nnpost: 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/nnpost - from package: nn

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

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