masterguard: 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 CentOS possible default full paths are:

/sbin/masterguard - from package: nut

You may install the required package with command yum install {package}

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