Due to having a very unstable connection in China, I wrote a script to alert me when my internet is down. If the internet is down, it will say so every 5 seconds until it is back up. If it is up, it will say this once and then shut up. The log messages are a delta.

check_internet.rb

#!/usr/bin/env ruby

require 'logger'

class SimpleDaemon
  def self.start pid, pidfile, outfile, errfile
    unless pid.nil?
      raise "Fork failed" if pid == -1
      write pid, pidfile if kill pid, pidfile
      exit
    else
      redirect outfile, errfile
    end
  end
 
  def self.write pid, pidfile
    File.open pidfile, "w" do |f|
      f.write pid
    end
  rescue ::Exception => e
    $stderr.puts "While writing the PID to file, unexpected #{e.class}: #{e}"
    Process.kill "HUP", pid
  end
 
  def self.kill(pid, pidfile)
    opid = open(pidfile).read.strip.to_i
    Process.kill "HUP", opid
    true
  rescue Errno::ENOENT
    $stdout.puts "#{pidfile} did not exist: Errno::ENOENT"
    true
  rescue Errno::ESRCH
    $stdout.puts "The process #{opid} did not exist: Errno::ESRCH"
    true
  rescue Errno::EPERM
    $stderr.puts "Lack of privileges to manage the process #{opid}: Errno::EPERM"
    false
  rescue ::Exception => e
    $stderr.puts "While signaling the PID, unexpected #{e.class}: #{e}"
    false
  end
 
  def self.redirect outfile, errfile
    $stdin.reopen '/dev/null'
    out = File.new outfile, "a"
    err = File.new errfile, "a"
    $stdout.reopen out
    $stderr.reopen err
    $stdout.sync = $stderr.sync = true
  end
end

$0 = "Internet Status Checker"

SimpleDaemon.start fork, (ARGV[0] || '/tmp/daemon.pid'), (ARGV[1] || '/tmp/daemon.stdout.log'), (ARGV[2] || '/tmp/daemon.stderr.log')
 
Signal.trap("HUP") { $stdout.puts "SIGHUP and exit"; exit }
Signal.trap("INT") { $stdout.puts "SIGINT and exit"; exit }
Signal.trap("QUIT") { $stdout.puts "SIGQUIT and exit"; exit }

log = Logger.new('status_internet.txt', 'daily')
log.level = Logger::INFO

log.info "Script started..."

ping_count = 3
server = "www.baidu.com"
server2 = "8.8.8.8"
down = true

loop do
  log.debug "Pinging #{server}"
  result = `ping -qoc #{ping_count} #{server}`
  
  if ($?.exitstatus == 0) then
    log.info "Internet is up!" unless down == false
    `say Internet up` if down == true
    down = false
  else
    result = `ping -qoc #{ping_count} #{server2}`
    if($?.exitstatus == 0) then
      log.info "Baidu.com not reachable, probably a DNS issue"
      `say Baidu down`
    else
      log.info "Internet down!" unless down == true
      `say Internet down`
      down = true
    end
  end
  
  sleep 5
end