1. Chapter 3: The Shell

2. Kernel and Utilities
Unix
Kernel
System
Utilities
Disks
Memory

3. Kernel Kernel is the heart of the Unix Systems
Resides in the memory from boot-up till shutdown

4. Utilities Utilities Resides in the computer disks
Brought only when invoked
Every command in UNIX is considered utility

5. The Shell The Shell Is a utility program
Loaded into the memory whenever you log in
The most often selected program in UNIX

6. The Login Shell
UNIX
System
Kernel
Getty
Getty
Getty

7. The Login Process starts Login init Login Program Displays Password:
Determines the baud rate, displays the login
Also known as the Unix System
Getty
program
disappears
Wait for input+
enter key
init
Login
Login
Program
Displays
Password:
File
etc/passwd
Password in
etc/shadow
begins
verifies
checks
Also known as the Unix System
Determines the baud rate, displays the login

8. Once password is verified, login program initiates the program to execute.

9. Command Cycle $ Shell Shell $ls ls shell $ls foo rje Waits for input
Looks for the command on the disk
Asks the Kernel to initiate the program then sleeps
foo rje $ ls
$ls foo rje
shell

10. Shell’s Responsibilities
Program Execution
Variable and Name Substitution
I/O Redirection
Pipeline Hookup
Environment Control

11. Thank You
Any questions?