# Extension Map Files

The "extension map" format is the same as that used in NCSA httpd 1.0.

Basically, a extension map is a configuration file that maps file extensions to MIME types. An example would be mapping file extension ".gif" to MIME type `image/gif`.

Here is an example extension map file:

    application/postscript         ai eps ps
    application/rtf                rtf
    application/slate
    application/x-tex              tex
    application/x-texinfo          texinfo texi
    application/x-troff            t tr roff
    audio/basic                    au snd
    audio/x-aiff                   aif aiff aifc
    audio/x-wav                    wav
    image/gif                      gif
    image/ief                      ief
    image/jpeg                     jpeg jpg jpe
    image/tiff                     tiff tif
    image/x-xwindowdump            xwd
    text/html                      html
    text/plain                     txt
    video/mpeg                     mpeg mpg mpe
    video/quicktime                qt mov
    video/x-msvideo                avi
    video/x-sgi-movie              movie

Note that each MIME type can be mapped to zero or more file extensions.

Note also that extension mapping is case insensitive.

Note finally that comments (lines starting with "#") are not supported until 2.0 prerelease 6, and that leading whitespace is not allowed -- the first character of the content-type should be the first character on a line.

## Where Do Extension Map Files Go?

There can be a global extension map; the X resource `globalExtensionMap` gives the filename. The default is "/usr/local/lib/mosaic/mime.types". This is generally the location for system- or site-wide viewer configuration.

There can also be a personal extension map; the X resource `personalExtensionMap` gives the filename (the value of the environment variable `HOME` is prepended to this). The default is ".mime.types". This is generally the location for per-user configuration.

Note that Mosaic is configured to map some extensions to MIME types by default. To turn off these defaults, set the X resource `useDefaultExtensionMap` to false. We strongly recommend that this resource be left true; simply override as necessary.

Entries in the personal extension map take precedence over entries in the global extension map, which in turn take precedence over the built-in defaults.

## Related Information

For information on how to map MIME types to external viewers and on the mailcap format, see here.

For information on file extensions mapped to MIME types by default in Mosaic 2.0pre4, see here.

For the list of MIME types recognized by default by Mosaic 2.0pre4, see here.