Here we create a plain LXC & AUFS container from scratch on Ubuntu Raring without Docker.

Overview

The objective of this exercise is to make you familiar how you can create a docker’esque LXC container yourself. This is how we’ll do it:

  • Create a filesystem we can use as write disk so our container can write, but it won’t pollute our base filesystem.
  • Combine the root filesystem with our container so we have an unified filesystem for our container.
  • Create a container and run /bin/bash

Creating the writable file system

For a lot of this we need to be sudo. So lets go for it:

sudo -i

We want to mount our parent filesystem read-only, and put all changes on top of this made in the container into a specific file called mycontainerrw.img.

Let’s start by creating a mountable filessystem for our writes, this will create a 500mb empty image. The fs parameters is the filestream, the bs the block size, the count number of blocks:

dd if=/dev/zero of=mycontainerrw.img bs=1M count=500

The command above basically creates a zero padded file of 500MB. Now we need to run mkfs on the file to make a filesystem out of this zero padded file:

mkfs mycontainerrw.img

Let’s create a mountpoint for it. It will nag that this is no block device. Whatever.

sudo mkdir /mnt/mycontainerrw
sudo mount -t mycontainerrw.img /mnt/mycontainerrw

Now lets create our container fs combing the rw and the ro images using AUFS. You can see we mount / as ro (read-only) and /dev/mycontainerrw as rw (read-write). This will mean that whenever we write to our /dev/mycontainer-fs we actually write to our mycontainerrw.img, leaving the root filesystem untouched. Amazeballs.

sudo mount -t aufs -o br=/dev/mycontainerrw=rw:/=ro -o udba=reval none \
/dev/mycontainer-fs

After we’ve created this, we can start creating our LXC container.

Setting up our LXC container

sudo lxc-create -n mycontainer

It will be created in the directory /var/lib/lxc/mycontainer so lets go there.

cd /var/lib/lxc/mycontainer

Let’s edit the config so we can mount our new made mycontainer-fs :) Remember. man lxc.conf to see what config options are available.

Here you can see we mount our unified mycontainer-fs in the config file.

lxc.network.type = veth
lxc.network.link = lxcbr0
lxc.network.flags = up

lxc.rootfs = /dev/mycontainer-fs

To start our container we do:

sudo lxc-execute -n mycontainer /bin/bash

Congratulations! You are now in a container, with AUFS. Every change you do now will be written to our mycontainerrw.img :-)

You can see that you can’t see what you typed. Not a clue why, I’ll will figure that out. To get out of your container do the following:

exit

This will say:

[1]+  Stopped sudo lxc-execute -n mycontainer /bin/bash

and then type:

fg

Your container should now be terminated.

Conclusion

As you can see it ain’t that hard to create a container with AUFS and LXC. It’s not hard to build something like a couple of shell scripts that allow for automation of this process like docker.

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