xenserver.rb: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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/ruby/vendor_ruby/fog/bin/xenserver.rb - from package: ruby-fog

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