Linux Containers - otherwise known as LXC - are a virtualisation system that's
in the Linux kernel right now and ready to use. You can use them to set up
vserver/openvz style guests on a host - e.g. separate processes, file systems,
but same kernel.
Word on the street is that vservers are being deprecated in Debian beyond
squeeze, so it seems like a good time to
learn about containers. Here is my five minute guide to getting them up and
running on your debian unstable (squeeze) box.
Setup
apt-get install lxc
You want kernel 2.6.29 or later, 2.6.31 is currently in unstable.
Once lxc is installed, lxc-checkconfig will check if your kernel has
everything enabled that is needed. It reports most things except for the memory
controller for me. As I haven't gotten around to playing with resource limiting
in the containers, this doesn't bother me.
You need to mount a cgroup filesystem somewhere to control things:
sudo mkdir /var/local/cgroup
sudo vim /etc/fstab
# add this line:
# cgroup /var/local/cgroup cgroup defaults 0 0
sudo mount cgroup
Networking Prep
You have to set up a bridge so the containers will be able to talk to the
outside world (and the outside world can talk back) .
This isn't hard, it just involves editing /etc/network/interfaces. Just make
sure you stop networking before making the changes:
/etc/init.d/networking stop
vim /etc/network/interfaces
# find the section talking about your physical interface, it's normally
# eth0 or eth1
auto eth0
iface eth0 inet manual # change from 'dhcp' to 'manual'
# add this section
auto br0
iface br0 inet dhcp
bridge_ports eth0
bridge_stp off
bridge_fd 0
bridge_maxwait 0
Then /etc/init.d/networking start. Try pinging something, it should work just
fine. If not, revert your changes and ask a network ninja to help you.
Creating Containers
The lxc-debian script in /usr/share/doc/lxc/examples is useful. I have
made some modifications to it, to make it a bit more friendly. You can get it
from my git repository:
git clone git://git.nigel.mcnie.name/lxc-debian.git
If you don't have git, just download it from here.
Put the lxc-debian script in /usr/local/bin, and put the init script at
/etc/init.d/lxc. Then you're ready to create your first container:
lxc-debian create
You'll have to pick a name and hostname, then some networking related things.
You can use route -n to work out your gateway if you don't know it already,
and just pick a free IP on your subnet if you don't know anything else to
choose.
Once you're done, it will download a bunch of packages with debootstrap, and
set up your container. The next time you create a container, it will use the
packages from the first time, so it'll only be slow once.
Starting and Accessing your Container
You start it with lxc-start -n [name]. This will dump you at the login
prompt - e.g., this is like starting a real server, it's in the foreground.
Login is 'root', no password.
You probably actually wanted to daemonize it, so halt it and then type
lxc-stop -n [name] in another terminal to shut it down .
To start it in the background, do lxc-start -n [name] -d. This will exit
immediately and the container will start. You can use lxc-info -n [name] to
find out whether it's started up yet, though they tend to start pretty quickly.
Once you're done, you can connect to a tty in the container with lxc-console -n
[name] -t 1. You can replace 1 with any tty number (1-6 are started for you).
Control-A, q exits.
Or, the lxc-debian script installs and configures an ssh server for you, so you
can just ssh root@[ipaddress] to get into it as root. I tend to use this
method all the time.
Update: (March '10) I see on the mailing list
that there is now some patches floating around to add an lxc-attach command
that will execute a command in a container (or a shell if none is specified).
They're not in a released version of lxc just yet, but I guess in a couple of
months they will be.
I want to remove my container
lxc-debian destroy and answer the questions. This basically does:
lxc-destroy -n [name]
rm -rf /path/to/rootfs
What Next?
Now that you can create, start, connect to and destroy containers, there's not
much else you need to know to use containers for development environments or
other such uses. Later, I might write an article about some more advanced
topics, such as resource limiting.
I'm interested in improving lxc-debian - if you are as well then get in touch,
I'd love to hear from you.
Resources
There's two mailing lists for LXC that may be of interest:
Like this post? Subscribe to my RSS feed and follow me on twitter to hear about new posts early.
Want to share this post?
Hi and welcome! In 2009 I quit my job to become an entrepreneur, founding 
