Ubuntu – How to enable X at boot time so that the system boots not in text mode

Yes, it is possible. I do it for games.

xinit session -- :1 -xf86config config.conf

Where session should be replaced by the session you'd like to start in the new Xorg display, and config.conf is the configuration file.

For starting it automatically, take a look at this answer.

First run this command for a graphical environment

sudo systemctl set-default graphical.target

Because you have used sudo systemctl set-default multi-user.target before.

Then repair the entries in /etc/default/grub

This statement is completely wrong:

GRUB_DEFAULT="quiet splash"

Open the configuration:

sudo nano /etc/default/grub

and replace the entry

GRUB_DEFAULT="quiet splash"

with

GRUB_DEFAULT=0

add the entry

GRUB_CMDLINE_LINUX="quiet splash"

After that run

sudo update-grub

• GRUB_DEFAULT

  The default menu entry. This may be a number, in which case it identifies the Nth entry in the generated menu counted from zero, or the title of a menu entry, or the special string ‘saved’. Using the title may be useful if you want to set a menu entry as the default even though there may be a variable number of entries before it.

• GRUB_CMDLINE_LINUX

  Command-line arguments to add to menu entries for the Linux kernel.

• GRUB_CMDLINE_LINUX_DEFAULT

  Unless ‘GRUB_DISABLE_RECOVERY’ is set to ‘true’, two menu entries will be generated for each Linux kernel: one default entry and one entry for recovery mode. This option lists command-line arguments to add only to the default menu entry, after those listed in ‘GRUB_CMDLINE_LINUX’.

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