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+'\" t
+.\" Copyright (C) 2007, Michael Kerrisk <mtk.manpages@gmail.com>
+.\" and Copyright (C) 2008, Linux Foundation, written by Michael Kerrisk
+.\"     <mtk.manpages@gmail.com>
+.\"
+.\" SPDX-License-Identifier: Linux-man-pages-copyleft
+.\"
+.\" 2007-05-31, mtk: Rewrite and substantial additional text.
+.\" 2008-12-03, mtk: Rewrote some pieces and fixed some errors
+.\"
+.TH bindresvport 3 2023-07-20 "Linux man-pages 6.05.01"
+.SH NAME
+bindresvport \- bind a socket to a privileged IP port
+.SH LIBRARY
+Standard C library
+.RI ( libc ", " \-lc )
+.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
+.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
+is set to indicate 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
+.B 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 lbx
+l l l.
+Interface	Attribute	Value
+T{
+.na
+.nh
+.BR bindresvport ()
+T}	Thread safety	T{
+.na
+.nh
+glibc\ >=\ 2.17: MT-Safe;
+.\" commit f6da27e53695ad1cc0e2a9490358decbbfdff5e5
+glibc\ <\ 2.17: MT-Unsafe
+T}
+.TE
+.sp 1
+.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 VERSIONS
+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 STANDARDS
+BSD.
+.SH SEE ALSO
+.BR bind (2),
+.BR getsockname (2)