1 ACCEPT(3C)               Standard C Library Functions               ACCEPT(3C)
   2 
   3 NAME
   4      accept - accept a connection on a socket
   5 
   6 LIBRARY
   7      Standard C Library (libc, -lc)
   8 
   9 SYNOPSIS
  10      #include <sys/types.h>
  11      #include <sys/socket.h>
  12 
  13      int
  14      accept(int s, struct sockaddr *restrict addr, socklen_t *addrlen);
  15 
  16      int
  17      accept4(int s, struct sockaddr *restrict addr, socklen_t *addrlen,
  18          int flags);
  19 
  20 DESCRIPTION
  21      The argument s is a socket that has been created with socket(3C) and
  22      bound to an address with bind(3C), and that is listening for connections
  23      after a call to listen(3C).  The accept() function extracts the first
  24      connection on the queue of pending connections, creates a new socket with
  25      the properties of s, and allocates a new file descriptor, ns, for the
  26      socket.  If no pending connections are present on the queue and the
  27      socket is not marked as non-blocking, accept() blocks the caller until a
  28      connection is present.  If the socket is marked as non-blocking and no
  29      pending connections are present on the queue, accept() returns an error
  30      as described below.  The accept() function uses the netconfig(4) file to
  31      determine the STREAMS device file name associated with s.  This is the
  32      device on which the connect indication will be accepted.  The accepted
  33      socket, ns, is used to read and write data to and from the socket that
  34      connected to ns.  It is not used to accept more connections.  The
  35      original socket (s) remains open for accepting further connections.
  36 
  37      The argument addr is a result parameter that is filled in with the
  38      address of the connecting entity as it is known to the communications
  39      layer.  The exact format of the addr parameter is determined by the
  40      domain in which the communication occurs.
  41 
  42      The argument addrlen is a value-result parameter.  Initially, it contains
  43      the amount of space pointed to by addr; on return it contains the length
  44      in bytes of the address returned.
  45 
  46      The accept() function is used with connection-based socket types,
  47      currently with SOCK_STREAM.
  48 
  49      The accept4() function allows flags that control the behavior of a
  50      successfully accepted socket.  If flags is 0, accept4() acts identically
  51      to accept().  Values for flags are constructed by a bitwise-inclusive-OR
  52      of flags from the following list, defined in <sys/socketvar.h>:
  53 
  54      SOCK_CLOEXEC
  55              The accepted socket will have the FD_CLOEXEC flag set as if
  56              fcntl(2) was called on it.  This flag is set before the socket is
  57              passed to the caller thus avoiding the race condition between
  58              accept() and fcntl(2).  See O_CLOEXEC in open(2) for more
  59              details.
  60 
  61      SOCK_NDELAY
  62              The accepted socket will have the O_NDELAY flag set as if
  63              fcntl(2) was called on it.  This sets the socket into non-
  64              blocking mode.  See O_NDELAY in fcntl.h(3HEAD) for more details.
  65 
  66      SOCK_NONBLOCK
  67              The accepted socket will have the O_NONBLOCK flag set as if
  68              fcntl(2) was called on it.  This sets the socket into non-
  69              blocking mode (POSIX; see standards(5)).  See O_NONBLOCK in
  70              fcntl.h(3HEAD) for more details.
  71 
  72      It is possible to select(3C) or poll(2) a socket for the purpose of an
  73      accept() by selecting or polling it for a read.  However, this will only
  74      indicate when a connect indication is pending; it is still necessary to
  75      call accept().
  76 
  77 RETURN VALUES
  78      The accept() function returns -1 on error.  If it succeeds, it returns a
  79      non-negative integer that is a descriptor for the accepted socket.
  80 
  81 ERRORS
  82      accept() and accept4() will fail if:
  83 
  84      [EBADF]            The descriptor is invalid.
  85 
  86      [ECONNABORTED]     The remote side aborted the connection before the
  87                         accept() operation completed.
  88 
  89      [EFAULT]           The addr parameter or the addrlen parameter is
  90                         invalid.
  91 
  92      [EINTR]            The accept() attempt was interrupted by the delivery
  93                         of a signal.
  94 
  95      [EMFILE]           The per-process descriptor table is full.
  96 
  97      [ENODEV]           The protocol family and type corresponding to s could
  98                         not be found in the netconfig file.
  99 
 100      [ENOMEM]           There was insufficient user memory available to
 101                         complete the operation.
 102 
 103      [ENOSR]            There were insufficient STREAMS resources available to
 104                         complete the operation.
 105 
 106      [ENOTSOCK]         The descriptor does not reference a socket.
 107 
 108      [EOPNOTSUPP]       The referenced socket is not of type SOCK_STREAM.
 109 
 110      [EPROTO]           A protocol error has occurred; for example, the
 111                         STREAMS protocol stack has not been initialized or the
 112                         connection has already been released.
 113 
 114      [EWOULDBLOCK]      The socket is marked as non-blocking and no
 115                         connections are present to be accepted.
 116 
 117      Additionally, accept4() will fail if:
 118 
 119      [EINVAL]           The flags value is invalid.  The flags argument can
 120                         only be the bitwise inclusive-OR of SOCK_CLOEXEC,
 121                         SOCK_NONBLOCK, and SOCK_NDELAY.
 122 
 123 MT-LEVEL
 124      Safe
 125 
 126 SEE ALSO
 127      fcntl(2), poll(2), bind(3C), connect(3C), listen(3C), select(3C),
 128      sockaddr(3C), socket(3C), fcntl.h(3HEAD), socket.h(3HEAD), netconfig(4),
 129      attributes(5), standards(5)
 130 
 131 illumos                         August 2, 2018                         illumos