How to set GNOME as my default desktop environment?

Question

I just downloaded GNOME-Shell. And at login screen it's give me to choose to set desktop environment, But I want to set GNOME as my default desktop environment. Although I tried the possible suggestions on this site like

pnath@ubuntu:~$ sudo /usr/lib/lightdm/lightdm-set-defaults -s gnome-shell
[sudo] password for pnath: 
sudo: /usr/lib/lightdm/lightdm-set-defaults: command not found
pnath@ubuntu:~$ 

And this

gksu gedit /etc/lightdm/lightdm.conf

and this:

Open a terminal and cd to /etc/lightdm/lightdm.d, create a file called 50-ubuntu.conf with the following command sudo nano 50-ubuntu.conf.

Add the following two lines.

[SeatDefaults]
user-session=gnome

then reboot and gnome should be your default session.

When I tried output is this:

pnath@ubuntu:~$ cd /etc/lightdm/lightdm.d
bash: cd: /etc/lightdm/lightdm.d: No such file or directory
pnath@ubuntu:~$ 

this did not change anything

Please give me any other solution

Solution

(This answer was tested with Ubuntu 14.04. It is probably not useful for newer Ubuntu editions)

I do not know about ligthDM (@muru confirm that lightDM behave the same), but if you use gdm as display manager the default session is simply the last one you choose (at least, it was --- I hope they didn't change this; can't test now because I removed all desktops minus the gnome-shell one).

To install gdm (which, by the way, is the best thing to do if you want gnome-shell --- I had problems with gnome-shell + lightDM), simply

sudo apt-get install gdm

If you have it already installed, just

sudo dpkg-reconfigure gdm 

will ask you which display manager to use.

Then when you login, you choose Gnome as the desktop you want, and the subsequent login that will be the default.

Comments

[Purnendu Nath]

Yes when I chose gdm , it's simply change login screen but not theme

[muru]

"the default session is simply the last one you choose" - also holds for LightDM.

[Purnendu Nath]

Yes by default Gnome has started but Icon theme does not changed why ?

[Rmano]

@muru thanks --- I suspected it. PriyankaNath, install and use gnome-tweak-tool to change the icon theme --- this is a different matter than default Desktop Environment; none of the changes you comment in the question will do anything in that direction.

[Mehdi]

sudo dpkg-reconfigure gdm has no effect for me. I'm not prompted to chosse any thing. No error meessage.

[Rmano]

@Mehdi the answer was posted for Ubuntu 14.04 (see the date!). A lot of things changed in the Ubuntu graphic stack... I added a warning.