pidns.c

#include <unistd.h>
#include <sched.h>
#include <stdio.h>

int _start_container(void *arg)
{
  return execl("/bin/bash", "bash", "-c", "echo $$", (char*) NULL);
}

int main(int argc, char *argv[]){
  int pid;

  // We don't share memory with the parent, so just start growing the stack
  // from here.
  char child_stack[1];

  pid = clone(
      _start_container,
      child_stack,
      CLONE_NEWPID,
      0
  );

  waitpid(pid, NULL, 0);
}