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28 .\" @(#)unix.4 8.1 (Berkeley) 6/9/93
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 file system pathnames for addressing.
59 addresses are variable-length file system pathnames of
60 at most 104 characters.
64 .Bd -literal -offset indent
76 causes a socket file to be created in the file system.
79 removed when the socket is closed \(em
81 must be used to remove the file.
89 can be calculated by the macro
95 field must be terminated by a
97 character to be used with
107 protocol family does not support broadcast addressing or any form
110 matching on incoming messages.
111 All addresses are absolute- or relative-pathnames
115 Normal file system access-control mechanisms are also
116 applied when referencing pathnames; e.g., the destination
122 .Sh PASSING FILE DESCRIPTORS
125 sockets support the communication of
127 file descriptors through the use of the
136 Any valid descriptor may be sent in a message.
137 The file descriptor(s) to be passed are described using a
139 that is defined in the include file
141 The type of the message is
143 and the data portion of the messages is an array of integers
144 representing the file descriptors to be passed.
145 The number of descriptors being passed is defined
146 by the length field of the message;
147 the length field is the sum of the size of the header
148 plus the size of the array of file descriptors.
150 The received descriptor is a
152 of the sender's descriptor, as if it were created via
155 .Li fcntl(fd, F_DUPFD_CLOEXEC, 0)
161 Descriptors that are awaiting delivery, or that are
162 purposely not received, are automatically closed by the system
163 when the destination socket is closed.
166 domain sockets support a number of socket options which can be set with
170 .Bl -tag -width ".Dv LOCAL_CONNWAIT"
172 This option may be enabled on
178 This option provides a mechanism for the receiver to
179 receive the credentials of the process as a
186 structure points to a buffer that contains a
188 structure followed by a variable length
190 structure, defined in
195 uid_t sc_uid; /* real user id */
196 uid_t sc_euid; /* effective user id */
197 gid_t sc_gid; /* real group id */
198 gid_t sc_egid; /* effective group id */
199 int sc_ngroups; /* number of supplemental groups */
200 gid_t sc_groups[1]; /* variable length */
206 macro computes the size of the
208 structure for a specified number
212 fields have the following values:
214 cmsg_len = CMSG_LEN(SOCKCREDSIZE(ngroups))
215 cmsg_level = SOL_SOCKET
216 cmsg_type = SCM_CREDS
223 sockets credentials are passed only on the first read from a socket,
224 then system clears the option on socket.
225 .It Dv LOCAL_CONNWAIT
228 sockets, this option causes the
230 function to block until
232 has been called on the listening socket.
233 .It Dv LOCAL_PEERCRED
238 socket returns credentials of the remote side.
239 These will arrive in the form of a filled in
241 structure, defined in
246 u_int cr_version; /* structure layout version */
247 uid_t cr_uid; /* effective user id */
248 short cr_ngroups; /* number of groups */
249 gid_t cr_groups[XU_NGROUPS]; /* groups */
254 fields should be checked against
258 The credentials presented to the server (the
260 caller) are those of the client when it called
262 the credentials presented to the client (the
264 caller) are those of the server when it called
266 This mechanism is reliable; there is no way for either party to influence
267 the credentials presented to its peer except by calling the appropriate
272 under different effective credentials.
274 To reliably obtain peer credentials on a
292 .%T "An Introductory 4.3 BSD Interprocess Communication Tutorial"
297 .%T "An Advanced 4.3 BSD Interprocess Communication Tutorial"