kblackbox: 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/kblackbox - from package: kdegames

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

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