ACCEPT(3SOCKET)ACCEPT(3SOCKET)NAME
accept - accept a connection on a socket
SYNOPSIS
cc [ flag ... ] file ... -lsocket-lnsl [ library ... ]
#include <sys/types.h>
#include <sys/socket.h>
int accept(int s, struct sockaddr *addr, socklen_t *addrlen);
int accept4(int s, struct sockaddr *addr, socklen_t *addrlen,
int flags);
DESCRIPTION
The argument s is a socket that has been created with socket(3SOCKET)
and bound to an address with bind(3SOCKET), and that is listening for
connections after a call to listen(3SOCKET). The accept() function
extracts the first connection on the queue of pending connections, cre‐
ates a new socket with the properties of s, and allocates a new file
descriptor, ns, for the socket. If no pending connections are present
on the queue and the socket is not marked as non-blocking, accept()
blocks the caller until a connection is present. If the socket is
marked as non-blocking and no pending connections are present on the
queue, accept() returns an error as described below. The accept()
function uses the netconfig(4) file to determine the STREAMS device
file name associated with s. This is the device on which the connect
indication will be accepted. The accepted socket, ns, is used to read
and write data to and from the socket that connected to ns. It is not
used to accept more connections. The original socket (s) remains open
for accepting further connections.
The argument addr is a result parameter that is filled in with the
address of the connecting entity as it is known to the communications
layer. The exact format of the addr parameter is determined by the
domain in which the communication occurs.
The argument addrlen is a value-result parameter. Initially, it con‐
tains the amount of space pointed to by addr; on return it contains the
length in bytes of the address returned.
The accept() function is used with connection-based socket types, cur‐
rently with SOCK_STREAM.
The accept4() function allows flags that control the behavior of a suc‐
cessfully accepted socket. If flags is 0, accept4() acts identically
to accept(). Values for flags are constructed by a bitwise-inclusive-OR
of flags from the following list, defined in <sys/socketvar.h>.
SOCK_CLOEXEC
The accepted socket will have the FD_CLOEXEC flag set as if
fcntl() was called on it. This flag is set before the
socket is passed to the caller thus avoiding the race con‐
dition between accept() and fcntl(). See, O_CLOEXEC in
open(2) for more details.
SOCK_NDELAY
The accepted socket will have the O_NDELAY flag set as if
fcntl() was called on it. This sets the socket into non-
blocking mode. See O_NDELAY in fcntl.h(3HEAD) for more
details.
SOCK_NONBLOCK
The accepted socket will have the O_NONBLOCK flag set as if
fcntl() was called on it. This sets the socket into non-
blocking mode (POSIX; see standards(5)). See O_NONBLOCK in
fcntl.h(3HEAD) for more details.
It is possible to select(3C) or poll(2) a socket for the purpose of an
accept() by selecting or polling it for a read. However, this will only
indicate when a connect indication is pending; it is still necessary to
call accept().
RETURN VALUES
The accept() function returns −1 on error. If it succeeds, it returns a
non-negative integer that is a descriptor for the accepted socket.
ERRORSaccept() and accept4() will fail if:
EBADF
The descriptor is invalid.
ECONNABORTED
The remote side aborted the connection before the
accept() operation completed.
EFAULT
The addr parameter or the addrlen parameter is invalid.
EINTR
The accept() attempt was interrupted by the delivery of
a signal.
EMFILE
The per-process descriptor table is full.
ENODEV
The protocol family and type corresponding to s could
not be found in the netconfig file.
ENOMEM
There was insufficient user memory available to com‐
plete the operation.
ENOSR
There were insufficient STREAMS resources available to
complete the operation.
ENOTSOCK
The descriptor does not reference a socket.
EOPNOTSUPP
The referenced socket is not of type SOCK_STREAM.
EPROTO
A protocol error has occurred; for example, the STREAMS
protocol stack has not been initialized or the connec‐
tion has already been released.
EWOULDBLOCK
The socket is marked as non-blocking and no connections
are present to be accepted.
Additionally, accept4() will fail if:
EINVAL
The flags value is invalid. The flags argument can only
be the bitwise inclusive-OR of SOCK_CLOEXEC, SOCK_NON‐
BLOCK, and SOCK_NDELAY.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌───────────────┬─────────────────┐
│ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├───────────────┼─────────────────┤
│MT-Level │ Safe │
└───────────────┴─────────────────┘
SEE ALSOpoll(2), bind(3SOCKET), connect(3SOCKET), listen(3SOCKET), select(3C),
socket.h(3HEAD), socket(3SOCKET), netconfig(4), attributes(5),
fcntl.h(3HEAD), fcntl(2), standards(5)
Apr 19, 2013 ACCEPT(3SOCKET)