how do I ensure that I install a NON-Snap version of an application (Thunderbird)

[mörgæs]

Not necessarily. In Xubuntu 19.10, chromium-browser is only available as a snap.
I gather that's true for all variants, and it's the only way Chromium will be available on *buntu in the future.

Now I have tested in Xubuntu 19.10 and yes, it's indeed the case.

sudo apt install chromium-browser

installs snapd without asking for permission (!) and installs at the same time chromium as a snap package.

Both were simple to remove so no harm done but still I would like to receive a clear warning from apt.

It seems like I have to use the dry run option

sudo apt install <some package> --dry-run

every time in the future so I know what is going to be added to my systems.

[howefield]

installs snapd without asking for permission (!) and installs at the same time chromium as a snap package.

Both were simple to remove so no harm done but still I would like to receive a clear warning from apt.

Sure snapd wasn't already installed ?

Installing with snapd already installed

hugh@eoan:~$  sudo apt install chromium-browser
[sudo] password for hugh: 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following NEW packages will be installed
  chromium-browser
0 to upgrade, 1 to newly install, 0 to remove and 0 not to upgrade.
Need to get 48.7 kB of archives.
After this operation, 163 kB of additional disk space will be used.
Get:1 http://gb.archive.ubuntu.com/ubuntu eoan-updates/universe amd64 chromium-browser amd64 77.0.3865.120-0ubuntu1.19.10.1 [48.7 kB]
Fetched 48.7 kB in 5s (9,446 B/s)         
Preconfiguring packages ...
Selecting previously unselected package chromium-browser.
(Reading database ... 182581 files and directories currently installed.)
Preparing to unpack .../chromium-browser_77.0.3865.120-0ubuntu1.19.10.1_amd64.deb ...
=> Installing the chromium snap
==> Checking connectivity with the snap store
==> Installing the chromium snap
Warning: /snap/bin was not found in your $PATH. If you've not restarted your session since you
         installed snapd, try doing that. Please see https://forum.snapcraft.io/t/9469 for more
         details.

chromium 79.0.3945.79 from Canonical✓ installed
=> Snap installation complete
Unpacking chromium-browser (77.0.3865.120-0ubuntu1.19.10.1) ...
Setting up chromium-browser (77.0.3865.120-0ubuntu1.19.10.1) ...
Processing triggers for mime-support (3.63ubuntu1) ...
Processing triggers for hicolor-icon-theme (0.17-2) ...
Processing triggers for gnome-menus (3.32.0-1ubuntu1) ...
Processing triggers for desktop-file-utils (0.24-1ubuntu1) ...

And without snapd already installed, there is a clear warning as is usually the case when apt wants to install packages other than those explicitly asked for.

hugh@eoan:~$  sudo apt install chromium-browser
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following additional packages will be installed:
  snapd
The following NEW packages will be installed
  chromium-browser snapd
0 to upgrade, 2 to newly install, 0 to remove and 0 not to upgrade.
Need to get 18.8 MB of archives.
After this operation, 80.5 MB of additional disk space will be used.
Do you want to continue? [Y/n] n
Abort.
hugh@eoan:~$

This is vanilla Ubuntu, not Xubuntu but I believe snapd is present in a default Xubuntu installation.

[mörgæs]

A case of jump-to-conclusion from my side. I get the same output as yours.

Sorry for the detour.

[pjstock]

maybe I should back up one minute and ask whether my problem (with being able to access files from any location) has to do with permissions or something more global and not with specific applications.

Because I notice that other Snap apps that I have installed (like Kolourpaint) also cannot access a file from other than my Home location. (so I cannot open or import an image into Kolourpaint from my other HDDs. I have to copy the image over to a folder in Home and open it from there. And that is a bore.)

Before I go purging all my Snap installed apps, is there anything I can do to make them work more fluidly? to allow me to just attach a file from anywhere to an email for instance, or import an image for modification to Kolourpaint, but from anywhere.

Peter

[Dennis N]

maybe I should back up one minute and ask whether my problem (with being able to access files from any location) has to do with permissions or something more global and not with specific applications.

Not file permissions, but depends on whether a specific interface is (or can be) connected.

Most users keep personal files in home folder, and that access is provided in snap applications that read/write your files through the home interface. You also get USB access via /media/<username> and access to /mnt if the snap is able to utilize the removable-media interface.

You can check it removable-media access is available:

snap connections | grep removable-media

On this computer, only two snaps (chromium and firefox) have it:

dmn@Sydney-VM:~$ snap connections | grep removable-media
removable-media           chromium:removable-media                   :removable-media                 manual
removable-media           firefox:removable-media                    :removable-media                 manual

If the third column isn't blank, then it's connected. 'Manual' means it was manually connected (enabled) by the user.

[TheFu]

Because I notice that other Snap apps that I have installed (like Kolourpaint) also cannot access a file from other than my Home location. (so I cannot open or import an image into Kolourpaint from my other HDDs. I have to copy the image over to a folder in Home and open it from there. And that is a bore.)

Before I go purging all my Snap installed apps, is there anything I can do to make them work more fluidly? to allow me to just attach a file from anywhere to an email for instance, or import an image for modification to Kolourpaint, but from anywhere.

By default, snaps only allow access to your HOME.
You can tell them to allow access to storage under /mnt/ or /media/ , but not everywhere, by using the

$ snap connect chromium:removable-media

Just replace the program/snap name with the specific program (that is a snap package install) you want to have that access. I don't have the snap subsystem or I'd look up in the manpage exactly how to do the snap connect stuff. It will not help other programs that are not snap packages.

It is a failure/feature of snap confinement NOT to allow access elsewhere. Which is dependent on your view.

[Dennis N]

You can tell them to allow access to storage under /mnt/ or /media/ , but not everywhere, by using the

$ snap connect chromium:removable-media

Just replace the program/snap name with the specific program (that is a snap package install) you want to have that access.

This only works if the snap has the necessary plug. Chromium has the plug, as output in post #25 shows, but for kolourpaint the connect command fails because it doesn't have that plug:

dmn@Tyana-vm:~$ snap connect kolourpaint:removable-media
error: snap "kolourpaint" has no plug named "removable-media"

Here are all supported interfaces in kolourpaint snap:

dmn@Tyana-vm:~$ snap connections kolourpaint
Interface                             Plug                               Slot                                                  Notes                                                         
content[kde-frameworks-5-core18-all]  kolourpaint:kde-frameworks-5-plug  kde-frameworks-5-core18:kde-frameworks-5-core18-slot  -                                                             
desktop                               kolourpaint:desktop                :desktop                                              -                                                             
desktop-legacy                        kolourpaint:desktop-legacy         :desktop-legacy                                       -                                                             
home                                  kolourpaint:home                   :home                                                 -                                                             
network                               kolourpaint:network                :network                                              -
network-bind                          kolourpaint:network-bind           :network-bind                                         -
opengl                                kolourpaint:opengl                 :opengl                                               -
pulseaudio                            kolourpaint:pulseaudio             :pulseaudio                                           -
unity7                                kolourpaint:unity7                 :unity7                                               -
x11                                   kolourpaint:x11                    :x11                                                  -