１ ubuntu用户名修改
/etc/hostname
2 开机时串口root用户自动登录
/lib/systemd/system/serial-getty\@.service
ExecStart=-/sbin/agetty --keep-baud -a root 115200,38400,9600 %I $TERM
取消root用户自动登录，删除-a root
3 创建新用户
useradd -s '/bin/bash' -m -G adm,sudo newuser
passwd newuser