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Date: Sun, 30 Dec 2012 20:48:00 +0000
Subject: Re: Tarfile and usernames
From: Nicholas Cole <nicholas.cole@gmail.com>
To: Albert Hopkins <marduk@letterboxes.org>
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On Sun, Dec 30, 2012 at 8:07 PM, Albert Hopkins <marduk@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,

N.

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<div dir=3D"ltr"><br><div class=3D"gmail_extra"><br><br><div class=3D"gmail=
_quote">On Sun, Dec 30, 2012 at 8:07 PM, Albert Hopkins <span dir=3D"ltr">&=
lt;<a href=3D"mailto:marduk@letterboxes.org" target=3D"_blank">marduk@lette=
rboxes.org</a>&gt;</span> wrote:<blockquote class=3D"gmail_quote" style=3D"=
margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div><div class=3D"im">
<div>=A0</div>
<div>On Sun, Dec 30, 2012, at 01:57 PM, Nicholas Cole wrote:<br></div>
<blockquote type=3D"cite"><div dir=3D"ltr">Dear List,<div>=A0</div>
<div>I&#39;m hoping to use the tarfile module in the standard library to mo=
ve some files between computers.=A0<br></div>
<div>=A0</div>
<div>I can&#39;t see documented anywhere what this library does with userid=
s and groupids. =A0I can&#39;t guarantee that the computers involved will h=
ave the same users and groups, and would like the archives to be extracted =
so that the files are all owned by the extracting user.=A0<br>
</div>
<div>=A0</div>
<div>Essentially, I do *not* with to preserve the owner and groups specifie=
d in the archives.<br></div>
</div>
</blockquote></div><div dir=3D"ltr"><div>=A0</div>
<div>Each &quot;member&quot; in the tar file has misc. metadata associated =
with it, which can be retrieved with the get_info() method. =A0You can add/=
modify this metadata if creating a TarFile.<br></div>
<div>=A0</div>
<div>However, it should be stated that by default (on *nix anyway) if the u=
ser is not root then user/groups are assigned to the user exctracting the f=
ile (because only root can assign userids/non-member-groups). =A0 The TarFi=
le extract*() methods pretty much inherit the same behavior as the *nix tar=
 command. =A0So if you are extracting as a non-root user, you should expect=
 the same behavoir. =A0If you are extracting as root but don&#39;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.<span class=3D"HO=
EnZb"><font color=3D"#888888"><br>
</font></span></div><span class=3D"HOEnZb"><font color=3D"#888888">
<div>=A0</div></font></span></div></div></blockquote><div><br></div><div st=
yle>Thank you for this. =A0I guess that since the behaviour is not defined =
in the documentation, it would probably be safest to inherit and change cho=
wn into a no op. =A0</div>
<div style><br></div><div style>I know that on *most* systems these days or=
dinary users cannot chown, and also that people shouldn&#39;t be running th=
ings as root. =A0But you can&#39;t be too careful - and predicting what a g=
iven user will do is always dangerous!</div>
<div style><br></div><div style>Best wishes,</div><div style><br></div><div=
 style>N.</div><div style><br></div><div style><br></div></div></div></div>

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