パスワードの最小長さを変更する方法
/etc/pam.d/common-password の次の行を書き換える。
# here are the per-package modules (the "Primary" block) password [success=1 default=ignore] pam_unix.so obscure sha512
↓
# here are the per-package modules (the "Primary" block) password [success=1 default=ignore] pam_unix.so minlen=0 sha512