PHP-FPM - ERROR: failed to prepare the stderr pipe: Too many open files (24)

Symptoms

When you see these errors in one of the PHP-FRPM error log files at

/opt/cpanel/ea-php??/root/usr/var/log/php-fpm/error.log

Description 

Websites may not be loading and this error is seen:

PHP-FPM - ERROR: failed to prepare the stderr pipe: Too many open files (24)

Workaround

Increase rlimit_files and then rebuild the PHP-FPM configs and restart PHP-FPM by doing the following.

Modify

/var/cpanel/ApachePHPFPM/system_pool_defaults.yaml

and add this line

rlimit_files: 4096

then modify

/etc/security/limits.conf

and add the following

* soft nofile 4096
* hard nofile 4096

and then run the following

/scripts/php_fpm_config --rebuild
/scripts/restartsrv_apache_php_fpm --hard