[Bug]: Update of signal-desktop to the most recent version (6.0.0) fails (on Ubuntu 20.04)

[joergsteffens]

What happened?

Update of signal-desktop to the most recent version (6.0.0) fails:

# snap refresh signal-desktop 
error: cannot perform the following tasks:
- Sicherheitsprofile für Snap "signal-desktop" (406) einrichten (cannot update mount namespace of snap "signal-desktop": cannot update preserved namespace of snap "signal-desktop": cannot update snap namespace: remove /usr/bin/gjs: read-only file system)

Currently, I'm using version 5.63.0.

What should have happened?

At best, the signal-desktop snaps gets updated automatically. I found this problem only because I've been manually using the snap command.

Output of snap info $snap_name

# snap info signal-desktop  
name:      signal-desktop
summary:   Private messaging from your desktop.
publisher: Snapcrafters
store-url: https://snapcraft.io/signal-desktop
contact:   https://github.com/snapcrafters/signal-desktop/issues
license:   AGPL-3.0-only
description: |
  Private messaging from your desktop.
  
  To use the Signal desktop app, Signal must first be installed on your phone.
  
  **Are you having issues?**
  
  Let us know by creating a new issue here: https://github.com/snapcrafters/signal-desktop/issues
  
  **Authors**
  
  This snap is maintained by the Snapcrafters community, and is not necessarily endorsed or
  officially maintained by the upstream developers.
commands:
  - signal-desktop
snap-id:      r4LxMVp7zWramXsJQAKdamxy6TAWlaDD
tracking:     latest/stable
refresh-date: today at 18:20 CET
channels:
  latest/stable:    6.0.0  2022-12-01 (406) 196MB -
  latest/candidate: ^                             
  latest/beta:      5.62.0 2022-11-24 (400) 192MB -
  latest/edge:      6.0.0  2022-11-30 (406) 196MB -
installed:          5.63.0            (401) 196MB -

Output of snap connections $snap_name

# snap connections signal-desktop
Interface                 Plug                            Slot                             Notes
audio-playback            signal-desktop:audio-playback   :audio-playback                  -
audio-record              signal-desktop:audio-record     :audio-record                    -
browser-support           signal-desktop:browser-support  :browser-support                 -
camera                    signal-desktop:camera           :camera                          -
content[gnome-3-28-1804]  signal-desktop:gnome-3-28-1804  gnome-3-28-1804:gnome-3-28-1804  -
content[gtk-3-themes]     signal-desktop:gtk-3-themes     gtk-common-themes:gtk-3-themes   -
content[icon-themes]      signal-desktop:icon-themes      gtk-common-themes:icon-themes    -
content[sound-themes]     signal-desktop:sound-themes     gtk-common-themes:sound-themes   -
desktop                   signal-desktop:desktop          :desktop                         -
desktop-legacy            signal-desktop:desktop-legacy   :desktop-legacy                  -
gsettings                 signal-desktop:gsettings        :gsettings                       -
home                      signal-desktop:home             :home                            -
network                   signal-desktop:network          :network                         -
opengl                    signal-desktop:opengl           :opengl                          -
removable-media           signal-desktop:removable-media  -                                -
unity7                    signal-desktop:unity7           :unity7                          -
wayland                   signal-desktop:wayland          :wayland                         -
x11                       signal-desktop:x11              :x11                             -

Output of snap version

# snap version
snap    2.57.6
snapd   2.57.6
series  16
ubuntu  20.04
kernel  5.4.0-126-generic

Relevant log output

Dec  4 18:18:19 ting snap[2072361]: fdo.go:203: Cannot remove D-Bus signal matcher: read unix @->/run/user/121/bus: use of closed network connection
Dec  4 18:18:27 ting systemd[1]: Mounting Mount unit for signal-desktop, revision 406...
Dec  4 18:18:27 ting systemd[1]: Mounted Mount unit for signal-desktop, revision 406.
Dec  4 18:18:30 ting snapd[1938316]: taskrunner.go:271: [change 486 "Sicherheitsprofile für Snap \"signal-desktop\" (406) einrichten" task] failed: cannot update mount namespace of snap "signal-desktop": cannot update preserved namespace of snap "signal-desktop": cannot update snap namespace: remove /usr/bin/gjs: read-only file system
Dec  4 18:18:31 ting systemd[1]: snap-signal\x2ddesktop-406.mount: Succeeded.
Dec  4 18:18:31 ting systemd[5261]: snap-signal\x2ddesktop-406.mount: Succeeded.
Dec  4 18:18:31 ting systemd[950526]: snap-signal\x2ddesktop-406.mount: Succeeded.

Teminal output of app

No response

[lucyllewy]

This is also, like #80, an issue with snapd and not something we can influence from the signal desktop snap. Again, posting about the issue in the snapcraft forum in the snapd category/tag can raise more awareness of the issue. I have encountered similar issues in the past, with random snaps, and there is no consistency. The workaround I have found to succeed in most cases is to close all instances of the snap's apps (in the case of signal desktop you need to close the app completely by using the indicator tray icon's menu; i.e. separate from your taskbar - on ubuntu this is found in the top right of your screen). Once all instances are closed you need to execute these two commands in a terminal to tear down the confinement state so that the mount namespace is removed and then request the snap be refreshed again:

sudo /usr/lib/snapd/snap-discard-ns signal-desktop
sudo snap refresh signal-desktop

[joergsteffens]

Thank you for your quick response.
Your proposal worked well, so the update succeeded.
I'd not call this end-user friendly, but I understand that this is not, as I initially assumed, a problem of the signal-desktop snap, but a general snapd problem.
Thanks for your help. I'm closing this issue now.

[merlijn-sebrechts]

FYI: I'm creating a bunch of PR's to update the description of the gnome snaps to state you should not manually remove them: ubuntu/gnome-sdk#92

[sarahscheffler]

Posting this here for anyone else who found this trying to solve this issue: For me, /usr/lib/snapd/snap-discard-ns didn't exist. (Fedora 38, snap 2.58.3-1.fc38) Instead what worked for me was:

sudo /usr/libexec/snapd/snap-discard-ns signal-desktop