kdekillall: 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/kdekillall - from package: kdesdk

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

On Debian possible default full paths are:

/usr/bin/kdekillall - from package: kdesdk-scripts

You may install the required package with command apt-get install {package}

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