I saw that in nextcloud box guide commands linux comand are empty.
I made a backup in ubuntu 16.04 conecting SD card with this comand
sudo dd if=/dev/sdx of=/path/to/image.iso bs=1M
i obtained sdx through “sudo fdisk -l” and choose path where sd card was located.
The reverse comand would be:
sudo dd if=/path/to/image.iso of=/dev/sdx bs=1M
I tried to use the backup in another SD card that is working as the original.
Maybe someone could find this interesting and can modify the guide.