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TCP(7P) TCP(7P)

the second threshold, TCP terminates the connection. The default value for

this option is the current value of the ndd tunable

tcp_ip_abort_cinterval

. See ndd(1M) online help for details on

the tcp_ip_abort_cinterval default value.

TCP_NODELAY is set, the system sends small amounts of output immediately rather than gathering

them into a single packet after an acknowledgement is received. If

TCP_NODELAY is not set, the system

sends data when it is presented, if there is no outstanding unacknowledged data. If there is outstanding

unacknowledged data, the system gathers small amounts of data to be sent in a single packet once an ack-

nowledgement is received. For clients such as window managers that send a stream of mouse events which

receive no replies, this packetization may cause signiﬁcant delays. The

TCP_NODELAY

option can be used

to avoid this situation. Note, however, that setting the

TCP_NODELAY option may result in a large

number of small packets being sent over the network.

By default,

TCP_NODELAY is not set when a socket is created.

The option level to use for accessing the

TCP option with the setsockopt() or getsockopt() calls

is the protocol number for

TCP which is available from

getprotobyname()

(see getprotoent (3N)).

If the

SO_KEEPALIVE socket option is enabled on an established TCP connection and the connection has

been idle for two hours, TCP sends a packet to the remote socket, expecting the remote TCP to ack-

nowledge that the connection is still active. If the remote TCP does not respond in a timely manner, TCP

continues to send keepalive packets according to its normal retransmission algorithm. If the remote TCP

does not respond within a particular time limit, TCP drops the connection. The next socket system call (for

example, recv()) returns an error, and errno is set to ETIMEDOUT. See getsockopt(2) for details on

enabling

SO_KEEPALIVE .

The default send and receives buffer size is 32768 bytes (see WARNINGS below). The send and receive

buffer sizes for

TCP stream sockets can be altered by using the SO_SNDBUF and SO_RCVBUF

options of

the

setsockopt() system call or the XTI_SNDBUF and XTI_RCVBUF options of the

t_optmgmt() system call. Refer to getsockopt(2) or t_optmgmt (3) for details.

The maximum transmit buffer size for a TCP stream socket is 2147483647 bytes. The maximum receive

buffer size for a TCP stream socket is 1073725440 bytes. These maximum values can be lowered using the

ndd variables tcp_xmit_hiwater_max and tcp_recv_hiwater_max.

ERRORS

One of the following errors may be returned in errno if a socket operation fails. For a more detailed list

of errors, see the man pages for speciﬁc system calls.

[EISCONN] The socket is already connected.

[ENOBUFS] No buffer space is available for an internal data structure.

[ETIMEDOUT] Connection dropped due to excessive retransmissions.

[ECONNRESET] The connection was forcibly closed by the peer socket.

[ECONNREFUSED] Remote peer actively refuses connection establishment (usually because no

process is listening to the port).

[EADDRINUSE] The speciﬁed address is already in use.

[EADDRNOTAVAIL] The speciﬁed address is not available on this machine.

WARNINGS

The default socket buffer size might increase without notice in a future release or patch. Therefore, if an

application calls setsockopt() with SO_RCVBUF, it should do so before calling listen(),orit

should ﬁrst call getsockopt() with SO_RCVBUF and ensure that the intended new receive buffer size

is not less than the current buffer size. These programming conventions are consistent with TCP protocol

restrictions against reducing the TCP receive window after a connection has been established.

AUTHOR

The socket interfaces to TCP were developed by the University of California, Berkeley.