Master of Science in Computer Science - Computer Science Introductory Course

Laboratory Work 1: Processes

Translated from a French version designed by Bertrand Dupouy

I.A number of usefull shell commands

Try the following commands:
```
who (list of users logged in)
who am i 
ps -l (list of processes attached to the terminal)
ps -axl (list of running processes)
```
identify the following processes :
- init with pid 1 and the swapper-scheduler with pid 0.
- daemons (marked with ?),
- those executing a shell (sh, csh ou ksh),
Sending a command in the background ( use &) : Sleep n results in the calling process pausing for n seconds. Send the following command sequence and observe the results. ps -l and sleep 20& and sleep 30& and ps -l
Using exec.
1. type: exec ps
  What happens ? Why ?
  Hint : for exec, as for other commands (built in commands) the shell does not create a new process (does not call fork).
2. After finding the pid of the process runing the current shell, do: exec sh
  What is the pid of the process that executes sh ? Why ?

II.Introduction to programming in this environment

Create a directory in which you will do subsequent work

cd To move to your home directory 
mkdir TPproc
cd TPproc

To compile your program files, use the gcc command (if the file to be comiled is named exo1.c :

gcc exo1.c -o exo1
or
gcc -Wall exo1.c -o exo1

III. Exercises on process creation (fork)

III.1 Functions used

fork()
This function creates a new process. It returns a value n that indicates: :

n > 0	we are in the parent process
n = 0	we are in the child process
n = -1	fork failed and no process was created

getpid(): returns the calling process identifier (pid)
getppid(): returns the parent pid

III.2 Exercise 1

After compiling exo1.c, execute exo1 several time.
What happens ? Why ?
To get a copy of exo1.c, click here
Add the following instruction after the fork call:
if (value == 0) sleep (4);
What happens ? Why ?

III. 3 Exercise 2

To get a copy of fork-mul.c, click here.
Compile fork-mul.c, and execute it.

After execution and using the following diagram, note the process numbers and note the order in which the printf are executed in order to find the order in which processes are executed.

Note:
If you see a process whose pid is 1, it is the init process that is the parent of all processes. Init adopts all orphan processes (those whose parent terminated).

Licence de droits d'usage ©(Copyright) Bertrand Dupouy- Contact : Petr Kuznetsov (surname . name @ telecom-paristech.fr) - Last Modified, september 26, 2013.