Suspend does not work in the login screen

[Mikko Rantalainen]

After booting the system and login screen is displayed top right gear-icon contains option to Suspend. However, selecting that action has no results at all (no error message, nothing in any file under /var/log or journalctl). I would like to get the suspend action to work similar to older Ubuntu versions (this system used to run Ubuntu 16.04 LTS and I did a fresh install of 18.04.1 LTS).

I have removed package gdm3 and installed lightdm instead because I like the lightdm interface better for our use case.

Looking at the source code in liblightdm-gobject/power.c suggests that lightdm_get_can_suspend() returns true because I get the suspend option. However, selecting the option does nothing so I would guess that lightdm_suspend() is called but somehow none of the g_debug() log messages never appear anywhere so I cannot debug the problem any further. (The above is just a guess because I didn't have enough time to read the source well enough to figure out if this is the codepath I'm trying to activate.)

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: lightdm 1.26.0-0ubuntu1
ProcVersionSignature: Ubuntu 4.18.0-13.14~18.04.1-lowlatency 4.18.17
Uname: Linux 4.18.0-13-lowlatency x86_64
ApportVersion: 2.20.9-0ubuntu7.5
Architecture: amd64
CurrentDesktop: MATE
Date: Sun Jan 6 22:23:20 2019
EcryptfsInUse: Yes
InstallationDate: Installed on 2019-01-05 (1 days ago)
InstallationMedia: Ubuntu 18.04.1 LTS "Bionic Beaver" - Release amd64 (20180725)
SourcePackage: lightdm
UpgradeStatus: No upgrade log present (probably fresh install)

[Mikko Rantalainen (mira)]

Does anybody care about lightdm bugs? I'm still seeing this issue but I haven't found a way to debug it. Is there some environment variable or some other method that can make all g_debug() messages visible from lightdm? Currently no log seems to contain any of the g_debug() messages in the lightdm source code.