mupdate: 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/lib/cyrus/bin/mupdate - from package: cyrus-murder

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

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