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 process1 (parent process). This process1 has forked another process process2(child process). Using script, I'm able to get the pid of process1 using the command:

cat /path/of/file/to/be/executed

but i'm unable to fetch the pid of the child process.

Answer 1

Just use :

pgrep -P $your_process1_pid

Answer 2

I am not sure if I understand you correctly, does this help?

ps --ppid <pid of the parent>

Answer 3

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 4

The shell process is $$ since it is a special parameter

On Linux, the proc(5) filesystem gives a lot of information about processes. Perhaps pgrep(1) (which accesses /proc) might help too.

So try cat /proc/$$/status to get the status of the shell process.

Hence, its parent process id could be retrieved with e.g.

  parpid=$(awk '/PPid:/{print $2}' /proc/$$/status)

Then use $parpid in your script to refer to the parent process pid (the parent of the shell).

But I don't think you need it!

Read some Bash Guide (or with caution advanced bash scripting guide, which has mistakes) and advanced linux programming.

Notice that some server daemon processes (wich usually need to be unique) are explicitly writing their pid into /var/run, e.g. the  sshd server daemon is writing its pid into the textual file /var/run/sshd.pid). You may want to add such a feature into your own server-like programs (coded in C, C++, Ocaml, Go, Rust or some other compiled language).

Answer 5

ps -axf | grep parent_pid 

Above command prints respective processes generated from parent_pid, hope it helps. +++++++++++++++++++++++++++++++++++++++++++

root@root:~/chk_prgrm/lp#

 parent...18685

 child... 18686


root@root:~/chk_prgrm/lp# ps axf | grep frk

 18685 pts/45   R      0:11  |       \_ ./frk

 18686 pts/45   R      0:11  |       |   \_ ./frk

 18688 pts/45   S+     0:00  |       \_ grep frk

Answer 6

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

Answer 7

#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;

}