rfdf: 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 CentOS possible default full paths are:

/usr/bin/rfdf - from package: dpm

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/rfdf - from package: dpm

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

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