Chapter 3: The Shell

Kernel and Utilities Unix Kernel System Utilities Disks Memory

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

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

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

The Login Shell UNIX System Kernel Getty Getty Getty

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

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

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

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

Thank You Any questions?