How to find `.desktop` file location for a particular application
A much faster and more universal search is with locate command:
$ locate *image*desktop
/usr/share/app-install/desktop/gimagereader:gimagereader-gtk.desktop
/usr/share/app-install/desktop/gnome-disk-utility:gnome-disk-image-mounter.desktop
/usr/share/app-install/desktop/gnome-disk-utility:gnome-disk-image-writer.desktop
/usr/share/app-install/desktop/imagej:imagej.desktop
/usr/share/app-install/desktop/imagemagick-6.q16:display-im6.q16.desktop
/usr/share/app-install/desktop/imagemagick:display-im6.desktop
/usr/share/app-install/desktop/imagevis3d:imagevis3d.desktop
/usr/share/app-install/desktop/kimagemapeditor:kde4__kimagemapeditor.desktop
/usr/share/app-install/desktop/simple-image-reducer:simple-image-reducer.desktop
/usr/share/app-install/desktop/trimage:trimage.desktop
/usr/share/applications/gnome-disk-image-mounter.desktop
/usr/share/applications/gnome-disk-image-writer.desktop
/usr/share/applications/screensavers/tessellimage.desktop
locate can search millions of files in a few seconds where it would take find many many minutes:
$ time find / -name '*image*.desktop'
real 0m52.563s
user 0m6.271s
sys 0m9.002s
$ time locate *image*desktop
real 0m0.705s
user 0m0.693s
sys 0m0.012s
Notice how grep was eliminated from original method and find command was ammended.
The disadvantage of locate is the database is updated daily. If you just installed the application you are searching for today, you will first need to run:
sudo updatedb
The name of the desktop file alone may not reveal sufficient information. The fundamental approach is to search the content of all .desktop files of the system to find the relevant one(s).
For example, the image viewer is displayed as Image Viewer in the Applications overview. Gnome Shell obtained that label from the .desktop file. To find the .desktop file (or files) that contains this string, execute
find / -name '*.desktop' -exec grep -H 'Image Viewer' {} \; 2>/dev/null
This uses find to find all .desktop files on the system. For each of the found files, grep is invoked, which searches for a string in the file, in this example Image Viewer. The 2>/dev/null suppresses the permission errors you inevitably get searching the root drive without root permissions.