Apache > HTTP Server > Documentation > Version 2.4


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This glossary defines some of the common terminology related to Apache in particular, and web serving in general. More information on each concept is provided in the links.



Access Control
The restriction of access to network realms. In an Apache context usually the restriction of access to certain URLs.
See: Authentication, Authorization, and Access Control
An unambiguous formula or set of rules for solving a problem in a finite number of steps. Algorithms for encryption are usually called Ciphers.
APache eXtension Tool (apxs)
A perl script that aids in compiling module sources into Dynamic Shared Objects (DSOs) and helps install them in the Apache Web server.
See: Manual Page: apxs
Apache Portable Runtime (APR)
A set of libraries providing many of the basic interfaces between the server and the operating system. APR is developed parallel to the Apache HTTP Server as an independent project.
See: Apache Portable Runtime Project
The positive identification of a network entity such as a server, a client, or a user.
See: Authentication, Authorization, and Access Control
A data record used for authenticating network entities such as a server or a client. A certificate contains X.509 information pieces about its owner (called the subject) and the signing Certification Authority (called the issuer), plus the owner's public key and the signature made by the CA. Network entities verify these signatures using CA certificates.
See: SSL/TLS Encryption
Certificate Signing Request (CSR)
An unsigned certificate for submission to a Certification Authority, which signs it with the Private Key of their CA Certificate. Once the CSR is signed, it becomes a real certificate.
See: SSL/TLS Encryption
Certification Authority (CA)
A trusted third party whose purpose is to sign certificates for network entities it has authenticated using secure means. Other network entities can check the signature to verify that a CA has authenticated the bearer of a certificate.
See: SSL/TLS Encryption
An algorithm or system for data encryption. Examples are DES, IDEA, RC4, etc.
See: SSL/TLS Encryption
The result after Plaintext is passed through a Cipher.
See: SSL/TLS Encryption
Common Gateway Interface (CGI)
A standard definition for an interface between a web server and an external program that allows the external program to service requests. There is an Informational RFC which covers the specifics.
See: Dynamic Content with CGI
Configuration Directive
See: Directive
Configuration File
A text file containing Directives that control the configuration of Apache.
See: Configuration Files
An HTTP method for proxying raw data channels over HTTP. It can be used to encapsulate other protocols, such as the SSL protocol.
An area in the configuration files where certain types of directives are allowed.
See: Terms Used to Describe Apache Directives
Digital Signature
An encrypted text block that validates a certificate or other file. A Certification Authority creates a signature by generating a hash of the Public Key embedded in a Certificate, then encrypting the hash with its own Private Key. Only the CA's public key can decrypt the signature, verifying that the CA has authenticated the network entity that owns the Certificate.
See: SSL/TLS Encryption
A configuration command that controls one or more aspects of Apache's behavior. Directives are placed in the Configuration File
See: Directive Index
Dynamic Shared Object (DSO)
Modules compiled separately from the Apache httpd binary that can be loaded on-demand.
See: Dynamic Shared Object Support
Environment Variable (env-variable)
Named variables managed by the operating system shell and used to store information and communicate between programs. Apache also contains internal variables that are referred to as environment variables, but are stored in internal Apache structures, rather than in the shell environment.
See: Environment Variables in Apache
Diminished in cryptographic strength (and security) in order to comply with the United States' Export Administration Regulations (EAR). Export-crippled cryptographic software is limited to a small key size, resulting in Ciphertext which usually can be decrypted by brute force.
See: SSL/TLS Encryption
A process that is applied to data that is sent or received by the server. Input filters process data sent by the client to the server, while output filters process documents on the server before they are sent to the client. For example, the INCLUDES output filter processes documents for Server Side Includes.
See: Filters
Fully-Qualified Domain-Name (FQDN)
The unique name of a network entity, consisting of a hostname and a domain name that can resolve to an IP address. For example, www is a hostname, example.com is a domain name, and www.example.com is a fully-qualified domain name.
An internal Apache representation of the action to be