Add a custom MIME type for all users

To add a custom MIME type for all users on the system and register a default application for that MIME type, you need to create a new MIME type specification file in the /usr/share/mime/packages/ directory and a .desktop file in the /usr/share/applications/ directory.

Add a custom application/x-newtype MIME Type for All Users

  1. Create the /usr/share/mime/packages/application-x-newtype.xml file:

    <?xml version="1.0" encoding="UTF-8"?>
    <mime-info xmlns="">
      <mime-type type="application/x-newtype">
        <comment>new mime type</comment>
        <glob pattern="*.xyz"/>

    The sample application-x-newtype.xml file above defines a new MIME type application/x-newtype and assigns file names with the .xyz extension to that MIME type.

  2. Create a new .desktop file named, for example, myapplication1.desktop, and place it in the /usr/share/applications/ directory:

    [Desktop Entry]
    Name=My Application 1

    The sample myapplication1.desktop file above associates the application/x-newtype MIME type with an application named My Application 1, which is run by a command myapplication1.

  3. As root, update the MIME database for your changes to take effect:

    # update-mime-database /usr/share/mime
  4. As root, update the application database:

    # update-desktop-database /usr/share/applications
  5. To verify that you have successfully associated *.xyz files with the application/x-newtype MIME type, first create an empty file, for example

    $ touch

    Then run the gio info command:

    $ gio info | grep "standard::content-type"
      standard::content-type: application/x-newtype
  6. To verify that myapplication1.desktop has been correctly set as the default registered application for the application/x-newtype MIME type, run the gio mime command:

    $ gio mime application/x-newtype
    Default application for “application/x-newtype”: myapplication1.desktop
    Registered applications:
    Recommended applications: