munpack: 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/munpack - from package: mpack

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

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