为什么`du`的输出通常与`du -b`如此不同

cat theFile | wc -c

mmap

mount

/

stat -fc %s .

4096

1 4095 4096 4097

#!/usr/bin/env bash
for size in 1 4095 4096 4097; do
  dd if=/dev/zero of=f bs=1 count=\"${size}\" status=none
  echo \"size     ${size}\"
  echo \"real     $(du --block-size=1 f)\"
  echo \"apparent $(du --block-size=1 --apparent-size f)\"
  echo
done

size     1
real     4096   f
apparent 1      f

size     4095
real     4096   f
apparent 4095   f

size     4096
real     4096   f
apparent 4096   f

size     4097
real     8192   f
apparent 4097   f

4096

4096

4097

8192

2 * 4096

dd seek=1G if=/dev/zero of=f bs=1 count=1 status=none
du --block-size=1 f
du --block-size=1 --apparent f

8192    f
1073741825      f

print apparent sizes, rather than disk usage; although the apparent size is usually smaller, it may be
larger due to holes in (`sparse\') files, internal fragmentation, indirect blocks, and the like

du -bm

du -m

-b

--apparent-size --block-size=1

m

1M

-bh

-h

-bh

--apparent-size --block-size=1 --human-readable