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SOCKET(2) | System Calls Manual | SOCKET(2) |
NAME¶
socket
—
create an endpoint for communication
LIBRARY¶
Standard C Library (libc, -lc)SYNOPSIS¶
#include
<sys/types.h>
#include
<sys/socket.h>
int
socket
(int
domain, int
type, int
protocol);
DESCRIPTION¶
Thesocket
() system call creates an endpoint
for communication and returns a descriptor.
The domain argument specifies a communications
domain within which communication will take place; this selects the protocol
family which should be used. These families are defined in the include file
<sys/socket.h>
.
The currently understood formats are:
PF_LOCAL Host-internal protocols, formerly called PF_UNIX, PF_UNIX Host-internal protocols, deprecated, use PF_LOCAL, PF_INET Internet version 4 protocols, PF_PUP PUP protocols, like BSP, PF_APPLETALK AppleTalk protocols, PF_ROUTE Internal Routing protocol, PF_LINK Link layer interface, PF_IPX Novell Internet Packet eXchange protocol, PF_RTIP Help Identify RTIP packets, PF_PIP Help Identify PIP packets, PF_ISDN Integrated Services Digital Network, PF_KEY Internal key-management function, PF_INET6 Internet version 6 protocols, PF_NATM Native ATM access, PF_ATM ATM, PF_NETGRAPH Netgraph sockets
SOCK_STREAM Stream socket, SOCK_DGRAM Datagram socket, SOCK_RAW Raw-protocol interface, SOCK_RDM Reliably-delivered packet, SOCK_SEQPACKET Sequenced packet stream
SOCK_STREAM
type provides sequenced,
reliable, two-way connection based byte streams. An out-of-band data
transmission mechanism may be supported. A
SOCK_DGRAM
socket supports datagrams
(connectionless, unreliable messages of a fixed (typically small) maximum
length). A SOCK_SEQPACKET
socket may
provide a sequenced, reliable, two-way connection-based data transmission path
for datagrams of fixed maximum length; a consumer may be required to read an
entire packet with each read system call. This facility is protocol specific,
and presently unimplemented. SOCK_RAW
sockets provide access to internal network protocols and interfaces. The types
SOCK_RAW
, which is available only to the
super-user, and SOCK_RDM
, which is planned,
but not yet implemented, are not described here.
Additionally, the following flags are allowed in the
type argument:
SOCK_CLOEXEC Set close-on-exec on the new descriptor, SOCK_NONBLOCK Set non-blocking mode on the new socket
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 connection to another socket is created with a
connect(2) system call. Once connected, data may
be transferred using read(2) and
write(2) calls or some variant of the
send(2) and recv(2)
functions. (Some protocol families, such as the Internet family, support the
notion of an “implied connect”, which permits data to be sent
piggybacked onto a connect operation by using the
sendto(2) system call.) 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
ensure 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 an extended period (e.g. 5 minutes). By default, a
SIGPIPE
signal is raised if a process sends
on a broken stream, but this behavior may be inhibited via
setsockopt(2).
SOCK_SEQPACKET
sockets employ the same system
calls as SOCK_STREAM
sockets. The only
difference is that read(2) calls will return only
the amount of data requested, and any remaining in the arriving packet will be
discarded.
SOCK_DGRAM
and
SOCK_RAW
sockets allow sending of datagrams
to correspondents named in send(2) calls.
Datagrams are generally received with
recvfrom(2), which returns the next datagram with
its return address.
An fcntl(2) system call can be used to specify a
process group to receive a SIGURG
signal
when the out-of-band data arrives. It may also enable non-blocking I/O and
asynchronous notification of I/O events via
SIGIO
.
The operation of sockets is controlled by socket level
options. These options are defined in the file
<sys/socket.h>
.
The setsockopt(2) and
getsockopt(2) system calls are used to set and
get options, respectively.
RETURN VALUES¶
A -1 is returned if an error occurs, otherwise the return value is a descriptor referencing the socket.ERRORS¶
Thesocket
() system call fails if:
- [
EACCES
] - Permission to create a socket of the specified type and/or protocol is denied.
- [
EAFNOSUPPORT
] - The address family (domain) is not supported or the specified domain is not supported by this protocol family.
- [
EMFILE
] - The per-process descriptor table is full.
- [
ENFILE
] - The system file table is full.
- [
ENOBUFS
] - Insufficient buffer space is available. The socket cannot be created until sufficient resources are freed.
- [
EPERM
] - User has insufficient privileges to carry out the requested operation.
- [
EPROTONOSUPPORT
] - The protocol type or the specified protocol is not supported within this domain.
- [
EPROTOTYPE
] - The socket type is not supported by the protocol.
SEE ALSO¶
accept(2), bind(2), connect(2), getpeername(2), getsockname(2), getsockopt(2), ioctl(2), listen(2), read(2), recv(2), select(2), send(2), shutdown(2), socketpair(2), write(2), getprotoent(3), netgraph(4), protocols(5) An Introductory 4.3 BSD Interprocess Communication Tutorial, PS1, 7. BSD Interprocess Communication Tutorial, PS1, 8.HISTORY¶
Thesocket
() system call appeared in
4.2BSD.March 19, 2013 | Debian |