Change the disk image filename as if it had been created with size size. Only images in raw format can be resized in both directions, whereas qcow2 images can be grown but cannot be shrunk.
Use the following to set the size of the disk image filename to size bytes:
qemu-img resize filename size
You can also resize relative to the current size of the disk image. To give a size relative to the current size, prefix the number of bytes with
+ to grow, or
- to reduce the size of the disk image by that number of bytes. Adding a unit suffix allows you to set the image size in kilobytes (K), megabytes (M), gigabytes (G) or terabytes (T).
qemu-img resize filename [+|-]size[K|M|G|T]
Before using this command to shrink a disk image, you must use file system and partitioning tools inside the VM itself to reduce allocated file systems and partition sizes accordingly. Failure to do so will result in data loss.
After using this command to grow a disk image, you must use file system and partitioning tools inside the VM to actually begin using the new space on the device.