Running different PHP applications as different users

Often you run different web applications on the same web servers. For security reasons, it is strongly recommended to run them in separate PHP-FPM processes under different user accounts. This way permissions can be set so that the user account of one PHP application, cannot access the files from another PHP application. Also open_basedir can be set so that accessing any files outside the base directory becomes impossible.

To create a separate PHP-FPM process for a PHP application on Debian Stretch with PHP 7.0, create a file /etc/php/7.0/fpm/pool.d/webapp.conf with these contents:

user = webapp_php
group = webapp_php
listen = /run/php/php7.0-webapp-fpm.sock
listen.owner = www-data = www-data
pm = dynamic
pm.max_children = 12
pm.start_servers = 1
pm.min_spare_servers = 1
pm.max_spare_servers = 2
pm.max_requests = 5000
rlimit_core = unlimited
php_admin_value[open_basedir] = /home/webapp/public_html

Replace webapp by a unique name for your web application. You can actually copy the default www.conf file and adapt it to your needs.

Create the webapp_php, with /bin/false as shell and login disabled to secure it against login attacks:

# adduser --system --disabled-login webapp_php --shell /bin/false --no-create-home --home /home/webapp webapp_php

In the above example the webapp is located in /home/webapp, but you can of course also use a directory somewhere in /var/www.

I strongly recommend against making all your PHP files in /home/webapp owned by webapp_php. This is a dangerous situation, because PHP can overwrite the code itself. This makes it possible for malware to overwrite your PHP files with malicious code. Only make the directories where PHP really needs to be able to write into (for example a directory where files uploaded in your web applications are stored), writable for the webapp_php user. Your code itself should be owned by a different user than webapp_php. It can be a dedicated user account, or just root.

Finally we need to configure Apache to contact the right php-fpm instance for the web application. Create a file /etc/apache2/conf-available/php7.0-webapp-fpm.conf:

<Directory /home/webapp/public_html>

# Redirect to local php-fpm if mod_php is not available
    <IfModule proxy_fcgi_module>
        # Enable http authorization headers
        <IfModule setenvif_module>
        SetEnvIfNoCase ^Authorization$ "(. )" HTTP_AUTHORIZATION=$1

        <FilesMatch ". \.ph(p[3457]?|t|tml)$">
            SetHandler "proxy:unix:/run/php/php7.0-webapp-fpm.sock|fcgi://localhost-webapp"
        <FilesMatch ". \.phps$">
            # Deny access to raw php sources by default
            # To re-enable it's recommended to enable access to the files
            # only in specific virtual host or directory
            Require all denied
        # Deny access to files without filename (e.g. '.php')
        <FilesMatch "^\.ph(p[3457]?|t|tml|ps)$">
            Require all denied

This file is based on the default php7.0-fpm.conf. You will need to create a symlink to make sure this gets activated:

# cd /etc/apache2/conf-enabled
# ln -s ../conf-available/php7.0-webapp-fpm.conf .

Now restart your Apache and PHP-FPM services and you should be ready. You can see the user your code in /home/webapp/public_html is being run as in the output of the phpinfo() function.

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