Linux System

7/30/2019 Linux System

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The Linux SystemSpeaker :

Bilal Ahmad



What is Linux?



What is Linux?

A Unix-like Operating System

A famous open source project

Free to use, distribute, modify under a compatible licence

Produced by a large developer and user community

A combination of many projects

Cost of commercial development estimated at USD 7 billion



Contents to be Discussed

• Linux History

• Design Principles

• Process Management

• Scheduling

• Memory Management

• File Systems• Input and Output

• Network Structure

• Security




• Linux History



• Scheduling




• Security



Linux History• Linux is a modern, free

operating system based on

UNIX standards

• First developed as a small butself-contained kernel in 1991 by

Linus Torvalds, with the majordesign goal of UNIXcompatibility



Linux History

• Its history has been one of collaboration by many users from all around the world,

corresponding almost exclusively over theInternet.

• It has been designed to run efficiently andreliably on common PC hardware, but also runson a variety of other platforms.



Linux History

GNU project started 1984 toproduce a Unix-like OS

1. Founded by Richard Stallman

2. Wrote the GNU manifesto in 1985 outliningphilosophy

3.Software that is free means more than free of

charge



Linux Distributions

• Early distributions included SLS and Slack ware.

▫ Red Hat and Debian are popular distributions from

commercial and noncommercial sources, respectively.



Linux Licensing

• The Linux kernel is distributed under the GNUGeneral Public License (GPL), the terms of which are set out by the Free SoftwareFoundation.




• Linux History



• Scheduling




• Security



Design principles

• Linux is a multiuser, multitasking system with afull set of UNIX-compatible tools.

• Its file system adheres to traditional UNIXsemantics, and it fully implements the standard

UNIX networking model

• Main design goals are speed, efficiency, andstandardization.



Components of Linux System



Components of Linux System• The kernel is responsible for maintaining the important

abstractions of the operating system

• The system libraries define a standard set of functionsthrough which applications interact with the kernel, and which implement much of the operating-system

functionality that does not need the full privileges of kernel code.

• The system utilities perform individual specialized

management tasks.




• Linux History



• Scheduling




• Security



Process Management• UNIX process management separates the creation of

processes and the running of a new program into two

distinct operations.▫ The fork system call creates a new process

▫ A new program is run after a call to execute

• Under UNIX, a process encompasses all the informationthat the operating system must maintain to track thecontext of a single execution of a single program.

• Under Linux, process properties fall into three groups:the process’s “identity, environment, and context .”



Process identity• Process ID (PID). The unique identifier for the

process; used to specify processes to the

operating system when an application makes asystem call to signal, modify, or wait for anotherprocess.



Process Environment

• The process’s environment is inherited from itsparent, and is composed of two null-terminated

vectors:

- The argument vector lists the command-line argumentsused to invoke the running program; conventionally starts

with the name of the program itself.

- The environment vector is a list of “NAME=VALUE” pairsthat associates named environment variables with arbitrary

textual values.



Process Context• The (constantly changing) state of a running program at

any point in time

• The scheduling context is the most important part of the process context; it is the information that thescheduler needs to suspend and restart the process




• Linux History



• Scheduling




• Security



Scheduling• The job of allocating CPU

time to different tasks

within an operating system• While scheduling is

normally thought of as therunning and interrupting of

processes, in Linux,scheduling also includes therunning of the variouskernel tasks



Process Scheduling

• Linux uses two process-scheduling algorithms:

▫ A time-sharing algorithm for fair preemptive

scheduling between multiple processes.

▫ A real-time algorithm for tasks where absolutepriorities are more important than fairness.

• A process’s scheduling class defines whichalgorithm to apply.



Process Scheduling

• Linux implements the FIFO and round-robinreal-time scheduling classes; in both cases, each

process has a priority in addition to itsscheduling class



Content 5

• Linux History



• Scheduling




• Security



Memory Management

• Linux’s physical memory -management systemdeals with allocating and freeing pages, groups

of pages, and small blocks of memory •

• It has additional mechanisms for handling

virtual memory, memory mapped into theaddress space of running processes



Memory Management

• Splits memory into 3 different zones due tohardware characteristics



Splitting of Memory



Content 6

• Linux History



• Scheduling




• Security



File Systems• To the user, Linux’s file

system appears as ahierarchical directory

tree obeying UNIXsemantics.

• Internally, the kernelhides implementation

details and manages themultiple different filesystems via anabstraction layer, that is,the virtual file system(VFS).



Content 7

• Linux History



• Scheduling




• Security



Input and Output

• The Linux device-oriented file system accessesdisk storage through two caches:

▫ Data is cached in the page cache, which is unified with the virtual memory system.

▫ Metadata is cached in the buffer cache, a separatecache indexed by the physical disk block.



Input and output

• Linux splits all devices into three classes:

• 1. Block devices

• 2. Character devices

• 3. Network devices



Content 8

• Linux History



• Scheduling




• Security



Network Structure• Networking is a key area of functionality for

Linux.

▫ It supports the standard Internet protocols forUNIX to UNIX communications

▫ It also implements protocols native to non UNIXoperating systems, in particular, protocols used onPC networks, such as AppleTalk and IPX



Network Structure• Internally, networking in the Linux kernel is

implemented by three layers of software:

▫ The socket interface

▫ Protocol drivers

▫ Network device drivers



Content 9• Linux History



• Scheduling




• Security



Security• The pluggable authentication modules (PAM)

system is available under Linux.

• PAM is based on a shared library that can beused by any system component that needs toauthenticate users.



Security• Access control under UNIX systems, including Linux, is

performed through the use of unique numeric identifiers

(uid and gid).



Thank you

Linux System

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