Answer by Hai Lang for If I can, how do I install Ubuntu from Ubuntu?

I think this link that may help: How do I install Ubuntu to a USB key? (without using Startup Disk Creator)

In short:

1. Install qemu-kvm package and dependencies if not yet done so.

   sudo apt-get install qemu-kvm

2. Run virtual machine with external HDD (assume it is mounted at /dev/sdb) as internal drive and Ubuntu ISO file as cdrom. Add more ram to virtual machine with -m 2GB if you have plenty of ram on your machine to speed up installation process.

   sudo kvm /dev/sdb -cdrom ~/.cache/testdrive/iso/ubuntu_natty-desktop-i386.iso

Personally, I prefer to run any installer on target PC/laptop instead of remove HDD from it and install at another PC/laptop.