fpdns: 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/fpdns - from package: fpdns

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

On Debian possible default full paths are:

/usr/bin/fpdns - from package: fpdns

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

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