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Chapter 18. Web Servers
HTTP
(Hypertext Transfer Protocol) server, or a web server, is a network service that serves content to a client over the web. This typically means web pages, but any other documents can be served as well.
- Apache HTTP Server
- nginx
Important
18.1. The Apache HTTP Server
httpd
service, and covers advanced topics such as adding server modules, setting up virtual hosts, or configuring the secure HTTP server.
httpd
service configuration accordingly. This section reviews some of the newly added features, outlines important changes, and guides you through the update of older configuration files.
18.1.1. New Features
- Support for large files on 32-bit architectures, allowing the web server to handle files greater than 2GB.
- A new structure for authentication and authorization support, replacing the authentication modules provided in previous versions.
18.1.2. Notable Changes
httpd
service configuration:
18.1.3. Updating the Configuration
- Make sure all module names are correct, since they may have changed. Adjust the
LoadModule
directive for each module that has been renamed. - Recompile all third party modules before attempting to load them. This typically means authentication and authorization modules.
- If you use the Apache HTTP Secure Server, see Section 18.1.9, “Enabling the mod_ssl Module” for important information on enabling the Secure Sockets Layer (SSL) protocol.
~]# service httpd configtest
Syntax OK
18.1.4. Running the httpd Service
httpd
service, make sure you have the httpd installed. You can do so by using the following command:
~]# yum install httpd
18.1.4.1. Starting the Service
httpd
service, type the following at a shell prompt as root
:
~]# service httpd start
Starting httpd: [ OK ]
~]# chkconfig httpd on
Note
18.1.4.2. Stopping the Service
httpd
service, type the following at a shell prompt as root
:
~]# service httpd stop
Stopping httpd: [ OK ]
~]# chkconfig httpd off
18.1.4.3. Restarting the Service
httpd
service:
- To restart the service completely, enter the following command as
root
:~]#
service httpd restart
Stopping httpd: [ OK ] Starting httpd: [ OK ]This stops the runninghttpd
service and immediately starts it again. Use this command after installing or removing a dynamically loaded module such as PHP. - To only reload the configuration, as
root
, type:~]#
service httpd reload
This causes the runninghttpd
service to reload its configuration file. Any requests being currently processed will be interrupted, which may cause a client browser to display an error message or render a partial page. - To reload the configuration without affecting active requests, enter the following command as
root
:~]#
service httpd graceful
This causes the runninghttpd
service to reload its configuration file. Any requests being currently processed will use the old configuration.
18.1.4.4. Verifying the Service Status
httpd
service is running, type the following at a shell prompt:
~]# service httpd status
httpd (pid 19014) is running...
18.1.5. Editing the Configuration Files
httpd
service is started, by default, it reads the configuration from locations that are listed in Table 18.1, “The httpd service configuration files”.
httpd
service.
~]# service httpd configtest
Syntax OK
18.1.5.1. Common httpd.conf Directives
/etc/httpd/conf/httpd.conf
configuration file:
-
<Directory>
- The
<Directory>
directive allows you to apply certain directives to a particular directory only. It takes the following form:<Directory directory> directive … </Directory>
The directory can be either a full path to an existing directory in the local file system, or a wildcard expression.This directive can be used to configure additionalcgi-bin
directories for server-side scripts located outside the directory that is specified byScriptAlias
. In this case, theExecCGI
andAddHandler
directives must be supplied, and the permissions on the target directory must be set correctly (that is,0755
).Example 18.1. Using the <Directory> directive
<Directory /var/www/html> Options Indexes FollowSymLinks AllowOverride None Order allow,deny Allow from all </Directory>
-
<IfDefine>
- The
IfDefine
directive allows you to use certain directives only when a particular parameter is supplied on the command line. It takes the following form:<IfDefine [!]parameter> directive … </IfDefine>
The parameter can be supplied at a shell prompt using the-D
parameter command-line option (for example,httpd -DEnableHome
). If the optional exclamation mark (that is,!
) is present, the enclosed directives are used only when the parameter is not specified.Example 18.2. Using the <IfDefine> directive
<IfDefine EnableHome> UserDir public_html </IfDefine>
-
<IfModule>
- The
<IfModule>
directive allows you to use certain directive only when a particular module is loaded. It takes the following form:<IfModule [!]module> directive … </IfModule>
The module can be identified either by its name, or by the file name. If the optional exclamation mark (that is,!
) is present, the enclosed directives are used only when the module is not loaded.Example 18.3. Using the <IfModule> directive
<IfModule mod_disk_cache.c> CacheEnable disk / CacheRoot /var/cache/mod_proxy </IfModule>
-
<Location>
- The
<Location>
directive allows you to apply certain directives to a particular URL only. It takes the following form:<Location url> directive … </Location>
The url can be either a path relative to the directory specified by theDocumentRoot
directive (for example,/server-info
), or an external URL such ashttp://example.com/server-info
.Example 18.4. Using the <Location> directive
<Location /server-info> SetHandler server-info Order deny,allow Deny from all Allow from .example.com </Location>
-
<Proxy>
- The
<Proxy>
directive allows you to apply certain directives to the proxy server only. It takes the following form:<Proxy pattern> directive … </Proxy>
The pattern can be an external URL, or a wildcard expression (for example,http://example.com/*
).Example 18.5. Using the <Proxy> directive
<Proxy *> Order deny,allow Deny from all Allow from .example.com </Proxy>
-
<VirtualHost>
- The
<VirtualHost>
directive allows you apply certain directives to particular virtual hosts only. It takes the following form:<VirtualHost address[:port]…> directive … </VirtualHost>
The address can be an IP address, a fully qualified domain name, or a special form as described in Table 18.2, “Available <VirtualHost> options”.Table 18.2. Available <VirtualHost> options Option Description *
Represents all IP addresses. _default_
Represents unmatched IP addresses. Example 18.6. Using the <VirtualHost> directive
<VirtualHost *:80> ServerAdmin webmaster@penguin.example.com DocumentRoot /www/docs/penguin.example.com ServerName penguin.example.com ErrorLog logs/penguin.example.com-error_log CustomLog logs/penguin.example.com-access_log common </VirtualHost>
-
AccessFileName
- The
AccessFileName
directive allows you to specify the file to be used to customize access control information for each directory. It takes the following form:AccessFileName filename…
The filename is a name of the file to look for in the requested directory. By default, the server looks for.htaccess
.For security reasons, the directive is typically followed by theFiles
tag to prevent the files beginning with.ht
from being accessed by web clients. This includes the.htaccess
and.htpasswd
files.Example 18.7. Using the AccessFileName directive
AccessFileName .htaccess <Files ~ "^\.ht"> Order allow,deny Deny from all Satisfy All </Files>
-
Action
- The
Action
directive allows you to specify a CGI script to be executed when a certain media type is requested. It takes the following form:Action content-type path
The content-type has to be a valid MIME type such astext/html
,image/png
, orapplication/pdf
. The path refers to an existing CGI script, and must be relative to the directory specified by theDocumentRoot
directive (for example,/cgi-bin/process-image.cgi
).Example 18.8. Using the Action directive
Action image/png /cgi-bin/process-image.cgi
-
AddDescription
- The
AddDescription
directive allows you to specify a short description to be displayed in server-generated directory listings for a given file. It takes the following form:AddDescription "description" filename…
The description should be a short text enclosed in double quotes (that is,"
). The filename can be a full file name, a file extension, or a wildcard expression.Example 18.9. Using the AddDescription directive
AddDescription "GZIP compressed tar archive" .tgz
-
AddEncoding
- The
AddEncoding
directive allows you to specify an encoding type for a particular file extension. It takes the following form:AddEncoding encoding extension…
The encoding has to be a valid MIME encoding such asx-compress
,x-gzip
, etc. The extension is a case sensitive file extension, and is conventionally written with a leading dot (for example,.gz
).This directive is typically used to instruct web browsers to decompress certain file types as they are downloaded.Example 18.10. Using the AddEncoding directive
AddEncoding x-gzip .gz .tgz
-
AddHandler
- The
AddHandler
directive allows you to map certain file extensions to a selected handler. It takes the following form:AddHandler handler extension…
The handler has to be a name of a previously defined handler. The extension is a case sensitive file extension, and is conventionally written with a leading dot (for example,.cgi
).This directive is typically used to treat files with the.cgi
extension as CGI scripts regardless of the directory they are in. Additionally, it is also commonly used to process server-parsed HTML and image-map files.Example 18.11. Using the AddHandler option
AddHandler cgi-script .cgi
-
AddIcon
- The
AddIcon
directive allows you to specify an icon to be displayed for a particular file in server-generated directory listings. It takes the following form:AddIcon path pattern…
The path refers to an existing icon file, and must be relative to the directory specified by theDocumentRoot
directive (for example,/icons/folder.png
). The pattern can be a file name, a file extension, a wildcard expression, or a special form as described in the following table:Table 18.3. Available AddIcon options Option Description ^^DIRECTORY^^
Represents a directory. ^^BLANKICON^^
Represents a blank line. Example 18.12. Using the AddIcon directive
AddIcon /icons/text.png .txt README
-
AddIconByEncoding
- The
AddIconByEncoding
directive allows you to specify an icon to be displayed for a particular encoding type in server-generated directory listings. It takes the following form:AddIconByEncoding path encoding…
The path refers to an existing icon file, and must be relative to the directory specified by theDocumentRoot
directive (for example,/icons/compressed.png
). The encoding has to be a valid MIME encoding such asx-compress
,x-gzip
, etc.Example 18.13. Using the AddIconByEncoding directive
AddIconByEncoding /icons/compressed.png x-compress x-gzip
-
AddIconByType
- The
AddIconByType
directive allows you to specify an icon to be displayed for a particular media type in server-generated directory listings. It takes the following form:AddIconByType path content-type…
The path refers to an existing icon file, and must be relative to the directory specified by theDocumentRoot
directive (for example,/icons/text.png
). The content-type has to be either a valid MIME type (for example,text/html
orimage/png
), or a wildcard expression such astext/*
,image/*
, etc.Example 18.14. Using the AddIconByType directive
AddIconByType /icons/video.png video/*
-
AddLanguage
- The
AddLanguage
directive allows you to associate a file extension with a specific language. It takes the following form:AddLanguage language extension…
The language has to be a valid MIME language such ascs
,en
, orfr
. The extension is a case sensitive file extension, and is conventionally written with a leading dot (for example,.cs
).This directive is especially useful for web servers that serve content in multiple languages based on the client's language settings.Example 18.15. Using the AddLanguage directive
AddLanguage cs .cs .cz
-
AddType
- The
AddType
directive allows you to define or override the media type for a particular file extension. It takes the following form:AddType content-type extension…
The content-type has to be a valid MIME type such astext/html
,image/png
, etc. The extension is a case sensitive file extension, and is conventionally written with a leading dot (for example,.cs
).Example 18.16. Using the AddType directive
AddType application/x-gzip .gz .tgz
-
Alias
- The
Alias
directive allows you to refer to files and directories outside the default directory specified by theDocumentRoot
directive. It takes the following form:Alias url-path real-path
The url-path must be relative to the directory specified by theDocumentRoot
directive (for example,/images/
). The real-path is a full path to a file or directory in the local file system.This directive is typically followed by theDirectory
tag with additional permissions to access the target directory. By default, the/icons/
alias is created so that the icons from/var/www/icons/
are displayed in server-generated directory listings.Example 18.17. Using the Alias directive
Alias /icons/ /var/www/icons/ <Directory "/var/www/icons"> Options Indexes MultiViews FollowSymLinks AllowOverride None Order allow,deny Allow from all <Directory>
-
Allow
- The
Allow
directive allows you to specify which clients have permission to access a given directory. It takes the following form:Allow from client…
The client can be a domain name, an IP address (both full and partial), a network/netmask pair, orall
for all clients.Example 18.18. Using the Allow directive
Allow from 192.168.1.0/255.255.255.0
-
AllowOverride
- The
AllowOverride
directive allows you to specify which directives in a.htaccess
file can override the default configuration. It takes the following form:AllowOverride type…
The type has to be one of the available grouping options as described in Table 18.4, “Available AllowOverride options”.Table 18.4. Available AllowOverride options Option Description All
All directives in .htaccess
are allowed to override earlier configuration settings.None
No directive in .htaccess
is allowed to override earlier configuration settings.AuthConfig
Allows the use of authorization directives such as AuthName
,AuthType
, orRequire
.FileInfo
Allows the use of file type, metadata, and mod_rewrite
directives such asDefaultType
,RequestHeader
, orRewriteEngine
, as well as theAction
directive.Indexes
Allows the use of directory indexing directives such as AddDescription
,AddIcon
, orFancyIndexing
.Limit
Allows the use of host access directives, that is, Allow
,Deny
, andOrder
.Options
[=option,…]Allows the use of the Options
directive. Additionally, you can provide a comma-separated list of options to customize which options can be set using this directive.Example 18.19. Using the AllowOverride directive
AllowOverride FileInfo AuthConfig Limit
-
BrowserMatch
- The
BrowserMatch
directive allows you to modify the server behavior based on the client's web browser type. It takes the following form:BrowserMatch pattern variable…
The pattern is a regular expression to match the User-Agent HTTP header field. The variable is an environment variable that is set when the header field matches the pattern.By default, this directive is used to deny connections to specific browsers with known issues, and to disable keepalives and HTTP header flushes for browsers that are known to have problems with these actions.Example 18.20. Using the BrowserMatch directive
BrowserMatch "Mozilla/2" nokeepalive
-
CacheDefaultExpire
- The
CacheDefaultExpire
option allows you to set how long to cache a document that does not have any expiration date or the date of its last modification specified. It takes the following form:CacheDefaultExpire time
The time is specified in seconds. The default option is3600
(that is, one hour).Example 18.21. Using the CacheDefaultExpire directive
CacheDefaultExpire 3600
-
CacheDisable
- The
CacheDisable
directive allows you to disable caching of certain URLs. It takes the following form:CacheDisable path
The path must be relative to the directory specified by theDocumentRoot
directive (for example,/files/
).Example 18.22. Using the CacheDisable directive
CacheDisable /temporary
-
CacheEnable
- The
CacheEnable
directive allows you to specify a cache type to be used for certain URLs. It takes the following form:CacheEnable type url
The type has to be a valid cache type as described in Table 18.5, “Available cache types”. The url can be a path relative to the directory specified by theDocumentRoot
directive (for example,/images/
), a protocol (for example,ftp://
), or an external URL such ashttp://example.com/
.Table 18.5. Available cache types Type Description mem
The memory-based storage manager. disk
The disk-based storage manager. fd
The file descriptor cache. Example 18.23. Using the CacheEnable directive
CacheEnable disk /
-
CacheLastModifiedFactor
- The
CacheLastModifiedFactor
directive allows you to customize how long to cache a document that does not have any expiration date specified, but that provides information about the date of its last modification. It takes the following form:CacheLastModifiedFactor number
The number is a coefficient to be used to multiply the time that passed since the last modification of the document. The default option is0.1
(that is, one tenth).Example 18.24. Using the CacheLastModifiedFactor directive
CacheLastModifiedFactor 0.1
-
CacheMaxExpire
- The
CacheMaxExpire
directive allows you to specify the maximum amount of time to cache a document. It takes the following form:CacheMaxExpire time
The time is specified in seconds. The default option is86400
(that is, one day).Example 18.25. Using the CacheMaxExpire directive
CacheMaxExpire 86400
-
CacheNegotiatedDocs
- The
CacheNegotiatedDocs
directive allows you to enable caching of the documents that were negotiated on the basis of content. It takes the following form:CacheNegotiatedDocs option
The option has to be a valid keyword as described in Table 18.6, “Available CacheNegotiatedDocs options”. Since the content-negotiated documents may change over time or because of the input from the requester, the default option isOff
.Table 18.6. Available CacheNegotiatedDocs options Option Description On
Enables caching the content-negotiated documents. Off
Disables caching the content-negotiated documents. Example 18.26. Using the CacheNegotiatedDocs directive
CacheNegotiatedDocs On
-
CacheRoot
- The
CacheRoot
directive allows you to specify the directory to store cache files in. It takes the following form:CacheRoot directory
The directory must be a full path to an existing directory in the local file system. The default option is/var/cache/mod_proxy/
.Example 18.27. Using the CacheRoot directive
CacheRoot /var/cache/mod_proxy
-
CustomLog
- The
CustomLog
directive allows you to specify the log file name and the log file format. It takes the following form:CustomLog path format
The path refers to a log file, and must be relative to the directory that is specified by theServerRoot
directive (that is,/etc/httpd/
by default). The format has to be either an explicit format string, or a format name that was previously defined using theLogFormat
directive.Example 18.28. Using the CustomLog directive
CustomLog logs/access_log combined
-
DefaultIcon
- The
DefaultIcon
directive allows you to specify an icon to be displayed for a file in server-generated directory listings when no other icon is associated with it. It takes the following form:DefaultIcon path
The path refers to an existing icon file, and must be relative to the directory specified by theDocumentRoot
directive (for example,/icons/unknown.png
).Example 18.29. Using the DefaultIcon directive
DefaultIcon /icons/unknown.png
-
DefaultType
- The
DefaultType
directive allows you to specify a media type to be used in case the proper MIME type cannot be determined by the server. It takes the following form:DefaultType content-type
The content-type has to be a valid MIME type such astext/html
,image/png
,application/pdf
, etc.Example 18.30. Using the DefaultType directive
DefaultType text/plain
-
Deny
- The
Deny
directive allows you to specify which clients are denied access to a given directory. It takes the following form:Deny from client…
The client can be a domain name, an IP address (both full and partial), a network/netmask pair, orall
for all clients.Example 18.31. Using the Deny directive
Deny from 192.168.1.1
-
DirectoryIndex
- The
DirectoryIndex
directive allows you to specify a document to be served to a client when a directory is requested (that is, when the URL ends with the/
character). It takes the following form:DirectoryIndex filename…
The filename is a name of the file to look for in the requested directory. By default, the server looks forindex.html
, andindex.html.var
.Example 18.32. Using the DirectoryIndex directive
DirectoryIndex index.html index.html.var
-
DocumentRoot
- The
DocumentRoot
directive allows you to specify the main directory from which the content is served. It takes the following form:DocumentRoot directory
The directory must be a full path to an existing directory in the local file system. The default option is/var/www/html/
.Example 18.33. Using the DocumentRoot directive
DocumentRoot /var/www/html
-
ErrorDocument
- The
ErrorDocument
directive allows you to specify a document or a message to be displayed as a response to a particular error. It takes the following form:ErrorDocument error-code action
The error-code has to be a valid code such as403
(Forbidden),404
(Not Found), or500
(Internal Server Error). The action can be either a URL (both local and external), or a message string enclosed in double quotes (that is,"
).Example 18.34. Using the ErrorDocument directive
ErrorDocument 403 "Access Denied" ErrorDocument 404 /404-not_found.html
-
ErrorLog
- The
ErrorLog
directive allows you to specify a file to which the server errors are logged. It takes the following form:ErrorLog path
The path refers to a log file, and can be either absolute, or relative to the directory that is specified by theServerRoot
directive (that is,/etc/httpd/
by default). The default option islogs/error_log
Example 18.35. Using the ErrorLog directive
ErrorLog logs/error_log
-
ExtendedStatus
- The
ExtendedStatus
directive allows you to enable detailed server status information. It takes the following form:ExtendedStatus option
The option has to be a valid keyword as described in Table 18.7, “Available ExtendedStatus options”. The default option isOff
.Table 18.7. Available ExtendedStatus options Option Description On
Enables generating the detailed server status. Off
Disables generating the detailed server status. Example 18.36. Using the ExtendedStatus directive
ExtendedStatus On
-
Group
- The
Group
directive allows you to specify the group under which thehttpd
service will run. It takes the following form:Group group
The group has to be an existing UNIX group. The default option isapache
.Note thatGroup
is no longer supported inside<VirtualHost>
, and has been replaced by theSuexecUserGroup
directive.Example 18.37. Using the Group directive
Group apache
-
HeaderName
- The
HeaderName
directive allows you to specify a file to be prepended to the beginning of the server-generated directory listing. It takes the following form:HeaderName filename
The filename is a name of the file to look for in the requested directory. By default, the server looks forHEADER.html
.Example 18.38. Using the HeaderName directive
HeaderName HEADER.html
-
HostnameLookups
- The
HostnameLookups
directive allows you to enable automatic resolving of IP addresses. It takes the following form:HostnameLookups option
The option has to be a valid keyword as described in Table 18.8, “Available HostnameLookups options”. To conserve resources on the server, the default option isOff
.Table 18.8. Available HostnameLookups options Option Description On
Enables resolving the IP address for each connection so that the host name can be logged. However, this also adds a significant processing overhead. Double
Enables performing the double-reverse DNS lookup. In comparison to the above option, this adds even more processing overhead. Off
Disables resolving the IP address for each connection. Note that when the presence of host names is required in server log files, it is often possible to use one of the many log analyzer tools that perform the DNS lookups more efficiently.Example 18.39. Using the HostnameLookups directive
HostnameLookups Off
-
Include
- The
Include
directive allows you to include other configuration files. It takes the following form:Include filename
Thefilename
can be an absolute path, a path relative to the directory specified by theServerRoot
directive, or a wildcard expression. All configuration files from the/etc/httpd/conf.d/
directory are loaded by default.Example 18.40. Using the Include directive
Include conf.d/*.conf
-
IndexIgnore
- The
IndexIgnore
directive allows you to specify a list of file names to be omitted from the server-generated directory listings. It takes the following form:IndexIgnore filename…
The filename option can be either a full file name, or a wildcard expression.Example 18.41. Using the IndexIgnore directive
IndexIgnore .??* *~ *# HEADER* README* RCS CVS *,v *,t
-
IndexOptions
- The
IndexOptions
directive allows you to customize the behavior of server-generated directory listings. It takes the following form:IndexOptions option…
The option has to be a valid keyword as described in Table 18.9, “Available directory listing options”. The default options areCharset=UTF-8
,FancyIndexing
,HTMLTable
,NameWidth=*
, andVersionSort
.Table 18.9. Available directory listing options Option Description Charset
=encodingSpecifies the character set of a generated web page. The encoding has to be a valid character set such as UTF-8
orISO-8859-2
.Type
=content-typeSpecifies the media type of a generated web page. The content-type has to be a valid MIME type such as text/html
ortext/plain
.DescriptionWidth
=valueSpecifies the width of the description column. The value can be either a number of characters, or an asterisk (that is, *
) to adjust the width automatically.FancyIndexing
Enables advanced features such as different icons for certain files or possibility to re-sort a directory listing by clicking on a column header. FolderFirst
Enables listing directories first, always placing them above files. HTMLTable
Enables the use of HTML tables for directory listings. IconsAreLinks
Enables using the icons as links. IconHeight
=valueSpecifies an icon height. The value is a number of pixels. IconWidth
=valueSpecifies an icon width. The value is a number of pixels. IgnoreCase
Enables sorting files and directories in a case-sensitive manner. IgnoreClient
Disables accepting query variables from a client. NameWidth
=valueSpecifies the width of the file name column. The value can be either a number of characters, or an asterisk (that is, *
) to adjust the width automatically.ScanHTMLTitles
Enables parsing the file for a description (that is, the title
element) in case it is not provided by theAddDescription
directive.ShowForbidden
Enables listing the files with otherwise restricted access. SuppressColumnSorting
Disables re-sorting a directory listing by clicking on a column header. SuppressDescription
Disables reserving a space for file descriptions. SuppressHTMLPreamble
Disables the use of standard HTML preamble when a file specified by the HeaderName
directive is present.SuppressIcon
Disables the use of icons in directory listings. SuppressLastModified
Disables displaying the date of the last modification field in directory listings. SuppressRules
Disables the use of horizontal lines in directory listings. SuppressSize
Disables displaying the file size field in directory listings. TrackModified
Enables returning the Last-Modified
andETag
values in the HTTP header.VersionSort
Enables sorting files that contain a version number in the expected manner. XHTML
Enables the use of XHTML 1.0 instead of the default HTML 3.2. Example 18.42. Using the IndexOptions directive
IndexOptions FancyIndexing VersionSort NameWidth=* HTMLTable Charset=UTF-8
-
KeepAlive
- The
KeepAlive
directive allows you to enable persistent connections. It takes the following form:KeepAlive option
The option has to be a valid keyword as described in Table 18.10, “Available KeepAlive options”. The default option isOff
.Table 18.10. Available KeepAlive options Option Description On
Enables the persistent connections. In this case, the server will accept more than one request per connection. Off
Disables the keep-alive connections. Note that when the persistent connections are enabled, on a busy server, the number of child processes can increase rapidly and eventually reach the maximum limit, slowing down the server significantly. To reduce the risk, it is recommended that you setKeepAliveTimeout
to a low number, and monitor the/var/log/httpd/logs/error_log
log file carefully.Example 18.43. Using the KeepAlive directive
KeepAlive Off
-
KeepAliveTimeout
- The
KeepAliveTimeout
directive allows you to specify the amount of time to wait for another request before closing the connection. It takes the following form:KeepAliveTimeout time
The time is specified in seconds. The default option is15
.Example 18.44. Using the KeepAliveTimeout directive
KeepAliveTimeout 15
-
LanguagePriority
- The
LanguagePriority
directive allows you to customize the precedence of languages. It takes the following form:LanguagePriority language…
The language has to be a valid MIME language such ascs
,en
, orfr
.This directive is especially useful for web servers that serve content in multiple languages based on the client's language settings.Example 18.45. Using the LanguagePriority directive
LanguagePriority sk cs en
-
Listen
- The Listen directive allows you to specify IP addresses or ports to listen to. It takes the following form:
Listen [ip-address:]port [protocol]
The ip-address is optional and unless supplied, the server will accept incoming requests on a given port from all IP addresses. Since the protocol is determined automatically from the port number, it can be usually omitted. The default option is to listen to port80
.Note that if the server is configured to listen to a port under 1024, only superuser will be able to start thehttpd
service.Example 18.46. Using the Listen directive
Listen 80
-
LoadModule
- The
LoadModule
directive allows you to load a Dynamic Shared Object (DSO) module. It takes the following form:LoadModule name path
The name has to be a valid identifier of the required module. The path refers to an existing module file, and must be relative to the directory in which the libraries are placed (that is,/usr/lib/httpd/
on 32-bit and/usr/lib64/httpd/
on 64-bit systems by default).See Section 18.1.6, “Working with Modules” for more information on the Apache HTTP Server's DSO support.Example 18.47. Using the LoadModule directive
LoadModule php5_module modules/libphp5.so
-
LogFormat
- The LogFormat directive allows you to specify a log file format. It takes the following form:
LogFormat format name
The format is a string consisting of options as described in Table 18.11, “Common LogFormat options”. The name can be used instead of the format string in theCustomLog
directive.Table 18.11. Common LogFormat options Option Description %b
Represents the size of the response in bytes. %h
Represents the IP address or host name of a remote client. %l
Represents the remote log name if supplied. If not, a hyphen (that is, -
) is used instead.%r
Represents the first line of the request string as it came from the browser or client. %s
Represents the status code. %t
Represents the date and time of the request. %u
If the authentication is required, it represents the remote user. If not, a hyphen (that is, -
) is used instead.%{field}
Represents the content of the HTTP header field. The common options include %{Referer}
(the URL of the web page that referred the client to the server) and%{User-Agent}
(the type of the web browser making the request).Example 18.48. Using the LogFormat directive
LogFormat "%h %l %u %t \"%r\" %>s %b" common
-
LogLevel
- The
LogLevel
directive allows you to customize the verbosity level of the error log. It takes the following form:LogLevel option
The option has to be a valid keyword as described in Table 18.12, “Available LogLevel options”. The default option iswarn
.Table 18.12. Available LogLevel options Option Description emerg
Only the emergency situations when the server cannot perform its work are logged. alert
All situations when an immediate action is required are logged. crit
All critical conditions are logged. error
All error messages are logged. warn
All warning messages are logged. notice
Even normal, but still significant situations are logged. info
Various informational messages are logged. debug
Various debugging messages are logged. Example 18.49. Using the LogLevel directive
LogLevel warn
-
MaxKeepAliveRequests
- The
MaxKeepAliveRequests
directive allows you to specify the maximum number of requests for a persistent connection. It takes the following form:MaxKeepAliveRequests number
A high number can improve the performance of the server. Note that using0
allows unlimited number of requests. The default option is100
.Example 18.50. Using the MaxKeepAliveRequests option
MaxKeepAliveRequests 100
-
NameVirtualHost
- The
NameVirtualHost
directive allows you to specify the IP address and port number for a name-based virtual host. It takes the following form:NameVirtualHost ip-address[:port]
The ip-address can be either a full IP address, or an asterisk (that is,*
) representing all interfaces. Note that IPv6 addresses have to be enclosed in square brackets (that is,[
and]
). The port is optional.Name-based virtual hosting allows one Apache HTTP Server to serve different domains without using multiple IP addresses.Important
Name-based virtual hosts only work with non-secure HTTP connections. If using virtual hosts with a secure server, use IP address-based virtual hosts instead.Example 18.51. Using the NameVirtualHost directive
NameVirtualHost *:80
-
Options
- The
Options
directive allows you to specify which server features are available in a particular directory. It takes the following form:Options option…
The option has to be a valid keyword as described in Table 18.13, “Available server features”.Table 18.13. Available server features Option Description ExecCGI
Enables the execution of CGI scripts. FollowSymLinks
Enables following symbolic links in the directory. Includes
Enables server-side includes. IncludesNOEXEC
Enables server-side includes, but does not allow the execution of commands. Indexes
Enables server-generated directory listings. MultiViews
Enables content-negotiated “MultiViews”. SymLinksIfOwnerMatch
Enables following symbolic links in the directory when both the link and the target file have the same owner. All
Enables all of the features above with the exception of MultiViews
.None
Disables all of the features above. Important
TheSymLinksIfOwnerMatch
option is not a security feature as it can be bypassed by an attacker.Example 18.52. Using the Options directive
Options Indexes FollowSymLinks
-
Order
- The
Order
directive allows you to specify the order in which theAllow
andDeny
directives are evaluated. It takes the following form:Order option
The option has to be a valid keyword as described in Table 18.14, “Available Order options”. The default option isallow,deny
.Table 18.14. Available Order options Option Description allow,deny
Allow
directives are evaluated first.deny,allow
Deny
directives are evaluated first.Example 18.53. Using the Order directive
Order allow,deny
-
PidFile
- The
PidFile
directive allows you to specify a file to which the process ID (PID) of the server is stored. It takes the following form:PidFile path
The path refers to a pid file, and can be either absolute, or relative to the directory that is specified by theServerRoot
directive (that is,/etc/httpd/
by default). The default option isrun/httpd.pid
.Example 18.54. Using the PidFile directive
PidFile run/httpd.pid
-
ProxyRequests
- The
ProxyRequests
directive allows you to enable forward proxy requests. It takes the following form:ProxyRequests option
The option has to be a valid keyword as described in Table 18.15, “Available ProxyRequests options”. The default option isOff
.Table 18.15. Available ProxyRequests options Option Description On
Enables forward proxy requests. Off
Disables forward proxy requests. Example 18.55. Using the ProxyRequests directive
ProxyRequests On
-
ReadmeName
- The
ReadmeName
directive allows you to specify a file to be appended to the end of the server-generated directory listing. It takes the following form:ReadmeName filename
The filename is a name of the file to look for in the requested directory. By default, the server looks forREADME.html
.Example 18.56. Using the ReadmeName directive
ReadmeName README.html
-
Redirect
- The
Redirect
directive allows you to redirect a client to another URL. It takes the following form:Redirect [status] path url
The status is optional, and if provided, it has to be a valid keyword as described in Table 18.16, “Available status options”. The path refers to the old location, and must be relative to the directory specified by theDocumentRoot
directive (for example,/docs
). The url refers to the current location of the content (for example,http://docs.example.com
).Table 18.16. Available status options Status Description permanent
Indicates that the requested resource has been moved permanently. The 301
(Moved Permanently) status code is returned to a client.temp
Indicates that the requested resource has been moved only temporarily. The 302
(Found) status code is returned to a client.seeother
Indicates that the requested resource has been replaced. The 303
(See Other) status code is returned to a client.gone
Indicates that the requested resource has been removed permanently. The 410
(Gone) status is returned to a client.Note that for more advanced redirection techniques, you can use themod_rewrite
module that is part of the Apache HTTP Server installation.Example 18.57. Using the Redirect directive
Redirect permanent /docs http://docs.example.com
-
ScriptAlias
- The
ScriptAlias
directive allows you to specify the location of CGI scripts. It takes the following form:ScriptAlias url-path real-path
The url-path must be relative to the directory specified by theDocumentRoot
directive (for example,/cgi-bin/
). The real-path is a full path to a file or directory in the local file system.This directive is typically followed by theDirectory
tag with additional permissions to access the target directory. By default, the/cgi-bin/
alias is created so that the scripts located in the/var/www/cgi-bin/
are accessible.TheScriptAlias
directive is used for security reasons to prevent CGI scripts from being viewed as ordinary text documents.Example 18.58. Using the ScriptAlias directive
ScriptAlias /cgi-bin/ /var/www/cgi-bin/ <Directory "/var/www/cgi-bin"> AllowOverride None Options None Order allow,deny Allow from all </Directory>
-
ServerAdmin
- The
ServerAdmin
directive allows you to specify the email address of the server administrator to be displayed in server-generated web pages. It takes the following form:ServerAdmin email
The default option isroot@localhost
.This directive is commonly set towebmaster@hostname
, where hostname is the address of the server. Once set, aliaswebmaster
to the person responsible for the web server in/etc/aliases
, and as superuser, run thenewaliases
command.Example 18.59. Using the ServerAdmin directive
ServerAdmin webmaster@penguin.example.com
-
ServerName
- The
ServerName
directive allows you to specify the host name and the port number of a web server. It takes the following form:ServerName hostname[:port]
The hostname has to be a fully qualified domain name (FQDN) of the server. The port is optional, but when supplied, it has to match the number specified by theListen
directive.When using this directive, make sure that the IP address and server name pair are included in the/etc/hosts
file.Example 18.60. Using the ServerName directive
ServerName penguin.example.com:80
-
ServerRoot
- The
ServerRoot
directive allows you to specify the directory in which the server operates. It takes the following form:ServerRoot directory
The directory must be a full path to an existing directory in the local file system. The default option is/etc/httpd/
.Example 18.61. Using the ServerRoot directive
ServerRoot /etc/httpd
-
ServerSignature
- The
ServerSignature
directive allows you to enable displaying information about the server on server-generated documents. It takes the following form:ServerSignature option
The option has to be a valid keyword as described in Table 18.17, “Available ServerSignature options”. The default option isOn
.Table 18.17. Available ServerSignature options Option Description On
Enables appending the server name and version to server-generated pages. Off
Disables appending the server name and version to server-generated pages. EMail
Enables appending the server name, version, and the email address of the system administrator as specified by the ServerAdmin
directive to server-generated pages.Example 18.62. Using the ServerSignature directive
ServerSignature On
-
ServerTokens
- The
ServerTokens
directive allows you to customize what information is included in the Server response header. It takes the following form:ServerTokens option
The option has to be a valid keyword as described in Table 18.18, “Available ServerTokens options”. The default option isOS
.Table 18.18. Available ServerTokens options Option Description Prod
Includes the product name only (that is, Apache
).Major
Includes the product name and the major version of the server (for example, 2
).Minor
Includes the product name and the minor version of the server (for example, 2.2
).Min
Includes the product name and the minimal version of the server (for example, 2.2.15
).OS
Includes the product name, the minimal version of the server, and the type of the operating system it is running on (for example, Red Hat
).Full
Includes all the information above along with the list of loaded modules. Note that for security reasons, it is recommended to reveal as little information about the server as possible.Example 18.63. Using the ServerTokens directive
ServerTokens Prod
-
SuexecUserGroup
- The
SuexecUserGroup
directive allows you to specify the user and group under which the CGI scripts will be run. It takes the following form:SuexecUserGroup user group
The user has to be an existing user, and the group must be a valid UNIX group.For security reasons, the CGI scripts should not be run with root privileges. Note that in<VirtualHost>
,SuexecUserGroup
replaces theUser
andGroup
directives.Example 18.64. Using the SuexecUserGroup directive
SuexecUserGroup apache apache
-
Timeout
- The
Timeout
directive allows you to specify the amount of time to wait for an event before closing a connection. It takes the following form:Timeout time
The time is specified in seconds. The default option is60
.Example 18.65. Using the Timeout directive
Timeout 60
-
TypesConfig
- The
TypesConfig
allows you to specify the location of the MIME types configuration file. It takes the following form:TypesConfig path
The path refers to an existing MIME types configuration file, and can be either absolute, or relative to the directory that is specified by theServerRoot
directive (that is,/etc/httpd/
by default). The default option is/etc/mime.types
.Note that instead of editing/etc/mime.types
, the recommended way to add MIME type mapping to the Apache HTTP Server is to use theAddType
directive.Example 18.66. Using the TypesConfig directive
TypesConfig /etc/mime.types
-
UseCanonicalName
- The
UseCanonicalName
allows you to specify the way the server refers to itself. It takes the following form:UseCanonicalName option
The option has to be a valid keyword as described in Table 18.19, “Available UseCanonicalName options”. The default option isOff
.Table 18.19. Available UseCanonicalName options Option Description On
Enables the use of the name that is specified by the ServerName
directive.Off
Disables the use of the name that is specified by the ServerName
directive. The host name and port number provided by the requesting client are used instead.DNS
Disables the use of the name that is specified by the ServerName
directive. The host name determined by a reverse DNS lookup is used instead.Example 18.67. Using the UseCanonicalName directive
UseCanonicalName Off
-
User
- The
User
directive allows you to specify the user under which thehttpd
service will run. It takes the following form:User user
The user has to be an existing UNIX user. The default option isapache
.For security reasons, thehttpd
service should not be run with root privileges. Note thatUser
is no longer supported inside<VirtualHost>
, and has been replaced by theSuexecUserGroup
directive.Example 18.68. Using the User directive
User apache
-
UserDir
- The
UserDir
directive allows you to enable serving content from users' home directories. It takes the following form:UserDir option
The option can be either a name of the directory to look for in user's home directory (typicallypublic_html
), or a valid keyword as described in Table 18.20, “Available UserDir options”. The default option isdisabled
.Table 18.20. Available UserDir options Option Description enabled
user…Enables serving content from home directories of given users. disabled
[user…]Disables serving content from home directories, either for all users, or, if a space separated list of users is supplied, for given users only. Note
In order for the web server to access the content, the permissions on relevant directories and files must be set correctly. Make sure that all users are able to access the home directories, and that they can access and read the content of the directory specified by theUserDir
directive. For example:~]#
chmod a+x /home/username/
~]#chmod a+rx /home/username/public_html/
All files in this directory must be set accordingly.Example 18.69. Using the UserDir directive
UserDir public_html
18.1.5.2. Common ssl.conf Directives
/etc/httpd/conf.d/ssl.conf
:
-
SetEnvIf
- The
SetEnvIf
directive allows you to set environment variables based on the headers of incoming connections. It takes the following form:SetEnvIf option pattern [!]variable[=value]…
The option can be either a HTTP header field, a previously defined environment variable name, or a valid keyword as described in Table 18.21, “Available SetEnvIf options”. The pattern is a regular expression. The variable is an environment variable that is set when the option matches the pattern. If the optional exclamation mark (that is,!
) is present, the variable is removed instead of being set.Table 18.21. Available SetEnvIf options Option Description Remote_Host
Refers to the client's host name. Remote_Addr
Refers to the client's IP address. Server_Addr
Refers to the server's IP address. Request_Method
Refers to the request method (for example, GET
).Request_Protocol
Refers to the protocol name and version (for example, HTTP/1.1
).Request_URI
Refers to the requested resource. TheSetEnvIf
directive is used to disable HTTP keepalives, and to allow SSL to close the connection without a closing notification from the client browser. This is necessary for certain web browsers that do not reliably shut down the SSL connection.Example 18.70. Using the SetEnvIf directive
SetEnvIf User-Agent ".*MSIE.*" \ nokeepalive ssl-unclean-shutdown \ downgrade-1.0 force-response-1.0
/etc/httpd/conf.d/ssl.conf
file to be present, the mod_ssl needs to be installed. See Section 18.1.8, “Setting Up an SSL Server” for more information on how to install and configure an SSL server.
18.1.5.3. Common Multi-Processing Module Directives
IfModule
. By default, the server-pool is defined for both the prefork
and worker
MPMs.
/etc/httpd/conf/httpd.conf
:
-
MaxClients
- The
MaxClients
directive allows you to specify the maximum number of simultaneously connected clients to process at one time. It takes the following form:MaxClients number
A high number can improve the performance of the server, although it is not recommended to exceed256
when using theprefork
MPM.Example 18.71. Using the MaxClients directive
MaxClients 256
-
MaxRequestsPerChild
- The
MaxRequestsPerChild
directive allows you to specify the maximum number of request a child process can serve before it dies. It takes the following form:MaxRequestsPerChild number
Setting the number to0
allows unlimited number of requests.TheMaxRequestsPerChild
directive is used to prevent long-lived processes from causing memory leaks.Example 18.72. Using the MaxRequestsPerChild directive
MaxRequestsPerChild 4000
-
MaxSpareServers
- The
MaxSpareServers
directive allows you to specify the maximum number of spare child processes. It takes the following form:MaxSpareServers number
This directive is used by theprefork
MPM only.Example 18.73. Using the MaxSpareServers directive
MaxSpareServers 20
-
MaxSpareThreads
- The
MaxSpareThreads
directive allows you to specify the maximum number of spare server threads. It takes the following form:MaxSpareThreads number
The number must be greater than or equal to the sum ofMinSpareThreads
andThreadsPerChild
. This directive is used by theworker
MPM only.Example 18.74. Using the MaxSpareThreads directive
MaxSpareThreads 75
-
MinSpareServers
- The
MinSpareServers
directive allows you to specify the minimum number of spare child processes. It takes the following form:MinSpareServers number
Note that a high number can create a heavy processing load on the server. This directive is used by theprefork
MPM only.Example 18.75. Using the MinSpareServers directive
MinSpareServers 5
-
MinSpareThreads
- The
MinSpareThreads
directive allows you to specify the minimum number of spare server threads. It takes the following form:MinSpareThreads number
This directive is used by theworker
MPM only.Example 18.76. Using the MinSpareThreads directive
MinSpareThreads 75
-
StartServers
- The
StartServers
directive allows you to specify the number of child processes to create when the service is started. It takes the following form:StartServers number
Since the child processes are dynamically created and terminated according to the current traffic load, it is usually not necessary to change this value.Example 18.77. Using the StartServers directive
StartServers 8
-
ThreadsPerChild
- The
ThreadsPerChild
directive allows you to specify the number of threads a child process can create. It takes the following form:ThreadsPerChild number
This directive is used by theworker
MPM only.Example 18.78. Using the ThreadsPerChild directive
ThreadsPerChild 25
18.1.6. Working with Modules
httpd
service is distributed along with a number of Dynamic Shared Objects (DSOs), which can be dynamically loaded or unloaded at runtime as necessary. By default, these modules are located in /usr/lib/httpd/modules/
on 32-bit and in /usr/lib64/httpd/modules/
on 64-bit systems.
18.1.6.1. Loading a Module
LoadModule
directive as described in Section 18.1.5.1, “Common httpd.conf Directives”. Note that modules provided by a separate package often have their own configuration file in the /etc/httpd/conf.d/
directory.
Example 18.79. Loading the mod_ssl DSO
LoadModule ssl_module modules/mod_ssl.so
httpd
service.
18.1.6.2. Writing a Module
root
:
~]# yum install httpd-devel
apxs
) utility required to compile a module.
~]# apxs -i -a -c module_name.c
18.1.7. Setting Up Virtual Hosts
/etc/httpd/conf/httpd.conf
as an example, remove the hash sign (that is, #
) from the beginning of each line, and customize the options according to your requirements as shown in Example 18.80, “Example virtual host configuration”.
Example 18.80. Example virtual host configuration
NameVirtualHost *:80 <VirtualHost *:80> ServerAdmin webmaster@penguin.example.com DocumentRoot /www/docs/penguin.example.com ServerName penguin.example.com ServerAlias www.penguin.example.com ErrorLog logs/penguin.example.com-error_log CustomLog logs/penguin.example.com-access_log common </VirtualHost>
ServerName
must be a valid DNS name assigned to the machine. The <VirtualHost>
container is highly customizable, and accepts most of the directives available within the main server configuration. Directives that are not supported within this container include User
and Group
, which were replaced by SuexecUserGroup
.
Note
Listen
directive in the global settings section of the /etc/httpd/conf/httpd.conf
file accordingly.
httpd
service.
18.1.8. Setting Up an SSL Server
mod_ssl
, a module that uses the OpenSSL toolkit to provide the SSL/TLS support, is commonly referred to as the SSL server. Red Hat Enterprise Linux also supports the use of Mozilla NSS as the TLS implementation. Support for Mozilla NSS is provided by the mod_nss
module.
18.1.8.1. An Overview of Certificates and Security
Web Browser | Link |
---|---|
Mozilla Firefox | Mozilla root CA list. |
Opera | Information on root certificates used by Opera. |
Internet Explorer | Information on root certificates used by Microsoft Windows. |
Chromium | Information on root certificates used by the Chromium project. |
18.1.9. Enabling the mod_ssl Module
mod_ssl
, you cannot have another application or module, such as mod_nss
configured to use the same port. Port 443
is the default port for HTTPS.
mod_ssl
module and the OpenSSL toolkit, install the mod_ssl and openssl packages. Enter the following command as root
:
~]# yum install mod_ssl openssl
mod_ssl
configuration file at /etc/httpd/conf.d/ssl.conf
, which is included in the main Apache HTTP Server configuration file by default. For the module to be loaded, restart the httpd
service as described in Section 18.1.4.3, “Restarting the Service”.
Important
SSL
, if it is enabled, and using only TLSv1.1
or TLSv1.2
. Backwards compatibility can be achieved using TLSv1.0
. Many products Red Hat supports have the ability to use SSLv2
or SSLv3
protocols. However, the use of SSLv2
or SSLv3
is now strongly recommended against.
18.1.9.1. Enabling and Disabling SSL and TLS in mod_ssl
SSLProtocol
directive in the “## SSL Global Context” section of the configuration file and removing it everywhere else, or edit the default entry under “# SSL Protocol support” in all “VirtualHost” sections. If you do not specify it in the per-domain VirtualHost section then it will inherit the settings from the global section. To make sure that a protocol version is being disabled the administrator should either only specify SSLProtocol
in the “SSL Global Context” section, or specify it in all per-domain VirtualHost sections.
Procedure 18.1. Disable SSLv2 and SSLv3
- As
root
, open the/etc/httpd/conf.d/ssl.conf
file and search for all instances of theSSLProtocol
directive. By default, the configuration file contains one section that looks as follows:~]#
This section is within the VirtualHost section.vi /etc/httpd/conf.d/ssl.conf
# SSL Protocol support: # List the enable protocol levels with which clients will be able to # connect. Disable SSLv2 access by default: SSLProtocol all -SSLv2 - Edit the
SSLProtocol
line as follows:# SSL Protocol support: # List the enable protocol levels with which clients will be able to # connect. Disable SSLv2 access by default: SSLProtocol all -SSLv2 -SSLv3
Repeat this action for all VirtualHost sections. Save and close the file. - Verify that all occurrences of the
SSLProtocol
directive have been changed as follows:~]#
This step is particularly important if you have more than the one default VirtualHost section.grep SSLProtocol /etc/httpd/conf.d/ssl.conf
SSLProtocol all -SSLv2 -SSLv3 - Restart the Apache daemon as follows:
~]#
Note that any sessions will be interrupted.service httpd restart
Procedure 18.2. Disable All SSL and TLS Protocols Except TLS 1 and Up
- As
root
, open the/etc/httpd/conf.d/ssl.conf
file and search for all instances ofSSLProtocol
directive. By default the file contains one section that looks as follows:~]#
vi /etc/httpd/conf.d/ssl.conf
# SSL Protocol support: # List the enable protocol levels with which clients will be able to # connect. Disable SSLv2 access by default: SSLProtocol all -SSLv2 - Edit the
SSLProtocol
line as follows:# SSL Protocol support: # List the enable protocol levels with which clients will be able to # connect. Disable SSLv2 access by default: SSLProtocol -all +TLSv1 +TLSv1.1 +TLSv1.2
Save and close the file. - Verify the change as follows:
~]#
grep SSLProtocol /etc/httpd/conf.d/ssl.conf
SSLProtocol -all +TLSv1 +TLSv1.1 +TLSv1.2 - Restart the Apache daemon as follows:
~]#
Note that any sessions will be interrupted.service httpd restart
Procedure 18.3. Testing the Status of SSL and TLS Protocols
openssl s_client -connect
command. The command has the following form: openssl s_client -connect hostname:port -protocolWhere port is the port to test and protocol is the protocol version to test for. To test the SSL server running locally, use
localhost
as the host name. For example, to test the default port for secure HTTPS connections, port 443
to see if SSLv3 is enabled, issue a command as follows:
~]#
The above output indicates that the handshake failed and therefore no cipher was negotiated.openssl s_client -connect localhost:443 -ssl3
CONNECTED(00000003) 139809943877536:error:14094410:SSL routines:SSL3_READ_BYTES:sslv3 alert handshake failure:s3_pkt.c:1257:SSL alert number 40 139809943877536:error:1409E0E5:SSL routines:SSL3_WRITE_BYTES:ssl handshake failure:s3_pkt.c:596: output omitted New, (NONE), Cipher is (NONE) Secure Renegotiation IS NOT supported Compression: NONE Expansion: NONE SSL-Session: Protocol : SSLv3 output truncated~]$
The above output indicates that no failure of the handshake occurred and a set of ciphers was negotiated.openssl s_client -connect localhost:443 -tls1_2
CONNECTED(00000003) depth=0 C = --, ST = SomeState, L = SomeCity, O = SomeOrganization, OU = SomeOrganizationalUnit, CN = localhost.localdomain, emailAddress = root@localhost.localdomain output omitted New, TLSv1/SSLv3, Cipher is ECDHE-RSA-AES256-GCM-SHA384 Server public key is 2048 bit Secure Renegotiation IS supported Compression: NONE Expansion: NONE SSL-Session: Protocol : TLSv1.2 output truncated
openssl s_client
command options are documented in the s_client(1)
manual page.
18.1.10. Enabling the mod_nss Module
mod_nss
, the HTTPS server cannot simultaneously use mod_ssl
with its default settings as mod_ssl
will use port 443
by default, however this is the default HTTPS port. If is recommend to remove the package if it is not required.
root
:
~]# yum remove mod_ssl
Note
mod_ssl
is required for other purposes, modify the /etc/httpd/conf.d/ssl.conf
file to use a port other than 443
to prevent mod_ssl
conflicting with mod_nss
when its port to listen on is changed to 443
.
mod_nss
and mod_ssl
can only co-exist at the same time if they use unique ports. For this reason mod_nss
by default uses 8443
, but the default port for HTTPS is port 443
. The port is specified by the Listen
directive as well as in the VirtualHost name or address.
Procedure 18.4. Configuring mod_nss
- Install mod_nss as
root
:~]#
yum install mod_nss
This will create themod_nss
configuration file at/etc/httpd/conf.d/nss.conf
. The/etc/httpd/conf.d/
directory is included in the main Apache HTTP Server configuration file by default. For the module to be loaded, restart thehttpd
service as described in Section 18.1.4.3, “Restarting the Service”. - As
root
, open the/etc/httpd/conf.d/nss.conf
file and search for all instances of theListen
directive.Edit theListen 8443
line as follows:Listen 443
Port443
is the default port forHTTPS
. - Edit the default
VirtualHost _default_:8443
line as follows:VirtualHost _default_:443
Edit any other non-default virtual host sections if they exist. Save and close the file. - Mozilla NSS stores certificates in a server certificate database indicated by the
NSSCertificateDatabase
directive in the/etc/httpd/conf.d/nss.conf
file. By default the path is set to/etc/httpd/alias
, the NSS database created during installation.To view the default NSS database, issue a command as follows:~]#
In the above command output,certutil -L -d /etc/httpd/alias
Certificate Nickname Trust Attributes SSL,S/MIME,JAR/XPI cacert CTu,Cu,Cu Server-Cert u,u,u alpha u,pu,uServer-Cert
is the defaultNSSNickname
. The-L
option lists all the certificates, or displays information about a named certificate, in a certificate database. The-d
option specifies the database directory containing the certificate and key database files. See thecertutil(1)
man page for more command line options. - To configure mod_nss to use another database, edit the
NSSCertificateDatabase
line in the/etc/httpd/conf.d/nss.conf
file. The default file has the following lines within the VirtualHost section.# Server Certificate Database: # The NSS security database directory that holds the certificates and # keys. The database consists of 3 files: cert8.db, key3.db and secmod.db. # Provide the directory that these files exist. NSSCertificateDatabase /etc/httpd/alias
In the above command output,alias
is the default NSS database directory,/etc/httpd/alias/
. - To apply a password to the default NSS certificate database, use the following command as
root
:~]#
certutil -W -d /etc/httpd/alias
Enter Password or Pin for "NSS Certificate DB": Enter a password which will be used to encrypt your keys. The password should be at least 8 characters long, and should contain at least one non-alphabetic character. Enter new password: Re-enter password: Password changed successfully. - Before deploying the HTTPS server, create a new certificate database using a certificate signed by a certificate authority (CA).
Example 18.81. Adding a Certificate to the Mozilla NSS database
Thecertutil
command is used to add a CA certificate to the NSS database files:certutil
-d
/etc/httpd/nss-db-directory/
-A
-n
"CA_certificate"-t
CT,,
-a
-i
certificate.pem
The above command adds a CA certificate stored in a PEM-formatted file named certificate.pem. The-d
option specifies the NSS database directory containing the certificate and key database files, the-n
option sets a name for the certificate,-t
CT,,
means that the certificate is trusted to be used in TLS clients and servers. The-A
option adds an existing certificate to a certificate database. If the database does not exist it will be created. The-a
option allows the use of ASCII format for input or output, and the-i
option passes thecertificate.pem
input file to the command.See thecertutil(1)
man page for more command line options. - The NSS database should be password protected to safeguard the private key.
Example 18.82. Setting_a_Password_for_a_Mozilla_NSS_database
Thecertutil
tool can be used to set a password for an NSS database as follows:certutil -W -d /etc/httpd/nss-db-directory/
For example, for the default database, issue a command asroot
as follows:~]#
certutil -W -d /etc/httpd/alias
Enter Password or Pin for "NSS Certificate DB": Enter a password which will be used to encrypt your keys. The password should be at least 8 characters long, and should contain at least one non-alphabetic character. Enter new password: Re-enter password: Password changed successfully. - Configure
mod_nss
to use the NSS internal software token by changing the line with theNSSPassPhraseDialog
directive as follows:~]#
This is to avoid manual password entry on system start. The software token exists in the NSS database but you can also have a physical token containing your certificates.vi /etc/httpd/conf.d/nss.conf
NSSPassPhraseDialog file:/etc/httpd/password.conf - If the SSL Server Certificate contained in the NSS database is an RSA certificate, make certain that the
NSSNickname
parameter is uncommented and matches the nickname displayed in step 4 above:~]#
vi /etc/httpd/conf.d/nss.conf
NSSNickname Server-CertIf the SSL Server Certificate contained in the NSS database is an ECC certificate, make certain that theNSSECCNickname
parameter is uncommented and matches the nickname displayed in step 4 above:~]#
vi /etc/httpd/conf.d/nss.conf
NSSECCNickname Server-CertMake certain that theNSSCertificateDatabase
parameter is uncommented and points to the NSS database directory displayed in step 4 or configured in step 5 above:~]#
Replacevi /etc/httpd/conf.d/nss.conf
NSSCertificateDatabase /etc/httpd/alias/etc/httpd/alias
with the path to the certificate database to be used. - Create the
/etc/httpd/password.conf
file asroot
:~]#
Add a line with the following form:vi /etc/httpd/password.conf
internal:password
Replacing password with the password that was applied to the NSS security databases in step 6 above. - Apply the appropriate ownership and permissions to the
/etc/httpd/password.conf
file:~]#
chgrp apache /etc/httpd/password.conf
~]# chmod 640 /etc/httpd/password.conf ~]# ls -l /etc/httpd/password.conf -rw-r-----. 1 root apache 10 Dec 4 17:13 /etc/httpd/password.conf - To configure
mod_nss
to use the NSS the software token in/etc/httpd/password.conf
, edit/etc/httpd/conf.d/nss.conf
as follows:~]#
vi /etc/httpd/conf.d/nss.conf
- Restart the Apache server for the changes to take effect as described in Section 18.1.4.3, “Restarting the Service”
Important
SSL
, if it is enabled, and using only TLSv1.1
or TLSv1.2
. Backwards compatibility can be achieved using TLSv1.0
. Many products Red Hat supports have the ability to use SSLv2
or SSLv3
protocols. However, the use of SSLv2
or SSLv3
is now strongly recommended against.
18.1.10.1. Enabling and Disabling SSL and TLS in mod_nss
NSSProtocol
directive in the “## SSL Global Context” section of the configuration file and removing it everywhere else, or edit the default entry under “# SSL Protocol” in all “VirtualHost” sections. If you do not specify it in the per-domain VirtualHost section then it will inherit the settings from the global section. To make sure that a protocol version is being disabled the administrator should either only specify NSSProtocol
in the “SSL Global Context” section, or specify it in all per-domain VirtualHost sections.
Procedure 18.5. Disable All SSL and TLS Protocols Except TLS 1 and Up in mod_nss
- As
root
, open the/etc/httpd/conf.d/nss.conf
file and search for all instances of theNSSProtocol
directive. By default, the configuration file contains one section that looks as follows:~]#
This section is within the VirtualHost section.vi /etc/httpd/conf.d/nss.conf
# SSL Protocol: output omitted # Since all protocol ranges are completely inclusive, and no protocol in the # middle of a range may be excluded, the entry "NSSProtocol SSLv3,TLSv1.1" # is identical to the entry "NSSProtocol SSLv3,TLSv1.0,TLSv1.1". NSSProtocol TLSv1.0,TLSv1.1,TLSv1.2 - Edit the
NSSProtocol
line as follows:# SSL Protocol: NSSProtocol TLSv1.0,TLSv1.1,TLSv1.2
Repeat this action for all VirtualHost sections. - Edit the
Listen 8443
line as follows:Listen 443
- Edit the default
VirtualHost _default_:8443
line as follows:VirtualHost _default_:443
Edit any other non-default virtual host sections if they exist. Save and close the file. - Verify that all occurrences of the
NSSProtocol
directive have been changed as follows:~]#
This step is particularly important if you have more than one VirtualHost section.grep NSSProtocol /etc/httpd/conf.d/nss.conf
# middle of a range may be excluded, the entry "NSSProtocol SSLv3,TLSv1.1" # is identical to the entry "NSSProtocol SSLv3,TLSv1.0,TLSv1.1". NSSProtocol TLSv1.0,TLSv1.1,TLSv1.2 - Restart the Apache daemon as follows:
~]#
Note that any sessions will be interrupted.service httpd restart
Procedure 18.6. Testing the Status of SSL and TLS Protocols in mod_nss
openssl s_client -connect
command. Install the openssl package as root
:
~]# yum install openssl
openssl s_client -connect
command has the following form: openssl s_client -connect hostname:port -protocolWhere port is the port to test and protocol is the protocol version to test for. To test the SSL server running locally, use
localhost
as the host name. For example, to test the default port for secure HTTPS connections, port 443
to see if SSLv3 is enabled, issue a command as follows:
~]#
The above output indicates that the handshake failed and therefore no cipher was negotiated.openssl s_client -connect localhost:443 -ssl3
CONNECTED(00000003) 3077773036:error:1408F10B:SSL routines:SSL3_GET_RECORD:wrong version number:s3_pkt.c:337: output omitted New, (NONE), Cipher is (NONE) Secure Renegotiation IS NOT supported Compression: NONE Expansion: NONE SSL-Session: Protocol : SSLv3 output truncated~]$
The above output indicates that no failure of the handshake occurred and a set of ciphers was negotiated.openssl s_client -connect localhost:443 -tls1_2
CONNECTED(00000003) depth=1 C = US, O = example.com, CN = Certificate Shack output omitted New, TLSv1/SSLv3, Cipher is AES256-SHA Server public key is 1024 bit Secure Renegotiation IS supported Compression: NONE Expansion: NONE SSL-Session: Protocol : TLSv1.2 Cipher : AES256-SHA output truncated
openssl s_client
command options are documented in the s_client(1)
manual page.
18.1.11. Using an Existing Key and Certificate
- You are changing the IP address or domain name.Certificates are issued for a particular IP address and domain name pair. If one of these values changes, the certificate becomes invalid.
- You have a certificate from VeriSign, and you are changing the server software.VeriSign, a widely used certificate authority, issues certificates for a particular software product, IP address, and domain name. Changing the software product renders the certificate invalid.
/etc/pki/tls/private/
and /etc/pki/tls/certs/
directories respectively. You can do so by issuing the following commands as root
:
~]#mv
key_file.key
/etc/pki/tls/private/hostname.key
~]#mv
certificate.crt
/etc/pki/tls/certs/hostname.crt
/etc/httpd/conf.d/ssl.conf
configuration file:
SSLCertificateFile /etc/pki/tls/certs/hostname.crt SSLCertificateKeyFile /etc/pki/tls/private/hostname.key
httpd
service as described in Section 18.1.4.3, “Restarting the Service”.
Example 18.83. Using a key and certificate from the Red Hat Secure Web Server
~]#mv /etc/httpd/conf/httpsd.key /etc/pki/tls/private/penguin.example.com.key
~]#mv /etc/httpd/conf/httpsd.crt /etc/pki/tls/certs/penguin.example.com.crt
18.1.12. Generating a New Key and Certificate
root
:
~]# yum install crypto-utils mod_ssl
Important
~]# openssl req -x509 -new -set_serial number -key hostname.key -out hostname.crt
Note
root
:
~]# rm /etc/pki/tls/private/hostname.key
genkey
command as root
, followed by the appropriate host name (for example, penguin.example.com
):
~]# genkey
hostname
- Review the target locations in which the key and certificate will be stored.
Figure 18.1. Running the genkey utility
Use the Tab key to select thebutton, and press Enter to proceed to the next screen. - Using the up and down arrow keys, select a suitable key size. Note that while a larger key increases the security, it also increases the response time of your server. The NIST recommends using
2048 bits
. See NIST Special Publication 800-131A.Figure 18.2. Selecting the key size
Once finished, use the Tab key to select thebutton, and press Enter to initiate the random bits generation process. Depending on the selected key size, this may take some time. - Decide whether you want to send a certificate request to a certificate authority.
Figure 18.3. Generating a certificate request
Use the Tab key to selectto compose a certificate request, or to generate a self-signed certificate. Then press Enter to confirm your choice. - Using the Spacebar key, enable (
[*]
) or disable ([ ]
) the encryption of the private key.Figure 18.4. Encrypting the private key
Use the Tab key to select thebutton, and press Enter to proceed to the next screen. - If you have enabled the private key encryption, enter an adequate passphrase. Note that for security reasons, it is not displayed as you type, and it must be at least five characters long.
Figure 18.5. Entering a passphrase
Use the Tab key to select thebutton, and press Enter to proceed to the next screen.Important
Entering the correct passphrase is required in order for the server to start. If you lose it, you will need to generate a new key and certificate. - Customize the certificate details.
Figure 18.6. Specifying certificate information
Use the Tab key to select thebutton, and press Enter to finish the key generation. - If you have previously enabled the certificate request generation, you will be prompted to send it to a certificate authority.
Figure 18.7. Instructions on how to send a certificate request
Press Enter to return to a shell prompt.
/etc/httpd/conf.d/ssl.conf
configuration file:
SSLCertificateFile /etc/pki/tls/certs/hostname.crt SSLCertificateKeyFile /etc/pki/tls/private/hostname.key
httpd
service as described in Section 18.1.4.3, “Restarting the Service”, so that the updated configuration is loaded.
18.1.13. Configure the Firewall for HTTP and HTTPS Using the Command Line
HTTP
and HTTPS
traffic by default. To enable the system to act as a web server, enable ports and protocols as required. The default port for HTTP
is 80
and the default port for HTTPS
is 443
. In both cases the TCP
should be allowed to pass through the firewall.
80
for HTTP
using the command line, issue the following command as root
:
~]# lokkit --port=80:tcp --update
Note that this will restart the firewall as long as it has not been disabled with the --disabled
option. Active connections will be terminated and time out on the initiating machine. Use the lokkit --help
command to view the built in help.
443
for HTTPS
using the command line, issue the following command as root
:
~]# lokkit --port=443:tcp --update
Note that this will restart the firewall as long as it has not been disabled with the --disabled
option. Active connections will be terminated and time out on the initiating machine. See the /etc/services
file for list of services and their associated ports.
/etc/sysconfig/system-config-firewall
file thoroughly after editing. To apply the settings in /etc/sysconfig/system-config-firewall
, issue the following command as root
:
~]# lokkit --update
HTTPS
to pass through the firewall, by editing the configuration file, become the root
user and add the following line to /etc/sysconfig/system-config-firewall
:
--port=443:tcpNote that these changes will not take effect even if the firewall is reloaded or the system rebooted. To apply the changes in
/etc/sysconfig/system-config-firewall
, issue the following command as root
:
~]# lokkit --update
18.1.13.1. Checking Network Access for Incoming HTTPS and HTTPS Using the Command Line
root
:
~]# less /etc/sysconfig/system-config-firewall
# Configuration file for system-config-firewall
--enabled
--service=ssh
In this example taken from a default installation, the firewall is enabled but HTTP
and HTTPS
have not been allowed to pass through.
HTTP
is enabled, the following line appears as output in addition to the lines shown above:
--port=80:tcp
HTTP
traffic for clients, issue the following command as root
:
~]# iptables -L -n | grep 'tcp.*80'
ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:80
HTTPS
is enabled, the following line appears as output in addition to the lines shown above:
--port=443:tcp
HTTPS
traffic for clients, issue the following command as root
:
~]# iptables -L -n | grep 'tcp.*443'
ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:443
18.1.14. Additional Resources
Installed Documentation
httpd(8)
— The manual page for thehttpd
service containing the complete list of its command-line options.genkey(1)
— The manual page forgenkey
utility, provided by the crypto-utils package.
Installable Documentation
- http://localhost/manual/ — The official documentation for the Apache HTTP Server with the full description of its directives and available modules. Note that in order to access this documentation, you must have the httpd-manual package installed, and the web server must be running.Before accessing the documentation, issue the following commands as
root
:~]#
yum install httpd-manual
~]#service httpd graceful
Online Documentation
- http://httpd.apache.org/ — The official website for the Apache HTTP Server with documentation on all the directives and default modules.
- http://www.openssl.org/ — The OpenSSL home page containing further documentation, frequently asked questions, links to the mailing lists, and other useful resources.