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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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RECV(3P) POSIX Programmer's Manual RECV(3P)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
recv — receive a message from a connected socket
#include <sys/socket.h>
ssize_t recv(int socket, void *buffer, size_t length, int flags);
The recv() function shall receive a message from a connection-mode
or connectionless-mode socket. It is normally used with connected
sockets because it does not permit the application to retrieve the
source address of received data.
The recv() function takes the following arguments:
socket Specifies the socket file descriptor.
buffer Points to a buffer where the message should be stored.
length Specifies the length in bytes of the buffer pointed to
by the buffer argument.
flags Specifies the type of message reception. Values of this
argument are formed by logically OR'ing zero or more of
the following values:
MSG_PEEK Peeks at an incoming message. The data is
treated as unread and the next recv() or
similar function shall still return this
data.
MSG_OOB Requests out-of-band data. The significance
and semantics of out-of-band data are
protocol-specific.
MSG_WAITALL On SOCK_STREAM sockets this requests that
the function block until the full amount of
data can be returned. The function may
return the smaller amount of data if the
socket is a message-based socket, if a
signal is caught, if the connection is
terminated, if MSG_PEEK was specified, or if
an error is pending for the socket.
The recv() function shall return the length of the message written
to the buffer pointed to by the buffer argument. For message-based
sockets, such as SOCK_DGRAM and SOCK_SEQPACKET, the entire message
shall be read in a single operation. If a message is too long to
fit in the supplied buffer, and MSG_PEEK is not set in the flags
argument, the excess bytes shall be discarded. For stream-based
sockets, such as SOCK_STREAM, message boundaries shall be ignored.
In this case, data shall be returned to the user as soon as it
becomes available, and no data shall be discarded.
If the MSG_WAITALL flag is not set, data shall be returned only up
to the end of the first message.
If no messages are available at the socket and O_NONBLOCK is not
set on the socket's file descriptor, recv() shall block until a
message arrives. If no messages are available at the socket and
O_NONBLOCK is set on the socket's file descriptor, recv() shall
fail and set errno to [EAGAIN] or [EWOULDBLOCK].
Upon successful completion, recv() shall return the length of the
message in bytes. If no messages are available to be received and
the peer has performed an orderly shutdown, recv() shall return 0.
Otherwise, -1 shall be returned and errno set to indicate the
error.
The recv() function shall fail if:
EAGAIN or EWOULDBLOCK
The socket's file descriptor is marked O_NONBLOCK and no
data is waiting to be received; or MSG_OOB is set and no
out-of-band data is available and either the socket's file
descriptor is marked O_NONBLOCK or the socket does not
support blocking to await out-of-band data.
EBADF The socket argument is not a valid file descriptor.
ECONNRESET
A connection was forcibly closed by a peer.
EINTR The recv() function was interrupted by a signal that was
caught, before any data was available.
EINVAL The MSG_OOB flag is set and no out-of-band data is
available.
ENOTCONN
A receive is attempted on a connection-mode socket that is
not connected.
ENOTSOCK
The socket argument does not refer to a socket.
EOPNOTSUPP
The specified flags are not supported for this socket type
or protocol.
ETIMEDOUT
The connection timed out during connection establishment,
or due to a transmission timeout on active connection.
The recv() function may fail if:
EIO An I/O error occurred while reading from or writing to the
file system.
ENOBUFS
Insufficient resources were available in the system to
perform the operation.
ENOMEM Insufficient memory was available to fulfill the request.
The following sections are informative.
None.
The recv() function is equivalent to recvfrom() with null pointer
address and address_len arguments, and to read() if the socket
argument refers to a socket and the flags argument is 0.
The select() and poll() functions can be used to determine when
data is available to be received.
None.
None.
poll(3p), pselect(3p), read(3p), recvmsg(3p), recvfrom(3p),
send(3p), sendmsg(3p), sendto(3p), shutdown(3p), socket(3p),
write(3p)
The Base Definitions volume of POSIX.1‐2017, sys_socket.h(0p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics Engineers,
Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard,
the original IEEE and The Open Group Standard is the referee
document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page
are most likely to have been introduced during the conversion of
the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 RECV(3P)
Pages that refer to this page: sys_socket.h(0p), recvfrom(3p), recvmsg(3p), send(3p), sendmsg(3p), sendto(3p), shutdown(3p), sockatmark(3p), socket(3p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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