SOCKET(2) COMMAND REFERENCE SOCKET(2)
NAME
socket - create an endpoint for communication
SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
s = socket(af, type, protocol)
int s, af, type, protocol;
DESCRIPTION
Socket creates an endpoint for communication and returns a
descriptor.
The af parameter specifies an address format with which
addresses specified in later operations using the socket
should be interpreted. These formats are defined in the
include file <sys/socket.h>. The currently understood
formats are:
AF_UNIX (UTek path names),
AF_INET (ARPA Internet addresses),
AF_PUP (Xerox PUP-I Internet addresses), and
AF_IMPLINK (IMP "host at IMP" addresses).
The socket has the indicated type which specifies the
semantics of communication. Currently defined types are:
SOCK_STREAM
SOCK_DGRAM
SOCK_RAW
A SOCK_STREAM type provides sequenced, reliable, two-way
connection based byte streams with an out-of-band data
transmission mechanism. A SOCK_DGRAM socket supports
datagrams (connectionless, unreliable messages of a fixed
(typically small) maximum length). SOCK_RAW sockets provide
access to internal network interfaces. SOCK_RAW is
available only to the super-user.
The protocol specifies a particular protocol to be used with
the socket. Normally only a single protocol exists to
support a particular socket type using a given address
format. However, it is possible that many protocols may
exist in which case a particular protocol must be specified
in this manner. The protocol number to use is particular to
the "communication domain" in which communication is to take
place.
Sockets of type SOCK_STREAM are full-duplex byte streams,
similar to pipes. A stream socket must be in a connected
state before any data may be sent or received on it. A
Printed 4/6/89 1
SOCKET(2) COMMAND REFERENCE SOCKET(2)
connection to another socket is created with a connect(2)
call. Once connected, data may be transferred using read(2)
and write(2) calls or some variant of the send(2) and
recv(2) calls. When a session has been completed a close(2)
may be performed. Out-of-band data may also be transmitted
as described in send(2) and received as described in
recv(2).
The communications protocols used to implement a SOCK_STREAM
insure that data is not lost or duplicated. If a piece of
data for which the peer protocol has buffer space cannot be
successfully transmitted within a reasonable length of time,
then the connection is considered broken and calls will
indicate an error with -1 returns and with ETIMEDOUT as the
specific code in the global variable errno. The protocols
optionally keep sockets "warm" by forcing transmissions
roughly every minute in the absence of other activity. An
error is then indicated if no response can be elicited on an
otherwise idle connection for a extended period (e.g. 5
minutes). A SIGPIPE signal is raised if a process sends on
a broken stream; this causes naive processes, which do not
handle the signal, to exit.
SOCK_DGRAM and SOCK_RAW sockets allow sending of datagrams
to correspondents named in send(2) calls. It is also
possible to receive datagrams at such a socket with recv(2).
An fcntl(2) call can be used to specify a process group to
receive a SIGURG signal when the out-of-band data arrives.
The operation of sockets is controlled by socket level
options. These options are defined in the file
<sys/socket.h> and explained below. Setsockopt(2) and
getsockopt(2) are used to set and get options, respectively.
SO_DEBUG turn on recording of debugging information.
SO_REUSEADDR allow local address reuse.
SO_KEEPALIVE keep connections alive.
SO_DONTROUTE do no apply routing on outgoing messages.
SO_LINGER linger on close if data present.
SO_DONTLINGER do not linger on close.fP
SO_DEBUG enables debugging in the underlying protocol
modules. SO_REUSEADDR indicates the rules used in
validating addresses supplied in a bind(2) call should allow
reuse of local addresses. SO_KEEPALIVE enables the periodic
transmission of messages on a connected socket. Should the
connected party fail to respond to these messages, the
connection is considered broken and processes using the
socket are notified via a SIGPIPE signal. SO_DONTROUTE
indicates that outgoing messages should bypass the standard
routing facilities. Instead, messages are directed to the
Printed 4/6/89 2
SOCKET(2) COMMAND REFERENCE SOCKET(2)
appropriate network interface according to the network
portion of the destination address. SO_LINGER and
SO_DONTLINGER control the actions taken when unsent messages
are queued on socket and a close(2) is performed. If the
socket promises reliable delivery of data and SO_LINGER is
set, the system will block the process on the close attempt
until it is able to transmit the data or until it decides it
is unable to deliver the information (a timeout period,
termed the linger interval, is specified in the setsockopt
call when SO_LINGER is requested). If SO_DONTLINGER is
specified and a close is issued, the system will process the
close in a manner which allows the process to continue as
quickly as possible.
DIAGNOSTICS
The socket call fails if:
[EAFNOSUPPORT] The specified address family is not supported
in this version of the system.
[ESOCKTNOSUPPORT]
The specified socket type is not supported in
this address family.
[EPROTONOSUPPORT]
The specified protocol is not supported.
[EMFILE] The per-process descriptor table is full.
[ENOBUFS] No buffer space is available. The socket
cannot be created.
RETURN VALUE
A -1 is returned if an error occurs, otherwise the return
value is a descriptor referencing the socket.
CAVEATS
The use of keepalives is a questionable feature for this
layer.
SEE ALSO
accept(2), bind(2), connect(2), getsockname(2),
getsockopt(2), ioctl(2), listen(2), recv(2), select(2),
send(2), shutdown(2), and socketpair(2).
Printed 4/6/89 3
%%index%%
na:288,97;
sy:385,1126;
de:1511,2040;3911,3005;7276,1044;
di:8320,713;
rv:9033,238;
ca:9271,153;
se:9424,433;
%%index%%000000000143