xen-dir: 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/lib/xen-common/bin/xen-dir - from package: xen-utils-common

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

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