How to Get Child Process from Parent Process

How to get child process from parent process

Just use :

pgrep -P $your_process1_pid

How to get child PID in C?

fork already returns the child's pid. Just store the return value.

look at man 2 fork:

RETURN VALUES

 Upon successful completion, fork() returns a value of 0 to the child process and
 returns the process ID of the child process to the parent process.  Otherwise, a
 value of -1 is returned to the parent process, no child process is created, and
 the global variable errno is set to indicate the error.

getting child process ID from the parent using C

After a minute of googling I found this page, where everything you need is written:

System call fork() is used to create processes. It takes no arguments and returns a process ID.

I highlighted the part which is importand for you, so you don't need to do anything to get the process IDs of the children. You have them already in fork1 and fork2!

Here is some code which will print the PIDs from parent and children.

#include <stdio.h>

int main() {
  int fork1 = fork();
  if (fork1 < 0) {
    printf("error\n");
  } else if (fork1 == 0) {
    printf("I'm child 1\n");
    printf("child 1: parent: %i\n", getppid());
    printf("child 1: my pid: %i\n", getpid());
  } else {
    int fork2 = fork();
    if (fork2 < 0) {
      printf("error\n");
    } else if (fork2 == 0) {
      printf("I'm child 2\n");
      printf("child 2: parent: %i\n", getppid());
      printf("child 2: my pid: %i\n", getpid());
    } else {
      printf("I'm the parent\n");
      printf("The PIDs are:\n");
      printf("parent: %i\n", getpid());
      printf("child 1: %i\n", fork1);
      printf("child 2: %i\n", fork2);
    }
  }
  return 0;
}

How to find all child process of a parent process (in C)

Following would be very basic steps you would like to do:

PS: Assuming you have not completed recursive function calls yet.

STEP1: First get the process id PID
STEP2:Find the child process IDs for PID and maintain a list (array) of them.
STEP3:Repeat STEP2 for all child process IDs saved in the list

Child process starts after parent process

The explanation is simple.
Scheduling of processes is up to the kernel. If this is a single core processor then in this run it decided to suspend the child execution and allow the parent process to run first. The parent ran for a few loops before being suspended in favor of the child, and so forth.

In a multiprocessor system both process can run in tandem but the console device will alternate the output depending on timing of interrupts.

There is no assurance a different run will result in the same output. There is also no assurance that different kernel version won't do something else.

If you want the processes to alternate between loops now is the time to learn interprocess communication.

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