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accept - accept a connection on a socket

 

NAME

      accept - accept a connection on a socket
 

LIBRARY

      Standard C Library (libc, -lc)
 

SYNOPSIS

      #include <sys/types.h>
      #include <sys/socket.h>
 
      int
      accept(int s, struct sockaddr * restrict addr,
              socklen_t * restrict addrlen);
 

DESCRIPTION

      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
      listen(2).  The accept() system call extracts the first connection
      request on the queue of pending connections, creates a new socket, and
      allocates a new file descriptor for the socket which inherits the state
      of the O_NONBLOCK property from the original socket s.
 
      If no pending connections are present on the queue, and the original
      socket is not marked as non-blocking, accept() blocks the caller until a
      connection is present.  If the original 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 argument that is filled-in with the address
      of the connecting entity, as known to the communications layer.  The
      exact format of the addr argument is determined by the domain in which
      the communication is occurring.  A null pointer may be specified for addr
      if the address information is not desired; in this case, addrlen is not
      used and should also be null.  Otherwise, the addrlen argument is a
      value-result argument; 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.  This call is used with connection-based
      socket types, currently with SOCK_STREAM.
 
      It is possible to select(2) a socket for the purposes of doing an
      accept() by selecting it for read.
 
      For certain protocols which require an explicit confirmation, such as ISO
      or DATAKIT, accept() can be thought of as merely dequeueing the next con‐
      nection request and not implying confirmation.  Confirmation can be
      implied by a normal read or write on the new file descriptor, and rejec‐
      tion can be implied by closing the new socket.
 
      For some applications, performance may be enhanced by using an
      accept_filter(9) to pre-process incoming connections.
      The call returns -1 on error.  If it succeeds, it returns a non-negative
      integer that is a descriptor for the accepted socket.
 

ERRORS

      The accept() system call will fail if:
 
      [EBADF]            The descriptor is invalid.
 
      [EINTR]            The accept() operation was interrupted.
 
      [EMFILE]           The per-process descriptor table is full.
 
      [ENFILE]           The system file table is full.
 
      [ENOTSOCK]         The descriptor references a file, not a socket.
 
      [EINVAL]           listen(2) has not been called on the socket descrip‐
                         tor.
 
      [EINVAL]           The addrlen argument is negative.
 
      [EFAULT]           The addr argument is not in a writable part of the
                         user address space.
 
      [EWOULDBLOCK]      The socket is marked non-blocking and no connections
                         are present to be accepted.
 
      [ECONNABORTED]     A connection arrived, but it was closed while waiting
                         on the listen queue.
      bind(2), connect(2), getpeername(2), listen(2), select(2), socket(2),
      accept_filter(9)
 

HISTORY

      The accept() system call appeared in 4.2BSD.
 

Sections

Based on BSD UNIX
FreeBSD is an advanced operating system for x86 compatible (including Pentium and Athlon), amd64 compatible (including Opteron, Athlon64, and EM64T), UltraSPARC, IA-64, PC-98 and ARM architectures. It is derived from BSD, the version of UNIX developed at the University of California, Berkeley. It is developed and maintained by a large team of individuals. Additional platforms are in various stages of development.