Linux

Please tell us the exact command you are using.

Could be fun if you're trying to tar up the tar file you're creating...

Consider: sparse files.

A sparse file that shows 10MB used space when copied or tar-ed may occupy exponentially more file space in the new file or tar file.... Those things are the bane of backups.

I am not saying this applies here but it should be considered when the backup of nnGB will not fit in a backup file of nnGB + a tiny amount.

Sparse file have "holes", this has nice diagrams:

Sparse file - Wikipedia, the free encyclopedia

Also note that you can mount file systems in such a way as to "obscure" an underlying group of files. Ex:
a directory tree with 2GB total in the whole thing :/path/to/confusion
If you mount a file system on /path/to/confusion on the confusion directory, all of the files are there but they no longer are visible to some tools. Results of du versus df is one of them.

This may produce the same weird results being discussed. Again, you may want to consider it. Look in fstab for confirmation.

Hi friends,

I tried that command ..
But it didn't show any output.
Will you please tell me how to solve this................

A good start would be to tell us what command you run, as already asked.