Task 1
======

ps -fu [username]
kill -9 pid

Task 2
======

To start a process: nice -n +5 top

(higher nice value means lower priority)

For running process:   renice +5 pid

Task 3
======

#include <stdio.h>

main()
{
int pid;

 /* child process is created using fork */
 pid = fork();
 /* fork returns -1 if the child process cannot be created */
 if (pid < 0) 
   {
    /* Show error message */
    fprintf(stderr,"Fork failed");
    /* exit program with error status */
    exit(-1);
   }
 /* pid is zero for child */
 if (pid == 0)
   {
      /* Execute top program in child process*/
      execlp("/usr/local/bin/top","top",NULL);
   }
 /* pid is nonzero positive integer for parent */
 else
   { 
     /* wait until child has executed */
     wait(NULL);
     /* Show message */
     printf("Child complete\n");
     /* Exit program with a succesfull status 0*/
     exit(0);
   }
}



Task 4
======

#include <stdio.h>

main()

{
 /* Create 1st child and execute top in it */
 /* NOTE: if execlp is succesfully executed, then child is terminated */
 if (fork() == 0) {execlp("/bin/who","who",NULL);}
 /* Create 2nd child and execute top in it */
 if (fork() == 0) {execlp("/bin/finger","finger",NULL);}
 /* This is in parent process */
 /* Wait all processes (wait will return -1, if there are not childs)*/
 while(wait(NULL) != -1);
 printf("Childs completed\n");
 /* exit program */
 exit(0);
}

Task 5
======

#include <stdio.h>
#include <string.h>

main()
{
  int putki[2], pid, N;
  /* create pipe, if pipe returns -1 it cannot be created */
  if (pipe(putki) != 0) {perror("pipe"); exit(1);}
  /* create a child */
  pid = fork();
  if (pid == -1) {perror("fork"); exit(1);}
  if (pid != 0) {
    /* this is in parent process */
    char message1[1024];
    /* close pipe writing fd, it is not needed */
    close(putki[1]); 
    /* read from pipe */
    if (read(putki[0],message1,1024) < 0) {perror("read putki"); exit(1);}
    /* Show message read from pipe */
    printf("Child: %s\n",message1);
    /* close pipe reading fd */ 
    close(putki[0]);
    printf("Parent: Yes.\n");
  }else{
    char message2[1024];
    /* close pipe reading fd, it is not needed */
    close(putki[0]); 
    /* copy a string */
    strcpy(message2,"Can you hear me ?");
    /* alculate the length of a string */
    /* NOTE: The strlen() function calculates the length of the string */
    /* not including the terminating `\0' character */
    N=strlen(message2);
    /* write message2 to a pipe */
    if (write(putki[1],message2,N+1) != N+1) {perror("write putki"); exit(2);}
    /* close pipe writing fd, it is not needed*/
    close(putki[1]);
  }
  /* exit a program */
  exit(0);
}