refdb-backup: 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/refdb-backup - from package: refdb-clients

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