Getting the revision of a snap from snapd

snapcraft
1

In the context of snapcraft pushing its own snap into the LXD container, along with the core snap, I was looking at how to get the relevant information. While I know the SNAP_REVISION for snapcraft itself, I don’t know what core snap revision is currently being used.

There seem to be several ways to get a revision right now:

  • readlink /var/snap/core/current 1689
  • snap list core Name Version Rev Developer Notes core 16-2 1689 canonical - Not very suitable for parsing. Is this format stable?
  • snap info core name: core summary: “snapd runtime environment” publisher: canonical description: | The core runtime environment for snapd type: core tracking: stable installed: 16-2 (1689) 83MB - refreshed: 2017-04-11 14:28:54 +0200 CEST channels: The installed value is what I’d be interested in, except it doesn’t seem to lend itself well to parsing.
2

I think using the snapd API is a good option:

$ curl -s --unix-socket /run/snapd.socket http:/v2/snaps/core
{"type":"sync","status-code":200,"status":"OK","result":{"apps":[],"broken":"","channel":"stable","confinement":"strict","contact":"mailto:snappy-canonical-storeaccount@canonical.com","description":"The core runtime environment for snapd","developer":"canonical","devmode":false,"icon":"","id":"99T7MUlRhtI3U0QFgl5mXXESAiSwt776","install-date":"2017-04-11T05:28:54-07:00","installed-size":83349504,"jailmode":false,"name":"core","private":false,"resource":"/v2/snaps/core","revision":"1689","status":"active","summary":"snapd runtime environment","tracking-channel":"stable","trymode":false,"type":"os","version":"16-2"}}
3

Question, can we always install any revision?

Like, install core rev 1000 even when the latest released core is rev 5000?

4

I think the goal is to install the version of core on the host, right? Which is a simple matter of grabbing the snap out of /var/lib/snapd/snaps/, as well as its assertion from snap known.

2 Likes
5

That’s indeed what I’m doing in my PR and also the only way to do it (because the store only allows for the publisher to download specific revisions).

6

btw you probably also need to set a refresh schedule so that you don’t get a refresh in the middle of things inside inside the lxd

7

What would I set it to, though? Can I set it to eg. “never” and take care of it manually? The example given in the announcement of that feature uses specific times when it “might” run.

8

no, “never” is not supported

9

How should this be used then? The snaps snapcraft cares about will be the versions it specifically injected, so it would be counter-productive for them to be updated.

10

Perhaps that’s a case for not getting their assertions. Then they can’t be updated.