no interfaces when installing only core18

[Oliver Grawert]

i recently had to test an armbian image, out of curiosity i installed snapd ...
installing "htop" as the first snap pulls in core18 (but not core) since htop uses "base:core18"

ogra@nanopct4:~$ sudo snap install htop
htop 2.2.0 from Maximiliano Bertacchini (maxiberta) installed
ogra@nanopct4:~$ snap interfaces
Slot Plug
- htop:mount-observe
- htop:network-control
- htop:process-control
- htop:system-observe

only installing core manually gets me the system interfaces:

ogra@nanopct4:~$ sudo snap install core
ogra@nanopct4:~$ snap interfaces
Slot Plug
:account-control -
:accounts-service -
:adb-support -
:alsa -
:autopilot-introspection -
:avahi-control -
:avahi-observe -
:block-devices -
[...]
:wayland -
:x11 -
- htop:mount-observe
- htop:network-control
- htop:process-control
- htop:system-observe

if interfaces can not be provided by core18, the core(16) snap should always be installed alongside ... (or better, make core18 provide them ;) )

note that the OS kernel of this armbian image does not seem to support confinement anyway so there is no impact of not having the interfaces, yet this looks like a bug :)

[Omer Akram (om26er)]

The applies to a Ubuntu Server instance on a VPS like DigitalOcean or Scaleway, where no snap is preinstalled. So installing any snap that has `base: core18` set doesn't work.

[林博仁(Buo-ren, Lin) (buo-ren-lin)]

Applies to Fedora as well, which doesn't have snapd+core installed in the first place.

[Zygmunt Krynicki (zyga)]

This is trivial to reproduce on a machine that doesn't have core installed:

zyga@bionic:~$ snap version
snap 2.37.4+18.04.1
snapd 2.37.4+18.04.1
series 16
ubuntu 18.04
kernel 4.15.0-46-generic

zyga@bionic:~$ sudo snap install htop
htop 2.2.0 from Maximiliano Bertacchini (maxiberta) installed

zyga@bionic:~$ snap list
Name Version Rev Tracking Publisher Notes
core18 18 782 stable canonical✓ base
htop 2.2.0 1168 stable maxiberta -

zyga@bionic:~$ snap interface
Slot Plug
- htop:mount-observe
- htop:network-control
- htop:process-control
- htop:system-observe

The root cause is that snapd creates implicit slots on a snap that must exist. The snap is either "core" or "snapd" (preferring "snapd" if it exists on startup).

[Alan Pope 🍺🐧🐱 🦄 (popey)]

I've seen this reported multiple times over the weekend. Seems Lubuntu and Pop!_OS! don't ship any snaps by default (although Lubuntu ships snapd) and as such, anyone who installs a core18 snap _first_ will have a bad experience.

[Zygmunt Krynicki (zyga)]

Long time ago we have explored the ability to associate interfaces with a virtual snap called "system" but that idea was declined. As such all snaps must install snapd snap (which is currently not available as a stable feature) or install the core snap.

[Michael Vogt (mvo)]

I created a PR for this https://github.com/snapcore/snapd/pull/6778

[Alvaro Uria (aluria)]

Is this fix also going to be released in Xenial? Newer versions of the grafana snap (still in edge) use core18, and I also hit this bug on fresh installs (socket error: permission denied). Installing core snap fixed the problem.

[Michael Vogt (mvo)]

The fix is in "-proposed" now and will soon land in -updates.