rootstrap binary package in Ubuntu Trusty amd64

 Rootstrap was originally written to provide a facility for building
 filesystems for use with User-mode Linux, but can be useful in other
 applications as well.
 .
 It uses a modular set of shell scripts to create the filesystem
 image, install a base system, and customize it for a particular
 application. Currently, it only builds Debian systems, but the
 architecture is such that other base systems could be used instead.
 .
 Use of rootstrap does not require root access, or special privileges
 of any kind. This is because it builds the filesystem inside a
 User-mode Linux system running under an
 unprivileged uid.
 .
 Filesystem creation with rootstrap is quick and painless. With a
 local mirror and a single command, a fresh Debian filesystem
 can be created in about 3 minutes on relatively modest hardware.

Source package