1. A system for the execution of immutable file system images, the system comprising: a file system tree including a plurality of mutually exclusive sub-trees, each sub-tree comprising individual software components of a software distribution. a plurality of immutable file system images wherein a separate immutable file system image corresponds to each of the plurality of mutually exclusive sub-trees and wherein each separate immutable file system image includes a file system structure; and a virtual file system associated with the plurality of immutable file system images, wherein at run-time the virtual file system interposes the file system structure of each separate immutable file system image dynamically forming the software distribution based on the plurality of immutable file system images.