CONNECT(2) Linux Programmer's Manual CONNECT(2)
NAME
connect - initiate a connection on a socket
SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
int connect(int sockfd, const struct sockaddr *serv_addr, socklen_t addrlen);
DESCRIPTION
The connect() system call connects the socket referred to by the file descriptor
sockfd to the address specified by serv_addr. The addrlen argument specifies the
size of serv_addr. The format of the address in serv_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 serv_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 serv_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.
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(2).)
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.
EADDRNOTAVAIL
Non-existent interface was requested or the requested address was not local.
EALREADY
The socket is non-blocking 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 non-blocking and the connection cannot be completed immedi-
ately. It is possible to select(2) or poll(2) for completion by selecting
the socket for writing. After select(2) indicates writability, use getsock-
opt(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.
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).
NOTE
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).
BUGS
Unconnecting a socket by calling connect() with a AF_UNSPEC address is not yet
implemented.
SEE ALSO
accept(2), bind(2), getsockname(2), listen(2), path_resolution(2), socket(2)
Linux 2.6.7 2004-06-23 CONNECT(2)
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