|SEND(2)||System Calls Manual||SEND(2)|
LIBRARY¶Standard C Library (libc, -lc)
s, const void *msg,
s, const void *msg,
const struct sockaddr
s, const struct msghdr
s, struct mmsghdr *
restrict msgvec, size_t
sendmmsg() functions, and
sendmsg() system calls are used to transmit one or more messages (with the
sendmmsg() call) to another socket. The
send() function may be used only when the socket is in a connected state, while
sendmmsg() may be used at any time.
The address of the target is given by to
with tolen specifying its size. The length of the
message is given by len. If the message is too long to
pass atomically through the underlying protocol, the error
EMSGSIZE is returned, and the message is not
sendmmsg() function sends multiple
messages at a call. They are given by the msgvec
vector along with vlen specifying the vector size. The
number of octets sent per each message is placed in the
msg_len field of each processed element of the vector
No indication of failure to deliver is implicit in a
send(). Locally detected errors are indicated by a
return value of -1.
If no messages space is available at the socket to hold the
message to be transmitted, then
blocks, unless the socket has been placed in non-blocking I/O mode. The
select(2) system call may be used to determine when it is
possible to send more data.
The flags argument may include one or more of the following:
#define MSG_OOB 0x00001 /* process out-of-band data */ #define MSG_DONTROUTE 0x00004 /* bypass routing, use direct interface */ #define MSG_EOR 0x00008 /* data completes record */ #define MSG_EOF 0x00100 /* data completes transaction */ #define MSG_NOSIGNAL 0x20000 /* do not generate SIGPIPE on EOF */
MSG_OOB is used to send
“out-of-band” data on sockets that support this notion (e.g.
SOCK_STREAM); the underlying protocol must also
support “out-of-band” data.
used to indicate a record mark for protocols which support the concept.
MSG_EOF requests that the sender side of a socket be
shut down, and that an appropriate indication be sent at the end of the
specified data; this flag is only implemented for
SOCK_STREAM sockets in the
PF_INET protocol family.
MSG_DONTROUTE is usually used only by diagnostic or
MSG_NOSIGNAL is used to prevent
SIGPIPE generation when writing a socket that may be
See recv(2) for a description of the msghdr structure and the mmsghdr structure.
sendmsg() calls return the number of octets sent. The
sendmmsg() call returns the number of messages sent. If an error occurred a value of -1 is returned.
sendmmsg() functions and
sendmsg() system calls fail if:
- An invalid descriptor was specified.
- The destination address is a broadcast address, and
SO_BROADCASThas not been set on the socket.
- The argument s is not a socket.
- An invalid user space address was specified for an argument.
- The socket requires that message be sent atomically, and the size of the message to be sent made this impossible.
- The socket is marked non-blocking and the requested operation would block.
- The system was unable to allocate an internal buffer. The operation may succeed when buffers become available.
- The output queue for a network interface was full. This generally indicates that the interface has stopped sending, but may be caused by transient congestion.
- The remote host was unreachable.
- A destination address was specified and the socket is already connected.
- The socket received an ICMP destination unreachable message from the last message sent. This typically means that the receiver is not listening on the remote port.
- The remote host was down.
- The remote network was down.
- The process using a
SOCK_RAWsocket was jailed and the source address specified in the IP header did not match the IP address bound to the prison.
- The socket is unable to send anymore data
SBS_CANTSENDMOREhas been set on the socket). This typically means that the socket is not connected.
SEE ALSO¶fcntl(2), getsockopt(2), recv(2), select(2), socket(2), write(2), CMSG_DATA(3)
send() function appeared in 4.2BSD. The
sendmmsg() function appeared in FreeBSD 11.0.
sendmsg() does not necessarily block until the data has been transferred, it is possible to transfer an open file descriptor across an
AF_UNIXdomain socket (see recv(2)), then
close() it before it has actually been sent, the result being that the receiver gets a closed file descriptor. It is left to the application to implement an acknowledgment mechanism to prevent this from happening.
|August 19, 2018||Linux 4.19.0-6-amd64|