Re: [gentoo-user] Compression tools Compared

[Matt Randolph]

Matt Randolph wrote:

> Nick Rout wrote:
>
>> On Sat, 2005-08-13 at 09:36 -0400, Jerry McBride wrote:
>>
>>
>>> On Saturday 13 August 2005 01:32 am, Nick Rout wrote:
>>>
>>>
>>>> On Sat, 2005-08-13 at 00:58 -0400, Jerry McBride wrote:
>>>>
>>>>
>>>>> Anyone else here subscribe to the LINUX JOURNAL?
>>>>>
>>>>> In the September issue there's a neat article titled tha same as the
>>>>> subject line of this message.
>>>>>
>>>>> The skinny is, there's some really nice file compressors out there
>>>>> and I
>>>>> never heard of two of them... Anyone else know about LZMA or 7ZA?
>>>>>
>>>>> The two mentioned compression tools work pretty much like gzip.
>>>>> You tar
>>>>> up your files, pipe to the compression filter and then on to the
>>>>> target
>>>>> file. Below is a small example of what I've been seeing here at the
>>>>> shack.
>>>>>
>>>>> -rw-r--r--  1 root root 12359680 Aug 12 23:57 backup.tar
>>>>> -rw-r--r--  1 root root  3536665 Aug 13 00:01 backup.tar.7z
>>>>> -rw-r--r--  1 root root  4438465 Aug 13 00:08 backup.tar.bz2
>>>>> -rw-r--r--  1 root root  4747637 Aug 13 00:03 backup.tar.gz
>>>>> -rw-r--r--  1 root root  2731412 Aug 13 00:10 backup.tar.lzma
>>>>> -rw-r--r--  1 root root  5125474 Aug 13 00:16 backup.tar.lzop
>>>>>
>>>>> What you're seeing are the results of compressing /lib on my gentoo
>>>>> powered laptop. I've not bothered with timing the processes as the
>>>>> better
>>>>> compression rates are at the cost of speed and memory usage. Not
>>>>> good for
>>>>> "while you wait" processing, but just plain perfect for backups and
>>>>> what-have-you on servers... One side note, 7za does not record
>>>>> user/group
>>>>> info...
>>>>>
>>>>
>>>> Are you saying it removes user/group info from the tar file?
>>>>
>>>>
>>>
>>> Not "removed", it's never put there... :')
>>>
>>
>>
>>
>> I'm sorry but how do you create a tar file without preserving the
>> usernames and permissions?
>>
>>
>>
>
> This may be a case of a different paradigm being used by 7-zip than
> that used by traditional (*nix) compression tools.  If my memory
> serves me, the 7-zip format is very similar to the pkzip format in its
> usage.  By that I mean that one is not required to make a tarball
> before compressing multiple files.  The format allows you to skip the
> tar step and make an archive consisting of whichever files and
> directories you wish.
>
> The problem, I'm guessing, is that the 7-zip archive format was
> developed in the Windows world where users and groups and permissions
> have no meaning (I think that has changed or is changing in the NT/XP
> world, but I don't know and don't especially care).  Hence, these
> attributes aren't accomodated by this format.  I assume the 7-zip
> extractor program sets the user and group of the extracted files to
> that of whomever extracts them.
>
> What everyone has rightly pointed out, namely that you can make a
> tarball and then compress that, is exactly right.  That IS how one
> would use 7-zip with a proper operating system.
>
> The original poster most likely used the 7-zip archiver as a
> stand-alone tool, rather than using it in conjunction with tar.  This
> is not altogether surprising as one typically compresses a directory
> with a single tar command (and an implied pipe) rather than explicitly
> piping the output of tar to the compression utility.  Since there is
> no --7-zip switch in tar, the OP couldn't simply 'tar -7cf
> backup.tar.7zip lib/'.  The OP probably simply 7-zipped his directory
> without tarring it first and consequently ran into the limitations of
> the archive format.
>
"-rw-r--r--  1 root root  3536665 Aug 13 00:01 backup.tar.7z"

Oops!  I should read more carefully.

-- 
"Pluralitas non est ponenda sine necessitate" - W. of O.

-- 
gentoo-user@g.o mailing list