rdiscount: 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/rdiscount - from package: ruby-rdiscount

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

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