zupdate: 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/zupdate - from package: zutils

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

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