Strange behavior of tar
 

Hello forum,

I write a short script which automates some backup-jobs. I describe my problem by an example.

find /etc -print > /tmp/backup.list

gives me a list of all files to back up (I want to perform incremental backups using the option -mtime -1).
Then I pack them into an tar.bz2 with the following command:

tar -cjv -T /tmp/backup.list -f backup.tar.bz2

If I look over the resulting archive I realize that the directories below /etc are stored twice in the archive. The next directorylevel is stored three times, so that

tar -tjf backup.tar.bz2|grep XF86Config

shows this file three times.

In /tmp/backup.list every file is present just one time!

In this case I'm really helpless and need your kindly advice.

:scratch: Frank Becker

Everything is OK. If you tar /xxx all the files and directories will be tared. Next you add /xxx/yyy so you make additional backup for subdir :)

Thanks to dorian above, he's right. Tar is seeing directory names like /etc/X11 and tarring the whole thing, then it's tarring the individual files within that directory. Just use:

tar -cjvf backup.tar.bz2 /etc

tar is smart enough to recurse subdirectories automatically and add files there.

You could still use your find /etc -print > backup.list for verification of archives.

Thanks jrmann,

now I know why there are duplicate entries in the tar-archive.

But, do you have any solution to perform incremental backups with find/tar? I don't want to save the complete directory with all files if there is any file to backup. In this case, if there are any changes in /etc/X11/XF86Config I just want to backup the entiere file and not the whole directory.

Thanks for your help

Frank

Your best bet would be to use rsync, it has an incremental backup mode and checks a variety of conditions based on whatever you specify(hint, man rsync). You could create a folder that you would purge->rsync->tar daily for incremental backups of a non-critical nature. There are many well documented solutions involving rsync(and tar if you choose to go that route) if you just google a bit.