cdown: 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/cdown - from package: cdtool

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

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