samba_dnsupdate: 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/samba_dnsupdate - from package: samba

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

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