Mini test 2

Question 1

Processes

Answer 1

an instance of a running program

Question 2

functionality of Processes

Answer 2

provides logical control flow and private address space

Question 3

management of Processes

Answer 3

OS uses context switching and virtual memory

Question 4

purpose of fork

Answer 4

creates a new child process

Question 5

behavior of forking

Answer 5

returns twice: once in the parent (child’s PID) and once in the child (0)

Question 6

characteristics of forking

Answer 6

child gets a copy of the parent’s address space and file descriptors

Question 7

exec function

Answer 7

replaces the current process memory with a new program

Question 8

exec usage

Answer 8

execve is a common variant that loads and runs a program

Question 9

details of exec

Answer 9

maintains PID but overwrites memory, stack, and code

Question 10

Process Graphs

Answer 10

visualize the partial ordering of operations in concurrent programs

Question 11

features of Process Graphs

Answer 11

nodes represent operations; edges indicate execution order

Question 12

Zombies

Answer 12

processes that have completed execution but still have an entry in the process table

Question 13

cause of Zombies

Answer 13

occur when a parent process doesn’t immediately perform a wait to collect the child’s termination status

Question 14

resolution of Zombies

Answer 14

parent performs reaping using wait or waitpid

Question 15

functionality of wait

Answer 15

pauses the parent until any child terminates; reaps zombie processes

Question 16

functionality of waitpid

Answer 16

more specific that wait, can wait for a specific process

Question 17

wait/waitpid options

Answer 17

can use various flags to modify behavior, such as non-blocking waits

Question 18

Signals

Answer 18

notifications sent to a process by the OS indication that an event has occurred

Question 19

types of Signals

Answer 19

identified by integer IDs, like SIGINT for interrupt and SIGKILL for termination

Question 20

behavior of Signals

Answer 20

can be ignore, terminate the process, or be caught by a custom handler

Question 21

Traps

Answer 21

intentional, such as system calls of breakpoints; control returns to next instruction

Question 22

Faults

Answer 22

unintentional but can be recoverable; may re-execute the faulting instruction

Question 23

Aborts

Answer 23

unintentional and unrecoverable; leads to program termination

Question 24

Signal Handlers

Answer 24

custom functions defined by a program to respond to specific signals

Question 25

installation of Signal Handlers

Answer 25

use signal() or sigaction() to set a handler

Question 26

safety of Signal Handlers

Answer 26

handlers should be simple and only use async-signal-safe functions

Question 27

Blocking Signals mechanism

Answer 27

prevents the process from receiving certain signals temporally

Question 28

Blocking Signals usage

Answer 28

useful during critical sections of code to avoid interruptions

Question 29

Blocking Signals methods

Answer 29

sigprocmask() to block/unblock signals and sigsuspend() to wait for a set of blocked signals to occur

Question 30

I/O Basics

Answer 30

Involves copying data between main memory and external sources like disk drives and terminals

Question 31

I/O Unix Model

Answer 31

Treats all I/O devices as files, allowing for uniform file operations across devices

Question 32

Open files

Answer 32

open() system call is used to access a file; returns a file descriptor if successful

Question 33

Close file

Answer 33

close() system call releases resources associated with a file; important to check return status for errors

Question 34

File Descriptor

Answer 34

Small, non-negative integer that identifies an open file for the process

Question 35

Open File

Answer 35

Represents an actual instance of an open file, including its current position, access modes, and links to file data

Question 36

V-node Tables

Answer 36

Low-level structures that store metadata about a file, such as permissions, owner, size, and pointers to data blocks

Question 37

Shared/Unshared I/O Between Parent and Child Processes Inheritance

Answer 37

Child process inherits open file descriptors from its parent upon fork()

Question 38

Shared/Unshared I/O Between Parent and Child Processes Independence

Answer 38

Despite sharing file descriptors, file offset and file status flags are copied, allowing independent file operations

Question 39

Redirection (dup2) Purpose

Answer 39

dup2() system call is used to copy a file descriptor to another, replacing the latter, useful for I/O redirection

Question 40

Redirection (dup2) Common Use

Answer 40

Redirect output or input of a process to/from a file or another process

Question 41

Pipes Functionality

Answer 41

Allows for one-way communication between two processes; typically used to connect the output of one process to the input of another

Question 42

Pipes Implementation

Answer 42

Created using the pipe() system call which returns two file descriptors; one for reading and the other for writing