Installing and configuring a web server is not much more difficult than installing an FTP server. Once your web server is up and running, other Internet users can view documents you publish on your Linux system.
Configuring a web server can be as easy or as difficult as you choose. Like other web servers, Apache provides seemingly countless options. Fortunately, Debian GNU/Linux automatically configures Apache when you install it. However, the configuration options selected by the install scripts may not suit your needs. In that case, you can modify the configuration files.
Apache's configuration files reside in the directory
/etc/apache. For historical reasons that no longer apply, Apache has three configuration files:
-
access.conf
-
Specifies what hosts and users are allowed access to what documents and services
-
httpd.conf
-
Specifies options that govern the operation of the
httpd daemon
-
srm.conf
-
Specifies how your server's documents and organized and formatted
Currently, you can place Apache configuration commands in any of these files. However, each of these files must exist, even if it is empty; otherwise, the
httpd daemon will refuse to run. As distributed, the files contain a default configuration. Before starting the web server, you should revise the
ServerName option of the
httpd.conf file. The three following subsections describe other options that you may wish to specify. You can scan them to see what options are available and specify options that interest you. A more complete description of the options is available in Apache's online documentation. Also, the Apache web site (
https://www.apache.org/) provides a tutorial on Apache configuration. To change an option, simply open the related file by using your favorite text editor, change the file as you wish, and save the file.
The subsections assume some familiarity with HTML and web servers. If you find that some options are obscure, don't fret; your web server will serve ordinary HTML pages even if you set no options other than
ServerName.
The
access.conf file specifies a default set of permissions that govern access to documents and services. It then specifies sets of permissions that override the default permissions for particular documents and services. The usual practice is to specify a quite restrictive set of default permissions, relaxing these permissions to provide access to particular documents and services.
The file contains a mixture of comments (lines beginning with #) and directives. Comments are ignored by the server.
The default permissions are specified as follows:
<Directory />
Options None
AllowOverride None
</Directory>
The paired tags
<Directory> and
</Directory> enclose a list of options that pertain to the
/ directory, the directory specified in the
<Directory> tag. The options are:
-
Options None, which specifies that no special server features are enabled for the specified directory or its subdirectories.
-
AllowOverride None, which specifies that access specifications cannot be overridden by an
.htaccess file.
Table 12.2 describes special server features that are available.
Table 12.2: Special Server Features
|
Option |
Description |
ExecCGI |
Execution of CGI scripts is permitted in this directory. |
FollowSymLinks |
The server will follow symbolic links in this directory. |
Includes |
Server-side includes are permitted. |
IncludesNOEXEC |
Server-side includes, except
#exec and
#include, are permitted in this directory. |
Indexes |
If the directory contains no index file (for example,
index.html), the server will prepare a formatted index. |
MultiViews |
Content-negotiated MultiViews are permitted in this directory. MultiViews permit, for example, a client browser to select a document in a particular language from a set of documents. |
SymLinksIfOwnerMatch |
The server will follow symbolic links for which the target file or directory has the same owner as the link. |
Unless the specification for a directory specifies
AllowOverride None, you can override the specified options by placing an
.htaccess file in the directory or one of its subdirectories. The
.htaccess file can contain specifications of the same sort as the
access.conf file; the server applies the specifications in the
.htaccess file in preference to those specified in the
access.conf file.
After the restrictive default specifications come some more relaxed specifications:
<Directory /home/httpd/html>
Options Indexes Includes FollowSymLinks
AllowOverride None
order allow,deny
allow from all
</Directory>
These specifications apply to the directory
/home/httpd/html and its subdirectories. Here,
the
Indexes,
Includes, and
FollowSymLinks options are specified. As for the
root directory, use of
.htaccess files is
forbidden, via
AllowOverride None. Here, unlike the
specification for the root directory, the hosts allowed to access
documents are services are specified. The
order
allow,deny directive specifies that any
deny directives will be applied after any
allow directives, and will therefore take
precedence. No
deny directives appear in this
specification; the
allow from all directive permits
any host to access documents and services within the
/home/httpd/html directory and its
subdirectories.
Another specification allows execution of CGI scripts within the
/home/httpd/cgi-bin directory and its subdirectories:
<Directory /home/httpd/cgi-bin>
AllowOverride None
Options ExecCGI
</Directory>
The final specification in the default configuration lets the local host access HTML documents within the
/usr/doc directory and its subdirectories:
<Directory /usr/doc>
order deny,allow
deny from all
allow from localhost
Options Indexes FollowSymLinks
</Directory>
The
srm.conf file specifies the organization and format of documents provided by your web server. As was the case with the
access.conf file, you don't need to make any changes to the
srm.conf file, though you may wish to do so.
The
DocumentRoot directive specifies the directory that contains your HTML files. When a web client accesses the root directory, the server actually fetches files from the directory specified as
DocumentRoot:
DocumentRoot /home/httpd/html
The UserDir directive specifies the name of the subdirectory that the server appends to a user's home directory when a client makes a
~user request:
UserDir public_html
This directive specifies that a reference to
~user will be translated to a reference to
/home/user/public_html.
The
DirectoryIndex directive specifies the name of the file (or names of the files) used a directory indexes:
DirectoryIndex index.html index.shtml index.cgi
The
FancyIndexing directive specifies whether icons are used to produce fancy directory indexes:
FancyIndexing on
The
AddIcon and
AddIconByType directives associate icons with files of given types:
AddIconByType (TXT,/icons/text.gif) text/*
AddIcon /icons/binary.gif .bin .exe
The default configuration includes many such directives. If you wish to add support for a new type of file, you may want to add a directive associating an icon with the new file type.
The DefaultIcon directive specifies the icon used for file types not explicitly associated with an icon:
DefaultIcon /icons/unknown.gif
The
ReadmeName directive specifies the name of a file used by the server to produce readme entries:
ReadmeName README
The server will first look for the file README.html and then for the file README.
The similar
HeaderName directive specifies the name of a file that the server will prepend to a generated index:
HeaderName HEADER
The
IndexIgnore directive specifies a set of file names that should not be included in a generated index. These are often specified by using wildcard characters:
IndexIgnore .??* *~ *# HEADER* README* RCS
The
AccessFileName directive specifies the name of the file that, if present, overrides access control specifications for a directory:
AccessFileName .htaccess
The
TypesConfig directive identifies the
mime.types file, which describes multimedia files:
TypesConfig /etc/mime.types
The
DefaultType directive specifies the default MIME type for documents:
DefaultType text/plain
The
AddEncoding directive instructs compatible browsers to uncompress information as it's downloaded:
AddEncoding x-compress Z
AddEncoding x-gzip gz
The
Redirect directive lets you provide a forwarding address for documents that have moved. The default configuration includes no
Redirects, which have this simple form:
Redirect old-URL new-URL
The
Alias directive lets you refer to a directory by using an alias. For example, the following directive provides a more convenient way of referring to the
/home/httpd/icons directory:
Alias /icons/ /home/httpd/icons/
The
ScriptAlias directive lets users refer to the CGI directory as simply
/cgi-bin/:
ScriptAlias /cgi-bin/ /home/httpd/cgi-bin/
The following sets of specifications work around problems with several browsers. First, two directives that disable
keepalive for browsers that do not support it:
BrowserMatch "Mozilla/2" nokeepalive
BrowserMatch "MSIE 4\.0b2;" nokeepalive downgrade-1.0 force-response-1.0
The final directives force use of HTTP version 1.0 responses for several browsers that do not support HTTP 1.1:
BrowserMatch "RealPlayer 4\.0" force-response-1.0
BrowserMatch "Java/1\.0" force-response-1.0
BrowserMatch "JDK/1\.0" force-response-1.0
The
httpd.conf file specifies options related to the
httpd daemon. You should specify the
ServerName option before starting your web server.
The
ServerType directory specifies whether the web server is started via
inetd or standalone:
ServerType standalone
The
port directive specifies the port on which the web server listens for client requests:
Port 80
The
HostnameLookups directive specifies whether clients are logged by IP address (off) or hostname (on):
HostnameLookups off
The
User and
Group directives specify the userid and group under which the
httpd daemon runs. The daemon initially runs as
root and then switches to the specified userid and group. The default configuration specifies the userid as
nobody, a standard Unix userid that has very limited permissions. A user or process running as
nobody can access files only in ways permitted to all users; generally, this means the user or process cannot modify files. The group
nobody has similarly constrained privileges:
User nobody
Group nobody
The
ServerAdmin directive specifies the email address of the server administrator:
ServerAdmin root@localhost
The
ServerRoot directive specifies the directory that contains the configuration, error, and log files:
ServerRoot /etc/httpd
The
BindAddress directive provides for virtual hosts. It specifies the IP address to which the server should listen. It is normally disabled by a comment token:
#BindAddress *
The
ErrorLog directive specifies the location of the error log file:
ErrorLog logs/error_log
The
LogLevel directive specifies the verbosity of the server log. Possible values include
debug,
info,
notice,
warn,
error,
crit,
alert, and
emerg:
LogLevel warn
The
LogFormat directive specifies format names that can be used with the
CustomLog directive:
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
CustomLog logs/access_log common
For more information about
LogFormat and
CustomLog, see the Apache documentation.
The
PidFile directive specifies the file in which the server should log its process id:
PidFile /var/run/httpd.pid
The
ScoreBoardFile directive specifies the name of the file used to store internal server process data:
ScoreBoardFile /var/run/httpd.scoreboard
The
LockFile directive specifies the file used to providing locking. You'll need to change this option only if you NFS mount the directory used by the server for logging:
#LockFile /var/lock/httpd.lock
The
ServerName directive specifies the hostname of the system on which your server runs. Depending on your network configuration, you may not need to specify this directive:
ServerName host.domain.com
The
UseCanonicalName directive specifies whether the server will return a canonical URL formed from the
ServerName and
Port directives (on) or the hostname and port supplied by the client (off):
UseCanonicalName on
The
CacheNegotiatedDocs directive instructs browsers not to cache documents; it is usually disabled by prefixing it with a comment token (#):
#CacheNegotiatedDocs
The
Timeout directive specifies the maximum number of seconds the server will wait for certain responses, such as the next packet in a sequence of TCP packets:
Timeout 300
The
KeepAlive directive specifies that connections are persistent; that is, that a client can make multiple requests per connection:
KeepAlive On
The
MaxKeepAliveRequests directive specifies the maximum number of requests permitted during a persistent connection:
MaxKeepAliveRequests 100
The value 0 denotes an unlimited number of requests.
The
KeepAliveTimeout directive specifies the maximum number of seconds during which the server will wait for the next request:
KeepAliveTimeout 15
The
MinSpareServers and
MaxSpareServers directives respectively fix the minimum and maximum number of spare server processes the server will create. Having an available server expedites handling of an incoming request:
MinSpareServers 8
MaxSpareServers 20
The
StartServers directive specifies the initial number of server processes:
StartServers 10
The
MaxClients directive specifies the maximum number of simultaneous server processes. When this number is reached, requests from additional clients are locked out:
MaxClients 150
The default values of these options are higher than necessary for most workstation users. Your system will perform more efficiently (and perhaps more reliably) if you change the directives to specify the following values:
MinSpareServers 3
MaxSpareServers 6
StartServers 3
MaxClients 20
The
MaxRequestsPerChild directive specifies the number of requests a child process can handle before expiring. This ensures that processes are periodically recreated, minimizing problems due to software errors such as memory leaks:
MaxRequestsPerChild 100
The
ProxyRequests directive specifies whether the proxy server is enabled; it is normally disabled:
#ProxyRequests On
When the proxy server is active, the following directives specify various caching options. They are normally disabled:
#CacheRoot /var/cache/httpd
#CacheSize 5
#CacheGcInterval 4
#CacheMaxExpire 24
#CacheLastModifiedFactor 0.1
#CacheDefaultExpire 1
#NoCache a_domain.com another_domain.edu joes.garage_sale.com
The
Listen directive lets your bind Apache to a
specific IP address or port, in addition to the default IP address and
port. It is generally disabled:
#Listen 3000
#Listen 12.34.56.78:80
The
<VirtualHost> and
</VirtualHost> tags enclose a series of options that establish a virtual host, useful if your system has multiple IP addresses. The options can include any of the options described in this subsection. The tags and options are normally disabled:
#<VirtualHost host.some_domain.com>
#ServerAdmin [email protected]_domain.com
#DocumentRoot /www/docs/host.some_domain.com
#ServerName host.some_domain.com
#ErrorLog logs/host.some_domain.com-error_log
#TransferLog logs/host.some_domain.com-access_log
#</VirtualHost>
