Setup LXC-Container in Debian Jessie

10 April 2016

LXC-Containers are very useful. They are more leightweight than virtual machines and not as static as docker-containers. That’s why I like them especially for my server environments. In this article I will show a very basic setup of LXC-Containers on Debian Jessie.

Creating a Network-Bridge

I use a network-bridge with a dummy-interface for my virtual internal network:


This is a sample /etc/network/interface for the LXC-Host:

auto br0
iface br0 inet static
bridge_ports dummy0
bridge_fd 2.0
bridge_maxwait 1

Installing dnsmasq

It’s possible to use the dns-server of the provider. But I always prefer a dns-forwarder like dnsmasq on the lxc-host:

apt-get install dnsmasq

dnsmasq should listen on br0-only. So we edit /etc/dnsmasq.conf:


..and restart the service:

service dnsmasq restart 

Installing LXC

apt-get install lxc

Creating a LXC-Container

If /var/lib/lxc is located on a btrfs, then we can automatically create a subvolume using option “-B btrfs”:

lxc-create -n CONTAINERNAME -t debian -B btrfs -- -r jessie

Otherwise we can just call lxc-create without -B:

lxc-create -n CONTAINERNAME -t debian -- -r jessie

If the container was created, we can edit it’s config /var/lib/lxc/CONTAINERNAME/config:

# Parameters passed to the template: -r jessie
# For additional config options, please look at lxc.container.conf(5) = empty
lxc.rootfs = /var/lib/lxc/sec/rootfs

# Common configuration
lxc.include = /usr/share/lxc/config/debian.common.conf

# Container specific configuration
lxc.mount = /var/lib/lxc/sec/fstab
lxc.utsname = CONTAINERNAME
lxc.arch = amd64
lxc.autodev = 1
lxc.kmsg = 0
lxc.tty = 6 = 1 = veth = veth0 = up = br0

Now let’s chroot into the container and install some packages we need:

chroot chroot /var/lib/lxc/CONTAINERNAME/rootfs/ /bin/bash
apt-get update && apt-get install iputils-ping dnsutils resolvconf vim rsyslog logrotate

Still in the chroot-system we could also edit our network-config in /etc/network/interfaces:

auto lo
iface lo inet loopback

auto veth0
iface veth0 inet static

Using “exit” we can escape from our chroot.

Starting the Container

lxc-start -d -n CONTAINERNAME

Get a Console for a Container

lxc-console -n CONTAINERNAME

The exit the console just call “ctrl+a q”

Firewalling and Routing

Normally I prefer to install shorewall to have the full power of greyskull. But for this example I will just use a very simple iptables-script.


        iptables -P FORWARD ACCEPT
	echo 1 > /proc/sys/net/ipv4/ip_forward
	iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

We can execute this script manually or use it in the /etc/network/interfaces for an up-directive. Since this script is not meant to run in production(because it’s not secure!) I will not publish an example how to autostart it using the interfaces-file.

Final Words

LXC is a very cool technique to run containers. It’s even possible to run containers inside a virtual machine(for example kvm). I prefer to install my containers on BTRFS-filesystems and use Snapper to automatically create and manage snapshots.

[ Linux  Sysadmin  Network  Virtualization  ]
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