1.\" Copyright (c) 1983, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" From: @(#)send.2 8.2 (Berkeley) 2/21/94 29.\" $FreeBSD: src/lib/libc/sys/send.2,v 1.10.2.6 2001/12/14 18:34:01 ru Exp $ 30.\" 31.Dd October 6, 2010 32.Dt SEND 2 33.Os 34.Sh NAME 35.Nm send , 36.Nm sendto , 37.Nm sendmsg 38.Nd send a message from a socket 39.Sh LIBRARY 40.Lb libc 41.Sh SYNOPSIS 42.In sys/types.h 43.In sys/socket.h 44.Ft ssize_t 45.Fn send "int s" "const void *msgbuf" "size_t len" "int flags" 46.Ft ssize_t 47.Fn sendto "int s" "const void *msgbuf" "size_t len" "int flags" "const struct sockaddr *to" "socklen_t tolen" 48.Ft ssize_t 49.Fn sendmsg "int s" "const struct msghdr *msg" "int flags" 50.Sh DESCRIPTION 51.Fn Send , 52.Fn sendto , 53and 54.Fn sendmsg 55are used to transmit a message to another socket. 56.Fn Send 57may be used only when the socket is in a 58.Em connected 59state, while 60.Fn sendto 61and 62.Fn sendmsg 63may be used at any time. 64.Pp 65The socket file descriptor is given by 66.Fa s . 67.Fa msgbuf 68points to a buffer containing the message. 69.Fa msg 70points to a 71.Fa msghdr 72structure. 73The address of the target is given by 74.Fa to 75with 76.Fa tolen 77specifying its size. 78The length of the message is given by 79.Fa len . 80If the message is too long to pass atomically through the 81underlying protocol, the error 82.Er EMSGSIZE 83is returned, and 84the message is not transmitted. 85.Pp 86No indication of failure to deliver is implicit in a 87.Fn send . 88Locally detected errors are indicated by a return value of -1. 89.Pp 90If no messages space is available at the socket to hold 91the message to be transmitted, then 92.Fn send 93normally blocks, unless the socket has been placed in 94non-blocking I/O mode. 95The 96.Xr select 2 97call may be used to determine when it is possible to 98send more data. 99.Pp 100The 101.Fa flags 102parameter may include one or more of the following: 103.Bd -literal 104#define MSG_OOB 0x1 /* process out-of-band data */ 105#define MSG_PEEK 0x2 /* peek at incoming message */ 106#define MSG_DONTROUTE 0x4 /* bypass routing, use direct interface */ 107#define MSG_EOR 0x8 /* data completes record */ 108#define MSG_EOF 0x100 /* data completes transaction */ 109#define MSG_NOSIGNAL 0x400 /* No SIGPIPE to unconnected socket stream */ 110.Ed 111.Pp 112The flag 113.Dv MSG_OOB 114is used to send 115.Dq out-of-band 116data on sockets that support this notion (e.g.\& 117.Dv SOCK_STREAM ) ; 118the underlying protocol must also support 119.Dq out-of-band 120data. 121.Dv MSG_EOR 122is used to indicate a record mark for protocols which support the 123concept. 124.Dv MSG_EOF 125requests that the sender side of a socket be shut down, and that an 126appropriate indication be sent at the end of the specified data; 127this flag is only implemented for 128.Dv SOCK_STREAM 129sockets in the 130.Dv PF_INET 131protocol family. 132.Dv MSG_DONTROUTE 133is usually used only by diagnostic or routing programs. 134.Dv MSG_NOSIGNAL 135requests not to send the 136.Dv SIGPIPE 137signal if an attempt to 138.Nm 139is made on a stream-oriented socket that is no longer connected. 140.Pp 141See 142.Xr recv 2 143for a description of the 144.Fa msghdr 145structure. 146.Sh RETURN VALUES 147Upon successful completion the number of characters which were sent is 148returned. Otherwise -1 is returned and the global variable 149.Va errno 150is set to indicate the error. 151.Sh ERRORS 152.Fn Send , 153.Fn sendto , 154and 155.Fn sendmsg 156fail if: 157.Bl -tag -width Er 158.It Bq Er EBADF 159An invalid descriptor was specified. 160.It Bq Er EACCES 161The destination address is a broadcast address, and 162.Dv SO_BROADCAST 163has not been set on the socket. 164.It Bq Er ENOTSOCK 165The argument 166.Fa s 167is not a socket. 168.It Bq Er EFAULT 169An invalid user space address was specified for a parameter. 170.It Bq Er EMSGSIZE 171The socket requires that message be sent atomically, 172and the size of the message to be sent made this impossible. 173.It Bq Er EAGAIN 174The socket is marked non-blocking and the requested operation 175would block. 176.It Bq Er ENOBUFS 177The system was unable to allocate an internal buffer. 178The operation may succeed when buffers become available. 179.It Bq Er ENOBUFS 180The output queue for a network interface was full. 181This generally indicates that the interface has stopped sending, 182but may be caused by transient congestion. 183.It Bq Er EHOSTUNREACH 184The remote host was unreachable. 185.It Bq Er ECONNREFUSED 186The socket received an ICMP destination unreachable message 187from the last message sent. This typically means that the 188receiver is not listening on the remote port. 189.It Bq Er EHOSTDOWN 190The remote host was down. 191.It Bq Er EPIPE 192The socket is unable to send anymore data (SS_CANTSENDMORE has 193been set on the socket). This typically means that the socket 194is not connected. 195.El 196.Sh SEE ALSO 197.Xr fcntl 2 , 198.Xr getsockopt 2 , 199.Xr recv 2 , 200.Xr select 2 , 201.Xr socket 2 , 202.Xr write 2 203.Sh HISTORY 204The 205.Fn send 206function call appeared in 207.Bx 4.2 . 208.Sh BUGS 209Because 210.Fn sendmsg 211doesn't necessarily block until the data has been transferred, it 212is possible to transfer an open file descriptor across an 213.Dv AF_UNIX 214domain socket 215(see 216.Xr recv 2 ) , 217then 218.Fn close 219it before it has actually been sent, the result being that the receiver 220gets a closed file descriptor. It is left to the application to 221implement an acknowledgment mechanism to prevent this from happening. 222