Virtualization (LXC Containers)

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As of Fall 2009, we use Linux containers to maintain virtual machines, most notably caffeine, which is hosted on glomag. The various commands to manipulate Linux containers are prefixed with "lxc-"; see their individual manpages for usage.

Creating a new container

Create a new container using `lxc-create`:

# Create new container "containername" with root fs located at /vm/containername
lxc-create --dir=/vm/containername -n containername --template download

This will prompt you for distribution, release, and architecture. (Architecture *must* match host machine.)

# List containers
lxc-ls

to ensure that your container has been successfully created; it should be listed. You can also list its root directory if you like. To start it in the background and obtain a root shell, do

# Start and attach a root shell
lxc-start -d -n containername
lxc-attach -n containername

Now you're ready to configure your machine.

Networking

Networking might not be enabled on your container by default. If this is the case (easily checked with `ifconfig`), you'll need to modify its config file, located at /var/lib/lxc/containername/config:

# Network configuration
lxc.network.type = veth
lxc.network.flags = up

# that's the interface defined above in host's interfaces file
lxc.network.link = br0

# name of network device inside the container,
# defaults to eth0, you could choose a name freely
# lxc.network.name = lxcnet0

lxc.network.hwaddr = DE:AD:BE:EF:70:10 # your favourite fake MAC

# the ip may be set to 0.0.0.0/24 or skip this line
# if you like to use a dhcp client inside the container
lxc.network.ipv4 = 129.97.134.XXX/24

# define a gateway to have access to the internet
lxc.network.ipv4.gateway = 129.97.134.1

Management Quick Guide

To manage containers, use the lxc-* tools, which require root privilege. Some examples (replace caffeine with the appropriate container name):

# check if caffeine is running
lxc-info -n caffeine

# start caffeine in the background
lxc-start -d -n caffeine

# stop caffeine gracefully
lxc-halt -n caffeine

# stop caffeine forcefully
lxc-stop -n caffeine

# launch a TTY console for the container
lxc-console -n caffeine

To install Linux container support on a recent Debian (squeeze or newer) system:

  • Install the lxc and bridge-utils packages.
  • Create a bridged network interface (this can be configured in /etc/network/interfaces as though it were a normal Ethernet device, with the additional bridge_ports parameter. This is usually called br0 (can be created manually with brctl). LXC will create a virtual Ethernet device and add it to the bridge when each container starts.

To start caffeine, run the following command as root on glomag:

lxc-start -d -n caffeine

Containers are stored on the host filesystem in /var/lib/lxc (root filesystems are symlinked to the appropriate directory on /vm).