create replica of ext4 filesystem and re-use it

Question

Is there a way that I can use my Linux ext4 file system, as such and then use it on some other computer.

I have a dual-boot of Windows 7 and Ubuntu 10.04 and my partition table looks like this:

My question might not be clear, so explaining it with an example.

Can I copy my Linux partition on a flash drive and then use it on a different PC, with or without any need to install Ubuntu on new PC, by simply booting from the copied ext4 partition.
This way, I can easily port my Ubuntu packages and other applications, settings etc. from one PC to other.

If it's a very stupid question, please don't mind.

Answer 1

1. The simplest way is to create an empty partition of exactly the same size¹, then dd over the data.

   dd if=<inputfile> of=<outputfile>
   

   For example, if you were to copy from /dev/sda3 to /dev/sdc1, you would use dd if=/dev/sda3 of=/dev/sdc1.

   (You can copy into a regular file too, but it wouldn't be easily bootable, although you can loop-mount such a copy in an already-running system.)

2. To make the copy bootable, you will need to install a bootloader into the flash drive.

   grub would work, but I'm not sure if the latest version supports specifying the root partition by UUID. (It used to be an Ubuntu-specific patch.) UUIDs are needed because grub needs a filesystem identifier that stays the same among computers.

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¹ The partition and the filesystem store their sizes independently; therefore, the partition must be as big as the filesystem thinks it is. You can create a larger partition and later grow the copied filesystem, though. Most filesystems can be shrunk too.