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

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

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