mirror of https://github.com/mkerrisk/man-pages
205 lines
6.9 KiB
Plaintext
205 lines
6.9 KiB
Plaintext
.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
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.TH "RECVFROM" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
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.\" recvfrom
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.SH PROLOG
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This manual page is part of the POSIX Programmer's Manual.
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The Linux implementation of this interface may differ (consult
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the corresponding Linux manual page for details of Linux behavior),
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or the interface may not be implemented on Linux.
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.SH NAME
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recvfrom \- receive a message from a socket
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.SH SYNOPSIS
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.LP
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\fB#include <sys/socket.h>
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.br
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.sp
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ssize_t recvfrom(int\fP \fIsocket\fP\fB, void *restrict\fP \fIbuffer\fP\fB,
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size_t\fP \fIlength\fP\fB,
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.br
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\ \ \ \ \ \ int\fP \fIflags\fP\fB, struct sockaddr *restrict\fP \fIaddress\fP\fB,
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.br
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\ \ \ \ \ \ socklen_t *restrict\fP \fIaddress_len\fP\fB);
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.br
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\fP
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.SH DESCRIPTION
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.LP
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The \fIrecvfrom\fP() function shall receive a message from a connection-mode
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or connectionless-mode socket. It is normally used
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with connectionless-mode sockets because it permits the application
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to retrieve the source address of received data.
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.LP
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The \fIrecvfrom\fP() function takes the following arguments:
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.TP 7
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\fIsocket\fP
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Specifies the socket file descriptor.
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.TP 7
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\fIbuffer\fP
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Points to the buffer where the message should be stored.
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.TP 7
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\fIlength\fP
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Specifies the length in bytes of the buffer pointed to by the \fIbuffer\fP
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argument.
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.TP 7
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\fIflags\fP
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Specifies the type of message reception. Values of this argument are
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formed by logically OR'ing zero or more of the following
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values:
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.TP 7
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MSG_PEEK
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.RS
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Peeks at an incoming message. The data is treated as unread and the
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next \fIrecvfrom\fP() or similar function shall still
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return this data.
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.RE
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.TP 7
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MSG_OOB
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.RS
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Requests out-of-band data. The significance and semantics of out-of-band
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data are protocol-specific.
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.RE
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.TP 7
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MSG_WAITALL
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.RS
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On SOCK_STREAM sockets this requests that the function block until
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the full amount of data can be returned. The function may
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return the smaller amount of data if the socket is a message-based
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socket, if a signal is caught, if the connection is terminated,
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if MSG_PEEK was specified, or if an error is pending for the socket.
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.RE
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.sp
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.TP 7
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\fIaddress\fP
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A null pointer, or points to a \fBsockaddr\fP structure in which the
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sending address is to be stored. The length and format of
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the address depend on the address family of the socket.
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.TP 7
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\fIaddress_len\fP
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Specifies the length of the \fBsockaddr\fP structure pointed to by
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the \fIaddress\fP argument.
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.sp
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.LP
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The \fIrecvfrom\fP() function shall return the length of the message
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written to the buffer pointed to by the \fIbuffer\fP
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argument. For message-based sockets, such as SOCK_RAW, SOCK_DGRAM,
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and SOCK_SEQPACKET, the entire message shall be read in a single operation.
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If a message is too long to fit
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in the supplied buffer, and MSG_PEEK is not set in the \fIflags\fP
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argument, the excess bytes shall be discarded. For stream-based
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sockets, such as SOCK_STREAM, message boundaries shall be ignored.
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In this case, data shall be returned to the user as soon as it
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becomes available, and no data shall be discarded.
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.LP
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If the MSG_WAITALL flag is not set, data shall be returned only up
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to the end of the first message.
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.LP
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Not all protocols provide the source address for messages. If the
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\fIaddress\fP argument is not a null pointer and the protocol
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provides the source address of messages, the source address of the
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received message shall be stored in the \fBsockaddr\fP
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structure pointed to by the \fIaddress\fP argument, and the length
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of this address shall be stored in the object pointed to by the
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\fIaddress_len\fP argument.
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.LP
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If the actual length of the address is greater than the length of
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the supplied \fBsockaddr\fP structure, the stored address
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shall be truncated.
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.LP
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If the \fIaddress\fP argument is not a null pointer and the protocol
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does not provide the source address of messages, the value
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stored in the object pointed to by \fIaddress\fP is unspecified.
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.LP
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If no messages are available at the socket and O_NONBLOCK is not set
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on the socket's file descriptor, \fIrecvfrom\fP() shall
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block until a message arrives. If no messages are available at the
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socket and O_NONBLOCK is set on the socket's file descriptor,
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\fIrecvfrom\fP() shall fail and set \fIerrno\fP to [EAGAIN] or [EWOULDBLOCK].
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.SH RETURN VALUE
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.LP
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Upon successful completion, \fIrecvfrom\fP() shall return the length
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of the message in bytes. If no messages are available to
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be received and the peer has performed an orderly shutdown, \fIrecvfrom\fP()
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shall return 0. Otherwise, the function shall return
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-1 and set \fIerrno\fP to indicate the error.
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.SH ERRORS
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.LP
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The \fIrecvfrom\fP() function shall fail if:
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.TP 7
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.B EAGAIN \fRor\fP EWOULDBLOCK
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.sp
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The socket's file descriptor is marked O_NONBLOCK and no data is waiting
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to be received; or MSG_OOB is set and no out-of-band data
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is available and either the socket's file descriptor is marked O_NONBLOCK
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or the socket does not support blocking to await
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out-of-band data.
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.TP 7
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.B EBADF
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The \fIsocket\fP argument is not a valid file descriptor.
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.TP 7
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.B ECONNRESET
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A connection was forcibly closed by a peer.
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.TP 7
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.B EINTR
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A signal interrupted \fIrecvfrom\fP() before any data was available.
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.TP 7
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.B EINVAL
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The MSG_OOB flag is set and no out-of-band data is available.
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.TP 7
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.B ENOTCONN
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A receive is attempted on a connection-mode socket that is not connected.
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.TP 7
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.B ENOTSOCK
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The \fIsocket\fP argument does not refer to a socket.
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.TP 7
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.B EOPNOTSUPP
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The specified flags are not supported for this socket type.
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.TP 7
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.B ETIMEDOUT
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The connection timed out during connection establishment, or due to
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a transmission timeout on active connection.
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.sp
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.LP
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The \fIrecvfrom\fP() function may fail if:
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.TP 7
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.B EIO
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An I/O error occurred while reading from or writing to the file system.
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.TP 7
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.B ENOBUFS
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Insufficient resources were available in the system to perform the
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operation.
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.TP 7
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.B ENOMEM
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Insufficient memory was available to fulfill the request.
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.sp
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.LP
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\fIThe following sections are informative.\fP
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.SH EXAMPLES
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.LP
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None.
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.SH APPLICATION USAGE
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.LP
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The \fIselect\fP() and \fIpoll\fP() functions can
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be used to determine when data is available to be received.
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.SH RATIONALE
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.LP
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None.
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.SH FUTURE DIRECTIONS
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.LP
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None.
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.SH SEE ALSO
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.LP
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\fIpoll\fP(), \fIread\fP(), \fIrecv\fP(), \fIrecvmsg\fP(), \fIselect\fP(),
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\fIsend\fP(), \fIsendmsg\fP(), \fIsendto\fP(), \fIshutdown\fP()
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,
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\fIsocket\fP(), \fIwrite\fP(), the Base Definitions volume of
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IEEE\ Std\ 1003.1-2001, \fI<sys/socket.h>\fP
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.SH COPYRIGHT
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Portions of this text are reprinted and reproduced in electronic form
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from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
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-- Portable Operating System Interface (POSIX), The Open Group Base
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Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
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Electrical and Electronics Engineers, Inc and The Open Group. In the
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event of any discrepancy between this version and the original IEEE and
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The Open Group Standard, the original IEEE and The Open Group Standard
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is the referee document. The original Standard can be obtained online at
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http://www.opengroup.org/unix/online.html .
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