UNIT 3
UNIX/LINUX OPERATING SYSTEM
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Introduction to Linux
UNIT 3
UNIX/LINUX OPERATING SYSTEM
Introduction to Unix
History of UNIX
What is LINUX
LINUX Distributions
Unix OS Structure
Unix File System
Unix Directories, Files and Inodes
Users, Groups and Permissions
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Introduction to Linux
UNIX Structure
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Introduction to Linux
Kernel Service
▪ A border between the kernel level and the user level code
➢ Supported by the hardware protection
▪ Kernel is working in an isolated address range
➢ Impossible to get access to that address space from the user level
▪ Any interaction between the two levels is possible only via
system calls
➢ Strictly controlled by the kernel
▪ System calls are mostly synchronous for user level
application
➢ Kernel might continue some work after returning results to the
user level
▪ System calls are mostly implemented by the means of
hardware exceptions
➢ Change the CPU working mode and the current virtual memory 8
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Introduction to Linux
Kernel Service
▪ Kernel strictly controls system call arguments before
executing the call
➢ Each argument is copied to the kernel address space to guarantee
that it will not be changed during the execution of the system call
➢ The address space where the result of the system call will be
placed has to belong to the process who made the call
➢ To ensure safe protection mechanisms, operating systems must
use the hardware protection associated with the CPU privileged
mode.
➢ If system call got an error, it returns -1 and sets global errno
variable.
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Introduction to Linux
UNIX
Linux is a free Unix-type operating system originally
created by Linus Torvalds with the assistance of
developers around the world.
Unix is a multi-user, multi-tasking operating system.
You can have many users logged into a system
simultaneously, each running many programs.
It's the kernel's job to keep each process and user
separate and to regulate access to system hardware,
including cpu, memory, disk and other I/O devices.
Being written in this high-level language greatly decreased
the effort needed to port it to new machines.
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Introduction to Linux
History of UNIX
First Version was created in Bell Labs in 1969.
Some of the Bell Labs programmers who had
worked on this project, Ken Thompson, Dennis
Ritchie, Rudd Canaday, and Doug McIlroy
designed and implemented the first version of the
Unix File System on a PDP-7 along with a few
utilities. It was given the name UNIX by Brian
Kernighan.
00:00:00 Hours, Jan 1, 1970 is time zero for UNIX. It
is also called as epoch.
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Introduction to Linux
What is LINUX
Linux is a free Unix-type operating system
originally created by Linus Torvalds with the
assistance of developers around the world.
It originated in 1991 as a personal project of Linus
Torvalds, a Finnish graduate student.
The Kernel version 1.0 was released in 1994 and
today the most recent stable version is 2.6.9
Developed under the GNU General Public License ,
the source code for Linux is freely available to
everyone.
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Linux File Management
