So this morning (5 August 2016) on Ubuntu 16.04 LTS I tried doing an apt-get update / apt-get upgrade security pass and it rendered my gnome3 installation unable to log in anyone through the GUI. Going to a tty screen _does_ allow login; trying through the GUI does not, on any account, including guest.

After searching a couple of hours for possible fixes and getting nowhere, I restored my previous root image, fortunately made only a few days ago. After restoring from dd-created image and booting/logging-in successfully, trying again to apt-get update / apt-get upgrade produced the same results: no ability to log in under gnome3.

Syslog was unrevealing but the first error was saying that org.gnome.SessionManager was not being provided by any .desktop file, and as far as I can find from searching, that is a harmless warning message. The closest thing to a relevant error I found indicated that it is in fact not generally provided by a .service file but is launched via /usr/bin/gnome-session which I have and which had correct executable permissions. I also have/had the correct xml file for the service. But all of that could've been completely irrelevant.

----- Here is a saved .xsession-errors file:

openConnection: connect: No such file or directory
cannot connect to brltty at :0
upstart: gnome-session (GNOME) main process (3277) terminated with status 1
upstart: logrotate main process (3137) killed by TERM signal
upstart: bamfdaemon main process (3213) killed by TERM signal
upstart: upstart-dbus-session-bridge main process (3258) terminated with status 1
upstart: Disconnected from notified D-Bus bus

----- Here is the list of packages it wants to update: firefox firefox-locale-en firefox-locale-ja grub-common grub-pc grub-pc-bin grub2-common less libegl1-mesa libgbm1 libgl1-mesa-dri libgl1-mesa-glx libglapi-mesa libgles1-mesa libgles2-mesa libllvm3.8 libwayland-egl1-mesa libxatracker2 mesa-vdpau-drivers snapd xserver-common xserver-xephyr xserver-xorg-core

----- And here's some low-level data which may and may not have any relevance:

Video driver: nvidia-367.27 (32-bit) from NVIDIA-Linux-x86-367.27 downloaded from their website.

$ cat /proc/version
Linux version 4.4.0-31-lowlatency (buildd@lgw01-58) (gcc version 5.3.1 20160413 (Ubuntu 5.3.1-14ubuntu2.1) ) #50-Ubuntu SMP PREEMPT Wed Jul 13 00:50:28 UTC 2016

$ lsb_release -a
LSB Version:	core-9.20160110ubuntu0.2-ia32:core-9.20160110ubuntu0.2-noarch:printing-9.20160110ubuntu0.2-ia32:printing-9.20160110ubuntu0.2-noarch:security-9.20160110ubuntu0.2-ia32:security-9.20160110ubuntu0.2-noarch
Distributor ID:	Ubuntu
Description:	Ubuntu 16.04.1 LTS
Release:	16.04
Codename:	xenial

$ cat /etc/X11/xorg.conf
# nvidia-xconfig: X configuration file generated by nvidia-xconfig
# nvidia-xconfig:  version 367.27  (buildmeister@swio-display-x64-rhel04-11)  Thu Jun  9 19:26:08 PDT 2016


Section "ServerLayout"
    Identifier     "Layout0"
    Screen      0  "Screen0" 0 0
    InputDevice    "Keyboard0" "CoreKeyboard"
    InputDevice    "Mouse0" "CorePointer"
EndSection

Section "Files"
EndSection

Section "InputDevice"

    # generated from default
    Identifier     "Mouse0"
    Driver         "mouse"
    Option         "Protocol" "auto"
    Option         "Device" "/dev/psaux"
    Option         "Emulate3Buttons" "no"
    Option         "ZAxisMapping" "4 5"
EndSection

Section "InputDevice"

    # generated from default
    Identifier     "Keyboard0"
    Driver         "kbd"
EndSection

Section "Monitor"
    Identifier     "Monitor0"
    VendorName     "Unknown"
    ModelName      "Unknown"
    HorizSync       28.0 - 33.0
    VertRefresh     43.0 - 72.0
    Option         "DPMS"
EndSection

Section "Device"
    Identifier     "Device0"
    Driver         "nvidia"
    VendorName     "NVIDIA Corporation"
EndSection

Section "Screen"
    Identifier     "Screen0"
    Device         "Device0"
    Monitor        "Monitor0"
    DefaultDepth    24
    DefaultFbBPP    32
    Option         "TransparentIndex" "0"
    SubSection     "Display"
        Depth       24
    EndSubSection
EndSection

----- contact

If anyone has any interest in contacting me about any of this, use the contact form at crimeandtheforcesofevil.com.