Ubuntu Core: how the file-system works

[Mark Shuttleworth]

On 20/01/17 05:59, Luca Dionisi wrote:
> First of all I need to understand how the file-system works. Because I
> need to edit some system files.

Ubuntu Core is designed to offer a super-reliable and predictable
upgrade experience, so core system files are often fixed ("immutable").
It will be interesting to know what you need at the base level so we can
expose it as a standard config element.

> My first question to the list is: why don't I see two partitions on
> the disk? I recall having read that Ubuntu Core was able to rollback to
> the previous version of "core" snap thanks to a second partition.
> Do I miss something?

In 15.04 we had an A/B partition system. Now we have evolved to
something much better, which is mountable compressed filesystems. The
A/B filesystems are now single files on the base filesystem. That's
better because it lets us use space much more efficiently, or decide
later we want three or four versions instead of just A/B versions, etc.

Mark