kdesu: 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/kdesu - from package: kdebase-runtime

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

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