【现象】
1.登录界面无法输入账号密码，只有一个“重试”按钮可以点，如下图所示：
2.终端界面输入用户名后，无法输入密码，直接报了“Login incorrect”，如下图所示：
【排查】
查看 /etc/pam.d/ 目录下的 lightdm 和 login 文件，发现这两个文件已经被清空。
【处理】
添加上相关内容后，重启后，系统正常进入。
1.cat /etc/pam.d/lightdm
#%PAM-1.0
auth [success=done ignore=ignore default=bad] pam_selinux_permit.so
auth required pam_env.so
auth substack system-auth
-auth optional pam_gnome_keyring.so
-auth optional pam_kwallet5.so
-auth optional pam_kwallet.so
auth include postlogin
account required pam_nologin.so
account include system-auth
password include system-auth
session required pam_selinux.so close
session required pam_loginuid.so
session optional pam_console.so
-session optional pam_ck_connector.so
session required pam_selinux.so open
session optional pam_keyinit.so force revoke
session required pam_namespace.so
session include system-auth
-session optional pam_gnome_keyring.so auto_start
-session optional pam_kwallet5.so
-session optional pam_kwallet.so
session optional pam_lastlog.so silent
session include postlogin
2.cat /etc/pam.d/login
#%PAM-1.0
auth substack system-auth
auth include postlogin
account required pam_nologin.so
account include system-auth
password include system-auth
# pam_selinux.so close should be the first session rule
session required pam_selinux.so close
session required pam_loginuid.so
# pam_selinux.so open should only be followed by sessions to be executed in the user context
session required pam_selinux.so open
session required pam_namespace.so
session optional pam_keyinit.so force revoke
session include system-auth
session include postlogin
-session optional pam_ck_connector.so
如果还有其他类似问题，可以检查一下相同目录下的其他文件，例如sshd、ukui-screensaver-qt等。