man3/bindresvport.3

   1 .\" Copyright (C) 2007, Michael Kerrisk <mtk.manpages@gmail.com>
   2 .\" and Copyright (C) 2008, Linux Foundation, written by Michael Kerrisk
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  27 .\" 2007-05-31, mtk: Rewrite and substantial additional text.
  28 .\" 2008-12-03, mtk: Rewrote some pieces and fixed some errors
  29 .\"
  30 .TH BINDRESVPORT 3  2017-09-15 "" "Linux Programmer's Manual"
  31 .SH NAME
  32 bindresvport \- bind a socket to a privileged IP port
  33 .SH SYNOPSIS
  34 .nf
  35 .B #include <sys/types.h>
  36 .B #include <netinet/in.h>
  37 .PP
  38 .BI "int bindresvport(int " sockfd ", struct sockaddr_in *" sin );
  39 .fi
  40 .SH DESCRIPTION
  41 .PP
  42 .BR bindresvport ()
  43 is used to bind the socket referred to by the
  44 file descriptor
  45 .I sockfd
  46 to a privileged anonymous IP port,
  47 that is, a port number arbitrarily selected from the range 512 to 1023.
  48 .\" Glibc actually starts searching with a port # in the range 600 to 1023
  49 .PP
  50 If the
  51 .BR bind (2)
  52 performed by
  53 .BR bindresvport ()
  54 is successful, and
  55 .I sin
  56 is not NULL, then
  57 .I sin\->sin_port
  58 returns the port number actually allocated.
  59 .PP
  60 .I sin
  61 can be NULL, in which case
  62 .I sin\->sin_family
  63 is implicitly taken to be
  64 .BR AF_INET .
  65 However, in this case,
  66 .BR bindresvport ()
  67 has no way to return the port number actually allocated.
  68 (This information can later be obtained using
  69 .BR getsockname (2).)
  70 .SH RETURN VALUE
  71 .BR bindresvport ()
  72 returns 0 on success; otherwise \-1 is returned and
  73 .I errno
  74 set to indicate the cause of the error.
  75 .SH ERRORS
  76 .BR bindresvport ()
  77 can fail for any of the same reasons as
  78 .BR bind (2).
  79 In addition, the following errors may occur:
  80 .TP
  81 .BR EACCES
  82 The calling process was not privileged
  83 (on Linux: the calling process did not have the
  84 .B CAP_NET_BIND_SERVICE
  85 capability in the user namespace governing its network namespace).
  86 .TP
  87 .B EADDRINUSE
  88 All privileged ports are in use.
  89 .TP
  90 .BR EAFNOSUPPORT " (" EPFNOSUPPORT " in glibc 2.7 and earlier)"
  91 .I sin
  92 is not NULL and
  93 .I sin->sin_family
  94 is not
  95 .BR AF_INET .
  96 .SH ATTRIBUTES
  97 For an explanation of the terms used in this section, see
  98 .BR attributes (7).
  99 .TS
 100 allbox;
 101 lb lb lb
 102 l l lw23.
 103 Interface       Attribute       Value
 104 T{
 105 .BR bindresvport ()
 106 T}      Thread safety   T{
 107 glibc >= 2.17: MT-Safe
 108 .\" commit f6da27e53695ad1cc0e2a9490358decbbfdff5e5
 109 .br
 110 glibc < 2.17: MT-Unsafe
 111 T}
 112 .TE
 113 .PP
 114 The
 115 .BR bindresvport ()
 116 function uses a static variable that was not protected by a lock
 117 before glibc 2.17, rendering the function MT-Unsafe.
 118 .SH CONFORMING TO
 119 Not in POSIX.1.
 120 Present on the BSDs, Solaris, and many other systems.
 121 .SH NOTES
 122 Unlike some
 123 .BR bindresvport ()
 124 implementations,
 125 the glibc implementation ignores any value that the caller supplies in
 126 .IR sin\->sin_port .
 127 .SH SEE ALSO
 128 .BR bind (2),
 129 .BR getsockname (2)