29
Jun
2

PHP Tutorial – Forking using wget in the background

by jestep

I see a lot of people asking on how to use a fork to run a php script or web page in the background.

Here's a quick script I created using linux's wget to run another process in the background. You could use this to automatically upload something to another server, or just about anything that needs to happen after a user action.

Note: you must have exec enabled for this to work. This is a security risk, so make sure you know the potential damage that can be done by enabling exec, and by the script that you are running. Make absolutely sure to sanitize any input being transferred to the executed script.

In my case, I needed to initiate a file upload to a remote server after a certain action was taken. Because of the nature of the upload, it would have taken about 30 seconds before displaying any response to my user, which is an unacceptable delay.

First, make the script that needs to run in the background.

PLAIN TEXT
PHP:
  1. <?php
  2.  
  3. //ALWAYS USE THIS FOR UNATTENDED SCRIPTS, YOU DON'T WANT THEM RUNNING FOREVER
  5.  
  6. /*
  7. SCRIPT THAT DOES SOMETHING YOU WANT TO RUN IN THE BACKGROUND
  8. THIS SCRIPT CAN DO ANYTHING. IT IS A NORMAL PHP SCRIPT
  9. HOWEVER, DO NOT MAKE A SCRIPT THAT WILL OUTPUT TO THE BROWSER
  10. AS NOBODY WILL EVER SEE IT
  11. */
  12.  
  13. //YOU CAN ALSO USE sleep($seconds) TO RUN THIS AFTER A SPECIFIED AMOUNT OF TIME
  14. sleep(30);
  15.  
  16. $output = 'SOME DATA THAT I GENERATED';
  17.  
  18. $ftp_user_name = 'user';
  19. $ftp_user_pass = 'pass';
  20. $ftp_server = 'ftp.someplace.com';
  21. $ftp_dir='/this_folder/';
  22.  
  23. $destination_file = date('Y-m-d');
  24.  
  25. // connect, login, and transfer the file
  26. $conn_id = @ftp_connect($ftp_server);
  27. $login_result = @ftp_login($conn_id, $ftp_user_name, $ftp_user_pass);
  28. @ftp_put($conn_id, $destination_file.'.csv', $output);

Next, make the script that executes the background script.

PLAIN TEXT
PHP:
  1. <?php
  2.  
  3. //DO A BUNCH OF STUFF HERE...
  4.  
  5. //LOCATION OF THE PAGE YOU WANT TO EXECUTE IN THE BACKGROUND
  6. $page_to_execute = 'http://www.mysite.com/background_script.php';
  7.  
  8. /*
  9. COMMAND TO EXECUTE THE PAGE USING WGET
  10. YOU CAN SEND GET VARIABLES USING THIS
  11. BE ABSOLUTELY SURE TO PROTECT AGAINST INJECTION
  12. */
  13. $command = 'wget -q '.$page_to_execute;
  14.  
  15. //ALTERNATELY TO WGET YOU COULD USE SOMETHING LIKE
  16. //$command = "nohup /usr/local/bin/php -f ".$page_to_execute;
  17.  
  18. /*
  19. NOW EXECUTE THE PAGE IN THE BACKGROUND
  20. THIS WILL NOT RETURN ANY ERROR IF IT FAILS
  21. YOU WILL NEED TO WATCH YOUR SERVER LOGS
  22. TO PROPERLY DEBUG
  23. */
  24.  
  25. @exec( "$command> /dev/null &", $arrOutput );

There you have it. This will run a script in the background (any web page that you specify). I do not use a local path to the file, because it will often break and can pose additional security risks. Using the above code, the server can only execute wget, and the actual page is parsed just like any other page on your website.

Again, make sure you understand the potential problems enabling exec can cause. There are also other ways of doing this such as running php from the exec command (path/to/php my_script). These can pose much greater security risks if they are not properly coded.

Lastly, this should be run on user or administrator initiated event, and not on events such as page views. This could spawn a huge number of processes if it is ever allowed to run based on every page view or something similar.

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2 Comments:
  1. Jonathan 29 Jun, 2009

    Are the two scripts on different machines? Why not simply call the php CLI from exec?

  2. jestep 29 Jun, 2009

    In this case they were.

    Normally I would go with php cli:
    php -f /path/to/page > /dev/null &

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