# Apache Core Features

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

- AccessConfig
- AccessFileName
- AllowOverride
- AuthName
- AuthType
- BindAdress
- DefaultType
- <Directory>
- DocumentRoot
- ErrorDocument
- ErrorLog
- Group
- IdentityCheck
- <Limit>
- MaxClients
- MaxRequestsPerChild
- MaxSpareServers
- MinSpareServers
- Options
- PidFile
- Port
- require
- ResourceConfig
- ServerAdmin
- ServerName
- ServerRoot
- ServerType
- StartServers
- TimeOut
- User
- <VirtualHost>

## 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:

  - it limits the amount of memory that process can consume by (accidental) memory leakage;
  - by giving processes a finite lifetime, it helps reduce the number of processes when the server load reduces.

  ## 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:

  - require user userid userid ...

    Only the named users can access the directory.

  - require group group-name group-name ...

    Only users in the named groups can access the directory.

  - require valid-user

    All valid users can access the directory.

  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.