Tarfile and usernames

Nicholas Cole nicholas.cole at gmail.com
Sun Dec 30 21:48:00 CET 2012

On Sun, Dec 30, 2012 at 8:07 PM, Albert Hopkins <marduk at letterboxes.org>wrote:
> On Sun, Dec 30, 2012, at 01:57 PM, Nicholas Cole wrote:
> Dear List,
> I'm hoping to use the tarfile module in the standard library to move some
> files between computers.
> I can't see documented anywhere what this library does with userids and
> groupids.  I can't guarantee that the computers involved will have the same
> users and groups, and would like the archives to be extracted so that the
> files are all owned by the extracting user.
> Essentially, I do *not* with to preserve the owner and groups specified in
> the archives.
> Each "member" in the tar file has misc. metadata associated with it, which
> can be retrieved with the get_info() method.  You can add/modify this
> metadata if creating a TarFile.
> However, it should be stated that by default (on *nix anyway) if the user
> is not root then user/groups are assigned to the user exctracting the file
> (because only root can assign userids/non-member-groups).   The TarFile
> extract*() methods pretty much inherit the same behavior as the *nix tar
> command.  So if you are extracting as a non-root user, you should expect
> the same behavoir.  If you are extracting as root but don't want to change
> user/groups may have to extract it manually or create your own class by
> inheriting TarFile and overriding the .chown() method.

Thank you for this.  I guess that since the behaviour is not defined in the
documentation, it would probably be safest to inherit and change chown into
a no op.

I know that on *most* systems these days ordinary users cannot chown, and
also that people shouldn't be running things as root.  But you can't be too
careful - and predicting what a given user will do is always dangerous!

Best wishes,

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