mirror of https://github.com/mkerrisk/man-pages
232 lines
7.3 KiB
Plaintext
232 lines
7.3 KiB
Plaintext
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.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
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.TH "SENDMSG" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
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.\" sendmsg
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.SH NAME
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sendmsg \- send a message on a socket using a message structure
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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 sendmsg(int\fP \fIsocket\fP\fB, const struct msghdr *\fP\fImessage\fP\fB,
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int\fP \fIflags\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 \fIsendmsg\fP() function shall send a message through a connection-mode
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or connectionless-mode socket. If the socket is
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connectionless-mode, the message shall be sent to the address specified
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by \fBmsghdr\fP. If the socket is connection-mode, the
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destination address in \fBmsghdr\fP shall be ignored.
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.LP
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The \fIsendmsg\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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\fImessage\fP
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Points to a \fBmsghdr\fP structure, containing both the destination
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address and the buffers for the outgoing message. The
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length and format of the address depend on the address family of the
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socket. The \fImsg_flags\fP member is ignored.
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.TP 7
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\fIflags\fP
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Specifies the type of message transmission. The application may specify
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0 or the following flag:
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.TP 7
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MSG_EOR
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.RS
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Terminates a record (if supported by the protocol).
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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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Sends out-of-band data on sockets that support out-of-bound data.
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The significance and semantics of out-of-band data are
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protocol-specific.
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.RE
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.sp
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.sp
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.LP
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The \fImsg_iov\fP and \fImsg_iovlen\fP fields of \fImessage\fP specify
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zero or more buffers containing the data to be sent.
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\fImsg_iov\fP points to an array of \fBiovec\fP structures; \fImsg_iovlen\fP
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shall be set to the dimension of this array. In
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each \fBiovec\fP structure, the \fIiov_base\fP field specifies a storage
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area and the \fIiov_len\fP field gives its size in
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bytes. Some of these sizes can be zero. The data from each storage
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area indicated by \fImsg_iov\fP is sent in turn.
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.LP
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Successful completion of a call to \fIsendmsg\fP() does not guarantee
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delivery of the message. A return value of -1 indicates
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only locally-detected errors.
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.LP
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If space is not available at the sending socket to hold the message
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to be transmitted and the socket file descriptor does not
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have O_NONBLOCK set, the \fIsendmsg\fP() function shall block until
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space is available. If space is not available at the sending
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socket to hold the message to be transmitted and the socket file descriptor
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does have O_NONBLOCK set, the \fIsendmsg\fP() function
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shall fail.
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.LP
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If the socket protocol supports broadcast and the specified address
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is a broadcast address for the socket protocol,
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\fIsendmsg\fP() shall fail if the SO_BROADCAST option is not set for
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the socket.
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.LP
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The socket in use may require the process to have appropriate privileges
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to use the \fIsendmsg\fP() function.
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.SH RETURN VALUE
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.LP
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Upon successful completion, \fIsendmsg\fP() shall return the number
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of bytes sent. Otherwise, -1 shall be returned and
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\fIerrno\fP set to indicate the error.
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.SH ERRORS
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.LP
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The \fIsendmsg\fP() function shall fail if:
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.TP 7
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.B EAGAIN \fRor\fP EWOULDBLOCK
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The socket's file descriptor is marked O_NONBLOCK and the requested
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operation would block.
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.TP 7
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.B EAFNOSUPPORT
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Addresses in the specified address family cannot be used with this
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socket.
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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 \fIsendmsg\fP() before any data was transmitted.
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.TP 7
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.B EINVAL
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The sum of the \fIiov_len\fP values overflows an \fBssize_t\fP.
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.TP 7
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.B EMSGSIZE
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The message is too large to be sent all at once (as the socket requires),
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or the \fImsg_iovlen\fP member of the \fBmsghdr\fP
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structure pointed to by \fImessage\fP is less than or equal to 0 or
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is greater than {IOV_MAX}.
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.TP 7
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.B ENOTCONN
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The socket is connection-mode but 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 \fIsocket\fP argument is associated with a socket that does not
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support one or more of the values set in
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\fIflags\fP.
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.TP 7
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.B EPIPE
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The socket is shut down for writing, or the socket is connection-mode
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and is no longer connected. In the latter case, and if
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the socket is of type SOCK_STREAM, the SIGPIPE signal is generated
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to the calling thread.
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.sp
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.LP
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If the address family of the socket is AF_UNIX, then \fIsendmsg\fP()
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shall 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 ELOOP
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A loop exists in symbolic links encountered during resolution of the
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pathname in the socket address.
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.TP 7
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.B ENAMETOOLONG
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A component of a pathname exceeded {NAME_MAX} characters, or an entire
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pathname exceeded {PATH_MAX} characters.
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.TP 7
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.B ENOENT
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A component of the pathname does not name an existing file or the
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path name is an empty string.
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.TP 7
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.B ENOTDIR
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A component of the path prefix of the pathname in the socket address
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is not a directory.
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.sp
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.LP
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The \fIsendmsg\fP() function may fail if:
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.TP 7
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.B EACCES
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Search permission is denied for a component of the path prefix; or
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write access to the named socket is denied.
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.TP 7
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.B EDESTADDRREQ
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The socket is not connection-mode and does not have its peer address
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set, and no destination address was specified.
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.TP 7
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.B EHOSTUNREACH
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The destination host cannot be reached (probably because the host
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is down or a remote router cannot reach it).
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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 EISCONN
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A destination address was specified and the socket is already connected.
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.TP 7
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.B ENETDOWN
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The local network interface used to reach the destination is down.
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.TP 7
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.B ENETUNREACH
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No route to the network is present.
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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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If the address family of the socket is AF_UNIX, then \fIsendmsg\fP()
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may fail if:
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.TP 7
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.B ELOOP
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More than {SYMLOOP_MAX} symbolic links were encountered during resolution
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of the pathname in the socket address.
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.TP 7
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.B ENAMETOOLONG
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Pathname resolution of a symbolic link produced an intermediate result
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whose length exceeds {PATH_MAX}.
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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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Done.
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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 it is possible to send more data.
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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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\fIgetsockopt\fP() , \fIpoll\fP() , \fIrecv\fP() , \fIrecvfrom\fP()
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, \fIrecvmsg\fP() , \fIselect\fP() , \fIsend\fP() , \fIsendto\fP()
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, \fIsetsockopt\fP() , \fIshutdown\fP() , \fIsocket\fP() , the Base
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Definitions volume of 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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