Linux Setup

Linux is the most common environment for deployed PHP applications, and it is also a common local development environment through native Linux, WSL, containers, and dev containers.

The useful skill is not memorising one distribution's package names. It is proving which PHP runtime is active, where configuration is loaded from, which extensions are enabled, and whether CLI PHP and PHP-FPM match the project.

Package Managers And PHP Versions

Linux distributions install PHP through package managers.

Debian and Ubuntu use apt:

apt-cache policy php
php -v

Fedora, RHEL, and similar systems use dnf:

dnf list installed "php*"
php -v

Arch uses pacman:

pacman -Qs php
php -v

Use the package manager to understand what is installed, but use php -v to prove what your shell actually runs.

Find The Active Binary

Check the active CLI PHP binary:

which php
which -a php
php -v

which -a php is useful when several PHP binaries are visible on PATH. The first one is the one your shell runs.

If the project runs in Docker, WSL, or a remote server, run these checks inside that environment. Your host machine's PHP may be irrelevant.

Configuration Paths

Linux package layouts vary by distribution. Debian-style systems often use versioned directories such as:

/etc/php/8.3/cli/php.ini
/etc/php/8.3/fpm/php.ini
/etc/php/8.3/mods-available
/etc/php/8.3/cli/conf.d
/etc/php/8.3/fpm/conf.d

Other distributions may use paths such as:

/etc/php.ini
/etc/php.d

The reliable command is:

php --ini

Also check:

php -i | grep "Loaded Configuration File"
php -i | grep "Scan this dir"

CLI and FPM may load different php.ini files. A setting can be correct for terminal commands and wrong for web requests.

Extensions

List loaded extensions:

php -m
php -m | grep mbstring
php -m | grep pdo

Common project extensions include:

mbstring
intl
pdo
pdo_mysql
curl
zip
gd
opcache
redis

From PHP:

<?php

declare(strict_types=1);

foreach (['mbstring', 'intl', 'pdo', 'opcache'] as $extension) {
    echo $extension . ': ';
    echo extension_loaded($extension) ? 'loaded' : 'missing';
    echo PHP_EOL;
}

// Prints:
// mbstring: loaded
// intl: loaded
// pdo: loaded
// opcache: loaded

If an extension is installed but not loaded, inspect the .ini files under the active configuration scan directory.

PHP-FPM Services

Production-style Linux PHP commonly uses PHP-FPM behind Nginx, Apache, or Caddy.

Check services with systemd:

systemctl status php-fpm
systemctl status php8.3-fpm
systemctl list-units "php*"

The exact service name depends on the distribution and PHP version.

Check FPM configuration and pools:

php-fpm -v
php-fpm -tt

On some systems the command may be versioned, such as php-fpm8.3.

Do not assume CLI PHP and FPM are the same runtime. Check both when debugging web-only problems.

Permissions And Users

Linux services run as users. PHP-FPM may run as www-data, nginx, apache, or a project-specific user.

Permission bugs often look like application bugs:

• uploads fail
• cache cannot be written
• logs do not appear
• sessions fail
• generated files are owned by the wrong user

Useful checks:

whoami
id
ps aux | grep php-fpm
ls -la storage

The user running CLI commands may not be the same user running web requests.

Composer Platform Checks

Run the project-level platform check:

composer check-platform-reqs

If this fails, compare:

which php
php -v
php -m
php --ini

Composer errors about missing extensions usually mean the active CLI runtime does not match the project requirements.

Linux Setup Checklist

For a Linux setup note, record:

1. Distribution and version.
2. Whether PHP runs on the host, in WSL, in Docker, or on a remote server.
3. What which php and php -v return.
4. What php --ini returns.
5. Which extensions are required.
6. Whether PHP-FPM is used and what the service is called.
7. Which user runs PHP-FPM.
8. Whether composer check-platform-reqs passes.

This checklist gives you enough information to debug setup, extension, and permission issues without guessing.

What You Should Be Able To Do

After this lesson, you should be able to verify Linux PHP from the terminal, inspect configuration paths, check extensions, distinguish CLI from PHP-FPM, identify service users, and confirm Composer platform requirements.

For junior PHP work, this matters because Linux is where many PHP applications ultimately run. Knowing how to inspect the runtime makes you useful in both development and deployment conversations.