The easiest way to change the MAC address of a Linux’ NIC is to use macchanger that, by default, sets a random address using macchanger -r <name_of_the_interface>. However, You need to set the interface down before doing so, which you might not do often enough as a lazy fuck you are (myself included).

So, to execute it systematically at startup on a systemd based Linux system, simply create the following unit /etc/systemd/system/macspoof.service (change wlan0 with the interface of your choice).

[Unit]
Description=macchanger on wlan0
Wants=network-pre.target
Before=network-pre.target
After=sys-subsystem-net-devices-wlan0.device

[Service]
ExecStart=/usr/bin/macchanger -r wlan0
Type=oneshot

[Install]
WantedBy=multi-user.target 

Reload the units

systemctl daemon-reload

Enable the service macspoof.service

systemctl enable macspoof.service

Et voilà. Check with ip addr and compare it with the one after your next boot