bug#35408: External monitor not working with GDM

[Ben Sturmfels <ben@sturm.com.au>]

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On Thu, 2019-04-25 at 14:16 +0200, Danny Milosavljevic wrote:
> On Thu, 25 Apr 2019 21:41:27 +1000
> Ben Sturmfels <ben@sturm.com.au> wrote:
> 
> > Apr 25 20:30:54 localhost gdm:
> > gdm_session_set_environment_variable:
> > assertion 'value != NULL' failed 
> 
> Yeah, that one again.  It might make sense to patch that so the
> assertion actually prints name and value passed.
> 
> You can also set "debug"'s "Enable=true" in gnu/services/xorg.scm ,
> in gdm-configuration-file , but it will only help in a limited way
> here.

Thanks Danny, I'll try enabling debugging in a second and see if I can
get some more info.

For what it's worth, I've attached my minimal system config that won't
start GDM on either internal or external monitor. It's very close to
what's in the manual. This is on an X200 with Libreboot running Guix
System 33023baac8ec548fe64ce8e4eb48840b5411ee4c.

Regards,
Ben

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(use-modules (gnu) (gnu system nss))
(use-service-modules desktop xorg)
(use-package-modules certs gnome)

(operating-system
 (host-name "Mars")
 (timezone "Australia/Melbourne")
 (locale "en_AU.utf8")

 ;; Choose US English keyboard layout.  The "altgr-intl"
 ;; variant provides dead keys for accented characters.
 (keyboard-layout (keyboard-layout "us" "altgr-intl"))

 ;; Assuming /dev/sdX is the target hard disk, and "my-root" is
 ;; the label of the target root file system.
 ;;
 ;; Using "target" here, rather than "device" suppresses a deprecation warning
 ;; from `guix reconfigure`.
 (bootloader (bootloader-configuration
              (bootloader grub-bootloader)
              (target "/dev/sda")))

 ;; Specify a mapped device for the encrypted root partition.
 ;; The UUID is that returned by 'cryptsetup luksUUID'.
 (mapped-devices
  (list (mapped-device
         (source (uuid "7c901f8e-c9fe-4e4d-989b-25a966e27df0"))
         (target "myroot")
         (type luks-device-mapping))
        (mapped-device
         (source (uuid "a63a607b-4fd8-4093-be93-c6265744e8b8"))
         (target "myhome")
         (type luks-device-mapping))))

 (file-systems (append
                (list (file-system
                       (device (file-system-label "mars-root"))
                       (mount-point "/")
                       (type "ext4")
                       (dependencies mapped-devices))
                      (file-system
                       (device (file-system-label "mars-home"))
                       (mount-point "/home")
                       (type "ext4")
                       (dependencies mapped-devices)))
                %base-file-systems))

 ;; This is where user accounts are specified.  The "root"
 ;; account is implicit, and is initially created with the
 ;; empty password.
 (users (cons (user-account
               (name "ben")
               (comment "Ben Sturmfels")
               (group "users")
               ;; Adding the account to the "wheel" group
               ;; makes it a sudoer.  Adding it to "audio"
               ;; and "video" allows the user to play sound
               ;; and access the webcam.
               (supplementary-groups '("wheel" "netdev"
                                       "audio" "video"
                                       "kvm" ; Needed for guix system vm
                                       ;; "docker"
                                       ))
               (home-directory "/home/ben"))
              %base-user-accounts))

 ;; Globally-installed packages.
 (packages (append
            (list gvfs ; for user mounts
                  nss-certs ; for HTTPS access
                  )
            %base-packages))

 ;; Add GNOME and/or Xfce---we can choose at the log-in
 ;; screen with F1.  Use the "desktop" services, which
 ;; include the X11 log-in service, networking with Wicd,
 ;; and more.
 (services (append
            (list (service gnome-desktop-service-type)
                  (service xfce-desktop-service-type)
                  (set-xorg-configuration
                   (xorg-configuration
                    (keyboard-layout keyboard-layout))))
            %desktop-services))

 ;; Allow resolution of '.local' host names with mDNS.
 (name-service-switch %mdns-host-lookup-nss))