Apache Core Features

These configuration parameters control the core Apache features, and are always available.

AccessConfig directive

Syntax: AccessConfig filename
Default: AccessConfig conf/access.conf
Context: server config, virtual host
Status: core

The server will read this file for more directives after reading the ResourceConfig file. Filename is relative to the ServerRoot. This feature can be disabled using:

AccessConfig /dev/null
Historically, this file only contained <Directory> sections; in fact it can now contain any server directive allowed in the server config context.


AccessFileName directive

Syntax: AccessFileName filename
Default: AccessFileName .htaccess
Context: server config, virtual host
Status: core

When returning a document to the client the server looks for an access control file with this name in every directory of the path to the document, if access control files are enabled for that directory. For example:

AccessFileName .acl
before returning the document /usr/local/web/index.html, the server will read /.acl, /usr/.acl, /usr/local/.acl and /usr/local/web/.acl for directives, unless they have been disabled with
<Directory />
AllowOverride None
</Directory>


AllowOverride directive

Syntax: AllowOverride override override ...
Default: AllowOverride All
Context: directory
Status: core

When the server finds an .htaccess file (as specified by AccessFileName) it needs to know which directives declared in that file can override earlier access information.

Override can be set to None, in which case the server will not read the file, All in which case the server will allow all the directives, or one or more of the following:

AuthConfig
Allow use of the authorization directives (AuthDBMGroupFile, AuthDBMUserFile, AuthGroupFile, AuthName, AuthType, AuthUserFile and require).
FileInfo
Allow use of the directives controlling document types (AddEncoding, AddLanguage, AddType, DefaultType and LanguagePriority).
Indexes
Allow use of the directives controlling directory indexing (AddDescription, AddIcon, AddIconByEncoding, AddIconByType, DefaultIcon, DirectoryIndex, FancyIndexing, HeaderName, IndexIgnore, IndexOptions and ReadmeName).
Limit
Allow use of the directives controlling host access (allow, deny and order).
Options
Allow use of the directives controlling specific directory features (Options and XBitHack).


AuthName directive

Syntax: AuthName auth-domain
Context: directory, .htaccess
Override: AuthConfig
Status: core

This directive sets the name of the authorization realm for a directory. This realm is given to the client so that the user knows which username and password to send. It must be accompanied by AuthType and require directives, and directives such as AuthUserFile and AuthGroupFile to work.


AuthType directive

Syntax: AuthType type
Context: directory, .htaccess
Override: AuthConfig
Status: core

This directive selects the type of user authentication for a directory. Only Basic is currently implemented. It must be accompanied by AuthName and require directives, and directives such as AuthUserFile and AuthGroupFile to work.


BindAddress directive

Syntax: BindAddress saddr
Default: BindAddress *
Context: server config
Status: core

A Unix® http server can either listen on for connections to every IP address of the server machine, or just one IP address of the server machine. Saddr can be

  • *
  • An IP address
  • A fully-qualified internet domain name
  • If the value is *, then the server will listen for connections on every IP address, otherwise it will only listen on the IP address specified.

    This option can be used as an alternative method for supporting virtual hosts instead of using <VirtualHost> sections.


    DefaultType directive

    Syntax: DefaultType mime-type
    Default: DefaultType text/html
    Context: server config, virtual host, directory, .htaccess
    Override: FileInfo
    Status: core

    There will be times when the server is asked to provide a document whose type cannot be determined by its MIME types mappings.

    The server must inform the client of the content-type of the document, so in the event of an unknown type it uses the DefaultType. For example:

    DefaultType image/gif
    would be appropriate for a directory which contained many gif images with filenames missing the .gif extension.


    <Directory> directive

    Syntax: <Directory directory> ... </Directory>
    Context: server config, virtual host
    Status: Core.

    <Directory> and </Directory> are used to enclose a group of directives which will apply only to the named directory and sub-directories of that directory. Any directive which is allowed in a directory context may be used. Directory is either the full path to a directory, or a wildcard string. In a wildcard string, `?' matches any single character, and `*' matches any sequences of characters. Example:

    <Directory /usr/local/httpd/htdocs>
    Options Indexes FollowSymLinks
    </Directory>
    If multiple directory sections match the directory (or its parents) containing a document, then the directives are applied in the order of shortest match first, interspersed with the directives from the .htaccess files. For example, with
    <Directory />
    AllowOverride None
    </Directory>

    <Directory /home/*>
    AllowOverride FileInfo
    </Directory>
    The for access to the document /home/web/dir/doc.html the steps are:
  • Apply directive AllowOverride None (disabling .htaccess files).
  • Apply directive AllowOverride FileInfo (for directory /home/web).
  • Apply any FileInfo directives in /home/web/.htaccess
  • The directory sections typically occur in the access.conf file, but they may appear in any configuration file. <Directory> directives cannot nest, and cannot appear in a <Limit> section.


    DocumentRoot directive

    Syntax: DocumentRoot directory-filename
    Default: DocumentRoot /usr/local/etc/httpd/htdocs
    Context: server config, virtual host
    Status: core

    This directive sets the directory from which httpd will serve files. Unless matched by a directive like Alias, the server appends the path from the requested URL to the document root to make the path to the document. Example:

    DocumentRoot /usr/web
    then an access to http://www.my.host.com/index.html refers to /usr/web/index.html.

    There appears to be a bug in mod_dir which causes problems when the DocumentRoot has a trailing slash (i.e. "DocumentRoot /usr/web/") so please avoid that.


    ErrorDocument directive

    Syntax: ErrorDocument error-code document
    Context server config, virtual host
    Status: core

    In the event of a problem or error, Apache can be configured to do one of four things,

    1. behave like NCSA httpd 1.3
    2. output a customized message
    3. redirect to a local URL to handle the problem/error
    4. redirect to an external URL to handle the problem/error

    2-4 are configured using ErrorDocument, which is followed by the HTTP response code and a message or URL.

    Messages in this context, begin with a single quote ("), which does not form part of the message itself. Apache will sometime offer additional information regarding the problem/error. This can be embedded into the message using %s

    URLs will begin with a slash (/) for local URLs, or will be a full URL which the client can resolve. Examples:

    ErrorDocument 500 /cgi-bin/tester
    ErrorDocument 404 /cgi-bin/bad_urls.pl
    ErrorDocument 401 http://www2.foo.bar/subscription_info.html
    ErrorDocument 403 "Sorry can't allow you access today
    See Also: documentation of customizable responses.


    ErrorLog directive

    Syntax: ErrorLog filename
    Default: ErrorLog logs/error_log
    Context: server config, virtual host
    Status: core

    The error log directive sets the name of the file to which the server will log any errors it encounters. If the filename does not begin with a slash (/) then it is assumed to be relative to the ServerRoot. Example:

    ErrorLog /dev/null
    This effectively turns off error logging.


    Group directive

    Syntax: Group unix-group
    Default: Group #-1
    Context: server config
    Status: core

    The Group directive sets the group under which the server will answer requests. In order to use this directive, the standalone server must be run initially as root. Unix-group is one of:

    A group name
    Refers to the given group by name.
    # followed by a group number.
    Refers to a group by its number.
    It is recommended that you set up a new group specifically for running the server. Some admins use user nobody, but this is not always possible or desirable.

    Note: if you start the server as a non-root user, it will fail to change to the specified, and will instead continue to run as the group of the original user.

    SECURITY: See User for a discussion of the security considerations.


    IdentityCheck directive

    Syntax: IdentityCheck boolean
    Default: IdentityCheck off
    Context: server config
    Status: core

    This directive enables RFC931-compliant logging of the remote user name for each connection, where the client machine runs identd or something similar. This information is logged in the access log. Boolean is either on or off.

    The information should not trusted in any way except for rudimentary usage tracking.


    <Limit> directive

    Syntax: <Limit method method ... > ... </Limit>
    Context: any
    Status: core

    <Limit> and </Limit> are used to enclose a group of access control directives which will then apply only to the specified access methods, where method is any valid HTTP method. Any directive except another <Limit> or <Directory> may be used; the majority will be unaffected by the <Limit>. Example:

    <Limit GET POST>
    require valid-user
    </Limit>
    If an access control directive appears outside a <Limit> directive, then it applies to all access methods.


    MaxClients directive

    Syntax: MaxClients number
    Default: MaxClients 150
    Context: server config
    Status: core

    The MaxClients directive sets the limit on the number of simultaneous requests that can be supported; not more than this number of child server processes will be created.


    MaxRequestsPerChild directive

    Syntax: MaxRequestsPerChild number
    Default: MaxRequestsPerChild 0
    Context: server config
    Status: core

    The MaxRequestsPerChild directive sets the limit on the number of requests that an individual child server process will handle. After MaxRequestsPerChild requests, the child process will die. If MaxRequestsPerChild is 0, then the process will never expire.

    Setting MaxRequestsPerChild to a non-zero limit has two beneficial effects:


    MaxSpareServers directive

    Syntax: MaxSpareServers number
    Default: MaxSpareServers 10
    Context: server config
    Status: core

    The MaxSpareServers directive sets the desired maximum number of idle child server processes. An idle process is one which is not handling a request. If there are more than MaxSpareServers idle, then the parent process will kill off the excess processes.

    Tuning of this parameter should only be necessary on very busy sites. Setting this parameter to a large number is almost always a bad idea.

    See also MinSpareServers and StartServers.


    MinSpareServers directive

    Syntax: MinSpareServers number
    Default: MinSpareServers 5
    Context: server config
    Status: core

    The MinSpareServers directive sets the desired minimum number of idle child server processes. An idle process is one which is not handling a request. If there are fewer than MinSpareServers idle, then the parent process creates new children at a maximum rate of 1 per second.

    Tuning of this parameter should only be necessary on very busy sites. Setting this parameter to a large number is almost always a bad idea.

    See also MaxSpareServers and StartServers.


    Options directive

    Syntax: Options option option ...
    Context: server config, virtual host, directory, .htaccess
    Override: Options
    Status: core

    The Options directive controls which server features are available in a particular directory.

    option can be set to None, in which case none of the extra features are enabled, or one or more of the following:

    All
    All options except for MultiViews.
    ExecCGI
    Execution of CGI scripts is permitted.
    FollowSymLinks
    The server will follow symbolic links in this directory.
    Includes
    Server-side includes are permitted.
    IncludesNOEXEC
    Server-side includes are permitted, but the #exec command and #include of CGI scripts are disabled.
    Indexes
    If a URL which maps to a directory is requested, and the there is no DirectoryIndex (e.g. index.html) in that directory, then the server will return a formatted listing of the directory.
    MultiViews
    Ccontent negotiatad MultiViews are allowed.
    SymLinksIfOwnerMatch
    The server will only follow symbolic links for which the target file or directory is owned by the same user id as the link.
    If multiple Options could apply to a directory, then the most specific one is taken complete; the options are not merged. For example:
    <Directory /web/docs>
    Options Indexes FollowSymLinks
    </Directory>
    <Directory /web/docs/spec>
    Options Includes
    </Directory>
    then only Includes will be set for the /web/docs/spec directory.


    PidFile directive

    Syntax: PidFile filename
    Default: PidFile logs/httpd.pid
    Context: server config
    Status: core

    The PidFile directive sets the file to which the server records the process id of the daemon. If the filename does not begin with a slash (/) then it is assumed to be relative to the ServerRoot. The PidFile is only used in standalone mode.

    It is often useful to be able to send the server a signal, so that it closes and then reopens its ErrorLog and TransferLog, and re-reads its configuration files. This is done by sending a SIGHUP (kill -1) signal to the process id listed in the PidFile.


    Port directive

    Syntax: Port number
    Default: Port 80
    Context: server config
    Status: core

    The Port directive sets the network port on which the server listens. Num is a number from 0 to 65535; some port numbers (especially below 1024) are reserved for particular protocols. See /etc/services for a list of some defined ports; the standard port for the http protocol is 80.

    Port 80 is one of Unix's special ports. All ports numbered below 1024 are reserved for system use, i.e. regular (non-root) users cannot make use of them; instead they can only use higher port numbers.

    To use port 80, you must start the server from the root account. After binding to the port and before accepting requests, Apache will change to a low privileged user as set by the User directive.

    If you cannot use port 80, choose any other unused port. Non-root users will have to choose a port number higher than 1023, such as 8000.

    SECURITY: if you do start the server as root, be sure not to set User to root. If you run the server as root whilst handling connections, your site may be open to a major security attack.


    require directive

    Syntax: require entity-name entity entity...
    Context: directory, .htaccess
    Override: AuthConfig
    Status: core

    This directive selects which authenticated users can access a directory. The allowed syntaxes are:

    If require appears in a <Limit> section, then it restricts access to the named methods, otherwise it restricts access for all methods. Example:

    AuthType Basic
    AuthName somedomain
    AuthUserFile /web/users
    AuthGroupFile /web/groups
    Limit <GET POST>
    require group admin
    </Limit>
    Require must be accompanied by AuthName and AuthType directives, and directives such as AuthUserFile and AuthGroupFile (to define users and groups) in order to work correctly.


    ResourceConfig directive

    Syntax: ResourceConfig filename
    Default: ResourceConfig conf/srm.conf
    Context: server config, virtual host
    Status: core

    The server will read this file for more directives after reading the httpd.conf file. Filename is relative to the ServerRoot. This feature can be disabled using:

    ResourceConfig /dev/null
    Historically, this file contained most directives except for server configuration directives and <Directory>. sections; in fact it can now contain any server directive allowed in the server config context.

    See also AccessConfig.


    ServerAdmin directive

    Syntax: ServerAdmin email-address
    Context: server config, virtual host
    Status: core

    The ServerAdmin sets the e-mail address that the server includes in any error messages it returns to the client.

    It may be worth setting up a dedicated address for this, e.g.

    ServerAdmin www-admin@foo.bar.com
    as users do not always mention that they are talking about the server!


    ServerName directive

    Syntax: ServerName fully-qualified domain name
    Context: server config, virtual host
    Status: core

    The ServerName directive sets the hostname of the server; this is only used when creating redirection URLs. If it is not specified, then the server attempts to deduce it from its own IP address; however this may not work reliably, or may not return the preferred hostname. For example:

    ServerName www.wibble.com
    would be used if the canonical (main) name of the actual machine were monster.wibble.com.


    ServerRoot directive

    Syntax: ServerRoot directory-filename
    Default: ServerRoot /usr/local/etc/httpd
    Context: server config
    Status: core

    The ServerRoot directive sets the directory in which the server lives. Typically it will contain the subdirectories conf/ and logs/. Relative paths for other configuration files are taken as relative to this directory.


    ServerType directive

    Syntax: ServerType type
    Default: ServerType standalone
    Context: server config
    Status: core

    The ServerType directive sets how the server is executed by the system. Type is one of

    inetd
    The server will be run from the system process inetd; the command to start the server is added to /etc/inetd.conf
    standalone
    The server will run as a daemon process; the command to start the server is added to the system startup scripts. (/etc/rc.local or /etc/rc3.d/....)
    Inetd is the lesser used of the two options. For each http connection received, a new copy of the server is started from scratch; after the connection is complete, this program exits. There is a high price to pay per connection, but for security reasons, some admins prefer this option.

    Standalone is the most common setting for ServerType since it is far more efficient. The server is started once, and services all subsequent connections. If you intend running Apache to serve a busy site, standalone will probably be your only option.

    SECURITY: if you are paranoid about security, run in inetd mode. Security cannot be guaranteed in either, but whilst most people are happy to use standalone, inetd is probably least prone to attack.


    StartServers directive

    Syntax: StartServers number
    Default: StartServers 5
    Context: server config
    Status: core

    The StartServers directive sets the number of child server processes created on startup. As the number of processes is dynamically controlled depending on the load, there is usually little reason to adjust this parameter.

    See also MinSpareServers and MaxSpareServers.


    TimeOut directive

    Syntax: TimeOut number
    Default: TimeOut 1200
    Context: server config
    Status: core

    The TimeOut directive sets the maximum time that the server will wait for the receipt of a request and the completion of a request, in seconds. So if it takes more than TimeOut seconds for a client to send a request or receive a response, the server will break off the connection. Thus TimeOut limits the maximum a transfer can take; for large files, and slow networks transfer times can be large.


    User directive

    Syntax: User unix-userid
    Default: User #-1
    Context: server config
    Status: core

    The User directive sets the userid as which the server will answer requests. In order to use this directive, the standalone server must be run initially as root. Unix-userid is one of:

    A username
    Refers to the given user by name.
    # followed by a user number.
    Refers to a user by their number.
    The user should have no privileges which result in it being able to access files which are not intended to be visible to the outside world, and similarly, the user should not be able to execute code which is not meant for httpd requests. It is recommended that you set up a new user and group specifically for running the server. Some admins use user nobody, but this is not always possible or desirable.

    Notes: If you start the server as a non-root user, it will fail to change to the lesser privileged user, and will instead continue to run as that original user. If you do start the server as root, then it is normal for the parent process to remain running as root.

    SECURITY: Don't set User (or Group) to root unless you know exactly what you are doing, and what the dangers are.


    <VirtualHost> directive

    Syntax: <VirtualHost addr> ... </Directory>
    Context: server config
    Status: Core.

    <VirtualHost> and </VirtualHost> are used to enclose a group of directives which will apply only to a particular virtual host. Any directive which is allowed in a virtual host context may be used. When the server receives a request for a document on a particular virtual host, it uses the configuration directives enclosed in the <VirtualHost> section. Addr can be

  • The IP address of the virtual host
  • A fully qualified domain name for the IP address of the virtual host.
  • Example:
    <VirtualHost host.foo.com>
    ServerAdmin webmaster@host.foo.com
    DocumentRoot /www/docs/host.foo.com
    ServerName host.foo.com
    ErrorLog logs/host.foo.com-error_log
    TransferLog logs/host.foo.com-access_log
    </VirtualHost>
    Currently, each VirtualHost must correspond to a different IP address for the server, so the server machine must be configured to accept IP packets for multiple addresses. If the machine does not have multiple network interfaces, then this can be accomplished with the ifconfig alias command (if your OS supports it), or with kernel patches like VIF (for SunOS(TM) 4.1.x).

    See also information on Virtual Hosts.


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