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8 <title>Glossary - Apache HTTP Server</title>
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15 <p class="apache">Apache HTTP Server Version 2.0</p>
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19 <a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="./">Version 2.0</a></div><div id="page-content"><div id="preamble"><h1>Glossary</h1>
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28 <p>This glossary defines some of the common terminology related to Apache in
29 particular, and web serving in general. More information on each concept
30 is provided in the links.</p>
32 <div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
34 <h2><a name="definitions" id="definitions">Definitions</a></h2>
37 <dt><a name="accesscontrol" id="accesscontrol">Access Control</a></dt>
38 <dd>The restriction of access to network realms. In an Apache context
39 usually the restriction of access to certain <em>URLs</em>.<br /> See: <a href="howto/auth.html">Authentication, Authorization, and Access
43 <dt><a name="algorithm" id="algorithm">Algorithm</a></dt>
45 <dd>An unambiguous formula or set of rules for solving a problem in a finite
46 number of steps. Algorithms for encryption are usually called
50 <dt><a name="apacheextensiontool" id="apacheextensiontool">APache
51 eXtension Tool</a> <a name="apxs" id="apxs">(apxs)</a></dt>
52 <dd>A perl script that aids in compiling <span title="see glossary">→</span> <a href="./glossary.html#module">module</a> sources into Dynamic Shared Objects
53 (<span title="see glossary">→</span> <a href="./glossary.html#dso">DSO</a>s) and helps install them in the
54 Apache Web server.<br />
55 See: Manual Page: <code class="program"><a href="./programs/apxs.html">apxs</a></code>
58 <dt><a name="authentication" id="authentication">Authentication</a></dt>
59 <dd>The positive identification of a network entity such as a server, a
60 client, or a user.<br />
61 See: <a href="howto/auth.html">Authentication, Authorization, and Access
65 <dt><a name="certificate" id="certificate">Certificate</a></dt>
66 <dd>A data record used for authenticating network entities such
67 as a server or a client. A certificate contains X.509 information pieces
68 about its owner (called the subject) and the signing <span title="see glossary">→</span> <a href="./glossary.html#certificationauthority">Certification Authority</a> (called
69 the issuer), plus the owner's <span title="see glossary">→</span> <a href="./glossary.html#publickey">public
71 signature made by the CA. Network entities verify these signatures
72 using CA certificates.<br />
73 See: <a href="ssl/">SSL/TLS Encryption</a>
76 <dt><a name="certificatsigningrequest" id="certificatsigningrequest">Certificate Signing Request</a>
77 <a name="csr" id="csr">(CSR)</a></dt>
78 <dd>An unsigned <span title="see glossary">→</span> <a href="./glossary.html#certificate">certificate</a> for
79 submission to a <span title="see glossary">→</span> <a href="./glossary.html#certificationauthority">Certification
80 Authority</a>, which signs it with the <span title="see glossary">→</span> <a href="./glossary.html#privatekey">Private Key</a> of their CA
81 <em>Certificate</em>. Once the CSR is signed, it becomes a real
83 See: <a href="ssl/">SSL/TLS Encryption</a>
86 <dt><a name="certificationauthority" id="certificationauthority">Certification Authority</a>
87 <a name="ca" id="ca">(CA)</a></dt>
88 <dd>A trusted third party whose purpose is to sign certificates for network
89 entities it has authenticated using secure means. Other network entities
90 can check the signature to verify that a CA has authenticated the bearer
91 of a certificate.<br />
92 See: <a href="ssl/">SSL/TLS Encryption</a>
95 <dt><a name="cipher" id="cipher">Cipher</a></dt>
96 <dd>An algorithm or system for data encryption. Examples are DES, IDEA, RC4,
98 See: <a href="ssl/">SSL/TLS Encryption</a>
101 <dt><a name="ciphertext" id="ciphertext">Ciphertext</a></dt>
102 <dd>The result after <span title="see glossary">→</span> <a href="./glossary.html#plaintext">Plaintext</a> is
103 passed through a <span title="see glossary">→</span> <a href="./glossary.html#cipher">Cipher</a>.<br /> See: <a href="ssl/">SSL/TLS Encryption</a>
106 <dt><a name="commongatewayinterface" id="commongatewayinterface">Common
107 Gateway Interface</a> <a name="cgi" id="cgi">(CGI)</a></dt>
108 <dd>A standard definition for an interface between a web server and an
109 external program that allows the external program to service requests.
110 The interface was originally defined by <a href="http://hoohoo.ncsa.uiuc.edu/cgi/overview.html">NCSA</a> but there
111 is also an <a href="http://cgi-spec.golux.com/">RFC project</a>.<br />
112 See: <a href="howto/cgi.html">Dynamic Content with CGI</a>
115 <dt><a name="configurationdirective" id="configurationdirective">Configuration Directive</a></dt>
116 <dd>See: <span title="see glossary">→</span> <a href="./glossary.html#directive">Directive</a></dd>
118 <dt><a name="configurationfile" id="configurationfile">Configuration
120 <dd>A text file containing <span title="see glossary">→</span> <a href="./glossary.html#directive">Directives</a>
121 that control the configuration of Apache.<br />
122 See: <a href="configuring.html">Configuration Files</a>
125 <dt><a name="connect" id="connect">CONNECT</a></dt>
126 <dd>An HTTP <span title="see glossary">→</span> <a href="./glossary.html#method">method</a> for proxying raw data
127 channels over HTTP. It can be used to encapsulate other protocols, such as
131 <dt><a name="context" id="context">Context</a></dt>
132 <dd>An area in the <span title="see glossary">→</span> <a href="./glossary.html#configurationfile">configuration
133 files</a> where certain types of <span title="see glossary">→</span> <a href="./glossary.html#directive">directives</a> are allowed.<br />
134 See: <a href="mod/directive-dict.html#Context">Terms Used to Describe
135 Apache Directives</a>
138 <dt><a name="digitalsignature" id="digitalsignature">Digital
140 <dd>An encrypted text block that validates a certificate or other file. A
141 <span title="see glossary">→</span> <a href="./glossary.html#certificationauthority">Certification Authority</a>
142 creates a signature by generating a hash of the <em>Public Key</em>
143 embedded in a <em>Certificate</em>, then encrypting the hash with its own
144 <em>Private Key</em>. Only the CA's public key can decrypt the signature,
145 verifying that the CA has authenticated the network entity that owns the
146 <em>Certificate</em>.<br />
147 See: <a href="ssl/">SSL/TLS Encryption</a>
150 <dt><a name="directive" id="directive">Directive</a></dt>
151 <dd>A configuration command that controls one or more aspects of Apache's
152 behavior. Directives are placed in the <span title="see glossary">→</span> <a href="./glossary.html#configurationfile">Configuration File</a><br />
153 See: <a href="mod/directives.html">Directive Index</a>
156 <dt><a name="dynamicsharedobject" id="dynamicsharedobject">Dynamic
157 Shared Object</a> <a name="dso" id="dso">(DSO)</a></dt>
158 <dd><span title="see glossary">→</span> <a href="./glossary.html#module">Modules</a> compiled separately from the
159 Apache <code class="program"><a href="./programs/httpd.html">httpd</a></code> binary that can be loaded on-demand.<br />
160 See: <a href="dso.html">Dynamic Shared Object Support</a>
163 <dt><a name="environmentvariable" id="environmentvariable">Environment
164 Variable</a> <a name="env-variable" id="env-variable">(env-variable)</a></dt>
165 <dd>Named variables managed by the operating system shell and used to store
166 information and communicate between programs. Apache also contains
167 internal variables that are referred to as environment variables, but are
168 stored in internal Apache structures, rather than in the shell
170 See: <a href="env.html">Environment Variables in Apache</a>
173 <dt><a name="export-crippled" id="export-crippled">Export-Crippled</a></dt>
174 <dd>Diminished in cryptographic strength (and security) in order to comply
175 with the United States' Export Administration Regulations (EAR).
176 Export-crippled cryptographic software is limited to a small key size,
177 resulting in <em>Ciphertext</em> which usually can be decrypted by brute
179 See: <a href="ssl/">SSL/TLS Encryption</a>
182 <dt><a name="filter" id="filter">Filter</a></dt>
183 <dd>A process that is applied to data that is sent or received by the
184 server. Input filters process data sent by the client to the server,
185 while output filters process documents on the server before they are sent
186 to the client. For example, the <code>INCLUDES</code> output filter
187 processes documents for <span title="see glossary">→</span> <a href="./glossary.html#ssi">Server Side
189 See: <a href="filter.html">Filters</a>
192 <dt><a name="fully-qualifieddomain-name" id="fully-qualifieddomain-name">Fully-Qualified Domain-Name</a>
193 <a name="fqdn" id="fqdn">(FQDN)</a></dt>
194 <dd>The unique name of a network entity, consisting of a hostname and a
195 domain name that can resolve to an IP address. For example,
196 <code>www</code> is a hostname, <code>example.com</code> is a domain name,
197 and <code>www.example.com</code> is a fully-qualified domain name.
200 <dt><a name="handler" id="handler">Handler</a></dt>
201 <dd>An internal Apache representation of the action to be performed when a
202 file is called. Generally, files have implicit handlers, based on the file
203 type. Normally, all files are simply served by the server, but certain
204 file types are "handled" separately. For example, the
205 <code>cgi-script</code> handler designates files to be processed as
206 <span title="see glossary">→</span> <a href="./glossary.html#cgi">CGIs</a>.<br />
207 See: <a href="handler.html">Apache's Handler Use</a>
210 <dt><a name="hash" id="hash">Hash</a></dt>
211 <dd>A mathematical one-way, irreversable algorithm generating a string with
212 fixed-length from another string of any length. Different input strings
213 will usually produce different hashes (depending on the hash function).
216 <dt><a name="header" id="header">Header</a></dt>
217 <dd>The part of the <span title="see glossary">→</span> <a href="./glossary.html#http">HTTP</a> request and
218 response that is sent before the actual content, and that contains
219 meta-information describing the content.
222 <dt><a name="htaccess" id="htaccess">.htaccess</a></dt>
223 <dd>A <span title="see glossary">→</span> <a href="./glossary.html#configurationfile">configuration file</a> that
224 is placed inside the web tree and applies configuration <span title="see glossary">→</span> <a href="./glossary.html#directive">directives</a> to the directory where it is
225 placed and all sub-directories. Despite its name, this file can hold
226 almost any type of directive, not just access-control directives.<br />
227 See: <a href="configuring.html">Configuration Files</a>
230 <dt><a name="httpd.conf" id="httpd.conf">httpd.conf</a></dt>
231 <dd>The main Apache <span title="see glossary">→</span> <a href="./glossary.html#configurationfile">configuration
232 file</a>. The default location is
233 <code>/usr/local/apache2/conf/httpd.conf</code>, but it may be moved using
234 run-time or compile-time configuration.<br />
235 See: <a href="configuring.html">Configuration Files</a>
238 <dt><a name="hypertexttransferprotocol" id="hypertexttransferprotocol">HyperText Transfer Protocol</a>
239 <a name="http" id="hhtp">(HTTP)</a></dt>
240 <dd>The standard transmission protocol used on the World Wide Web. Apache
241 implements version 1.1 of the protocol, referred to as HTTP/1.1 and
242 defined by <a href="http://ietf.org/rfc/rfc2616.txt">RFC 2616</a>.
245 <dt><a name="https" id="https">HTTPS</a></dt>
246 <dd>The HyperText Transfer Protocol (Secure), the standard encrypted
247 communication mechanism on the World Wide Web. This is actually just HTTP
248 over <span title="see glossary">→</span> <a href="./glossary.html#ssl">SSL</a>.<br />
249 See: <a href="ssl/">SSL/TLS Encryption</a>
252 <dt><a name="method" id="method">Method</a></dt>
253 <dd>In the context of <span title="see glossary">→</span> <a href="./glossary.html#http">HTTP</a>, an action to
254 perform on a resource, specified on the request line by the client. Some
255 of the methods available in HTTP are <code>GET</code>, <code>POST</code>,
256 and <code>PUT</code>.
259 <dt><a name="messagedigest" id="messagedigest">Message Digest</a></dt>
260 <dd>A hash of a message, which can be used to verify that the contents of
261 the message have not been altered in transit.<br />
262 See: <a href="ssl/">SSL/TLS Encryption</a>
265 <dt><a name="mime-type" id="mime-type">MIME-type</a></dt>
266 <dd>A way to describe the kind of document being transmitted. Its name
267 comes from that fact that its format is borrowed from the Multipurpose
268 Internet Mail Extensions. It consists of a major type and a minor type,
269 separated by a slash. Some examples are <code>text/html</code>,
270 <code>image/gif</code>, and <code>application/octet-stream</code>. In
271 HTTP, the MIME-type is transmitted in the <code>Content-Type</code>
272 <span title="see glossary">→</span> <a href="./glossary.html#header">header</a>.<br />
273 See: <a href="mod/mod_mime.html">mod_mime</a>
276 <dt><a name="module" id="module">Module</a></dt>
277 <dd>An independent part of a program. Much of Apache's functionality is
278 contained in modules that you can choose to include or exclude. Modules
279 that are compiled into the Apache <code class="program"><a href="./programs/httpd.html">httpd</a></code> binary are
280 called <dfn>static modules</dfn>, while modules that are stored
281 separately and can be optionally loaded at run-time are called
282 <dfn>dynamic modules</dfn> or <span title="see glossary">→</span> <a href="./glossary.html#dso">DSOs</a>.
283 Modules that are included by default
284 are called <dfn>base modules</dfn>. Many modules are available for Apache
285 that are not distributed as part of the Apache HTTP Server <span title="see glossary">→</span> <a href="./glossary.html#tarball">tarball</a>. These are referred to as
286 <dfn>third-party modules</dfn>.<br />
287 See: <a href="mod/">Module Index</a>
290 <dt><a name="modulemagicnumber" id="modulemagicnumber">Module Magic
291 Number</a> (<a name="mmn" id="mmn">MMN</a>)</dt>
292 <dd>Module Magic Number is a constant defined in the Apache source code that
293 is associated with binary compatibility of modules. It is changed when
294 internal Apache structures, function calls and other significant parts of
295 API change in such a way that binary compatibility cannot be guaranteed
296 any more. On MMN change, all third party modules have to be at least
297 recompiled, sometimes even slightly changed in order to work with the new
301 <dt><a name="openssl" id="openssl">OpenSSL</a></dt>
302 <dd>The Open Source toolkit for SSL/TLS<br />
303 See <a href="http://www.openssl.org/">http://www.openssl.org/</a>#
306 <dt><a name="passphrase" id="passphrase">Pass Phrase</a></dt>
307 <dd>The word or phrase that protects private key files. It prevents
308 unauthorized users from encrypting them. Usually it's just the secret
309 encryption/decryption key used for <span title="see glossary">→</span> <a href="./glossary.html#cipher">Ciphers</a>.<br />
310 See: <a href="ssl/">SSL/TLS Encryption</a>
313 <dt><a name="plaintext" id="plaintext">Plaintext</a></dt>
314 <dd>The unencrypted text.</dd>
316 <dt><a name="privatekey" id="privatekey">Private Key</a></dt>
317 <dd>The secret key in a <span title="see glossary">→</span> <a href="./glossary.html#publickeycryptography">Public Key
318 Cryptography</a> system, used to decrypt incoming messages and
319 sign outgoing ones.<br />
320 See: <a href="ssl/">SSL/TLS Encryption</a>
323 <dt><a name="proxy" id="proxy">Proxy</a></dt>
324 <dd>An intermediate server that sits between the client and the <em>origin
325 server</em>. It accepts requests from clients, transmits those requests
326 on to the origin server, and then returns the response from the origin
327 server to the client. If several clients request the same content, the
328 proxy can deliver that content from its cache, rather than requesting it
329 from the origin server each time, thereby reducing response time.<br />
330 See: <a href="mod/mod_proxy.html">mod_proxy</a>
333 <dt><a name="publickey" id="publickey">Public Key</a></dt>
334 <dd>The publicly available key in a <span title="see glossary">→</span> <a href="./glossary.html#publickeycryptography">Public Key Cryptography</a> system,
335 used to encrypt messages bound for its owner and to decrypt signatures
336 made by its owner.<br />
337 See: <a href="ssl/">SSL/TLS Encryption</a>
340 <dt><a name="publickeycryptography" id="publickeycryptography">Public Key Cryptography</a></dt>
341 <dd>The study and application of asymmetric encryption systems, which use
342 one key for encryption and another for decryption. A corresponding pair of
343 such keys constitutes a key pair. Also called Asymmetric Cryptography.
345 See: <a href="ssl/">SSL/TLS Encryption</a>
348 <dt><a name="regularexpresion" id="regularexpresion">Regular Expression</a>
349 <a name="regex" id="regex">(Regex)</a></dt>
350 <dd>A way of describing a pattern in text - for example, "all the words that
351 begin with the letter A" or "every 10-digit phone number" or even "Every
352 sentence with two commas in it, and no capital letter Q". Regular
353 expressions are useful in Apache because they let you apply certain
354 attributes against collections of files or resources in very flexible ways
355 - for example, all .gif and .jpg files under any "images" directory could
356 be written as "<code>/images/.*(jpg|gif)$</code>". Apache uses Perl
357 Compatible Regular Expressions provided by the <a href="http://www.pcre.org/">PCRE</a> library.
360 <dt><a name="reverseproxy" id="reverseproxy">Reverse Proxy</a></dt>
361 <dd>A <span title="see glossary">→</span> <a href="./glossary.html#proxy">proxy</a> server that appears to the client
362 as if it is an <em>origin server</em>. This is useful to hide the real
363 origin server from the client for security reasons, or to load balance.
366 <dt><a name="securesocketslayer" id="securesocketslayer">Secure Sockets
367 Layer</a> <a name="ssl" id="ssl">(SSL)</a></dt>
368 <dd>A protocol created by Netscape Communications Corporation for general
369 communication authentication and encryption over TCP/IP networks. The most
370 popular usage is <em>HTTPS</em>, i.e. the HyperText Transfer Protocol (HTTP)
372 See: <a href="ssl/">SSL/TLS Encryption</a>
375 <dt><a name="serversideincludes" id="serversideincludes">Server Side
376 Includes</a> <a name="ssi" id="ssi">(SSI)</a></dt>
377 <dd>A technique for embedding processing directives inside HTML files.<br />
378 See: <a href="howto/ssi.html">Introduction to Server Side Includes</a>
381 <dt><a name="session" id="session">Session</a></dt>
382 <dd>The context information of a communication in general.</dd>
384 <dt><a name="ssleay" id="ssleay">SSLeay</a></dt>
385 <dd>The original SSL/TLS implementation library developed by Eric A.
389 <dt><a name="symmetriccryptophraphy" id="symmetriccryptophraphy">Symmetric
390 Cryptography</a></dt>
391 <dd>The study and application of <em>Ciphers</em> that use a single secret key
392 for both encryption and decryption operations.<br />
393 See: <a href="ssl/">SSL/TLS Encryption</a>
396 <dt><a name="tarball" id="tarball">Tarball</a></dt>
397 <dd>A package of files gathered together using the <code>tar</code> utility.
398 Apache distributions are stored in compressed tar archives or using
402 <dt><a name="transportlayersecurity" id="transportlayersecurity">Transport
403 Layer Security</a> <a name="tls" id="tls">(TLS)</a></dt>
404 <dd>The successor protocol to SSL, created by the Internet Engineering Task
405 Force (IETF) for general communication authentication and encryption over
406 TCP/IP networks. TLS version 1 is nearly identical with SSL version 3.<br />
407 See: <a href="ssl/">SSL/TLS Encryption</a>
410 <dt><a name="uniformresourcelocator" id="uniformresourcelocator">Uniform
411 Resource Locator</a> <a name="url" id="url">(URL)</a></dt>
412 <dd>The name/address of a resource on the Internet. This is the common
413 informal term for what is formally called a <span title="see glossary">→</span> <a href="./glossary.html#uniformresourceidentifier">Uniform Resource Identifier</a>.
414 URLs are usually made up of a scheme, like <code>http</code> or
415 <code>https</code>, a hostname, and a path. A URL for this page is
416 <code>http://httpd.apache.org/docs/2.0/glossary.html</code>.
419 <dt><a name="uniformresourceidentifier" id="uniformresourceidentifier">Uniform Resource Identifier</a>
420 <a name="URI" id="URI">(URI)</a></dt>
421 <dd>A compact string of characters for identifying an abstract or physical
422 resource. It is formally defined by <a href="http://www.ietf.org/rfc/rfc2396.txt">RFC 2396</a>. URIs used on the
423 world-wide web are commonly referred to as <span title="see glossary">→</span> <a href="./glossary.html#url">URLs</a>.
426 <dt><a name="virtualhosting" id="virtualhosting">Virtual Hosting</a></dt>
427 <dd>Serving multiple websites using a single instance of Apache. <em>IP
428 virtual hosting</em> differentiates between websites based on their IP
429 address, while <em>name-based virtual hosting</em> uses only the name of the
430 host and can therefore host many sites on the same IP address.<br />
431 See: <a href="vhosts/">Apache Virtual Host documentation</a>
434 <dt><a name="x.509" id="x.509">X.509</a></dt>
435 <dd>An authentication certificate scheme recommended by the International
436 Telecommunication Union (ITU-T) which is used for SSL/TLS authentication.<br /> See: <a href="ssl/">SSL/TLS Encryption</a>
440 <div class="bottomlang">
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447 <p class="apache">Copyright 2009 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
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