/usr/share/xfce4/panel-plugins/cellmodem.desktop is in xfce4-cellmodem-plugin 0.0.5.dfsg-5ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 | [Xfce Panel]
Type=X-XFCE-PanelPlugin
Encoding=UTF-8
Name=Cellular Modem Monitor
Name[cs]=Monitorování modemu pro mobilní telefon
Name[pt]=Monitor de Modem Celular
Comment=Monitor line quality and type of Cellular Modems
Icon=xfce-mouse
X-XFCE-Exec=/usr/lib/x86_64-linux-gnu/xfce4/panel-plugins/xfce4-cellmodem-plugin
|