ubuntu 20.04 允许root登录

echo 'greeter-show-manual-login = true' >> /usr/share/lightdm/lightdm.conf.d/50-ubuntu.conf
sed -i 's/.*pam_succeed_if.so.*/#&/' /etc/pam.d/gdm-autologin
sed -i 's/.*pam_succeed_if.so.*/#&/' /etc/pam.d/gdm-password
# 删除最后一行后添加
echo 'tty -s mesg n 2> /dev/null || true' >> /root/.profile
echo 'mesg n || true' >> /root/.profile