linux slide

7/31/2019 Linux Slide

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What is Linux?Linux is, in simplest terms, an operating system. It is the software on a computer that enables

applications and the computer operator to access the devices on the computer to performdesired functions. The operating system (OS) relays instructions from an application to, forinstance, the computer's processor. The processor performs the instructed task, then sends

the results back to the application via the operating system.


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Features of Linux Key features of Linux Operating System:

Following are the key features of the Linux operatingsystem:

Multitasking: several programs running at the sametime.

Multiuser: several users on the same machine at thesame time (and no two-user licenses!).

Multiplatform: runs on many different CPUs, not just

Intel. Multiprocessor/multithreading: it has native kernelsupport for multiple independent threads of controlwithin a single process memory space.


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Advantages OF Linux Linux Advantages Low cost: You dont need to spend time and money to obtain licenses

since Linux and much of its software come with the GNU General PublicLicense. You can start to work immediately without worrying that yoursoftware may stop working anytime because the free trial version expires.Additionally, there are large repositories from which you can freelydownload high quality software for almost any task you can think of.

Stability: Linux doesnt need to be rebooted periodically to maintainperformance levels. It doesnt freeze up or slow down over time due tomemory leaks and such. Continuous up-times of hundreds of days (up to ayear or more) are not uncommon.

Performance: Linux provides persistent high performance on workstationsand on networks. It can handle unusually large numbers of userssimultaneously, and can make old computers sufficiently responsive to beuseful again.


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Advantages OF Linux Network friendliness: Linux was developed by a group of

programmers over the Internet and has therefore strongsupport for network functionality; client and server systemscan be easily set up on any computer running Linux. It canperform tasks such as network backups faster and morereliably than alternative systems. Flexibility: Linux can beused for high performance server applications, desktopapplications, and embedded systems. You can save diskspace by only installing the components needed for aparticular use. You can restrict the use of specificcomputers by installing for example only selected officeapplications instead of the whole suite.

Compatibility: It runs all common Unix software packagesand can process all common file formats.


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Advantages OF Linux Multitasking: Linux is designed to do many things at the

same time; e.g., a large printing job in the backgroundwont slow down your other work. Security: Linux is one of the most secure operating systems. Walls and flexible fileaccess permission systems prevent access by unwantedvisitors or viruses. Linux users have to option to select andsafely download software, free of charge, from onlinerepositories containing thousands of high quality packages.No purchase transactions requiring credit card numbers orother sensitive personal information are necessary. OpenSource: If you develop software that requires knowledge ormodification of the operating system code, Linuxs sourcecode is at your fingertips. Most Linux applications are OpenSource as well.


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Kernal What is Kernel? Explain the task it performs. Answer

Kernel is used in UNIX like systems and is considered to be the heart of theoperating system. It is responsible for communication between hardware andsoftware components. It is primarily used for managing the systems resources aswell.

Kernel Activities: The Kernel task manager allows tasks to run concurrently. Managing the computer resources: Kernel allows the other programs to run and

use the resources. Resources include i/o devices, CPU, memory. Kernel is responsible for Process management. It allows multiple processes to run

simultaneously allowing user to multitask. Kernel has an access to the systems memory and allows the processes to access

the memory when required. Processes may also need to access the devices attached to the system. Kernel

assists the processes in doing so. For the processes to access and make use of these services, system calls are

used.


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Basics Architecture of Linux System


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What Is Difference Between DOS andWindows

Both Dos and Windows are Operating systems. But, they possess some features which makethem differentiate. These features are listed below:Dos is only single tasking while Windows is multitasking.Dos is based on plain interface while Windows is based on Graphical user interface (GUI).Dos is difficult to learn and understand while Windows is easy to learn and understand.Dos is less preferable by users while Windows is more preferable operating system.

Limited users can work on dos while in Windows there are many users.We cannot see mouse in Dos while in Windows we can see and use mouse to click on icons orlinks.Simple text commands are written in Dos while in Windows we operate computer with thehelp of mouse.n Dos we cannot Play games, watch movies and listen songs while in Windows we can enjoyplaying games, watching movies and listening songs.n Dos new hardware cannot work properly while in Windows it can detect and installs softwareautomatically.Application and system softwares did not work properly in Dos while in Windows it runs at agreat speed.Dos is not user friendly while Windows operating system is user friendly.Dos performs operations speedily as compared with Windows operating system.


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LINUX DIRECTORY STURUCTURE


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1. /bin Contains several useful commands that are of use to both

the system administrator as well as non-privileged users. Usually contains the shells like bash, csh, etc.... and

commonly used commands like cp, mv, rm, cat, ls. Also contains programs which boot scripts may depend

on There are no (real) subdirectories in /bin


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1. /bin detail

cat chgrp chmod chown cp date

dd df dmesg echo false

Utility to concatenate files to standard output Utility to change file group ownership Utility to change file access permissions Utility to change file owner and group Utility to copy files and directories Utility to print or set the system data and time

Utility to convert and copy a file Utility to report filesystem disk space usage Utility to print or control the kernel message buffer Utility to display a line of text Utility to do nothing, unsuccessfully


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7. /lib

Contains kernel modules and those sharedlibrary images (the C programming codelibrary) needed to boot the system and runthe commands in the root filesystem, ie. bybinaries in /bin and /sbin

Windows equivalent to a shared library wouldbe a DLL (dynamically linked library) file


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4. /etc detail

/etc/hosts : This file is used to define a system name anddomain combination with a specific IP address

127.0.0.1 localhost ::1 localhost ip6-localhost ip6-loopback fe00::0 ip6-localnet ff00::0 ip6-mcastprefix ff02::1 ip6-allnodes ff02::2 ip6-allrouters ff02::3 ip6-allhosts 192.168.0.99 debian.localdomain.com debian

192.168.0.1 ws001


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5. /home

The user home directories Accessible only to its owner and the system

administrator Contains the users personal configuration

files Quite large to be used as Users Documents

Space


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10. /mnt

This is a generic mount point under mounted

(mount is to make a filesystem available tothe system) the filesystems or devices. When a filesystem no longer needs to be

mounted, it can be unmounted with umount mount /dev/hda2 /home umount /dev/hda2


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File System Implementation


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File

Sequence of bytes, with no structure as far asthe operating system is concerned. The onlyoperations are to read and write bytes.

Interpretation of the data is left to theapplication using it.

File descriptor a handle to a file that the OSprovides the user so that it can use the file


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File Metadata

Owner: the user who owns this file. Permissions: who is allowed to access this file.

Modification time: when this file was lastmodified. Size: how many bytes of data are there.

Data location: where on the disk the files datais stored.


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Hardware background: Direct MemoryAccess

When a process needs a block from the disk, thecpu needs to copy the requested block from thedisk to the main memory.

This is a waste of cpu time. If we could exempt the cpu from this job, it will

be available to run other ready processes. This is the reason that the operating system uses

the DMA feature of the disk controller. Disk access is always in full blocks .


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Direct Memory Access Cont.

OS passes the needed parameters to the disk controller(address on disk, address on main memory, amount of data to copy)

The running process is transferred to the blockedqueue and a new process from the ready queue isselected to run.

The controller transfers the requested data from thedisk to the main memory using DMA.

The controller sends an interrupt to the cpu, indicatingthe IO operation has been finished.

The waiting process is transferred to the ready queue.


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Disk Layout

Boot Block for loading the OS (optional) Swap area (optional)

Super Block File system management i-nodes File metadata Data blocks Actual file data


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Super Block

Manages the allocation of blockson the file system area

This block contains: The size of the file system A list of free blocks available on the fs A list of free i-nodes in the fs

And more... Using this information it is possible to allocate

disk block for saving file data or file metadata


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Mapping File Blocks It is inefficient to save each file as a consecutive

data block. Why?

How do we find the blocks that togetherconstitute the file?

How do we find the right block if we want to accessthe file at a particular offset?

How do we make sure not to spend too much space

on management data? We need an efficient way to save files of varying

sizes.


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Typical Distribution of File Sizes

Many very small files that use little disk space Some intermediate files

Very few large files that use a large part of thedisk space


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The Unix i-node In Unix, files are represented internally by a structure

known as an inode, which includes an index of diskblocks.

The index is arranged in a hierarchical manner: Few direct pointers, which list the first blocks of the file

(Good for small files) One single indirect pointer - points to a whole block of

additional direct pointers (Good for intermediate files)

One double indirect pointer - points to a block of indirect pointers. (Good for large files) One triple indirect pointer - points to a block of double

indirect pointers. (Good for very large files)


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i-node Structure


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system administrator is responsible

The system administrator is responsible for following things: User administration (setup and maintaining account) Maintaining system Verify that peripherals are working properly Quickly arrange repair for hardware in occasion of hardware failure Monitor system performance Create file systems Install software Create a backup and recover policy Monitor network communication

Update system as soon as new version of OS and application softwarecomes out Implement the policies for the use of the computer system and network Setup security policies for users. A sysadmin must have a strong grasp of

computer security (e.g. firewalls and intrusion detection systems).


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Linux Installation requirement

Requirement MinimumRecommended

Version Linux 2.2 and 2.4 with glibc2.1 or greater

CPU 400 MHz 800+ MHz

RAM 32 MB (fileto fileencoding)96 MB (livebroadcasting)

256 MB


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System Startup and Shutdown The Boot Process The Initialization Process and Startup Scripts

linuxconf and Managing Your Services Shutting Down the Linux System When the System Crashes This chapter explains how to start your Red Hat Linux

system, what happens when it starts, and how toproperly shut it down. It also covers system crashesand what to do if your system won't boot.