ACCEPT(3SOCKET) Sockets Library Functions ACCEPT(3SOCKET)

accept - accept a connection on a socket

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);

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/socketvar.h>.


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.


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.


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().

The accept() function returns −1 on error. If it succeeds, it returns a non-negative integer that is a descriptor for the accepted socket.

accept() and accept4() will fail if:


The descriptor is invalid.


The remote side aborted the connection before the accept() operation completed.


The addr parameter or the addrlen parameter is invalid.


The accept() attempt was interrupted by the delivery of a signal.


The per-process descriptor table is full.


The protocol family and type corresponding to s could not be found in the netconfig file.


There was insufficient user memory available to complete the operation.


There were insufficient STREAMS resources available to complete the operation.


The descriptor does not reference a socket.


The referenced socket is not of type SOCK_STREAM.


A protocol error has occurred; for example, the STREAMS protocol stack has not been initialized or the connection has already been released.


The socket is marked as non-blocking and no connections are present to be accepted.

Additionally, accept4() will fail if:


The flags value is invalid. The flags argument can only be the bitwise inclusive-OR of SOCK_CLOEXEC, SOCK_NONBLOCK, and SOCK_NDELAY.

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

MT-Level Safe

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)

April 19, 2013 OmniOS