A network service allows remote users to connect to your server to access information or perform certain functions. Examples of network services include SSH and Telnet, which allow you to log into your server, as well as the FTP, email and HTTP (Web) services.
Network services are provided by server applications, which are also referred to as daemons. A daemon is a program that listens for and accepts connections to the server, and services requests for access or information. For example, when someone sends email to a user account on your server, it is the Sendmail server application that receives the mail and prepares it to be picked up by the user. When someone visits your Web site, it is the Apache Web server application that receives the request and returns the appropriate page to the visitor.
All server applications are run in one of two ways: as a standalone application or as an application invoked (spawned) by the xinetd application. In general, applications are run in standalone mode when speed is critical or high traffic is expected, whereas the applications invoked through xinetd are done so for efficiency and to reduce overhead and resource drain on the server.
Each of the standalone server applications that are run on your server can be found on the Network Services menu, along with a brief status report, as shown below:
Applications that run in standalone mode are constantly running, listening for requests. Your server runs Apache, Sendmail, MySQL, and SSH as standalone applications. Xinetd is a standalone application that in turn runs other applications on your server as needed.
Applications invoked through xinetd are executed only when a service is requested, and terminate when the request has been fulfilled.
The status of the applications invoked by xinetd can be viewed by clicking the Service Control link under the Network Services menu. The table below lists all the server applications that xinetd is configured to listen for by default, along with a description of each application:
For instructions on enabling and disabling the applications invoked by xinetd, see the next section.