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Re: Extensions to Tar
Re: Extensions to Tar
Wed, 3 Apr 2002 15:28:51 -0800 (PST)
> Date: Sun, 31 Mar 2002 13:04:36 +0100 (BST)
> From: Chris Wilson <address@hidden>
> > Look at the 'pax' command for a description of the format.
> I've had a look at this document, and it says that A-Z typeflags are
> reserved for custom implementations. I noticed that all the GNUTYPE_*
> typeflags were also in the A-Z range with a similar comment, and that Y
> and E were unused, so I added mine to that list. Is that okay?
It's OK as far as I know, but it would be helpful if you looked for
other software to see what it did with those letters. I would look at
the letters that the latest 'star' uses, for example.
> > With ssh you can give them only the ability to run a certain command,
> > presumably rmt or a wrapper for rmt. Isn't that enough to give you
> > want you want?
> Maybe, I'll look into it. The main problem is that it doesn't work for
> multi-volume file archives
Doesn't rmt have the same problem? I don't see why a wrapper would fail
for multi-volume files, if plain rmt succeeds.
> > You should be able to do that by telling tar to read
> > the archive from stdin and write it to stdout, updating as you go.
> How do I tell tar to do that?
tar -u -f -
It's not much used, though, and it could well be buggy.
> > Why? You don't trust the time stamps?
> That's why I ask. I know rsync uses checksums (md5 I think) to compare
> files, and I know programs like tar can restore an archive and fudge the
> timestamps so it wouldn't be backed up by an incremental restore. Or am I
You are not mistaken about mtimes. However, you can tell tar to use
ctimes, and the operating system does not let you fudge ctimes.
> > here. And if you're paranoid enough to want a cryptographic checksum,
> > you should use a better one than MD5; SHA1 say.
> Is MD5 really that insecure?
That depends on how you measure security. Let's put it this way:
better safe than sorry. As far as I know, MD5 has not been cracked in
general, but there have been a bit of progress in cracking it, and
this is enough to convince me to not use it for new applications.