How to get child process from parent process

Question

Is it possible to get the child process id from parent process id in shell script?

I have a file to execute using shell script, which leads to a new process

Answer 1

To get the child process and thread, pstree -p PID. It also show the hierarchical tree

Answer 2

You can get the pids of all child processes of a given parent process <pid> by reading the /proc/<pid>/task/<tid>/children entry.

This file contain the pids of first level child processes.

For more information head over to https://lwn.net/Articles/475688/

Answer 3

For the case when the process tree of interest has more than 2 levels (e.g. Chromium spawns 4-level deep process tree), pgrep isn't of much use. As others have mentioned above, procfs files contain all the information about processes and one just needs to read them. I built a CLI tool called Procpath which does exactly this. It reads all /proc/N/stat files, represents the contents as a JSON tree and expose it to JSONPath queries.

To get all descendant process' comma-separated PIDs of a non-root process (for the root it's ..stat.pid) it's:

$ procpath query -d, "..children[?(@.stat.pid == 24243)]..pid"
24243,24259,24284,24289,24260,24262,24333,24337,24439,24570,24592,24606,...

Answer 4

Just use :

pgrep -P $your_process1_pid

Answer 5

I'v written a scrpit to get all child process pids of a parent process. Here is the code.Hope it helps.

function getcpid() {
    cpids=`pgrep -P $1|xargs`
#    echo "cpids=$cpids"
    for cpid in $cpids;
    do
        echo "$cpid"
        getcpid $cpid
    done
}

getcpid $1

Answer 6

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

int main()
{
    // Create a child process     
    int pid = fork();

    if (pid > 0)
    {

            int j=getpid();

            printf("in parent process %d\n",j);
    }
    // Note that pid is 0 in child process
    // and negative if fork() fails
    else if (pid == 0)
    {





            int i=getppid();
            printf("Before sleep %d\n",i);

            sleep(5);
            int k=getppid();

            printf("in child process %d\n",k);
    }

    return 0;

}