The kernel resides in memory from boot until shutdown and is responsible for executing programs. Utilities reside on disk and are loaded into memory as needed by the shell. The shell is a command line interpreter that displays a prompt, executes commands by asking the kernel to run the program, and waits for the program to terminate before accepting new commands. Logging into the shell connects through a network to the Apache server using putty which performs password authentication before launching the login program.

1. Kernels, Shells, and Popcorn

2. The Kernel
• The Unix system is logically divided into two pieces:
• 1. The Kernel – is the heart of the Unix system and resides in the computer’s memory
fro the time the machine is booted until shutdown.
• 2. The Utilities – reside on the computer’s disk and are only brought into memory as
requested.
• Virtually every command

3. The Shell
• The Shell is a command line interpreter interface.
• It is a utility program.
• When the shell starts up it displays a command prompt with a dollar sign($) at
your terminal.
• It then waits for your to execute a command.
• Once a command is executed the shell
searches the disk for the program and then asks
the kernel to initiate the program’s execution.
• The kernel creates a copy of the program
into memory and begins its execution. This
copy is known as a process.
• While the program is executing the shell
“goes to sleep” until the program terminates.
Shell
Kernel

4. The Shell’s Responsibilities

5. Logging into the Shell
• Our terminals connect to the Apache Server, Navajo, through a network.
• We connect over the network via a program, putty, that ssh’s into the server.
• After login checks the password you typed against the one stored in /etc/shadow,
it then checks for the name of the program to execute in /etc/password.
getty
Unix
System
kernel
/usr/bin/
Unix
System
kernel
login
Unix
System
kernel