sisu: 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/sisu - from package: sisu

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

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