what are parent and child processes all about?


 
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# 1  
what are parent and child processes all about?

I don't follow what these are...

this is what my text says...

"When a process is started, a duplicate of that process is created. This new process is called the child and the process that created it is called the parent. The child process then replaces the copy for the code the parent process created with the code the child process is supposted to execute."

The last sentance confuses me the most. Actually the entire thing confsues me. Why is a child process started anyways? Why does the parent process spawn a child process in the first place? And what's all this code copy stuff all about?

The next paragraph states...

"While the command is executing, the shell waits until the child process has completed. After is completes, the parent process terminates the child process, and a prompt is displated, ready for a new command"

Why does this happen? I guess it goes back to my confusion about why the child process is created in the first place.
# 2  
Good example.

When you use a command like grep or find, they kick off subprocesses (children processes) that actually do the work.

EXAMPLE #1
The parent ( the command that you typed.) "find . -name somefile -print " kicks off subprocesses that actually go out and search for the file that you specified. When they are done they report back to the find command.

EXAMPLE #2
Using grep if you are trying to do something like matching a pattern(s) in a file to print out the lines.

cat filename|grep patterna

This command will actually spawn 2 processes. The cat command, the parent, and the grep command, the child. When the child (grep) finishes it returns to the parent (cat) with the result.

Example #3
Do a ps -aef |grep sh" to find your telnet session. Find your login and do a ps -aef |grep on that PID. All of your commands are technically children of your telnet session as you will see.
 

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