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/.