killall: 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/killall - from package: psmisc

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

On Debian possible default full paths are:

/usr/bin/killall - from package: psmisc

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

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