Want to change an app's icon on Ubuntu? Especially, Terminator's icon looks ugly?

ubuntu_change_app_icon.md

This guide applies if you want to override/create the icon for an application on Ubuntu.

Terminator is a popular terminal emulator that comes with a handy screen-split feature if you are not comfortable with the classic tmux solution. However, one thing of Terminator that put me off is its dark-red icon -- it feels so out of place with the rest of the icons in the side bar! In contrast the icon of Ubuntu's own Terminal app has an arguably sleekier look that fits very neatly with neighbors. Fortunately though, Ubuntu allows replacing the icon.

Step 1

Copy Terminator's *.desktop file into your home directory's ~/.local/share/applications:

$ cp /usr/share/applications/terminator.desktop ~/.local/share/applications/terminator.desktop

Explanations:

1. In GNOME desktop environment (the GUI layer of Ubuntu) a *.desktop file configs how an app is to be launched, how it appears in menus, etc. A full specification of the file format is at the web page https://specifications.freedesktop.org/desktop-entry-spec/latest/ The file format is shared among the desktop environments using Wayland, a core component of Linux-based operating systems' GUI support.
2. If you installed Terminator normally, its *.desktop file will be under /usr/share/applications.
3. Files in directory ~/.local/share/applications will override the corresponding *.desktop files in /usr/share/applications.
4. Do not edit the original usr/share/applications/terminator.desktop, as it will be restored after program upgrades.
5. By the way, you could create a new *.desktop config in ~/.local/share/applications for an app if it doesn't have one already. In this file, you can designate an icon and a launch command, etc.

Step 2

Edit that latter file, so that its Icon points to Terminal's icon:

$ cat ~/.local/share/applications/terminator.desktop
[Desktop Entry]
Name=Terminator
...
Icon=/usr/share/icons/Yaru/256x256/apps/org.gnome.Terminal.png
...

Explanations:

1. Yaru is Ubuntu's default theme and it holds many nice-looking icon files. If the icon is not here, you can use /usr/share/icons/hicolor/scalable/apps/org.gnome.Terminal.svg instead. If a theme isn't present in /usr/share/icons, the directory hicolor is the fallback to look for icons according to specification https://specifications.freedesktop.org/icon-theme-spec/latest/#directory_layout.
2. Only the "Icon" line needs to be modified. The rest of the file content was copied from Step 1.
3. By the way, you can point this Icon entry to a *.svg or a *.png file you created.

Step 3

Close Terminator. You can see its icon in the side bar flashes and changes look. No reboot necessary.