How can I set the hardware mac address permanently?

ThatDataGuy

6/25/23, 11:31 PM

I have a headless ARM server running 20.04.4, which for reasons I cannot understand has all it's NICs with hardware macs of all zeros, and sets the current mac randomly on every reboot.

╰─ macchanger eth2
Current MAC:   2a:77:19:7c:b4:e4 (unknown)
Permanent MAC: 00:00:00:00:00:00 (XEROX CORPORATION)

I run a pi hole on my network and it also handles the DHCP service, and can only assign static IPs based on reported mac address. This means that my server gets a new IP address on every reboot, which is problematic when there is an issue with the pi hole.

I want my server to keep a mac address for a given interface even when reboots happen.

I've tried

ip link set eth2 address 2A:77:19:7C:B4:E4

but that got wiped during a reboot.

I've tried using a link file with systemd-networkd, but this appears to have no effect either.

sudo nano /etc/systemd/network/10-eth2.link

[Match]
PermanentMACAddress=00:00:00:00:00:00

[Link]
MACAddress=2A:77:19:7C:B4:E4

Digging around, I found these log entries in

journalctl -b -u systemd-udevd.service

eth2: Could not generate persistent MAC: No data available
Feb 25 23:23:42 macchiatobin systemd-udevd[480]: ethtool: autonegotiation is unset or enabled, the speed and duplex are not writable.

How else can I set my mac address to the same value permanently, or on start up so it is the same value on every boot?

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systemd-networkd

heynnema

6/26/23, 12:11 AM

I assume that you're running netplan. See https://netplan.io/ and search the reference and design pages for "mac address". Then you might try using the **match** (by name... eth0, eth1, etc.) and **macaddress** qualifiers.

Score:0

Ubuntu

ThatDataGuy

6/27/23, 12:25 AM

I was able to solve this as follows.

I created this file:

/etc/netplan/config.yaml

with contents:

network:
    version: 2
    renderer: networkd
    ethernets:
        eth0:
            macaddress: ba:e4:64:bc:81:d7
        eth1:
            macaddress: c2:1c:fb:6b:fb:73
        eth2:
            macaddress: 2A:77:19:7C:B4:E4
        eth3:
            macaddress: ba:2a:5c:54:35:60

where eth0/1/2/3 are the interfaces on my machine. I was then able to apply these instantly using

sudo netplan apply

these settings are then persisted after reboots.

Note that there is a bug in the pihole dhcp server that doesn't remove a dynamic lease when using the UI. You can edit the file at /etc/pihole/dhcp.leases and remove the lease directly. Then use

sudo pihole restartdns

This setup now assigns the same mac address for the interfaces, and the dhcp server does the rest.

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