Posted on Dec 26, 2014 By copyninja under devops

LXC - Linux Containers allows us to run multiple isolated Linux system under same control host. This will be useful for testing application without changing our existing system.

To create an LXC container we use the lxc-create command, it can accepts the template option, with which we can choose the OS we would like to run under the virtual isolated environment. On a Debian system I see following templates supported

[vasudev@rudra: ~/ ]% ls /usr/share/lxc/templates
lxc-alpine*    lxc-archlinux*  lxc-centos*  lxc-debian*    lxc-fedora*  lxc-openmandriva*  lxc-oracle*  lxc-sshd*    lxc-ubuntu-cloud*
lxc-altlinux*  lxc-busybox*    lxc-cirros*  lxc-download*  lxc-gentoo*  lxc-opensuse*      lxc-plamo*   lxc-ubuntu*

For my application testing I wanted to create a Debian container for my By default the template provided by lxc package creates Debian stable container. This can be changed by passing the option to debootstrap after -- as shown below.

sudo MIRROR=http://localhost:9999/debian lxc-create -t debian \
     -f   container.conf -n container-name -- -r sid

-r switch is used to specify the release, MIRROR environment variable is used to choose the required Debian mirror. I wanted to use my own local approx installation, so I can save some bandwidth.

container.conf is the configuration file used for creating the LXC, in my case it contains basic information on how container networking should b setup. The configuration is basically taken from LXC Debian wiki

lxc.utsname = aptoffline-dev = veth = up = br0.1 = eth0 = = vethvm1

I'm using VLAN setup described in Debian wiki: LXC VLAN Networking page. Below is my interfaces file.

iface eth0.1 inet manual

iface br0.1  inet manual
   bridge_ports eth0.1
   bridge_fd 0
   bridge_maxwait 0

Before launching the LXC make sure you run below command

sudo ifup eth0.1
sudo ifup br0.1

# Also give ip to bridge in same subnet as
sudo ip addr add dev br0.1

I'm giving ip address to bridge so that I can communicate with container from my control host, once it comes up.

Now start the container using below command

sudo lxc-start -n container -d -c tty8

We are starting lxc in daemon mode and attaching it to console tty8. If you want, you can drop -d and -c option to start lxc in foreground. But its better you start it in background and attach using lxc-console command shown below.

sudo lxc-console -n container -t tty8

You can detach from console using Ctrl+a q combination and let lxc execute in background.

Its also possible to simply ssh into the running container since we have enabled networking.

Stopping the container should be done using lxc-stop command, but without -k switch (kill) this command never returned. Even with timeout container is not stopped.

sudo lxc-stop -n container

-r can be used for reboot of container. Since I couldn't get clean shutdown I normally attach the console and issue a halt command in container itself. Not sure if this is the right way, but it gets the thing done.

I consider Linux container as a better alternative for spawning a virtual Linux environment instead of running a full blown VM like Virtualbox or VMware.