The article delves into the foundational aspects of container technology, emphasizing the role of the Unix system call chroot in understanding containers. It explains how containers, often described as "light-weight VMs" due to their shared kernel with the host, are essentially processes that utilize chroot to create isolated environments. The text explores the historical development of chroot since its inception in Unix v7 in 1979 and demonstrates a hands-on approach to building a simple container runtime called "chrun" using chroot, which can mimic some functionalities of Docker by pulling and running images. The article also highlights the educational value of understanding containers as chrooted processes, thus demystifying their operation and opening up new possibilities, such as native OS X containers. Despite the existence of advanced container runtimes like runC and gVisor, the article posits that a fundamental grasp of chroot provides valuable insights into containerization's underlying principles.