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-.\" Copyright (c) 1983, 1990, 1991 The Regents of the University of California.
-.\" All rights reserved.
-.\"
-.\" SPDX-License-Identifier: BSD-4-Clause-UC
-.\"
-.\" Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu>
-.\" Modified 1996-10-21 by Eric S. Raymond <esr@thyrsus.com>
-.\" Modified 1998-2000 by Andi Kleen to match Linux 2.2 reality
-.\" Modified 2002-04-23 by Roger Luethi <rl@hellgate.ch>
-.\" Modified 2004-06-17 by Michael Kerrisk <mtk.manpages@gmail.com>
-.\" 2008-12-04, mtk, Add documentation of accept4()
-.\"
-.TH accept 2 2023-10-31 "Linux man-pages 6.7"
-.SH NAME
-accept, accept4 \- accept a connection on a socket
-.SH LIBRARY
-Standard C library
-.RI ( libc ", " \-lc )
-.SH SYNOPSIS
-.nf
-.B #include <sys/socket.h>
-.P
-.BI "int accept(int " sockfd ", struct sockaddr *_Nullable restrict " addr ,
-.BI " socklen_t *_Nullable restrict " addrlen );
-.P
-.BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */"
-.B #include <sys/socket.h>
-.P
-.BI "int accept4(int " sockfd ", struct sockaddr *_Nullable restrict " addr ,
-.BI " socklen_t *_Nullable restrict " addrlen ", int " flags );
-.fi
-.SH DESCRIPTION
-The
-.BR accept ()
-system call is used with connection-based socket types
-.RB ( SOCK_STREAM ,
-.BR SOCK_SEQPACKET ).
-It extracts the first connection request on the queue of pending
-connections for the listening socket,
-.IR sockfd ,
-creates a new connected socket, and returns a new file
-descriptor referring to that socket.
-The newly created socket is not in the listening state.
-The original socket
-.I sockfd
-is unaffected by this call.
-.P
-The argument
-.I sockfd
-is a socket that has been created with
-.BR socket (2),
-bound to a local address with
-.BR bind (2),
-and is listening for connections after a
-.BR listen (2).
-.P
-The argument
-.I addr
-is a pointer to a
-.I sockaddr
-structure.
-This structure is filled in with the address of the peer socket,
-as known to the communications layer.
-The exact format of the address returned
-.I addr
-is determined by the socket's address family (see
-.BR socket (2)
-and the respective protocol man pages).
-When
-.I addr
-is NULL, nothing is filled in; in this case,
-.I addrlen
-is not used, and should also be NULL.
-.P
-The
-.I addrlen
-argument is a value-result argument:
-the caller must initialize it to contain the
-size (in bytes) of the structure pointed to by
-.IR addr ;
-on return it will contain the actual size of the peer address.
-.P
-The returned address is truncated if the buffer provided is too small;
-in this case,
-.I addrlen
-will return a value greater than was supplied to the call.
-.P
-If no pending
-connections are present on the queue, and the socket is not marked as
-nonblocking,
-.BR accept ()
-blocks the caller until a connection is present.
-If the socket is marked
-nonblocking and no pending connections are present on the queue,
-.BR accept ()
-fails with the error
-.B EAGAIN
-or
-.BR EWOULDBLOCK .
-.P
-In order to be notified of incoming connections on a socket, you can use
-.BR select (2),
-.BR poll (2),
-or
-.BR epoll (7).
-A readable event will be delivered when a new connection is attempted and you
-may then call
-.BR accept ()
-to get a socket for that connection.
-Alternatively, you can set the socket to deliver
-.B SIGIO
-when activity occurs on a socket; see
-.BR socket (7)
-for details.
-.P
-If
-.I flags
-is 0, then
-.BR accept4 ()
-is the same as
-.BR accept ().
-The following values can be bitwise ORed in
-.I flags
-to obtain different behavior:
-.TP 16
-.B SOCK_NONBLOCK
-Set the
-.B O_NONBLOCK
-file status flag on the open file description (see
-.BR open (2))
-referred to by the new file descriptor.
-Using this flag saves extra calls to
-.BR fcntl (2)
-to achieve the same result.
-.TP
-.B SOCK_CLOEXEC
-Set the close-on-exec
-.RB ( FD_CLOEXEC )
-flag on the new file descriptor.
-See the description of the
-.B O_CLOEXEC
-flag in
-.BR open (2)
-for reasons why this may be useful.
-.SH RETURN VALUE
-On success,
-these system calls return a file descriptor
-for the accepted socket (a nonnegative integer).
-On error, \-1 is returned,
-.I errno
-is set to indicate the error, and
-.I addrlen
-is left unchanged.
-.SS Error handling
-Linux
-.BR accept ()
-(and
-.BR accept4 ())
-passes already-pending network errors on the new socket
-as an error code from
-.BR accept ().
-This behavior differs from other BSD socket
-implementations.
-For reliable operation the application should detect
-the network errors defined for the protocol after
-.BR accept ()
-and treat
-them like
-.B EAGAIN
-by retrying.
-In the case of TCP/IP, these are
-.BR ENETDOWN ,
-.BR EPROTO ,
-.BR ENOPROTOOPT ,
-.BR EHOSTDOWN ,
-.BR ENONET ,
-.BR EHOSTUNREACH ,
-.BR EOPNOTSUPP ,
-and
-.BR ENETUNREACH .
-.SH ERRORS
-.TP
-.BR EAGAIN " or " EWOULDBLOCK
-.\" Actually EAGAIN on Linux
-The socket is marked nonblocking and no connections are
-present to be accepted.
-POSIX.1-2001 and POSIX.1-2008
-allow either error to be returned for this case,
-and do not require these constants to have the same value,
-so a portable application should check for both possibilities.
-.TP
-.B EBADF
-.I sockfd
-is not an open file descriptor.
-.TP
-.B ECONNABORTED
-A connection has been aborted.
-.TP
-.B EFAULT
-The
-.I addr
-argument is not in a writable part of the user address space.
-.TP
-.B EINTR
-The system call was interrupted by a signal that was caught
-before a valid connection arrived; see
-.BR signal (7).
-.TP
-.B EINVAL
-Socket is not listening for connections, or
-.I addrlen
-is invalid (e.g., is negative).
-.TP
-.B EINVAL
-.RB ( accept4 ())
-invalid value in
-.IR flags .
-.TP
-.B EMFILE
-The per-process limit on the number of open file descriptors has been reached.
-.TP
-.B ENFILE
-The system-wide limit on the total number of open files has been reached.
-.TP
-.B ENOBUFS
-.TQ
-.B ENOMEM
-Not enough free memory.
-This often means that the memory allocation is limited by the socket buffer
-limits, not by the system memory.
-.TP
-.B ENOTSOCK
-The file descriptor
-.I sockfd
-does not refer to a socket.
-.TP
-.B EOPNOTSUPP
-The referenced socket is not of type
-.BR SOCK_STREAM .
-.TP
-.B EPERM
-Firewall rules forbid connection.
-.TP
-.B EPROTO
-Protocol error.
-.P
-In addition, network errors for the new socket and as defined
-for the protocol may be returned.
-Various Linux kernels can
-return other errors such as
-.BR ENOSR ,
-.BR ESOCKTNOSUPPORT ,
-.BR EPROTONOSUPPORT ,
-.BR ETIMEDOUT .
-The value
-.B ERESTARTSYS
-may be seen during a trace.
-.SH VERSIONS
-On Linux, the new socket returned by
-.BR accept ()
-does \fInot\fP inherit file status flags such as
-.B O_NONBLOCK
-and
-.B O_ASYNC
-from the listening socket.
-This behavior differs from the canonical BSD sockets implementation.
-.\" Some testing seems to show that Tru64 5.1 and HP-UX 11 also
-.\" do not inherit file status flags -- MTK Jun 05
-Portable programs should not rely on inheritance or noninheritance
-of file status flags and always explicitly set all required flags on
-the socket returned from
-.BR accept ().
-.SH STANDARDS
-.TP
-.BR accept ()
-POSIX.1-2008.
-.TP
-.BR accept4 ()
-Linux.
-.SH HISTORY
-.TP
-.BR accept ()
-POSIX.1-2001, SVr4, 4.4BSD
-.RB ( accept ()
-first appeared in 4.2BSD).
-.\" The BSD man page documents five possible error returns
-.\" (EBADF, ENOTSOCK, EOPNOTSUPP, EWOULDBLOCK, EFAULT).
-.\" POSIX.1-2001 documents errors
-.\" EAGAIN, EBADF, ECONNABORTED, EINTR, EINVAL, EMFILE,
-.\" ENFILE, ENOBUFS, ENOMEM, ENOTSOCK, EOPNOTSUPP, EPROTO, EWOULDBLOCK.
-.\" In addition, SUSv2 documents EFAULT and ENOSR.
-.TP
-.BR accept4 ()
-Linux 2.6.28,
-glibc 2.10.
-.SH NOTES
-There may not always be a connection waiting after a
-.B SIGIO
-is delivered or
-.BR select (2),
-.BR poll (2),
-or
-.BR epoll (7)
-return a readability event because the connection might have been
-removed by an asynchronous network error or another thread before
-.BR accept ()
-is called.
-If this happens, then the call will block waiting for the next
-connection to arrive.
-To ensure that
-.BR accept ()
-never blocks, the passed socket
-.I sockfd
-needs to have the
-.B O_NONBLOCK
-flag set (see
-.BR socket (7)).
-.P
-For certain protocols which require an explicit confirmation,
-such as DECnet,
-.BR accept ()
-can be thought of as merely dequeuing the next connection request and not
-implying confirmation.
-Confirmation can be implied by
-a normal read or write on the new file descriptor, and rejection can be
-implied by closing the new socket.
-Currently, only DECnet has these semantics on Linux.
-.\"
-.SS The socklen_t type
-In the original BSD sockets implementation (and on other older systems)
-.\" such as Linux libc4 and libc5, SunOS 4, SGI
-the third argument of
-.BR accept ()
-was declared as an \fIint\ *\fP.
-A POSIX.1g draft
-standard wanted to change it into a \fIsize_t\ *\fPC;
-.\" SunOS 5 has 'size_t *'
-later POSIX standards and glibc 2.x have
-.IR "socklen_t\ * ".
-.SH EXAMPLES
-See
-.BR bind (2).
-.SH SEE ALSO
-.BR bind (2),
-.BR connect (2),
-.BR listen (2),
-.BR select (2),
-.BR socket (2),
-.BR socket (7)