mjhjmtu

Running Arch Linux (KDE). I performed an uneventful update today using pacman -Syu. No errors were encountered. Upon rebooting the system no user can log in. In sddm every user is greeted with "Login failed". In a virtual console, every user receives the message "login incorrect".

What could have happened? What would be the steps to fix it?

Initially, I was unable to ssh into the machine either, but after 3 reboots, I got in via ssh (with a key file).

As root, I created a new temp user and set a password. That user was able to ssh into the machine, but is not able to log in at the virtual console.

Here are the additional steps I tried so far (withotu resolution):

• I updated the passwords for all users and tried to login at the virtual console as each user.


• I restored /etc/shadow and /etc/gshadow from the pre-update snapshot and tried again


• checked pwck and grpck -- each returned no errors


• 
  systemctl --failed shows no errors


• UPDATE 1: while logged in via ssh I can su to another user, enter that user's password and authentication succeeds. I can do this for all users from the ssh session. However, no users can log in on a virtual console or via sddm still.


• UPDATE 2: I edited /etc/shadow and removed the password hash for the test user account I created (see above), leaving the user with an empty password. Upon logging in on the virtual console, I get an immediate login failure as soon as I enter the username and return key.

For concern that I won't be able to ssh back in, I am not logging out or rebooting the machine until I solve the issue.

Responses to comments:

1. Here is the output when running journalctl -f on one terminal or tty and attempting to log in on a virtual console (at the command line).

for testuser1 at virtual console:

Jan 03 14:25:44 client1 login[1506]: FAILED LOGIN 1 FROM tty2 FOR testuser1, Authentication failure 
Jan 03 14:25:58 client1 login[1506]: FAILED LOGIN 2 FROM tty2 FOR testuser1, Authentication failure 
Jan 03 14:26:06 client1 login[1506]: FAILED LOGIN 3 FROM tty2 FOR testuser1, Authentication failure 
Jan 03 14:26:13 client1 login[1506]: FAILED LOGIN 4 FROM tty2 FOR testuser1, Authentication failure 

Here is the log info when attempting to log an actual user in via sddm:

Jan 03 14:36:01 client1 sddm-helper[1594]: [PAM] authenticate: Authentication failure
Jan 03 14:36:01 client1 sddm-helper[1594]: [PAM] returning.
Jan 03 14:36:01 client1 sddm[622]: Authentication error: "Authentication failure"
Jan 03 14:36:01 client1 sddm-greeter[687]: Message received from daemon: LoginFailed
Jan 03 14:36:01 client1 sddm-helper[1594]: [PAM] Ended.
Jan 03 14:36:01 client1 sddm[622]: Auth: sddm-helper exited with 1

2. the disk is only 15% full




3. regarding "are the users on the X group? Who has the ownership of the desktop configurations?", I do not understand this question. File ownerships were not changed by running pacman -Syu. And X would not affect logging in at the virtual console, so I don't believe this is relevant to the issue.




4. a diff on the prior snapshot and /etc/pam.d shows no differences. In particular, /etc/pam.d/system-auth and /etc/pam.d/su are unchanged from before the update.