The size parameter specifies the requested new size of the filesystem. The size of the filesystem may never be larger than the size of the partition. Optionally, the size parameter may be suffixed by one of the following units designators: 's', 'K', 'M', 'G', or 'T', for 512 byte sectors, kilobytes, megabytes, gigabytes, or terabytes, respectively. If size parameter is not specified, it will default to the size of the partition.
This program does not manipulate the size of partitions. If you wish to enlarge a filesystem, you must make sure you can expand the size of the underlying partition first. This can be done using fdisk(8) by deleting the partition and recreating it with a larger size or using lvextend(8), if you are using the logical volume manager lvm(8)
If you wish to shrink a nilfs2 partition, first use nilfs-resize to shrink the size of filesystem. Then you may use fdisk(8) to shrink the size of the partition. When shrinking the size of the partition, make sure you do not make it smaller than the new size of the nilfs2 filesystem.