xkoules: 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 CentOS possible default full paths are:

/usr/bin/xkoules - from package: koules-x11

You may install the required package with command yum install {package}

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