Temperature monitor

crontab

# m h  dom mon dow   command

# User environment wrapper provided by .rvm
*/5 * * * * /home/username/.rvm/wrappers/ruby-2.3.3/ruby /var/scripts/temperature.rb

monitrc

# To check one of the files via monit and send email to an extra address:
  check file vorzimmer with path /var/scripts/rrd-data/vorzimmer.txt
     if match "Alarm!" then alert
     if timestamp > 15 minutes then alert  
       alert email@example.com

temperatures.rb

require 'nokogiri'
require 'open-uri'
require "rrd"

# that's how the database has been created:
#rrd.create start: Time.now - 10.seconds, step: 5.minutes do
#  datasource "abstellraum", type: :gauge, heartbeat: 10.minutes, min: 0, max: 50
#  datasource "vorzimmer", type: :gauge, heartbeat: 10.minutes, min: 0, max: 50
#  archive :average, every: 5.minutes, during: 1.day
#  archive :average, every: 30.minutes, during: 1.week
#  archive :average, every: 1.day, during: 1.year
#end

# read temperature sensor webserver page
doc = Nokogiri::HTML(open("http://1.2.3.4/ipwe.cgi", :http_basic_authentication => ["username", "super_secret_password"]))

# get data for one room 
vorzimmer = doc.css("html body form table tbody tr:nth-child(2) td:nth-child(4)").text[/[0-9\.]+/]

# get data for another room
abstellraum = doc.css("html body form table tbody tr:nth-child(3) td:nth-child(4)").text[/[0-9\.]+/]

# open rrd database file
rrd_file = "/var/scripts/rrd-data/temperatures.rrd"
rrd = RRD::Base.new(rrd_file)

# store data in it
rrd.update Time.now, abstellraum.to_f, vorzimmer.to_f

# create small text files for monit escalation email
[[:vorzimmer, vorzimmer.to_f, 15] , [:abstellraum, abstellraum.to_f, 10]].each do |key, value, limit|
  status = value < limit ? "#{Time.now()} - Alarm! temperature #{value}°C to low in #{key}\n" : "#{Time.now()} - ok\n"
  File.open("/var/scripts/rrd-data/#{key}.txt", 'a') { |file| file.write(status) }
end


# create a nice graph from it
graph = RRD.graph "/var/www/html/today.png", title: "Temperatures today",
                                             width: 800,
                                             height: 250,
                                             color: ["FONT#000000", "BACK#ffffff"], 
                                             start: Time.now - 1.day,
                                             end: Time.now  do
  line rrd_file, abstellraum: :average,
                 color: "#0022ee", 
                 label: "First room"
  line rrd_file, vorzimmer: :average,
                 color: "#22ee00", 
                 label: "Second room"
end