I had installed Kubuntu 15.04 sometime ago. I upgraded to 15.10, things were going fine till I added
ubuntu-desktop to use Unity DE.
When booting with systemd, on startup or login, I get black or white screen for all Virtual Terminamls (TV's / TTY's) including TV7 graphical one. In some rare cases flickering screen between lightdm & sddm GUI, and that's how I got to know that both were running and may be the cause of this problem (black screen).
It works fine: when booting with upstart or switching DM back to sddm.
Flickering screen between KDE/sddm Unity/lightdm
ps ax | grep dm
1377 ? SLsl 0:00 /usr/sbin/lightdm 1459 tty7 Ssl+ 1:10 /usr/bin/X -core :0 -seat seat0 -auth /var/run/lightdm/root/:0 -nolisten tcp vt7 -novtswitch 1526 ? Ssl 0:00 /usr/bin/sddm 1626 ? SLl 0:00 lightdm --session-child 12 19 3843 pts/2 S+ 0:00 grep --color=auto dm
systemctl status default.target
● graphical.target - Graphical Interface Loaded: loaded (/lib/systemd/system/graphical.target; static; vendor preset: enabled) Active: active since Fri 2015-11-13 09:46:21 CET; 50min ago Docs: man:systemd.special(7) Nov 13 09:46:21 BlueSkies systemd: Reached target Graphical Interface.
sudo dpkg-reconfigure lightdm
Default display manager: gdm * lightdm sddm xdm
ls -l /etc/systemd/system/display-manager.service
lrwxrwxrwx 1 root root 35 Nov 13 17:26 /etc/systemd/system/display-manager.service -> /lib/systemd/system/lightdm.service
I don't want to remove any DM, also I do want to keep LightDM as default. So, is there a canonical answer to How to set the default DM for this mixed release 15.10 (systemd/upstart)?
I could find many similar question without the answer I'm looking for:
- lightdm black screen after installing plasma5 in Ubuntu
- lightdm doesn't show up
- kubuntu 15.04 upgrade: many problems
- No login screen on startup, works after logging in and logging out again
Dual boot ubunuty/windows 10 partition on Dell xps 13, see Palantir's answer:
I found the kubuntu installer would not handle full disk encryption correctly, so I installed with Ubuntu installer, and added the kubuntu-desktop package later. I had serious problems with LightDM (it would appear and immediately disappear after boot, also it would not allow me to switch VTs), so I switched to KDE's sddm and its login manager (hint: sudo dpkg-reconfigure lightdm).