xdg-utils

xdg-utils provides the official utilities for managing XDG MIME Applications.

xdg-desktop-menu(1) - Install desktop menu items
xdg-desktop-icon(1) - copies desktop entries to the user's desktop
xdg-email(1) - Compose a new email in the user's preferred email client, potentially with subject and other info filled in
xdg-icon-resource(1) - Install icon resources
xdg-mime(1) - Query and install MIME types and associations
xdg-open(1) - Open a file or URI in the user's preferred application
xdg-screensaver(1) - Enable, disable, or suspend the screensaver
xdg-settings(1) - Get or set the default web browser and URL handlers

Installation

Usage

Environment variables

Note: A normally functioning desktop environment should automatically set these variables. This section is only necessary for understanding how xdg-utils works, i.e. for troubleshooting purposes.

xdg-utils attempts to integrate with your desktop environment by invoking the specialized programs it provides, where applicable. The evaluation of the current environment is as follows [1]:

If the standardized XDG_CURRENT_DESKTOP environment variable is set to a recognized desktop environment, the corresponding value is used.
If any classic fallbacks or environment-specific variables, such as KDE's KDE_FULL_SESSION, are present, then the corresponding value is used.
If the legacy DESKTOP_SESSION environment variable is set to a recognized desktop environment, the corresponding value is used.

During this process, if any match is found, the DE variable is internally overwritten with the detected desktop environment's normalized value. Hence, DE is both a legacy environment variable, and an internal state variable for xdg-utils. As an example, if XDG_CURRENT_DESKTOP is KDE, xdg-utils will internally set DE to kde. If no match is found, then any pre-existing DE value will be used, in such a way that XDG_CURRENT_DESKTOP=KDE is equivalent to XDG_CURRENT_DESKTOP being unset, and having DE=kde. This implementation detail is worth noting because it has the consequence that a pre-set DE is ignored if a desktop environment is otherwise detected.

Values of the variables that xdg-utils recognizes are:

Desktop Environment	`XDG_CURRENT_DESKTOP`	`DE`	`DESKTOP_SESSION`
–	`X-Generic`¹	`generic`	–
Cinnamon	`Cinnamon`, `X-Cinnamon`	`deepin`	–
Deepin	`Deepin`, `DEEPIN`, `deepin`¹	`cinnamon`	–
Enlightenment	`ENLIGHTENMENT`¹	`enlightenment`	–
GNOME	`GNOME`²	`gnome`	`gnome`
GNOME Flashback	`GNOME-Flashback`, `GNOME-Flashback:GNOME`²	`gnome`	`gnome`
KDE Plasma	`KDE`	`kde`	–
LXDE	`LXDE`	`lxde`	`LXDE`
LXQt	`LXQt`	`lxqt`	–
MATE	`MATE`	`mate`	`mate`
Xfce	`XFCE`	`xfce`	`xfce`, `xfce4`, `Xfce Session`

This is not an environment registered with freedesktop.org.
GNOME variations, including the GNOME Classic mode, are all regarded as the same by xdg-utils.

Note that this is only a list of what the scripts provided by xdg-utils are capable of detecting. The scripts will still perform generic, environment-agnostic actions under the following conditions:

The generic routine was asked for, via XDG_CURRENT_DESKTOP=X-Generic or DE=generic.
Environment detection failed. All relevant environment variables were unrecognized or unset, and the classic fallbacks did not reveal anything.
Environment-specific actions were performed, but failed, e.g. due to a missing program.

xdg-mime

xdg-mime(1) is a script for directly querying and modifying default MIME applications. It is used within other scripts, such as xdg-open, and is also a useful troubleshooting tool.

Determine a file's MIME type:

$ xdg-mime query filetype photo.jpeg
image/jpeg

Determine the default application for a MIME type:

$ xdg-mime query default image/jpeg
gimp.desktop

Change the default application for a MIME type:

$ xdg-mime default feh.desktop image/jpeg

Debug default application for MIME type:

$ env XDG_UTILS_DEBUG_LEVEL=10  xdg-mime query default text/html
Checking /home/user/.config/mimeapps.list
Checking /home/user/.local/share/applications/defaults.list and /home/user/.local/share/applications/mimeinfo.cache
Checking /usr/local/share/applications/defaults.list and /usr/local/share/applications/mimeinfo.cache
Checking /usr/share/applications/defaults.list and /usr/share/applications/mimeinfo.cache
qutebrowser.desktop

When it is necessary to determine the MIME type of a file, xdg-mime attempts to use the right program for the desktop environment:

Desktop Environment	Program	Package
Cinnamon	`gio`	glib2
GNOME
GNOME Flashback
LXDE
MATE
Xfce
Deepin	–	–
Enlightenment
LXQt
KDE Plasma	`kmimetypefinder`	kde-cli-tools

In the generic case, xdg-mime will:

Delegate to mimetype if present. Requires the perl-file-mimeinfo package to be installed.
Delegate to file if present.

xdg-open

xdg-open(1) is a resource opener used by many applications, implementing the XDG MIME Applications standard while integrating with the system's desktop environment as much as possible.

If a desktop environment was detected, its provided handler will be invoked [2]:

Desktop Environment	Program	Package
Cinnamon	`gio`	glib2
GNOME
GNOME Flashback
MATE
Deepin	`dde-open`	deepin-api
Enlightenment	`enlightenment_open`	enlightenment
KDE Plasma	`kde-open`¹	kde-cli-tools
LXDE	`pcmanfm`	pcmanfm
LXQt	–	–
Xfce	`exo-open`²	exo

If KDE_SESSION_VERSION is unset, then kfmclient from konqueror will be used instead. KDE Plasma should set this variable under any condition, though.
gio from glib2 will also be tried.

In the generic case, xdg-open will:

Query #xdg-mime for the default desktop entry associated with the resource, parse the desktop entry, and execute its command.
Delegate to run-mailcap if present. Requires the run-mailcap^AUR package to be installed.
Delegate to mimeopen if present. Requires the perl-file-mimeinfo package to be installed.

Tip: To see which backend xdg-open will use, set XDG_UTILS_DEBUG_LEVEL=3.

Since xdg-mime relies on perl-file-mimeinfo package to implement the XDG MIME Applications standard, if you are not using a desktop environment, you should either install perl-file-mimeinfo, or consider a different resource opener.

xdg-settings

See xdg-settings(1).

Shortcut to open all web MIME types with a single application:

$ xdg-settings set default-web-browser firefox.desktop

Shortcut for setting the default application for a URL scheme:

$ xdg-settings set default-url-scheme-handler irc xchat.desktop

Tips and Tricks

URL scheme handlers

To set the default application for a URL scheme you may also need to change the default application for the x-scheme-handler/* MIME types:

$ xdg-mime default firefox.desktop x-scheme-handler/https x-scheme-handler/http