In Ubuntu it is easy to create bootable USB from iso file. If you did not download iso file, first download iso file from Ubuntu. and save on Desktop or where you want but remember the location of directory. Lets create it step by step with pictures.

Condition: Your USB Flashdrive must be empty. 

1. Go to search box and type "Disk Creator" and you will get option as below and click to open the application.

Choose Startup Disk Creator Application on Search Box

2. Choose your directory where your downloaded iso file has been kept and choose your USB Flash-drive to create bootable on the second option "Disk to use" and next specify how much stored in reserved extra space (Recommended 1GB).

Choose other option to select your directory of iso file
Choose other option to select your directory of iso file

Select the directory of iso file
Select the directory of iso file (where your iso file)

3. Click "Mark Startup Disk" option. It will start copying files automatically till 40% or more. Before completion it will be required to authenticate your system and provide it by entering your system password.

Start installing and provide password to authenticate
Provide your password to authenticate

4. After installing complete let quit to finish.

Installing Complete Disk creator
Installing Complete
5. Go to your USB device and you will show bootable files.

Showcase of bootable files

Hurray ! You are ready to boot from USB.

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