module-assistant: 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/module-assistant - from package: module-assistant

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

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