SlickStack uses PHP-FPM to execute WordPress and other approved PHP requests passed from Nginx.

PHP-FPM packages, extensions, configuration files, process limits, OPcache settings, permissions, restarts, and basic service recovery are managed by SlickStack. The standard layout uses one local PHP version and one www pool for the production, staging, and development sites on the server.

• PHP versions
• Configuration files
• Installation behavior
• Nginx connection
• RAM autotuning
• PHP settings
• PHP extensions
• OPcache
• Restarts and recovery
• Scope

SlickStack selects the PHP version from the detected Ubuntu LTS version:

The installer also sets the matching PHP CLI binary as the system default.

An Ubuntu release remaining accepted by the SlickStack installer does not mean its bundled PHP branch still receives security fixes from the PHP project. New servers should normally use Ubuntu 24.04 and PHP 8.3. Older accepted combinations are retained for existing SlickStack servers and should be upgraded deliberately rather than treated as equivalent new-install choices.

For the active PHP version, SlickStack installs and manages:

/etc/php/<version>/fpm/php.ini
/etc/php/<version>/cli/php.ini
/etc/php/<version>/fpm/php-fpm.conf
/etc/php/<version>/fpm/pool.d/www.conf

PHP 8.3 also uses a separate managed OPcache file:

/etc/php/8.3/mods-available/opcache.ini

PHP-FPM and PHP runtime errors are written to:

/var/www/logs/php-error.log

The same generated php.ini is installed for both PHP-FPM and PHP CLI so common resource, upload, serialization, socket, and security settings remain aligned.

ss-install-php-config retrieves the appropriate boilerplates, applies current ss-config values, autotunes resource settings, installs the generated files, resets permissions, and restarts PHP-FPM.

The relevant commands are:

sudo bash /var/www/ss-install-php-packages
sudo bash /var/www/ss-install-php-config
sudo bash /var/www/ss-restart-php
sudo bash /var/www/ss-purge-opcache

Direct edits under /etc/php/ may be replaced the next time ss-install or ss-install-php-config runs. Persistent changes should use supported variables in ss-config whenever possible.

The standard www pool runs as www-data and listens locally over TCP:

127.0.0.1:9000

Nginx sends approved PHP requests to the same address using FastCGI. The PHP-FPM pool only allows local clients, clears inherited environment variables, and restricts executable script extensions to .php.

SlickStack uses this TCP listener instead of a Unix socket so the connection remains consistent across its production, staging, development, Adminer, and Multisite Nginx templates.

During ss-install-php-config, SlickStack detects total physical RAM and applies conservative PHP-FPM and OPcache limits. These values are designed to prevent small servers from spawning more PHP workers than their memory can safely support.

The current autotuner uses ondemand process management for every RAM tier, with a 10-second idle timeout. Worker and memory values are regenerated during installation, so manually editing those generated values is not persistent.

Common PHP settings can be controlled through ss-config, including:

• execution and input time limits
• memory, POST, and upload limits
• input variables and multipart body limits
• disabled PHP functions and classes
• allow_url_fopen and socket timeout behavior
• additional PHP extensions

Several baseline settings are intentionally enforced in the templates. User-level .user.ini files are disabled, PHP version exposure and displayed errors are disabled, errors are logged centrally, allow_url_include is disabled, and PHP uploads use the WordPress temporary directory under /var/www/html/wp-content/temp.

SlickStack installs PHP-FPM with the common extensions expected by WordPress, including database, image, internationalization, XML, archive, SOAP, SQLite, cURL, and multibyte string support.

Memcached extensions are also installed for WordPress object caching. Additional version-matched Ubuntu PHP packages may be requested with the PHP_EXTENSIONS variable in ss-config.

Custom extensions must exist in the configured Ubuntu repositories and must be compatible with the PHP version selected for that Ubuntu release.

OPcache is installed and enabled as part of the managed PHP environment. Its memory allocation is autotuned by RAM, while settings such as revalidation frequency, accelerated file limits, wasted-memory percentage, huge code pages, preload, and blacklist paths can be configured through ss-config.

PHP 8.3 includes configurable JIT settings, but the JIT buffer is set to 0 by default, which leaves JIT disabled.

To clear cached PHP scripts after a deployment or troubleshooting change, run:

sudo bash /var/www/ss-purge-opcache

Purging OPcache during a traffic spike can temporarily increase CPU and PHP-FPM load while scripts are compiled again.

ss-restart-php forcefully restarts the installed php*-fpm service. PHP-FPM is also restarted automatically after SlickStack installs new PHP packages or configuration files.

The SlickStack cron that runs every two minutes checks the version-specific PHP-FPM systemd service. If systemd reports that the service is inactive or failed, SlickStack runs ss-restart-php to recover from failures such as an out-of-memory kill.

This watchdog checks service state rather than application response quality. A PHP-FPM service that remains active but responds slowly or has exhausted its workers will not be restarted solely by this check.

The standard SlickStack configuration assumes:

• one PHP version selected by Ubuntu release
• one local www PHP-FPM pool
• one TCP listener on 127.0.0.1:9000
• shared PHP-FPM service for production, staging, and development

Multiple PHP versions, separate per-site pools, remote PHP-FPM servers, containerized PHP, and custom socket layouts are outside the standard managed configuration. Such changes require coordinated PHP-FPM and Nginx edits and may be overwritten by future SlickStack installations.