You need to set open file descriptor rlimit for the PHP master process. The default value is system defined but one can increase it as per needs.
php-fpm too many open files error and solution
Edit php-fpm.conf# vi /etc/php/7.0/fpm/php-fpm.conf
Find rlimit_files;rlimit_files = 1024
And update it as follows (or as per your need):rlimit_files = 4096
Save and close the file. Restart php7-0.fpm, run:# systemctl restart php7.0-fpm
Increase FD limit at the OS level
Find user/group name:$ grep ^user /etc/php/7.0/fpm/pool.d/www.conf$ grep ^group /etc/php/7.0/fpm/pool.d/www.conf
www-data www-data
Edit /etc/security/limits.conf, enter:# vi /etc/security/limits.conf
Append as follows (replace user/group name with your actual names):
www-data soft nofile 4096 www-data hard nofile 4096
Restart required process. Save and close the file. Verify it:$ su - www-data
To see the hard and soft values, issue the command as follows:$ ulimit -Hn$ ulimit -Sn
Reference: www.cyberciti.biz
