Why does du show that an 83GB file uses zero space?

Question

In home/{user}, I have a file called ntfs.txt whose total size of files is 83,3GB and whose size on disk is 0B. Its owned and group are both root. The last time it was accessed is the 24/07/2012. ls -l /home/romain/ntfs.txt outputs -rw------- 1 root root 83346727424 janv. 15 2012 /home/{user}/ntfs.txt and du /home/romain/ntfs.txt gives 0 /home/{user}/ntfs.txt. Previously, I had a Wubi install which I moved to a separated partition later. I also just got rid of Windows, but the file is still here. What's with its strange size? Can I delete it?

Answer 1

It's probably a sparse file

The most common case where du and ls return wildly different sizes is for sparse files, which are often created by download accelerators or bittorrent clients. ls gives you the size allocated (which the application will gradually fill up), while du gives you the actual size used.

If the actual size is 0, then there really is no data in it and it's safe to move or delete it (not that it would save you any disk space, since it's using none).

Experiment yourself with sparse files:

You can duplicate this weird scenario easily enough, with a 1-gigabyte file that takes ZERO space:

$ dd if=/dev/zero of=SparseFile bs=1 seek=1G count=0
$ ls -l SparseFile
-rw-rw-r-- 1 izx izx 1073741824 Jul 24 03:53 SparseFile
$ du SparseFile
0 SparseFile
$ stat SparseFile
  File: `SparseFile'
  Size: 1073741824  Blocks: 0          IO Block: 4096   regular file
Device: 805h/2053d  Inode: 400321      Links: 1
Access: (0664/-rw-rw-r--)  Uid: ( 1000/     izx)   Gid: ( 1000/     izx)