mred: 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/mred - from package: racket

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

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