restoring FC1 to *new* partition from tar archive

Jeff Vian jvian10 at
Mon May 10 04:48:09 UTC 2004

Joe(theWordy)Philbrook wrote:

>It would appear that on May 9, Luciano Miguel Ferreira Rocha did say:
>>On Sun, May 09, 2004 at 08:21:43AM -0500, Jeff Vian wrote:
>>>I think you are confusing /restore/ with /use/.  
>>>It can be /restored/ using any system. The ownership is numeric and does 
>>>not change on a differnent system.
>>No, I'm not confusing it, and no, the ownership isn't numeric. At least,
>>in my experience. I've created backups of redhat and fedora installs, in
>>single user mode, and restore them under live cds (knoppix or self-made).
>>If I didn't use the option I described, some files would end with
>>different numeric ids than they should. In particular, the knoppix cd has
>>different values for cups and other system accounts, and when restoring
>>the files would use those values.
>>When booting the restored system, those files would have invalid
>>>The user ids are a problem if /used/ on a system where the group and 
>>>passwd files define different userids for the owners.
>>Not as such. As tar uncompresses using user and group names (in _my_
>>experience), the extracted files will be usable by the users on that
>>Of course, if you consider the "use" of such backup as above, then it
>>still is a problem.
>>Luciano Rocha
>Now I'm getting a little confused... I found two relevant items under
>info tar.
>=> `--numeric-owner'
>=>      This option will notify `tar' that it should use numeric user and
>=>      group IDs when creating a `tar' file, rather than names.
>Which option isn't even mentioned in man tar. Now here is the part I
>don't understand. If it's supposed to be more reliable when extracting
>to a different system, How would it deal with file belonging to
>user=goodDube has UID=1001 on the source file system when on the
>destination file system UID=1001 is held by user=EvilTwin???
>-> `--same-owner'
>->      When extracting an archive, `tar' will attempt to preserve the
>->      owner specified in the `tar' archive with this option present.
>->      This is the default behavior for the superuser; this option has an
>->      effect only for ordinary users.
>Which option is listed (sparsely) in man tar, and sounds like it will
>try to keep the same owner, based on the user name of owner. 
>What happens  when the filesystem that is creating/extracting the
>tar file has different UID numbers for some users than the
>source/destination file system. Does it actually think to look up the
>users in the destination system's passwd file (that would be a neat
>trick) or does it fall back on it's own passwd file?
>I'm guessing that when --numeric-owner is used then in the first
>scenario EvilTwin would become the new file owner. And that in the
>second scenario the UID from the source file would be used even when
>tar thinks it may belong to an unknown user on the destination system.
>I'm also guessing that when --numeric-owner is NOT used, then in the
>first scenario tar would look up the username "goodDube" in the passwd
>file and use that users UID. But that in the second scenario, it would
>wind up assigning the user id from it's own filesystems passwd file
>which may not match the user id of the destination filesystem's passwd
>Sheesh, this is confusing. It's sounding more and more like the fact
>that mdk didn't appear to mess up my FC1 is probably a fluke.
>If I wanted to use the --numeric-owner option, do I need to use it
>during both the "tar -c" AND the "tar -x" process, or only during the
I am going to let someone else address the questions about the options 
in info and man.  My answer is based on experience and practical usage.

In my many years of experience I have never used the numeric option, and 
seldom used the -p option

I routinely use tar -cvf  (or czvf) to create the file and tar -xvf (or 
xzvf) to extract it.  

AFAICT the numeric UID/GID is stored in the file from the source system, 
and the numeric UID/GID is extracted with the file on the destination 
system.  On systems where the username/UID pair from the source does not 
match the username/UID pair from the destination, the file on the 
destination is owned automatically by the user with the UID of the 
original file.

I can and have tested this repeatedly and have found nothing unusual as 
long as I remember that the ownership for extracted files will go to the 
user with the matching UID and not necessarily to the matching username. 
If there is no username that has a matching UID then the ownership 
displays as the numeric UID  (see my earlier post on this for an example)

There are many options for tar that I seldom use and thus am not 
familiar with.  But in my experience, your results are common.  YMMV

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