CMPSC 311 | Exam 2 (Spring 2025)

Notes

Hypervisor

virtual machine monitor

Operating system (OS)

software that manages machine hardware, provides interface with said hardware, and provides abstractions that system software can build upon

Type 1 Hypervisor

a hypervisor that runs on the host machine

Type 2 Hypervisor

a hypervisor that runs on the operating system

Layer

collection of system functions that support abstractions to services/apps above

Abstraction

The process of hiding and simplifying unnecessary or messy details into something more readable and/or ergonomic

Process

structures that form independent programs running concurrently within OSes

File

An abstraction of a data object

Data file

A type of file to be used for interpretation and manipulation from a program

Virtual memory

A combination of memory addresses and disk addresses to create “more memory” than physically possible

Word size

Number of bits processed simultaneously by a computer’s processor or memory

Address

Unique identifiers for byte locations in memory

Applications programmer interface (API)

A set of methods used to manipulate an abstraction; a library of calls that use the abstraction

Low-level language

A programming language that has low amounts of abstraction and is overall higher performance, more control of system hardware

High-level language

A programming language that is built for productivity and ease of access rather than performance, more useful for system software

GNU

One of the collections of softwares to be used within operating systems

Open source

Describes when a user of the source is allowed to review, modify, and distribute software with no cost to anyone; variants of this can allow charging for derivative works

System call

A call from user-level processes that allow them to safely enter the OS and call methods from it

Unprivileged (User) mode

The mode that the CPU runs in when user-level processes run

Privileged (Kernel) mode

The mode that the CPU runs in when the OS runs

Application

A complete program for ordinary users

Application library

An application-specific tool

Command interpreter/shell

Shell program that interpets built-in commands and can run programs and shell scripts

System utility

Tools that are independent from applications, used to tune system software

Device driver

Program that implements an interface to real hardware, such as mice or keyboards

Kernel module

A software module that can be loaded and unloaded on a system, increasing a kernel’s functionality without needing recompilation

Command line interface

The user interface within a terminal

/usr

In Linux: installed software

/etc

In Linux: configuration files

/home

In Linux: user files

/dev

In Linux: devices and their files

/tmp

In Linux: temporary files

Root

The “super user” within Linux, can access any file

su

This CLI command that, upon verification, grants administrative privileges

sudo

This CLI command that temporarily gives administrative privileges without the requirement of logging in as root

ls

This CLI command lists files and directories within the current directory

mv

This CLI command renames files, as well as move files between directories

rm

This CLI command removes a given file from existence

rmdir

This CLI command removes an empty directory from existence

rm -r

This CLI command removes the current directory and all its contained files from existence

cat

This CLI command reads the contents of a given file (STDIN) and prints to terminal (STDOUT)

touch

This CLI command creates a file with the given name and an optional file extension

pwd

This CLI command prints out the current working directory

cd

This CLI command moves the current working directory

mkdir

This CLI command creates a new directory within the current directory

cd ..

This CLI command moves the current working directory to the parent directory if it exists

man

This CLI command prints out documentation for a given command (others similar command are help and tldr)

Binary file

A separate program executed by the shell

/lib

Location of shared library files used by core systems programs

/sbin

Location of system binaries for vital system tasks

Alias (term)

Shortcut defined by a user to avoid typing long commands or command sequences

> (within CLI)

Within the CLI this operator redirects the output or error of a command by overwriting a file

>> (within CLI)

Within the CLI this operator redirects the output or error of a command by appending to a file

< (within CLI)

Within the CLI this operator reads an input from a file rather than the standard input (which usually is the keyboard)

cp

This CLI command copies the contents of one file into another file

history

This CLI command lists the history of all commands since system startup

alias (CLI command)

This CLI command creates an alias that can be used as a shortcut for inputting multiple commands

echo

This CLI command prints a given string of text within the terminal STDOUT

Syntax: command “string”

ls -a

This CLI command lists the contents of the directory including usually hidden dot files

Object file

A file that contains machine code produced by a compiler, will be linked in a later process to be turned into an executable file

const

A variable modifier in C that makes a variable’s value final and unchangeable

&[variablename]

This C operator takes the address of a variable rather than its value

*[variablename]

This C operator “dereferences” a pointer, giving access to the pointed variable’s value

Pass-by-value

This term describes when a variable’s value is passed into a function, which bars the function from modifying that variable directly

Pass-by-reference

This term describes when a variable’s address is passed into a function, allowing that variable to be modified within the function

Array

A way to store multiple values in a single variable, though it has no methods and can’t keep track of its own length

String

An array of char, terminated by the string \0. Can be initialized with char as well.

malloc()

Allocates memory for program usage; returns NULL if memory can’t be allocated, else returns a void pointer corresponding to the first byte of the memory allocated

Syntax: function(size)

free()

Frees up memory that was heap-allocated/manually allocated

Syntax: function(*pointer)

assert()

Checks for statements in the code that must always be true, where the process aborts if is not true; syntax function(expression)

Debugger

A program that runs your program within a controlled environment

GDB (Term)

The GNU Debugger

gdb (CLI command)

Runs the GDB debugger, has syntax function(program)

run (GDB command)

Within GDB, starts the program; arguments can be passed down to this function

Syntax: function (arguments)

list (GDB command)

Within GDB, shows ten lines of code at a time given a line number or a function name

Syntax: function (line number or function name)

Breakpoint

A position in the code you wish for a debugger to stop and wait for your commands; each one is assigned a number to be referenced later

break (GDB command)

Within GDB, creates a breakpoint; each one is assigned a number that can be referenced later

Syntax: function (function_name) OR function (line_number)

delete (GDB command)

Within GDB, deletes a breakpoint

Syntax: function (breakpoint_ID)

cond (GDB command)

Within GDB, modifies a given breakpoint such that it will only call the debugger if the condition is true (i.e. a conditional breakpoint)

Syntax: function (breakpoint_ID) (expression)

info breakpoints (GDB command)

Within GDB, allows the user to see information about their current breakpoints

save breakpoints (GDB command)

Within GDB, lets the user save their current breakpoints to a file for later use

Syntax: function (file name)

source (GDB command)

Within GDB, lets the user load saved breakpoints for use

Syntax: function (file name)

Watchpoint

This stops execution and calls the debugger whenever the state of a specific variable changes, without a particular place where it happens. Also known as a data breakpoint

watch (GDB command)

Within GDB, creates a watchpoint for a specific variable

Syntax: function (variable name)

where (GDB command)

Within GDB, tells the user where they are in the command, along with a stack

up (GDB command)

Within GDB, moves up the stack

print (GDB command)

Within GDB, prints the value of any variable in the program.

Syntax: function[/(format)] (variable)

x (GDB command)

Within GDB, examines regions of memory given an address

Syntax: function[/<num><format><size>] address

next (GDB command)

Within GDB, moves the program forward one statement

step (GDB command)

Within GDB, moves the program forward one statement, and steps into a function if applicable

continue (GDB command)

Within GDB, runs the program until it hits another breakpoint or the program ends

finish (GDB command)

Within GDB, runs the function until it returns a value

Box & Arrow Diagrams

Method where all variables, pointers, array elements, etc. are listed in a table

Buffer

A memory region that has some temporary use, typically referenced through a pointer.

General purpose buffer

A buffer defined with type void, doesn’t have a data type and requires casting for access to its data

memcpy()

Copies memory from one region to another

Syntax: function(*dest, *src, length); length must be explicit

memset()

Fills memory with a constant given byte

Syntax: function(*buf, byteVal, length)

memcmp()

Compares the first length bytes of two buffers; negative if buf1 is less than buf2, and so on

Syntax: function(*buf1, *buf2, length)

Dynamic memory

Memory that is allocated and returned by a function, where its size isn’t known by the caller; memory must be deallocated manually

sizeof()

Returns the size (in bytes) of the variable given

Syntax: function(variable)