[Duplicity-talk] Re: Help me replace tar!

[Joerg Schilling]

>From address@hidden  Thu Oct 16 02:55:53 2003

>On Thu, 16 Oct 2003 00:59:41 +0200 (CEST)
>Joerg Schilling <address@hidden> wrote:
>> Star is very close to the standard. In fact, it is the TAR
>> implementation that AFAIK is closest to the standard.
>> 
>> THE way to go for an archiver is to use the extensible POSIX.1-2001
>> format.  Star is the first tar implementation for the POSIX.1-2001
>> tar format aka. PAX.  During the last two years, star did add a lot
>> of features based on POSIX.1-2001 extensions. This allows star to
>> implement things that other tar implementations cannot do.

>Where can I get a copy of this POSIX.1-2001 standard?  When I first
>wrote the relevant portions of duplicity, one of the main reasons I
>used GNU tar format was because I could easily download a clear
>description of it.

Are you sure? I don't know any description of the archive format used by GNU 
tar. All I could do when implementing GNU tar compatibility inside star was to
read the GNU tar source and check the behavior :-( .... This is why I know that
GNU tar is full of bugs.

The POSIX standard is at the Open Group. Go to www.opengroup.org and register
for free html view of the SUSv3 standard. This has been taken as the 
POSIX.1-2001 by ISO.

>>From what I've heard though, I agree that your star is superior to GNU
>tar.  Not sure why distributions haven't moved to make it standard.

There may be several reasons:

-       Linux users seems to be a lot more conservative than you believe.

-       GNU tar is far from the POSIX archive standard, so if you move to star,
        your machine may be used fine, but other people who only have GNU tar
        may get into problems because GNU tar may have problems to read
        even POSIX.1-1988 archives.

-       GNU tar is far away from SUSv2. Star implements a standard compliant
        command line syntax, GNU tar does not. This is the reason why I recently
        created the "gnutar" program on top of the star archiver library.
        Note that the complete functionality is only available with the star
        command line interface.

Also note that United Linux added star because they added ACL support and star
is the only program that is able to archive ACLs on Linux.

>> In the future, there will be a star based backup that is not worse in any 
>> specific feature compared to ufsdump/ufsrestore. This will include a compact 
>> full directory at the beginning of the tape...

>And this is part of the POSIX-1.2001 standard?

No, but it uses an extension method that is documented in POSIX.1-2001.
When I am ready with the incremental dump/restore implementation, I will try to
introduce my extensions to the successor to POSIX.1-2001.

>> You may also like to check the archive format documentation
>> 
>> http://www.fokus.gmd.de/usr/schilling/private/star.html
>> http://www.fokus.gmd.de/usr/schilling/private/man/star.4.html

>This lists some keywords and extensions to the basic format, but not
>the basic format itself.

This should be widely known, but I am willing to make it more complete after
the implementation is reday. I started too late and for this reason only things 
are documented that have been added after august 2001.

Jörg

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