How to install PHP on Linux

PHP 5 installation

We will set up PHP as a shared module, being loaded into Apache2 dynamically during the server startup. These instructions are known to work for PHP versions: 5.0.4 through 5.2.1 .
prerequisites

At this point Apache web server must be installed. If you want MySQL support in PHP, MySQL server also must have been installed prior to the next steps.
download source

Get the source from http://www.php.net/downloads.php . At the time of writing this tutorial the best available version was 5.1.5 ( php-5.1.5.tar.gz ).
unpack, configure, compile

Go to the directory whith the downloaded file and enter:
tar -xzf php-5.2.1.tar.gz
cd php-5.2.1
./configure --prefix=/usr/local/php --with-apxs2=/usr/local/apache2/bin/apxs --with-mysql=/usr/local/mysql

The configuration options ought to be self-explaining; --prefix specifies the location where PHP is to be installed, --with-apxs2 with correct path pointing to bin/apxs in the Apache installation directory is mandatory for the installator to work. Since PHP 5, you need to explicitly bundle PHP with MySQL by --with-mysql directive (make sure you specified path to where MySQL is installed on your system).

There are many other options which turn on additional features. For all available configuration options and their default values type ./configure --help.

Tip: If you are performing an upgrade, you may want to copy config.nice from the old PHP installation directory (if available) to where you unpacked the new PHP tarball file. Run ./config.nice instead of ./configure. This way all the previous configure options will be applied to the new installation effortlessly.

Once you entered ./configure with all the options you need, compile and install the software:
make
make install
edit httpd.conf

All necessary changes to httpd.conf (Apache configuration file) should have already been made automatically during the installation, so usually you need not do anything. Anyways, check that following lines were added to your httpd.conf file:
LoadModule php5_module modules/libphp5.so
AddType application/x-httpd-php .php

If not, add them manually.
create php.ini file

Importanly, you have to create php.ini configuration file. Choose one of the pre-made files (preferably php.ini-recommended) residing inside the php-5.2.1/ directory (it's the folder to which the downloaded archive was extracted). Copy the file to the lib/ directory in the PHP installation directory.
cp php-5.2.1/php.ini-recommended /usr/local/php/lib/php.ini

If you need to, edit the php.ini file:
vi /usr/local/php/lib/php.ini

However, the default settings should work for everyone in most cases.
restart apache server

After everything is set up, restart Apache:
/usr/local/bin/apachectl stop
/usr/local/bin/apachectl start

Alternatively, simply enter:
/usr/local/bin/apachectl restart