1 <?xml version="1.0" standalone="no" ?>
2 <!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
3 "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd"
8 <title>D-Bus Specification</title>
9 <releaseinfo>Version 0.17</releaseinfo>
10 <date>(not final)</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>
55 <revnumber>current</revnumber>
56 <date><ulink url='http://cgit.freedesktop.org/dbus/dbus/log/doc/dbus-specification.xml'>commit log</ulink></date>
57 <authorinitials></authorinitials>
58 <revremark></revremark>
61 <revnumber>0.16</revnumber>
62 <date>11 April 2011</date>
63 <authorinitials></authorinitials>
64 <revremark>add path_namespace, arg0namespace; argNpath matches object
68 <revnumber>0.15</revnumber>
69 <date>3 November 2010</date>
70 <authorinitials></authorinitials>
71 <revremark></revremark>
74 <revnumber>0.14</revnumber>
75 <date>12 May 2010</date>
76 <authorinitials></authorinitials>
77 <revremark></revremark>
80 <revnumber>0.13</revnumber>
81 <date>23 Dezember 2009</date>
82 <authorinitials></authorinitials>
83 <revremark></revremark>
86 <revnumber>0.12</revnumber>
87 <date>7 November, 2006</date>
88 <authorinitials></authorinitials>
89 <revremark></revremark>
92 <revnumber>0.11</revnumber>
93 <date>6 February 2005</date>
94 <authorinitials></authorinitials>
95 <revremark></revremark>
98 <revnumber>0.10</revnumber>
99 <date>28 January 2005</date>
100 <authorinitials></authorinitials>
101 <revremark></revremark>
104 <revnumber>0.9</revnumber>
105 <date>7 Januar 2005</date>
106 <authorinitials></authorinitials>
107 <revremark></revremark>
110 <revnumber>0.8</revnumber>
111 <date>06 September 2003</date>
112 <authorinitials></authorinitials>
113 <revremark>First released document.</revremark>
118 <sect1 id="introduction">
119 <title>Introduction</title>
121 D-Bus is a system for low-latency, low-overhead, easy to use
122 interprocess communication (IPC). In more detail:
126 D-Bus is <emphasis>low-latency</emphasis> because it is designed
127 to avoid round trips and allow asynchronous operation, much like
133 D-Bus is <emphasis>low-overhead</emphasis> because it uses a
134 binary protocol, and does not have to convert to and from a text
135 format such as XML. Because D-Bus is intended for potentially
136 high-resolution same-machine IPC, not primarily for Internet IPC,
137 this is an interesting optimization.
142 D-Bus is <emphasis>easy to use</emphasis> because it works in terms
143 of <firstterm>messages</firstterm> rather than byte streams, and
144 automatically handles a lot of the hard IPC issues. Also, the D-Bus
145 library is designed to be wrapped in a way that lets developers use
146 their framework's existing object/type system, rather than learning
147 a new one specifically for IPC.
154 The base D-Bus protocol is a one-to-one (peer-to-peer or client-server)
155 protocol, specified in <xref linkend="message-protocol"/>. That is, it is
156 a system for one application to talk to a single other
157 application. However, the primary intended application of the protocol is the
158 D-Bus <firstterm>message bus</firstterm>, specified in <xref
159 linkend="message-bus"/>. The message bus is a special application that
160 accepts connections from multiple other applications, and forwards
165 Uses of D-Bus include notification of system changes (notification of when
166 a camera is plugged in to a computer, or a new version of some software
167 has been installed), or desktop interoperability, for example a file
168 monitoring service or a configuration service.
172 D-Bus is designed for two specific use cases:
176 A "system bus" for notifications from the system to user sessions,
177 and to allow the system to request input from user sessions.
182 A "session bus" used to implement desktop environments such as
187 D-Bus is not intended to be a generic IPC system for any possible
188 application, and intentionally omits many features found in other
189 IPC systems for this reason.
193 At the same time, the bus daemons offer a number of features not found in
194 other IPC systems, such as single-owner "bus names" (similar to X
195 selections), on-demand startup of services, and security policies.
196 In many ways, these features are the primary motivation for developing
197 D-Bus; other systems would have sufficed if IPC were the only goal.
201 D-Bus may turn out to be useful in unanticipated applications, but future
202 versions of this spec and the reference implementation probably will not
203 incorporate features that interfere with the core use cases.
207 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
208 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
209 document are to be interpreted as described in RFC 2119. However, the
210 document could use a serious audit to be sure it makes sense to do
211 so. Also, they are not capitalized.
214 <sect2 id="stability">
215 <title>Protocol and Specification Stability</title>
217 The D-Bus protocol is frozen (only compatible extensions are allowed) as
218 of November 8, 2006. However, this specification could still use a fair
219 bit of work to make interoperable reimplementation possible without
220 reference to the D-Bus reference implementation. Thus, this
221 specification is not marked 1.0. To mark it 1.0, we'd like to see
222 someone invest significant effort in clarifying the specification
223 language, and growing the specification to cover more aspects of the
224 reference implementation's behavior.
227 Until this work is complete, any attempt to reimplement D-Bus will
228 probably require looking at the reference implementation and/or asking
229 questions on the D-Bus mailing list about intended behavior.
230 Questions on the list are very welcome.
233 Nonetheless, this document should be a useful starting point and is
234 to our knowledge accurate, though incomplete.
240 <sect1 id="message-protocol">
241 <title>Message Protocol</title>
244 A <firstterm>message</firstterm> consists of a
245 <firstterm>header</firstterm> and a <firstterm>body</firstterm>. If you
246 think of a message as a package, the header is the address, and the body
247 contains the package contents. The message delivery system uses the header
248 information to figure out where to send the message and how to interpret
249 it; the recipient interprets the body of the message.
253 The body of the message is made up of zero or more
254 <firstterm>arguments</firstterm>, which are typed values, such as an
255 integer or a byte array.
259 Both header and body use the same type system and format for
260 serializing data. Each type of value has a wire format.
261 Converting a value from some other representation into the wire
262 format is called <firstterm>marshaling</firstterm> and converting
263 it back from the wire format is <firstterm>unmarshaling</firstterm>.
266 <sect2 id="message-protocol-signatures">
267 <title>Type Signatures</title>
270 The D-Bus protocol does not include type tags in the marshaled data; a
271 block of marshaled values must have a known <firstterm>type
272 signature</firstterm>. The type signature is made up of <firstterm>type
273 codes</firstterm>. A type code is an ASCII character representing the
274 type of a value. Because ASCII characters are used, the type signature
275 will always form a valid ASCII string. A simple string compare
276 determines whether two type signatures are equivalent.
280 As a simple example, the type code for 32-bit integer (<literal>INT32</literal>) is
281 the ASCII character 'i'. So the signature for a block of values
282 containing a single <literal>INT32</literal> would be:
286 A block of values containing two <literal>INT32</literal> would have this signature:
293 All <firstterm>basic</firstterm> types work like
294 <literal>INT32</literal> in this example. To marshal and unmarshal
295 basic types, you simply read one value from the data
296 block corresponding to each type code in the signature.
297 In addition to basic types, there are four <firstterm>container</firstterm>
298 types: <literal>STRUCT</literal>, <literal>ARRAY</literal>, <literal>VARIANT</literal>,
299 and <literal>DICT_ENTRY</literal>.
303 <literal>STRUCT</literal> has a type code, ASCII character 'r', but this type
304 code does not appear in signatures. Instead, ASCII characters
305 '(' and ')' are used to mark the beginning and end of the struct.
306 So for example, a struct containing two integers would have this
311 Structs can be nested, so for example a struct containing
312 an integer and another struct:
316 The value block storing that struct would contain three integers; the
317 type signature allows you to distinguish "(i(ii))" from "((ii)i)" or
322 The <literal>STRUCT</literal> type code 'r' is not currently used in the D-Bus protocol,
323 but is useful in code that implements the protocol. This type code
324 is specified to allow such code to interoperate in non-protocol contexts.
328 Empty structures are not allowed; there must be at least one
329 type code between the parentheses.
333 <literal>ARRAY</literal> has ASCII character 'a' as type code. The array type code must be
334 followed by a <firstterm>single complete type</firstterm>. The single
335 complete type following the array is the type of each array element. So
336 the simple example is:
340 which is an array of 32-bit integers. But an array can be of any type,
341 such as this array-of-struct-with-two-int32-fields:
345 Or this array of array of integer:
352 The phrase <firstterm>single complete type</firstterm> deserves some
353 definition. A single complete type is a basic type code, a variant type code,
354 an array with its element type, or a struct with its fields.
355 So the following signatures are not single complete types:
365 And the following signatures contain multiple complete types:
375 Note however that a single complete type may <emphasis>contain</emphasis>
376 multiple other single complete types.
380 <literal>VARIANT</literal> has ASCII character 'v' as its type code. A marshaled value of
381 type <literal>VARIANT</literal> will have the signature of a single complete type as part
382 of the <emphasis>value</emphasis>. This signature will be followed by a
383 marshaled value of that type.
387 A <literal>DICT_ENTRY</literal> works exactly like a struct, but rather
388 than parentheses it uses curly braces, and it has more restrictions.
389 The restrictions are: it occurs only as an array element type; it has
390 exactly two single complete types inside the curly braces; the first
391 single complete type (the "key") must be a basic type rather than a
392 container type. Implementations must not accept dict entries outside of
393 arrays, must not accept dict entries with zero, one, or more than two
394 fields, and must not accept dict entries with non-basic-typed keys. A
395 dict entry is always a key-value pair.
399 The first field in the <literal>DICT_ENTRY</literal> is always the key.
400 A message is considered corrupt if the same key occurs twice in the same
401 array of <literal>DICT_ENTRY</literal>. However, for performance reasons
402 implementations are not required to reject dicts with duplicate keys.
406 In most languages, an array of dict entry would be represented as a
407 map, hash table, or dict object.
411 The following table summarizes the D-Bus types.
416 <entry>Conventional Name</entry>
418 <entry>Description</entry>
423 <entry><literal>INVALID</literal></entry>
424 <entry>0 (ASCII NUL)</entry>
425 <entry>Not a valid type code, used to terminate signatures</entry>
427 <entry><literal>BYTE</literal></entry>
428 <entry>121 (ASCII 'y')</entry>
429 <entry>8-bit unsigned integer</entry>
431 <entry><literal>BOOLEAN</literal></entry>
432 <entry>98 (ASCII 'b')</entry>
433 <entry>Boolean value, 0 is <literal>FALSE</literal> and 1 is <literal>TRUE</literal>. Everything else is invalid.</entry>
435 <entry><literal>INT16</literal></entry>
436 <entry>110 (ASCII 'n')</entry>
437 <entry>16-bit signed integer</entry>
439 <entry><literal>UINT16</literal></entry>
440 <entry>113 (ASCII 'q')</entry>
441 <entry>16-bit unsigned integer</entry>
443 <entry><literal>INT32</literal></entry>
444 <entry>105 (ASCII 'i')</entry>
445 <entry>32-bit signed integer</entry>
447 <entry><literal>UINT32</literal></entry>
448 <entry>117 (ASCII 'u')</entry>
449 <entry>32-bit unsigned integer</entry>
451 <entry><literal>INT64</literal></entry>
452 <entry>120 (ASCII 'x')</entry>
453 <entry>64-bit signed integer</entry>
455 <entry><literal>UINT64</literal></entry>
456 <entry>116 (ASCII 't')</entry>
457 <entry>64-bit unsigned integer</entry>
459 <entry><literal>DOUBLE</literal></entry>
460 <entry>100 (ASCII 'd')</entry>
461 <entry>IEEE 754 double</entry>
463 <entry><literal>STRING</literal></entry>
464 <entry>115 (ASCII 's')</entry>
465 <entry>UTF-8 string (<emphasis>must</emphasis> be valid UTF-8). Must be nul terminated and contain no other nul bytes.</entry>
467 <entry><literal>OBJECT_PATH</literal></entry>
468 <entry>111 (ASCII 'o')</entry>
469 <entry>Name of an object instance</entry>
471 <entry><literal>SIGNATURE</literal></entry>
472 <entry>103 (ASCII 'g')</entry>
473 <entry>A type signature</entry>
475 <entry><literal>ARRAY</literal></entry>
476 <entry>97 (ASCII 'a')</entry>
479 <entry><literal>STRUCT</literal></entry>
480 <entry>114 (ASCII 'r'), 40 (ASCII '('), 41 (ASCII ')')</entry>
481 <entry>Struct; type code 114 'r' is reserved for use in
482 bindings and implementations to represent the general
483 concept of a struct, and must not appear in signatures
484 used on D-Bus.</entry>
486 <entry><literal>VARIANT</literal></entry>
487 <entry>118 (ASCII 'v') </entry>
488 <entry>Variant type (the type of the value is part of the value itself)</entry>
490 <entry><literal>DICT_ENTRY</literal></entry>
491 <entry>101 (ASCII 'e'), 123 (ASCII '{'), 125 (ASCII '}') </entry>
492 <entry>Entry in a dict or map (array of key-value pairs).
493 Type code 101 'e' is reserved for use in bindings and
494 implementations to represent the general concept of a
495 dict or dict-entry, and must not appear in signatures
496 used on D-Bus.</entry>
498 <entry><literal>UNIX_FD</literal></entry>
499 <entry>104 (ASCII 'h')</entry>
500 <entry>Unix file descriptor</entry>
503 <entry>(reserved)</entry>
504 <entry>109 (ASCII 'm')</entry>
505 <entry>Reserved for <ulink
506 url="https://bugs.freedesktop.org/show_bug.cgi?id=27857">a
507 'maybe' type compatible with the one in GVariant</ulink>,
508 and must not appear in signatures used on D-Bus until
509 specified here</entry>
512 <entry>(reserved)</entry>
513 <entry>42 (ASCII '*')</entry>
514 <entry>Reserved for use in bindings/implementations to
515 represent any <firstterm>single complete type</firstterm>,
516 and must not appear in signatures used on D-Bus.</entry>
519 <entry>(reserved)</entry>
520 <entry>63 (ASCII '?')</entry>
521 <entry>Reserved for use in bindings/implementations to
522 represent any <firstterm>basic type</firstterm>, and must
523 not appear in signatures used on D-Bus.</entry>
526 <entry>(reserved)</entry>
527 <entry>64 (ASCII '@'), 38 (ASCII '&'),
528 94 (ASCII '^')</entry>
529 <entry>Reserved for internal use by bindings/implementations,
530 and must not appear in signatures used on D-Bus.
531 GVariant uses these type-codes to encode calling
541 <sect2 id="message-protocol-marshaling">
542 <title>Marshaling (Wire Format)</title>
545 Given a type signature, a block of bytes can be converted into typed
546 values. This section describes the format of the block of bytes. Byte
547 order and alignment issues are handled uniformly for all D-Bus types.
551 A block of bytes has an associated byte order. The byte order
552 has to be discovered in some way; for D-Bus messages, the
553 byte order is part of the message header as described in
554 <xref linkend="message-protocol-messages"/>. For now, assume
555 that the byte order is known to be either little endian or big
560 Each value in a block of bytes is aligned "naturally," for example
561 4-byte values are aligned to a 4-byte boundary, and 8-byte values to an
562 8-byte boundary. To properly align a value, <firstterm>alignment
563 padding</firstterm> may be necessary. The alignment padding must always
564 be the minimum required padding to properly align the following value;
565 and it must always be made up of nul bytes. The alignment padding must
566 not be left uninitialized (it can't contain garbage), and more padding
567 than required must not be used.
571 Given all this, the types are marshaled on the wire as follows:
576 <entry>Conventional Name</entry>
577 <entry>Encoding</entry>
578 <entry>Alignment</entry>
583 <entry><literal>INVALID</literal></entry>
584 <entry>Not applicable; cannot be marshaled.</entry>
587 <entry><literal>BYTE</literal></entry>
588 <entry>A single 8-bit byte.</entry>
591 <entry><literal>BOOLEAN</literal></entry>
592 <entry>As for <literal>UINT32</literal>, but only 0 and 1 are valid values.</entry>
595 <entry><literal>INT16</literal></entry>
596 <entry>16-bit signed integer in the message's byte order.</entry>
599 <entry><literal>UINT16</literal></entry>
600 <entry>16-bit unsigned integer in the message's byte order.</entry>
603 <entry><literal>INT32</literal></entry>
604 <entry>32-bit signed integer in the message's byte order.</entry>
607 <entry><literal>UINT32</literal></entry>
608 <entry>32-bit unsigned integer in the message's byte order.</entry>
611 <entry><literal>INT64</literal></entry>
612 <entry>64-bit signed integer in the message's byte order.</entry>
615 <entry><literal>UINT64</literal></entry>
616 <entry>64-bit unsigned integer in the message's byte order.</entry>
619 <entry><literal>DOUBLE</literal></entry>
620 <entry>64-bit IEEE 754 double in the message's byte order.</entry>
623 <entry><literal>STRING</literal></entry>
624 <entry>A <literal>UINT32</literal> indicating the string's
625 length in bytes excluding its terminating nul, followed by
626 non-nul string data of the given length, followed by a terminating nul
633 <entry><literal>OBJECT_PATH</literal></entry>
634 <entry>Exactly the same as <literal>STRING</literal> except the
635 content must be a valid object path (see below).
641 <entry><literal>SIGNATURE</literal></entry>
642 <entry>The same as <literal>STRING</literal> except the length is a single
643 byte (thus signatures have a maximum length of 255)
644 and the content must be a valid signature (see below).
650 <entry><literal>ARRAY</literal></entry>
652 A <literal>UINT32</literal> giving the length of the array data in bytes, followed by
653 alignment padding to the alignment boundary of the array element type,
654 followed by each array element. The array length is from the
655 end of the alignment padding to the end of the last element,
656 i.e. it does not include the padding after the length,
657 or any padding after the last element.
658 Arrays have a maximum length defined to be 2 to the 26th power or
659 67108864. Implementations must not send or accept arrays exceeding this
666 <entry><literal>STRUCT</literal></entry>
668 A struct must start on an 8-byte boundary regardless of the
669 type of the struct fields. The struct value consists of each
670 field marshaled in sequence starting from that 8-byte
677 <entry><literal>VARIANT</literal></entry>
679 A variant type has a marshaled
680 <literal>SIGNATURE</literal> followed by a marshaled
681 value with the type given in the signature. Unlike
682 a message signature, the variant signature can
683 contain only a single complete type. So "i", "ai"
684 or "(ii)" is OK, but "ii" is not. Use of variants may not
685 cause a total message depth to be larger than 64, including
686 other container types such as structures.
689 1 (alignment of the signature)
692 <entry><literal>DICT_ENTRY</literal></entry>
700 <entry><literal>UNIX_FD</literal></entry>
701 <entry>32-bit unsigned integer in the message's byte
702 order. The actual file descriptors need to be
703 transferred out-of-band via some platform specific
704 mechanism. On the wire, values of this type store the index to the
705 file descriptor in the array of file descriptors that
706 accompany the message.</entry>
714 <sect3 id="message-protocol-marshaling-object-path">
715 <title>Valid Object Paths</title>
718 An object path is a name used to refer to an object instance.
719 Conceptually, each participant in a D-Bus message exchange may have
720 any number of object instances (think of C++ or Java objects) and each
721 such instance will have a path. Like a filesystem, the object
722 instances in an application form a hierarchical tree.
726 The following rules define a valid object path. Implementations must
727 not send or accept messages with invalid object paths.
731 The path may be of any length.
736 The path must begin with an ASCII '/' (integer 47) character,
737 and must consist of elements separated by slash characters.
742 Each element must only contain the ASCII characters
748 No element may be the empty string.
753 Multiple '/' characters cannot occur in sequence.
758 A trailing '/' character is not allowed unless the
759 path is the root path (a single '/' character).
768 <sect3 id="message-protocol-marshaling-signature">
769 <title>Valid Signatures</title>
771 An implementation must not send or accept invalid signatures.
772 Valid signatures will conform to the following rules:
776 The signature ends with a nul byte.
781 The signature is a list of single complete types.
782 Arrays must have element types, and structs must
783 have both open and close parentheses.
788 Only type codes and open and close parentheses are
789 allowed in the signature. The <literal>STRUCT</literal> type code
790 is not allowed in signatures, because parentheses
796 The maximum depth of container type nesting is 32 array type
797 codes and 32 open parentheses. This implies that the maximum
798 total depth of recursion is 64, for an "array of array of array
799 of ... struct of struct of struct of ..." where there are 32
805 The maximum length of a signature is 255.
810 Signatures must be nul-terminated.
819 <sect2 id="message-protocol-messages">
820 <title>Message Format</title>
823 A message consists of a header and a body. The header is a block of
824 values with a fixed signature and meaning. The body is a separate block
825 of values, with a signature specified in the header.
829 The length of the header must be a multiple of 8, allowing the body to
830 begin on an 8-byte boundary when storing the entire message in a single
831 buffer. If the header does not naturally end on an 8-byte boundary
832 up to 7 bytes of nul-initialized alignment padding must be added.
836 The message body need not end on an 8-byte boundary.
840 The maximum length of a message, including header, header alignment padding,
841 and body is 2 to the 27th power or 134217728. Implementations must not
842 send or accept messages exceeding this size.
846 The signature of the header is:
850 Written out more readably, this is:
852 BYTE, BYTE, BYTE, BYTE, UINT32, UINT32, ARRAY of STRUCT of (BYTE,VARIANT)
857 These values have the following meanings:
863 <entry>Description</entry>
868 <entry>1st <literal>BYTE</literal></entry>
869 <entry>Endianness flag; ASCII 'l' for little-endian
870 or ASCII 'B' for big-endian. Both header and body are
871 in this endianness.</entry>
874 <entry>2nd <literal>BYTE</literal></entry>
875 <entry><firstterm>Message type</firstterm>. Unknown types must be ignored.
876 Currently-defined types are described below.
880 <entry>3rd <literal>BYTE</literal></entry>
881 <entry>Bitwise OR of flags. Unknown flags
882 must be ignored. Currently-defined flags are described below.
886 <entry>4th <literal>BYTE</literal></entry>
887 <entry>Major protocol version of the sending application. If
888 the major protocol version of the receiving application does not
889 match, the applications will not be able to communicate and the
890 D-Bus connection must be disconnected. The major protocol
891 version for this version of the specification is 1.
895 <entry>1st <literal>UINT32</literal></entry>
896 <entry>Length in bytes of the message body, starting
897 from the end of the header. The header ends after
898 its alignment padding to an 8-boundary.
902 <entry>2nd <literal>UINT32</literal></entry>
903 <entry>The serial of this message, used as a cookie
904 by the sender to identify the reply corresponding
905 to this request. This must not be zero.
909 <entry><literal>ARRAY</literal> of <literal>STRUCT</literal> of (<literal>BYTE</literal>,<literal>VARIANT</literal>)</entry>
910 <entry>An array of zero or more <firstterm>header
911 fields</firstterm> where the byte is the field code, and the
912 variant is the field value. The message type determines
913 which fields are required.
921 <firstterm>Message types</firstterm> that can appear in the second byte
927 <entry>Conventional name</entry>
928 <entry>Decimal value</entry>
929 <entry>Description</entry>
934 <entry><literal>INVALID</literal></entry>
936 <entry>This is an invalid type.</entry>
939 <entry><literal>METHOD_CALL</literal></entry>
941 <entry>Method call.</entry>
944 <entry><literal>METHOD_RETURN</literal></entry>
946 <entry>Method reply with returned data.</entry>
949 <entry><literal>ERROR</literal></entry>
951 <entry>Error reply. If the first argument exists and is a
952 string, it is an error message.</entry>
955 <entry><literal>SIGNAL</literal></entry>
957 <entry>Signal emission.</entry>
964 Flags that can appear in the third byte of the header:
969 <entry>Conventional name</entry>
970 <entry>Hex value</entry>
971 <entry>Description</entry>
976 <entry><literal>NO_REPLY_EXPECTED</literal></entry>
978 <entry>This message does not expect method return replies or
979 error replies; the reply can be omitted as an
980 optimization. However, it is compliant with this specification
981 to return the reply despite this flag and the only harm
982 from doing so is extra network traffic.
986 <entry><literal>NO_AUTO_START</literal></entry>
988 <entry>The bus must not launch an owner
989 for the destination name in response to this message.
997 <sect3 id="message-protocol-header-fields">
998 <title>Header Fields</title>
1001 The array at the end of the header contains <firstterm>header
1002 fields</firstterm>, where each field is a 1-byte field code followed
1003 by a field value. A header must contain the required header fields for
1004 its message type, and zero or more of any optional header
1005 fields. Future versions of this protocol specification may add new
1006 fields. Implementations must ignore fields they do not
1007 understand. Implementations must not invent their own header fields;
1008 only changes to this specification may introduce new header fields.
1012 Again, if an implementation sees a header field code that it does not
1013 expect, it must ignore that field, as it will be part of a new
1014 (but compatible) version of this specification. This also applies
1015 to known header fields appearing in unexpected messages, for
1016 example: if a signal has a reply serial it must be ignored
1017 even though it has no meaning as of this version of the spec.
1021 However, implementations must not send or accept known header fields
1022 with the wrong type stored in the field value. So for example a
1023 message with an <literal>INTERFACE</literal> field of type
1024 <literal>UINT32</literal> would be considered corrupt.
1028 Here are the currently-defined header fields:
1033 <entry>Conventional Name</entry>
1034 <entry>Decimal Code</entry>
1036 <entry>Required In</entry>
1037 <entry>Description</entry>
1042 <entry><literal>INVALID</literal></entry>
1045 <entry>not allowed</entry>
1046 <entry>Not a valid field name (error if it appears in a message)</entry>
1049 <entry><literal>PATH</literal></entry>
1051 <entry><literal>OBJECT_PATH</literal></entry>
1052 <entry><literal>METHOD_CALL</literal>, <literal>SIGNAL</literal></entry>
1053 <entry>The object to send a call to,
1054 or the object a signal is emitted from.
1056 <literal>/org/freedesktop/DBus/Local</literal> is reserved;
1057 implementations should not send messages with this path,
1058 and the reference implementation of the bus daemon will
1059 disconnect any application that attempts to do so.
1063 <entry><literal>INTERFACE</literal></entry>
1065 <entry><literal>STRING</literal></entry>
1066 <entry><literal>SIGNAL</literal></entry>
1068 The interface to invoke a method call on, or
1069 that a signal is emitted from. Optional for
1070 method calls, required for signals.
1071 The special interface
1072 <literal>org.freedesktop.DBus.Local</literal> is reserved;
1073 implementations should not send messages with this
1074 interface, and the reference implementation of the bus
1075 daemon will disconnect any application that attempts to
1080 <entry><literal>MEMBER</literal></entry>
1082 <entry><literal>STRING</literal></entry>
1083 <entry><literal>METHOD_CALL</literal>, <literal>SIGNAL</literal></entry>
1084 <entry>The member, either the method name or signal name.</entry>
1087 <entry><literal>ERROR_NAME</literal></entry>
1089 <entry><literal>STRING</literal></entry>
1090 <entry><literal>ERROR</literal></entry>
1091 <entry>The name of the error that occurred, for errors</entry>
1094 <entry><literal>REPLY_SERIAL</literal></entry>
1096 <entry><literal>UINT32</literal></entry>
1097 <entry><literal>ERROR</literal>, <literal>METHOD_RETURN</literal></entry>
1098 <entry>The serial number of the message this message is a reply
1099 to. (The serial number is the second <literal>UINT32</literal> in the header.)</entry>
1102 <entry><literal>DESTINATION</literal></entry>
1104 <entry><literal>STRING</literal></entry>
1105 <entry>optional</entry>
1106 <entry>The name of the connection this message is intended for.
1107 Only used in combination with the message bus, see
1108 <xref linkend="message-bus"/>.</entry>
1111 <entry><literal>SENDER</literal></entry>
1113 <entry><literal>STRING</literal></entry>
1114 <entry>optional</entry>
1115 <entry>Unique name of the sending connection.
1116 The message bus fills in this field so it is reliable; the field is
1117 only meaningful in combination with the message bus.</entry>
1120 <entry><literal>SIGNATURE</literal></entry>
1122 <entry><literal>SIGNATURE</literal></entry>
1123 <entry>optional</entry>
1124 <entry>The signature of the message body.
1125 If omitted, it is assumed to be the
1126 empty signature "" (i.e. the body must be 0-length).</entry>
1129 <entry><literal>UNIX_FDS</literal></entry>
1131 <entry><literal>UINT32</literal></entry>
1132 <entry>optional</entry>
1133 <entry>The number of Unix file descriptors that
1134 accompany the message. If omitted, it is assumed
1135 that no Unix file descriptors accompany the
1136 message. The actual file descriptors need to be
1137 transferred via platform specific mechanism
1138 out-of-band. They must be sent at the same time as
1139 part of the message itself. They may not be sent
1140 before the first byte of the message itself is
1141 transferred or after the last byte of the message
1151 <sect2 id="message-protocol-names">
1152 <title>Valid Names</title>
1154 The various names in D-Bus messages have some restrictions.
1157 There is a <firstterm>maximum name length</firstterm>
1158 of 255 which applies to bus names, interfaces, and members.
1160 <sect3 id="message-protocol-names-interface">
1161 <title>Interface names</title>
1163 Interfaces have names with type <literal>STRING</literal>, meaning that
1164 they must be valid UTF-8. However, there are also some
1165 additional restrictions that apply to interface names
1168 <listitem><para>Interface names are composed of 1 or more elements separated by
1169 a period ('.') character. All elements must contain at least
1173 <listitem><para>Each element must only contain the ASCII characters
1174 "[A-Z][a-z][0-9]_" and must not begin with a digit.
1178 <listitem><para>Interface names must contain at least one '.' (period)
1179 character (and thus at least two elements).
1182 <listitem><para>Interface names must not begin with a '.' (period) character.</para></listitem>
1183 <listitem><para>Interface names must not exceed the maximum name length.</para></listitem>
1188 Interface names should start with the reversed DNS domain name of
1189 the author of the interface (in lower-case), like interface names
1190 in Java. It is conventional for the rest of the interface name
1191 to consist of words run together, with initial capital letters
1192 on all words ("CamelCase"). Several levels of hierarchy can be used.
1193 It is also a good idea to include the major version of the interface
1194 in the name, and increment it if incompatible changes are made;
1195 this way, a single object can implement several versions of an
1196 interface in parallel, if necessary.
1200 For instance, if the owner of <literal>example.com</literal> is
1201 developing a D-Bus API for a music player, they might define
1202 interfaces called <literal>com.example.MusicPlayer1</literal>,
1203 <literal>com.example.MusicPlayer1.Track</literal> and
1204 <literal>com.example.MusicPlayer1.Seekable</literal>.
1208 D-Bus does not distinguish between the concepts that would be
1209 called classes and interfaces in Java: either can be identified on
1210 D-Bus by an interface name.
1213 <sect3 id="message-protocol-names-bus">
1214 <title>Bus names</title>
1216 Connections have one or more bus names associated with them.
1217 A connection has exactly one bus name that is a <firstterm>unique
1218 connection name</firstterm>. The unique connection name remains
1219 with the connection for its entire lifetime.
1220 A bus name is of type <literal>STRING</literal>,
1221 meaning that it must be valid UTF-8. However, there are also
1222 some additional restrictions that apply to bus names
1225 <listitem><para>Bus names that start with a colon (':')
1226 character are unique connection names. Other bus names
1227 are called <firstterm>well-known bus names</firstterm>.
1230 <listitem><para>Bus names are composed of 1 or more elements separated by
1231 a period ('.') character. All elements must contain at least
1235 <listitem><para>Each element must only contain the ASCII characters
1236 "[A-Z][a-z][0-9]_-". Only elements that are part of a unique
1237 connection name may begin with a digit, elements in
1238 other bus names must not begin with a digit.
1242 <listitem><para>Bus names must contain at least one '.' (period)
1243 character (and thus at least two elements).
1246 <listitem><para>Bus names must not begin with a '.' (period) character.</para></listitem>
1247 <listitem><para>Bus names must not exceed the maximum name length.</para></listitem>
1251 Note that the hyphen ('-') character is allowed in bus names but
1252 not in interface names.
1256 Like <link linkend="message-protocol-names-interface">interface
1257 names</link>, well-known bus names should start with the
1258 reversed DNS domain name of the author of the interface (in
1259 lower-case), and it is conventional for the rest of the well-known
1260 bus name to consist of words run together, with initial
1261 capital letters. As with interface names, including a version
1262 number in well-known bus names is a good idea; it's possible to
1263 have the well-known bus name for more than one version
1264 simultaneously if backwards compatibility is required.
1268 If a well-known bus name implies the presence of a "main" interface,
1269 that "main" interface is often given the same name as
1270 the well-known bus name, and situated at the corresponding object
1271 path. For instance, if the owner of <literal>example.com</literal>
1272 is developing a D-Bus API for a music player, they might define
1273 that any application that takes the well-known name
1274 <literal>com.example.MusicPlayer1</literal> should have an object
1275 at the object path <literal>/com/example/MusicPlayer1</literal>
1276 which implements the interface
1277 <literal>com.example.MusicPlayer1</literal>.
1280 <sect3 id="message-protocol-names-member">
1281 <title>Member names</title>
1283 Member (i.e. method or signal) names:
1285 <listitem><para>Must only contain the ASCII characters
1286 "[A-Z][a-z][0-9]_" and may not begin with a
1287 digit.</para></listitem>
1288 <listitem><para>Must not contain the '.' (period) character.</para></listitem>
1289 <listitem><para>Must not exceed the maximum name length.</para></listitem>
1290 <listitem><para>Must be at least 1 byte in length.</para></listitem>
1294 <sect3 id="message-protocol-names-error">
1295 <title>Error names</title>
1297 Error names have the same restrictions as interface names.
1302 <sect2 id="message-protocol-types">
1303 <title>Message Types</title>
1305 Each of the message types (<literal>METHOD_CALL</literal>, <literal>METHOD_RETURN</literal>, <literal>ERROR</literal>, and
1306 <literal>SIGNAL</literal>) has its own expected usage conventions and header fields.
1307 This section describes these conventions.
1309 <sect3 id="message-protocol-types-method">
1310 <title>Method Calls</title>
1312 Some messages invoke an operation on a remote object. These are
1313 called method call messages and have the type tag <literal>METHOD_CALL</literal>. Such
1314 messages map naturally to methods on objects in a typical program.
1317 A method call message is required to have a <literal>MEMBER</literal> header field
1318 indicating the name of the method. Optionally, the message has an
1319 <literal>INTERFACE</literal> field giving the interface the method is a part of. In the
1320 absence of an <literal>INTERFACE</literal> field, if two interfaces on the same object have
1321 a method with the same name, it is undefined which of the two methods
1322 will be invoked. Implementations may also choose to return an error in
1323 this ambiguous case. However, if a method name is unique
1324 implementations must not require an interface field.
1327 Method call messages also include a <literal>PATH</literal> field
1328 indicating the object to invoke the method on. If the call is passing
1329 through a message bus, the message will also have a
1330 <literal>DESTINATION</literal> field giving the name of the connection
1331 to receive the message.
1334 When an application handles a method call message, it is required to
1335 return a reply. The reply is identified by a <literal>REPLY_SERIAL</literal> header field
1336 indicating the serial number of the <literal>METHOD_CALL</literal> being replied to. The
1337 reply can have one of two types; either <literal>METHOD_RETURN</literal> or <literal>ERROR</literal>.
1340 If the reply has type <literal>METHOD_RETURN</literal>, the arguments to the reply message
1341 are the return value(s) or "out parameters" of the method call.
1342 If the reply has type <literal>ERROR</literal>, then an "exception" has been thrown,
1343 and the call fails; no return value will be provided. It makes
1344 no sense to send multiple replies to the same method call.
1347 Even if a method call has no return values, a <literal>METHOD_RETURN</literal>
1348 reply is required, so the caller will know the method
1349 was successfully processed.
1352 The <literal>METHOD_RETURN</literal> or <literal>ERROR</literal> reply message must have the <literal>REPLY_SERIAL</literal>
1356 If a <literal>METHOD_CALL</literal> message has the flag <literal>NO_REPLY_EXPECTED</literal>,
1357 then as an optimization the application receiving the method
1358 call may choose to omit the reply message (regardless of
1359 whether the reply would have been <literal>METHOD_RETURN</literal> or <literal>ERROR</literal>).
1360 However, it is also acceptable to ignore the <literal>NO_REPLY_EXPECTED</literal>
1361 flag and reply anyway.
1364 Unless a message has the flag <literal>NO_AUTO_START</literal>, if the
1365 destination name does not exist then a program to own the destination
1366 name will be started before the message is delivered. The message
1367 will be held until the new program is successfully started or has
1368 failed to start; in case of failure, an error will be returned. This
1369 flag is only relevant in the context of a message bus, it is ignored
1370 during one-to-one communication with no intermediate bus.
1372 <sect4 id="message-protocol-types-method-apis">
1373 <title>Mapping method calls to native APIs</title>
1375 APIs for D-Bus may map method calls to a method call in a specific
1376 programming language, such as C++, or may map a method call written
1377 in an IDL to a D-Bus message.
1380 In APIs of this nature, arguments to a method are often termed "in"
1381 (which implies sent in the <literal>METHOD_CALL</literal>), or "out" (which implies
1382 returned in the <literal>METHOD_RETURN</literal>). Some APIs such as CORBA also have
1383 "inout" arguments, which are both sent and received, i.e. the caller
1384 passes in a value which is modified. Mapped to D-Bus, an "inout"
1385 argument is equivalent to an "in" argument, followed by an "out"
1386 argument. You can't pass things "by reference" over the wire, so
1387 "inout" is purely an illusion of the in-process API.
1390 Given a method with zero or one return values, followed by zero or more
1391 arguments, where each argument may be "in", "out", or "inout", the
1392 caller constructs a message by appending each "in" or "inout" argument,
1393 in order. "out" arguments are not represented in the caller's message.
1396 The recipient constructs a reply by appending first the return value
1397 if any, then each "out" or "inout" argument, in order.
1398 "in" arguments are not represented in the reply message.
1401 Error replies are normally mapped to exceptions in languages that have
1405 In converting from native APIs to D-Bus, it is perhaps nice to
1406 map D-Bus naming conventions ("FooBar") to native conventions
1407 such as "fooBar" or "foo_bar" automatically. This is OK
1408 as long as you can say that the native API is one that
1409 was specifically written for D-Bus. It makes the most sense
1410 when writing object implementations that will be exported
1411 over the bus. Object proxies used to invoke remote D-Bus
1412 objects probably need the ability to call any D-Bus method,
1413 and thus a magic name mapping like this could be a problem.
1416 This specification doesn't require anything of native API bindings;
1417 the preceding is only a suggested convention for consistency
1423 <sect3 id="message-protocol-types-signal">
1424 <title>Signal Emission</title>
1426 Unlike method calls, signal emissions have no replies.
1427 A signal emission is simply a single message of type <literal>SIGNAL</literal>.
1428 It must have three header fields: <literal>PATH</literal> giving the object
1429 the signal was emitted from, plus <literal>INTERFACE</literal> and <literal>MEMBER</literal> giving
1430 the fully-qualified name of the signal. The <literal>INTERFACE</literal> header is required
1431 for signals, though it is optional for method calls.
1435 <sect3 id="message-protocol-types-errors">
1436 <title>Errors</title>
1438 Messages of type <literal>ERROR</literal> are most commonly replies
1439 to a <literal>METHOD_CALL</literal>, but may be returned in reply
1440 to any kind of message. The message bus for example
1441 will return an <literal>ERROR</literal> in reply to a signal emission if
1442 the bus does not have enough memory to send the signal.
1445 An <literal>ERROR</literal> may have any arguments, but if the first
1446 argument is a <literal>STRING</literal>, it must be an error message.
1447 The error message may be logged or shown to the user
1452 <sect3 id="message-protocol-types-notation">
1453 <title>Notation in this document</title>
1455 This document uses a simple pseudo-IDL to describe particular method
1456 calls and signals. Here is an example of a method call:
1458 org.freedesktop.DBus.StartServiceByName (in STRING name, in UINT32 flags,
1459 out UINT32 resultcode)
1461 This means <literal>INTERFACE</literal> = org.freedesktop.DBus, <literal>MEMBER</literal> = StartServiceByName,
1462 <literal>METHOD_CALL</literal> arguments are <literal>STRING</literal> and <literal>UINT32</literal>, <literal>METHOD_RETURN</literal> argument
1463 is <literal>UINT32</literal>. Remember that the <literal>MEMBER</literal> field can't contain any '.' (period)
1464 characters so it's known that the last part of the name in
1465 the "IDL" is the member name.
1468 In C++ that might end up looking like this:
1470 unsigned int org::freedesktop::DBus::StartServiceByName (const char *name,
1471 unsigned int flags);
1473 or equally valid, the return value could be done as an argument:
1475 void org::freedesktop::DBus::StartServiceByName (const char *name,
1477 unsigned int *resultcode);
1479 It's really up to the API designer how they want to make
1480 this look. You could design an API where the namespace wasn't used
1481 in C++, using STL or Qt, using varargs, or whatever you wanted.
1484 Signals are written as follows:
1486 org.freedesktop.DBus.NameLost (STRING name)
1488 Signals don't specify "in" vs. "out" because only
1489 a single direction is possible.
1492 It isn't especially encouraged to use this lame pseudo-IDL in actual
1493 API implementations; you might use the native notation for the
1494 language you're using, or you might use COM or CORBA IDL, for example.
1499 <sect2 id="message-protocol-handling-invalid">
1500 <title>Invalid Protocol and Spec Extensions</title>
1503 For security reasons, the D-Bus protocol should be strictly parsed and
1504 validated, with the exception of defined extension points. Any invalid
1505 protocol or spec violations should result in immediately dropping the
1506 connection without notice to the other end. Exceptions should be
1507 carefully considered, e.g. an exception may be warranted for a
1508 well-understood idiosyncrasy of a widely-deployed implementation. In
1509 cases where the other end of a connection is 100% trusted and known to
1510 be friendly, skipping validation for performance reasons could also make
1511 sense in certain cases.
1515 Generally speaking violations of the "must" requirements in this spec
1516 should be considered possible attempts to exploit security, and violations
1517 of the "should" suggestions should be considered legitimate (though perhaps
1518 they should generate an error in some cases).
1522 The following extension points are built in to D-Bus on purpose and must
1523 not be treated as invalid protocol. The extension points are intended
1524 for use by future versions of this spec, they are not intended for third
1525 parties. At the moment, the only way a third party could extend D-Bus
1526 without breaking interoperability would be to introduce a way to negotiate new
1527 feature support as part of the auth protocol, using EXTENSION_-prefixed
1528 commands. There is not yet a standard way to negotiate features.
1532 In the authentication protocol (see <xref linkend="auth-protocol"/>) unknown
1533 commands result in an ERROR rather than a disconnect. This enables
1534 future extensions to the protocol. Commands starting with EXTENSION_ are
1535 reserved for third parties.
1540 The authentication protocol supports pluggable auth mechanisms.
1545 The address format (see <xref linkend="addresses"/>) supports new
1551 Messages with an unknown type (something other than
1552 <literal>METHOD_CALL</literal>, <literal>METHOD_RETURN</literal>,
1553 <literal>ERROR</literal>, <literal>SIGNAL</literal>) are ignored.
1554 Unknown-type messages must still be well-formed in the same way
1555 as the known messages, however. They still have the normal
1561 Header fields with an unknown or unexpected field code must be ignored,
1562 though again they must still be well-formed.
1567 New standard interfaces (with new methods and signals) can of course be added.
1577 <sect1 id="auth-protocol">
1578 <title>Authentication Protocol</title>
1580 Before the flow of messages begins, two applications must
1581 authenticate. A simple plain-text protocol is used for
1582 authentication; this protocol is a SASL profile, and maps fairly
1583 directly from the SASL specification. The message encoding is
1584 NOT used here, only plain text messages.
1587 In examples, "C:" and "S:" indicate lines sent by the client and
1588 server respectively.
1590 <sect2 id="auth-protocol-overview">
1591 <title>Protocol Overview</title>
1593 The protocol is a line-based protocol, where each line ends with
1594 \r\n. Each line begins with an all-caps ASCII command name containing
1595 only the character range [A-Z_], a space, then any arguments for the
1596 command, then the \r\n ending the line. The protocol is
1597 case-sensitive. All bytes must be in the ASCII character set.
1599 Commands from the client to the server are as follows:
1602 <listitem><para>AUTH [mechanism] [initial-response]</para></listitem>
1603 <listitem><para>CANCEL</para></listitem>
1604 <listitem><para>BEGIN</para></listitem>
1605 <listitem><para>DATA <data in hex encoding></para></listitem>
1606 <listitem><para>ERROR [human-readable error explanation]</para></listitem>
1607 <listitem><para>NEGOTIATE_UNIX_FD</para></listitem>
1610 From server to client are as follows:
1613 <listitem><para>REJECTED <space-separated list of mechanism names></para></listitem>
1614 <listitem><para>OK <GUID in hex></para></listitem>
1615 <listitem><para>DATA <data in hex encoding></para></listitem>
1616 <listitem><para>ERROR</para></listitem>
1617 <listitem><para>AGREE_UNIX_FD</para></listitem>
1621 Unofficial extensions to the command set must begin with the letters
1622 "EXTENSION_", to avoid conflicts with future official commands.
1623 For example, "EXTENSION_COM_MYDOMAIN_DO_STUFF".
1626 <sect2 id="auth-nul-byte">
1627 <title>Special credentials-passing nul byte</title>
1629 Immediately after connecting to the server, the client must send a
1630 single nul byte. This byte may be accompanied by credentials
1631 information on some operating systems that use sendmsg() with
1632 SCM_CREDS or SCM_CREDENTIALS to pass credentials over UNIX domain
1633 sockets. However, the nul byte must be sent even on other kinds of
1634 socket, and even on operating systems that do not require a byte to be
1635 sent in order to transmit credentials. The text protocol described in
1636 this document begins after the single nul byte. If the first byte
1637 received from the client is not a nul byte, the server may disconnect
1641 A nul byte in any context other than the initial byte is an error;
1642 the protocol is ASCII-only.
1645 The credentials sent along with the nul byte may be used with the
1646 SASL mechanism EXTERNAL.
1649 <sect2 id="auth-command-auth">
1650 <title>AUTH command</title>
1652 If an AUTH command has no arguments, it is a request to list
1653 available mechanisms. The server must respond with a REJECTED
1654 command listing the mechanisms it understands, or with an error.
1657 If an AUTH command specifies a mechanism, and the server supports
1658 said mechanism, the server should begin exchanging SASL
1659 challenge-response data with the client using DATA commands.
1662 If the server does not support the mechanism given in the AUTH
1663 command, it must send either a REJECTED command listing the mechanisms
1664 it does support, or an error.
1667 If the [initial-response] argument is provided, it is intended for use
1668 with mechanisms that have no initial challenge (or an empty initial
1669 challenge), as if it were the argument to an initial DATA command. If
1670 the selected mechanism has an initial challenge and [initial-response]
1671 was provided, the server should reject authentication by sending
1675 If authentication succeeds after exchanging DATA commands,
1676 an OK command must be sent to the client.
1679 The first octet received by the server after the \r\n of the BEGIN
1680 command from the client must be the first octet of the
1681 authenticated/encrypted stream of D-Bus messages.
1684 If BEGIN is received by the server, the first octet received
1685 by the client after the \r\n of the OK command must be the
1686 first octet of the authenticated/encrypted stream of D-Bus
1690 <sect2 id="auth-command-cancel">
1691 <title>CANCEL Command</title>
1693 At any time up to sending the BEGIN command, the client may send a
1694 CANCEL command. On receiving the CANCEL command, the server must
1695 send a REJECTED command and abort the current authentication
1699 <sect2 id="auth-command-data">
1700 <title>DATA Command</title>
1702 The DATA command may come from either client or server, and simply
1703 contains a hex-encoded block of data to be interpreted
1704 according to the SASL mechanism in use.
1707 Some SASL mechanisms support sending an "empty string";
1708 FIXME we need some way to do this.
1711 <sect2 id="auth-command-begin">
1712 <title>BEGIN Command</title>
1714 The BEGIN command acknowledges that the client has received an
1715 OK command from the server, and that the stream of messages
1719 The first octet received by the server after the \r\n of the BEGIN
1720 command from the client must be the first octet of the
1721 authenticated/encrypted stream of D-Bus messages.
1724 <sect2 id="auth-command-rejected">
1725 <title>REJECTED Command</title>
1727 The REJECTED command indicates that the current authentication
1728 exchange has failed, and further exchange of DATA is inappropriate.
1729 The client would normally try another mechanism, or try providing
1730 different responses to challenges.
1732 Optionally, the REJECTED command has a space-separated list of
1733 available auth mechanisms as arguments. If a server ever provides
1734 a list of supported mechanisms, it must provide the same list
1735 each time it sends a REJECTED message. Clients are free to
1736 ignore all lists received after the first.
1739 <sect2 id="auth-command-ok">
1740 <title>OK Command</title>
1742 The OK command indicates that the client has been
1743 authenticated. The client may now proceed with negotiating
1744 Unix file descriptor passing. To do that it shall send
1745 NEGOTIATE_UNIX_FD to the server.
1748 Otherwise, the client must respond to the OK command by
1749 sending a BEGIN command, followed by its stream of messages,
1750 or by disconnecting. The server must not accept additional
1751 commands using this protocol after the BEGIN command has been
1752 received. Further communication will be a stream of D-Bus
1753 messages (optionally encrypted, as negotiated) rather than
1757 If a client sends BEGIN the first octet received by the client
1758 after the \r\n of the OK command must be the first octet of
1759 the authenticated/encrypted stream of D-Bus messages.
1762 The OK command has one argument, which is the GUID of the server.
1763 See <xref linkend="addresses"/> for more on server GUIDs.
1766 <sect2 id="auth-command-error">
1767 <title>ERROR Command</title>
1769 The ERROR command indicates that either server or client did not
1770 know a command, does not accept the given command in the current
1771 context, or did not understand the arguments to the command. This
1772 allows the protocol to be extended; a client or server can send a
1773 command present or permitted only in new protocol versions, and if
1774 an ERROR is received instead of an appropriate response, fall back
1775 to using some other technique.
1778 If an ERROR is sent, the server or client that sent the
1779 error must continue as if the command causing the ERROR had never been
1780 received. However, the the server or client receiving the error
1781 should try something other than whatever caused the error;
1782 if only canceling/rejecting the authentication.
1785 If the D-Bus protocol changes incompatibly at some future time,
1786 applications implementing the new protocol would probably be able to
1787 check for support of the new protocol by sending a new command and
1788 receiving an ERROR from applications that don't understand it. Thus the
1789 ERROR feature of the auth protocol is an escape hatch that lets us
1790 negotiate extensions or changes to the D-Bus protocol in the future.
1793 <sect2 id="auth-command-negotiate-unix-fd">
1794 <title>NEGOTIATE_UNIX_FD Command</title>
1796 The NEGOTIATE_UNIX_FD command indicates that the client
1797 supports Unix file descriptor passing. This command may only
1798 be sent after the connection is authenticated, i.e. after OK
1799 was received by the client. This command may only be sent on
1800 transports that support Unix file descriptor passing.
1803 On receiving NEGOTIATE_UNIX_FD the server must respond with
1804 either AGREE_UNIX_FD or ERROR. It shall respond the former if
1805 the transport chosen supports Unix file descriptor passing and
1806 the server supports this feature. It shall respond the latter
1807 if the transport does not support Unix file descriptor
1808 passing, the server does not support this feature, or the
1809 server decides not to enable file descriptor passing due to
1810 security or other reasons.
1813 <sect2 id="auth-command-agree-unix-fd">
1814 <title>AGREE_UNIX_FD Command</title>
1816 The AGREE_UNIX_FD command indicates that the server supports
1817 Unix file descriptor passing. This command may only be sent
1818 after the connection is authenticated, and the client sent
1819 NEGOTIATE_UNIX_FD to enable Unix file descriptor passing. This
1820 command may only be sent on transports that support Unix file
1824 On receiving AGREE_UNIX_FD the client must respond with BEGIN,
1825 followed by its stream of messages, or by disconnecting. The
1826 server must not accept additional commands using this protocol
1827 after the BEGIN command has been received. Further
1828 communication will be a stream of D-Bus messages (optionally
1829 encrypted, as negotiated) rather than this protocol.
1832 <sect2 id="auth-command-future">
1833 <title>Future Extensions</title>
1835 Future extensions to the authentication and negotiation
1836 protocol are possible. For that new commands may be
1837 introduced. If a client or server receives an unknown command
1838 it shall respond with ERROR and not consider this fatal. New
1839 commands may be introduced both before, and after
1840 authentication, i.e. both before and after the OK command.
1843 <sect2 id="auth-examples">
1844 <title>Authentication examples</title>
1848 <title>Example of successful magic cookie authentication</title>
1850 (MAGIC_COOKIE is a made up mechanism)
1852 C: AUTH MAGIC_COOKIE 3138363935333137393635383634
1858 <title>Example of finding out mechanisms then picking one</title>
1861 S: REJECTED KERBEROS_V4 SKEY
1862 C: AUTH SKEY 7ab83f32ee
1863 S: DATA 8799cabb2ea93e
1864 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f
1870 <title>Example of client sends unknown command then falls back to regular auth</title>
1874 C: AUTH MAGIC_COOKIE 3736343435313230333039
1880 <title>Example of server doesn't support initial auth mechanism</title>
1882 C: AUTH MAGIC_COOKIE 3736343435313230333039
1883 S: REJECTED KERBEROS_V4 SKEY
1884 C: AUTH SKEY 7ab83f32ee
1885 S: DATA 8799cabb2ea93e
1886 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f
1892 <title>Example of wrong password or the like followed by successful retry</title>
1894 C: AUTH MAGIC_COOKIE 3736343435313230333039
1895 S: REJECTED KERBEROS_V4 SKEY
1896 C: AUTH SKEY 7ab83f32ee
1897 S: DATA 8799cabb2ea93e
1898 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f
1900 C: AUTH SKEY 7ab83f32ee
1901 S: DATA 8799cabb2ea93e
1902 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f
1908 <title>Example of skey cancelled and restarted</title>
1910 C: AUTH MAGIC_COOKIE 3736343435313230333039
1911 S: REJECTED KERBEROS_V4 SKEY
1912 C: AUTH SKEY 7ab83f32ee
1913 S: DATA 8799cabb2ea93e
1916 C: AUTH SKEY 7ab83f32ee
1917 S: DATA 8799cabb2ea93e
1918 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f
1924 <title>Example of successful magic cookie authentication with successful negotiation of Unix FD passing</title>
1926 (MAGIC_COOKIE is a made up mechanism)
1928 C: AUTH MAGIC_COOKIE 3138363935333137393635383634
1930 C: NEGOTIATE_UNIX_FD
1936 <title>Example of successful magic cookie authentication with unsuccessful negotiation of Unix FD passing</title>
1938 (MAGIC_COOKIE is a made up mechanism)
1940 C: AUTH MAGIC_COOKIE 3138363935333137393635383634
1942 C: NEGOTIATE_UNIX_FD
1949 <sect2 id="auth-states">
1950 <title>Authentication state diagrams</title>
1953 This section documents the auth protocol in terms of
1954 a state machine for the client and the server. This is
1955 probably the most robust way to implement the protocol.
1958 <sect3 id="auth-states-client">
1959 <title>Client states</title>
1962 To more precisely describe the interaction between the
1963 protocol state machine and the authentication mechanisms the
1964 following notation is used: MECH(CHALL) means that the
1965 server challenge CHALL was fed to the mechanism MECH, which
1971 CONTINUE(RESP) means continue the auth conversation
1972 and send RESP as the response to the server;
1978 OK(RESP) means that after sending RESP to the server
1979 the client side of the auth conversation is finished
1980 and the server should return "OK";
1986 ERROR means that CHALL was invalid and could not be
1992 Both RESP and CHALL may be empty.
1996 The Client starts by getting an initial response from the
1997 default mechanism and sends AUTH MECH RESP, or AUTH MECH if
1998 the mechanism did not provide an initial response. If the
1999 mechanism returns CONTINUE, the client starts in state
2000 <emphasis>WaitingForData</emphasis>, if the mechanism
2001 returns OK the client starts in state
2002 <emphasis>WaitingForOK</emphasis>.
2006 The client should keep track of available mechanisms and
2007 which it mechanisms it has already attempted. This list is
2008 used to decide which AUTH command to send. When the list is
2009 exhausted, the client should give up and close the
2014 <title><emphasis>WaitingForData</emphasis></title>
2022 MECH(CHALL) returns CONTINUE(RESP) → send
2024 <emphasis>WaitingForData</emphasis>
2028 MECH(CHALL) returns OK(RESP) → send DATA
2029 RESP, goto <emphasis>WaitingForOK</emphasis>
2033 MECH(CHALL) returns ERROR → send ERROR
2034 [msg], goto <emphasis>WaitingForData</emphasis>
2042 Receive REJECTED [mechs] →
2043 send AUTH [next mech], goto
2044 WaitingForData or <emphasis>WaitingForOK</emphasis>
2049 Receive ERROR → send
2051 <emphasis>WaitingForReject</emphasis>
2056 Receive OK → send
2057 BEGIN, terminate auth
2058 conversation, authenticated
2063 Receive anything else → send
2065 <emphasis>WaitingForData</emphasis>
2073 <title><emphasis>WaitingForOK</emphasis></title>
2078 Receive OK → send BEGIN, terminate auth
2079 conversation, <emphasis>authenticated</emphasis>
2084 Receive REJECT [mechs] → send AUTH [next mech],
2085 goto <emphasis>WaitingForData</emphasis> or
2086 <emphasis>WaitingForOK</emphasis>
2092 Receive DATA → send CANCEL, goto
2093 <emphasis>WaitingForReject</emphasis>
2099 Receive ERROR → send CANCEL, goto
2100 <emphasis>WaitingForReject</emphasis>
2106 Receive anything else → send ERROR, goto
2107 <emphasis>WaitingForOK</emphasis>
2115 <title><emphasis>WaitingForReject</emphasis></title>
2120 Receive REJECT [mechs] → send AUTH [next mech],
2121 goto <emphasis>WaitingForData</emphasis> or
2122 <emphasis>WaitingForOK</emphasis>
2128 Receive anything else → terminate auth
2129 conversation, disconnect
2138 <sect3 id="auth-states-server">
2139 <title>Server states</title>
2142 For the server MECH(RESP) means that the client response
2143 RESP was fed to the the mechanism MECH, which returns one of
2148 CONTINUE(CHALL) means continue the auth conversation and
2149 send CHALL as the challenge to the client;
2155 OK means that the client has been successfully
2162 REJECT means that the client failed to authenticate or
2163 there was an error in RESP.
2168 The server starts out in state
2169 <emphasis>WaitingForAuth</emphasis>. If the client is
2170 rejected too many times the server must disconnect the
2175 <title><emphasis>WaitingForAuth</emphasis></title>
2181 Receive AUTH → send REJECTED [mechs], goto
2182 <emphasis>WaitingForAuth</emphasis>
2188 Receive AUTH MECH RESP
2192 MECH not valid mechanism → send REJECTED
2194 <emphasis>WaitingForAuth</emphasis>
2198 MECH(RESP) returns CONTINUE(CHALL) → send
2200 <emphasis>WaitingForData</emphasis>
2204 MECH(RESP) returns OK → send OK, goto
2205 <emphasis>WaitingForBegin</emphasis>
2209 MECH(RESP) returns REJECT → send REJECTED
2211 <emphasis>WaitingForAuth</emphasis>
2219 Receive BEGIN → terminate
2220 auth conversation, disconnect
2226 Receive ERROR → send REJECTED [mechs], goto
2227 <emphasis>WaitingForAuth</emphasis>
2233 Receive anything else → send
2235 <emphasis>WaitingForAuth</emphasis>
2244 <title><emphasis>WaitingForData</emphasis></title>
2252 MECH(RESP) returns CONTINUE(CHALL) → send
2254 <emphasis>WaitingForData</emphasis>
2258 MECH(RESP) returns OK → send OK, goto
2259 <emphasis>WaitingForBegin</emphasis>
2263 MECH(RESP) returns REJECT → send REJECTED
2265 <emphasis>WaitingForAuth</emphasis>
2273 Receive BEGIN → terminate auth conversation,
2280 Receive CANCEL → send REJECTED [mechs], goto
2281 <emphasis>WaitingForAuth</emphasis>
2287 Receive ERROR → send REJECTED [mechs], goto
2288 <emphasis>WaitingForAuth</emphasis>
2294 Receive anything else → send ERROR, goto
2295 <emphasis>WaitingForData</emphasis>
2303 <title><emphasis>WaitingForBegin</emphasis></title>
2308 Receive BEGIN → terminate auth conversation,
2309 client authenticated
2315 Receive CANCEL → send REJECTED [mechs], goto
2316 <emphasis>WaitingForAuth</emphasis>
2322 Receive ERROR → send REJECTED [mechs], goto
2323 <emphasis>WaitingForAuth</emphasis>
2329 Receive anything else → send ERROR, goto
2330 <emphasis>WaitingForBegin</emphasis>
2340 <sect2 id="auth-mechanisms">
2341 <title>Authentication mechanisms</title>
2343 This section describes some new authentication mechanisms.
2344 D-Bus also allows any standard SASL mechanism of course.
2346 <sect3 id="auth-mechanisms-sha">
2347 <title>DBUS_COOKIE_SHA1</title>
2349 The DBUS_COOKIE_SHA1 mechanism is designed to establish that a client
2350 has the ability to read a private file owned by the user being
2351 authenticated. If the client can prove that it has access to a secret
2352 cookie stored in this file, then the client is authenticated.
2353 Thus the security of DBUS_COOKIE_SHA1 depends on a secure home
2357 Throughout this description, "hex encoding" must output the digits
2358 from a to f in lower-case; the digits A to F must not be used
2359 in the DBUS_COOKIE_SHA1 mechanism.
2362 Authentication proceeds as follows:
2366 The client sends the username it would like to authenticate
2372 The server sends the name of its "cookie context" (see below); a
2373 space character; the integer ID of the secret cookie the client
2374 must demonstrate knowledge of; a space character; then a
2375 randomly-generated challenge string, all of this hex-encoded into
2381 The client locates the cookie and generates its own
2382 randomly-generated challenge string. The client then concatenates
2383 the server's decoded challenge, a ":" character, its own challenge,
2384 another ":" character, and the cookie. It computes the SHA-1 hash
2385 of this composite string as a hex digest. It concatenates the
2386 client's challenge string, a space character, and the SHA-1 hex
2387 digest, hex-encodes the result and sends it back to the server.
2392 The server generates the same concatenated string used by the
2393 client and computes its SHA-1 hash. It compares the hash with
2394 the hash received from the client; if the two hashes match, the
2395 client is authenticated.
2401 Each server has a "cookie context," which is a name that identifies a
2402 set of cookies that apply to that server. A sample context might be
2403 "org_freedesktop_session_bus". Context names must be valid ASCII,
2404 nonzero length, and may not contain the characters slash ("/"),
2405 backslash ("\"), space (" "), newline ("\n"), carriage return ("\r"),
2406 tab ("\t"), or period ("."). There is a default context,
2407 "org_freedesktop_general" that's used by servers that do not specify
2411 Cookies are stored in a user's home directory, in the directory
2412 <filename>~/.dbus-keyrings/</filename>. This directory must
2413 not be readable or writable by other users. If it is,
2414 clients and servers must ignore it. The directory
2415 contains cookie files named after the cookie context.
2418 A cookie file contains one cookie per line. Each line
2419 has three space-separated fields:
2423 The cookie ID number, which must be a non-negative integer and
2424 may not be used twice in the same file.
2429 The cookie's creation time, in UNIX seconds-since-the-epoch
2435 The cookie itself, a hex-encoded random block of bytes. The cookie
2436 may be of any length, though obviously security increases
2437 as the length increases.
2443 Only server processes modify the cookie file.
2444 They must do so with this procedure:
2448 Create a lockfile name by appending ".lock" to the name of the
2449 cookie file. The server should attempt to create this file
2450 using <literal>O_CREAT | O_EXCL</literal>. If file creation
2451 fails, the lock fails. Servers should retry for a reasonable
2452 period of time, then they may choose to delete an existing lock
2453 to keep users from having to manually delete a stale
2454 lock. <footnote><para>Lockfiles are used instead of real file
2455 locking <literal>fcntl()</literal> because real locking
2456 implementations are still flaky on network
2457 filesystems.</para></footnote>
2462 Once the lockfile has been created, the server loads the cookie
2463 file. It should then delete any cookies that are old (the
2464 timeout can be fairly short), or more than a reasonable
2465 time in the future (so that cookies never accidentally
2466 become permanent, if the clock was set far into the future
2467 at some point). If no recent keys remain, the
2468 server may generate a new key.
2473 The pruned and possibly added-to cookie file
2474 must be resaved atomically (using a temporary
2475 file which is rename()'d).
2480 The lock must be dropped by deleting the lockfile.
2486 Clients need not lock the file in order to load it,
2487 because servers are required to save the file atomically.
2492 <sect1 id="addresses">
2493 <title>Server Addresses</title>
2495 Server addresses consist of a transport name followed by a colon, and
2496 then an optional, comma-separated list of keys and values in the form key=value.
2497 Each value is escaped.
2501 <programlisting>unix:path=/tmp/dbus-test</programlisting>
2502 Which is the address to a unix socket with the path /tmp/dbus-test.
2505 Value escaping is similar to URI escaping but simpler.
2509 The set of optionally-escaped bytes is:
2510 <literal>[0-9A-Za-z_-/.\]</literal>. To escape, each
2511 <emphasis>byte</emphasis> (note, not character) which is not in the
2512 set of optionally-escaped bytes must be replaced with an ASCII
2513 percent (<literal>%</literal>) and the value of the byte in hex.
2514 The hex value must always be two digits, even if the first digit is
2515 zero. The optionally-escaped bytes may be escaped if desired.
2520 To unescape, append each byte in the value; if a byte is an ASCII
2521 percent (<literal>%</literal>) character then append the following
2522 hex value instead. It is an error if a <literal>%</literal> byte
2523 does not have two hex digits following. It is an error if a
2524 non-optionally-escaped byte is seen unescaped.
2528 The set of optionally-escaped bytes is intended to preserve address
2529 readability and convenience.
2533 A server may specify a key-value pair with the key <literal>guid</literal>
2534 and the value a hex-encoded 16-byte sequence. <xref linkend="uuids"/>
2535 describes the format of the <literal>guid</literal> field. If present,
2536 this UUID may be used to distinguish one server address from another. A
2537 server should use a different UUID for each address it listens on. For
2538 example, if a message bus daemon offers both UNIX domain socket and TCP
2539 connections, but treats clients the same regardless of how they connect,
2540 those two connections are equivalent post-connection but should have
2541 distinct UUIDs to distinguish the kinds of connection.
2545 The intent of the address UUID feature is to allow a client to avoid
2546 opening multiple identical connections to the same server, by allowing the
2547 client to check whether an address corresponds to an already-existing
2548 connection. Comparing two addresses is insufficient, because addresses
2549 can be recycled by distinct servers, and equivalent addresses may look
2550 different if simply compared as strings (for example, the host in a TCP
2551 address can be given as an IP address or as a hostname).
2555 Note that the address key is <literal>guid</literal> even though the
2556 rest of the API and documentation says "UUID," for historical reasons.
2560 [FIXME clarify if attempting to connect to each is a requirement
2561 or just a suggestion]
2562 When connecting to a server, multiple server addresses can be
2563 separated by a semi-colon. The library will then try to connect
2564 to the first address and if that fails, it'll try to connect to
2565 the next one specified, and so forth. For example
2566 <programlisting>unix:path=/tmp/dbus-test;unix:path=/tmp/dbus-test2</programlisting>
2571 <sect1 id="transports">
2572 <title>Transports</title>
2574 [FIXME we need to specify in detail each transport and its possible arguments]
2576 Current transports include: unix domain sockets (including
2577 abstract namespace on linux), launchd, TCP/IP, and a debug/testing transport
2578 using in-process pipes. Future possible transports include one that
2579 tunnels over X11 protocol.
2582 <sect2 id="transports-unix-domain-sockets">
2583 <title>Unix Domain Sockets</title>
2585 Unix domain sockets can be either paths in the file system or on Linux
2586 kernels, they can be abstract which are similar to paths but
2587 do not show up in the file system.
2591 When a socket is opened by the D-Bus library it truncates the path
2592 name right before the first trailing Nul byte. This is true for both
2593 normal paths and abstract paths. Note that this is a departure from
2594 previous versions of D-Bus that would create sockets with a fixed
2595 length path name. Names which were shorter than the fixed length
2596 would be padded by Nul bytes.
2599 Unix domain sockets are not available on windows.
2601 <sect3 id="transports-unix-domain-sockets-addresses">
2602 <title>Server Address Format</title>
2604 Unix domain socket addresses are identified by the "unix:" prefix
2605 and support the following key/value pairs:
2612 <entry>Values</entry>
2613 <entry>Description</entry>
2619 <entry>(path)</entry>
2620 <entry>path of the unix domain socket. If set, the "tmpdir" and "abstract" key must not be set.</entry>
2623 <entry>tmpdir</entry>
2624 <entry>(path)</entry>
2625 <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>
2628 <entry>abstract</entry>
2629 <entry>(string)</entry>
2630 <entry>unique string (path) in the abstract namespace. If set, the "path" or "tempdir" key must not be set.</entry>
2637 <sect2 id="transports-launchd">
2638 <title>launchd</title>
2640 launchd is a open-source server management system that replaces init, inetd
2641 and cron on Apple Mac OS X versions 10.4 and above. It provides a common session
2642 bus address for each user and deprecates the X11-enabled D-Bus launcher on OSX.
2646 launchd allocates a socket and provides it with the unix path through the
2647 DBUS_LAUNCHD_SESSION_BUS_SOCKET variable in launchd's environment. Every process
2648 spawned by launchd (or dbus-daemon, if it was started by launchd) can access
2649 it through its environment.
2650 Other processes can query for the launchd socket by executing:
2651 $ launchctl getenv DBUS_LAUNCHD_SESSION_BUS_SOCKET
2652 This is normally done by the D-Bus client library so doesn't have to be done
2656 launchd is not available on Microsoft Windows.
2658 <sect3 id="transports-launchd-addresses">
2659 <title>Server Address Format</title>
2661 launchd addresses are identified by the "launchd:" prefix
2662 and support the following key/value pairs:
2669 <entry>Values</entry>
2670 <entry>Description</entry>
2676 <entry>(environment variable)</entry>
2677 <entry>path of the unix domain socket for the launchd created dbus-daemon.</entry>
2684 <sect2 id="transports-tcp-sockets">
2685 <title>TCP Sockets</title>
2687 The tcp transport provides TCP/IP based connections between clients
2688 located on the same or different hosts.
2691 Using tcp transport without any additional secure authentification mechanismus
2692 over a network is unsecure.
2695 Windows notes: Because of the tcp stack on windows does not provide sending
2696 credentials over a tcp connection, the EXTERNAL authentification
2697 mechanismus does not work.
2699 <sect3 id="transports-tcp-sockets-addresses">
2700 <title>Server Address Format</title>
2702 TCP/IP socket addresses are identified by the "tcp:" prefix
2703 and support the following key/value pairs:
2710 <entry>Values</entry>
2711 <entry>Description</entry>
2717 <entry>(string)</entry>
2718 <entry>dns name or ip address</entry>
2722 <entry>(number)</entry>
2723 <entry>The tcp port the server will open. A zero value let the server
2724 choose a free port provided from the underlaying operating system.
2725 libdbus is able to retrieve the real used port from the server.
2729 <entry>family</entry>
2730 <entry>(string)</entry>
2731 <entry>If set, provide the type of socket family either "ipv4" or "ipv6". If unset, the family is unspecified.</entry>
2738 <sect2 id="transports-nonce-tcp-sockets">
2739 <title>Nonce-secured TCP Sockets</title>
2741 The nonce-tcp transport provides a secured TCP transport, using a
2742 simple authentication mechanism to ensure that only clients with read
2743 access to a certain location in the filesystem can connect to the server.
2744 The server writes a secret, the nonce, to a file and an incoming client
2745 connection is only accepted if the client sends the nonce right after
2746 the connect. The nonce mechanism requires no setup and is orthogonal to
2747 the higher-level authentication mechanisms described in the
2748 Authentication section.
2752 On start, the server generates a random 16 byte nonce and writes it
2753 to a file in the user's temporary directory. The nonce file location
2754 is published as part of the server's D-Bus address using the
2755 "noncefile" key-value pair.
2757 After an accept, the server reads 16 bytes from the socket. If the
2758 read bytes do not match the nonce stored in the nonce file, the
2759 server MUST immediately drop the connection.
2760 If the nonce match the received byte sequence, the client is accepted
2761 and the transport behaves like an unsecured tcp transport.
2764 After a successful connect to the server socket, the client MUST read
2765 the nonce from the file published by the server via the noncefile=
2766 key-value pair and send it over the socket. After that, the
2767 transport behaves like an unsecured tcp transport.
2769 <sect3 id="transports-nonce-tcp-sockets-addresses">
2770 <title>Server Address Format</title>
2772 Nonce TCP/IP socket addresses uses the "nonce-tcp:" prefix
2773 and support the following key/value pairs:
2780 <entry>Values</entry>
2781 <entry>Description</entry>
2787 <entry>(string)</entry>
2788 <entry>dns name or ip address</entry>
2792 <entry>(number)</entry>
2793 <entry>The tcp port the server will open. A zero value let the server
2794 choose a free port provided from the underlaying operating system.
2795 libdbus is able to retrieve the real used port from the server.
2799 <entry>family</entry>
2800 <entry>(string)</entry>
2801 <entry>If set, provide the type of socket family either "ipv4" or "ipv6". If unset, the family is unspecified.</entry>
2804 <entry>noncefile</entry>
2805 <entry>(path)</entry>
2806 <entry>file location containing the secret</entry>
2814 <sect1 id="meta-transports">
2815 <title>Meta Transports</title>
2817 Meta transports are a kind of transport with special enhancements or
2818 behavior. Currently available meta transports include: autolaunch
2821 <sect2 id="meta-transports-autolaunch">
2822 <title>Autolaunch</title>
2823 <para>The autolaunch transport provides a way for dbus clients to autodetect
2824 a running dbus session bus and to autolaunch a session bus if not present.
2826 <sect3 id="meta-transports-autolaunch-addresses">
2827 <title>Server Address Format</title>
2829 Autolaunch addresses uses the "autolaunch:" prefix and support the
2830 following key/value pairs:
2837 <entry>Values</entry>
2838 <entry>Description</entry>
2843 <entry>scope</entry>
2844 <entry>(string)</entry>
2845 <entry>scope of autolaunch (Windows only)
2849 "*install-path" - limit session bus to dbus installation path.
2850 The dbus installation path is determined from the location of
2851 the shared dbus library. If the library is located in a 'bin'
2852 subdirectory the installation root is the directory above,
2853 otherwise the directory where the library lives is taken as
2856 <install-root>/bin/[lib]dbus-1.dll
2857 <install-root>/[lib]dbus-1.dll
2863 "*user" - limit session bus to the recent user.
2868 other values - specify dedicated session bus like "release",
2880 <sect3 id="meta-transports-autolaunch-windows-implementation">
2881 <title>Windows implementation</title>
2883 On start, the server opens a platform specific transport, creates a mutex
2884 and a shared memory section containing the related session bus address.
2885 This mutex will be inspected by the dbus client library to detect a
2886 running dbus session bus. The access to the mutex and the shared memory
2887 section are protected by global locks.
2890 In the recent implementation the autolaunch transport uses a tcp transport
2891 on localhost with a port choosen from the operating system. This detail may
2892 change in the future.
2895 Disclaimer: The recent implementation is in an early state and may not
2896 work in all cirumstances and/or may have security issues. Because of this
2897 the implementation is not documentated yet.
2902 <sect1 id="naming-conventions">
2903 <title>Naming Conventions</title>
2906 D-Bus namespaces are all lowercase and correspond to reversed domain
2907 names, as with Java. e.g. "org.freedesktop"
2910 Interface, signal, method, and property names are "WindowsStyleCaps", note
2911 that the first letter is capitalized, unlike Java.
2914 Object paths are normally all lowercase with underscores used rather than
2920 <title>UUIDs</title>
2922 A working D-Bus implementation uses universally-unique IDs in two places.
2923 First, each server address has a UUID identifying the address,
2924 as described in <xref linkend="addresses"/>. Second, each operating
2925 system kernel instance running a D-Bus client or server has a UUID
2926 identifying that kernel, retrieved by invoking the method
2927 org.freedesktop.DBus.Peer.GetMachineId() (see <xref
2928 linkend="standard-interfaces-peer"/>).
2931 The term "UUID" in this document is intended literally, i.e. an
2932 identifier that is universally unique. It is not intended to refer to
2933 RFC4122, and in fact the D-Bus UUID is not compatible with that RFC.
2936 The UUID must contain 128 bits of data and be hex-encoded. The
2937 hex-encoded string may not contain hyphens or other non-hex-digit
2938 characters, and it must be exactly 32 characters long. To generate a
2939 UUID, the current reference implementation concatenates 96 bits of random
2940 data followed by the 32-bit time in seconds since the UNIX epoch (in big
2944 It would also be acceptable and probably better to simply generate 128
2945 bits of random data, as long as the random number generator is of high
2946 quality. The timestamp could conceivably help if the random bits are not
2947 very random. With a quality random number generator, collisions are
2948 extremely unlikely even with only 96 bits, so it's somewhat academic.
2951 Implementations should, however, stick to random data for the first 96 bits
2956 <sect1 id="standard-interfaces">
2957 <title>Standard Interfaces</title>
2959 See <xref linkend="message-protocol-types-notation"/> for details on
2960 the notation used in this section. There are some standard interfaces
2961 that may be useful across various D-Bus applications.
2963 <sect2 id="standard-interfaces-peer">
2964 <title><literal>org.freedesktop.DBus.Peer</literal></title>
2966 The <literal>org.freedesktop.DBus.Peer</literal> interface
2969 org.freedesktop.DBus.Peer.Ping ()
2970 org.freedesktop.DBus.Peer.GetMachineId (out STRING machine_uuid)
2974 On receipt of the <literal>METHOD_CALL</literal> message
2975 <literal>org.freedesktop.DBus.Peer.Ping</literal>, an application should do
2976 nothing other than reply with a <literal>METHOD_RETURN</literal> as
2977 usual. It does not matter which object path a ping is sent to. The
2978 reference implementation handles this method automatically.
2981 On receipt of the <literal>METHOD_CALL</literal> message
2982 <literal>org.freedesktop.DBus.Peer.GetMachineId</literal>, an application should
2983 reply with a <literal>METHOD_RETURN</literal> containing a hex-encoded
2984 UUID representing the identity of the machine the process is running on.
2985 This UUID must be the same for all processes on a single system at least
2986 until that system next reboots. It should be the same across reboots
2987 if possible, but this is not always possible to implement and is not
2989 It does not matter which object path a GetMachineId is sent to. The
2990 reference implementation handles this method automatically.
2993 The UUID is intended to be per-instance-of-the-operating-system, so may represent
2994 a virtual machine running on a hypervisor, rather than a physical machine.
2995 Basically if two processes see the same UUID, they should also see the same
2996 shared memory, UNIX domain sockets, process IDs, and other features that require
2997 a running OS kernel in common between the processes.
3000 The UUID is often used where other programs might use a hostname. Hostnames
3001 can change without rebooting, however, or just be "localhost" - so the UUID
3005 <xref linkend="uuids"/> explains the format of the UUID.
3009 <sect2 id="standard-interfaces-introspectable">
3010 <title><literal>org.freedesktop.DBus.Introspectable</literal></title>
3012 This interface has one method:
3014 org.freedesktop.DBus.Introspectable.Introspect (out STRING xml_data)
3018 Objects instances may implement
3019 <literal>Introspect</literal> which returns an XML description of
3020 the object, including its interfaces (with signals and methods), objects
3021 below it in the object path tree, and its properties.
3024 <xref linkend="introspection-format"/> describes the format of this XML string.
3027 <sect2 id="standard-interfaces-properties">
3028 <title><literal>org.freedesktop.DBus.Properties</literal></title>
3030 Many native APIs will have a concept of object <firstterm>properties</firstterm>
3031 or <firstterm>attributes</firstterm>. These can be exposed via the
3032 <literal>org.freedesktop.DBus.Properties</literal> interface.
3036 org.freedesktop.DBus.Properties.Get (in STRING interface_name,
3037 in STRING property_name,
3039 org.freedesktop.DBus.Properties.Set (in STRING interface_name,
3040 in STRING property_name,
3042 org.freedesktop.DBus.Properties.GetAll (in STRING interface_name,
3043 out DICT<STRING,VARIANT> props);
3047 The available properties and whether they are writable can be determined
3048 by calling <literal>org.freedesktop.DBus.Introspectable.Introspect</literal>,
3049 see <xref linkend="standard-interfaces-introspectable"/>.
3052 An empty string may be provided for the interface name; in this case,
3053 if there are multiple properties on an object with the same name,
3054 the results are undefined (picking one by according to an arbitrary
3055 deterministic rule, or returning an error, are the reasonable
3059 If one or more properties change on an object, the
3060 <literal>org.freedesktop.DBus.Properties.PropertiesChanged</literal>
3061 signal may be emitted (this signal was added in 0.14):
3065 org.freedesktop.DBus.Properties.PropertiesChanged (STRING interface_name,
3066 DICT<STRING,VARIANT> changed_properties,
3067 ARRAY<STRING> invalidated_properties);
3071 where <literal>changed_properties</literal> is a dictionary
3072 containing the changed properties with the new values and
3073 <literal>invalidated_properties</literal> is an array of
3074 properties that changed but the value is not conveyed.
3077 Whether the <literal>PropertiesChanged</literal> signal is
3078 supported can be determined by calling
3079 <literal>org.freedesktop.DBus.Introspectable.Introspect</literal>. Note
3080 that the signal may be supported for an object but it may
3081 differ how whether and how it is used on a per-property basis
3082 (for e.g. performance or security reasons). Each property (or
3083 the parent interface) must be annotated with the
3084 <literal>org.freedesktop.DBus.Property.EmitsChangedSignal</literal>
3085 annotation to convey this (usually the default value
3086 <literal>true</literal> is sufficient meaning that the
3087 annotation does not need to be used). See <xref
3088 linkend="introspection-format"/> for details on this
3094 <sect1 id="introspection-format">
3095 <title>Introspection Data Format</title>
3097 As described in <xref linkend="standard-interfaces-introspectable"/>,
3098 objects may be introspected at runtime, returning an XML string
3099 that describes the object. The same XML format may be used in
3100 other contexts as well, for example as an "IDL" for generating
3101 static language bindings.
3104 Here is an example of introspection data:
3106 <!DOCTYPE node PUBLIC "-//freedesktop//DTD D-BUS Object Introspection 1.0//EN"
3107 "http://www.freedesktop.org/standards/dbus/1.0/introspect.dtd">
3108 <node name="/org/freedesktop/sample_object">
3109 <interface name="org.freedesktop.SampleInterface">
3110 <method name="Frobate">
3111 <arg name="foo" type="i" direction="in"/>
3112 <arg name="bar" type="s" direction="out"/>
3113 <arg name="baz" type="a{us}" direction="out"/>
3114 <annotation name="org.freedesktop.DBus.Deprecated" value="true"/>
3116 <method name="Bazify">
3117 <arg name="bar" type="(iiu)" direction="in"/>
3118 <arg name="bar" type="v" direction="out"/>
3120 <method name="Mogrify">
3121 <arg name="bar" type="(iiav)" direction="in"/>
3123 <signal name="Changed">
3124 <arg name="new_value" type="b"/>
3126 <property name="Bar" type="y" access="readwrite"/>
3128 <node name="child_of_sample_object"/>
3129 <node name="another_child_of_sample_object"/>
3134 A more formal DTD and spec needs writing, but here are some quick notes.
3138 Only the root <node> element can omit the node name, as it's
3139 known to be the object that was introspected. If the root
3140 <node> does have a name attribute, it must be an absolute
3141 object path. If child <node> have object paths, they must be
3147 If a child <node> has any sub-elements, then they
3148 must represent a complete introspection of the child.
3149 If a child <node> is empty, then it may or may
3150 not have sub-elements; the child must be introspected
3151 in order to find out. The intent is that if an object
3152 knows that its children are "fast" to introspect
3153 it can go ahead and return their information, but
3154 otherwise it can omit it.
3159 The direction element on <arg> may be omitted,
3160 in which case it defaults to "in" for method calls
3161 and "out" for signals. Signals only allow "out"
3162 so while direction may be specified, it's pointless.
3167 The possible directions are "in" and "out",
3168 unlike CORBA there is no "inout"
3173 The possible property access flags are
3174 "readwrite", "read", and "write"
3179 Multiple interfaces can of course be listed for
3185 The "name" attribute on arguments is optional.
3191 Method, interface, property, and signal elements may have
3192 "annotations", which are generic key/value pairs of metadata.
3193 They are similar conceptually to Java's annotations and C# attributes.
3194 Well-known annotations:
3201 <entry>Values (separated by ,)</entry>
3202 <entry>Description</entry>
3207 <entry>org.freedesktop.DBus.Deprecated</entry>
3208 <entry>true,false</entry>
3209 <entry>Whether or not the entity is deprecated; defaults to false</entry>
3212 <entry>org.freedesktop.DBus.GLib.CSymbol</entry>
3213 <entry>(string)</entry>
3214 <entry>The C symbol; may be used for methods and interfaces</entry>
3217 <entry>org.freedesktop.DBus.Method.NoReply</entry>
3218 <entry>true,false</entry>
3219 <entry>If set, don't expect a reply to the method call; defaults to false.</entry>
3222 <entry>org.freedesktop.DBus.Property.EmitsChangedSignal</entry>
3223 <entry>true,invalidates,false</entry>
3226 If set to <literal>false</literal>, the
3227 <literal>org.freedesktop.DBus.Properties.PropertiesChanged</literal>
3229 linkend="standard-interfaces-properties"/> is not
3230 guaranteed to be emitted if the property changes.
3233 If set to <literal>invalidates</literal> the signal
3234 is emitted but the value is not included in the
3238 If set to <literal>true</literal> the signal is
3239 emitted with the value included.
3242 The value for the annotation defaults to
3243 <literal>true</literal> if the enclosing interface
3244 element does not specify the annotation. Otherwise it
3245 defaults to the value specified in the enclosing
3254 <sect1 id="message-bus">
3255 <title>Message Bus Specification</title>
3256 <sect2 id="message-bus-overview">
3257 <title>Message Bus Overview</title>
3259 The message bus accepts connections from one or more applications.
3260 Once connected, applications can exchange messages with other
3261 applications that are also connected to the bus.
3264 In order to route messages among connections, the message bus keeps a
3265 mapping from names to connections. Each connection has one
3266 unique-for-the-lifetime-of-the-bus name automatically assigned.
3267 Applications may request additional names for a connection. Additional
3268 names are usually "well-known names" such as
3269 "org.freedesktop.TextEditor". When a name is bound to a connection,
3270 that connection is said to <firstterm>own</firstterm> the name.
3273 The bus itself owns a special name, <literal>org.freedesktop.DBus</literal>.
3274 This name routes messages to the bus, allowing applications to make
3275 administrative requests. For example, applications can ask the bus
3276 to assign a name to a connection.
3279 Each name may have <firstterm>queued owners</firstterm>. When an
3280 application requests a name for a connection and the name is already in
3281 use, the bus will optionally add the connection to a queue waiting for
3282 the name. If the current owner of the name disconnects or releases
3283 the name, the next connection in the queue will become the new owner.
3287 This feature causes the right thing to happen if you start two text
3288 editors for example; the first one may request "org.freedesktop.TextEditor",
3289 and the second will be queued as a possible owner of that name. When
3290 the first exits, the second will take over.
3294 Messages may have a <literal>DESTINATION</literal> field (see <xref
3295 linkend="message-protocol-header-fields"/>). If the
3296 <literal>DESTINATION</literal> field is present, it specifies a message
3297 recipient by name. Method calls and replies normally specify this field.
3298 The message bus must send messages (of any type) with the
3299 <literal>DESTINATION</literal> field set to the specified recipient,
3300 regardless of whether the recipient has set up a match rule matching
3305 Signals normally do not specify a destination; they are sent to all
3306 applications with <firstterm>message matching rules</firstterm> that
3311 When the message bus receives a method call, if the
3312 <literal>DESTINATION</literal> field is absent, the call is taken to be
3313 a standard one-to-one message and interpreted by the message bus
3314 itself. For example, sending an
3315 <literal>org.freedesktop.DBus.Peer.Ping</literal> message with no
3316 <literal>DESTINATION</literal> will cause the message bus itself to
3317 reply to the ping immediately; the message bus will not make this
3318 message visible to other applications.
3322 Continuing the <literal>org.freedesktop.DBus.Peer.Ping</literal> example, if
3323 the ping message were sent with a <literal>DESTINATION</literal> name of
3324 <literal>com.yoyodyne.Screensaver</literal>, then the ping would be
3325 forwarded, and the Yoyodyne Corporation screensaver application would be
3326 expected to reply to the ping.
3330 <sect2 id="message-bus-names">
3331 <title>Message Bus Names</title>
3333 Each connection has at least one name, assigned at connection time and
3334 returned in response to the
3335 <literal>org.freedesktop.DBus.Hello</literal> method call. This
3336 automatically-assigned name is called the connection's <firstterm>unique
3337 name</firstterm>. Unique names are never reused for two different
3338 connections to the same bus.
3341 Ownership of a unique name is a prerequisite for interaction with
3342 the message bus. It logically follows that the unique name is always
3343 the first name that an application comes to own, and the last
3344 one that it loses ownership of.
3347 Unique connection names must begin with the character ':' (ASCII colon
3348 character); bus names that are not unique names must not begin
3349 with this character. (The bus must reject any attempt by an application
3350 to manually request a name beginning with ':'.) This restriction
3351 categorically prevents "spoofing"; messages sent to a unique name
3352 will always go to the expected connection.
3355 When a connection is closed, all the names that it owns are deleted (or
3356 transferred to the next connection in the queue if any).
3359 A connection can request additional names to be associated with it using
3360 the <literal>org.freedesktop.DBus.RequestName</literal> message. <xref
3361 linkend="message-protocol-names-bus"/> describes the format of a valid
3362 name. These names can be released again using the
3363 <literal>org.freedesktop.DBus.ReleaseName</literal> message.
3366 <sect3 id="bus-messages-request-name">
3367 <title><literal>org.freedesktop.DBus.RequestName</literal></title>
3371 UINT32 RequestName (in STRING name, in UINT32 flags)
3378 <entry>Argument</entry>
3380 <entry>Description</entry>
3386 <entry>STRING</entry>
3387 <entry>Name to request</entry>
3391 <entry>UINT32</entry>
3392 <entry>Flags</entry>
3402 <entry>Argument</entry>
3404 <entry>Description</entry>
3410 <entry>UINT32</entry>
3411 <entry>Return value</entry>
3418 This method call should be sent to
3419 <literal>org.freedesktop.DBus</literal> and asks the message bus to
3420 assign the given name to the method caller. Each name maintains a
3421 queue of possible owners, where the head of the queue is the primary
3422 or current owner of the name. Each potential owner in the queue
3423 maintains the DBUS_NAME_FLAG_ALLOW_REPLACEMENT and
3424 DBUS_NAME_FLAG_DO_NOT_QUEUE settings from its latest RequestName
3425 call. When RequestName is invoked the following occurs:
3429 If the method caller is currently the primary owner of the name,
3430 the DBUS_NAME_FLAG_ALLOW_REPLACEMENT and DBUS_NAME_FLAG_DO_NOT_QUEUE
3431 values are updated with the values from the new RequestName call,
3432 and nothing further happens.
3438 If the current primary owner (head of the queue) has
3439 DBUS_NAME_FLAG_ALLOW_REPLACEMENT set, and the RequestName
3440 invocation has the DBUS_NAME_FLAG_REPLACE_EXISTING flag, then
3441 the caller of RequestName replaces the current primary owner at
3442 the head of the queue and the current primary owner moves to the
3443 second position in the queue. If the caller of RequestName was
3444 in the queue previously its flags are updated with the values from
3445 the new RequestName in addition to moving it to the head of the queue.
3451 If replacement is not possible, and the method caller is
3452 currently in the queue but not the primary owner, its flags are
3453 updated with the values from the new RequestName call.
3459 If replacement is not possible, and the method caller is
3460 currently not in the queue, the method caller is appended to the
3467 If any connection in the queue has DBUS_NAME_FLAG_DO_NOT_QUEUE
3468 set and is not the primary owner, it is removed from the
3469 queue. This can apply to the previous primary owner (if it
3470 was replaced) or the method caller (if it updated the
3471 DBUS_NAME_FLAG_DO_NOT_QUEUE flag while still stuck in the
3472 queue, or if it was just added to the queue with that flag set).
3478 Note that DBUS_NAME_FLAG_REPLACE_EXISTING results in "jumping the
3479 queue," even if another application already in the queue had specified
3480 DBUS_NAME_FLAG_REPLACE_EXISTING. This comes up if a primary owner
3481 that does not allow replacement goes away, and the next primary owner
3482 does allow replacement. In this case, queued items that specified
3483 DBUS_NAME_FLAG_REPLACE_EXISTING <emphasis>do not</emphasis>
3484 automatically replace the new primary owner. In other words,
3485 DBUS_NAME_FLAG_REPLACE_EXISTING is not saved, it is only used at the
3486 time RequestName is called. This is deliberate to avoid an infinite loop
3487 anytime two applications are both DBUS_NAME_FLAG_ALLOW_REPLACEMENT
3488 and DBUS_NAME_FLAG_REPLACE_EXISTING.
3491 The flags argument contains any of the following values logically ORed
3498 <entry>Conventional Name</entry>
3499 <entry>Value</entry>
3500 <entry>Description</entry>
3505 <entry>DBUS_NAME_FLAG_ALLOW_REPLACEMENT</entry>
3509 If an application A specifies this flag and succeeds in
3510 becoming the owner of the name, and another application B
3511 later calls RequestName with the
3512 DBUS_NAME_FLAG_REPLACE_EXISTING flag, then application A
3513 will lose ownership and receive a
3514 <literal>org.freedesktop.DBus.NameLost</literal> signal, and
3515 application B will become the new owner. If DBUS_NAME_FLAG_ALLOW_REPLACEMENT
3516 is not specified by application A, or DBUS_NAME_FLAG_REPLACE_EXISTING
3517 is not specified by application B, then application B will not replace
3518 application A as the owner.
3523 <entry>DBUS_NAME_FLAG_REPLACE_EXISTING</entry>
3527 Try to replace the current owner if there is one. If this
3528 flag is not set the application will only become the owner of
3529 the name if there is no current owner. If this flag is set,
3530 the application will replace the current owner if
3531 the current owner specified DBUS_NAME_FLAG_ALLOW_REPLACEMENT.
3536 <entry>DBUS_NAME_FLAG_DO_NOT_QUEUE</entry>
3540 Without this flag, if an application requests a name that is
3541 already owned, the application will be placed in a queue to
3542 own the name when the current owner gives it up. If this
3543 flag is given, the application will not be placed in the
3544 queue, the request for the name will simply fail. This flag
3545 also affects behavior when an application is replaced as
3546 name owner; by default the application moves back into the
3547 waiting queue, unless this flag was provided when the application
3548 became the name owner.
3556 The return code can be one of the following values:
3562 <entry>Conventional Name</entry>
3563 <entry>Value</entry>
3564 <entry>Description</entry>
3569 <entry>DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER</entry>
3570 <entry>1</entry> <entry>The caller is now the primary owner of
3571 the name, replacing any previous owner. Either the name had no
3572 owner before, or the caller specified
3573 DBUS_NAME_FLAG_REPLACE_EXISTING and the current owner specified
3574 DBUS_NAME_FLAG_ALLOW_REPLACEMENT.</entry>
3577 <entry>DBUS_REQUEST_NAME_REPLY_IN_QUEUE</entry>
3580 <entry>The name already had an owner,
3581 DBUS_NAME_FLAG_DO_NOT_QUEUE was not specified, and either
3582 the current owner did not specify
3583 DBUS_NAME_FLAG_ALLOW_REPLACEMENT or the requesting
3584 application did not specify DBUS_NAME_FLAG_REPLACE_EXISTING.
3588 <entry>DBUS_REQUEST_NAME_REPLY_EXISTS</entry> <entry>3</entry>
3589 <entry>The name already has an owner,
3590 DBUS_NAME_FLAG_DO_NOT_QUEUE was specified, and either
3591 DBUS_NAME_FLAG_ALLOW_REPLACEMENT was not specified by the
3592 current owner, or DBUS_NAME_FLAG_REPLACE_EXISTING was not
3593 specified by the requesting application.</entry>
3596 <entry>DBUS_REQUEST_NAME_REPLY_ALREADY_OWNER</entry>
3598 <entry>The application trying to request ownership of a name is already the owner of it.</entry>
3606 <sect3 id="bus-messages-release-name">
3607 <title><literal>org.freedesktop.DBus.ReleaseName</literal></title>
3611 UINT32 ReleaseName (in STRING name)
3618 <entry>Argument</entry>
3620 <entry>Description</entry>
3626 <entry>STRING</entry>
3627 <entry>Name to release</entry>
3637 <entry>Argument</entry>
3639 <entry>Description</entry>
3645 <entry>UINT32</entry>
3646 <entry>Return value</entry>
3653 This method call should be sent to
3654 <literal>org.freedesktop.DBus</literal> and asks the message bus to
3655 release the method caller's claim to the given name. If the caller is
3656 the primary owner, a new primary owner will be selected from the
3657 queue if any other owners are waiting. If the caller is waiting in
3658 the queue for the name, the caller will removed from the queue and
3659 will not be made an owner of the name if it later becomes available.
3660 If there are no other owners in the queue for the name, it will be
3661 removed from the bus entirely.
3663 The return code can be one of the following values:
3669 <entry>Conventional Name</entry>
3670 <entry>Value</entry>
3671 <entry>Description</entry>
3676 <entry>DBUS_RELEASE_NAME_REPLY_RELEASED</entry>
3677 <entry>1</entry> <entry>The caller has released his claim on
3678 the given name. Either the caller was the primary owner of
3679 the name, and the name is now unused or taken by somebody
3680 waiting in the queue for the name, or the caller was waiting
3681 in the queue for the name and has now been removed from the
3685 <entry>DBUS_RELEASE_NAME_REPLY_NON_EXISTENT</entry>
3687 <entry>The given name does not exist on this bus.</entry>
3690 <entry>DBUS_RELEASE_NAME_REPLY_NOT_OWNER</entry>
3692 <entry>The caller was not the primary owner of this name,
3693 and was also not waiting in the queue to own this name.</entry>
3701 <sect3 id="bus-messages-list-queued-owners">
3702 <title><literal>org.freedesktop.DBus.ListQueuedOwners</literal></title>
3706 ARRAY of STRING ListQueuedOwners (in STRING name)
3713 <entry>Argument</entry>
3715 <entry>Description</entry>
3721 <entry>STRING</entry>
3722 <entry>The well-known bus name to query, such as
3723 <literal>com.example.cappuccino</literal></entry>
3733 <entry>Argument</entry>
3735 <entry>Description</entry>
3741 <entry>ARRAY of STRING</entry>
3742 <entry>The unique bus names of connections currently queued
3743 for the name</entry>
3750 This method call should be sent to
3751 <literal>org.freedesktop.DBus</literal> and lists the connections
3752 currently queued for a bus name (see
3753 <xref linkend="term-queued-owner"/>).
3758 <sect2 id="message-bus-routing">
3759 <title>Message Bus Message Routing</title>
3763 <sect3 id="message-bus-routing-match-rules">
3764 <title>Match Rules</title>
3766 An important part of the message bus routing protocol is match
3767 rules. Match rules describe what messages can be sent to a client
3768 based on the contents of the message. When a message is routed
3769 through the bus it is compared to clients' match rules. If any
3770 of the rules match, the message is dispatched to the client.
3771 If none of the rules match the message never leaves the bus. This
3772 is an effective way to control traffic over the bus and to make sure
3773 only relevant message need to be processed by the client.
3776 Match rules are added using the AddMatch bus method
3777 (see <xref linkend="bus-messages-add-match"/>). Rules are
3778 specified as a string of comma separated key/value pairs.
3779 Excluding a key from the rule indicates a wildcard match.
3780 For instance excluding the the member from a match rule but
3781 adding a sender would let all messages from that sender through.
3782 An example of a complete rule would be
3783 "type='signal',sender='org.freedesktop.DBus',interface='org.freedesktop.DBus',member='Foo',path='/bar/foo',destination=':452345.34',arg2='bar'"
3786 The following table describes the keys that can be used to create
3788 The following table summarizes the D-Bus types.
3794 <entry>Possible Values</entry>
3795 <entry>Description</entry>
3800 <entry><literal>type</literal></entry>
3801 <entry>'signal', 'method_call', 'method_return', 'error'</entry>
3802 <entry>Match on the message type. An example of a type match is type='signal'</entry>
3805 <entry><literal>sender</literal></entry>
3806 <entry>A bus or unique name (see <xref linkend="term-bus-name"/>
3807 and <xref linkend="term-unique-name"/> respectively)
3809 <entry>Match messages sent by a particular sender. An example of a sender match
3810 is sender='org.freedesktop.Hal'</entry>
3813 <entry><literal>interface</literal></entry>
3814 <entry>An interface name (see <xref linkend="message-protocol-names-interface"/>)</entry>
3815 <entry>Match messages sent over or to a particular interface. An example of an
3816 interface match is interface='org.freedesktop.Hal.Manager'.
3817 If a message omits the interface header, it must not match any rule
3818 that specifies this key.</entry>
3821 <entry><literal>member</literal></entry>
3822 <entry>Any valid method or signal name</entry>
3823 <entry>Matches messages which have the give method or signal name. An example of
3824 a member match is member='NameOwnerChanged'</entry>
3827 <entry><literal>path</literal></entry>
3828 <entry>An object path (see <xref linkend="message-protocol-marshaling-object-path"/>)</entry>
3829 <entry>Matches messages which are sent from or to the given object. An example of a
3830 path match is path='/org/freedesktop/Hal/Manager'</entry>
3833 <entry><literal>path_namespace</literal></entry>
3834 <entry>An object path</entry>
3837 Matches messages which are sent from or to an
3838 object for which the object path is either the
3839 given value, or that value followed by one or
3840 more path components.
3845 <literal>path_namespace='/com/example/foo'</literal>
3846 would match signals sent by
3847 <literal>/com/example/foo</literal>
3849 <literal>/com/example/foo/bar</literal>,
3851 <literal>/com/example/foobar</literal>.
3855 Using both <literal>path</literal> and
3856 <literal>path_namespace</literal> in the same match
3857 rule is not allowed.
3862 This match key was added in version 0.16 of the
3863 D-Bus specification and implemented by the bus
3864 daemon in dbus 1.5.0 and later.
3870 <entry><literal>destination</literal></entry>
3871 <entry>A unique name (see <xref linkend="term-unique-name"/>)</entry>
3872 <entry>Matches messages which are being sent to the given unique name. An
3873 example of a destination match is destination=':1.0'</entry>
3876 <entry><literal>arg[0, 1, 2, 3, ...]</literal></entry>
3877 <entry>Any string</entry>
3878 <entry>Arg matches are special and are used for further restricting the
3879 match based on the arguments in the body of a message. Only arguments of type
3880 STRING can be matched in this way. An example of an argument match
3881 would be arg3='Foo'. Only argument indexes from 0 to 63 should be
3885 <entry><literal>arg[0, 1, 2, 3, ...]path</literal></entry>
3886 <entry>Any string</entry>
3888 <para>Argument path matches provide a specialised form of wildcard matching for
3889 path-like namespaces. They can match arguments whose type is either STRING or
3890 OBJECT_PATH. As with normal argument matches,
3891 if the argument is exactly equal to the string given in the match
3892 rule then the rule is satisfied. Additionally, there is also a
3893 match when either the string given in the match rule or the
3894 appropriate message argument ends with '/' and is a prefix of the
3895 other. An example argument path match is arg0path='/aa/bb/'. This
3896 would match messages with first arguments of '/', '/aa/',
3897 '/aa/bb/', '/aa/bb/cc/' and '/aa/bb/cc'. It would not match
3898 messages with first arguments of '/aa/b', '/aa' or even '/aa/bb'.</para>
3900 <para>This is intended for monitoring “directories” in file system-like
3901 hierarchies, as used in the <citetitle>dconf</citetitle> configuration
3902 system. An application interested in all nodes in a particular hierarchy would
3903 monitor <literal>arg0path='/ca/example/foo/'</literal>. Then the service could
3904 emit a signal with zeroth argument <literal>"/ca/example/foo/bar"</literal> to
3905 represent a modification to the “bar” property, or a signal with zeroth
3906 argument <literal>"/ca/example/"</literal> to represent atomic modification of
3907 many properties within that directory, and the interested application would be
3908 notified in both cases.</para>
3911 This match key was added in version 0.12 of the
3912 D-Bus specification, implemented for STRING
3913 arguments by the bus daemon in dbus 1.2.0 and later,
3914 and implemented for OBJECT_PATH arguments in dbus 1.5.0
3921 <entry><literal>arg0namespace</literal></entry>
3922 <entry>Like a bus name, except that the string is not
3923 required to contain a '.' (period)</entry>
3925 <para>Match messages whose first argument is of type STRING, and is a bus name
3926 or interface name within the specified namespace. This is primarily intended
3927 for watching name owner changes for a group of related bus names, rather than
3928 for a single name or all name changes.</para>
3930 <para>Because every valid interface name is also a valid
3931 bus name, this can also be used for messages whose
3932 first argument is an interface name.</para>
3934 <para>For example, the match rule
3935 <literal>member='NameOwnerChanged',arg0namespace='com.example.backend'</literal>
3936 matches name owner changes for bus names such as
3937 <literal>com.example.backend.foo</literal>,
3938 <literal>com.example.backend.foo.bar</literal>, and
3939 <literal>com.example.backend</literal> itself.</para>
3941 <para>See also <xref linkend='bus-messages-name-owner-changed'/>.</para>
3944 This match key was added in version 0.16 of the
3945 D-Bus specification and implemented by the bus
3946 daemon in dbus 1.5.0 and later.
3957 <sect2 id="message-bus-starting-services">
3958 <title>Message Bus Starting Services</title>
3960 The message bus can start applications on behalf of other applications.
3961 In CORBA terms, this would be called <firstterm>activation</firstterm>.
3962 An application that can be started in this way is called a
3963 <firstterm>service</firstterm>.
3966 With D-Bus, starting a service is normally done by name. That is,
3967 applications ask the message bus to start some program that will own a
3968 well-known name, such as <literal>org.freedesktop.TextEditor</literal>.
3969 This implies a contract documented along with the name
3970 <literal>org.freedesktop.TextEditor</literal> for which objects
3971 the owner of that name will provide, and what interfaces those
3975 To find an executable corresponding to a particular name, the bus daemon
3976 looks for <firstterm>service description files</firstterm>. Service
3977 description files define a mapping from names to executables. Different
3978 kinds of message bus will look for these files in different places, see
3979 <xref linkend="message-bus-types"/>.
3982 Service description files have the ".service" file
3983 extension. The message bus will only load service description files
3984 ending with .service; all other files will be ignored. The file format
3985 is similar to that of <ulink
3986 url="http://standards.freedesktop.org/desktop-entry-spec/desktop-entry-spec-latest.html">desktop
3987 entries</ulink>. All service description files must be in UTF-8
3988 encoding. To ensure that there will be no name collisions, service files
3989 must be namespaced using the same mechanism as messages and service
3994 [FIXME the file format should be much better specified than "similar to
3995 .desktop entries" esp. since desktop entries are already
3996 badly-specified. ;-)]
3997 These sections from the specification apply to service files as well:
4000 <listitem><para>General syntax</para></listitem>
4001 <listitem><para>Comment format</para></listitem>
4005 <title>Example service description file</title>
4007 # Sample service description file
4009 Names=org.freedesktop.ConfigurationDatabase;org.gnome.GConf;
4010 Exec=/usr/libexec/gconfd-2
4015 When an application asks to start a service by name, the bus daemon tries to
4016 find a service that will own that name. It then tries to spawn the
4017 executable associated with it. If this fails, it will report an
4018 error. [FIXME what happens if two .service files offer the same service;
4019 what kind of error is reported, should we have a way for the client to
4023 The executable launched will have the environment variable
4024 <literal>DBUS_STARTER_ADDRESS</literal> set to the address of the
4025 message bus so it can connect and request the appropriate names.
4028 The executable being launched may want to know whether the message bus
4029 starting it is one of the well-known message buses (see <xref
4030 linkend="message-bus-types"/>). To facilitate this, the bus must also set
4031 the <literal>DBUS_STARTER_BUS_TYPE</literal> environment variable if it is one
4032 of the well-known buses. The currently-defined values for this variable
4033 are <literal>system</literal> for the systemwide message bus,
4034 and <literal>session</literal> for the per-login-session message
4035 bus. The new executable must still connect to the address given
4036 in <literal>DBUS_STARTER_ADDRESS</literal>, but may assume that the
4037 resulting connection is to the well-known bus.
4040 [FIXME there should be a timeout somewhere, either specified
4041 in the .service file, by the client, or just a global value
4042 and if the client being activated fails to connect within that
4043 timeout, an error should be sent back.]
4046 <sect3 id="message-bus-starting-services-scope">
4047 <title>Message Bus Service Scope</title>
4049 The "scope" of a service is its "per-", such as per-session,
4050 per-machine, per-home-directory, or per-display. The reference
4051 implementation doesn't yet support starting services in a different
4052 scope from the message bus itself. So e.g. if you start a service
4053 on the session bus its scope is per-session.
4056 We could add an optional scope to a bus name. For example, for
4057 per-(display,session pair), we could have a unique ID for each display
4058 generated automatically at login and set on screen 0 by executing a
4059 special "set display ID" binary. The ID would be stored in a
4060 <literal>_DBUS_DISPLAY_ID</literal> property and would be a string of
4061 random bytes. This ID would then be used to scope names.
4062 Starting/locating a service could be done by ID-name pair rather than
4066 Contrast this with a per-display scope. To achieve that, we would
4067 want a single bus spanning all sessions using a given display.
4068 So we might set a <literal>_DBUS_DISPLAY_BUS_ADDRESS</literal>
4069 property on screen 0 of the display, pointing to this bus.
4074 <sect2 id="message-bus-types">
4075 <title>Well-known Message Bus Instances</title>
4077 Two standard message bus instances are defined here, along with how
4078 to locate them and where their service files live.
4080 <sect3 id="message-bus-types-login">
4081 <title>Login session message bus</title>
4083 Each time a user logs in, a <firstterm>login session message
4084 bus</firstterm> may be started. All applications in the user's login
4085 session may interact with one another using this message bus.
4088 The address of the login session message bus is given
4089 in the <literal>DBUS_SESSION_BUS_ADDRESS</literal> environment
4090 variable. If that variable is not set, applications may
4091 also try to read the address from the X Window System root
4092 window property <literal>_DBUS_SESSION_BUS_ADDRESS</literal>.
4093 The root window property must have type <literal>STRING</literal>.
4094 The environment variable should have precedence over the
4095 root window property.
4097 <para>The address of the login session message bus is given in the
4098 <literal>DBUS_SESSION_BUS_ADDRESS</literal> environment variable. If
4099 DBUS_SESSION_BUS_ADDRESS is not set, or if it's set to the string
4100 "autolaunch:", the system should use platform-specific methods of
4101 locating a running D-Bus session server, or starting one if a running
4102 instance cannot be found. Note that this mechanism is not recommended
4103 for attempting to determine if a daemon is running. It is inherently
4104 racy to attempt to make this determination, since the bus daemon may
4105 be started just before or just after the determination is made.
4106 Therefore, it is recommended that applications do not try to make this
4107 determination for their functionality purposes, and instead they
4108 should attempt to start the server.</para>
4110 <sect4 id="message-bus-types-login-x-windows">
4111 <title>X Windowing System</title>
4113 For the X Windowing System, the application must locate the
4114 window owner of the selection represented by the atom formed by
4118 <para>the literal string "_DBUS_SESSION_BUS_SELECTION_"</para>
4122 <para>the current user's username</para>
4126 <para>the literal character '_' (underscore)</para>
4130 <para>the machine's ID</para>
4136 The following properties are defined for the window that owns
4138 <informaltable frame="all">
4147 <para>meaning</para>
4153 <para>_DBUS_SESSION_BUS_ADDRESS</para>
4157 <para>the actual address of the server socket</para>
4163 <para>_DBUS_SESSION_BUS_PID</para>
4167 <para>the PID of the server process</para>
4176 At least the _DBUS_SESSION_BUS_ADDRESS property MUST be
4177 present in this window.
4181 If the X selection cannot be located or if reading the
4182 properties from the window fails, the implementation MUST conclude
4183 that there is no D-Bus server running and proceed to start a new
4184 server. (See below on concurrency issues)
4188 Failure to connect to the D-Bus server address thus obtained
4189 MUST be treated as a fatal connection error and should be reported
4194 As an alternative, an implementation MAY find the information
4195 in the following file located in the current user's home directory,
4196 in subdirectory .dbus/session-bus/:
4199 <para>the machine's ID</para>
4203 <para>the literal character '-' (dash)</para>
4207 <para>the X display without the screen number, with the
4208 following prefixes removed, if present: ":", "localhost:"
4209 ."localhost.localdomain:". That is, a display of
4210 "localhost:10.0" produces just the number "10"</para>
4216 The contents of this file NAME=value assignment pairs and
4217 lines starting with # are comments (no comments are allowed
4218 otherwise). The following variable names are defined:
4225 <para>Variable</para>
4229 <para>meaning</para>
4235 <para>DBUS_SESSION_BUS_ADDRESS</para>
4239 <para>the actual address of the server socket</para>
4245 <para>DBUS_SESSION_BUS_PID</para>
4249 <para>the PID of the server process</para>
4255 <para>DBUS_SESSION_BUS_WINDOWID</para>
4259 <para>the window ID</para>
4268 At least the DBUS_SESSION_BUS_ADDRESS variable MUST be present
4273 Failure to open this file MUST be interpreted as absence of a
4274 running server. Therefore, the implementation MUST proceed to
4275 attempting to launch a new bus server if the file cannot be
4280 However, success in opening this file MUST NOT lead to the
4281 conclusion that the server is running. Thus, a failure to connect to
4282 the bus address obtained by the alternative method MUST NOT be
4283 considered a fatal error. If the connection cannot be established,
4284 the implementation MUST proceed to check the X selection settings or
4285 to start the server on its own.
4289 If the implementation concludes that the D-Bus server is not
4290 running it MUST attempt to start a new server and it MUST also
4291 ensure that the daemon started as an effect of the "autolaunch"
4292 mechanism provides the lookup mechanisms described above, so
4293 subsequent calls can locate the newly started server. The
4294 implementation MUST also ensure that if two or more concurrent
4295 initiations happen, only one server remains running and all other
4296 initiations are able to obtain the address of this server and
4297 connect to it. In other words, the implementation MUST ensure that
4298 the X selection is not present when it attempts to set it, without
4299 allowing another process to set the selection between the
4300 verification and the setting (e.g., by using XGrabServer /
4307 [FIXME specify location of .service files, probably using
4308 DESKTOP_DIRS etc. from basedir specification, though login session
4309 bus is not really desktop-specific]
4313 <sect3 id="message-bus-types-system">
4314 <title>System message bus</title>
4316 A computer may have a <firstterm>system message bus</firstterm>,
4317 accessible to all applications on the system. This message bus may be
4318 used to broadcast system events, such as adding new hardware devices,
4319 changes in the printer queue, and so forth.
4322 The address of the system message bus is given
4323 in the <literal>DBUS_SYSTEM_BUS_ADDRESS</literal> environment
4324 variable. If that variable is not set, applications should try
4325 to connect to the well-known address
4326 <literal>unix:path=/var/run/dbus/system_bus_socket</literal>.
4329 The D-Bus reference implementation actually honors the
4330 <literal>$(localstatedir)</literal> configure option
4331 for this address, on both client and server side.
4336 [FIXME specify location of system bus .service files]
4341 <sect2 id="message-bus-messages">
4342 <title>Message Bus Messages</title>
4344 The special message bus name <literal>org.freedesktop.DBus</literal>
4345 responds to a number of additional messages.
4348 <sect3 id="bus-messages-hello">
4349 <title><literal>org.freedesktop.DBus.Hello</literal></title>
4360 <entry>Argument</entry>
4362 <entry>Description</entry>
4368 <entry>STRING</entry>
4369 <entry>Unique name assigned to the connection</entry>
4376 Before an application is able to send messages to other applications
4377 it must send the <literal>org.freedesktop.DBus.Hello</literal> message
4378 to the message bus to obtain a unique name. If an application without
4379 a unique name tries to send a message to another application, or a
4380 message to the message bus itself that isn't the
4381 <literal>org.freedesktop.DBus.Hello</literal> message, it will be
4382 disconnected from the bus.
4385 There is no corresponding "disconnect" request; if a client wishes to
4386 disconnect from the bus, it simply closes the socket (or other
4387 communication channel).
4390 <sect3 id="bus-messages-list-names">
4391 <title><literal>org.freedesktop.DBus.ListNames</literal></title>
4395 ARRAY of STRING ListNames ()
4402 <entry>Argument</entry>
4404 <entry>Description</entry>
4410 <entry>ARRAY of STRING</entry>
4411 <entry>Array of strings where each string is a bus name</entry>
4418 Returns a list of all currently-owned names on the bus.
4421 <sect3 id="bus-messages-list-activatable-names">
4422 <title><literal>org.freedesktop.DBus.ListActivatableNames</literal></title>
4426 ARRAY of STRING ListActivatableNames ()
4433 <entry>Argument</entry>
4435 <entry>Description</entry>
4441 <entry>ARRAY of STRING</entry>
4442 <entry>Array of strings where each string is a bus name</entry>
4449 Returns a list of all names that can be activated on the bus.
4452 <sect3 id="bus-messages-name-exists">
4453 <title><literal>org.freedesktop.DBus.NameHasOwner</literal></title>
4457 BOOLEAN NameHasOwner (in STRING name)
4464 <entry>Argument</entry>
4466 <entry>Description</entry>
4472 <entry>STRING</entry>
4473 <entry>Name to check</entry>
4483 <entry>Argument</entry>
4485 <entry>Description</entry>
4491 <entry>BOOLEAN</entry>
4492 <entry>Return value, true if the name exists</entry>
4499 Checks if the specified name exists (currently has an owner).
4503 <sect3 id="bus-messages-name-owner-changed">
4504 <title><literal>org.freedesktop.DBus.NameOwnerChanged</literal></title>
4508 NameOwnerChanged (STRING name, STRING old_owner, STRING new_owner)
4515 <entry>Argument</entry>
4517 <entry>Description</entry>
4523 <entry>STRING</entry>
4524 <entry>Name with a new owner</entry>
4528 <entry>STRING</entry>
4529 <entry>Old owner or empty string if none</entry>
4533 <entry>STRING</entry>
4534 <entry>New owner or empty string if none</entry>
4541 This signal indicates that the owner of a name has changed.
4542 It's also the signal to use to detect the appearance of
4543 new names on the bus.
4546 <sect3 id="bus-messages-name-lost">
4547 <title><literal>org.freedesktop.DBus.NameLost</literal></title>
4551 NameLost (STRING name)
4558 <entry>Argument</entry>
4560 <entry>Description</entry>
4566 <entry>STRING</entry>
4567 <entry>Name which was lost</entry>
4574 This signal is sent to a specific application when it loses
4575 ownership of a name.
4579 <sect3 id="bus-messages-name-acquired">
4580 <title><literal>org.freedesktop.DBus.NameAcquired</literal></title>
4584 NameAcquired (STRING name)
4591 <entry>Argument</entry>
4593 <entry>Description</entry>
4599 <entry>STRING</entry>
4600 <entry>Name which was acquired</entry>
4607 This signal is sent to a specific application when it gains
4608 ownership of a name.
4612 <sect3 id="bus-messages-start-service-by-name">
4613 <title><literal>org.freedesktop.DBus.StartServiceByName</literal></title>
4617 UINT32 StartServiceByName (in STRING name, in UINT32 flags)
4624 <entry>Argument</entry>
4626 <entry>Description</entry>
4632 <entry>STRING</entry>
4633 <entry>Name of the service to start</entry>
4637 <entry>UINT32</entry>
4638 <entry>Flags (currently not used)</entry>
4648 <entry>Argument</entry>
4650 <entry>Description</entry>
4656 <entry>UINT32</entry>
4657 <entry>Return value</entry>
4662 Tries to launch the executable associated with a name. For more information, see <xref linkend="message-bus-starting-services"/>.
4666 The return value can be one of the following values:
4671 <entry>Identifier</entry>
4672 <entry>Value</entry>
4673 <entry>Description</entry>
4678 <entry>DBUS_START_REPLY_SUCCESS</entry>
4680 <entry>The service was successfully started.</entry>
4683 <entry>DBUS_START_REPLY_ALREADY_RUNNING</entry>
4685 <entry>A connection already owns the given name.</entry>
4694 <sect3 id="bus-messages-update-activation-environment">
4695 <title><literal>org.freedesktop.DBus.UpdateActivationEnvironment</literal></title>
4699 UpdateActivationEnvironment (in ARRAY of DICT<STRING,STRING> environment)
4706 <entry>Argument</entry>
4708 <entry>Description</entry>
4714 <entry>ARRAY of DICT<STRING,STRING></entry>
4715 <entry>Environment to add or update</entry>
4720 Normally, session bus activated services inherit the environment of the bus daemon. This method adds to or modifies that environment when activating services.
4723 Some bus instances, such as the standard system bus, may disable access to this method for some or all callers.
4726 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.
4731 <sect3 id="bus-messages-get-name-owner">
4732 <title><literal>org.freedesktop.DBus.GetNameOwner</literal></title>
4736 STRING GetNameOwner (in STRING name)
4743 <entry>Argument</entry>
4745 <entry>Description</entry>
4751 <entry>STRING</entry>
4752 <entry>Name to get the owner of</entry>
4762 <entry>Argument</entry>
4764 <entry>Description</entry>
4770 <entry>STRING</entry>
4771 <entry>Return value, a unique connection name</entry>
4776 Returns the unique connection name of the primary owner of the name
4777 given. If the requested name doesn't have an owner, returns a
4778 <literal>org.freedesktop.DBus.Error.NameHasNoOwner</literal> error.
4782 <sect3 id="bus-messages-get-connection-unix-user">
4783 <title><literal>org.freedesktop.DBus.GetConnectionUnixUser</literal></title>
4787 UINT32 GetConnectionUnixUser (in STRING bus_name)
4794 <entry>Argument</entry>
4796 <entry>Description</entry>
4802 <entry>STRING</entry>
4803 <entry>Unique or well-known bus name of the connection to
4804 query, such as <literal>:12.34</literal> or
4805 <literal>com.example.tea</literal></entry>
4815 <entry>Argument</entry>
4817 <entry>Description</entry>
4823 <entry>UINT32</entry>
4824 <entry>Unix user ID</entry>
4829 Returns the Unix user ID of the process connected to the server. If
4830 unable to determine it (for instance, because the process is not on the
4831 same machine as the bus daemon), an error is returned.
4835 <sect3 id="bus-messages-get-connection-unix-process-id">
4836 <title><literal>org.freedesktop.DBus.GetConnectionUnixProcessID</literal></title>
4840 UINT32 GetConnectionUnixProcessID (in STRING bus_name)
4847 <entry>Argument</entry>
4849 <entry>Description</entry>
4855 <entry>STRING</entry>
4856 <entry>Unique or well-known bus name of the connection to
4857 query, such as <literal>:12.34</literal> or
4858 <literal>com.example.tea</literal></entry>
4868 <entry>Argument</entry>
4870 <entry>Description</entry>
4876 <entry>UINT32</entry>
4877 <entry>Unix process id</entry>
4882 Returns the Unix process ID of the process connected to the server. If
4883 unable to determine it (for instance, because the process is not on the
4884 same machine as the bus daemon), an error is returned.
4888 <sect3 id="bus-messages-add-match">
4889 <title><literal>org.freedesktop.DBus.AddMatch</literal></title>
4893 AddMatch (in STRING rule)
4900 <entry>Argument</entry>
4902 <entry>Description</entry>
4908 <entry>STRING</entry>
4909 <entry>Match rule to add to the connection</entry>
4914 Adds a match rule to match messages going through the message bus (see <xref linkend='message-bus-routing-match-rules'/>).
4915 If the bus does not have enough resources the <literal>org.freedesktop.DBus.Error.OOM</literal>
4919 <sect3 id="bus-messages-remove-match">
4920 <title><literal>org.freedesktop.DBus.RemoveMatch</literal></title>
4924 RemoveMatch (in STRING rule)
4931 <entry>Argument</entry>
4933 <entry>Description</entry>
4939 <entry>STRING</entry>
4940 <entry>Match rule to remove from the connection</entry>
4945 Removes the first rule that matches (see <xref linkend='message-bus-routing-match-rules'/>).
4946 If the rule is not found the <literal>org.freedesktop.DBus.Error.MatchRuleNotFound</literal>
4951 <sect3 id="bus-messages-get-id">
4952 <title><literal>org.freedesktop.DBus.GetId</literal></title>
4956 GetId (out STRING id)
4963 <entry>Argument</entry>
4965 <entry>Description</entry>
4971 <entry>STRING</entry>
4972 <entry>Unique ID identifying the bus daemon</entry>
4977 Gets the unique ID of the bus. The unique ID here is shared among all addresses the
4978 bus daemon is listening on (TCP, UNIX domain socket, etc.) and its format is described in
4979 <xref linkend="uuids"/>. Each address the bus is listening on also has its own unique
4980 ID, as described in <xref linkend="addresses"/>. The per-bus and per-address IDs are not related.
4981 There is also a per-machine ID, described in <xref linkend="standard-interfaces-peer"/> and returned
4982 by org.freedesktop.DBus.Peer.GetMachineId().
4983 For a desktop session bus, the bus ID can be used as a way to uniquely identify a user's session.
4991 <appendix id="implementation-notes">
4992 <title>Implementation notes</title>
4993 <sect1 id="implementation-notes-subsection">
5001 <glossary><title>Glossary</title>
5003 This glossary defines some of the terms used in this specification.
5006 <glossentry id="term-bus-name"><glossterm>Bus Name</glossterm>
5009 The message bus maintains an association between names and
5010 connections. (Normally, there's one connection per application.) A
5011 bus name is simply an identifier used to locate connections. For
5012 example, the hypothetical <literal>com.yoyodyne.Screensaver</literal>
5013 name might be used to send a message to a screensaver from Yoyodyne
5014 Corporation. An application is said to <firstterm>own</firstterm> a
5015 name if the message bus has associated the application's connection
5016 with the name. Names may also have <firstterm>queued
5017 owners</firstterm> (see <xref linkend="term-queued-owner"/>).
5018 The bus assigns a unique name to each connection,
5019 see <xref linkend="term-unique-name"/>. Other names
5020 can be thought of as "well-known names" and are
5021 used to find applications that offer specific functionality.
5026 <glossentry id="term-message"><glossterm>Message</glossterm>
5029 A message is the atomic unit of communication via the D-Bus
5030 protocol. It consists of a <firstterm>header</firstterm> and a
5031 <firstterm>body</firstterm>; the body is made up of
5032 <firstterm>arguments</firstterm>.
5037 <glossentry id="term-message-bus"><glossterm>Message Bus</glossterm>
5040 The message bus is a special application that forwards
5041 or routes messages between a group of applications
5042 connected to the message bus. It also manages
5043 <firstterm>names</firstterm> used for routing
5049 <glossentry id="term-name"><glossterm>Name</glossterm>
5052 See <xref linkend="term-bus-name"/>. "Name" may
5053 also be used to refer to some of the other names
5054 in D-Bus, such as interface names.
5059 <glossentry id="namespace"><glossterm>Namespace</glossterm>
5062 Used to prevent collisions when defining new interfaces or bus
5063 names. The convention used is the same one Java uses for defining
5064 classes: a reversed domain name.
5069 <glossentry id="term-object"><glossterm>Object</glossterm>
5072 Each application contains <firstterm>objects</firstterm>, which have
5073 <firstterm>interfaces</firstterm> and
5074 <firstterm>methods</firstterm>. Objects are referred to by a name,
5075 called a <firstterm>path</firstterm>.
5080 <glossentry id="one-to-one"><glossterm>One-to-One</glossterm>
5083 An application talking directly to another application, without going
5084 through a message bus. One-to-one connections may be "peer to peer" or
5085 "client to server." The D-Bus protocol has no concept of client
5086 vs. server after a connection has authenticated; the flow of messages
5087 is symmetrical (full duplex).
5092 <glossentry id="term-path"><glossterm>Path</glossterm>
5095 Object references (object names) in D-Bus are organized into a
5096 filesystem-style hierarchy, so each object is named by a path. As in
5097 LDAP, there's no difference between "files" and "directories"; a path
5098 can refer to an object, while still having child objects below it.
5103 <glossentry id="term-queued-owner"><glossterm>Queued Name Owner</glossterm>
5106 Each bus name has a primary owner; messages sent to the name go to the
5107 primary owner. However, certain names also maintain a queue of
5108 secondary owners "waiting in the wings." If the primary owner releases
5109 the name, then the first secondary owner in the queue automatically
5110 becomes the new owner of the name.
5115 <glossentry id="term-service"><glossterm>Service</glossterm>
5118 A service is an executable that can be launched by the bus daemon.
5119 Services normally guarantee some particular features, for example they
5120 may guarantee that they will request a specific name such as
5121 "org.freedesktop.Screensaver", have a singleton object
5122 "/org/freedesktop/Application", and that object will implement the
5123 interface "org.freedesktop.ScreensaverControl".
5128 <glossentry id="term-service-description-files"><glossterm>Service Description Files</glossterm>
5131 ".service files" tell the bus about service applications that can be
5132 launched (see <xref linkend="term-service"/>). Most importantly they
5133 provide a mapping from bus names to services that will request those
5134 names when they start up.
5139 <glossentry id="term-unique-name"><glossterm>Unique Connection Name</glossterm>
5142 The special name automatically assigned to each connection by the
5143 message bus. This name will never change owner, and will be unique
5144 (never reused during the lifetime of the message bus).
5145 It will begin with a ':' character.