Increasing the PHP memory_limit Setting

If you've built PHP applications for even a short period of time, chances are you've encountered this dreaded error:

PHP Fatal error: Allowed memory size of X bytes exhausted (tried to allocate Y bytes)

This error occurs when the executing PHP script consumes more memory than what has been allocated using PHP's memory_limit setting. Keep in mind this setting imposes a cap on each PHP process, meaning if the memory_limit setting was 128MB and there were four simultaneously executing PHP scripts with each requiring 100MB, then none would produce the above PHP fatal error because each was under the 128MB maximum memory allocation.

The memory_limit value is often set quite low, for instance to 128MB:

memory_limit = 128M

Because many web application servers are configured with much higher amounts of RAM than in years past, you can almost certainly increase the setting to 512 MB or even higher. This is typically done by changing the memory_limit setting found in your server's php.ini file.

Finding Your php.ini File

It would seem trivial to find your server's php.ini configuration file, however there is a catch. Modern PHP installations come with two php.ini files: one for use in conjunction with CLI-based PHP applications, and another for web-based PHP applications. If you SSH into the server and run the following command you'll be presented with the location of the php.ini file used for the former:

$ php --ini | grep Configuration
Configuration File (php.ini) Path: /etc/php/7.3/cli
Loaded Configuration File:         /etc/php/7.3/cli/php.ini

However if you instead use the find command you'll locate two php.ini files:

$ find . -name php.ini
./etc/php/7.3/fpm/php.ini
./etc/php/7.3/cli/php.ini

The php.ini file found in the fpm directory is used by PHP-FPM, so that's the version you'll want to modify. After making the change, restart your PHP-FPM daemon:

$ sudo service php7.3-fpm restart