Apache HOWTO documentation
Description: Some 'how to' tips for the Apache httpd server
Keywords: apache,redirect,robots,rotate,logfiles

### Apache HTTP Server Version 1.3

# Apache HOWTO documentation

How to:

- redirect an entire server or directory to a single URL
- reset your log files
- stop/restrict robots
- proxy SSL requests through your non-SSL server

## 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]

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\n" .
>           "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 names) - 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 you're 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.

## How to proxy SSL requests through your non-SSL Apache server
(submitted by David Sedlock)

SSL uses port 443 for requests for secure pages. If your browser just sits there for a long time when you attempt to access a secure page over your Apache proxy, then the proxy may not be configured to handle SSL. You need to instruct Apache to listen on port 443 in addition to any of the ports on which it is already listening:

        Listen 80
        Listen 443

Then set the security proxy in your browser to 443. That might be it!

If your proxy is sending requests to another proxy, then you may have to set the directive ProxyRemote differently. Here are my settings:

        ProxyRemote http://nicklas:80/ http://proxy.mayn.franken.de:8080
        ProxyRemote http://nicklas:443/ http://proxy.mayn.franken.de:443

Requests on port 80 of my proxy `nicklas` are forwarded to `proxy.mayn.franken.de:8080`, while requests on port 443 are forwarded to `proxy.mayn.franken.de:443`. If the remote proxy is not set up to handle port 443, then the last directive can be left out. SSL requests will only go over the first proxy.

Note that your Apache does NOT have to be set up to serve secure pages with SSL. Proxying SSL is a different thing from using it.

### Apache HTTP Server Version 1.3