Reparent Command to Init in Namespace

reparent.c

#include <stdlib.h>
#include <stdio.h>
#include <sched.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

int main() {
  // NOTE: replace <pid> with PID of init, or take as an arg. This was shorter :)
  // Enter namespace.
  int fd = open("/proc/<pid>/ns/pid", O_RDWR);
  if (fd < 0) {
    printf("Failed to open NS file\n");
    return 1;   
  }     

  if (setns(fd, 0) == -1) { 
    printf("Failed to setns()\n");
    return 1;   
  }     

  // Double fork the child and sleep indefinitely.
  int pid = fork();
  if (pid == 0) {
    pid = fork();
    if (pid == 0) {
      // Here we would typically exec.
      while (1) {       
        sleep(3600);            
      }                 
    }           
  }     
  return 0;
}

@xemul - this seems to be a solution to properly re-parenting a forked process to the namespace's init. This is discussed here if you'd like to comment.