man2/bind.2

   1 .\" Copyright 1993 Rickard E. Faith (faith@cs.unc.edu)
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  64 .\" Modified Mon Oct 21 23:05:29 EDT 1996 by Eric S. Raymond <esr@thyrsus.com>
  65 .\" Modified 1998 by Andi Kleen
  66 .\" $Id: bind.2,v 1.3 1999/04/23 19:56:07 freitag Exp $
  67 .\" Modified 2004-06-23 by Michael Kerrisk <mtk.manpages@gmail.com>
  68 .\"
  69 .TH BIND 2 2019-03-06 "Linux" "Linux Programmer's Manual"
  70 .SH NAME
  71 bind \- bind a name to a socket
  72 .SH SYNOPSIS
  73 .nf
  74 .BR "#include <sys/types.h>" "          /* See NOTES */"
  75 .B #include <sys/socket.h>
  76 .PP
  77 .BI "int bind(int " sockfd ", const struct sockaddr *" addr ,
  78 .BI "         socklen_t " addrlen );
  79 .fi
  80 .SH DESCRIPTION
  81 When a socket is created with
  82 .BR socket (2),
  83 it exists in a name space (address family) but has no address assigned to it.
  84 .BR bind ()
  85 assigns the address specified by
  86 .I addr
  87 to the socket referred to by the file descriptor
  88 .IR sockfd .
  89 .I addrlen
  90 specifies the size, in bytes, of the address structure pointed to by
  91 .IR addr .
  92 Traditionally, this operation is called \(lqassigning a name to a socket\(rq.
  93 .PP
  94 It is normally necessary to assign a local address using
  95 .BR bind ()
  96 before a
  97 .B SOCK_STREAM
  98 socket may receive connections (see
  99 .BR accept (2)).
 100 .PP
 101 The rules used in name binding vary between address families.
 102 Consult the manual entries in Section 7 for detailed information.
 103 For
 104 .BR AF_INET ,
 105 see
 106 .BR ip (7);
 107 for
 108 .BR AF_INET6 ,
 109 see
 110 .BR ipv6 (7);
 111 for
 112 .BR AF_UNIX ,
 113 see
 114 .BR unix (7);
 115 for
 116 .BR AF_APPLETALK ,
 117 see
 118 .BR ddp (7);
 119 for
 120 .BR AF_PACKET ,
 121 see
 122 .BR packet (7);
 123 for
 124 .BR AF_X25 ,
 125 see
 126 .BR x25 (7);
 127 and for
 128 .BR AF_NETLINK ,
 129 see
 130 .BR netlink (7).
 131 .PP
 132 The actual structure passed for the
 133 .I addr
 134 argument will depend on the address family.
 135 The
 136 .I sockaddr
 137 structure is defined as something like:
 138 .PP
 139 .in +4n
 140 .EX
 141 struct sockaddr {
 142     sa_family_t sa_family;
 143     char        sa_data[14];
 144 }
 145 .EE
 146 .in
 147 .PP
 148 The only purpose of this structure is to cast the structure
 149 pointer passed in
 150 .I addr
 151 in order to avoid compiler warnings.
 152 See EXAMPLE below.
 153 .SH RETURN VALUE
 154 On success, zero is returned.
 155 On error, \-1 is returned, and
 156 .I errno
 157 is set appropriately.
 158 .SH ERRORS
 159 .TP
 160 .B EACCES
 161 .\" e.g., privileged port in AF_INET domain
 162 The address is protected, and the user is not the superuser.
 163 .TP
 164 .B EADDRINUSE
 165 The given address is already in use.
 166 .TP
 167 .B EADDRINUSE
 168 (Internet domain sockets)
 169 The port number was specified as zero in the socket address structure,
 170 but, upon attempting to bind to an ephemeral port,
 171 it was determined that all port numbers in the ephemeral port range
 172 are currently in use.
 173 See the discussion of
 174 .I /proc/sys/net/ipv4/ip_local_port_range
 175 .BR ip (7).
 176 .TP
 177 .B EBADF
 178 .I sockfd
 179 is not a valid file descriptor.
 180 .TP
 181 .B EINVAL
 182 The socket is already bound to an address.
 183 .\" This may change in the future: see
 184 .\" .I linux/unix/sock.c for details.
 185 .TP
 186 .B EINVAL
 187 .I addrlen
 188 is wrong, or
 189 .I addr
 190 is not a valid address for this socket's domain.
 191 .TP
 192 .B ENOTSOCK
 193 The file descriptor
 194 .I sockfd
 195 does not refer to a socket.
 196 .PP
 197 The following errors are specific to UNIX domain
 198 .RB ( AF_UNIX )
 199 sockets:
 200 .TP
 201 .B EACCES
 202 Search permission is denied on a component of the path prefix.
 203 (See also
 204 .BR path_resolution (7).)
 205 .TP
 206 .B EADDRNOTAVAIL
 207 A nonexistent interface was requested or the requested
 208 address was not local.
 209 .TP
 210 .B EFAULT
 211 .I addr
 212 points outside the user's accessible address space.
 213 .TP
 214 .B ELOOP
 215 Too many symbolic links were encountered in resolving
 216 .IR addr .
 217 .TP
 218 .B ENAMETOOLONG
 219 .I addr
 220 is too long.
 221 .TP
 222 .B ENOENT
 223 A component in the directory prefix of the socket pathname does not exist.
 224 .TP
 225 .B ENOMEM
 226 Insufficient kernel memory was available.
 227 .TP
 228 .B ENOTDIR
 229 A component of the path prefix is not a directory.
 230 .TP
 231 .B EROFS
 232 The socket inode would reside on a read-only filesystem.
 233 .SH CONFORMING TO
 234 POSIX.1-2001, POSIX.1-2008, SVr4, 4.4BSD
 235 .RB ( bind ()
 236 first appeared in 4.2BSD).
 237 .\" SVr4 documents an additional
 238 .\" .B ENOSR
 239 .\" general error condition, and
 240 .\" additional
 241 .\" .B EIO
 242 .\" and
 243 .\" .B EISDIR
 244 .\" UNIX-domain error conditions.
 245 .SH NOTES
 246 POSIX.1 does not require the inclusion of
 247 .IR <sys/types.h> ,
 248 and this header file is not required on Linux.
 249 However, some historical (BSD) implementations required this header
 250 file, and portable applications are probably wise to include it.
 251 .PP
 252 For background on the
 253 .I socklen_t
 254 type, see
 255 .BR accept (2).
 256 .SH BUGS
 257 The transparent proxy options are not described.
 258 .\" FIXME Document transparent proxy options
 259 .SH EXAMPLE
 260 An example of the use of
 261 .BR bind ()
 262 with Internet domain sockets can be found in
 263 .BR getaddrinfo (3).
 264 .PP
 265 The following example shows how to bind a stream socket in the UNIX
 266 .RB ( AF_UNIX )
 267 domain, and accept connections:
 268 .\" listen.7 refers to this example.
 269 .\" accept.7 refers to this example.
 270 .\" unix.7 refers to this example.
 271 .PP
 272 .EX
 273 #include <sys/socket.h>
 274 #include <sys/un.h>
 275 #include <stdlib.h>
 276 #include <stdio.h>
 277 #include <string.h>
 278
 279 #define MY_SOCK_PATH "/somepath"
 280 #define LISTEN_BACKLOG 50
 281
 282 #define handle_error(msg) \e
 283     do { perror(msg); exit(EXIT_FAILURE); } while (0)
 284
 285 int
 286 main(int argc, char *argv[])
 287 {
 288     int sfd, cfd;
 289     struct sockaddr_un my_addr, peer_addr;
 290     socklen_t peer_addr_size;
 291
 292     sfd = socket(AF_UNIX, SOCK_STREAM, 0);
 293     if (sfd == \-1)
 294         handle_error("socket");
 295
 296     memset(&my_addr, 0, sizeof(struct sockaddr_un));
 297                         /* Clear structure */
 298     my_addr.sun_family = AF_UNIX;
 299     strncpy(my_addr.sun_path, MY_SOCK_PATH,
 300             sizeof(my_addr.sun_path) \- 1);
 301
 302     if (bind(sfd, (struct sockaddr *) &my_addr,
 303             sizeof(struct sockaddr_un)) == \-1)
 304         handle_error("bind");
 305
 306     if (listen(sfd, LISTEN_BACKLOG) == \-1)
 307         handle_error("listen");
 308
 309     /* Now we can accept incoming connections one
 310        at a time using accept(2) */
 311
 312     peer_addr_size = sizeof(struct sockaddr_un);
 313     cfd = accept(sfd, (struct sockaddr *) &peer_addr,
 314                  &peer_addr_size);
 315     if (cfd == \-1)
 316         handle_error("accept");
 317
 318     /* Code to deal with incoming connection(s)... */
 319
 320     /* When no longer required, the socket pathname, MY_SOCK_PATH
 321        should be deleted using unlink(2) or remove(3) */
 322 }
 323 .EE
 324 .SH SEE ALSO
 325 .BR accept (2),
 326 .BR connect (2),
 327 .BR getsockname (2),
 328 .BR listen (2),
 329 .BR socket (2),
 330 .BR getaddrinfo (3),
 331 .BR getifaddrs (3),
 332 .BR ip (7),
 333 .BR ipv6 (7),
 334 .BR path_resolution (7),
 335 .BR socket (7),
 336 .BR unix (7)