system-config-cluster: 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/system-config-cluster - from package: system-config-cluster

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

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