namespace.c

#define _GNU_SOURCE
#include <sched.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/mount.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/wait.h>

void setup_mount_namespace() {

    if (mount(NULL, "/", NULL, MS_REC|MS_PRIVATE, NULL) == -1) {
        perror("Error in making mounts private");
        exit(EXIT_FAILURE);
    }

    if (mount("proc", "/proc", "proc", MS_NOSUID | MS_NOEXEC | MS_NODEV, NULL) == -1) {
        perror("Error while mounting /proc");
        exit(EXIT_FAILURE);
    }

    if (mount("tmpfs", "/tmp", "tmpfs", MS_NOSUID|MS_NODEV|MS_NOEXEC, "size=256m,mode=1777") == -1) {
        perror("Error in mounting private /tmp");
        exit(EXIT_FAILURE);
    }
}

int main() {
    if (unshare(CLONE_NEWPID | CLONE_NEWNS | CLONE_NEWNET | CLONE_NEWUTS) == -1) {
        perror("unshare");
        exit(EXIT_FAILURE);
    }

    printf("Namespaces created successfully.\n");

    pid_t child = fork();
    if (child == -1) {
        perror("fork");
        exit(EXIT_FAILURE);
    }

    if (child == 0) {
        printf("Namespace isolated. PID: %d\n", getpid());
        printf("  Parent PID in isolated namespace: %d\n", getppid());
        sethostname("container", 10);
        setup_mount_namespace();
        printf("Starting shell inside isolated namespace...\n");
        execlp("/bin/bash", "/bin/bash", NULL);
        perror("execlp");
        exit(EXIT_FAILURE);
    }

    waitpid(child, NULL, 0);
    return 0;
}