The file httpd.conf is the main server-configuration file. First, copy httpd.conf-dist to httpd.conf and edit it. We only cover some of the more important options here; the file httpd.conf-dist is vastly commented.

The ServerType directive is used to specify how the server will run—either as a standalone daemon (as seen here) or from inetd. For various reasons, it’s usually best to run httpd in standalone mode. Otherwise, inetd must spawn a new instance of httpd for each incoming connection.

One tricky item here is the port number specification. You may wish to run httpd as a user other than root (that is, you may not have root access on the machine in question and wish to run httpd as yourself). In this case, you must use a port numbered 1024 or above. For example, if we specify:

Port 2112

we may run httpd as a regular user. In this case, HTTP URLs to this machine must be specified as in the following example:

If no port number is given in the URL (as is the usual case), port 80 is assumed.

With

DocumentRoot 
 /usr/local/httpd/htdocs

we specify the DocumentRoot directive, where documents to be provided via HTTP are stored. These documents are written in HTML.

For example, if someone were to access the URL:

the actual file accessed would be /usr/local/httpd/htdocs/fruits.html.

The UserDir directive specifies a directory each user may create in his home directory for storing public HTML files. For example, if we were to use the URL:

the actual file accessed would be ~mdw/public_html/linux-info.html.

The following lines enable the indexing features of httpd :

# If a URL is received with a directory but no filename, retrieve this
# file as the index (if it exists).
DirectoryIndex index.html

# Turn on 'fancy' directory indexes
IndexOptions FancyIndexing

In this case, if a browser attempts to access a directory URL, the file index.html in that directory is returned, if it exists. Otherwise, httpd generates a “fancy” index with icons representing various file types. Figure 5-2 shows an example of such an index.

Icons are assigned using the AddIcon directive, as seen here:

# Set up various icons for use with fancy indexes, by filename
# E.g., we use DocumentRoot/icons/movie.xbm for files ending
#     in .mpg and .qt
AddIcon /icons/movie.xbm .mpg
AddIcon /icons/back.xbm ..
AddIcon /icons/menu.xbm ^^DIRECTORY^^
AddIcon /icons/blank.xbm ^^BLANKICON^^
DefaultIcon 
 /icons/unknown.xbm

The icon filenames (such as /icons/movie.xbm) are relative to DocumentRoot by default. (There are other ways to specify pathnames to documents and icons—for example, by using aliases. This is discussed later.) There is also an AddIconByType directive, which lets you specify an icon for a document based on the document’s MIME type, and an AddIconByEncoding directive, which lets you specify an icon for a document based on the document’s encoding (i.e., whether and how it is compressed).

You can also specify an icon to be used when none of the above matches. This is done with the DefaultIcon directive.

The optional ReadmeName and HeaderName directives specify the names of files to be included in the index generated by httpd:

ReadmeName README
HeaderName HEADER

Here, if the file README.html exists in the current directory, it will be appended to the index. The file README will be appended if README.html does not exist. Likewise, HEADER.html or HEADER will be included at the top of the index generated by httpd. You can use these files to describe the contents of a particular directory when an index is requested by the browser:

# Local access filename.
AccessFileName .htaccess

# Default MIME type for documents.
DefaultType text/plain

The AccessFileName directive specifies the name of the local configuration file for each directory. (This is described later in this chapter.) The DefaultType directive specifies the MIME type for documents not listed in mime.types.

The following lines specify directories for useful files:

# Set location of icons.
Alias 
 /icons/ /usr/local/html/icons/

# Set location of CGI binaries.
ScriptAlias 
 /cgi-bin/ /usr/local/httpd/cgi-bin/

The Alias directive specifies an alias for any of the files that would normally not be visible through the web server. Earlier, we used the AddIcon directive to set icon names using pathnames such as /icons/movie.xbm. Here, we specify that the pathname /icons/ should be translated to /usr/local/html/icons/. Therefore, the various icon files should be stored in the latter directory. You can use Alias to set aliases for other pathnames as well.

The ScriptAlias directive is similar, but it sets the actual location of CGI scripts on the system. Here, we wish to store scripts in the directory /usr/local/httpd/cgi-bin/. Any time a URL is used with a leading directory component of /cgi-bin/, it is translated into the actual directory name. More information on CGI and scripts is included in the book CGI Programming with Perl, by Scott Guelich, Shishir Gundavaram, and Gunther Birznieks (O’Reilly).

<Directory> entries specify the options and attributes for a particular directory, as in the following:

# Set options for the cgi-bin script directory.
<Directory /usr/local/html/cgi-bin>
Options Indexes FollowSymLinks
</Directory>

Here, we specify that the CGI script directory should have the access options Indexes and FollowSymLinks. A number of access options are available. These include the following:

There are other options as well; see the httpd documentation for details.

Next, we configure a very strict default configuration for the complete filesystem.

# Default configuration
<Directory />

# Turn all features off
Options None

# Do not allow local files to override configuration.
AllowOverride None

# In fact, do not allow access 
 to any of the files.
Order allow,deny
Deny from all

</Directory>

We have started by denying access to the complete filesystem. Now we proceed to explicitly allow access to the files we want Apache to serve. At the very least we need to enable several options and other attributes for /usr/local/httpd/htdocs, the directory containing our HTML documents. This configuration applies to the base directory and the subdirectories below it.

# Configuration for the web server files.
<Directory /usr/local/httpd/htdocs>

# Allow automatic indexes and controlled symbolic links.
Options Indexes SymLinksIfOwnerMatch

# Allow the local access file, .htaccess, to override
# any attributes listed here.
AllowOverride All

# Allow unrestricted access to files in this directory.
Order allow,deny
Allow from all

</Directory>

Here, we turn on the Indexes and SymLinksIfOwnerMatch options for this directory. The AllowOverride option allows the local access file (named .htaccess) in each directory that contains documents to override any of the attributes given here. The .htaccess file has essentially the same format as the global configuration but applies only to the directory in which it is located. This way, we can specify attributes for particular directories by including a .htaccess file in those directories instead of listing the attributes in the global file.

The primary use for local access files is to allow individual users to set the access permissions for personal HTML directories (such as ~/public_html) without having to ask the system administrator to modify the global access file. Security issues are associated with this, however. For example, a user might enable access permissions in her own directory such that any browser can run expensive server-side CGI scripts. If you disable the AllowOverride feature, users cannot get around the access attributes specified in the global configuration. This can be done by using:

AllowOverride None

which effectively disables local .htaccess files.

The <Limit GET> field is used to specify access rules for browsers attempting to retrieve documents from this server. In this case, we specify Order allow,deny, which means that allow rules should be evaluated before deny rules. We then instate the rule Allow from all, which simply means any host may retrieve documents from the server. If you wish to deny access from a particular machine or domain, you could add the line:

Deny from ..nuts.com biffnet.biffs-house.us

The first entry denies access from all sites in the nuts.com domain. The second denies access from the site biffnet.biffs-house.us.

The srm.conf and access.conf files should be kept empty. In earlier Apache versions, srm.conf stood for Server Resource Map and listed facilities provided by the server, and access.conf controlled access to Apache files. All the resources originally placed in those files are now listed in the main httpd .conf file.

Now you’re ready to run httpd, allowing your machine to service HTTP URLs. As mentioned previously, you can run httpd from inetd or as a standalone server. Here, we describe how to run httpd in standalone mode.

All that’s required to start httpd is to run the command:

httpd -f configuration-file

where configuration-file is the pathname of httpd.conf. For example:

/usr/sbin/httpd -f /etc/httpd/httpd.conf

starts up httpd, with configuration files found in /etc/httpd.

Watch the httpd error logs (the location of which is given in httpd.conf) for any errors that might occur when trying to start up the server or when accessing documents. Remember you must run httpd as root if it is to use a port numbered 1023 or less. Once you have httpd working to your satisfaction, you can start it automatically at boot time by including the appropriate httpd command line in one of your system rc files, such as /etc/init.d/boot.local.

Apache also provides a utility called apachectl that is more convienent for starting, stopping, and reloading the httpd process. In particular, calling:

apachectl configtest

is a good way of checking whether the configuration file is actually correct before starting the server. Finally, we should mention that you can also start, restart, and stop Apache by using /etc/init.d/apache plus one of the parameters start, restart, or stop.

Of course, in order to request documents via HTTP from your browser, you’ll need to write them, something that we cannot cover in this book. Two good sources for HTML information are the O’Reilly books HTML & XML: The Definitive Guide and HTML Pocket Reference by Jennifer Niederst. To set up a back-end database to your web server, start with Chapter 25.