dyndns_tool: 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/sbin/dyndns_tool - from package: dms-core

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

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