Apache HOWTO documentation

How to:

redirect an entire server or directory to a single URL
reset your log files
stop/restrict robots

How to redirect an entire server or directory to a single URL

There are two chief ways to redirect all requests for an entire server to a single location: one which requires the use of mod_rewrite, and another which uses a CGI script.

First: if all you need to do is migrate a server from one name to another, simply use the Redirect directive, as supplied by mod_alias:

  Redirect / http://www.apache.org/

Since Redirect will forward along the complete path, however, it may not be appropriate - for example, when the directory structure has changed after the move, and you simply want to direct people to the home page.

The best option is to use the standard Apache module mod_rewrite. If that module is compiled in, the following lines:

RewriteEngine On
RewriteRule /.* http://www.apache.org/ [R]

This will send an HTTP 302 Redirect back to the client, and no matter what they gave in the original URL, they'll be sent to "http://www.apache.org". The second option is to set up a ScriptAlias pointing to a cgi script which outputs a 301 or 302 status and the location of the other server.

By using a cgi-script you can intercept various requests and treat them specially, e.g. you might want to intercept POST requests, so that the client isn't redirected to a script on the other server which expects POST information (a redirect will lose the POST information.) You might also want to use a CGI script if you don't want to compile mod_rewrite into your server.

Here's how to redirect all requests to a script... In the server configuration file,

ScriptAlias / /usr/local/httpd/cgi-bin/redirect_script

and here's a simple perl script to redirect requests:

#!/usr/local/bin/perl

print "Status: 302 Moved Temporarily\r
Location: http://www.some.where.else.com/\r\n\r\n";

How to reset your log files

Sooner or later, you'll want to reset your log files (access_log and error_log) because they are too big, or full of old information you don't need.

access.log typically grows by 1Mb for each 10,000 requests.

Most people's first attempt at replacing the logfile is to just move the logfile or remove the logfile. This doesn't work.

Apache will continue writing to the logfile at the same offset as before the logfile moved. This results in a new logfile being created which is just as big as the old one, but it now contains thousands (or millions) of null characters.

The correct procedure is to move the logfile, then signal Apache to tell it to reopen the logfiles.

Apache is signaled using the SIGHUP (-1) signal. e.g.

mv access_log access_log.old kill -1 `cat httpd.pid`

Note: httpd.pid is a file containing the process id of the Apache httpd daemon, Apache saves this in the same directory as the log files.

Many people use this method to replace (and backup) their logfiles on a nightly or weekly basis.

How to stop or restrict robots

Ever wondered why so many clients are interested in a file called robots.txt which you don't have, and never did have?

These clients are called robots (also known as crawlers, spiders and other cute name) - special automated clients which wander around the web looking for interesting resources.

Most robots are used to generate some kind of web index which is then used by a search engine to help locate information.

robots.txt provides a means to request that robots limit their activities at the site, or more often than not, to leave the site alone.

When the first robots were developed, they had a bad reputation for sending hundreds/thousands of requests to each site, often resulting in the site being overloaded. Things have improved dramatically since then, thanks to Guidelines for Robot Writers, but even so, some robots may exhibit unfriendly behavior which the webmaster isn't willing to tolerate, and will want to stop.

Another reason some webmasters want to block access to robots, is to stop them indexing dynamic information. Many search engines will use the data collected from your pages for months to come - not much use if your serving stock quotes, news, weather reports or anything else that will be stale by the time people find it in a search engine.

If you decide to exclude robots completely, or just limit the areas in which they can roam, create a robots.txt file; refer to the robot information pages provided by Martijn Koster for the syntax.