xen-ringwatch: 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/xen-ringwatch - from package: xen-utils-4.4

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

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