mirror of https://github.com/mkerrisk/man-pages
169 lines
4.1 KiB
Groff
169 lines
4.1 KiB
Groff
.\" Copyright (c) 2012 YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
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.\" and Copyright (c) 2012 Michael Kerrisk <mtk.manpages@gmail.com>
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.\"
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.\" %%%LICENSE_START(VERBATIM)
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of
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.\" this manual under the conditions for verbatim copying, provided that
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.\" the entire resulting derived work is distributed under the terms of
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.\" a permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume
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.\" no responsibility for errors or omissions, or for damages resulting
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.\" from the use of the information contained herein. The author(s) may
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.\" not have taken the same level of care in the production of this
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.\" manual, which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\" %%%LICENSE_END
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.\"
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.TH IF_NAMEINDEX 3 2020-06-09 "GNU" "Linux Programmer's Manual"
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.SH NAME
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if_nameindex, if_freenameindex \- get network interface names and indexes
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.SH SYNOPSIS
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.nf
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.B #include <net/if.h>
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.PP
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.BI "struct if_nameindex *if_nameindex(" void );
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.BI "void if_freenameindex(struct if_nameindex *" "ptr" );
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.fi
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.SH DESCRIPTION
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The
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.BR if_nameindex ()
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function returns an array of
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.I if_nameindex
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structures, each containing information
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about one of the network interfaces on the local system.
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The
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.I if_nameindex
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structure contains at least the following entries:
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.PP
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.in +4n
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.EX
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unsigned int if_index; /* Index of interface (1, 2, ...) */
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char *if_name; /* Null-terminated name ("eth0", etc.) */
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.EE
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.in
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.PP
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The
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.I if_index
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field contains the interface index.
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The
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.I if_name
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field points to the null-terminated interface name.
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The end of the array is indicated by entry with
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.I if_index
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set to zero and
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.I if_name
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set to NULL.
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.PP
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The data structure returned by
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.BR if_nameindex ()
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is dynamically allocated and should be freed using
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.BR if_freenameindex ()
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when no longer needed.
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.SH RETURN VALUE
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On success,
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.BR if_nameindex ()
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returns pointer to the array;
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on error, NULL is returned, and
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.I errno
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is set appropriately.
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.SH ERRORS
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.BR if_nameindex ()
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may fail and set
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.I errno
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if:
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.TP
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.B ENOBUFS
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Insufficient resources available.
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.PP
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.BR if_nameindex ()
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may also fail for any of the errors specified for
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.BR socket (2),
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.BR bind (2),
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.BR ioctl (2),
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.BR getsockname (2),
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.BR recvmsg (2),
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.BR sendto (2),
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or
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.BR malloc (3).
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.SH VERSIONS
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The
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.BR if_nameindex ()
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function first appeared in glibc 2.1, but before glibc 2.3.4,
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the implementation supported only interfaces with IPv4 addresses.
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Support of interfaces that don't have IPv4 addresses is available only
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on kernels that support netlink.
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.SH ATTRIBUTES
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For an explanation of the terms used in this section, see
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.BR attributes (7).
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.TS
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allbox;
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lb lb lb
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l l l.
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Interface Attribute Value
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T{
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.BR if_nameindex (),
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.br
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.BR if_freenameindex ()
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T} Thread safety MT-Safe
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.TE
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.sp 1
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.SH CONFORMING TO
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POSIX.1-2001, POSIX.1-2008, RFC\ 3493.
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.PP
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This function first appeared in BSDi.
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.SH EXAMPLES
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The program below demonstrates the use of the functions described
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on this page.
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An example of the output this program might produce is the following:
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.PP
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.in +4n
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.EX
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$ \fB./a.out\fI
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1: lo
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2: wlan0
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3: em1
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.EE
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.in
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.SS Program source
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.EX
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#include <net/if.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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int
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main(int argc, char *argv[])
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{
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struct if_nameindex *if_ni, *i;
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if_ni = if_nameindex();
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if (if_ni == NULL) {
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perror("if_nameindex");
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exit(EXIT_FAILURE);
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}
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for (i = if_ni; ! (i\->if_index == 0 && i\->if_name == NULL); i++)
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printf("%u: %s\en", i\->if_index, i\->if_name);
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if_freenameindex(if_ni);
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exit(EXIT_SUCCESS);
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}
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.EE
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.SH SEE ALSO
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.BR getsockopt (2),
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.BR setsockopt (2),
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.BR getifaddrs (3),
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.BR if_indextoname (3),
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.BR if_nametoindex (3),
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.BR ifconfig (8)
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