Nginx Insight Guide How To Guide For Nginx & PHP-FPM Debugging

Nginx and PHP-FPM debugging is a last resort to figure out issues you may have with Nginx and PHP-FPM which normal logs can no provide any insight into.

If you have a lot of free disk space, you can enable debug nginx version and compile a nginx debug build of nginx with NGINX_DEBUG=y variable via persistent config /etc/centminmod/custom_config.inc outlined at centminmod.com/upgrade.html#persistent so place in file /etc/centminmod/custom_config.inc

Code:

NGINX_DEBUG=y

then recompile nginx via centmin.sh menu option 4 and then in your nginx error_log directive add debug option outlined at debugging log and restart nginx and check logs

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They will be very very very verbose and lot alot to disk usage logged to error logs, so ensure you have a lot of disk free space.

You can minimise this by limiting it to specific ip based client connections too

After debugging is done, reverse the debug now by setting NGINX_DEBUG=n and recompile Nginx again

Also check output for these commands - post output wrapped in CODE tags

Code (Text):

php -v

Code (Text):

php -m

Code (Text):

php-config --configure-options

Examples with strace below:

• Debugging Stuck PHP-FPM Process With Strace - Coffee Coder
• Why you should be using strace – Brandon Wamboldt
• Linux application/script debugging with 'strace'
• markus-perl/php-strace · GitHub

With gdb backtrace and PHP debug compiled mode where centmin.sh has a PHPDEBUGMODE variable which you can set to PHPDEBUGMODE=y and recompile php via centmin.sh menu option 5 to enable debug mode for PHP-FPM. After troubleshooting set PHPDEBUGMODE=n and recompile php via centmin.sh menu option 5 again to disable debug mode.

Code:

PHPDEBUGMODE=n # --enable-debug PHP compile flag

• PHP :: Generating a gdb backtrace

Centmin Mod is provide as is, so short of scripted related bugs or issues, any further optimisation to the web stack components - nginx, php-fpm, mariadb mysql, csf firewall etc or web app specific configurations are left to the Centmin Mod user to deal with. So I do not provide any free support for such. Interpretation of the debug logs and outputs are left for you to figure out.

You'll need to tune your PHP-FPM settings and this is left up to end user to do but here's a thread for starters to enable php status page output outlined at PHP-FPM - CentminMod.com LEMP Nginx web stack for CentOS and PHP-FPM - pm.max_children which outlines the official PHP-FPM config documentation as well. Also read How to troubleshoot & optimize PHP-FPM server?