mrd6sh: 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/mrd6sh - from package: mrd6

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

Error in other languages:
mrd6sh: bevel nie gevind nie
mrd6sh: comandă negăsită
mrd6sh: comando não encontrado
mrd6sh: commande introuvable
mrd6sh: command not found
mrd6sh: käsku ei ole
mrd6sh: không tìm thấy lệnh
mrd6sh: komanda nerasta
mrd6sh: Kommando nicht gefunden.
mrd6sh: kommandot finns inte
mrd6sh: komut yok
mrd6sh: nie znaleziono polecenia
mrd6sh: níor aimsíodh an t-ordú
mrd6sh: no se encontró la orden
mrd6sh: no s'ha trobat l'ordre
mrd6sh: opdracht niet gevonden
mrd6sh: parancs nem található
mrd6sh: perintah tidak ditemukan
mrd6sh: príkaz nenájdený
mrd6sh: příkaz nenalezen
mrd6sh: команда не найдена
mrd6sh: командата не е открита
mrd6sh: 命令找不到
mrd6sh: コマンドが見つかりません