lightdm/login session fails to resume after display is locked and goes to black

[Patrick Barabe]

Logging in after a fresh boot works fine. Subsequently, after locking the screen (either Super + L or allow to auto-lock) and letting the screen turn off automatically, then attempting to wake the machine, only a black screen and the mouse cursor are visible. The desktop and authentication prompt do not re-appear, and though the mouse cursor moves, the machine doesn't respond to keyboard entry except to switch to a virtual console with Ctrl + Alt + 1 (2, 3, etc). From there it's possible to reboot or kill -HUP lightdm, but in either case, the active Unity login session is lost. I've check various log files, including /var/log/lightdm/* but haven't noticed any obvious culprits.

This started after the following system updates on 2017-07-25 (/var/log/apt/history.log):
Start-Date: 2017-07-25 08:32:14
Commandline: apt upgrade
Requested-By: myusername (1000)
Upgrade: libfwup0:amd64 (0.5-2ubuntu4, 0.5-2ubuntu5), unity-control-center-faces:amd64 (15.04.0+16.04.20160705-0ubuntu1, 15.04.0+16.04.20170214-0ubuntu1), linux-libc-dev:amd64 (4.4.0-83.106, 4.4.0-87.110), xserver-common:amd64 (2:1.18.4-0ubuntu0.2, 2:1.18.4-0ubuntu0.3), libgtk2.0-bin:amd64 (2.24.30-1ubuntu1, 2.24.30-1ubuntu1.16.04.1), imagemagick:amd64 (8:6.8.9.9-7ubuntu5.7, 8:6.8.9.9-7ubuntu5.8), libsystemd0:amd64 (229-4ubuntu17, 229-4ubuntu19), libmagickwand-6.q16-2:amd64 (8:6.8.9.9-7ubuntu5.7, 8:6.8.9.9-7ubuntu5.8), libgail-common:amd64 (2.24.30-1ubuntu1, 2.24.30-1ubuntu1.16.04.1), libgtk2.0-0:amd64 (2.24.30-1ubuntu1, 2.24.30-1ubuntu1.16.04.1), coreutils:amd64 (8.25-2ubuntu2, 8.25-2ubuntu3~16.04), udev:amd64 (229-4ubuntu17, 229-4ubuntu19), libepoxy0:amd64 (1.3.1-1ubuntu0.16.04.1, 1.3.1-1ubuntu0.16.04.2), libgail18:amd64 (2.24.30-1ubuntu1, 2.24.30-1ubuntu1.16.04.1), fwupdate:amd64 (0.5-2ubuntu4, 0.5-2ubuntu5), libudev1:amd64 (229-4ubuntu17, 229-4ubuntu19), unity-control-center:amd64 (15.04.0+16.04.20160705-0ubuntu1, 15.04.0+16.04.20170214-0ubuntu1), imagemagick-6.q16:amd64 (8:6.8.9.9-7ubuntu5.7, 8:6.8.9.9-7ubuntu5.8), libmagickcore-6.q16-2-extra:amd64 (8:6.8.9.9-7ubuntu5.7, 8:6.8.9.9-7ubuntu5.8), systemd-sysv:amd64 (229-4ubuntu17, 229-4ubuntu19), session-shortcuts:amd64 (1.2, 1.2ubuntu0.16.04.1), libpam-systemd:amd64 (229-4ubuntu17, 229-4ubuntu19), systemd:amd64 (229-4ubuntu17, 229-4ubuntu19), libmagickcore-6.q16-2:amd64 (8:6.8.9.9-7ubuntu5.7, 8:6.8.9.9-7ubuntu5.8), libgtk2.0-common:amd64 (2.24.30-1ubuntu1, 2.24.30-1ubuntu1.16.04.1), xserver-xorg-core-hwe-16.04:amd64 (2:1.18.4-1ubuntu6.1~16.04.1, 2:1.18.4-1ubuntu6.1~16.04.2), libunity-control-center1:amd64 (15.04.0+16.04.20160705-0ubuntu1, 15.04.0+16.04.20170214-0ubuntu1), imagemagick-common:amd64 (8:6.8.9.9-7ubuntu5.7, 8:6.8.9.9-7ubuntu5.8), fwupdate-signed:amd64 (1.11+0.5-2ubuntu4, 1.11.1+0.5-2ubuntu5)
End-Date: 2017-07-25 08:34:11

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: lightdm 1.18.3-0ubuntu1.1
ProcVersionSignature: Ubuntu 4.10.0-27.30~16.04.2-generic 4.10.17
Uname: Linux 4.10.0-27-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.10
Architecture: amd64
CurrentDesktop: Unity
Date: Wed Jul 26 12:43:23 2017
EcryptfsInUse: Yes
InstallationDate: Installed on 2017-05-19 (68 days ago)
InstallationMedia: Ubuntu 16.04.2 LTS "Xenial Xerus" - Release amd64 (20170215.2)
SourcePackage: lightdm
UpgradeStatus: No upgrade log present (probably fresh install)

[Patrick Barabe (uazpbarabe)]

This is running on Xenial/16.04. Buggy behavior is similar to that described in https://bugs.launchpad.net/ubuntu/+source/lightdm/+bug/1543888

[Patrick Barabe (uazpbarabe)]

This issue does not appear to persist after today's updates.

/var/log/apt/history.log:

Start-Date: 2017-07-28 11:43:40
Commandline: apt upgrade
Requested-By: myusername (1000)
Install: linux-headers-4.10.0-28-generic:amd64 (4.10.0-28.32~16.04.2, automatic), linux-image-4.10.0-28-generic:amd64 (4.10.0-28.32~16.04.2, automatic), libllvm4.0:amd64 (1:4.0-1ubuntu1~16.04.1, automatic), libinput-bin:amd64 (1.6.3-1ubuntu1~16.04.1, automatic), libxfont2:amd64 (1:2.0.1-3~ubuntu16.04.1, automatic), linux-headers-4.10.0-28:amd64 (4.10.0-28.32~16.04.2, automatic), xserver-xorg-legacy-hwe-16.04:amd64 (2:1.19.3-1ubuntu1~16.04.2, automatic), linux-image-extra-4.10.0-28-generic:amd64 (4.10.0-28.32~16.04.2, automatic)
Upgrade: xserver-xorg-video-qxl-hwe-16.04:amd64 (0.1.4-3ubuntu3~16.04.1, 0.1.5-2build1~16.04.1), update-manager-core:amd64 (1:16.04.6, 1:16.04.7), xserver-xorg-video-vesa-hwe-16.04:amd64 (1:2.3.4-1build2~16.04.1, 1:2.3.4-1build3~16.04.1), libdrm-nouveau2:amd64 (2.4.70-1~ubuntu16.04.1, 2.4.76-1~ubuntu16.04.1), whoopsie:amd64 (0.2.52.3, 0.2.52.4), libwacom-common:amd64 (0.18-1, 0.22-1~ubuntu16.04.1), linux-image-generic-hwe-16.04:amd64 (4.10.0.27.30, 4.10.0.28.31), libkmod2:amd64 (22-1ubuntu4, 22-1ubuntu5), libglapi-mesa:amd64 (12.0.6-0ubuntu0.16.04.1, 17.0.7-0ubuntu0.16.04.1), update-manager:amd64 (1:16.04.6, 1:16.04.7), binutils:amd64 (2.26.1-1ubuntu1~16.04.3, 2.26.1-1ubuntu1~16.04.4), libwhoopsie0:amd64 (0.2.52.3, 0.2.52.4), xserver-xorg-video-amdgpu-hwe-16.04:amd64 (1.1.2-1~16.04.1, 1.3.0-0ubuntu1~16.04.1), linux-generic-hwe-16.04:amd64 (4.10.0.27.30, 4.10.0.28.31), gnome-software:amd64 (3.20.1+git20170524.0.ea2fe2b0-0ubuntu0.16.04.1, 3.20.5-0ubuntu0.16.04.5), xfonts-utils:amd64 (1:7.7+3, 1:7.7+3ubuntu0.16.04.2), xserver-xorg-input-synaptics-hwe-16.04:amd64 (1.8.3-1ubuntu1~16.04.1, 1.9.0-1ubuntu1~16.04.1), libxatracker2:amd64 (12.0.6-0ubuntu0.16.04.1, 17.0.7-0ubuntu0.16.04.1), libwacom-bin:amd64 (0.18-1, 0.22-1~ubuntu16.04.1), libegl1-mesa:amd64 (12.0.6-0ubuntu0.16.04.1, 17.0.7-0ubuntu0.16.04.1), kmod:amd64 (22-1ubuntu4, 22-1ubuntu5), xserver-xorg-hwe-16.04:amd64 (1:7.7+13ubuntu4~16.04.2, 1:7.7+16ubuntu3~16.04.1), libgbm1:amd64 (12.0.6-0ubuntu0.16.04.1, 17.0.7-0ubuntu0.16.04.1), libwayland-client0:amd64 (1.9.0-1, 1.12.0-1~ubuntu16.04.1), xserver-xorg-video-all-hwe-16.04:amd64 (1:7.7+13ubuntu4~16.04.2, 1:7.7+16ubuntu3~16.04.1), libappstream-glib8:amd64 (0.5.13-1ubuntu4, 0.5.13-1ubuntu5), libdrm-amdgpu1:amd64 (2.4.70-1~ubuntu16.04.1, 2.4.76-1~ubuntu16.04.1), xserver-xorg-video-fbdev-hwe-16.04:amd64 (1:0.4.4-1build5~16.04.1, 1:0.4.4-1build6~16.04.1), python3-distupgrade:amd64 (1:16.04.21, 1:16.04.22), ubuntu-software:amd64 (3.20.1+git20170524.0.ea2fe2b0-0ubuntu0.16.04.1, 3.20.5-0ubuntu0.16.04.5), python3-update-manager:amd64 (1:16.04.6, 1:16.04.7), ubuntu-release-upgrader-core:amd64 (1:16.04.21, 1:16.04.22), libwayland-egl1-mesa:amd64 (12.0.6-0ubuntu0.16.04.1, 17.0.7-0ubuntu0.16.04.1), xserver-xorg-video-vmware-hwe-16.04:amd64 (1:13.1.0-2ubuntu3~16.04.1, 1:13.2.1-1build1~16.04.1), libxfont1:amd64 (1:1.5.1-1, 1:1.5.1-1ubuntu0.16.04.1), libdrm2:amd64 (2.4.70-1~ubuntu16.04.1, 2.4.76-1~ubuntu16.04.1), libgl1-mesa-dri:amd64 (12.0.6-0ubuntu0.16.04.1,...