tinydyndns-update: 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/tinydyndns-update - from package: tinydyndns

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

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