Re: [Bug-tar] tar, multi-volume and long filenames

[Joerg Schilling]

Ingo von Borstel <address@hidden> wrote:

> Hi there,
>
> I just discovered a phenomenon that tar exits with errorcode one in my
> backup script - and I'm not sure about the cause. The situation is as
> follows:
>
> address@hidden:~/backup> tar --version
> tar (GNU tar) 1.15.1
>
> My backupscript basically looks like this, omitting variable initilization:
>
> ### begin shell script ###
> tar --create --one-file-system
> --exclude-from=/home/ingo/backup/homeingo_exclude.txt
> --file=$backupfilename --tape-length=2000000 --recursion --multi-volume
> --new-volume-script="/home/ingo/backup/volumechange.sh
> $backupfileprefix" --totals /home/ingo/*
>
> /home/ingo/backup/volumechange.sh $backupfileprefix
> ### end shell script ###
>
> Now that works fine for four volumes, the fifth is only created as a
> zero sized file and the script / tar exits with a cron notification that
> reads like
>
> ### begin error message ###
> From: Cron Daemon <address@hidden>
> To:  <address@hidden>
> Subject: Cron <address@hidden> /home/name/backup/makeremotebackup.sh
> tar: Removing leading `/' from member names
> tar:
> home/name/icaps/pfc092005/auswertung/flug1_10/13.09.2005_parabola10_overview_frame00220_T04095175.bmp:
> file name
> too long to be stored in a GNU multivolume header
> tar: Error is not recoverable: exiting now
> ### end error message ###

>From what I know, GNU tar is unable to split an archive inside a 
"long filename" speudo tar file.

The last time I checked, GNU tar was also unable to extrect a folloup volume
from a multi-volume archive in case that the last file has not been split 
across volumes.

The problem seems to be caused by the way GNU tar splits archives in 
multi-volume mode. It may be possible that this method could be fixed for
simple tar implementations like GNU tar but it is definitely not possible
to let a buffered tar implementation like "star" split archives using
the GNU tar method.

You may like to have a look at star ftp://ftp.berlios.de/pub/star/alpha/
Star uses a different method for multi volume archives that is less
sensitive to the content of the location of the archive where the split is done.

If you like to have a look at the star archive format definition.

http://cdrecord.berlios.de/old/private/man/star.4.html

or the star pages:
 
http://cdrecord.berlios.de/old/private/star

The reason whyt star has no such problems is caused by th fact that it
is using an offset based algorithm instead of a file name based one.

Jörg

-- 
 EMail:address@hidden (home) Jörg Schilling D-13353 Berlin
       address@hidden                (uni)  
       address@hidden     (work) Blog: http://schily.blogspot.com/
 URL:  http://cdrecord.berlios.de/old/private/ ftp://ftp.berlios.de/pub/schily