Linux getting all network interface names

Question

I need to collect all the interface names, even the ones that aren't up at the moment. Like ifconfig -a.

getifaddrs() is iterating through same interface name multiple times. How can I collect all the interface names just once using getifaddrs()?

Thanks Joachim but isn't there any other way without extra processing? — tez, Oct 07 '13 at 14:49

score 27 · Accepted Answer · answered Oct 07 '13 at 15:00

You could check which entries from getifaddrs belong to the AF_PACKET family. On my system that seems to list all interfaces:

struct ifaddrs *addrs,*tmp;

getifaddrs(&addrs);
tmp = addrs;

while (tmp)
{
    if (tmp->ifa_addr && tmp->ifa_addr->sa_family == AF_PACKET)
        printf("%s\n", tmp->ifa_name);

    tmp = tmp->ifa_next;
}

freeifaddrs(addrs);

Hugues · Answer 2 · 2020-04-09T10:16:03.553

getifaddrs() will only return your interfaces addresses, not the interfaces themselves.

What if any of your interface has no address, or no address of the requested family, as suggested with the 'AF_PACKET' one ?

Here, an example where I’ve got a tunnel interface (with an OpenVPN connexion), and where I’m listing all entries from getifaddrs() for each of my network interfaces:

[0] 1: lo                address family: 17 (AF_PACKET) b4:11:00:00:00:01
                         address family: 2 (AF_INET)    address: <127.0.0.1>
                         address family: 10 (AF_INET6)  address: <::1>
[...]

[5] 10: tun0             address family: 2 (AF_INET)    address: <172.16.0.14>
[EOF]

Bam. No AF_PACKET on the "tun0" interface, but it DOES exist on the system.

You should, instead, use if_nameindex() syscall, which does exactly what you want. In other words, with no arguments, it returns a list of all interfaces on your system:

#include <net/if.h>
#include <stdio.h>

int main (void)
{
    struct if_nameindex *if_nidxs, *intf;

    if_nidxs = if_nameindex();
    if ( if_nidxs != NULL )
    {
        for (intf = if_nidxs; intf->if_index != 0 || intf->if_name != NULL; intf++)
        {
            printf("%s\n", intf->if_name);
        }

        if_freenameindex(if_nidxs);
    }

    return 0;
}

And voilà.

Your example code is leaking the memory. According to the documentation ([if_nameindex](http://man7.org/linux/man-pages/man3/if_nameindex.3.html)) if_nameindex() function dynamically allocates memory that later should be freed by calling if_freenameindex(). — fetch, Sep 30 '17 at 13:35
Hello `void main (void)` is improper. You should use `int main()` or `int main(void)` Also main should return a value. — f3xy, Apr 03 '20 at 17:02
Just updated, and checkd the `gcc -Wall` does not produces anymore errors. Thx ;-) — Hugues, Apr 15 '20 at 08:23

ldav1s · Answer 3 · 2013-10-07T15:51:20.610

6

It seems that ifconfig -a only lists active interfaces (at least on Fedora 19). I know I have at least one more network card that I'm not seeing. Anyway, I get the same list as:

ls -1 /sys/class/net

Which could easily be done programatically.

edited Oct 07 '13 at 15:51

answered Oct 07 '13 at 15:46

ldav1s

14,864
2
46
52

score 2 · Answer 4 · answered Oct 07 '13 at 14:50

2

You are on the right track (it is getifaddrs). It returns each interface once per family, so you get eth0 for ipv4 and one for ipv6. If you just want each interface once you will have to uniq the output yourself.

answered Oct 07 '13 at 14:50

aet

6,977
3
24
25

score 2 · Answer 5 · answered Oct 08 '13 at 07:17

2

I thing this show you all interface, at least for me

ip link show

ls -1 /sys/class/net

only show interface name

lo
p4p1

answered Oct 08 '13 at 07:17

Makaro

33
4

score 1 · Answer 6 · answered Feb 16 '16 at 21:26

I need the main device that is being used by the system (assuming there is only one) such as eth0 wlan0 or whatever RHEL7 is trying to do...

The best I hacked together was this:

#!/bin/bash
# -- Get me the interface for the main ip on system

for each in $(ls -1 /sys/class/net) ;do 

    result=$(ip addr show $each | awk '$1 == "inet" {gsub(/\/.*$/, "", $2); print $2}' | grep "$(hostname -I | cut -d' ' -f1)")

    if [ ! -z "${result// }" ] && [ -d /sys/class/net/${each// } ] ;then
            echo "Device: $each IP: $result"
            break;
    fi

done

Sample output:

    ./maineth.sh  
    Device: enp0s25 IP: 192.168.1.6

Linux getting all network interface names

6 Answers6

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