Installing Ubuntu on Pen Drive (recommended for Lenovo laptops)

Installing Ubuntu on a pen drive is not a very long task. Its very simple due to the softwares available on the internet. All you need is:

• A 8GB Pen Drive (recommended) 
• Ubuntu 14.04 iso (recommended). You can download 15.04, but I had some issues with WiFi on it.
• A UUI (Universal USB Installer) down loaded from pendrivelinux.com

The whole process of downloading and installing took me 40 minutes with an internet connection of 14Mbps.

The steps are given below:

1. Download the Ubuntu 14.04 iso (make note of the download location).
2. Download the UUI
3. Plug in your empty pen drive. Take backup of your drive if you have data stored on it.
4. Execute the UUI
5. Select Ubuntu from the first drop down list.
6. The next bar requires you to enter the location of the iso file. Click on the ... (Browse) button and select the iso file from the location you noted while installing.
7. Select your pen drive from the next drop down list. 
8. Check the box saying Format pen drive (recommended).
9. Choose the amount of storage space you want on your pen drive using the slider(recommended). I chose about 3.5GB (5384MB).
10. Click on next.
11. During the process your bar wouldn't move at point. DO NOT WORRY. Your process will complete in 20-30 minutes.
12. After the process is complete restart your computer.
13. On the first screen hit F12 or the required key to open the multiboot menu.
14. Select USB HDD on the list.
15. Ubuntu will boot up from your drive.
16. MAKE SURE you click TRY Ubuntu and NOT Install Ubuntu because installing Ubuntu will install it on your native Hard disk of your computer.
17. Ubuntu will now start.

SOME Troubleshooting

I did the same process on a Lenovo Z570 and after installing and trying to boot Ubuntu from my pen drive using multi boot I did not get the screen where I can select try Ubuntu or install Ubuntu. This is how I solved it:

• When you boot up your laptop open the BIOS menu by hitting F2.
• Go to the boot preference tab or option and shift the USB HDD to the top of the list.
• Now reboot your computer and everything will work fine.

NEW EDIT

There has always been a persistence issue with Ubuntu on pen drive because the steps above are instructions to installing live ubuntu on your pen drive. Persistence means to preserve your home file system and save all your documents and application on the ubuntu image of your pen drive. Though the casper-rw file created during the above procedure is meant for persistence, it is not reliable (It definitely didn't work out for me). So to over come this problem you have to install ubuntu on your pen drive. This would use up your whole pen drive (recommended 16GB), So take backup of the data on your pen drive.

Installing Ubuntu

For this you would need a drive (CD or pen drive) that already has Live ubuntu installed on it. Boot this drive. For convenience of conversation we would call this as "live drive" and the other as "Ubuntu drive".

Steps:

•  Boot your live drive
• Plug in your Ubuntu drive
• click on install Ubuntu (Beware this procedure takes your Hard Drive as the default drive so pay attention before clicking next)
• Select your language.
• Don't install any updates and any third party applications now, we'll do it later.
• Now it would ask you for the location to install ubuntu click on the last option Custom and click Next (NOT Install).
• Select your pen drive from the list that pops up.
• Format your Ubuntu drive to get 'unallocated' space on the pen drive.
• Divide  Ubuntu drive as follows:

• 8GB : /
• 300MB : /boot
• 1GB : swap
• Keep the rest for /home (Here is where you store your files, so you can decide the size yourself)

• The process will take maximum 40 minutes.
• After that shut down your computer.
• Plug-in your Ubuntu drive and boot from it.
• You Now Have Fully Functioning Ubuntu.
• Now go to the dash and open the Disks (Disk Manager) application.
• Go to the partition of you pen drive (NOT your Hard Disk), it is usually on the top of the list.
• Select the 'unallocated' space and click on the gears below it to format it. Format it to a FAT32 File system and give it a suitable, distinct name and click Format. This part of your pen drive would act like a normal pen drive and can be used to transfer data from any computer to any other (no matter if it is a windows, Mac or Linux)

 Now if thought of keeping some unallocated space on your Ubuntu drive thinking that you can use this later as a FAT32 partition, you have made a TERRIBLE MISTAKE because windows recognizes only one partition on a pen drive and that usually is the primary partition. So there is no point in leaving even 1MB as external FAT32 storage.

Installing ubuntu on a pen drive is indeed your first step towards Linux and safe installation without touching your hard disk, but ubuntu uses unity ui which is heavy and eats lot of space. I would instead recommend using Lubuntu as it uses the LXDE and is very light and does all the same things that ubuntu does.