autodns-dhcp_ddns: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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/sbin/autodns-dhcp_ddns - from package: autodns-dhcp

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