setns

setns.c

#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");
}