This is standard behaviour of all desktop messengers (Skype, Viber, Telegram, ..). All of them minimizes itself in system tray when Alt+F4 or close button is activated and they are running in background (instead of closing completely).
How can I force Signal messenger to behave the same way?
Jiří Doubravský solution worked for Gnome on Ubuntu 19.04.
Add --use-tray-icon option inside the Exec line in /usr/share/applications/signal-desktop.desktop from:
Exec=/opt/Signal/signal-desktop --no-sandbox %U
To:
Exec=/opt/Signal/signal-desktop --use-tray-icon --no-sandbox %U
Restarted Signal a couple times and the tray icon shows up. Strange that this isn't enabled by default.
You can use optional arguments to start the application
--start-in-tray and/or --use-tray-icon
Startup launcher: Add both arguments.
Desktop launcher icon:
Add just the second one argument. In menulibre, search for "Signal" and change command from "/opt/Signal/signal-desktop" %U to "/opt/Signal/signal-desktop" --use-tray-icon %U
source: https://github.com/signalapp/Signal-Desktop/issues/2911#issuecomment-439545459
A one-liner. Personally I have this saved on my desktop since Signal updates seem to to remove it.
sudo sed -i 's/signal-desktop --no-sandbox %U/signal-desktop --use-tray-icon --no-sandbox %U/g' /usr/share/applications/signal-desktop.desktop
sed is find and replace matching signal-desktop --no-sandbox %U and replacing with signal-desktop --use-tray-icon --no-sandbox %U
I propose building onto robmsmt's one-liner to account for different launch options I've encountered in the wild (without --no-sandbox, with lowercase %u, and 'empty' option --), probably depending on Signal version and/or distro used.
sed -i '/^Exec/ {/--use-tray-icon/ !s/$/ --use-tray-icon/}' /usr/share/applications/signal-desktop.desktop (Needs sudo)
This will match a line starting with Exec and appending --use-tray-icon to the end of that line unless the line already contains --use-tray-icon.
I previously suggested using incron to automatically run such script when the desktop file is modified, but sadly upon closer inspection it didn't actually work as the files are not really modified but completely replaced during an upgrade. I didn't manage to get incron to work with that, but you might want to take a look if you're interested and more savvy. It should be safe though to run that script as a good 'ol cron job as root (sudo crontab -e) e.g. at reboot (adding @reboot script.sh to the table). It obviously doesn't take effect immediately after Signal upgrade, but will have to suffice until I figure out what's up with incron.
Instead of editing a root owned file that gets overwritten when the package manager installs a new version of signal-desktop, I recommend to create a custom .desktop file in your home folder, and add the --use-tray-icon flag there. The local user-specific .desktop files should automatically take precedence over the system-wide file.
mkdir -p ~/.local/share/applications/
cp /usr/share/applications/signal-desktop.desktop ~/.local/share/applications/signal-desktop.desktop
sed -i 's/Exec=signal-desktop /Exec=signal-desktop --use-tray-icon /' ~/.local/share/applications/signal-desktop.desktop
To do this for the flatpak version of Signal use flatseal. With flatseal you can easily edit this flatpaks environment variables:
Set them to 1 to accomplish setting of above mentioned flags. Editing the flatpaks desktop file did not work for me.
