mad: 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/mad - from package: mmv

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

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