默認 系統 root 登錄 圖形界面，出現 登錄失敗。解決方法如下：
1，登錄普通用戶, 打開終端執行命令, 使用su root或sudo -i切換到root用戶(必須)
su root
按照提示輸入密碼即可切換用戶。
若root賬戶密碼忘記，使用如下命令重設后再切換。
sudo passwd root
2，在終端中輸入如下命令，打開文件
gedit /etc/pam.d/gdm-autologin
將打開的文件中第三行前加#，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，保存並退出,繼續在終端執行
gedit /etc/pam.d/gdm-password
將打開的文件中第三行語句加#注釋掉，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，保存並退出。在終端繼續執行
gedit /root/.profile
將打開的文件中“mesg n 2> /dev/null || true” 改為
tty -s&&mesg n 2> /dev/null || true
5，保存並退出。
6，重啟電腦，即可以root用戶登錄。