mdu: 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:

/usr/bin/mdu - from package: mtools

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

On Debian possible default full paths are:

/usr/bin/mdu - from package: mtools

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

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