I installed gdm for a while as my display manager, and after removing it, lightdm does not start by itself. I instead have to login to a tty, and run sudo start lightdm.
Running dpkg-reconfigure lightdm does not work either:
dpkg-maintscript-helper: warning: environment variable DPKG_MAINTSCRIPT_NAME missing
dpkg-maintscript-helper: warning: environment variable DPKG_MAINTSCRIPT_PACKAGE missingI've also tried reinstalling lightdm completely, but it does not work as well
My /var/log/boot.log has the following lines:
* Starting LightDM Display Manager
* Starting ACPI daemon
* Starting anac(h)ronistic cron
* Starting save kernel messages
* Stopping LightDM Display Manager 6 Answers
Run a terminal and enter cat /etc/X11/default-display-manager. Probably says lightdm if you recently uninstalled GDM. /etc/init/lightdm.conf doesn't accept lightdm as a setting - however, /usr/bin/lightdm or /usr/sbin/lightdm work. So open /etc/X11/default-display-manager in your favorite text editor and replace whatever is there with the following line:
/usr/bin/lightdm
or
/usr/sbin/lightdm
Reboot and lightdm should start and bring you to the logon screen as usual.
1My solution was to run:
rm /etc/systemd/system/default.target
systemctl set-default graphical.targetThis will replace the default target file, which in my case must have prevented systemd from reaching the graphical target, with a symlink to the graphical target. After this, lightdm (and gdm when selected with dpkg-reconfigure) starts automatically.
/etc/X11/default-display-manager was already set to the correct value so this appears to be a different root cause from OP's.
More information on systemd targets here.
2It happens for me when removing gnome apps including gdm,and moving to kde.
I fixed it by running:
sudo dpkg-reconfigure lightdmand choosing kdm as default instead of lightdm
Alright, I think I finally figured it out! Everyone's suggestion in response to this problem is to get the right legacy nVidia card. Easier said than done. I had a really hard time tracking down the right driver, since it seemed to have disappeared from repositories (at least Ubuntu's). Here's what worked for me. Depending on your nVidia card, you might need to download a different file, but they're all listed at . I needed the legacy 96xx driver for my GeForce 2 MX 400. So, after weeks of trying to fix this, I just ran these commands and it finally worked! The URL used in the wget command is just the URL of the file that the nVidia website wanted me to download.
wget
sudo sh NVIDIA-Linux-x86-96.43.23-pkg1.run
sudo rebootIn my case, I have to reinstall ubuntu-desktop to get it to work again.
sudo apt install xorg
sudo apt-get install --reinstall ubuntu-desktopIf the system seems not to boot up, you can try switch tty with CTRL+FX Buttons, with X being a number from 1 to 7. Usually, the lightdm does not start completely, but systemd is able to start all services needed, as their own login manager. Changing tty will let you purge and reinstall the login manager packages and let your distribuition configure It to you automatically. On Ubuntu after the tty change:
0sudo apt-get purge lightdm && sudo apt-get install lightdm
