I want my linux to always boot into command line on startup and when later I want , I can start GUI, but how do that. I want to know the safest method and please provide step by step explanation to cancel Graphical user interface on startup.

Most probably your computer is set to boot at run-level 5. First you need to know run levels,

Runlevel 0 and 6: halt and reboot the machine, respectively.
Runlevel 1: No services running, only root can login.
Runlevel 2: Users can login but no networking.
Runlevel 3: Networking and text-mode.
Runlevel 4: unused.
Runlevel 5: GUI.

So , you need run level 3 on boot. It can be done by modifying /etc/inittab

You should see something like following :

Code:

id:5:initdefault

Change it to :

Code:

id:3:initdefault

Hmm.. it appears "code" blockquote is not working properly on eTI...