Networks connect computers so that the different systems can share information. For users and system administrators, Unix systems have traditionally provided a set of simple but valuable network services that let you check whether systems are running, refer to files residing on remote systems, communicate via electronic mail, and so on.
For most commands to work over a network, each system must be continuously running a server process in the background, silently waiting to handle the user’s request. This kind of process is commonly called a daemon.
Most Unix networking commands are based on Internet protocols. These are standardized ways of communicating across a network on hierarchical layers. The protocols range from addressing and packet routing at a relatively low layer to finding users and executing user commands at a higher layer.
The basic user commands that most systems support over Internet protocols are generally called TCP/IP commands, named after the two most common protocols. You can use all of these commands to communicate with other Unix systems including Linux systems. Because all modern operating systems support TCP/IP, commands can also be used to communicate with non-Unix systems.
Mac OS X includes several applications that bring graphical interfaces to these commands. Some, such as Network Utility, are little more than Aqua-window wrappers to the basic command-line tools. Others, like the Network preferences pane, bundle them into programs ...