What is difference between ls -lh and du -sh?

Question

$ ls -lh file1.tar

-rw-r--r-- 1 wnice wnice 40K Aug  6 20:41 file1.tar

$ du -sh file1.tar

80K     file1.tar

Why is it showing different sizes of same file? Please help me understand

Answer 1

The du command shows how much disk space is used for the given file.

In contrast, the ls command shows the size of the file. The space used can be larger than the file size, depending on the filesystem used.

For example, we can create a file with the size 1 byte like this (just one newline character in the file):

echo > tmp.txt

Then check its size using ls -l which shows the size one byte:

ls -l tmp.txt 
-rw-r--r-- 1 elias elias 1 aug  6 17:50 tmp.txt

Then check the used space using du:

du -h tmp.txt 
4,0K    tmp.txt

So the used disk space was in this example 4 kilobytes, although the filesize is only one byte.