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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON |
CONNECT(2) Linux Programmer's Manual CONNECT(2)
connect - initiate a connection on a socket
#include <sys/types.h> /* See NOTES */
#include <sys/socket.h>
int connect(int sockfd, const struct sockaddr *addr,
socklen_t addrlen);
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).
If the connection or binding succeeds, zero is returned. On error,
-1 is returned, and errno is set appropriately.
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 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
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 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.
POSIX.1-2001, POSIX.1-2008, SVr4, 4.4BSD, (the connect() function
first appeared in 4.2BSD).
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.
An example of the use of connect() is shown in getaddrinfo(3).
accept(2), bind(2), getsockname(2), listen(2), socket(2),
path_resolution(7)
This page is part of release 4.12 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2016-12-12 CONNECT(2)
Pages that refer to this page: pmsocks(1), telnet-probe(1), accept(2), bind(2), getpeername(2), listen(2), recv(2), select(2), select_tut(2), shutdown(2), socket(2), socketcall(2), syscalls(2), write(2), getaddrinfo(3), ldap_get_option(3), rtime(3), slapd-asyncmeta(5), slapd-ldap(5), slapd-meta(5), ddp(7), ip(7), netlink(7), packet(7), sctp(7), signal(7), signal-safety(7), sock_diag(7), socket(7), tcp(7), udp(7), unix(7)