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 ACCEPT 3SOCKET "June 21, 2024"
 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, creates 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(5) 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 contains
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,
currently with SOCK_STREAM.


The accept4() function allows flags that control the behavior of a
successfully 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/socket.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 condition between accept() and
fcntl(). See, O_CLOEXEC in open(2) for more details.



SOCK_CLOFORK


The accepted socket will have the FD_CLOFORK 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 condition between accept() and
fcntl(). See, O_CLOFORK 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(7)). 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.

 ERRORS
accept() 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 complete 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 connection 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_CLOFORK,
SOCK_NONBLOCK, and SOCK_NDELAY.




 ATTRIBUTES
See attributes(7) for descriptions of the following attributes:






ATTRIBUTE TYPE ATTRIBUTE VALUE
MT-Level Safe



 SEE ALSO
poll(2), bind(3SOCKET), connect(3SOCKET),
listen(3SOCKET), sockaddr(3SOCKET), select(3C),
socket.h(3HEAD), socket(3SOCKET), netconfig(5),
attributes(7), fcntl.h(3HEAD), fcntl(2), standards(7)