Operating Systems Concepts Quiz

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Questions and Answers

Which of the following functions are considered direct system calls? (Select all that apply)

  • int open(const char *pathname, int flags, mode_t mode) (correct)
  • void assert(scalar expression)
  • int pause(void) (correct)
  • void *malloc(size_t size)

Which of these statements is true regarding kernel modules and execution modes? (Select all that apply)

  • A loaded kernel module executes in user mode.
  • A program executed with root permissions runs in user mode.
  • Transition from user mode into system can be caused by an interrupt or a system call. (correct)
  • Regular programs execute in kernel mode.

Which function is used to suspend the execution of the calling thread for a specified time? (Select all that apply)

  • int pause(void) (correct)
  • ssize_t write(int fd, const void *buf, size_t count)
  • void *malloc(size_t size)
  • unsigned int sleep(unsigned int seconds) (correct)

Which function is NOT a system call? (Select all that apply)

<p>void *malloc(size_t size) (A)</p> Signup and view all the answers

Which of the following descriptions correctly identifies execution modes? (Select all that apply)

<p>User mode restricts access to certain system resources. (B), Interrupts can cause a transition from user mode to system mode. (C)</p> Signup and view all the answers

Which statement accurately describes parallel execution?

<p>Parallel execution is concerned with doing many things at once. (A)</p> Signup and view all the answers

What best describes the difference between concurrency and parallelism?

<p>Concurrency is focused on handling multiple tasks over time, while parallelism executes them simultaneously. (C)</p> Signup and view all the answers

Which of the following statements about a kernel's efficiency is true?

<p>A kernel must incorporate concurrency to enhance performance. (A)</p> Signup and view all the answers

How does a hardware trap related to invalid pointers operate?

<p>It is synchronous to the execution of the current process. (B)</p> Signup and view all the answers

What is the role of the perror() function in C programming?

<p>It writes a specified message followed by the last error description to the standard error stream. (A)</p> Signup and view all the answers

Which scenario illustrates asynchronous behavior in processes?

<p>Receiving user-generated interrupts that do not block the running process. (C)</p> Signup and view all the answers

Which statement about standard output and standard error file descriptors is accurate?

<p>Standard output is 0 while standard error is 1. (B)</p> Signup and view all the answers

Why is handling runtime errors important in C programming?

<p>Unhandled errors can cause programs to terminate unexpectedly. (D)</p> Signup and view all the answers

What does the function void perror(const char *s) accomplish?

<p>Writes a message to the standard error stream followed by the last error description. (C)</p> Signup and view all the answers

Which statement accurately describes dynamic libraries?

<p>A dynamically linked executable runs the dynamic linker before main() is called. (C)</p> Signup and view all the answers

In terms of error handling, what does the global symbol errno indicate?

<p>It indicates the error code of the last occurred error. (A)</p> Signup and view all the answers

What is a microkernel architecture primarily characterized by?

<p>Minimizing kernel size by executing core functions in user space. (C)</p> Signup and view all the answers

Which statement is true regarding a program exiting with a non-zero exit code?

<p>It can signal varying types of errors. (B)</p> Signup and view all the answers

What is a potential consequence of bypassing standard I/O streams in C?

<p>It requires implementing additional error handling mechanisms. (C)</p> Signup and view all the answers

Which of the following correctly describes modular architecture in operating systems?

<p>It facilitates simpler development of new kernel components. (A)</p> Signup and view all the answers

How is standard output normally managed in a terminal context?

<p>It is buffered, which may delay detecting write failures. (D)</p> Signup and view all the answers

What is a common trait of operating systems that employ a layered architecture?

<p>It allows for modular updates of specific system parts without affecting the entire system. (A)</p> Signup and view all the answers

In the context of operating systems, what function does access control mechanisms serve?

<p>They enable enforcement of access control policies. (B)</p> Signup and view all the answers

What distinguishes a dynamic library from a static library?

<p>Dynamic libraries require linking at runtime rather than compile time. (D)</p> Signup and view all the answers

What happens when an error is encountered in a system call?

<p>The call returns a negative error code to signify failure. (D)</p> Signup and view all the answers

Why might error messages not be sent to standard output?

<p>They can confuse users by mixing with normal output. (A)</p> Signup and view all the answers

What defines the functionality of user-space components in a microkernel architecture?

<p>They execute non-critical services that support kernel functionality. (C)</p> Signup and view all the answers

Flashcards

Parallel Execution

Performing multiple tasks simultaneously on different processors.

Concurrency

Managing multiple tasks as if they were happening simultaneously, even though they might not be.

Concurrent Execution

Executing multiple tasks in an interleaved manner on a single processor.

Kernel Efficiency

A kernel needs concurrency to efficiently handle multiple requests/tasks.

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Synchronous Error

An error that occurs immediately during program execution.

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Asynchronous Error

An error that occurs at a later time, and may not be related to the current task or thread.

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strerror Function

Converts an error code to a descriptive string.

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perror Function

Prints an error message to standard error.

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System Call

A function that directly interacts with the kernel to request an operation, such as accessing hardware or managing resources.

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Direct System Call

A function that is directly implemented as a system call, bypassing any library or middleware layers.

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User Mode vs. System Mode

User mode allows regular programs to run, while system mode grants access to sensitive system resources and operations, reserved for the kernel.

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System Call Example

The open() function is a direct system call that requests the kernel to open a file.

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Kernel Module Execution

A loaded kernel module, like a mini-program within the kernel, always executes in system mode.

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Dynamic Linking

A technique where a program's dependencies are loaded at runtime, allowing for more modularity and updates.

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Static Linking

A technique where a program's dependencies are combined into a single executable file during compilation.

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Dynamic Library

A collection of code and data that can be shared by multiple programs at runtime.

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Dynamic Linker

The program responsible for loading and linking dynamic libraries at runtime.

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Microkernel Architecture

A kernel architecture where only essential functions are in the core kernel, with other services like device drivers running as user-level processes.

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Modular Kernel Architecture

A kernel architecture where the kernel is divided into modules that can be loaded or unloaded dynamically.

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Layered Kernel Architecture

A kernel architecture where system services are organized in layers, with each layer accessing only the layer below it.

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Runtime Error

An error that occurs during program execution.

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Error Code

A numeric value indicating the type of runtime error.

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errno

A global variable that holds the error code of the last system call.

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Standard Input (stdin)

The input stream for a program, usually the keyboard.

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Standard Output (stdout)

The output stream for a program, usually the console.

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Standard Error (stderr)

A separate output stream for error messages.

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Redirection

The ability to change the source or destination of standard input, output, or error streams.

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Study Notes

Correct Statements About Operating Systems and Programming

  • Concurrency and Parallelism: Concurrency involves dealing with multiple tasks seemingly simultaneously, while parallelism involves executing multiple tasks truly simultaneously on multiple processors. Concurrent execution is possible even on a single processor. Concurrency and parallelism can be combined.

  • Kernel Efficiency and Concurrency: A kernel needs to exploit concurrency for efficiency.

  • Synchronous vs. Asynchronous Events: Hardware traps (e.g., invalid pointer dereferencing) are synchronous events. Software interrupts triggered by user actions are asynchronous. System calls can be considered potentially synchronous but not always. The kernel handles asynchronous interrupts independently of running processes.

  • Runtime Error Handling (C): The perror function writes error messages to standard error, while the strerror function converts error codes into strings. Unhandled runtime errors can lead to exceptions. Error messages should be written to standard error, not standard output.

  • Dynamic Linking: Dynamic libraries can be shared among multiple programs. A dynamically linked executable uses a dynamic linker before the main function is called. Dynamically linked programs might need more memory than statically linked programs. Static linking typically results in smaller executables. Updating a dynamic library often requires restarting programs that use it.

  • Operating System Architectures: Microkernels typically have a layered architecture with two layers. Microkernels implement device drivers, while memory management and multitasking fall under the operating system kernel. Modular architectures are valuable for simplified development of kernel modules, such as device drivers and filesystems. Virtual machine kernel architectures often benefit from three or more privilege levels. Modular architectures allow loading only necessary modules, making the kernel smaller.

  • System Call Error Reporting: System calls often return -1 to indicate errors. The errno variable contains the last error code, allowing programs to check for errors. Programs exiting with non-zero exit codes signify errors.

  • Mechanism and Policy: Mechanisms enforce things, while policies dictate how those mechanisms should be used. Systems are designed to be adaptable to various situations through this separation. Operating systems provide mechanisms for controlling access, letting users configure the specific policies.

  • Standard I/O Streams: Standard output and standard error are typically sent to the terminal in a terminal session. The standard input is often line-buffered in a terminal. The standard output and standard error streams used by C libraries are internally buffered for performance. Standard input's redirection is common, allowing other program results or file input.

  • System Calls in C: open, write, and pause are direct system calls. malloc, assert, and sleep are not direct system calls.

  • System Mode and User Mode: Kernel modules execute in system mode. Transitions to system mode can be triggered by interrupts or system calls. Root permissions allow programs to function in system mode but standard programs run in user mode.

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