killer: 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 Debian possible default full paths are:

/usr/sbin/killer - from package: killer

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

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