Sorting out old password hashes
https://archlinux.org/news/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.