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socket(3c)
socket(3C) Standard C Library Functions socket(3C)
NAME
socket - create an endpoint for communication
SYNOPSIS
#include <sys/socket.h>
int socket(int domain, int type, int protocol);
DESCRIPTION
The socket() function creates an endpoint for communication and returns
a descriptor.
The domain argument specifies the protocol family within which communi‐
cation takes place. The protocol family is generally the same as the
address family for the addresses supplied in later operations on the
socket. These families are defined in <sys/socket.h>.
The currently supported protocol families are:
PF_UNIX UNIX system internal protocols
PF_INET Internet Protocol Version 4 (IPv4)
PF_INET6 Internet Protocol Version 6 (IPv6)
The socket has the indicated type, which specifies the communication
semantics. Currently defined types are:
SOCK_STREAM
SOCK_DGRAM
SOCK_SEQPACKET
SOCK_RAW
SOCK_RDM
There must be an entry in the netconfig(5) file for at least each pro‐
tocol family and type required. If a non-zero protocol has been speci‐
fied but no exact match for the protocol family, type, and protocol is
found, then the first entry containing the specified family and type
with a protocol value of zero will be used.
A 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, un‐
reliable messages of a fixed (typically small) maximum length). A
SOCK_SEQPACKET socket may provide a sequenced, reliable, two-way con‐
nection-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 not
implemented for any protocol family. SOCK_RAW sockets provide access to
internal network interfaces. The types SOCK_RAW, which is available
only to a user with the net_rawaccess privilege, and SOCK_RDM, for
which no implementation currently exists, are not described here.
The protocol parameter is a protocol-family-specific value which speci‐
fies a particular protocol to be used with the socket. Normally this
value is zero, as commonly only a single protocol exists to support a
particular socket type within a given protocol family. However, multi‐
ple protocols may exist, in which case a particular protocol may be
specified in this manner.
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 connection to another socket is created
with a connect(3C) call. Once connected, data may be transferred using
read(2) and write(2) calls or some variant of the send(3C) and recv(3C)
calls. When a session has been completed, a close(2) may be performed.
Out-of-band data may also be transmitted as described on the send(3C)
manual page and received as described on the recv(3C) manual page.
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 proto‐
cols optionally keep sockets "warm" by forcing transmissions roughly
every minute in the absence of other activity. An error is then indi‐
cated if no response can be elicited on an otherwise idle connection
for a extended period (for instance 5 minutes). A SIGPIPE signal is
raised if a thread sends on a broken stream; this causes naive
processes, which do not handle the signal, to exit.
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 datagrams to be sent to corre‐
spondents named in sendto(3C) calls. Datagrams are generally received
with recvfrom(3C), which returns the next datagram with its return ad‐
dress.
An fcntl(2) call can be used to specify a process group to receive a
SIGURG signal when the out-of-band data arrives. It can also enable
non-blocking I/O.
The operation of sockets is controlled by socket level options. These
options are defined in the file <sys/socket.h>. setsockopt(3C) and get‐
sockopt(3C) are used to set and get options, respectively.
Some file descriptor flags can be specified at socket creation time to
avoid race conditions. These options are passed by using a bitwise-in‐
clusive-OR of values from the following list with the value passed for
the type parameter to the socket(). See the open(2) man page for de‐
tails on what each flag does.
SOCK_CLOEXEC If set, the O_CLOEXEC flag is set for the new file
descriptor.
SOCK_CLOFORK If set, the O_CLOFORK flag is set for the new file
descriptor.
SOCK_NONBLOCK If set, the O_NONBLOCK flag is set for the new file
descriptor.
SOCK_NDELAY If set, the O_NDELAY flag is set for the new file de‐
scriptor.
SOCK_NOSIGPIPE If set, the O_NOSIGPIPE flag is set for the new file
descriptor.
RETURN VALUES
Upon successful completion, a descriptor referencing the socket is re‐
turned. Otherwise, -1 is returned and errno is set to indicate the er‐
ror.
ERRORS
The socket() function will fail if:
EACCES Permission to create a socket of the specified type
or protocol is denied.
EAGAIN There were insufficient resources available to com‐
plete the operation.
EAFNOSUPPORT The specified address family is not supported by the
protocol family.
EMFILE The per-process descriptor table is full.
ENOMEM Insufficient user memory is available.
ENOSR There were insufficient STREAMS resources available
to complete the operation.
EPFNOSUPPORT The specified protocol family is not supported.
EPROTONOSUPPORT The protocol type is not supported by the address
family.
EPROTOTYPE The socket type is not supported by the protocol.
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Interface StabilityCommitted _ MT-LevelAsync-Signal-
Safe _ StandardSee standards(7).
SEE ALSO
close(2), fcntl(2), ioctl(2), read(2), write(2), accept(3C), bind(3C),
connect(3C), getsockname(3C), getsockopt(3C), listen(3C), recv(3C),
recvmmsg(3C), send(3C), sendfile(3C), sendfilev(3C), sendmmsg(3C), set‐
sockopt(3C), shutdown(3C), sockatmark(3C), socketpair(3C), in.h(3HEAD),
socket.h(3HEAD), attributes(7)
NOTES
Historically, AF_* was commonly used in places where PF_* was meant.
New code should be careful to use PF_* as necessary.
HISTORY
The socket() function has been present since the initial release of So‐
laris.
Support for PF_UNIX and PF_INET protocol families has been present
since the initial release of Solaris. Support for PF_INET6 was added in
Solaris 8.
Support for PF_NCA sockets was added in Solaris 8 7/01 (Update 5), and
removed in Oracle Solaris 11.4.
Support for SOCK_* flags as part of the type parameter was added to Or‐
acle Solaris in the 11.4 release.
Oracle Solaris 11.4 2 Feb 2021 socket(3C)