Chapter 2

Question 1

what is a command interpreter

Answer 1

same thing as a CLI or command line interface

Question 2

what are system calls?

Answer 2

provide an interface to the services made available by the operating system

Question 3

why are API’s preferable to directly calling system calls?

Answer 3

API’s provide a level of abstraction to ensure portability they are also generally simplified interfaces compared to the sys call. API’s are the interface between user mode and kernel mode

Question 4

what are the ways parameters are passed to system calls?

Answer 4

through registers, in a block of memory with the address of the memory being put in the register

Question 5

what is a process control system call?

Answer 5

manages the creation and termination of processes, loading and executing programs, getting and setting process attributes, allocating and freeing memory

Question 6

what is a file management system call?

Answer 6

creates, deletes files. opens and clsoes files, reads and writes or moves, gets and sets file attributes

Question 7

what are device management system calls?

Answer 7

request and release device, read write to the device, get and set device attributes, attach and detach devices

Question 8

what are information maintenance system calls?

Answer 8

get/set time or date, get/set system data, get/set process, file or device attributes

Question 9

what are communication system calls?

Answer 9

handles interprocess communication

Question 10

what two types of constructs are so similar that unix treats them as the same?

Answer 10

device management and file system

Question 11

what is the general purpose of information maintenance system calls?

Answer 11

to simply transfer information between the user program and the operating system. just generic things that may not fit exclusively into the various buckets, like version numbers or date time. they also critically provide stack traces

Question 12

name the two types of interprocess communications

Answer 12

message passing model and shared-memory model

Question 13

how are daemons used for interprocess communication?

Answer 13

a daemon wates for a connection in a client/server model and then facilitates communication with read_message() and write_message()

Question 14

what are protection system calls?

Answer 14

they provide mechanisms for controlling access to resources. like setting and getting permissions

Question 15

what is the difference between system services and system calls?

Answer 15

system calls are singular things, system services can be an abstraction of multiple system calls and other logic

Question 16

what is a linker?

Answer 16

a linker combines various object files into a single binary, like including libaries into the final binary output

Question 17

what is a loader?

Answer 17

a loader prepares the computer and memory space to run the binary

Question 18

what is a DLL?

Answer 18

dynamically linked libraries, it is used to not link every possible library file and instead pulls them in dynamically during run time

Question 19

why are applications OS specific

Answer 19

mainly comes down to system calls and various other OS specifics

Question 20

what are some solutions to this?

Answer 20

interpreters, virtual machines like the JVM, and cross compilation

Question 21

what do ELF files attempt to solve?

Answer 21

provides a common binary format with headers, instructions and variables that the OS can consistently understand how to run and load

Question 22

what is an ABI?

Answer 22

application binary interface, used to define how different components of binary code can interface for a given OS

Question 23

what problem do ABI’s solve?

Answer 23

they define a common interface to define how things like system calls are encoded at the binary level to ensure that registers in a specific architecture are used

Question 24

what is a monolithic OS structure?

Answer 24

when the kernel is placed into a single static binary file that runs in a single address space

Question 25

what is a layered OS design structure?

Answer 25

an os separated into smaller components that have specific and limited functionality

Question 26

what advantage do layered OS designs have?

Answer 26

they are less coupled, changes in one area do not necessarily impact another area of the OS or kernel

Question 27

what type of structure do modern OS’s use?

Answer 27

they use a hybrid of monolithic and layered as layered can be slow. the kernel is monolithic for performance

Question 28

what is a microkernel?

Answer 28

removes all nonessential components and makes them part of user space in the OS

Question 29

what are Loadable Kernel Modules?

Answer 29

LKM’s provide a small kernel with other modules that can be dynamically loaded while the kernel is still loading that would otherwise require the kernel to be recompiled

Question 30

what is a boot loader?

Answer 30

it locates the kernel and loads it into memory

Question 31

what does grub do?

Answer 31

grub allows you to load different OS kernels into memory, can boot multiple OS’s

Question 32

what are OS counters?

Answer 32

they keep track of various stats of processes running on the OS, crucial for system monitoring for data tools like top or vmstat

Question 33

what is tracing in the OS?

Answer 33

provides detailed event by event information about system behavior. used for debugging or to find out what went wrong with

Question 34

what does the BCC do?

Answer 34

provided tracing at the kernel level, is a higher level abstraction on top of eBPF