Comment 0 for bug 1781418

As of lately, something about the login session breaks horribly when logging in via Lightdm/Slick-Greeter. I'm not quite certain what causes the issue, however here are the symptoms:

* The user when logged in, seems not be in any group except for its main group (e.g. `groups` yields just `username`). This is not the case when checking groups in TTY, after starting the X-server from TTY or when executing `sudo -u <username> groups`.
* Login works (with the described symptoms), but when trying to log out after having logged in from the greeter, the DM just restarts and apparently creates a new session (without requesting my password, so that the keyring needs to be manually unlocked)
* On every login attempt there seems to occur the following error in /var/log/auth.log:

```
Jul 12 16:20:32 GlaDOS dbus-daemon[1231]: [system] Rejected send message, 2 matched rules; type="method_ca
ll", sender=":1.220" (uid=1000 pid=11258 comm="lightdm --session-child 13 22 " label="unconfined") interfa
ce="org.freedesktop.login1.Manager" member="ReleaseSession" error name="(unset)" requested_reply="0" desti
nation="org.freedesktop.login1" (uid=0 pid=1267 comm="/lib/systemd/systemd-logind " label="unconfined")
Jul 12 16:20:32 GlaDOS lightdm: pam_systemd(lightdm:session): Failed to release session: Access denied
```
* Executing the command from the error message (`lightdm --session-child 13 22`) produces the following errors:
```
Error reading from daemon: Bad file descriptor
Error reading from daemon: Bad file descriptor
Error reading from daemon: Bad file descriptor
Error reading from daemon: Bad file descriptor
Error reading from daemon: Bad file descriptor
Error reading from daemon: Bad file descriptor
Error reading from daemon: Bad file descriptor
Error reading from daemon: Bad file descriptor
Error reading from daemon: Bad file descriptor
Error reading from daemon: Bad file descriptor
Failed to start PAM: System error
```

Things I have tried so far:
- `apt install --reinstall --purge slick-greeter lightdm*`
- `apt install --reinstall --purge dbus dbus-x11 dbus-user-session`

My System:

Architecture: amd64
System: Ubuntu 18.04 Budgie 64bit
Desktop-Manager: Budgie-Desktop
Session: budgie-desktop
Greeter: Slick-Greeter

I'm thankful for any clues on how to further debug these issues. I don't even know when they started - maybe an package update is to blame, but the only possibly relevant updates I have found in /var/log/apt/history.log are glx-related. I'll attach the latest apt history anyways.