sudo modprobe loop
sudo losetup -f
sudo losetup /dev/loop0 myimage.img
sudo partprobe /dev/loop0
sudo gparted /dev/loop0
sudo losetup -d /dev/loop0
fdisk -l myimage.img
Disk myimage.img: 6144 MB, 6144000000 bytes, 12000000 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000ea37d
Device Boot Start End Blocks Id System
myimage.img1 2048 9181183 4589568 b W95 FAT32
truncate --size=$[(9181183+1)*512] myimage.img
Източник: https://askubuntu.com/questions/1174487/re-size-the-img-for-smaller-sd-card-how-to-shrink-a-bootable-sd-card-image