mpmv: 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/mpmv - from package: mpdtoys

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

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