sisu6: 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/sisu6 - from package: sisu

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

Error in other languages:
sisu6: bevel nie gevind nie
sisu6: comandă negăsită
sisu6: comando não encontrado
sisu6: commande introuvable
sisu6: command not found
sisu6: käsku ei ole
sisu6: không tìm thấy lệnh
sisu6: komanda nerasta
sisu6: Kommando nicht gefunden.
sisu6: kommandot finns inte
sisu6: komut yok
sisu6: nie znaleziono polecenia
sisu6: níor aimsíodh an t-ordú
sisu6: no se encontró la orden
sisu6: no s'ha trobat l'ordre
sisu6: opdracht niet gevonden
sisu6: parancs nem található
sisu6: perintah tidak ditemukan
sisu6: príkaz nenájdený
sisu6: příkaz nenalezen
sisu6: команда не найдена
sisu6: командата не е открита
sisu6: 命令找不到
sisu6: コマンドが見つかりません