Andrew Hudson - Fedora™ Unleashed, 2008 edition

You perform runtime configuration of your server with configuration directives, which are commands that set options for the httpddaemon. The directives are used to tell the server about various options you want to enable, such as the location of files important to the server configuration and operation. Apache supports nearly 300 configuration directives with the following syntax:

directive option option...

Each directive is specified on a single line. See the following sections for some sample directives and how to use them. Some directives set only a value such as a filename, whereas others enable you to specify various options. Some special directives, called sections , look like HTML tags. Section directives are surrounded by angle brackets, such as < directive >. Sections usually enclose a group of directives that apply only to the directory specified in the section:

somedir/in/your/tree >

directive option option

directive option option

All sections are closed with a matching section tag that looks like this: </ directive >. Note that section tags, like any other directives, are specified one per line.

After installing and starting Apache, you'll find an index of directives at http://localhost/manual/mod/directives.html.

Most of the default settings in the config file are okay to keep, particularly if you've installed the server in a default location and aren't doing anything unusual on your server. In general, if you don't understand what a particular directive is for, you should leave it set to the default value.

The following sections describe some of the configuration file settings you might want to change concerning operation of your server.

The ServerRootdirective sets the absolute path to your server directory. This directive tells the server where to find all the resources and configuration files. Many of these resources are specified in the configuration files relative to the ServerRootdirectory.

Your ServerRootdirective should be set to /etc/httpdif you installed the RPM or /usr/local/apache(or whatever directory you chose when you compiled Apache) if you installed from the source.

The Listendirective indicates on which port you want your server to run. By default, this is set to 80, which is the standard HTTP port number. You might want to run your server on another port — for example, when running a test server that you don't want people to find by accident. Don't confuse this with real security! See the "File System Authentication and Access Control" section for more information about how to secure parts of your web server.

The Userand Groupdirectives should be set to the UID and group ID ( GID ) the server uses to process requests. In Fedora, set these configurations to a user with few or no privileges. In this case, they're set to user apacheand group apache— a user defined specifically to run Apache. If you want to use a different UID or GID, be aware that the server runs with the permissions of the user and group set here. That means in the event of a security breach, whether on the server or (more likely) in your own CGI programs, those programs run with the assigned UID. If the server runs as root or some other privileged user, someone can exploit the security holes and do nasty things to your site. Always think in terms of the specified user running a command such as rm -rf /because that would wipe all files from your system. That should convince you that leaving apacheas a user with no privileges is probably a good thing.

Instead of using names to specify the Userand Groupdirectives, you can specify them with the UID and GID numbers. If you use numbers, be sure that the numbers you specify correspond to the user and group you want and that they're preceded by the pound (#) symbol.

Here's how these directives look if specified by name:

User apache

Group apache

Here's the same specification by UID and GID:

User #48

Group #48

If you find a user on your system (other than root) with a UID and GID of 0, your system has been compromised by a malicious user.

The ServerAdmindirective should be set to the address of the webmaster managing the server. This address should be a valid email address or alias, such as webmaster@gnulix.org, because this address is returned to a visitor when a problem occurs on the server.

The ServerName directive sets the hostname that the server returns. Set it to a fully qualified domain name (FQDN). For example, set it to www.your.domain rather than simply www. This is particularly important if this machine will be accessible from the Internet rather than just on your local network.

You don't need to set this unless you want a name other than the machine's canonical name returned. If this value isn't set, the server will figure out the name by itself and set it to its canonical name. However, you might want the server to return a friendlier address, such as www.your.domain . Whatever you do, ServerName should be a real domain name service (DNS) name for your network. If you're administering your own DNS, remember to add an alias for your host. If someone else manages the DNS for you, ask that person to set this name for you.

Set this directive to the absolute path of your document tree, which is the top directory from which Apache serves files. By default, it's set to /var/www/html/usage. If you built the source code yourself, DocumentRootis set to /usr/local/apache/htdocs(if you didn't choose another directory when you compiled Apache). Prior to version 1.3.4, this directive appears in srm.conf.

The UserDirdirective disables or enables and defines the directory (relative to a local user's home directory) where that user can put public HTML documents. It's relative because each user has her own HTML directory. This setting is disabled by default but can be enabled to store user web content under any directory.

The default setting for this directive, if enabled, is public_html. Each user can create a directory called public_htmlunder her home directory, and HTML documents placed in that directory are available as http://servername / ~ username , where username is the username of the particular user. Prior to version Apache version 1.3.4, this directive appears in srm.conf.

The DirectoryIndexdirective indicates which file should be served as the index for a directory, such as which file should be served if the URL http:// servername/_SomeDirectory /is requested.

It's often useful to put a list of files here so that if index.html(the default value) isn't found, another file can be served instead. The most useful application of this is to have a CGI program run as the default action in a directory. If you have users who make their web pages on Windows, you might want to add index.htmas well. In that case, the directive would look like DirectoryIndex index.html index.cgi index.htm. Prior to version 1.3.4, this directive appears in srm.conf.