Ubuntu Core is a version of Ubuntu that’s fully transactional and entirely based on snap packages.
Most of the system is read-only. All installed applications come from snap packages and all updates are done using transactions. Meaning that should anything go wrong at any point during a package or system update, the system will be able to revert to the previous state and report the failure.
The current release of Ubuntu Core is called series 16 and was released in November 2016.
Note that on Ubuntu Core systems, only snap packages using confinement can be installed (no “classic” snaps) and that a good number of snaps will not fully work in this environment or will require some manual intervention (creating user and groups, …). Ubuntu Core gets improved on a weekly basis as new releases of snapd and the “core” snap are put out.
### Requirements
As far as LXD is concerned, Ubuntu Core is just another Linux distribution. That being said, snapd does require unprivileged FUSE mounts and AppArmor namespacing and stacking, so you will need the following:
* An up to date Ubuntu system using the official Ubuntu kernel
* An up to date version of LXD
### Creating an Ubuntu Core container
The Ubuntu Core images are currently published on the community image server.
The container will take a few seconds to start, first executing a first stage loader that determines what read-only image to use and setup the writable layers. You don’t want to interrupt the container in that stage and “lxc exec” will likely just fail as pretty much nothing is available at that point.
Seconds later, “lxc list” will show the container IP address, indicating that it’s booted into Ubuntu Core:
You can then interact with that container the same way you would any other:
```
stgraber@dakara:~$ lxc exec ubuntu-core bash
root@ubuntu-core:~# snap list
Name Version Rev Developer Notes
core 16.04.1 394 canonical -
pc 16.04-0.8 9 canonical -
pc-kernel 4.4.0-45-4 37 canonical -
root@ubuntu-core:~#
```
### Updating the container
If you’ve been tracking the development of Ubuntu Core, you’ll know that those versions above are pretty old. That’s because the disk images that are used as the source for the Ubuntu Core LXD images are only refreshed every few months. Ubuntu Core systems will automatically update once a day and then automatically reboot to boot onto the new version (and revert if this fails).
If you want to immediately force an update, you can do it with:
```
stgraber@dakara:~$ lxc exec ubuntu-core bash
root@ubuntu-core:~# snap refresh
pc-kernel (stable) 4.4.0-53-1 from 'canonical' upgraded
core (stable) 16.04.1 from 'canonical' upgraded
root@ubuntu-core:~# snap version
snap 2.17
snapd 2.17
series 16
root@ubuntu-core:~#
```
And then reboot the system and check the snapd version again:
```
root@ubuntu-core:~# reboot
root@ubuntu-core:~#
stgraber@dakara:~$ lxc exec ubuntu-core bash
root@ubuntu-core:~# snap version
snap 2.21
snapd 2.21
series 16
root@ubuntu-core:~#
```
You can get an history of all snapd interactions with
If you ever wanted to try Ubuntu Core, this is a great way to do it. It’s also a great tool for snap authors to make sure their snap is fully self-contained and will work in all environments.
Ubuntu Core is a great fit for environments where you want to ensure that your system is always up to date and is entirely reproducible. This does come with a number of constraints that may or may not work for you.
And lastly, a word of warning. Those images are considered as good enough for testing, but aren’t officially supported at this point. We are working towards getting fully supported Ubuntu Core LXD images on the official Ubuntu image server in the near future.
### Extra information
The main LXD website is at:[https://linuxcontainers.org/lxd][2] Development happens on Github at:[https://github.com/lxc/lxd][3]
Mailing-list support happens on:[https://lists.linuxcontainers.org][4]
IRC support happens in: #lxcontainers on irc.freenode.net
