Extract file from tar home/

g geleem at bellsouth.net
Thu Jun 10 04:17:43 UTC 2010


Ed Greshko wrote:
> On 06/10/2010 09:20 AM, g wrote:
>> Ed Greshko wrote:
>>   
>>> On 06/09/2010 10:30 AM, g wrote:
>>>     
>>>> what do you do if archive file gets broken?
>>>>   
>>>>       
>>> In the past 10+ years that has not happened.  If it does, I'll let you
>>> know what I did.  FWIW, I always compress my archive files.
>>>     
>> may you continue to be blessed with such good fortune.
>>
>> post it on list. i promise not to laugh. :)
>>   
> OK...  For the fun of it I dug up an old CD-RW disk that had a
> compressed tar file on it with a photo archive.  If I recall correctly,
> the disk was written on a Liteon drive that lasted less than 6 months in
> my system of the time.  The CD was written in February of 2002 and was
> stored in a box packed up in 2002 when I moved offices.  It hadn't see
> the light of day until today.  Extracted the full archive without problem.
> 
> Of course this is only one file on one old CD-RW disk.  It doesn't prove
> anything.  Just like...
>> i used to compress archives. unfortunately, i did lose some one time.
>> it was then that i decided that i would limit my archive sizes to
>> smaller files.
>>
>>   

> ...there is no evidence that you wouldn't have lost data even if the
> archive size was smaller or uncompressed.

this is true.

but, in making smaller tar files or compressed files, there is less lost
if file becomes corrupt.

this is my point.

with cpio, if archive gets corrupt, only thing lost is in corrupt area.

but, even then not all will be lost, depending on type of file, and media
that cpio is sent to.

i normally cpio to tapes, but i also cpio to hard drive and then copy to
cd/dvd.


in example, on a hard drive or cd/dvd, if corrupt file is a text file or some
data base files.

cpio file that is corrupt, is removed by determining where in cpio file it is
located and using 'head -c', 'tail -c' dump of corrupt file, within cpio
file, to a new file, which is then run with 'head -c', 'tail -c', until a
file is built of corrupt file and then is edited with a hex file editor.

takes time, but is doable.

ie, a text file, and corrupted area contains non printable/usable bytes,
editor is then use to change bytes to 'spaces' and then can be recovered.
only loss is where spaces where inserted.

if a data base file, and you know how data is structured and store, patching
can/may be done to recover file with a hex editor.

i have never tried to recover a binary file. normally they can be replaced.

granted, it takes time, but recovery is possible.

if file is compressed, then, for all practical purposes, file is lost, unless
a binary program file.

so, to c.y.o.a., or in my case, c.m.o.a, i usually make 2 backups.

and yes, i have had cases where both backups had corruption, but luckily, it
was not same file in both backups.

nes pa?


-- 

peace out.

tc,hago.

g
.

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