where are the icon of application bar?

Solution 1:

Icons on the application bar most commonly are installed under /usr/share/icons or sometimes (more traditional) under /usr/share/pixmaps/ for systemwide icons, and in ~/.icons and/or ~/.local/share/icons for user icons. The latter, if installed, override the systemwide installed ones.

Apparently, the installer of your application did not correctly install an icon, or the icon installed is not in a valid format.

• Find a suitable icon (graphics file in .png, .svg or .xpm format), and copy it into .local/share/icons in your home folder. Create the folder if it does not exist.
• Find the installed .desktop launcher for clementine. Open it and note the name of the icon referenced in the launcher on the Icon= line.
• Rename your icon file in .local/share/icons accordingly (name only, not the extension).

Desktop launchers are commonly installed under /usr/share/applications for regular applications installed using APT. However, you can find where with the findcommand:

find / -name '*.desktop' -exec grep -H "Name=Clementine" {} \; 2>/dev/null

This example assumes you are seeing "Clementine" in the application overview. If it is "clementine", substitute that instead.