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XXXXXXXXXXlabs/lab5.md at master · ITF22519/labshttps:github.com/ITF22519/labslomastelab5/lab5.md 1/8ITF22519 / labs PrivateCode Issues Pull requests Actions Projects Security Insightslabs / lab5 / lab5.mdanlam Update lab5.md Latest commit 428f5cf 13 days ago  History 1 contributoLearn Git and GitHub without any code!Using the Hello World guide, you’ll start a anch, write comments, and open a pull request.Read the guide master Go to file298 lines (234 sloc XXXXXXXXXXKB   ITF XXXXXXXXXXIntroduction to Operating SystemsAutumn 2020Lab 5: Introduction to Unix ProcessesBefore you start, remember to commit  and push  your previous lab to your git repository. Then, try to pull  the new lab:$ cd ITF22519/labs $ git pull upstream master $ git pull origin master $ cd lab5Please remember these steps for the future labs.Raw Blamehttps:github.com/ITF22519https:github.com/ITF22519/labshttps:github.com/ITF22519/labshttps:github.com/ITF22519/labs/issueshttps:github.com/ITF22519/labs/pullshttps:github.com/ITF22519/labs/actionshttps:github.com/ITF22519/labs/projectshttps:github.com/ITF22519/labs/securityhttps:github.com/ITF22519/labs/network/dependencieshttps:github.com/ITF22519/labshttps:github.com/ITF22519/labs/tree/mastelab5https:github.com/anlamhttps:github.com/anlamhttps:github.com/ITF22519/labs/commit/428f5cfa19c8ce3f50025c0e13408b76c5fa1230https:github.com/ITF22519/labs/commit/428f5cfa19c8ce3f50025c0e13408b76c5fa1230https:github.com/ITF22519/labs/commits/mastelab5/lab5.mdhttps:guides.github.com/activities/hello-worldhttps:github.com/ITF22519/labs/find/mastehttps:github.com/ITF22519/labsaw/mastelab5/lab5.mdhttps:github.com/ITF22519/labslame/mastelab5/lab5.mdx-github-client:openRepo/https:github.com/ITF22519/labs?anch=master&filepath=lab5%2Flab5.mdhttps:github.com/login?return_to=%2FITF22519%2Flabs%2Fblob%2Fmaster%2Flab5%2Flab5.mdhttps:github.com/login?return_to=%2FITF22519%2Flabs%2Fblob%2Fmaster%2Flab5%2Flab5.md XXXXXXXXXXlabs/lab5.md at master · ITF22519/labshttps:github.com/ITF22519/labslomastelab5/lab5.md 2/8I wrote this lab using Markdown ( .md ) which is a very simple markup language for documentation. You can find an example ofmarkdown here. I was thinking maybe you should also try using markdown to write your reports (or enter your answers of the laexercises directly into this file). This is not mandatory, just a suggestion. I just wanted to introduce to you a very cool language thatdevelopers use to document their code.About Unix Processes1. When a system is booted, the first user space process is systemd  (or /sbin/init  depending on your Linux Distribution), and has aPID of 1. This process will in turn launch startup scripts and eventually login prompts. If you do a ps -el , you should see that process1 is systemd . It will be the ancestor of all other user processes on the system.2. When you login or start a terminal, a process for the shell is started. The shell will then launch other processes, which will be childrenof the shell. If the parent process dies (for example, you exit the shell), systemd  will adopt the orphaned processes (on Linux andmany other Unix variants).3. The status of a Unix process is shown as the second column of the process table (viewed by executing the ps  command). Some ofthe states are R: running, S: sleeping, Z: zombie.Process TableThe program print_pid.c  prints out its process id as well as its parent’s id, and then sleeps for 2 minutes. Run the program print_pid.ctwice, both times as a background process (i.e. suffix it with an ampersand “ & ”):$ ./print_pid & Ctrl+C $ ./print_pid & Ctrl+CPay attention to the id of the parent processes printed by this program. Once both processes are running as background processes, viewthe process table (use ps -l  to view only the processes running on your terminal, or ps -el  to view all processes on the system). If yousee the message “I am awake”, the process has finished and will no longer show up in the process table. The first line from a ps -l  isduplicated here:F S     UID     PID  PPID   C PRI    NI ADDR     SZ WCHAN     TTY   TIME CMDA short description of the fields could be found here: https:docs.oracle.com/cd/E XXXXXXXXXX/ XXXXXXXXXX/spprocess-47/index.html. Youshould be able to find more details of these fields in the ps  manual page ( man ps ).Exercise 1 (10 pts)(8 pts) In the report, include only relevant lines from ps -l  for your programs, and point out the following items:process name (Process CMD)process state (decode the letter!)process ID (PID)parent process ID (PPID)(2 pts) Find out the name of the process that started your print_pid  programs. What is it, and what does it do?https:github.com/ITF22519/demo-markdownhttps:docs.oracle.com/cd/E XXXXXXXXXX/ XXXXXXXXXX/spprocess-47/index.html XXXXXXXXXXlabs/lab5.md at master · ITF22519/labshttps:github.com/ITF22519/labslomastelab5/lab5.md 3/8Kill processesNow that you know how to find a PID for a running program, you can use kill  to terminate an unwanted process. Just type killfollowed by the process ID. If a process refuses to terminate, kill -9  followed by the process ID will terminate any process you havepermission to kill. You might also try killall  to kill all processes with the same name (try man killall  for more information).$ killall print_pidThe fork() system callThe fork()  call creates a child that is a copy of the parent process. Because the child is a copy, both it and its parent process begin fromjust after the fork() . All of the statements after a call to fork()  are executed by both the parent and child processes. However, bothprocesses are now separate and changes in one do not affect the other.The code fragment below calls fork()  once, which results in the creation of one child process. Then, each process prints out its id and theparent’s id.int main() {     fork();     printf("Process %d's parent process ID is %d
", getpid(), getppid());     return 0; }The output of this program could be:Process 14427's parent process ID is 6891Process 14428's parent process ID is 14427Here, the id of the main function is 14427, the child id is 14428, and the id of bash shell is 6891. The process tree of this program isshowed below.Exercise 2 (10 pts)Compile and execute the program fork_ex1.c .https:github.com/ITF22519/labslomastelab5/img/process_tree.png XXXXXXXXXXlabs/lab5.md at master · ITF22519/labshttps:github.com/ITF22519/labslomastelab5/lab5.md 4/8(1 pts) Include the output of the program.(5 pts) Draw the process tree (label processes with PIDs).(4 pts) Explain how the tree was built.Make the new Process do Something DifferentSince the fork()  function call creates a clone of the parent process and returns different values for the parent and child processes. Usingthese two return values, the child process can be made to do something that is not the same as the parent. Firstly, we can use the fact thatthe value returned by fork()  is zero for the child. To differentiate between which process is which, the simplest is to use an if statement.Exercise 3 (5 pts)The program fork_ex2.c  prints different messages in the child and parent processes. Complete the condition of the if statements in thisprogram.Waiting on the Child ProcessWhen running the program fork_ex2.c , the parent and child process will each execute at their own pace, and either can finish executionefore the other. In the event that this is not the desired behavior, there are two system calls that the parent can run that will guaranteethat the parent waits for the child process to exit. The two functions are wait()  and waitpid() . Full information on what each of thesefunctions do and how they are used can be found at the manual page:$ man 2 waitTo use wait()  to make the parent process wait for the child process to complete, the following snippet of code is used:#include  #include  ... int status = 0; ... child = fork(); if(child == 0) {         does something cool } else if(child > 0) {  XXXXXXXXXXwait(&status);  XXXXXXXXXXprintf("child process is done, status is: %d
", status);  XXXXXXXXXXreturn 0; } else {  XXXXXXXXXXpeor("fork");  XXXXXXXXXXexit(-1); } XXXXXXXXXXlabs/lab5.md at master · ITF22519/labshttps:github.com/ITF22519/labslomastelab5/lab5.md 5/8This snippet will make sure that the parent suspends execution until one of its children terminates. In the event that there are multiplechildren, and knowledge of a specific child process’ termination is of importance, then waitpid()  should be used to tell the parentprocess to wait. The code snippet to do that is:#include  #include  ... int status = 0; ... child = fork(); if(child == 0) {         does something cool } else if(child > 0) {  XXXXXXXXXXwaitpid(child, &status, 0);  XXXXXXXXXXprintf("child process is done, status is: %d
", status);  XXXXXXXXXXreturn 0; } else {  XXXXXXXXXXpeor("fork");  XXXXXXXXXXexit(-1); }This will guarantee that the parent process wait for the child process with the process id stored in child  to terminate before continuing.Note that, as shown in the man pages for wait() , to make this snippet of code work like the previous snippet, change the value of thefirst argument for waitpid()  (the argument that is occupied by the variable child ) to -1  and the behavior of this snippet and theprevious snippet would be the same. So effectively:wait(&status);         is the same as waitpid(-1, &status, 0);The call to the wait()  function results in a number of actions:If the calling process has no children, wait()  returns -1 .If the calling process has a child that has terminated (a zombie), that child’s PID is returned and it is removed from the process table.Otherwise, the call blocks (suspends the process) until a child terminates. The waitpid()  function allows the WNOHANG  flag to bespecified to return immediately in all cases.It is highly recommended that the student read through the man page for wait()  and waitpid()  to fully understand how to use wait()and waitpid()  and experiment with multiple fork()  and wait()  programs until fully comfortable with what is actually happening. Whatis presented here is merely a quick overview of how to use the two.Exercise 4 (5 pts)Summarize the usage of wait()  and waitpid() .Making a Process Run Another

Shivani · Accepted Answer

Solution/lab4/Array.txt
10
12
14
65
32
12
46
53
15
67
23
Solution/lab4/lab4_ex1.c
/*Lab4: Exercise 1 
Write a program that (1) gets a character from user input (2) gets a string from user input
and (3) calculates the number of input character in the input string. */
#include 
#include 
int main()
{
	char ch;
	char str[100];
	int count=0;
	
	printf("Enter a character: ");
	ch=getchar();
	fflush(stdin);
	
    printf("Enter a string: ");
    gets(str);
    int i=0;
	while(*(str+i) != '\0')
	{
        if (*(str+i) == ch)
			count++;
		i++;
	}
    
	printf("The number of input character in the string is: %d", count);
    return 0;
}
Solution/lab4/lab4_ex2.c
/* Lab-4: Ex2
Use pointers to write a program that gets integers from a user, puts the integers in an array,
and prints out the integers in reverse order. */
#include 
#include 
int main()
{
	int n; // number of elements in the array
	int *A; // Array
	int itr;
	
	printf("
Enter the size of array:");
	scanf("%d", &n);
	fflush(stdin);
										 
	A = malloc(n*sizeof(int)); // memory allocation
	A = (int*)malloc(n*sizeof(int));
	if (A== NULL)
	{
		printf("Error in Memory Allocation");
		exit (0);
	}
	
	printf("Input values for the array: ");
	for(itr=0; itr=0;itr--)
		printf(" %d",*(A+itr));
	
	free(A);
	
	return 0;
}
Solution/lab4/lab4_ex3.c
/* Lab4: Ex3: 
Write a program that (a) reads the first element of Array.txt and assigns it to a variable
n, (b) creates an array A with the size n and dynamically allocates memory for A, (c) reads
the next n elements of Array.txt and assigns these elements with the corresponding elements
in array A - if there are not enough n valid elements in Array.txt, print out error message,
(d) prints array A and (e) finds the maximum element of A */
#include 
#include 
int main()
{
    FILE    *fp;
    int     *A;
    int     n, i;
    fp = fopen("Array.txt", "r");
    if(NULL == fp)
    {
        printf("Unable to open file
");
        exit(-1);
    }
	
	// reading the first line of the file
	fscanf(fp, "%d", &n);
	
	// Allocating memory to the array
	A = malloc(n*sizeof(int));
	printf("Number of elements in the array: %d",n);
	
	// reading numbers from the file into the array
	for(i=0;i max)
			max = *(A+i);
	}
	printf("
Maximum element of the array: %d", max);
	
    fclose(fp); //Close the file pointer
    return 0;
}
Solution/lab4/lab4_task1.c
/* Lab-4: Task-1: Calculate the number of a character in a string */
#include 
int main() 
{
	char s[] = "This Is The Operating System Course";
	char ch = 'e';
	int count = 0; // store the number of e in string s
	
	int itr=0; // iterator to iterate through the string
	while(s[itr] != 0)
	{
		if(s[itr] == ch)
		{
			count++;
		}
		itr++;
	}
	printf("The character %c appears %d times
", ch, count);
	return 0;
}
Solution/lab4/lab4_task2.c
/* Lab-4: Task-2: Arithmetic Operators Using Pointer */
#include 
int main() 
{
	int num1, num2;
	int *p1, *p2;
	int sum, diff, mul, div;
	
	printf("
Enter one integer: ");
	scanf("%d", &num1);
	fflush(stdin);
	
	printf("Enter another integer: ");
	scanf("%d", &num2);
	fflush(stdin);
	
	/* assigning to pointers*/
	p1 = &num1;
	p2 = &num2;
	
	printf("
The first integer is stored at the address: %p", p1);
	printf("
The second integer is stored at the address: %p", p2);
	
	sum = *p1 + *p2;
	diff = *p1 - *p2;
	mul = *p1 * *p2;
	div = *p1 / *p2;
	
	printf("
Summation: %d", sum);
	printf("
Difference: %d", diff);
	printf("
Multiplication: %d", mul);
	printf("
Division: %d", div);	
}
Solution/lab4/lab4_task3.c
/* Lab-4: Task-3: Fixing bugs */
#include
void change(int *ptr1, int *ptr2) 
{
	int temp;
	
	temp = *ptr1;
	*ptr1 = *ptr2;
	*ptr2 = temp;
}
int main() 
{
	int num1, num2;
	
	printf("
Enter the first number: ");
	scanf("%d", &num1);
	printf("
Enter the second number: ");
	scanf("%d", &num2);
	
	change(&num1, &num2);
	
	printf("

After changing two numbers:");
	printf("
The first number is: %d", num1);
	printf("
The second number is: %d
", num2);
	
	return 0;
}
Solution/lab4/lab4_task4.c
/* Lab-4: Task-4: program that prints out the number of characters in a string */
#include
int calStringLength(char *tmpStr);
int main()
{
	char str[20];
	int length;
	
	printf("Enter a string you want to count: ");
	gets(str);
	
	length = calStringLength(str);
	printf("Its length is: %d", length);
}
int calStringLength(char *tmpStr)
{
	int count = 0;
	
	while (*tmpStr != '\0')
	{
		count++;
		tmpStr++;
	}
	
	return(count);
}
Solution/lab4/lab4_task5.c
/* Lab-4: Task-5:  **
* code to read the content of file Array.txt which includes 10 integers and put
these integers into an array A. Write your code to (a) print each element of A on the
terminal, (b) calculate the summation of all elements in A, and (c) print the summation on
the terminal. **/
#include 
#include 
int main()
{
    FILE    *fp;
    int     *A;
    int     n=10, i;
    fp = fopen("Array.txt", "r");
    if(NULL == fp)
    {
        printf("Unable to open file
");
        exit(-1);
    }
	
	// Allocating memory to the array
	A = malloc(10*sizeof(int));
	
	// reading numbers from the file into the array
	for(i=0;i
#include 
int main()
{
	int n; // number of elements in the array
	int *A; // Array
	int itr;
	
	// YOUR code to get array size, put it in variable n
	printf("
Number of elements in the array:");
	scanf("%d", &n);
	fflush(stdin);
	// End of array size
										 
	A = malloc(n*sizeof(int)); // memory allocation
	
	// MY code for memory allocation
	A = (int*)malloc(n*sizeof(int));
	if (A== NULL)
	{
		printf("Error in Memory Allocation");
		exit (0);
	}
	// END of my code
	
	// YOUR code to fill out elements of the array
	printf("Enter array elements: ");
	for(itr=0; itr
#include
int main()
{
	int m, n;
	
	printf("Enter the nmuber of rows and columns for matrix: ");
	scanf("%d%d", &m, &n);
	
	int **a;
	
	//Allocate memory to matrix
	a = (int **) malloc(m * sizeof(int *));
	
	for(int i=0; i
#include 
#include 
#include 
#include 
#include 
void main (int argc, char *argv[])
{
    if(argc   
");
        exit(0);
    }
    
    int num1 = atoi(argv[2]);
    int num2 = atoi(argv[3]);
    int result = 0;
    
    if(strcmp(argv[1], "add") == 0)
    {
        result = num1 + num2;
    }
    else if(strcmp(argv[1], "sub") == 0)
    {
        result = num1 - num2;
    }
    else if(strcmp(argv[1], "mul") == 0)
    {
        result = num1 * num2;
    }
    else if(strcmp(argv[1], "div") == 0)
    {
        result = num1/num2;
    }
    else 
    {
        printf("Unknown Operator: %s
", argv[1]);
        exit(0);
    }
    
    printf("%d %s %d equals %d
", num1, argv[1], num2, result);

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