Saturday, March 15, 2003

Web Server Tutorial - Part 2

n the first part of this series on Apache Web server, we looked at how Web communication takes place. Here we deal with DSO and the main server configuration.

Dynamic Shared Object (DSO) Support

To be able to use the functionality of a module which was built as a DSO you have to place corresponding 'LoadModule' lines at this location so the directives contained in it are actually available before they are used. Please read the file README.DSO in the Apache 1.3 distribution for more details about the DSO mechanism and run 'httpd -l' for the list of already built-in (statically linked and thus always available) modules in your httpd binary.

Note: The order in which modules are loaded is important. Don't change the order below without expert advice.


LoadModule foo_module modules/
LoadModule mmap_static_module modules/
LoadModule vhost_alias_module modules/
LoadModule env_module modules/
LoadModule config_log_module modules/
LoadModule agent_log_module modules/
LoadModule referer_log_module modules/
LoadModule mime_magic_module modules/
LoadModule mime_module modules/
LoadModule negotiation_module modules/
LoadModule status_module modules/
LoadModule info_module modules/
LoadModule includes_module modules/
LoadModule autoindex_module modules/
LoadModule dir_module modules/
LoadModule cgi_module modules/
LoadModule asis_module modules/
LoadModule imap_module modules/
LoadModule action_module modules/
LoadModule speling_module modules/
LoadModule userdir_module modules/
LoadModule alias_module modules/
LoadModule rewrite_module modules/
LoadModule access_module modules/
LoadModule auth_module modules/
LoadModule anon_auth_module modules/
LoadModule db_auth_module modules/
LoadModule digest_module modules/
LoadModule proxy_module modules/
LoadModule cern_meta_module modules/
LoadModule expires_module modules/
LoadModule headers_module modules/
LoadModule usertrack_module modules/
LoadModule example_module modules/
LoadModule unique_id_module modules/
LoadModule setenvif_module modules/
LoadModule bandwidth_module modules/
LoadModule put_module modules/

Extra Modules

LoadModule perl_module modules/
LoadModule php_module modules/
LoadModule php3_module modules/

Reconstruction of the complete module list from all available modules (static and shared ones) to achieve correct module execution order is necessary (whenever you change the LoadModule section above update this too).

AddModule mod_mmap_static.c
AddModule mod_vhost_alias.c
AddModule mod_env.c
AddModule mod_log_config.c
AddModule mod_log_agent.c
AddModule mod_log_referer.c
AddModule mod_mime_magic.c
AddModule mod_mime.c
AddModule mod_negotiation.c
AddModule mod_status.c
AddModule mod_info.c
AddModule mod_include.c
AddModule mod_autoindex.c
AddModule mod_dir.c
AddModule mod_cgi.c
AddModule mod_asis.c
AddModule mod_imap.c
AddModule mod_actions.c
AddModule mod_speling.c
AddModule mod_userdir.c
AddModule mod_alias.c
AddModule mod_rewrite.c
AddModule mod_access.c
AddModule mod_auth.c
AddModule mod_auth_anon.c
AddModule mod_auth_db.c
AddModule mod_digest.c
AddModule mod_proxy.c
AddModule mod_cern_meta.c
AddModule mod_expires.c
AddModule mod_headers.c
AddModule mod_usertrack.c
AddModule mod_example.c
AddModule mod_unique_id.c
AddModule mod_so.c
AddModule mod_setenvif.c
AddModule mod_bandwidth.c
AddModule mod_put.c

Extra Modules

AddModule mod_perl.c
AddModule mod_php.c
AddModule mod_php3.c

ExtendedStatus: Controls whether Apache will generate "full" status information (ExtendedStatus On) or just basic information (ExtendedStatus Off) when the "server-status" handler is called. The default is Off.
ExtendedStatus On

Section 2: 'Main' server configuration

The directives in this section set up the values used by the 'main' server, which responds to any requests that aren't handled by a definition. These values also provide defaults for any containers you may define later in the file. All of these directives may appear inside containers, in which case these default settings will be overridden for the virtual host being defined.

If your ServerType directive (set earlier in the 'Global Environment' section) is set to "inetd", the next few directives don't have any effect since their settings are defined by the inetd configuration.
Skip ahead to the ServerAdmin directive.

Port: The port to which the standalone server listens. For ports <1023,>User/Group: The name (or number) of the user/group to run httpd as:
On SCO (ODT 3) use "User nouser" and "Group nogroup".
On HPUX you may not be able to use shared memory as anybody, and the suggested workaround is to create a user www and use that user.

Note: Some kernels refuse to setgid(Group) or semctl(IPC_SET) when the value of (unsigned)Group is above 60000; don't use Group nobody on these systems!
User nobody
Group nobody

ServerAdmin: Your address, where problems with the server should be emailed. This address appears on some server-generated pages, such as error documents.
ServerAdmin root@localhost

ServerName: Allows you to set a host name which is sent back to your server if it's different than the one the program would get (i.e., use "www" instead of the host's real name).

Note: You cannot just invent host names and hope they work. The name you define here must be a valid DNS name for your host. If you don't understand this, ask your network administrator.
If your host doesn't have a registered DNS name, enter its IP address here.
You will have to access it by its address (e.g., anyway, and this will make redirections work in a sensible way.
ServerName localhost

DocumentRoot: The directory out of which you will serve your documents. By default, all requests are taken from this directory, but symbolic links and aliases may be used to point to other locations.
DocumentRoot "/home/httpd/html"
Each directory to which Apache has access, can be configured with respect to which services and features are allowed and/or disabled in that directory (and its subdirectories).
First, we configure the "default" to be a very restrictive set of permissions.

Options FollowSymLinks
AllowOverride None

Note: From this point forward you must specifically allow particular features to be enabled - so if something's not working as you might expect, make sure that you have specifically enabled it below.
This should be changed to whatever you set DocumentRoot to.

This may also be "None", "All", or any combination of "Indexes", "Includes", "FollowSymLinks", "ExecCGI", or "MultiViews".
Note: "MultiViews" must be named explicitly --- "Options All" doesn't give it to you.
Options Indexes Includes FollowSymLinks
This controls which options the .htaccess files in directories can override. Can also be "All", or any combination of "Options", "FileInfo", "AuthConfig", and "Limit"
AllowOverride all

Controls who can get stuff from this server.
Order allow,deny
Allow from all

UserDir: The name of the directory which is appended onto a user's home directory if a ~user request is received.
UserDir public_html

Control access to UserDir directories. The following is an example for a site where these directories are restricted to read-only.

AllowOverride FileInfo AuthConfig Limit
Options MultiViews Indexes SymLinksIfOwnerMatch IncludesNoExec

Order allow,deny
Allow from all

Order deny,allow
Deny from all

DirectoryIndex: Name of the file or files to use as a pre-written HTML directory index. Separate multiple entries with spaces.
DirectoryIndex index.html index.htm index.shtml index.cgi

AccessFileName: The name of the file to look for in each directory for access control information.
AccessFileName .htaccess

The following lines prevent .htaccess files from being viewed by Web clients. Since .htaccess files often contain authorization information, access is disallowed for security reasons. Comment these lines out if you want Web visitors to see the contents of .htaccess files. If you change the AccessFileName directive above, be sure to make the corresponding changes here.
Also, folks tend to use names such as .htpasswd for password files, so this will protect those as well.

Order allow,deny
Deny from all

CacheNegotiatedDocs: By default, Apache sends "Pragma: no-cache" with each document that was negotiated on the basis of content. This asks proxy servers not to cache the document. Uncommenting the following line disables this behavior, and proxies will be allowed to cache the documents.

UseCanonicalName: (new for 1.3) With this setting turned on, whenever Apache needs to construct a self-referencing URL (a URL that refers back to the server the response is coming from) it will use ServerName and Port to form a "canonical" name. With this setting off, Apache will use the hostname:port that the client supplied, when possible. This also affects SERVER_NAME and SERVER_PORT in CGI scripts.
UseCanonicalName On

TypesConfig: Describes where the mime.types file (or equivalent) is to be found.
TypesConfig /etc/mime.types

DefaultType is the default MIME type the server will use for a document if it cannot otherwise determine one, such as from filename extensions.
If your server contains mostly text or HTML documents, "text/plain" is a good value. If most of your content is binary, such as applications or images, you may want to use "application/octet-stream" instead to keep browsers from trying to display binary files as though they are text.
DefaultType text/plain

The mod_mime_magic module allows the server to use various hints from the contents of the file itself to determine its type. The MIMEMagicFile directive tells the module where the hint definitions are located.
mod_mime_magic is not part of the default server (you have to add it yourself with a LoadModule [see the DSO paragraph in the 'Global Environment' section], or recompile the server and include mod_mime_magic as part of the configuration), so it's enclosed in an container.
This means that the MIMEMagicFile directive will only be processed if the module is part of the server.

MIMEMagicFile share/magic

HostnameLookups: Log the names of clients or just their IP addresses e.g., (on) or (off).
The default is off because it'd be overall better for the net if people had to knowingly turn this feature on, since enabling it means that each client request will result in AT LEAST one lookup request to thenameserver.
HostnameLookups Off

ErrorLog: The location of the error log file.
If you do not specify an ErrorLog directive within a container, error messages relating to that virtual host will be logged here. If you do define an error logfile for a container, that host's errors will be logged there and not here.
ErrorLog /var/log/httpd/error_log

LogLevel: Control the number of messages logged to the error_log.
Possible values include: debug, info, notice, warn, error, crit, alert, emerg.
LogLevel warn

The following directives define some format nicknames for use with a CustomLog directive (see below).
LogFormat "%h %l %u %t "%r" %>s %b "%{Referer}i" "%{User-Agent}i"" combined
LogFormat "%h %l %u %t "%r" %>s %b" common
LogFormat "%{Referer}i -> %U" referer
LogFormat "%{User-agent}i" agent

The location and format of the access logfile (Common Logfile Format).
If you do not define any access logfiles within a container, they will be logged here. Contrariwise, if you do define per- access logfiles, transactions will be logged therein and not in this file.
CustomLog /var/log/httpd/access_log common

If you would like to have agent and referer logfiles, uncomment the following directives.
CustomLog /var/log/httpd/referer_log referer
CustomLog /var/log/httpd/agent_log agent

If you prefer a single logfile with access, agent, and referrer information (Combined Logfile Format) you can use the following directive.
CustomLog /var/log/httpd/access_log combined

Optionally add a line containing the server version and virtual host name to server-generated pages (error documents, FTP directory listings, mod_status and mod_info output etc., but not CGI generated documents).
Set to "EMail" to also include a mailto: link to the ServerAdmin.
Set to one of: On | Off | EMail
ServerSignature On

Aliases: Add here as many aliases as you need (with no limit). The format is
Alias fakename realname
Note: If you include a trailing / on fakename then the server will require it to be present in the URL. So "/icons" isn't aliased in this example, only "/icons/"..
Alias /icons/ "/home/httpd/icons/"

Options Indexes MultiViews
AllowOverride None
Order allow,deny
Allow from all

ScriptAlias: This controls which directories contain server scripts.
ScriptAliases are essentially the same as Aliases, except that documents in the realname directory are treated as applications and run by the server when requested rather than as documents sent to the client.
The same rules about trailing "/" apply to ScriptAlias directives as to Alias.
ScriptAlias /cgi-bin/ "/home/httpd/cgi-bin/"

"/home/httpd/cgi-bin" should be changed to whatever your ScriptAliased
CGI directory exists, if you have that configured.

AllowOverride None
Options ExecCGI
Order allow,deny
Allow from all

Redirect: Allows you to tell clients about documents which used to exist in your server's namespace, but do not anymore. This allows you to tell the clients where to look for the relocated document.
Format: Redirect old-URL new-URL

Directives controlling the display of server-generated directory listings.

FancyIndexing: Asks whether you want fancy directory indexing or standard IndexOptions FancyIndexing

AddIcon* directives: Tell the server which icon to show for different files or filename extensions. These are only displayed for FancyIndexed directories.
AddIconByEncoding (CMP,/icons/compressed.gif) x-compress x-gzip
AddIconByType (TXT,/icons/text.gif) text/*
AddIconByType (IMG,/icons/image2.gif) image/*
AddIconByType (SND,/icons/sound2.gif) audio/*
AddIconByType (VID,/icons/movie.gif) video/*
AddIcon /icons/binary.gif .bin .exe
AddIcon /icons/binhex.gif .hqx
AddIcon /icons/tar.gif .tar
AddIcon /icons/world2.gif .wrl .wrl.gz .vrml .vrm .iv
AddIcon /icons/compressed.gif .Z .z .tgz .gz .zip
AddIcon /icons/a.gif .ps .ai .eps
AddIcon /icons/layout.gif .html .shtml .htm .pdf
AddIcon /icons/text.gif .txt
AddIcon /icons/c.gif .c
AddIcon /icons/p.gif .pl .py
AddIcon /icons/f.gif .for
AddIcon /icons/dvi.gif .dvi
AddIcon /icons/uuencoded.gif .uu
AddIcon /icons/script.gif .conf .sh .shar .csh .ksh .tcl
AddIcon /icons/tex.gif .tex
AddIcon /icons/bomb.gif core

AddIcon /icons/back.gif ..
AddIcon /icons/hand.right.gif README
AddIcon /icons/folder.gif ^^DIRECTORY^^
AddIcon /icons/blank.gif ^^BLANKICON^^

DefaultIcon: Which icon to show for files, which do not have an icon explicitly set.
DefaultIcon /icons/unknown.gif

AddDescription: Allows you to place a short description after a file in server-generated indexes. These are only displayed for FancyIndexed directories.
Format: AddDescription "description" filename
AddDescription "GZIP compressed document" .gz
AddDescription "tar archive" .tar
AddDescription "GZIP compressed tar archive" .tgz

ReadmeName: The name of the README file the server will look for by default, and append to directory listings.
HeaderName: the name of a file, which should be prepended to directory indexes.
The server will first look for name.html and include it if found. If name.html doesn't exist, the server will then look for name.txt and include it as plaintext if found.
ReadmeName README
HeaderName HEADER

IndexIgnore: A set of filenames which directory indexing should ignore and not include in the listing. Shell-style wildcarding is permitted.
IndexIgnore .??* *~ * HEADER* README* RCS CVS *,v *,t

AddEncoding: Allows you to have certain browsers (Mosaic/X 2.1+) uncompress information on the fly.
Note: Not all browsers support this. Despite the name similarity, the following Add* directives have nothing to do with the FancyIndexing customization directives above.
AddEncoding x-compress Z
AddEncoding x-gzip gz tgz

AddLanguage: Allows you to specify the language of a document. You can then use content negotiation to give a browser a file in a language it can understand. Note that the suffix does not have to be the same as the language keyword --- those with documents in Polish (whose net-standard language code is pl) may wish to use "AddLanguage pl .po" to avoid the ambiguity with the common suffix for perl scripts.
AddLanguage en .en
AddLanguage fr .fr
AddLanguage de .de
AddLanguage da .da
AddLanguage el .el
AddLanguage it .it

LanguagePriority: Allows you to give precedence to some languages in case of a tie during content negotiation.
Just list the languages in decreasing order of preference.
LanguagePriority en fr de

AddType: Allows you to tweak mime.types without actually editing it, or to make certain files to be certain types.
For example, the PHP3 module (not part of the Apache distribution - see will typically use:

AddType application/x-httpd-php3 .php3
AddType application/x-httpd-php3-source .phps

The following is for PHP/FI (PHP2):

AddType application/x-httpd-php .phtml

AddType application/x-tar .tgz

AddHandler: Allows you to map certain file extensions to "handlers", actions unrelated to filetype. These can be either built into the server or added with the Action command (see below)
If you want to use server side includes, or CGI outside ScriptAliased directories, uncomment the following lines.
To use CGI scripts:
AddHandler cgi-script .cgi

To use server-parsed HTML files
AddType text/html .shtml
AddHandler server-parsed .shtml

Uncomment the following line to enable Apache's send-asis HTTP file feature
AddHandler send-as-is asis

If you wish to use server-parsed imagemap files, use
AddHandler imap-file map

To enable type maps, you might want to use
AddHandler type-map var

Action: Lets you define media types that will execute a script whenever a matching file is called. This eliminates the need for repeated URL pathnames for oft-used CGI file processors.
Format: Action media/type /cgi-script/location
Format: Action handler-name /cgi-script/location

MetaDir: Specifies the name of the directory in which Apache can find meta information files. These files contain additional HTTP headers to include when sending the document
MetaDir .web

MetaSuffix: Specifies the file name suffix for the file containing the meta information.
MetaSuffix .meta