Ubuntu – In Ubuntu 15.04 can’t do graphical log in

bootgraphicslightdmsystemdtext-mode

I have done clean install recently of Ubuntu Desktop 15.04.
And I was able to log in to the graphical environment until I enabled "boot to text" like said there: How do I disable X at boot time so that the system boots in text mode?
1. commented out 

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

2. added "text" to 

GRUB_CMDLINE_LINUX="text"

3. uncommented 

GRUB_TERMINAL=console

4. 

sudo update-grub

5. 

sudo systemctl set-default multi-user.target

Now system does not load gui, just text prompt.
When I want the GUI, I start it using

sudo systemctl start lightdm

graphical login prompt appear, but when I pass the password screen flickers and again password prompt appears.
I even reverted all changes back: grub file and 

sudo systemctl set-default graphical.target

How can I log in to the GUI now, please?

Best Answer

Based on the bug report, reported March 21, 2015 Ubuntu 15.04 Xserver does not start or freezes with systemd + lightdm. More detail regarding the impact of this change and how to switch from systemd to upstart and back again is available on this page.

To check to see if your system is using systemd vs. upstart you can test by issuing the command sudo initctl version which will return upstart if upstart is handling init. another useful method is to issue the command dpkg -S /sbin/init which will tell you which package installed it (in my case on 14.04 it's upstart) you can find more very good answers on how to do so from our friends at Unix & Linux. Further detail regarding identifying the init system is also available.

To see if your lightdm works under upstart as designed, you can install the upstart-sysv package, which will remove ubuntu-standard and systemd-sysv (but should not remove anything else. Give the developers a heads up if it does!), and run sudo update-initramfs -u. After that, grub's "Advanced options" menu will have a corresponding "Ubuntu, with Linux ... (systemd)" entry where you can do an one-time boot with systemd.

You can revert back to systemd installing systemd-sysv and ubuntu-standard packages.

Another option appears to be to use gdm under systemd instead of lightdm under upstart.

Further sources (not linked elsewhere):

https://unix.stackexchange.com/questions/196166/how-to-find-out-if-a-system-uses-sysv-upstart-or-systemd-initsystem

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