NF: 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/NF - from package: byobu

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

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