0

There is a commonly discussed method of starting a background process in PHP using the exec or shell_exec functionality.

I have had success with this in the past with batch email sending, and sending data to APIs in the background.

In a PHP page that you would call by ajax, you do something like this:

echo 'process running';
shell_exec('/usr/bin/php -q path_to_background_script.php  > /dev/null &' );
exit;

The background process normally runs as if called by the owner of the php user like a terminal process.

Recently however, under a FASTCGI system (ea-php56) I have found this method has stopped working.

Instead of one process beginning from one web-request to the calling page, I am getting the background script continually terminating and being re-spawned with a new process id. Interestingly, the only way to stop this continual re-spawning is to disable the line in the calling script that starts the process. The re-spawning stops immediately when you save the calling file without the call to the background script. This tells me that it is actually the calling script (requested by the browser) which is actually being re-spawned.

This is what the re-spawning looks like from the root terminal. Notice the PID changes everytime I look: 

[root@*** public_html]# ps -ef | grep php
*user*    725     1  7 23:53 ?        00:00:00 /opt/cpanel/ea-php56/root/usr/bin/php-cgi /home/*user*/public_html/background-script_exec.php
root       727 32411  0 23:53 pts/1    00:00:00 grep php
[root@dev public_html]# ps -ef | grep php
*user*    757     1  5 23:53 ?        00:00:00 /opt/cpanel/ea-php56/root/usr/bin/php-cgi /home/*user*/public_html/background-script_exec.php
root       759 32411  0 23:53 pts/1    00:00:00 grep php
[root@dev public_html]# ps -ef | grep php
*user*    781     1 12 23:54 ?        00:00:00 /opt/cpanel/ea-php56/root/usr/bin/php-cgi /home/*user*/public_html/background-script_exec.php

I have tried disabling "PHP-FPM service for cPanel Daemons". I have tried 'ignore_user_abort()'. fastcgi_finish_request() function is not available so could not try that. I have tried creating a shell script instead to call the background PHP script, which I call from the calling script - but this also does exactly the same thing.

Apart from disabling the ability to trigger background scripts from a PHP web-page, this new PHP FastCGI behaviour is creating an erratic re-spawning process that does not stop without intervention mentioned above. It has made shell_exec / exec functions unstable!

Problem seems similar to that reported here: php exec/shell_exec/system/popen/proc_open runs calling script itself infinite number of times on linux

but, suggestion reported here does not help in this case.

Community
  • 1
  • 1
Gordon Rouse
  • 301
  • 3
  • 6

1 Answers1

0

This seems to solve the problem. Using the 'php5-cli' instead of 'php'

shell_exec('/usr/bin/php5-cli path_to_background_script.php  > /dev/null &' );

I had early tried 'php-cli' and found it did not exist - I did not think to check to see that it was named differently!

If having similar problems, have a look for the php binaries:

>>ls /usr/bin/php*
>>/usr/bin/php  /usr/bin/php5  /usr/bin/php5-cli  /usr/bin/php-config  /usr/bin/phpize

use the one which is for command line, and it should then run properly.

-note that this issue was specifically on a linux cpanel easy-apache fastcgi-php system running on Centos.

Gordon Rouse
  • 301
  • 3
  • 6