Detect and download the most recent stable Ubuntu kernel version

download_recent_stable_kernel.rb

require 'nokogiri'
require 'net/http'
require 'uri'
require 'byebug'
require 'open-uri'

class LinuxKernel
  OFFICIAL_KERNEL_URL = 'https://www.kernel.org/'.freeze
  UBUNTU_KERNEL_BASE_URL  = 'http://kernel.ubuntu.com/~kernel-ppa/mainline/'.freeze

  def initialize
    @sections = {}
  end

  def exists?
    File.directory? version
  end

  def version
    return @version if @version
    @version = Nokogiri::HTML(official_web_page).css('td#latest_link a').text
  end

  def available?
    Net::HTTP.get_response(ubuntu_kernel_uri).is_a? Net::HTTPSuccess
  end

  def links_available?
    files.all? do |kernel_file|
      Net::HTTP.get_response(kernel_file[:uri]).is_a? Net::HTTPSuccess
    end
  end

  def download!
    Dir.mkdir version
    files.each do |kernel_file|
      print "- #{kernel_file[:basename]}"
      download = open kernel_file[:uri]
      IO.copy_stream(download, "#{version}/#{kernel_file[:basename]}")
      puts " [downloaded]"
    end
    save_install_command
  end

  private

  attr_reader :sections

  def links
    return @links if @links
    detect_url_parts
    @links = [
      "linux-headers-#{sections[:first]}_#{sections[:second]}_all.deb",
      "linux-headers-#{sections[:first]}-generic_#{sections[:second]}_amd64.deb",
      "linux-image-#{sections[:first]}-generic_#{sections[:second]}_amd64.deb"
    ]
  end

  def files
    links.map do |file|
      {
        basename: file,
        uri: ubuntu_kernel_uri.tap { |uri| uri.path << file }
      }
    end
  end

  def save_install_command
    File.open("#{version}/install_command.txt", "w") do |file|
      file.puts 'sudo dpkg -i *.deb'
    end
  end

  def detect_url_parts
    page = Nokogiri::HTML ubuntu_kernel_page
    link_text = page.css('a:contains("generic")').css('a:contains("amd64")').first.text
    link_match = link_text.match(/linux-headers-(.+)-generic_(.+)_amd64/)
    if link_match
      @sections[:first] = link_match[1]
      @sections[:second] = link_match[2]
    end
  end

  def official_web_page
    @official_web_page ||= Net::HTTP.get official_uri
  end

  def official_uri
    URI.parse OFFICIAL_KERNEL_URL
  end

  def ubuntu_kernel_page
    @ubuntu_kernel_page ||= Net::HTTP.get ubuntu_kernel_uri
  end

  def ubuntu_kernel_uri
    URI.parse "#{UBUNTU_KERNEL_BASE_URL}v#{version}/"
  end
end

linux_kernel = LinuxKernel.new
if linux_kernel.exists?
  puts "You already downloaded the recent stable kernel [#{linux_kernel.version}]"
elsif linux_kernel.available?
  puts "Downloading v#{linux_kernel.version}"
  if linux_kernel.links_available?
    linux_kernel.download!
    puts "Done!"
    puts ""
    puts "Installing: sudo dpkg -i #{linux_kernel.version}/*.deb"
  else
    puts "Error checking the status of new kernel files"
  end
end

Example output:

$ rb download_recent_stable_kernel.rb
Downloading v4.15.1
- linux-headers-4.15.1-041501_4.15.1-041501.201802031831_all.deb [downloaded]
- linux-headers-4.15.1-041501-generic_4.15.1-041501.201802031831_amd64.deb [downloaded]
- linux-image-4.15.1-041501-generic_4.15.1-041501.201802031831_amd64.deb [downloaded]
Done!

Installing: sudo dpkg -i 4.15.1/*.deb