systemd-ask-password: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/bin/systemd-ask-password - from package: systemd

You may install the required package with command apt-get install {package}

Error in other languages:
systemd-ask-password: bevel nie gevind nie
systemd-ask-password: comandă negăsită
systemd-ask-password: comando não encontrado
systemd-ask-password: commande introuvable
systemd-ask-password: command not found
systemd-ask-password: käsku ei ole
systemd-ask-password: không tìm thấy lệnh
systemd-ask-password: komanda nerasta
systemd-ask-password: Kommando nicht gefunden.
systemd-ask-password: kommandot finns inte
systemd-ask-password: komut yok
systemd-ask-password: nie znaleziono polecenia
systemd-ask-password: níor aimsíodh an t-ordú
systemd-ask-password: no se encontró la orden
systemd-ask-password: no s'ha trobat l'ordre
systemd-ask-password: opdracht niet gevonden
systemd-ask-password: parancs nem található
systemd-ask-password: perintah tidak ditemukan
systemd-ask-password: príkaz nenájdený
systemd-ask-password: příkaz nenalezen
systemd-ask-password: команда не найдена
systemd-ask-password: командата не е открита
systemd-ask-password: 命令找不到
systemd-ask-password: コマンドが見つかりません