can not active screen after second time lock screen with command dm-tool lock.

[Hacksign]

What I have done:
1. login system, then lock screen with command dm-tool lock.
2. active screen and unlock.
3. lock the screen again with dm-tool lock.
What happend :
screen remain blank after second time lock screen.no matter how I click keyboard/move mouse ...
I just can not lightup the screen

below is the log:
```
[root@XSign lightdm]# cat x-0.log

X.Org X Server 1.18.3
Release Date: 2016-04-04
X Protocol Version 11, Revision 0
Build Operating System: Linux 4.2.5-1-ARCH x86_64
Current Operating System: Linux XSign 4.4.5-1-ARCH #1 SMP PREEMPT Thu Mar 10 07:38:19 CET 2016 x86_64
Kernel command line: initrd=\initramfs-linux.img root=/dev/sda3 rw
Build Date: 05 April 2016 05:24:02PM

Current version of pixman: 0.34.0
 Before reporting problems, check http://wiki.x.org
 to make sure that you have the latest version.
Markers: (--) probed, (**) from config file, (==) default setting,
 (++) from command line, (!!) notice, (II) informational,
 (WW) warning, (EE) error, (NI) not implemented, (??) unknown.
(==) Log file: "/var/log/Xorg.0.log", Time: Thu Apr 14 14:06:18 2016
(==) Using config directory: "/etc/X11/xorg.conf.d"
(==) Using system config directory "/usr/share/X11/xorg.conf.d"
xf86: remove device 0 /sys/devices/pci0000:00/0000:00:02.0/drm/card0
failed to find screen to remove
```

[Douglas Moyes (aragorn-stellimare)]

I've seem this happen to. I'll have to switch to a virtual terminal, run "sudo systemctl restart lightdm" to get the display back (of course, if CTL-ALT-BS wasn't disabled now by default in window managers, this fix would require fewer keystrokes).

This might be an issue with the nVidia driver as I've seen screen blanking screw up any session. While the window manager recognizes some key strokes. The biggest issue here is there is no way for the user to configure LightDM screen blanking options without editing a text file.

We'll want to get more input here to se if it is a Nvidia driver issue or a generic issue with screen blanking in Linux

System specs for refrence:
01:00.0 VGA compatible controller: NVIDIA Corporation GM206 [GeForce GTX 960] (rev a1)
AMD FX(tm)-8350 Eight-Core Processor

Relevant packages:
liblightdm-gobject-1-0/bionic,now 1.26.0-0ubuntu1 amd64 [installed,automatic]
lightdm/bionic,now 1.26.0-0ubuntu1 amd64 [installed,automatic]
lightdm-gtk-greeter/bionic,now 2.0.5-0ubuntu1 amd64 [installed,automatic]
lightdm-gtk-greeter-settings/bionic,bionic,now 1.2.2-1 all [installed,automatic]

libnvidia-cfg1-390/bionic-updates,bionic-security,now 390.116-0ubuntu0.18.04.1 amd64 [installed]
libnvidia-common-390/bionic-updates,bionic-updates,bionic-security,bionic-security,now 390.116-0ubuntu0.18.04.1 all [installed]
libnvidia-compute-390/bionic-updates,bionic-security,now 390.116-0ubuntu0.18.04.1 amd64 [installed]
libnvidia-decode-390/bionic-updates,bionic-security,now 390.116-0ubuntu0.18.04.1 amd64 [installed]
libnvidia-encode-390/bionic-updates,bionic-security,now 390.116-0ubuntu0.18.04.1 amd64 [installed]
libnvidia-fbc1-390/bionic-updates,bionic-security,now 390.116-0ubuntu0.18.04.1 amd64 [installed]
libnvidia-gl-390/bionic-updates,bionic-security,now 390.116-0ubuntu0.18.04.1 amd64 [installed]
libnvidia-ifr1-390/bionic-updates,bionic-security,now 390.116-0ubuntu0.18.04.1 amd64 [installed]
nvidia-compute-utils-390/bionic-updates,bionic-security,now 390.116-0ubuntu0.18.04.1 amd64 [installed]
nvidia-dkms-390/bionic-updates,bionic-security,now 390.116-0ubuntu0.18.04.1 amd64 [installed]
nvidia-driver-390/bionic-updates,bionic-security,now 390.116-0ubuntu0.18.04.1 amd64 [installed]
nvidia-kernel-common-390/bionic-updates,bionic-security,now 390.116-0ubuntu0.18.04.1 amd64 [installed]
nvidia-kernel-source-390/bionic-updates,bionic-security,now 390.116-0ubuntu0.18.04.1 amd64 [installed,automatic]
nvidia-prime/bionic-updates,bionic-updates,now 0.8.8.2 all [installed]
nvidia-settings/bionic-updates,now 390.77-0ubuntu0.18.04.1 amd64 [installed]
nvidia-utils-390/bionic-updates,bionic-security,now 390.116-0ubuntu0.18.04.1 amd64 [installed,automatic]
xserver-xorg-video-nvidia-390/bionic-updates,bionic-security,now 390.116-0ubuntu0.18.04.1 amd64 [installed,automatic]

[Douglas Moyes (aragorn-stellimare)]

BTW, for thsoe affected by the bug, the lightdm config file is located in /usr/share/lightdm/lightdm-gtk-greeter.conf.d/30_xubuntu.conf on Ubuntu 18.04.

This usually happens after my system has been left idle for hours.

[Crispin (crispinh)]

I'm getting this (or something very similar) on Arch - version 1.30
The first time I lock my session it works fine but the second time it kicks me to the "this session is locked you will be redirected to the greeter" message and then I have to go into a virtual terminal and restart lightdm (which restarts my login session)
I've tried it with the GTK and slick greeters and both of them have the problem.
Here's my `/var/log/lightdm/lightdm.log from the second time I lock & unlock in a session: https://gist.github.com/crispinha/f1c28d6d670ea9dd6f4f82ce8d6659e7