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THE LINUX SYSTEMTHE LINUX SYSTEM

Designed by:Nilesh Jaiswar

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INDEXINDEX

• History

• Design principals

• Components of linux system

• Kernel modules

• Process management

• Process and threads

• Scheduling in linux

• Process scheduling

• Memory management

• File systems

• I/O in linux

• Interprocess communication

• Linux networking structure

• Security

• Conclusion

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HISTORYHISTORY

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DESIGN PRINCIPLESDESIGN PRINCIPLES

LINUX: A Multitasking, Multiuser and full set of UNIX compatible tools.

It is capable of operating under 4Mb of RAM

It contains POSIX standards. It act as a interface for both the

programmer and the user.

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USER INTERFACEUSER INTERFACE

Users operate linux through CLI and GUI.

On desktop systems: KDE Plasma Desktop,GNOME and Xfce.

Linux kernel and other components are free and open source software.

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COMPONENTS OF LINUX SYSTEMCOMPONENTS OF LINUX SYSTEM

Linux system consists of three main bodies:

• The kernel

• The system libraries

• The system utilities

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KERNEL MODULESKERNEL MODULES

Three components of the module:

• Module management

• Driver Registration

• Conflict Resolution

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PROCESS MANAGEMENTPROCESS MANAGEMENT

Two different operations:•The creation of process•Running of new program

Terms in linux:•Fork-a new process is created by fork system call.•Execve-a new program is run after a execve call•Clone-creates a new process sharing parent data structure having it’s own identity.

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PROCESS MANAGEMENTPROCESS MANAGEMENT

Process properties:

• Process identity:

a. Process ID(PID):

b. Credentials:

c. Personality:

• Process environment:

• Process context: a. Scheduling context:

b. Accounting:

c. File table:

d. File system context:

e. Single handler table:

f. Virtual memory context:

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Processes and ThreadsProcesses and Threads

• Threads are light weight processes(LWPs)

• Processes are heavy weight processes(HWPs)

• Fundamental parts of process:

a. code(text)

b. data(vm)

c. stack

d. file I/O

e. signal table

• Threads: user level and kernel level

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PROCESSES AND THREADSPROCESSES AND THREADS

1. REPRESENT THE EXECUTION OF SINGLE PROGRAM

2. TWO SEPARATE PROCESSES WILL HAVE THEIR OWN INDEPENDENT ADDRESS SPACE

1. REPRESENT SEPARATE , CONCURRENT EXECUTION WITHIN SINGLE PROCESS

2. TWO THREADS WITHIN A PROCESS SHARE SAME ADDRESS SPACE

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SCHEDULINGSCHEDULING

• The linux scheduler is a pre-emptive , priority-based algorithm

• Two separate priority ranges :

1. Real-time range( 0 to 99)

2. ice-value range (100 to 140)

• Once kernel code start running , then it is the only kernel code till the following event occurs.

1. An interrupt

2. A page fault

3. A kernel code call to the scheduler function itself

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PROCESS SCHEDULINGPROCESS SCHEDULING

Linux supports two process scheduling algorithms• Time- sharing algorithm

• Real- time task algorithm

1.First-in first-out (FIFO)

2.Round Robin

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MEMORY MANAGEMENTMEMORY MANAGEMENT

Two components in Memory management:• Physical memory management

• Virtual memory

Physical memory management: This deals with allocation and deallocation of pages, group of pages and blocks of memory.

Virtual memory: it is the memory mapped into the address

space of running process.

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PHYSICAL MEMORY MANAGEMENT

•Physical memory manager is a page allocator, which uses “buddy heap” algorithm in order to keep track of available address space . Ex. Splitting of memory in buddy heap.

16 KB

8KB

8 KB

8 KB

4 KB

4 KB

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VIRTUAL MEMORYVIRTUAL MEMORY

• Virtual memory is responsible for maintaining the address space visible to each process.

• There are two situations where the kernel creates a new virtual address space

a) when a process runs a new program with the “exec” system call.

b) When a new process is created by the “fork” system call.

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FILE SYSTEMSFILE SYSTEMS

• Linux file system retains UNIX’s features. here file can be anything capable of handling I/O of stream of data.

• The virtual file system is designed using object oriented principles. It consists of two components,

i. A set of definition which define what a file object is allowed to look like.

ii. A layer of software to manipulate those objects.

3 main object defined by VTS are

i. Inode object

ii. File object structure

iii. File system object

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I/O IN LINUXI/O IN LINUX

Linux splits all the I/O devices into three groups

a. Block devices

b. Character devices

c. Network devices

• Block devices include all devices that allow random access like HDD, floppy disk & CD-ROMS.

• Character devices include other devices with the main exception of network devices like Magnetic tap devices.

• Network devices are dealt differently from both devices.

user cannot transfer directly data to network devices

but communicate indirectly. Ex. Tty discipline.

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Inter-Process Communication

VARIOUS types of MECHANISM

• SIGNAL

• PIPES

• FISOS

• Message Queues

• Semaphores

• Shared Memory

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LINUX NETWORK STRUCTURE

Linux kernel is implemented using the three layers of software internally-

• System call interface

• Protocol agnostic interface

• Network protocols

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SECURITY

In Linux, Security issues can be classified in two group-

• AUTHENTICATION

• ACCESS CONTROL

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Conclusion

“When is it best to use Linux and when should some other operating system be preferred?”

It all depends on the user

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REFERENCES

•www. Wikipedia.com•www.trimble.com•www.wiley.com•Book: Operating system concepts