undertaker-checkpatch: 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-checkpatch - from package: undertaker

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

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