Unix Inter-Process Communication (IPC)

Inter Process Communication. IPC is used to pass information

between two or more processes.

Schemes are pipes, shared memory & semaphore.

Below are the different IPC methods

1. Semaphores

2. FIFO's (Also called Named Pipes)

3. Message Queues

4. Shared Memory

by calling system call fork() to create child process which

handles the other.

There r two main advantage :

1.you can use console to execute your command.

2.More importantly if one is connected through remote

console and as there is no controlling terminal attached to

background process even if your terminal get disconnected

the process continues (with help of nohup in shell script

or by using setsid in C)

When command is given then unix os will fork the shell i.e

will creat a new process and will execute the command using

exec command...something like suppose you gave command "ls"

in the shell then...

fork();

exec(ls);

It will give you the result and after this the child process

will die.

The processes like vhand, bdflush, sched are housed in

kernel file or /unix system which are known as daemons.

These files run in the background without users

request.These are created when the system boots up and

remains active till it shut down or hang. These are not

linked to any user or any terminal .We can't kill a daemon.

A system that has been taken over using Remote Control

Software. Zombies are often used to send spam or to attack

remote servers with an overwhelming amount of traffic (a

Distributed Denial of Service Attack).