Computer File Sharing Systems

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Questions and Answers

What is a common method of sharing files on distributed systems?

File Transfer Protocol (FTP)

Remote Desktop Connection

Network File System (NFS) (correct)

World Wide Web

What identifies users and allows permissions and protections to be per-user?

File IDs

User IDs (correct)

Group IDs

System IDs

What is the primary goal of a protection scheme in file sharing?

To allow access to all users

To share files across a network

To deny access to all users

To control what can be done and by whom (correct)

What is the mode of access for the owner of a file in Unix/Linux?

RWX Signup and view all the answers

What is the command to attach a group to a file in Unix/Linux?

chgrp G game Signup and view all the answers

What is the purpose of an Access-Control List (ACL) in Windows?

To manage file permissions Signup and view all the answers

What is the term for sharing files on a multi-user system?

File Sharing Signup and view all the answers

What is the term for a set of files stored on a disk?

File System Signup and view all the answers

What is the main advantage of using the modified free-list approach in storing free blocks?

Faster lookup of free blocks Signup and view all the answers

What is the benefit of using a balanced tree instead of a linked list to store free-space list entries?

It allows for efficient lookup, insertion, and deletion Signup and view all the answers

What is the purpose of keeping a count of free contiguous blocks in the counting approach?

To keep track of the number of free blocks allocated simultaneously Signup and view all the answers

What is the main advantage of grouping free blocks in the modified free-list approach?

Storing a large number of free blocks efficiently Signup and view all the answers

What is the main purpose of the counting approach in free-space management?

To manage allocation and freeing of contiguous blocks Signup and view all the answers

What is the main advantage of using a balanced tree in the counting approach?

Efficient lookup, insertion, and deletion operations Signup and view all the answers

What is the main purpose of the modified free-list approach?

To quickly find a large number of free blocks Signup and view all the answers

What is the main difference between the modified free-list approach and the standard linked-list approach?

The modified approach stores a large number of free blocks efficiently Signup and view all the answers

What is the effect of increasing the number of disks in an array?

Data-transfer rates are higher, but the system is more expensive. Signup and view all the answers

What is the consequence of protecting more bits with a single parity bit?

The space overhead due to parity bits is lower, but the chance of data loss due to a second disk failure is higher. Signup and view all the answers

What is the goal of system protection?

To ensure the security and integrity of the system. Signup and view all the answers

What is the domain of protection in an operating system?

System security and data integrity. Signup and view all the answers

What is the consequence of a second disk failure before the first failed disk is repaired?

Data loss is guaranteed. Signup and view all the answers

What is the primary concern in system protection?

Ensuring the integrity and security of the system. Signup and view all the answers

What is the total number of cylinder moves in the SCAN algorithm example?

236 Signup and view all the answers

What is the primary advantage of the C-SCAN algorithm over the SCAN algorithm?

More uniform wait time Signup and view all the answers

How does the C-SCAN algorithm treat the cylinders on the disk?

As a circular list that wraps around from the last cylinder to the first one Signup and view all the answers

What is the total number of cylinder moves in the C-SCAN algorithm example?

382 Signup and view all the answers

What is the main difference between the SCAN and LOOK algorithms?

The arm only goes as far as the last request in each direction, then reverses direction Signup and view all the answers

What is the relationship between the C-LOOK and C-SCAN algorithms?

C-LOOK is a version of C-SCAN, and LOOK is a version of SCAN Signup and view all the answers

What is the primary purpose of the saved set-user-ID and saved set-group-ID?

To store copies of the effective user ID and effective group ID when a program is executed Signup and view all the answers

What are the two IDs that identify who the user really is?

Real user ID and real group ID Signup and view all the answers

What determines file access permissions for a user?

Effective user ID, effective group ID, and supplementary group IDs Signup and view all the answers

What is the function used to set the real user ID and effective user ID?

setuid Signup and view all the answers

What happens when a process has superuser privileges and calls the setuid function?

The real user ID, effective user ID, and saved set-user-ID are set to uid Signup and view all the answers

When a user tries to open a file, what IDs are used for access tests?

Effective user ID and effective group ID Signup and view all the answers

What is the purpose of the access and faccessat functions?

To test accessibility based on the real user and group IDs Signup and view all the answers

What is the consequence of calling the setuid function without superuser privileges, when uid does not equal either the real user ID or the saved set-user-ID?

The function returns an error and errno is set to EPERM Signup and view all the answers

Study Notes

Operating Systems

Operating systems manage free space in the file system using various techniques, including the free-list approach and the counting approach.

Grouping

A modification of the free-list approach stores addresses of n free blocks in the first free block, with the last block containing addresses of another n free blocks.
This approach allows for quick retrieval of addresses of a large number of free blocks.

Counting

The counting approach keeps track of the address of the first free block and the number (n) of free contiguous blocks that follow the first block.
Each entry in the free-space list consists of a disk address and a count, and can be stored in a balanced tree for efficient lookup, insertion, and deletion.

File Management

File management involves file sharing, access control, and protection schemes to ensure secure access to files.

File sharing is desirable in multi-user systems and can be implemented through protection schemes.
On distributed systems, files can be shared across a network using methods like Network File System (NFS).
User IDs, group IDs, and owner permissions determine file access rights.

Remote File Systems

Remote file systems allow file system access between systems, either manually via programs like FTP or automatically using distributed file systems.
The World Wide Web is another way to access remote files semi-automatically.

Protection

File owners should be able to control what can be done to their files and by whom.
Types of access include read, write, execute, append, delete, and list.

Access Lists and Groups

Unix/Linux systems have three classes of users: owner, group, and public.
Access modes include read, write, and execute (RWX).
Users can be grouped together using commands like chgrp.

Windows Access-Control List Management

Windows uses Access-Control Lists (ACLs) to manage file access.

Files and Directories - System Calls

System calls for file management include create, delete, open, close, read, write, and seek.

I/O Management, System Protection, and Security

I/O management involves managing input/output operations between devices and programs.
System protection involves achieving security goals like confidentiality, integrity, and availability.

System Protection - Goals, Principles, and Domain of Protection

System protection aims to prevent unauthorized access, use, disclosure, modification, or destruction of resources.
Principles of protection include least privilege, separation of privilege, and accountability.
The domain of protection includes hardware, software, and human elements.

SCAN Algorithm

The SCAN algorithm (also called the elevator algorithm) schedules disk I/O requests to minimize head movement.
The algorithm moves the head from one end of the disk to the other, servicing requests as it goes.

C-SCAN Algorithm

The C-SCAN algorithm is a variant of SCAN that provides a more uniform wait time.
The head moves from one end of the disk to the other, servicing requests, and then immediately returns to the beginning of the disk without servicing any requests on the return trip.
C-SCAN treats the cylinders as a circular list that wraps around from the last cylinder to the first one.

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Description

Learn about the concepts and methods of file sharing in multi-user and distributed systems, including remote file systems and networking protocols.