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diyC

A simple educational Linux container runtime.

It is intentionally simple and leaves a lot of stuff out. It is a single C file of roughly 500 lines including comments showing the core features of the Linux used to build containers. It includes also the creation of a container from an image to clarify how images and containers are related.

Documentation

http://wvi.cz/diyC/ or pure markdown in the docs directory.

Prerequisites

This is a educational piece of software and has not been tested on many systems, here are the prerequisites:

  • recent Linux kernel supporting needed namespaces and cgroups
  • overlayfs
  • ip tool (iproute2 package)
  • iptables
  • gcc
  • make
  • bash

Apart from overlayfs most of the distros are prepared and ready, if not please consult your distro package manager. Overlayfs is in the mainline kernel so it should be straightforward.

Note: Kernel needs to be configured to support following namespaces PID, mount, network and UTS, cgroups are needed as well. Most of the GNU/Linux distros have this support enabled by default.

Installation

  1. make setup

It creates the necessary directory structure as well as prepares the networking part like iptables rules, bridge (diyc0) and so on. To remove the networking bits like bridge and iptables rules run make net-clean which removes them all.

  1. make

Builds the runtime.

  1. Done

It also builds a nsexec which executes a local command in namespaces. See nsexec --help to see what namespaces are available. Usage is very simple sudo ./nsexec -pnu myhost bash will start a new bash in new pid, network and UTS namespace.