Sorting out old password hashes

Starting with libxcrypt 4.4.21, weak password hashes (such as MD5 and SHA1) are no longer accepted for new passwords. Users that still have their passwords stored with a weak hash will be asked to update their password on their next login.

If the login just fails (for example from display manager) switch to a virtual terminal (Ctrl-Alt-F2) and log in there once.