xl: 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-4.4/bin/xl - from package: xen-utils-4.4
/usr/sbin/xl - from package: xen-utils-common

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

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