Computer does not return from lock normally

[LochDhu10yr]

When I lock the computer from the whisker menu, the screen goes blank. It will remain blank even if I move the mouse, click or press keys. I can get the screen back on with Ctrl-Alt-F1 for a command prompt. Or Ctrl-Alt-F7 gives me large white text on a black background, saying "This session is locked. You'll be redirected to the unlock dialog automatically in a few seconds." And in a few seconds I do get an unlock dialog in a few seconds. The system works normally thereafter.

If I close the laptop lid while the laptop is plugged in, the screen is blank when I reopen it as above. Ctrl-Alt-F1 works as above. Ctrl-Alt-F7 produces the "This session is locked" message, but it does not proceed to the unlock dialog. This forces me to restart the computer. Power Manager is set to lock the screen when I close the laptop lid.

If I close the laptop lid while the laptop is on battery power, the screen is blank when I reopen it as above. Ctrl-Alt-F1 works as above. Ctrl-Alt-F7 has no effect. This forces me to restart the computer. Power Manager is set to switch off the display when I close the laptop lid.

If is suspend the laptop from the whisker menu, on restore it behaves the same as locking the computer. Ctrl-Alt-F7 allows me to get to the unlock dialog and continue using the computer.

This is a System76 Galadro Ultra Pro.
$ lsb_release -rd
Description: Ubuntu 18.04.2 LTS
Release: 18.04
$ apt-cache policy light-locker
light-locker:
  Installed: 1.8.0-1ubuntu1
  Candidate: 1.8.0-1ubuntu1
  Version table:
 *** 1.8.0-1ubuntu1 500
        500 http://us.archive.ubuntu.com/ubuntu bionic/universe amd64 Packages
        100 /var/lib/dpkg/status
$ lscpu
Architecture: x86_64
CPU op-mode(s): 32-bit, 64-bit
Byte Order: Little Endian
CPU(s): 8
On-line CPU(s) list: 0-7
Thread(s) per core: 2
Core(s) per socket: 4
Socket(s): 1
NUMA node(s): 1
Vendor ID: GenuineIntel
CPU family: 6
Model: 70
Model name: Intel(R) Core(TM) i7-4750HQ CPU @ 2.00GHz
Stepping: 1
CPU MHz: 798.169
CPU max MHz: 3200.0000
CPU min MHz: 800.0000
BogoMIPS: 3990.40
Virtualization: VT-x
L1d cache: 32K
L1i cache: 32K
L2 cache: 256K
L3 cache: 6144K
L4 cache: 131072K
NUMA node0 CPU(s): 0-7
Flags: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc cpuid aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx est tm2 ssse3 sdbg fma cx16 xtpr pdcm pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm cpuid_fault epb invpcid_single pti ssbd ibrs ibpb stibp tpr_shadow vnmi flexpriority ept vpid fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid xsaveopt dtherm ida arat pln pts md_clear flush_l1d

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: light-locker 1.8.0-1ubuntu1
ProcVersionSignature: Ubuntu 4.18.0-21.22~18.04.1-generic 4.18.20
Uname: Linux 4.18.0-21-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.6
Architecture: amd64
CurrentDesktop: XFCE
Date: Sat Jun 15 15:50:29 2019
InstallationDate: Installed on 2019-06-13 (2 days ago)
InstallationMedia: Xubuntu 18.04.2 LTS "Bionic Beaver" - Release amd64 (20190210)
SourcePackage: light-locker
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[micsu (micsu-z)]

There are several workarounds:
1) change light-locker to another locker, eg
- XScreenSaver
- xfce4-screensaver
- physlock
- Slock
more details: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=846278

2) keep light-locker but change the greeter to another greeter, eg
- slick-greeter
more details: https://github.com/the-cavalry/light-locker/issues/114#issuecomment-474709454

[Jarno Suni (jarnos)]

I have similar issue, but I do not get the unlock dialog even after the Ctrl-Alt-F1 Ctrl-Alt-F7 trick. However, the issue does not occur, if I use nouveau graphics driver instead of nvidia driver (which I had selected in Additional Drivers dialog). See also Bug #1811402

xfce4-screensaver is not available for 18.04

[Jarno Suni (jarnos)]

Besides, even with nvidia driver, I can unlock by typing password, even if screen is blank.

[Josep Pujadas-Jubany (jpujades)]

Same problem. Very easy to test/reproduce doing:

$ light-locker-command -l

I can return to my session doing Ctrl+Alt+F1 + Ctrl+Alt+F7 and waiting unlock for the greeter.

Lubuntu 18.04.3 64 bit fresh install + updates

$ lsb_release -d
Description: Ubuntu 18.04.3 LTS

$ uname -rm
5.0.0-27-generic x86_64

Acer TravelMate B118-M (TMB118-M-C4AL manufactured date 2019/05/23)

[Josep Pujadas-Jubany (jpujades)]

@jarnos at #5

You are right!

It not depends of the video card! It happens also with my i915 video card.

After black screen with:

$ light-locker-command -l

typed my user password and hit the Enter key and returned to my session!!!

[Josep Pujadas-Jubany (jpujades)]

Here you have the bug explained:

https://github.com/the-cavalry/light-locker/issues/114

It's 1 year old!

[Josep Pujadas-Jubany (jpujades)]

slick-greeter is a good workaround but I had to configure it manually. Perhaps for this some people is saying that doesn't work for them.

apt-get install slick-greeter
cd /etc/lightdm/lightdm.conf.d
cp -p /usr/share/lightdm/lightdm.conf.d/50-slick-greeter.conf .

lightdm --show-config

shows:

I greeter-session=slick-greeter

reboot and it works! No more blank screen when light-locker is activated.