How to reload Ethernet udev rules without reboot

19 July 2018

This note detail how to update udev rules for an Ethernet connection and have them take effect without rebooting the machine. The critical part is using rmmod and modprobe to remove and re-load the networking module for the Ethernet connection, which effectively “unplugs” and “replugs” the connection, causing the udev rules to take effect. Note that this will cause brief downtime for the specific network interface, but avoids rebooting the entire machine.

First lets run ip addr to show the interfaces we are starting with:

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: ens33u1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether aa:bb:cc:dd:ee:ff brd ff:ff:ff:ff:ff:ff
    inet 192.168.0.12/24 brd 192.168.0.255 scope global dynamic ens33u1
       valid_lft 2460sec preferred_lft 2460sec
    inet6 fe80::20c:29ff:fe1a:4605/64 scope link
       valid_lft forever preferred_lft forever

Next we add our udev rule, which should give the Ethernet interface with the MAC address aa:bb:cc:dd:ee:ff the interface name ethfoo.

/etc/udev/rules.d/70-persistent-net.rules §

SUBSYSTEM=="net", ATTR{address}=="aa:bb:cc:dd:ee:ff", NAME="ethfoo"

At this point, most advice online states you only need to run:

udevadm control --reload-rules
udevadm trigger

However this is not enough. It is necessary to unload and reload the module used for networking on that interface.

Examples of module names I’ve come across are:

ixgbe
tg3
e1000
asix
vmxnet3

The easiest way to find out which modules applies to your Ethernet connection is to physically unplug the cable (or virtually remove it if running a VM) and then run dmesg | tail to see the latest dmesg log. You should see something like this:

[11267.360808] usb 1-2: USB disconnect, device number 8
[11267.363008] asix 1-2:1.0 ens33u1: unregister 'asix' usb-0000:02:01.0-2, ASIX AX88772 USB 2.0 Ethernet

Or this:

[ 5740.147559] vmxnet3 0000:03:00.0 ens160: NIC Link is Down
[ 5747.098256] vmxnet3 0000:03:00.0 ens160: NIC Link is Up 10000 Mbps

In the first case I now know that the ens33u1 interface uses the asix module.

To unload and reload the module I run:

rmmod asix
modprobe asix

Finally I can run ip addr and see that the udev rules have taken effect - it is now called ethfoo:

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: ethfoo: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether aa:bb:cc:dd:ee:ff brd ff:ff:ff:ff:ff:ff
    inet 192.168.0.12/24 brd 192.168.0.255 scope global dynamic ethfoo
       valid_lft 2460sec preferred_lft 2460sec
    inet6 fe80::20c:29ff:fe1a:4605/64 scope link
       valid_lft forever preferred_lft forever