（1）普通用户登录系统，打开终端，输入：sudo passwd root(使用root权限为root更改密码)

（2）设置root密码；

（3）重复root密码；

Jaking@ubuntu:~$ sudo passwd root
[sudo] password for uplooking:
Enter new UNIX password:
Retype new UNIX password:
passwd: password updated successfully
Jaking@ubuntu:~$ su - root
Password:
root@ubuntu:~#

vim /usr/share/lightdm/lightdm.conf.d/50-ubuntu.conf

打开文件，在文件尾加入两行：

greeter-show-manual-login=true
all-guest=false
root@ubuntu:~# cat /usr/share/lightdm/lightdm.conf.d/50-ubuntu.conf
[Seat:*]
user-session=ubuntu
greeter-show-manual-login=true
all-guest=false

gdm-autologin文件注释掉auth required pam_success_if.so user!=root quiet_success 这一行

gdm-password文件注释掉auth required pam_success_if.so user!=root quiet_success 这一行

root@ubuntu:~# cd /etc/pam.d
root@ubuntu:/etc/pam.d# cat gdm-autologin | grep auth
auth requisite pam_nologin.so
#auth required pam_succeed_if.so user != root quiet_success
auth optional pam_gdm.so
auth optional pam_gnome_keyring.so
auth required pam_permit.so
root@ubuntu:/etc/pam.d# cat gdm-password | grep auth
auth requisite pam_nologin.so
#auth required pam_succeed_if.so user != root quiet_success
@include common-auth
auth optional pam_gnome_keyring.so

将 mesg n 改为 tty -s && mesg n

root@ubuntu:~# cat /root/.profile
# ~/.profile: executed by Bourne-compatible login s.

if [ "$BASH" ]; then
if [ -f ~/.bashrc ]; then
. ~/.bashrc
fi
fi

tty -s && mesg n || true

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