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Full Discussion: Fork()
Top Forums Programming Fork() Post 302386636 by thegeek on Wednesday 13th of January 2010 02:40:08 AM
Old 01-13-2010
Yes, you are right.

An example to clarify the matter better,

Code:
use strict;
use warnings;

print "PARENT 1: $$\n";
my $pid = fork ();
if ( $pid )  {
    print "Parent of 1st fork $$\n";
} else {
    print "Child of 1st fork $$\n";
}

my $next_pid = fork ();

if ( $next_pid )  {
    print "Parent of next fork $$\n";
} else {
    print "Child of next fork $$\n";
}

And its output,
Code:
PARENT 1: 27844
Child of 1st fork 27845
Child of next fork 27846
Parent of next fork 27845
Parent of 1st fork 27844
Child of next fork 27847
Parent of next fork 27844

It is so clear that, the first process id is: 27844, which gets forked into another as: 27845.

Then the next is two parents: 27844, 27845 which gets two childs as: 27846, 27847.
 

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LEARN ABOUT REDHAT

fork

FORK(2) 						     Linux Programmer's Manual							   FORK(2)

NAME

       fork - create a child process

SYNOPSIS

       #include <sys/types.h>
       #include <unistd.h>

       pid_t fork(void);

DESCRIPTION

       fork  creates a child process that differs from the parent process only in its PID and PPID, and in the fact that resource utilizations are
       set to 0.  File locks and pending signals are not inherited.

       Under Linux, fork is implemented using copy-on-write pages, so the only penalty incurred by fork is the time and memory required to  dupli-
       cate the parent's page tables, and to create a unique task structure for the child.

RETURN VALUE

       On success, the PID of the child process is returned in the parent's thread of execution, and a 0 is returned in the child's thread of exe-
       cution.	On failure, a -1 will be returned in the parent's context, no child process will be created, and errno will be set appropriately.

ERRORS

       EAGAIN fork cannot allocate sufficient memory to copy the parent's page tables and allocate a task structure for the child.

       ENOMEM fork failed to allocate the necessary kernel structures because memory is tight.

CONFORMING TO

       The fork call conforms to SVr4, SVID, POSIX, X/OPEN, BSD 4.3.

SEE ALSO

       clone(2), execve(2), vfork(2), wait(2)

Linux 1.2.9							    1995-06-10								   FORK(2)
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