tkill: 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/bin/tkill - from package: lam-runtime

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

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