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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 *serv_addr,
                   socklen_t addrlen);

DESCRIPTION

       The  connect()  system call connects the socket referred to by the file
       descriptor sockfd to the address specified by serv_addr.   The  addrlen
       argument specifies the size of serv_addr.  The format of the address in
       serv_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 serv_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 serv_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

       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 connection 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 PF_INET see the net.ipv4.ip_local_port_range  sysctl
              in ip(7) on how to increase the number of local ports.

       EALREADY
              The socket is non-blocking 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  non-blocking  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.

       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 3.01 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/.