main.c

#define _GNU_SOURCE
#include <err.h>
#include <sched.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>
#include <sys/mount.h>

int main(int argc, char *argv[])

{
  if (chroot("./rootfs_alpine") == -1)
    err(EXIT_FAILURE, "chroot");
  if (chdir("/") == -1)
    err(EXIT_FAILURE, "chdir");

  if (unshare(CLONE_NEWPID | CLONE_NEWNS) == -1)
    err(EXIT_FAILURE, "unshare");

  int pid = fork();
  if (pid == -1)
    err(EXIT_FAILURE, "fork");

  if (pid == 0)
  {
    if (mount("proc", "proc", "proc", 0, NULL) == -1)
    {
      err(EXIT_FAILURE, "mount");
    }

    if (execvp(argv[1], &argv[1]) == -1)
    {
      err(EXIT_FAILURE, "execvp");
    }
  }
  else
  {
    int status;
    wait(&status);
    exit(WEXITSTATUS(status));
  }
}