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8 <title>D-Bus Specification</title>
9 <releaseinfo>Version 0.22</releaseinfo>
10 <date>2013-10-09</date>
13 <firstname>Havoc</firstname>
14 <surname>Pennington</surname>
16 <orgname>Red Hat, Inc.</orgname>
18 <email>hp@pobox.com</email>
23 <firstname>Anders</firstname>
24 <surname>Carlsson</surname>
26 <orgname>CodeFactory AB</orgname>
28 <email>andersca@codefactory.se</email>
33 <firstname>Alexander</firstname>
34 <surname>Larsson</surname>
36 <orgname>Red Hat, Inc.</orgname>
38 <email>alexl@redhat.com</email>
43 <firstname>Sven</firstname>
44 <surname>Herzberg</surname>
46 <orgname>Imendio AB</orgname>
48 <email>sven@imendio.com</email>
53 <firstname>Simon</firstname>
54 <surname>McVittie</surname>
56 <orgname>Collabora Ltd.</orgname>
58 <email>simon.mcvittie@collabora.co.uk</email>
63 <firstname>David</firstname>
64 <surname>Zeuthen</surname>
66 <orgname>Red Hat, Inc.</orgname>
68 <email>davidz@redhat.com</email>
75 <revnumber>0.22</revnumber>
76 <date>2013-10-09</date>
77 <authorinitials></authorinitials>
78 <revremark>add GetConnectionCredentials, document
79 GetAtdAuditSessionData, document GetConnectionSELinuxSecurityContext,
80 document and correct .service file syntax and naming
84 <revnumber>0.21</revnumber>
85 <date>2013-04-25</date>
86 <authorinitials>smcv</authorinitials>
87 <revremark>allow Unicode noncharacters in UTF-8 (Unicode
88 Corrigendum #9)</revremark>
91 <revnumber>0.20</revnumber>
92 <date>22 February 2013</date>
93 <authorinitials>smcv, walters</authorinitials>
94 <revremark>reorganise for clarity, remove false claims about
95 basic types, mention /o/fd/DBus</revremark>
98 <revnumber>0.19</revnumber>
99 <date>20 February 2012</date>
100 <authorinitials>smcv/lp</authorinitials>
101 <revremark>formally define unique connection names and well-known
102 bus names; document best practices for interface, bus, member and
103 error names, and object paths; document the search path for session
104 and system services on Unix; document the systemd transport</revremark>
107 <revnumber>0.18</revnumber>
108 <date>29 July 2011</date>
109 <authorinitials>smcv</authorinitials>
110 <revremark>define eavesdropping, unicast, broadcast; add eavesdrop
111 match keyword; promote type system to a top-level section</revremark>
114 <revnumber>0.17</revnumber>
115 <date>1 June 2011</date>
116 <authorinitials>smcv/davidz</authorinitials>
117 <revremark>define ObjectManager; reserve extra pseudo-type-codes used
118 by GVariant</revremark>
121 <revnumber>0.16</revnumber>
122 <date>11 April 2011</date>
123 <authorinitials></authorinitials>
124 <revremark>add path_namespace, arg0namespace; argNpath matches object
128 <revnumber>0.15</revnumber>
129 <date>3 November 2010</date>
130 <authorinitials></authorinitials>
131 <revremark></revremark>
134 <revnumber>0.14</revnumber>
135 <date>12 May 2010</date>
136 <authorinitials></authorinitials>
137 <revremark></revremark>
140 <revnumber>0.13</revnumber>
141 <date>23 Dezember 2009</date>
142 <authorinitials></authorinitials>
143 <revremark></revremark>
146 <revnumber>0.12</revnumber>
147 <date>7 November, 2006</date>
148 <authorinitials></authorinitials>
149 <revremark></revremark>
152 <revnumber>0.11</revnumber>
153 <date>6 February 2005</date>
154 <authorinitials></authorinitials>
155 <revremark></revremark>
158 <revnumber>0.10</revnumber>
159 <date>28 January 2005</date>
160 <authorinitials></authorinitials>
161 <revremark></revremark>
164 <revnumber>0.9</revnumber>
165 <date>7 Januar 2005</date>
166 <authorinitials></authorinitials>
167 <revremark></revremark>
170 <revnumber>0.8</revnumber>
171 <date>06 September 2003</date>
172 <authorinitials></authorinitials>
173 <revremark>First released document.</revremark>
178 <sect1 id="introduction">
179 <title>Introduction</title>
181 D-Bus is a system for low-overhead, easy to use
182 interprocess communication (IPC). In more detail:
186 D-Bus is <emphasis>low-overhead</emphasis> because it uses a
187 binary protocol, and does not have to convert to and from a text
188 format such as XML. Because D-Bus is intended for potentially
189 high-resolution same-machine IPC, not primarily for Internet IPC,
190 this is an interesting optimization. D-Bus is also designed to
191 avoid round trips and allow asynchronous operation, much like
197 D-Bus is <emphasis>easy to use</emphasis> because it works in terms
198 of <firstterm>messages</firstterm> rather than byte streams, and
199 automatically handles a lot of the hard IPC issues. Also, the D-Bus
200 library is designed to be wrapped in a way that lets developers use
201 their framework's existing object/type system, rather than learning
202 a new one specifically for IPC.
209 The base D-Bus protocol is a one-to-one (peer-to-peer or client-server)
210 protocol, specified in <xref linkend="message-protocol"/>. That is, it is
211 a system for one application to talk to a single other
212 application. However, the primary intended application of the protocol is the
213 D-Bus <firstterm>message bus</firstterm>, specified in <xref
214 linkend="message-bus"/>. The message bus is a special application that
215 accepts connections from multiple other applications, and forwards
220 Uses of D-Bus include notification of system changes (notification of when
221 a camera is plugged in to a computer, or a new version of some software
222 has been installed), or desktop interoperability, for example a file
223 monitoring service or a configuration service.
227 D-Bus is designed for two specific use cases:
231 A "system bus" for notifications from the system to user sessions,
232 and to allow the system to request input from user sessions.
237 A "session bus" used to implement desktop environments such as
242 D-Bus is not intended to be a generic IPC system for any possible
243 application, and intentionally omits many features found in other
244 IPC systems for this reason.
248 At the same time, the bus daemons offer a number of features not found in
249 other IPC systems, such as single-owner "bus names" (similar to X
250 selections), on-demand startup of services, and security policies.
251 In many ways, these features are the primary motivation for developing
252 D-Bus; other systems would have sufficed if IPC were the only goal.
256 D-Bus may turn out to be useful in unanticipated applications, but future
257 versions of this spec and the reference implementation probably will not
258 incorporate features that interfere with the core use cases.
262 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
263 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
264 document are to be interpreted as described in RFC 2119. However, the
265 document could use a serious audit to be sure it makes sense to do
266 so. Also, they are not capitalized.
269 <sect2 id="stability">
270 <title>Protocol and Specification Stability</title>
272 The D-Bus protocol is frozen (only compatible extensions are allowed) as
273 of November 8, 2006. However, this specification could still use a fair
274 bit of work to make interoperable reimplementation possible without
275 reference to the D-Bus reference implementation. Thus, this
276 specification is not marked 1.0. To mark it 1.0, we'd like to see
277 someone invest significant effort in clarifying the specification
278 language, and growing the specification to cover more aspects of the
279 reference implementation's behavior.
282 Until this work is complete, any attempt to reimplement D-Bus will
283 probably require looking at the reference implementation and/or asking
284 questions on the D-Bus mailing list about intended behavior.
285 Questions on the list are very welcome.
288 Nonetheless, this document should be a useful starting point and is
289 to our knowledge accurate, though incomplete.
295 <sect1 id="type-system">
296 <title>Type System</title>
299 D-Bus has a type system, in which values of various types can be
300 serialized into a sequence of bytes referred to as the
301 <firstterm>wire format</firstterm> in a standard way.
302 Converting a value from some other representation into the wire
303 format is called <firstterm>marshaling</firstterm> and converting
304 it back from the wire format is <firstterm>unmarshaling</firstterm>.
308 The D-Bus protocol does not include type tags in the marshaled data; a
309 block of marshaled values must have a known <firstterm>type
310 signature</firstterm>. The type signature is made up of zero or more
311 <firstterm id="term-single-complete-type">single complete
312 types</firstterm>, each made up of one or more
313 <firstterm>type codes</firstterm>.
317 A type code is an ASCII character representing the
318 type of a value. Because ASCII characters are used, the type signature
319 will always form a valid ASCII string. A simple string compare
320 determines whether two type signatures are equivalent.
324 A single complete type is a sequence of type codes that fully describes
325 one type: either a basic type, or a single fully-described container type.
326 A single complete type is a basic type code, a variant type code,
327 an array with its element type, or a struct with its fields (all of which
328 are defined below). So the following signatures are not single complete
339 And the following signatures contain multiple complete types:
349 Note however that a single complete type may <emphasis>contain</emphasis>
350 multiple other single complete types, by containing a struct or dict
354 <sect2 id="basic-types">
355 <title>Basic types</title>
358 The simplest type codes are the <firstterm id="term-basic-type">basic
359 types</firstterm>, which are the types whose structure is entirely
360 defined by their 1-character type code. Basic types consist of
361 fixed types and string-like types.
365 The <firstterm id="term-fixed-type">fixed types</firstterm>
366 are basic types whose values have a fixed length, namely BYTE,
367 BOOLEAN, DOUBLE, UNIX_FD, and signed or unsigned integers of length
372 As a simple example, the type code for 32-bit integer (<literal>INT32</literal>) is
373 the ASCII character 'i'. So the signature for a block of values
374 containing a single <literal>INT32</literal> would be:
378 A block of values containing two <literal>INT32</literal> would have this signature:
385 The characteristics of the fixed types are listed in this table.
391 <entry>Conventional name</entry>
392 <entry>ASCII type-code</entry>
393 <entry>Encoding</entry>
398 <entry><literal>BYTE</literal></entry>
399 <entry><literal>y</literal> (121)</entry>
400 <entry>Unsigned 8-bit integer</entry>
403 <entry><literal>BOOLEAN</literal></entry>
404 <entry><literal>b</literal> (98)</entry>
405 <entry>Boolean value: 0 is false, 1 is true, any other value
406 allowed by the marshalling format is invalid</entry>
409 <entry><literal>INT16</literal></entry>
410 <entry><literal>n</literal> (110)</entry>
411 <entry>Signed (two's complement) 16-bit integer</entry>
414 <entry><literal>UINT16</literal></entry>
415 <entry><literal>q</literal> (113)</entry>
416 <entry>Unsigned 16-bit integer</entry>
419 <entry><literal>INT32</literal></entry>
420 <entry><literal>i</literal> (105)</entry>
421 <entry>Signed (two's complement) 32-bit integer</entry>
424 <entry><literal>UINT32</literal></entry>
425 <entry><literal>u</literal> (117)</entry>
426 <entry>Unsigned 32-bit integer</entry>
429 <entry><literal>INT64</literal></entry>
430 <entry><literal>x</literal> (120)</entry>
431 <entry>Signed (two's complement) 64-bit integer
432 (mnemonic: x and t are the first characters in "sixty" not
433 already used for something more common)</entry>
436 <entry><literal>UINT64</literal></entry>
437 <entry><literal>t</literal> (116)</entry>
438 <entry>Unsigned 64-bit integer</entry>
441 <entry><literal>DOUBLE</literal></entry>
442 <entry><literal>d</literal> (100)</entry>
443 <entry>IEEE 754 double-precision floating point</entry>
446 <entry><literal>UNIX_FD</literal></entry>
447 <entry><literal>h</literal> (104)</entry>
448 <entry>Unsigned 32-bit integer representing an index into an
449 out-of-band array of file descriptors, transferred via some
450 platform-specific mechanism (mnemonic: h for handle)</entry>
458 The <firstterm id="term-string-like-type">string-like types</firstterm>
459 are basic types with a variable length. The value of any string-like
460 type is conceptually 0 or more Unicode codepoints encoded in UTF-8,
461 none of which may be U+0000. The UTF-8 text must be validated
462 strictly: in particular, it must not contain overlong sequences
463 or codepoints above U+10FFFF.
467 Since D-Bus Specification version 0.21, in accordance with Unicode
468 Corrigendum #9, the "noncharacters" U+FDD0..U+FDEF, U+nFFFE and
469 U+nFFFF are allowed in UTF-8 strings (but note that older versions of
470 D-Bus rejected these noncharacters).
474 The marshalling formats for the string-like types all end with a
475 single zero (NUL) byte, but that byte is not considered to be part of
480 The characteristics of the string-like types are listed in this table.
486 <entry>Conventional name</entry>
487 <entry>ASCII type-code</entry>
488 <entry>Validity constraints</entry>
493 <entry><literal>STRING</literal></entry>
494 <entry><literal>s</literal> (115)</entry>
495 <entry>No extra constraints</entry>
498 <entry><literal>OBJECT_PATH</literal></entry>
499 <entry><literal>o</literal> (111)</entry>
501 <link linkend="message-protocol-marshaling-object-path">a
502 syntactically valid object path</link></entry>
505 <entry><literal>SIGNATURE</literal></entry>
506 <entry><literal>g</literal> (103)</entry>
508 <firstterm linkend="term-single-complete-type">single
509 complete types</firstterm></entry>
516 <sect3 id="message-protocol-marshaling-object-path">
517 <title>Valid Object Paths</title>
520 An object path is a name used to refer to an object instance.
521 Conceptually, each participant in a D-Bus message exchange may have
522 any number of object instances (think of C++ or Java objects) and each
523 such instance will have a path. Like a filesystem, the object
524 instances in an application form a hierarchical tree.
528 Object paths are often namespaced by starting with a reversed
529 domain name and containing an interface version number, in the
531 <link linkend="message-protocol-names-interface">interface
533 <link linkend="message-protocol-names-bus">well-known
535 This makes it possible to implement more than one service, or
536 more than one version of a service, in the same process,
537 even if the services share a connection but cannot otherwise
538 co-operate (for instance, if they are implemented by different
543 For instance, if the owner of <literal>example.com</literal> is
544 developing a D-Bus API for a music player, they might use the
545 hierarchy of object paths that start with
546 <literal>/com/example/MusicPlayer1</literal> for its objects.
550 The following rules define a valid object path. Implementations must
551 not send or accept messages with invalid object paths.
555 The path may be of any length.
560 The path must begin with an ASCII '/' (integer 47) character,
561 and must consist of elements separated by slash characters.
566 Each element must only contain the ASCII characters
572 No element may be the empty string.
577 Multiple '/' characters cannot occur in sequence.
582 A trailing '/' character is not allowed unless the
583 path is the root path (a single '/' character).
591 <sect3 id="message-protocol-marshaling-signature">
592 <title>Valid Signatures</title>
594 An implementation must not send or accept invalid signatures.
595 Valid signatures will conform to the following rules:
599 The signature is a list of single complete types.
600 Arrays must have element types, and structs must
601 have both open and close parentheses.
606 Only type codes, open and close parentheses, and open and
607 close curly brackets are allowed in the signature. The
608 <literal>STRUCT</literal> type code
609 is not allowed in signatures, because parentheses
610 are used instead. Similarly, the
611 <literal>DICT_ENTRY</literal> type code is not allowed in
612 signatures, because curly brackets are used instead.
617 The maximum depth of container type nesting is 32 array type
618 codes and 32 open parentheses. This implies that the maximum
619 total depth of recursion is 64, for an "array of array of array
620 of ... struct of struct of struct of ..." where there are 32
626 The maximum length of a signature is 255.
633 When signatures appear in messages, the marshalling format
634 guarantees that they will be followed by a nul byte (which can
635 be interpreted as either C-style string termination or the INVALID
636 type-code), but this is not conceptually part of the signature.
642 <sect2 id="container-types">
643 <title>Container types</title>
646 In addition to basic types, there are four <firstterm>container</firstterm>
647 types: <literal>STRUCT</literal>, <literal>ARRAY</literal>, <literal>VARIANT</literal>,
648 and <literal>DICT_ENTRY</literal>.
652 <literal>STRUCT</literal> has a type code, ASCII character 'r', but this type
653 code does not appear in signatures. Instead, ASCII characters
654 '(' and ')' are used to mark the beginning and end of the struct.
655 So for example, a struct containing two integers would have this
660 Structs can be nested, so for example a struct containing
661 an integer and another struct:
665 The value block storing that struct would contain three integers; the
666 type signature allows you to distinguish "(i(ii))" from "((ii)i)" or
671 The <literal>STRUCT</literal> type code 'r' is not currently used in the D-Bus protocol,
672 but is useful in code that implements the protocol. This type code
673 is specified to allow such code to interoperate in non-protocol contexts.
677 Empty structures are not allowed; there must be at least one
678 type code between the parentheses.
682 <literal>ARRAY</literal> has ASCII character 'a' as type code. The array type code must be
683 followed by a <firstterm>single complete type</firstterm>. The single
684 complete type following the array is the type of each array element. So
685 the simple example is:
689 which is an array of 32-bit integers. But an array can be of any type,
690 such as this array-of-struct-with-two-int32-fields:
694 Or this array of array of integer:
701 <literal>VARIANT</literal> has ASCII character 'v' as its type code. A marshaled value of
702 type <literal>VARIANT</literal> will have the signature of a single complete type as part
703 of the <emphasis>value</emphasis>. This signature will be followed by a
704 marshaled value of that type.
708 Unlike a message signature, the variant signature can
709 contain only a single complete type. So "i", "ai"
710 or "(ii)" is OK, but "ii" is not. Use of variants may not
711 cause a total message depth to be larger than 64, including
712 other container types such as structures.
716 A <literal>DICT_ENTRY</literal> works exactly like a struct, but rather
717 than parentheses it uses curly braces, and it has more restrictions.
718 The restrictions are: it occurs only as an array element type; it has
719 exactly two single complete types inside the curly braces; the first
720 single complete type (the "key") must be a basic type rather than a
721 container type. Implementations must not accept dict entries outside of
722 arrays, must not accept dict entries with zero, one, or more than two
723 fields, and must not accept dict entries with non-basic-typed keys. A
724 dict entry is always a key-value pair.
728 The first field in the <literal>DICT_ENTRY</literal> is always the key.
729 A message is considered corrupt if the same key occurs twice in the same
730 array of <literal>DICT_ENTRY</literal>. However, for performance reasons
731 implementations are not required to reject dicts with duplicate keys.
735 In most languages, an array of dict entry would be represented as a
736 map, hash table, or dict object.
741 <title>Summary of types</title>
744 The following table summarizes the D-Bus types.
749 <entry>Conventional Name</entry>
751 <entry>Description</entry>
756 <entry><literal>INVALID</literal></entry>
757 <entry>0 (ASCII NUL)</entry>
758 <entry>Not a valid type code, used to terminate signatures</entry>
760 <entry><literal>BYTE</literal></entry>
761 <entry>121 (ASCII 'y')</entry>
762 <entry>8-bit unsigned integer</entry>
764 <entry><literal>BOOLEAN</literal></entry>
765 <entry>98 (ASCII 'b')</entry>
766 <entry>Boolean value, 0 is <literal>FALSE</literal> and 1 is <literal>TRUE</literal>. Everything else is invalid.</entry>
768 <entry><literal>INT16</literal></entry>
769 <entry>110 (ASCII 'n')</entry>
770 <entry>16-bit signed integer</entry>
772 <entry><literal>UINT16</literal></entry>
773 <entry>113 (ASCII 'q')</entry>
774 <entry>16-bit unsigned integer</entry>
776 <entry><literal>INT32</literal></entry>
777 <entry>105 (ASCII 'i')</entry>
778 <entry>32-bit signed integer</entry>
780 <entry><literal>UINT32</literal></entry>
781 <entry>117 (ASCII 'u')</entry>
782 <entry>32-bit unsigned integer</entry>
784 <entry><literal>INT64</literal></entry>
785 <entry>120 (ASCII 'x')</entry>
786 <entry>64-bit signed integer</entry>
788 <entry><literal>UINT64</literal></entry>
789 <entry>116 (ASCII 't')</entry>
790 <entry>64-bit unsigned integer</entry>
792 <entry><literal>DOUBLE</literal></entry>
793 <entry>100 (ASCII 'd')</entry>
794 <entry>IEEE 754 double</entry>
796 <entry><literal>STRING</literal></entry>
797 <entry>115 (ASCII 's')</entry>
798 <entry>UTF-8 string (<emphasis>must</emphasis> be valid UTF-8). Must be nul terminated and contain no other nul bytes.</entry>
800 <entry><literal>OBJECT_PATH</literal></entry>
801 <entry>111 (ASCII 'o')</entry>
802 <entry>Name of an object instance</entry>
804 <entry><literal>SIGNATURE</literal></entry>
805 <entry>103 (ASCII 'g')</entry>
806 <entry>A type signature</entry>
808 <entry><literal>ARRAY</literal></entry>
809 <entry>97 (ASCII 'a')</entry>
812 <entry><literal>STRUCT</literal></entry>
813 <entry>114 (ASCII 'r'), 40 (ASCII '('), 41 (ASCII ')')</entry>
814 <entry>Struct; type code 114 'r' is reserved for use in
815 bindings and implementations to represent the general
816 concept of a struct, and must not appear in signatures
817 used on D-Bus.</entry>
819 <entry><literal>VARIANT</literal></entry>
820 <entry>118 (ASCII 'v') </entry>
821 <entry>Variant type (the type of the value is part of the value itself)</entry>
823 <entry><literal>DICT_ENTRY</literal></entry>
824 <entry>101 (ASCII 'e'), 123 (ASCII '{'), 125 (ASCII '}') </entry>
825 <entry>Entry in a dict or map (array of key-value pairs).
826 Type code 101 'e' is reserved for use in bindings and
827 implementations to represent the general concept of a
828 dict or dict-entry, and must not appear in signatures
829 used on D-Bus.</entry>
831 <entry><literal>UNIX_FD</literal></entry>
832 <entry>104 (ASCII 'h')</entry>
833 <entry>Unix file descriptor</entry>
836 <entry>(reserved)</entry>
837 <entry>109 (ASCII 'm')</entry>
838 <entry>Reserved for <ulink
839 url="https://bugs.freedesktop.org/show_bug.cgi?id=27857">a
840 'maybe' type compatible with the one in GVariant</ulink>,
841 and must not appear in signatures used on D-Bus until
842 specified here</entry>
845 <entry>(reserved)</entry>
846 <entry>42 (ASCII '*')</entry>
847 <entry>Reserved for use in bindings/implementations to
848 represent any <firstterm>single complete type</firstterm>,
849 and must not appear in signatures used on D-Bus.</entry>
852 <entry>(reserved)</entry>
853 <entry>63 (ASCII '?')</entry>
854 <entry>Reserved for use in bindings/implementations to
855 represent any <firstterm>basic type</firstterm>, and must
856 not appear in signatures used on D-Bus.</entry>
859 <entry>(reserved)</entry>
860 <entry>64 (ASCII '@'), 38 (ASCII '&'),
861 94 (ASCII '^')</entry>
862 <entry>Reserved for internal use by bindings/implementations,
863 and must not appear in signatures used on D-Bus.
864 GVariant uses these type-codes to encode calling
875 <sect1 id="message-protocol-marshaling">
876 <title>Marshaling (Wire Format)</title>
879 D-Bus defines a marshalling format for its type system, which is
880 used in D-Bus messages. This is not the only possible marshalling
881 format for the type system: for instance, GVariant (part of GLib)
882 re-uses the D-Bus type system but implements an alternative marshalling
887 <title>Byte order and alignment</title>
890 Given a type signature, a block of bytes can be converted into typed
891 values. This section describes the format of the block of bytes. Byte
892 order and alignment issues are handled uniformly for all D-Bus types.
896 A block of bytes has an associated byte order. The byte order
897 has to be discovered in some way; for D-Bus messages, the
898 byte order is part of the message header as described in
899 <xref linkend="message-protocol-messages"/>. For now, assume
900 that the byte order is known to be either little endian or big
905 Each value in a block of bytes is aligned "naturally," for example
906 4-byte values are aligned to a 4-byte boundary, and 8-byte values to an
907 8-byte boundary. To properly align a value, <firstterm>alignment
908 padding</firstterm> may be necessary. The alignment padding must always
909 be the minimum required padding to properly align the following value;
910 and it must always be made up of nul bytes. The alignment padding must
911 not be left uninitialized (it can't contain garbage), and more padding
912 than required must not be used.
916 As an exception to natural alignment, <literal>STRUCT</literal> and
917 <literal>DICT_ENTRY</literal> values are always aligned to an 8-byte
918 boundary, regardless of the alignments of their contents.
923 <title>Marshalling basic types</title>
926 To marshal and unmarshal fixed types, you simply read one value
927 from the data block corresponding to each type code in the signature.
928 All signed integer values are encoded in two's complement, DOUBLE
929 values are IEEE 754 double-precision floating-point, and BOOLEAN
930 values are encoded in 32 bits (of which only the least significant
935 The string-like types are all marshalled as a
936 fixed-length unsigned integer <varname>n</varname> giving the
937 length of the variable part, followed by <varname>n</varname>
938 nonzero bytes of UTF-8 text, followed by a single zero (nul) byte
939 which is not considered to be part of the text. The alignment
940 of the string-like type is the same as the alignment of
941 <varname>n</varname>.
945 For the STRING and OBJECT_PATH types, <varname>n</varname> is
946 encoded in 4 bytes, leading to 4-byte alignment.
947 For the SIGNATURE type, <varname>n</varname> is encoded as a single
948 byte. As a result, alignment padding is never required before a
954 <title>Marshalling containers</title>
957 Arrays are marshalled as a <literal>UINT32</literal>
958 <varname>n</varname> giving the length of the array data in bytes,
959 followed by alignment padding to the alignment boundary of the array
960 element type, followed by the <varname>n</varname> bytes of the
961 array elements marshalled in sequence. <varname>n</varname> does not
962 include the padding after the length, or any padding after the
967 For instance, if the current position in the message is a multiple
968 of 8 bytes and the byte-order is big-endian, an array containing only
969 the 64-bit integer 5 would be marshalled as:
972 00 00 00 08 <lineannotation>8 bytes of data</lineannotation>
973 00 00 00 00 <lineannotation>padding to 8-byte boundary</lineannotation>
974 00 00 00 00 00 00 00 05 <lineannotation>first element = 5</lineannotation>
979 Arrays have a maximum length defined to be 2 to the 26th power or
980 67108864. Implementations must not send or accept arrays exceeding this
985 Structs and dict entries are marshalled in the same way as their
986 contents, but their alignment is always to an 8-byte boundary,
987 even if their contents would normally be less strictly aligned.
991 Variants are marshalled as the <literal>SIGNATURE</literal> of
992 the contents (which must be a single complete type), followed by a
993 marshalled value with the type given by that signature. The
994 variant has the same 1-byte alignment as the signature, which means
995 that alignment padding before a variant is never needed.
996 Use of variants may not cause a total message depth to be larger
997 than 64, including other container types such as structures.
1002 <title>Summary of D-Bus marshalling</title>
1005 Given all this, the types are marshaled on the wire as follows:
1010 <entry>Conventional Name</entry>
1011 <entry>Encoding</entry>
1012 <entry>Alignment</entry>
1017 <entry><literal>INVALID</literal></entry>
1018 <entry>Not applicable; cannot be marshaled.</entry>
1021 <entry><literal>BYTE</literal></entry>
1022 <entry>A single 8-bit byte.</entry>
1025 <entry><literal>BOOLEAN</literal></entry>
1026 <entry>As for <literal>UINT32</literal>, but only 0 and 1 are valid values.</entry>
1029 <entry><literal>INT16</literal></entry>
1030 <entry>16-bit signed integer in the message's byte order.</entry>
1033 <entry><literal>UINT16</literal></entry>
1034 <entry>16-bit unsigned integer in the message's byte order.</entry>
1037 <entry><literal>INT32</literal></entry>
1038 <entry>32-bit signed integer in the message's byte order.</entry>
1041 <entry><literal>UINT32</literal></entry>
1042 <entry>32-bit unsigned integer in the message's byte order.</entry>
1045 <entry><literal>INT64</literal></entry>
1046 <entry>64-bit signed integer in the message's byte order.</entry>
1049 <entry><literal>UINT64</literal></entry>
1050 <entry>64-bit unsigned integer in the message's byte order.</entry>
1053 <entry><literal>DOUBLE</literal></entry>
1054 <entry>64-bit IEEE 754 double in the message's byte order.</entry>
1057 <entry><literal>STRING</literal></entry>
1058 <entry>A <literal>UINT32</literal> indicating the string's
1059 length in bytes excluding its terminating nul, followed by
1060 non-nul string data of the given length, followed by a terminating nul
1067 <entry><literal>OBJECT_PATH</literal></entry>
1068 <entry>Exactly the same as <literal>STRING</literal> except the
1069 content must be a valid object path (see above).
1075 <entry><literal>SIGNATURE</literal></entry>
1076 <entry>The same as <literal>STRING</literal> except the length is a single
1077 byte (thus signatures have a maximum length of 255)
1078 and the content must be a valid signature (see above).
1084 <entry><literal>ARRAY</literal></entry>
1086 A <literal>UINT32</literal> giving the length of the array data in bytes, followed by
1087 alignment padding to the alignment boundary of the array element type,
1088 followed by each array element.
1094 <entry><literal>STRUCT</literal></entry>
1096 A struct must start on an 8-byte boundary regardless of the
1097 type of the struct fields. The struct value consists of each
1098 field marshaled in sequence starting from that 8-byte
1105 <entry><literal>VARIANT</literal></entry>
1107 The marshaled <literal>SIGNATURE</literal> of a single
1108 complete type, followed by a marshaled value with the type
1109 given in the signature.
1112 1 (alignment of the signature)
1115 <entry><literal>DICT_ENTRY</literal></entry>
1117 Identical to STRUCT.
1123 <entry><literal>UNIX_FD</literal></entry>
1124 <entry>32-bit unsigned integer in the message's byte
1125 order. The actual file descriptors need to be
1126 transferred out-of-band via some platform specific
1127 mechanism. On the wire, values of this type store the index to the
1128 file descriptor in the array of file descriptors that
1129 accompany the message.</entry>
1141 <sect1 id="message-protocol">
1142 <title>Message Protocol</title>
1145 A <firstterm>message</firstterm> consists of a
1146 <firstterm>header</firstterm> and a <firstterm>body</firstterm>. If you
1147 think of a message as a package, the header is the address, and the body
1148 contains the package contents. The message delivery system uses the header
1149 information to figure out where to send the message and how to interpret
1150 it; the recipient interprets the body of the message.
1154 The body of the message is made up of zero or more
1155 <firstterm>arguments</firstterm>, which are typed values, such as an
1156 integer or a byte array.
1160 Both header and body use the D-Bus <link linkend="type-system">type
1161 system</link> and format for serializing data.
1164 <sect2 id="message-protocol-messages">
1165 <title>Message Format</title>
1168 A message consists of a header and a body. The header is a block of
1169 values with a fixed signature and meaning. The body is a separate block
1170 of values, with a signature specified in the header.
1174 The length of the header must be a multiple of 8, allowing the body to
1175 begin on an 8-byte boundary when storing the entire message in a single
1176 buffer. If the header does not naturally end on an 8-byte boundary
1177 up to 7 bytes of nul-initialized alignment padding must be added.
1181 The message body need not end on an 8-byte boundary.
1185 The maximum length of a message, including header, header alignment padding,
1186 and body is 2 to the 27th power or 134217728. Implementations must not
1187 send or accept messages exceeding this size.
1191 The signature of the header is:
1195 Written out more readably, this is:
1197 BYTE, BYTE, BYTE, BYTE, UINT32, UINT32, ARRAY of STRUCT of (BYTE,VARIANT)
1202 These values have the following meanings:
1207 <entry>Value</entry>
1208 <entry>Description</entry>
1213 <entry>1st <literal>BYTE</literal></entry>
1214 <entry>Endianness flag; ASCII 'l' for little-endian
1215 or ASCII 'B' for big-endian. Both header and body are
1216 in this endianness.</entry>
1219 <entry>2nd <literal>BYTE</literal></entry>
1220 <entry><firstterm>Message type</firstterm>. Unknown types must be ignored.
1221 Currently-defined types are described below.
1225 <entry>3rd <literal>BYTE</literal></entry>
1226 <entry>Bitwise OR of flags. Unknown flags
1227 must be ignored. Currently-defined flags are described below.
1231 <entry>4th <literal>BYTE</literal></entry>
1232 <entry>Major protocol version of the sending application. If
1233 the major protocol version of the receiving application does not
1234 match, the applications will not be able to communicate and the
1235 D-Bus connection must be disconnected. The major protocol
1236 version for this version of the specification is 1.
1240 <entry>1st <literal>UINT32</literal></entry>
1241 <entry>Length in bytes of the message body, starting
1242 from the end of the header. The header ends after
1243 its alignment padding to an 8-boundary.
1247 <entry>2nd <literal>UINT32</literal></entry>
1248 <entry>The serial of this message, used as a cookie
1249 by the sender to identify the reply corresponding
1250 to this request. This must not be zero.
1254 <entry><literal>ARRAY</literal> of <literal>STRUCT</literal> of (<literal>BYTE</literal>,<literal>VARIANT</literal>)</entry>
1255 <entry>An array of zero or more <firstterm>header
1256 fields</firstterm> where the byte is the field code, and the
1257 variant is the field value. The message type determines
1258 which fields are required.
1266 <firstterm>Message types</firstterm> that can appear in the second byte
1272 <entry>Conventional name</entry>
1273 <entry>Decimal value</entry>
1274 <entry>Description</entry>
1279 <entry><literal>INVALID</literal></entry>
1281 <entry>This is an invalid type.</entry>
1284 <entry><literal>METHOD_CALL</literal></entry>
1286 <entry>Method call.</entry>
1289 <entry><literal>METHOD_RETURN</literal></entry>
1291 <entry>Method reply with returned data.</entry>
1294 <entry><literal>ERROR</literal></entry>
1296 <entry>Error reply. If the first argument exists and is a
1297 string, it is an error message.</entry>
1300 <entry><literal>SIGNAL</literal></entry>
1302 <entry>Signal emission.</entry>
1309 Flags that can appear in the third byte of the header:
1314 <entry>Conventional name</entry>
1315 <entry>Hex value</entry>
1316 <entry>Description</entry>
1321 <entry><literal>NO_REPLY_EXPECTED</literal></entry>
1323 <entry>This message does not expect method return replies or
1324 error replies; the reply can be omitted as an
1325 optimization. However, it is compliant with this specification
1326 to return the reply despite this flag and the only harm
1327 from doing so is extra network traffic.
1331 <entry><literal>NO_AUTO_START</literal></entry>
1333 <entry>The bus must not launch an owner
1334 for the destination name in response to this message.
1342 <sect3 id="message-protocol-header-fields">
1343 <title>Header Fields</title>
1346 The array at the end of the header contains <firstterm>header
1347 fields</firstterm>, where each field is a 1-byte field code followed
1348 by a field value. A header must contain the required header fields for
1349 its message type, and zero or more of any optional header
1350 fields. Future versions of this protocol specification may add new
1351 fields. Implementations must ignore fields they do not
1352 understand. Implementations must not invent their own header fields;
1353 only changes to this specification may introduce new header fields.
1357 Again, if an implementation sees a header field code that it does not
1358 expect, it must ignore that field, as it will be part of a new
1359 (but compatible) version of this specification. This also applies
1360 to known header fields appearing in unexpected messages, for
1361 example: if a signal has a reply serial it must be ignored
1362 even though it has no meaning as of this version of the spec.
1366 However, implementations must not send or accept known header fields
1367 with the wrong type stored in the field value. So for example a
1368 message with an <literal>INTERFACE</literal> field of type
1369 <literal>UINT32</literal> would be considered corrupt.
1373 Here are the currently-defined header fields:
1378 <entry>Conventional Name</entry>
1379 <entry>Decimal Code</entry>
1381 <entry>Required In</entry>
1382 <entry>Description</entry>
1387 <entry><literal>INVALID</literal></entry>
1390 <entry>not allowed</entry>
1391 <entry>Not a valid field name (error if it appears in a message)</entry>
1394 <entry><literal>PATH</literal></entry>
1396 <entry><literal>OBJECT_PATH</literal></entry>
1397 <entry><literal>METHOD_CALL</literal>, <literal>SIGNAL</literal></entry>
1398 <entry>The object to send a call to,
1399 or the object a signal is emitted from.
1401 <literal>/org/freedesktop/DBus/Local</literal> is reserved;
1402 implementations should not send messages with this path,
1403 and the reference implementation of the bus daemon will
1404 disconnect any application that attempts to do so.
1408 <entry><literal>INTERFACE</literal></entry>
1410 <entry><literal>STRING</literal></entry>
1411 <entry><literal>SIGNAL</literal></entry>
1413 The interface to invoke a method call on, or
1414 that a signal is emitted from. Optional for
1415 method calls, required for signals.
1416 The special interface
1417 <literal>org.freedesktop.DBus.Local</literal> is reserved;
1418 implementations should not send messages with this
1419 interface, and the reference implementation of the bus
1420 daemon will disconnect any application that attempts to
1425 <entry><literal>MEMBER</literal></entry>
1427 <entry><literal>STRING</literal></entry>
1428 <entry><literal>METHOD_CALL</literal>, <literal>SIGNAL</literal></entry>
1429 <entry>The member, either the method name or signal name.</entry>
1432 <entry><literal>ERROR_NAME</literal></entry>
1434 <entry><literal>STRING</literal></entry>
1435 <entry><literal>ERROR</literal></entry>
1436 <entry>The name of the error that occurred, for errors</entry>
1439 <entry><literal>REPLY_SERIAL</literal></entry>
1441 <entry><literal>UINT32</literal></entry>
1442 <entry><literal>ERROR</literal>, <literal>METHOD_RETURN</literal></entry>
1443 <entry>The serial number of the message this message is a reply
1444 to. (The serial number is the second <literal>UINT32</literal> in the header.)</entry>
1447 <entry><literal>DESTINATION</literal></entry>
1449 <entry><literal>STRING</literal></entry>
1450 <entry>optional</entry>
1451 <entry>The name of the connection this message is intended for.
1452 Only used in combination with the message bus, see
1453 <xref linkend="message-bus"/>.</entry>
1456 <entry><literal>SENDER</literal></entry>
1458 <entry><literal>STRING</literal></entry>
1459 <entry>optional</entry>
1460 <entry>Unique name of the sending connection.
1461 The message bus fills in this field so it is reliable; the field is
1462 only meaningful in combination with the message bus.</entry>
1465 <entry><literal>SIGNATURE</literal></entry>
1467 <entry><literal>SIGNATURE</literal></entry>
1468 <entry>optional</entry>
1469 <entry>The signature of the message body.
1470 If omitted, it is assumed to be the
1471 empty signature "" (i.e. the body must be 0-length).</entry>
1474 <entry><literal>UNIX_FDS</literal></entry>
1476 <entry><literal>UINT32</literal></entry>
1477 <entry>optional</entry>
1478 <entry>The number of Unix file descriptors that
1479 accompany the message. If omitted, it is assumed
1480 that no Unix file descriptors accompany the
1481 message. The actual file descriptors need to be
1482 transferred via platform specific mechanism
1483 out-of-band. They must be sent at the same time as
1484 part of the message itself. They may not be sent
1485 before the first byte of the message itself is
1486 transferred or after the last byte of the message
1496 <sect2 id="message-protocol-names">
1497 <title>Valid Names</title>
1499 The various names in D-Bus messages have some restrictions.
1502 There is a <firstterm>maximum name length</firstterm>
1503 of 255 which applies to bus names, interfaces, and members.
1505 <sect3 id="message-protocol-names-interface">
1506 <title>Interface names</title>
1508 Interfaces have names with type <literal>STRING</literal>, meaning that
1509 they must be valid UTF-8. However, there are also some
1510 additional restrictions that apply to interface names
1513 <listitem><para>Interface names are composed of 1 or more elements separated by
1514 a period ('.') character. All elements must contain at least
1518 <listitem><para>Each element must only contain the ASCII characters
1519 "[A-Z][a-z][0-9]_" and must not begin with a digit.
1523 <listitem><para>Interface names must contain at least one '.' (period)
1524 character (and thus at least two elements).
1527 <listitem><para>Interface names must not begin with a '.' (period) character.</para></listitem>
1528 <listitem><para>Interface names must not exceed the maximum name length.</para></listitem>
1533 Interface names should start with the reversed DNS domain name of
1534 the author of the interface (in lower-case), like interface names
1535 in Java. It is conventional for the rest of the interface name
1536 to consist of words run together, with initial capital letters
1537 on all words ("CamelCase"). Several levels of hierarchy can be used.
1538 It is also a good idea to include the major version of the interface
1539 in the name, and increment it if incompatible changes are made;
1540 this way, a single object can implement several versions of an
1541 interface in parallel, if necessary.
1545 For instance, if the owner of <literal>example.com</literal> is
1546 developing a D-Bus API for a music player, they might define
1547 interfaces called <literal>com.example.MusicPlayer1</literal>,
1548 <literal>com.example.MusicPlayer1.Track</literal> and
1549 <literal>com.example.MusicPlayer1.Seekable</literal>.
1553 D-Bus does not distinguish between the concepts that would be
1554 called classes and interfaces in Java: either can be identified on
1555 D-Bus by an interface name.
1558 <sect3 id="message-protocol-names-bus">
1559 <title>Bus names</title>
1561 Connections have one or more bus names associated with them.
1562 A connection has exactly one bus name that is a <firstterm>unique
1563 connection name</firstterm>. The unique connection name remains
1564 with the connection for its entire lifetime.
1565 A bus name is of type <literal>STRING</literal>,
1566 meaning that it must be valid UTF-8. However, there are also
1567 some additional restrictions that apply to bus names
1570 <listitem><para>Bus names that start with a colon (':')
1571 character are unique connection names. Other bus names
1572 are called <firstterm>well-known bus names</firstterm>.
1575 <listitem><para>Bus names are composed of 1 or more elements separated by
1576 a period ('.') character. All elements must contain at least
1580 <listitem><para>Each element must only contain the ASCII characters
1581 "[A-Z][a-z][0-9]_-". Only elements that are part of a unique
1582 connection name may begin with a digit, elements in
1583 other bus names must not begin with a digit.
1587 <listitem><para>Bus names must contain at least one '.' (period)
1588 character (and thus at least two elements).
1591 <listitem><para>Bus names must not begin with a '.' (period) character.</para></listitem>
1592 <listitem><para>Bus names must not exceed the maximum name length.</para></listitem>
1596 Note that the hyphen ('-') character is allowed in bus names but
1597 not in interface names.
1601 Like <link linkend="message-protocol-names-interface">interface
1602 names</link>, well-known bus names should start with the
1603 reversed DNS domain name of the author of the interface (in
1604 lower-case), and it is conventional for the rest of the well-known
1605 bus name to consist of words run together, with initial
1606 capital letters. As with interface names, including a version
1607 number in well-known bus names is a good idea; it's possible to
1608 have the well-known bus name for more than one version
1609 simultaneously if backwards compatibility is required.
1613 If a well-known bus name implies the presence of a "main" interface,
1614 that "main" interface is often given the same name as
1615 the well-known bus name, and situated at the corresponding object
1616 path. For instance, if the owner of <literal>example.com</literal>
1617 is developing a D-Bus API for a music player, they might define
1618 that any application that takes the well-known name
1619 <literal>com.example.MusicPlayer1</literal> should have an object
1620 at the object path <literal>/com/example/MusicPlayer1</literal>
1621 which implements the interface
1622 <literal>com.example.MusicPlayer1</literal>.
1625 <sect3 id="message-protocol-names-member">
1626 <title>Member names</title>
1628 Member (i.e. method or signal) names:
1630 <listitem><para>Must only contain the ASCII characters
1631 "[A-Z][a-z][0-9]_" and may not begin with a
1632 digit.</para></listitem>
1633 <listitem><para>Must not contain the '.' (period) character.</para></listitem>
1634 <listitem><para>Must not exceed the maximum name length.</para></listitem>
1635 <listitem><para>Must be at least 1 byte in length.</para></listitem>
1640 It is conventional for member names on D-Bus to consist of
1641 capitalized words with no punctuation ("camel-case").
1642 Method names should usually be verbs, such as
1643 <literal>GetItems</literal>, and signal names should usually be
1644 a description of an event, such as <literal>ItemsChanged</literal>.
1647 <sect3 id="message-protocol-names-error">
1648 <title>Error names</title>
1650 Error names have the same restrictions as interface names.
1654 Error names have the same naming conventions as interface
1655 names, and often contain <literal>.Error.</literal>; for instance,
1656 the owner of <literal>example.com</literal> might define the
1657 errors <literal>com.example.MusicPlayer.Error.FileNotFound</literal>
1658 and <literal>com.example.MusicPlayer.Error.OutOfMemory</literal>.
1659 The errors defined by D-Bus itself, such as
1660 <literal>org.freedesktop.DBus.Error.Failed</literal>, follow a
1666 <sect2 id="message-protocol-types">
1667 <title>Message Types</title>
1669 Each of the message types (<literal>METHOD_CALL</literal>, <literal>METHOD_RETURN</literal>, <literal>ERROR</literal>, and
1670 <literal>SIGNAL</literal>) has its own expected usage conventions and header fields.
1671 This section describes these conventions.
1673 <sect3 id="message-protocol-types-method">
1674 <title>Method Calls</title>
1676 Some messages invoke an operation on a remote object. These are
1677 called method call messages and have the type tag <literal>METHOD_CALL</literal>. Such
1678 messages map naturally to methods on objects in a typical program.
1681 A method call message is required to have a <literal>MEMBER</literal> header field
1682 indicating the name of the method. Optionally, the message has an
1683 <literal>INTERFACE</literal> field giving the interface the method is a part of. In the
1684 absence of an <literal>INTERFACE</literal> field, if two interfaces on the same object have
1685 a method with the same name, it is undefined which of the two methods
1686 will be invoked. Implementations may also choose to return an error in
1687 this ambiguous case. However, if a method name is unique
1688 implementations must not require an interface field.
1691 Method call messages also include a <literal>PATH</literal> field
1692 indicating the object to invoke the method on. If the call is passing
1693 through a message bus, the message will also have a
1694 <literal>DESTINATION</literal> field giving the name of the connection
1695 to receive the message.
1698 When an application handles a method call message, it is required to
1699 return a reply. The reply is identified by a <literal>REPLY_SERIAL</literal> header field
1700 indicating the serial number of the <literal>METHOD_CALL</literal> being replied to. The
1701 reply can have one of two types; either <literal>METHOD_RETURN</literal> or <literal>ERROR</literal>.
1704 If the reply has type <literal>METHOD_RETURN</literal>, the arguments to the reply message
1705 are the return value(s) or "out parameters" of the method call.
1706 If the reply has type <literal>ERROR</literal>, then an "exception" has been thrown,
1707 and the call fails; no return value will be provided. It makes
1708 no sense to send multiple replies to the same method call.
1711 Even if a method call has no return values, a <literal>METHOD_RETURN</literal>
1712 reply is required, so the caller will know the method
1713 was successfully processed.
1716 The <literal>METHOD_RETURN</literal> or <literal>ERROR</literal> reply message must have the <literal>REPLY_SERIAL</literal>
1720 If a <literal>METHOD_CALL</literal> message has the flag <literal>NO_REPLY_EXPECTED</literal>,
1721 then as an optimization the application receiving the method
1722 call may choose to omit the reply message (regardless of
1723 whether the reply would have been <literal>METHOD_RETURN</literal> or <literal>ERROR</literal>).
1724 However, it is also acceptable to ignore the <literal>NO_REPLY_EXPECTED</literal>
1725 flag and reply anyway.
1728 Unless a message has the flag <literal>NO_AUTO_START</literal>, if the
1729 destination name does not exist then a program to own the destination
1730 name will be started before the message is delivered. The message
1731 will be held until the new program is successfully started or has
1732 failed to start; in case of failure, an error will be returned. This
1733 flag is only relevant in the context of a message bus, it is ignored
1734 during one-to-one communication with no intermediate bus.
1736 <sect4 id="message-protocol-types-method-apis">
1737 <title>Mapping method calls to native APIs</title>
1739 APIs for D-Bus may map method calls to a method call in a specific
1740 programming language, such as C++, or may map a method call written
1741 in an IDL to a D-Bus message.
1744 In APIs of this nature, arguments to a method are often termed "in"
1745 (which implies sent in the <literal>METHOD_CALL</literal>), or "out" (which implies
1746 returned in the <literal>METHOD_RETURN</literal>). Some APIs such as CORBA also have
1747 "inout" arguments, which are both sent and received, i.e. the caller
1748 passes in a value which is modified. Mapped to D-Bus, an "inout"
1749 argument is equivalent to an "in" argument, followed by an "out"
1750 argument. You can't pass things "by reference" over the wire, so
1751 "inout" is purely an illusion of the in-process API.
1754 Given a method with zero or one return values, followed by zero or more
1755 arguments, where each argument may be "in", "out", or "inout", the
1756 caller constructs a message by appending each "in" or "inout" argument,
1757 in order. "out" arguments are not represented in the caller's message.
1760 The recipient constructs a reply by appending first the return value
1761 if any, then each "out" or "inout" argument, in order.
1762 "in" arguments are not represented in the reply message.
1765 Error replies are normally mapped to exceptions in languages that have
1769 In converting from native APIs to D-Bus, it is perhaps nice to
1770 map D-Bus naming conventions ("FooBar") to native conventions
1771 such as "fooBar" or "foo_bar" automatically. This is OK
1772 as long as you can say that the native API is one that
1773 was specifically written for D-Bus. It makes the most sense
1774 when writing object implementations that will be exported
1775 over the bus. Object proxies used to invoke remote D-Bus
1776 objects probably need the ability to call any D-Bus method,
1777 and thus a magic name mapping like this could be a problem.
1780 This specification doesn't require anything of native API bindings;
1781 the preceding is only a suggested convention for consistency
1787 <sect3 id="message-protocol-types-signal">
1788 <title>Signal Emission</title>
1790 Unlike method calls, signal emissions have no replies.
1791 A signal emission is simply a single message of type <literal>SIGNAL</literal>.
1792 It must have three header fields: <literal>PATH</literal> giving the object
1793 the signal was emitted from, plus <literal>INTERFACE</literal> and <literal>MEMBER</literal> giving
1794 the fully-qualified name of the signal. The <literal>INTERFACE</literal> header is required
1795 for signals, though it is optional for method calls.
1799 <sect3 id="message-protocol-types-errors">
1800 <title>Errors</title>
1802 Messages of type <literal>ERROR</literal> are most commonly replies
1803 to a <literal>METHOD_CALL</literal>, but may be returned in reply
1804 to any kind of message. The message bus for example
1805 will return an <literal>ERROR</literal> in reply to a signal emission if
1806 the bus does not have enough memory to send the signal.
1809 An <literal>ERROR</literal> may have any arguments, but if the first
1810 argument is a <literal>STRING</literal>, it must be an error message.
1811 The error message may be logged or shown to the user
1816 <sect3 id="message-protocol-types-notation">
1817 <title>Notation in this document</title>
1819 This document uses a simple pseudo-IDL to describe particular method
1820 calls and signals. Here is an example of a method call:
1822 org.freedesktop.DBus.StartServiceByName (in STRING name, in UINT32 flags,
1823 out UINT32 resultcode)
1825 This means <literal>INTERFACE</literal> = org.freedesktop.DBus, <literal>MEMBER</literal> = StartServiceByName,
1826 <literal>METHOD_CALL</literal> arguments are <literal>STRING</literal> and <literal>UINT32</literal>, <literal>METHOD_RETURN</literal> argument
1827 is <literal>UINT32</literal>. Remember that the <literal>MEMBER</literal> field can't contain any '.' (period)
1828 characters so it's known that the last part of the name in
1829 the "IDL" is the member name.
1832 In C++ that might end up looking like this:
1834 unsigned int org::freedesktop::DBus::StartServiceByName (const char *name,
1835 unsigned int flags);
1837 or equally valid, the return value could be done as an argument:
1839 void org::freedesktop::DBus::StartServiceByName (const char *name,
1841 unsigned int *resultcode);
1843 It's really up to the API designer how they want to make
1844 this look. You could design an API where the namespace wasn't used
1845 in C++, using STL or Qt, using varargs, or whatever you wanted.
1848 Signals are written as follows:
1850 org.freedesktop.DBus.NameLost (STRING name)
1852 Signals don't specify "in" vs. "out" because only
1853 a single direction is possible.
1856 It isn't especially encouraged to use this lame pseudo-IDL in actual
1857 API implementations; you might use the native notation for the
1858 language you're using, or you might use COM or CORBA IDL, for example.
1863 <sect2 id="message-protocol-handling-invalid">
1864 <title>Invalid Protocol and Spec Extensions</title>
1867 For security reasons, the D-Bus protocol should be strictly parsed and
1868 validated, with the exception of defined extension points. Any invalid
1869 protocol or spec violations should result in immediately dropping the
1870 connection without notice to the other end. Exceptions should be
1871 carefully considered, e.g. an exception may be warranted for a
1872 well-understood idiosyncrasy of a widely-deployed implementation. In
1873 cases where the other end of a connection is 100% trusted and known to
1874 be friendly, skipping validation for performance reasons could also make
1875 sense in certain cases.
1879 Generally speaking violations of the "must" requirements in this spec
1880 should be considered possible attempts to exploit security, and violations
1881 of the "should" suggestions should be considered legitimate (though perhaps
1882 they should generate an error in some cases).
1886 The following extension points are built in to D-Bus on purpose and must
1887 not be treated as invalid protocol. The extension points are intended
1888 for use by future versions of this spec, they are not intended for third
1889 parties. At the moment, the only way a third party could extend D-Bus
1890 without breaking interoperability would be to introduce a way to negotiate new
1891 feature support as part of the auth protocol, using EXTENSION_-prefixed
1892 commands. There is not yet a standard way to negotiate features.
1896 In the authentication protocol (see <xref linkend="auth-protocol"/>) unknown
1897 commands result in an ERROR rather than a disconnect. This enables
1898 future extensions to the protocol. Commands starting with EXTENSION_ are
1899 reserved for third parties.
1904 The authentication protocol supports pluggable auth mechanisms.
1909 The address format (see <xref linkend="addresses"/>) supports new
1915 Messages with an unknown type (something other than
1916 <literal>METHOD_CALL</literal>, <literal>METHOD_RETURN</literal>,
1917 <literal>ERROR</literal>, <literal>SIGNAL</literal>) are ignored.
1918 Unknown-type messages must still be well-formed in the same way
1919 as the known messages, however. They still have the normal
1925 Header fields with an unknown or unexpected field code must be ignored,
1926 though again they must still be well-formed.
1931 New standard interfaces (with new methods and signals) can of course be added.
1941 <sect1 id="auth-protocol">
1942 <title>Authentication Protocol</title>
1944 Before the flow of messages begins, two applications must
1945 authenticate. A simple plain-text protocol is used for
1946 authentication; this protocol is a SASL profile, and maps fairly
1947 directly from the SASL specification. The message encoding is
1948 NOT used here, only plain text messages.
1951 In examples, "C:" and "S:" indicate lines sent by the client and
1952 server respectively.
1954 <sect2 id="auth-protocol-overview">
1955 <title>Protocol Overview</title>
1957 The protocol is a line-based protocol, where each line ends with
1958 \r\n. Each line begins with an all-caps ASCII command name containing
1959 only the character range [A-Z_], a space, then any arguments for the
1960 command, then the \r\n ending the line. The protocol is
1961 case-sensitive. All bytes must be in the ASCII character set.
1963 Commands from the client to the server are as follows:
1966 <listitem><para>AUTH [mechanism] [initial-response]</para></listitem>
1967 <listitem><para>CANCEL</para></listitem>
1968 <listitem><para>BEGIN</para></listitem>
1969 <listitem><para>DATA <data in hex encoding></para></listitem>
1970 <listitem><para>ERROR [human-readable error explanation]</para></listitem>
1971 <listitem><para>NEGOTIATE_UNIX_FD</para></listitem>
1974 From server to client are as follows:
1977 <listitem><para>REJECTED <space-separated list of mechanism names></para></listitem>
1978 <listitem><para>OK <GUID in hex></para></listitem>
1979 <listitem><para>DATA <data in hex encoding></para></listitem>
1980 <listitem><para>ERROR</para></listitem>
1981 <listitem><para>AGREE_UNIX_FD</para></listitem>
1985 Unofficial extensions to the command set must begin with the letters
1986 "EXTENSION_", to avoid conflicts with future official commands.
1987 For example, "EXTENSION_COM_MYDOMAIN_DO_STUFF".
1990 <sect2 id="auth-nul-byte">
1991 <title>Special credentials-passing nul byte</title>
1993 Immediately after connecting to the server, the client must send a
1994 single nul byte. This byte may be accompanied by credentials
1995 information on some operating systems that use sendmsg() with
1996 SCM_CREDS or SCM_CREDENTIALS to pass credentials over UNIX domain
1997 sockets. However, the nul byte must be sent even on other kinds of
1998 socket, and even on operating systems that do not require a byte to be
1999 sent in order to transmit credentials. The text protocol described in
2000 this document begins after the single nul byte. If the first byte
2001 received from the client is not a nul byte, the server may disconnect
2005 A nul byte in any context other than the initial byte is an error;
2006 the protocol is ASCII-only.
2009 The credentials sent along with the nul byte may be used with the
2010 SASL mechanism EXTERNAL.
2013 <sect2 id="auth-command-auth">
2014 <title>AUTH command</title>
2016 If an AUTH command has no arguments, it is a request to list
2017 available mechanisms. The server must respond with a REJECTED
2018 command listing the mechanisms it understands, or with an error.
2021 If an AUTH command specifies a mechanism, and the server supports
2022 said mechanism, the server should begin exchanging SASL
2023 challenge-response data with the client using DATA commands.
2026 If the server does not support the mechanism given in the AUTH
2027 command, it must send either a REJECTED command listing the mechanisms
2028 it does support, or an error.
2031 If the [initial-response] argument is provided, it is intended for use
2032 with mechanisms that have no initial challenge (or an empty initial
2033 challenge), as if it were the argument to an initial DATA command. If
2034 the selected mechanism has an initial challenge and [initial-response]
2035 was provided, the server should reject authentication by sending
2039 If authentication succeeds after exchanging DATA commands,
2040 an OK command must be sent to the client.
2043 The first octet received by the server after the \r\n of the BEGIN
2044 command from the client must be the first octet of the
2045 authenticated/encrypted stream of D-Bus messages.
2048 If BEGIN is received by the server, the first octet received
2049 by the client after the \r\n of the OK command must be the
2050 first octet of the authenticated/encrypted stream of D-Bus
2054 <sect2 id="auth-command-cancel">
2055 <title>CANCEL Command</title>
2057 At any time up to sending the BEGIN command, the client may send a
2058 CANCEL command. On receiving the CANCEL command, the server must
2059 send a REJECTED command and abort the current authentication
2063 <sect2 id="auth-command-data">
2064 <title>DATA Command</title>
2066 The DATA command may come from either client or server, and simply
2067 contains a hex-encoded block of data to be interpreted
2068 according to the SASL mechanism in use.
2071 Some SASL mechanisms support sending an "empty string";
2072 FIXME we need some way to do this.
2075 <sect2 id="auth-command-begin">
2076 <title>BEGIN Command</title>
2078 The BEGIN command acknowledges that the client has received an
2079 OK command from the server, and that the stream of messages
2083 The first octet received by the server after the \r\n of the BEGIN
2084 command from the client must be the first octet of the
2085 authenticated/encrypted stream of D-Bus messages.
2088 <sect2 id="auth-command-rejected">
2089 <title>REJECTED Command</title>
2091 The REJECTED command indicates that the current authentication
2092 exchange has failed, and further exchange of DATA is inappropriate.
2093 The client would normally try another mechanism, or try providing
2094 different responses to challenges.
2096 Optionally, the REJECTED command has a space-separated list of
2097 available auth mechanisms as arguments. If a server ever provides
2098 a list of supported mechanisms, it must provide the same list
2099 each time it sends a REJECTED message. Clients are free to
2100 ignore all lists received after the first.
2103 <sect2 id="auth-command-ok">
2104 <title>OK Command</title>
2106 The OK command indicates that the client has been
2107 authenticated. The client may now proceed with negotiating
2108 Unix file descriptor passing. To do that it shall send
2109 NEGOTIATE_UNIX_FD to the server.
2112 Otherwise, the client must respond to the OK command by
2113 sending a BEGIN command, followed by its stream of messages,
2114 or by disconnecting. The server must not accept additional
2115 commands using this protocol after the BEGIN command has been
2116 received. Further communication will be a stream of D-Bus
2117 messages (optionally encrypted, as negotiated) rather than
2121 If a client sends BEGIN the first octet received by the client
2122 after the \r\n of the OK command must be the first octet of
2123 the authenticated/encrypted stream of D-Bus messages.
2126 The OK command has one argument, which is the GUID of the server.
2127 See <xref linkend="addresses"/> for more on server GUIDs.
2130 <sect2 id="auth-command-error">
2131 <title>ERROR Command</title>
2133 The ERROR command indicates that either server or client did not
2134 know a command, does not accept the given command in the current
2135 context, or did not understand the arguments to the command. This
2136 allows the protocol to be extended; a client or server can send a
2137 command present or permitted only in new protocol versions, and if
2138 an ERROR is received instead of an appropriate response, fall back
2139 to using some other technique.
2142 If an ERROR is sent, the server or client that sent the
2143 error must continue as if the command causing the ERROR had never been
2144 received. However, the the server or client receiving the error
2145 should try something other than whatever caused the error;
2146 if only canceling/rejecting the authentication.
2149 If the D-Bus protocol changes incompatibly at some future time,
2150 applications implementing the new protocol would probably be able to
2151 check for support of the new protocol by sending a new command and
2152 receiving an ERROR from applications that don't understand it. Thus the
2153 ERROR feature of the auth protocol is an escape hatch that lets us
2154 negotiate extensions or changes to the D-Bus protocol in the future.
2157 <sect2 id="auth-command-negotiate-unix-fd">
2158 <title>NEGOTIATE_UNIX_FD Command</title>
2160 The NEGOTIATE_UNIX_FD command indicates that the client
2161 supports Unix file descriptor passing. This command may only
2162 be sent after the connection is authenticated, i.e. after OK
2163 was received by the client. This command may only be sent on
2164 transports that support Unix file descriptor passing.
2167 On receiving NEGOTIATE_UNIX_FD the server must respond with
2168 either AGREE_UNIX_FD or ERROR. It shall respond the former if
2169 the transport chosen supports Unix file descriptor passing and
2170 the server supports this feature. It shall respond the latter
2171 if the transport does not support Unix file descriptor
2172 passing, the server does not support this feature, or the
2173 server decides not to enable file descriptor passing due to
2174 security or other reasons.
2177 <sect2 id="auth-command-agree-unix-fd">
2178 <title>AGREE_UNIX_FD Command</title>
2180 The AGREE_UNIX_FD command indicates that the server supports
2181 Unix file descriptor passing. This command may only be sent
2182 after the connection is authenticated, and the client sent
2183 NEGOTIATE_UNIX_FD to enable Unix file descriptor passing. This
2184 command may only be sent on transports that support Unix file
2188 On receiving AGREE_UNIX_FD the client must respond with BEGIN,
2189 followed by its stream of messages, or by disconnecting. The
2190 server must not accept additional commands using this protocol
2191 after the BEGIN command has been received. Further
2192 communication will be a stream of D-Bus messages (optionally
2193 encrypted, as negotiated) rather than this protocol.
2196 <sect2 id="auth-command-future">
2197 <title>Future Extensions</title>
2199 Future extensions to the authentication and negotiation
2200 protocol are possible. For that new commands may be
2201 introduced. If a client or server receives an unknown command
2202 it shall respond with ERROR and not consider this fatal. New
2203 commands may be introduced both before, and after
2204 authentication, i.e. both before and after the OK command.
2207 <sect2 id="auth-examples">
2208 <title>Authentication examples</title>
2212 <title>Example of successful magic cookie authentication</title>
2214 (MAGIC_COOKIE is a made up mechanism)
2216 C: AUTH MAGIC_COOKIE 3138363935333137393635383634
2222 <title>Example of finding out mechanisms then picking one</title>
2225 S: REJECTED KERBEROS_V4 SKEY
2226 C: AUTH SKEY 7ab83f32ee
2227 S: DATA 8799cabb2ea93e
2228 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f
2234 <title>Example of client sends unknown command then falls back to regular auth</title>
2238 C: AUTH MAGIC_COOKIE 3736343435313230333039
2244 <title>Example of server doesn't support initial auth mechanism</title>
2246 C: AUTH MAGIC_COOKIE 3736343435313230333039
2247 S: REJECTED KERBEROS_V4 SKEY
2248 C: AUTH SKEY 7ab83f32ee
2249 S: DATA 8799cabb2ea93e
2250 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f
2256 <title>Example of wrong password or the like followed by successful retry</title>
2258 C: AUTH MAGIC_COOKIE 3736343435313230333039
2259 S: REJECTED KERBEROS_V4 SKEY
2260 C: AUTH SKEY 7ab83f32ee
2261 S: DATA 8799cabb2ea93e
2262 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f
2264 C: AUTH SKEY 7ab83f32ee
2265 S: DATA 8799cabb2ea93e
2266 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f
2272 <title>Example of skey cancelled and restarted</title>
2274 C: AUTH MAGIC_COOKIE 3736343435313230333039
2275 S: REJECTED KERBEROS_V4 SKEY
2276 C: AUTH SKEY 7ab83f32ee
2277 S: DATA 8799cabb2ea93e
2280 C: AUTH SKEY 7ab83f32ee
2281 S: DATA 8799cabb2ea93e
2282 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f
2288 <title>Example of successful magic cookie authentication with successful negotiation of Unix FD passing</title>
2290 (MAGIC_COOKIE is a made up mechanism)
2292 C: AUTH MAGIC_COOKIE 3138363935333137393635383634
2294 C: NEGOTIATE_UNIX_FD
2300 <title>Example of successful magic cookie authentication with unsuccessful negotiation of Unix FD passing</title>
2302 (MAGIC_COOKIE is a made up mechanism)
2304 C: AUTH MAGIC_COOKIE 3138363935333137393635383634
2306 C: NEGOTIATE_UNIX_FD
2313 <sect2 id="auth-states">
2314 <title>Authentication state diagrams</title>
2317 This section documents the auth protocol in terms of
2318 a state machine for the client and the server. This is
2319 probably the most robust way to implement the protocol.
2322 <sect3 id="auth-states-client">
2323 <title>Client states</title>
2326 To more precisely describe the interaction between the
2327 protocol state machine and the authentication mechanisms the
2328 following notation is used: MECH(CHALL) means that the
2329 server challenge CHALL was fed to the mechanism MECH, which
2335 CONTINUE(RESP) means continue the auth conversation
2336 and send RESP as the response to the server;
2342 OK(RESP) means that after sending RESP to the server
2343 the client side of the auth conversation is finished
2344 and the server should return "OK";
2350 ERROR means that CHALL was invalid and could not be
2356 Both RESP and CHALL may be empty.
2360 The Client starts by getting an initial response from the
2361 default mechanism and sends AUTH MECH RESP, or AUTH MECH if
2362 the mechanism did not provide an initial response. If the
2363 mechanism returns CONTINUE, the client starts in state
2364 <emphasis>WaitingForData</emphasis>, if the mechanism
2365 returns OK the client starts in state
2366 <emphasis>WaitingForOK</emphasis>.
2370 The client should keep track of available mechanisms and
2371 which it mechanisms it has already attempted. This list is
2372 used to decide which AUTH command to send. When the list is
2373 exhausted, the client should give up and close the
2378 <title><emphasis>WaitingForData</emphasis></title>
2386 MECH(CHALL) returns CONTINUE(RESP) → send
2388 <emphasis>WaitingForData</emphasis>
2392 MECH(CHALL) returns OK(RESP) → send DATA
2393 RESP, goto <emphasis>WaitingForOK</emphasis>
2397 MECH(CHALL) returns ERROR → send ERROR
2398 [msg], goto <emphasis>WaitingForData</emphasis>
2406 Receive REJECTED [mechs] →
2407 send AUTH [next mech], goto
2408 WaitingForData or <emphasis>WaitingForOK</emphasis>
2413 Receive ERROR → send
2415 <emphasis>WaitingForReject</emphasis>
2420 Receive OK → send
2421 BEGIN, terminate auth
2422 conversation, authenticated
2427 Receive anything else → send
2429 <emphasis>WaitingForData</emphasis>
2437 <title><emphasis>WaitingForOK</emphasis></title>
2442 Receive OK → send BEGIN, terminate auth
2443 conversation, <emphasis>authenticated</emphasis>
2448 Receive REJECTED [mechs] → send AUTH [next mech],
2449 goto <emphasis>WaitingForData</emphasis> or
2450 <emphasis>WaitingForOK</emphasis>
2456 Receive DATA → send CANCEL, goto
2457 <emphasis>WaitingForReject</emphasis>
2463 Receive ERROR → send CANCEL, goto
2464 <emphasis>WaitingForReject</emphasis>
2470 Receive anything else → send ERROR, goto
2471 <emphasis>WaitingForOK</emphasis>
2479 <title><emphasis>WaitingForReject</emphasis></title>
2484 Receive REJECTED [mechs] → send AUTH [next mech],
2485 goto <emphasis>WaitingForData</emphasis> or
2486 <emphasis>WaitingForOK</emphasis>
2492 Receive anything else → terminate auth
2493 conversation, disconnect
2502 <sect3 id="auth-states-server">
2503 <title>Server states</title>
2506 For the server MECH(RESP) means that the client response
2507 RESP was fed to the the mechanism MECH, which returns one of
2512 CONTINUE(CHALL) means continue the auth conversation and
2513 send CHALL as the challenge to the client;
2519 OK means that the client has been successfully
2526 REJECTED means that the client failed to authenticate or
2527 there was an error in RESP.
2532 The server starts out in state
2533 <emphasis>WaitingForAuth</emphasis>. If the client is
2534 rejected too many times the server must disconnect the
2539 <title><emphasis>WaitingForAuth</emphasis></title>
2545 Receive AUTH → send REJECTED [mechs], goto
2546 <emphasis>WaitingForAuth</emphasis>
2552 Receive AUTH MECH RESP
2556 MECH not valid mechanism → send REJECTED
2558 <emphasis>WaitingForAuth</emphasis>
2562 MECH(RESP) returns CONTINUE(CHALL) → send
2564 <emphasis>WaitingForData</emphasis>
2568 MECH(RESP) returns OK → send OK, goto
2569 <emphasis>WaitingForBegin</emphasis>
2573 MECH(RESP) returns REJECTED → send REJECTED
2575 <emphasis>WaitingForAuth</emphasis>
2583 Receive BEGIN → terminate
2584 auth conversation, disconnect
2590 Receive ERROR → send REJECTED [mechs], goto
2591 <emphasis>WaitingForAuth</emphasis>
2597 Receive anything else → send
2599 <emphasis>WaitingForAuth</emphasis>
2608 <title><emphasis>WaitingForData</emphasis></title>
2616 MECH(RESP) returns CONTINUE(CHALL) → send
2618 <emphasis>WaitingForData</emphasis>
2622 MECH(RESP) returns OK → send OK, goto
2623 <emphasis>WaitingForBegin</emphasis>
2627 MECH(RESP) returns REJECTED → send REJECTED
2629 <emphasis>WaitingForAuth</emphasis>
2637 Receive BEGIN → terminate auth conversation,
2644 Receive CANCEL → send REJECTED [mechs], goto
2645 <emphasis>WaitingForAuth</emphasis>
2651 Receive ERROR → send REJECTED [mechs], goto
2652 <emphasis>WaitingForAuth</emphasis>
2658 Receive anything else → send ERROR, goto
2659 <emphasis>WaitingForData</emphasis>
2667 <title><emphasis>WaitingForBegin</emphasis></title>
2672 Receive BEGIN → terminate auth conversation,
2673 client authenticated
2679 Receive CANCEL → send REJECTED [mechs], goto
2680 <emphasis>WaitingForAuth</emphasis>
2686 Receive ERROR → send REJECTED [mechs], goto
2687 <emphasis>WaitingForAuth</emphasis>
2693 Receive anything else → send ERROR, goto
2694 <emphasis>WaitingForBegin</emphasis>
2704 <sect2 id="auth-mechanisms">
2705 <title>Authentication mechanisms</title>
2707 This section describes some new authentication mechanisms.
2708 D-Bus also allows any standard SASL mechanism of course.
2710 <sect3 id="auth-mechanisms-sha">
2711 <title>DBUS_COOKIE_SHA1</title>
2713 The DBUS_COOKIE_SHA1 mechanism is designed to establish that a client
2714 has the ability to read a private file owned by the user being
2715 authenticated. If the client can prove that it has access to a secret
2716 cookie stored in this file, then the client is authenticated.
2717 Thus the security of DBUS_COOKIE_SHA1 depends on a secure home
2721 Throughout this description, "hex encoding" must output the digits
2722 from a to f in lower-case; the digits A to F must not be used
2723 in the DBUS_COOKIE_SHA1 mechanism.
2726 Authentication proceeds as follows:
2730 The client sends the username it would like to authenticate
2736 The server sends the name of its "cookie context" (see below); a
2737 space character; the integer ID of the secret cookie the client
2738 must demonstrate knowledge of; a space character; then a
2739 randomly-generated challenge string, all of this hex-encoded into
2745 The client locates the cookie and generates its own
2746 randomly-generated challenge string. The client then concatenates
2747 the server's decoded challenge, a ":" character, its own challenge,
2748 another ":" character, and the cookie. It computes the SHA-1 hash
2749 of this composite string as a hex digest. It concatenates the
2750 client's challenge string, a space character, and the SHA-1 hex
2751 digest, hex-encodes the result and sends it back to the server.
2756 The server generates the same concatenated string used by the
2757 client and computes its SHA-1 hash. It compares the hash with
2758 the hash received from the client; if the two hashes match, the
2759 client is authenticated.
2765 Each server has a "cookie context," which is a name that identifies a
2766 set of cookies that apply to that server. A sample context might be
2767 "org_freedesktop_session_bus". Context names must be valid ASCII,
2768 nonzero length, and may not contain the characters slash ("/"),
2769 backslash ("\"), space (" "), newline ("\n"), carriage return ("\r"),
2770 tab ("\t"), or period ("."). There is a default context,
2771 "org_freedesktop_general" that's used by servers that do not specify
2775 Cookies are stored in a user's home directory, in the directory
2776 <filename>~/.dbus-keyrings/</filename>. This directory must
2777 not be readable or writable by other users. If it is,
2778 clients and servers must ignore it. The directory
2779 contains cookie files named after the cookie context.
2782 A cookie file contains one cookie per line. Each line
2783 has three space-separated fields:
2787 The cookie ID number, which must be a non-negative integer and
2788 may not be used twice in the same file.
2793 The cookie's creation time, in UNIX seconds-since-the-epoch
2799 The cookie itself, a hex-encoded random block of bytes. The cookie
2800 may be of any length, though obviously security increases
2801 as the length increases.
2807 Only server processes modify the cookie file.
2808 They must do so with this procedure:
2812 Create a lockfile name by appending ".lock" to the name of the
2813 cookie file. The server should attempt to create this file
2814 using <literal>O_CREAT | O_EXCL</literal>. If file creation
2815 fails, the lock fails. Servers should retry for a reasonable
2816 period of time, then they may choose to delete an existing lock
2817 to keep users from having to manually delete a stale
2818 lock. <footnote><para>Lockfiles are used instead of real file
2819 locking <literal>fcntl()</literal> because real locking
2820 implementations are still flaky on network
2821 filesystems.</para></footnote>
2826 Once the lockfile has been created, the server loads the cookie
2827 file. It should then delete any cookies that are old (the
2828 timeout can be fairly short), or more than a reasonable
2829 time in the future (so that cookies never accidentally
2830 become permanent, if the clock was set far into the future
2831 at some point). If no recent keys remain, the
2832 server may generate a new key.
2837 The pruned and possibly added-to cookie file
2838 must be resaved atomically (using a temporary
2839 file which is rename()'d).
2844 The lock must be dropped by deleting the lockfile.
2850 Clients need not lock the file in order to load it,
2851 because servers are required to save the file atomically.
2856 <sect1 id="addresses">
2857 <title>Server Addresses</title>
2859 Server addresses consist of a transport name followed by a colon, and
2860 then an optional, comma-separated list of keys and values in the form key=value.
2861 Each value is escaped.
2865 <programlisting>unix:path=/tmp/dbus-test</programlisting>
2866 Which is the address to a unix socket with the path /tmp/dbus-test.
2869 Value escaping is similar to URI escaping but simpler.
2873 The set of optionally-escaped bytes is:
2874 <literal>[0-9A-Za-z_-/.\]</literal>. To escape, each
2875 <emphasis>byte</emphasis> (note, not character) which is not in the
2876 set of optionally-escaped bytes must be replaced with an ASCII
2877 percent (<literal>%</literal>) and the value of the byte in hex.
2878 The hex value must always be two digits, even if the first digit is
2879 zero. The optionally-escaped bytes may be escaped if desired.
2884 To unescape, append each byte in the value; if a byte is an ASCII
2885 percent (<literal>%</literal>) character then append the following
2886 hex value instead. It is an error if a <literal>%</literal> byte
2887 does not have two hex digits following. It is an error if a
2888 non-optionally-escaped byte is seen unescaped.
2892 The set of optionally-escaped bytes is intended to preserve address
2893 readability and convenience.
2897 A server may specify a key-value pair with the key <literal>guid</literal>
2898 and the value a hex-encoded 16-byte sequence. <xref linkend="uuids"/>
2899 describes the format of the <literal>guid</literal> field. If present,
2900 this UUID may be used to distinguish one server address from another. A
2901 server should use a different UUID for each address it listens on. For
2902 example, if a message bus daemon offers both UNIX domain socket and TCP
2903 connections, but treats clients the same regardless of how they connect,
2904 those two connections are equivalent post-connection but should have
2905 distinct UUIDs to distinguish the kinds of connection.
2909 The intent of the address UUID feature is to allow a client to avoid
2910 opening multiple identical connections to the same server, by allowing the
2911 client to check whether an address corresponds to an already-existing
2912 connection. Comparing two addresses is insufficient, because addresses
2913 can be recycled by distinct servers, and equivalent addresses may look
2914 different if simply compared as strings (for example, the host in a TCP
2915 address can be given as an IP address or as a hostname).
2919 Note that the address key is <literal>guid</literal> even though the
2920 rest of the API and documentation says "UUID," for historical reasons.
2924 [FIXME clarify if attempting to connect to each is a requirement
2925 or just a suggestion]
2926 When connecting to a server, multiple server addresses can be
2927 separated by a semi-colon. The library will then try to connect
2928 to the first address and if that fails, it'll try to connect to
2929 the next one specified, and so forth. For example
2930 <programlisting>unix:path=/tmp/dbus-test;unix:path=/tmp/dbus-test2</programlisting>
2935 <sect1 id="transports">
2936 <title>Transports</title>
2938 [FIXME we need to specify in detail each transport and its possible arguments]
2940 Current transports include: unix domain sockets (including
2941 abstract namespace on linux), launchd, systemd, TCP/IP, an executed subprocess and a debug/testing transport
2942 using in-process pipes. Future possible transports include one that
2943 tunnels over X11 protocol.
2946 <sect2 id="transports-unix-domain-sockets">
2947 <title>Unix Domain Sockets</title>
2949 Unix domain sockets can be either paths in the file system or on Linux
2950 kernels, they can be abstract which are similar to paths but
2951 do not show up in the file system.
2955 When a socket is opened by the D-Bus library it truncates the path
2956 name right before the first trailing Nul byte. This is true for both
2957 normal paths and abstract paths. Note that this is a departure from
2958 previous versions of D-Bus that would create sockets with a fixed
2959 length path name. Names which were shorter than the fixed length
2960 would be padded by Nul bytes.
2963 Unix domain sockets are not available on Windows.
2965 <sect3 id="transports-unix-domain-sockets-addresses">
2966 <title>Server Address Format</title>
2968 Unix domain socket addresses are identified by the "unix:" prefix
2969 and support the following key/value pairs:
2976 <entry>Values</entry>
2977 <entry>Description</entry>
2983 <entry>(path)</entry>
2984 <entry>path of the unix domain socket. If set, the "tmpdir" and "abstract" key must not be set.</entry>
2987 <entry>tmpdir</entry>
2988 <entry>(path)</entry>
2989 <entry>temporary directory in which a socket file with a random file name starting with 'dbus-' will be created by the server. This key can only be used in server addresses, not in client addresses. If set, the "path" and "abstract" key must not be set.</entry>
2992 <entry>abstract</entry>
2993 <entry>(string)</entry>
2994 <entry>unique string (path) in the abstract namespace. If set, the "path" or "tempdir" key must not be set.</entry>
3001 <sect2 id="transports-launchd">
3002 <title>launchd</title>
3004 launchd is an open-source server management system that replaces init, inetd
3005 and cron on Apple Mac OS X versions 10.4 and above. It provides a common session
3006 bus address for each user and deprecates the X11-enabled D-Bus launcher on OSX.
3010 launchd allocates a socket and provides it with the unix path through the
3011 DBUS_LAUNCHD_SESSION_BUS_SOCKET variable in launchd's environment. Every process
3012 spawned by launchd (or dbus-daemon, if it was started by launchd) can access
3013 it through its environment.
3014 Other processes can query for the launchd socket by executing:
3015 $ launchctl getenv DBUS_LAUNCHD_SESSION_BUS_SOCKET
3016 This is normally done by the D-Bus client library so doesn't have to be done
3020 launchd is not available on Microsoft Windows.
3022 <sect3 id="transports-launchd-addresses">
3023 <title>Server Address Format</title>
3025 launchd addresses are identified by the "launchd:" prefix
3026 and support the following key/value pairs:
3033 <entry>Values</entry>
3034 <entry>Description</entry>
3040 <entry>(environment variable)</entry>
3041 <entry>path of the unix domain socket for the launchd created dbus-daemon.</entry>
3048 <sect2 id="transports-systemd">
3049 <title>systemd</title>
3051 systemd is an open-source server management system that
3052 replaces init and inetd on newer Linux systems. It supports
3053 socket activation. The D-Bus systemd transport is used to acquire
3054 socket activation file descriptors from systemd and use them
3055 as D-Bus transport when the current process is spawned by
3056 socket activation from it.
3059 The systemd transport accepts only one or more Unix domain or
3060 TCP streams sockets passed in via socket activation.
3063 The systemd transport is not available on non-Linux operating systems.
3066 The systemd transport defines no parameter keys.
3069 <sect2 id="transports-tcp-sockets">
3070 <title>TCP Sockets</title>
3072 The tcp transport provides TCP/IP based connections between clients
3073 located on the same or different hosts.
3076 Using tcp transport without any additional secure authentification mechanismus
3077 over a network is unsecure.
3080 Windows notes: Because of the tcp stack on Windows does not provide sending
3081 credentials over a tcp connection, the EXTERNAL authentification
3082 mechanismus does not work.
3084 <sect3 id="transports-tcp-sockets-addresses">
3085 <title>Server Address Format</title>
3087 TCP/IP socket addresses are identified by the "tcp:" prefix
3088 and support the following key/value pairs:
3095 <entry>Values</entry>
3096 <entry>Description</entry>
3102 <entry>(string)</entry>
3103 <entry>dns name or ip address</entry>
3107 <entry>(number)</entry>
3108 <entry>The tcp port the server will open. A zero value let the server
3109 choose a free port provided from the underlaying operating system.
3110 libdbus is able to retrieve the real used port from the server.
3114 <entry>family</entry>
3115 <entry>(string)</entry>
3116 <entry>If set, provide the type of socket family either "ipv4" or "ipv6". If unset, the family is unspecified.</entry>
3123 <sect2 id="transports-nonce-tcp-sockets">
3124 <title>Nonce-secured TCP Sockets</title>
3126 The nonce-tcp transport provides a secured TCP transport, using a
3127 simple authentication mechanism to ensure that only clients with read
3128 access to a certain location in the filesystem can connect to the server.
3129 The server writes a secret, the nonce, to a file and an incoming client
3130 connection is only accepted if the client sends the nonce right after
3131 the connect. The nonce mechanism requires no setup and is orthogonal to
3132 the higher-level authentication mechanisms described in the
3133 Authentication section.
3137 On start, the server generates a random 16 byte nonce and writes it
3138 to a file in the user's temporary directory. The nonce file location
3139 is published as part of the server's D-Bus address using the
3140 "noncefile" key-value pair.
3142 After an accept, the server reads 16 bytes from the socket. If the
3143 read bytes do not match the nonce stored in the nonce file, the
3144 server MUST immediately drop the connection.
3145 If the nonce match the received byte sequence, the client is accepted
3146 and the transport behaves like an unsecured tcp transport.
3149 After a successful connect to the server socket, the client MUST read
3150 the nonce from the file published by the server via the noncefile=
3151 key-value pair and send it over the socket. After that, the
3152 transport behaves like an unsecured tcp transport.
3154 <sect3 id="transports-nonce-tcp-sockets-addresses">
3155 <title>Server Address Format</title>
3157 Nonce TCP/IP socket addresses uses the "nonce-tcp:" prefix
3158 and support the following key/value pairs:
3165 <entry>Values</entry>
3166 <entry>Description</entry>
3172 <entry>(string)</entry>
3173 <entry>dns name or ip address</entry>
3177 <entry>(number)</entry>
3178 <entry>The tcp port the server will open. A zero value let the server
3179 choose a free port provided from the underlaying operating system.
3180 libdbus is able to retrieve the real used port from the server.
3184 <entry>family</entry>
3185 <entry>(string)</entry>
3186 <entry>If set, provide the type of socket family either "ipv4" or "ipv6". If unset, the family is unspecified.</entry>
3189 <entry>noncefile</entry>
3190 <entry>(path)</entry>
3191 <entry>file location containing the secret</entry>
3198 <sect2 id="transports-exec">
3199 <title>Executed Subprocesses on Unix</title>
3201 This transport forks off a process and connects its standard
3202 input and standard output with an anonymous Unix domain
3203 socket. This socket is then used for communication by the
3204 transport. This transport may be used to use out-of-process
3205 forwarder programs as basis for the D-Bus protocol.
3208 The forked process will inherit the standard error output and
3209 process group from the parent process.
3212 Executed subprocesses are not available on Windows.
3214 <sect3 id="transports-exec-addresses">
3215 <title>Server Address Format</title>
3217 Executed subprocess addresses are identified by the "unixexec:" prefix
3218 and support the following key/value pairs:
3225 <entry>Values</entry>
3226 <entry>Description</entry>
3232 <entry>(path)</entry>
3233 <entry>Path of the binary to execute, either an absolute
3234 path or a binary name that is searched for in the default
3235 search path of the OS. This corresponds to the first
3236 argument of execlp(). This key is mandatory.</entry>
3239 <entry>argv0</entry>
3240 <entry>(string)</entry>
3241 <entry>The program name to use when executing the
3242 binary. If omitted the same value as specified for path=
3243 will be used. This corresponds to the second argument of
3247 <entry>argv1, argv2, ...</entry>
3248 <entry>(string)</entry>
3249 <entry>Arguments to pass to the binary. This corresponds
3250 to the third and later arguments of execlp(). If a
3251 specific argvX is not specified no further argvY for Y > X
3252 are taken into account.</entry>
3260 <sect1 id="meta-transports">
3261 <title>Meta Transports</title>
3263 Meta transports are a kind of transport with special enhancements or
3264 behavior. Currently available meta transports include: autolaunch
3267 <sect2 id="meta-transports-autolaunch">
3268 <title>Autolaunch</title>
3269 <para>The autolaunch transport provides a way for dbus clients to autodetect
3270 a running dbus session bus and to autolaunch a session bus if not present.
3272 <sect3 id="meta-transports-autolaunch-addresses">
3273 <title>Server Address Format</title>
3275 Autolaunch addresses uses the "autolaunch:" prefix and support the
3276 following key/value pairs:
3283 <entry>Values</entry>
3284 <entry>Description</entry>
3289 <entry>scope</entry>
3290 <entry>(string)</entry>
3291 <entry>scope of autolaunch (Windows only)
3295 "*install-path" - limit session bus to dbus installation path.
3296 The dbus installation path is determined from the location of
3297 the shared dbus library. If the library is located in a 'bin'
3298 subdirectory the installation root is the directory above,
3299 otherwise the directory where the library lives is taken as
3302 <install-root>/bin/[lib]dbus-1.dll
3303 <install-root>/[lib]dbus-1.dll
3309 "*user" - limit session bus to the recent user.
3314 other values - specify dedicated session bus like "release",
3326 <sect3 id="meta-transports-autolaunch-windows-implementation">
3327 <title>Windows implementation</title>
3329 On start, the server opens a platform specific transport, creates a mutex
3330 and a shared memory section containing the related session bus address.
3331 This mutex will be inspected by the dbus client library to detect a
3332 running dbus session bus. The access to the mutex and the shared memory
3333 section are protected by global locks.
3336 In the recent implementation the autolaunch transport uses a tcp transport
3337 on localhost with a port choosen from the operating system. This detail may
3338 change in the future.
3341 Disclaimer: The recent implementation is in an early state and may not
3342 work in all cirumstances and/or may have security issues. Because of this
3343 the implementation is not documentated yet.
3350 <title>UUIDs</title>
3352 A working D-Bus implementation uses universally-unique IDs in two places.
3353 First, each server address has a UUID identifying the address,
3354 as described in <xref linkend="addresses"/>. Second, each operating
3355 system kernel instance running a D-Bus client or server has a UUID
3356 identifying that kernel, retrieved by invoking the method
3357 org.freedesktop.DBus.Peer.GetMachineId() (see <xref
3358 linkend="standard-interfaces-peer"/>).
3361 The term "UUID" in this document is intended literally, i.e. an
3362 identifier that is universally unique. It is not intended to refer to
3363 RFC4122, and in fact the D-Bus UUID is not compatible with that RFC.
3366 The UUID must contain 128 bits of data and be hex-encoded. The
3367 hex-encoded string may not contain hyphens or other non-hex-digit
3368 characters, and it must be exactly 32 characters long. To generate a
3369 UUID, the current reference implementation concatenates 96 bits of random
3370 data followed by the 32-bit time in seconds since the UNIX epoch (in big
3374 It would also be acceptable and probably better to simply generate 128
3375 bits of random data, as long as the random number generator is of high
3376 quality. The timestamp could conceivably help if the random bits are not
3377 very random. With a quality random number generator, collisions are
3378 extremely unlikely even with only 96 bits, so it's somewhat academic.
3381 Implementations should, however, stick to random data for the first 96 bits
3386 <sect1 id="standard-interfaces">
3387 <title>Standard Interfaces</title>
3389 See <xref linkend="message-protocol-types-notation"/> for details on
3390 the notation used in this section. There are some standard interfaces
3391 that may be useful across various D-Bus applications.
3393 <sect2 id="standard-interfaces-peer">
3394 <title><literal>org.freedesktop.DBus.Peer</literal></title>
3396 The <literal>org.freedesktop.DBus.Peer</literal> interface
3399 org.freedesktop.DBus.Peer.Ping ()
3400 org.freedesktop.DBus.Peer.GetMachineId (out STRING machine_uuid)
3404 On receipt of the <literal>METHOD_CALL</literal> message
3405 <literal>org.freedesktop.DBus.Peer.Ping</literal>, an application should do
3406 nothing other than reply with a <literal>METHOD_RETURN</literal> as
3407 usual. It does not matter which object path a ping is sent to. The
3408 reference implementation handles this method automatically.
3411 On receipt of the <literal>METHOD_CALL</literal> message
3412 <literal>org.freedesktop.DBus.Peer.GetMachineId</literal>, an application should
3413 reply with a <literal>METHOD_RETURN</literal> containing a hex-encoded
3414 UUID representing the identity of the machine the process is running on.
3415 This UUID must be the same for all processes on a single system at least
3416 until that system next reboots. It should be the same across reboots
3417 if possible, but this is not always possible to implement and is not
3419 It does not matter which object path a GetMachineId is sent to. The
3420 reference implementation handles this method automatically.
3423 The UUID is intended to be per-instance-of-the-operating-system, so may represent
3424 a virtual machine running on a hypervisor, rather than a physical machine.
3425 Basically if two processes see the same UUID, they should also see the same
3426 shared memory, UNIX domain sockets, process IDs, and other features that require
3427 a running OS kernel in common between the processes.
3430 The UUID is often used where other programs might use a hostname. Hostnames
3431 can change without rebooting, however, or just be "localhost" - so the UUID
3435 <xref linkend="uuids"/> explains the format of the UUID.
3439 <sect2 id="standard-interfaces-introspectable">
3440 <title><literal>org.freedesktop.DBus.Introspectable</literal></title>
3442 This interface has one method:
3444 org.freedesktop.DBus.Introspectable.Introspect (out STRING xml_data)
3448 Objects instances may implement
3449 <literal>Introspect</literal> which returns an XML description of
3450 the object, including its interfaces (with signals and methods), objects
3451 below it in the object path tree, and its properties.
3454 <xref linkend="introspection-format"/> describes the format of this XML string.
3457 <sect2 id="standard-interfaces-properties">
3458 <title><literal>org.freedesktop.DBus.Properties</literal></title>
3460 Many native APIs will have a concept of object <firstterm>properties</firstterm>
3461 or <firstterm>attributes</firstterm>. These can be exposed via the
3462 <literal>org.freedesktop.DBus.Properties</literal> interface.
3466 org.freedesktop.DBus.Properties.Get (in STRING interface_name,
3467 in STRING property_name,
3469 org.freedesktop.DBus.Properties.Set (in STRING interface_name,
3470 in STRING property_name,
3472 org.freedesktop.DBus.Properties.GetAll (in STRING interface_name,
3473 out DICT<STRING,VARIANT> props);
3477 It is conventional to give D-Bus properties names consisting of
3478 capitalized words without punctuation ("CamelCase"), like
3479 <link linkend="message-protocol-names-member">member names</link>.
3480 For instance, the GObject property
3481 <literal>connection-status</literal> or the Qt property
3482 <literal>connectionStatus</literal> could be represented on D-Bus
3483 as <literal>ConnectionStatus</literal>.
3486 Strictly speaking, D-Bus property names are not required to follow
3487 the same naming restrictions as member names, but D-Bus property
3488 names that would not be valid member names (in particular,
3489 GObject-style dash-separated property names) can cause interoperability
3490 problems and should be avoided.
3493 The available properties and whether they are writable can be determined
3494 by calling <literal>org.freedesktop.DBus.Introspectable.Introspect</literal>,
3495 see <xref linkend="standard-interfaces-introspectable"/>.
3498 An empty string may be provided for the interface name; in this case,
3499 if there are multiple properties on an object with the same name,
3500 the results are undefined (picking one by according to an arbitrary
3501 deterministic rule, or returning an error, are the reasonable
3505 If one or more properties change on an object, the
3506 <literal>org.freedesktop.DBus.Properties.PropertiesChanged</literal>
3507 signal may be emitted (this signal was added in 0.14):
3511 org.freedesktop.DBus.Properties.PropertiesChanged (STRING interface_name,
3512 DICT<STRING,VARIANT> changed_properties,
3513 ARRAY<STRING> invalidated_properties);
3517 where <literal>changed_properties</literal> is a dictionary
3518 containing the changed properties with the new values and
3519 <literal>invalidated_properties</literal> is an array of
3520 properties that changed but the value is not conveyed.
3523 Whether the <literal>PropertiesChanged</literal> signal is
3524 supported can be determined by calling
3525 <literal>org.freedesktop.DBus.Introspectable.Introspect</literal>. Note
3526 that the signal may be supported for an object but it may
3527 differ how whether and how it is used on a per-property basis
3528 (for e.g. performance or security reasons). Each property (or
3529 the parent interface) must be annotated with the
3530 <literal>org.freedesktop.DBus.Property.EmitsChangedSignal</literal>
3531 annotation to convey this (usually the default value
3532 <literal>true</literal> is sufficient meaning that the
3533 annotation does not need to be used). See <xref
3534 linkend="introspection-format"/> for details on this
3539 <sect2 id="standard-interfaces-objectmanager">
3540 <title><literal>org.freedesktop.DBus.ObjectManager</literal></title>
3542 An API can optionally make use of this interface for one or
3543 more sub-trees of objects. The root of each sub-tree implements
3544 this interface so other applications can get all objects,
3545 interfaces and properties in a single method call. It is
3546 appropriate to use this interface if users of the tree of
3547 objects are expected to be interested in all interfaces of all
3548 objects in the tree; a more granular API should be used if
3549 users of the objects are expected to be interested in a small
3550 subset of the objects, a small subset of their interfaces, or
3554 The method that applications can use to get all objects and
3555 properties is <literal>GetManagedObjects</literal>:
3559 org.freedesktop.DBus.ObjectManager.GetManagedObjects (out DICT<OBJPATH,DICT<STRING,DICT<STRING,VARIANT>>> objpath_interfaces_and_properties);
3563 The return value of this method is a dict whose keys are
3564 object paths. All returned object paths are children of the
3565 object path implementing this interface, i.e. their object
3566 paths start with the ObjectManager's object path plus '/'.
3569 Each value is a dict whose keys are interfaces names. Each
3570 value in this inner dict is the same dict that would be
3571 returned by the <link
3572 linkend="standard-interfaces-properties">org.freedesktop.DBus.Properties.GetAll()</link>
3573 method for that combination of object path and interface. If
3574 an interface has no properties, the empty dict is returned.
3577 Changes are emitted using the following two signals:
3581 org.freedesktop.DBus.ObjectManager.InterfacesAdded (OBJPATH object_path,
3582 DICT<STRING,DICT<STRING,VARIANT>> interfaces_and_properties);
3583 org.freedesktop.DBus.ObjectManager.InterfacesRemoved (OBJPATH object_path,
3584 ARRAY<STRING> interfaces);
3588 The <literal>InterfacesAdded</literal> signal is emitted when
3589 either a new object is added or when an existing object gains
3590 one or more interfaces. The
3591 <literal>InterfacesRemoved</literal> signal is emitted
3592 whenever an object is removed or it loses one or more
3593 interfaces. The second parameter of the
3594 <literal>InterfacesAdded</literal> signal contains a dict with
3595 the interfaces and properties (if any) that have been added to
3596 the given object path. Similarly, the second parameter of the
3597 <literal>InterfacesRemoved</literal> signal contains an array
3598 of the interfaces that were removed. Note that changes on
3599 properties on existing interfaces are not reported using this
3600 interface - an application should also monitor the existing <link
3601 linkend="standard-interfaces-properties">PropertiesChanged</link>
3602 signal on each object.
3605 Applications SHOULD NOT export objects that are children of an
3606 object (directly or otherwise) implementing this interface but
3607 which are not returned in the reply from the
3608 <literal>GetManagedObjects()</literal> method of this
3609 interface on the given object.
3612 The intent of the <literal>ObjectManager</literal> interface
3613 is to make it easy to write a robust client
3614 implementation. The trivial client implementation only needs
3615 to make two method calls:
3619 org.freedesktop.DBus.AddMatch (bus_proxy,
3620 "type='signal',name='org.example.App',path_namespace='/org/example/App'");
3621 objects = org.freedesktop.DBus.ObjectManager.GetManagedObjects (app_proxy);
3625 on the message bus and the remote application's
3626 <literal>ObjectManager</literal>, respectively. Whenever a new
3627 remote object is created (or an existing object gains a new
3628 interface), the <literal>InterfacesAdded</literal> signal is
3629 emitted, and since this signal contains all properties for the
3630 interfaces, no calls to the
3631 <literal>org.freedesktop.Properties</literal> interface on the
3632 remote object are needed. Additionally, since the initial
3633 <literal>AddMatch()</literal> rule already includes signal
3634 messages from the newly created child object, no new
3635 <literal>AddMatch()</literal> call is needed.
3640 The <literal>org.freedesktop.DBus.ObjectManager</literal>
3641 interface was added in version 0.17 of the D-Bus
3648 <sect1 id="introspection-format">
3649 <title>Introspection Data Format</title>
3651 As described in <xref linkend="standard-interfaces-introspectable"/>,
3652 objects may be introspected at runtime, returning an XML string
3653 that describes the object. The same XML format may be used in
3654 other contexts as well, for example as an "IDL" for generating
3655 static language bindings.
3658 Here is an example of introspection data:
3660 <!DOCTYPE node PUBLIC "-//freedesktop//DTD D-BUS Object Introspection 1.0//EN"
3661 "http://www.freedesktop.org/standards/dbus/1.0/introspect.dtd">
3662 <node name="/com/example/sample_object">
3663 <interface name="com.example.SampleInterface">
3664 <method name="Frobate">
3665 <arg name="foo" type="i" direction="in"/>
3666 <arg name="bar" type="s" direction="out"/>
3667 <arg name="baz" type="a{us}" direction="out"/>
3668 <annotation name="org.freedesktop.DBus.Deprecated" value="true"/>
3670 <method name="Bazify">
3671 <arg name="bar" type="(iiu)" direction="in"/>
3672 <arg name="bar" type="v" direction="out"/>
3674 <method name="Mogrify">
3675 <arg name="bar" type="(iiav)" direction="in"/>
3677 <signal name="Changed">
3678 <arg name="new_value" type="b"/>
3680 <property name="Bar" type="y" access="readwrite"/>
3682 <node name="child_of_sample_object"/>
3683 <node name="another_child_of_sample_object"/>
3688 A more formal DTD and spec needs writing, but here are some quick notes.
3692 Only the root <node> element can omit the node name, as it's
3693 known to be the object that was introspected. If the root
3694 <node> does have a name attribute, it must be an absolute
3695 object path. If child <node> have object paths, they must be
3701 If a child <node> has any sub-elements, then they
3702 must represent a complete introspection of the child.
3703 If a child <node> is empty, then it may or may
3704 not have sub-elements; the child must be introspected
3705 in order to find out. The intent is that if an object
3706 knows that its children are "fast" to introspect
3707 it can go ahead and return their information, but
3708 otherwise it can omit it.
3713 The direction element on <arg> may be omitted,
3714 in which case it defaults to "in" for method calls
3715 and "out" for signals. Signals only allow "out"
3716 so while direction may be specified, it's pointless.
3721 The possible directions are "in" and "out",
3722 unlike CORBA there is no "inout"
3727 The possible property access flags are
3728 "readwrite", "read", and "write"
3733 Multiple interfaces can of course be listed for
3739 The "name" attribute on arguments is optional.
3745 Method, interface, property, and signal elements may have
3746 "annotations", which are generic key/value pairs of metadata.
3747 They are similar conceptually to Java's annotations and C# attributes.
3748 Well-known annotations:
3755 <entry>Values (separated by ,)</entry>
3756 <entry>Description</entry>
3761 <entry>org.freedesktop.DBus.Deprecated</entry>
3762 <entry>true,false</entry>
3763 <entry>Whether or not the entity is deprecated; defaults to false</entry>
3766 <entry>org.freedesktop.DBus.GLib.CSymbol</entry>
3767 <entry>(string)</entry>
3768 <entry>The C symbol; may be used for methods and interfaces</entry>
3771 <entry>org.freedesktop.DBus.Method.NoReply</entry>
3772 <entry>true,false</entry>
3773 <entry>If set, don't expect a reply to the method call; defaults to false.</entry>
3776 <entry>org.freedesktop.DBus.Property.EmitsChangedSignal</entry>
3777 <entry>true,invalidates,false</entry>
3780 If set to <literal>false</literal>, the
3781 <literal>org.freedesktop.DBus.Properties.PropertiesChanged</literal>
3783 linkend="standard-interfaces-properties"/> is not
3784 guaranteed to be emitted if the property changes.
3787 If set to <literal>invalidates</literal> the signal
3788 is emitted but the value is not included in the
3792 If set to <literal>true</literal> the signal is
3793 emitted with the value included.
3796 The value for the annotation defaults to
3797 <literal>true</literal> if the enclosing interface
3798 element does not specify the annotation. Otherwise it
3799 defaults to the value specified in the enclosing
3808 <sect1 id="message-bus">
3809 <title>Message Bus Specification</title>
3810 <sect2 id="message-bus-overview">
3811 <title>Message Bus Overview</title>
3813 The message bus accepts connections from one or more applications.
3814 Once connected, applications can exchange messages with other
3815 applications that are also connected to the bus.
3818 In order to route messages among connections, the message bus keeps a
3819 mapping from names to connections. Each connection has one
3820 unique-for-the-lifetime-of-the-bus name automatically assigned.
3821 Applications may request additional names for a connection. Additional
3822 names are usually "well-known names" such as
3823 "com.example.TextEditor". When a name is bound to a connection,
3824 that connection is said to <firstterm>own</firstterm> the name.
3827 The bus itself owns a special name,
3828 <literal>org.freedesktop.DBus</literal>, with an object
3829 located at <literal>/org/freedesktop/DBus</literal> that
3830 implements the <literal>org.freedesktop.DBus</literal>
3831 interface. This service allows applications to make
3832 administrative requests of the bus itself. For example,
3833 applications can ask the bus to assign a name to a connection.
3836 Each name may have <firstterm>queued owners</firstterm>. When an
3837 application requests a name for a connection and the name is already in
3838 use, the bus will optionally add the connection to a queue waiting for
3839 the name. If the current owner of the name disconnects or releases
3840 the name, the next connection in the queue will become the new owner.
3844 This feature causes the right thing to happen if you start two text
3845 editors for example; the first one may request "com.example.TextEditor",
3846 and the second will be queued as a possible owner of that name. When
3847 the first exits, the second will take over.
3851 Applications may send <firstterm>unicast messages</firstterm> to
3852 a specific recipient or to the message bus itself, or
3853 <firstterm>broadcast messages</firstterm> to all interested recipients.
3854 See <xref linkend="message-bus-routing"/> for details.
3858 <sect2 id="message-bus-names">
3859 <title>Message Bus Names</title>
3861 Each connection has at least one name, assigned at connection time and
3862 returned in response to the
3863 <literal>org.freedesktop.DBus.Hello</literal> method call. This
3864 automatically-assigned name is called the connection's <firstterm>unique
3865 name</firstterm>. Unique names are never reused for two different
3866 connections to the same bus.
3869 Ownership of a unique name is a prerequisite for interaction with
3870 the message bus. It logically follows that the unique name is always
3871 the first name that an application comes to own, and the last
3872 one that it loses ownership of.
3875 Unique connection names must begin with the character ':' (ASCII colon
3876 character); bus names that are not unique names must not begin
3877 with this character. (The bus must reject any attempt by an application
3878 to manually request a name beginning with ':'.) This restriction
3879 categorically prevents "spoofing"; messages sent to a unique name
3880 will always go to the expected connection.
3883 When a connection is closed, all the names that it owns are deleted (or
3884 transferred to the next connection in the queue if any).
3887 A connection can request additional names to be associated with it using
3888 the <literal>org.freedesktop.DBus.RequestName</literal> message. <xref
3889 linkend="message-protocol-names-bus"/> describes the format of a valid
3890 name. These names can be released again using the
3891 <literal>org.freedesktop.DBus.ReleaseName</literal> message.
3894 <sect3 id="bus-messages-request-name">
3895 <title><literal>org.freedesktop.DBus.RequestName</literal></title>
3899 UINT32 RequestName (in STRING name, in UINT32 flags)
3906 <entry>Argument</entry>
3908 <entry>Description</entry>
3914 <entry>STRING</entry>
3915 <entry>Name to request</entry>
3919 <entry>UINT32</entry>
3920 <entry>Flags</entry>
3930 <entry>Argument</entry>
3932 <entry>Description</entry>
3938 <entry>UINT32</entry>
3939 <entry>Return value</entry>
3946 This method call should be sent to
3947 <literal>org.freedesktop.DBus</literal> and asks the message bus to
3948 assign the given name to the method caller. Each name maintains a
3949 queue of possible owners, where the head of the queue is the primary
3950 or current owner of the name. Each potential owner in the queue
3951 maintains the DBUS_NAME_FLAG_ALLOW_REPLACEMENT and
3952 DBUS_NAME_FLAG_DO_NOT_QUEUE settings from its latest RequestName
3953 call. When RequestName is invoked the following occurs:
3957 If the method caller is currently the primary owner of the name,
3958 the DBUS_NAME_FLAG_ALLOW_REPLACEMENT and DBUS_NAME_FLAG_DO_NOT_QUEUE
3959 values are updated with the values from the new RequestName call,
3960 and nothing further happens.
3966 If the current primary owner (head of the queue) has
3967 DBUS_NAME_FLAG_ALLOW_REPLACEMENT set, and the RequestName
3968 invocation has the DBUS_NAME_FLAG_REPLACE_EXISTING flag, then
3969 the caller of RequestName replaces the current primary owner at
3970 the head of the queue and the current primary owner moves to the
3971 second position in the queue. If the caller of RequestName was
3972 in the queue previously its flags are updated with the values from
3973 the new RequestName in addition to moving it to the head of the queue.
3979 If replacement is not possible, and the method caller is
3980 currently in the queue but not the primary owner, its flags are
3981 updated with the values from the new RequestName call.
3987 If replacement is not possible, and the method caller is
3988 currently not in the queue, the method caller is appended to the
3995 If any connection in the queue has DBUS_NAME_FLAG_DO_NOT_QUEUE
3996 set and is not the primary owner, it is removed from the
3997 queue. This can apply to the previous primary owner (if it
3998 was replaced) or the method caller (if it updated the
3999 DBUS_NAME_FLAG_DO_NOT_QUEUE flag while still stuck in the
4000 queue, or if it was just added to the queue with that flag set).
4006 Note that DBUS_NAME_FLAG_REPLACE_EXISTING results in "jumping the
4007 queue," even if another application already in the queue had specified
4008 DBUS_NAME_FLAG_REPLACE_EXISTING. This comes up if a primary owner
4009 that does not allow replacement goes away, and the next primary owner
4010 does allow replacement. In this case, queued items that specified
4011 DBUS_NAME_FLAG_REPLACE_EXISTING <emphasis>do not</emphasis>
4012 automatically replace the new primary owner. In other words,
4013 DBUS_NAME_FLAG_REPLACE_EXISTING is not saved, it is only used at the
4014 time RequestName is called. This is deliberate to avoid an infinite loop
4015 anytime two applications are both DBUS_NAME_FLAG_ALLOW_REPLACEMENT
4016 and DBUS_NAME_FLAG_REPLACE_EXISTING.
4019 The flags argument contains any of the following values logically ORed
4026 <entry>Conventional Name</entry>
4027 <entry>Value</entry>
4028 <entry>Description</entry>
4033 <entry>DBUS_NAME_FLAG_ALLOW_REPLACEMENT</entry>
4037 If an application A specifies this flag and succeeds in
4038 becoming the owner of the name, and another application B
4039 later calls RequestName with the
4040 DBUS_NAME_FLAG_REPLACE_EXISTING flag, then application A
4041 will lose ownership and receive a
4042 <literal>org.freedesktop.DBus.NameLost</literal> signal, and
4043 application B will become the new owner. If DBUS_NAME_FLAG_ALLOW_REPLACEMENT
4044 is not specified by application A, or DBUS_NAME_FLAG_REPLACE_EXISTING
4045 is not specified by application B, then application B will not replace
4046 application A as the owner.
4051 <entry>DBUS_NAME_FLAG_REPLACE_EXISTING</entry>
4055 Try to replace the current owner if there is one. If this
4056 flag is not set the application will only become the owner of
4057 the name if there is no current owner. If this flag is set,
4058 the application will replace the current owner if
4059 the current owner specified DBUS_NAME_FLAG_ALLOW_REPLACEMENT.
4064 <entry>DBUS_NAME_FLAG_DO_NOT_QUEUE</entry>
4068 Without this flag, if an application requests a name that is
4069 already owned, the application will be placed in a queue to
4070 own the name when the current owner gives it up. If this
4071 flag is given, the application will not be placed in the
4072 queue, the request for the name will simply fail. This flag
4073 also affects behavior when an application is replaced as
4074 name owner; by default the application moves back into the
4075 waiting queue, unless this flag was provided when the application
4076 became the name owner.
4084 The return code can be one of the following values:
4090 <entry>Conventional Name</entry>
4091 <entry>Value</entry>
4092 <entry>Description</entry>
4097 <entry>DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER</entry>
4098 <entry>1</entry> <entry>The caller is now the primary owner of
4099 the name, replacing any previous owner. Either the name had no
4100 owner before, or the caller specified
4101 DBUS_NAME_FLAG_REPLACE_EXISTING and the current owner specified
4102 DBUS_NAME_FLAG_ALLOW_REPLACEMENT.</entry>
4105 <entry>DBUS_REQUEST_NAME_REPLY_IN_QUEUE</entry>
4108 <entry>The name already had an owner,
4109 DBUS_NAME_FLAG_DO_NOT_QUEUE was not specified, and either
4110 the current owner did not specify
4111 DBUS_NAME_FLAG_ALLOW_REPLACEMENT or the requesting
4112 application did not specify DBUS_NAME_FLAG_REPLACE_EXISTING.
4116 <entry>DBUS_REQUEST_NAME_REPLY_EXISTS</entry> <entry>3</entry>
4117 <entry>The name already has an owner,
4118 DBUS_NAME_FLAG_DO_NOT_QUEUE was specified, and either
4119 DBUS_NAME_FLAG_ALLOW_REPLACEMENT was not specified by the
4120 current owner, or DBUS_NAME_FLAG_REPLACE_EXISTING was not
4121 specified by the requesting application.</entry>
4124 <entry>DBUS_REQUEST_NAME_REPLY_ALREADY_OWNER</entry>
4126 <entry>The application trying to request ownership of a name is already the owner of it.</entry>
4134 <sect3 id="bus-messages-release-name">
4135 <title><literal>org.freedesktop.DBus.ReleaseName</literal></title>
4139 UINT32 ReleaseName (in STRING name)
4146 <entry>Argument</entry>
4148 <entry>Description</entry>
4154 <entry>STRING</entry>
4155 <entry>Name to release</entry>
4165 <entry>Argument</entry>
4167 <entry>Description</entry>
4173 <entry>UINT32</entry>
4174 <entry>Return value</entry>
4181 This method call should be sent to
4182 <literal>org.freedesktop.DBus</literal> and asks the message bus to
4183 release the method caller's claim to the given name. If the caller is
4184 the primary owner, a new primary owner will be selected from the
4185 queue if any other owners are waiting. If the caller is waiting in
4186 the queue for the name, the caller will removed from the queue and
4187 will not be made an owner of the name if it later becomes available.
4188 If there are no other owners in the queue for the name, it will be
4189 removed from the bus entirely.
4191 The return code can be one of the following values:
4197 <entry>Conventional Name</entry>
4198 <entry>Value</entry>
4199 <entry>Description</entry>
4204 <entry>DBUS_RELEASE_NAME_REPLY_RELEASED</entry>
4205 <entry>1</entry> <entry>The caller has released his claim on
4206 the given name. Either the caller was the primary owner of
4207 the name, and the name is now unused or taken by somebody
4208 waiting in the queue for the name, or the caller was waiting
4209 in the queue for the name and has now been removed from the
4213 <entry>DBUS_RELEASE_NAME_REPLY_NON_EXISTENT</entry>
4215 <entry>The given name does not exist on this bus.</entry>
4218 <entry>DBUS_RELEASE_NAME_REPLY_NOT_OWNER</entry>
4220 <entry>The caller was not the primary owner of this name,
4221 and was also not waiting in the queue to own this name.</entry>
4229 <sect3 id="bus-messages-list-queued-owners">
4230 <title><literal>org.freedesktop.DBus.ListQueuedOwners</literal></title>
4234 ARRAY of STRING ListQueuedOwners (in STRING name)
4241 <entry>Argument</entry>
4243 <entry>Description</entry>
4249 <entry>STRING</entry>
4250 <entry>The well-known bus name to query, such as
4251 <literal>com.example.cappuccino</literal></entry>
4261 <entry>Argument</entry>
4263 <entry>Description</entry>
4269 <entry>ARRAY of STRING</entry>
4270 <entry>The unique bus names of connections currently queued
4271 for the name</entry>
4278 This method call should be sent to
4279 <literal>org.freedesktop.DBus</literal> and lists the connections
4280 currently queued for a bus name (see
4281 <xref linkend="term-queued-owner"/>).
4286 <sect2 id="message-bus-routing">
4287 <title>Message Bus Message Routing</title>
4290 Messages may have a <literal>DESTINATION</literal> field (see <xref
4291 linkend="message-protocol-header-fields"/>), resulting in a
4292 <firstterm>unicast message</firstterm>. If the
4293 <literal>DESTINATION</literal> field is present, it specifies a message
4294 recipient by name. Method calls and replies normally specify this field.
4295 The message bus must send messages (of any type) with the
4296 <literal>DESTINATION</literal> field set to the specified recipient,
4297 regardless of whether the recipient has set up a match rule matching
4302 When the message bus receives a signal, if the
4303 <literal>DESTINATION</literal> field is absent, it is considered to
4304 be a <firstterm>broadcast signal</firstterm>, and is sent to all
4305 applications with <firstterm>message matching rules</firstterm> that
4306 match the message. Most signal messages are broadcasts.
4310 Unicast signal messages (those with a <literal>DESTINATION</literal>
4311 field) are not commonly used, but they are treated like any unicast
4312 message: they are delivered to the specified receipient,
4313 regardless of its match rules. One use for unicast signals is to
4314 avoid a race condition in which a signal is emitted before the intended
4315 recipient can call <xref linkend="bus-messages-add-match"/> to
4316 receive that signal: if the signal is sent directly to that recipient
4317 using a unicast message, it does not need to add a match rule at all,
4318 and there is no race condition. Another use for unicast signals,
4319 on message buses whose security policy prevents eavesdropping, is to
4320 send sensitive information which should only be visible to one
4325 When the message bus receives a method call, if the
4326 <literal>DESTINATION</literal> field is absent, the call is taken to be
4327 a standard one-to-one message and interpreted by the message bus
4328 itself. For example, sending an
4329 <literal>org.freedesktop.DBus.Peer.Ping</literal> message with no
4330 <literal>DESTINATION</literal> will cause the message bus itself to
4331 reply to the ping immediately; the message bus will not make this
4332 message visible to other applications.
4336 Continuing the <literal>org.freedesktop.DBus.Peer.Ping</literal> example, if
4337 the ping message were sent with a <literal>DESTINATION</literal> name of
4338 <literal>com.yoyodyne.Screensaver</literal>, then the ping would be
4339 forwarded, and the Yoyodyne Corporation screensaver application would be
4340 expected to reply to the ping.
4344 Message bus implementations may impose a security policy which
4345 prevents certain messages from being sent or received.
4346 When a message cannot be sent or received due to a security
4347 policy, the message bus should send an error reply, unless the
4348 original message had the <literal>NO_REPLY</literal> flag.
4351 <sect3 id="message-bus-routing-eavesdropping">
4352 <title>Eavesdropping</title>
4354 Receiving a unicast message whose <literal>DESTINATION</literal>
4355 indicates a different recipient is called
4356 <firstterm>eavesdropping</firstterm>. On a message bus which acts as
4357 a security boundary (like the standard system bus), the security
4358 policy should usually prevent eavesdropping, since unicast messages
4359 are normally kept private and may contain security-sensitive
4364 Eavesdropping is mainly useful for debugging tools, such as
4365 the <literal>dbus-monitor</literal> tool in the reference
4366 implementation of D-Bus. Tools which eavesdrop on the message bus
4367 should be careful to avoid sending a reply or error in response to
4368 messages intended for a different client.
4372 Clients may attempt to eavesdrop by adding match rules
4373 (see <xref linkend="message-bus-routing-match-rules"/>) containing
4374 the <literal>eavesdrop='true'</literal> match. If the message bus'
4375 security policy does not allow eavesdropping, the match rule can
4376 still be added, but will not have any practical effect. For
4377 compatibility with older message bus implementations, if adding such
4378 a match rule results in an error reply, the client may fall back to
4379 adding the same rule with the <literal>eavesdrop</literal> match
4384 <sect3 id="message-bus-routing-match-rules">
4385 <title>Match Rules</title>
4387 An important part of the message bus routing protocol is match
4388 rules. Match rules describe the messages that should be sent to a
4389 client, based on the contents of the message. Broadcast signals
4390 are only sent to clients which have a suitable match rule: this
4391 avoids waking up client processes to deal with signals that are
4392 not relevant to that client.
4395 Messages that list a client as their <literal>DESTINATION</literal>
4396 do not need to match the client's match rules, and are sent to that
4397 client regardless. As a result, match rules are mainly used to
4398 receive a subset of broadcast signals.
4401 Match rules can also be used for eavesdropping
4402 (see <xref linkend="message-bus-routing-eavesdropping"/>),
4403 if the security policy of the message bus allows it.
4406 Match rules are added using the AddMatch bus method
4407 (see <xref linkend="bus-messages-add-match"/>). Rules are
4408 specified as a string of comma separated key/value pairs.
4409 Excluding a key from the rule indicates a wildcard match.
4410 For instance excluding the the member from a match rule but
4411 adding a sender would let all messages from that sender through.
4412 An example of a complete rule would be
4413 "type='signal',sender='org.freedesktop.DBus',interface='org.freedesktop.DBus',member='Foo',path='/bar/foo',destination=':452345.34',arg2='bar'"
4416 The following table describes the keys that can be used to create
4423 <entry>Possible Values</entry>
4424 <entry>Description</entry>
4429 <entry><literal>type</literal></entry>
4430 <entry>'signal', 'method_call', 'method_return', 'error'</entry>
4431 <entry>Match on the message type. An example of a type match is type='signal'</entry>
4434 <entry><literal>sender</literal></entry>
4435 <entry>A bus or unique name (see <xref linkend="term-bus-name"/>
4436 and <xref linkend="term-unique-name"/> respectively)
4438 <entry>Match messages sent by a particular sender. An example of a sender match
4439 is sender='org.freedesktop.Hal'</entry>
4442 <entry><literal>interface</literal></entry>
4443 <entry>An interface name (see <xref linkend="message-protocol-names-interface"/>)</entry>
4444 <entry>Match messages sent over or to a particular interface. An example of an
4445 interface match is interface='org.freedesktop.Hal.Manager'.
4446 If a message omits the interface header, it must not match any rule
4447 that specifies this key.</entry>
4450 <entry><literal>member</literal></entry>
4451 <entry>Any valid method or signal name</entry>
4452 <entry>Matches messages which have the give method or signal name. An example of
4453 a member match is member='NameOwnerChanged'</entry>
4456 <entry><literal>path</literal></entry>
4457 <entry>An object path (see <xref linkend="message-protocol-marshaling-object-path"/>)</entry>
4458 <entry>Matches messages which are sent from or to the given object. An example of a
4459 path match is path='/org/freedesktop/Hal/Manager'</entry>
4462 <entry><literal>path_namespace</literal></entry>
4463 <entry>An object path</entry>
4466 Matches messages which are sent from or to an
4467 object for which the object path is either the
4468 given value, or that value followed by one or
4469 more path components.
4474 <literal>path_namespace='/com/example/foo'</literal>
4475 would match signals sent by
4476 <literal>/com/example/foo</literal>
4478 <literal>/com/example/foo/bar</literal>,
4480 <literal>/com/example/foobar</literal>.
4484 Using both <literal>path</literal> and
4485 <literal>path_namespace</literal> in the same match
4486 rule is not allowed.
4491 This match key was added in version 0.16 of the
4492 D-Bus specification and implemented by the bus
4493 daemon in dbus 1.5.0 and later.
4499 <entry><literal>destination</literal></entry>
4500 <entry>A unique name (see <xref linkend="term-unique-name"/>)</entry>
4501 <entry>Matches messages which are being sent to the given unique name. An
4502 example of a destination match is destination=':1.0'</entry>
4505 <entry><literal>arg[0, 1, 2, 3, ...]</literal></entry>
4506 <entry>Any string</entry>
4507 <entry>Arg matches are special and are used for further restricting the
4508 match based on the arguments in the body of a message. Only arguments of type
4509 STRING can be matched in this way. An example of an argument match
4510 would be arg3='Foo'. Only argument indexes from 0 to 63 should be
4514 <entry><literal>arg[0, 1, 2, 3, ...]path</literal></entry>
4515 <entry>Any string</entry>
4517 <para>Argument path matches provide a specialised form of wildcard matching for
4518 path-like namespaces. They can match arguments whose type is either STRING or
4519 OBJECT_PATH. As with normal argument matches,
4520 if the argument is exactly equal to the string given in the match
4521 rule then the rule is satisfied. Additionally, there is also a
4522 match when either the string given in the match rule or the
4523 appropriate message argument ends with '/' and is a prefix of the
4524 other. An example argument path match is arg0path='/aa/bb/'. This
4525 would match messages with first arguments of '/', '/aa/',
4526 '/aa/bb/', '/aa/bb/cc/' and '/aa/bb/cc'. It would not match
4527 messages with first arguments of '/aa/b', '/aa' or even '/aa/bb'.</para>
4529 <para>This is intended for monitoring “directories” in file system-like
4530 hierarchies, as used in the <citetitle>dconf</citetitle> configuration
4531 system. An application interested in all nodes in a particular hierarchy would
4532 monitor <literal>arg0path='/ca/example/foo/'</literal>. Then the service could
4533 emit a signal with zeroth argument <literal>"/ca/example/foo/bar"</literal> to
4534 represent a modification to the “bar” property, or a signal with zeroth
4535 argument <literal>"/ca/example/"</literal> to represent atomic modification of
4536 many properties within that directory, and the interested application would be
4537 notified in both cases.</para>
4540 This match key was added in version 0.12 of the
4541 D-Bus specification, implemented for STRING
4542 arguments by the bus daemon in dbus 1.2.0 and later,
4543 and implemented for OBJECT_PATH arguments in dbus 1.5.0
4550 <entry><literal>arg0namespace</literal></entry>
4551 <entry>Like a bus name, except that the string is not
4552 required to contain a '.' (period)</entry>
4554 <para>Match messages whose first argument is of type STRING, and is a bus name
4555 or interface name within the specified namespace. This is primarily intended
4556 for watching name owner changes for a group of related bus names, rather than
4557 for a single name or all name changes.</para>
4559 <para>Because every valid interface name is also a valid
4560 bus name, this can also be used for messages whose
4561 first argument is an interface name.</para>
4563 <para>For example, the match rule
4564 <literal>member='NameOwnerChanged',arg0namespace='com.example.backend'</literal>
4565 matches name owner changes for bus names such as
4566 <literal>com.example.backend.foo</literal>,
4567 <literal>com.example.backend.foo.bar</literal>, and
4568 <literal>com.example.backend</literal> itself.</para>
4570 <para>See also <xref linkend='bus-messages-name-owner-changed'/>.</para>
4573 This match key was added in version 0.16 of the
4574 D-Bus specification and implemented by the bus
4575 daemon in dbus 1.5.0 and later.
4581 <entry><literal>eavesdrop</literal></entry>
4582 <entry><literal>'true'</literal>, <literal>'false'</literal></entry>
4583 <entry>Since D-Bus 1.5.6, match rules do not
4584 match messages which have a <literal>DESTINATION</literal>
4585 field unless the match rule specifically
4587 (see <xref linkend="message-bus-routing-eavesdropping"/>)
4588 by specifying <literal>eavesdrop='true'</literal>
4589 in the match rule. <literal>eavesdrop='false'</literal>
4590 restores the default behaviour. Messages are
4591 delivered to their <literal>DESTINATION</literal>
4592 regardless of match rules, so this match does not
4593 affect normal delivery of unicast messages.
4594 If the message bus has a security policy which forbids
4595 eavesdropping, this match may still be used without error,
4596 but will not have any practical effect.
4597 In older versions of D-Bus, this match was not allowed
4598 in match rules, and all match rules behaved as if
4599 <literal>eavesdrop='true'</literal> had been used.
4608 <sect2 id="message-bus-starting-services">
4609 <title>Message Bus Starting Services</title>
4611 The message bus can start applications on behalf of other applications.
4612 In CORBA terms, this would be called <firstterm>activation</firstterm>.
4613 An application that can be started in this way is called a
4614 <firstterm>service</firstterm>.
4617 With D-Bus, starting a service is normally done by name. That is,
4618 applications ask the message bus to start some program that will own a
4619 well-known name, such as <literal>com.example.TextEditor</literal>.
4620 This implies a contract documented along with the name
4621 <literal>com.example.TextEditor</literal> for which object
4622 the owner of that name will provide, and what interfaces those
4626 To find an executable corresponding to a particular name, the bus daemon
4627 looks for <firstterm>service description files</firstterm>. Service
4628 description files define a mapping from names to executables. Different
4629 kinds of message bus will look for these files in different places, see
4630 <xref linkend="message-bus-types"/>.
4633 Service description files have the ".service" file
4634 extension. The message bus will only load service description files
4635 ending with .service; all other files will be ignored. The file format
4636 is similar to that of <ulink
4637 url="http://standards.freedesktop.org/desktop-entry-spec/desktop-entry-spec-latest.html">desktop
4638 entries</ulink>. All service description files must be in UTF-8
4639 encoding. To ensure that there will be no name collisions, service files
4640 must be namespaced using the same mechanism as messages and service
4645 On the well-known system bus, the name of a service description file
4646 must be its well-known name plus <literal>.service</literal>,
4648 <literal>com.example.ConfigurationDatabase.service</literal>.
4652 On the well-known session bus, services should follow the same
4653 service description file naming convention as on the system bus,
4654 but for backwards compatibility they are not required to do so.
4658 [FIXME the file format should be much better specified than "similar to
4659 .desktop entries" esp. since desktop entries are already
4660 badly-specified. ;-)]
4661 These sections from the specification apply to service files as well:
4664 <listitem><para>General syntax</para></listitem>
4665 <listitem><para>Comment format</para></listitem>
4668 Service description files must contain a
4669 <literal>D-BUS Service</literal> group with at least the keys
4670 <literal>Name</literal> (the well-known name of the service)
4671 and <literal>Exec</literal> (the command to be executed).
4674 <title>Example service description file</title>
4676 # Sample service description file
4678 Name=com.example.ConfigurationDatabase
4679 Exec=/usr/bin/sample-configd
4685 Additionally, service description files for the well-known system
4686 bus on Unix must contain a <literal>User</literal> key, whose value
4687 is the name of a user account (e.g. <literal>root</literal>).
4688 The system service will be run as that user.
4692 When an application asks to start a service by name, the bus daemon tries to
4693 find a service that will own that name. It then tries to spawn the
4694 executable associated with it. If this fails, it will report an
4699 On the well-known system bus, it is not possible for two .service files
4700 in the same directory to offer the same service, because they are
4701 constrained to have names that match the service name.
4705 On the well-known session bus, if two .service files in the same
4706 directory offer the same service name, the result is undefined.
4707 Distributors should avoid this situation, for instance by naming
4708 session services' .service files according to their service name.
4712 If two .service files in different directories offer the same
4713 service name, the one in the higher-priority directory is used:
4714 for instance, on the system bus, .service files in
4715 /usr/local/share/dbus-1/system-services take precedence over those
4716 in /usr/share/dbus-1/system-services.
4719 The executable launched will have the environment variable
4720 <literal>DBUS_STARTER_ADDRESS</literal> set to the address of the
4721 message bus so it can connect and request the appropriate names.
4724 The executable being launched may want to know whether the message bus
4725 starting it is one of the well-known message buses (see <xref
4726 linkend="message-bus-types"/>). To facilitate this, the bus must also set
4727 the <literal>DBUS_STARTER_BUS_TYPE</literal> environment variable if it is one
4728 of the well-known buses. The currently-defined values for this variable
4729 are <literal>system</literal> for the systemwide message bus,
4730 and <literal>session</literal> for the per-login-session message
4731 bus. The new executable must still connect to the address given
4732 in <literal>DBUS_STARTER_ADDRESS</literal>, but may assume that the
4733 resulting connection is to the well-known bus.
4736 [FIXME there should be a timeout somewhere, either specified
4737 in the .service file, by the client, or just a global value
4738 and if the client being activated fails to connect within that
4739 timeout, an error should be sent back.]
4742 <sect3 id="message-bus-starting-services-scope">
4743 <title>Message Bus Service Scope</title>
4745 The "scope" of a service is its "per-", such as per-session,
4746 per-machine, per-home-directory, or per-display. The reference
4747 implementation doesn't yet support starting services in a different
4748 scope from the message bus itself. So e.g. if you start a service
4749 on the session bus its scope is per-session.
4752 We could add an optional scope to a bus name. For example, for
4753 per-(display,session pair), we could have a unique ID for each display
4754 generated automatically at login and set on screen 0 by executing a
4755 special "set display ID" binary. The ID would be stored in a
4756 <literal>_DBUS_DISPLAY_ID</literal> property and would be a string of
4757 random bytes. This ID would then be used to scope names.
4758 Starting/locating a service could be done by ID-name pair rather than
4762 Contrast this with a per-display scope. To achieve that, we would
4763 want a single bus spanning all sessions using a given display.
4764 So we might set a <literal>_DBUS_DISPLAY_BUS_ADDRESS</literal>
4765 property on screen 0 of the display, pointing to this bus.
4770 <sect2 id="message-bus-types">
4771 <title>Well-known Message Bus Instances</title>
4773 Two standard message bus instances are defined here, along with how
4774 to locate them and where their service files live.
4776 <sect3 id="message-bus-types-login">
4777 <title>Login session message bus</title>
4779 Each time a user logs in, a <firstterm>login session message
4780 bus</firstterm> may be started. All applications in the user's login
4781 session may interact with one another using this message bus.
4784 The address of the login session message bus is given
4785 in the <literal>DBUS_SESSION_BUS_ADDRESS</literal> environment
4786 variable. If that variable is not set, applications may
4787 also try to read the address from the X Window System root
4788 window property <literal>_DBUS_SESSION_BUS_ADDRESS</literal>.
4789 The root window property must have type <literal>STRING</literal>.
4790 The environment variable should have precedence over the
4791 root window property.
4793 <para>The address of the login session message bus is given in the
4794 <literal>DBUS_SESSION_BUS_ADDRESS</literal> environment variable. If
4795 DBUS_SESSION_BUS_ADDRESS is not set, or if it's set to the string
4796 "autolaunch:", the system should use platform-specific methods of
4797 locating a running D-Bus session server, or starting one if a running
4798 instance cannot be found. Note that this mechanism is not recommended
4799 for attempting to determine if a daemon is running. It is inherently
4800 racy to attempt to make this determination, since the bus daemon may
4801 be started just before or just after the determination is made.
4802 Therefore, it is recommended that applications do not try to make this
4803 determination for their functionality purposes, and instead they
4804 should attempt to start the server.</para>
4806 <sect4 id="message-bus-types-login-x-windows">
4807 <title>X Windowing System</title>
4809 For the X Windowing System, the application must locate the
4810 window owner of the selection represented by the atom formed by
4814 <para>the literal string "_DBUS_SESSION_BUS_SELECTION_"</para>
4818 <para>the current user's username</para>
4822 <para>the literal character '_' (underscore)</para>
4826 <para>the machine's ID</para>
4832 The following properties are defined for the window that owns
4834 <informaltable frame="all">
4843 <para>meaning</para>
4849 <para>_DBUS_SESSION_BUS_ADDRESS</para>
4853 <para>the actual address of the server socket</para>
4859 <para>_DBUS_SESSION_BUS_PID</para>
4863 <para>the PID of the server process</para>
4872 At least the _DBUS_SESSION_BUS_ADDRESS property MUST be
4873 present in this window.
4877 If the X selection cannot be located or if reading the
4878 properties from the window fails, the implementation MUST conclude
4879 that there is no D-Bus server running and proceed to start a new
4880 server. (See below on concurrency issues)
4884 Failure to connect to the D-Bus server address thus obtained
4885 MUST be treated as a fatal connection error and should be reported
4890 As an alternative, an implementation MAY find the information
4891 in the following file located in the current user's home directory,
4892 in subdirectory .dbus/session-bus/:
4895 <para>the machine's ID</para>
4899 <para>the literal character '-' (dash)</para>
4903 <para>the X display without the screen number, with the
4904 following prefixes removed, if present: ":", "localhost:"
4905 ."localhost.localdomain:". That is, a display of
4906 "localhost:10.0" produces just the number "10"</para>
4912 The contents of this file NAME=value assignment pairs and
4913 lines starting with # are comments (no comments are allowed
4914 otherwise). The following variable names are defined:
4921 <para>Variable</para>
4925 <para>meaning</para>
4931 <para>DBUS_SESSION_BUS_ADDRESS</para>
4935 <para>the actual address of the server socket</para>
4941 <para>DBUS_SESSION_BUS_PID</para>
4945 <para>the PID of the server process</para>
4951 <para>DBUS_SESSION_BUS_WINDOWID</para>
4955 <para>the window ID</para>
4964 At least the DBUS_SESSION_BUS_ADDRESS variable MUST be present
4969 Failure to open this file MUST be interpreted as absence of a
4970 running server. Therefore, the implementation MUST proceed to
4971 attempting to launch a new bus server if the file cannot be
4976 However, success in opening this file MUST NOT lead to the
4977 conclusion that the server is running. Thus, a failure to connect to
4978 the bus address obtained by the alternative method MUST NOT be
4979 considered a fatal error. If the connection cannot be established,
4980 the implementation MUST proceed to check the X selection settings or
4981 to start the server on its own.
4985 If the implementation concludes that the D-Bus server is not
4986 running it MUST attempt to start a new server and it MUST also
4987 ensure that the daemon started as an effect of the "autolaunch"
4988 mechanism provides the lookup mechanisms described above, so
4989 subsequent calls can locate the newly started server. The
4990 implementation MUST also ensure that if two or more concurrent
4991 initiations happen, only one server remains running and all other
4992 initiations are able to obtain the address of this server and
4993 connect to it. In other words, the implementation MUST ensure that
4994 the X selection is not present when it attempts to set it, without
4995 allowing another process to set the selection between the
4996 verification and the setting (e.g., by using XGrabServer /
5003 On Unix systems, the session bus should search for .service files
5004 in <literal>$XDG_DATA_DIRS/dbus-1/services</literal> as defined
5006 <ulink url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG Base Directory Specification</ulink>.
5007 Implementations may also search additional locations, which
5008 should be searched with lower priority than anything in
5009 XDG_DATA_HOME, XDG_DATA_DIRS or their respective defaults;
5010 for example, the reference implementation also
5011 looks in <literal>${datadir}/dbus-1/services</literal> as
5012 set at compile time.
5015 As described in the XDG Base Directory Specification, software
5016 packages should install their session .service files to their
5017 configured <literal>${datadir}/dbus-1/services</literal>,
5018 where <literal>${datadir}</literal> is as defined by the GNU
5019 coding standards. System administrators or users can arrange
5020 for these service files to be read by setting XDG_DATA_DIRS or by
5021 symlinking them into the default locations.
5025 <sect3 id="message-bus-types-system">
5026 <title>System message bus</title>
5028 A computer may have a <firstterm>system message bus</firstterm>,
5029 accessible to all applications on the system. This message bus may be
5030 used to broadcast system events, such as adding new hardware devices,
5031 changes in the printer queue, and so forth.
5034 The address of the system message bus is given
5035 in the <literal>DBUS_SYSTEM_BUS_ADDRESS</literal> environment
5036 variable. If that variable is not set, applications should try
5037 to connect to the well-known address
5038 <literal>unix:path=/var/run/dbus/system_bus_socket</literal>.
5041 The D-Bus reference implementation actually honors the
5042 <literal>$(localstatedir)</literal> configure option
5043 for this address, on both client and server side.
5048 On Unix systems, the system bus should default to searching
5049 for .service files in
5050 <literal>/usr/local/share/dbus-1/system-services</literal>,
5051 <literal>/usr/share/dbus-1/system-services</literal> and
5052 <literal>/lib/dbus-1/system-services</literal>, with that order
5053 of precedence. It may also search other implementation-specific
5054 locations, but should not vary these locations based on environment
5058 The system bus is security-sensitive and is typically executed
5059 by an init system with a clean environment. Its launch helper
5060 process is particularly security-sensitive, and specifically
5061 clears its own environment.
5066 Software packages should install their system .service
5067 files to their configured
5068 <literal>${datadir}/dbus-1/system-services</literal>,
5069 where <literal>${datadir}</literal> is as defined by the GNU
5070 coding standards. System administrators can arrange
5071 for these service files to be read by editing the system bus'
5072 configuration file or by symlinking them into the default
5078 <sect2 id="message-bus-messages">
5079 <title>Message Bus Messages</title>
5081 The special message bus name <literal>org.freedesktop.DBus</literal>
5082 responds to a number of additional messages.
5085 <sect3 id="bus-messages-hello">
5086 <title><literal>org.freedesktop.DBus.Hello</literal></title>
5097 <entry>Argument</entry>
5099 <entry>Description</entry>
5105 <entry>STRING</entry>
5106 <entry>Unique name assigned to the connection</entry>
5113 Before an application is able to send messages to other applications
5114 it must send the <literal>org.freedesktop.DBus.Hello</literal> message
5115 to the message bus to obtain a unique name. If an application without
5116 a unique name tries to send a message to another application, or a
5117 message to the message bus itself that isn't the
5118 <literal>org.freedesktop.DBus.Hello</literal> message, it will be
5119 disconnected from the bus.
5122 There is no corresponding "disconnect" request; if a client wishes to
5123 disconnect from the bus, it simply closes the socket (or other
5124 communication channel).
5127 <sect3 id="bus-messages-list-names">
5128 <title><literal>org.freedesktop.DBus.ListNames</literal></title>
5132 ARRAY of STRING ListNames ()
5139 <entry>Argument</entry>
5141 <entry>Description</entry>
5147 <entry>ARRAY of STRING</entry>
5148 <entry>Array of strings where each string is a bus name</entry>
5155 Returns a list of all currently-owned names on the bus.
5158 <sect3 id="bus-messages-list-activatable-names">
5159 <title><literal>org.freedesktop.DBus.ListActivatableNames</literal></title>
5163 ARRAY of STRING ListActivatableNames ()
5170 <entry>Argument</entry>
5172 <entry>Description</entry>
5178 <entry>ARRAY of STRING</entry>
5179 <entry>Array of strings where each string is a bus name</entry>
5186 Returns a list of all names that can be activated on the bus.
5189 <sect3 id="bus-messages-name-exists">
5190 <title><literal>org.freedesktop.DBus.NameHasOwner</literal></title>
5194 BOOLEAN NameHasOwner (in STRING name)
5201 <entry>Argument</entry>
5203 <entry>Description</entry>
5209 <entry>STRING</entry>
5210 <entry>Name to check</entry>
5220 <entry>Argument</entry>
5222 <entry>Description</entry>
5228 <entry>BOOLEAN</entry>
5229 <entry>Return value, true if the name exists</entry>
5236 Checks if the specified name exists (currently has an owner).
5240 <sect3 id="bus-messages-name-owner-changed">
5241 <title><literal>org.freedesktop.DBus.NameOwnerChanged</literal></title>
5245 NameOwnerChanged (STRING name, STRING old_owner, STRING new_owner)
5252 <entry>Argument</entry>
5254 <entry>Description</entry>
5260 <entry>STRING</entry>
5261 <entry>Name with a new owner</entry>
5265 <entry>STRING</entry>
5266 <entry>Old owner or empty string if none</entry>
5270 <entry>STRING</entry>
5271 <entry>New owner or empty string if none</entry>
5278 This signal indicates that the owner of a name has changed.
5279 It's also the signal to use to detect the appearance of
5280 new names on the bus.
5283 <sect3 id="bus-messages-name-lost">
5284 <title><literal>org.freedesktop.DBus.NameLost</literal></title>
5288 NameLost (STRING name)
5295 <entry>Argument</entry>
5297 <entry>Description</entry>
5303 <entry>STRING</entry>
5304 <entry>Name which was lost</entry>
5311 This signal is sent to a specific application when it loses
5312 ownership of a name.
5316 <sect3 id="bus-messages-name-acquired">
5317 <title><literal>org.freedesktop.DBus.NameAcquired</literal></title>
5321 NameAcquired (STRING name)
5328 <entry>Argument</entry>
5330 <entry>Description</entry>
5336 <entry>STRING</entry>
5337 <entry>Name which was acquired</entry>
5344 This signal is sent to a specific application when it gains
5345 ownership of a name.
5349 <sect3 id="bus-messages-start-service-by-name">
5350 <title><literal>org.freedesktop.DBus.StartServiceByName</literal></title>
5354 UINT32 StartServiceByName (in STRING name, in UINT32 flags)
5361 <entry>Argument</entry>
5363 <entry>Description</entry>
5369 <entry>STRING</entry>
5370 <entry>Name of the service to start</entry>
5374 <entry>UINT32</entry>
5375 <entry>Flags (currently not used)</entry>
5385 <entry>Argument</entry>
5387 <entry>Description</entry>
5393 <entry>UINT32</entry>
5394 <entry>Return value</entry>
5399 Tries to launch the executable associated with a name. For more information, see <xref linkend="message-bus-starting-services"/>.
5403 The return value can be one of the following values:
5408 <entry>Identifier</entry>
5409 <entry>Value</entry>
5410 <entry>Description</entry>
5415 <entry>DBUS_START_REPLY_SUCCESS</entry>
5417 <entry>The service was successfully started.</entry>
5420 <entry>DBUS_START_REPLY_ALREADY_RUNNING</entry>
5422 <entry>A connection already owns the given name.</entry>
5431 <sect3 id="bus-messages-update-activation-environment">
5432 <title><literal>org.freedesktop.DBus.UpdateActivationEnvironment</literal></title>
5436 UpdateActivationEnvironment (in ARRAY of DICT<STRING,STRING> environment)
5443 <entry>Argument</entry>
5445 <entry>Description</entry>
5451 <entry>ARRAY of DICT<STRING,STRING></entry>
5452 <entry>Environment to add or update</entry>
5457 Normally, session bus activated services inherit the environment of the bus daemon. This method adds to or modifies that environment when activating services.
5460 Some bus instances, such as the standard system bus, may disable access to this method for some or all callers.
5463 Note, both the environment variable names and values must be valid UTF-8. There's no way to update the activation environment with data that is invalid UTF-8.
5468 <sect3 id="bus-messages-get-name-owner">
5469 <title><literal>org.freedesktop.DBus.GetNameOwner</literal></title>
5473 STRING GetNameOwner (in STRING name)
5480 <entry>Argument</entry>
5482 <entry>Description</entry>
5488 <entry>STRING</entry>
5489 <entry>Name to get the owner of</entry>
5499 <entry>Argument</entry>
5501 <entry>Description</entry>
5507 <entry>STRING</entry>
5508 <entry>Return value, a unique connection name</entry>
5513 Returns the unique connection name of the primary owner of the name
5514 given. If the requested name doesn't have an owner, returns a
5515 <literal>org.freedesktop.DBus.Error.NameHasNoOwner</literal> error.
5519 <sect3 id="bus-messages-get-connection-unix-user">
5520 <title><literal>org.freedesktop.DBus.GetConnectionUnixUser</literal></title>
5524 UINT32 GetConnectionUnixUser (in STRING bus_name)
5531 <entry>Argument</entry>
5533 <entry>Description</entry>
5539 <entry>STRING</entry>
5540 <entry>Unique or well-known bus name of the connection to
5541 query, such as <literal>:12.34</literal> or
5542 <literal>com.example.tea</literal></entry>
5552 <entry>Argument</entry>
5554 <entry>Description</entry>
5560 <entry>UINT32</entry>
5561 <entry>Unix user ID</entry>
5566 Returns the Unix user ID of the process connected to the server. If
5567 unable to determine it (for instance, because the process is not on the
5568 same machine as the bus daemon), an error is returned.
5572 <sect3 id="bus-messages-get-connection-unix-process-id">
5573 <title><literal>org.freedesktop.DBus.GetConnectionUnixProcessID</literal></title>
5577 UINT32 GetConnectionUnixProcessID (in STRING bus_name)
5584 <entry>Argument</entry>
5586 <entry>Description</entry>
5592 <entry>STRING</entry>
5593 <entry>Unique or well-known bus name of the connection to
5594 query, such as <literal>:12.34</literal> or
5595 <literal>com.example.tea</literal></entry>
5605 <entry>Argument</entry>
5607 <entry>Description</entry>
5613 <entry>UINT32</entry>
5614 <entry>Unix process id</entry>
5619 Returns the Unix process ID of the process connected to the server. If
5620 unable to determine it (for instance, because the process is not on the
5621 same machine as the bus daemon), an error is returned.
5625 <sect3 id="bus-messages-get-connection-credentials">
5626 <title><literal>org.freedesktop.DBus.GetConnectionCredentials</literal></title>
5630 DICT<STRING,VARIANT> GetConnectionCredentials (in STRING bus_name)
5637 <entry>Argument</entry>
5639 <entry>Description</entry>
5645 <entry>STRING</entry>
5646 <entry>Unique or well-known bus name of the connection to
5647 query, such as <literal>:12.34</literal> or
5648 <literal>com.example.tea</literal></entry>
5658 <entry>Argument</entry>
5660 <entry>Description</entry>
5666 <entry>DICT<STRING,VARIANT></entry>
5667 <entry>Credentials</entry>
5675 Returns as many credentials as possible for the process connected to
5676 the server. If unable to determine certain credentials (for instance,
5677 because the process is not on the same machine as the bus daemon,
5678 or because this version of the bus daemon does not support a
5679 particular security framework), or if the values of those credentials
5680 cannot be represented as documented here, then those credentials
5685 Keys in the returned dictionary not containing "." are defined
5686 by this specification. Bus daemon implementors supporting
5687 credentials frameworks not mentioned in this document should either
5688 contribute patches to this specification, or use keys containing
5689 "." and starting with a reversed domain name.
5695 <entry>Value type</entry>
5696 <entry>Value</entry>
5701 <entry>UnixUserID</entry>
5702 <entry>UINT32</entry>
5703 <entry>The numeric Unix user ID, as defined by POSIX</entry>
5706 <entry>ProcessID</entry>
5707 <entry>UINT32</entry>
5708 <entry>The numeric process ID, on platforms that have
5709 this concept. On Unix, this is the process ID defined by
5718 This method was added in D-Bus 1.7 to reduce the round-trips
5719 required to list a process's credentials. In older versions, calling
5720 this method will fail: applications should recover by using the
5721 separate methods such as
5722 <xref linkend="bus-messages-get-connection-unix-user"/>
5727 <sect3 id="bus-messages-get-adt-audit-session-data">
5728 <title><literal>org.freedesktop.DBus.GetAdtAuditSessionData</literal></title>
5732 ARRAY of BYTE GetAdtAuditSessionData (in STRING bus_name)
5739 <entry>Argument</entry>
5741 <entry>Description</entry>
5747 <entry>STRING</entry>
5748 <entry>Unique or well-known bus name of the connection to
5749 query, such as <literal>:12.34</literal> or
5750 <literal>com.example.tea</literal></entry>
5760 <entry>Argument</entry>
5762 <entry>Description</entry>
5768 <entry>ARRAY of BYTE</entry>
5769 <entry>auditing data as returned by
5770 adt_export_session_data()</entry>
5775 Returns auditing data used by Solaris ADT, in an unspecified
5776 binary format. If you know what this means, please contribute
5777 documentation via the D-Bus bug tracking system.
5778 This method is on the core DBus interface for historical reasons;
5779 the same information should be made available via
5780 <xref linkend="bus-messages-get-connection-credentials"/>
5785 <sect3 id="bus-messages-get-connection-selinux-security-context">
5786 <title><literal>org.freedesktop.DBus.GetConnectionSELinuxSecurityContext</literal></title>
5790 ARRAY of BYTE GetConnectionSELinuxSecurityContext (in STRING bus_name)
5797 <entry>Argument</entry>
5799 <entry>Description</entry>
5805 <entry>STRING</entry>
5806 <entry>Unique or well-known bus name of the connection to
5807 query, such as <literal>:12.34</literal> or
5808 <literal>com.example.tea</literal></entry>
5818 <entry>Argument</entry>
5820 <entry>Description</entry>
5826 <entry>ARRAY of BYTE</entry>
5827 <entry>some sort of string of bytes, not necessarily UTF-8,
5828 not including '\0'</entry>
5833 Returns the security context used by SELinux, in an unspecified
5834 format. If you know what this means, please contribute
5835 documentation via the D-Bus bug tracking system.
5836 This method is on the core DBus interface for historical reasons;
5837 the same information should be made available via
5838 <xref linkend="bus-messages-get-connection-credentials"/>
5844 <sect3 id="bus-messages-add-match">
5845 <title><literal>org.freedesktop.DBus.AddMatch</literal></title>
5849 AddMatch (in STRING rule)
5856 <entry>Argument</entry>
5858 <entry>Description</entry>
5864 <entry>STRING</entry>
5865 <entry>Match rule to add to the connection</entry>
5870 Adds a match rule to match messages going through the message bus (see <xref linkend='message-bus-routing-match-rules'/>).
5871 If the bus does not have enough resources the <literal>org.freedesktop.DBus.Error.OOM</literal>
5875 <sect3 id="bus-messages-remove-match">
5876 <title><literal>org.freedesktop.DBus.RemoveMatch</literal></title>
5880 RemoveMatch (in STRING rule)
5887 <entry>Argument</entry>
5889 <entry>Description</entry>
5895 <entry>STRING</entry>
5896 <entry>Match rule to remove from the connection</entry>
5901 Removes the first rule that matches (see <xref linkend='message-bus-routing-match-rules'/>).
5902 If the rule is not found the <literal>org.freedesktop.DBus.Error.MatchRuleNotFound</literal>
5907 <sect3 id="bus-messages-get-id">
5908 <title><literal>org.freedesktop.DBus.GetId</literal></title>
5912 GetId (out STRING id)
5919 <entry>Argument</entry>
5921 <entry>Description</entry>
5927 <entry>STRING</entry>
5928 <entry>Unique ID identifying the bus daemon</entry>
5933 Gets the unique ID of the bus. The unique ID here is shared among all addresses the
5934 bus daemon is listening on (TCP, UNIX domain socket, etc.) and its format is described in
5935 <xref linkend="uuids"/>. Each address the bus is listening on also has its own unique
5936 ID, as described in <xref linkend="addresses"/>. The per-bus and per-address IDs are not related.
5937 There is also a per-machine ID, described in <xref linkend="standard-interfaces-peer"/> and returned
5938 by org.freedesktop.DBus.Peer.GetMachineId().
5939 For a desktop session bus, the bus ID can be used as a way to uniquely identify a user's session.
5947 <appendix id="implementation-notes">
5948 <title>Implementation notes</title>
5949 <sect1 id="implementation-notes-subsection">
5957 <glossary><title>Glossary</title>
5959 This glossary defines some of the terms used in this specification.
5962 <glossentry id="term-bus-name"><glossterm>Bus Name</glossterm>
5965 The message bus maintains an association between names and
5966 connections. (Normally, there's one connection per application.) A
5967 bus name is simply an identifier used to locate connections. For
5968 example, the hypothetical <literal>com.yoyodyne.Screensaver</literal>
5969 name might be used to send a message to a screensaver from Yoyodyne
5970 Corporation. An application is said to <firstterm>own</firstterm> a
5971 name if the message bus has associated the application's connection
5972 with the name. Names may also have <firstterm>queued
5973 owners</firstterm> (see <xref linkend="term-queued-owner"/>).
5974 The bus assigns a unique name to each connection,
5975 see <xref linkend="term-unique-name"/>. Other names
5976 can be thought of as "well-known names" and are
5977 used to find applications that offer specific functionality.
5981 See <xref linkend="message-protocol-names-bus"/> for details of
5982 the syntax and naming conventions for bus names.
5987 <glossentry id="term-message"><glossterm>Message</glossterm>
5990 A message is the atomic unit of communication via the D-Bus
5991 protocol. It consists of a <firstterm>header</firstterm> and a
5992 <firstterm>body</firstterm>; the body is made up of
5993 <firstterm>arguments</firstterm>.
5998 <glossentry id="term-message-bus"><glossterm>Message Bus</glossterm>
6001 The message bus is a special application that forwards
6002 or routes messages between a group of applications
6003 connected to the message bus. It also manages
6004 <firstterm>names</firstterm> used for routing
6010 <glossentry id="term-name"><glossterm>Name</glossterm>
6013 See <xref linkend="term-bus-name"/>. "Name" may
6014 also be used to refer to some of the other names
6015 in D-Bus, such as interface names.
6020 <glossentry id="namespace"><glossterm>Namespace</glossterm>
6023 Used to prevent collisions when defining new interfaces, bus names
6024 etc. The convention used is the same one Java uses for defining
6025 classes: a reversed domain name.
6026 See <xref linkend="message-protocol-names-bus"/>,
6027 <xref linkend="message-protocol-names-interface"/>,
6028 <xref linkend="message-protocol-names-error"/>,
6029 <xref linkend="message-protocol-marshaling-object-path"/>.
6034 <glossentry id="term-object"><glossterm>Object</glossterm>
6037 Each application contains <firstterm>objects</firstterm>, which have
6038 <firstterm>interfaces</firstterm> and
6039 <firstterm>methods</firstterm>. Objects are referred to by a name,
6040 called a <firstterm>path</firstterm>.
6045 <glossentry id="one-to-one"><glossterm>One-to-One</glossterm>
6048 An application talking directly to another application, without going
6049 through a message bus. One-to-one connections may be "peer to peer" or
6050 "client to server." The D-Bus protocol has no concept of client
6051 vs. server after a connection has authenticated; the flow of messages
6052 is symmetrical (full duplex).
6057 <glossentry id="term-path"><glossterm>Path</glossterm>
6060 Object references (object names) in D-Bus are organized into a
6061 filesystem-style hierarchy, so each object is named by a path. As in
6062 LDAP, there's no difference between "files" and "directories"; a path
6063 can refer to an object, while still having child objects below it.
6068 <glossentry id="term-queued-owner"><glossterm>Queued Name Owner</glossterm>
6071 Each bus name has a primary owner; messages sent to the name go to the
6072 primary owner. However, certain names also maintain a queue of
6073 secondary owners "waiting in the wings." If the primary owner releases
6074 the name, then the first secondary owner in the queue automatically
6075 becomes the new owner of the name.
6080 <glossentry id="term-service"><glossterm>Service</glossterm>
6083 A service is an executable that can be launched by the bus daemon.
6084 Services normally guarantee some particular features, for example they
6085 may guarantee that they will request a specific name such as
6086 "com.example.Screensaver", have a singleton object
6087 "/com/example/Application", and that object will implement the
6088 interface "com.example.Screensaver.Control".
6093 <glossentry id="term-service-description-files"><glossterm>Service Description Files</glossterm>
6096 ".service files" tell the bus about service applications that can be
6097 launched (see <xref linkend="term-service"/>). Most importantly they
6098 provide a mapping from bus names to services that will request those
6099 names when they start up.
6104 <glossentry id="term-unique-name"><glossterm>Unique Connection Name</glossterm>
6107 The special name automatically assigned to each connection by the
6108 message bus. This name will never change owner, and will be unique
6109 (never reused during the lifetime of the message bus).
6110 It will begin with a ':' character.
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