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>
1187 <sect3 id="message-protocol-names-bus">
1188 <title>Bus names</title>
1190 Connections have one or more bus names associated with them.
1191 A connection has exactly one bus name that is a unique connection
1192 name. The unique connection name remains with the connection for
1193 its entire lifetime.
1194 A bus name is of type <literal>STRING</literal>,
1195 meaning that it must be valid UTF-8. However, there are also
1196 some additional restrictions that apply to bus names
1199 <listitem><para>Bus names that start with a colon (':')
1200 character are unique connection names.
1203 <listitem><para>Bus names are composed of 1 or more elements separated by
1204 a period ('.') character. All elements must contain at least
1208 <listitem><para>Each element must only contain the ASCII characters
1209 "[A-Z][a-z][0-9]_-". Only elements that are part of a unique
1210 connection name may begin with a digit, elements in
1211 other bus names must not begin with a digit.
1215 <listitem><para>Bus names must contain at least one '.' (period)
1216 character (and thus at least two elements).
1219 <listitem><para>Bus names must not begin with a '.' (period) character.</para></listitem>
1220 <listitem><para>Bus names must not exceed the maximum name length.</para></listitem>
1224 Note that the hyphen ('-') character is allowed in bus names but
1225 not in interface names.
1228 <sect3 id="message-protocol-names-member">
1229 <title>Member names</title>
1231 Member (i.e. method or signal) names:
1233 <listitem><para>Must only contain the ASCII characters
1234 "[A-Z][a-z][0-9]_" and may not begin with a
1235 digit.</para></listitem>
1236 <listitem><para>Must not contain the '.' (period) character.</para></listitem>
1237 <listitem><para>Must not exceed the maximum name length.</para></listitem>
1238 <listitem><para>Must be at least 1 byte in length.</para></listitem>
1242 <sect3 id="message-protocol-names-error">
1243 <title>Error names</title>
1245 Error names have the same restrictions as interface names.
1250 <sect2 id="message-protocol-types">
1251 <title>Message Types</title>
1253 Each of the message types (<literal>METHOD_CALL</literal>, <literal>METHOD_RETURN</literal>, <literal>ERROR</literal>, and
1254 <literal>SIGNAL</literal>) has its own expected usage conventions and header fields.
1255 This section describes these conventions.
1257 <sect3 id="message-protocol-types-method">
1258 <title>Method Calls</title>
1260 Some messages invoke an operation on a remote object. These are
1261 called method call messages and have the type tag <literal>METHOD_CALL</literal>. Such
1262 messages map naturally to methods on objects in a typical program.
1265 A method call message is required to have a <literal>MEMBER</literal> header field
1266 indicating the name of the method. Optionally, the message has an
1267 <literal>INTERFACE</literal> field giving the interface the method is a part of. In the
1268 absence of an <literal>INTERFACE</literal> field, if two interfaces on the same object have
1269 a method with the same name, it is undefined which of the two methods
1270 will be invoked. Implementations may also choose to return an error in
1271 this ambiguous case. However, if a method name is unique
1272 implementations must not require an interface field.
1275 Method call messages also include a <literal>PATH</literal> field
1276 indicating the object to invoke the method on. If the call is passing
1277 through a message bus, the message will also have a
1278 <literal>DESTINATION</literal> field giving the name of the connection
1279 to receive the message.
1282 When an application handles a method call message, it is required to
1283 return a reply. The reply is identified by a <literal>REPLY_SERIAL</literal> header field
1284 indicating the serial number of the <literal>METHOD_CALL</literal> being replied to. The
1285 reply can have one of two types; either <literal>METHOD_RETURN</literal> or <literal>ERROR</literal>.
1288 If the reply has type <literal>METHOD_RETURN</literal>, the arguments to the reply message
1289 are the return value(s) or "out parameters" of the method call.
1290 If the reply has type <literal>ERROR</literal>, then an "exception" has been thrown,
1291 and the call fails; no return value will be provided. It makes
1292 no sense to send multiple replies to the same method call.
1295 Even if a method call has no return values, a <literal>METHOD_RETURN</literal>
1296 reply is required, so the caller will know the method
1297 was successfully processed.
1300 The <literal>METHOD_RETURN</literal> or <literal>ERROR</literal> reply message must have the <literal>REPLY_SERIAL</literal>
1304 If a <literal>METHOD_CALL</literal> message has the flag <literal>NO_REPLY_EXPECTED</literal>,
1305 then as an optimization the application receiving the method
1306 call may choose to omit the reply message (regardless of
1307 whether the reply would have been <literal>METHOD_RETURN</literal> or <literal>ERROR</literal>).
1308 However, it is also acceptable to ignore the <literal>NO_REPLY_EXPECTED</literal>
1309 flag and reply anyway.
1312 Unless a message has the flag <literal>NO_AUTO_START</literal>, if the
1313 destination name does not exist then a program to own the destination
1314 name will be started before the message is delivered. The message
1315 will be held until the new program is successfully started or has
1316 failed to start; in case of failure, an error will be returned. This
1317 flag is only relevant in the context of a message bus, it is ignored
1318 during one-to-one communication with no intermediate bus.
1320 <sect4 id="message-protocol-types-method-apis">
1321 <title>Mapping method calls to native APIs</title>
1323 APIs for D-Bus may map method calls to a method call in a specific
1324 programming language, such as C++, or may map a method call written
1325 in an IDL to a D-Bus message.
1328 In APIs of this nature, arguments to a method are often termed "in"
1329 (which implies sent in the <literal>METHOD_CALL</literal>), or "out" (which implies
1330 returned in the <literal>METHOD_RETURN</literal>). Some APIs such as CORBA also have
1331 "inout" arguments, which are both sent and received, i.e. the caller
1332 passes in a value which is modified. Mapped to D-Bus, an "inout"
1333 argument is equivalent to an "in" argument, followed by an "out"
1334 argument. You can't pass things "by reference" over the wire, so
1335 "inout" is purely an illusion of the in-process API.
1338 Given a method with zero or one return values, followed by zero or more
1339 arguments, where each argument may be "in", "out", or "inout", the
1340 caller constructs a message by appending each "in" or "inout" argument,
1341 in order. "out" arguments are not represented in the caller's message.
1344 The recipient constructs a reply by appending first the return value
1345 if any, then each "out" or "inout" argument, in order.
1346 "in" arguments are not represented in the reply message.
1349 Error replies are normally mapped to exceptions in languages that have
1353 In converting from native APIs to D-Bus, it is perhaps nice to
1354 map D-Bus naming conventions ("FooBar") to native conventions
1355 such as "fooBar" or "foo_bar" automatically. This is OK
1356 as long as you can say that the native API is one that
1357 was specifically written for D-Bus. It makes the most sense
1358 when writing object implementations that will be exported
1359 over the bus. Object proxies used to invoke remote D-Bus
1360 objects probably need the ability to call any D-Bus method,
1361 and thus a magic name mapping like this could be a problem.
1364 This specification doesn't require anything of native API bindings;
1365 the preceding is only a suggested convention for consistency
1371 <sect3 id="message-protocol-types-signal">
1372 <title>Signal Emission</title>
1374 Unlike method calls, signal emissions have no replies.
1375 A signal emission is simply a single message of type <literal>SIGNAL</literal>.
1376 It must have three header fields: <literal>PATH</literal> giving the object
1377 the signal was emitted from, plus <literal>INTERFACE</literal> and <literal>MEMBER</literal> giving
1378 the fully-qualified name of the signal. The <literal>INTERFACE</literal> header is required
1379 for signals, though it is optional for method calls.
1383 <sect3 id="message-protocol-types-errors">
1384 <title>Errors</title>
1386 Messages of type <literal>ERROR</literal> are most commonly replies
1387 to a <literal>METHOD_CALL</literal>, but may be returned in reply
1388 to any kind of message. The message bus for example
1389 will return an <literal>ERROR</literal> in reply to a signal emission if
1390 the bus does not have enough memory to send the signal.
1393 An <literal>ERROR</literal> may have any arguments, but if the first
1394 argument is a <literal>STRING</literal>, it must be an error message.
1395 The error message may be logged or shown to the user
1400 <sect3 id="message-protocol-types-notation">
1401 <title>Notation in this document</title>
1403 This document uses a simple pseudo-IDL to describe particular method
1404 calls and signals. Here is an example of a method call:
1406 org.freedesktop.DBus.StartServiceByName (in STRING name, in UINT32 flags,
1407 out UINT32 resultcode)
1409 This means <literal>INTERFACE</literal> = org.freedesktop.DBus, <literal>MEMBER</literal> = StartServiceByName,
1410 <literal>METHOD_CALL</literal> arguments are <literal>STRING</literal> and <literal>UINT32</literal>, <literal>METHOD_RETURN</literal> argument
1411 is <literal>UINT32</literal>. Remember that the <literal>MEMBER</literal> field can't contain any '.' (period)
1412 characters so it's known that the last part of the name in
1413 the "IDL" is the member name.
1416 In C++ that might end up looking like this:
1418 unsigned int org::freedesktop::DBus::StartServiceByName (const char *name,
1419 unsigned int flags);
1421 or equally valid, the return value could be done as an argument:
1423 void org::freedesktop::DBus::StartServiceByName (const char *name,
1425 unsigned int *resultcode);
1427 It's really up to the API designer how they want to make
1428 this look. You could design an API where the namespace wasn't used
1429 in C++, using STL or Qt, using varargs, or whatever you wanted.
1432 Signals are written as follows:
1434 org.freedesktop.DBus.NameLost (STRING name)
1436 Signals don't specify "in" vs. "out" because only
1437 a single direction is possible.
1440 It isn't especially encouraged to use this lame pseudo-IDL in actual
1441 API implementations; you might use the native notation for the
1442 language you're using, or you might use COM or CORBA IDL, for example.
1447 <sect2 id="message-protocol-handling-invalid">
1448 <title>Invalid Protocol and Spec Extensions</title>
1451 For security reasons, the D-Bus protocol should be strictly parsed and
1452 validated, with the exception of defined extension points. Any invalid
1453 protocol or spec violations should result in immediately dropping the
1454 connection without notice to the other end. Exceptions should be
1455 carefully considered, e.g. an exception may be warranted for a
1456 well-understood idiosyncrasy of a widely-deployed implementation. In
1457 cases where the other end of a connection is 100% trusted and known to
1458 be friendly, skipping validation for performance reasons could also make
1459 sense in certain cases.
1463 Generally speaking violations of the "must" requirements in this spec
1464 should be considered possible attempts to exploit security, and violations
1465 of the "should" suggestions should be considered legitimate (though perhaps
1466 they should generate an error in some cases).
1470 The following extension points are built in to D-Bus on purpose and must
1471 not be treated as invalid protocol. The extension points are intended
1472 for use by future versions of this spec, they are not intended for third
1473 parties. At the moment, the only way a third party could extend D-Bus
1474 without breaking interoperability would be to introduce a way to negotiate new
1475 feature support as part of the auth protocol, using EXTENSION_-prefixed
1476 commands. There is not yet a standard way to negotiate features.
1480 In the authentication protocol (see <xref linkend="auth-protocol"/>) unknown
1481 commands result in an ERROR rather than a disconnect. This enables
1482 future extensions to the protocol. Commands starting with EXTENSION_ are
1483 reserved for third parties.
1488 The authentication protocol supports pluggable auth mechanisms.
1493 The address format (see <xref linkend="addresses"/>) supports new
1499 Messages with an unknown type (something other than
1500 <literal>METHOD_CALL</literal>, <literal>METHOD_RETURN</literal>,
1501 <literal>ERROR</literal>, <literal>SIGNAL</literal>) are ignored.
1502 Unknown-type messages must still be well-formed in the same way
1503 as the known messages, however. They still have the normal
1509 Header fields with an unknown or unexpected field code must be ignored,
1510 though again they must still be well-formed.
1515 New standard interfaces (with new methods and signals) can of course be added.
1525 <sect1 id="auth-protocol">
1526 <title>Authentication Protocol</title>
1528 Before the flow of messages begins, two applications must
1529 authenticate. A simple plain-text protocol is used for
1530 authentication; this protocol is a SASL profile, and maps fairly
1531 directly from the SASL specification. The message encoding is
1532 NOT used here, only plain text messages.
1535 In examples, "C:" and "S:" indicate lines sent by the client and
1536 server respectively.
1538 <sect2 id="auth-protocol-overview">
1539 <title>Protocol Overview</title>
1541 The protocol is a line-based protocol, where each line ends with
1542 \r\n. Each line begins with an all-caps ASCII command name containing
1543 only the character range [A-Z_], a space, then any arguments for the
1544 command, then the \r\n ending the line. The protocol is
1545 case-sensitive. All bytes must be in the ASCII character set.
1547 Commands from the client to the server are as follows:
1550 <listitem><para>AUTH [mechanism] [initial-response]</para></listitem>
1551 <listitem><para>CANCEL</para></listitem>
1552 <listitem><para>BEGIN</para></listitem>
1553 <listitem><para>DATA <data in hex encoding></para></listitem>
1554 <listitem><para>ERROR [human-readable error explanation]</para></listitem>
1555 <listitem><para>NEGOTIATE_UNIX_FD</para></listitem>
1558 From server to client are as follows:
1561 <listitem><para>REJECTED <space-separated list of mechanism names></para></listitem>
1562 <listitem><para>OK <GUID in hex></para></listitem>
1563 <listitem><para>DATA <data in hex encoding></para></listitem>
1564 <listitem><para>ERROR</para></listitem>
1565 <listitem><para>AGREE_UNIX_FD</para></listitem>
1569 Unofficial extensions to the command set must begin with the letters
1570 "EXTENSION_", to avoid conflicts with future official commands.
1571 For example, "EXTENSION_COM_MYDOMAIN_DO_STUFF".
1574 <sect2 id="auth-nul-byte">
1575 <title>Special credentials-passing nul byte</title>
1577 Immediately after connecting to the server, the client must send a
1578 single nul byte. This byte may be accompanied by credentials
1579 information on some operating systems that use sendmsg() with
1580 SCM_CREDS or SCM_CREDENTIALS to pass credentials over UNIX domain
1581 sockets. However, the nul byte must be sent even on other kinds of
1582 socket, and even on operating systems that do not require a byte to be
1583 sent in order to transmit credentials. The text protocol described in
1584 this document begins after the single nul byte. If the first byte
1585 received from the client is not a nul byte, the server may disconnect
1589 A nul byte in any context other than the initial byte is an error;
1590 the protocol is ASCII-only.
1593 The credentials sent along with the nul byte may be used with the
1594 SASL mechanism EXTERNAL.
1597 <sect2 id="auth-command-auth">
1598 <title>AUTH command</title>
1600 If an AUTH command has no arguments, it is a request to list
1601 available mechanisms. The server must respond with a REJECTED
1602 command listing the mechanisms it understands, or with an error.
1605 If an AUTH command specifies a mechanism, and the server supports
1606 said mechanism, the server should begin exchanging SASL
1607 challenge-response data with the client using DATA commands.
1610 If the server does not support the mechanism given in the AUTH
1611 command, it must send either a REJECTED command listing the mechanisms
1612 it does support, or an error.
1615 If the [initial-response] argument is provided, it is intended for use
1616 with mechanisms that have no initial challenge (or an empty initial
1617 challenge), as if it were the argument to an initial DATA command. If
1618 the selected mechanism has an initial challenge and [initial-response]
1619 was provided, the server should reject authentication by sending
1623 If authentication succeeds after exchanging DATA commands,
1624 an OK command must be sent to the client.
1627 The first octet received by the server after the \r\n of the BEGIN
1628 command from the client must be the first octet of the
1629 authenticated/encrypted stream of D-Bus messages.
1632 If BEGIN is received by the server, the first octet received
1633 by the client after the \r\n of the OK command must be the
1634 first octet of the authenticated/encrypted stream of D-Bus
1638 <sect2 id="auth-command-cancel">
1639 <title>CANCEL Command</title>
1641 At any time up to sending the BEGIN command, the client may send a
1642 CANCEL command. On receiving the CANCEL command, the server must
1643 send a REJECTED command and abort the current authentication
1647 <sect2 id="auth-command-data">
1648 <title>DATA Command</title>
1650 The DATA command may come from either client or server, and simply
1651 contains a hex-encoded block of data to be interpreted
1652 according to the SASL mechanism in use.
1655 Some SASL mechanisms support sending an "empty string";
1656 FIXME we need some way to do this.
1659 <sect2 id="auth-command-begin">
1660 <title>BEGIN Command</title>
1662 The BEGIN command acknowledges that the client has received an
1663 OK command from the server, and that the stream of messages
1667 The first octet received by the server after the \r\n of the BEGIN
1668 command from the client must be the first octet of the
1669 authenticated/encrypted stream of D-Bus messages.
1672 <sect2 id="auth-command-rejected">
1673 <title>REJECTED Command</title>
1675 The REJECTED command indicates that the current authentication
1676 exchange has failed, and further exchange of DATA is inappropriate.
1677 The client would normally try another mechanism, or try providing
1678 different responses to challenges.
1680 Optionally, the REJECTED command has a space-separated list of
1681 available auth mechanisms as arguments. If a server ever provides
1682 a list of supported mechanisms, it must provide the same list
1683 each time it sends a REJECTED message. Clients are free to
1684 ignore all lists received after the first.
1687 <sect2 id="auth-command-ok">
1688 <title>OK Command</title>
1690 The OK command indicates that the client has been
1691 authenticated. The client may now proceed with negotiating
1692 Unix file descriptor passing. To do that it shall send
1693 NEGOTIATE_UNIX_FD to the server.
1696 Otherwise, the client must respond to the OK command by
1697 sending a BEGIN command, followed by its stream of messages,
1698 or by disconnecting. The server must not accept additional
1699 commands using this protocol after the BEGIN command has been
1700 received. Further communication will be a stream of D-Bus
1701 messages (optionally encrypted, as negotiated) rather than
1705 If a client sends BEGIN the first octet received by the client
1706 after the \r\n of the OK command must be the first octet of
1707 the authenticated/encrypted stream of D-Bus messages.
1710 The OK command has one argument, which is the GUID of the server.
1711 See <xref linkend="addresses"/> for more on server GUIDs.
1714 <sect2 id="auth-command-error">
1715 <title>ERROR Command</title>
1717 The ERROR command indicates that either server or client did not
1718 know a command, does not accept the given command in the current
1719 context, or did not understand the arguments to the command. This
1720 allows the protocol to be extended; a client or server can send a
1721 command present or permitted only in new protocol versions, and if
1722 an ERROR is received instead of an appropriate response, fall back
1723 to using some other technique.
1726 If an ERROR is sent, the server or client that sent the
1727 error must continue as if the command causing the ERROR had never been
1728 received. However, the the server or client receiving the error
1729 should try something other than whatever caused the error;
1730 if only canceling/rejecting the authentication.
1733 If the D-Bus protocol changes incompatibly at some future time,
1734 applications implementing the new protocol would probably be able to
1735 check for support of the new protocol by sending a new command and
1736 receiving an ERROR from applications that don't understand it. Thus the
1737 ERROR feature of the auth protocol is an escape hatch that lets us
1738 negotiate extensions or changes to the D-Bus protocol in the future.
1741 <sect2 id="auth-command-negotiate-unix-fd">
1742 <title>NEGOTIATE_UNIX_FD Command</title>
1744 The NEGOTIATE_UNIX_FD command indicates that the client
1745 supports Unix file descriptor passing. This command may only
1746 be sent after the connection is authenticated, i.e. after OK
1747 was received by the client. This command may only be sent on
1748 transports that support Unix file descriptor passing.
1751 On receiving NEGOTIATE_UNIX_FD the server must respond with
1752 either AGREE_UNIX_FD or ERROR. It shall respond the former if
1753 the transport chosen supports Unix file descriptor passing and
1754 the server supports this feature. It shall respond the latter
1755 if the transport does not support Unix file descriptor
1756 passing, the server does not support this feature, or the
1757 server decides not to enable file descriptor passing due to
1758 security or other reasons.
1761 <sect2 id="auth-command-agree-unix-fd">
1762 <title>AGREE_UNIX_FD Command</title>
1764 The AGREE_UNIX_FD command indicates that the server supports
1765 Unix file descriptor passing. This command may only be sent
1766 after the connection is authenticated, and the client sent
1767 NEGOTIATE_UNIX_FD to enable Unix file descriptor passing. This
1768 command may only be sent on transports that support Unix file
1772 On receiving AGREE_UNIX_FD the client must respond with BEGIN,
1773 followed by its stream of messages, or by disconnecting. The
1774 server must not accept additional commands using this protocol
1775 after the BEGIN command has been received. Further
1776 communication will be a stream of D-Bus messages (optionally
1777 encrypted, as negotiated) rather than this protocol.
1780 <sect2 id="auth-command-future">
1781 <title>Future Extensions</title>
1783 Future extensions to the authentication and negotiation
1784 protocol are possible. For that new commands may be
1785 introduced. If a client or server receives an unknown command
1786 it shall respond with ERROR and not consider this fatal. New
1787 commands may be introduced both before, and after
1788 authentication, i.e. both before and after the OK command.
1791 <sect2 id="auth-examples">
1792 <title>Authentication examples</title>
1796 <title>Example of successful magic cookie authentication</title>
1798 (MAGIC_COOKIE is a made up mechanism)
1800 C: AUTH MAGIC_COOKIE 3138363935333137393635383634
1806 <title>Example of finding out mechanisms then picking one</title>
1809 S: REJECTED KERBEROS_V4 SKEY
1810 C: AUTH SKEY 7ab83f32ee
1811 S: DATA 8799cabb2ea93e
1812 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f
1818 <title>Example of client sends unknown command then falls back to regular auth</title>
1822 C: AUTH MAGIC_COOKIE 3736343435313230333039
1828 <title>Example of server doesn't support initial auth mechanism</title>
1830 C: AUTH MAGIC_COOKIE 3736343435313230333039
1831 S: REJECTED KERBEROS_V4 SKEY
1832 C: AUTH SKEY 7ab83f32ee
1833 S: DATA 8799cabb2ea93e
1834 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f
1840 <title>Example of wrong password or the like followed by successful retry</title>
1842 C: AUTH MAGIC_COOKIE 3736343435313230333039
1843 S: REJECTED KERBEROS_V4 SKEY
1844 C: AUTH SKEY 7ab83f32ee
1845 S: DATA 8799cabb2ea93e
1846 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f
1848 C: AUTH SKEY 7ab83f32ee
1849 S: DATA 8799cabb2ea93e
1850 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f
1856 <title>Example of skey cancelled and restarted</title>
1858 C: AUTH MAGIC_COOKIE 3736343435313230333039
1859 S: REJECTED KERBEROS_V4 SKEY
1860 C: AUTH SKEY 7ab83f32ee
1861 S: DATA 8799cabb2ea93e
1864 C: AUTH SKEY 7ab83f32ee
1865 S: DATA 8799cabb2ea93e
1866 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f
1872 <title>Example of successful magic cookie authentication with successful negotiation of Unix FD passing</title>
1874 (MAGIC_COOKIE is a made up mechanism)
1876 C: AUTH MAGIC_COOKIE 3138363935333137393635383634
1878 C: NEGOTIATE_UNIX_FD
1884 <title>Example of successful magic cookie authentication with unsuccessful negotiation of Unix FD passing</title>
1886 (MAGIC_COOKIE is a made up mechanism)
1888 C: AUTH MAGIC_COOKIE 3138363935333137393635383634
1890 C: NEGOTIATE_UNIX_FD
1897 <sect2 id="auth-states">
1898 <title>Authentication state diagrams</title>
1901 This section documents the auth protocol in terms of
1902 a state machine for the client and the server. This is
1903 probably the most robust way to implement the protocol.
1906 <sect3 id="auth-states-client">
1907 <title>Client states</title>
1910 To more precisely describe the interaction between the
1911 protocol state machine and the authentication mechanisms the
1912 following notation is used: MECH(CHALL) means that the
1913 server challenge CHALL was fed to the mechanism MECH, which
1919 CONTINUE(RESP) means continue the auth conversation
1920 and send RESP as the response to the server;
1926 OK(RESP) means that after sending RESP to the server
1927 the client side of the auth conversation is finished
1928 and the server should return "OK";
1934 ERROR means that CHALL was invalid and could not be
1940 Both RESP and CHALL may be empty.
1944 The Client starts by getting an initial response from the
1945 default mechanism and sends AUTH MECH RESP, or AUTH MECH if
1946 the mechanism did not provide an initial response. If the
1947 mechanism returns CONTINUE, the client starts in state
1948 <emphasis>WaitingForData</emphasis>, if the mechanism
1949 returns OK the client starts in state
1950 <emphasis>WaitingForOK</emphasis>.
1954 The client should keep track of available mechanisms and
1955 which it mechanisms it has already attempted. This list is
1956 used to decide which AUTH command to send. When the list is
1957 exhausted, the client should give up and close the
1962 <title><emphasis>WaitingForData</emphasis></title>
1970 MECH(CHALL) returns CONTINUE(RESP) → send
1972 <emphasis>WaitingForData</emphasis>
1976 MECH(CHALL) returns OK(RESP) → send DATA
1977 RESP, goto <emphasis>WaitingForOK</emphasis>
1981 MECH(CHALL) returns ERROR → send ERROR
1982 [msg], goto <emphasis>WaitingForData</emphasis>
1990 Receive REJECTED [mechs] →
1991 send AUTH [next mech], goto
1992 WaitingForData or <emphasis>WaitingForOK</emphasis>
1997 Receive ERROR → send
1999 <emphasis>WaitingForReject</emphasis>
2004 Receive OK → send
2005 BEGIN, terminate auth
2006 conversation, authenticated
2011 Receive anything else → send
2013 <emphasis>WaitingForData</emphasis>
2021 <title><emphasis>WaitingForOK</emphasis></title>
2026 Receive OK → send BEGIN, terminate auth
2027 conversation, <emphasis>authenticated</emphasis>
2032 Receive REJECT [mechs] → send AUTH [next mech],
2033 goto <emphasis>WaitingForData</emphasis> or
2034 <emphasis>WaitingForOK</emphasis>
2040 Receive DATA → send CANCEL, goto
2041 <emphasis>WaitingForReject</emphasis>
2047 Receive ERROR → send CANCEL, goto
2048 <emphasis>WaitingForReject</emphasis>
2054 Receive anything else → send ERROR, goto
2055 <emphasis>WaitingForOK</emphasis>
2063 <title><emphasis>WaitingForReject</emphasis></title>
2068 Receive REJECT [mechs] → send AUTH [next mech],
2069 goto <emphasis>WaitingForData</emphasis> or
2070 <emphasis>WaitingForOK</emphasis>
2076 Receive anything else → terminate auth
2077 conversation, disconnect
2086 <sect3 id="auth-states-server">
2087 <title>Server states</title>
2090 For the server MECH(RESP) means that the client response
2091 RESP was fed to the the mechanism MECH, which returns one of
2096 CONTINUE(CHALL) means continue the auth conversation and
2097 send CHALL as the challenge to the client;
2103 OK means that the client has been successfully
2110 REJECT means that the client failed to authenticate or
2111 there was an error in RESP.
2116 The server starts out in state
2117 <emphasis>WaitingForAuth</emphasis>. If the client is
2118 rejected too many times the server must disconnect the
2123 <title><emphasis>WaitingForAuth</emphasis></title>
2129 Receive AUTH → send REJECTED [mechs], goto
2130 <emphasis>WaitingForAuth</emphasis>
2136 Receive AUTH MECH RESP
2140 MECH not valid mechanism → send REJECTED
2142 <emphasis>WaitingForAuth</emphasis>
2146 MECH(RESP) returns CONTINUE(CHALL) → send
2148 <emphasis>WaitingForData</emphasis>
2152 MECH(RESP) returns OK → send OK, goto
2153 <emphasis>WaitingForBegin</emphasis>
2157 MECH(RESP) returns REJECT → send REJECTED
2159 <emphasis>WaitingForAuth</emphasis>
2167 Receive BEGIN → terminate
2168 auth conversation, disconnect
2174 Receive ERROR → send REJECTED [mechs], goto
2175 <emphasis>WaitingForAuth</emphasis>
2181 Receive anything else → send
2183 <emphasis>WaitingForAuth</emphasis>
2192 <title><emphasis>WaitingForData</emphasis></title>
2200 MECH(RESP) returns CONTINUE(CHALL) → send
2202 <emphasis>WaitingForData</emphasis>
2206 MECH(RESP) returns OK → send OK, goto
2207 <emphasis>WaitingForBegin</emphasis>
2211 MECH(RESP) returns REJECT → send REJECTED
2213 <emphasis>WaitingForAuth</emphasis>
2221 Receive BEGIN → terminate auth conversation,
2228 Receive CANCEL → send REJECTED [mechs], goto
2229 <emphasis>WaitingForAuth</emphasis>
2235 Receive ERROR → send REJECTED [mechs], goto
2236 <emphasis>WaitingForAuth</emphasis>
2242 Receive anything else → send ERROR, goto
2243 <emphasis>WaitingForData</emphasis>
2251 <title><emphasis>WaitingForBegin</emphasis></title>
2256 Receive BEGIN → terminate auth conversation,
2257 client authenticated
2263 Receive CANCEL → send REJECTED [mechs], goto
2264 <emphasis>WaitingForAuth</emphasis>
2270 Receive ERROR → send REJECTED [mechs], goto
2271 <emphasis>WaitingForAuth</emphasis>
2277 Receive anything else → send ERROR, goto
2278 <emphasis>WaitingForBegin</emphasis>
2288 <sect2 id="auth-mechanisms">
2289 <title>Authentication mechanisms</title>
2291 This section describes some new authentication mechanisms.
2292 D-Bus also allows any standard SASL mechanism of course.
2294 <sect3 id="auth-mechanisms-sha">
2295 <title>DBUS_COOKIE_SHA1</title>
2297 The DBUS_COOKIE_SHA1 mechanism is designed to establish that a client
2298 has the ability to read a private file owned by the user being
2299 authenticated. If the client can prove that it has access to a secret
2300 cookie stored in this file, then the client is authenticated.
2301 Thus the security of DBUS_COOKIE_SHA1 depends on a secure home
2305 Throughout this description, "hex encoding" must output the digits
2306 from a to f in lower-case; the digits A to F must not be used
2307 in the DBUS_COOKIE_SHA1 mechanism.
2310 Authentication proceeds as follows:
2314 The client sends the username it would like to authenticate
2320 The server sends the name of its "cookie context" (see below); a
2321 space character; the integer ID of the secret cookie the client
2322 must demonstrate knowledge of; a space character; then a
2323 randomly-generated challenge string, all of this hex-encoded into
2329 The client locates the cookie and generates its own
2330 randomly-generated challenge string. The client then concatenates
2331 the server's decoded challenge, a ":" character, its own challenge,
2332 another ":" character, and the cookie. It computes the SHA-1 hash
2333 of this composite string as a hex digest. It concatenates the
2334 client's challenge string, a space character, and the SHA-1 hex
2335 digest, hex-encodes the result and sends it back to the server.
2340 The server generates the same concatenated string used by the
2341 client and computes its SHA-1 hash. It compares the hash with
2342 the hash received from the client; if the two hashes match, the
2343 client is authenticated.
2349 Each server has a "cookie context," which is a name that identifies a
2350 set of cookies that apply to that server. A sample context might be
2351 "org_freedesktop_session_bus". Context names must be valid ASCII,
2352 nonzero length, and may not contain the characters slash ("/"),
2353 backslash ("\"), space (" "), newline ("\n"), carriage return ("\r"),
2354 tab ("\t"), or period ("."). There is a default context,
2355 "org_freedesktop_general" that's used by servers that do not specify
2359 Cookies are stored in a user's home directory, in the directory
2360 <filename>~/.dbus-keyrings/</filename>. This directory must
2361 not be readable or writable by other users. If it is,
2362 clients and servers must ignore it. The directory
2363 contains cookie files named after the cookie context.
2366 A cookie file contains one cookie per line. Each line
2367 has three space-separated fields:
2371 The cookie ID number, which must be a non-negative integer and
2372 may not be used twice in the same file.
2377 The cookie's creation time, in UNIX seconds-since-the-epoch
2383 The cookie itself, a hex-encoded random block of bytes. The cookie
2384 may be of any length, though obviously security increases
2385 as the length increases.
2391 Only server processes modify the cookie file.
2392 They must do so with this procedure:
2396 Create a lockfile name by appending ".lock" to the name of the
2397 cookie file. The server should attempt to create this file
2398 using <literal>O_CREAT | O_EXCL</literal>. If file creation
2399 fails, the lock fails. Servers should retry for a reasonable
2400 period of time, then they may choose to delete an existing lock
2401 to keep users from having to manually delete a stale
2402 lock. <footnote><para>Lockfiles are used instead of real file
2403 locking <literal>fcntl()</literal> because real locking
2404 implementations are still flaky on network
2405 filesystems.</para></footnote>
2410 Once the lockfile has been created, the server loads the cookie
2411 file. It should then delete any cookies that are old (the
2412 timeout can be fairly short), or more than a reasonable
2413 time in the future (so that cookies never accidentally
2414 become permanent, if the clock was set far into the future
2415 at some point). If no recent keys remain, the
2416 server may generate a new key.
2421 The pruned and possibly added-to cookie file
2422 must be resaved atomically (using a temporary
2423 file which is rename()'d).
2428 The lock must be dropped by deleting the lockfile.
2434 Clients need not lock the file in order to load it,
2435 because servers are required to save the file atomically.
2440 <sect1 id="addresses">
2441 <title>Server Addresses</title>
2443 Server addresses consist of a transport name followed by a colon, and
2444 then an optional, comma-separated list of keys and values in the form key=value.
2445 Each value is escaped.
2449 <programlisting>unix:path=/tmp/dbus-test</programlisting>
2450 Which is the address to a unix socket with the path /tmp/dbus-test.
2453 Value escaping is similar to URI escaping but simpler.
2457 The set of optionally-escaped bytes is:
2458 <literal>[0-9A-Za-z_-/.\]</literal>. To escape, each
2459 <emphasis>byte</emphasis> (note, not character) which is not in the
2460 set of optionally-escaped bytes must be replaced with an ASCII
2461 percent (<literal>%</literal>) and the value of the byte in hex.
2462 The hex value must always be two digits, even if the first digit is
2463 zero. The optionally-escaped bytes may be escaped if desired.
2468 To unescape, append each byte in the value; if a byte is an ASCII
2469 percent (<literal>%</literal>) character then append the following
2470 hex value instead. It is an error if a <literal>%</literal> byte
2471 does not have two hex digits following. It is an error if a
2472 non-optionally-escaped byte is seen unescaped.
2476 The set of optionally-escaped bytes is intended to preserve address
2477 readability and convenience.
2481 A server may specify a key-value pair with the key <literal>guid</literal>
2482 and the value a hex-encoded 16-byte sequence. <xref linkend="uuids"/>
2483 describes the format of the <literal>guid</literal> field. If present,
2484 this UUID may be used to distinguish one server address from another. A
2485 server should use a different UUID for each address it listens on. For
2486 example, if a message bus daemon offers both UNIX domain socket and TCP
2487 connections, but treats clients the same regardless of how they connect,
2488 those two connections are equivalent post-connection but should have
2489 distinct UUIDs to distinguish the kinds of connection.
2493 The intent of the address UUID feature is to allow a client to avoid
2494 opening multiple identical connections to the same server, by allowing the
2495 client to check whether an address corresponds to an already-existing
2496 connection. Comparing two addresses is insufficient, because addresses
2497 can be recycled by distinct servers, and equivalent addresses may look
2498 different if simply compared as strings (for example, the host in a TCP
2499 address can be given as an IP address or as a hostname).
2503 Note that the address key is <literal>guid</literal> even though the
2504 rest of the API and documentation says "UUID," for historical reasons.
2508 [FIXME clarify if attempting to connect to each is a requirement
2509 or just a suggestion]
2510 When connecting to a server, multiple server addresses can be
2511 separated by a semi-colon. The library will then try to connect
2512 to the first address and if that fails, it'll try to connect to
2513 the next one specified, and so forth. For example
2514 <programlisting>unix:path=/tmp/dbus-test;unix:path=/tmp/dbus-test2</programlisting>
2519 <sect1 id="transports">
2520 <title>Transports</title>
2522 [FIXME we need to specify in detail each transport and its possible arguments]
2524 Current transports include: unix domain sockets (including
2525 abstract namespace on linux), launchd, TCP/IP, and a debug/testing transport
2526 using in-process pipes. Future possible transports include one that
2527 tunnels over X11 protocol.
2530 <sect2 id="transports-unix-domain-sockets">
2531 <title>Unix Domain Sockets</title>
2533 Unix domain sockets can be either paths in the file system or on Linux
2534 kernels, they can be abstract which are similar to paths but
2535 do not show up in the file system.
2539 When a socket is opened by the D-Bus library it truncates the path
2540 name right before the first trailing Nul byte. This is true for both
2541 normal paths and abstract paths. Note that this is a departure from
2542 previous versions of D-Bus that would create sockets with a fixed
2543 length path name. Names which were shorter than the fixed length
2544 would be padded by Nul bytes.
2547 Unix domain sockets are not available on windows.
2549 <sect3 id="transports-unix-domain-sockets-addresses">
2550 <title>Server Address Format</title>
2552 Unix domain socket addresses are identified by the "unix:" prefix
2553 and support the following key/value pairs:
2560 <entry>Values</entry>
2561 <entry>Description</entry>
2567 <entry>(path)</entry>
2568 <entry>path of the unix domain socket. If set, the "tmpdir" and "abstract" key must not be set.</entry>
2571 <entry>tmpdir</entry>
2572 <entry>(path)</entry>
2573 <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>
2576 <entry>abstract</entry>
2577 <entry>(string)</entry>
2578 <entry>unique string (path) in the abstract namespace. If set, the "path" or "tempdir" key must not be set.</entry>
2585 <sect2 id="transports-launchd">
2586 <title>launchd</title>
2588 launchd is a open-source server management system that replaces init, inetd
2589 and cron on Apple Mac OS X versions 10.4 and above. It provides a common session
2590 bus address for each user and deprecates the X11-enabled D-Bus launcher on OSX.
2594 launchd allocates a socket and provides it with the unix path through the
2595 DBUS_LAUNCHD_SESSION_BUS_SOCKET variable in launchd's environment. Every process
2596 spawned by launchd (or dbus-daemon, if it was started by launchd) can access
2597 it through its environment.
2598 Other processes can query for the launchd socket by executing:
2599 $ launchctl getenv DBUS_LAUNCHD_SESSION_BUS_SOCKET
2600 This is normally done by the D-Bus client library so doesn't have to be done
2604 launchd is not available on Microsoft Windows.
2606 <sect3 id="transports-launchd-addresses">
2607 <title>Server Address Format</title>
2609 launchd addresses are identified by the "launchd:" prefix
2610 and support the following key/value pairs:
2617 <entry>Values</entry>
2618 <entry>Description</entry>
2624 <entry>(environment variable)</entry>
2625 <entry>path of the unix domain socket for the launchd created dbus-daemon.</entry>
2632 <sect2 id="transports-tcp-sockets">
2633 <title>TCP Sockets</title>
2635 The tcp transport provides TCP/IP based connections between clients
2636 located on the same or different hosts.
2639 Using tcp transport without any additional secure authentification mechanismus
2640 over a network is unsecure.
2643 Windows notes: Because of the tcp stack on windows does not provide sending
2644 credentials over a tcp connection, the EXTERNAL authentification
2645 mechanismus does not work.
2647 <sect3 id="transports-tcp-sockets-addresses">
2648 <title>Server Address Format</title>
2650 TCP/IP socket addresses are identified by the "tcp:" prefix
2651 and support the following key/value pairs:
2658 <entry>Values</entry>
2659 <entry>Description</entry>
2665 <entry>(string)</entry>
2666 <entry>dns name or ip address</entry>
2670 <entry>(number)</entry>
2671 <entry>The tcp port the server will open. A zero value let the server
2672 choose a free port provided from the underlaying operating system.
2673 libdbus is able to retrieve the real used port from the server.
2677 <entry>family</entry>
2678 <entry>(string)</entry>
2679 <entry>If set, provide the type of socket family either "ipv4" or "ipv6". If unset, the family is unspecified.</entry>
2686 <sect2 id="transports-nonce-tcp-sockets">
2687 <title>Nonce-secured TCP Sockets</title>
2689 The nonce-tcp transport provides a secured TCP transport, using a
2690 simple authentication mechanism to ensure that only clients with read
2691 access to a certain location in the filesystem can connect to the server.
2692 The server writes a secret, the nonce, to a file and an incoming client
2693 connection is only accepted if the client sends the nonce right after
2694 the connect. The nonce mechanism requires no setup and is orthogonal to
2695 the higher-level authentication mechanisms described in the
2696 Authentication section.
2700 On start, the server generates a random 16 byte nonce and writes it
2701 to a file in the user's temporary directory. The nonce file location
2702 is published as part of the server's D-Bus address using the
2703 "noncefile" key-value pair.
2705 After an accept, the server reads 16 bytes from the socket. If the
2706 read bytes do not match the nonce stored in the nonce file, the
2707 server MUST immediately drop the connection.
2708 If the nonce match the received byte sequence, the client is accepted
2709 and the transport behaves like an unsecured tcp transport.
2712 After a successful connect to the server socket, the client MUST read
2713 the nonce from the file published by the server via the noncefile=
2714 key-value pair and send it over the socket. After that, the
2715 transport behaves like an unsecured tcp transport.
2717 <sect3 id="transports-nonce-tcp-sockets-addresses">
2718 <title>Server Address Format</title>
2720 Nonce TCP/IP socket addresses uses the "nonce-tcp:" prefix
2721 and support the following key/value pairs:
2728 <entry>Values</entry>
2729 <entry>Description</entry>
2735 <entry>(string)</entry>
2736 <entry>dns name or ip address</entry>
2740 <entry>(number)</entry>
2741 <entry>The tcp port the server will open. A zero value let the server
2742 choose a free port provided from the underlaying operating system.
2743 libdbus is able to retrieve the real used port from the server.
2747 <entry>family</entry>
2748 <entry>(string)</entry>
2749 <entry>If set, provide the type of socket family either "ipv4" or "ipv6". If unset, the family is unspecified.</entry>
2752 <entry>noncefile</entry>
2753 <entry>(path)</entry>
2754 <entry>file location containing the secret</entry>
2762 <sect1 id="meta-transports">
2763 <title>Meta Transports</title>
2765 Meta transports are a kind of transport with special enhancements or
2766 behavior. Currently available meta transports include: autolaunch
2769 <sect2 id="meta-transports-autolaunch">
2770 <title>Autolaunch</title>
2771 <para>The autolaunch transport provides a way for dbus clients to autodetect
2772 a running dbus session bus and to autolaunch a session bus if not present.
2774 <sect3 id="meta-transports-autolaunch-addresses">
2775 <title>Server Address Format</title>
2777 Autolaunch addresses uses the "autolaunch:" prefix and support the
2778 following key/value pairs:
2785 <entry>Values</entry>
2786 <entry>Description</entry>
2791 <entry>scope</entry>
2792 <entry>(string)</entry>
2793 <entry>scope of autolaunch (Windows only)
2797 "*install-path" - limit session bus to dbus installation path.
2798 The dbus installation path is determined from the location of
2799 the shared dbus library. If the library is located in a 'bin'
2800 subdirectory the installation root is the directory above,
2801 otherwise the directory where the library lives is taken as
2804 <install-root>/bin/[lib]dbus-1.dll
2805 <install-root>/[lib]dbus-1.dll
2811 "*user" - limit session bus to the recent user.
2816 other values - specify dedicated session bus like "release",
2828 <sect3 id="meta-transports-autolaunch-windows-implementation">
2829 <title>Windows implementation</title>
2831 On start, the server opens a platform specific transport, creates a mutex
2832 and a shared memory section containing the related session bus address.
2833 This mutex will be inspected by the dbus client library to detect a
2834 running dbus session bus. The access to the mutex and the shared memory
2835 section are protected by global locks.
2838 In the recent implementation the autolaunch transport uses a tcp transport
2839 on localhost with a port choosen from the operating system. This detail may
2840 change in the future.
2843 Disclaimer: The recent implementation is in an early state and may not
2844 work in all cirumstances and/or may have security issues. Because of this
2845 the implementation is not documentated yet.
2850 <sect1 id="naming-conventions">
2851 <title>Naming Conventions</title>
2854 D-Bus namespaces are all lowercase and correspond to reversed domain
2855 names, as with Java. e.g. "org.freedesktop"
2858 Interface, signal, method, and property names are "WindowsStyleCaps", note
2859 that the first letter is capitalized, unlike Java.
2862 Object paths are normally all lowercase with underscores used rather than
2868 <title>UUIDs</title>
2870 A working D-Bus implementation uses universally-unique IDs in two places.
2871 First, each server address has a UUID identifying the address,
2872 as described in <xref linkend="addresses"/>. Second, each operating
2873 system kernel instance running a D-Bus client or server has a UUID
2874 identifying that kernel, retrieved by invoking the method
2875 org.freedesktop.DBus.Peer.GetMachineId() (see <xref
2876 linkend="standard-interfaces-peer"/>).
2879 The term "UUID" in this document is intended literally, i.e. an
2880 identifier that is universally unique. It is not intended to refer to
2881 RFC4122, and in fact the D-Bus UUID is not compatible with that RFC.
2884 The UUID must contain 128 bits of data and be hex-encoded. The
2885 hex-encoded string may not contain hyphens or other non-hex-digit
2886 characters, and it must be exactly 32 characters long. To generate a
2887 UUID, the current reference implementation concatenates 96 bits of random
2888 data followed by the 32-bit time in seconds since the UNIX epoch (in big
2892 It would also be acceptable and probably better to simply generate 128
2893 bits of random data, as long as the random number generator is of high
2894 quality. The timestamp could conceivably help if the random bits are not
2895 very random. With a quality random number generator, collisions are
2896 extremely unlikely even with only 96 bits, so it's somewhat academic.
2899 Implementations should, however, stick to random data for the first 96 bits
2904 <sect1 id="standard-interfaces">
2905 <title>Standard Interfaces</title>
2907 See <xref linkend="message-protocol-types-notation"/> for details on
2908 the notation used in this section. There are some standard interfaces
2909 that may be useful across various D-Bus applications.
2911 <sect2 id="standard-interfaces-peer">
2912 <title><literal>org.freedesktop.DBus.Peer</literal></title>
2914 The <literal>org.freedesktop.DBus.Peer</literal> interface
2917 org.freedesktop.DBus.Peer.Ping ()
2918 org.freedesktop.DBus.Peer.GetMachineId (out STRING machine_uuid)
2922 On receipt of the <literal>METHOD_CALL</literal> message
2923 <literal>org.freedesktop.DBus.Peer.Ping</literal>, an application should do
2924 nothing other than reply with a <literal>METHOD_RETURN</literal> as
2925 usual. It does not matter which object path a ping is sent to. The
2926 reference implementation handles this method automatically.
2929 On receipt of the <literal>METHOD_CALL</literal> message
2930 <literal>org.freedesktop.DBus.Peer.GetMachineId</literal>, an application should
2931 reply with a <literal>METHOD_RETURN</literal> containing a hex-encoded
2932 UUID representing the identity of the machine the process is running on.
2933 This UUID must be the same for all processes on a single system at least
2934 until that system next reboots. It should be the same across reboots
2935 if possible, but this is not always possible to implement and is not
2937 It does not matter which object path a GetMachineId is sent to. The
2938 reference implementation handles this method automatically.
2941 The UUID is intended to be per-instance-of-the-operating-system, so may represent
2942 a virtual machine running on a hypervisor, rather than a physical machine.
2943 Basically if two processes see the same UUID, they should also see the same
2944 shared memory, UNIX domain sockets, process IDs, and other features that require
2945 a running OS kernel in common between the processes.
2948 The UUID is often used where other programs might use a hostname. Hostnames
2949 can change without rebooting, however, or just be "localhost" - so the UUID
2953 <xref linkend="uuids"/> explains the format of the UUID.
2957 <sect2 id="standard-interfaces-introspectable">
2958 <title><literal>org.freedesktop.DBus.Introspectable</literal></title>
2960 This interface has one method:
2962 org.freedesktop.DBus.Introspectable.Introspect (out STRING xml_data)
2966 Objects instances may implement
2967 <literal>Introspect</literal> which returns an XML description of
2968 the object, including its interfaces (with signals and methods), objects
2969 below it in the object path tree, and its properties.
2972 <xref linkend="introspection-format"/> describes the format of this XML string.
2975 <sect2 id="standard-interfaces-properties">
2976 <title><literal>org.freedesktop.DBus.Properties</literal></title>
2978 Many native APIs will have a concept of object <firstterm>properties</firstterm>
2979 or <firstterm>attributes</firstterm>. These can be exposed via the
2980 <literal>org.freedesktop.DBus.Properties</literal> interface.
2984 org.freedesktop.DBus.Properties.Get (in STRING interface_name,
2985 in STRING property_name,
2987 org.freedesktop.DBus.Properties.Set (in STRING interface_name,
2988 in STRING property_name,
2990 org.freedesktop.DBus.Properties.GetAll (in STRING interface_name,
2991 out DICT<STRING,VARIANT> props);
2995 The available properties and whether they are writable can be determined
2996 by calling <literal>org.freedesktop.DBus.Introspectable.Introspect</literal>,
2997 see <xref linkend="standard-interfaces-introspectable"/>.
3000 An empty string may be provided for the interface name; in this case,
3001 if there are multiple properties on an object with the same name,
3002 the results are undefined (picking one by according to an arbitrary
3003 deterministic rule, or returning an error, are the reasonable
3007 If one or more properties change on an object, the
3008 <literal>org.freedesktop.DBus.Properties.PropertiesChanged</literal>
3009 signal may be emitted (this signal was added in 0.14):
3013 org.freedesktop.DBus.Properties.PropertiesChanged (STRING interface_name,
3014 DICT<STRING,VARIANT> changed_properties,
3015 ARRAY<STRING> invalidated_properties);
3019 where <literal>changed_properties</literal> is a dictionary
3020 containing the changed properties with the new values and
3021 <literal>invalidated_properties</literal> is an array of
3022 properties that changed but the value is not conveyed.
3025 Whether the <literal>PropertiesChanged</literal> signal is
3026 supported can be determined by calling
3027 <literal>org.freedesktop.DBus.Introspectable.Introspect</literal>. Note
3028 that the signal may be supported for an object but it may
3029 differ how whether and how it is used on a per-property basis
3030 (for e.g. performance or security reasons). Each property (or
3031 the parent interface) must be annotated with the
3032 <literal>org.freedesktop.DBus.Property.EmitsChangedSignal</literal>
3033 annotation to convey this (usually the default value
3034 <literal>true</literal> is sufficient meaning that the
3035 annotation does not need to be used). See <xref
3036 linkend="introspection-format"/> for details on this
3041 <sect2 id="standard-interfaces-objectmanager">
3042 <title><literal>org.freedesktop.DBus.ObjectManager</literal></title>
3044 An API can optionally make use of this interface for one or
3045 more sub-trees of objects. The root of each sub-tree implements
3046 this interface so other applications can get all objects,
3047 interfaces and properties in a single method call. It is
3048 appropriate to use this interface if users of the tree of
3049 objects are expected to be interested in all interfaces of all
3050 objects in the tree; a more granular API should be used if
3051 users of the objects are expected to be interested in a small
3052 subset of the objects, a small subset of their interfaces, or
3056 The method that applications can use to get all objects and
3057 properties is <literal>GetManagedObjects</literal>:
3061 org.freedesktop.DBus.ObjectManager.GetManagedObjects (out DICT<OBJPATH,DICT<STRING,DICT<STRING,VARIANT>>> objpath_interfaces_and_properties);
3065 The return value of this method is a dict whose keys are
3066 object paths. All returned object paths are children of the
3067 object path implementing this interface, i.e. their object
3068 paths start with the ObjectManager's object path plus '/'.
3071 Each value is a dict whose keys are interfaces names. Each
3072 value in this inner dict is the same dict that would be
3073 returned by the <link
3074 linkend="standard-interfaces-properties">org.freedesktop.DBus.Properties.GetAll()</link>
3075 method for that combination of object path and interface. If
3076 an interface has no properties, the empty dict is returned.
3079 Changes are emitted using the following two signals:
3083 org.freedesktop.DBus.ObjectManager.InterfacesAdded (OBJPATH object_path,
3084 DICT<STRING,DICT<STRING,VARIANT>> interfaces_and_properties);
3085 org.freedesktop.DBus.ObjectManager.InterfacesRemoved (OBJPATH object_path,
3086 ARRAY<STRING> interfaces);
3090 The <literal>InterfacesAdded</literal> signal is emitted when
3091 either a new object is added or when an existing object gains
3092 one or more interfaces. The
3093 <literal>InterfacesRemoved</literal> signal is emitted
3094 whenever an object is removed or it loses one or more
3095 interfaces. The second parameter of the
3096 <literal>InterfacesAdded</literal> signal contains a dict with
3097 the interfaces and properties (if any) that have been added to
3098 the given object path. Similarly, the second parameter of the
3099 <literal>InterfacesRemoved</literal> signal contains an array
3100 of the interfaces that were removed. Note that changes on
3101 properties on existing interfaces are not reported using this
3102 interface - an application should also monitor the existing <link
3103 linkend="standard-interfaces-properties">PropertiesChanged</link>
3104 signal on each object.
3107 Applications SHOULD NOT export objects that are children of an
3108 object (directly or otherwise) implementing this interface but
3109 which are not returned in the reply from the
3110 <literal>GetManagedObjects()</literal> method of this
3111 interface on the given object.
3114 The intent of the <literal>ObjectManager</literal> interface
3115 is to make it easy to write a robust client
3116 implementation. The trivial client implementation only needs
3117 to make two method calls:
3121 org.freedesktop.DBus.AddMatch (bus_proxy,
3122 "type='signal',name='org.example.App',path_namespace='/org/example/App'");
3123 objects = org.freedesktop.DBus.ObjectManager.GetManagedObjects (app_proxy);
3127 on the message bus and the remote application's
3128 <literal>ObjectManager</literal>, respectively. Whenever a new
3129 remote object is created (or an existing object gains a new
3130 interface), the <literal>InterfacesAdded</literal> signal is
3131 emitted, and since this signal contains all properties for the
3132 interfaces, no calls to the
3133 <literal>org.freedesktop.Properties</literal> interface on the
3134 remote object are needed. Additionally, since the initial
3135 <literal>AddMatch()</literal> rule already includes signal
3136 messages from the newly created child object, no new
3137 <literal>AddMatch()</literal> call is needed.
3142 The <literal>org.freedesktop.DBus.ObjectManager</literal>
3143 interface was added in version 0.17 of the D-Bus
3150 <sect1 id="introspection-format">
3151 <title>Introspection Data Format</title>
3153 As described in <xref linkend="standard-interfaces-introspectable"/>,
3154 objects may be introspected at runtime, returning an XML string
3155 that describes the object. The same XML format may be used in
3156 other contexts as well, for example as an "IDL" for generating
3157 static language bindings.
3160 Here is an example of introspection data:
3162 <!DOCTYPE node PUBLIC "-//freedesktop//DTD D-BUS Object Introspection 1.0//EN"
3163 "http://www.freedesktop.org/standards/dbus/1.0/introspect.dtd">
3164 <node name="/org/freedesktop/sample_object">
3165 <interface name="org.freedesktop.SampleInterface">
3166 <method name="Frobate">
3167 <arg name="foo" type="i" direction="in"/>
3168 <arg name="bar" type="s" direction="out"/>
3169 <arg name="baz" type="a{us}" direction="out"/>
3170 <annotation name="org.freedesktop.DBus.Deprecated" value="true"/>
3172 <method name="Bazify">
3173 <arg name="bar" type="(iiu)" direction="in"/>
3174 <arg name="bar" type="v" direction="out"/>
3176 <method name="Mogrify">
3177 <arg name="bar" type="(iiav)" direction="in"/>
3179 <signal name="Changed">
3180 <arg name="new_value" type="b"/>
3182 <property name="Bar" type="y" access="readwrite"/>
3184 <node name="child_of_sample_object"/>
3185 <node name="another_child_of_sample_object"/>
3190 A more formal DTD and spec needs writing, but here are some quick notes.
3194 Only the root <node> element can omit the node name, as it's
3195 known to be the object that was introspected. If the root
3196 <node> does have a name attribute, it must be an absolute
3197 object path. If child <node> have object paths, they must be
3203 If a child <node> has any sub-elements, then they
3204 must represent a complete introspection of the child.
3205 If a child <node> is empty, then it may or may
3206 not have sub-elements; the child must be introspected
3207 in order to find out. The intent is that if an object
3208 knows that its children are "fast" to introspect
3209 it can go ahead and return their information, but
3210 otherwise it can omit it.
3215 The direction element on <arg> may be omitted,
3216 in which case it defaults to "in" for method calls
3217 and "out" for signals. Signals only allow "out"
3218 so while direction may be specified, it's pointless.
3223 The possible directions are "in" and "out",
3224 unlike CORBA there is no "inout"
3229 The possible property access flags are
3230 "readwrite", "read", and "write"
3235 Multiple interfaces can of course be listed for
3241 The "name" attribute on arguments is optional.
3247 Method, interface, property, and signal elements may have
3248 "annotations", which are generic key/value pairs of metadata.
3249 They are similar conceptually to Java's annotations and C# attributes.
3250 Well-known annotations:
3257 <entry>Values (separated by ,)</entry>
3258 <entry>Description</entry>
3263 <entry>org.freedesktop.DBus.Deprecated</entry>
3264 <entry>true,false</entry>
3265 <entry>Whether or not the entity is deprecated; defaults to false</entry>
3268 <entry>org.freedesktop.DBus.GLib.CSymbol</entry>
3269 <entry>(string)</entry>
3270 <entry>The C symbol; may be used for methods and interfaces</entry>
3273 <entry>org.freedesktop.DBus.Method.NoReply</entry>
3274 <entry>true,false</entry>
3275 <entry>If set, don't expect a reply to the method call; defaults to false.</entry>
3278 <entry>org.freedesktop.DBus.Property.EmitsChangedSignal</entry>
3279 <entry>true,invalidates,false</entry>
3282 If set to <literal>false</literal>, the
3283 <literal>org.freedesktop.DBus.Properties.PropertiesChanged</literal>
3285 linkend="standard-interfaces-properties"/> is not
3286 guaranteed to be emitted if the property changes.
3289 If set to <literal>invalidates</literal> the signal
3290 is emitted but the value is not included in the
3294 If set to <literal>true</literal> the signal is
3295 emitted with the value included.
3298 The value for the annotation defaults to
3299 <literal>true</literal> if the enclosing interface
3300 element does not specify the annotation. Otherwise it
3301 defaults to the value specified in the enclosing
3310 <sect1 id="message-bus">
3311 <title>Message Bus Specification</title>
3312 <sect2 id="message-bus-overview">
3313 <title>Message Bus Overview</title>
3315 The message bus accepts connections from one or more applications.
3316 Once connected, applications can exchange messages with other
3317 applications that are also connected to the bus.
3320 In order to route messages among connections, the message bus keeps a
3321 mapping from names to connections. Each connection has one
3322 unique-for-the-lifetime-of-the-bus name automatically assigned.
3323 Applications may request additional names for a connection. Additional
3324 names are usually "well-known names" such as
3325 "org.freedesktop.TextEditor". When a name is bound to a connection,
3326 that connection is said to <firstterm>own</firstterm> the name.
3329 The bus itself owns a special name, <literal>org.freedesktop.DBus</literal>.
3330 This name routes messages to the bus, allowing applications to make
3331 administrative requests. For example, applications can ask the bus
3332 to assign a name to a connection.
3335 Each name may have <firstterm>queued owners</firstterm>. When an
3336 application requests a name for a connection and the name is already in
3337 use, the bus will optionally add the connection to a queue waiting for
3338 the name. If the current owner of the name disconnects or releases
3339 the name, the next connection in the queue will become the new owner.
3343 This feature causes the right thing to happen if you start two text
3344 editors for example; the first one may request "org.freedesktop.TextEditor",
3345 and the second will be queued as a possible owner of that name. When
3346 the first exits, the second will take over.
3350 Messages may have a <literal>DESTINATION</literal> field (see <xref
3351 linkend="message-protocol-header-fields"/>). If the
3352 <literal>DESTINATION</literal> field is present, it specifies a message
3353 recipient by name. Method calls and replies normally specify this field.
3354 The message bus must send messages (of any type) with the
3355 <literal>DESTINATION</literal> field set to the specified recipient,
3356 regardless of whether the recipient has set up a match rule matching
3361 Signals normally do not specify a destination; they are sent to all
3362 applications with <firstterm>message matching rules</firstterm> that
3367 When the message bus receives a method call, if the
3368 <literal>DESTINATION</literal> field is absent, the call is taken to be
3369 a standard one-to-one message and interpreted by the message bus
3370 itself. For example, sending an
3371 <literal>org.freedesktop.DBus.Peer.Ping</literal> message with no
3372 <literal>DESTINATION</literal> will cause the message bus itself to
3373 reply to the ping immediately; the message bus will not make this
3374 message visible to other applications.
3378 Continuing the <literal>org.freedesktop.DBus.Peer.Ping</literal> example, if
3379 the ping message were sent with a <literal>DESTINATION</literal> name of
3380 <literal>com.yoyodyne.Screensaver</literal>, then the ping would be
3381 forwarded, and the Yoyodyne Corporation screensaver application would be
3382 expected to reply to the ping.
3386 <sect2 id="message-bus-names">
3387 <title>Message Bus Names</title>
3389 Each connection has at least one name, assigned at connection time and
3390 returned in response to the
3391 <literal>org.freedesktop.DBus.Hello</literal> method call. This
3392 automatically-assigned name is called the connection's <firstterm>unique
3393 name</firstterm>. Unique names are never reused for two different
3394 connections to the same bus.
3397 Ownership of a unique name is a prerequisite for interaction with
3398 the message bus. It logically follows that the unique name is always
3399 the first name that an application comes to own, and the last
3400 one that it loses ownership of.
3403 Unique connection names must begin with the character ':' (ASCII colon
3404 character); bus names that are not unique names must not begin
3405 with this character. (The bus must reject any attempt by an application
3406 to manually request a name beginning with ':'.) This restriction
3407 categorically prevents "spoofing"; messages sent to a unique name
3408 will always go to the expected connection.
3411 When a connection is closed, all the names that it owns are deleted (or
3412 transferred to the next connection in the queue if any).
3415 A connection can request additional names to be associated with it using
3416 the <literal>org.freedesktop.DBus.RequestName</literal> message. <xref
3417 linkend="message-protocol-names-bus"/> describes the format of a valid
3418 name. These names can be released again using the
3419 <literal>org.freedesktop.DBus.ReleaseName</literal> message.
3422 <sect3 id="bus-messages-request-name">
3423 <title><literal>org.freedesktop.DBus.RequestName</literal></title>
3427 UINT32 RequestName (in STRING name, in UINT32 flags)
3434 <entry>Argument</entry>
3436 <entry>Description</entry>
3442 <entry>STRING</entry>
3443 <entry>Name to request</entry>
3447 <entry>UINT32</entry>
3448 <entry>Flags</entry>
3458 <entry>Argument</entry>
3460 <entry>Description</entry>
3466 <entry>UINT32</entry>
3467 <entry>Return value</entry>
3474 This method call should be sent to
3475 <literal>org.freedesktop.DBus</literal> and asks the message bus to
3476 assign the given name to the method caller. Each name maintains a
3477 queue of possible owners, where the head of the queue is the primary
3478 or current owner of the name. Each potential owner in the queue
3479 maintains the DBUS_NAME_FLAG_ALLOW_REPLACEMENT and
3480 DBUS_NAME_FLAG_DO_NOT_QUEUE settings from its latest RequestName
3481 call. When RequestName is invoked the following occurs:
3485 If the method caller is currently the primary owner of the name,
3486 the DBUS_NAME_FLAG_ALLOW_REPLACEMENT and DBUS_NAME_FLAG_DO_NOT_QUEUE
3487 values are updated with the values from the new RequestName call,
3488 and nothing further happens.
3494 If the current primary owner (head of the queue) has
3495 DBUS_NAME_FLAG_ALLOW_REPLACEMENT set, and the RequestName
3496 invocation has the DBUS_NAME_FLAG_REPLACE_EXISTING flag, then
3497 the caller of RequestName replaces the current primary owner at
3498 the head of the queue and the current primary owner moves to the
3499 second position in the queue. If the caller of RequestName was
3500 in the queue previously its flags are updated with the values from
3501 the new RequestName in addition to moving it to the head of the queue.
3507 If replacement is not possible, and the method caller is
3508 currently in the queue but not the primary owner, its flags are
3509 updated with the values from the new RequestName call.
3515 If replacement is not possible, and the method caller is
3516 currently not in the queue, the method caller is appended to the
3523 If any connection in the queue has DBUS_NAME_FLAG_DO_NOT_QUEUE
3524 set and is not the primary owner, it is removed from the
3525 queue. This can apply to the previous primary owner (if it
3526 was replaced) or the method caller (if it updated the
3527 DBUS_NAME_FLAG_DO_NOT_QUEUE flag while still stuck in the
3528 queue, or if it was just added to the queue with that flag set).
3534 Note that DBUS_NAME_FLAG_REPLACE_EXISTING results in "jumping the
3535 queue," even if another application already in the queue had specified
3536 DBUS_NAME_FLAG_REPLACE_EXISTING. This comes up if a primary owner
3537 that does not allow replacement goes away, and the next primary owner
3538 does allow replacement. In this case, queued items that specified
3539 DBUS_NAME_FLAG_REPLACE_EXISTING <emphasis>do not</emphasis>
3540 automatically replace the new primary owner. In other words,
3541 DBUS_NAME_FLAG_REPLACE_EXISTING is not saved, it is only used at the
3542 time RequestName is called. This is deliberate to avoid an infinite loop
3543 anytime two applications are both DBUS_NAME_FLAG_ALLOW_REPLACEMENT
3544 and DBUS_NAME_FLAG_REPLACE_EXISTING.
3547 The flags argument contains any of the following values logically ORed
3554 <entry>Conventional Name</entry>
3555 <entry>Value</entry>
3556 <entry>Description</entry>
3561 <entry>DBUS_NAME_FLAG_ALLOW_REPLACEMENT</entry>
3565 If an application A specifies this flag and succeeds in
3566 becoming the owner of the name, and another application B
3567 later calls RequestName with the
3568 DBUS_NAME_FLAG_REPLACE_EXISTING flag, then application A
3569 will lose ownership and receive a
3570 <literal>org.freedesktop.DBus.NameLost</literal> signal, and
3571 application B will become the new owner. If DBUS_NAME_FLAG_ALLOW_REPLACEMENT
3572 is not specified by application A, or DBUS_NAME_FLAG_REPLACE_EXISTING
3573 is not specified by application B, then application B will not replace
3574 application A as the owner.
3579 <entry>DBUS_NAME_FLAG_REPLACE_EXISTING</entry>
3583 Try to replace the current owner if there is one. If this
3584 flag is not set the application will only become the owner of
3585 the name if there is no current owner. If this flag is set,
3586 the application will replace the current owner if
3587 the current owner specified DBUS_NAME_FLAG_ALLOW_REPLACEMENT.
3592 <entry>DBUS_NAME_FLAG_DO_NOT_QUEUE</entry>
3596 Without this flag, if an application requests a name that is
3597 already owned, the application will be placed in a queue to
3598 own the name when the current owner gives it up. If this
3599 flag is given, the application will not be placed in the
3600 queue, the request for the name will simply fail. This flag
3601 also affects behavior when an application is replaced as
3602 name owner; by default the application moves back into the
3603 waiting queue, unless this flag was provided when the application
3604 became the name owner.
3612 The return code can be one of the following values:
3618 <entry>Conventional Name</entry>
3619 <entry>Value</entry>
3620 <entry>Description</entry>
3625 <entry>DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER</entry>
3626 <entry>1</entry> <entry>The caller is now the primary owner of
3627 the name, replacing any previous owner. Either the name had no
3628 owner before, or the caller specified
3629 DBUS_NAME_FLAG_REPLACE_EXISTING and the current owner specified
3630 DBUS_NAME_FLAG_ALLOW_REPLACEMENT.</entry>
3633 <entry>DBUS_REQUEST_NAME_REPLY_IN_QUEUE</entry>
3636 <entry>The name already had an owner,
3637 DBUS_NAME_FLAG_DO_NOT_QUEUE was not specified, and either
3638 the current owner did not specify
3639 DBUS_NAME_FLAG_ALLOW_REPLACEMENT or the requesting
3640 application did not specify DBUS_NAME_FLAG_REPLACE_EXISTING.
3644 <entry>DBUS_REQUEST_NAME_REPLY_EXISTS</entry> <entry>3</entry>
3645 <entry>The name already has an owner,
3646 DBUS_NAME_FLAG_DO_NOT_QUEUE was specified, and either
3647 DBUS_NAME_FLAG_ALLOW_REPLACEMENT was not specified by the
3648 current owner, or DBUS_NAME_FLAG_REPLACE_EXISTING was not
3649 specified by the requesting application.</entry>
3652 <entry>DBUS_REQUEST_NAME_REPLY_ALREADY_OWNER</entry>
3654 <entry>The application trying to request ownership of a name is already the owner of it.</entry>
3662 <sect3 id="bus-messages-release-name">
3663 <title><literal>org.freedesktop.DBus.ReleaseName</literal></title>
3667 UINT32 ReleaseName (in STRING name)
3674 <entry>Argument</entry>
3676 <entry>Description</entry>
3682 <entry>STRING</entry>
3683 <entry>Name to release</entry>
3693 <entry>Argument</entry>
3695 <entry>Description</entry>
3701 <entry>UINT32</entry>
3702 <entry>Return value</entry>
3709 This method call should be sent to
3710 <literal>org.freedesktop.DBus</literal> and asks the message bus to
3711 release the method caller's claim to the given name. If the caller is
3712 the primary owner, a new primary owner will be selected from the
3713 queue if any other owners are waiting. If the caller is waiting in
3714 the queue for the name, the caller will removed from the queue and
3715 will not be made an owner of the name if it later becomes available.
3716 If there are no other owners in the queue for the name, it will be
3717 removed from the bus entirely.
3719 The return code can be one of the following values:
3725 <entry>Conventional Name</entry>
3726 <entry>Value</entry>
3727 <entry>Description</entry>
3732 <entry>DBUS_RELEASE_NAME_REPLY_RELEASED</entry>
3733 <entry>1</entry> <entry>The caller has released his claim on
3734 the given name. Either the caller was the primary owner of
3735 the name, and the name is now unused or taken by somebody
3736 waiting in the queue for the name, or the caller was waiting
3737 in the queue for the name and has now been removed from the
3741 <entry>DBUS_RELEASE_NAME_REPLY_NON_EXISTENT</entry>
3743 <entry>The given name does not exist on this bus.</entry>
3746 <entry>DBUS_RELEASE_NAME_REPLY_NOT_OWNER</entry>
3748 <entry>The caller was not the primary owner of this name,
3749 and was also not waiting in the queue to own this name.</entry>
3757 <sect3 id="bus-messages-list-queued-owners">
3758 <title><literal>org.freedesktop.DBus.ListQueuedOwners</literal></title>
3762 ARRAY of STRING ListQueuedOwners (in STRING name)
3769 <entry>Argument</entry>
3771 <entry>Description</entry>
3777 <entry>STRING</entry>
3778 <entry>The well-known bus name to query, such as
3779 <literal>com.example.cappuccino</literal></entry>
3789 <entry>Argument</entry>
3791 <entry>Description</entry>
3797 <entry>ARRAY of STRING</entry>
3798 <entry>The unique bus names of connections currently queued
3799 for the name</entry>
3806 This method call should be sent to
3807 <literal>org.freedesktop.DBus</literal> and lists the connections
3808 currently queued for a bus name (see
3809 <xref linkend="term-queued-owner"/>).
3814 <sect2 id="message-bus-routing">
3815 <title>Message Bus Message Routing</title>
3819 <sect3 id="message-bus-routing-match-rules">
3820 <title>Match Rules</title>
3822 An important part of the message bus routing protocol is match
3823 rules. Match rules describe what messages can be sent to a client
3824 based on the contents of the message. When a message is routed
3825 through the bus it is compared to clients' match rules. If any
3826 of the rules match, the message is dispatched to the client.
3827 If none of the rules match the message never leaves the bus. This
3828 is an effective way to control traffic over the bus and to make sure
3829 only relevant message need to be processed by the client.
3832 Match rules are added using the AddMatch bus method
3833 (see <xref linkend="bus-messages-add-match"/>). Rules are
3834 specified as a string of comma separated key/value pairs.
3835 Excluding a key from the rule indicates a wildcard match.
3836 For instance excluding the the member from a match rule but
3837 adding a sender would let all messages from that sender through.
3838 An example of a complete rule would be
3839 "type='signal',sender='org.freedesktop.DBus',interface='org.freedesktop.DBus',member='Foo',path='/bar/foo',destination=':452345.34',arg2='bar'"
3842 The following table describes the keys that can be used to create
3844 The following table summarizes the D-Bus types.
3850 <entry>Possible Values</entry>
3851 <entry>Description</entry>
3856 <entry><literal>type</literal></entry>
3857 <entry>'signal', 'method_call', 'method_return', 'error'</entry>
3858 <entry>Match on the message type. An example of a type match is type='signal'</entry>
3861 <entry><literal>sender</literal></entry>
3862 <entry>A bus or unique name (see <xref linkend="term-bus-name"/>
3863 and <xref linkend="term-unique-name"/> respectively)
3865 <entry>Match messages sent by a particular sender. An example of a sender match
3866 is sender='org.freedesktop.Hal'</entry>
3869 <entry><literal>interface</literal></entry>
3870 <entry>An interface name (see <xref linkend="message-protocol-names-interface"/>)</entry>
3871 <entry>Match messages sent over or to a particular interface. An example of an
3872 interface match is interface='org.freedesktop.Hal.Manager'.
3873 If a message omits the interface header, it must not match any rule
3874 that specifies this key.</entry>
3877 <entry><literal>member</literal></entry>
3878 <entry>Any valid method or signal name</entry>
3879 <entry>Matches messages which have the give method or signal name. An example of
3880 a member match is member='NameOwnerChanged'</entry>
3883 <entry><literal>path</literal></entry>
3884 <entry>An object path (see <xref linkend="message-protocol-marshaling-object-path"/>)</entry>
3885 <entry>Matches messages which are sent from or to the given object. An example of a
3886 path match is path='/org/freedesktop/Hal/Manager'</entry>
3889 <entry><literal>path_namespace</literal></entry>
3890 <entry>An object path</entry>
3893 Matches messages which are sent from or to an
3894 object for which the object path is either the
3895 given value, or that value followed by one or
3896 more path components.
3901 <literal>path_namespace='/com/example/foo'</literal>
3902 would match signals sent by
3903 <literal>/com/example/foo</literal>
3905 <literal>/com/example/foo/bar</literal>,
3907 <literal>/com/example/foobar</literal>.
3911 Using both <literal>path</literal> and
3912 <literal>path_namespace</literal> in the same match
3913 rule is not allowed.
3918 This match key was added in version 0.16 of the
3919 D-Bus specification and implemented by the bus
3920 daemon in dbus 1.5.0 and later.
3926 <entry><literal>destination</literal></entry>
3927 <entry>A unique name (see <xref linkend="term-unique-name"/>)</entry>
3928 <entry>Matches messages which are being sent to the given unique name. An
3929 example of a destination match is destination=':1.0'</entry>
3932 <entry><literal>arg[0, 1, 2, 3, ...]</literal></entry>
3933 <entry>Any string</entry>
3934 <entry>Arg matches are special and are used for further restricting the
3935 match based on the arguments in the body of a message. Only arguments of type
3936 STRING can be matched in this way. An example of an argument match
3937 would be arg3='Foo'. Only argument indexes from 0 to 63 should be
3941 <entry><literal>arg[0, 1, 2, 3, ...]path</literal></entry>
3942 <entry>Any string</entry>
3944 <para>Argument path matches provide a specialised form of wildcard matching for
3945 path-like namespaces. They can match arguments whose type is either STRING or
3946 OBJECT_PATH. As with normal argument matches,
3947 if the argument is exactly equal to the string given in the match
3948 rule then the rule is satisfied. Additionally, there is also a
3949 match when either the string given in the match rule or the
3950 appropriate message argument ends with '/' and is a prefix of the
3951 other. An example argument path match is arg0path='/aa/bb/'. This
3952 would match messages with first arguments of '/', '/aa/',
3953 '/aa/bb/', '/aa/bb/cc/' and '/aa/bb/cc'. It would not match
3954 messages with first arguments of '/aa/b', '/aa' or even '/aa/bb'.</para>
3956 <para>This is intended for monitoring “directories” in file system-like
3957 hierarchies, as used in the <citetitle>dconf</citetitle> configuration
3958 system. An application interested in all nodes in a particular hierarchy would
3959 monitor <literal>arg0path='/ca/example/foo/'</literal>. Then the service could
3960 emit a signal with zeroth argument <literal>"/ca/example/foo/bar"</literal> to
3961 represent a modification to the “bar” property, or a signal with zeroth
3962 argument <literal>"/ca/example/"</literal> to represent atomic modification of
3963 many properties within that directory, and the interested application would be
3964 notified in both cases.</para>
3967 This match key was added in version 0.12 of the
3968 D-Bus specification, implemented for STRING
3969 arguments by the bus daemon in dbus 1.2.0 and later,
3970 and implemented for OBJECT_PATH arguments in dbus 1.5.0
3977 <entry><literal>arg0namespace</literal></entry>
3978 <entry>Like a bus name, except that the string is not
3979 required to contain a '.' (period)</entry>
3981 <para>Match messages whose first argument is of type STRING, and is a bus name
3982 or interface name within the specified namespace. This is primarily intended
3983 for watching name owner changes for a group of related bus names, rather than
3984 for a single name or all name changes.</para>
3986 <para>Because every valid interface name is also a valid
3987 bus name, this can also be used for messages whose
3988 first argument is an interface name.</para>
3990 <para>For example, the match rule
3991 <literal>member='NameOwnerChanged',arg0namespace='com.example.backend'</literal>
3992 matches name owner changes for bus names such as
3993 <literal>com.example.backend.foo</literal>,
3994 <literal>com.example.backend.foo.bar</literal>, and
3995 <literal>com.example.backend</literal> itself.</para>
3997 <para>See also <xref linkend='bus-messages-name-owner-changed'/>.</para>
4000 This match key was added in version 0.16 of the
4001 D-Bus specification and implemented by the bus
4002 daemon in dbus 1.5.0 and later.
4013 <sect2 id="message-bus-starting-services">
4014 <title>Message Bus Starting Services</title>
4016 The message bus can start applications on behalf of other applications.
4017 In CORBA terms, this would be called <firstterm>activation</firstterm>.
4018 An application that can be started in this way is called a
4019 <firstterm>service</firstterm>.
4022 With D-Bus, starting a service is normally done by name. That is,
4023 applications ask the message bus to start some program that will own a
4024 well-known name, such as <literal>org.freedesktop.TextEditor</literal>.
4025 This implies a contract documented along with the name
4026 <literal>org.freedesktop.TextEditor</literal> for which objects
4027 the owner of that name will provide, and what interfaces those
4031 To find an executable corresponding to a particular name, the bus daemon
4032 looks for <firstterm>service description files</firstterm>. Service
4033 description files define a mapping from names to executables. Different
4034 kinds of message bus will look for these files in different places, see
4035 <xref linkend="message-bus-types"/>.
4038 Service description files have the ".service" file
4039 extension. The message bus will only load service description files
4040 ending with .service; all other files will be ignored. The file format
4041 is similar to that of <ulink
4042 url="http://standards.freedesktop.org/desktop-entry-spec/desktop-entry-spec-latest.html">desktop
4043 entries</ulink>. All service description files must be in UTF-8
4044 encoding. To ensure that there will be no name collisions, service files
4045 must be namespaced using the same mechanism as messages and service
4050 [FIXME the file format should be much better specified than "similar to
4051 .desktop entries" esp. since desktop entries are already
4052 badly-specified. ;-)]
4053 These sections from the specification apply to service files as well:
4056 <listitem><para>General syntax</para></listitem>
4057 <listitem><para>Comment format</para></listitem>
4061 <title>Example service description file</title>
4063 # Sample service description file
4065 Names=org.freedesktop.ConfigurationDatabase;org.gnome.GConf;
4066 Exec=/usr/libexec/gconfd-2
4071 When an application asks to start a service by name, the bus daemon tries to
4072 find a service that will own that name. It then tries to spawn the
4073 executable associated with it. If this fails, it will report an
4074 error. [FIXME what happens if two .service files offer the same service;
4075 what kind of error is reported, should we have a way for the client to
4079 The executable launched will have the environment variable
4080 <literal>DBUS_STARTER_ADDRESS</literal> set to the address of the
4081 message bus so it can connect and request the appropriate names.
4084 The executable being launched may want to know whether the message bus
4085 starting it is one of the well-known message buses (see <xref
4086 linkend="message-bus-types"/>). To facilitate this, the bus must also set
4087 the <literal>DBUS_STARTER_BUS_TYPE</literal> environment variable if it is one
4088 of the well-known buses. The currently-defined values for this variable
4089 are <literal>system</literal> for the systemwide message bus,
4090 and <literal>session</literal> for the per-login-session message
4091 bus. The new executable must still connect to the address given
4092 in <literal>DBUS_STARTER_ADDRESS</literal>, but may assume that the
4093 resulting connection is to the well-known bus.
4096 [FIXME there should be a timeout somewhere, either specified
4097 in the .service file, by the client, or just a global value
4098 and if the client being activated fails to connect within that
4099 timeout, an error should be sent back.]
4102 <sect3 id="message-bus-starting-services-scope">
4103 <title>Message Bus Service Scope</title>
4105 The "scope" of a service is its "per-", such as per-session,
4106 per-machine, per-home-directory, or per-display. The reference
4107 implementation doesn't yet support starting services in a different
4108 scope from the message bus itself. So e.g. if you start a service
4109 on the session bus its scope is per-session.
4112 We could add an optional scope to a bus name. For example, for
4113 per-(display,session pair), we could have a unique ID for each display
4114 generated automatically at login and set on screen 0 by executing a
4115 special "set display ID" binary. The ID would be stored in a
4116 <literal>_DBUS_DISPLAY_ID</literal> property and would be a string of
4117 random bytes. This ID would then be used to scope names.
4118 Starting/locating a service could be done by ID-name pair rather than
4122 Contrast this with a per-display scope. To achieve that, we would
4123 want a single bus spanning all sessions using a given display.
4124 So we might set a <literal>_DBUS_DISPLAY_BUS_ADDRESS</literal>
4125 property on screen 0 of the display, pointing to this bus.
4130 <sect2 id="message-bus-types">
4131 <title>Well-known Message Bus Instances</title>
4133 Two standard message bus instances are defined here, along with how
4134 to locate them and where their service files live.
4136 <sect3 id="message-bus-types-login">
4137 <title>Login session message bus</title>
4139 Each time a user logs in, a <firstterm>login session message
4140 bus</firstterm> may be started. All applications in the user's login
4141 session may interact with one another using this message bus.
4144 The address of the login session message bus is given
4145 in the <literal>DBUS_SESSION_BUS_ADDRESS</literal> environment
4146 variable. If that variable is not set, applications may
4147 also try to read the address from the X Window System root
4148 window property <literal>_DBUS_SESSION_BUS_ADDRESS</literal>.
4149 The root window property must have type <literal>STRING</literal>.
4150 The environment variable should have precedence over the
4151 root window property.
4153 <para>The address of the login session message bus is given in the
4154 <literal>DBUS_SESSION_BUS_ADDRESS</literal> environment variable. If
4155 DBUS_SESSION_BUS_ADDRESS is not set, or if it's set to the string
4156 "autolaunch:", the system should use platform-specific methods of
4157 locating a running D-Bus session server, or starting one if a running
4158 instance cannot be found. Note that this mechanism is not recommended
4159 for attempting to determine if a daemon is running. It is inherently
4160 racy to attempt to make this determination, since the bus daemon may
4161 be started just before or just after the determination is made.
4162 Therefore, it is recommended that applications do not try to make this
4163 determination for their functionality purposes, and instead they
4164 should attempt to start the server.</para>
4166 <sect4 id="message-bus-types-login-x-windows">
4167 <title>X Windowing System</title>
4169 For the X Windowing System, the application must locate the
4170 window owner of the selection represented by the atom formed by
4174 <para>the literal string "_DBUS_SESSION_BUS_SELECTION_"</para>
4178 <para>the current user's username</para>
4182 <para>the literal character '_' (underscore)</para>
4186 <para>the machine's ID</para>
4192 The following properties are defined for the window that owns
4194 <informaltable frame="all">
4203 <para>meaning</para>
4209 <para>_DBUS_SESSION_BUS_ADDRESS</para>
4213 <para>the actual address of the server socket</para>
4219 <para>_DBUS_SESSION_BUS_PID</para>
4223 <para>the PID of the server process</para>
4232 At least the _DBUS_SESSION_BUS_ADDRESS property MUST be
4233 present in this window.
4237 If the X selection cannot be located or if reading the
4238 properties from the window fails, the implementation MUST conclude
4239 that there is no D-Bus server running and proceed to start a new
4240 server. (See below on concurrency issues)
4244 Failure to connect to the D-Bus server address thus obtained
4245 MUST be treated as a fatal connection error and should be reported
4250 As an alternative, an implementation MAY find the information
4251 in the following file located in the current user's home directory,
4252 in subdirectory .dbus/session-bus/:
4255 <para>the machine's ID</para>
4259 <para>the literal character '-' (dash)</para>
4263 <para>the X display without the screen number, with the
4264 following prefixes removed, if present: ":", "localhost:"
4265 ."localhost.localdomain:". That is, a display of
4266 "localhost:10.0" produces just the number "10"</para>
4272 The contents of this file NAME=value assignment pairs and
4273 lines starting with # are comments (no comments are allowed
4274 otherwise). The following variable names are defined:
4281 <para>Variable</para>
4285 <para>meaning</para>
4291 <para>DBUS_SESSION_BUS_ADDRESS</para>
4295 <para>the actual address of the server socket</para>
4301 <para>DBUS_SESSION_BUS_PID</para>
4305 <para>the PID of the server process</para>
4311 <para>DBUS_SESSION_BUS_WINDOWID</para>
4315 <para>the window ID</para>
4324 At least the DBUS_SESSION_BUS_ADDRESS variable MUST be present
4329 Failure to open this file MUST be interpreted as absence of a
4330 running server. Therefore, the implementation MUST proceed to
4331 attempting to launch a new bus server if the file cannot be
4336 However, success in opening this file MUST NOT lead to the
4337 conclusion that the server is running. Thus, a failure to connect to
4338 the bus address obtained by the alternative method MUST NOT be
4339 considered a fatal error. If the connection cannot be established,
4340 the implementation MUST proceed to check the X selection settings or
4341 to start the server on its own.
4345 If the implementation concludes that the D-Bus server is not
4346 running it MUST attempt to start a new server and it MUST also
4347 ensure that the daemon started as an effect of the "autolaunch"
4348 mechanism provides the lookup mechanisms described above, so
4349 subsequent calls can locate the newly started server. The
4350 implementation MUST also ensure that if two or more concurrent
4351 initiations happen, only one server remains running and all other
4352 initiations are able to obtain the address of this server and
4353 connect to it. In other words, the implementation MUST ensure that
4354 the X selection is not present when it attempts to set it, without
4355 allowing another process to set the selection between the
4356 verification and the setting (e.g., by using XGrabServer /
4363 [FIXME specify location of .service files, probably using
4364 DESKTOP_DIRS etc. from basedir specification, though login session
4365 bus is not really desktop-specific]
4369 <sect3 id="message-bus-types-system">
4370 <title>System message bus</title>
4372 A computer may have a <firstterm>system message bus</firstterm>,
4373 accessible to all applications on the system. This message bus may be
4374 used to broadcast system events, such as adding new hardware devices,
4375 changes in the printer queue, and so forth.
4378 The address of the system message bus is given
4379 in the <literal>DBUS_SYSTEM_BUS_ADDRESS</literal> environment
4380 variable. If that variable is not set, applications should try
4381 to connect to the well-known address
4382 <literal>unix:path=/var/run/dbus/system_bus_socket</literal>.
4385 The D-Bus reference implementation actually honors the
4386 <literal>$(localstatedir)</literal> configure option
4387 for this address, on both client and server side.
4392 [FIXME specify location of system bus .service files]
4397 <sect2 id="message-bus-messages">
4398 <title>Message Bus Messages</title>
4400 The special message bus name <literal>org.freedesktop.DBus</literal>
4401 responds to a number of additional messages.
4404 <sect3 id="bus-messages-hello">
4405 <title><literal>org.freedesktop.DBus.Hello</literal></title>
4416 <entry>Argument</entry>
4418 <entry>Description</entry>
4424 <entry>STRING</entry>
4425 <entry>Unique name assigned to the connection</entry>
4432 Before an application is able to send messages to other applications
4433 it must send the <literal>org.freedesktop.DBus.Hello</literal> message
4434 to the message bus to obtain a unique name. If an application without
4435 a unique name tries to send a message to another application, or a
4436 message to the message bus itself that isn't the
4437 <literal>org.freedesktop.DBus.Hello</literal> message, it will be
4438 disconnected from the bus.
4441 There is no corresponding "disconnect" request; if a client wishes to
4442 disconnect from the bus, it simply closes the socket (or other
4443 communication channel).
4446 <sect3 id="bus-messages-list-names">
4447 <title><literal>org.freedesktop.DBus.ListNames</literal></title>
4451 ARRAY of STRING ListNames ()
4458 <entry>Argument</entry>
4460 <entry>Description</entry>
4466 <entry>ARRAY of STRING</entry>
4467 <entry>Array of strings where each string is a bus name</entry>
4474 Returns a list of all currently-owned names on the bus.
4477 <sect3 id="bus-messages-list-activatable-names">
4478 <title><literal>org.freedesktop.DBus.ListActivatableNames</literal></title>
4482 ARRAY of STRING ListActivatableNames ()
4489 <entry>Argument</entry>
4491 <entry>Description</entry>
4497 <entry>ARRAY of STRING</entry>
4498 <entry>Array of strings where each string is a bus name</entry>
4505 Returns a list of all names that can be activated on the bus.
4508 <sect3 id="bus-messages-name-exists">
4509 <title><literal>org.freedesktop.DBus.NameHasOwner</literal></title>
4513 BOOLEAN NameHasOwner (in STRING name)
4520 <entry>Argument</entry>
4522 <entry>Description</entry>
4528 <entry>STRING</entry>
4529 <entry>Name to check</entry>
4539 <entry>Argument</entry>
4541 <entry>Description</entry>
4547 <entry>BOOLEAN</entry>
4548 <entry>Return value, true if the name exists</entry>
4555 Checks if the specified name exists (currently has an owner).
4559 <sect3 id="bus-messages-name-owner-changed">
4560 <title><literal>org.freedesktop.DBus.NameOwnerChanged</literal></title>
4564 NameOwnerChanged (STRING name, STRING old_owner, STRING new_owner)
4571 <entry>Argument</entry>
4573 <entry>Description</entry>
4579 <entry>STRING</entry>
4580 <entry>Name with a new owner</entry>
4584 <entry>STRING</entry>
4585 <entry>Old owner or empty string if none</entry>
4589 <entry>STRING</entry>
4590 <entry>New owner or empty string if none</entry>
4597 This signal indicates that the owner of a name has changed.
4598 It's also the signal to use to detect the appearance of
4599 new names on the bus.
4602 <sect3 id="bus-messages-name-lost">
4603 <title><literal>org.freedesktop.DBus.NameLost</literal></title>
4607 NameLost (STRING name)
4614 <entry>Argument</entry>
4616 <entry>Description</entry>
4622 <entry>STRING</entry>
4623 <entry>Name which was lost</entry>
4630 This signal is sent to a specific application when it loses
4631 ownership of a name.
4635 <sect3 id="bus-messages-name-acquired">
4636 <title><literal>org.freedesktop.DBus.NameAcquired</literal></title>
4640 NameAcquired (STRING name)
4647 <entry>Argument</entry>
4649 <entry>Description</entry>
4655 <entry>STRING</entry>
4656 <entry>Name which was acquired</entry>
4663 This signal is sent to a specific application when it gains
4664 ownership of a name.
4668 <sect3 id="bus-messages-start-service-by-name">
4669 <title><literal>org.freedesktop.DBus.StartServiceByName</literal></title>
4673 UINT32 StartServiceByName (in STRING name, in UINT32 flags)
4680 <entry>Argument</entry>
4682 <entry>Description</entry>
4688 <entry>STRING</entry>
4689 <entry>Name of the service to start</entry>
4693 <entry>UINT32</entry>
4694 <entry>Flags (currently not used)</entry>
4704 <entry>Argument</entry>
4706 <entry>Description</entry>
4712 <entry>UINT32</entry>
4713 <entry>Return value</entry>
4718 Tries to launch the executable associated with a name. For more information, see <xref linkend="message-bus-starting-services"/>.
4722 The return value can be one of the following values:
4727 <entry>Identifier</entry>
4728 <entry>Value</entry>
4729 <entry>Description</entry>
4734 <entry>DBUS_START_REPLY_SUCCESS</entry>
4736 <entry>The service was successfully started.</entry>
4739 <entry>DBUS_START_REPLY_ALREADY_RUNNING</entry>
4741 <entry>A connection already owns the given name.</entry>
4750 <sect3 id="bus-messages-update-activation-environment">
4751 <title><literal>org.freedesktop.DBus.UpdateActivationEnvironment</literal></title>
4755 UpdateActivationEnvironment (in ARRAY of DICT<STRING,STRING> environment)
4762 <entry>Argument</entry>
4764 <entry>Description</entry>
4770 <entry>ARRAY of DICT<STRING,STRING></entry>
4771 <entry>Environment to add or update</entry>
4776 Normally, session bus activated services inherit the environment of the bus daemon. This method adds to or modifies that environment when activating services.
4779 Some bus instances, such as the standard system bus, may disable access to this method for some or all callers.
4782 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.
4787 <sect3 id="bus-messages-get-name-owner">
4788 <title><literal>org.freedesktop.DBus.GetNameOwner</literal></title>
4792 STRING GetNameOwner (in STRING name)
4799 <entry>Argument</entry>
4801 <entry>Description</entry>
4807 <entry>STRING</entry>
4808 <entry>Name to get the owner of</entry>
4818 <entry>Argument</entry>
4820 <entry>Description</entry>
4826 <entry>STRING</entry>
4827 <entry>Return value, a unique connection name</entry>
4832 Returns the unique connection name of the primary owner of the name
4833 given. If the requested name doesn't have an owner, returns a
4834 <literal>org.freedesktop.DBus.Error.NameHasNoOwner</literal> error.
4838 <sect3 id="bus-messages-get-connection-unix-user">
4839 <title><literal>org.freedesktop.DBus.GetConnectionUnixUser</literal></title>
4843 UINT32 GetConnectionUnixUser (in STRING bus_name)
4850 <entry>Argument</entry>
4852 <entry>Description</entry>
4858 <entry>STRING</entry>
4859 <entry>Unique or well-known bus name of the connection to
4860 query, such as <literal>:12.34</literal> or
4861 <literal>com.example.tea</literal></entry>
4871 <entry>Argument</entry>
4873 <entry>Description</entry>
4879 <entry>UINT32</entry>
4880 <entry>Unix user ID</entry>
4885 Returns the Unix user ID of the process connected to the server. If
4886 unable to determine it (for instance, because the process is not on the
4887 same machine as the bus daemon), an error is returned.
4891 <sect3 id="bus-messages-get-connection-unix-process-id">
4892 <title><literal>org.freedesktop.DBus.GetConnectionUnixProcessID</literal></title>
4896 UINT32 GetConnectionUnixProcessID (in STRING bus_name)
4903 <entry>Argument</entry>
4905 <entry>Description</entry>
4911 <entry>STRING</entry>
4912 <entry>Unique or well-known bus name of the connection to
4913 query, such as <literal>:12.34</literal> or
4914 <literal>com.example.tea</literal></entry>
4924 <entry>Argument</entry>
4926 <entry>Description</entry>
4932 <entry>UINT32</entry>
4933 <entry>Unix process id</entry>
4938 Returns the Unix process ID of the process connected to the server. If
4939 unable to determine it (for instance, because the process is not on the
4940 same machine as the bus daemon), an error is returned.
4944 <sect3 id="bus-messages-add-match">
4945 <title><literal>org.freedesktop.DBus.AddMatch</literal></title>
4949 AddMatch (in STRING rule)
4956 <entry>Argument</entry>
4958 <entry>Description</entry>
4964 <entry>STRING</entry>
4965 <entry>Match rule to add to the connection</entry>
4970 Adds a match rule to match messages going through the message bus (see <xref linkend='message-bus-routing-match-rules'/>).
4971 If the bus does not have enough resources the <literal>org.freedesktop.DBus.Error.OOM</literal>
4975 <sect3 id="bus-messages-remove-match">
4976 <title><literal>org.freedesktop.DBus.RemoveMatch</literal></title>
4980 RemoveMatch (in STRING rule)
4987 <entry>Argument</entry>
4989 <entry>Description</entry>
4995 <entry>STRING</entry>
4996 <entry>Match rule to remove from the connection</entry>
5001 Removes the first rule that matches (see <xref linkend='message-bus-routing-match-rules'/>).
5002 If the rule is not found the <literal>org.freedesktop.DBus.Error.MatchRuleNotFound</literal>
5007 <sect3 id="bus-messages-get-id">
5008 <title><literal>org.freedesktop.DBus.GetId</literal></title>
5012 GetId (out STRING id)
5019 <entry>Argument</entry>
5021 <entry>Description</entry>
5027 <entry>STRING</entry>
5028 <entry>Unique ID identifying the bus daemon</entry>
5033 Gets the unique ID of the bus. The unique ID here is shared among all addresses the
5034 bus daemon is listening on (TCP, UNIX domain socket, etc.) and its format is described in
5035 <xref linkend="uuids"/>. Each address the bus is listening on also has its own unique
5036 ID, as described in <xref linkend="addresses"/>. The per-bus and per-address IDs are not related.
5037 There is also a per-machine ID, described in <xref linkend="standard-interfaces-peer"/> and returned
5038 by org.freedesktop.DBus.Peer.GetMachineId().
5039 For a desktop session bus, the bus ID can be used as a way to uniquely identify a user's session.
5047 <appendix id="implementation-notes">
5048 <title>Implementation notes</title>
5049 <sect1 id="implementation-notes-subsection">
5057 <glossary><title>Glossary</title>
5059 This glossary defines some of the terms used in this specification.
5062 <glossentry id="term-bus-name"><glossterm>Bus Name</glossterm>
5065 The message bus maintains an association between names and
5066 connections. (Normally, there's one connection per application.) A
5067 bus name is simply an identifier used to locate connections. For
5068 example, the hypothetical <literal>com.yoyodyne.Screensaver</literal>
5069 name might be used to send a message to a screensaver from Yoyodyne
5070 Corporation. An application is said to <firstterm>own</firstterm> a
5071 name if the message bus has associated the application's connection
5072 with the name. Names may also have <firstterm>queued
5073 owners</firstterm> (see <xref linkend="term-queued-owner"/>).
5074 The bus assigns a unique name to each connection,
5075 see <xref linkend="term-unique-name"/>. Other names
5076 can be thought of as "well-known names" and are
5077 used to find applications that offer specific functionality.
5082 <glossentry id="term-message"><glossterm>Message</glossterm>
5085 A message is the atomic unit of communication via the D-Bus
5086 protocol. It consists of a <firstterm>header</firstterm> and a
5087 <firstterm>body</firstterm>; the body is made up of
5088 <firstterm>arguments</firstterm>.
5093 <glossentry id="term-message-bus"><glossterm>Message Bus</glossterm>
5096 The message bus is a special application that forwards
5097 or routes messages between a group of applications
5098 connected to the message bus. It also manages
5099 <firstterm>names</firstterm> used for routing
5105 <glossentry id="term-name"><glossterm>Name</glossterm>
5108 See <xref linkend="term-bus-name"/>. "Name" may
5109 also be used to refer to some of the other names
5110 in D-Bus, such as interface names.
5115 <glossentry id="namespace"><glossterm>Namespace</glossterm>
5118 Used to prevent collisions when defining new interfaces or bus
5119 names. The convention used is the same one Java uses for defining
5120 classes: a reversed domain name.
5125 <glossentry id="term-object"><glossterm>Object</glossterm>
5128 Each application contains <firstterm>objects</firstterm>, which have
5129 <firstterm>interfaces</firstterm> and
5130 <firstterm>methods</firstterm>. Objects are referred to by a name,
5131 called a <firstterm>path</firstterm>.
5136 <glossentry id="one-to-one"><glossterm>One-to-One</glossterm>
5139 An application talking directly to another application, without going
5140 through a message bus. One-to-one connections may be "peer to peer" or
5141 "client to server." The D-Bus protocol has no concept of client
5142 vs. server after a connection has authenticated; the flow of messages
5143 is symmetrical (full duplex).
5148 <glossentry id="term-path"><glossterm>Path</glossterm>
5151 Object references (object names) in D-Bus are organized into a
5152 filesystem-style hierarchy, so each object is named by a path. As in
5153 LDAP, there's no difference between "files" and "directories"; a path
5154 can refer to an object, while still having child objects below it.
5159 <glossentry id="term-queued-owner"><glossterm>Queued Name Owner</glossterm>
5162 Each bus name has a primary owner; messages sent to the name go to the
5163 primary owner. However, certain names also maintain a queue of
5164 secondary owners "waiting in the wings." If the primary owner releases
5165 the name, then the first secondary owner in the queue automatically
5166 becomes the new owner of the name.
5171 <glossentry id="term-service"><glossterm>Service</glossterm>
5174 A service is an executable that can be launched by the bus daemon.
5175 Services normally guarantee some particular features, for example they
5176 may guarantee that they will request a specific name such as
5177 "org.freedesktop.Screensaver", have a singleton object
5178 "/org/freedesktop/Application", and that object will implement the
5179 interface "org.freedesktop.ScreensaverControl".
5184 <glossentry id="term-service-description-files"><glossterm>Service Description Files</glossterm>
5187 ".service files" tell the bus about service applications that can be
5188 launched (see <xref linkend="term-service"/>). Most importantly they
5189 provide a mapping from bus names to services that will request those
5190 names when they start up.
5195 <glossentry id="term-unique-name"><glossterm>Unique Connection Name</glossterm>
5198 The special name automatically assigned to each connection by the
5199 message bus. This name will never change owner, and will be unique
5200 (never reused during the lifetime of the message bus).
5201 It will begin with a ':' character.