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This file documents Boa, an HTTP daemon for UN*X like machines.
START-INFO-DIR-ENTRY
* Boa: (boa). The Boa Webserver
END-INFO-DIR-ENTRY
Welcome to the documentation for Boa, a high performance HTTP Server
for UN*X-alike computers, covered by the GNU General Public License
(Gnu_License). The on-line, updated copy of this documentation lives at
http://www.boa.org/ (http://www.boa.org/)
Copyright (C) 1996-2001 Jon Nelson and Larry Doolittle
Last Updated: 2 Jan 2001, $Revision: #1 $
Introduction
************
Boa is a single-tasking HTTP server. That means that unlike
traditional web servers, it does not fork for each incoming connection,
nor does it fork many copies of itself to handle multiple connections.
It internally multiplexes all of the ongoing HTTP connections, and
forks only for CGI programs (which must be separate processes),
automatic directory generation, and automatic file gunzipping.
Preliminary tests show Boa is capable of handling several thousand hits
per second on a 300 MHz Pentium and dozens of hits per second on a
lowly 20 MHz 386/SX.
The primary design goals of Boa are speed and security. Security, in
the sense of _can't be subverted by a malicious user,_ not _fine
grained access control and encrypted communications_. Boa is not
intended as a feature-packed server; if you want one of those, check out
WN (`http://hopf.math.nwu.edu/') from John Franks. Modifications to
Boa that improve its speed, security, robustness, and portability, are
eagerly sought. Other features may be added if they can be achieved
without hurting the primary goals.
Boa was created in 1991 by Paul Phillips (<psp@well.com>). It is now
being maintained and enhanced by Larry Doolittle (<ldoolitt@boa.org>)
and Jon Nelson (<jnelson@boa.org>). Please see the acknowledgement
section for further details.
GNU/Linux is the development platform at the moment, other OS's are
known to work. If you'd like to contribute to this effort, contact
Larry or Jon via e-mail.
Installation and Usage
**********************
Boa is currently being developed and tested on GNU/Linux/i386. The
code is straightforward (more so than most other servers), so it should
run easily on most modern Unix-alike platforms. Recent versions of Boa
worked fine on FreeBSD, SunOS 4.1.4, GNU/Linux-SPARC, and HP-UX 9.0.
Pre-1.2.0 GNU/Linux kernels may not work because of deficient mmap()
implementations.
Installation
============
1. Unpack
1. Choose, and cd into, a convenient directory for the package.
2. `tar -xvzf boa-0.94.tar.gz', or for those of you with an
archaic (non-GNU) tar; `gzip -cd &lt; boa-0.94.tar.gz | tar
-xvf -'
3. Read the documentation. Really.
2. Build
1. cd into the src directory.
2. (optional) Change the default SERVER_ROOT by setting the
#define at the top of src/defines.h
3. Type `./configure; make'
4. Report any errors to the maintainers for resolution, or strike
out on your own.
3. Configure
1. Choose a user and server port under which Boa can run. The
traditional port is 80, and user nobody (create if you
need to) is often a good selection for security purposes.
If you don't have (or choose not to use) root privileges, you
can not use port numbers less than 1024, nor can you
switch user id.
2. Choose a server root. The conf directory within the
server root must hold your copy of the configuration file
_boa.conf_
3. Choose locations for log files, CGI programs (if any), and
the base of your URL tree.
4. Set the location of the mime.types file.
5. Edit _conf/boa.conf_ according to your choices above
(this file documents itself). Read through this file to
see what other features you can configure.
4. Start
* Start Boa. If you didn't build the right SERVER_ROOT into the
binary, you can specify it on the command line with the
-c option (command line takes precedence).
Example: ./boa -c /usr/local/boa
5. Test
* At this point the server should run and serve documents.
If not, check the error_log file for clues.
6. Install
* Copy the binary to a safe place, and put the invocation into
your system startup scripts. Use the same -c option you
used in your initial tests.
Files Used by Boa
=================
`boa.conf'
This file is the sole configuration file for Boa. The directives
in this file are defined in the DIRECTIVES section.
`mime.types'
The MimeTypes <filename> defines what Content-Type Boa will send
in an HTTP/1.0 or better transaction. Set to /dev/null if you
do not want to load a mime types file. Do *not* comment out
(better use AddType!)
Compile-Time and Command-Line Options
=====================================
SERVER_ROOT
-C
The default server root as #defined by SERVER_ROOT in `defines.h'
can be overridden on the commandline using the `-c' option. The
server root must hold your local copy of the configuration file
`boa.conf'.
Example: /usr/sbin/boa -c /etc/boa
boa.conf Directives
===================
The Boa configuration file is parsed with a lex/yacc or flex/bison
generated parser. If it reports an error, the line number will be
provided; it should be easy to spot. The syntax of each of these rules
is very simple, and they can occur in any order. Where possible, these
directives mimic those of NCSA httpd 1.3; I (Paul Phillips) saw no
reason to introduce gratuitous differences.
Note: the "ServerRoot" is not in this configuration file. It can be
compiled into the server (see `defines.h') or specified on the command
line with the `-c' option.
The following directives are contained in the `boa.conf' file, and most,
but not all, are required.
`Port <Integer>'
This is the port that Boa runs on. The default port for http
servers is 80. If it is less than 1024, the server must be
started as root.
`Listen <IP>'
The Internet address to bind(2) to, in quadded-octet form
(numbers). If you leave it out, it binds to all addresses
(INADDR_ANY).
The name you provide gets run through inet_aton(3), so you have to
use dotted quad notation. This configuration is too important
to trust some DNS.
You only get one "Listen" directive, if you want service on
multiple IP addresses, you have three choices:
1. Run boa without a "Listen" directive:
* All addresses are treated the same; makes sense if the
addresses are localhost, ppp, and eth0.
* Use the VirtualHost directive below to point requests to
different files. Should be good for a very large
number of addresses (web hosting clients).
2. Run one copy of boa per IP address:
* Each instance has its own configuration with its own
"Listen" directive. No big deal up to a few tens of
addresses. Nice separation between clients.
`User <username or UID>'
The name or UID the server should run as. For Boa to attempt this,
the server must be started as root.
`Group <groupname or GID>'
The group name or GID the server should run as. For Boa to attempt
this, the server must be started as root.
`ServerAdmin <email address>'
The email address where server problems should be sent. Note: this
is not currently used.
`ErrorLog <filename>'
The location of the error log file. If this does not start with /,
it is considered relative to the server root. Set to /dev/null if
you don't want errors logged.
`AccessLog <filename>'
The location of the access log file. If this does not start with
/, it is considered relative to the server root. Comment out or
set to /dev/null (less effective) to disable access logging.
`VerboseCGILogs'
This is a logical switch and does not take any parameters. Comment
out to disable. All it does is switch on or off logging of when
CGIs are launched and when the children return.
`CgiLog <filename>'
The location of the CGI error log file. If specified, this is
the file that the stderr of CGIs is tied to. Otherwise, writes
to stderr meet the bit bucket.
`ServerName <server_name>'
The name of this server that should be sent back to clients if
different than that returned by gethostname.
`VirtualHost'
This is a logical switch and does not take any parameters.
Comment out to disable. Given DocumentRoot /var/www, requests on
interface `A' or IP `IP-A' become /var/www/IP-A. Example:
http://localhost/ becomes /var/www/127.0.0.1
`DocumentRoot <directory>'
The root directory of the HTML documents. If this does not start
with /, it is considered relative to the server root.
`UserDir <directory>'
The name of the directory which is appended onto a user's home
directory if a ~user request is received.
`DirectoryIndex <filename>'
Name of the file to use as a pre-written HTML directory index.
Please make and use these files. On the fly creation of directory
indexes can be slow.
`DirectoryMaker <full pathname to program>'
Name of the program used to generate on-the-fly directory
listings. The program must take one or two command-line
arguments, the first being the directory to index (absolute), and
the second, which is optional, should be the "title" of the
document be. Comment out if you don't want on the fly directory
listings. If this does not start with /, it is considered
relative to the server root.
`DirectoryCache <directory>'
DirectoryCache: If DirectoryIndex doesn't exist, and
DirectoryMaker has been commented out, the the on-the-fly
indexing of Boa can be used to generate indexes of directories.
Be warned that the output is extremely minimal and can cause
delays when slow disks are used. Note: The DirectoryCache must be
writable by the same user/group that Boa runs as.
`KeepAliveMax <integer>'
Number of KeepAlive requests to allow per connection. Comment out,
or set to 0 to disable keepalive processing.
`KeepAliveTimeout <integer>'
Number of seconds to wait before keepalive connections time out.
`MimeTypes <file>'
The location of the mime.types file. If this does not start with
/, it is considered relative to the server root. Comment out to
avoid loading mime.types (better use AddType!)
`DefaultType <mime type>'
MIME type used if the file extension is unknown, or there is no
file extension.
`AddType <mime type> <extension> extension...'
Associates a MIME type with an extension or extensions.
`Redirect, Alias, and ScriptAlias'
Redirect, Alias, and ScriptAlias all have the same semantics -
they match the beginning of a request and take appropriate action.
Use Redirect for other servers, Alias for the same server, and
ScriptAlias to enable directories for script execution.
`Redirect <path1> <path2>'
allows you to tell clients about documents which used to exist
in your server's namespace, but do not anymore. This allows you
tell the clients where to look for the relocated document.
`Alias <path1> <path2>'
aliases one path to another. Of course, symbolic links in the
file system work fine too.
`ScriptAlias <path1> <path2>'
maps a virtual path to a directory for serving scripts.
Security
========
Boa has been designed to use the existing file system security. In
`boa.conf', the directives _user_ and _group_ determine who Boa will
run as, if launched by root. By default, the user/group is
nobody/nogroup. This allows quite a bit of flexibility. For example,
if you want to disallow access to otherwise accessible directories or
files, simply make them inaccessible to nobody/nogroup. If the user
that Boa runs as is "boa" and the groups that "boa" belongs to include
"web-stuff" then files/directories accessible by users with group
"web-stuff" will also be accessible to Boa.
The February 2000 hoo-rah from CERT advisory CA-2000-02
(http://www.cert.org/advisories/CA-2000-02.html) has little to do with
Boa. As of version 0.94.4, Boa's escaping rules have been cleaned up a
little, but they weren't that bad before. The example CGI programs
have been updated to show what effort is needed there. If you write,
maintain, or use CGI programs under Boa (or any other server) it's
worth your while to read and understand this advisory. The real
problem, however, boils down to browser and web page designers
emphasizing frills over content and security. The market leading
browsers assume (incorrectly) that all web pages are trustworthy.
Limits and Design Philosophy
****************************
There are many issues that become more difficult to resolve in a single
tasking web server than in the normal forking model. Here is a partial
list - there are probably others that haven't been encountered yet.
Limits
======
* Slow file systems
The file systems being served should be much faster than the
network connection to the HTTP requests, or performance will
suffer. For instance, if a document is served from a CD-ROM, the
whole server (including all other currently incomplete data
transfers) will stall while the CD-ROM spins up. This is a
consequence of the fact that Boa mmap()'s each file being served,
and lets the kernel read and cache pages as best it knows how.
When the files come from a local disk (the faster the better),
this is no problem, and in fact delivers nearly ideal performance
under heavy load. Avoid serving documents from NFS and CD-ROM
unless you have even slower inbound net connections (e.g., POTS
SLIP).
* DNS lookups
Writing a nonblocking gethostbyaddr is a difficult and not very
enjoyable task. Paul Phillips experimented with several methods,
including a separate logging process, before removing hostname
lookups entirely. There is a companion program with Boa
`util/resolver.pl' that will postprocess the logfiles and replace
IP addresses with hostnames, which is much faster no matter what
sort of server you run.
* Identd lookups
Same difficulties as hostname lookups; not included. Boa
provides a REMOTE_PORT environment variable, in addition to
REMOTE_ADDR, so that a CGI program can do its own ident. See the
end of examples/cgi-test.cgi.
* Password file lookups via NIS
If users are allowed to serve HTML from their home directories,
password file lookups can potentially block the process. To lessen
the impact, each user's home directory is cached by Boa so it need
only be looked up once.
* Running out of file descriptors
Since a file descriptor is needed for every ongoing connection
(two for non-nph CGIs, directories, and automatic gunzipping of
files), it is possible though highly improbable to run out of file
descriptors. The symptoms of this conditions may vary with your
particular unix variant, but you will probably see log entries
giving an error message for accept. Try to build your kernel to
give an adequate number for your usage - GNU/Linux provides 256
out of the box, more than enough for most people.
Differences between Boa and other web servers
=============================================
In the pursuit of speed and simplicity, some aspects of Boa differ from
the popular web servers. In no particular order:
* REMOTE_HOST environment variable not set for CGI programs
The REMOTE_HOST environment variable is not set for CGI programs,
for reasons already described. This is easily worked around
because the IP address is provided in the REMOTE_HOST variable,
so (if the CGI program actually cares) gethostbyaddr or a
variant can be used.
* There are no server side includes (SSI) in Boa
We don't like them, and they are too slow to parse. We will
consider more efficient alternatives.
* There are no access control features
Boa will follow symbolic links, and serve any file that it can
read. The expectation is that you will configure Boa to run as
user "nobody", and only files configured world readable will come
out.
* No chroot option
There is no option to run chrooted. If anybody wants this, and is
willing to try out experimental code, contact the maintainers.
Unexpected Behavior
===================
* SIGHUP handling
Like any good server, Boa traps SIGHUP and rereads `boa.conf'.
However, under normal circumstances, it has already given away
permissions, so many items listed in `boa.conf' can not take
effect. No attempt is made to change uid, gid, log files, or
server port. All other configuration changes should take place
smoothly.
* Relative URL handling
Not all browsers handle relative URLs correctly. Boa will not
cover up for this browser bug, and will typically report 404 Not
Found for URL's containing odd combinations of "../" 's.
Note: As of version 0.95.0 (unreleased) the URL parser has been
rewritten and *does* correctly handle relative URLs.
Appendix
********
License
=======
This program is distributed under the GNU General Public License
(http://www.gnu.org/copyleft/gpl.html). as noted in each source file:
/*
* Boa, an http server
* Copyright (C) 1995 Paul Phillips <psp@well.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 1, or (at your option)
* any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*
*/
Acknowledgments
===============
Paul Phillips wrote the first versions of Boa, up to and including
version 0.91. Version 0.92 of Boa was officially released December 1996
by Larry Doolittle. Version 0.93 was the development version of 0.94,
which was released in February 2000.
The Boa Webserver is currently (Feb 2000) maintained and enhanced by
Larry Doolittle (<ldoolitt@boa.org>) and Jon Nelson (<jnelson@boa.org>).
We would like to thank Russ Nelson (<nelson@crynwr.com>) for hosting
the web site (http://www.boa.org).
We would also like to thank Paul Philips for writing code that is worth
maintaining and supporting.
Many people have contributed to Boa, including (but not limited to)
Charles F. Randall (<randall@goldsys.com>) Christoph Lameter
(<<chris@waterf.org>>), Russ Nelson (<<nelson@crynwr.com>>), Alain
Magloire (<<alain.magloire@rcsm.ee.mcgill.ca>>), and more recently, M.
Drew Streib (<<dtype@linux.com>>).
Paul Phillips records his acknowledgments as follows:
Thanks to everyone in the WWW community, in general a great bunch
of people. Special thanks to Clem Taylor
(<<ctaylor@eecis.udel.edu>>), who provided invaluable feedback on
many of my ideas, and offered good ones of his own. Also thanks
to John Franks, author of wn, for writing what I believe is the
best webserver out there.
Reference Documents
===================
Links to documents relevant to Boa (http://www.boa.org/) development
and usage. Incomplete, we're still working on this. NCSA has a decent
page (http://hoohoo.ncsa.uiuc.edu/docs/Library.html) along these lines,
too.
Also see Yahoo's List
`http://www.yahoo.com/Computers_and_Internet/Software/Internet/World_Wide_Web/Servers/'
* W3O HTTP page
`http://www.w3.org/pub/WWW/Protocols/'
* RFC 1945 HTTP-1.0 (informational)
`http://ds.internic.net/rfc/rfc1945.txt'
* IETF Working Group Draft 07 of HTTP-1.1
`http://www.w3.org/pub/WWW/Protocols/HTTP/1.1/draft-ietf-http-v11-spec-07.txt'
* HTTP: A protocol for networked information
`http://www.w3.org/pub/WWW/Protocols/HTTP/HTTP2.html'
* The Common Gateway Interface (CGI)
`http://hoohoo.ncsa.uiuc.edu/cgi/overview.html'
* RFC 1738 URL syntax and semantics
`http://ds.internic.net/rfc/rfc1738.txt'
* RFC 1808 Relative URL syntax and semantics
`http://ds.internic.net/rfc/rfc1808.txt'
Other HTTP Servers
==================
For unix-alike platforms, with published source code.
* tiny/turbo/throttling httpd very similar to Boa, with a throttling
feature
`http://www.acme.com/software/thttpd/'
* Roxen: based on ulpc interpreter, non-forking (interpreter
implements threading), GPL'd
`http://www.roxen.com/'
* WN: featureful, GPL'd
`http://hopf.math.nwu.edu/'
* Apache: fast, PD
`http://www.apache.org/'
* NCSA: standard, legal status?
`http://hoohoo.ncsa.uiuc.edu/'
* CERN: standard, PD, supports proxy
`http://www.w3.org/pub/WWW/Daemon/Status.html'
* xs-httpd 2.0: small, fast, pseudo-GPL'd
`http://www.stack.nl/~sven/xs-httpd/'
* bozohttpd.tar.gz sources, in perl
`ftp://ftp.eterna.com.au/bozo/bsf/attware/bozohttpd.tar.gz'
* Squid is actually an "Internet Object Cache"
`http://squid.nlanr.net/Squid/'
Also worth mentioning is Zeus. It is commercial, with a free demo, so
it doesn't belong on the list above. Zeus seems to be based on
technology similar to Boa and thttpd, but with more bells and whistles.
`http://www.zeus.co.uk/products/server/'
Benchmarks
==========
* ZeusBench (broken link)
`http://www.zeus.co.uk/products/server/intro/bench2/zeusbench.shtml'
* WebBench (binary-ware)
`http://web1.zdnet.com/zdbop/webbench/webbench.html'
* WebStone
`http://www.mindcraft.com/benchmarks/webstone/'
* SpecWeb96
`http://www.specbench.org/osg/web96/'
Tools
=====
* Analog logfile analyzer
`http://www.statslab.cam.ac.uk/s~ret1/analog/'
* wwwstat logfile analyzer
`http://www.ics.uci.edu/pub/websoft/wwwstat/'
* gwstat wwwstat postprocessor
`http://dis.cs.umass.edu/stats/gwstat.html'
* The Webalizer logfile analyzer
`http://www.usagl.net/webalizer/'
* cgiwrap
`http://www.umr.edu/c~giwrap/'
* suEXEC (Boa would need to be ..umm.. "adjusted" to support this)
`http://www.apache.org/docs/suexec.html'
Note: References last checked: 06 October 1997
Authors
=======
* Conversion from linuxdoc SGML to texinfo by Jon Nelson
* Conversion to linuxdoc SGML by Jon Nelson
* Original HTML documentation by Larry Doolittle
* Copyright (C) 1996-2001 Jon Nelson and Larry Doolittle
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