預設 系統 root 登入 圖形介面，出現 登入失敗。解決方法如下：

1，登入普通使用者, 開啟終端執行命令, 使用su root或sudo -i切換到root使用者(必須)

su root

按照提示輸入密碼即可切換使用者。

若root賬戶密碼忘記，使用如下命令重設後再切換。

sudo passwd root

2，在終端中輸入如下命令，開啟檔案

gedit /etc/pam.d/gdm-autologin

將開啟的檔案中第三行前加#，如下注釋掉語句 “auth required pam_succeed_if.so user != root quiet_success”

#%PAM-1.0
 

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
@include common-account
# SELinux needs to be the first session rule. This ensures that any 
 

# lingering context has been cleared. Without this it is possible 
# that a module could execute code in the wrong domain.
session [success=ok ignore=ignore module_unknown=ignore default=bad]        pam_selinux.so close
session required        pam_loginuid.so
# SELinux needs to intervene at login time to ensure that the process
 

# starts in the proper default security context. Only sessions which are
# intended to run in the user's context should be run after this.
session [success=ok ignore=ignore module_unknown=ignore default=bad]        pam_selinux.so open
session optional        pam_keyinit.so force revoke
session required        pam_limits.so
session required        pam_env.so readenv=1
session required        pam_env.so readenv=1 user_readenv=1 envfile=/etc/default/locale
@include common-session
session optional        pam_gnome_keyring.so auto_start
@include common-password

3，儲存並退出,繼續在終端執行

gedit /etc/pam.d/gdm-password

將開啟的檔案中第三行語句加#註釋掉，如下圖

#%PAM-1.0
auth    requisite       pam_nologin.so
#auth    required    pam_succeed_if.so user != root quiet_success
@include common-auth
auth    optional        pam_gnome_keyring.so
@include common-account
# SELinux needs to be the first session rule. This ensures that any 
# lingering context has been cleared. Without this it is possible 
# that a module could execute code in the wrong domain.
session [success=ok ignore=ignore module_unknown=ignore default=bad]        pam_selinux.so close
session required        pam_loginuid.so
# SELinux needs to intervene at login time to ensure that the process
# starts in the proper default security context. Only sessions which are
# intended to run in the user's context should be run after this.
# pam_selinux.so changes the SELinux context of the used TTY and configures
# SELinux in order to transition to the user context with the next execve()
# call.
session [success=ok ignore=ignore module_unknown=ignore default=bad]        pam_selinux.so open
session optional        pam_keyinit.so force revoke
session required        pam_limits.so
session required        pam_env.so readenv=1
session required        pam_env.so readenv=1 user_readenv=1 envfile=/etc/default/locale
@include common-session
session optional        pam_gnome_keyring.so auto_start
@include common-password

4，儲存並退出。在終端繼續執行

gedit /root/.profile

將開啟的檔案中“mesg n 2> /dev/null || true” 改為

tty -s&&mesg n 2> /dev/null || true

5，儲存並退出。

6，重啟電腦，即可以root使用者登入。

參考文章：解決Ubuntu使用ROOT賬戶登入圖形介面報錯認證失敗_D&T的部落格-CSDN部落格