kspaceduel: 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/kspaceduel - from package: kdegames

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

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