undertaker: 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/undertaker - from package: undertaker

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

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