connect(2)

NAME

       connect - initiate a connection on a socket

SYNOPSIS

       #include <sys/types.h>
       #include <sys/socket.h>

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

DESCRIPTION

       The file descriptor sockfd must refer to a socket.  If the
       socket is of type SOCK_DGRAM then the serv_addr address 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 another socket.  The
       other socket  is  specified  by  serv_addr,  which  is  an
       address (of length addrlen) in the communications space of
       the socket.   Each  communications  space  interprets  the
       serv_addr parameter in its own way.

       Generally,  connection-based protocol sockets may success­
       fully connect only once; connectionless  protocol  sockets
       may  use  connect  multiple times to change their associa­
       tion.  Connectionless sockets may dissolve the association
       by  connecting  to an address with the sa_family member of
       sockaddr set to AF_UNSPEC.

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.

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

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

       ENOTSOCK
              The  file  descriptor  is  not  associated  with  a
              socket.

       EISCONN
              The socket is already connected.

       ECONNREFUSED
              No one listening on the remote address.





       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.

       ENETUNREACH
              Network is unreachable.

       EADDRINUSE
              Local address is already in use.

       EINPROGRESS
              The  socket is non-blocking and the connection can­
              not be completed immediately.  It  is  possible  to
              select(2)  or  poll(2)  for completion by selecting
              the socket  for  writing.  After  select  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).

       EALREADY
              The socket is non-blocking and a  previous  connec­
              tion attempt has not yet been completed.

       EAGAIN No more free local ports or insufficient entries in
              the   routing   cache.   For   PF_INET   see    the
              net.ipv4.ip_local_port_range sysctl in ip(7) on how
              to increase the number of local ports.

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

       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.

CONFORMING TO

       SVr4, 4.4BSD (the connect function first appeared  in  BSD
       4.2).   SVr4  documents the additional general error codes
       EADDRNOTAVAIL,  EINVAL,  EAFNOSUPPORT,  EALREADY,   EINTR,
       EPROTOTYPE,  and ENOSR.  It also documents many additional
       error conditions not described here.

NOTE

       The third argument of connect is in reality  an  int  (and
       this  is  what  BSD  4.*  and libc4 and libc5 have).  Some
       POSIX confusion resulted in the  present  socklen_t.   The



       draft  standard  has  not  been  adopted  yet,  but glibc2
       already follows it and also has socklen_t. See also

BUGS

       Unconnecting a socket by calling connect with a  AF_UNSPEC
       address is not yet implemented.

SEE ALSO

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