Lab 2 (5 points)
CS550, Operating Systems
Introduction to UNIX and C

Name: _____________________________________________

This assignment is based upon the UNIX labs from the CS2351 course at Oklahoma State University, available at cs.okstate.edu/newuser/index.html. The purpose of this lesson is to learn to use the various UNIX commands, to learn about command line compilers, editors, and to establish an account with the Extreme Science and Engineering Discovery Environment (XSEDE). It is recommended that you complete this assignment with the Littlefe cluster, however, you may use Cygwin, your own copy of BCCD, or another Linux variant to complete it.

Command Line Compilers

First, you will experiment with the C command line compiler called gcc.

Create a file called hello_loop.c with nano. Type the following code into the text editor:

#include <stdio.h>

int main(int argc, char ** argv)
{
  int i;
  for(i = 0; i < 100; i++)
      printf("Hello %d\n", i)
  }
}

Compile the code with the following command:

gcc hello_loop.c -o hello_loop.exe

What happened? ______________________________________________________

Fix any errors in the code and recompile.

When running the code, you will use a pipe to send the output of the program to another UNIX command called more. Pipes are a one way form of interprocess communication. Just like water, data flows through a pipe in one direction. Execute your code as follows:

./hello_loop.exe | more

What happened? ________________________________________________________

Use the spacebar and the "b" character to page up and page down through your output. The "q" character will get you out of more.

Many UNIX and Linux systems support less. Try piping your program to less. What happens? ________________________________________________________

Next, you will experiment with another program using the C command line compiler called gcc.

Create a file called test_args.c with nano. Type the following code into the text editor:

#include <stdio.h>

int main(int argc, char ** argv)
{
  int i;
  if(argc > 0)
  {
    for(i = 0; i < argc; i++)
      printf("%s\n", argv[i])
  }
  return 0;
}

Compile the code with the following command:

gcc test_args.c -o test_args.exe

What happened? ______________________________________________________

Fix any errors in the code and recompile.

When running the code, you will pass parameters into the code via the command line. These parameters are called command line arguments. Note that you can also use command line arguments in Java. Execute your code as follows:

./test_args.exe arg1 arg2 arg3

What happened? ________________________________________________________

Now execute your code as follows:

./test_args.exe

What happened? ________________________________________________________

Complete the next program, and name it lab2.c:

//lab2.c
//<your name goes here>
//This program determines if a number is prime.

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int main(int argc, char ** argv)
{
  //Declare and initialize a counter i and an input
  //variable num.
  int num, i = 2;

  //Read in num using scanf

  //Use a count controlled loop to check if num is prime.
  //Hint: use the sqrt function from the math library to
  //find the square root of num.
  while(...)
  {
    //Replace the ... in the if statement with the condition to
    //determine if num is divisible by i
    if(...)
    {
      //Print a message stating num is not prime.

      exit(0);
    }
    //increment i
  }

  //Print a message stating that num is prime.

  return 0;
}

Hand in a printout of your code file (lab2.c), and a printout of a sample output file you created.

To compile your program use the following command:

gcc lab2.c -lm -o lab2.exe

Introducing MPI

Finally, you will experiment with the Message Passing Interface (MPI) enhanced C command line compiler called mpicc. Note that the MPI library allows for C programs to be executed as multiple independent processes.

Create a file called do_nothing.c with nano. Type the following code into the text editor:

#include <stdio.h>
#include <stdlib.h>
#include <mpi.h>

int main(int argc, char ** argv)
{
  int number_of_processes;
  int my_rank;
  int mpi_error_code;
  int i, j = 0;
  mpi_error_code = MPI_Init(&argc, &argv);
    mpi_error_code = MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
    mpi_error_code = MPI_Comm_size(MPI_COMM_WORLD, &number_of_processes);
    for(i = 0; i < 100000000; i++)
      j = i + 1;
    printf("%d o%d: Hello, world!\n", my_rank, number_of_processes);
  mpi_error_code = MPI_Finalize();
  return 0;
}

Note that all the code inside of MPI_Init through MPI_Finalize will run as number_of_processes processes. Compile the code with the following command:

mpicc do_nothing.c -o do_nothing.exe

What happened? ______________________________________________________

Fix any errors in the code and recompile.

Remove the line containing MPI_Init and recompile.

What happened? ______________________________________________________

Replace the line containing MPI_Init, and remove the line containing MPI_Finalize and recompile.

What happened? ______________________________________________________

Replace the missing line in your code, fix all errors and recompile.  Open a second terminal (or PuTTY) window. If you are opening a second window to a remote system such as Littlefe, you will need to login again.  Run the command called top. This command shows the current system statistics, including CPU usage by each process, and it updates on a regular basis. Execute your code as follows in the first terminal window:

mpirun -n 8 do_nothing.exe

On LittleFe use:

mpirun -n 8 -machinefile machines-openmpi do_nothing.exe

Note that the -n 8 tells the operating system to create 8 processes.

What happened in the first terminal window? ________________________________________________________

What happened in the second terminal window? ________________________________________________________

Replace the -n 8 with -n 16 to tell the operating system to create 16 processes.  Hint: you can use the up and down arrows at the command line to scroll through your history of commands.

What happened in the first terminal window? ________________________________________________________

What happened in the second terminal window? ________________________________________________________

Now press the character "q" in the second terminal window and run the command:

mpirun -n 16 do_nothing.exe

On LittleFe use:

mpirun -n 16 -machinefile machines-openmpi do_nothing.exe

While the program is running, run the following command in the second terminal window:

ps -fu username

Where username is your username.  The ps command outputs a list of the current running processes.

What happened in the first terminal window? ________________________________________________________

What happened in the second terminal window? ________________________________________________________

Using Other UNIX Commands

Using nano write a short java program with an infinite loop. Compile and run this program at the command line. While this program is running, use ps to find its process id number. Then use the kill command to terminate the process. Submit a copy of your code and the output from ps with this homework.

The grep command allows you to find patterns in files. Run the command:

grep -n MPI do_nothing.c

What does the "-n" option do?__________________________________________

Attach the output of the grep command to this homework.

Investigate the sort, diff, and uniq commands. The man pages would also be a good place to look. Explain each in one or two short sentences.

Run the command:

man sort

What does the sort command do?_____________________________________________________________________
__________________________________________________________________________________________________

Run the command:

man diff

What does the diff command do?_____________________________________________________________________
__________________________________________________________________________________________________

Run the command:

man uniq

What does the uniq command do?_____________________________________________________________________
__________________________________________________________________________________________________