.\" Copyright (C) 2007, Michael Kerrisk <mtk.manpages@gmail.com>
.\" and Copyright (C) 2008, Linux Foundation, written by Michael Kerrisk
.\"     <mtk.manpages@gmail.com>
.\"
.\" %%%LICENSE_START(VERBATIM)
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date.  The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein.  The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\" %%%LICENSE_END
.\"
.\" 2007-05-31, mtk: Rewrite and substantial additional text.
.\" 2008-12-03, mtk: Rewrote some pieces and fixed some errors
.\"
.TH BINDRESVPORT 3  2017-09-15 "" "Linux Programmer's Manual"
.SH NAME
bindresvport \- bind a socket to a privileged IP port
.SH SYNOPSIS
.nf
.B #include <sys/types.h>
.B #include <netinet/in.h>
.PP
.BI "int bindresvport(int " sockfd ", struct sockaddr_in *" sin );
.fi
.SH DESCRIPTION
.PP
.BR bindresvport ()
is used to bind the socket referred to by the
file descriptor
.I sockfd
to a privileged anonymous IP port,
that is, a port number arbitrarily selected from the range 512 to 1023.
.\" Glibc actually starts searching with a port # in the range 600 to 1023
.PP
If the
.BR bind (2)
performed by
.BR bindresvport ()
is successful, and
.I sin
is not NULL, then
.I sin\->sin_port
returns the port number actually allocated.
.PP
.I sin
can be NULL, in which case
.I sin\->sin_family
is implicitly taken to be
.BR AF_INET .
However, in this case,
.BR bindresvport ()
has no way to return the port number actually allocated.
(This information can later be obtained using
.BR getsockname (2).)
.SH RETURN VALUE
.BR bindresvport ()
returns 0 on success; otherwise \-1 is returned and
.I errno
set to indicate the cause of the error.
.SH ERRORS
.BR bindresvport ()
can fail for any of the same reasons as
.BR bind (2).
In addition, the following errors may occur:
.TP
.BR EACCES
The calling process was not privileged
(on Linux: the calling process did not have the
.B CAP_NET_BIND_SERVICE
capability in the user namespace governing its network namespace).
.TP
.B EADDRINUSE
All privileged ports are in use.
.TP
.BR EAFNOSUPPORT " (" EPFNOSUPPORT " in glibc 2.7 and earlier)"
.I sin
is not NULL and
.I sin->sin_family
is not
.BR AF_INET .
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lb lb lb
l l lw23.
Interface	Attribute	Value
T{
.BR bindresvport ()
T}	Thread safety	T{
glibc >= 2.17: MT-Safe
.\" commit f6da27e53695ad1cc0e2a9490358decbbfdff5e5
.br
glibc < 2.17: MT-Unsafe
T}
.TE
.PP
The
.BR bindresvport ()
function uses a static variable that was not protected by a lock
before glibc 2.17, rendering the function MT-Unsafe.
.SH CONFORMING TO
Not in POSIX.1.
Present on the BSDs, Solaris, and many other systems.
.SH NOTES
Unlike some
.BR bindresvport ()
implementations,
the glibc implementation ignores any value that the caller supplies in
.IR sin\->sin_port .
.SH SEE ALSO
.BR bind (2),
.BR getsockname (2)
.SH COLOPHON
This page is part of release 5.04 of the Linux
.I man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
\%https://www.kernel.org/doc/man\-pages/.