mycontainer

A tiny toy container runtime written in 200 lines of C.

quick start

Prerequisites

mycontainer runs smoothly with the following prerequisites:

• make
• gcc
• ip
• docker
• Linux distribution with control group v2

The following build instructions were tested under Ubuntu 22.04.

Step 1: make rootfs from docker image

First, we should make a rootfs for our container. There are many ways to build rootfs from scratch, namely, busybox, shell command lines, and etc. In this document, I will demostrate an unusual way to build a rootfs, which take advantages of docker images.

1. export an archive from a docker image(centos for example)

   docker export $(docker create centos) --output="centos.tar"

2. extract the archive to a directory

   mkdir rootfs
   tar -xf centos.tar -C rootfs

3. check the rootfs

   $ ls rootfs
   bin  etc   lib    lost+found  mnt  proc  run   srv  tmp  var
   dev  home  lib64  media       opt  root  sbin  sys  usr

Step 2: compile and run

1. edit macro ROOT_PATH in main.c, change it to the absolute path of your own rootfs

   -#define ROOT_PATH "/home/haooops/Documents/CST/Projects/mycontainer/rootfs"
   +#define ROOT_PATH "/absolute/path/to/your/own/rootfs"

2. compile and run

   make run

   The shell will ask for your root password. After entering the password, the container will start up.

3. check if the container is in a new PID namespace

   ps -e

   the shell will show:

   [root@75a80a52 /]# ps -e
       PID TTY          TIME CMD
         1 ?        00:00:00 bash
        12 ?        00:00:00 ps

4. check the network

   ip a

   the shell will show:

   [root@75a80a52 /]# ip a
   1: lo: <LOOPBACK> mtu 65536 qdisc noop state DOWN group default qlen 1000
       link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
   2: eth0@if30: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
       link/ether f2:bc:91:44:c8:40 brd ff:ff:ff:ff:ff:ff link-netnsid 0
       inet 172.17.0.82/16 scope global eth0
       valid_lft forever preferred_lft forever
       inet6 fe80::f0bc:91ff:fe44:c840/64 scope link 
       valid_lft forever preferred_lft forever

   The container is at ip address 172.17.0.82/16.