A network service allows remote users to connect to your Freedom server to access information or perform certain functions. You are already familiar with the SSH, Telnet, and other network services, which allow you to log into your Freedom server, and you have probably used other network services such as FTP, email or the HTTP (Web) services.
Network services are provided by server applications, which are also referred to as daemons. A daemon is a program that listens on a network port, accepts connections, and services requests for access or information. For example, when someone sends email to a user account on your server, it is the Sendmail 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. Applications that run in standalone mode are constantly running, listening for requests. Applications invoked through xinetd are executed only when a service is requested, and terminate when the request has been fulfilled. In general, applications are run as standalone daemons when speed is critical or high traffic is expected. Likewise, the applications spawned through xinetd are done so for efficiency and to reduce overhead and resource drain on the server.
The following table displays the basic network services that are provided by default on every Freedom server as well as the server applications that power these services:
|
Network Service Name |
Description |
Server Application |
Execution Mode |
|
HTTP / HTTPS |
Serves Web pages in both standard and secure modes |
Apache (httpd) |
Standalone |
|
SMTP |
Sends outbound mail from the server and receives inbound mail to the server |
Sendmail |
Standalone |
|
FTP |
Efficient, platform independent file transfer |
ProFTPd |
Xinetd Spawned |
|
SSH |
Secure login and remote shell access |
SSHD |
Standalone |
|
Telnet |
Login and remote shell access |
Telnetd |
Xinetd Spawned |
|
POP3 / POP3S |
Provides remote retrieval of waiting email messages in both standard and secure modes |
Qpopper |
Xinetd Spawned |
|
IMAP4 / IMAP4S |
Provides retrieval, storage and management of email messages in both standard and secure modes |
IMAPd |
Xinetd Spawned |
|
netbios-ssn / netbios-ns |
Provides direct file sharing with Microsoft Windows PCs |
Samba (smbd / nmbd) |
Xinetd Spawned |
|
MySQL |
Network accessible SQL database service |
Mysqld |
Standalone |
Each of these network services and the server applications that power them are described in the Provided Services and Applications section of this guide.