Step 2: Select and enter Advanced options for Ubuntu, from there select the kernel named as recovery mode as shown in the screenshot below: Recover Mode. Step 3: Select root – by dropping to the root shell prompt as shown in the screenshot. Root Kernel. Step 4: Now the file system is read-only. Issue with one or more configuration files: system-auth-ac and password-auth-ac, sssd module were commented in configuration file below: $ grep sss /etc/pam.d/system-auth-ac # auth sufficient pam_sss.so use_first_pass # account [default=bad success=ok user_unknown=ignore] pam_sss.so # password sufficient pam_sss.so use_authtok # session.