This document discusses Linux containers and provides an overview of their internals. It notes that containers were not originally based on any standard but that the Open Container Initiative (OCI) later established standards. It describes key components of containers like OCI-compliant images and runtimes, chroot technology, and union mount file systems. It also discusses cgroups and how they were introduced in Linux kernels starting in version 2.6.24 to provide kernel-level resource controls for processes like CPU and disk limits.