xnbd-wrapper-ctl: 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-wrapper-ctl - from package: xnbd-server

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

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