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 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 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  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.

       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 3.54 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/.