Ubuntu LTS (Dapper) uses a Debian based Apache layout which differs from the 'classic' layout you may have encountered from other distributions.
The differences are not huge and, indeed, help in configuring and deploying websites.
Assuming you have used apt-get to install Apache, move into the config folder and have a look:
cd /etc/apache2 ls
You will see this:
The folders are highlighted in blue. Let's look at those first:
Inside here will be files containing the configurations for each site you want to serve. Have a look now and see that there is one site (default) available. Although we'll look in detail later at the sites configuration files, you can take a look now:
As I say, we'll look in more detail at the actual configuration later.
Do note that a file in sites-available does not mean they are active. You need to enable them first. Which brings us to...
These are symlinks to whichever sites you want to enable.
So if you had 5 sites configured and available (i.e. in the sites-available folder), nothing would happen until you enabled them to be served.
Have a look at the default contents:
ls -l sites-enabled
You will see this:
Apart from the horrible colour format of the symlink, you will see it is named 000-default and points to an 'available' site at /etc/apache2/sites-available/default.
This means that the 'default' site has been enabled. Without the symlink in this folder it would remain available (in the sites-available folder) but not active.
The other thing to note is the naming. It's possible for a domain to point to your Slice IP but have no site configuration file. In these cases, the first enabled site (alphabetically) will be displayed i.e. 000-default's config will be used.
Well, I guess you get the idea already but this folder holds the modules that are available to be loaded.
Have a look:
A fair list is available from our base install but remember that they are not all enabled, merely available for use. Which brings us to...
This contains a list of symlinks to the modules that are enabled. Have a look and compare it to the list of modules available:
This list is a lot shorter than the list of available modules (meaning not all the available modules are enabled) and includes php5.conf - which is handy as we installed PHP5 earlier.
a2en and a2dis
Being a good sysadmin, we like to get stuck in and create our vhosts and now we know how the symlinks work we could go ahead and 'ln -s' until all our sites are enabled.
However, there are some commands that make this process much easier.
They are a2enmod, a2ensite, a2dismod and a2dissite.
This will delete the symlink to a site you have previously enabled.
For example, let's disable the default site:
sudo a2dissite default
The symlink in sites-enabled has been deleted and the output is as follows:
Site default disabled; run /etc/init.d/apache2 reload to fully disable.
Reload Apache as indicated to ensure the site is fully disabled. You can test this by visiting your Slice IP address. Instead of the nice 'It Works!' page, you will now get a 404 Not Found message.
Let's enable the default site again:
sudo a2ensite default
Site default installed; run /etc/init.d/apache2 reload to enable.
Reload Apache and visit your Slice IP - the default is now being served again.
In the same way as just shown, a2dismod will disable any modules you have previously enabled:
sudo a2dismod php5
Module php5 disabled; run /etc/init.d/apache2 force-reload to fully disable.
That will disable the php5 module and if you look in the mods-enabled folder, you will see that the symlinks php5.conf and php5.load have been deleted.
I reckon you've got it now, but to enable the php5 module simply enter:
sudo a2enmod php5
Module php5 installed; run /etc/init.d/apache2 force-reload to enable.
And a quick check will show that indeed, the php5.conf and php5.load symlinks are back in the mods-enabled folder.
Don't forget to reload Apache after each site or module change.
We'll talk about site configurations and the main apache2.conf file in the next articles.