New snapd updates process

[Michael Vogt]

Hello,

we will enable an additional way to ship snapd updates soon. With the
next update of the "ubuntu-core" snap we will automatically run snapd
from this image [1]. This allows quicker and more seamless updates for
snapd. Which of course means you get the bugfixes and new features
quicker :) 

Additionally we plan to use the channels mechanism to give you more
choices on what version of snapd to run. We will have the latest daily
version of snapd available in the "edge" channel. We also plan to
pre-release all our stable releases in the "candidate" channel first
so that users can use/test them early.

This means with:

$ snap refresh --candidate ubuntu-core

you can start tracking the candidate channel and get early access to
the releases.


To disable this feature (e.g. if you need to ensure you are on a
particular version for some reason), you can set SNAP_REEXEC=0
in your environment. You also need to tweak the systemd service:

# mkdir /etc/systemd/system/snapd.service.d/
# cat > /etc/systemd/system/snapd.service.d/local.conf <<EOF
[Service]
Environment="SNAP_REEXEC=0"
EOF

We will still do SRUs when we need to do bigger packaging related
changes, but less frequently than we do currently.

Please let us know if you have any questions!

Cheers,
 Michael

[1] Technically: when the snapd from the deb file runs it will
re-execute itself from /snap/ubuntu-core/current/usr/lib/snapd.