what is the most reliable command to find actual size of a file linux

Question

Recently I tried to find out the size of a file using various command and it showed huge differences.

ls -ltr showed its size around 34GB (bytes rounded off by me ) while du -sh filename showed it to be around 11GB. while stat command showed the same to be around 34GB . Any idea which is the most reliable command to find actual size of the file ?

There was some copy operation performed on it and we are unsure of if this was appropriately done as after a certain time source file from where copy was being performed was removed by a job of ours.

Answer 1

There are several notions of file size, as explained in that other guy's answer and the wikipage figure on sparse files.

However, you might want to use both ls(1) & stat(1) commands.

If coding in C, consider using stat(2) & lseek(2) syscalls.

See also the references in this answer.

Answer 2

There is no inaccuracy or reliability issue here, you're just comparing two different numbers: logical size vs physical size.

Here's Wikipedia's illustration for sparse files:

ls shows the gray+green areas, the logical length of the file. du (without --apparent-size) shows only the green areas, since those are the ones that take up space.

You can create a sparse file with dd count=0 bs=1M seek=100 of=myfile.

ls shows 100MiB because that's how long the file is:

$ ls -lh myfile
-rw-r----- 1 me me 100M Jul 15 10:57 myfile

du shows 0, because that's how much data it's allocated:

$ du myfile
0 myfile

Answer 3

ls -l --block-size=M

will give you a long format listing (needed to actually see the file size) and round file sizes up to the nearest MiB.

If you want MB (10^6 bytes) rather than MiB (2^20 bytes) units, use --block-size=MB instead.

If you don't want the M suffix attached to the file size, you can use something like --block-size=1M. Thanks Stéphane Chazelas for suggesting this.

This is described in the man page for ls; man ls and search for SIZE. It allows for units other than MB/MiB as well, and from the looks of it (I didn't try that) arbitrary block sizes as well (so you could see the file size as number of 412-byte blocks, if you want to).

Note that the --block-size parameter is a GNU extension on top of the Open Group's ls, so this may not work if you don't have a GNU userland (which most Linux installations do). The ls from GNU coreutils 8.5 does support --block-size as described above.