nagstamon: 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/nagstamon - from package: nagstamon

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

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