		 (group "users")
		 (supplementary-groups '("wheel"))
		 (home-directory "/home/glc3"))
		(user-account
		 (name "glc4")
		 (comment "glc4")
		 (group "users")
		 (supplementary-groups '("wheel"))
		 (home-directory "/home/glc4"))
		%base-user-accounts))
  (packages
   (cons*
    glibc-utf8-locales
    parted
    ;;    gcc-5 sqlite libgcrypt gnu-make autoconf automake pkg-config gnu-gettext graphviz help2man ;; guix
    ;; comment out above because 'configure.ac:46: error: possibly undefined macro: PKG_CHECK_MODULES'
    %base-packages
    )
   )
  (services (cons* (dhcp-client-service)
                   (lsh-service #:port-number 22)
                   %base-services)))