Recently in our Personal Computer are installed more than one Operation System, es; Ubuntu and XP, or Ubuntu and Vista, Ubuntu and Mac OSX etc. GRUB is a multiboot boot loader. GRand Unified Bootloader, which was originally designed and implemented by Erich Stefan Boleyn. Boot loader is the first software program that runs when a computer starts. It is responsible for loading and transferring control to the operating system kernel software.
From GRUB menu you can select you Operating System. By default this menu have a timeout by 3 or 10 seconds.
Here is a short guide how to change this time.
Open Terminal Window and write:
sudo gedit /boot/grub/menu.lst
Enter you user password. This command will open menu.lst with gedit editor.
From gedit editor CTRL + F and find “timeout”
Edit the value near “timeout”. The timeout value is in seconds. Save the file, and when you reboot you will have that many seconds to choose the menu item you want.