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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