update-kboot: 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/sbin/update-kboot - from package: kboot-utils

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

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