rsbackup: 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/rsbackup - from package: rsbackup

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

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