deb-systemd-helper: 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:

/usr/bin/deb-systemd-helper - from package: init-system-helpers

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

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