[LightDM] After restart of lightdm display is black

Sat Mar 10 18:08:03 UTC 2018

I have lightdm 1:1.24.1-3 installed on and Intel NUC. it is enabled and started.
● lightdm.service - Light Display Manager
   Loaded: loaded (/usr/lib/systemd/system/lightdm.service; enabled; vendor preset: disabled)
   Active: active (running) since Fri 2018-03-09 14:50:28 EST; 15min ago
     Docs: man:lightdm(1)
 Main PID: 749 (lightdm)
    Tasks: 6 (limit: 4915)
   CGroup: /system.slice/lightdm.service
           ├─749 /usr/bin/lightdm
           └─755 /usr/lib/xorg-server/Xorg :0 -seat seat0 -auth /run/lightdm/root/:0 -nolisten tcp
vt7 -novtswitch

I have been running this system, OS, and configuration for over two years with no issues at all.

Mar 09 14:50:28 appenzeller systemd[1]: Starting Light Display Manager...
Mar 09 14:50:28 appenzeller systemd[1]: Started Light Display Manager.
Mar 09 14:50:28 appenzeller lightdm[749]: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
Mar 09 14:50:29 appenzeller lightdm[771]: pam_unix(lightdm-greeter:session): session opened for user
lightdm by (uid=0)

sytem data from inxi -F

System:    Host: appenzeller Kernel: 4.15.7-1-ARCH x86_64 bits: 64 Desktop: Cinnamon 3.6.7  Distro:
Arch Linux
Machine:   Device: desktop Mobo: Intel model: NUC5i5MYBE v: H47797-205 serial: N/A
           UEFI: Intel v: MYBDWi5v.86A.0026.2015.0820.1501 date: 08/20/2015
CPU:       Dual core Intel Core i5-5300U (-MT-MCP-) cache: 3072 KB
           clock speeds: max: 2900 MHz 1: 2290 MHz 2: 2037 MHz 3: 2143 MHz 4: 2093 MHz
Graphics:  Card: Intel HD Graphics 5500
           Display Server: X.Org 1.19.6 driver: i915 Resolution: 3840x2160 at 30.00hz
           OpenGL: renderer: llvmpipe (LLVM 5.0, 256 bits) version: 3.3 Mesa 17.3.6
Audio:     Card-1 Intel Wildcat Point-LP High Definition Audio Controller driver: snd_hda_intel
           Card-2 Intel Broadwell-U Audio Controller driver: snd_hda_intel
           Card-3 GN Netcom driver: USB Audio
           Sound: Advanced Linux Sound Architecture v: k4.15.7-1-ARCH
Network:   Card: Intel Ethernet Connection (3) I218-LM driver: e1000e
           IF: enp0s25 state: up speed: 1000 Mbps duplex: full mac: b8:ae:ed:79:c4:74
Drives:    HDD Total Size: 128.0GB (52.4% used)
           ID-1: /dev/sda model: TS128GMTS800 size: 128.0GB
Partition: ID-1: / size: 44G used: 24G (56%) fs: ext4 dev: /dev/sda2
           ID-2: /home size: 70G used: 36G (54%) fs: ext4 dev: /dev/sda4
           ID-3: swap-1 size: 4.29GB used: 0.00GB (0%) fs: swap dev: /dev/sda3
Sensors:   System Temperatures: cpu: 29.8C mobo: 27.8C
           Fan Speeds (in rpm): cpu: N/A
Info:      Processes: 140 Uptime: 1 min Memory: 375.5/15911.8MB Client: Shell (bash) inxi: 2.3.56

I had just updated the system with these packages:
[2018-03-09 07:22] [ALPM] upgraded libxml2 (2.9.7+4+g72182550-2 -> 2.9.8-1)
[2018-03-09 07:22] [ALPM] upgraded libinput (1.10.1-1 -> 1.10.2-1)
[2018-03-09 07:22] [ALPM] upgraded harfbuzz (1.7.5-1 -> 1.7.6-1)
[2018-03-09 07:22] [ALPM] upgraded libunistring (0.9.8-1 -> 0.9.9-1)
[2018-03-09 07:22] [ALPM] upgraded xcb-proto (1.12-3 -> 1.13-1)
[2018-03-09 07:22] [ALPM] upgraded libxcb (1.12-1 -> 1.13-1)
[2018-03-09 07:22] [ALPM] upgraded libdrm (2.4.90-3 -> 2.4.91-1)
[2018-03-09 07:22] [ALPM] upgraded qt5-base (5.10.1-3 -> 5.10.1-4)
[2018-03-09 07:22] [ALPM] upgraded akonadi (17.12.2-2 -> 17.12.3-1)
[2018-03-09 07:22] [ALPM] upgraded kmime (17.12.2-1 -> 17.12.3-1)
[2018-03-09 07:22] [ALPM] upgraded akonadi-mime (17.12.2-1 -> 17.12.3-1)
[2018-03-09 07:22] [ALPM] upgraded ksmtp (17.12.2-1 -> 17.12.3-1)
[2018-03-09 07:22] [ALPM] upgraded kmailtransport (17.12.2-1 -> 17.12.3-1)
[2018-03-09 07:22] [ALPM] upgraded kcalcore (17.12.2-1 -> 17.12.3-1)
[2018-03-09 07:22] [ALPM] upgraded kpimtextedit (17.12.2-1 -> 17.12.3-1)
[2018-03-09 07:22] [ALPM] upgraded kidentitymanagement (17.12.2-1 -> 17.12.3-1)
[2018-03-09 07:22] [ALPM] upgraded kcalutils (17.12.2-1 -> 17.12.3-1)
[2018-03-09 07:22] [ALPM] upgraded kcontacts (17.12.2-1 -> 17.12.3-1)
[2018-03-09 07:22] [ALPM] upgraded akonadi-contacts (17.12.2-1 -> 17.12.3-1)
[2018-03-09 07:22] [ALPM] upgraded akonadi-calendar (17.12.2-1 -> 17.12.3-1)
[2018-03-09 07:22] [ALPM] upgraded akonadi-search (17.12.2-1 -> 17.12.3-1)
[2018-03-09 07:22] [ALPM] upgraded libkleo (17.12.2-1 -> 17.12.3-1)
[2018-03-09 07:22] [ALPM] upgraded kldap (17.12.2-1 -> 17.12.3-1)
[2018-03-09 07:22] [ALPM] upgraded libkdepim (17.12.2-1 -> 17.12.3-1)
[2018-03-09 07:22] [ALPM] upgraded kimap (17.12.2-1 -> 17.12.3-1)
[2018-03-09 07:22] [ALPM] upgraded pimcommon (17.12.2-1 -> 17.12.3-1)
[2018-03-09 07:22] [ALPM] upgraded grantleetheme (17.12.2-1 -> 17.12.3-1)
[2018-03-09 07:22] [ALPM] upgraded kdepim-apps-libs (17.12.2-1 -> 17.12.3-1)
[2018-03-09 07:22] [ALPM] upgraded calendarsupport (17.12.2-1 -> 17.12.3-1)
[2018-03-09 07:22] [ALPM] upgraded libgravatar (17.12.2-1 -> 17.12.3-1)
[2018-03-09 07:22] [ALPM] upgraded kmbox (17.12.2-1 -> 17.12.3-1)
[2018-03-09 07:22] [ALPM] upgraded messagelib (17.12.2-1 -> 17.12.3-1)
[2018-03-09 07:22] [ALPM] upgraded akonadiconsole (17.12.2-1 -> 17.12.3-1)

I ran checkrestart which suggested among others that I restart lightdm.service.
The monitor immediately went black.  Nothing I have tried has brought back the display. The keyboard
still works. I tested by ctrl-alt-F2 and logging in.

I can ssh into the machine where I:
Removed and reinstalled lightdm

lightdm is running
750 ?     Ssl    0:00 /usr/bin/lightdm
756 tty7  Ssl+   0:35 /usr/lib/xorg-server/Xorg :0 -seat seat0 -auth /run/lightdm/root/:0 -nolisten
tcp vt7 -novtswitch
772 ?     Sl     0:00 lightdm --session-child 17 20
783 ?     Ssl    0:26 /usr/bin/lightdm-webkit2-greeter
988 ?     S<     0:00 /usr/NX/bin/nxexec --node --user lightdm --priority realtime --mode 0 --pid 12

and obviously waiting for a login.

Ran startx from tty2, Xorg and cinnamon run
 2424 tty2     Sl     0:00 /usr/lib/xorg-server/Xorg -nolisten tcp :1 vt2 -auth
/tmp/serverauth.V1TL95uMJO

 2430 tty2     Sl     0:00 cinnamon-session
 2473 tty2     Sl     0:00 /usr/lib/cinnamon-settings-daemon/csd-keyboard
 2474 tty2     Sl     0:00 /usr/lib/cinnamon-settings-daemon/csd-automount
 2475 tty2     Sl     0:00 /usr/lib/cinnamon-settings-daemon/csd-cursor
 2476 tty2     Sl     0:00 /usr/lib/cinnamon-settings-daemon/csd-wacom
 2477 tty2     Sl     0:00 /usr/lib/cinnamon-settings-daemon/csd-a11y-keyboard
 2478 tty2     Sl     0:00 /usr/lib/cinnamon-settings-daemon/csd-orientation
 2481 tty2     Sl     0:00 /usr/lib/cinnamon-settings-daemon/csd-screensaver-proxy
 2484 tty2     Sl     0:00 /usr/lib/cinnamon-settings-daemon/csd-print-notifications
 2489 tty2     Sl     0:00 /usr/lib/cinnamon-settings-daemon/csd-sound
 2498 tty2     Sl     0:00 /usr/lib/cinnamon-settings-daemon/csd-xrandr
 2500 tty2     Sl     0:00 /usr/lib/cinnamon-settings-daemon/csd-power
 2502 tty2     Sl     0:00 /usr/lib/cinnamon-settings-daemon/csd-xsettings
 2504 tty2     Sl     0:00 /usr/lib/cinnamon-settings-daemon/csd-clipboard
 2510 tty2     Sl     0:00 /usr/lib/cinnamon-settings-daemon/csd-color
 2513 tty2     Sl     0:00 /usr/lib/cinnamon-settings-daemon/csd-background
 2516 tty2     Sl     0:00 /usr/lib/cinnamon-settings-daemon/csd-a11y-settings
 2519 tty2     Sl     0:00 /usr/lib/cinnamon-settings-daemon/csd-housekeeping
 2521 tty2     Sl     0:00 /usr/lib/cinnamon-settings-daemon/csd-mouse
 2526 tty2     Sl     0:00 /usr/lib/cinnamon-settings-daemon/csd-media-keys
 2606 tty2     Sl     0:00 /usr/lib/cinnamon-settings-daemon/csd-printer
 2640 tty2     Sl     0:00 /usr/bin/python3 /usr/bin/cinnamon-launcher
 2650 tty2     Sl     0:07 cinnamon --replace
 2679 tty2     Sl     0:00 /usr/bin/python3 /usr/bin/cinnamon-killer-daemon
 2913 tty2     Sl     0:01 cinnamon-screensaver

Tried switching display ports, switching cables, switching monitors.
Then I tried booting a live ISO, the display was still blank. 
I tried to enter the BIOS to check if fast boot was turned on but again no display.
I removed the xf86-video-intel driver, as suggested by Antergos, still blank.

So my last hope before using the machine as a paper weight is to ask what does lightdm do on a
restart. Is there some very low level system writing taking place that could hopefully be manually
reversed. Any suggestions would be welcome.

Thank you