rdd-copy: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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/rdd-copy - from package: rdd

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