Php-Fpm 7 server reached pm.max_children

To adjust the settings, you’ll need to find your php-fpm.conf or www.conf depending on what version of PHP-FPM you have installed. In my case, I had to edit /etc/php/7.0/fpm/pool.d/www.conf. You’ll want to look for the following settings and make adjustments based on your server specs:

[php-fpm-pool-settings] pm = dynamic pm.max_children = 25 pm.start_servers = 10 pm.min_spare_servers = 5 pm.max_spare_servers = 20 pm.max_requests = 500 

To get an idea of what to use for the pm.max_children, you can use this calculation: pm.max_children = Total RAM dedicated to the web server / Max child process size. Remember to leave some RAM for extra services you have running on your system.

Depending on the name of your service, you can try on of the following:

sudo systemctl restart php-fpm sudo systemctl restart php7.0-fpm 

the following command will help us to determine the memory used by each (PHP-FPM) child process:

ps -ylC php-fpm --sort:rss 

You can check an average memory usage by single PHP-FPM process with this handy command:

ps --no-headers -o "rss,cmd" -C php-fpm | awk '{ sum+=$1 } END { printf ("%d%s\n", sum/NR/1024,"M") }' 

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This command is supported by Php-Fpm 7. Use this ps -ylC php-fpm7.0 --sort:rss

For php 7.3 use this command:

ps -ylC php-fpm7.3 --sort:rss 

I had a bit different case but thought it to be worth mentioning here. In my case the reason behind the server reached pm.max_children setting error was invalid redirection configuration. That put my WordPress process into an infinite redirection loop that took all the PHP processes of the machine. From the client perspective the browser threw 504 Gateway timed out error.

In my Nginx configuration I had a redirection from a naked domain to www:

server_name akselipalen.com; return 301 http://www.akselipalen.com; 

I had to add $request_uri to the url like this:

server_name akselipalen.com; return 301 http://www.akselipalen.com$request_uri; 

The actual reason is a bit unknown but it seems that WordPress often wants to redirect to another URL. In my case, I had also just moved the WordPress instance from blog.akselipalen.com to www.akselipalen.com from the dashboard settings and ensured the correct new siteurl and home values via mysql console. The correct settings did not help the problem until I made the update to the Nginx redirection config.