bsd/man/man2/listen.2

   1 .\"     $OpenBSD: listen.2,v 1.2 1996/03/19 23:15:16 niklas Exp $
   2 .\"     $NetBSD: listen.2,v 1.7 1996/02/16 20:38:45 phil Exp $
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  35 .\"     @(#)listen.2    8.2 (Berkeley) 12/11/93
  36 .\"
  37 .Dd March 18, 2015
  38 .Dt LISTEN 2
  39 .Os BSD 4.2
  40 .Sh NAME
  41 .Nm listen
  42 .Nd listen for connections on a socket
  43 .Sh SYNOPSIS
  44 .Fd #include <sys/socket.h>
  45 .Ft int
  46 .Fo listen
  47 .Fa "int socket"
  48 .Fa "int backlog"
  49 .Fc
  50 .Sh DESCRIPTION
  51 Creation of socket-based connections requires several operations.
  52 First, a socket is created with
  53 .Xr socket 2 .
  54 Next, a willingness to accept incoming connections and
  55 a queue limit for incoming connections are specified with
  56 .Fn listen .
  57 Finally, the connections are
  58 accepted with
  59 .Xr accept 2 .
  60 The
  61 .Fn listen
  62 call applies only to sockets of type
  63 .Dv SOCK_STREAM.
  64 .\"or
  65 .\".Dv SOCK_SEQPACKET.
  66 .Pp
  67 The
  68 .Fa backlog
  69 parameter defines the maximum length
  70 for the queue of pending connections.
  71 If a connection
  72 request arrives with the queue full,
  73 the client may receive an error with an indication of
  74 .Er ECONNREFUSED .
  75 Alternatively, if the underlying protocol supports retransmission,
  76 the request may be ignored so that retries may succeed.
  77 .Sh RETURN VALUES
  78 .Rv -std listen
  79 .Sh ERRORS
  80 .Fn Listen
  81 will fail if:
  82 .Bl -tag -width Er
  83 .\" ==========
  84 .It Bq Er EACCES
  85 The current process has insufficient privileges.
  86 .\" ==========
  87 .It Bq Er EBADF
  88 The argument
  89 .Fa socket
  90 is not a valid file descriptor.
  91 .\" ==========
  92 .It Bq Er EDESTADDRREQ
  93 The socket is not bound to a local address
  94 and the protocol does not support listening on an unbound socket.
  95 .\" ==========
  96 .It Bq Er EINVAL
  97 .Fa socket
  98 is already connected.
  99 .\" ==========
 100 .It Bq Er ENOTSOCK
 101 The argument
 102 .Fa socket
 103 does not reference a socket.
 104 .\" ==========
 105 .It Bq Er EOPNOTSUPP
 106 The socket is not of a type that supports the operation
 107 .Fn listen .
 108 .El
 109 .Sh SEE ALSO
 110 .Xr accept 2 ,
 111 .Xr connect 2 ,
 112 .Xr connectx 2 ,
 113 .Xr socket 2
 114 .Sh BUGS
 115 The
 116 .Fa backlog
 117 is currently limited (silently) to 128.
 118 .Sh HISTORY
 119 The
 120 .Fn listen
 121 function call appeared in
 122 .Bx 4.2 .