Why file size appears to change when you move a file from one Unix-like system to another

On Unix-like (that is, Linux) systems, the ls -s and du commands both report the size of files in blocks. However, the length of a block can differ between operating systems. For example, in some Unix-like operating systems, blocks are 512 bytes long; in others, blocks are 1 kilobyte (KB) long.

Some Unix-like systems that restrict the amount of storage space their users can have measure storage space in bytes rather than blocks. If you move a file from such a system to one that measures storage capacity in blocks, the du and ls -s commands will report a file size different from the one reported on the previous system; however, this does not mean the file size has actually changed.

On UITS research supercomputers at Indiana University, the du and ls -s commands both report file sizes in 1-KB blocks.