UNIX for Advanced & Expert Users

Can someone please verify for me if tar compresses the directory or filesystem it is asked to back up??

reason am asking is I checked the size of the /home directory before running a tar command

now, after I ran the tar command and the tar was done extracting the directory from the archive, I check the size of the directory extracted from the archive and lo and behold, it was way smaller that the original size of the home directory. why is this so??

i checked the contents of the extracted directory and everything was in there, just like it was before I tared it.

my question is, does tar automatically compress files???. by the way the commad I used was: tar cf backedup /home

the system am using is red hat 7.2

AFAIK tar does not automatically compress files, at least, for the GNU tar I am using.

For example, I usually compress a directory and then bzip it by

tar cvjf something.tar.bz2 somedir/

You need extra options (-j or -z etc.) for compression.

A directory entry is a name and an inode number and a directory is a file that contains several directory entries. A literal interpretation of "size of directory" is, well, the size of the directory.

A second interpretation of "size of directory" is the total of the directory size and all of the files it contains. No one seems to use this intrepretation very much.

A third intrepretation of "size of directory" is total of the directory size and all files in any subdirectory.

Which of these did you think that you meant? And what command are you using to obtain it?

Directories grow as more files are added to them. But they do not shrink (with most file systems) as files are deleted.

It is possible that someone added a lot of files to /home and later deleted them. The size of /home itself would not shrink when they were deleted. Another possibility is that someone did this to a subdirectory deep in /home. The subdirectory would be big enough to only hold its current contents after you untarred.