.\" Copyright (C) 2007, Michael Kerrisk <mtk.manpages@gmail.com>

.\" and Copyright (C) 2008, Linux Foundation, written by Michael Kerrisk

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.\" 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 4.15 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/.