kxkb: 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/kxkb - from package: kdebase-workspace

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

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