Guide for cloning drives to make a minimal image

minimal-image.md

• https://serverfault.com/questions/96592
• https://unix.stackexchange.com/questions/44234
• https://serverfault.com/questions/4906
• https://serverfault.com/a/853753
• https://serverfault.com/a/796767

It is recommended that you only have 2 partitions, boot and root, and that your boot partition is located before your root partition.

Use seperate live OS and follow steps in order.

For root partition where {a} is the partition name and {b} is the entire drive to clone

• sudo mount /dev/{a} /mnt
• sudo e4defrag /mnt
• sudo fstrim /mnt may not work unless on a SSD
• sudo umount /mnt
• sudo e2fsck -f /dev/{a}
• sudo resize2fs -M /dev/{a} note the block count and block size
• fdisk -u -l /dev/{b} note the drive's sector size and your partition's start sector
• sudo fdisk dev/{b} list the partitions using p and note the start sector, delete the partition, then create a new one
  • start sector is the same as before it was deleted
  • end sector is calculated using the following

  fs_size = block_count * block_size
  fs_sectors = fs_size/sector_size
  part_sectors = ((fs_sectors-1)/2048+1)*2048
  end_sector = start_sector + part_sectors - 1

  • do NOT remove the ext4 signature
• sudo zerofree /dev/{a}

Then where {c} is the drive's block size, and {d} is the new end sector + 1 (use fdisk -u -l /dev/{b} if you forgot)

• dd if=/dev/{b} bs={c} count={d} | pigz > image.iso.gz

If you have a really small root partition (less than 200MB) or you have an REALLY powerful CPU, use pigz -11 for better compression.

To flash the image on Linux, use one of the following where {x} is the device you would like to flash:

• pigz -cd image.iso.gz | dd of=/dev/{x}
• gunzip -c image.iso.gz | dd of=/dev/{x}

On windows, use Etcher or Rufus to flash.