Eu encontrei uma solução em outro fórum. Para todas as pessoas com o mesmo problema, talvez essa abordagem também possa ajudar:
Meu provedor alterou a senha do root e tentou o "chsh -s / bin / bash root", o que não funcionou, porque a senha não foi aceita e ocorreu o seguinte erro: "chsh: PAM authentication failed".
dave_mystic deu a solução:
The real problem is in /etc/pam.d/chsh. In that file, the line which prevents users from changing back to a normal shell after being assigned a special shell appears before the line that authorizes all changes from the root.
Unfortunately, the following line was firing first, disallowing a change because the users shell was NOT in the list of available shells. The authorization line from me being 'root' via sudo never fired because it was never checked after the first line fired.
auth required pam_shells.so
The solution was to temporarily comment out the line in /etc/pam.d/chsh, change the users shell to the correct shell, and then remove the comment in the line.
Fonte: link
Então eu comentei a linha mencionada e depois disso consegui alterar o shell.