— accept a connection on a
s, struct sockaddr
s, struct sockaddr
The argument s is a socket that has been
created with socket(2), bound to an address with
bind(2), and is listening for connections after a
call extracts the first connection request on the queue of pending
connections, creates a new socket with the same non-blocking I/O mode as
s, and allocates a new file descriptor for the socket
with the close-on-exec flag clear.
system call is similar, however the non-blocking I/O mode of the new socket
is determined by the
SOCK_NONBLOCK flag in the
flags argument and the close-on-exec flag on the new
file descriptor is determined by the
flag in the flags argument.
If no pending connections are present on the queue,
and the socket is not marked as non-blocking,
blocks the caller until a connection is present. If the socket is marked
non-blocking and no pending connections are present on the queue,
accept() returns an error as described below. The
accepted socket may not be used to accept more connections. The original
socket s remains open.
The argument addr is a result parameter that is filled in with the address of the connecting entity as known to the communications layer. The exact format of the addr parameter is determined by the domain in which the communication is occurring. The structure sockaddr_storage exists for greater portability. It is large enough to hold any of the types that may be returned in the addr parameter.
The addrlen is a value-result parameter; it
should initially contain the amount of space pointed to by
addr; on return it will contain the actual length (in
bytes) of the address returned. If addrlen does not
point to enough space to hold the entire socket address, the result will be
truncated to the initial value of addrlen (in bytes).
This call is used with connection-based socket types, currently with
It is possible to
poll(2) a socket for the purposes of doing an
by selecting it for read.
accept4() return a non-negative integer, the
accepted socket file descriptor. Otherwise, a value of -1 is returned and
errno is set to indicate the error.
The following code uses struct sockaddr_storage to allocate enough space for the returned address:
#include <sys/types.h> #include <sys/socket.h> struct sockaddr_storage addr; socklen_t len = sizeof(addr); int retcode; retcode = accept(s, (struct sockaddr *)&addr, &len); if (retcode == -1) err(1, "accept");
accept4() will fail if:
- The descriptor is invalid.
- The descriptor doesn't reference a socket.
- The referenced socket is not of type
- A signal was caught before a connection arrived.
- The referenced socket is not listening for connections (that is, listen(2) has not yet been called).
- The addr or addrlen parameter is not in a valid part of the process address space.
- The socket is marked non-blocking and no connections are present to be accepted.
- The per-process descriptor table is full.
- The system file table is full.
- A connection has been aborted.
accept4() will fail if
- flags is invalid.
bind(2), connect(2), listen(2), poll(2), select(2), socket(2)
accept() function conforms to
IEEE Std 1003.1-2008 (“POSIX.1”). The
accept4() function is expected to conform to a
future revision of that standard.
accept() system call first appeared in
ENFILE is returned, new connections are neither
dequeued nor discarded. Thus considerable care is required in