/usr/share/mimelnk/application/x-raster-mrsid.desktop is in qgis 2.8.6+dfsg-1build1.
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 | [Desktop Entry]
Type=MimeType
MimeType=application/x-raster-mrsid
Hidden=false
Comment=MrSID raster data
Comment[de]=MrSID-Rasterdaten
Icon=qgis-mime
Patterns=*.sid;
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