My SD card is much larger than the UBOS image. How do I use the rest of the space?

It would be best if you don’t burn the UBOS image to your large SD Card, but instead to a temporary SD card. Then you boot from the temporary card, and use ubos-install to create a clean new installation on your large SD Card. ubos-install will use all available space. Then you can discard your temporary SD card.

You can also expand the file system, but note that this is an expert-level operation; you can very easily screw your existing UBOS installation and all data on it. So be very careful. In principle, it should work like this: first determine what filesystem your UBOS root partition runs on. On most devices, UBOS runs on “btrfs” but it might be “ext4”. Then, use a command specific to that filesystem type to expand the filesystem, such as btrfs filesystem resize (for “btrfs) or resize2fs (for “ext4”). Alternatively, you can add a second device to the btrfs filesystem pool.