Thursday, January 12, 2017

Configuration Directives in httpd conf

Configuration Directives in httpd conf



The Apache HTTP Server configuration file is /etc/httpd/conf/httpd.conf. The httpd.conf file is well-commented and mostly self-explanatory. The default configuration works for most situations; however, it is a good idea to become familiar some of the more important configuration options.

Warning

With the release of Apache HTTP Server 2.2, many configuration options have changed. If migrating from version 1.3 to 2.2, please firstly read Section 21.2.2, “Migrating Apache HTTP Server 1.3 Configuration Files to 2.0”.

21.5.1. General Configuration Tips

If configuring the Apache HTTP Server, edit /etc/httpd/conf/httpd.conf and then either reload, restart, or stop and start the httpd process as outlined in Section 21.3, “Starting and Stopping httpd”.
Before editing httpd.conf, make a copy the original file. Creating a backup makes it easier to recover from mistakes made while editing the configuration file.
If a mistake is made and the Web server does not work correctly, first review recently edited passages in httpd.conf to verify there are no typos.
Next look in the Web servers error log, /var/log/httpd/error_log. The error log may not be easy to interpret, depending on your level of expertise. However, the last entries in the error log should provide useful information.
The following subsections contain a list of short descriptions for many of the directives included inhttpd.conf. These descriptions are not exhaustive. For more information, refer to the Apache documentation online at http://httpd.apache.org/docs/2.2/.
For more information about mod_ssl directives, refer to the documentation online athttp://httpd.apache.org/docs/2.2/mod/mod_ssl.html.

AccessFileName
AccessFileName names the file which the server should use for access control information in each directory. The default is .htaccess.
Immediately after the AccessFileName directive, a set of Files tags apply access control to any file beginning with a .ht. These directives deny Web access to any .htaccess files (or other files which begin with .ht) for security reasons.
Action
Action specifies a MIME content type and CGI script pair, so that when a file of that media type is requested, a particular CGI script is executed.
AddDescription
When using FancyIndexing as an IndexOptions parameter, the AddDescription directive can be used to display user-specified descriptions for certain files or file types in a server generated directory listing. The AddDescription directive supports listing specific files, wildcard expressions, or file extensions.
AddEncoding
AddEncoding names file name extensions which should specify a particular encoding type. AddEncodingcan also be used to instruct some browsers to uncompress certain files as they are downloaded.
AddHandler
AddHandler maps file extensions to specific handlers. For example, the cgi-script handler can be matched with the extension .cgi to automatically treat a file ending with .cgi as a CGI script. The following is a sample AddHandler directive for the .cgi extension.
AddHandler cgi-script .cgi
This directive enables CGIs outside of the cgi-bin to function in any directory on the server which has the ExecCGI option within the directories container. Refer to Directory for more information about setting the ExecCGI option for a directory.
In addition to CGI scripts, the AddHandler directive is used to process server-parsed HTML and image-map files.
AddIcon
AddIcon specifies which icon to show in server generated directory listings for files with certain extensions. For example, the Web server is set to show the icon binary.gif for files with .bin or .exeextensions.
AddIconByEncoding
This directive names icons which are displayed by files with MIME encoding in server generated directory listings. For example, by default, the Web server shows the compressed.gif icon next to MIME encoded x-compress and x-gzip files in server generated directory listings.
AddIconByType
This directive names icons which are displayed next to files with MIME types in server generated directory listings. For example, the server shows the icon text.gif next to files with a mime-type oftext, in server generated directory listings.
AddLanguage
AddLanguage associates file name extensions with specific languages. This directive is useful for Apache HTTP Servers which serve content in multiple languages based on the client Web browsers language settings.
AddType
Use the AddType directive to define or override a default MIME type and file extension pairs. The following example directive tells the Apache HTTP Server to recognize the .tgz file extension:
AddType application/x-tar .tgz
Alias
The Alias setting allows directories outside the DocumentRoot directory to be accessible. Any URL ending in the alias automatically resolves to the alias path. By default, one alias for an icons/ directory is already set up. An icons/ directory can be accessed by the Web server, but the directory is not in theDocumentRoot.
Allow
Allow specifies which client can access a given directory. The client can be all, a domain name, an IP address, a partial IP address, a network/netmask pair, and so on. The DocumentRoot directory is configured to Allow requests from all, meaning everyone has access.
AllowOverride
The AllowOverride directive sets whether any Options can be overridden by the declarations in an.htaccess file. By default, both the root directory and the DocumentRoot are set to allow no .htaccessoverrides.
BrowserMatch
The BrowserMatch directive allows the server to define environment variables and take appropriate actions based on the User-Agent HTTP header field — which identifies the clients Web browser type. By default, the Web server uses BrowserMatch to deny connections to specific browsers with known problems and also to disable keepalives and HTTP header flushes for browsers that are known to have problems with those actions.
Cache Directives
A number of commented cache directives are supplied by the default Apache HTTP Server configuration file. In most cases, uncommenting these lines by removing the hash mark (#) from the beginning of the line is sufficient. The following, however, is a list of some of the more important cache-related directives.
  • CacheEnable — Specifies whether the cache is a disk, memory, or file descriptor cache. By defaultCacheEnable configures a disk cache for URLs at or below /.
  • CacheRoot — Specifies the name of the directory containing cached files. The default CacheRoot is the/var/httpd/proxy/ directory.
  • CacheSize — Specifies how much space the cache can use in kilobytes. The default CacheSize is 5 KB.
The following is a list of some of the other common cache-related directives.
  • CacheMaxExpire — Specifies how long HTML documents are retained (without a reload from the originating Web server) in the cache. The default is 24 hours (86400 seconds).
  • CacheLastModifiedFactor — Specifies the creation of an expiry (expiration) date for a document which did not come from its originating server with its own expiry set. The defaultCacheLastModifiedFactor is set to 0.1, meaning that the expiry date for such documents equals one-tenth of the amount of time since the document was last modified.
  • CacheDefaultExpire — Specifies the expiry time in hours for a document that was received using a protocol that does not support expiry times. The default is set to 1 hour (3600 seconds).
  • NoProxy — Specifies a space-separated list of subnets, IP addresses, domains, or hosts whose content is not cached. This setting is most useful for Intranet sites.
CacheNegotiatedDocs
By default, the Web server asks proxy servers not to cache any documents which were negotiated on the basis of content (that is, they may change over time or because of the input from the requester). IfCacheNegotiatedDocs is set to on, this function is disabled and proxy servers are allowed to cache such documents.
CustomLog
CustomLog identifies the log file and the log file format. By default, the access log is recorded to the/var/log/httpd/access_log file while errors are recorded in the /var/log/httpd/error_log file.
The default CustomLog format is the combined log file format, as illustrated here:
remotehost rfc931 user date "request" status bytes referrer user-agent
DefaultIcon
DefaultIcon specifies the icon displayed in server generated directory listings for files which have no other icon specified. The unknown.gif image file is the default.
DefaultType
DefaultType sets a default content type for the Web server to use for documents whose MIME types cannot be determined. The default is text/plain.
Deny
Deny works similar to Allow, except it specifies who is denied access. The DocumentRoot is not configured to Deny requests from anyone by default.
Directory
 and  tags create a container used to enclose a group of configuration directives which apply only to a specific directory and its subdirectories. Any directive which is applicable to a directory may be used within Directory tags.
By default, very restrictive parameters are applied to the root directory (/), using the Options (refer toOptions) and AllowOverride (refer to AllowOverride) directives. Under this configuration, any directory on the system which needs more permissive settings has to be explicitly given those settings.
In the default configuration, another Directory container is configured for the DocumentRoot which assigns less rigid parameters to the directory tree so that the Apache HTTP Server can access the files residing there.
The Directory container can be also be used to configure additional cgi-bin directories for server-side applications outside of the directory specified in the ScriptAlias directive (refer to ScriptAlias for more information).
To accomplish this, the Directory container must set the ExecCGI option for that directory.
For example, if CGI scripts are located in /home/my_cgi_directory, add the following Directory container to the httpd.conf file:
 Options +ExecCGI
Next, the AddHandler directive must be uncommented to identify files with the .cgi extension as CGI scripts. Refer to AddHandler for instructions on setting AddHandler.
For this to work, permissions for CGI scripts, and the entire path to the scripts, must be set to 0755.
DirectoryIndex
The DirectoryIndex is the default page served by the server when a user requests an index of a directory by specifying a forward slash (/) at the end of the directory name.
When a user requests the page http://example/this_directory/, they get either the DirectoryIndexpage, if it exists, or a server-generated directory list. The default for DirectoryIndex is index.html and the index.html.var type map. The server tries to find either of these files and returns the first one it finds. If it does not find one of these files and Options Indexes is set for that directory, the server generates and returns a listing, in HTML format, of the subdirectories and files within the directory, unless the directory listing feature is turned off.
DocumentRoot
DocumentRoot is the directory which contains most of the HTML files which are served in response to requests. The default DocumentRoot, for both the non-secure and secure Web servers, is the/var/www/html directory. For example, the server might receive a request for the following document:
http://example.com/foo.html
The server looks for the following file in the default directory:
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