I was curious and installed GNOME desktop environment alongside with Unity. Then I felt it's not the flavor I like. I already uninstalled it by doing a complete removal via Synaptic Package Manager. However, the process of uninstalling was very quick compared to the installing process. It seemed that the 'complete removal' happened to be 'incomplete removal'. Till now, I am still given options to choose which desktop environment I want to use (whether it's Unity as the default environment or some other types of GNOME) whenever my laptop is opening the login window. I don't like it. How do I get rid of this space-consuming GNOME entirely (it said over 500 MB space required)?
If GUI is troubling you, login through CUI(Ctrl+Alt+F1)
Check if "ppa-purge" package is installed or not.
dpkg -l | grep ppa-purge
If it returns the value, "ppa-purge" is installed. If not, install it as follows;
sudo apt-get install ppa-purge
After that run the following commands;
sudo ppa-purge ppa:gnome3-team/gnome3-next sudo ppa-purge ppa:gnome3-team/gnome3-staging sudo ppa-purge ppa:gnome3-team/gnome3 sudo apt-get remove gnome-shell ubuntu-gnome-desktop
Reboot system and login through Unity.
I'd like to share an experience that happened to solve problem. I went to Synaptic Package Manager and typed 'GNOME Flashback' on its 'rebuilding search index' space. Then it showed me some file packages which had been installed including a package named 'gnome-session-flashback'. I did a complete removal to it. Soon after that I restarted my laptop. Then, voila! There were no other desktop environments I had to pick but my one and only Unity. Thank you for your support, people! I've got what I want.