Introduction

Both the KDE and GNOME desktop environments have adopted a similar format for "desktop entries," or configuration files describing how a particular program is to be launched, how it appears in menus, etc. It is to the larger community's benefit that a unified standard be agreed upon by all parties such that interoperation between the two environments, and indeed any additional environments that implement the specification, becomes simpler.

Basic format of the file

These desktop entry files should have an extension of ".desktop" or ".kdelnk". ".kdelnk" is deprecated, and is only maintained for backwards compatibility. Determining file type on basis of extension makes determining the file type very easy and quick. When no file extension is present, the desktop system should fall back to recognition via "magic detection." Desktop entries which describe how a directory is to be formatted/displayed should be simply called ".directory".

The basic format of the desktop entry file requires that there be a "group" header named "[Desktop Entry]". For backwards compatibility, implementations may also support the header "[KDE Desktop Entry]". This "group" entry denotes that all {key,value} pairs following it belong in the Desktop Entry group. There may be other groups present in the file (see MIME types discussion below), but this is the most important group which explicitly needs to be supported. This group should also be used as the "magic key" for automatic mime type detection. There should be nothing proceeding this group in the desktop entry file but possibly one or more comments (see below).

Lines beginning with a "#" are considered comments and will be ignored, however they should be preserved across reads / writes of the desktop entry file.

Compliant implementations MUST not remove any fields from the file, even if they don't support them. Such fields must be maintained in a list somewhere, and if the file is "rewritten," they will be included. This ensures that any desktop-specific extensions will be preserved even if another system accesses and changes the file.

Entries in the file are {key,value} pairs in the format:

Name=Value

Space before and after the equals sign should be supported; the "=" sign is the actual delimiter.

Possible value types

The value types recognized are string, localestring, regular expression, boolean (encoded as the string true/false), and numeric.

The difference between string and localestring is that the value for a string key must contain only ASCII characters and while the value of a localestring key may contain localized encodings. (See section 5.)

Some keys can have multiple values; these should be separated by a semicolon. Those keys which have several values should have a semicolon as the trailing character.

Recognized desktop entry keys

Keys may be postfixed by [locale], where locale is the LOCALE type of the entry. locale must be of the form lang[_COUNTRY][.ENCODING], where either _COUNTRY or .ENCODING may be omitted. If a postfixed key occurs, the same key must be also present without the postfix.

When reading in the desktop entry file, the value of the key is selected by matching the current POSIX locale for the LC_MESSAGES category against the locale postfixes of all occurrences of the key, with the .ENCODING part stripped. (The .ENCODING is used when the Encoding key for the desktop entry file is Legacy-Mixed, see the Appendix called The Legacy-Mixed encoding.)

The matching is done as follows: if the current value of LC_MESSAGES is lang_country.encoding@modifier, then, if a key for lang_country is present, it will be used. Otherwise, if a key for lang is present, it will be used. If both of these are missing, the required key without a locale specified is used. The encoding and modifier from the LC_MESSAGES value are ignored.

For example, if the current value of the LC_MESSAGES category is de_DE, and the desktop file includes:

 Name=Foo
 Name[de]=Foo auf Deutsch

Then the value used for the name key will be 'Foo auf Deutsch'. However, if a value is specified for Name[de_DE], then that will be used instead.

Case is significant. The keys "Name" and "NAME" are not equivalent. The same holds for group names. Key values are case sensitive as well.

Keys are either OPTIONAL or REQUIRED. If a key is optional it may or may not be present in the file. However, if it isn't, the implementation of the standard should not blow up, it must provide some sane defaults. Additionally, keys either MUST or MAY be supported by a particular implementation.

Some keys only make sense in the context when another particular key is also present.

Some example keys: Name[C], Comment[it].

Notes:

1. possible values are Application, Link, FSDevice, MimeType, Directory, Service, ServiceType

2. historically these have been represented by the numeric entries 0 or 1. With this version of the standard they are now to be represented as a boolean string. However, if an implementation is reading a pre-1.0 desktop entry, it should interpret 0 and 1 as false and true, respectively.

3. historically this has been a comma separated list. This is inconsistent with other lists which are separated by a semicolon. When reading a pre-1.0 desktop entry, comma separated lists should continue to be supported.

4. while the version field is not required to be present, it should be in all newer implementations of the Desktop Entry specification. If the version number is not present, a "pre-standard" desktop entry file is to be assumed.

Character set encoding of the file

Desktop entry files are encoded as lines of 8-bit characters separated by LF characters.

Except for comments and values of type localestring, only ASCII characters are permitted in the file:

• Key names must contain only the characters 'A-Za-z0-9-'

• Group names may contain all ASCII characters except for control characters and '[' and ']'.

• Values of type string may contain all ASCII characters except for control characters.

• Values of type boolean must either be the string 'true' or 'false'

• Numeric values must be a valid floating point number as recognized by the %f specifier for scanf.

Comment lines are uninterpreted and may contain any character (except for LF). However, using UTF-8 for comment lines that contain characters not in ASCII is encouraged.

The encoding for values of type localestring is determined by the Encoding field of the desktop entry. This field should always be present. (However, many legacy files may not include it.)

Only two values for Encoding are currently defined: 'UTF-8', and 'Legacy-Mixed', and desktop files must not use any other value. Implementations must support the UTF-8 encoding, and may choose to support Legacy-Mixed in addition. For this reason, authors of desktop files are encouraged to use the value 'UTF-8'.

If the file specifies an unsupported encoding, the implementation should either ignore the file, or, if the user has requested a direct operation on the file (such as opening it for editing), display an appropriate error indication to the user.

In the absence of an Encoding line, the implementation may choose to autodetect the encoding of the file by using such factors as:

• The location of the file on the filesystem

• Whether the contents of the file are valid UTF-8

If the implementation does not perform such auto-detection, it should treat a file without an Encoding key in the same way as a file with an unsupported Encoding Key.

List of valid Exec parameter variables

Each "Exec" field may take a number of arguments which will be expanded by the file manager or program launcher and passed to the program if necessary. Recognized fields are as follows:

Detailed discussion of supporting MIME types

It is in every desktop's best interest to have thorough support for mime types. The old /etc/mailcap and /etc/mime.types files are rather limited in scope and frankly, are outdated. Various desktop systems have come up with different ways of extending this original system, but none are compatible with each other. The Desktop Entry Standard hopes to be able to provide the beginnings of a solution to this problem.

At a very basic level, the "Exec" key provides the default action to take when the program described by a desktop entry is used to open a document or data file. Usually this consists of some action along the lines of "kedit %f" or "ee %f". This is a good start, but it isn't as flexible as it can be.

Let us first establish that a program which supports a MIME type or multiple mime types may be able to support multiple actions on those MIME types as well. The desktop entry may want to define additional actions in addition to the default. The toplevel "Exec" key describes the default action; Let us define this action to also be known as the "Open" action. Additional actions which might be possible include View, Edit, Play, etc. A further revision of this document will probably specify several "standard" actions in addition to the default "Open" action, but in all cases, the number of actions is arbitrary.

Let us use a sound player as a simple example. Call it sp. The default Exec (Open) action for this program would likely look something like:

Exec=sp %u

However, imagine the sound player also supports editing of sound files in a graphical manner. We might wish to define an additional action which could accomodate this. Adding the action would be performed like this:

Actions=Edit;

[Desktop Action Edit]
Exec=sp -edit %u

As you can see, defining the action "edit" will enable an additional group of the name [Desktop Action actionname] to be read. This group can contain an additional Exec line, as well as possibly other information like a new Name, Comment, Icon, and Path. Thus right-clicking on a .wav file will show both the default "Open" action and this "Edit" action to both be displayed as choices in the context-menu. A left click (double or single, whichever the file manager implements) would cause the default action to take place. These are implementation-specific details which are up to the implementer, and are not enforced by this standard.

If no DefaultApp is specified for a particular MIME type, any one of the programs registered which claim to be able to handle the MIME type may become the default handler. This behaviour is undefined and implementation-specific. KDE doesn't use a DefaultApp anymore, but assigns a Preference number to each program, so that the highest number is the one chosen for handling the MIME type.

Extending the format

If the standard is to be amended with a new {key,value} pair which should be applicable to all supporting parties, a group discussion will take place. This is the preferred method for introducing changes. If one particular party wishes to add a field for personal use, they should prefix the key with the string "X-PRODUCT", i.e. "X-NewDesktop-Foo", following the precedent set by other IETF and RFC standards.

Alternatively, fields can be placed in their own group, where they may then have arbitrary key names. If this is the case, the group should follow the scheme outlined above, i.e. [X-PRODUCT GROUPNAME] or something similar. These steps will avoid namespace clashes between different yet similar environments.