nnadmin: 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/nnadmin - from package: nn

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

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