njb-fwupgrade: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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/njb-fwupgrade - from package: libnjb-tools

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