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Apache HTTP Server
Server-Wide Configuration
This document explains some of the directives provided by the
core server which are used to configure
the basic operations of the server.
The ServerAdmin and ServerTokens directives control what
information about the server will be presented in server-generated documents such as error
messages. The ServerTokens directive sets the value of the Server HTTP response
header field.
The ServerName and UseCanonicalName directives are used by the
server to determine how to construct self-referential URLs. For example, when a client
requests a directory, but does not include the trailing slash in the directory name, Apache
must redirect the client to the full name including the trailing slash so that the client will
correctly resolve relative references in the document.
These directives control the locations of the various files that Apache needs for proper
operation. When the pathname used does not begin with a slash "/", the files are
located relative to the ServerRoot. Be careful about locating files in paths
which are writable by non-root users. See the
security tips documentation
for more details.
When ServerType is set to its recommended value of Standalone,
Apache 1.3 for Unix is a pre-forking web server. A single control process is responsible for
launching child processes which listen for connections and serve them when they arrive. Apache
always tries to maintain several spare or idle server processes, which stand ready to
serve incoming requests. In this way, clients do not need to wait for a new child processes to
be forked before their requests can be served.
The StartServers, MinSpareServers, MaxSpareServers,
and MaxServers regulate how the parent process creates children to serve
requests. In general, Apache is very self-regulating, so most sites do not need to adjust
these directives from their default values. Sites which need to serve more than 256
simultaneous requests may need to increase MaxClients, while sites with limited
memory may need to decrease MaxClients to keep the server from thrashing
(swapping memory to disk and back). More information about tuning process creation is provided
in the performance hints
documentation.
While the parent process is usually started as root under Unix in order to bind to port 80,
the child processes are launched by Apache as a less-privileged user. The User
and Group directives are used to set the privileges of the Apache child
processes. The child processes must be able to read all the content that will be served, but
should have as few privileges beyond that as possible. In addition, unless
suexec is used, these directives also set
the privileges which will be inherited by CGI scripts.
MaxRequestsPerChild controls how frequently the server recycles processes by
killing old ones and launching new ones.
Under Windows, Apache launches one control process and one child process. The child process
creates multiple threads to serve requests. The number of threads is controlled by the ThreadsPerChild
directive.
When Apache starts, it connects to some port and address on the local machine and waits for
incoming requests. By default, it listens to all addresses on the machine, and to the port as
specified by the Port directive in the server configuration. However, it can be
told to listen to more than one port, to listen to only selected addresses, or a combination.
This is often combined with the
Virtual Host
feature which determines how Apache responds to different IP addresses, hostnames and ports.
There are two directives used to restrict or specify which addresses and ports Apache
listens to. The BindAddress directive is used to restrict the server to listening
to a single IP address. The Listen directive can be used to specify multiple IP
addresses and/or Ports to which Apache will listen.
The ListenBackLog, SendBufferSize, and TimeOut
directives are used to adjust how Apache interacts with the network.AcceptFilter
controls a BSD specific filter optimization. See the BSD section on
performance hints documentation. AcceptMutex
controls which accept mutex method will be used. For an explanation of what this is and why
it's needed, see the performance
tuning guide
The KeepAlive, KeepAliveTimeout, and MaxKeepAliveRequests
directives are used to configure how Apache handles persistent connections.
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The LimitRequest* directives are used to place limits on the amount of
resources Apache will use in reading requests from clients. By limiting these values, some
kinds of denial of service attacks can be mitigated.
The RLimit* directives are used to limit the amount of resources which can be
used by processes forked off from the Apache children. In particular, this will control
resources used by CGI scripts and SSI exec commands.
The ThreadStackSize directive is used only on Netware to control the stack
size.
Apache HTTP Server
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