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kHTTPd  -  Kernel httpd accelerator

(C) 1999 by Arjan van de Ven
Licensed under the terms of the GNU General Public License

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1. Introduction
---------------
   kHTTPd is a http-daemon (webserver) for Linux. kHTTPd is different from 
   other webservers in that it runs from within the Linux-kernel as a module 
   (device-driver).

   kHTTPd handles only static (file based) web-pages, and passes all requests
   for non-static information to a regular userspace-webserver such as Apache or 
   Zeus. The userspace-daemon doesn't have to be altered in any way.

   Static web-pages are not a very complex thing to serve, but these are very
   important nevertheless, since virtually all images are static, and a large
   portion of the html-pages are static also. A "regular" webserver has little
   added value for static pages, it is simply a "copy file to network"-operation.
   This can be done very efficiently from within the Linux-kernel, for example 
   the nfs (network file system) daemon performs a similar task and also runs 
   in the kernel.

   By "accelerating" the simple case within the kernel, userspace daemons can
   do what they are very good at: Generating user-specific, dynamic content.

   Note: This document sometimes uses "Apache" instead of "any webserver you
   ever might want to use", just for reasons of readability.
   

2. Quick Start  
--------------

   1) compile and load the module
   2) configure the module in /proc/sys/net/khttpd if needed
   3) echo 1 > /proc/sys/net/khttpd/start

   unloading:
 
   echo 1 > /proc/sys/net/khttpd/stop
   echo 1 > /proc/sys/net/khttpd/unload 
   rmmod khttpd
   


3. Configuration 
----------------

   Modes of operation
   ==================


   There are two recommended modes of operation:

   1) "Apache" is main webserver, kHTTPd is assistant
	clientport   -> 80
  	serverport   -> 8080 (or whatever)

   2) kHTTPd is main webserver, "Apache" is assistant
	clientport   -> 8080 (or whatever)
 	serverport   -> 80

   
   Configuring kHTTPd
   ==================

   Before you can start using kHTTPd, you have to configure it. This
   is done through the /proc filesystem, and can thus be done from inside
   a script. Most parameters can only be set when kHTTPd is not active.

   The following things need configuration:

   1) The port where kHTTPd should listen for requests
   2) The port (on "localhost") where "Apache" is listening
   3) The location of the documents (documentroot)
   4) The strings that indicate dynamic content (optional)
      [  "cgi-bin" is added by default ]

   It is very important that the documentroot for kHTTPd matches the
   documentroot for the userspace-daemon, as kHTTPd might "redirect"
   any request to this userspace-daemon.

   A typical script (for the first mode of operation) to do this would 
   look like:

#!/bin/sh
modprobe khttpd
echo 80 > /proc/sys/net/khttpd/clientport
echo 8080 > /proc/sys/net/khttpd/serverport
echo /var/www > /proc/sys/net/khttpd/documentroot
echo php3 > /proc/sys/net/khttpd/dynamic
echo shtml > /proc/sys/net/khttpd/dynamic
echo 1 > /proc/sys/net/khttpd/start

   For the second mode of operation, this would be:

#!/bin/sh
modprobe khttpd
echo 8080 > /proc/sys/net/khttpd/clientport
echo 80 > /proc/sys/net/khttpd/serverport
echo /var/www > /proc/sys/net/khttpd/documentroot
echo php3 > /proc/sys/net/khttpd/dynamic
echo shtml > /proc/sys/net/khttpd/dynamic
echo 1 > /proc/sys/net/khttpd/start

   In this case, you also have to change the configuration of the 
   userspace-daemon. For Apache, you do this by changing

   Port 80

   to 

   Port 8080


   
   Stopping kHTTPd
   ===============
   In order to change the configuration, you should stop kHTTPd by typing
   echo 1 > /proc/sys/net/khttpd/stop
   on a command-prompt.

   If you want to unload the module, you should type
   echo 1 > /proc/sys/net/khttpd/unload
   after stopping kHTTPd first.

   If this doesn't work fast enough for you (the commands above can wait for 
   a remote connection to close down), you can send the daemons a "HUP"
   signal after you told them to stop. This will cause the daemon-threads to
   stop immediately. 

   Note that the daemons will restart immediately if they are not told to
   stop.

   

4. Permissions
--------------
   The security model of kHTTPd is very strict. It can be, since there is a 
   userspace daemon that can handle the complex exceptions. 

   kHTTPd only serves a file if

	1)  There is no "?" in the URL
	2)  The URL starts with a "/"
	3)  The file indicated by the URL exists
	4)  The file is world-readable (*)
	5)  The file is not a directory, executable or has the Sticky-bit
	    set (*)
	6)  The URL doesn't contain any "forbidden" substrings such as ".."
	    and "cgi-bin" (*)
	7)  The mime-type is known (*)

   The items marked with a (*) are configurable through the
   sysctl-parameters in /proc/sys/net/khttpd.


   In all cases where any of the above conditions isn't met, the
   userspace-daemon is handed the request.



5. Parameters
-------------
   The following parameters are settable through /proc/sys/net/khttpd:
 
	Name		Default		Description

	serverport	8080		The port where kHTTPd listens on

	clientport	80		The port of the userspace
					http-daemon

	threads		2		The number of server-threads. Should
					be 1 per CPU for small websites, 2
					per CPU for big (the active files
					do not fit in the RAM) websites.

	documentroot	/var/www	the directory where the
					document-files are

	start		0		Set to 1 to start kHTTPd 
					(this also resets "stop" to 0)

	stop		0		Set to 1 to stop kHTTPd
					(this also resets "start" to 0)

	unload		0		Set to 1 to prepare kHTTPd for
					unloading of the module

	sloppymime	0		If set to 1, unknown mime-types are
					set to text/html. If set to 0,
					files with unknown mime-types are
					handled by the userspace daemon

	perm_required	S_IROTH		Minimum permissions required
					(for values see "man 2 stat")
	
	perm_forbid	dir+sticky+	Permission-mask with "forbidden"
			execute		permissions.
					(for values see "man 2 stat")

	dynamic		cgi-bin ..	Strings that, if they are a subset
					of the URL, indicate "dynamic
					content"

	maxconnect	1000		Maximum number of concurrent
					connections

6. More information
-------------------
   More information about the architecture of kHTTPd, the mailinglist and
   configuration-examples can be found at the kHTTPd homepage:

	http://www.fenrus.demon.nl

   Bugreports, patches, etc can be send to the mailinglist
   ([e-mail]) or to [e-mail]