SEND(2) System Calls Manual SEND(2)
send, sendto, sendmsg - send a message from a socket
int send(s, msg, len, flags)
int len, flags;
int sendto(s, msg, len, flags, to, tolen)
int len, flags;
struct sockaddr *to;
int sendmsg(s, msg, flags)
struct msghdr *msg;
s is a socket created with socket(2). send(), sendto(), and sendmsg()
are used to transmit a message to another socket. send() may be used
only when the socket is in a connected state, while sendto() and
sendmsg() 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, then the
error EMSGSIZE is returned, and the message is not transmitted.
No indication of failure to deliver is implicit in a send(). Return
values of -1 indicate some locally detected errors.
If no buffer space is available at the socket to hold the message to be
transmitted, then send() normally blocks, unless the socket has been
placed in non-blocking I/O mode. The select(2) call may be used to
determine when it is possible to send more data.
If the process calling send(), sendmsg() or sendto() receives a signal
before any data are buffered to be sent, the system call is restarted
unless the calling process explicitly set the signal to interrupt these
calls using sigvec() or sigaction() (see the discussions of SV_INTER-
RUPT on sigvec(2), and SA_INTERRUPT on sigaction(3V)).
The flags parameter is formed by ORing one or more of the following:
MSG_OOB Send ``out-of-band'' data on sockets that support
this notion. The underlying protocol must also
support ``out-of-band'' data. Currently, only
SOCK_STREAM sockets created in the AF_INET address
family support out-of-band data.
MSG_DONTROUTE The SO_DONTROUTE option is turned on for the dura-
tion of the operation. This is usually used only
by diagnostic or routing programs.
See recv(2) for a description of the msghdr structure.
On success, these functions return the number of bytes sent. On fail-
ure, they return -1 and set errno to indicate the error.
EBADF s is an invalid descriptor.
EFAULT The data was specified to be sent to a non-existent
or protected part of the process address space.
EINTR The calling process received a signal before any
data could be buffered to be sent, and the signal
was set to interrupt the system call.
EINVAL len is not the size of a valid address for the
specified address family.
EMSGSIZE The socket requires that message be sent atomi-
cally, and the size of the message to be sent made
ENOBUFS The system was unable to allocate an internal buf-
fer. The operation may succeed when buffers become
ENOBUFS The output queue for a network interface was full.
This generally indicates that the interface has
stopped sending, but may be caused by transient
ENOTSOCK s is a descriptor for a file, not a socket.
EWOULDBLOCK The socket is marked non-blocking and the requested
operation would block.
connect(2), fcntl(2V), getsockopt(2), recv(2), select(2), socket(2),
21 January 1990 SEND(2)