raspberry pi 備份 縮小分割區

1. 備份整塊區塊. sd card.
    windows : Win32DiskImager
    Linux : sudo dd bs=4M if=/dev/mmcblok0 | zip backup-raspbian.zip -
          看狀態改用 : sudo dd bs=4M if=/dev/mmcblok0 status=progress | zip backup-raspbian.zip -
          解壓 unzip backup-raspbian.zip backup-raspbian.img
2. fdisk -l backup-raspbian.img
    記下要掛載修改的start address. 通常是last partition.
    假設主要Linux : start : 8192 磁區 在第一個partition. 每個sector 512byte
3. 掛載loop
    sudo losetup /dev/loop10 backup-raspbian.img -o $((512*8192))
4. 用gparted resize
    sudo gparted /dev/loop10
    點resize 不要縮到有資料的地方
    記下最後resize 的size.  假設是5447008K
5. 重新掛整個img 在loop上
    sudo losetup --detach /dev/loop10
    sudo losetup /dev/loop10 backup-raspbian.img
6. fdisk /dev/loop10
      Command (m for help): d
      Selected partition 1
      Partition 1 has been deleted.

      Command (m for help): n
      Partition type
         p   primary (0 primary, 0 extended, 4 free)
         e   extended (container for logical partitions)
      Select (default p): p
      Partition number (1-4, default 1):
      First sector (2048-62333951, default 2048): 8192
      Last sector, +sectors or +size{K,M,G,T,P} (8192-62333951, default 62333951): +5447008K

      Created a new partition 1 of type 'Linux' and of size 5.2 GiB.
      Partition #1 contains a ext4 signature.

      Do you want to remove the signature? [Y]es/[N]o: N

      Command (m for help): w

     出現 Re-reading the partition table failed.: Invalid argument
        使用 partprobe 指令

7. truncate
    sudo losetup --detach /dev/loop10
    fdisk -l backup-raspbian.img
      記下最後磁區的end . 假設是 10901503
    truncate -s $((512*(10901503+1))) backup-raspbian.img


https://blog.cavedu.com/2018/03/22/raspberry-pi-
%E4%B8%8D%E5%86%8D%E5%82%99%E4%BB%BD%E6%95%B4%E5%BC%B5sd%E5%8D%A1%EF%BC%8C%E7%B8%AE%E5%B0%8Fraspberrypi%E5%82%99%E4%BB%BD%E5%AE%B9%E9%87%8F/