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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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CONNECT(3P) POSIX Programmer's Manual CONNECT(3P)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
connect — connect a socket
#include <sys/socket.h>
int connect(int socket, const struct sockaddr *address,
socklen_t address_len);
The connect() function shall attempt to make a connection on a
connection-mode socket or to set or reset the peer address of a
connectionless-mode socket. The function takes the following
arguments:
socket Specifies the file descriptor associated with the
socket.
address Points to a sockaddr structure containing the peer
address. The length and format of the address depend
on the address family of the socket.
address_len Specifies the length of the sockaddr structure
pointed to by the address argument.
If the socket has not already been bound to a local address,
connect() shall bind it to an address which, unless the socket's
address family is AF_UNIX, is an unused local address.
If the initiating socket is not connection-mode, then connect()
shall set the socket's peer address, and no connection is made.
For SOCK_DGRAM sockets, the peer address identifies where all
datagrams are sent on subsequent send() functions, and limits the
remote sender for subsequent recv() functions. If the sa_family
member of address is AF_UNSPEC, the socket's peer address shall
be reset. Note that despite no connection being made, the term
``connected'' is used to describe a connectionless-mode socket
for which a peer address has been set.
If the initiating socket is connection-mode, then connect() shall
attempt to establish a connection to the address specified by the
address argument. If the connection cannot be established
immediately and O_NONBLOCK is not set for the file descriptor for
the socket, connect() shall block for up to an unspecified
timeout interval until the connection is established. If the
timeout interval expires before the connection is established,
connect() shall fail and the connection attempt shall be aborted.
If connect() is interrupted by a signal that is caught while
blocked waiting to establish a connection, connect() shall fail
and set errno to [EINTR], but the connection request shall not be
aborted, and the connection shall be established asynchronously.
If the connection cannot be established immediately and
O_NONBLOCK is set for the file descriptor for the socket,
connect() shall fail and set errno to [EINPROGRESS], but the
connection request shall not be aborted, and the connection shall
be established asynchronously. Subsequent calls to connect() for
the same socket, before the connection is established, shall fail
and set errno to [EALREADY].
When the connection has been established asynchronously,
pselect(), select(), and poll() shall indicate that the file
descriptor for the socket is ready for writing.
The socket in use may require the process to have appropriate
privileges to use the connect() function.
Upon successful completion, connect() shall return 0; otherwise,
-1 shall be returned and errno set to indicate the error.
The connect() function shall fail if:
EADDRNOTAVAIL
The specified address is not available from the local
machine.
EAFNOSUPPORT
The specified address is not a valid address for the
address family of the specified socket.
EALREADY
A connection request is already in progress for the
specified socket.
EBADF The socket argument is not a valid file descriptor.
ECONNREFUSED
The target address was not listening for connections or
refused the connection request.
EINPROGRESS
O_NONBLOCK is set for the file descriptor for the socket
and the connection cannot be immediately established; the
connection shall be established asynchronously.
EINTR The attempt to establish a connection was interrupted by
delivery of a signal that was caught; the connection shall
be established asynchronously.
EISCONN
The specified socket is connection-mode and is already
connected.
ENETUNREACH
No route to the network is present.
ENOTSOCK
The socket argument does not refer to a socket.
EPROTOTYPE
The specified address has a different type than the socket
bound to the specified peer address.
ETIMEDOUT
The attempt to connect timed out before a connection was
made.
If the address family of the socket is AF_UNIX, then connect()
shall fail if:
EIO An I/O error occurred while reading from or writing to the
file system.
ELOOP A loop exists in symbolic links encountered during
resolution of the pathname in address.
ENAMETOOLONG
The length of a component of a pathname is longer than
{NAME_MAX}.
ENOENT A component of the pathname does not name an existing file
or the pathname is an empty string.
ENOTDIR
A component of the path prefix of the pathname in address
names an existing file that is neither a directory nor a
symbolic link to a directory, or the pathname in address
contains at least one non-<slash> character and ends with
one or more trailing <slash> characters and the last
pathname component names an existing file that is neither
a directory nor a symbolic link to a directory.
The connect() function may fail if:
EACCES Search permission is denied for a component of the path
prefix; or write access to the named socket is denied.
EADDRINUSE
Attempt to establish a connection that uses addresses that
are already in use.
ECONNRESET
Remote host reset the connection request.
EHOSTUNREACH
The destination host cannot be reached (probably because
the host is down or a remote router cannot reach it).
EINVAL The address_len argument is not a valid length for the
address family; or invalid address family in the sockaddr
structure.
ELOOP More than {SYMLOOP_MAX} symbolic links were encountered
during resolution of the pathname in address.
ENAMETOOLONG
The length of a pathname exceeds {PATH_MAX}, or pathname
resolution of a symbolic link produced an intermediate
result with a length that exceeds {PATH_MAX}.
ENETDOWN
The local network interface used to reach the destination
is down.
ENOBUFS
No buffer space is available.
EOPNOTSUPP
The socket is listening and cannot be connected.
The following sections are informative.
None.
If connect() fails, the state of the socket is unspecified.
Conforming applications should close the file descriptor and
create a new socket before attempting to reconnect.
None.
None.
accept(3p), bind(3p), close(3p), getsockname(3p), poll(3p),
pselect(3p), send(3p), shutdown(3p), socket(3p)
The Base Definitions volume of POSIX.1‐2017, sys_socket.h(0p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any
discrepancy between this version and the original IEEE and The
Open Group Standard, the original IEEE and The Open Group
Standard is the referee document. The original Standard can be
obtained online at http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page
are most likely to have been introduced during the conversion of
the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 CONNECT(3P)
Pages that refer to this page: netinet_in.h(0p), sys_socket.h(0p), accept(3p), bind(3p), freeaddrinfo(3p), listen(3p), pselect(3p), send(3p), socket(3p)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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