gem install net-ssh notify

ssh_tail.rb

# -*- coding: utf-8 -*-
require 'rubygems'
require 'net/ssh'
require 'notify'

def daemonize(&block)
  if Process.respond_to? :daemon
    Process.daemon(&block)
  else
    require 'WEBrick'
    WEBrick::Daemon.start(&block)
  end
end

hostname = 'remote_host_name'
user = 'username'
key = '~/.ssh/id_rsa'
path = '/path/to/file.log'

daemonize {
  Net::SSH.start(hostname, user, :keys => [key]) do |ssh|
    ssh.open_channel do |ch|
      ch.on_data do |c,data|
        Notify.notify hostname, data
      end
      ch.exec "tail -f #{path}"
    end
    ssh.loop
  end
}