/usr/share/mimelnk/application/x-excellon.desktop is in pcb-common 20110918-4.
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 10 | [Desktop Entry]
Encoding=UTF-8
Comment=Excellon drill file
Comment[nl]=Excellon boor bestand
Comment[ru]=Файл сверловки Excellon
MimeType=application/x-excellon
Type=MimeType
Icon=application-x-excellon
Patterns=*.cnc
X-KDE-IsAlso=text/plain
|