+ /* Store current mount namespace */
+ r = namespace_open(0, NULL, &initial_mntns_fd, NULL, NULL);
+ if (r < 0)
+ return log_error_errno(r, "Can't fetch current mount namespace: %m");
+
+ /* Switch to a new mount namespace, isolate ourself and unmount etc_machine_id in our new namespace */
+ if (unshare(CLONE_NEWNS) < 0)
+ return log_error_errno(errno, "Failed to enter new namespace: %m");
+
+ if (mount(NULL, "/", NULL, MS_SLAVE | MS_REC, NULL) < 0)
+ return log_error_errno(errno, "Couldn't make-rslave / mountpoint in our private namespace: %m");
+
+ if (umount(etc_machine_id) < 0)
+ return log_error_errno(errno, "Failed to unmount transient %s file in our private namespace: %m", etc_machine_id);
+
+ /* Update a persistent version of etc_machine_id */
+ fd = open(etc_machine_id, O_RDWR|O_CREAT|O_CLOEXEC|O_NOCTTY, 0444);
+ if (fd < 0)
+ return log_error_errno(errno, "Cannot open for writing %s. This is mandatory to get a persistent machine-id: %m", etc_machine_id);
+
+ r = write_machine_id(fd, id);
+ if (r < 0)
+ return log_error_errno(r, "Cannot write %s: %m", etc_machine_id);
+
+ fd = safe_close(fd);
+
+ /* Return to initial namespace and proceed a lazy tmpfs unmount */
+ r = namespace_enter(-1, initial_mntns_fd, -1, -1);
+ if (r < 0)
+ return log_warning_errno(r, "Failed to switch back to initial mount namespace: %m.\nWe'll keep transient %s file until next reboot.", etc_machine_id);
+
+ if (umount2(etc_machine_id, MNT_DETACH) < 0)
+ return log_warning_errno(errno, "Failed to unmount transient %s file: %m.\nWe keep that mount until next reboot.", etc_machine_id);