Why does my headless browser script open Firefox, causing issues in a cron job?

I created a script intended for execution via a cron job, using a headless browser approach. I utilized the Headless gem, aiming for it to operate without a graphical display. However, upon running the script, Firefox still launches, which seems counterproductive to the concept of headless operation. I expected it to function similarly to PhantomJS, executing in the background without display access. Am I misunderstanding the functionality of this gem? Also, when I previously tried using PhantomJS, it timed out when attempting to access the email input field on a Google login page. Below is my script example:

#coding: utf-8
require 'watir-webdriver'
require 'headless'

# Start headless session
headless = Headless.new
browser = Watir::Browser.start 'http://app.example.com/admin'
# Perform login steps here

# Fetch yesterday's data
# Close browser after data retrieval
browser.close
headless.destroy

# Log timestamp
current_time = Time.now
puts "Data retrieved at: " + current_time.inspect
"

When I execute the script outside of the cron environment, it functions correctly, but it fails while being run by cron. Any advice would be appreciated!

It seems like the core of your issue lies with the way your script interacts with the headless environment when being executed in a cron job. Let’s break down the problem and address it step-by-step. Here are the points you should consider and modifications you can make to your script to ensure it works correctly with cron and in a headless manner:

  1. Initialization of Headless Session: Ensure you initialize and start the headless session properly using the begin and end block to make sure it is correctly managed.

  2. Providing Display Number: When setting up a headless session, explicitly provide a display number which can sometimes avoid conflicts.

  3. Running Cron with a Full Path: Ensure your cron job uses the full path to the ruby executable and the script to avoid environment-specific issues.

  4. Logging Errors for Debugging: Add error handling and logging to understand where it might be failing when executed via cron.

Here’s an updated version of your script to incorporate these suggestions:

#coding: utf-8
require 'watir-webdriver'
require 'headless'

begin
  # Start headless session
  headless = Headless.new(display: 99)
  headless.start

  # Start browser session with headless
  browser = Watir::Browser.start 'http://app.example.com/admin'
  # Perform login steps here

  # Fetch yesterday's data
  # Close browser after data retrieval
  browser.close
rescue Exception => e
  # Log an error message with timestamp
  File.open('/path/to/your/logfile.log', 'a') do |f|
    f.puts "Error at: #{Time.now} - #{e.message}"
  end
ensure
  headless.destroy if headless
end

# Log timestamp of data retrieval
current_time = Time.now
puts "Data retrieved at: " + current_time.inspect

Additional Tips:

  • Make your script executable by adding the shebang at the top: #!/usr/bin/env ruby
  • In your crontab file, ensure you have something like:
    * * * * * /usr/bin/ruby /path/to/your_script.rb >> /path/to/your_output.log 2>&1
    
  • Check environment variables since cron runs with a limited environment compared to your user session.
  • Look into cron output or log files (/var/log/syslog or /var/log/cron) for potential errors.

By making these adjustments, your script should execute in a fully headless manner within the cron job environment.