ipcluster3: 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/ipcluster3 - from package: ipython3

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

Error in other languages:
ipcluster3: bevel nie gevind nie
ipcluster3: comandă negăsită
ipcluster3: comando não encontrado
ipcluster3: commande introuvable
ipcluster3: command not found
ipcluster3: käsku ei ole
ipcluster3: không tìm thấy lệnh
ipcluster3: komanda nerasta
ipcluster3: Kommando nicht gefunden.
ipcluster3: kommandot finns inte
ipcluster3: komut yok
ipcluster3: nie znaleziono polecenia
ipcluster3: níor aimsíodh an t-ordú
ipcluster3: no se encontró la orden
ipcluster3: no s'ha trobat l'ordre
ipcluster3: opdracht niet gevonden
ipcluster3: parancs nem található
ipcluster3: perintah tidak ditemukan
ipcluster3: príkaz nenájdený
ipcluster3: příkaz nenalezen
ipcluster3: команда не найдена
ipcluster3: командата не е открита
ipcluster3: 命令找不到
ipcluster3: コマンドが見つかりません