NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON

CONNECT(2)                Linux Programmer's Manual               CONNECT(2)

NAME         top

       connect - initiate a connection on a socket

SYNOPSIS         top

       #include <sys/types.h>          /* See NOTES */
       #include <sys/socket.h>

       int connect(int sockfd, const struct sockaddr *addr,
                   socklen_t addrlen);

DESCRIPTION         top

       The connect() system call connects the socket referred to by the file
       descriptor sockfd to the address specified by addr.  The addrlen
       argument specifies the size of addr.  The format of the address in
       addr is determined by the address space of the socket sockfd; see
       socket(2) for further details.

       If the socket sockfd is of type SOCK_DGRAM, then addr is the address
       to which datagrams are sent by default, and the only address from
       which datagrams are received.  If the socket is of type SOCK_STREAM
       or SOCK_SEQPACKET, this call attempts to make a connection to the
       socket that is bound to the address specified by addr.

       Generally, connection-based protocol sockets may successfully
       connect() only once; connectionless protocol sockets may use
       connect() multiple times to change their association.  Connectionless
       sockets may dissolve the association by connecting to an address with
       the sa_family member of sockaddr set to AF_UNSPEC (supported on Linux
       since kernel 2.2).

RETURN VALUE         top

       If the connection or binding succeeds, zero is returned.  On error,
       -1 is returned, and errno is set appropriately.

ERRORS         top

       The following are general socket errors only.  There may be other
       domain-specific error codes.

       EACCES For UNIX domain sockets, which are identified by pathname:
              Write permission is denied on the socket file, or search
              permission is denied for one of the directories in the path
              prefix.  (See also path_resolution(7).)

       EACCES, EPERM
              The user tried to connect to a broadcast address without
              having the socket broadcast flag enabled or the connection
              request failed because of a local firewall rule.

       EADDRINUSE
              Local address is already in use.

       EADDRNOTAVAIL
              (Internet domain sockets) The socket referred to by sockfd had
              not previously been bound to an address and, upon attempting
              to bind it 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
              in ip(7).

       EAFNOSUPPORT
              The passed address didn't have the correct address family in
              its sa_family field.

       EAGAIN Insufficient entries in the routing cache.

       EALREADY
              The socket is nonblocking and a previous connection attempt
              has not yet been completed.

       EBADF  The file descriptor is not a valid index in the descriptor
              table.

       ECONNREFUSED
              No-one listening on the remote address.

       EFAULT The socket structure address is outside the user's address
              space.

       EINPROGRESS
              The socket is nonblocking and the connection cannot be
              completed immediately.  It is possible to select(2) or poll(2)
              for completion by selecting the socket for writing.  After
              select(2) indicates writability, use getsockopt(2) to read the
              SO_ERROR option at level SOL_SOCKET to determine whether
              connect() completed successfully (SO_ERROR is zero) or
              unsuccessfully (SO_ERROR is one of the usual error codes
              listed here, explaining the reason for the failure).

       EINTR  The system call was interrupted by a signal that was caught;
              see signal(7).

       EISCONN
              The socket is already connected.

       ENETUNREACH
              Network is unreachable.

       ENOTSOCK
              The file descriptor is not associated with a socket.

       EPROTOTYPE
              The socket type does not support the requested communications
              protocol.  This error can occur, for example, on an attempt to
              connect a UNIX domain datagram socket to a stream socket.

       ETIMEDOUT
              Timeout while attempting connection.  The server may be too
              busy to accept new connections.  Note that for IP sockets the
              timeout may be very long when syncookies are enabled on the
              server.

CONFORMING TO         top

       SVr4, 4.4BSD, (the connect() function first appeared in 4.2BSD),
       POSIX.1-2001.

NOTES         top

       POSIX.1-2001 does not require the inclusion of <sys/types.h>, and
       this header file is not required on Linux.  However, some historical
       (BSD) implementations required this header file, and portable
       applications are probably wise to include it.

       The third argument of connect() is in reality an int (and this is
       what 4.x BSD and libc4 and libc5 have).  Some POSIX confusion
       resulted in the present socklen_t, also used by glibc.  See also
       accept(2).

       If connect() fails, consider the state of the socket as unspecified.
       Portable applications should close the socket and create a new one
       for reconnecting.

EXAMPLE         top

       An example of the use of connect() is shown in getaddrinfo(3).

SEE ALSO         top

       accept(2), bind(2), getsockname(2), listen(2), socket(2),
       path_resolution(7)

COLOPHON         top

       This page is part of release 3.73 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       http://www.kernel.org/doc/man-pages/.

Linux                            2014-09-06                       CONNECT(2)