def boot_time
      raw = procfs_file("uptime") { |file| file.read }
      Time.now - raw.split(/\s/).first.to_f
    end
def boot_time
      raw = procfs_file("uptime") { |file| file.read }
      Time.now - raw.split(/\s/).first.to_f
    end
Fetches the boot time of the system.
 @return [Time] the boot time as regular time object.
 @example
   Vmstat.boot_time # => 2012-10-09 18:42:37 +0200