rbldns-data: 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/rbldns-data - from package: ndjbdns

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

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