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28 .\" @(#)unix.4 8.1 (Berkeley) 6/9/93
29 .\" $FreeBSD: src/share/man/man4/unix.4,v 1.3.2.4 2002/04/22 08:59:53 dd Exp $
36 .Nd UNIX-domain protocol family
43 protocol family is a collection of protocols
44 that provides local (on-machine) interprocess
45 communication through the normal
56 filesystem pathnames for addressing.
59 addresses are variable-length filesystem pathnames of
60 at most 104 characters.
64 .Bd -literal -offset indent
67 sa_family_t sun_family;
76 causes a socket file to be created in the filesystem.
79 removed when the socket is closed \(em
81 must be used to remove the file.
85 protocol family does not support broadcast addressing or any form
88 matching on incoming messages.
89 All addresses are absolute- or relative-pathnames
93 Normal filesystem access-control mechanisms are also
94 applied when referencing pathnames; e.g., the destination
103 protocol family is comprised of simple
104 transport protocols that support the
114 sockets also support the communication of
116 file descriptors through the use of the
125 Any valid descriptor may be sent in a message.
126 The file descriptor(s) to be passed are described using a
128 that is defined in the include file
130 The type of the message is
132 and the data portion of the messages is an array of integers
133 representing the file descriptors to be passed.
134 The number of descriptors being passed is defined
135 by the length field of the message;
136 the length field is the sum of the size of the header
137 plus the size of the array of file descriptors.
139 The received descriptor is a
141 of the sender's descriptor, as if it were created via
144 .Li fcntl(fd, F_DUPFD_CLOEXEC, 0)
150 Descriptors that are awaiting delivery, or that are
151 purposely not received, are automatically closed by the system
152 when the destination socket is closed.
154 The effective credentials (i.e., the user ID and group list) of a
157 socket may be obtained using the
160 This may be used by a server to obtain and verify the credentials of
161 its client, and vice versa by the client to verify the credentials
163 These will arrive in the form of a filled in
167 The credentials presented to the server (the
169 caller) are those of the client when it called
171 the credentials presented to the client (the
173 caller) are those of the server when it called
175 This mechanism is reliable; there is no way for either party to influence
176 the credentials presented to its peer except by calling the appropriate
181 under different effective credentials.
186 .%T "An Introductory 4.3 BSD Interprocess Communication Tutorial"
191 .%T "An Advanced 4.3 BSD Interprocess Communication Tutorial"