Introduction to MIME Types
A Multipurpose Internet Mail Extension
[MIME] type identifies the format of a file.
Applications such as Internet browsers and email applications use the MIME
type of a file to decide which actions to perform on it. For example, an
email application can use the MIME type to detect the format of an
attachment and choose an appropriate viewer for the file, such as opening
a text document with gedit.
As another example, the Nautilus file
manager needs to know the MIME type of a file to perform the following
Open the file in an appropriate application.
Display a string that describes the type of file.
Display an appropriate icon to represent the file.
Display a list of other applications that can open the
MIME types were originally proposed as a standard for identifying
the message body of an e-mail message. Now, many systems use MIME types to
identify the format of arbitrary files on the file system. MIME types are
composed of a top-level media type followed by a
subtype identifier, separated by a forward slash
character, “/”. One example of a MIME type
is image/jpeg. The media type in this example is
“image” and the subtype identifier is
“jpeg”. The top-level media type is meant
to be a general categorization about the content of the file, while the
subtype identifer is meant to specifically identify the format of the
There are eight media types currently blessed by the
IANA [Internet Assigned Naming Authority]. These eight
media types are application, audio, image, message, model, multipart, text, video. Many subtypes exist for each media type; for more
information, see MIME Media
Types at the IANA web
Implementation of MIME types in GNOME follows the XDG
shared mime info specification. This specification provides the
Standard locations for all MIME related files.
A standard way for applications to register information about a
new MIME type.
A standard way to retrieve the MIME type for a file.
A standard way to retrieve information about a MIME type.
The rest of the chapter describes the files and directories that
make up the MIME database, details about source XML files, how to create
or modify MIME types, how to register applications as handlers for certain
MIME types and finally, how to add an application to the GNOME