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.

       EADDRNOTAVAIL
              (Internet  domain sockets) The socket referred to by sockfd had not previously been
              bound to an address and, upon attempting to bind it to an ephemeral  port,  it  was
              determined  that all port numbers in the ephemeral port range are currently in use.
              See the discussion of /proc/sys/net/ipv4/ip_local_port_range in ip(7).

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

       EAGAIN For nonblocking UNIX domain sockets, the socket is nonblocking, and the  connection
              cannot be completed immediately.  For other socket families, there are insufficient
              entries in the routing cache.

       EALREADY
              The socket is nonblocking and a  previous  connection  attempt  has  not  yet  been
              completed.

       EBADF  sockfd is not a valid open file descriptor.

       ECONNREFUSED
              A connect() on a stream socket found 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.
              (UNIX domain sockets failed with EAGAIN instead.)  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 sockfd does not refer to a socket.

       EPROTOTYPE
              The socket type does not support the requested communications protocol.  This error
              can occur, for example, on an attempt to connect a UNIX domain datagram socket to a
              stream 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

       POSIX.1-2001, POSIX.1-2008, SVr4, 4.4BSD, (connect() first appeared in 4.2BSD).

NOTES

       POSIX.1  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.

       For background on the socklen_t type, see accept(2).

       If   connect()  fails,  consider  the  state  of  the  socket  as  unspecified.   Portable
       applications should close the socket and create a new one for reconnecting.

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

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