[SOLVED] Can't restore lightdm login greeter

[froggit9000]

Initially I installed SID and had the XFCE desktop environment plus a basic login greeter screen, which was using 'lightdm' as far as I am aware.
A basic login box was displayed, asking for username and password. No users were displayed, which is how I like it, for security purposes.

Then recently I installed the GNOME desktop environment and I think the installer asked me to select the display manager.
I think I selected 'sddm' which was probably a mistake. I think I should have selected 'lightdm'.
Now when I boot, the login greeter is different, and I want to restore the login greeter back to how I initially had it - lightdm.

Now after booting and seeing the login greeter, if I press CTRL-ALT-F1 I can see the boot log messages and I see:

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Started sddm.service - Simple Desktop Display Manager

I had a look at how to restore the lightdm display manager/greeter and I saw:

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# /usr/sbin/dpkg-reconfigure lightdm

I ran that and selected 'lightdm'.

After rebooting however, I still see the system appears to be starting SDDM and a list of users are displayed, allowing me to select one and enter the password.

Does anyone have any ideas how I can restore the lightdm login greeter that I had originally?

Thanks in advance.

[RedGreen925]

Does anyone have any ideas how I can restore the lightdm login greeter that I had originally?

Thanks in advance.

Use apt remove --purge sddm to remove it from the system if it does not ask for your choice of login manager when doing it run the reconfigure command again. Reboot and find out if it has worked for you if getting no login screen when done then login to the console and apt install --reinstall lightdm to reinstall it and try startx to see if worked then.

Edit: If is says X is already running then pkill X to kill it off and have it respawn.

[amin11]

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sudo systemctl disable sddm.service

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sudo systemctl enable lightdm.service

If the second command gives an error, place that error with the output of the following command here

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systemctl status lightdm.service

[froggit9000]

After executing the commands suggested above, the system boots to an unresponsive black screen.

After selecting recovery mode from grub boot loader, I can login as root but there is no network.

I cannot copy and paste any messages therefore.

Any suggestions?

[amin11]

Output Send the following commands(with image)

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sudo systemctl enable lightdm.service

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systemctl status lightdm.service

and reboot you computer

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sudo reboot

[froggit9000]

After executing

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sudo systemctl enable lightdm.service

I can see some output, too much to type here on my phone, but I will try to copy some info:

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The unit files have no installation config (WantedBy=, RequiredBy=, UpheldBy=, Also= or Alias= settings in the [Install] section, and DefaultInstance= for template units.  This means they are not meant to enabled or disabled using systemctl.

Possible reasons for having these kinds of units are:
- a unit may be statically enabled...
- A unit's purpose may be to act as a helper...
- a unit may be started when needed by activation...
- in case of template units, the unit is meant to be enabled with some instance name specified. 

[froggit9000]

I remembered there was an extra display manager installed called 'gdm3' so i executed:

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# dpkg-reconfigure gdm3
# exit (to resume start-up from recovery mode)

So now I can boot into gdm3 display manager and I have network connection.

Any help to restore lightdm is appreciated.

Note from previous output shown above that it complained about use of systemctl to enable lightdm service.

[amin11]

So run

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sudo apt install --reinstall lightdm

And

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sudo systemctl disable gdm3.service

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sudo systemctl enable lightdm.service

If the lightdm service fails to activate again, activate the gdm3 service before turning off the computer.

[froggit9000]

Thanks amin11, it's working again now.

It seems that the config file for lightdm got overwritten, perhaps with the 'apt install --reinstall lightdm',
so I had to uncomment and edit the following lines in /etc/lightdm/lightdm.conf:

greeter-session=lightdm-gtk-greeter
user-session=xfce

I found the following helped sort this:
https://christitus.com/lightdm-configuration
https://youtu.be/_dYqisDIcC0