This document mainly introduces automatic login under Ubuntu.

Edit file /usr/share/lightdm/lightdm.conf.d/50-greeter-wrapper.conf to add the configuration below:

[SeatDefaults]
greeter-session=lightdm-gtk-greeter
autologin-user=khadas

For tty1-tty6:

sudo cp /lib/systemd/system/getty@.service /lib/systemd/system/getty@.service.backup
sudo sed -i "s/ExecStart=.*/ExecStart=-\/sbin\/agetty --noclear --autologin root \%I \$TERM/g" /lib/systemd/system/getty@.service

For ttyS0:

sudo cp /lib/systemd/system/serial-getty@.service /lib/systemd/system/serial-getty@.service.backup
sudo sed -i "s/ExecStart=.*/ExecStart=-\/sbin\/agetty --autologin root --keep-baud 115200,38400,9600 \%I \$TERM/g" /lib/systemd/system/serial-getty@.service

sudo mv /lib/systemd/system/getty@.service.backup /lib/systemd/system/getty@.service
sudo mv /lib/systemd/system/serial-getty@.service.backup /lib/systemd/system/serial-getty@.service