CONNECT(2) Linux Programmer's Manual CONNECT(2)
NAME
connect - initiate a connection on a socket(2,7,n)
SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
int connect(int sockfd, const struct sockaddr *serv_addr, socklen_t
addrlen);
DESCRIPTION
The file(1,n) descriptor sockfd must refer to a socket. If the socket(2,7,n) is of
type SOCK_DGRAM then the serv_addr address is the address to which
datagrams are sent by default, and the only address from which data-
grams are received. If the socket(2,7,n) is of type SOCK_STREAM or SOCK_SEQ-
PACKET, this call attempts to make a connection to another socket. The
other socket(2,7,n) is specified by serv_addr, which is an address (of length
addrlen) in(1,8) the communications space of the socket. Each communica-
tions space interprets the serv_addr parameter in(1,8) its own way.
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(7,n,1 builtins) to AF_UNSPEC.
RETURN VALUE
If the connection or binding succeeds, zero is returned. On error(8,n), -1
is returned, and errno is set(7,n,1 builtins) appropriately.
ERRORS
The following are general socket(2,7,n) errors only. There may be other
domain-specific error(8,n) codes.
EACCES For Unix domain sockets, which are identified by pathname: Write
permission is denied on the socket(2,7,n) file(1,n), or search permission is
denied for one of the directories in(1,8) the path prefix. (See also
path_resolution(2).)
EACCES, EPERM
The user tried to connect to a broadcast address without having
the socket(2,7,n) broadcast flag enabled or the connection request
failed because of a local firewall rule.
EADDRINUSE
Local address is already in(1,8) use.
EAFNOSUPPORT
The passed address didn't have the correct address family in(1,8) its
sa_family field.
EAGAIN No more free local ports or insufficient entries in(1,8) the routing
cache. For PF_INET see the net.ipv4.ip_local_port_range sysctl(2,5,8)
in(1,8) ip(7,8)(7) on how to increase the number of local ports.
EALREADY
The socket(2,7,n) is non-blocking and a previous connection attempt has
not yet been completed.
EBADF The file(1,n) descriptor is not a valid index in(1,8) the descriptor ta-
ble.
ECONNREFUSED
No one listening on the remote address.
EFAULT The socket(2,7,n) structure address is outside the user's address
space.
EINPROGRESS
The socket(2,7,n) is non-blocking and the connection cannot be com-
pleted immediately. It is possible to select(2,7,2 select_tut)(2) or poll(2) for
completion by selecting the socket(2,7,n) for writing. After select(2,7,2 select_tut)
indicates writability, use getsockopt(2) to read(2,n,1 builtins) the SO_ERROR
option at level SOL_SOCKET to determine whether connect com-
pleted successfully (SO_ERROR is zero) or unsuccessfully
(SO_ERROR is one of the usual error(8,n) codes listed here, explain-
ing the reason for the failure).
EISCONN
The socket(2,7,n) is already connected.
ENETUNREACH
Network is unreachable.
ENOTSOCK
The file(1,n) descriptor is not associated with a socket.
ETIMEDOUT
Timeout while attempting connection. The server may be too busy
to accept(2,8) new connections. Note that for IP sockets the timeout(1,3x,3x cbreak)
may be very long when syncookies are enabled on the server.
CONFORMING TO
SVr4, 4.4BSD (the connect function first appeared in(1,8) BSD 4.2). SVr4
documents the additional general error(8,n) codes EADDRNOTAVAIL, EINVAL,
EAFNOSUPPORT, EALREADY, EINTR, EPROTOTYPE, and ENOSR. It also docu-
ments many additional error(8,n) conditions not described here.
NOTE
The third argument of connect is in(1,8) reality an int (and this is what
BSD 4.* and libc4 and libc5 have). Some POSIX confusion resulted in(1,8)
the present socklen_t, also used by glibc. See also accept(2,8)(2).
BUGS
Unconnecting a socket(2,7,n) by calling connect with a AF_UNSPEC address is
not yet implemented.
SEE ALSO
accept(2,8)(2), bind(2,n,1 builtins)(2), getsockname(2), listen(1,2,7)(2), path_resolution(2),
socket(2,7,n)(2)
Linux 2.6.7 2004-06-23 CONNECT(2)