Question

I am running php scripts in parallel on an AWS lamp server. Right now I have a cron job set up to run each script at 10 min intervals, and then the script is set to exit after running for 20mins. I limit the time each script runs to keep from running out of memory on the server. I have tried to plug the memory holes as best I can, but as I work on this, timing out the script is a good interim solution.

The problem is I get too many scripts running at the same time. So rather than use cron to run the scripts at set intervals, how can I script the server to

A) monitor how many instances of specific php script are running at any given moment

B) if that number drops below n (say 4 instances) the server would fire up another instance of the php script?

Thanks for the help still learning my way around linux!

Answer 1

The best way would likely be to write your own daemon which runs, forks child processes, monitors them, and will restart them as needed.

Take a look at http://php.net/manual/en/book.pcntl.php

However, in your case, there may be a simpler answer… Put a one minute crontab in place which calls your loader script, like this:

* * * * *  /usr/bin/php /path/to/loader.php

The loader script can be a simple shell script (or php script). Run this command in the shell. It will return the number of instances of the script you are running.

ps aux | grep "/usr/bin/php /path/to/thing/you/run.php" | grep -v grep | wc -l

If # instances > 3, then do not start one. Otherwise, start one. If in PHP, you can simply include the desired file. If in bash, just write /usr/bin/php /path/to/thing/you/run.php

Hope it helps some!