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LXD and LXC#

LXC - Linux Containers, a userspace interface using the host’s kernel LXD - An extension to LXC adding a Rest API - an alternative to LXC’s tools

The lightervisor

A System container manager, offering a similar user experience to virtual machines but using linux containers instead.

  • Image based with pre-made images for a wide number of linux distributions
  • Built around a REST API
  • Designed to run full machine containers - as opposed to docker and rocket that run process based containers
  • High density - number of containers you can run
  • Feels the same as a full machine
  • Security focus - all processes not run as root

The LXD daemon only works on Linux but the client tool (lxc) is available on most platforms


View loaded images

lxc image list

You can also view available images on their website

There are 3 default image servers:

  • ubuntu
  • ubuntu-daily
  • images

List stable ubuntu images

lxc image list ubuntu: | less

Launch an image

lxc launch ubuntu:18.04 first

View current server configuration

lxc config show

The new image will be visible in the list now

lxc list

Get running details

lxc info first
lxc config show first

Limiting Resources#

By default your container comes with no resource limitation and inherits from the parent environment

free -m
lxc exec first -- free -m

To apply a memory limit to a container

lxc config set first limits.memory 128MB

Confirm it has been applied

lxc exec first -- free -m


LXD supports snapshotting and restoring container snapshots

Make a snapshot called clean:

lxc snapshot first clean

Restore everything to the snapshotted state:

lxc restore first clean

Confirm everything is back to normal

lxc exec first -- bash

Creating Images#

To publish an existing container

lxc publish first/clean --alias clean-ubuntu

Delete the initial contains

lxc stop first
lxc delete first

Launch a container from the existing image

lxc launch clean-ubuntu second

Stop and delete

lxc delete --force second

Accessing files from the container#

Pull a file from the container

lxc file pull second/etc/hosts .

Push a file to the container

lxc file push hosts second/etc/hosts

Access log files

lxc file pull second/var/log/syslog - | less

Use a remote image server#

List available images

lxc image list images: | less

Spawn a centos container

lxc launch images:centos/7 third

Confirm it is centos

lxc exec third -- cat /etc/redhat-release

Delete it

lxc delete -f third

List all configured remotes

lxc remote list

List remote container images

lxc list tryit:

List images

lxc image list tryit:

Launch a local image on a remote LXD

lxc launch clean-ubuntu tryit:fourth

Spawn a shell inside the remote

lxc exec tryit:fourth bash

Copy that container

lxc copy tryit:fourth tryit:fifth

Move it back to our local lxd

lxc move tryit:fifth sixth


Drop in replacement for libVirt KVM driver - to manage LXD containers in an Openstack cloud.


In KVM the virtual machine has all the same things as bare metal - bios, bootloader, linux kernel, host OS then can you only run your workload. In LXD there is none of that, containers run as processes directly on the host - no bios, no device drivers.


Intel server 4 core, 16 Gb and setup ubuntu on it. Launch KVM instances with an ubuntu image until we run out of hypervisor resources and do the same thing with LXD.

The VM’s were 512mb.

KVM launched 36. LXD launched over 600, of the same image. A much lower memory footprint.

LXD is frugal with memory

Startup Time#

How fast the instances are created

LXD - 1.5 seconds KVM - 25 seconds

  • 37 KVM instances launched in 943 seconds
  • 536 LXD guests in 828 seconds

Network Latency#

KVM packet through networking layer into host, to bridge and wake up other host etc. With LXD with the same test, there is not as much to go through so apps communicate 50% faster

Even local latency with 2 threads needing to be scheduled and context switched between, LXD was 50% faster.

OS Limitations#

You can run a windows or mac VM on a KVM instance. Only something that runs on a linux container will work on LXD. You could run centOS but you will get the ubuntu kernel.


On LXD cannot mount within a guest instances, you have to ask lxd to mount it.

Fits with OpenStack to provide the networking and storage components


If you are not in a privileged container you won’t be able to create another lxc instance inside that container.

lxc config set myvm2 security.privileged true
lxc config set myvm2 security.nesting true

or with profile:

lxc profile edit customer
  • security.nesting -
  • security.privileged -