#define _GNU_SOURCE
#include <fcntl.h>
#include <sched.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>

#define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \
	} while (0)

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

	if (argc < 3) {
		fprintf(stderr, "%s /proc/PID/ns/FILE cmd args...\n", argv[0]);
		exit(EXIT_FAILURE);
	}

	fd = open(argv[1], O_RDONLY);   /* Get descriptor for namespace */
	if (fd == -1)
		errExit("open");

	//if (setns(fd, CLONE_NEWNS) == -1)
	if (setns(fd, 0) == -1)         /* Join that namespace */
		errExit("setns");

	execvp(argv[2], &argv[2]);      /* Execute a command in namespace */
	errExit("execvp");
}