main()
{
fork(); fork(); fork();
printf("Hello World!");
} 

Answer:

"Hello World" will be printed 8 times.
Explanation:
2^n times where n is the number of calls to fork() 
 

List the system calls used for process management:

System calls Description
- fork() To create a new process
- exec() To execute a new program in a process
- wait() To wait until a created process completes its execution
- exit() To exit from a process execution
- getpid() To get a process identifier of the current process
- getppid() To get parent process identifier
- nice() To bias the existing priority of a process
- brk() To increase/decrease the data segment size of a process.
 

How can you get/set an environment variable from a program?

Getting the value of an environment variable is done by using `getenv()'. Setting the value of an environment variable is done by using `putenv()'.
 

How can a parent and child process communicate?

A parent and child can communicate through any of the normal inter-process communication schemes (pipes, sockets, message queues, shared memory), but also have some special ways to communicate that take advantage of their relationship  as a parent and child. One of the most obvious is that the parent can get the exit status of the child.
 

What is a zombie?

When a program forks and the child finishes before the parent, the kernel still keeps some of its information about the child in case the parent might need it - for example, the parent may need to check the child's exit status. To be able to get this information, the parent calls `wait()'; In the interval between the child terminating and the parent calling `wait()', the child is said to be a `zombie' (If you do `ps', the child will have a `Z' in its status field to indicate this.)
 

What are the process states in Unix? 

As a process executes it changes state according to its circumstances. Unix processes have the following states:
Running : The process is either running or it is ready to run .
Waiting : The process is waiting for an event or for a resource.
Stopped : The process has been stopped, usually by receiving a signal.
Zombie : The process is dead but have not been removed from the process table.

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