Public Network Internal Network
FIGURE 1-1
Using Linux as
a firewall
Firewall
Rules
Allowed Traffic
Allowed Traffic
Disallowed Traffic
FIGURE 1-2
Firewalls block or
allow traffic based
on rules.
Use the Linux User Interface 15
CERTIFICATION OBJECTIVE 1.02
Use the Linux User Interface
For an operating system to be useful, it must provide some means for the user to
communicate with it. Users need a way to tell the operating system what it should
do, such as running a program, copying a file, or shutting down. These tasks are done
using a user interface. Linux provides two types of user interfaces:
?– Command-Line Interface (CLI) With the command-line interface, the
user communicates with the Linux operating system by typing commands at a
command prompt, as shown in Figure 1-3.
?– Graphical User Interface (GUI) In addition to a command-line interface,
Linux also offers users an easy-to-use graphical user interface. While most
network administrators are at ease with the Linux CLI, most end users aren??™t.
They are much more comfortable with a GUI. Because of the dominance
of Windows in the home computer market, most end users have never even
used a command-line type of interface.
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