socket(3SOCKET) Sockets Library Functions socket(3SOCKET)
socket - create an endpoint for communication
cc [ flag ... ] file ... -lsocket -lnsl [ library ... ]
int socket(int domain, int type, int protocol);
The socket() function creates an endpoint for communication and returns a descriptor.
The domain argument specifies the protocol family within which communication 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)
PF_NCA Network Cache and Accelerator (NCA) protocols
The socket has the indicated type, which specifies the communication semantics. Currently defined types are:
There must be an entry in the netconfig(4) file for at least each protocol family and type required. If a non-zero protocol has been spec-
ified 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, 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
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
The protocol parameter is a protocol-family-specific value which specifies 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, mul-
tiple 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(3SOCKET) call. Once connected, data may be trans-
ferred using read(2) and write(2) calls or some variant of the send(3SOCKET) and recv(3SOCKET) 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(3SOCKET) manual page and received as described
on the recv(3SOCKET) manual page.
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 (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 correspondents named in sendto(3SOCKET) calls. Datagrams are generally
received with recvfrom(3SOCKET), which returns the next datagram with its return address.
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
The operation of sockets is controlled by socket level options. These options are defined in the file <sys/socket.h>. setsockopt(3SOCKET)
and getsockopt(3SOCKET) are used to set and get options, respectively.
Upon successful completion, a descriptor referencing the socket is returned. Otherwise, -1 is returned and errno is set to indicate the
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 complete 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.
See attributes(5) for descriptions of the following attributes:
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|MT-Level |Safe |
nca(1), close(2), fcntl(2), ioctl(2), read(2), write(2), accept(3SOCKET), bind(3SOCKET), connect(3SOCKET), getsockname(3SOCKET), getsock-
opt(3SOCKET), in.h(3HEAD),listen(3SOCKET), recv(3SOCKET), setsockopt(3SOCKET), send(3SOCKET), shutdown(3SOCKET), socket.h(3HEAD), socket-
Historically, AF_* was commonly used in places where PF_* was meant. New code should be careful to use PF_* as necessary.
SunOS 5.11 28 Jan 2009 socket(3SOCKET)