352 lines
9.2 KiB
Groff
352 lines
9.2 KiB
Groff
.\" Copyright (c) 1983, 1991, 1993
|
|
.\" The Regents of the University of California. All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 3. Neither the name of the University nor the names of its contributors
|
|
.\" may be used to endorse or promote products derived from this software
|
|
.\" without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.\" From: @(#)socket.2 8.1 (Berkeley) 6/4/93
|
|
.\"
|
|
.Dd January 15, 2023
|
|
.Dt SOCKET 2
|
|
.Os
|
|
.Sh NAME
|
|
.Nm socket
|
|
.Nd create an endpoint for communication
|
|
.Sh LIBRARY
|
|
.Lb libc
|
|
.Sh SYNOPSIS
|
|
.In sys/socket.h
|
|
.Ft int
|
|
.Fn socket "int domain" "int type" "int protocol"
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Fn socket
|
|
system call
|
|
creates an endpoint for communication and returns a descriptor.
|
|
.Pp
|
|
The
|
|
.Fa 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
|
|
.In sys/socket.h .
|
|
The currently understood formats are:
|
|
.Pp
|
|
.Bd -literal -offset indent -compact
|
|
PF_LOCAL Host-internal protocols (alias for PF_UNIX),
|
|
PF_UNIX Host-internal protocols,
|
|
PF_INET Internet version 4 protocols,
|
|
PF_INET6 Internet version 6 protocols,
|
|
PF_DIVERT Firewall packet diversion/re-injection,
|
|
PF_ROUTE Internal routing protocol,
|
|
PF_KEY Internal key-management function,
|
|
PF_NETGRAPH Netgraph sockets,
|
|
PF_NETLINK Netlink protocols,
|
|
PF_BLUETOOTH Bluetooth protocols,
|
|
PF_INET_SDP OFED socket direct protocol (IPv4),
|
|
AF_HYPERV HyperV sockets
|
|
.Ed
|
|
.Pp
|
|
Each protocol family is connected to an address family, which has the
|
|
same name except that the prefix is
|
|
.Dq Dv AF_
|
|
in place of
|
|
.Dq Dv PF_ .
|
|
Other protocol families may be also defined, beginning with
|
|
.Dq Dv PF_ ,
|
|
with corresponding address families.
|
|
.Pp
|
|
The socket has the indicated
|
|
.Fa type ,
|
|
which specifies the semantics of communication.
|
|
Currently
|
|
defined types are:
|
|
.Pp
|
|
.Bd -literal -offset indent -compact
|
|
SOCK_STREAM Stream socket,
|
|
SOCK_DGRAM Datagram socket,
|
|
SOCK_RAW Raw-protocol interface,
|
|
SOCK_SEQPACKET Sequenced packet stream
|
|
.Ed
|
|
.Pp
|
|
A
|
|
.Dv SOCK_STREAM
|
|
type provides sequenced, reliable,
|
|
two-way connection based byte streams.
|
|
An out-of-band data transmission mechanism may be supported.
|
|
A
|
|
.Dv SOCK_DGRAM
|
|
socket supports
|
|
datagrams (connectionless, unreliable messages of
|
|
a fixed (typically small) maximum length).
|
|
A
|
|
.Dv 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 may have protocol-specific properties.
|
|
.Dv SOCK_RAW
|
|
sockets provide access to internal network protocols and interfaces.
|
|
The
|
|
.Dv SOCK_RAW
|
|
type is available only to the super-user and is described in
|
|
.Xr ip 4
|
|
and
|
|
.Xr ip6 4 .
|
|
.Pp
|
|
Additionally, the following flags are allowed in the
|
|
.Fa type
|
|
argument:
|
|
.Pp
|
|
.Bd -literal -offset indent -compact
|
|
SOCK_CLOEXEC Set close-on-exec on the new descriptor,
|
|
SOCK_NONBLOCK Set non-blocking mode on the new socket
|
|
.Ed
|
|
.Pp
|
|
The
|
|
.Fa protocol
|
|
argument
|
|
specifies a particular protocol to be used with the socket.
|
|
Normally only a single protocol exists to support a particular
|
|
socket type within a given protocol family.
|
|
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
|
|
.Dq "communication domain"
|
|
in which communication
|
|
is to take place; see
|
|
.Xr protocols 5 .
|
|
.Pp
|
|
The
|
|
.Fa protocol
|
|
argument may be set to zero (0) to request the default
|
|
implementation of a socket type for the protocol, if any.
|
|
.Pp
|
|
Sockets of type
|
|
.Dv SOCK_STREAM
|
|
are full-duplex byte streams, similar
|
|
to pipes.
|
|
A stream socket must be in a
|
|
.Em connected
|
|
state before any data may be sent or received
|
|
on it.
|
|
A connection to another socket is created with a
|
|
.Xr connect 2
|
|
system call.
|
|
Once connected, data may be transferred using
|
|
.Xr read 2
|
|
and
|
|
.Xr write 2
|
|
calls or some variant of the
|
|
.Xr send 2
|
|
and
|
|
.Xr recv 2
|
|
functions.
|
|
(Some protocol families, such as the Internet family,
|
|
support the notion of an
|
|
.Dq implied connect ,
|
|
which permits data to be sent piggybacked onto a connect operation by
|
|
using the
|
|
.Xr sendto 2
|
|
system call.)
|
|
When a session has been completed a
|
|
.Xr close 2
|
|
may be performed.
|
|
Out-of-band data may also be transmitted as described in
|
|
.Xr send 2
|
|
and received as described in
|
|
.Xr recv 2 .
|
|
.Pp
|
|
The communications protocols used to implement a
|
|
.Dv 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
|
|
.Er ETIMEDOUT
|
|
as the specific code
|
|
in the global variable
|
|
.Va errno .
|
|
The protocols optionally keep sockets
|
|
.Dq 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
|
|
.Dv SIGPIPE
|
|
signal is raised if a process sends
|
|
on a broken stream, but this behavior may be inhibited via
|
|
.Xr setsockopt 2 .
|
|
.Pp
|
|
.Dv SOCK_SEQPACKET
|
|
sockets employ the same system calls
|
|
as
|
|
.Dv SOCK_STREAM
|
|
sockets.
|
|
The only difference
|
|
is that
|
|
.Xr read 2
|
|
calls will return only the amount of data requested,
|
|
and any remaining in the arriving packet will be discarded.
|
|
.Pp
|
|
.Dv SOCK_DGRAM
|
|
and
|
|
.Dv SOCK_RAW
|
|
sockets allow sending of datagrams to correspondents
|
|
named in
|
|
.Xr send 2
|
|
calls.
|
|
Datagrams are generally received with
|
|
.Xr recvfrom 2 ,
|
|
which returns the next datagram with its return address.
|
|
.Pp
|
|
An
|
|
.Xr fcntl 2
|
|
system call can be used to specify a process group to receive
|
|
a
|
|
.Dv 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
|
|
.Dv SIGIO .
|
|
.Pp
|
|
The operation of sockets is controlled by socket level
|
|
.Em options .
|
|
These options are defined in the file
|
|
.In sys/socket.h .
|
|
The
|
|
.Xr setsockopt 2
|
|
and
|
|
.Xr getsockopt 2
|
|
system calls are used to set and get options, respectively.
|
|
.Sh RETURN VALUES
|
|
A -1 is returned if an error occurs, otherwise the return
|
|
value is a descriptor referencing the socket.
|
|
.Sh ERRORS
|
|
The
|
|
.Fn socket
|
|
system call fails if:
|
|
.Bl -tag -width Er
|
|
.It Bq Er EACCES
|
|
Permission to create a socket of the specified type and/or protocol
|
|
is denied.
|
|
.It Bq Er EAFNOSUPPORT
|
|
The address family (domain) is not supported or the
|
|
specified domain is not supported by this protocol family.
|
|
.It Bq Er EMFILE
|
|
The per-process descriptor table is full.
|
|
.It Bq Er ENFILE
|
|
The system file table is full.
|
|
.It Bq Er ENOBUFS
|
|
Insufficient buffer space is available.
|
|
The socket cannot be created until sufficient resources are freed.
|
|
.It Bq Er EPERM
|
|
User has insufficient privileges to carry out the requested operation.
|
|
.It Bq Er EPROTONOSUPPORT
|
|
The protocol type or the specified protocol is not supported
|
|
within this domain.
|
|
.It Bq Er EPROTOTYPE
|
|
The socket type is not supported by the protocol.
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr accept 2 ,
|
|
.Xr bind 2 ,
|
|
.Xr connect 2 ,
|
|
.Xr divert 4 ,
|
|
.Xr getpeername 2 ,
|
|
.Xr getsockname 2 ,
|
|
.Xr getsockopt 2 ,
|
|
.Xr ioctl 2 ,
|
|
.Xr ip 4 ,
|
|
.Xr ip6 4 ,
|
|
.Xr listen 2 ,
|
|
.Xr read 2 ,
|
|
.Xr recv 2 ,
|
|
.Xr select 2 ,
|
|
.Xr send 2 ,
|
|
.Xr shutdown 2 ,
|
|
.Xr socketpair 2 ,
|
|
.Xr write 2 ,
|
|
.Xr CMSG_DATA 3 ,
|
|
.Xr getprotoent 3 ,
|
|
.Xr netgraph 4 ,
|
|
.Xr protocols 5
|
|
.Rs
|
|
.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial"
|
|
.%B PS1
|
|
.%N 7
|
|
.Re
|
|
.Rs
|
|
.%T "BSD Interprocess Communication Tutorial"
|
|
.%B PS1
|
|
.%N 8
|
|
.Re
|
|
.Sh STANDARDS
|
|
The
|
|
.Fn socket
|
|
function conforms to
|
|
.St -p1003.1-2008 .
|
|
The
|
|
.Tn POSIX
|
|
standard specifies only the
|
|
.Dv AF_INET ,
|
|
.Dv AF_INET6 ,
|
|
and
|
|
.Dv AF_UNIX
|
|
constants for address families, and requires the use of
|
|
.Dv AF_*
|
|
constants for the
|
|
.Fa domain
|
|
argument of
|
|
.Fn socket .
|
|
The
|
|
.Dv SOCK_CLOEXEC
|
|
flag is expected to conform to the next revision of the
|
|
.Tn POSIX
|
|
standard.
|
|
The
|
|
.Dv SOCK_RDM
|
|
.Fa type ,
|
|
the
|
|
.Dv PF_*
|
|
constants, and other address families are
|
|
.Fx
|
|
extensions.
|
|
.Sh HISTORY
|
|
The
|
|
.Fn socket
|
|
system call appeared in
|
|
.Bx 4.2 .
|