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Windows file association steps:

1. Right click on a file with the extension you want to associate.
2. Select properties.
3. On General tab, click the change button on the "Opens with" line.
4. Click on the "More Apps" link
5. Scroll to the bottom of the list
6. Click on the "Look for another app on this PC" link
7. Navigate to the installation of HDFView.
8. Select the HDFView.exe file.
9. Click the open button.
10. Click "OK" button
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Linux file associations steps:

1. Right click on a file with the extension you want to associate.
2. Select "Open With ..." or "Open With Other Application"
3. Depending on system, search for HDFView and select application.
   There may be other options such as "run in a terminal"

The associations can also be changed/updated in the mime mapping files.
   global associations : /usr/share/applications/mimeapps.list
   or                  : /etc/gnome/defaults.list

   user associations   : ~/.local/share/applications/mimeapps.list
   or                  : ~/.config/mimeapps.list

Command to change the files:
  xdg-mime

