kill: 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:

/bin/kill - from package: util-linux-ng
/usr/bin/kill - from package: util-linux-ng

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

On Debian possible default full paths are:

/bin/kill - from package: procps
/usr/lib/klibc/bin/kill - from package: klibc-utils

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

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