xen-update-image: 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/xen-update-image - from package: xen-tools

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

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