rfrename: 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/rfrename - from package: dpm

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

On Debian possible default full paths are:

/usr/bin/rfrename - from package: dpm

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

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