getting child processes with libproc

Question

Like adviced in this post I use libproc to get a list of all running processes. In comparison to the treeview of htop miss I the ability to get all child processes of a parent process. Is there a way or function to get them?

alk · Answer 1 · 2013-06-18T17:20:07.057

0

You can pull the parent-pid from the child's info provided by /proc/<child-pid>/stat.

As far as I know /proc does not provide this info the other way round.

To get the tree just read in the parent-pid attribute for all pids and then build up the reverse index yourself.

edited Jun 18 '13 at 17:20

answered Jun 18 '13 at 17:13

alk

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One of the main problems is that the `/proc` (and the `libproc` also) didn't lists the child-pids at all. So I only get the parent-pids and not the child-pids. – arbyter Jun 19 '13 at 07:13
@arbyter: Yes sure, but knowing who is the parent-pid of a pid makes you know that this pid is the child of what it carries as it's parent. So you are capable to build the tree your own, **after** you read out the parent-pid for **all* pids. – alk Jun 19 '13 at 07:32

score 0 · Answer 2 · answered Jun 20 '13 at 08:07

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In /proc/<pid>/task I have found what I had searched for. All child-processes are listed there. Unfortunately I have to write my own code to get the infos out of the structure, but that should be manageable :).

answered Jun 20 '13 at 08:07

arbyter

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score 0 · Answer 3 · answered May 10 '20 at 22:13

If you're struck using libproc (e.g. on systems without linux's /proc filesystem), you can use proc_listpids.

XNU (macOS' kernel) also offers proc_listchildpids, which just calls proc_listpids, but returning the number of PIDs instead of raw byte count.

int
proc_listchildpids(pid_t ppid, void * buffer, int buffersize)
{
    int numpids;
    numpids = proc_listpids(PROC_PPID_ONLY, (uint32_t)ppid, buffer, buffersize);
    if (numpids == -1) {
        return -1;
    } else {
        return numpids / sizeof(int);
    }
}

I feel like that's more of a trap than a convience, so I just prefered to call proc_listpids directly, myself.

getting child processes with libproc

3 Answers3