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

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

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