How do I find out which snaps are using which versions of the runtime

Question

I have Gnome 3.26, 3.28 and 3.34 on my machine (Ubuntu 18.04) and want to know if I can get rid of any of them to save disk space. Is there some kind of snap command I can run that will show me?

Answer 1

Snap Commands to track connections

• You may use command below to list all slots/plugs used.

  snap connections
  

  or for specific app, example:

  $ snap connections snap-store
  Interface                 Plug                                      Slot                             Notes
  appstream-metadata        snap-store:appstream-metadata             :appstream-metadata              -
  content[gnome-3-38-2004]  snap-store:gnome-3-38-2004                gnome-3-38-2004:gnome-3-38-2004  -
  content[gtk-3-themes]     snap-store:gtk-3-themes                   gtk-common-themes:gtk-3-themes   -
  content[icon-themes]      snap-store:icon-themes                    gtk-common-themes:icon-themes    -
  content[sound-themes]     snap-store:sound-themes                   gtk-common-themes:sound-themes   -
  dbus                      -                                         snap-store:packagekit-svc        -
  dbus                      -                                         snap-store:snap-store            -
  desktop                   snap-store:desktop                        :desktop                         -
  desktop-legacy            snap-store:desktop-legacy                 :desktop-legacy                  -
  ...
  

  or probably best option with reverse search:

  $ snap connections gnome-3-38-2004 
  Interface                 Plug                                       Slot                             Notes
  content[gnome-3-38-2004]  firefox:gnome-3-38-2004                    gnome-3-38-2004:gnome-3-38-2004  -
  content[gnome-3-38-2004]  snap-store:gnome-3-38-2004                 gnome-3-38-2004:gnome-3-38-2004  -
  content[gnome-3-38-2004]  snapd-desktop-integration:gnome-3-38-2004  gnome-3-38-2004:gnome-3-38-2004 
  

• It may be worth adding, search by interface too:

  $ snap interface content | grep gnome
    - firefox:gnome-3-38-2004
    - snap-store:gnome-3-38-2004
    - snapd-desktop-integration:gnome-3-38-2004
    - gnome-3-38-2004:gnome-3-38-2004
  

Explaining snap connection

Due to the objective nature of snaps. Snap runs regular apps in confined environment. So each snap app that depends on another app, its developer has to declare the "connection" (or we may say plug-slot), mook765's answer here has used it for his approach (snap.yaml contains the dependencies declaration). The type of the connection is called "interface" content[gnome-3-38-2004]. And each connection composed of (one "slot" which is connected to either no, one or many "plugs"). Slot gnome-3-38-2004:gnome-3-38-2004 in this case is provided by gnome core snap, app declares and uses a plug ex:snap-store:gnome-3-38-2004 to that slot.

A good reference to read more: snapcraft.io: gnome-3-38-extension - plugs

Removing gnome-extension snap (Test)

Connections may auto/manually be connected or disconnected, that why I expect snap doesn't force uninstalling of dependent apps. I tested it within Ubuntu 22.04 in Virtual-box. Snap disconnects plug/slot and then removes the app. The app fails to run anyway.

$ snap remove gnome-3-38-2004
gnome-3-38-2004 removed
$ snap connections snap-store 
Interface                 Plug                                      Slot                            Notes
appstream-metadata        snap-store:appstream-metadata             :appstream-metadata             -
content                   snap-store:gnome-3-38-2004                -                               -
content[gtk-3-themes]     snap-store:gtk-3-themes                   gtk-common-themes:gtk-3-themes  -
content[icon-themes]      snap-store:icon-themes                    gtk-common-themes:icon-themes   -
content[sound-themes]     snap-store:sound-themes                   gtk-common-themes:sound-themes  -
dbus                      -                                         snap-store:packagekit-svc       -
...
$ snap-store
ERROR: not connected to the gnome-3-38-2004 content interface.
$ firefox
ERROR: not connected to the gnome-3-38-2004 content interface.

Answer 2

You can find out the dependencies of a snap by examining it's snap.yaml-file which is

/snap/<snapname>/<revision>/meta/snap.yaml

The commands

~$ grep "default-provider:" /snap/*/*/meta/snap.yaml
~$ grep "base:" /snap/*/*/meta/snap.yaml

will produce a list of all needed dependencies for all installed snaps, a dependency not listed can safely be removed. See the example in this answer.