This is actually somewhat a "derivative" that comes from the genius idea of the Live CD which lets users run a pre-installed OS using a bootable CD/DVD without having to install it on a HDD. Although CD and DVD's are not dead :) but other than storing movies and backing up data, most prefer to use the USB drives these days.
They're pretty small, easy to carry, re-writeable, quiet and much faster than CDs. So, by using a USB or pen drive to run GNU/Linux OS rather than using the conventional CD will give us the ability to experience the OS in general, in much faster way. Although haven't yet come out that much... but with the introduction of the USB 3.0, oh man.... they're dauntingly fast!.
Anyhow, the problem is that, unlike creating a boo-table Live CD using a disk image which is pretty easy since all the CD/DVD burners support this by default, yet when it comes to creating a bootable Live USB GNU/Linux "disk" is a bit hard.
Although you can do this by using the Linux command line but again, it ain't that user friendly.
Even if you do it manually using the command line but it can't let us create a "pendrive Linux" which contains more than one OS. Well, you'll be glad to know that there is an excellent utility called "Multisystem" which does exactly that!.
It's a GUI written in GTK+ toolkit and once installed you can use it to ...
*. Install more than one GNU/Linux distribution into a USB drive and create a multiboot Live USB drive!.
*. Supports a huge list of distributions by default.
*. Drag-n-Drop support.
*. Also supports removable hard drives, Memory cards, SSD drives as well.
*. If you have installed Virtualbox, then Multisystem even lets you run it via the Virtual environment.
|The default Grub menu...|
*. USB stick has to be formated using the FAT32 file system.
That's about it actually. Once you show the app where the .iso files are, it'll extract them (can use more than one OS as said before) to the pendrive or any supported storage media and then it'll automatically install the proper boot-images + the Grub boot-loader as well.
If you use Ubuntu 11.04 Natty Narwhal, then you can install Multisystem by entering the below command in your command line (Terminal).
sudo apt-add-repository 'deb http://liveusb.info/multisystem/depot all main'I actually can't give you a screenshot of mine because it needs you to have an empty USB drive... I don't have much space to put the "data" inside mine.
wget -q http://liveusb.info/multisystem/depot/multisystem.asc -O- | sudo apt-key add -
sudo apt-get update
sudo apt-get install multisystem
|This was as far as I could "go" because of the "not empty" USB stick :/...|
Anyhow, if you want to test a multiboot or singe boot Pendrive Linux "environment", then I highly suggest Multisystem, this is one hell of an application!.