connect — initiate a connection on a socket
#include <sys/types.h> /* See NOTES */ #include <sys/socket.h>
int
connect( |
int | sockfd, |
| const struct sockaddr * | serv_addr, | |
| socklen_t | addrlen); |
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 (supported since 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.
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).)
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.
Local address is already in use.
The passed address didn't have the correct address
family in its sa_family field.
No more free local ports or insufficient entries in
the routing cache. For PF_INET see the net.ipv4.ip_local_port_range
sysctl in ip(7) on how to
increase the number of local ports.
The socket is non-blocking and a previous connection attempt has not yet been completed.
The file descriptor is not a valid index in the descriptor table.
No-one listening on the remote address.
The socket structure address is outside the user's address space.
The socket is non-blocking 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).
The system call was interrupted by a signal that was caught.
The socket is already connected.
Network is unreachable.
The file descriptor is not associated with a socket.
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 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.
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).