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



NAME
       connect - initiate a connection on a socket

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

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

DESCRIPTION
       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  con-
       necting to an address with the sa_family member of sockaddr set to AF_UNSPEC (supported on Linux since kernel 2.2).

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

ERRORS
       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  connec-
              tion request failed because of a local firewall rule.

       EADDRINUSE
              Local address is already in use.

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

       EAGAIN No  more  free  local  ports  or  insufficient  entries  in the routing cache.  For AF_INET see the description of
              /proc/sys/net/ipv4/ip_local_port_range ip(7) for information on how to increase the number of local ports.

       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 getsock-
              opt(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.

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

NOTES
       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).

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

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

COLOPHON
       This page is part of release 3.25 of the Linux man-pages project.  A description of the project,  and  information  about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                                                      2008-12-03                                                 CONNECT(2)