LXC setup on Debian jessie

Here's how to setup LXC-based "chroots" on Debian jessie. While this is documented on the Debian wiki, I had to tweak a few things to get the networking to work on my machine.

Start by installing (as root) the necessary packages:

apt install lxc libvirt-clients debootstrap

Network setup

I decided to use the default /etc/lxc/default.conf configuration (no change needed here):

lxc.network.type = veth
lxc.network.flags = up
lxc.network.link = virbr0
lxc.network.hwaddr = 00:FF:AA:xx:xx:xx
lxc.network.ipv4 = 0.0.0.0/24

That configuration requires that the veth kernel module be loaded. If you have any kinds of module-loading restrictions enabled, you probably need to add the following to /etc/modules and reboot:

veth

Next, I had to make sure that the "guests" could connect to the outside world through the "host":

  1. Enable IPv4 forwarding by putting this in /etc/sysctl.conf:

    net.ipv4.ip_forward=1

  2. and then applying it using:

    sysctl -p

  3. Ensure that the network bridge is automatically started on boot:

    virsh -c lxc:/// net-start default
virsh -c lxc:/// net-autostart default

  4. and that it's not blocked by the host firewall, by putting this in /etc/network/iptables.up.rules:

    -A INPUT -d 224.0.0.251 -s 192.168.122.1 -j ACCEPT
-A INPUT -d 192.168.122.255 -s 192.168.122.1 -j ACCEPT
-A INPUT -d 192.168.122.1 -s 192.168.122.0/24 -j ACCEPT

  5. and applying the rules using:

    iptables-apply

Creating a container

Creating a new container (in /var/lib/lxc/) is simple:

sudo MIRROR=http://httpredir.debian.org/debian lxc-create -n sid64 -t debian -- -r sid -a amd64

You can start or stop it like this:

sudo lxc-start -n sid64 -d
sudo lxc-stop -n sid64

Connecting to a guest using ssh

The ssh server is configured to require pubkey-based authentication for root logins, so you'll need to log into the console:

sudo lxc-stop -n sid64
sudo lxc-start -n sid64 -F

Since the root password is randomly generated, you'll need to reset it before you can login as root:

sudo lxc-attach -n sid64 passwd

Then login as root and install a text editor inside the container because the root image doesn't have one by default:

apt install vim

then paste your public key in /root/.ssh/authorized_keys.

Then you can exit the console (using Ctrl+a q) and ssh into the container. You can find out what IP address the container received from DHCP by typing this command:

sudo lxc-ls --fancy

Mounting your home directory inside a container

In order to have my home directory available within the container, I created a user account for myself inside the container and then added the following to the container config file (/var/lib/lxc/sid64/config):

lxc.mount.entry=/home/francois /var/lib/lxc/sid64/rootfs/home/francois none bind 0 0

before restarting the container:

lxc-stop -n sid64
lxc-start -n sid64 -d

Fixing locale errors

If you see a bunch of errors like these when you start your container:

perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
LANGUAGE = (unset),
LC_ALL = (unset),
LANG = "fr_CA.utf8"
    are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").

then log into the container as root and use:

dpkg-reconfigure locales

to enable the same locales as the ones you have configured in the host.

If you see these errors while reconfiguring the locales package:

Generating locales (this might take a while)...
  en_US.UTF-8...cannot change mode of new locale archive: No such file or directory
 done
  fr_CA.UTF-8...cannot change mode of new locale archive: No such file or directory
 done
Generation complete.

and see the following dmesg output on the host:

[235350.947808] audit: type=1400 audit(1441664940.224:225): apparmor="DENIED" operation="chmod" info="Failed name lookup - deleted entry" error=-2 profile="/usr/bin/lxc-start" name="/usr/lib/locale/locale-archive.WVNevc" pid=21651 comm="localedef" requested_mask="w" denied_mask="w" fsuid=0 ouid=0

then AppArmor is interfering with the locale-gen binary and the work-around I found is to temporarily shutdown AppArmor on the host:

lxc-stop -n sid64
service apparmor teardown
lxc-start -n sid64 -d

and then start up it later once the locales have been updates:

lxc-stop -n sid64
service apparmor start
lxc-start -n sid64 -d

AppArmor support

If you are running AppArmor, your container probably won't start until you add the following to the container config (/var/lib/lxc/sid64/config):

lxc.aa_allow_incomplete = 1