Run PHP Applications under CGI with Apache on Ubuntu 9.10 (Karmic)

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In most cases, we recommend using the mod_php module to run PHP scripts with the Apache HTTP server. This embeds a PHP interpreter in the web server process and makes running PHP applications easy. The embedded interpreter approach, however, is not without challenges. When the PHP interpreter is embedded in the web server process, PHP scripts are executed by and with the permissions of the web server’s user. In smaller deployments, this is perfectly acceptable, but in larger deployments and operations it can create security risks. While Apache’s itk message passing module (mpm) makes it possible to run Apache processes under user processes in a per-virtual host setup, this is incompatible with the embedded interpreter. The itk module is compatible with PHP running as a CGI process.

Additionally, in our experience, mod_php is incompatible with the mod_rails or Phusion Passenger method of running Ruby On Rails. In these cases, if you want to run PHP and Rails applications within a single instance of Apache, you must run PHP scripts as CGI processes using the method outlined below.

Before beginning this guide we assume that you’ve completed the Setting Up and Securing a Compute Instance. If you are new to Linux server administration, we recommend considering the beginner’s guide, and the article concerning systems administration basics. If you’re interested in learning more about the Apache HTTP server, we encourage you to consider our extensive documentation on Apache configuration.

Enable Universe Repositories

Edit your /etc/apt/sources.list file to enable the “universe” repositories by removing the hash symbol in front of the universe lines. The file should resemble the following example:

File: /etc/apt/sources.list
## main & restricted repositories
deb karmic main restricted
deb-src karmic main restricted

deb karmic-security main restricted
deb-src karmic-security main restricted

## universe repositories
deb karmic universe
deb-src karmic universe
deb karmic-updates universe
deb-src karmic-updates universe

deb karmic-security universe
deb-src karmic-security universe

When you have saved this file, issue the following command to refresh your system’s package database:

apt-get update
apt-get upgrade

We’re now ready to begin installing Apache with PHP-CGI.

Installing Apache and PHP

If you have not already installed the Apache HTTP server, issue the following command to install the packages for Apache:

apt-get install apache2

You can now configure virtual hosting in accordance with the needs of your server. To install the PHP CGI binaries, issue the following command:

apt-get install php5-cgi

When this process completes, we can configure Apache to hand PHP scripts to the CGI process for rendering these scripts.

Configure Apache for PHP CGI

In order to set up Apache to use PHP-CGI on Ubuntu systems, you must enable the mod_actions module. Issue the following command:

a2enmod actions

The required directives can be set anywhere in Apache’s configuration tree. We recommend creating the php-cgi.conf file in Apache’s conf.d/ directory and setting these variables there. For Ubuntu systems, this is located at /etc/apache2/conf.d/. You may also choose to place these settings in your /etc/apache2/httpd.conf file. Regardless of their location, the relevant settings are:

File: Apache Configuration Block
ScriptAlias /local-bin /usr/bin
AddHandler application/x-httpd-php5 php
Action application/x-httpd-php5 /local-bin/php-cgi

In this example, the path to the php-cgi binary is /usr/bin/php-cgi. All files with the php extension will be handed to the PHP CGI binary.

You may also choose to put these configuration directives within a virtual hosting block. If you do not have mod_php enabled or installed, you can use this to selectively enable PHP for certain virtual hosts. Furthermore, if your deployment requires multiple versions of PHP, you can specify virtual host specific handlers by specifying paths to various versions of php-cgi.

The configuration file for the CGI executable of PHP is located at /etc/php5/cgi/php.ini. You can modify this file to suit the needs of your deployment.

File: /etc/php5/cgi/php.ini
display_errors = Off
log_errors = On
error_log = /var/log/php.log
max_execution_time = 30
memory_limit = 64M
register_globals = Off

If you need support for MySQL in PHP, then you must install the php5-mysql package with the following command:

apt-get install php5-mysql

When php-cgi is configured, you can now safely enable the itk message passing module for Apache. The installation process for itk will restart the Apache process. If you choose to use PHP CGI with the default or existing message passing module, then restart Apache by issuing the following command:

/etc/init.d/apache2 restart

Enabling the “itk” Message Passing Module

The default Apache configuration uses a message passing module called worker which uses a threaded approach to efficiently handling HTTP requests. An alternative MPM is prefork which does not use threads and is compatible with non-thread-safe libraries. Both the worker and prefork modules require that all requests be handled by a process running under a user with particular permissions. On Ubuntu systems, Apache processes run under the www-data user.

This may not be ideal if you have multiple users running publicly accessible scripts on your server. In some of these cases it is prudent to isolate virtual hosts under specific user accounts using an alternative message passing module, known as itk or mpm-itk. Functionally, mpm-itk is quite similar to prefork however itk can processes requests for each virtual host or each site under a specified user account. This useful in situations where you’re hosting a number of distinct sites and you need to isolate sites on the basis of user privileges.

Begin by installing the mpm-itk module:

apt-get install apache2-mpm-itk

Now, in the <VirtualHost > entries for your sites (the site-specific files in /etc/apache2/sites-avalible/) add the following sub-block:

File: Apache Virtual Hosting Configuration Block
<IfModule mpm_itk_module>
   AssignUserId webeditor webgroup

In this example, webeditor is the name of the user of the specific site in question, and webgroup is the name of the user group that “owns” the web server related files and processes for this host. Remember that you must create the user accounts and groups using the useradd command. Consider our documentation of user groups and permissions for more information about creating the necessary users and groups.

More Information

You may wish to consult the following resources for additional information on this topic. While these are provided in the hope that they will be useful, please note that we cannot vouch for the accuracy or timeliness of externally hosted materials.

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