SEND(2) Linux Programmer's Manual SEND(2)
send, sendto, sendmsg - send a message from a socket
int send(int s, const void *msg, int len, unsigned int
int sendto(int s, const void *msg, int len, unsigned int
flags, const struct sockaddr *to, int tolen);
int sendmsg(int s, const struct msghdr *msg, unsigned int
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 speci-
fying 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 transmitted.
No indication of failure to deliver is implicit in a send.
Locally detected errors are indicated by a return value of
When the message does not fit into the send buffer of the
socket, send normally blocks, unless the socket has been
placed in non-blocking I/O mode. In non-blocking mode it
would return EAGAIN in this case. The select(2) call may
be used to determine when it is possible to send more
The flags parameter may include one or more of the follow-
#define MSG_OOB 0x1 /* process out-of-band data */
#define MSG_DONTROUTE 0x4 /* bypass routing, use direct interface */
#define MSG_DONTWAIT 0x40 /* don't block */
#define MSG_NOSIGNAL 0x2000 /* don't raise SIGPIPE */
Sends out-of-band data on sockets that support this
notion (e.g. SOCK_STREAM); the underlying protocol
must also support out-of-band data.
Bypasses the usual routing table lookup and sends
the packet directly to the interface described by
the destination address. This is usually used only
by diagnostic or routing programs.
Enables non-blocking operation; if the operation
would block, EAGAIN is returned.
Requests not to send SIGPIPE on errors on stream
oriented sockets when the other end breaks the con-
nection. The EPIPE error is still returned.
See recv(2) for a description of the msghdr structure. You
may send control information using the msg_control and
msg_controllen members. The maximum control buffer length
the kernel can process is limited by the net.core.opt-
mem_max sysctl; see socket(4).
The calls return the number of characters sent, or -1 if
an error occurred.
These are some standard errors generated by the socket
layer. Additional errors may be generated and returned
from the underlying protocol modules; see their respective
EBADF An invalid descriptor was specified.
The argument s is not a socket.
EFAULT An invalid user space address was specified for a
The socket requires that message be sent atomi-
cally, and the size of the message to be sent made
EAGAIN The socket is marked non-blocking and the
requested operation would block.
ENOBUFS The system was unable to allocate an internal mem-
ory block. The operation may succeed when buffers
EINTR A signal occurred.
ENOMEM No memory available.
EINVAL Invalid argument passed.
EPIPE The local end has been shut down on a connection
oriented socket. In this case the process will
also receive a SIGPIPE unless MSG_NOSIGNAL is set.
4.4BSD, SVr4, POSIX 1003.1g draft (these function calls
appeared in 4.2BSD).
fcntl(2), recv(2), select(2), getsockopt(2), socket(2),
write(2), socket(4), ip(4), tcp(4), udp(4)
BSD Man Page 24 July 1993 1