fdnsname: 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 Debian possible default full paths are:

/usr/bin/fdnsname - from package: firedns

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

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