rdup: 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/rdup - from package: rdup

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

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