Checklist 03

This is a general outline of the key concepts (arranged by topic) that you should know for the Exam 03.

Format

The exam will have the following format:

1. Code Snippets: Write Shell commands or Python code to perform certain tasks. (6 Points)

2. Short Answers: Briefly answer questions about:

   • Unix Philosophy (4 Points)

   • C

     • Compiling and Makefiles (6 Points)

     • Pointers, Arrays, Strings (6 Points)

     • Data Representation (6 Points)

     • Memory (6 Points)

   • System Calls

     • I/O, Files, Directories (6 Points)

     • Processes (6 Points)

     • Networking (6 Points)

3. Programming: Write some C code that uses system calls. (8 Points)

Parts 1 and 2 are to be done first on paper. After these parts are completed, part 3 can be done with the aid of your laptop and the Internet (but not other people).

Scripting

1. What is Unix?

   • What are the three tenets of the Unix Philosophy?

   • What are filters? What do they do and how are they related to the Unix Philosophy?

2. What are the principles of functional programming?

   • How does functional programming compare to procedural programming?

   • How is functional programming related to the Unix Philosophy?

3. What is concurrency and what is parallelism?

   • What makes concurrency challenging?

   • What are the different forms of parallelism?

Shell

How do you construct a unix pipeline to do the following:

1. Extract a fields or characters.

2. Search based on a pattern.

3. Count the number of lines.

4. Search a directory based on a pattern or file attribute.

5. List the processes on the current machine.

Python

1. How do you use map, filter, and lambda?

2. How do you use list comprehensions?

Sample Question

Given a list of integers called numbers, produce a new list called fives which consist only of the multiples of 5 by using filter and lambda.

Then, do the same thing using list comprehensions.

C

1. Why bother with C? Why not just Python or C++?

2. Why is C considered a systems programming language?

3. What is C's relationship to Unix?

Compiling and Makefiles

1. What is the compiler pipeline?

   • What exactly happens when you compile a program (ie. describe the compiler pipeline)?

   • What is the difference between a dynamic executable and a static executable?

   • What is the difference between a shared library and a static library?

2. How do you write a Makefile that utilizes rules and variables for a program that consists of multiple files?

Pointers, Arrays, Strings

1. What exactly is a pointer? array? string? How are they related?

2. What does it mean to dereference a pointer?

3. How do we get the address of a variable?

4. What are multiple ways to access an element of an array or string?

Data Representation

1. What is the difference between a struct and a union?

2. How much memory is allocated when we declare an int, float, double, char, array, string, or pointer?

3. What is the difference between little-endian and big-endian?

4. When we declare a variable, where is the data allocated (stack, heap, data, code)?

Memory

1. How do we dynamically allocate memory? How do we deallocate that memory?

2. When should we allocate on the stack? heap? data? What are the advantages and disadvantages of utilizing each memory segment?

3. How do we detect and fix memory errors such as: segmentation faults, invalid reads, uninitialized memory, and memory leaks?

Sample Question

An anagram is a word formed by rearranging the letters of another word. For instance, cinema is an anagram of iceman.  The following function determines if the two given strings are anagrams:

bool is_anagram(const char *s1, const char *s2) {
    int max = 0;

    for (const char *c = s1; c; c++) { if (*c > max) max = *c; }
    for (const char *c = s2; c; c++) { if (*c > max) max = *c; }

    int *counts1 = malloc(max * sizeof(int)), *counts2 = malloc(max * sizeof(int));

    for (const char *c = s1; c; c++) { counts1[(int)*c]++; }
    for (const char *c = s2; c; c++) { counts2[(int)*c]++; }

    for (int i = 0; i <= max; i++) if (counts1[i] != counts2[i]) { return false; }
    free(counts1); free(counts2);
    return true;
}

This function has the following memory errors: segmentation fault, invalid read, uninitialized memory, and memory leak.  Briefly describe how you would fix these errors.

System Calls

1. What exactly are system calls?

   • What is the difference between user mode and kernel mode?

   • What happens when an application performs a system call?

2. What are some reasons why system calls related to files, processes, and networking would fail?

   • How do we check these failures?

   • How do we get the error message related to these failures?

Files

1. What is the difference between open and fopen?

2. What exactly is a file descriptor and what system calls can we do with one?

3. How do we get the inode information for a file?

Sample Question

How would you use system calls in C to accomplish the following tasks:

• Display the contents of a file?

• Copy the contents of a file?

• Check if a file is a regular file, directory, or symlink?

• Check if a file is a readable, writable, or executable?

• Check the size of the file?

• Check the last modification time?

• List the contents of a directory? in sorted order?

Processes

1. What is a process?

   • What attributes or components does it have?

   • What system calls can you do with them?

2. What happens during the life cycle of a typical process?

   • After a fork, how does a process determine if they are the child or parent?

   • After a fork, who executes first: parent or child?

   • What happens when a process performs exec?

   • Why is it necessary to perform a wait?

   • What is the purpose of exit?

3. How do we prevent a fork bomb?

   • How do we prevent zombies?

   • Why would we want to prevent these situations?

4. What is a signal?

   • What does a signal do to a process?

   • How do we send a signal to another process?

   • How do we catch a signal and handle them?

   • What happens to system calls if a signal interrupts them?

Sample Question

Draw a diagram of the typical life cycle of a process.

Networking

1. What is networking?

   • What is bandwidth and latency and how do we measure them?

   • What is an IP address and what is a domain name?

   • What is a network port?

   • What is the basic difference between TCP and UDP?

2. What is a URL and what are its components?

3. How are sockets like files? How are they different?

4. What is HTTP?

   • What system calls does a typical HTTP client perform? What messages does it send and receive?

   • What system calls does a typical HTTP server perform? What messages does it send and receive?

Sample Question

Modify echo_client_refactored.c to implement a port scanner (ie. nc -z) or a HTTP client (ie. curl).