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If you have a Ubuntu installation that you want to convert to a live/installer disk image (able to be burned to DVD, "burned" to bootable USB, or used as an .iso to set up a virtual machine), this is one way to do it. I'm using Ubuntu 14.04.3 in this example, because it's the latest LTS (Long-Term Support release for Ubuntu). If you're using the newest version of Ubuntu (15.10, as of this writing), you may find How to create a custom live/installer disk image for Ubuntu 15.10 more helpful.
Make sure you have your Ubuntu installation exactly the way you want it before proceeding.
First, go to the Remastersys PPA.
Expand Technical details about this PPA.
Under Display sources.list entries for:, select Trusty (14.04).
You'll then see the sources in the input box change to something like this:
deb-src http://ppa.launchpad.net/mutse-young/remastersys/ubuntu trusty main
Put this command into the terminal to edit the sources.list (while also making a backup):
Now that the repository is set up, let's pull from it to get Remastersys actually installed:
Optional: Remastersys, by default, will just back up your whole system but not any of the logged-in users. If you want to make one of your user's the default user profile, run this command:
You can then burn it to a DVD (as a disk image—not data), use Startup Disk Creator to make a bootable USB, or use the .iso to install to a virtual disk using something like VMWare or VirtualBox.