rdup-up: 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-up - from package: rdup

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

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