To run Ubuntu from a USB stick, the first thing you need to do is insert a USB stick with at least 2GB of free space into your PC.
There are two process of creating a live usb disk.
Using ‘dd’ command in linux
open terminal in linux and type in following command.
It shows which one is your usb drive.
Your usb drive must be something like sdb* (* can be any number)
now run following command
sudo umount /dev/sdb*
sudo dd if=</path/to/ubuntu.iso> of=/dev/sdb*
wait for a while and its done.
The easiest way to put Ubuntu onto your stick is to use the USB installer provided at pendrivelinux.com. You’ll need to download and install and follow the instructions.Download Pendrive linux usb installer or Universal Usb installer
Select ‘Ubuntu’ from the dropdown list.
Click ‘Browse’ and open the downloaded ISO file.
Choose the USB drive and click ‘Create’.
After the process is completed, you are good to go! Happy booting!