bind(2) — Linux manual page

NAME \| LIBRARY \| SYNOPSIS \| DESCRIPTION \| RETURN VALUE \| ERRORS \| STANDARDS \| HISTORY \| BUGS \| EXAMPLES \| SEE ALSO \| COLOPHON

 bind(2)                    System Calls Manual                    bind(2)

NAME top

        bind - bind a name to a socket

LIBRARY top

        Standard C library (libc, -lc)

SYNOPSIS top

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

DESCRIPTION top

        When a socket is created with socket(2), it exists in a name space        (address family) but has no address assigned to it.  bind()        assigns the address specified by addr to the socket referred to by        the file descriptor sockfd.  addrlen specifies the size, in bytes,        of the address structure pointed to by addr.  Traditionally, this        operation is called “assigning a name to a socket”.         It is normally necessary to assign a local address using bind()        before a SOCK_STREAM socket may receive connections (see        accept(2)).         The rules used in name binding vary between address families.        Consult the manual entries in Section 7 for detailed information.        For AF_INET, see ip(7); for AF_INET6, see ipv6(7); for AF_UNIX,        see unix(7); for AF_APPLETALK, see ddp(7); for AF_PACKET, see        packet(7); for AF_X25, see x25(7); and for AF_NETLINK, see        netlink(7).         The actual structure passed for the addr argument will depend on        the address family.  The sockaddr structure is defined as        something like:             struct sockaddr {                sa_family_t sa_family;                char        sa_data[14];            }         The only purpose of this structure is to cast the structure        pointer passed in addr in order to avoid compiler warnings.  See        EXAMPLES below.

RETURN VALUE top

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

ERRORS top

EACCES The address is protected, and the user is not the superuser. EADDRINUSE The given address is already in use. EADDRINUSE (Internet domain sockets) The port number was specified as zero in the socket address structure, but, upon attempting to bind to an ephemeral port, it was determined that all port numbers in the ephemeral port range are currently in use. See the discussion of /proc/sys/net/ipv4/ip_local_port_range ip(7). EBADF sockfd is not a valid file descriptor. EINVAL The socket is already bound to an address. EINVAL addrlen is wrong, or addr is not a valid address for this socket's domain. ENOTSOCK The file descriptor sockfd does not refer to a socket. EADDRNOTAVAIL A nonexistent interface was requested or the requested address was not local. The following errors are specific to UNIX domain (AF_UNIX) sockets: EACCES Search permission is denied on a component of the path prefix. (See also path_resolution(7).) EFAULT addr points outside the user's accessible address space. ELOOP Too many symbolic links were encountered in resolving addr. ENAMETOOLONG addr is too long. ENOENT A component in the directory prefix of the socket pathname does not exist. ENOMEM Insufficient kernel memory was available. ENOTDIR A component of the path prefix is not a directory. EROFS The socket inode would reside on a read-only filesystem. Other errors may be generated by the underlying protocol modules.

STANDARDS top

        POSIX.1-2008.

HISTORY top

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

BUGS top

        The transparent proxy options are not described.

EXAMPLES top

        An example of the use of bind() with Internet domain sockets can        be found in getaddrinfo(3).         The following example shows how to bind a stream socket in the        UNIX (AF_UNIX) domain, and accept connections:         #include <stdio.h>        #include <stdlib.h>        #include <string.h>        #include <sys/socket.h>        #include <sys/un.h>        #include <unistd.h>         #define MY_SOCK_PATH "/somepath"        #define LISTEN_BACKLOG 50         #define handle_error(msg) \            do { perror(msg); exit(EXIT_FAILURE); } while (0)         int        main(void)        {            int                 sfd, cfd;            socklen_t           peer_addr_size;            struct sockaddr_un  my_addr, peer_addr;             sfd = socket(AF_UNIX, SOCK_STREAM, 0);            if (sfd == -1)                handle_error("socket");             memset(&my_addr, 0, sizeof(my_addr));            my_addr.sun_family = AF_UNIX;            strncpy(my_addr.sun_path, MY_SOCK_PATH,                    sizeof(my_addr.sun_path) - 1);             if (bind(sfd, (struct sockaddr *) &my_addr,                     sizeof(my_addr)) == -1)                handle_error("bind");             if (listen(sfd, LISTEN_BACKLOG) == -1)                handle_error("listen");             /* Now we can accept incoming connections one               at a time using accept(2). */             peer_addr_size = sizeof(peer_addr);            cfd = accept(sfd, (struct sockaddr *) &peer_addr,                         &peer_addr_size);            if (cfd == -1)                handle_error("accept");             /* Code to deal with incoming connection(s)... */             if (close(sfd) == -1)                handle_error("close");             if (unlink(MY_SOCK_PATH) == -1)                handle_error("unlink");        }

COLOPHON top

        This page is part of the man-pages (Linux kernel and C library        user-space interface documentation) project.  Information about        the project can be found at         ⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report        for this manual page, see        ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.        This page was obtained from the tarball man-pages-6.15.tar.gz        fetched from        ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on        2025-08-11.  If you discover any rendering problems in this HTML        version of the page, or you believe there is a better or more up-        to-date source for the page, or you have corrections or        improvements to the information in this COLOPHON (which is not        part of the original manual page), send a mail to        [email protected]  Linux man-pages 6.15            2025-05-17                        bind(2)

Pages that refer to this page: accept(2), connect(2), getpeername(2), getsockname(2), io_uring_enter2(2), io_uring_enter(2), landlock_add_rule(2), listen(2), pidfd_getfd(2), seccomp_unotify(2), socket(2), socketcall(2), syscalls(2), bindresvport(3), getaddrinfo(3), getifaddrs(3), if_nameindex(3), io_uring_prep_bind(3), sctp_bindx(3), sockaddr(3type), services(5), systemd.resource-control(5), systemd.socket(5), ddp(7), inotify(7), ip(7), ipv6(7), mctp(7), netlink(7), packet(7), raw(7), sctp(7), signal-safety(7), sock_diag(7), socket(7), tcp(7), udp(7), unix(7), vsock(7)