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32 .\" @(#)unix.4 8.1 (Berkeley) 6/9/93
40 .Nd UNIX-domain protocol family
47 protocol family is a collection of protocols
48 that provides local (on-machine) interprocess
49 communication through the normal
60 file system pathnames for addressing.
63 addresses are variable-length file system pathnames of
64 at most 104 characters.
68 .Bd -literal -offset indent
80 causes a socket file to be created in the file system.
83 removed when the socket is closed \(em
85 must be used to remove the file.
93 can be calculated by the macro
99 field must be terminated by a
101 character to be used with
111 protocol family does not support broadcast addressing or any form
114 matching on incoming messages.
115 All addresses are absolute- or relative-pathnames
119 Normal file system access-control mechanisms are also
120 applied when referencing pathnames; e.g., the destination
126 .Sh PASSING FILE DESCRIPTORS
129 sockets support the communication of
131 file descriptors through the use of the
140 Any valid descriptor may be sent in a message.
141 The file descriptor(s) to be passed are described using a
143 that is defined in the include file
145 The type of the message is
147 and the data portion of the messages is an array of integers
148 representing the file descriptors to be passed.
149 The number of descriptors being passed is defined
150 by the length field of the message;
151 the length field is the sum of the size of the header
152 plus the size of the array of file descriptors.
154 The received descriptor is a
156 of the sender's descriptor, as if it were created via
159 .Li fcntl(fd, F_DUPFD_CLOEXEC, 0)
165 Descriptors that are awaiting delivery, or that are
166 purposely not received, are automatically closed by the system
167 when the destination socket is closed.
170 domain sockets support a number of socket options which can be set with
174 .Bl -tag -width ".Dv LOCAL_CONNWAIT"
176 This option may be enabled on
182 This option provides a mechanism for the receiver to
183 receive the credentials of the process as a
190 structure points to a buffer that contains a
192 structure followed by a variable length
194 structure, defined in
199 uid_t sc_uid; /* real user id */
200 uid_t sc_euid; /* effective user id */
201 gid_t sc_gid; /* real group id */
202 gid_t sc_egid; /* effective group id */
203 int sc_ngroups; /* number of supplemental groups */
204 gid_t sc_groups[1]; /* variable length */
210 macro computes the size of the
212 structure for a specified number
216 fields have the following values:
218 cmsg_len = CMSG_LEN(SOCKCREDSIZE(ngroups))
219 cmsg_level = SOL_SOCKET
220 cmsg_type = SCM_CREDS
227 sockets credentials are passed only on the first read from a socket,
228 then system clears the option on socket.
229 .It Dv LOCAL_CONNWAIT
232 sockets, this option causes the
234 function to block until
236 has been called on the listening socket.
237 .It Dv LOCAL_PEERCRED
242 socket returns credentials of the remote side.
243 These will arrive in the form of a filled in
245 structure, defined in
250 u_int cr_version; /* structure layout version */
251 uid_t cr_uid; /* effective user id */
252 short cr_ngroups; /* number of groups */
253 gid_t cr_groups[XU_NGROUPS]; /* groups */
258 fields should be checked against
262 The credentials presented to the server (the
264 caller) are those of the client when it called
266 the credentials presented to the client (the
268 caller) are those of the server when it called
270 This mechanism is reliable; there is no way for either party to influence
271 the credentials presented to its peer except by calling the appropriate
276 under different effective credentials.
278 To reliably obtain peer credentials on a
296 .%T "An Introductory 4.3 BSD Interprocess Communication Tutorial"
301 .%T "An Advanced 4.3 BSD Interprocess Communication Tutorial"