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Re: [Bug-tar] incremental backup won't recognise snar file from previous

From: Helmut Waitzmann
Subject: Re: [Bug-tar] incremental backup won't recognise snar file from previous system
Date: Thu, 07 Dec 2006 05:20:15 +0100
User-agent: Gnus/5.1008 (Gnus v5.10.8) Emacs/21.4 (gnu/linux)

"Henry Andrew" <address@hidden> writes:

>I use /var/log/snar to record the files that were backed up so that
>future incrementals can refer to this file and only bakup the newest
>files.  This has been working perfectly for some tmie, but recently
>after a botched upgrade to the latest version of Ubuntu, I was forced to
>re-install my current version.  

So you use that version of tar, which you used to use before the botched
upgrade, right?

>As I have /home on a separate partition, this didn't involve restoring
>the archive, 

You didn't touch any file in the file hierarchy "/home", right?

>however, I did not backup /var/log/snar, but I have a copy of it on the
>DVD that I burnt the yearly archive to.
>Now, even though I have copied snar back to /var/log, using cp -p to
>make sure that it retains it's original timestamp, 

You restored latest version of the file "/var/log/snar", which was there
before the botched upgrade, right?

Then I think, your system behaves strange, in deed:

>my weekly backups are backing up every file on /home, as if it is unable
>to recognise the snar file.

If you know for certain, that your "/home" filesystem has not changed
during and since the botched upgrade, make a backup to "/dev/null", just
to create a new "/var/log/snar" GNU tar snapshot file.

If there might be changes in your "/home" file hierarchy, but you can
identify all of them, make a backup to "/dev/null" as above, and then
touch each of the changed inodes, to trigger a new backup.

To identify the changes, you could restore "/home" from the backup into
a different place, for example "/restored_home".  Maybe you have to use
GNU tar's option "--strip-components" to achieve that.

With "cmp" together with "find" you could traverse both hierarchies
finding files wich differ in their contents and files which are only in
one of both hierarchies.

There is no easy way to find inodes which differences consist of only the
filenames that are hardlinked to them, though.
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