To start new programs on the system, you
must somehow tell the kernel what program to start. The trick is interfacing with the
kernel to start the programs you want to run.
The shell is an interactive environment that allows Linux users (and administrators) access
to the kernel. The shell interacts with an input device (usually the console keyboard) and
an output device (usually the console monitor). The shell allows users to type commands
at the console, which are read and processed by the shell. Internal shell commands are
processed by the shell, while commands to start programs are passed to the kernel to run.
Figure 8.1 demonstrates how the shell interacts with the kernel and users.
User User User
Shell
Kernel
Shell Shell
System
Hardware
System
Memory
System
CPU
FIGURE 8.1 The Linux shell interacting with the kernel and the user.
As an interactive environment, the shell allows you to enter commands at what is called
the command prompt. Often, the commands entered are program names. When a
program name is entered, the shell attempts to find the program in the file system and
then passes the executable program to the kernel to be run on the system.
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