Canonical maintains an official set of Ubuntu-based images.
Images are arranged by Ubuntu release, and by image release date, with
current being the most recent. For example, the page that contains the most recently built image for Ubuntu 16.04 Xenial Xerus is Ubuntu 16.04 LTS (Xenial Xerus) Daily Build. Scroll to the bottom of the page for links to the images that can be downloaded directly.
If your deployment uses QEMU or KVM, we recommend using the images in qcow2 format. The most recent version of the 64-bit QCOW2 image for Ubuntu 16.04 is xenial-server-cloudimg-amd64-disk1.img.
In an Ubuntu cloud image, the login account is
ubuntu. eller root