Operating system Notes

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Introduction of Operating System

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PROCESS: Program to process, Lifecycle of the process, Process control block, IPC

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Scheduling

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Threads

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Memory Management

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File Management

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Synchronization

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Disk Management

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IO Management

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Protection And Security

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Q

1

What is access matrix with respect to system protection?

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Ans

Access Matrix is a security model of protection state in computer system. It is represented as a matrix. Access matrix is used to define the rights of each process executing in the domain with respect to each object. The rows of matrix represent domains and columns represent objects.

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Q

2

What is DOS attack? Explain the concept of DDoS attack.

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Ans

A Denial-of-Service (DoS) attack is an attack meant to shut down a machine or network, making it inaccessible to its intended users. DoS attacks accomplish this by flooding the target with traffic, or sending it information that triggers a crash. In both instances, the DoS attack deprives legitimate users (i.e. employees, members, or account holders) of the service or resource they expected.

Victims of DoS attacks often target web servers of high-profile organizations such as banking, commerce, and media companies, or government and trade organizations. Though DoS attacks do not typically result in the theft or loss of significant information or other assets, they can cost the victim a great deal of time and money to handle.

There are two general methods of DoS attacks: flooding services or crashing services. Flood attacks occur when the system receives too much traffic for the server to buffer, causing them to slow down and eventually stop. Popular flood attacks include:

Buffer overflow attacks – the most common DoS attack. The concept is to send more traffic to a network address than the programmers have built the system to handle. It includes the attacks listed below, in addition to others that are designed to exploit bugs specific to certain applications or networks

ICMP flood – leverages misconfigured network devices by sending spoofed packets that ping every computer on the targeted network, instead of just one specific machine. The network is then triggered to amplify the traffic. This attack is also known as the smurf attack or ping of death.

SYN flood – sends a request to connect to a server, but never completes the handshake. Continues until all open ports are saturated with requests and none are available for legitimate users to connect to

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Q

3

What do you mean by session hijacking with proper example?

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Ans

session hijacking also known as TCP session hijacking, is a method of taking over a web user session by surreptitiously obtaining the session ID and masquerading as the authorized user. Once the user's session ID has been accessed, the attacker can masquerade as that user and do anything the user is authorized to do on the network.

One of the most valuable byproducts of this type of attack is the ability to gain access to a server without having to authenticate to it. Once the attacker hijacks a session, they no longer have to worry about authenticating to the server as long as the communication session remains active. The attacker enjoys the same server access as the compromised user because the user has already authenticated to the server prior to the attack.

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Q

4

What do you mean by cryptography?

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Ans

Cryptography is a method of protecting information and communications through the use of codes, so that only those for whom the information is intended can read and process it. The prefix "crypt-" means "hidden" or "vault" -- and the suffix "-graphy" stands for "writing."

In computer science, cryptography refers to secure information and communication techniques derived from mathematical concepts and a set of rule-based calculations called algorithms, to transform messages in ways that are hard to decipher. These deterministic algorithms are used for cryptographic key generation, digital signing, verification to protect data privacy, web browsing on the internet, and confidential communications such as credit card transactions and email.

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