bind(2) - f36

1BIND(2)                    Linux Programmer's Manual                   BIND(2)
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NAME

6       bind - bind a name to a socket
7

SYNOPSIS

9       #include <sys/socket.h>
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11       int bind(int sockfd, const struct sockaddr *addr,
12                socklen_t addrlen);
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DESCRIPTION

15       When a socket is created with socket(2), it exists in a name space (ad‐
16       dress family) but has no address assigned to it.   bind()  assigns  the
17       address  specified  by  addr  to the socket referred to by the file de‐
18       scriptor sockfd.  addrlen specifies the size, in bytes, of the  address
19       structure  pointed to by addr.  Traditionally, this operation is called
20       “assigning a name to a socket”.
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22       It is normally necessary to assign a local address using bind()  before
23       a SOCK_STREAM socket may receive connections (see accept(2)).
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25       The  rules used in name binding vary between address families.  Consult
26       the manual entries in Section 7 for detailed information.  For AF_INET,
27       see  ip(7);  for  AF_INET6,  see ipv6(7); for AF_UNIX, see unix(7); for
28       AF_APPLETALK, see ddp(7); for AF_PACKET, see packet(7); for AF_X25, see
29       x25(7); and for AF_NETLINK, see netlink(7).
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31       The  actual  structure  passed for the addr argument will depend on the
32       address family.  The sockaddr structure is defined as something like:
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34           struct sockaddr {
35               sa_family_t sa_family;
36               char        sa_data[14];
37           }
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39       The only purpose of this structure is to  cast  the  structure  pointer
40       passed  in  addr in order to avoid compiler warnings.  See EXAMPLES be‐
41       low.
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RETURN VALUE

44       On success, zero is returned.  On error, -1 is returned, and  errno  is
45       set to indicate the error.
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ERRORS

48       EACCES The address is protected, and the user is not the superuser.
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50       EADDRINUSE
51              The given address is already in use.
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53       EADDRINUSE
54              (Internet  domain sockets) The port number was specified as zero
55              in the socket address structure, but, upon attempting to bind to
56              an  ephemeral  port,  it was determined that all port numbers in
57              the ephemeral port range are currently in use.  See the  discus‐
58              sion of /proc/sys/net/ipv4/ip_local_port_range ip(7).
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60       EBADF  sockfd is not a valid file descriptor.
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62       EINVAL The socket is already bound to an address.
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64       EINVAL addrlen  is  wrong,  or  addr  is  not  a valid address for this
65              socket's domain.
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67       ENOTSOCK
68              The file descriptor sockfd does not refer to a socket.
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70       The following errors are specific to UNIX domain (AF_UNIX) sockets:
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72       EACCES Search permission is denied on a component of the  path  prefix.
73              (See also path_resolution(7).)
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75       EADDRNOTAVAIL
76              A  nonexistent  interface was requested or the requested address
77              was not local.
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79       EFAULT addr points outside the user's accessible address space.
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81       ELOOP  Too many symbolic links were encountered in resolving addr.
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83       ENAMETOOLONG
84              addr is too long.
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86       ENOENT A component in the directory prefix of the socket pathname  does
87              not exist.
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89       ENOMEM Insufficient kernel memory was available.
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91       ENOTDIR
92              A component of the path prefix is not a directory.
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94       EROFS  The socket inode would reside on a read-only filesystem.
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CONFORMING TO

97       POSIX.1-2001,  POSIX.1-2008,  SVr4,  4.4BSD  (bind()  first appeared in
98       4.2BSD).
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NOTES

101       For background on the socklen_t type, see accept(2).
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BUGS

104       The transparent proxy options are not described.
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EXAMPLES

107       An example of the use of bind() with Internet  domain  sockets  can  be
108       found in getaddrinfo(3).
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110       The  following  example  shows  how to bind a stream socket in the UNIX
111       (AF_UNIX) domain, and accept connections:
112
113       #include <sys/socket.h>
114       #include <sys/un.h>
115       #include <stdlib.h>
116       #include <stdio.h>
117       #include <string.h>
118
119       #define MY_SOCK_PATH "/somepath"
120       #define LISTEN_BACKLOG 50
121
122       #define handle_error(msg) \
123           do { perror(msg); exit(EXIT_FAILURE); } while (0)
124
125       int
126       main(int argc, char *argv[])
127       {
128           int sfd, cfd;
129           struct sockaddr_un my_addr, peer_addr;
130           socklen_t peer_addr_size;
131
132           sfd = socket(AF_UNIX, SOCK_STREAM, 0);
133           if (sfd == -1)
134               handle_error("socket");
135
136           memset(&my_addr, 0, sizeof(my_addr));
137           my_addr.sun_family = AF_UNIX;
138           strncpy(my_addr.sun_path, MY_SOCK_PATH,
139                   sizeof(my_addr.sun_path) - 1);
140
141           if (bind(sfd, (struct sockaddr *) &my_addr,
142                   sizeof(my_addr)) == -1)
143               handle_error("bind");
144
145           if (listen(sfd, LISTEN_BACKLOG) == -1)
146               handle_error("listen");
147
148           /* Now we can accept incoming connections one
149              at a time using accept(2). */
150
151           peer_addr_size = sizeof(peer_addr);
152           cfd = accept(sfd, (struct sockaddr *) &peer_addr,
153                        &peer_addr_size);
154           if (cfd == -1)
155               handle_error("accept");
156
157           /* Code to deal with incoming connection(s)... */
158
159           /* When no longer required, the socket pathname, MY_SOCK_PATH
160              should be deleted using unlink(2) or remove(3). */
161       }
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COLOPHON

169       This page is part of release 5.13 of the Linux  man-pages  project.   A
170       description  of  the project, information about reporting bugs, and the
171       latest    version    of    this    page,    can     be     found     at
172       https://www.kernel.org/doc/man-pages/.
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176Linux                             2021-03-22                           BIND(2)