xnbd-watchdog: 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/xnbd-watchdog - from package: xnbd-client

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